Polyester production energy supply system

Abstract

The invention relates to the technical field of nitrogen purification or separation, and particularly discloses a polyester production energy supply system which comprises a nitrogen supply unit and a steam supply unit, and the nitrogen supply unit comprises an air compressor, an air purifier, an air dryer, an adsorption type nitrogen making machine, a nitrogen tank and nitrogen using equipment which are communicated in sequence. The steam supply unit comprises a heating boiler, a waste heat boiler, heat utilization equipment and steam utilization equipment, a flue gas pipeline is communicated between the heating boiler and the waste heat boiler, a circulating pipeline is communicated between the heating boiler and the heat utilization equipment, and a steam pipeline is communicated between the waste heat boiler and the steam utilization equipment; the adsorption type nitrogen making machine is communicated with a waste gas tank, a waste gas recycling pipe is communicated between the waste gas tank and the air purifier, and a combustion-supporting waste gas pipe is communicated between the waste gas tank and the heating boiler. By adopting the technical scheme provided by the invention, the technical problems that the nitrogen utilization rate is reduced and energy is wasted due to the fact that nitrogen-making waste gas is directly emptied by a nitrogen supply system in the prior art can be solved; and the quality of a polyester product can be ensured.

Description

Technical Field

[0001] The invention relates to the technical field of nitrogen purification or separation, and in particular to an energy supply system for polyester production. Background Art

[0002] In the polyester production process, the amount of nitrogen used is large, so the nitrogen supply system is an indispensable "energy" supply source for polyester production. Among them, the uses of nitrogen mainly include oxygen isolation protection for PTA transportation, nitrogen purge for PTA anti-caking, nitrogen sealing of ethylene glycol tanks, nitrogen sealing of thermal oil tanks, nitrogen for bubbler level gauges, and nitrogen for PET chip transportation.

[0003] The nitrogen supply system in the existing polyester production process includes an air compressor, an air dryer, an adsorption nitrogen generator and a nitrogen tank which are connected in sequence through pipelines. The inventors found that the adsorption nitrogen generator generates a large amount of waste gas during the nitrogen production process. The waste gas also contains a large amount of nitrogen. Direct exhaust treatment will reduce the utilization rate of nitrogen and lead to energy waste.

[0004] The prior art with announcement number CN113277486A discloses a combined nitrogen generator and a nitrogen making process thereof, which discloses that the gas introduced into the nitrogen generator is first dried by a dryer and then enters the nitrogen generator for adsorption and nitrogen making. Since the nitrogen making process requires not only adsorption but also desorption of the nitrogen making adsorbent, the waste gas generated by desorption is also dry gas after passing through the nitrogen making adsorbent, and through the adsorption of the nitrogen generator, the gas dew point moisture is lower, which is better than the dew point of the gas dried by the dryer itself. The waste gas can be completely used for desorption of the desiccant in the dryer. The waste gas generated by the desorption of the nitrogen generator enters the dryer through the regeneration gas path for desorption, avoiding direct discharge of the waste gas, which is beneficial to energy saving and consumption reduction.

[0005] However, the above system has the following problems:

[0006] The inventors discovered during the polyester production process that the waste gas generated by the nitrogen generator is not suitable for recycling, which can easily lead to unstable color value of polyester chips, thereby affecting the transparency of downstream products. Summary of the invention

[0007] The present invention is intended to provide an energy supply system for polyester production, so as to solve the technical problem that the waste gas generated by the nitrogen generator used in the polyester production process in the prior art is not suitable for recovery, and the color value of the polyester chip product is easily unstable.

[0008] In order to achieve the above object, the present invention adopts the following technical scheme:

[0009] A polyester production energy supply system comprises a nitrogen supply unit, wherein the nitrogen supply unit comprises an air compressor, an air dryer, an adsorption nitrogen generator, a nitrogen tank and nitrogen using equipment which are sequentially connected through a nitrogen production pipeline; an air purifier is arranged between the air compressor and the air dryer; the adsorption nitrogen generator is connected with an exhaust gas tank, and a recycled exhaust gas pipe is connected between the exhaust gas tank and the air purifier; and a combustion chamber is also included, a combustion-supporting exhaust gas pipe is connected between the exhaust gas tank and the combustion chamber, and a combustion-supporting air pipe is also connected to the combustion chamber.

[0010] Invention concept:

[0011] In order to solve the problem of unstable product color value caused by nitrogen recovery in the polyester production process, the inventor first thought of the oxygen content in the waste gas. Therefore, the inventor connected the waste gas from the waste gas tank to the air purifier, so that the recovered waste gas can first pass through the air purifier to remove other gases other than oxygen and nitrogen as much as possible, and then separately and centrally treat the nitrogen and oxygen mixed gas to ensure the amount of nitrogen. However, the inventor further analyzed and found that if the waste gas is recycled and mixed with the compressed air generated by the air compressor to form nitrogen-making gas, if the proportion of waste gas in the nitrogen-making gas is too high and the proportion of compressed air is too low, it may cause the separation efficiency of the nitrogen generator to decrease, the nitrogen production to decrease, and even fail to meet production needs; because the adsorption nitrogen generator mainly relies on compressed air to separate nitrogen through adsorbents, insufficient compressed air will directly affect the output and purity of nitrogen. Moreover, too high a proportion of waste gas also means that the compressed air effectively used to separate nitrogen is reduced, thereby reducing the efficiency of nitrogen production.

