Polyamide continuous drying process, fluidized continuous drying device and application

Abstract

The application discloses a kind of polyamide continuous drying processes, fluidization continuous drying device and application.The polyamide continuous drying process includes: the continuous self-flowing of the moisture-containing polyamide solid material passes through fluidization drying module, the fluidization drying module includes the hot drying section with hot gas stream inlet and hot gas stream outlet;Part of the hot gas stream discharged from the hot gas stream outlet of the hot drying section is used as reflux hot gas stream, and the reflux hot gas stream and the first supplementary air stream are combined and then introduced into the hot drying section through the hot gas stream inlet.By controlling the flow ratio of the reflux hot gas stream and the first supplementary air stream to be 1:1~15:1, the humidity and temperature in the hot drying section are within the preset steady-state range, so that the drying efficiency and color stability of the polyamide are considered.

Description

Technical Field

[0001] This invention relates to a continuous drying process for polyamide, a fluidized continuous drying apparatus, and its applications. Background Technology

[0002] The degree of dryness in the dehumidification and drying of solid materials has a significant impact on subsequent storage, transportation, processing, and application. Polyamide (nylon) molecules are rich in polar amide groups, exhibiting extremely high hygroscopicity, with an equilibrium water absorption rate of approximately 3% at room temperature. Residual moisture will trigger molecular chain hydrolysis and degradation during melt processing, leading to defects such as silver streaks and bubbles on the surface of the product, and significantly deteriorating its mechanical properties. Therefore, the moisture content of polyamide particles must be strictly controlled below 0.15%~0.2% before processing; this drying process is an indispensable and critical step before molding.

[0003] Currently, the mainstream technology for industrial continuous drying is fluidized bed drying, which typically employs a two-stage design: the incoming material first flows through the hot bed section, where the moisture is vaporized by high-temperature hot air and carried out with the carrier gas; the dried material then enters the cold bed section, is cooled by cold air, and is discharged. To ensure fluidization uniformity, both the hot and cold sections are usually purged with dry air. For special materials, inert gases such as nitrogen are used instead of dry air as the fluidizing carrier gas.

[0004] Existing patent documents disclose various fluidized bed drying systems and process schemes. Patents CN100376470C, CN213631192U, and CN203704617U all disclose drying processes based on room temperature air, where cold air is heated to form hot dry air, which is then sent into the hot section of the dryer, and discharged or partially reused after a single pass through the material. Patent CN117570762B describes an in-situ condensation dehumidification scheme without humidifying air discharge, relying on complex compressor equipment to achieve airflow pressurization and transmission. Patent CA2986740C does not utilize the high-value drying hot air that initially contacts the material; instead, the cooling waste air at the end is treated and reused. Patent DE602023001926T2 uses a complex circular drive material equipment, which causes the material to be repeatedly subjected to off-site hot drying and blowing. It is impossible to perform dual temperature-changing treatment of hot drying and cooling in a continuous process, and can only be hot dried. At the same time, the recycled airflow is repeatedly humidified without returning to its original state. In a complete processing process, the moisture content of the airflow in contact with the material increases over time. It is an uncontrollable steady-state airflow drying process, and it is impossible to regulate the airflow that pierces the material each time. From a system perspective, it has a complex structure, many moving parts, difficult control, large investment, poor stability, and is not suitable for high-requirement drying scenarios.

[0005] The drying effect of existing drying technologies is highly susceptible to interference from environmental factors such as workshop temperature and humidity. Moreover, to ensure the drying depth, it is often necessary to maintain a high hot air temperature. However, polyamides are sensitive to thermo-oxidative aging, and these high-temperature conditions can directly cause thermochromic discoloration of the particles, severely affecting the product's appearance quality. Therefore, existing drying processes cannot simultaneously meet the dual requirements of low moisture content and high color stability.

[0006] The information disclosed in the background section is only intended to enhance the understanding of the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to provide a continuous drying process for polyamide, suitable for pre-processing of polyamide particles. Through a regenerative fluidized bed drying module, it possesses excellent self-adaptability to external disturbances. Under the condition of achieving the same drying depth (meeting the moisture content standard), only minor adjustments to the operating variables are needed to maintain steady-state system operation, and the yellowing index (YI) of the particles fluctuates minimally before and after drying, thus balancing drying efficiency and color stability. For example, if there are situations such as misoperation, valve failure, abnormal heat medium supply, distributed control system (DCS) failure, or power outages causing deviation in the first makeup air flow, the regenerative cycle constructed based on this invention will not cause severe deviation and system shutdown in the hot drying section as in traditional full makeup air modes.

[0008] The present invention also aims to provide a fluidized continuous drying device and its application in polyamide drying. This fluidized continuous drying device has good adaptability to external disturbances. Under the condition of achieving the same drying depth (moisture content meets the standard), only minor corrections to the operating variables are needed to maintain steady-state operation of the system.

[0009] The first aspect of the present invention provides a continuous drying process for polyamide, comprising: Step S1: The wet polyamide solid material is continuously flowed through the fluidized bed drying module, which includes a hot drying section with a hot air inlet and a hot air outlet; Step S2: A portion of the hot airflow discharged from the hot airflow outlet of the hot drying section is used as a return hot airflow. The return hot airflow and the first supplementary airflow are combined and then introduced into the hot drying section through the hot airflow inlet. In step S2, the flow ratio of the return hot airflow to the first supplementary airflow is controlled to be 1:1 to 15:1, so that the humidity and temperature in the hot drying section are within a preset steady-state range.

[0010] In some preferred embodiments, in step S2, the flow rate ratio of the recirculating hot airflow to the first supplementary airflow is 5:1 to 15:1.

[0011] In some preferred embodiments, in step S2, the temperature difference between the first supplementary airflow and the return hot airflow is controlled to be 5% to 300% of the temperature of the return hot airflow.

[0012] In some preferred embodiments, the relative humidity when the first supplementary airflow and the return hot airflow enter the hot drying section is below 20%.

[0013] In some preferred embodiments, the relative humidity when the first supplementary airflow and the return hot airflow enter the hot drying section after merging is below 3%. More preferably, the relative humidity when the first supplementary airflow and the return hot airflow enter the hot drying section after merging is below 1%.

[0014] In some preferred embodiments, in step S2, the first supplementary airflow and the return hot airflow are combined and then enter the hot drying section at a temperature of 50~250°C. More preferably, the first supplementary airflow and the return hot airflow are combined and then enter the hot drying section at a temperature of 80~200°C. Even more preferably, the first supplementary airflow and the return hot airflow are combined and then enter the hot drying section at a temperature of 105~120°C.

[0015] In some specific and preferred embodiments, in step S2, the humidity and temperature in the hot drying section are kept within a preset steady-state range by controlling the following parameters: the flow ratio of the recirculating hot airflow to the first supplementary airflow is 5:1 to 15:1, the temperature difference between the first supplementary airflow and the recirculating hot airflow is 5% to 300% of the temperature of the recirculating hot airflow, the relative humidity of the first supplementary airflow entering the hot drying section is below 1%, and the temperature of the combined first supplementary airflow and the recirculating hot airflow entering the hot drying section is 105 to 120°C.

[0016] In some preferred embodiments, the first supplementary airflow enters the hot drying section after undergoing dust removal and / or charge control treatment; The flow rate of the residual hot airflow discharged from the hot airflow outlet of the hot drying section, excluding the return hot airflow, is 6% to 50% of the total hot airflow flow rate discharged from the hot airflow outlet of the hot drying section; The remaining hot air is fed into the first channel of the waste heat exchanger; fresh air, fresh inert gas, or treated exhaust gas from the cooling section of the fluidized drying module is fed into the second channel of the waste heat exchanger, where it exchanges heat with the remaining portion of the hot air flow and serves as the first supplementary air flow or as the second supplementary air flow into the cooling section, which is located behind or below the hot drying section.

