Energy-saving and cost-reducing industrial tower suitable for polyester industry

Abstract

The present application relates to the field of chemical equipment, in particular to the energy-saving and consumption-reducing design of polyester industrial chemical equipment, which is achieved by the following technical scheme: an energy-saving and consumption-reducing industrial tower suitable for polyester industry, comprising a tower body, a reboiler, a plurality of trays located in the tower body, a packing zone and a liquid distributor located above all the trays, a condenser and a collecting tank connected to the top of the tower body, a water return device connected to the liquid distributor, a plurality of overflow holes with different heights located on the overflow slope, and a water outlet channel through the water outlet hole. The present application aims to provide an energy-saving and consumption-reducing industrial tower suitable for polyester industry, which can reduce the reflux ratio, the number of reflux liquid settings, the load of the heat boiler and the consumption of the coal water slurry while ensuring the separation effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chemical equipment, in particular to the energy consumption reduction and optimization design of polyester industrial chemical equipment. BACKGROUND

[0002] The production of polyethylene terephthalate (PET) is a kind of polyester production, and the core chemical reactions include esterification and polycondensation. The former is to obtain polyethylene terephthalate (PET) + water by reacting purified terephthalic acid + ethylene glycol (EG); the latter is to obtain longer chain polyester molecules + ethylene glycol by reacting PET molecules (or oligomers) + PET molecules (or oligomers). The longer chain polyester molecules are the final polyester product.

[0003] However, this reaction is a reversible reaction, and if the small molecules (water and ethylene glycol) generated by the reaction are not removed, the reaction will quickly reach equilibrium and stay at a low polymerization degree stage, and high molecular weight polymers cannot be obtained. One of the functions of the industrial tower is to continuously separate water and ethylene glycol, so that the chemical equilibrium is broken and the reaction continues to proceed towards the target product, successfully generating more high molecular weight polymers.

[0004] In actual production, industrial towers are not single, but different stages of industrial towers (first esterification kettle, second esterification kettle, pre-polycondensation kettle) are connected in series to form a continuous multi-stage reactor system. For example, the Chinese patent document with application number CN202121207716.0 discloses a multi-stage series industrial tower, and the adjacent industrial towers are connected by flow paths. Different industrial towers absorb and remove different substances, for example, esterification towers remove more water, and pre-polycondensation towers need to remove more ethylene glycol.

[0005] Different stages of industrial towers have different functions, but the structure and principle are similar, all of which are reaction, distillation and separation working principle. Specifically, taking the esterification industrial tower as an example, the Chinese patent document with application number CN201510503526.6 discloses a structure of an industrial tower. The reactants react in the industrial tower, and a heating structure such as a reboiler is provided at the bottom of the tower to increase the temperature of the tower cavity and generate steam. The temperature is controlled within a reasonable range, and the boiling point difference between the reactants, water and ethylene glycol is used. At this temperature, ethylene glycol remains in the liquid phase, water is in the gas phase, rises to the top of the tower, and is condensed and collected by an air cooler for discharge.

[0006] However, the working principle of distillation and separation of such industrial tower exists the phenomenon of simple "single machine flash evaporation", that is, the water-EG mixture is heated to a temperature between the boiling points of water and EG (such as 120℃), and is affected by thermodynamic equilibrium. Finally, at such a temperature, the gas phase at the top of the tower will be about 92% water and 8% EG, and the liquid phase at the bottom of the tower will be 92% EG and 8% liquid phase, that is, such 8% will make the separation efficiency poor and the purity of the obtained separation product not enough. In order to solve this problem, there is a technical means of "reflux setting" in the industrial tower. Specifically, a feed inlet is arranged in the tower body, the feed inlet is arranged to return the feed liquid, and different industrial towers are arranged to return different feed liquids, such as water reflux, ethylene glycol (EG) reflux, or water and EG reflux. Under such technical means, on the one hand, due to the concentration gradient generated in the tower, it is further beneficial to separation; on the other hand, the gas-liquid two-phase countercurrent contact is more sufficient (steam rising vs. liquid descending), which ensures the separation effect and makes the water vapor collected at the top have higher purity and greatly reduced EG impurities. The control parameter of this process in the industry is the reflux ratio, that is, the reflux ratio R = reflux liquid flow L / tower top product production flow D, which represents the amount of liquid that needs to be refluxed to the tower top for every unit of product produced. Obviously, sufficient reflux ratio can ensure and improve the separation purity.