[0012] Based on the above situation, the inventor solved the problem of unstable product color value by using an air purifier to pre-treat the recycled waste gas and controlling the ratio of recycled waste gas to compressed air. However, the inventor also found that the above-mentioned "waste gas" is actually a mixture of nitrogen and oxygen with a high content, in which the oxygen content is about 30%, which is a relatively ideal combustion aid. It is not possible to maximize the utilization of waste gas by simply recycling part of the nitrogen. Therefore, the inventor led another part of the waste gas in the waste gas tank to the combustion chamber (for example, the combustion furnace of the heating boiler), mixed it with the air introduced by the combustion air pipe, and used it as a combustion-supporting gas to promote the full combustion of natural gas and reduce energy waste.

[0013] Beneficial effects:

[0014] 1. Reversely utilize the waste gas generated by the nitrogen generator, and use high-purity waste gas for backblowing, which not only improves the nitrogen production efficiency and reduces waste gas emissions, but also ensures the quality of the product. Specifically, in actual application, the large amount of waste gas generated by the adsorption nitrogen generator during the nitrogen production process is no longer directly emptied and processed. Instead, a waste gas tank is set up to store the waste gas, and the waste gas stored in the waste gas tank is merged into the compressed air through the recycled waste gas pipe. The mixed gas of compressed air and recycled waste gas is used as nitrogen-making gas and passed into the adsorption nitrogen generator for nitrogen production. In this way, not only can the nitrogen utilization rate per unit volume of compressed air be improved, thereby reducing energy waste, but also the amount of compressed air required to produce unit volume of nitrogen can be reduced, thereby reducing the energy consumption of the air compressor.

[0015] 2. This solution connects the recycled waste gas pipe between the waste gas tank and the air purifier, that is, the recycled waste gas is combined with the compressed air and introduced into the air purifier. After being purified and dried together with the compressed air, the recycled waste gas is introduced into the adsorption nitrogen generator for making nitrogen. Since the waste gas has been purified and dried, it is purified and dried together with the compressed air, which can reduce the workload of the air purifier and the air dryer, and can also ensure the cleanliness and dryness of the nitrogen-making gas introduced into the adsorption nitrogen generator, which is conducive to extending the service life of each equipment in the nitrogen supply unit. Moreover, the factory building previously used a high-purity nitrogen generator. After being improved by this technology, especially by adding an air purifier, the compressed air can be purified, and the nitrogen-making efficiency of the nitrogen generator can be improved. The use of an ordinary nitrogen generator can also meet production requirements.

[0016] 3. The waste gas generated by the nitrogen generator can not only be used to improve the efficiency of nitrogen production, but also as a combustion aid, which greatly reduces the cost of polyester production: This solution connects the combustion-supporting waste gas pipe between the waste gas tank and the combustion chamber. Part of the waste gas stored in the waste gas tank is reused for nitrogen production, and the other part is introduced into the combustion chamber through the combustion-supporting waste gas pipe, mixed with the air introduced from the combustion-supporting air pipe, and used as a combustion-supporting gas to promote the full combustion of natural gas and reduce energy waste. The waste gas is a nitrogen-oxygen mixture with an oxygen content of about 30%, which is an ideal combustion aid. Compared with the existing technology of using oxygen and air as combustion-supporting gases, this solution can reduce the cost of making or purchasing oxygen, thereby reducing the operating cost of the steam supply system.

[0017] Preferably, as a further improvement, the combustion chamber is used to supply heat to the steam supply unit; the steam supply unit includes a heating boiler, a waste heat boiler, a heat-using device and a steam-using device, a flue gas duct is connected between the heating boiler and the waste heat boiler, a circulation duct is connected between the heating boiler and the heat-using device, and a steam duct is connected between the waste heat boiler and the steam-using device; the combustion chamber is the combustion furnace of the heating boiler.

[0018] Beneficial effects: The inventors have found through research that the amount of steam used in the polyester production process is also very large; and the technology studied by the inventors can not only reduce the nitrogen supply cost and improve the nitrogen supply efficiency, but also reduce the cost of combustion aids in the combustion chamber of the steam supply system, achieving multiple goals at one stroke and bringing great progress to this field.

[0019] Preferably, as an improvement, at the nitrogen making gas inlet end of the adsorption nitrogen making machine, per unit time, the compressed air intake accounts for P1% of the total nitrogen making gas intake, 88≤P1<100; the recycled waste gas intake accounts for P2% of the total nitrogen making gas intake, 0<P2≤12.

[0020] Beneficial effect: When the waste gas is recycled to the adsorption nitrogen generator to produce nitrogen, the percentage of the recycled waste gas intake to the total nitrogen gas intake is controlled to be P2≤12, which can maximize the utilization of the waste gas and ensure the nitrogen production efficiency.

[0021] According to the inventor's analysis, if the proportion of waste gas in the nitrogen-generating gas is too high and exceeds 12%, the proportion of compressed air is too low, which may cause the separation efficiency of the nitrogen generator to decrease, the nitrogen production to decrease, and even fail to meet production needs. Because the adsorption nitrogen generator mainly relies on compressed air to separate nitrogen through adsorbents, insufficient compressed air will directly affect the output and purity of nitrogen; a high proportion of waste gas also means that the compressed air effectively used to separate nitrogen is reduced, thereby reducing the efficiency of nitrogen production.

[0022] Preferably, as an improvement, at the combustion-supporting gas inlet end of the heating boiler, the combustion-supporting air intake accounts for C1% of the total combustion-supporting gas intake per unit time, 73≤C1<100, and the combustion-supporting exhaust gas intake accounts for C2% of the total combustion-supporting gas intake, 0<C2≤27.