[0017] In some preferred embodiments, the moist polyamide solid material is polyamide particles, and the standard deviation of the ASTM D1925 yellowness index fluctuation of 98% of the data after drying of the polyamide particles is less than 0.15. More preferably, the standard deviation of the ASTM D1925 yellowness index fluctuation of 98% of the data after drying of the polyamide particles is less than 0.14, for example, 0.1~0.14. The "standard deviation of the ASTM D1925 yellowness index fluctuation of 98% of the data" is defined as follows: the standard deviation of the yellowness index fluctuation is obtained by statistical calculation based on the ASTM D1925 yellowness index of the products sampled every 30 minutes during 24 hours of continuous production; wherein, "98% of the data" refers to the standard deviation of the remaining samples after removing the highest and lowest 1% outliers from all sample data.

[0018] In some embodiments, the flow ratio of the recirculated hot airflow to the first supplementary airflow is controlled between 1:1 and 15:1. The closer the ratio is to 15:1, the higher the proportion of the recirculated hot airflow in the total exhaust of the hot drying section, the smaller the amount of the first supplementary airflow, the easier the steady-state control of the air intake of the hot drying section, the more stable the drying control of the material in the fluidized bed dryer, and the more convergent the indicators such as humidity and color of the final output product. At the same time, the less exhaust airflow is discharged from the hot drying section, the lower the cost of exhaust gas treatment, the lower the implementation cost of the first supplementary airflow, and the better the overall economic efficiency of the project.

[0019] In some embodiments, the temperature difference between the first supplementary airflow and the return hot airflow is controlled to be 5%-300% of the temperature of the return hot airflow. When the temperature of the first supplementary airflow increases and the temperature of the return hot airflow decreases, this ratio will often increase: if the temperature of the first supplementary airflow increases, the temperature requirements of its heating equipment and heat medium will need to be increased accordingly; if the temperature of the return hot airflow decreases, the thermal energy requirements of the first supplementary airflow will need to be increased accordingly to maintain the stability of the heat storage cycle.

[0020] In some embodiments, the relative humidity when the first supplementary airflow and the return hot airflow enter the hot drying section is controlled to be below 20%. The lower the humidity, the better the drying and dehumidification effect, but the higher the engineering implementation cost.

[0021] In some embodiments, the first supplementary airflow and the return hot airflow are mixed and then enter the hot drying section at a temperature of 50~250°C. The lower the temperature, the worse the drying and dehumidification effect; the higher the temperature, the more serious the negative effects such as aging, discoloration, and adhesion.

[0022] In some embodiments, the above-mentioned important parameters are controlled simultaneously. These parameters have a synergistic effect and need to be considered and adjusted in a comprehensive manner. They are also related to factors such as the physical properties of upstream and downstream materials and the structure of the fluidized bed dryer. In reality, industrial production often involves matching upstream material conditions and anchoring downstream material demand conditions, and comprehensively selecting and optimizing the supporting parameters under limited equipment operation conditions.

[0023] A second aspect of the present invention provides a fluidized continuous drying apparatus, comprising: A fluidized bed drying module is configured to allow a continuous flow of moist solid material or supersaturated slurry. The fluidized bed drying module includes a hot drying section, which has a hot air inlet for the hot air to enter and a hot air outlet for the hot air to exit. An air inlet module is used to supply airflow to the fluidized drying module; The air intake module includes: A return line is used to introduce a portion of the hot gas flow from the hot gas outlet as a return hot gas flow. The make-up air duct is used to introduce make-up airflow. At least a portion of the make-up airflow is used as the first make-up airflow and is combined with the return hot airflow before being introduced into the hot airflow inlet. The moisture content of the first make-up airflow is less than that of the return hot airflow. The flow ratio of the return hot airflow to the first make-up airflow is greater than 1:1, so that the humidity and temperature in the hot drying section are within a preset steady-state range. The fluidized continuous drying device further includes an exhaust module, which includes a first exhaust duct for discharging the remaining hot air from the hot air outlet, and the first exhaust duct is connected to the hot air outlet.

[0024] In some preferred embodiments, the flow rate ratio of the recirculating hot airflow to the first supplementary airflow is 1:1 to 15:1; and / or, the temperature difference between the first supplementary airflow and the recirculating hot airflow is 5% to 300% of the temperature of the recirculating hot airflow; and / or, the relative humidity of the first supplementary airflow entering the hot drying section is below 20%; and / or, the combined first supplementary airflow and the recirculating hot airflow enter the hot drying section at a temperature of 50 to 250°C; and / or, the flow rate of the remaining hot airflow is 6% to 50% of the total flow rate of the hot airflow discharged from the hot drying section.

[0025] In some preferred embodiments, the air intake module further includes: A first fan is used to drive the return hot airflow to flow in the return duct and / or drive the first supplementary airflow to flow in the supplementary air duct; The first heating device is used to heat the supplementary airflow in the make-up air duct, or to heat the return airflow in the return duct, or to heat the airflow after the return hot airflow and the first supplementary airflow are combined.

[0026] In some preferred embodiments, a condenser is installed on or before the make-up air duct to remove moisture from the make-up airflow in the make-up air duct.

[0027] In some preferred embodiments, the air intake module further includes: A first dust separation device is used to remove dust from the reflux hot airflow, and the first dust separation device is connected to the reflux pipeline; The first dust separation device includes a dust collector and / or a cyclone separator; And / or, the air intake module further includes a charge control device for processing the charge carried in the return hot airflow, the first supplementary airflow, or the airflow after the return hot airflow and the first supplementary airflow are combined. The charge control device is disposed on the first supplementary air duct, the return duct, or before the hot airflow inlet. The charge control device includes an electrostatic eliminator and / or a charge controller.

[0028] In some preferred embodiments, the exhaust module further includes a second exhaust duct, which and / or the first exhaust duct is connected to a second dust separation device to remove dust from the discharged exhaust gas. The second dust separation device includes a dust collector and / or a cyclone separator.

[0029] In some preferred embodiments, a waste heat exchanger is provided on the second exhaust duct and / or the first exhaust duct to utilize the energy of the waste gas in the second exhaust duct and / or the first exhaust duct.

[0030] In some preferred embodiments, the fluidized bed drying module includes a cooling section located behind the hot drying section. The cooling section has a cooling airflow inlet, a cooling airflow outlet, and a cooled material outlet. The cooling airflow inlet is connected to a cooling air duct, and the cooling air duct is connected to the make-up air duct to allow another portion of the make-up airflow to pass through the cooling air duct into the cooling airflow inlet.

[0031] In some preferred embodiments, the fluidized bed drying module includes a cooling section located behind the hot drying section. The cooling section has a cooling airflow inlet, a cooling airflow outlet, and a cooled material outlet. The cooling airflow inlet is connected to a cooling air duct, and / or the first exhaust duct is connected to the cooling air duct alone or in combination with the second exhaust duct, so as to reuse the exhaust gas discharged through the second exhaust duct and / or the first exhaust duct. Among them, a portion of the recycled waste gas is combined with the return hot gas flow and then introduced into the hot gas flow inlet, while the other portion is connected to the cooling air duct and introduced into the cooling air flow inlet; And / or, all the recycled exhaust gas is connected to the cooling air duct to enter the cooling air inlet.

[0032] In some further preferred embodiments, the fluidized continuous drying apparatus further includes an airflow pretreatment module for pretreating the supplementary airflow to be supplied to the fluidized drying module, the airflow pretreatment module comprising: The second fan is used to drive the supplementary airflow. A gas filter for filtering the makeup gas stream, and / or a condenser for removing moisture from the makeup gas stream.