[0007] However, when the flow of reflux is relatively large, that is, too much reflux liquid is refluxed into the tower body, although it is beneficial to improve the separation purity, but this part of the reflux liquid needs to be reheated to boiling in the tower, which undoubtedly makes the energy consumption of the whole industrial tower high and the consumption of fuel water coal slurry increases. SUMMARY

[0008] The purpose of the present application is to provide an energy-saving and consumption-reducing industrial tower suitable for polyester industry, which reduces the reflux ratio, reduces the setting of reflux liquid, and reduces the load of heat boiler and the consumption of water coal slurry under the premise of ensuring the separation effect.

[0009] The present application is realized by the following technical scheme: an energy-saving and consumption-reducing industrial tower suitable for polyester industry, comprising a tower body, a reboiler, a plurality of trays located in the tower body, a packing zone and a liquid distributor located above all the trays, a condenser and a collection tank connected to the top of the tower body, and a water reflux device connected to the liquid distributor, characterized in that the liquid distributor comprises a water inlet pipe connected to the water reflux device, a water placing disc connected to the water inlet pipe and extending in the horizontal direction, an overflow slope formed on the upper surface of the water placing disc, and a guide depression with a height lower than the overflow slope, a plurality of overflow holes with different heights are arranged on the overflow slope, and a water outlet channel is provided in the guide depression and communicates with the water outlet hole.

[0010] As a preferred embodiment of the present application, an air table is arranged above the water tray, and a nozzle for jet cleaning of the water outlet is arranged on the air table, and the jet used by the nozzle is nitrogen.

[0011] As a preferred embodiment of the present application, the nozzle is multiple, and each nozzle is directed to a different area of the water outlet, and the liquid distributor is further provided with a detection device for detecting the blockage of the water outlet in different areas.

[0012] As a preferred embodiment of the present application, the detection device is an industrial camera or a distributed optical fiber pressure sensor.

[0013] As a preferred embodiment of the present application, the detection device is that the bottom surface of the water tray is provided with a fine groove, and the optical fiber pressure sensor is embedded in the fine groove.

[0014] As a preferred embodiment of the present application, the number of layers of the tray is more than one, and further comprises an EG refluxer, and the EG refluxer comprises a de-azeotrope pipe connected with the tower body.

[0015] As a preferred embodiment of the present application, the EG refluxer further comprises a suppression pipe connected with the tower body.

[0016] As a preferred embodiment of the present application, the height of the suppression pipe is arranged to be higher than that of the de-azeotrope pipe, and the flow rate of EG flowing out of the de-azeotrope pipe is greater than that of the suppression pipe.

[0017] As a preferred embodiment of the present application, the optimal feeding height H of the suppression pipe is solved based on a genetic algorithm opt , the genetic algorithm realizes global minimization of the reflux ratio, and the constraint conditions comprise constraint condition one: comparison of separation efficiency with a preset value; and constraint condition two: comparison of DEG side reaction with a preset value.

[0018] As a preferred embodiment of the present application, the constraint conditions further comprise constraint condition three: temperature gradient constraint, that is, the temperature difference between the bottom temperature of the tower body and the temperature of the main reaction zone.

[0019] In summary, the present application has the following beneficial effects:

[0020] 1. Multiple porous overflow, uniform liquid falling, ensuring that the liquid can uniformly cover the entire cross section of the packing, preventing poor initial distribution from causing a decrease in packing efficiency. The liquid distributor improves the uniformity of the falling liquid, making the liquid film on the packing area 4 more uniform, thereby improving the separation effect and reducing the input of reflux water.

[0021] 2. Single-slope multi-hole design ensures the uniformity of the falling reflux liquid.

[0022] 3. The jet cleaning ensures the uniformity of the liquid distribution of the liquid distributor, avoiding the risk of dry zone in the packing zone, which may cause gas phase short circuit and wall flow leading to liquid phase enrichment.

[0023] 4. The distributed optical fiber pressure sensor can measure the stress pressure change of each area in a non-contact manner, realizing high-precision blockage positioning without disturbing the fluid.

[0024] 5. The gas sprayed by the nozzle can be nitrogen or argon, which avoids the oxidation of ethylene glycol caused by ordinary air.

[0025] 6. The azeotrope-breaking tube injects reflux EG, which can break the azeotrope barrier of water-EG and avoid the lockout of dehydration efficiency caused by azeotrope effect.

[0026] 7. The injection of reflux EG in the inhibition tube can inhibit the generation of byproduct DEG and prevent high-temperature gas phase from directly impacting the condenser at the top of the tower.