[0023] Beneficial effect: When the waste gas is introduced into the heating boiler to promote the full combustion of natural gas, the maximum value C2 of the intake volume of the combustion-supporting waste gas is controlled to be no more than 27% of the total intake volume of the combustion-supporting gas, which not only realizes the utilization of waste gas but also does not generate additional air pollution.

[0024] According to the inventor's analysis, if the proportion of combustion exhaust gas is too high and the proportion of combustion air is too low, the oxygen content will increase, resulting in nitrogen oxides (NO x ) emissions increase (incomplete combustion and excessive combustion temperature will lead to an increase in nitrogen oxides); nitrogen oxides not only cause serious environmental pollution problems such as acid rain and photochemical smog, but also run counter to the current stringent environmental regulations. If the proportion of combustion-supporting exhaust gas is too low, it will basically not play a regulatory role and the exhaust gas cannot be utilized.

[0025] Preferably, as an improvement, the waste heat boiler is connected to an air heat exchanger via a flue gas duct, and the air heat exchanger is connected to the heating boiler via a combustion-supporting air pipe.

[0026] Beneficial effects:

[0027] 1. The inventors also found during the research that the amount of steam used in the polyester production process is very large, so the steam supply system is also an indispensable "energy" supply source for polyester production; these steam are transported to the polyester device for lithium bromide refrigeration, low-emission heat transfer oil heating, and polyester catalyst heating. The steam supply system developed by the inventors in the first generation includes a heating boiler and a waste heat boiler. The heating boiler uses natural gas as raw material, oxygen and air as combustion-supporting gases, and heat transfer oil as medium. The hot oil circulation pump is used to force the medium to circulate in the liquid phase, and the heat energy is transported to the heat-using equipment in the polyester production process and then returned to the heating boiler for reheating; the flue gas outlet of the heating boiler is connected to the flue gas inlet of the waste heat boiler through a pipeline, and the waste heat boiler uses the waste heat of the flue gas to heat the desalted water to obtain steam. The steam outlet of the waste heat boiler is connected to the steam-using equipment in the polyester production process through a pipeline.

[0028] However, the inventors found that the above-mentioned first-generation technology still has the problems of low waste heat utilization and energy waste; specifically, the waste heat boiler of the steam supply system prepares steam by heating the desalted water by heating the flue gas of the heating boiler. The waste heat boiler can only utilize part of the sensible heat in the flue gas, and the remaining large amount of sensible heat and latent heat in the flue gas are not utilized, resulting in the steam supply system, which further leads to energy waste.

[0029] Therefore, the inventors conducted further research based on the above, combining these latent heat with the combustion-supporting exhaust gas pipe to improve the nitrogen supply efficiency and reduce the steam supply cost.

[0030] 2. When the heating boiler burns natural gas to heat the heat transfer oil, the flue gas generated has a temperature of about 310°C. The flue gas is passed into the waste heat boiler through the flue gas pipeline to heat the desalted water. After a heat exchange between the flue gas and the desalted water, the temperature drops to about 220°C. At this time, the sensible heat in the flue gas is partially utilized, and a large amount of sensible heat and latent heat remain. In this scheme, an air heat exchanger is connected downstream of the waste heat boiler, and the flue gas after the primary heat exchange in the waste heat boiler is passed into the air heat exchanger through the flue gas pipe. The flue gas undergoes secondary heat exchange with the combustion air in the air heat exchanger, and the combustion air is heated to about 140-180°C. The flue gas then enters the combustion exhaust gas pipe through the combustion air pipe to mix with the exhaust gas, and then enters the heating boiler, which is beneficial to improving the combustion effect of the gas on the natural gas after it enters the heating boiler, and ensures the full combustion of the natural gas. At this time, the temperature of the flue gas is reduced to 80-100°C, and a large amount of water vapor in the flue gas is condensed, which realizes the further utilization of the sensible heat in the flue gas, and utilizes a large amount of latent heat in the flue gas, thereby improving the waste heat utilization rate of the steam supply unit and reducing energy waste.

[0031] Preferably, as an improvement, the air heat exchanger is connected to a cold water heat exchanger through a flue gas duct, the cold water heat exchanger is connected to a soft water duct, and the soft water duct is also connected to a soft water tank.

[0032] Beneficial effect: This scheme connects the cold water heat exchanger downstream of the air heat exchanger, and passes the flue gas after secondary heat exchange in the air heat exchanger into the cold water heat exchanger through the flue gas pipe. At the same time, the soft water pipe passes the soft water into the cold water heat exchanger. The flue gas undergoes three heat exchanges with the soft water in the cold water heat exchanger, and the soft water is heated to 35-55°C. The heated soft water is transported to the soft water pool for storage through the soft water pipe, and can be supplied to polyester production and domestic water through pipelines, thereby reducing the energy consumption of polyester production and domestic water. At this time, the temperature of the flue gas is reduced to 40-50°C, and the water vapor in the flue gas is basically condensed, which not only realizes the further utilization of sensible heat and latent heat in the flue gas, thereby further improving the waste heat utilization rate of the steam supply unit and reducing energy waste. Moreover, the reduction of water vapor in the flue gas entering the furnace can further reduce its impact on the furnace, thereby ensuring the combustion effect as much as possible.

[0033] Preferably, as an improvement, the soft water tank is connected to a hot water heat exchanger through a soft water pipe, and the hot water heat exchanger is connected to a steam-using device through a steam pipe; the hot water heat exchanger is connected to a circulation pipe, and the hot water heat exchanger is located downstream of the heat-using device.

