Method and apparatus for washing crystalline product

Abstract

The present invention relates to a method and apparatus for washing a crystalline product. The method for washing a crystalline product of the present invention comprises: S1: washing a crude crystalline product to obtain a washing filtrate and a solid-phase crystalline product; and S2: melting the solid-phase crystalline product to obtain a melt of the crystalline product, wherein a first part of the melt is heated to obtain a heated melt; a part of the heated melt is returned to step S2 as a main stream, and the remaining part of the heated melt is returned to step S1 as a bypass stream; a second part of the melt is returned to step S1; and a third part of the melt is discharged as a purified crystalline product. The present invention also relates to the apparatus used for executing the method. The method and apparatus for washing a crystalline product of the present invention have the advantages of low energy consumption during washing, simple and efficient control, a simple process, and large-scale application.

Description

Method and apparatus for washing crystallized products Technical Field

[0001] This invention relates to the field of separation and purification technology, and specifically to a method and apparatus for washing and crystalline products. Background Technology

[0002] In industries such as chemical, food, and pharmaceutical, crystallization is a very common separation and purification method. Solvent crystallization requires the addition of a third substance to change the solubility of the target product, thereby allowing the target product to precipitate from the mother liquor. Melt crystallization, on the other hand, does not require the introduction of a third substance; it separates and purifies the components solely based on the differences in melting points among the components in the mother liquor. Therefore, melt crystallization has the advantages of simple process steps, high product purity, and low energy consumption.

[0003] Depending on the crystal formation state, melt crystallization is divided into suspension crystallization and layer crystallization. In the former, the precipitated crystals are suspended in the mother liquor as particles, while in the latter, the precipitated crystals adhere to the heat exchange interface and gradually grow along it. Each has its own applicable systems and fields of study. For suspension crystallization, solid-liquid separation is required through methods such as filtration or centrifugation to obtain the crystalline product. Furthermore, since the mother liquor is inevitably carried over, impurities are introduced. Therefore, when high purity is required for the crystalline product, the crude crystalline product after solid-liquid separation often needs to be washed to obtain the qualified target crystalline product.

[0004] Washing the crystallized product requires a washing solution. When a substance other than the target product is used as the washing solution (such as toluene used as the washing solution in early xylene crystallization separation processes), additional separation methods are needed to separate the washing solution from the target crystallized product for recycling. This complicates the process and increases energy consumption. Therefore, in improved processes, the molten target crystallized product is often used directly as the washing solution.

[0005] During the washing process of crystallized products, if the washing solution temperature is too high or the volume is too large, the crystal product is prone to melting and loss; if the washing solution temperature is too low or the volume is too small, it is difficult to achieve the desired purification effect, resulting in low product purity. Typically, the temperature of the crude crystallized product to be washed fluctuates over time or batch. For example, the temperature of the crude crystallized product to be washed may change due to fluctuations in the production process of the upstream crystallization unit or aging unit. Therefore, to ensure the purification effect, the temperature and volume of the washing solution need to be flexibly adjusted and strictly controlled.

[0006] CN101941882B proposes a method for separating para-xylene from mixed xylenes. In this method, the solid crystals after crystallization and solid-liquid separation are melted after heat exchange. Part of the melt is returned to the solid-liquid separator as washing liquid, while the remainder is sent to a product tank as para-xylene. This method requires melting all the solid crystals to the temperature required for the washing liquid, resulting in high energy consumption. Furthermore, it is difficult to adjust the temperature and volume of the washing liquid in a timely, rapid, and accurate manner. When the washing liquid temperature needs adjustment, the temperature of the entire melting equipment must be changed, which is detrimental to large-scale equipment design.

[0007] CN116768172A proposes a wet-process phosphoric acid suspension crystallization purification process. In this process, phosphoric acid crystals obtained after crystallization, solid-liquid separation, and washing are completely melted in a melting tank. A portion of the melt is cooled and returned to the solid-liquid separator as washing liquid, while the remainder is collected as the phosphoric acid product. This method not only requires a large amount of heat to melt all the phosphoric acid crystals in the melting tank and raise the temperature above the washing liquid temperature, but also requires additional cooling to lower the phosphoric acid crystals used as washing liquid back to the required washing temperature, resulting in energy waste. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems of high energy consumption and untimely and inefficient control of washing liquid temperature and dosage in existing crystallization product washing processes. To achieve the above objective, this invention provides a method and apparatus for washing crystallization products. This method and apparatus for washing crystallization products achieves the advantages of low energy consumption, simple and efficient control, simple process, and suitability for large-scale application.

[0009] The first aspect of the present invention provides a method for washing crystallized products, characterized in that the method includes:

[0010] S1: Wash the crude crystalline product to obtain a washing filtrate and a solid phase of crystalline product;

[0011] S2: Melt the solid-phase crystalline product to obtain a melt of the crystalline product;

[0012] In this process, the first part of the melt is heated to obtain a heated melt. A portion of the heated melt is returned to step S2 as the main flow, and the remaining portion of the heated melt is returned to step S1 as a bypass flow.

[0013] The second part of the melt returns to step S1;

[0014] The third portion of the melt is discharged as a purified crystalline product.

[0015] In one variation, the present invention provides a method for washing crystallized products, characterized in that the method comprises:

[0016] S1: Wash the crude crystalline product with a washing solution to obtain a washing filtrate and a solid phase of crystalline product;

[0017] S2: Melt the solid-phase crystalline product to obtain a melt of the crystalline product;

[0018] In this process, the first part of the melt is heated to obtain a heated melt. A portion of the heated melt is returned to step S2 as the main flow, and the remaining portion of the heated melt is returned to step S1 as a bypass flow.

[0019] The second part of the melt returns to step S1;

[0020] The third portion of the melt is discharged as a purified crystallized product, and

[0021] The method further includes at least one of the following control steps:

[0022] Control step C1: Obtain information on the flow rate of the washing liquid, and adjust the flow rate of the second part of the melt returning to step S1 based on the information;

[0023] Control step C2: Obtain information on the liquid level of the molten material of the crystallized product in step S2, and adjust the flow rate of the third part of the molten material based on the information;

[0024] Control step C3: Obtain information on the temperature of the first portion of the melt, and adjust the flow rate of the first portion of the melt based on the information;

[0025] Control step C5: Obtain information on the temperature of the washing liquid and adjust the flow rate of the main pipeline based on the information; and

[0026] Control step C6: Obtain information on the temperature of the heated melt and adjust the flow rate of the heating medium based on the information.

[0027] A second aspect of the present invention provides an apparatus for implementing the above-described method, the apparatus comprising: a scrubber for washing a crude crystalline product to obtain a solid crystalline product and a washing filtrate; and a melter comprising: a melting zone for melting the solid crystalline product to obtain a melt of the crystalline product; wherein the melter is provided with three outlet pipes; wherein a first outlet pipe is connected to a heat exchanger, wherein the heat exchanger is provided with a main outlet pipe connected to the melting zone; and an outlet bypass pipe connected to the scrubber; a second outlet pipe is connected to the scrubber; and a third outlet pipe is connected to a product outlet.

[0028] The third aspect of the present invention provides a method for washing a crystallized product, which is carried out in the apparatus described in the second aspect. The method includes: (1) washing the crude crystallized product with a washing liquid in a scrubber to obtain a solid-phase crystallized product and a washing filtrate; (2) introducing the solid-phase crystallized product into the melting zone of a melter for melting to obtain a melt of the crystallized product; wherein the melt enters the three outlet pipes respectively; a first portion of the melt is introduced into a heat exchanger through the first outlet pipe for heating to obtain a heated melt, a portion of the heated melt is returned to the melting zone as the main flow through the main outlet pipe, and the remaining portion of the heated melt is returned to the scrubber as the bypass flow through the outlet bypass pipe; a second portion of the melt is returned to the scrubber through the second outlet pipe; and a third portion of the melt is discharged from the product outlet through the third outlet pipe.

[0029] Compared with the prior art, the present invention has at least the following beneficial effects:

[0030] (1) In the method of the present invention, the first portion of the melt is heated to obtain a heated melt. A portion of the heated melt is returned to step S2 as the main flow, and the remaining portion of the heated melt is returned to step S1 as a bypass flow for use as washing liquid. On the one hand, the operation of the present invention ensures the washing liquid temperature while maintaining the bypass flow of the heated melt at a temperature lower than the washing liquid temperature. In the method of the present invention, only the washing liquid reaches the washing liquid temperature, while the purified crystallized product discharged as a product is at the melt temperature of the melt in the melt, which is lower than the washing liquid temperature. In contrast, in the prior art, all the melt in the melt is heated to the washing liquid temperature or even higher, with a portion of the heated melt being reused as washing liquid and another portion being discharged as a product. Accordingly, not only is the washing liquid at the washing liquid temperature, but the discharged product is also at the washing liquid temperature. That is to say, compared to the method of the present invention, the product is at a higher temperature in the prior art method, which obviously increases energy consumption. In the prior art solution where the melt is heated to a temperature higher than the washing liquid temperature, additional cooling is required, which further increases energy consumption. Therefore, the method of the present invention achieves the goal of reducing the heating load of the heat exchanger (and eliminating the cooling load of the heater). On the other hand, the operation of the present invention reduces the flow rate of the first portion of the molten material entering the heat exchanger, thereby reducing the total flow rate of the product stream pump used to discharge the molten material from the melt, and correspondingly reducing the energy consumption of the product pump. Combining the above two aspects, the goal of reducing energy consumption in the washing process is achieved.

[0031] (2) In the method of the present invention, the first portion of the melt is heated to obtain a heated melt. A portion of the heated melt is returned to step S2 as the main stream, and the remaining portion of the heated melt is returned to step S1 as a bypass stream for use as the washing liquid. Simultaneously, the second portion of the melt is also returned to step S1 as the washing liquid. Therefore, the portion of the heated melt returned to step S1 (i.e., the bypass stream) and the second portion of the melt together constitute the washing liquid used in step S1. The portion of the heated melt returned to step S1 and the second portion of the melt have different temperatures and flow rates. By controlling the ratio of the two, the temperature and amount of the washing liquid (as mentioned above, which are key factors affecting the purification effect) can be controlled in a timely and efficient manner, thereby achieving the desired purification effect efficiently.

[0032] (3) In the device of the present invention, the melter is provided with three outlet pipes, wherein the outlet pipes are respectively connected to the heat exchanger, the melting zone of the melter and the scrubber, so as to effectively return the crystalline product melts of different temperatures and flow rates to the scrubber and the melter, thereby realizing simple and efficient control of the washing and melting operation conditions.

[0033] (4) In the apparatus of the present invention, the melter includes a melting zone and a refining zone, wherein the melting zone and the refining zone are isolated by a baffle, and the outlet pipeline is located in the refining zone. In the configuration of the present invention, the baffle prevents the solid crystal product from the scrubber from entering the melting zone and thus entering the product pump, thereby ensuring the continuous and stable operation of the product pump. In a preferred embodiment, multiple liquid phase inlets are provided at the top or bottom of the melting zone of the melter, which are connected to the main outlet pipeline. This helps to disperse the main pipeline flow into the melting zone of the melter, accelerating the melting of the solid crystal product. This can shorten the residence time and reduce the size of the melter. In a preferred embodiment, a liquid phase inlet is provided at the bottom of the melting zone of the melter. Therefore, the main pipeline flow enters the melting zone of the melter, and the melting zone of the melter contains melt, the temperature of which is lower than that of the main pipeline flow. This can prevent the vapor volatilized from the main pipeline flow from flowing back into the scrubber, disrupting the washing process and causing product loss. Therefore, the apparatus of the present invention is more conducive to ensuring the smooth progress of the washing process and realizing large-scale production. Attached Figure Description

[0034] Figure 1 is a schematic diagram of the structure of a melt according to an embodiment of the present invention;

[0035] Figure 2 is a schematic flowchart of a washing method according to one embodiment of the present invention;

[0036] Figure 3 is a schematic flowchart of a washing method according to one embodiment of the present invention;

[0037] Figure 4 is a schematic flowchart of a washing method according to one embodiment of the prior art;

[0038] Figure 5 is a schematic flowchart of a washing method according to one embodiment of the prior art.

