Preheating anti-scaling system and method

Abstract

The present invention provides a preheating anti-scaling system and method, comprising: a preheating system, a seed crystal catcher, a circulation pump, and a subsequent treatment system; the preheating system, seed crystal catcher, and circulation pump are sequentially connected via pipelines to form a circulation loop; the inlet of the subsequent treatment system is connected to the seed crystal catcher, and the outlet of the subsequent treatment system is connected to the pipeline between the seed crystal catcher and the circulation pump. The present invention achieves particle size classification and circulation of seed crystals in the preheating system through the preheating system, while increasing the material flow rate within the preheating system and inhibiting the adhesion and deposition of small particles within the preheating system; in addition, the slurry generated by the subsequent treatment system itself is used for replenishment to ensure the stability of the seed crystal content in the preheating system, thereby achieving a better anti-scaling effect, achieving long-term stable operation of the preheating system, and effectively preventing scaling and corrosion damage to equipment, which is of great significance for the utilization of calcium sulfate wastewater or brine resources.

Description

Technical Field

[0001] The present invention relates to the technical field of resource utilization, and in particular to a preheating and anti-scaling system and method, and more particularly to a continuous preheating and anti-scaling system and method for circulating seed crystals. Background Art

[0002] In the process of resource utilization of calcium sulfate wastewater and brine, the calcium ions (Ca 2 +) and other ions such as carbonate (CO3 2 -) or sulfate (SO4 2 -) to form insoluble calcium salts. Especially in high-temperature thermal processes, these calcium salts have inverse solubility properties and are prone to scaling on heat exchange surfaces. The growth of scale reduces heat transfer efficiency, decreases production efficiency, increases equipment maintenance costs, and shortens equipment life.

[0003] When treating this type of water, scaling within the heat exchanger is generally mitigated using special descaling agents, regular inspections, pickling, and mechanical cleaning. Compared to these methods, the seed crystal anti-scaling method utilizes the preferential deposition of calcium sulfate on seed crystals to slow and inhibit scaling on the heat exchange surfaces. This method allows for continuous operation without the addition of softening agents, avoids the sludge generated by softening agents, and significantly reduces treatment costs. However, in salt production and industrial saline wastewater treatment, the seed crystal method is not particularly effective under certain conditions due to the unclear scaling patterns of calcium sulfate on heat exchange surfaces.

[0004] Existing technologies focus more on solving the scaling problem of heat exchangers in the preheating process by optimizing equipment structure, using external fields such as ultrasound, and adding scale inhibitors. At the same time, compared with the preheating system, the scaling prevention problem of heat exchange equipment in the evaporation and concentration section in the existing technology has received more attention. For example, patents CN202110414610.6, 202010093046.8, 201920169181.9 and 202110915768.1 all achieve scaling prevention of desulfurization wastewater evaporation heat exchangers by adding gypsum crystal seeds to the evaporator during the evaporation stage. Studies have shown that changes in the heat exchange surface temperature, the precipitation rate of calcium sulfate per unit time, the composition of the water sample and basic physical properties will affect the conditions for seed addition. Therefore, the amount of seed addition proposed in the above technology still needs to be further adjusted according to the operating conditions.

[0005] Unlike heat exchangers in the evaporation section, the preheating section experiences a larger temperature difference in the feed liquid temperature rise. The temperature difference in the heat exchange interface and the physical adhesion of solid particles on the heat exchange surface are the main causes of scaling on the heat exchange interface in the preheating system. On the one hand, the preheating section generally uses multi-stage preheating to raise the feed liquid temperature to 50-110°C. Due to the inverse solubility properties of sparingly soluble calcium salts (such as CaSO4 and CaCO3), the higher temperature heat exchange surface provides an excellent nucleation and growth site for these calcium salts. On the other hand, when the flow rate in the tube is low, suspended solid particles in the heated material tend to settle and adhere to the heat exchange surface, leading to scarring and increased scaling of the heat exchange surface. Patent CN201810995127.X adds NaOH to the brine preheating section to make it alkaline, and then uses a segmented plate heat exchanger to preheat the brine in two stages. It is still necessary to switch the flow channels and regularly disassemble and clean the calcium sulfate scale on the heat exchange surface of the preheater to ensure the heat exchange effect. Frequent disassembly, cleaning and switching increase the workload and complexity of production operations.