[0034] Beneficial effects: In this solution, a hot water heat exchanger is connected downstream of the soft water tank, and the hot water heat exchanger is connected to a circulation pipeline downstream of the heat-using equipment. When in use, the heated soft water stored in the soft water tank is transported to the hot water heat exchanger through the soft water pipeline, and at the same time, the heat transfer oil used by the heat-using equipment is introduced into the hot water heat exchanger through the circulation pipeline. The heated soft water exchanges heat with the heat transfer oil in the hot water heat exchanger, is further heated into water vapor, and is transported to the steam-using equipment through the steam pipeline for use; this solution utilizes the waste heat of the heat transfer oil to continue to heat the heated soft water into water vapor, which not only reduces energy waste, but also increases the steam source of the steam-using equipment, ensuring that the steam supply of the steam-using equipment is sufficient.

[0035] Preferably, as an improvement, the hot water heat exchanger is connected to a circulation branch pipe, and the other end of the circulation branch pipe is connected to the circulation pipeline upstream of the heat-using equipment.

[0036] Beneficial effect: This solution connects a circulation branch pipe to the hot water heat exchanger, and connects the other end of the circulation branch pipe to the circulation pipeline upstream of the heat-consuming equipment. When the amount of heat transfer oil output by the heating boiler is greater than the demand of the heat-consuming equipment, the excess heat transfer oil can be directly transported to the hot water heat exchanger through the circulation branch pipe to continue heating the heated soft water into water vapor. This can not only reduce the waste of heat transfer oil, but also improve the efficiency of generating water vapor by the hot water heat exchanger.

[0037] Preferably, as an improvement, a nitrogen oxide detector is provided at the smoke exhaust port of the smoke duct, and a smoke return pipe is connected to the smoke duct downstream of the cold water heat exchanger, and the other end of the smoke return pipe is connected to the heating boiler.

[0038] Beneficial effects: This solution sets a nitrogen oxide detector at the smoke outlet of the smoke duct, and detects the smoke at the smoke outlet through the nitrogen oxide detector. When the nitrogen oxide detector detects that the nitrogen oxide content of the smoke at the smoke outlet is high, the smoke after secondary heat exchange in the air heat exchanger is returned to the heating boiler through the smoke return pipe, so that the smoke is burned with natural gas in the combustion furnace of the heating boiler, reducing the content of nitrogen oxides in the exhaust flue gas. This solution monitors the nitrogen oxides in the smoke at the smoke outlet. When the nitrogen oxide content in the smoke exceeds the preset value, the smoke after secondary heat exchange is returned to the heating furnace for combustion treatment, that is, the smoke is refluxed upstream of the smoke outlet, which can ensure that the nitrogen oxide content of the smoke discharged from the smoke outlet meets the emission requirements of environmental monitoring for smoke.

[0039] Preferably, as an improvement, the other end of the flue gas return pipe is connected to the heating boiler and the combustion-supporting exhaust gas pipe respectively; and the connecting point between the flue gas return pipe and the combustion-supporting exhaust gas pipe is located on the side close to the exhaust gas tank, and a one-way valve is provided on the combustion-supporting exhaust gas pipe between the connecting point and the combustion-supporting air pipe.

[0040] Beneficial effects: When the nitrogen oxide detector detects that the nitrogen oxide content of the flue gas at the exhaust port is greater than the set value, the flue gas flows back from the return pipe; by connecting the outlet end of the flue gas return pipe with the heating boiler and the combustion-supporting exhaust gas pipe respectively, the return flue gas can be controlled more flexibly. When the return flue gas enters the combustion-supporting exhaust gas pipe through the flue gas return branch pipe, it can be mixed with the combustion-supporting exhaust gas, further reducing the temperature of the return flue gas, and condensing the water vapor in the flue gas again, so that the water vapor of the flue gas entering the furnace is basically removed, reducing the impact of the return flue gas on the furnace, and ensuring the combustion effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram of the structure of Example 1 of the present invention.

[0042] Figure 2 This is a schematic diagram of the nitrogen equipment used in Example 1 of the present invention.

[0043] Figure 3 This is a schematic diagram of the structure of Example 4 of the present invention (the flue gas return pipe and the branch pipeline of the heating boiler are not shown in the figure).

[0044] Figure 4 This is a schematic diagram of the structure of Example 5 of the present invention. DETAILED DESCRIPTION

[0045] The following is further described in detail through specific implementation methods:

[0046] The figure marks in the drawings of the specification include: nitrogen production pipeline 10, air compressor 11, air purifier 12, air dryer 13, adsorption nitrogen generator 14, nitrogen tank 15, nitrogen using equipment 16, waste gas tank 20, recycled waste gas pipe 21, combustion-supporting waste gas pipe 22, flue gas pipeline 30, heating boiler 31, waste heat boiler 32, air heat exchanger 33, cold water heat exchanger 34, nitrogen oxide detector 35, combustion-supporting air pipe 41, flue gas reflux pipe 42, soft water pipeline 50, soft water tank 51, hot water heat exchanger 52, circulation pipeline 60, heat using equipment 61, steam pipeline 70, steam using equipment 71, circulation branch pipe 80.

[0047] Example 1

[0048] A polyester production energy supply system, as shown in the following Figure 1 As shown, it includes a nitrogen supply unit and a steam supply unit. The nitrogen supply unit includes a nitrogen production pipeline 10 and an air compressor 11, an air purifier 12, an air dryer 13, an adsorption nitrogen generator 14, a nitrogen tank 15 and a nitrogen-using device 16 which are sequentially connected to the nitrogen production pipeline 10. The exhaust gas discharge port of the adsorption nitrogen generator 14 is connected to the exhaust tank 20 through a pipeline. The exhaust tank 20 is connected to a recycling exhaust pipe 21. The end of the recycling exhaust pipe 21 away from the exhaust tank 20 is connected to the air purifier 12. Specifically, the end of the recycling exhaust pipe 21 away from the exhaust tank 20 is connected to the nitrogen production pipeline 10 upstream of the air purifier 12.