[0033] In some preferred embodiments, the fluidized continuous drying apparatus is a plastic particle drying apparatus, and the fluidized drying module is configured to allow the plastic particles to flow continuously to reduce the moisture content of the plastic particles.

[0034] A third aspect of the present invention provides an application of the fluidized continuous drying apparatus described above in the drying of polyamides.

[0035] The present invention adopts the above solution, which has the following advantages compared with the prior art: The polyamide continuous drying process of this invention takes a portion of the hot airflow from the hot air outlet of the hot drying section and adds another portion of airflow. The two portions of airflow converge as the inlet airflow of the hot drying section to dry the polyamide solid material in the hot drying section. This can create a near-steady-state hot air circulation environment in the hot drying section, which is conducive to maintaining a stable drying environment in the hot drying section. Under the condition of achieving the same drying depth (moisture content meets the standard), only a small correction to the operating variables is needed to maintain the steady-state operation of the system. This avoids large-scale and large-amplitude control of high-flow-rate hot airflow, and can reduce or eliminate poor drying effect or fluctuations in the hot drying section. It is particularly suitable for the pre-processing of polyamide particles, which can not only obtain a better drying effect, but also avoid large changes in the properties of plastic particles during the drying process, especially the yellowness index changes little, thus taking into account both drying efficiency and color stability.

[0036] The fluidized continuous drying device of the present invention constructs a heat storage type fine-tuning hot air circulation in the hot drying section of the fluidized drying module. Utilizing its buffering effect, it can effectively offset the adverse fluctuations of heat exchangers, dampers, etc. in the hot drying section, forming a stable high-temperature drying environment in the hot drying section, thereby obtaining a final output product with more stable properties. This circulation makes full use of the waste heat of the exhaust air in the hot drying section, reduces the active adjustment of temperature and humidity parameters of the hot air inlet in the hot drying section, reduces the investment in related equipment, and reduces the difficulty of stable implementation in engineering practice. Attached Figure Description

[0037] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other similar combinations can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of a fluidized continuous drying apparatus according to an embodiment of the present invention.

[0039] Figure 2 This is a structural diagram of a fluidized continuous drying apparatus according to Embodiment 1 of the present invention.

[0040] Figure 3 This is a structural diagram of a fluidized continuous drying apparatus according to Embodiment 2 of the present invention.

[0041] Figure 4 This is a structural diagram of a fluidized continuous drying apparatus according to Embodiment 3 of the present invention.

[0042] Figure 5 This is a structural diagram of a fluidized continuous drying apparatus according to Embodiment 4 of the present invention.

[0043] Figure 6 This is a structural diagram of a drying device for comparison.

[0044] The attached figures are labeled as follows: 1. Fluidized bed drying module; 10. Fluidized bed dryer; 11. Hot drying section; 111. Hot air inlet; 112. Hot air outlet; 113. Feed inlet; 12. Cooling section; 121. Cooling air duct; 121a. Cooling section fan; 122. Second heating device; 123. Cooling air inlet; 124. Cooling air outlet; 125. Cooled material discharge outlet; 2. Air intake module; 21. Return duct; 22. Makeup air duct; 23. First fan; 24. First heating device; 25. First dust separation device; 3. Exhaust module; 31. First exhaust duct; 32. Second exhaust duct; 33. Second dust separation device; 34. Third fan; 35. Waste heat exchanger; 36. Waste gas condenser; 4. Airflow pretreatment module; 41. Gas filter; 42. Condenser; 43. Second fan; 44. Branch piping; 51. Gas inlet; 52. Gas outlet. Detailed Implementation

[0045] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art. It should be noted that the description of these embodiments is for the purpose of aiding understanding the present invention, but does not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0046] For drying polyamide particles, existing traditional drying methods are insufficient to meet the requirements of both low moisture content and high color stability. For example, patents CN203704617U, CN100376470C, and CN213631192U involve drastically raising the temperature of ambient cold air from zero starting point to the required process temperature in a single pass. This large-scale, large-amplitude control of high-flow-rate, rapidly changing hot air is used to cope with fluctuating moisture content of upstream materials. This is not conducive to precise matching and control of the hot air in actual engineering implementation, and can easily lead to poor or fluctuating drying effect of the dryer. For temperature-sensitive polyamide particles, this can easily cause product deterioration. All the air required for the hot drying section of the dryer must be controlled by the heater in a single pass. The air volume requiring temperature and humidity control is too large, which is not conducive to actual engineering implementation and places excessive demands on equipment performance and factory space. Patent CN117570762B relies on complex compressor equipment to achieve airflow pressurization and transmission. The separation of wet components from the wet material entering the system relies on a unique self-condensing water dryer; however, it also suffers from large temperature and humidity variations in the airflow and difficulty in adjusting and resetting parameters such as temperature, which is detrimental to the stable operation of the system.

[0047] Based on this, the following describes embodiments of a continuous polyamide drying process and embodiments of a fluidized continuous drying device that can be used for polyamide drying. This device is characterized by stable efficiency, easy operation, low initial investment and operating costs, independence from high-pressure systems, high-turbine air introduction equipment, high difficulty and unique self-condensing water dryers, high flexibility in air medium selection, energy saving, heat storage, in-situ air return capability, and long-term operation capability.

[0048] This fluidized bed continuous drying device includes a fluidized bed drying module. The fluidized bed drying module is a single fluidized bed dryer with a hot drying section and a cooling section, or it may include multiple fluidized bed dryers, with several at the front serving as the hot drying section and several at the rear serving as the cooling section. The material first enters the hot drying section of the fluidized bed drying module, and then flows through the cooling section. The main function of the hot drying section is to dry and separate the moisture from the source material, while the main function of the cooling section is to control the discharge temperature to a range acceptable to downstream processes. The hot drying section and cooling section have separate air inlets and outlets. The airflow, air temperature, and residence time distribution between the hot drying section and cooling section depend on the physical properties of the source material, including its composition, moisture content, temperature, flow rate, morphology, and particle size distribution.

[0049] The following Examples 1 to 5 specifically describe several fluidized continuous drying apparatuses.

[0050] Example 1 Figure 1 A simplified fluidized continuous drying apparatus according to Example 1 is shown. See also Figure 1 As shown, the fluidized continuous drying device mainly includes: fluidized drying module 1, air inlet module 2, and air outlet module 3.

[0051] The fluidized bed drying module 1 is configured to allow wet solid materials or supersaturated slurries to flow through it. In this embodiment, the fluidized bed drying module 1 includes a single fluidized bed dryer 10, which includes a fluidized bed through which the wet solid materials or supersaturated slurries continuously flow. The front section of the single fluidized bed dryer 10 serves as a hot drying section 11, and the rear section serves as a cooling section 12. The airflow in the hot drying section 11 and the cooling section 12 are isolated from each other, and the cooling section 12 is located behind the hot drying section 11. The upstream material enters through the feed inlet 113 at the front end of the fluidized bed drying module 1, is dried in the hot drying section 11, then cooled in the cooling section 12, and finally exits from the rear end of the fluidized bed drying module 1 downstream. The material flows horizontally or nearly horizontally (at an angle of less than 45 degrees to the horizontal plane) through the hot drying section 11, the cooling section 12, or the entire fluidized bed drying module 1. The hot drying section 11 specifically includes a hot air inlet 111 into which the heating airflow enters and a hot air outlet 112 into which the heating airflow exits; wherein, the hot air inlet 111 is located at the lower part of the hot drying section 11, and the hot air outlet 112 is located at the upper part of the hot drying section 11, and the hot airflow passes through the hot drying section 11 from bottom to top. The cooling section 12 has a cooling airflow inlet 123, a cooling airflow outlet 124, and a cooled material discharge outlet 125.