[0039] List of reference numerals: 1. Cylinder; 2. Baffle; 3. Solid inlet; 4. Liquid outlet; 5. Level gauge port; 6. Liquid inlet; I. Melting zone; II. Clarification zone; II-1. First clarification zone; II-2. Second clarification zone; 101. Crystal slurry; 102. Crystallization mother liquor; 103. Washing liquid; 104. Washing filtrate; 105. Solid crystallization product; 106. Melt of crystallization product; 107. First part melt; 108. Heated melt; 108-1. Main flow; 108-2. Bypass flow; 109. Second part melt; 110. Third part melt; 201. Heat exchange medium; 202. Cooling medium; C; 101. Scrubber; D; 101. Melter; P; 101. Product pump; E; 101. Heat exchanger; E; 102. Cooler; TC. Temperature monitoring equipment; LC. Level monitoring equipment; FC. Flow monitoring equipment; TI. Temperature measuring equipment; FI. Flow measuring equipment. Detailed Implementation

[0040] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0041] In this document, the terms "first," "second," "third," etc., are used to distinguish multiple different elements or materials, and are not used to define specific locations or relative relationships. In other words, in some embodiments, the terms "first," "second," "third," etc., can also be used interchangeably.

[0042] The first aspect of the present invention provides a method for washing crystallized products, the method comprising:

[0043] S1: Wash the crude crystalline product to obtain a washing filtrate and a solid phase of crystalline product;

[0044] S2: Melt the solid-phase crystalline product to obtain a melt of the crystalline product;

[0045] The first part of the melt is heated to obtain a heated melt. A portion of the heated melt is returned to step S2 as the main stream, and the remaining portion of the heated melt is returned to step S1 as a bypass stream. The second part of the melt is returned to step S1. The third part of the melt is discharged as a purified crystallized product.

[0046] As used herein, "crystallized product" is a general term referring to a stream containing the target crystalline product. "Crude crystalline product" refers to the crystalline product to be washed. The crude crystalline product contains the target crystalline product and impurities. In one embodiment, the content of the target crystals in the crude crystalline product (i.e., the purity of the crude crystalline product) is 95-99.5 wt%, preferably 97-99.5 wt%. "Purified crystalline product" refers to the crystalline product after washing. The purified crystalline product is rich in the target crystalline product, or even consists essentially of the target crystalline product. In one embodiment, the content of the target crystals in the purified crystalline product (i.e., the purity of the purified crystalline product) is 99-99.99 wt%, preferably 99.5-99.99 wt%.

[0047] The target crystal is selected from aromatic compounds. In one variation, the aromatic compound is selected from substituted or unsubstituted benzene and / or substituted or unsubstituted naphthalene. Preferably, the aromatic compound is selected from alkyl or halogen-substituted benzene and / or alkyl-substituted naphthalene, such as p-xylene, 2,6-diisopropylnaphthalene, mesitylene, or p-dichlorobenzene.

[0048] In one embodiment, the crude crystallized product is a crystal slurry from upstream, such as from a crystallization unit or an aging unit. Typically, the crystal slurry can be pretreated before being introduced into a washing step, particularly through solid-liquid separation in a solid-liquid separation device. The solid material obtained after this solid-liquid separation can be considered the crude crystallized product.

[0049] As is known, one of the factors affecting purification efficiency during the washing of crystalline products is the amount of washing solution used. Therefore, the amount of washing solution in step S1 needs to be determined based on the amount of crude crystalline product to be washed. This allows for timely and effective control of the washing solution amount in response to changes in the amount of crude crystalline product (if any), thus avoiding problems such as excessive washing solution leading to melting of the crystalline product or insufficient washing solution resulting in poor purification. At the start of the method, before the returned melt is used as washing solution, molten crystalline product needs to be added externally as washing solution. Accordingly, the amount of added molten crystalline product can be determined based on information about the amount of crude crystalline product.

[0050] The quantity of the crude crystallized product can be its flow rate, such as mass flow rate or volumetric flow rate. In this document, mass flow rate is used as a representative of the quantity of the stream. In one variation, the crude crystallized product is a crystal slurry from upstream, such as from a crystallization unit or aging unit. Accordingly, the flow rate (e.g., mass flow rate) of the crude crystallized product can be calculated by obtaining the flow rate (e.g., mass flow rate) and solid content of the crystal slurry, wherein the calculation is based on the following formula: Crude crystallized product (mass) flow rate = Crystal slurry (mass) flow rate × Crystal slurry solid content. For example, the crystal slurry (mass) flow rate and solid content are obtained by a flow measurement device. In another variation, the upstream crystal slurry can undergo solid-liquid separation to obtain crystallization mother liquor and crude crystallized product. In this case, the flow rate (e.g., mass flow rate) of the crude crystallized product can be calculated by obtaining the flow rate (e.g., mass flow rate) of the crystal slurry and the flow rate (e.g., mass flow rate) of the crystallization mother liquor, wherein the calculation is based on the following formula: Crude crystallized product (mass) flow rate = Crystal slurry (mass) flow rate - Crystallization mother liquor (mass) flow rate discharged after solid-liquid separation. For example, the (mass) flow rate of the crystal slurry and the (mass) flow rate of the crystallization mother liquor can be obtained separately using flow measurement equipment.

[0051] The present invention does not impose any particular limitation on the amount of washing liquid used. Preferably, the flow rate (e.g., mass flow rate) of the washing liquid is 0.2-0.4 times the flow rate (e.g., mass) of the crude crystallized product.

[0052] In one embodiment, the method of the present invention further includes: a control step C1: obtaining information on the flow rate of the washing liquid, and adjusting the flow rate of the second portion of the melt returning to step S1 based on the information. In a variant, a correspondence table relating the flow rate of the washing liquid to the flow rate of the second portion of the melt returning to step S1 is pre-established. Then, information on the flow rate of the washing liquid is obtained, and the flow rate of the second portion of the melt returning to step S1 is adjusted based on the information and the correspondence table.

[0053] In this document, for convenience, the adjusted flow rate (by mass) of the material is expressed as a multiple of the flow rate (by mass) of the coarse crystalline product. Preferably, the flow rate (by mass) of the second portion of the melt returned to step S1 is 0.03-0.35 times, more preferably 0.05-0.25 times, of the flow rate (by mass) of the coarse crystalline product, for example, 0.03 times, 0.04 times, 0.05 times, 0.08 times, 0.1 times, 0.12 times, 0.15 times, 0.2 times, 0.24 times, 0.26 times, 0.31 times, or 0.35 times. In control step C1, adjusting the amount (e.g., flow rate, such as mass flow rate) of the second portion of the melt returned to step S1 based on the aforementioned information can be accomplished through valve operation.

[0054] In one embodiment, the method of the present invention further includes: a control step C2: obtaining information on the liquid level of the melt of the crystallized product in step S2, and adjusting the flow rate of the third portion of the melt based on the information. Similarly, the adjustment can be based on a predetermined relational table. The adjustment can be performed by valve operation. The flow rate of the third portion of the melt is adjusted so that the liquid level of the melt of the crystallized product in step S2 remains constant or substantially constant. "Substantially constant" means that the absolute value of the difference in flow rate before and after the change is 5% or less of the flow rate before the change, preferably 3% or less, more preferably 1% or less.

[0055] In one embodiment, the (mass) flow rate of the third melt can be 0.5-0.9 times, preferably 0.6-0.8 times, of the (mass) flow rate of the crude crystallized product, for example, 0.5 times, 0.6 times, 0.65 times, 0.68 times, 0.7 times, 0.74 times, 0.8 times, or 0.9 times.

[0056] In one embodiment, the method of the present invention further includes: a control step C3: obtaining information on the temperature of the first portion of the melt, and adjusting the flow rate of the first portion of the melt based on the information. Without considering heat loss, the temperature of the first portion of the melt is the same as the temperatures of the second and third melts and the melt in the melter. Accordingly, the flow rate of the first portion of the melt can also be adjusted by obtaining information on the temperatures of the second and third melts or the melt in the melter. In a variant, the method of the present invention further includes: a control step C4: obtaining information on the temperature of the heated melt and the flow rate of the first portion of the melt, and adjusting the flow rate of the first portion of the melt based on the information. That is, control step C3 can be replaced by control step C4. Similarly, the adjustment can be based on a predetermined relational mapping table. The adjustment can be accomplished through valve operation.

[0057] In one embodiment, the (mass) flow rate of the first portion of the melt is 1-10 times, preferably 1-6 times, more preferably 1.5-3 times, of the (mass) flow rate of the crude crystallized product, for example, 1, 1.3, 1.65, 1.67, 1.75, 1.82, 2.33, 2.76, 3, 3.5, 5, 6, 7, 8, 9, or 10 times.

[0058] As is known, one of the factors affecting the purification effect during the washing of crystalline products is the temperature of the washing solution. Therefore, in one embodiment, the method of the present invention further includes: a control step C5: obtaining information on the temperature of the washing solution and adjusting the flow rate of the bypass stream based on the information. Similarly, the adjustment can be based on a predetermined relational table. The adjustment can be accomplished by valve operation. In the method of the present invention, a first portion of the melt is heated to obtain a heated melt. A portion of the heated melt is returned to step S2 as the main stream, and the remaining portion of the heated melt is returned to step S1 as a bypass stream for use as the washing solution. Simultaneously, a second portion of the melt is also returned to step S1 as the washing solution. The bypass stream returned to step S1 and the second portion of the melt returned to step S1 together serve as the washing solution used in step S1. Since the former is a heated melt and the latter is an unheated melt, the former will provide heat for heating the mixture of the two. Therefore, the temperature of the former is an important factor in adjusting the temperature of the washing solution (i.e., the mixture of the two). Accordingly, by controlling step C5, the temperature of the washing solution during washing can be controlled in a timely and effective manner in response to changes in the amount of crude crystalline product (if any), thereby avoiding problems such as the crystal product melting due to excessively high washing solution temperature or poor purification effect due to excessively low washing solution temperature.

[0059] In one embodiment, in control step C5, the temperature of the washing liquid is 10-30°C higher than the melting point of the target crystalline product, preferably 15-27°C, for example, 10°C, 12°C, 15°C, 16.7°C, 17.8°C, 19.5°C, 21.7°C, 23°C, 25°C, 27°C, 29°C, or 30°C higher than the melting point of the target crystalline product.

[0060] In the method of this invention, the bypass stream returned to step S1 and the second portion of the melt returned to step S1 are used together as the washing liquid in step S1. The amount (e.g., flow rate, particularly mass flow rate) of the bypass stream returned to S1 is adjusted by controlling step C5. Simultaneously, the amount (e.g., flow rate, such as mass flow rate) of the second portion of the melt returned to step S1 is adjusted by controlling step C1. Accordingly, the temperature and amount of the washing liquid can be easily and promptly changed, which better ensures the purification effect and thus allows for the efficient acquisition of purified crystalline products.

[0061] In the method of this invention, the first portion of the melt is heated to obtain a heated melt. A portion of the heated melt is returned to step S2 as the main stream, and the remaining portion is returned to step S1 as a bypass stream. Simultaneously, the second portion of the melt is returned to step S1. In one embodiment, the temperature of the heated melt is 30-75°C higher than the melting point of the target crystalline product, preferably 50-70°C, for example, 30°C, 36°C, 46°C, 56°C, 66°C, 70°C, 72°C, or 75°C higher. Simultaneously, the temperature of the heated melt should be lower than the vaporization temperature of the target crystalline product. The bypass stream returned to step S1 and the second portion of the melt returned to step S1 together serve as the washing liquid used in step S1. In this case, the temperature of the bypass stream is equal to the temperature of the main stream and also equal to the temperature of the heated melt. Furthermore, the temperature of the washing liquid is lower than the temperature of the bypass stream. The main stream returned to step S2 will provide the heat required for melting the solid-phase crystalline product in step S2. Accordingly, the temperature of the melt of the obtained crystalline product is lower than the temperature of the main stream returning to step S2.

[0062] In the method of this invention, the temperature of the melt is lower than the temperature of the washing liquid. In one embodiment, the temperature of the melt is 5-25°C lower than the temperature of the washing liquid, preferably 5-20°C lower, for example, 5°C, 7°C, 9°C, 10°C, 15°C, 17°C, 20°C, 23°C, or 25°C. For example, the melt temperature can be 5-18°C higher than the melting point of the target crystalline product, preferably 6-15°C, for example, 6°C, 8°C, 10°C, 12°C, or 14°C higher than the melting point of the target crystalline product, which ensures product transport while reducing process energy consumption. In the method of this invention, the temperature of the heated melt > the temperature of the washing liquid > the temperature of the melt > the melting point of the target crystalline product.