[0027] 8. The EG temperature in the azeotrope-breaking tube is lower than that in the inhibition tube, which avoids the destruction of the azeotrope zone balance and the liquid flooding caused by thermal shock in the middle of the tower.

[0028] 9. The inlet height of the inhibition tube is calculated by genetic algorithm, which maximizes the separation efficiency while minimizing the reflux ratio.

[0029] 10. The design of genetic algorithm includes three constraint conditions, which force the algorithm to meet the minimum water production requirement, avoid the deterioration of product quality caused by excessive DEG, and maintain the temperature difference gradient to ensure mass transfer efficiency and reaction balance. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a schematic diagram of Example 1;

[0031] Figure 2 is a schematic diagram of the liquid distributor in Example 1;

[0032] Figure 3 is a side cross-sectional view of Figure 2 .

[0033] In the figure:

[0034] 1. tower body, 2. tower plate, 3. liquid distributor, 31. insulation shell, 32. water inlet pipe, 33. water placement disc, 34. overflow slope, 35. flow guide depression, 36. water outlet hole, 37. overflow hole, 38. gas platform, 39. nozzle, 4. packing zone, 5. EG reflux device, 51. azeotrope-breaking tube, 52. inhibition tube, 6. water reflux device, 7. condenser, 8. collection tank, 9. reboiler. DETAILED DESCRIPTION

[0035] The present invention will be further described in detail below with reference to the accompanying drawings.

[0036] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

[0037] Example 1, as Figure 1 As shown, the industrial tower's main component is the tower body 1, where esterification and polycondensation reactions take place. The material enters the tower body 1, and a reboiler 9 provides heat. The material contains ethylene glycol (EG) and water, which need to be separated at different stages. Under high temperatures, water is heated and rises as a gas, while EG often remains in the liquid phase. As described in the background section, to avoid flash evaporation, reflux liquid needs to be added to the industrial tower. The reflux liquid is water and / or EG, with different requirements at different chemical reaction stages. Steam flows upwards, and the reflux liquid flows downwards, ensuring sufficient counter-current contact between the gas and liquid phases. Especially in the tray area shown in the diagram, multiple trays 2 are installed, typically 15-20. Tray 2 is one of the core internal components of the industrial tower, allowing steam to rise and forming an efficient gas-liquid contact section, providing more thorough gas-liquid heat exchange.

[0038] In addition to tray 2, the packing zone 4 exists to provide a larger gas-liquid contact interface in order to ensure separation efficiency. The principle is that the liquid spreads into a thin film on the surface of the packing, which greatly increases the gas-liquid contact area. The rising vapor comes into countercurrent contact with the liquid film in the packing channel, and small molecule components evaporate from the surface of the liquid film into the gas phase.

[0039] As the steam rises, it passes through multiple trays 2 and the packing zone 4, where it undergoes sufficient gas-liquid contact. Small molecule components, such as water, reach the top of the tower in gaseous form, are condensed by the condenser 7, and then enter the collection tank 8.

[0040] The above is the existing technology. The specific structure of the tray 2 and the structured packing in the packing zone 4 can be achieved using the corresponding technical means in the existing technology without any changes.

[0041] In this case, in order to reduce the amount of reflux liquid and lower the reflux ratio while ensuring the separation effect, the following technical improvements were used.

[0042] First, the liquid distributor 3 was completely redesigned. The water return device 6 uses a pump station and other structures to pump return water into the liquid distributor 3 in the tower body 1. For example... Figure 2 and Figure 3As shown, the backflow water enters the water inlet pipe 32 from the water backflow device 6, and then enters the inside of the tray body of the water tray 33, and gathers in the inside of the tray body. As the water increases, the water level in the inside of the tray body rises to a certain height. The upper surface of the water tray 3 is staggered, including a high overflow slope 34 and a low flow depression 35, and the overflow hole 37 is arranged on the high overflow slope 34. This makes the water level in the water tray 33 reach a predetermined height uniformly, and then overflow from the overflow hole 37, and then flow to the low flow depression 35 under the influence of gravity, and then fall from the water outlet of the flow depression 35, and then flow out from the water outlet hole 36, and then uniformly fall on the filler area 4 below.

[0043] Such porous overflow and uniform liquid falling ensure that the liquid can uniformly cover the entire cross section of the filler, preventing poor initial distribution from causing a decrease in the efficiency of the filler. The liquid distributor 3 improves the uniformity of the falling liquid, which makes the liquid film on the filler area 4 more uniform, thereby improving the separation effect and reducing the input of backflow water.