[0052] The air inlet module 2 is used to introduce airflow into the fluidized drying module 1, including introducing hot airflow into the hot drying section 11 and / or introducing cooling airflow into the cooling section 12. The air inlet module 2 mainly includes a return pipe 21 and a makeup air pipe 22. The return pipe 21 is used to introduce a portion of the hot airflow from the hot air outlet 112 as a return hot airflow. The makeup air pipe 22 is used to introduce makeup airflow. The makeup air pipe 22 and the return pipe 21 are connected together and then connected to the hot air inlet 111. The makeup airflow is used as the first makeup airflow, and the first makeup airflow and the return hot airflow are combined and then introduced into the hot air inlet 111. The moisture content of the first makeup airflow is less than that of the return hot airflow, and the flow ratio of the return hot airflow to the first makeup airflow is greater than 1:1, so that the humidity and temperature in the hot drying section 11 are within a preset steady-state range.

[0053] The exhaust module 3 includes a first exhaust duct 31 and a second exhaust duct 32. The first exhaust duct 31 is directly or indirectly connected to the hot air outlet 112 of the hot air section 11, and is used to discharge the residual hot air in the hot air flowing out of the hot air outlet 112. That is, the hot air discharged from the hot air section 11 is divided into two parts: most of it is used as return hot air and circulates back into the hot air section 11 through the return duct 21; a small part is used as residual hot air discharged through the first exhaust duct 31. The second exhaust duct 32 is connected to the cooling air outlet 124 of the cooling section 12, and discharges the exhaust gas flowing out of the cooling air outlet 124 of the cooling section 12.

[0054] Furthermore, the inlet and outlet airflow of the hot drying section 11 is controlled according to one or more of the following parameters (1) to (5) to create a steady-state drying environment within the hot drying section 11: (1) The flow ratio of the return hot air flow to the first supplementary air flow is 1:1 to 15:1, preferably 5:1 to 15:1; (2) The temperature difference between the first supplementary airflow and the return hot airflow is 5% to 300% of the temperature of the return hot airflow; in the embodiments, the temperatures are all in Celsius. (3) The relative humidity when the first supplementary airflow enters the hot drying section is less than 20%, preferably less than 3%, and more preferably less than 1%; (4) The combined first supplementary airflow and return hot airflow enter the hot drying section 11 at a temperature of 50~250°C, preferably at a temperature of 105~120°C; for most operating conditions, the temperature is controlled at 80~200°C; more specifically, it can be controlled at 105~120°C. (5) The flow rate of the remaining hot air is 6 to 50% of the total flow rate of the hot air discharged from the hot drying section 11.

[0055] Furthermore, the air intake module 2 also includes a first fan 23 and a first heating device 24. The first fan 23 is installed on the duct after the return duct 21 and the makeup air duct 22 are combined, driving the return hot airflow and the first makeup airflow to flow to the hot drying section 11 after they are combined in the makeup air duct 22. The first heating device 24 is installed on the makeup air duct 22 and is used to heat the makeup airflow in the makeup air duct 22. The first heating device 24 can be an electric heater, a steam heater, or other types of heat exchangers.

[0056] In the hot drying section 11, the recirculating hot airflow and the first supplementary airflow merge and enter the hot drying section 11. After exchanging heat and humidity with the materials therein, the airflow exits from the hot airflow outlet 112. Part of the airflow returns to the hot drying section 11, while the other part is directly discharged as waste gas or undergoes other treatment. In the cooling section 12, the cooling airflow inlet 123 is connected to a cooling air duct 121. A cooling section fan 121a can also be installed on the cooling air duct 121 to introduce cooling airflow into the cooling section 12. After the cooling airflow cools the materials flowing through the cooling section 12, it exits from the cooling airflow outlet 124 and is discharged through the second exhaust duct 32.

[0057] In this embodiment, the mechanism for constructing a near-steady-state drying environment is as follows: the humidifying hot air that quickly passes through the material in the hot drying section 11 is far from reaching moisture saturation and can still be recycled as drying air for the hot drying section 11. By recirculating a portion of the humidifying circulating hot air (returning hot airflow) discharged from the hot drying section 11 and simultaneously supplementing it with the first supplementary airflow, the hot air circulation in the hot drying section 11 can be maintained within a controllable steady-state range of moisture content. At the same time, the supplementary first supplementary airflow is heated to almost equal amount to compensate for the heat carried away by the remaining hot airflow discharged from the first exhaust duct 31, thereby maintaining the hot air circulation within the hot drying section 11 within a controllable steady-state range of temperature.

[0058] Therefore, by supplementing dryness and energy in the hot drying section 11, the internal energy changes of the material passing through the hot drying section 11, the natural heat dissipation loss of the entire hot drying section 11 cycle, and the heat energy and moisture components carried away by the residual hot air flow are offset, forming a heat storage and fine-tuning hot air circulation in the hot drying section 11. This circulation only requires active adjustment of the temperature and humidity parameters of a small amount of supplementary air (i.e., the first supplementary airflow introduced into the supplementary air pipe 22) to indirectly fine-tune the overall temperature and humidity state of the hot air circulation in the hot drying section 11; the difficulty of stabilizing the hot air circulation in the hot drying section 11 is greatly reduced; at the same time, due to the buffering effect of the return hot airflow, the adverse fluctuations of the first heating device 24 and the first fan 23 in the hot drying section 11 can be effectively offset, which is very beneficial to the stability of material property changes in the high temperature environment of the hot drying section 11, so as to ensure the stability of the properties of the final output product of this system. In addition, it indirectly achieves efficient utilization of the waste heat energy of the hot air discharged from the hot drying section 11, reducing the investment in the related first heating device 24 and auxiliary pipe valve components; combined with the disassembly and miniaturization of the first fan 23 and supporting dust removal facilities, it further reduces the difficulty of space layout for large-sized equipment in the factory.

[0059] Example 2 Figure 2 A specific fluidized continuous drying apparatus according to Example 2 is shown. (Refer to...) Figure 2 As shown, this embodiment has the same fluidized bed drying module 1 as in embodiment 1, and its structure will not be described in detail.

[0060] The air inlet module 2 in this embodiment also includes a first dust separation device 25, which is otherwise the same as the air inlet module in embodiment 1. The first dust separation device 25 is disposed on the return pipe 21 and is connected to the return pipe 21, and is used to remove dust from the return hot airflow. The first dust separation device 25 may specifically include a dust collector, such as a bag filter. The inlet airflow and outlet airflow of the hot drying section 11 are also controlled according to one or more of the parameters (1) to (5) described in embodiment 1, so as to build a steady drying environment in the hot drying section 11.

[0061] The exhaust module 3 in this embodiment includes the same first exhaust duct 31 and second exhaust duct 32 as in embodiment 1. In addition, the exhaust module 3 in this embodiment also includes a second dust separation device 33 and a third fan 34. The exhaust gases discharged from the first exhaust duct 31 and the second exhaust duct 32 are combined and enter the second dust separation device 33 for dust removal treatment, and are then discharged through the third fan 34. The second dust separation device 33 may specifically include a dust collector, such as a bag filter.

[0062] In this embodiment, the fluidized continuous drying device further includes an airflow pretreatment module 4, which pretreatments the supplementary airflow to the fluidized drying module 1. Specifically, the airflow pretreatment module 4 pretreatments the fresh air before supplementing it into the hot drying section 11 and the cooling section 12 of the fluidized drying module 1. The airflow pretreatment module 4 includes a gas filter 41, a condenser 42, and a second fan 43. The gas filter 41, the second fan 43, and the condenser 42 are arranged sequentially. The fresh air is first filtered by the gas filter 41, and then driven by the second fan 43 into the condenser 42 to remove moisture. The final treated fresh, dry, and cold airflow enters the make-up air duct 22. A portion of it serves as the first supplementary airflow to the hot drying section 11; the remaining portion serves as the second supplementary airflow, which enters the cooling section 12 through a branch line (cooling air duct 121) connected to the make-up air duct 22 as the cooling airflow.