[0063] In the method of the present invention, the first portion of the melt is heated to obtain a heated melt. A portion of the heated melt is returned to step S2 as the main stream, and the remaining portion of the heated melt is returned to step S1 as a bypass stream. The mixture of the bypass stream returned to step S1 and the second portion of the melt returned to step S1 is used as a washing liquid in step S1. In one embodiment, the (mass) flow rate ratio of the main stream to the bypass stream is (90-99):(1-10), preferably (94-98):(2-6). Accordingly, the bypass stream is 1-10% of the mass of the heated melt, preferably 2-6%, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%. In one embodiment, the bypass stream accounts for 10-60% of the mass of the washing liquid, preferably 20-50%, for example 10%, 11%, 16%, 20%, 24%, 26%, 30%, 24%, 38%, 43%, 45%, 50%, 55%, and 60%.

[0064] The present invention does not impose any particular limitations on the method used to heat the first portion of the liquid phase. Preferably, the first portion of the liquid phase is heated by heat exchange. The heat exchanger used for heating by heat exchange is a wall-mounted heat exchanger, such as a plate heat exchanger, a tubular heat exchanger, or a shell-and-tube heat exchanger. The present invention does not impose any particular limitations on the heating medium used for heating by heat exchange; for example, it can be a high-temperature material from the upstream or downstream operating unit, or it can be an external high-temperature material. Preferably, using a high-temperature material from the upstream or downstream operating unit as the heating medium of the heat exchanger can further reduce the overall energy consumption of the upstream and downstream processes.

[0065] In one embodiment, the method of the present invention further includes: a control step C6: obtaining information on the temperature of the heated melt and adjusting the flow rate of the heating medium based on the information. In a variant, the method of the present invention further includes: a control step C7: obtaining information on the temperature of a first portion of the melt and adjusting the flow rate of the heating medium based on the information. That is, control step C6 can be replaced by control step C7. Similarly, the adjustment can be based on a predetermined relational mapping table. The adjustment can be accomplished through valve operation.

[0066] In one variation, the present invention provides a method for washing crystallized products, characterized in that the method comprises:

[0067] S1: Wash the crude crystalline product with a washing solution to obtain a washing filtrate and a solid phase of crystalline product;

[0068] S2: Melt the solid-phase crystalline product to obtain a melt of the crystalline product;

[0069] In this process, the first part of the melt is heated to obtain a heated melt. A portion of the heated melt is returned to step S2 as the main flow, and the remaining portion of the heated melt is returned to step S1 as a bypass flow.

[0070] The second part of the melt returns to step S1;

[0071] The third portion of the melt is discharged as a purified crystallized product, and

[0072] The method further includes at least one of the following control steps:

[0073] Control step C1: Obtain information on the flow rate of the washing liquid, and adjust the flow rate of the second part of the melt returning to step S1 based on the information;

[0074] Control step C2: Obtain information on the liquid level of the molten material of the crystallized product in step S2, and adjust the flow rate of the third part of the molten material based on the information;

[0075] Control step C3: Obtain information on the temperature of the first portion of the melt, and adjust the flow rate of the first portion of the melt based on the information;

[0076] Control step C5: Obtain information on the temperature of the washing liquid and adjust the flow rate of the main pipeline based on the information; and

[0077] Control step C6: Obtain information on the temperature of the heated melt and adjust the flow rate of the heating medium based on the information.

[0078] Preferably, in the method of the present invention,

[0079] Control step C3 is replaced with: Control step C4: Obtaining information on the temperature of the heated melt and the flow rate of the first portion of the melt, and adjusting the flow rate of the first portion of the melt based on the information; and / or

[0080] Control step C6 is replaced with: Control step C7: Obtain information on the temperature of the first part of the melt, and adjust the flow rate of the heating medium based on the information.

[0081] In one embodiment, the method further includes: preparing a crude crystalline product, which is obtained by solid-liquid separation of an upstream crystal slurry.

[0082] In one implementation, the preparation and washing of the crude crystallized product are carried out simultaneously. For example, in a solid-liquid separator, the upstream crystal slurry is separated into a mother liquor and the crude crystallized product. The mother liquor is discharged, and the remaining crude crystallized product is washed to obtain a washing filtrate and a solid phase of the crystallized product. The solid-liquid separator can be a centrifuge, filter, washing tower, etc.

[0083] A second aspect of the present invention provides an apparatus for carrying out the above-described method, the apparatus comprising: a scrubber for washing a crude crystalline product to obtain a solid crystalline product and a washing filtrate; and a melter comprising: a melting zone for melting the solid crystalline product to obtain a melt of the crystalline product; wherein the melter is provided with three outlet pipes: a first outlet pipe connected to a heat exchanger, wherein the heat exchanger is provided with a main outlet pipe connected to the melting zone; and an outlet bypass pipe connected to the scrubber; a second outlet pipe connected to the scrubber; and a third outlet pipe connected to a product outlet.

[0084] In one embodiment, the apparatus of the present invention further includes: a valve disposed on a second outlet pipe, which is connected to a first controller, the first controller receiving information on the flow rate of the washing liquid and sending a signal to the valve to adjust the flow rate of the second portion of the melt flowing through the second outlet pipe to the washer. In a variant, the first controller is provided with a correspondence table relating the flow rate of the washing liquid to the flow rate of the second portion of the melt returning to step S1.

[0085] In one embodiment, the apparatus of the present invention further includes: a valve disposed on a third outlet pipe, which is connected to a second controller. The second controller receives information on the liquid level of the molten material of the crystallized product from a liquid level monitoring device disposed on the melt, and sends a signal to the valve to adjust the flow rate of the third portion of the molten material flowing through the third outlet pipe to the product outlet. In a variant, the second controller is provided with a correspondence table relating the liquid level of the molten material in the melt to the flow rate of the third portion of the molten material flowing to the product outlet.

[0086] In one embodiment, the apparatus of the present invention further includes: a valve disposed on a first outlet pipe, which is connected to a third controller, the third controller receiving information about the temperature of the first partial melt and sending a signal to the valve to adjust the flow rate of the first partial melt flowing through the first outlet pipe to the heat exchanger. Without considering heat loss, the temperature of the first partial melt is the same as the temperatures of the second and third melts and the melt in the melter. Accordingly, it is possible to obtain information about the temperatures of the second and third melts or the melt in the melter through an additional controller and send a signal to the valve disposed on the first outlet pipe to adjust the flow rate of the first partial melt flowing through the first outlet pipe to the heat exchanger. The additional controller may be disposed on the second outlet pipe, the third outlet pipe, or the melter. In a variation, the third controller includes a table showing the relationship between the temperature of the first partial melt and the flow rate of the first partial melt flowing to the heat exchanger. In one variation, the apparatus further includes a valve disposed in the first outlet pipe, which is connected to a fourth controller and a fifth controller. The fifth controller receives information about the temperature of the heated molten material and sends a signal to the fourth controller. The fourth controller receives information from the fifth controller and obtains information about the flow rate of the first portion of the molten material, and sends a signal to the valve to adjust the flow rate of the first portion of the molten material flowing through the first outlet pipe to the heat exchanger. In another variation, the apparatus further includes a valve disposed in the first outlet pipe, which is connected to a fifth controller. The fifth controller receives information about the temperature of the heated molten material and sends a signal to the valve to adjust the flow rate of the first portion of the molten material flowing through the first outlet pipe to the heat exchanger. In one variation, the fifth controller includes a table showing the relationship between the temperature of the heated molten material and the flow rate of the first portion of the molten material flowing to the heat exchanger.

[0087] In one embodiment, the apparatus of the present invention further includes: a valve disposed on the outlet bypass, which is connected to a sixth controller, the sixth controller receiving information about the washing liquid temperature and sending a signal to the valve to adjust the flow rate of the bypass stream flowing into the washer through the outlet bypass. In a variant, the sixth stream controller includes a table showing the relationship between the washing liquid temperature and the flow rate of the bypass stream. In another variant, the apparatus of the present invention further includes: a washing liquid inlet pipe disposed on the washer, equipped with a temperature monitoring device to provide washing liquid temperature information to the sixth controller.

[0088] In one embodiment, the apparatus of the present invention further includes: a valve disposed on the heat exchanger, which is connected to a seventh controller, the seventh controller receiving information about the temperature of the heated melt and sending a signal to the valve to adjust the flow rate of the heating medium flowing through the heat exchanger. In a variant, the seventh flow controller includes a table showing the relationship between the temperature of the heated melt and the flow rate of the heating medium flowing through the heat exchanger. In another variant, the apparatus of the present invention further includes: a valve disposed on the heat exchanger, which is connected to an eighth controller, the eighth controller receiving information about the temperature of a first portion of the melt and sending a signal to the valve to adjust the flow rate of the heating medium flowing through the heat exchanger. In another variant, the eighth controller includes a table showing the relationship between the temperature of the first portion of the melt and the flow rate of the heating medium flowing through the heat exchanger.

[0089] In one embodiment, the main outlet of the heat exchanger is connected to a liquid phase inlet located at the top or bottom of the molten zone, preferably at the bottom of the molten zone. In a variation, multiple liquid phase inlets are provided at the top or bottom of the molten zone, preferably the multiple liquid phase inlets are evenly distributed.

[0090] In one embodiment, the melt further includes at least one refining zone for receiving melt from the melting zone. The at least one refining zone refers to, for example, one, two, three, etc. In one embodiment, the melt includes one or two refining zones.

[0091] The at least one clarifying zone may be located on one or both sides of the molten zone. For example, when there are two clarifying zones, the two clarifying zones may be located on both sides of the molten zone respectively.

[0092] In one embodiment, the melting zone is separated from the at least one clarifying zone by a baffle, preferably without openings. The invention does not impose any particular limitation on the height of the baffle, but preferably the height of the baffle is 1 / 3 to 3 / 5 of the height of the melter.

[0093] The scrubber can be any type in the art, such as a centrifuge, pressure filter, vacuum filter, or scrubbing tower.

[0094] The heat exchanger can be any type of indirect heat exchanger in the art, such as a plate heat exchanger, a tube heat exchanger, a shell-and-tube heat exchanger, etc.

[0095] The controller can be a flow monitoring device, a temperature monitoring device, etc.

[0096] Inlets, outlets, or monitoring ports can be provided on the scrubber and melter. For example, to introduce the solid-phase crystallized product from the scrubber and the returned melt (i.e., the main stream entering the melter), a solid phase inlet and a liquid phase inlet are provided in the melting zone of the melter. The solid phase inlet and the liquid phase inlet can be the same port or different ports. One or multiple liquid phase inlets can be provided, evenly arranged. For example, to monitor the liquid level, a level gauge port is preferably provided in the clarification zone of the melter. For example, to draw out the melt from the melting zone, a liquid phase outlet is provided in the clarification zone of the melter. When there are two or more clarification zones, liquid phase outlets can be provided in each clarification zone.

[0097] Referring to Figure 1, (a), (b), (c), and (d) of Figure 1 respectively show schematic diagrams of the structures of different melters used in this invention.

[0098] As shown in Figure 1(a), the melter includes a cylinder 1, wherein the internal space of the cylinder 1 is divided into a melting zone I and a clarifying zone II by a baffle 2. A solid phase inlet 3 is provided at the top of the melting zone I, wherein the solid phase inlet 3 also serves as a liquid phase inlet. A liquid level gauge port 5 and a liquid phase outlet 4 are provided on the clarifying zone II.

[0099] As shown in Figure 1(b), the melter includes a cylinder 1, wherein the internal space of the cylinder 1 is divided into a melting zone I, a first clarification zone II-1 and a second clarification zone II-2 by two baffles 2. The first clarification zone II-1 and the second clarification zone II-2 are located on both sides of the melting zone I. A solid phase inlet 3 is provided at the top of the melting zone I, wherein the solid phase inlet 3 also serves as a liquid phase inlet. A liquid level gauge 5 and a molten liquid phase outlet 4 are provided on the first clarification zone II-1 and the second clarification zone II-2, respectively.

[0100] As shown in Figure 1(c), the melter includes a cylinder 1, wherein the internal space of the cylinder 1 is divided into a melting zone I and a clarifying zone II by a baffle 2. The top of the melting zone I is provided with a solid phase inlet 3 and a liquid phase inlet 6, and the clarifying zone II is provided with a liquid level gauge port 5 and a molten liquid phase outlet 4.