[0006] Therefore, in order to solve the scaling problem of the preheating system of desulfurization wastewater and calcium sulfate brine with similar water quality, it is urgent to propose a continuous heat exchange and anti-scaling process and system with circulating crystal seeds to achieve long-term stable operation of the preheating system and provide a solution to the scaling problem of the preheater. Summary of the Invention

[0007] The object of the present invention is to provide a preheating anti-scaling system and method, which can solve the scaling problem that occurs in the preheating system during the preheating treatment process and achieve long-term stable operation of the preheating system.

[0008] A first aspect of the present invention provides a preheating and anti-scaling system, comprising: a preheating system, a seed catcher, a circulation pump, and a subsequent processing system; the preheating system, seed catcher, and circulation pump are sequentially connected via pipelines to form a circulation loop; the inlet of the subsequent processing system is connected to the seed catcher, and the outlet of the subsequent processing system is connected to the pipeline between the seed catcher and the circulation pump.

[0009] In the present invention, the seed catcher utilizes the difference in sedimentation rates of particles of different particle sizes to capture and collect large-particle gypsum particles by expanding the pipeline diameter and setting a sleeve. When the material flows through the expanded port, the cross-sectional area becomes larger and the material flow rate slows down. The large-particle gypsum particles settle due to the advantage of gravity and are discharged from the sleeve outlet along with the circulating slurry as seed crystals. They are returned to the front end of the preheating system by the circulating pump and mixed with the material to be heated, thereby realizing seed crystal circulation, while small particles enter the subsequent processing system along with the high-temperature liquid.

[0010] Preferably, the seed catcher is provided with an inlet, a first outlet and a second outlet; the inlet of the seed catcher is connected to the outlet of the preheating system, the first outlet of the seed catcher is connected to the inlet of the circulation pump, and the second outlet of the seed catcher is connected to the inlet of the subsequent processing system.

[0011] Preferably, the subsequent processing system is an evaporation and concentration system, which is provided with an inlet, a first outlet and a second outlet; the inlet of the evaporation and concentration system is connected to the second outlet of the seed crystal catcher, the first outlet of the evaporation and concentration system is connected to the pipeline between the seed crystal catcher and the circulation pump, and the second outlet of the evaporation and concentration system is connected to the material output pipeline.

[0012] Preferably, the inlet of the preheating system is connected to the material input pipeline, and the outlet of the circulation pump is connected to the material input pipeline.

[0013] Preferably, the preheating system comprises: a plurality of preheaters connected in series, wherein the inlet of the first preheater is connected to the material input pipeline, and the outlet of the last preheater is connected to the inlet of the seed catcher.

[0014] A second aspect of the present invention provides a preheating anti-scaling method, which uses the above-mentioned preheating anti-scaling system and includes the following steps:

[0015] S1, the liquid material enters the preheating system and is heated to obtain a high-temperature liquid;

[0016] S2, the high-temperature liquid enters the seed crystal catcher for particle size classification, and the circulating slurry containing large particles is screened out and enters the circulation loop, and the remaining small particles enter the subsequent treatment system with the high-temperature liquid;

[0017] S3, the high-temperature liquid containing small particles is treated by the subsequent treatment system to obtain a supplementary slurry, which enters the circulation loop and mixes with the circulating slurry;

[0018] S4. The mixed slurry is transported back to the pipeline at the front end of the preheating system through the circulation pump, and is mixed with the liquid material and enters the preheating system.