[0049] The steam supply unit includes a heat-using device 61, a steam-using device 71, a flue gas duct 30, and a heating boiler 31, a waste heat boiler 32, an air heat exchanger 33 and a cold water heat exchanger 34 which are sequentially connected to the flue gas duct 30. The downstream of the cold water heat exchanger 34 is the exhaust port of the flue gas duct 30, and a nitrogen oxide detector 35 is installed at the exhaust port of the flue gas duct 30. A circulation duct 60 is connected between the heating boiler 31 and the heat-using device 61. Specifically, both ends of the circulation duct 60 are connected to the heating boiler 31, and the heat-using device 61 is connected to the circulation duct 60; a steam duct 70 is connected between the waste heat boiler 32 and the steam-using device 71. It is worth noting that a plurality of natural gas combustion points are arranged in the combustion furnace of the heating boiler 31 of the present technology, and the combustion points are evenly distributed in the combustion furnace; specifically, a combustion point centrally arranged in the existing combustion furnace is dispersed into a plurality of, for example, 10 combustion points. Such a dispersed design can reduce the concentration of energy, reduce the area with high local temperature, and make the overall heating more uniform.

[0050] The exhaust gas tank 20 is also connected to a combustion-supporting exhaust gas pipe 22, and one end of the combustion-supporting exhaust gas pipe 22 away from the exhaust gas tank 20 is connected to the heating boiler 31. The air heat exchanger 33 is connected to a combustion-supporting air pipe 41, the air inlet end of the combustion-supporting air pipe 41 is connected to a blower (not shown in the figure), and the air outlet end of the combustion-supporting air pipe 41 is connected to the heating boiler 31. The flue gas duct 30 downstream of the cold water heat exchanger 34 is connected to a flue gas return pipe 42, and the other end of the flue gas return pipe 42 is connected to the furnace of the heating boiler 31.

[0051] The cold water heat exchanger 34 is connected with a soft water pipe 50, the water inlet end of the soft water pipe 50 is connected with an external water source, and the water outlet end of the soft water pipe 50 is connected with a hot water heat exchanger 52; the soft water pipe 50 between the cold water heat exchanger 34 and the hot water heat exchanger 52 is also connected with a soft water tank 51. The hot water heat exchanger 52 is connected with a steam-using device 71 through a steam pipe 70; the hot water heat exchanger 52 is connected with a circulation pipe 60, and the hot water heat exchanger 52 is located downstream of the heat-using device 61. In this embodiment, the hot water heat exchanger 52 is a kettle-type heat exchanger, so that the soft water and the heat transfer oil can be fully contacted, thereby improving the heat exchange efficiency between the soft water and the heat transfer oil.

[0052] At the nitrogen-making gas inlet end of the adsorption nitrogen generator 14, the compressed air intake accounts for P1% of the total nitrogen-making gas intake per unit time, 88≤P1<100; the recycled waste gas intake accounts for P2% of the total nitrogen-making gas intake, 0<P2≤12; P1+P2=100%. That is, in the nitrogen-making pipeline 10 between the air dryer 13 and the adsorption nitrogen generator 14, the compressed air flow accounts for 88%~100% (not including 100%) of the total nitrogen-making gas flow, and the recycled waste gas flow accounts for 0~12% (not including 0) of the total nitrogen-making gas flow. In this embodiment, P1=88, P2=12.

[0053] At the combustion-supporting air intake end of the heating boiler 31, the combustion-supporting air intake volume accounts for C1% of the total combustion-supporting gas intake volume per unit time, 73≤C1<100, and the combustion-supporting exhaust gas intake volume accounts for C2% of the total combustion-supporting gas intake volume, 0<C2≤27; C1+C2=100%. That is, the combustion-supporting air flow rate in the combustion-supporting air pipe 41 accounts for 73%~100% (excluding 100%) of the total combustion-supporting gas flow rate in the combustion-supporting air pipe 41 and the combustion-supporting exhaust gas pipe 22, and the combustion-supporting exhaust gas flow rate in the combustion-supporting exhaust gas pipe 22 accounts for 0~27% (excluding 0) of the total combustion-supporting gas flow rate in the combustion-supporting air pipe 41 and the combustion-supporting exhaust gas pipe 22. In this embodiment, C1=73,C2=27. The air intake pipe of the air compressor 11, the recycled waste gas pipe 21, the combustion waste gas pipe 22, and the combustion air pipe 41 are all provided with one-way valves; the flue gas return pipe 42, the outlet end of the flue gas duct 30 and other positions are also provided with one-way valves, so that the controller can receive the signal of the nitrogen oxide detector 35 to control the switching of the flue gas return pipe 42 and the flue gas duct 30; the controller is a PLC. In addition, in this embodiment, the position of the valve can be set as needed, and the controller can be used to realize the opening and closing / switching. Since setting the valve at the position where it is required to be turned on and off and using the controller to control the valve are prior arts, they will not be elaborated here. For those skilled in the art, without departing from the technical solution of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent.