[0101] As shown in Figure 1(d), the melter includes a cylinder 1, wherein the internal space of the cylinder 1 is divided into a melting zone I and a clarifying zone II by a baffle 2. A solid phase inlet 3 is provided at the top of the melting zone I, and three liquid phase inlets 6 are provided at the bottom of the melting zone I. A liquid level gauge port 5 and a molten liquid phase outlet 4 are provided on the clarifying zone II.

[0102] The third aspect of the present invention provides a method for washing a crystallized product, which is carried out in the apparatus described in the second aspect. The method includes: (1) washing the crude crystallized product with a washing liquid in a scrubber to obtain a solid-phase crystallized product and a washing filtrate; (2) introducing the solid-phase crystallized product into the melting zone of a melter for melting to obtain a melt of the crystallized product; wherein the melt enters the three outlet pipes respectively; a first portion of the melt is introduced into the heat exchanger through the first outlet pipe connected to the heat exchanger for heating to obtain a heated melt, a portion of the heated melt is returned to the melting zone as the main flow through the main outlet pipe, and the remaining portion of the heated melt is returned to the scrubber as the bypass flow through the outlet bypass pipe; a second portion of the melt is returned to the scrubber through the second outlet pipe connected to the scrubber; and a third portion of the melt is discharged through the third outlet pipe as the product outlet as a purified crystallized product.

[0103] Referring to Figure 2, a flowchart of one embodiment of the method of the present invention is shown. In this embodiment, the flow of the material is shown as a solid line. Specifically, crystal slurry 101 is fed into a scrubber C101 for solid-liquid separation to obtain crystallization mother liquor 102 and crude crystal product. Crystallization mother liquor 102 is discharged from scrubber C101, while the crude crystal product remains in scrubber C101. The crude crystal product is washed in C101 by washing liquid 103 and undergoes solid-liquid separation to obtain washing filtrate 104 and solid-phase crystal product 105. Washing filtrate 104 is discharged from scrubber C101, while solid-phase crystal product 105 is fed into a melter D101. In melter D101, solid-phase crystal product 105 is melted to obtain melt 106 of the crystal product. The melt 106 is pumped by product pump P101 into the first outlet pipeline, the second outlet pipeline, and the third outlet pipeline, and discharged as the first portion melt 107, the second portion melt 109, and the third portion melt 110, respectively. The first portion melt 107 is fed into heat exchanger E101 for heating to obtain heated melt 108, wherein heat exchanger E101 uses heating medium 201 to provide heat. A portion of the heated melt 108 returns to the melting zone of melter D101 as main stream 108-1 through the main outlet of the heat exchanger, and the remainder returns to scrubber C101 as bypass stream 108-2 through the outlet bypass. The second portion melt 109 returns to scrubber C101. The mixture of bypass stream 108-2 and the second portion melt 109 returned to scrubber C101 is used as scrubbing liquid 103 in scrubber C101. The third portion melt 110 is discharged through the third outlet pipeline as a purified crystallized product.

[0104] Referring again to Figure 2, in the described embodiment, the process is controlled as shown by the dashed lines. Specifically, flow measurement devices FI, installed on the inlet and outlet pipes of the scrubber C101, measure the mass flow rate of the crystal slurry 101 and the mass flow rate of the crystallization mother liquor 102, respectively. The obtained mass flow rates are input to a flow monitoring device FC, installed on the inlet pipe of the washing liquid 103 of the scrubber C101, thereby obtaining information on the mass flow rate of the crude crystallized product and the mass flow rate of the washing liquid 103, and sending a signal to a valve installed on the second outlet pipe to adjust the mass flow rate of the second portion of melt 109 flowing through the second outlet pipe to the scrubber C101. A level monitoring device LC, installed on the melter D101, provides information on the level of the molten crystallized product and sends a signal to a valve installed on the third outlet pipe to adjust the mass flow rate of the third portion of melt 110 flowing through the third outlet pipe to the product outlet. The temperature monitoring device TC installed on the first outlet pipeline provides information on the temperature of the first portion of the melt 107 and sends a signal to the valve installed on the first outlet pipeline to adjust the mass flow rate of the first portion of the melt 107 flowing through the first outlet pipeline to the heat exchanger E101. The temperature monitoring device TC installed at the heat exchanger outlet provides information on the temperature of the heated melt 108 and sends a signal to the valve installed on the heat exchanger E101 to adjust the mass flow rate of the heating medium 201 flowing through the heat exchanger. The temperature monitoring device TC installed on the inlet pipeline of the washing liquid 103 of the scrubber C101 provides information on the temperature of the washing liquid and sends a signal to the valve installed on the outlet bypass to adjust the mass flow rate of the bypass stream 108-2 flowing into the scrubber C101 through the outlet bypass.

[0105] Referring to Figure 3, a flowchart of one embodiment of the method of the present invention is shown. In the embodiment shown in Figure 2, the material flow is the same as in the embodiment shown in Figure 2, but the process control is different, particularly the adjustment of the mass flow rate of the first portion of the melt 107 and the adjustment of the mass flow rate of the heating medium 201 flowing through the heat exchanger. Specifically, in the embodiment shown in Figure 3, a temperature monitoring device TC located at the heat exchanger outlet acquires the temperature information of the heated melt 108 and sends it to a flow monitoring device FC located on the first outlet pipeline of the melt D101. The flow monitoring device FC receives the temperature information of the heated melt 108 and acquires the mass flow rate information of the first portion of the melt 107, and then sends a signal to a valve located on the first outlet pipeline to adjust the mass flow rate of the first portion of the melt 107 flowing through the first outlet pipeline to the heat exchanger E101. The temperature monitoring device TC located on the first outlet pipeline provides the temperature information of the first portion of the melt 107 and sends a signal to a valve located on the heat exchanger E101 to adjust the mass flow rate of the heating medium 201 flowing through the heat exchanger.

[0106] Referring to Figure 4, a flowchart of one embodiment of the prior art is shown. In this embodiment, the flow of materials is shown as solid lines. Specifically, crystal slurry 101 is fed into a scrubber C101 for solid-liquid separation, yielding crystallization mother liquor 102 and crude crystal product. Crystallization mother liquor 102 is discharged from scrubber C101, while the crude crystal product remains in scrubber C101. The crude crystal product is washed in C101 by washing liquid 103, and solid-liquid separation is performed, yielding washing filtrate 104 and solid-phase crystal product 105. Washing filtrate 104 is discharged from scrubber C101, while solid-phase crystal product 105 is fed into a melter D101. In melter D101, solid-phase crystal product 105 is melted to obtain melt 106 of the crystal product. The melt 106 is pumped by product pump P101 into the first outlet pipeline, the second outlet pipeline, and the third outlet pipeline, and discharged as the first portion of melt 107, the second portion of melt 109, and the third portion of melt 110, respectively. The first portion of melt 107 is sent to heat exchanger E101 for heating to obtain heated melt 108. The heated melt 108 is returned entirely to the melting zone of melter D101. The second portion of melt 109 is returned to scrubber C101. The second portion of melt 109 returned to scrubber C101 is used as the washing liquid 103 of scrubber C101. The third portion of melt 110 is discharged through the third outlet pipeline as the product outlet, as the purified crystallized product.

[0107] Referring again to Figure 4, in the described embodiment, the process is controlled as shown by the dashed lines. Specifically, a flow monitoring device FC, located on the inlet pipe of the washing liquid 103 in the scrubber C101, provides information on the mass flow rate of the washing liquid 103 and signals a valve located on the second outlet pipe to adjust the mass flow rate of the second partial melt 109 flowing through the second outlet pipe to the scrubber C101. A level monitoring device LC, located on the melter D101, provides information on the level of the melt of the crystallized product and signals a valve located on the third outlet pipe to adjust the mass flow rate of the third partial melt 110 flowing through the third outlet pipe to the product outlet. A temperature monitoring device TC, located on the first outlet pipe, provides information on the temperature of the first partial melt 107 and signals a valve located on the first outlet pipe to adjust the mass flow rate of the first partial melt 107 flowing through the first outlet pipe to the heat exchanger E101. The temperature monitoring device TC installed on the first outlet pipeline provides information on the temperature of the first portion of the melt 107 and sends a signal to the valve installed on the heat exchanger E101 to adjust the mass flow rate of the heating medium 201 flowing through the heat exchanger.

[0108] Referring to Figure 5, a flowchart of one embodiment of the prior art is shown. In this embodiment, the flow of materials is shown as solid lines. Specifically, crystal slurry 101 is fed into a scrubber C101 for solid-liquid separation, yielding crystallization mother liquor 102 and crude crystal product. Crystallization mother liquor 102 is discharged from scrubber C101, while the crude crystal product remains in scrubber C101. The crude crystal product is washed in C101 by washing liquid 103 and undergoes solid-liquid separation, yielding washing filtrate 104 and solid-phase crystal product 105. Washing filtrate 104 is discharged from scrubber C101, while solid-phase crystal product 105 is fed into a melter D101. In melter D101, solid-phase crystal product 105 is melted to obtain a melt 106 of the crystal product. The melt 106 is pumped by product pump P101 into a first outlet pipe and a third outlet pipe, and discharged as a first portion of melt 107 and a third portion of melt 110, respectively. The first portion of the melt 107 is fed into heat exchanger E101 for heating, resulting in heated melt 108. Heat exchanger E101 uses heating medium 201 to provide heat. A portion of the heated melt 108 returns to the melting zone of melter D101 as main stream 108-1 via the main outlet of the heat exchanger, while the remainder is sent to cooler E102 as bypass stream 108-2 via the outlet bypass of the heat exchanger. In cooler E102, bypass stream 108-2 exchanges heat with cooling medium 202, resulting in cooled bypass stream 108-2, which is then sent to scrubber C101 via the scrubbing liquid inlet pipe to be used as scrubbing liquid 103. The third portion of the melt 110 is discharged through the third outlet pipe as a purified crystallized product.

[0109] Referring again to Figure 5, in the described embodiment, the process is controlled as shown by the dashed lines. Specifically, a level monitoring device LC installed on the melter D101 provides information on the level of the molten material of the crystallized product and signals a valve installed on the third outlet pipe to adjust the mass flow rate of the third portion of the melt 110 flowing through the third outlet pipe to the product outlet. A flow monitoring device FC installed on the first outlet pipe provides information on the mass flow rate of the first portion of the melt 107 and signals a valve installed on the first outlet pipe to adjust the mass flow rate of the first portion of the melt 107 flowing through the first outlet pipe to the heat exchanger E101. A temperature monitoring device TC installed on the first outlet pipe provides information on the temperature of the first portion of the melt 107 and signals a valve installed on the heat exchanger E101 to adjust the mass flow rate of the heating medium 201 flowing through the heat exchanger. A flow monitoring device FC installed on the outlet bypass provides information on the mass flow rate of the bypass stream 108-2 and signals a valve installed on the outlet bypass to adjust the mass flow rate of the bypass stream 108-2 flowing through the outlet bypass to the cooler E102. The temperature monitoring device TC installed on the inlet pipe of the washing liquid 103 in the scrubber C101 provides information on the temperature of the washing liquid and sends a signal to the valve installed on the cooler E102 to adjust the mass flow rate of the cooling medium 202 flowing through the cooler.

[0110] Example

[0111] The following embodiments are used to further illustrate this application, but are not intended to limit this application.

[0112] Sample purity testing:

[0113] The purity of the sample was obtained by gas chromatography analysis using an Agilent GC 6890 gas chromatograph.

[0114] Specifically:

[0115] The purity of the paraxylene samples was tested using the petrochemical industry standard SH / T 1486.1-2008 Petroleum paraxylene.

[0116] The purity of the dichlorobenzene sample was tested according to the chemical industry standard "HG / T 4489-2020".

[0117] The purity of the xylene sample was tested according to the enterprise standard "Q / PSHD009-2020".

[0118] The purity of 2,6-diisopropylnaphthalene samples was tested using the following method: FID detector, HP-PONA column (50m×0.2mm×0.50μm), injection volume 0.2~0.4μL (crystalline product dissolved in cyclohexane), split ratio 100:1, carrier gas pressure 41psi, flow rate 0.8ml / min, injection port temperature 250℃, detector temperature 300℃, and temperature program: hold at 200℃ for 5min, then increase to 300℃ at 5℃ / min, and hold at this temperature for 10min.