[0019] Preferably, in step S1, the liquid material includes: one or more of calcium sulfate type wastewater or calcium sulfate type brine, and the viscosity of the liquid material is 1.01 to 2.50 mPa·s. The preheating process of liquid materials with higher viscosity is prone to cause particles to adhere to and deposit on the heat exchange surface to form scale. If the viscosity of the water sample caused by the suspended solid content exceeds the viscosity range described in the present invention, it is particularly recommended to pretreat the water sample by sedimentation and then use the method described in the present invention to alleviate the scaling problem.

[0020] Preferably, in step S2, the particle size of the large particles is greater than or equal to 50 μm, and the particle size of the small particles is less than 50 μm.

[0021] Preferably, in step S3, the solid content of the supplementary slurry gypsum is controlled at 20%-50%, and the particle size of the particles in the supplementary slurry is greater than or equal to 50 μm.

[0022] Preferably, in step S4, the mixed slurry is mixed with the liquid material and enters the preheating system. According to the heat source temperature of the preheating system and the scaling differences of the heat exchange surfaces at different temperatures, the circulating slurry and the replenishing slurry flow are adjusted to control the solid content (mass percentage) of the gypsum seed in the preheating system to meet the following conditions, so as to achieve long-term stable operation of the preheating system without scaling for more than 3 months:

[0023] When the heat source temperature in the preheating system is greater than or equal to 80°C, the solid content of the gypsum seed crystals is controlled at 1.5% to 3%;

[0024] When the heat source temperature in the preheating system is less than 80° C., the solid content of the gypsum seed crystals is controlled at 1% to 10%.

[0025] The present invention has the following beneficial effects:

[0026] (1) The present invention not only realizes the circulation of gypsum crystal seeds in the preheating system by circulating the high-temperature liquid after preheating, but also increases the material flow rate in the preheating system by circulating the high-temperature liquid, thereby inhibiting the adhesion and deposition of small particles in the preheating system.

[0027] (2) The present invention utilizes the gypsum slurry generated by the subsequent treatment system itself for supplementation, which can ensure the stability of the seed crystal content in the preheating system. The surface properties of the gypsum seed crystal particles precipitated by the system itself have a higher consistency with the solute in the liquid phase, and a better anti-scaling effect can be obtained.

[0028] (3) The present invention realizes the gypsum seed particle size classification of the preheater system by setting a seed catcher and controlling the particle size distribution of the particles in the slurry, thereby reducing the proportion of small particle solids, thereby fundamentally slowing down the deposition of small particles on the heat exchange surface and reducing the risk of scaling of the heat exchange surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1 This is a schematic structural diagram of the preheating and anti-scaling system provided in Example 1 of the present invention.

[0031] Figure 2 This is a structural diagram of the preheating and anti-scaling system provided in Example 3 of the present invention.

[0032] Figure 3 This is a schematic structural diagram of the seed crystal catcher provided by the present invention.

[0033] Explanation of the reference numerals: 1. Preheating system; 1-1. Primary preheater; 1-2. Secondary preheater; 2. Seed catcher; 2-1. Inlet of seed catcher; 2-2. First outlet of seed catcher; 2-3. Second outlet of seed catcher; 3. Circulation pump; 4. Subsequent processing system. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction, and therefore should not be understood as limiting the present invention.

[0036] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined. In addition, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a communication between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0037] Example 1