[0054] A polyester production energy supply method, using the polyester production energy supply system, comprises the following steps:

[0055] (1) Nitrogen supply: The compressed air produced by the air compressor 11 flows in the nitrogen production pipeline 10, and after being purified and dried by the air purifier 12 and the air dryer 13, enters the adsorption nitrogen generator 14 as nitrogen production gas to produce nitrogen. The produced nitrogen is transported to the nitrogen tank 15 through the nitrogen production pipeline 10 for storage. The nitrogen stored in the nitrogen tank 15 is transported to the nitrogen using equipment 16 through the nitrogen production pipeline 10 for use; Figure 2As shown, the nitrogen-using equipment 16 can use nitrogen for PTA transportation oxygen isolation protection, PTA anti-caking nitrogen purging, ethylene glycol tank nitrogen sealing, thermal oil tank nitrogen sealing, bubbling level gauge nitrogen, PET slice transportation nitrogen, and PET polycondensation heat transfer nitrogen. The waste gas generated in the adsorption nitrogen production process is transported to the waste gas tank 20 through a pipeline for storage, and a part of the waste gas in the waste gas tank 20 is transported to the nitrogen production pipeline 10 upstream of the air purifier 12 through the recycled waste gas pipe 21. The recycled waste gas is mixed with compressed air and then purified and dried in turn, and enters the adsorption nitrogen generator 14 as nitrogen production gas for nitrogen production. In the above process, the inventor uses the air purifier to pre-treat the recycled waste gas and control the ratio of the recycled waste gas to the compressed air, which not only realizes the utilization of waste gas, but also reduces the nitrogen supply cost and ensures the color value of the polyester chip product is stable.

[0056] (2) Heat supply: The heating boiler 31 burns natural gas to heat the heat transfer oil. During the natural gas combustion process, another part of the waste gas in the waste gas tank 20 is transported to the heating boiler 31 through the combustion-supporting waste gas pipe 22, and mixed with the air transported to the heating boiler 31 through the combustion-supporting air pipe 41, and serves as a combustion-supporting gas to promote the full combustion of the natural gas. The heat transfer oil in the heating boiler 31 is heated to 315-317°C and then transported to the heat-using equipment 61 through the circulation pipe 60. After being used by the heat-using equipment 61, it is transported back to the heating boiler 31 through the circulation pipe 60 for reheating; the heat-using equipment 61 is used for refrigeration of lithium bromide refrigerators, heating of low-discharge heat transfer oil, heating of polyester catalysts, etc.

[0057] (3) Steam supply: The temperature of the flue gas generated by the combustion of the heating boiler 31 is about 310°C. The flue gas is transported to the waste heat boiler 32 through the flue gas pipeline 30. The flue gas performs a heat exchange with the desalted water in the waste heat boiler 32. The flue gas heats the desalted water into water vapor, which is transported to the heat-using equipment 61 through the steam pipeline 70 for use. The temperature of the flue gas after the primary heat exchange is reduced to about 220°C. At this time, the sensible heat in the flue gas is partially utilized, and a large amount of sensible heat and latent heat remain.

[0058] It is worth noting that after the flue gas completes the above-mentioned primary heat exchange, it is transported to the air heat exchanger 33 through the flue gas pipeline 30. The flue gas performs secondary heat exchange with the combustion air in the air heat exchanger 33, and the combustion air is heated to about 140-180°C. Then, the flue gas enters the combustion exhaust gas pipe 22 through the combustion air pipe 41 to mix with the exhaust gas. This process can achieve secondary cooling of the flue gas. The flue gas temperature after the secondary heat exchange is reduced to 80-100°C. At this time, a large amount of water vapor in the flue gas condenses, realizing further utilization of sensible heat in the flue gas, and utilizing a large amount of latent heat in the flue gas to heat the combustion air, thereby improving combustion efficiency. After the flue gas completes the secondary heat exchange, it is transported to the cold water heat exchanger 34 through the flue gas pipeline 30. The flue gas performs three heat exchanges with cold soft water in the cold water heat exchanger 34, and the cold soft water is heated to 35-55°C. The heated hot soft water is transported to the soft water pool 51 through the soft water pipeline 50 for storage, and can be used as polyester production and domestic water. After three heat exchanges, the flue gas temperature drops to 40-50°C. At this time, the water vapor in the flue gas has basically condensed, realizing the further utilization of the sensible heat and latent heat in the flue gas.

[0059] Part of the hot soft water stored in the soft water tank 51 is continuously transported to the hot water heat exchanger 52 through the soft water pipe 50. The hot soft water exchanges heat with the heat transfer oil in the hot water heat exchanger 52 and is heated by the heat transfer oil to become water vapor. The water vapor is transported to the steam equipment 71 through the steam pipe 70 for use.

[0060] It is worth mentioning that the flue gas after heat exchange in the cold water heat exchanger 34 will be detected by the nitrogen oxide detector 35 when it is discharged, and the content of nitrogen oxides in the discharged flue gas is controlled within 41-45 mg / m 3 , so that the content of nitrogen oxides is not higher than 50mg / m 3 When the nitrogen oxide detector 35 detects that the nitrogen oxide content of the smoke at the exhaust port is greater than 48 mg / m 3 The controller will control the valve on the flue gas return pipe 42 to open, and the flue gas will flow back to the furnace of the heating boiler 31 for combustion. It is worth noting that after the step-by-step heat exchange of this technology, the water vapor in the flue gas is condensed, so that the water vapor in the flue gas flowing back into the furnace of the heating boiler 31 is reduced, thereby maximizing the combustion efficiency.

[0061] Example 2

[0062] The difference between this embodiment and embodiment 1 is that P1=90, P2=10; C1=74, C2=26.