[0119] Example 1

[0120] In this embodiment, the flowchart shown in Figure 2 is used to wash the crystal slurry 101.

[0121] Washer C101 is a centrifuge.

[0122] The melter D101 adopts the structure shown in Figure 1(a), wherein the height of the baffle 2 is 1 / 3 of the height of the cylinder 1.

[0123] Heat exchanger E101 uses high-temperature material (100°C material) from the upstream paraxylene (PX) crystallization unit as heating medium 201.

[0124] Slurry 101 is a slurry from the upstream para-xylene (PX) crystallization unit at a temperature of 8.5°C. Slurry 101 undergoes pre-solid-liquid separation in scrubber C101 to obtain mother liquor 102 and crude crystallized product. As described above, gas chromatography analysis of the crude crystallized product confirms its purity (i.e., the PX content in the crude crystallized product) to be 99.3%. Flow measurement devices FI, installed on the inlet and outlet pipes of scrubber C101, measure the mass flow rate of slurry 101 and the mass flow rate of mother liquor 102, and use these two measurements to determine the mass flow rate of the crude crystallized product remaining in scrubber C101.

[0125] In this embodiment, the process is controlled as follows: A flow monitoring device FC, located on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve on the second outlet pipe to adjust the mass flow rate of the second partial melt 109 to 0.24 times the mass flow rate of the coarse crystallized product. A level monitoring device LC, located on the melter D101, sends a signal to a valve on the third outlet pipe to adjust the mass flow rate of the third partial melt 110 to 0.70 times the mass flow rate of the coarse crystallized product. A temperature monitoring device TC, located on the first outlet pipe, sends a signal to a valve on the first outlet pipe to adjust the mass flow rate of the first partial melt 107 to 2.02 times the mass flow rate of the coarse crystallized product. A temperature monitoring device TC, located at the heat exchanger outlet, sends a signal to a valve on the heat exchanger E101 to adjust the mass flow rate of the heating medium 201 flowing through the heat exchanger, so that the temperature of the heated melt 108 is 70°C. A temperature monitoring device TC, installed on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve installed on the outlet bypass to adjust the mass flow rate of the bypass stream 108-2 to 0.06 times the mass flow rate of the crude crystallized product (correspondingly, the bypass stream 108-2 is 2.97% of the mass of the heated melt 108). Through this control, the melter D101 operates at a temperature of 20°C, and the scrubber C101 operates at a temperature of 30°C and a mass flow rate of 0.3 times the mass flow rate of the crude crystallized product.

[0126] The energy consumption of the above process includes the heat consumption of heat exchanger E101 and the electrical energy consumption of product pump P101. The heat consumption of heat exchanger E101 is calculated based on the temperature difference and mass flow rate of the heating medium 201. The electrical energy consumption of product pump P101 is proportional to the mass flow rate of the materials passing through it (i.e., the sum of the mass flow rates of the first, second, and third melts).

[0127] In this embodiment, the heat consumption of heat exchanger E101 is 182.31 KJ, measured by the mass flow rate of a unit coarse crystallized product.

[0128] The total mass flow rate of the product stream via product pump P101 is 2.96 times that of the crude crystallization product.

[0129] As described above, the purified crystalline product (i.e., the third melt) was subjected to gas chromatography analysis, and its purity was determined to be 99.82%.

[0130] Comparative Example 1-1

[0131] Repeat Example 1, except that the flowchart shown in Figure 4 is used.

[0132] In this comparative example, the process is controlled as follows: A flow monitoring device FC, located on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve on the second outlet pipe to adjust the mass flow rate of the second portion of melt 109 to 0.3 times the mass flow rate of the coarse crystallized product. A level monitoring device LC, located on the melter D101, sends a signal to a valve on the third outlet pipe to adjust the mass flow rate of the third portion of melt 110 to 0.7 times the mass flow rate of the coarse crystallized product. A flow monitoring device FC, located on the first outlet pipe, sends a signal to a valve on the first outlet pipe to adjust the mass flow rate of the first portion of melt 107 to 2.77 times the mass flow rate of the coarse crystallized product. A temperature monitoring device TC, located on the first outlet pipe, sends a signal to a valve on the heat exchanger E101 to adjust the mass flow rate of the heating medium 201 flowing through the heat exchanger, so that the temperature of the heated melt 108 is 70°C. Through the above control, the melt D101 operates under the following conditions: the temperature is 30°C, and the scrubber C101 operates under the following conditions: the temperature of the scrubbing liquid 103 is 30°C and the amount is 0.3 times the mass flow rate of the crude crystallized product.

[0133] Comparative Example 1-1 and Example 1 were operated with the same conditions, and the yields of purified crystalline products were the same (i.e., the mass flow rate of the third melt was the same), and their purity was also the same, both being 99.82%. Under these conditions, the energy consumption of Comparative Example 1-1 and Example 1 can be better compared.

[0134] In this comparative example, the heat consumption of heat exchanger E101 is 200.40 KJ per unit mass flow rate of crude crystallized product. That is, compared with Example 1, the energy consumption of heat exchanger E101 in Comparative Example 1-1 increases by 9.92%.

[0135] As described above, the energy consumption of product pump P101 is directly proportional to the mass flow rate of the stream passing through it (i.e., the sum of the mass flow rates of the first, second, and third melts). In Example 1, the total mass flow rate of the stream passing through product pump P101 was 2.96 times the mass flow rate of the coarse crystalline product. In this comparative example, the total mass flow rate of the stream passing through product pump P101 was 3.77 times the mass flow rate of the coarse crystalline product. This means that, compared to Example 1, the energy consumption of product pump P101 in this comparative example increased by 27.36%.

[0136] Comparative Examples 1-2

[0137] Repeat Example 1, except that the flowchart shown in Figure 5 is used.

[0138] Cooler E102 uses a 20℃ ethylene glycol aqueous solution as the cooling medium 202.

[0139] In this comparative example, the process is controlled as follows: A level monitoring device LC installed on the melter D101 sends a signal to a valve on the third outlet pipeline to adjust the mass flow rate of the third portion of melt 110 to 0.7 times the mass flow rate of the coarse crystallized product. A flow monitoring device FC installed on the first outlet pipeline sends a signal to a valve on the first outlet pipeline to adjust the mass flow rate of the first portion of melt 107 to 2.32 times the mass flow rate of the coarse crystallized product. A temperature monitoring device TC installed on the first outlet pipeline sends a signal to a valve on the heat exchanger E101 to adjust the mass flow rate of the heating medium 201 flowing through the heat exchanger, so that the temperature of the heated melt 108 is 70°C. A flow monitoring device FC installed on the outlet bypass sends a signal to a valve on the outlet bypass to adjust the mass flow rate of the bypass stream 108-2 to 0.3 times the mass flow rate of the coarse crystallized product. The temperature monitoring device TC, installed on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to the valve installed on the cooler E102 to adjust the mass flow rate of the cooling medium 202 flowing through the cooler, so that the temperature of the bypass stream 108-2 is 30°C. Through the above control, the melter D101 operates under the following conditions: a temperature of 20°C, and the scrubber C101 operates under the following conditions: a washing liquid 103 temperature of 30°C and a dosage of 0.3 times the mass flow rate of the crude crystallized product.

[0140] Comparative Examples 1-2 and Example 1 operated the scrubber C101 under the same conditions, and the yields of purified crystalline products were the same (i.e., the mass flow rates of the third melt were the same), and their purities were also substantially the same. Under these conditions, the energy consumption of Comparative Examples 1-2 and Example 1 can be better compared.

[0141] In this comparative example, the total energy consumption of heat exchanger E101 and cooler E102, measured by the mass flow rate per unit of crude crystallized product, is 215.69 kJ. That is, compared to Example 1, the energy consumption of the heat exchangers and coolers in Comparative Examples 1-2 increases by 18.31%.

[0142] In Comparative Examples 1-2, the total mass flow rate of the product stream through product pump P101 was 3.02 times that of the crude crystallized product. That is, compared to Example 1, the energy consumption of product pump P101 in Comparative Examples 1-2 increased by 2.03%.

[0143] Example 2

[0144] Repeat Example 1, except that the flowchart shown in Figure 3 is used.

[0145] In this embodiment, the process is controlled as follows: A flow monitoring device FC, located on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve on the second outlet pipe to adjust the mass flow rate of the second portion of melt 109 to 0.25 times the mass flow rate of the coarse crystallized product. A level monitoring device LC, located on the melter D101, sends a signal to a valve on the third outlet pipe to adjust the mass flow rate of the third portion of melt 110 to 0.70 times the mass flow rate of the coarse crystallized product. A temperature monitoring device TC, located at the heat exchanger outlet, sends information about the temperature of the heated melt 108 to the flow monitoring device FC, located on the first outlet pipe of the melter D101. The latter receives the temperature information of the heated melt 108, obtains the mass flow rate information of the first portion of melt 107, and sends a signal to a valve on the first outlet pipe to adjust the mass flow rate of the first portion of melt 107 to 1.83 times the mass flow rate of the coarse crystallized product. Temperature monitoring device TC, installed on the first outlet pipeline, sends a signal to the valve on heat exchanger E101 to adjust the mass flow rate of heating medium 201 flowing through the heat exchanger, so that the temperature of the heated melt 108 is 75°C. Temperature monitoring device TC, installed on the inlet pipeline of washing liquid 103 in scrubber C101, sends a signal to the valve on the outlet bypass to adjust the mass flow rate of bypass stream 108-2 to 0.05 times the mass flow rate of the crude crystallized product (correspondingly, bypass stream 108-2 is 2.98% of the mass of the heated melt 108). Through the above control, melter D101 operates under the following conditions: temperature 20°C, and scrubber C101 operates under the following conditions: the amount of washing liquid 103 is 0.3 times the mass flow rate of the crude crystallized product, and the temperature is 30°C.

[0146] In this embodiment, the energy consumption of heat exchanger E101 is 182.31 KJ, measured by the mass flow rate of a unit crude crystallized product.

[0147] The total mass flow rate of the material through product pump P101 is 2.78 times the mass of the crude crystallized product.

[0148] As described above, the purified crystalline product (i.e., the third melt) was subjected to gas chromatography analysis, and its purity was determined to be 99.82%.

[0149] Comparative Example 2-1

[0150] Example 2 is repeated, except that the flowchart shown in Figure 4 is used.

[0151] In this comparative example, the process is controlled as follows: A flow monitoring device FC, located on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve on the second outlet pipe to adjust the mass flow rate of the second portion of melt 109 to 0.3 times the mass flow rate of the coarse crystallized product. A level monitoring device LC, located on the melter D101, sends a signal to a valve on the third outlet pipe to adjust the mass flow rate of the third portion of melt 110 to 0.7 times the mass flow rate of the coarse crystallized product. A flow monitoring device FC, located on the first outlet pipe, sends a signal to a valve on the first outlet pipe to adjust the mass flow rate of the first portion of melt 107 to 2.22 times the mass flow rate of the coarse crystallized product. A temperature monitoring device TC, located on the first outlet pipe, sends a signal to a valve on the heat exchanger E101 to adjust the mass flow rate of the heating medium 201 flowing through the heat exchanger, so that the temperature of the heated melt 108 is 80°C. Through the above control, the melt D101 is operated under the following conditions: temperature 30°C, and the scrubber C101 is operated under the following conditions: the amount of scrubbing liquid 103 is 0.3 times the mass flow rate of the crude crystallized product, and the temperature is 30°C.

[0152] As described above, the purified crystalline product (i.e., the third melt) was subjected to gas chromatography analysis, and its purity was determined to be 99.82%.

[0153] Comparative Example 2-1 and Example 2 operated the scrubber C101 under the same conditions, and the yields of purified crystalline products were the same (i.e., the mass flow rate of the third melt was the same), and their purity was also the same, both being 99.82%. Under these conditions, the energy consumption of Comparative Example 2-1 and Example 2 can be better compared.

[0154] In Comparative Example 2-1, the energy consumption of heat exchanger E101, measured per unit mass flow rate of coarse crystallized product, is 200.40 kJ. That is, compared to Example 2, the energy consumption of the heat exchanger in Comparative Example 2-1 increases by 9.92%.

[0155] In Comparative Example 2-1, the total mass flow rate of the material through product pump P101 was 3.22 times that of the crude crystallized product. That is, compared to Example 2, the energy consumption of the product pump in Comparative Example 2-1 increased by 15.83%.