[0038] This embodiment takes the treatment of calcium sulfate-containing desulfurization wastewater as an example. Figure 1As shown, a preheating anti-scaling system is provided, comprising: a preheating system 1, a seed catcher 2, a circulation pump 3 and a subsequent treatment system 4; the preheating system 1, the seed catcher 2 and the circulation pump 3 are connected in sequence through pipelines to form a circulation loop, and the gypsum crystals precipitated due to the temperature increase during the preheating process can provide seeds for the preheating system 1, and the circulating slurry containing gypsum crystals increases the material flow rate in the preheating system 1, reduces and inhibits the adhesion and deposition of solid particles on the heat exchange surface; the inlet of the subsequent treatment system 4 is connected to the seed catcher 2, and the outlet of the subsequent treatment system 4 is connected to the pipeline between the seed catcher 2 and the circulation pump 3. The supplementary slurry provided by the subsequent treatment system 4 is mixed with the circulating slurry as a seed and then supplemented to the front end of the preheating system 1, which can ensure the stability of the seed content in the preheating system 1, and the surface properties of the gypsum crystal particles precipitated by the system itself have higher consistency with the solute in the liquid phase, and a better anti-scaling effect can be obtained.

[0039] like Figure 3 As shown, in this embodiment, the seed catcher 2 is provided with an inlet, a first outlet and a second outlet; the inlet 2-1 of the seed catcher is connected to the outlet of the preheating system 1, the first outlet 2-2 of the seed catcher is connected to the inlet of the circulation pump 3, and the second outlet 2-3 of the seed catcher is connected to the inlet of the subsequent processing system 4.

[0040] In this embodiment, the subsequent processing system 4 is an evaporation concentration system, which is provided with an inlet, a first outlet, and a second outlet; the inlet of the evaporation concentration system is connected to the second outlet of the seed catcher 2, the first outlet of the evaporation concentration system is connected to the pipeline between the seed catcher 2 and the circulation pump 3, and the second outlet of the evaporation concentration system is connected to the material output pipeline.

[0041] In this embodiment, the inlet of the preheating system 1 is connected to the material input pipeline, and the outlet of the circulation pump 3 is connected to the material input pipeline.

[0042] In this embodiment, the preheating system 1 is a first-stage preheater, and the preheating tube is a bellows. The bellows can enhance the heat transfer performance and increase the turbulence of the fluid in the tube, thereby further slowing down the scaling rate and achieving better results.

[0043] This embodiment also provides a preheating anti-scaling method, which uses the preheating anti-scaling system of this embodiment, including the following steps:

[0044] S1, the calcium sulfate-containing desulfurization wastewater enters the preheating system 1 through the material input pipeline and is heated to obtain a high-temperature liquid;

[0045] Specifically, the calcium sulfate-containing desulfurization wastewater is desulfurization wastewater at room temperature of 18 to 25° C., the wastewater is saturated with calcium sulfate, the soluble solid content (TDS) is 4.00%, the insoluble solid content (SS) is 0.8%, and the wastewater viscosity is 1.15 mPa·s;

[0046] S2, the high-temperature liquid enters the seed crystal catcher 2 for particle size classification, and the circulating slurry containing large particles is screened out and enters the circulation loop, and the remaining small particles enter the evaporation and concentration system with the high-temperature liquid;

[0047] S3. The high-temperature liquid containing small particles is treated by the evaporation and concentration system to obtain supplementary slurry. The solid content of the supplementary slurry is controlled at 20%-50%. The supplementary slurry enters the circulation loop and mixes with the circulating slurry. The remaining materials enter other processing processes through the material output pipeline;

[0048] S4. The mixed slurry is transported back to the material input pipeline at the front end of the preheating system 1 through the circulation pump 3, and is mixed with the calcium sulfate-containing desulfurization wastewater and enters the preheating system 1.

[0049] In this embodiment, the preheating system 1 uses high-temperature liquid treated with 100°C high-temperature condensate to obtain a circulating slurry after passing through a seed catcher 2. The supplementary slurry is mixed with the circulating slurry on the pipeline in front of the circulation pump 3, and is transported by the circulation pump 3 to the front-end pipeline of the preheating system 1 to mix with the wastewater and then enter the preheating system 1. The solid content of the gypsum of the material before entering the preheating system 1 is controlled to be 1.5%, and the average particle size of the seed crystal is 50 μm. The preheating system 1 can maintain stable operation for 100 days without scaling.