[0044] Further, in the present embodiment, the overflow hole 37 on each overflow slope 34 is not one but multiple, which avoids the situation that some overflow holes 37 are blocked in an industrial environment with high temperature and acidic steam, so that the flow depression 35 in a certain area cannot obtain enough overflow water, which causes the "wall flow, dry area" phenomenon. The single-slope multi-hole design reduces the occurrence of such a situation, further ensuring the uniformity of the backflow liquid falling.

[0045] In the embodiment, above the water tray 33, a gas table 38 and a plurality of spray heads 39 are arranged. The spray heads 39 are arranged to direct to different areas of the water outlet. The spray heads 39 can be made of Hastelloy C276, which can resist high-temperature steam, especially high-temperature acidic steam. The control system can remotely control the different spray heads 39 to spray high-pressure gas, so as to clean the water outlet and the water outlet hole 36 in the designated area, avoiding blockage. The data acquisition of the blockage diagnosis system depends on the detection device. The bottom of the entire water tray 33 is distributed with a large number of water outlet holes 36 and water outlets connected thereto. The function of the detection device is to detect where the water outlet hole 36 and the water outlet are blocked, and then transmit the position information of the blockage to the control system, and the control system operates the corresponding spray head 39 to work. The communication of the data and the implementation of the control system can use the common control system and communication mode in the prior art, which will not be described here. The detection device can be implemented in various ways, for example, a high-temperature-resistant industrial camera can be used to shoot the picture of the bottom of the water tray 33, or the bottom of the water tray 33 can be artificially divided into a plurality of areas, and a thermal flow meter such as the Sierra SmartTrak series flow meter in the prior art is arranged in each area. A precision groove can also be opened on the bottom surface of the water tray 33, and a distributed fiber optic pressure sensor (FBG array) is embedded and installed in the groove, which can measure the stress pressure change of each area in a non-contact manner, so as to determine whether each area is blocked. Such a design makes the water tray 33 itself a "smart pressure field imaging board", which realizes high-precision blockage positioning without disturbing the fluid.

[0046] The gas sprayed by the spray head 39 can be nitrogen or argon, which avoids the oxidation of ethylene glycol (EG) caused by ordinary air.

[0047] The above design further ensures the uniformity of the liquid distribution of the liquid distributor, avoids the dry area of the packing zone 4, and avoids the risk of gas phase short circuit and wall flow caused by liquid phase enrichment.

[0048] In embodiment 2, the ethylene glycol (EG) reflux is further optimized based on embodiment 1.

[0049] As shown in Figure 1 , an EG reflux device is also arranged, which drives the EG reflux into the tower by a pump or the like. Different from the prior art, a double reflux is arranged in the case, which is independently controlled.

[0050] Specifically, a de-azeotrope pipe 51 and a suppression pipe 52 are arranged, the former enters the tower at a lower position, closer to the tower bottom. The latter is arranged at a higher position, generally at a middle or upper position of the tray zone, for example, between the 13th tray 2 and the 14th tray 2.

[0051] The azeotrope breaking pipe 51 injects the reflux EG, which can break the azeotrope barrier of water-EG, and this position is the main reaction zone of dehydration, and can also keep the concentration of the water / EG azeotrope zone within a reasonable range, and avoid the dehydration efficiency being locked by the azeotrope effect. The suppression pipe 52 injects the reflux EG, which has two effects, one of which is to inhibit the generation of the byproduct DEG, and the other of which is that it itself forms a "temperature buffer layer" at the middle and high positions in the tower, thereby preventing the high-temperature gas phase from directly impacting the condenser 7 at the top of the tower, and prolonging the service life of the air cooler in the condenser 7.

[0052] Further, since it is double-path independent control, the temperature and flow rate of the EG entering the tower through the azeotrope breaking pipe 51 and the suppression pipe 52 can be controlled. In this embodiment, the EG temperature in the azeotrope breaking pipe 51 is lower than the EG temperature in the suppression pipe 52, because if the former EG temperature is too low, it will destroy the azeotrope zone balance; and if the latter EG temperature is too low, it will cause thermal shock in the middle of the tower to cause flooding. The flow rate of the former is also greater than that of the latter, and the ratio is in the range of 1.2-1.8.

[0053] In Example 3, an intelligent calculation design for the height position of the inlet of the suppression pipe 52 is further added based on Example 2.

[0054] The inventor has found that the height of the inlet of the suppression pipe 52 will affect the reflux ratio and the separation efficiency, and the reasons are various. For example, when the height is different, the gas phase dew point temperature will also change, causing the relative volatility to change, and the separation difficulty to change. For another example, when the height is different, after the EG is injected, the EG concentration difference at a certain height position will also change, and then the mass transfer driving force will also change, and the reflux ratio under the same separation requirement will also change.