[0156] Example 3

[0157] Example 2 is repeated, except that the melter D101 adopts the structure shown in Figure 1(b), wherein the height of the baffle 2 is 1 / 2 of the height of the cylinder 1.

[0158] Crystal slurry 101 is derived from the upstream PX crystallization unit at a temperature of 7.5°C. Crystal slurry 101 undergoes pre-solid-liquid separation in scrubber C101 to obtain crystallization mother liquor 102 and crude crystallized product. As described above, gas chromatography analysis of the crude crystallized product confirms a purity of 99.1%.

[0159] In this embodiment, the process is controlled as follows: A flow monitoring device FC, located on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve on the second outlet pipe to adjust the mass flow rate of the second portion of melt 109 to 0.22 times the mass flow rate of the coarse crystallized product. The valve on the third outlet pipe is manually adjusted so that the mass flow rate of the third portion of melt 110 is 0.70 times the mass flow rate of the coarse crystallized product. A temperature monitoring device TC, located at the heat exchanger outlet, sends information about the temperature of the heated melt 108 to the flow monitoring device FC, located on the first outlet pipe of the melter D101. The latter receives the temperature information of the heated melt 108, obtains the mass flow rate information of the first portion of melt 107, and sends a signal to a valve on the first outlet pipe to adjust the mass flow rate of the first portion of melt 107 to 2.03 times the mass flow rate of the coarse crystallized product. Temperature monitoring device TC, installed on the first outlet pipeline, sends a signal to the valve on heat exchanger E101 to adjust the mass flow rate of heating medium 201 flowing through the heat exchanger, so that the temperature of the heated melt 108 is 73°C. Temperature monitoring device TC, installed on the inlet pipeline of washing liquid 103 in scrubber C101, sends a signal to the valve on the outlet bypass to adjust the mass flow rate of bypass stream 108-2 to 0.08 times the mass flow rate of the crude crystallized product (correspondingly, bypass stream 108-2 is 3.76% of the mass of the heated melt 108). Through the above control, melter D101 operates under the following conditions: temperature 22°C, and scrubber C101 operates under the following conditions: the amount of washing liquid 103 is 0.3 times the mass flow rate of the crude crystallized product, and the temperature is 35°C.

[0160] In this embodiment, the energy consumption of heat exchanger E101 is 187.74 KJ per unit mass flow rate of the crude crystallized product. The total mass flow rate of the material through product pump P101 is 2.96 times the mass flow rate of the crude crystallized product. As described above, gas chromatography analysis of the purified crystallized product (i.e., the third melt) determined its purity to be 99.84%.

[0161] Comparative Example 3-1

[0162] Example 3 is repeated, except that the flowchart shown in Figure 4 is used.

[0163] In this comparative example, the process is controlled as follows: A flow monitoring device FC, located on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve on the second outlet pipe to adjust the mass flow rate of the second portion of melt 109 to 0.3 times the mass flow rate of the coarse crystallized product. A valve on the third outlet pipe is manually adjusted so that the mass flow rate of the third portion of melt 110 is 0.70 times the mass flow rate of the coarse crystallized product. A flow monitoring device FC, located on the first outlet pipe, sends a signal to a valve on the first outlet pipe to adjust the mass flow rate of the first portion of melt 107 to 2.60 times the mass flow rate of the coarse crystallized product. A temperature monitoring device TC, located on the first outlet pipe, sends a signal to a valve on the heat exchanger E101 to adjust the mass flow rate of the heating medium 201 flowing through the heat exchanger so that the temperature of the heated melt 108 is 80°C. Through the above control, the melt D101 is operated under the following conditions: temperature 35°C, and the scrubber C101 is operated under the following conditions: the amount of scrubbing liquid 103 is 0.3 times the mass flow rate of the crude crystallized product, and the temperature is 35°C.

[0164] As described above, the purified crystalline product (i.e., the third melt) was subjected to gas chromatography analysis, and its purity was determined to be 99.84%.

[0165] In this comparative example, the energy consumption of heat exchanger E101 is 211.26 KJ per unit mass flow rate of coarse crystallized product. That is, compared with Example 3, the energy consumption of the heat exchanger in Comparative Example 3-1 increases by 12.53%.

[0166] In Comparative Example 3-1, the total mass flow rate of the material through product pump P101 was 3.60 times that of the crude crystallized product. That is, compared to Example 3, the energy consumption of the product pump in Comparative Example 3-1 increased by 21.62%.

[0167] Example 4

[0168] Example 2 is repeated, except that the scrubber C101 is a pressure filter. The melter D101 adopts the structure shown in Figure 1(c), wherein the height of the baffle 2 is 1 / 2 of the height of the cylinder 1.

[0169] Crystal slurry 101 is derived from the upstream PX aging unit at a temperature of 7°C. Crystal slurry 101 undergoes pre-solid-liquid separation in scrubber C101 to obtain crystallization mother liquor 102 and crude crystal product. As described above, gas chromatography analysis of the crude crystal product confirms a purity of 98.9%.

[0170] In this embodiment, the process is controlled as follows: A flow monitoring device FC, located on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve on the second outlet pipe to adjust the mass flow rate of the second portion of melt 109 to 0.27 times the mass flow rate of the coarse crystallized product. The valve on the third outlet pipe is manually adjusted so that the mass flow rate of the third portion of melt 110 is 0.65 times the mass flow rate of the coarse crystallized product. A temperature monitoring device TC, located at the heat exchanger outlet, sends information about the temperature of the heated melt 108 to the flow monitoring device FC, located on the first outlet pipe of the melter D101. The latter receives the temperature information of the heated melt 108, obtains the mass flow rate information of the first portion of melt 107, and sends a signal to a valve on the first outlet pipe to adjust the mass flow rate of the first portion of melt 107 to 2.49 times the mass flow rate of the coarse crystallized product. Temperature monitoring device TC, installed on the first outlet pipeline, sends a signal to the valve on heat exchanger E101 to adjust the mass flow rate of heating medium 201 flowing through the heat exchanger, so that the temperature of the heated melt 108 is 68°C. Temperature monitoring device TC, installed on the inlet pipeline of washing liquid 103 in scrubber C101, sends a signal to the valve on the outlet bypass to adjust the mass flow rate of bypass stream 108-2 to 0.08 times the mass flow rate of the crude crystallized product (correspondingly, bypass stream 108-2 is 3.26% of the mass of the heated melt 108). Through the above control, melter D101 operates under the following conditions: temperature 25°C, and scrubber C101 operates under the following conditions: the amount of washing liquid 103 is 0.35 times the mass flow rate of the crude crystallized product, and the temperature is 35°C.

[0171] In this embodiment, the energy consumption of heat exchanger E101 is 194.07 KJ per unit mass flow rate of the crude crystallized product. The total mass flow rate of the material through product pump P101 is 3.41 times the mass flow rate of the crude crystallized product. As described above, gas chromatography analysis of the purified crystallized product (i.e., the third melt) determined its purity to be 99.85%.

[0172] Comparative Example 4-1

[0173] Example 4 is repeated, except that the flowchart shown in Figure 4 is used.

[0174] In this comparative example, the process is controlled as follows: A flow monitoring device FC, located on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve on the second outlet pipe to adjust the mass flow rate of the second portion of melt 109 to 0.35 times the mass flow rate of the coarse crystallized product. A valve on the third outlet pipe is manually adjusted to ensure that the mass flow rate of the third portion of melt 110 is 0.65 times the mass flow rate of the coarse crystallized product. A flow monitoring device FC, located on the first outlet pipe, sends a signal to a valve on the first outlet pipe to adjust the mass flow rate of the first portion of melt 107 to 2.61 times the mass flow rate of the coarse crystallized product. A temperature monitoring device TC, located on the first outlet pipe, sends a signal to a valve on the heat exchanger E101 to adjust the mass flow rate of the heating medium 201 flowing through the heat exchanger, ensuring that the temperature of the heated melt 108 is 80°C. Through the above control, the melt D101 is operated under the following conditions: temperature 35°C, and the scrubber C101 is operated under the following conditions: the amount of scrubbing liquid 103 is 0.35 times the mass flow rate of the crude crystallized product, and the temperature is 35°C.

[0175] As described above, the purified crystalline product (i.e., the third melt) was analyzed by gas chromatography, and its purity was determined to be 99.85%.

[0176] In Comparative Example 4-1, the energy consumption of heat exchanger E101, measured per unit mass flow rate of coarse crystallized product, is 212.16 kJ. That is, compared to Example 4, the energy consumption of heat exchanger E101 in Comparative Example 4-1 increases by 9.32%.

[0177] In Comparative Example 4-1, the total mass flow rate of the product stream through product pump P101 was 3.61 times that of the crude crystallized product. That is, compared to Example 4, the energy consumption of the product pump in Comparative Example 4-1 increased by 5.87%.

[0178] Example 5

[0179] Example 2 is repeated, except that the scrubber C101 is a vacuum filter. The melter D101 adopts the structure shown in Figure 1(d), wherein the height of the baffle 2 is 3 / 5 of the height of the cylinder 1.

[0180] Crystal slurry 101 is a slurry from the upstream PX aging unit, with a temperature of 6.5°C. Crystal slurry 101 undergoes pre-solid-liquid separation in scrubber C101 to obtain crystallization mother liquor 102 and crude crystal product. As described above, gas chromatography analysis of the crude crystal product confirms its purity to be 98.7%.

[0181] In this embodiment, the process is controlled as follows: A flow monitoring device FC, located on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve on the second outlet pipe to adjust the mass flow rate of the second partial melt 109 to 0.27 times the mass flow rate of the coarse crystallized product. A level monitoring device LC, located on the melter D101, sends a signal to a valve on the third outlet pipe to adjust the mass flow rate of the third partial melt 110 to 0.65 times the mass flow rate of the coarse crystallized product. The valve on the first outlet pipe is manually adjusted so that the mass flow rate of the first partial melt 107 is 1.56 times the mass flow rate of the coarse crystallized product. The valve on the heat exchanger E101 is manually adjusted to adjust the mass flow rate of the heating medium 201 flowing through the heat exchanger so that the temperature of the heated melt 108 is 86°C. A temperature monitoring device TC, installed on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve on the outlet bypass to adjust the mass flow rate of the bypass stream 108-2 to 0.08 times the mass flow rate of the crude crystallized product (correspondingly, the bypass stream 108-2 is 5.11% of the mass of the heated melt 108). Through this control, the melter D101 operates at a temperature of 20°C, and the scrubber C101 operates at a washing liquid 103 volume of 0.35 times the mass flow rate of the crude crystallized product and a temperature of 35°C.

[0182] In Example 5, the energy consumption of heat exchanger E101 was 185.93 KJ per unit mass flow rate of the crude crystalline product. The total mass flow rate of the material through product pump P101 was 2.48 times the mass flow rate of the crude crystalline product. As described above, gas chromatography analysis of the purified crystalline product (i.e., the third melt) determined its purity to be 99.84%.

[0183] Comparative Example 5-1

[0184] Example 5 is repeated, except that the flowchart shown in Figure 4 is used.

[0185] In this comparative example, the process is controlled as follows: A flow monitoring device FC, located on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve on the second outlet pipe to adjust the mass flow rate of the second portion of melt 109 to 0.35 times the mass flow rate of the coarse crystallized product. A level monitoring device LC, located on the melter D101, sends a signal to a valve on the third outlet pipe to adjust the mass flow rate of the third portion of melt 110 to 0.65 times the mass flow rate of the coarse crystallized product. The valve on the first outlet pipe is manually adjusted to make the mass flow rate of the first portion of melt 107 2.07 times the mass flow rate of the coarse crystallized product. The valve on the heat exchanger E101 is manually adjusted to adjust the mass flow rate of the heating medium 201 flowing through the heat exchanger so that the temperature of the heated melt 108 is 92°C. Through the above control, the melt D101 is operated under the following conditions: temperature 35°C, and the scrubber C101 is operated under the following conditions: the amount of scrubbing liquid 103 is 0.35 times the mass flow rate of the crude crystallized product, and the temperature is 35°C.

[0186] As described above, the purified crystalline product (i.e., the third melt) was subjected to gas chromatography analysis, and its purity was determined to be 99.84%.