[0063] Furthermore, the first supplementary airflow, after being heated by the first heating device 24, merges with the return hot airflow after dust removal and is sent into the hot drying section 11 by the first fan 23. The second supplementary airflow, after being heated by the second heating device 122, is sent into the cooling section 12. The second heating device 122 is installed on the cooling air duct 121.

[0064] In this embodiment, the fluidized bed drying module 1 uses a single fluidized bed dryer 10. In other embodiments, the fluidized bed drying module 1 uses multiple fluidized bed dryers 10, which are connected sequentially. Several fluidized bed dryers 10 at the front serve as a hot drying section 11, and several fluidized bed dryers 10 at the rear serve as a cooling section 12. The material flows sequentially through these multiple fluidized bed dryers 10 from front to back. In yet another embodiment, the fluidized bed drying module 1 may only include a hot drying section without a cooling section; if it is a single fluidized bed dryer 10, the entire fluidized bed dryer serves as the hot drying section; that is, the material is not cooled after hot drying.

[0065] In this embodiment, the first fan 23 is installed on the duct after the return duct 21 and the make-up air duct 22 are combined, and the first heating device 24 is installed on the make-up air duct 22. In other embodiments, the first fan 23 may be installed on the return duct 21, and the first heating device 24 may be installed on the duct after the return duct 21 and the make-up air duct 22 are combined. That is, the first make-up airflow and the return hot airflow are combined and then heated to the required temperature (e.g., 80~200℃) by the first heating device 24.

[0066] In this embodiment, the first fan 23 is located behind the first dust separation device 25. In other embodiments, the first fan 23 may be located in front of the first dust separation device 25.

[0067] In this embodiment, the airflow pretreatment module 4 first condenses the airflow before distributing it to the heating section 11 and the cooling section 12. In other embodiments, the make-up air duct 22 can be directly connected to the gas filter 41, and a portion of the filtered gas is directly used as the first make-up airflow, which is then separately heated (by the first heating device 24). A portion of the gas filtered by the gas filter 41 is then separately condensed (processed by the condenser 42) and heated (by the second heating device 122) to become the cooling airflow to be introduced into the cooling section 12.

[0068] In this embodiment, the second heating device 122 is disposed on the cooling air duct 121. In other embodiments, the second heating device 122 may be disposed on the make-up air duct 22 or in front of the make-up air duct 22. That is, after the make-up airflow is heated as a whole by the second heating device 122, the airflow in the make-up air duct 22 is divided into two branches: a first make-up airflow and a second make-up airflow. The second make-up airflow can be directly introduced into the cooling section 12 without further heating.

[0069] In this embodiment, the second dust separation device 33 is a dust collector. In other embodiments, the second dust separation device 33 may be a cyclone separator.

[0070] Example 3 Figure 3 A specific fluidized continuous drying apparatus of Example 3 is shown. (Refer to...) Figure 3 As shown, the main difference between this embodiment and embodiment 2 lies in the exhaust module 3.

[0071] In this embodiment, the exhaust module 3 includes a waste heat exchanger 35, which can recover the waste heat of the hot and humid airflow discharged from the first exhaust duct 31, further reducing energy consumption. Specifically, the waste heat exchanger 35 has a first channel and a second channel, which are not connected to each other but are in direct or indirect contact for heat exchange. The first exhaust duct 31 is connected to the inlet of the first channel of the waste heat exchanger 35, and the outlet of the first channel is connected to the second dust separation device 33 via a combined pipe and the second exhaust duct 32. The airflow pretreatment module 4 is connected to the inlet of the second channel via a branch pipe 44, and the outlet of the second channel is connected to the makeup air duct 22.

[0072] The airflow pretreatment module 4 divides the filtered, condensed, and heated fresh air into two parts. One part is introduced into the cooling section 12, and the other part is sent to the waste heat exchanger 35 through the branch pipe 44. In the waste heat exchanger 35, the fresh air exchanges heat with the residual hot airflow discharged from the hot drying section 11. The heated fresh air is then introduced into the hot drying section 11 through the makeup air pipe 22 and merged with the dust-removed return hot airflow. The fresh airflow is further heated by the first heating device 24 and finally introduced into the hot drying section 11. The residual hot airflow discharges some heat in the waste heat exchanger 35 and merges with the exhaust gas in the second exhaust pipe 32. The exhaust gasflow is then processed by the second dust separation device 33 and discharged by the third fan 34.

[0073] Example 4 Figure 4 A specific fluidized continuous drying apparatus according to Example 4 is shown. (Refer to...) Figure 4 As shown, the main difference between this embodiment and embodiment 2 is that this embodiment uses inert gas to dry the material in the fluidized drying module 1.

[0074] Specifically, the fluidized continuous drying device has a gas inlet 51 and a gas outlet 52. The gas inlet 51 is connected to an inert gas source and to the airflow pretreatment module 4. The inert gas is first sent to the condenser 42 by the second fan 43 to remove the water vapor, and then divided into two parts. One part is introduced into the make-up air duct 22 as the first make-up airflow, and after dust removal and heating treatment, it is introduced into the hot drying section 11. The other part is heated by the second heating device 122 and then introduced into the cooling section 12. The exhaust gas from the first exhaust duct 31 and the second exhaust duct 32 is discharged through the gas outlet 52 after passing through the second dust separation device 33.

[0075] Furthermore, the fluidized bed drying module 1 employs two fluidized bed dryers 10a and 10b, which are arranged one after the other and interconnected. The front fluidized bed dryer 10a serves as the heating section 11, and the rear fluidized bed dryer 10b serves as the cooling section 12. The material flows sequentially through the fluidized bed dryers 10a and 10b from front to back.

[0076] Example 5 Figure 5 A specific fluidized continuous drying apparatus according to Example 5 is shown. (Refer to...) Figure 5 As shown, this embodiment also uses inert gas, and the main difference from embodiment 4 is that the positions of the gas inlet 51 and the gas outlet 52 are different.

[0077] Specifically, the make-up air duct 22 is directly connected to the gas inlet 51 to directly replenish inert gas from the inert gas source. This newly replenished first make-up airflow and the return hot airflow from the return duct 21 are combined and then treated by dust removal in the first dust separation device 25, and then heated by the first heating device 24 before entering the hot drying section 11.

[0078] The exhaust module 3 also includes a waste heat exchanger 35 and a waste gas condenser 36. The second dust separation device 33, the third fan 34, and the waste gas condenser 36 are connected in sequence, with the outlet of the waste gas condenser 36 connected to the waste heat exchanger 35. The gas outlet 52 is located behind the third fan 34 and in front of the waste gas condenser 36. The first exhaust duct 31 is also connected to the waste heat exchanger 35. The residual hot air flow from the first exhaust duct 31 into the waste heat exchanger 35, after heat exchange, merges with the dust-treated waste gas discharged from the cooling section 12 through the second exhaust duct 32. A portion of this merges with the waste gas discharged from the heating section 11 through the first exhaust duct 31. A portion of this merged gas is discharged through the gas outlet 52, while the remaining portion passes through the waste gas condenser 36, undergoes condensation, and then enters the waste heat exchanger 35. This merged gas then exchanges heat with the residual hot air flow from the heating section 11 through the first exhaust duct 31 in the waste heat exchanger 35. After being heated by the second heating device 122, the merged gas is then sent to the cooling section 12 through the cooling air duct 121.