[0055] In this embodiment, a genetic algorithm modeling is adopted. The genetic algorithm (Genetic Algorithm, GA) is a meta-heuristic search and optimization algorithm inspired by the natural evolution process. It simulates the "survival of the fittest" principle in biological evolution, and is used to find the optimal solution or approximate optimal solution of complex problems.

[0056] The fitness calculation of the genetic algorithm, i.e., the core definition of the Fitness calculation formula algorithm, in this case, the fitness formula is: wherein R = L / D, the reflux liquid flow L / the product extraction flow D at the top of the tower, i.e., the reflux ratio, 10 3 is the penalty weight coefficient. And Penalty is the penalty term. As can be seen from the formula, when the reflux ratio R is smaller, the penalty term ΣPenalty is closer to zero, and the fitness is greater.

[0057] The constraints of the algorithm are set as three, which are constraint one: comparison of separation efficiency and preset value; constraint two: comparison of DEG side reaction and preset value; and constraint three: temperature gradient constraint, temperature difference between tower bottom temperature inside tower body 1 and temperature of main reaction zone.

[0058] The three constraints are written in the penalty term formula in the above, and some constants are taken, in this embodiment, as follows:

[0059]

[0060] Specifically, 5450 is a preset critical value in this embodiment, and Qwater is the actual obtained esterification water yield (kg / h) calculated in the model. This makes the forced algorithm meet the minimum water yield requirement.

[0061] DEG is the mass fraction of diethylene glycol (%) calculated in the model, and 0.109 is a preset critical value in this embodiment. This ensures that the side reaction of the recombined components is controlled, and avoids product quality deterioration caused by too high DEG.

[0062] Tbottom-Tmiddle is the temperature difference between the tower bottom temperature and the tower middle temperature, 16 is a preset temperature difference critical value, the temperature difference gradient is maintained, and the mass transfer efficiency and reaction equilibrium are ensured.

[0063] The feeding height H is a decision variable of the genetic algorithm, and different feeding heights H result in different Qwater, EDG and Tbottom-Tmiddle. The feeding height H corresponding to the optimal solution calculated by the final algorithm is the best feeding height H. opt ​

Claims

1. Energy saving and consumption reducing industrial column suitable for polyester industry, comprising a column body (1), a reboiler (9), a plurality of trays (2) located in the column body (1), a packing zone (4) and a liquid distributor (3) located above all the trays (2), the top of the column body (1) is connected with a condenser (7) and a collection tank (8), the liquid distributor (3) is connected with a water reflux device (6), characterized in that: The liquid distributor (3) comprises a water inlet pipe (32) connected with the water reflux device (6), a water tray (33) connected with the water inlet pipe (32) and extending in the horizontal direction, an upper surface of the water tray (33) is formed with an overflow slope (34) and a guide depression (35) with a lower height than the overflow slope (34), a plurality of overflow holes (37) with different heights are arranged on the overflow slope (34), the guide depression (35) is provided with a water outlet channel penetrating the water outlet hole (36), the number of the tower plates (2) is more than 15, the liquid distributor (3) further comprises an EG reflux device (5), the EG reflux device (5) comprises a de-azeotrope pipe (51) connected with the tower body (1), the EG reflux device (5) further comprises a suppression pipe (52) connected with the tower body (1), the height of the suppression pipe (52) is arranged to be higher than that of the de-azeotrope pipe (51), and the flow of EG flowing out of the de-azeotrope pipe (51) is greater than that of the suppression pipe (52).

2. The energy efficient and cost effective industrial column suitable for polyester industry as claimed in claim 1, wherein: An air table (38) is arranged above the water tray (33), the air table (38) is provided with a spray head (39) for jet cleaning the water outlet channel, and the jet used by the spray head (39) is nitrogen.

3. The energy efficient and cost effective industrial column suitable for polyester industry as claimed in claim 2, wherein: The spray head (39) is a plurality of, respectively pointing to the water outlet channel in different areas, and the liquid distributor is further provided with a detection device for detecting the blockage of the water outlet channel in different areas.

4. The energy efficient and cost effective industrial column suitable for polyester industry as claimed in claim 3, wherein: The detection device is an industrial camera or a distributed optical fiber pressure sensor.

5. The energy efficient and cost effective industrial column suitable for polyester industry as claimed in claim 4 wherein: The detection device is provided with a precision groove on the bottom surface of the water tray (33), and the optical fiber pressure sensor is embedded in the precision groove.

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