[0187] In Comparative Example 5-1, the energy consumption of heat exchanger E101, measured per unit mass flow rate of coarse crystallized product, is 213.06 KJ. That is, compared to Example 5, the energy consumption of the heat exchanger in Comparative Example 5-1 increases by 14.59%.

[0188] In Comparative Example 5-1, the total mass flow rate of the material through product pump P101 was 3.07 times that of the crude crystallized product. That is, compared to Example 5, the energy consumption of the product pump in Comparative Example 5-1 increased by 23.79%.

[0189] Comparative Example 5-2

[0190] Example 5 is repeated, except that the flowchart shown in Figure 5 is used.

[0191] In this comparative example, the process is controlled as follows: The level monitoring device LC installed on the melter D101 sends a signal to the valve on the third outlet pipeline to adjust the mass flow rate of the third portion of melt 110 to 0.65 times the mass flow rate of the coarse crystallized product. The valve on the first outlet pipeline is manually adjusted so that the mass flow rate of the first portion of melt 107 is 1.87 times the mass flow rate of the coarse crystallized product. The valve on the heat exchanger E101 is manually adjusted to adjust the mass flow rate of the heating medium 201 flowing through the heat exchanger so that the temperature of the heated melt 108 is 75°C. The flow monitoring device FC installed on the outlet bypass sends a signal to the valve on the outlet bypass to adjust the mass flow rate of the bypass stream 108-2 to 0.35 times the mass flow rate of the coarse crystallized product. The temperature monitoring device TC, installed on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to the valve on the cooler E102 to adjust the mass flow rate of the cooling medium 202 flowing through the cooler, so that the temperature of the bypass stream 108-2 is 35°C. Through the above control, the melter D101 operates under the following conditions: temperature 20°C, and the scrubber C101 operates under the following conditions: the washing liquid 103 dosage is 0.35 times the mass flow rate of the crude crystallized product, and the temperature is 35°C.

[0192] As described above, the purified crystalline product (i.e., the third melt) was subjected to gas chromatography analysis, and its purity was determined to be 99.84%.

[0193] In Comparative Example 5-1, the total energy consumption of heat exchanger E101 and cooler E102, measured per unit mass flow rate of coarse crystallized product, is 213.06 kJ. That is, compared to Example 5, the energy consumption of the heat exchanger and cooler in Comparative Example 5-1 increases by 14.59%.

[0194] Furthermore, the total material flow rate through product pump P101 is 2.87 times the mass flow rate of the crude crystallized product. That is, compared to Example 5, the energy consumption of the product pump in Comparative Example 4-2 increased by 15.73%.

[0195] Example 6

[0196] Example 2 is repeated, except that the scrubber C101 is a vacuum filter. The melter D101 adopts the structure shown in Figure 1(a), wherein the height of the baffle 2 is 1 / 3 of the height of the cylinder 1.

[0197] Heat exchanger E101 uses high-temperature material (material at 160°C) from the upstream 2,6-diisopropylnaphthalene crystallization unit as heating medium 201.

[0198] Crystal slurry 101 is a slurry from the upstream 2,6-diisopropylnaphthalene crystallization unit, with a temperature of 60°C. Crystal slurry 101 undergoes pre-solid-liquid separation in scrubber C101 to obtain crystallization mother liquor 102 and crude crystal product. As described above, gas chromatography analysis of the crude crystal product confirms its purity (i.e., the content of 2,6-diisopropylnaphthalene in the crude crystal product) to be 97.5%.

[0199] In this embodiment, the process is controlled as follows: A flow monitoring device FC, located on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve on the second outlet pipe to adjust the mass flow rate of the second portion of melt 109 to 0.23 times the mass flow rate of the coarse crystallized product. A level monitoring device LC, located on the melter D101, sends a signal to a valve on the third outlet pipe to adjust the mass flow rate of the third portion of melt 110 to 0.7 times the mass flow rate of the coarse crystallized product. A temperature monitoring device TC, located at the heat exchanger outlet, sends information about the temperature of the heated melt 108 to the flow monitoring device FC, located on the first outlet pipe of the melter D101. The latter receives the temperature information of the heated melt 108, obtains the mass flow rate information of the first portion of melt 107, and sends a signal to a valve on the first outlet pipe to adjust the mass flow rate of the first portion of melt 107 to 2.42 times the mass flow rate of the coarse crystallized product. Temperature monitoring device TC, installed on the first outlet pipeline, sends a signal to the valve on heat exchanger E101 to adjust the mass flow rate of heating medium 201 flowing through the heat exchanger, so that the temperature of the heated melt 108 is 120°C. Temperature monitoring device TC, installed on the inlet pipeline of washing liquid 103 in scrubber C101, sends a signal to the valve on the outlet bypass to adjust the mass flow rate of bypass stream 108-2 to 0.08 times the mass flow rate of the crude crystallized product (correspondingly, bypass stream 108-2 is 3.10% of the mass of the heated melt 108). Through the above control, melter D101 operates under the following conditions: temperature 80°C, and scrubber C101 operates under the following conditions: the amount of washing liquid 103 is 0.3 times the mass flow rate of the crude crystallized product, and the temperature is 90°C.

[0200] In Example 6, the energy consumption of heat exchanger E101 was 136.53 KJ per unit mass flow rate of the crude crystallized product. The total mass flow rate of the material through product pump P101 was 3.34 times the mass flow rate of the crude crystallized product. As described above, gas chromatography analysis of the purified crystallized product (i.e., the third melt) determined its purity to be 99.56%.

[0201] Comparative Example 6-1

[0202] Example 6 is repeated, except that the flowchart shown in Figure 4 is used.

[0203] In this comparative example, the process is controlled as follows: A flow monitoring device FC, located on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve on the second outlet pipe to adjust the mass flow rate of the second portion of melt 109 to 0.3 times the mass flow rate of the coarse crystallized product. A level monitoring device LC, located on the melter D101, sends a signal to a valve on the third outlet pipe to adjust the mass flow rate of the third portion of melt 110 to 0.7 times the mass flow rate of the coarse crystallized product. A flow monitoring device FC, located on the first outlet pipe, sends a signal to a valve on the first outlet pipe to adjust the mass flow rate of the first portion of melt 107 to 3.55 times the mass flow rate of the coarse crystallized product. A temperature monitoring device TC, located on the first outlet pipe, sends a signal to a valve on the heat exchanger E101 to adjust the mass flow rate of the heating medium 201 flowing through the heat exchanger, so that the temperature of the heated melt 108 is 120°C. Through the above control, the melt D101 is operated under the following conditions: temperature of 90°C, and the scrubber C101 is operated under the following conditions: the amount of scrubbing liquid 103 is 0.3 times the mass flow rate of the crude crystallized product, and the temperature is 90°C.

[0204] As described above, the purified crystalline product (i.e., the third melt) was subjected to gas chromatography analysis, and its purity was determined to be 99.56%.

[0205] In Comparative Example 6-1, the energy consumption of heat exchanger E101, measured per unit mass flow rate of coarse crystallized product, is 150.66 kJ. That is, compared to Example 6, the energy consumption of the heat exchanger in Comparative Example 6-1 increases by 10.35%.

[0206] Furthermore, in Comparative Example 5-1, the total mass flow rate of the material through product pump P101 was 4.55 times that of the crude crystallized product. That is, compared to Example 6, the energy consumption of the product pump in Comparative Example 6-1 increased by 36.23%.

[0207] Example 7

[0208] Example 2 was repeated, except that the crystal slurry 101 was derived from the upstream p-dichlorobenzene crystallization unit at a temperature of 48°C. The crystal slurry 101 underwent pre-solid-liquid separation in scrubber C101 to obtain crystallization mother liquor 102 and crude crystallized product. As described above, gas chromatography analysis of the crude crystallized product determined its purity (i.e., the p-dichlorobenzene content in the crude crystallized product) to be 99%.

[0209] In this embodiment, the process is controlled as follows: A flow monitoring device FC, located on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve on the second outlet pipe to adjust the mass flow rate of the second portion of melt 109 to 0.17 times the mass flow rate of the coarse crystallized product. A level monitoring device LC, located on the melter D101, sends a signal to a valve on the third outlet pipe to adjust the mass flow rate of the third portion of melt 110 to 0.7 times the mass flow rate of the coarse crystallized product. A temperature monitoring device TC, located at the heat exchanger outlet, sends information about the temperature of the heated melt 108 to the flow monitoring device FC, located on the first outlet pipe of the melter D101. The latter receives the temperature information of the heated melt 108, obtains the mass flow rate information of the first portion of melt 107, and sends a signal to a valve on the first outlet pipe to adjust the mass flow rate of the first portion of melt 107 to 2.33 times the mass flow rate of the coarse crystallized product. Temperature monitoring device TC, installed on the first outlet pipeline, sends a signal to the valve on heat exchanger E101 to adjust the mass flow rate of heating medium 201 flowing through the heat exchanger, so that the temperature of the heated melt 108 is 95°C. Temperature monitoring device TC, installed on the inlet pipeline of washing liquid 103 in scrubber C101, sends a signal to the valve on the outlet bypass to adjust the mass flow rate of bypass stream 108-2 to 0.13 times the mass flow rate of the crude crystallized product (correspondingly, bypass stream 108-2 is 5.51% of the mass of the heated melt 108). Through the above control, melter D101 operates under the following conditions: temperature 60°C, and scrubber C101 operates under the following conditions: the amount of washing liquid 103 is 0.3 times the mass flow rate of the crude crystallized product, and the temperature is 75°C.

[0210] In Example 7, the energy consumption of heat exchanger E101 was 159.48 KJ per unit mass flow rate of the crude crystallized product. The total mass flow rate of the material through product pump P101 was 3.21 times the mass flow rate of the crude crystallized product. As described above, gas chromatography analysis of the purified crystallized product (i.e., the third melt) determined its purity to be 99.90%.

[0211] Comparative Example 7-1

[0212] Example 7 is repeated, except that the flowchart shown in Figure 4 is used.

[0213] In this comparative example, the process is controlled as follows: A flow monitoring device FC, located on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve on the second outlet pipe to adjust the mass flow rate of the second portion of melt 109 to 0.3 times the mass flow rate of the coarse crystallized product. A level monitoring device LC, located on the melter D101, sends a signal to a valve on the third outlet pipe to adjust the mass flow rate of the third portion of melt 110 to 0.7 times the mass flow rate of the coarse crystallized product. A flow monitoring device FC, located on the first outlet pipe, sends a signal to a valve on the first outlet pipe to adjust the mass flow rate of the first portion of melt 107 to 3.87 times the mass flow rate of the coarse crystallized product. A temperature monitoring device TC, located on the first outlet pipe, sends a signal to a valve on the heat exchanger E101 to adjust the mass flow rate of the heating medium 201 flowing through the heat exchanger, so that the temperature of the heated melt 108 is 100°C. Through the above control, the melt D101 is operated under the following conditions: temperature of 75°C, and the scrubber C101 is operated under the following conditions: the amount of scrubbing liquid 103 is 0.3 times the mass flow rate of the crude crystallized product, and the temperature is 75°C.

[0214] As described above, the purified crystalline product (i.e., the third melt) was analyzed by gas chromatography, and its purity was determined to be 99.90%.

[0215] In Comparative Example 7-1, the energy consumption of heat exchanger E101, measured per unit mass flow rate of coarse crystallized product, is 188.77 kJ. That is, compared to Example 7, the energy consumption of the heat exchanger in Comparative Example 7-1 increases by 18.37%.

[0216] Furthermore, in Comparative Example 7-1, the total mass flow rate of the material through product pump P101 was 4.87 times that of the crude crystallized product. That is, compared to Example 7, the energy consumption of the product pump in Comparative Example 7-1 increased by 51.71%.

[0217] Example 8

[0218] Example 2 is repeated, except that the scrubber C101 is a pressure filter. The melter D101 adopts the structure shown in Figure 1(a), wherein the height of the baffle 2 is 1 / 3 of the height of the cylinder 1.

[0219] Crystal slurry 101 is a slurry from the upstream mesitylene crystallization unit, with a temperature of 72°C. Crystal slurry 101 undergoes pre-solid-liquid separation in scrubber C101 to obtain crystallization mother liquor 102 and crude crystallized product. As described above, gas chromatography analysis of the crude crystallized product confirms its purity (i.e., the mesitylene content in the crude crystallized product) to be 98%.