[0079] The following Examples 6 to 10 specifically describe several continuous drying processes for polyamides.

[0080] Example 6 The polyamide particles were dried using the fluidized continuous drying apparatus described in Example 2, including the following steps: Step S1: Allow polyamide particles to continuously flow through the self-fluidized drying module 1; Step S2: A portion of the hot air discharged from the hot air outlet 112 of the hot air section 11 is used as a return hot air stream. The return hot air stream and the first supplementary air stream are combined and then introduced into the hot air section 11 through the hot air inlet 111. The flow ratio of the return hot air stream to the first supplementary air stream is 9:1.

[0081] Figure 2 This illustrates a specific working condition. Figure 2 The meanings of the parameters are as follows: M: Weight flow rate of the material; T: Temperature; Cw: Moisture content; F: Gas flow rate, measured by a flow meter; RH: Relative humidity, measured by a hygrometer.

[0082] Combination Figure 2 The specific drying process is as follows: Feeding: Polyamide pellets of 6000 kg / h are continuously fed into the fluidized bed dryer 10 through the feed inlet 113. The material temperature is 100℃, the relative moisture content is 0.25% kg / kg, the ASTM D1925 yellowness index is -5.2, and the standard deviation of the ASTM D1925 yellowness index fluctuation is 0.1.

[0083] Drying, cooling, and basic heat storage cycle: Air is filtered by air filter 41, then drawn in by the second fan 43, and then cooled and dehumidified by condenser 42 to become saturated air with a flow rate of 11000 kg / h, a temperature of 15.5°C, and a relative humidity of 100%, at which point the moisture content is 11 g / kg. This saturated air is then divided into two streams, used in the hot drying section 11 and the cooling section 12 of the fluidized bed dryer 10, respectively.

[0084] 1) A stream of saturated humid air enters the make-up air duct 22. After being heated by the first heating device 24, it is combined with the return hot air from the return duct 21 as the first make-up airflow. Under the delivery of the first fan 23, a total of 11,000 kg / h of hot dry air at 105°C enters the hot drying section 11 through the hot air inlet 111. After drying, the temperature changes to 103°C and is discharged from the hot air outlet 112: ① Most of it is purified by the first dust separation device 25 and enters the return duct 21. Before being drawn into the first fan 23, it is cooled down to 98°C and reused as the return hot airflow; ② In the hot airflow discharged from the hot air outlet 112, a small amount of humidifying air that is almost equal to that of the make-up air duct 22 is discharged through the first exhaust duct 31, completely carrying away the 6 kg / h of moisture lost during material drying; maintaining the humidity balance of the drying air system and constructing a heat storage and fine-tuning hot air circulation.

[0085] 2) The remaining portion of the 10,000 kg / h of saturated wet air is heated to 20°C by the second heating device 122, at which point the relative humidity changes to 75%, and then blown into the cooling section 12 of the fluidized bed dryer 10. After the material in the cooling section 12 is cooled to 50°C as required by the downstream process, it is discharged from the second exhaust duct 32 and merged with the small amount of humidifying air discharged from the first exhaust duct 31. After being purified by the second dust separation device 33, it is then discharged through the third fan 34.

[0086] Temperature and humidity balance regulation in heat storage circulation: The first supplementary airflow, with a flow rate of 1000 kg / h, is heated to 175°C by the first heating device 24, and the relative humidity is reduced to 0.2%. Then, it is combined with the return hot airflow from the return pipe 21 and enters the first fan 23, forming an airflow with a moisture content of 16.4 g / kg and a relative humidity of 2.2%. After humidification in the self-heating drying section 11, two streams of hot airflow are discharged from the hot air outlet 112. One is a small stream of 1006 kg / h of exhaust humidifying air discharged through the first exhaust pipe 31, and the other is the remaining 10000 kg / h of recirculated hot airflow. The relative humidity of both streams is 2.4%, and the moisture content is 16.9 g / kg. The relative humidity of the return hot airflow is 2.9% after cooling down before being incorporated into the first fan 23.

[0087] This cycle achieves relatively constant moisture and temperature in the circulating air system of the hot drying section 11 by actively adjusting a small amount of the first supplementary airflow, corresponding to an almost equal amount of automatically discharged small amount of humidifying air (residual hot airflow). This results in a continuous and relatively stable drying environment for the moisture in the dried polyamide particles, which helps to reduce the unstable discharge characteristics that often occur in fluidized bed dryers 10, such as over-drying causing discoloration and under-drying causing high moisture content.

[0088] Output: The moisture content of the polyamide ions after drying (GB / T12006.2-2009) is 0.15% kg / kg, the ASTM D1925 yellowness index is -5.14, and the standard deviation of the ASTM D1925 yellowness index fluctuation of 98% of the data is 0.12.

[0089] Example 7 In this embodiment, the flow ratio of the recirculating hot airflow to the first supplementary airflow is 1:1. In the temperature and humidity balance adjustment section of the heat storage cycle: the first supplementary airflow, with a flow rate of 5500 kg / h, is heated to 112°C by the first heating device 24, and the relative humidity is reduced to 1.2%; then it is combined with the recirculating hot airflow from the recirculation pipe 21 and enters the first fan 23, forming an airflow with a moisture content of 11.5 g / kg and a relative humidity of 1.55%; after humidification in the self-heating drying section 11, the two streams of hot airflow discharged from the hot airflow outlet 112 are a small stream of 5506 kg / h of exhaust humidifying air discharged through the first exhaust pipe 31 and the remaining 5500 kg / h reused as recirculating hot airflow. Both streams have a relative humidity of 1.75% and a moisture content of 12.1 g / kg, and the relative humidity of the recirculating hot airflow is 2% after cooling down before being incorporated into the first fan 23. Other aspects are the same as in embodiment 6.

[0090] Output: The moisture content of the polyamide ions after drying (GB / T12006.2-2009) is 0.15% kg / kg, the ASTM D1925 yellowness index is -5.08, and the standard deviation of the ASTM D1925 yellowness index fluctuation of 98% of the data is 0.14.

[0091] Example 8 In this embodiment, the flow ratio of the recirculating hot airflow to the first supplementary airflow is 15:1. In the temperature and humidity balance adjustment section of the heat storage cycle: the first supplementary airflow, with a flow rate of 687.5 kg / h, is heated to 210°C by the first heating device 24, and the relative humidity is reduced to 0.1%; then it is combined with the recirculating hot airflow from the recirculation pipe 21 and enters the first fan 23, forming an airflow with a moisture content of 19 g / kg and a relative humidity of 2.5%; after humidification in the self-heating drying section 11, the two streams of hot airflow discharged from the hot airflow outlet 112 are a small stream of 693.5 kg / h of exhaust humidifying air discharged through the first exhaust pipe 31 and the remaining 10312.5 kg / h reused as recirculating hot airflow. Both streams have a relative humidity of 2.8% and a moisture content of 19.5 g / kg, with the recirculating hot airflow having a relative humidity of 3.4% after cooling down before being incorporated into the first fan 23. Other aspects are the same as in embodiment 6.

[0092] Output: The moisture content of the polyamide ions after drying (GB / T12006.2-2009) is 0.15% kg / kg, the ASTM D1925 yellowness index is -5.11, and the standard deviation of the ASTM D1925 yellowness index fluctuation of 98% of the data is 0.11.