[0063] Example 3

[0064] The difference between this embodiment and embodiment 1 is that P1=92, P2=8; C1=75, C2=25.

[0065] Example 4

[0066] like Figure 3 As shown, the difference between this embodiment and embodiment 1 is that two branch pipelines are arranged at the other end of the flue gas return pipe 42, one of which is connected to the furnace of the heating boiler 31, and the other branch pipeline is connected to the combustion-supporting exhaust gas pipe 22; and the connecting point between the branch pipeline of the flue gas return pipe 42 and the combustion-supporting exhaust gas pipe 22 is arranged on the side close to the exhaust gas tank, and a one-way valve is arranged on the combustion-supporting exhaust gas pipe 22 between the connecting point and the combustion-supporting air pipe 41, so as to control the amount of exhaust gas entering the heating boiler 31. The mixture of the return flue gas and the combustion-supporting exhaust gas entering the combustion-supporting exhaust gas pipe 22 is called a mixed gas, and the mixed gas accounts for C2% of the total intake of the combustion-supporting gas, 0<C2≤27, and 27 is specifically taken in this embodiment. The intake volume is controlled by the one-way valve of the combustion-supporting exhaust gas pipe 22; after testing, the product color value (L value) and nitrogen oxide emission within the above range can still meet the standards.

[0067] It is worth emphasizing that since there are two branch pipes at the outlet end of the flue gas return pipe 42, valves are respectively set on the two branch pipes, and workers can judge whether to open the two branch pipes according to the flue gas return amount and time under actual working conditions, which is more flexible. Therefore, this part of the flue gas can be diverted, part of the flue gas is returned to the furnace of the heating boiler 31 for combustion, and the other part of the flue gas enters the combustion-supporting exhaust gas pipe 22 and mixes with the combustion-supporting exhaust gas to reduce the water vapor in the flue gas again, which can also improve the combustion effect. In other embodiments other than this embodiment, it is also possible to open only the branch pipe connected to the combustion-supporting exhaust gas pipe 22, and pass all the refluxed flue gas into the combustion-supporting exhaust gas pipe 22 to mix with the combustion-supporting exhaust gas, and then enter the furnace. The above design allows the refluxed flue gas to enter the combustion-supporting exhaust gas pipe 22 and mix with the combustion-supporting exhaust gas, and the temperature of the flue gas can be further reduced on the basis of Example 1, and the water vapor in the flue gas is reduced again, which can better ensure the combustion effect.

[0068] Example 5

[0069] A polyester production energy supply system, as shown in the following Figure 4 As shown, the difference from Example 4 is that the hot water heat exchanger 52 is connected to a circulation branch pipe 80, the end of the circulation branch pipe 80 away from the hot water heat exchanger 52 is connected to the circulation pipe 60, and the connection point between the circulation branch pipe 80 and the circulation pipe 60 is located upstream of the device.

[0070] This solution adds a circulation branch pipe 80. When the amount of heat transfer oil output by the heating boiler 31 is greater than the demand of the heat-consuming equipment 61, the excess heat transfer oil can be directly transported to the hot water heat exchanger 52 through the circulation branch pipe 80 to continue heating the heated soft water into water vapor. This can not only reduce the waste of heat transfer oil, but also improve the efficiency of the hot water heat exchanger 52 in generating water vapor.

[0071] Comparative Examples and Test Results

[0072] Control the compressed air intake volume and the recycled waste gas volume per unit time; and control the combustion-supporting waste gas intake volume and the combustion-supporting air intake volume per unit time at the combustion-supporting air intake end of the heating boiler 31; the difference between comparative examples 1-4 and embodiment 1 is shown in Table 1 below, and the rest is the same as embodiment 1. Embodiments 1-4 and comparative examples 1-4 were tested, and the conclusions are shown in Table 1.

[0073] Note: In the gas ratio column, in Examples 1-4, the ratio of the compressed air intake to the total nitrogen-making gas intake is recorded as P1; the ratio of the recycled exhaust gas intake to the total nitrogen-making gas intake is recorded as P2. In Examples 1-3, the ratio of the combustion-supporting air intake to the total combustion-supporting gas intake is recorded as C1; the ratio of the combustion-supporting exhaust gas intake to the total combustion-supporting gas intake is recorded as C2. In Example 4, the mixture of the reflux flue gas and the combustion-supporting exhaust gas entering the combustion-supporting exhaust gas pipe 22 is called a mixed gas, and the ratio of the mixed gas to the total combustion-supporting gas intake is recorded as C2.

[0074] In the test result column, the product color value is tested by HunterLab colorimeter (LabScan XE), and the product L value (whiteness) is above 80, which is qualified. Samples are taken every 8 hours every day (3 times a day), 500g each time, and the product color value (L value) of each sampling test is recorded as A; the sampling is carried out for 4 consecutive days, and then the color values ​​A of all products are added up to get the average value, and the average product color value (L value) is written in the table below.

[0075] In the test result column, nitrogen oxide emissions <50mg / m 3 During the production process, if the concentration of 3 , then record the value of this point and fill it in the table below; if it does not exceed, it will be displayed as <50mg / m 3 .

[0076] Table 1

[0077]

[0078] In summary, it can be seen from Examples 1-3 that the present scheme is used to recycle the waste gas generated by the nitrogen generator, and a part of the recycled waste gas is mixed with compressed air to form a mixed gas as nitrogen-making gas; the other part is mixed with the combustion-supporting air as combustion-supporting waste gas to achieve combustion-supporting heating of the boiler; by controlling the mixing ratio, the optimal waste gas recovery effect is achieved, which not only improves the nitrogen production efficiency and reduces the nitrogen production cost, but also extends the service life of the equipment; on the other hand, the combustion-supporting waste gas is combined with the flue gas of the heating boiler to heat the combustion-supporting waste gas and improve the combustion-supporting effect; and the nitrogen oxide emissions are reduced, and the standard emission is less than 80 mg / m 3, and our technology can reach <50mg / m 3 , far below the standard, with obvious environmental protection effect.