[0220] In this embodiment, the process is controlled as follows: A flow monitoring device FC, located on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve on the second outlet pipe to adjust the mass flow rate of the second portion of melt 109 to 0.23 times the mass flow rate of the coarse crystallized product. A level monitoring device LC, located on the melter D101, sends a signal to a valve on the third outlet pipe to adjust the mass flow rate of the third portion of melt 110 to 0.7 times the mass flow rate of the coarse crystallized product. A temperature monitoring device TC, located at the heat exchanger outlet, sends information about the temperature of the heated melt 108 to the flow monitoring device FC, located on the first outlet pipe of the melter D101. The latter receives the temperature information of the heated melt 108, obtains the mass flow rate information of the first portion of melt 107, and sends a signal to a valve on the first outlet pipe to adjust the mass flow rate of the first portion of melt 107 to 2.06 times the mass flow rate of the coarse crystallized product. Temperature monitoring device TC, installed on the first outlet pipeline, sends a signal to the valve on heat exchanger E101 to adjust the mass flow rate of heating medium 201 flowing through the heat exchanger, so that the temperature of the heated melt 108 is 130°C. Temperature monitoring device TC, installed on the inlet pipeline of washing liquid 103 in scrubber C101, sends a signal to the valve on the main outlet pipeline to adjust the mass flow rate of main pipeline stream 108-2 to 0.07 times the mass flow rate of the crude crystallized product (correspondingly, bypass stream 108-2 is 3.47% of the mass of the heated melt 108). Through the above control, melter D101 operates under the following conditions: temperature 88°C, and scrubber C101 operates under the following conditions: the amount of washing liquid 103 is 0.3 times the mass flow rate of the crude crystallized product, and the temperature is 98°C.

[0221] In Example 8, the energy consumption of heat exchanger E101 was 173.77 KJ per unit mass flow rate of the crude crystalline product. The total mass flow rate of the material through product pump P101 was 2.99 times the mass of the crude crystalline product. As described above, gas chromatography analysis of the purified crystalline product (i.e., the third melt) determined its purity to be 99.71%.

[0222] Comparative Example 8-1

[0223] Example 8 is repeated, except that the flowchart shown in Figure 4 is used.

[0224] In this comparative example, the process is controlled as follows: A flow monitoring device FC, located on the inlet pipe of the washing liquid 103 in the scrubber C101, sends a signal to a valve on the second outlet pipe to adjust the mass flow rate of the second portion of melt 109 to 0.3 times the mass flow rate of the coarse crystallized product. A level monitoring device LC, located on the melter D101, sends a signal to a valve on the third outlet pipe to adjust the mass flow rate of the third portion of melt 110 to 0.7 times the mass flow rate of the coarse crystallized product. A flow monitoring device FC, located on the first outlet pipe, sends a signal to a valve on the first outlet pipe to adjust the mass flow rate of the first portion of melt 107 to 2.60 times the mass flow rate of the coarse crystallized product. A temperature monitoring device TC, located on the first outlet pipe, sends a signal to a valve on the heat exchanger E101 to adjust the mass flow rate of the heating medium 201 flowing through the heat exchanger, so that the temperature of the heated melt 108 is 135°C. Through the above control, the melt D101 is operated under the following conditions: temperature of 98°C, and the scrubber C101 is operated under the following conditions: the amount of scrubbing liquid 103 is 0.3 times the mass flow rate of the crude crystallized product, and the temperature is 98°C.

[0225] As described above, the purified crystalline product (i.e., the third melt) was subjected to gas chromatography analysis, and its purity was determined to be 99.71%.

[0226] In Comparative Example 8-1, the energy consumption of heat exchanger E101, measured per unit mass flow rate of coarse crystallized product, is 193.89 kJ. That is, compared to Example 8, the energy consumption of the heat exchanger in Comparative Example 8-1 increases by 11.58%.

[0227] Furthermore, in Comparative Example 8-1, the total mass flow rate of the material through product pump P101 was 3.60 times that of the crude crystallized product. That is, compared to Example 8, the energy consumption of the product pump in Comparative Example 8-1 increased by 20.40%.

[0228] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for washing crystallized products, characterized in that, The method includes: S1: Wash the crude crystalline product to obtain a washing filtrate and a solid phase of crystalline product; S2: Melt the solid-phase crystalline product to obtain a melt of the crystalline product; In this process, the first part of the melt is heated to obtain a heated melt. A portion of the heated melt is returned to step S2 as the main flow, and the remaining portion of the heated melt is returned to step S1 as a bypass flow. The second part of the melt returns to step S1; The third portion of the melt is discharged as a purified crystalline product.

2. The method according to claim 1, further comprising: Control step C1: Obtain information on the flow rate of the washing liquid, and adjust the flow rate of the second part of the melt returning to step S1 based on the information.

3. The method according to claim 1 or 2, further comprising: Control step C2: Obtain information on the liquid level of the melt of the crystallized product in step S2, and adjust the flow rate of the third part of the melt based on the information.

4. The method according to any one of claims 1-3, further comprising: Control step C3: Obtain information on the temperature of the first portion of the melt, and adjust the flow rate of the first portion of the melt based on the information; or Control step C4: Obtain information on the temperature of the heated melt and the flow rate of the first portion of the melt, and adjust the flow rate of the first portion of the melt based on the information.

5. The method according to any one of claims 1-4, further comprising: Control step C5: Obtain information on the temperature of the washing liquid and adjust the flow rate of the main logistics path based on the information.

6. The method according to any one of claims 1-5, further comprising: Control step C6: Obtain information on the temperature of the heated melt and adjust the flow rate of the heating medium based on the information; or Control step C7: Obtain information on the temperature of the first part of the melt, and adjust the flow rate of the heating medium based on the information.

7. A method for washing crystallized products, characterized in that, The method includes: S1: Wash the crude crystalline product with a washing solution to obtain a washing filtrate and a solid phase of crystalline product; S2: Melt the solid-phase crystalline product to obtain a melt of the crystalline product; In this process, the first part of the melt is heated to obtain a heated melt. A portion of the heated melt is returned to step S2 as the main flow, and the remaining portion of the heated melt is returned to step S1 as a bypass flow. The second part of the melt returns to step S1; The third portion of the melt is discharged as a purified crystallized product, and The method further includes at least one of the following control steps: Control step C1: Obtain information on the flow rate of the washing liquid, and adjust the flow rate of the second part of the melt returning to step S1 based on the information; Control step C2: Obtain information on the liquid level of the molten material of the crystallized product in step S2, and adjust the flow rate of the third part of the molten material based on the information; Control step C3: Obtain information on the temperature of the first portion of the melt, and adjust the flow rate of the first portion of the melt based on the information; Control step C5: Obtain information on the temperature of the washing liquid and adjust the flow rate of the main pipeline based on the information; and Control step C6: Obtain information on the temperature of the heated melt and adjust the flow rate of the heating medium based on the information.

8. The method according to claim 7, wherein, Control step C3 is replaced by: Control step C4: Obtaining information on the temperature of the heated melt and the flow rate of the first portion of the melt, and adjusting the flow rate of the first portion of the melt based on the information; and / or Control step C6 is replaced by: Control step C7: Obtain information on the temperature of the first part of the melt, and adjust the flow rate of the heating medium based on the information.

9. The method according to any one of claims 1-8, wherein, The bypass stream comprises 1-10% of the mass of the heated melt, preferably 2-6%; or The mixture of the bypass stream returned to step S1 and the second portion of the melt returned to step S1 is a washing liquid for step S1, wherein the bypass stream accounts for 10-60% of the mass of the washing liquid, preferably 20-50%.

10. The method according to any one of claims 1-9, further comprising: The crude crystalline product is prepared by solid-liquid separation of the upstream crystal slurry.

11. The method according to any one of claims 1-10, wherein, The content of the target crystalline product in the crude crystalline product is 95-99.5 wt%, preferably 97-99.5 wt%. The target crystalline product is selected from aromatic compounds, preferably from substituted or unsubstituted benzene and / or substituted or unsubstituted naphthalene, more preferably from alkyl or halogen-substituted benzene and / or alkyl-substituted naphthalene, and most preferably from p-xylene, 2,6-diisopropylnaphthalene, mesitylene or p-dichlorobenzene.

12. The method according to claim 11, wherein, The temperature of the washing solution should be 10-30°C higher than the melting point of the target crystalline product, preferably 15-27°C; and / or The temperature of the heated melt is 30-75°C above the melting point of the target crystalline product, preferably 50-70°C; and / or The temperature of the melt is 5-25°C lower than the temperature of the washing liquid, preferably 5-20°C lower.

13. An apparatus for washing crystallized products, characterized in that, The device includes: Washer: Used to wash the crude crystalline product to obtain a solid crystalline product and washing filtrate; Melter: includes a melting zone, used to melt solid-phase crystalline products to obtain a melt of crystalline products; The melter is provided with three outlet pipes: the first outlet pipe is connected to the heat exchanger, wherein the heat exchanger is provided with an outlet main line connected to the melting zone and an outlet bypass line connected to the scrubber; the second outlet pipe is connected to the scrubber; and the third outlet pipe is connected to the product outlet.

14. The apparatus of claim 13, further comprising: A valve installed on the second outlet pipe is connected to a first controller. The first controller receives information about the flow rate of the washing liquid and sends a signal to the valve to adjust the flow rate of the second part of the melt flowing through the second outlet pipe to the washer.

15. The apparatus according to claim 13 or 14, further comprising: A valve installed in the third outlet pipeline is connected to a second controller. The second controller receives information about the liquid level of the molten material of the crystallized product from a liquid level monitoring device installed on the melter and sends a signal to the valve to adjust the flow rate of the third portion of the molten material flowing through the third outlet pipeline to the product outlet.

16. The apparatus according to any one of claims 13-15, further comprising: A valve installed in the first outlet pipe is connected to a third controller. The third controller receives information about the temperature of the first portion of the melt and sends a signal to the valve to adjust the flow rate of the first portion of the melt flowing through the first outlet pipe to the heat exchanger; or A valve installed in the first outlet pipe is connected to a fourth controller and a fifth controller. The fourth controller receives information about the flow rate of the first partial melt and sends a signal to the fifth controller. The fifth controller receives information from the fourth controller and obtains information about the temperature of the heated melt, and sends a signal to the valve to adjust the flow rate of the first partial melt flowing through the first outlet pipe to the heat exchanger.

17. The apparatus according to any one of claims 13-16, further comprising: A valve installed on the outlet bypass is connected to a sixth controller, which receives information about the washing liquid temperature and sends a signal to the valve to adjust the flow rate of the bypass material flowing into the washer through the outlet bypass. The detergent inlet pipe installed on the washer is equipped with a temperature monitoring device to provide the detergent temperature information to the sixth controller.

18. The apparatus according to any one of claims 13-17, further comprising: A valve installed on the heat exchanger is connected to a seventh controller, which receives information about the temperature of the heated molten material and sends a signal to the valve to adjust the flow rate of the heating medium through the heat exchanger; or A valve installed on the heat exchanger is connected to an eighth controller, which receives information about the temperature of the first portion of the melt and sends a signal to the valve to adjust the flow rate of the heating medium flowing through the heat exchanger.

19. The apparatus according to any one of claims 13-18, wherein: The melter further includes at least one clarifying zone for receiving melt from the melting zone; The melting zone and refining zone of the melter are separated by baffles; and / or A liquid phase inlet is provided at the top or bottom of the melting zone of the melt, which is connected to the main outlet of the heat exchanger; preferably, a liquid phase inlet is provided at the bottom of the melt, which is connected to the main outlet of the heat exchanger; preferably, multiple liquid phase inlets are provided.

20. A method for washing crystallized products, characterized in that, The method is performed in the apparatus according to any one of claims 13-19, and the washing method includes: (1) The crude crystalline product is washed with washing liquid in a scrubber to obtain a solid crystalline product and washing filtrate; (2) The solid crystalline product is introduced into the melting zone of the melter and melted to obtain a crystalline product melt, which is then introduced into the clarification zone of the melter. The melt introduced into the clarification zone enters the three outlet pipes respectively. The first part of the melt is introduced into the heat exchanger through the first outlet pipe for heating to obtain a heated melt. A part of the heated melt is returned to the melting zone as the main flow through the outlet main pipe, and the remaining part of the heated melt is returned to step (1) as the bypass flow through the outlet bypass. The second part of the melt is returned to step (1) through the second outlet pipe. The third part of the melt is discharged from the product outlet through the third outlet pipe.

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