[0093] Example 9 In this embodiment, the temperature difference between the first supplementary airflow and the return hot airflow is 100% of the temperature of the return hot airflow. In the temperature and humidity balance adjustment section of the heat storage cycle: the first supplementary airflow, with a flow rate of 786 kg / h, is heated to 196°C by the first heating device 24, and the relative humidity is reduced to 0.1%; then it is combined with the return hot airflow from the return pipe 21 and enters the first fan 23, forming an airflow with a moisture content of 18 g / kg and a relative humidity of 2.4%; after humidification in the self-heating drying section 11, the two streams of hot airflow discharged from the hot airflow outlet 112 are a small stream of humidifying airflow of 792 kg / h discharged through the first exhaust pipe 31 and the remaining 10214 kg / h reused as return hot airflow. Both streams have a relative humidity of 2.7% and a moisture content of 18.5 g / kg, and the relative humidity of the return hot airflow is 3.2% after cooling down before being incorporated into the first fan 23. Other aspects are the same as in embodiment 6.

[0094] Output: The moisture content of the polyamide ions after drying (GB / T12006.2-2009) is 0.15% kg / kg, the ASTM D1925 yellowness index is -5.13, and the standard deviation of the ASTM D1925 yellowness index fluctuation of 98% of the data is 0.11.

[0095] Example 10 In this embodiment, the moisture content of the first supplementary airflow is 13 g / kg.

[0096] Drying, cooling and basic heat storage cycle: After cooling and dehumidification by condenser 42, the air temperature is 18℃. After being heated by the second heating device 122, the air temperature is 25℃ (at this time, the relative humidity changes to 65%). Temperature and humidity balance regulation in heat storage circulation: The combined airflow into the first fan 23 has a moisture content of 18.4 g / kg and a relative humidity of 2.5%. After humidification in the self-heating drying section 11, the two hot airflows discharged from the hot airflow outlet 112 have a relative humidity of 2.7% and a moisture content of 18.9 g / kg. The return hot airflow has a relative humidity of 3.3% after cooling down before being combined into the first fan 23.

[0097] The rest is the same as in Example 6.

[0098] Output: The moisture content of the polyamide ions after drying (GB / T12006.2-2009) is 0.15% kg / kg, the ASTM D1925 yellowness index is -5.14, and the standard deviation of the ASTM D1925 yellowness index fluctuation of 98% of the data is 0.12.

[0099] Comparative Example 1 Figure 6 A conventional continuous drying scheme for polyamide particles is shown.

[0100] Feed: Polyamide pellets of 6000 kg / h are continuously fed into the inlet of fluidized bed dryer 1'. The material temperature is 100℃, the relative moisture content is 0.25% kg / kg, the ASTM D1925 yellowness index is -5.2, and the standard deviation of the ASTM D1925 yellowness index fluctuation is 0.1.

[0101] Drying: Air is supplied by fan 2' to gas filter 3' in the hot drying section. After filtration, the air is cooled and dehumidified by condenser 11' in the hot drying section, resulting in dehumidified cold air with a capacity of 11000 kg / h, a moisture content of 11 g / kg, a temperature of 15.5℃, and a relative humidity of 100%. This air is then heated to 105℃ by heater 8' in the hot drying section, with a relative humidity of 2.2%, before being blown into the hot drying section of fluidized bed dryer 1'. Air is supplied by fan 5' to gas filter 4' in the cooling section. After filtration, this air is cooled and dehumidified by condenser 6' in the cooling section, resulting in dehumidified cold air with a capacity of 10000 kg / h, a moisture content of 11 g / kg, a temperature of 15.5℃, and a relative humidity of 100%. This air is then heated to 20℃ by heater 7' in the cooling section, with a relative humidity of 74.5%, before being blown into the cooling section of fluidized bed dryer 1'.

[0102] Polyamide particles are dehumidified and dried in the hot drying section, and then cooled to 50°C in the cooling section to meet the downstream process requirements before being discharged downstream. The hot drying section of the fluidized bed dryer 1' discharges waste hot air at 11006 kg / h, 11.54 g / kg, 103°C, and 1.7% relative humidity, while the cooling section discharges waste cold air at 10000 kg / h, 11 g / kg, 70°C, and 3.9% relative humidity. After being combined and purified by the refrigerated dust collector 9', the air is then conveyed and discharged by the induced draft fan 10'.

[0103] Output: The moisture content of the dried polyamide pellets (GB / T 12006.2-2009) is 0.15% kg / kg, the ASTM D1925 yellowness index is -4.94, and the standard deviation of the ASTM D1925 yellowness index fluctuation of 98% of the data is 0.25.

[0104] Compared with Comparative Example 1, the yellowness index of the product obtained in Example 6 fluctuated less and the degree of yellowing was lower, and the drying process of Example 6 consumed less energy.

[0105] Compared to Comparative Example 1, the ASTM D1925 yellowness index fluctuation standard deviation of 98% of the data from Example 6 was lower, effectively improving the quality stability of fluidized bed dried polyamide particles, reducing batch-to-batch variability, and thus enhancing the product's commercial competitiveness. In Example 6, the hot air entering the drying section only needs to heat a small 1000 kg / h first supplementary airflow, reducing energy consumption by more than 80%. Simultaneously, the reduced heat exchange requirements of the first heating device in the drying section allow for a corresponding reduction in its heat exchange area, significantly decreasing equipment size and footprint. The engineering practice temperature and humidity control parameters of the hot air entering the drying section were also significantly reduced to approximately 15%. A finely tuned hot air circulation was constructed using a recirculating hot airflow, providing a large buffer margin for the incoming air in the drying section, and greatly improving the high-temperature stability of drying. The required airflow for the third fan was reduced by approximately 48%, and the volume and cost of the third fan and the preceding and following ducts were significantly reduced.

[0106] This invention utilizes the high-quality temperature and dryness resources contained in the humidifying air of the hot drying section of a fluidized bed dryer, which has been overlooked in previous solutions. It breaks away from the conventional thinking that all parameters of the hot air entering the hot drying section of a traditional fluidized bed dryer should be adjusted from zero. The humidifying hot dry air, which quickly passes through the material in the hot drying section and is far from reaching moisture saturation, is then replenished and finely adjusted for balance. It is then reintroduced into the hot drying section as a return hot air stream, becoming a highly reusable in-situ drying air. This constructs a heat storage-type fine-tuned hot air circulation in the hot drying section, achieving continuous drying operation. It does not rely on a special self-condensing water dryer, a high-configuration compressor, or an excessively high-pressure air turbine. It does not require extremely high system pressure resistance, has no forced air turbulence mixing, and can maintain long-term stability with low energy consumption.

[0107] In the regenerative fine-tuning hot air circulation of the hot drying section, the buffering effect of the recirculating hot airflow effectively offsets the adverse fluctuations caused by heating devices in the hot drying section, creating a more stable high-temperature drying environment. This results in a more stable final product. The circulation fully utilizes the residual heat of the hot airflow discharged from the hot drying section, reducing the need for active temperature and humidity control of the incoming hot airflow, minimizing equipment investment, and lowering the difficulty of implementation and control in engineering practice. This leads to lower construction costs and greater energy savings during construction and operation.

[0108] As indicated in this specification and claims, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, and these steps and elements do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0109] The “approximately” before the numerical value should be understood as including the range of experimental errors that inevitably occur in routine measurements, which may be affected by the measurement method, instrument accuracy, sample condition and environmental conditions.

[0110] It is further understood that the terms "first," "second," etc., are used to describe various types of information, but this information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another, and do not indicate a specific order or degree of importance. In fact, the expressions "first," "second," etc., are completely interchangeable. For example, without departing from the scope of this disclosure, first information can also be referred to as second information, and similarly, second information can also be referred to as first information.

[0111] The above embodiments are only for illustrating the technical concept and features of the present invention, and are preferred embodiments. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the scope of protection of the present invention.