[0050] Example 2

[0051] This embodiment is basically the same as Example 1, except that: the preheating system 1 uses high-temperature condensate water to treat the high-temperature liquid and then passes through the seed catcher 2 to obtain a circulating slurry, the replenishing slurry and the circulating slurry are mixed on the pipeline before the circulation pump 3, and are transported by the circulation pump 3 to the front end pipeline of the preheating system 1 to mix with the wastewater and then enter the preheating system 1. The gypsum solid content of the material before entering the preheating system 1 is controlled to be 10.0%, the average particle size of the seed crystals is 100 μm, and the preheating system 1 can maintain stable operation for 180 days without scaling.

[0052] Example 3

[0053] This embodiment is basically the same as embodiment 1, except that: Figure 2 As shown, the preheating system 1 is a first-stage preheater 1-1 and a second-stage preheater 1-2 connected in series, wherein the inlet of the first-stage preheater 1-1 is connected to the material input pipeline, and the outlet of the second-stage preheater 1-2 is connected to the inlet of the seed catcher 2.

[0054] High-temperature condensed water is used to perform secondary preheating on calcium sulfate saturated brine at 15-20°C. The brine is saturated with calcium sulfate, and the soluble solid content (TDS) is 20.00%. No insoluble solids are detected in the brine, and the viscosity of the brine is 1.90 mPa·s.

[0055] The first-stage preheater 1-1 and the second-stage preheater 1-2 use high-temperature condensed water of different temperatures, and the heat source temperatures are 50°C and 100°C respectively. The high-temperature liquid treated by the first-stage preheater 1-1 and the second-stage preheater 1-2 is passed through the seed catcher 2 to obtain circulating slurry. The supplementary slurry is mixed with the circulating slurry in the pipeline before the circulation pump 3, and is transported by the circulation pump 3 to the front-end pipeline of the first-stage preheater 1-1 and mixed with brine before entering the preheater. The gypsum solid content of the material before entering the first-stage preheater 1-1 is controlled to be 3.0%, and the average particle size of the seed crystals is 100μm. The first-stage preheater 1-1 and the second-stage preheater 1-2 can maintain stable operation for 180 days and 120 days respectively without scaling.

[0056] Comparative Example 1

[0057] This comparative example is basically the same as Example 1, except that: the high-temperature liquid preheated by the preheating system 1 was not circulated, and the slurry was not replenished, that is, the gypsum solid content of the wastewater to be preheated by the preheating system 1 was not adjusted. The preheating system 1 maintained stable operation for 20 days, and after 25 days, there was an obvious scale layer on the heat exchange surface.

[0058] Comparative Example 2

[0059] This comparative example is basically the same as Example 1, except that the average particle size of the particles in the supplementary slurry is 10-30 μm, the preheating system 1 maintains stable operation for 25 days, and after 35 days, there is an obvious scale layer on the heat exchange surface.

[0060] Comparative Example 3

[0061] This comparative example is basically the same as Example 1, except that: first, no circulating slurry is set, and the control of the seed amount of the preheating system 1 is achieved only by replenishing the slurry; second, the average particle size of the particles in the replenishing slurry is 10 to 30 μm, and the preheating system 1 maintains stable operation for 15 days. After 19 days, there is an obvious scale layer on the heat exchange surface.