Claims

1. A continuous drying process for polyamide, characterized in that, include: Step S1: The wet polyamide solid material is continuously flowed through the fluidized bed drying module, which includes a hot drying section with a hot air inlet and a hot air outlet; Step S2: A portion of the hot airflow discharged from the hot airflow outlet of the hot drying section is used as a return hot airflow. The return hot airflow and the first supplementary airflow are combined and then introduced into the hot drying section through the hot airflow inlet. In step S2, the flow ratio of the return hot airflow to the first supplementary airflow is controlled to be 1:1 to 15:1, so that the humidity and temperature in the hot drying section are within a preset steady-state range.

2. The continuous drying process for polyamide according to claim 1, characterized in that, In step S2, the temperature difference between the first supplementary airflow and the return hot airflow is controlled to be 5% to 300% of the temperature of the return hot airflow.

3. The continuous drying process for polyamide according to claim 1, characterized in that, The relative humidity when the first supplementary airflow and the return hot airflow enter the hot drying section is below 20%.

4. The continuous drying process for polyamide according to claim 3, characterized in that, The relative humidity when the first supplementary airflow and the return hot airflow enter the hot drying section is below 3%.

5. The continuous drying process for polyamide according to claim 1, characterized in that, In step S2, the first supplementary airflow and the return hot airflow are combined and then enter the hot drying section at a temperature of 50~250°C.

6. The continuous polyamide drying process according to claim 1, characterized in that, In step S2, the humidity and temperature in the hot drying section are kept within a preset steady-state range by controlling the following parameters: the flow ratio of the recirculating hot airflow to the first supplementary airflow is 5:1 to 15:1, the temperature difference between the first supplementary airflow and the recirculating hot airflow is 5% to 300% of the temperature of the recirculating hot airflow, the relative humidity of the first supplementary airflow when it enters the hot drying section is below 1%, and the temperature of the combined first supplementary airflow and the recirculating hot airflow when they enter the hot drying section is 105 to 120°C.

7. The continuous drying process for polyamide according to claim 1, characterized in that, The first supplementary airflow enters the hot drying section after undergoing dust removal and / or charge control treatment. The flow rate of the residual hot airflow discharged from the hot airflow outlet of the hot drying section, excluding the return hot airflow, is 6% to 50% of the total hot airflow discharged from the hot airflow outlet of the hot drying section; The remaining hot air is fed into the first channel of the waste heat exchanger; fresh air, fresh inert gas, or treated exhaust gas from the cooling section of the fluidized drying module is fed into the second channel of the waste heat exchanger, where it exchanges heat with the remaining portion of the hot air flow and serves as the first supplementary air flow or as the second supplementary air flow into the cooling section, which is located behind or below the hot drying section.

8. The continuous drying process for polyamide according to any one of claims 1 to 7, characterized in that, The moist polyamide solid material is polyamide particles, and the standard deviation of the ASTM D1925 yellowness index fluctuation of 98% of the data of the polyamide particles after drying is less than 0.

15.

9. A fluidized bed continuous drying apparatus, comprising: A fluidized bed drying module is configured to allow a continuous flow of moist solid material or supersaturated slurry. The fluidized bed drying module includes a hot drying section, which has a hot air inlet for the hot air to enter and a hot air outlet for the hot air to exit. An air inlet module is used to supply airflow to the fluidized drying module; The air intake module is characterized by comprising: A return line is used to introduce a portion of the hot gas flow from the hot gas outlet as a return hot gas flow. The make-up air duct is used to introduce make-up airflow. At least a portion of the make-up airflow is used as the first make-up airflow and is combined with the return hot airflow before being introduced into the hot airflow inlet. The moisture content of the first make-up airflow is less than that of the return hot airflow. The flow ratio of the return hot airflow to the first make-up airflow is greater than 1:1, so that the humidity and temperature in the hot drying section are within a preset steady-state range. The fluidized continuous drying device further includes an exhaust module, which includes a first exhaust duct for discharging the remaining hot air from the hot air outlet, and the first exhaust duct is connected to the hot air outlet.

10. The fluidized bed continuous drying apparatus according to claim 9, characterized in that, The flow ratio of the recirculating hot airflow to the first supplementary airflow is 1:1 to 15:1; and / or, the temperature difference between the first supplementary airflow and the recirculating hot airflow is 5% to 300% of the temperature of the recirculating hot airflow; and / or, the relative humidity of the first supplementary airflow entering the hot drying section is below 20%; and / or, the combined first supplementary airflow and the recirculating hot airflow enter the hot drying section at a temperature of 50 to 250°C; and / or, the flow rate of the remaining hot airflow is 6% to 50% of the total flow rate of the hot airflow discharged from the hot drying section.

11. The fluidized bed continuous drying apparatus according to claim 9, characterized in that, The air intake module also includes: A first fan is used to drive the return hot airflow to flow in the return duct and / or drive the first supplementary airflow to flow in the supplementary air duct; The first heating device is used to heat the supplementary airflow in the make-up air duct, or to heat the return airflow in the return duct, or to heat the airflow after the return hot airflow and the first supplementary airflow are combined.

12. The fluidized bed continuous drying apparatus according to claim 9, characterized in that, The air intake module also includes: A first dust separation device is used to remove dust from the reflux hot airflow, and the first dust separation device is connected to the reflux pipeline; The first dust separation device includes a dust collector and / or a cyclone separator; And / or, the air intake module further includes a charge control device for processing the charge carried in the return hot airflow, the first supplementary airflow, or the airflow after the return hot airflow and the first supplementary airflow are combined. The charge control device is disposed on the first supplementary air duct, the return duct, or before the hot airflow inlet. The charge control device includes an electrostatic eliminator and / or a charge controller.

13. The fluidized bed continuous drying apparatus according to claim 9, characterized in that, The exhaust module further includes a second exhaust duct, which and / or the first exhaust duct are connected to a second dust separation device to remove dust from the discharged exhaust gas. The second dust separation device includes a dust collector and / or a cyclone separator. Waste heat exchangers are installed on the second exhaust duct and / or the first exhaust duct to utilize the energy of the waste gas in the second exhaust duct and / or the first exhaust duct.

14. The fluidized bed continuous drying apparatus according to any one of claims 9 to 13, characterized in that, The fluidized bed drying module includes a cooling section located behind the hot drying section. The cooling section has a cooling airflow inlet, a cooling airflow outlet, and a cooled material outlet. The cooling airflow inlet is connected to a cooling air duct, and the cooling air duct is connected to the make-up air duct to allow another part of the make-up airflow to pass through the cooling air duct into the cooling airflow inlet. The fluidized bed drying module includes a cooling section located behind the hot drying section. The cooling section has a cooling airflow inlet, a cooling airflow outlet, and a cooled material outlet. The cooling airflow inlet is connected to a cooling air duct, and / or the first exhaust duct, either alone or combined with the second exhaust duct, is connected to the cooling air duct to reuse the exhaust gas discharged through the second exhaust duct and / or the first exhaust duct. Among them, a portion of the recycled waste gas is combined with the return hot gas flow and then introduced into the hot gas flow inlet, while the other portion is connected to the cooling air duct and introduced into the cooling air flow inlet; And / or, all the recycled exhaust gas is connected to the cooling air duct to enter the cooling air inlet; The fluidized continuous drying apparatus further includes an airflow pretreatment module for pretreating the supplementary airflow to be supplied to the fluidized drying module, the airflow pretreatment module comprising: The second fan is used to drive the supplementary airflow. Gas filters for filtering the makeup gas stream and / or condensers for removing moisture from the makeup gas stream; The fluidized continuous drying device is a plastic particle drying device, and the fluidized drying module is configured to allow plastic particles to flow continuously to reduce the moisture content of the plastic particles.

15. The application of a fluidized continuous drying apparatus according to any one of claims 9 to 14 in the drying of polyamide.

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