[0062] In summary, the present invention not only realizes the circulation of gypsum seeds in the preheating system through the circulation of high-temperature liquid after preheating, but also increases the material flow rate in the preheating system by circulating the high-temperature liquid, and suppresses the adhesion and deposition of small particles in the preheating system; the present invention uses the gypsum slurry generated by the subsequent treatment system itself for supplementation, which can ensure the stability of the seed content in the preheating system, and the surface properties of the gypsum seed particles precipitated by the system itself have a higher consistency with the solute in the liquid phase, which can obtain a better anti-scaling effect; the present invention realizes the gypsum seed particle size classification of the preheater system by setting a seed catcher and controlling the particle size distribution of the particles in the slurry, thereby reducing the proportion of small solid particles, thereby fundamentally slowing down the deposition of small particles on the heat exchange surface and reducing the risk of scaling on the heat exchange surface; the present invention clarifies the effective anti-scaling seed solid content control conditions for different heat source temperatures based on the differences in the scaling kinetics of the heat exchange surface at different temperatures, and the continuous preheating seed scaling prevention method is more accurately regulated.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preheating anti-scaling method, characterized in that: A preheating and anti-scaling system is used, comprising: a preheating system, a seed catcher, a circulation pump, and a subsequent treatment system; the preheating system, seed catcher, and circulation pump are sequentially connected via pipelines to form a circulation loop; the inlet of the subsequent treatment system is connected to the seed catcher, and the outlet of the subsequent treatment system is connected to the pipeline between the seed catcher and the circulation pump; the subsequent treatment system is an evaporation and concentration system; the seed catcher utilizes the difference in sedimentation rates of particles of different particle sizes to capture and collect large gypsum particles by expanding the pipeline and providing a casing. The large gypsum particles settle and are discharged from the casing outlet along with the circulating slurry, while the small gypsum particles enter the subsequent treatment system along with the high-temperature liquid; The preheating anti-scaling method comprises the following steps: S1. Liquid material enters a preheating system and is heated to obtain a high-temperature liquid; the liquid material comprises one or more of calcium sulfate type wastewater or calcium sulfate type brine, and the viscosity of the liquid material is 1.01-2.50 mPa·s; S2, the high-temperature liquid enters the seed crystal catcher for particle size classification, and the circulating slurry containing large particles is screened out and enters the circulation loop, and the remaining small particles enter the subsequent treatment system with the high-temperature liquid; the particle size of the large particles is greater than or equal to 50 μm; S3. The high-temperature liquid containing small particles is treated by a subsequent treatment system to obtain a supplementary slurry, which enters a circulation loop and is mixed with the circulating slurry. The gypsum solid content of the supplementary slurry is controlled at 20%-50%, and the particle size of the particles in the supplementary slurry is greater than or equal to 50μm. S4. The mixed slurry is transported back to the pipeline at the front end of the preheating system through the circulation pump, and is mixed with the liquid material and enters the preheating system; the mixed slurry is mixed with the liquid material and enters the preheating system. When the heat source temperature in the preheating system is greater than or equal to 80°C, the solid content of the gypsum seed crystal is controlled at 1.5%~3%; when the heat source temperature in the preheating system is less than 80°C, the solid content of the gypsum seed crystal is controlled at 1%~10%.

2. The preheating anti-scaling method according to claim 1, characterized in that: The seed catcher is provided with an inlet, a first outlet and a second outlet; the inlet of the seed catcher is connected to the outlet of the preheating system, the first outlet of the seed catcher is connected to the inlet of the circulation pump, and the second outlet of the seed catcher is connected to the inlet of the subsequent processing system.

3. The preheating anti-scaling method according to claim 2, characterized in that: The evaporation and concentration system is provided with an inlet, a first outlet and a second outlet; the inlet of the evaporation and concentration system is connected to the second outlet of the seed crystal catcher, the first outlet of the evaporation and concentration system is connected to the pipeline between the seed crystal catcher and the circulation pump, and the second outlet of the evaporation and concentration system is connected to the material output pipeline.

4. The preheating anti-scaling method according to claim 1, characterized in that: The inlet of the preheating system is connected to the material input pipeline, and the outlet of the circulation pump is connected to the material input pipeline.

5. The preheating anti-scaling method according to claim 1, characterized in that: The preheating system comprises: a plurality of preheaters connected in series, wherein the inlet of the first preheater is connected to the material input pipeline, and the outlet of the last preheater is connected to the inlet of the seed catcher.

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