[0079] In Example 4, a test was conducted on the situation where all the flue gas refluxed from the flue gas reflux pipe 42 was passed into the combustion-supporting exhaust gas pipe 22. The product color value had normal fluctuations, and the color value still met the standard, which could further control the emission of nitrogen oxides. According to the analysis of the inventor, it is speculated that the water vapor in this part of the flue gas is condensed again, so that when the flue gas enters the furnace of the heating boiler 31 for combustion, it will not affect the combustion efficiency. It is worth noting that, based on the detection of Example 1 and Example 4, if due to working conditions, a part of the flue gas refluxed from the flue gas reflux pipe 42 is used to directly enter the furnace, and the other part enters the combustion-supporting exhaust gas pipe 22, because the temperature of the combustion-supporting exhaust gas in the combustion-supporting exhaust gas pipe 22 is lower than that of the flue gas, the flue gas entering the combustion-supporting exhaust gas pipe 22 can still be condensed, thereby improving the combustion efficiency; this situation also falls within the protection scope of the present technology.

[0080] By comparing Comparative Example 1 with Example 1, it can be seen that when the intake of recycled waste gas is increased to 20%, it exceeds the maximum ratio of 12% of the intake of recycled waste gas to the total intake of nitrogen-making gas. The polyester chip product inspection failed, which was mainly reflected in the inspection of the polyester chip product by the quality inspection team, and the product color value was found to be unstable. According to the inference and analysis of the inventor, because the adsorption nitrogen generator mainly relies on compressed air to separate nitrogen through the adsorbent, the insufficient amount of compressed air will directly affect the output and purity of nitrogen. In other words, when the intake of recycled waste gas is too much, the separation efficiency of the nitrogen generator decreases, the nitrogen production decreases, and the production demand cannot be met.

[0081] By comparing Example 2 with Example 1, the inventor found that when the compressed air intake is increased and the recycled waste gas intake is reduced, the product color value is still up to standard, and the technology can achieve the corresponding effect. However, the inventor analyzed from another aspect that although increasing the compressed air intake can increase nitrogen output, it also requires more energy to produce and compress the air, resulting in increased costs; and the waste gas still contains a certain concentration of nitrogen and other recyclable gases that are not utilized, resulting in a waste of resources. Therefore, when controlling the recycled waste gas intake, this factor needs to be considered, and the recycled waste gas intake should not be reduced blindly. For example, it can be considered to be controlled at more than 5%.

[0082] In summary, this technology can not only achieve full recovery and utilization of waste gas by controlling the gas mixing amount, but also ensure the quality stability of the product.

[0083] By comparing Example 3 with Example 1, when the proportion of combustion air intake C1 is reduced to 72%, the proportion of combustion exhaust gas intake C2 is increased to 28%; when the maximum ratio of combustion exhaust gas intake to total combustion gas intake per unit time is exceeded, 27%, the nitrogen oxide emission is ≥50mg / m 3 The inventors have analyzed and speculated that the main reason is that the increase in oxygen content will make the combustion more intense, further increase the combustion temperature, and cause nitrogen oxides (NO x ) emissions will increase; nitrogen oxides will not only cause serious environmental pollution problems such as acid rain and photochemical smog, but also run counter to the current stringent environmental protection laws and regulations.

[0084] By comparing Example 4 with Example 1, when the proportion of combustion-supporting exhaust gas intake C2 is reduced to 10%, the inventors found that the product color value and nitrogen oxide emissions are still up to standard, and the technology can achieve the corresponding effect. However, the inventors also found that the exhaust gas utilization rate cannot be reduced too much blindly, and to avoid reducing its utilization rate, it can be controlled above 20%.

[0085] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A polyester production energy supply system, comprising a nitrogen supply unit, the nitrogen supply unit comprising an air compressor, an air dryer, an adsorption nitrogen generator, a nitrogen tank and a nitrogen using device which are sequentially connected through a nitrogen production pipeline, characterized in that: An air purifier is provided between the air compressor and the air dryer; the adsorption nitrogen generator is connected to a waste gas tank, and a recycled waste gas pipe is connected between the waste gas tank and the air purifier; It also includes a combustion chamber, a combustion-supporting exhaust gas pipe is connected between the exhaust gas tank and the combustion chamber, and a combustion-supporting air pipe is also connected to the combustion chamber.

2. A polyester production energy supply system according to claim 1, characterized in that: The combustion chamber is used to supply heat to the steam supply unit; the steam supply unit includes a heating boiler, a waste heat boiler, heat-using equipment and steam-using equipment, a flue gas pipe is connected between the heating boiler and the waste heat boiler, a circulation pipe is connected between the heating boiler and the heat-using equipment, and a steam pipe is connected between the waste heat boiler and the steam-using equipment; the combustion chamber is the combustion furnace of the heating boiler.

3. A polyester production energy supply system according to claim 2, characterized in that: At the nitrogen making gas inlet end of the adsorption nitrogen making machine, per unit time, the compressed air intake accounts for P1% of the total nitrogen making gas intake, 88≤P1<100; the recycled waste gas intake accounts for P2% of the total nitrogen making gas intake, 0<P2≤12.

4. A polyester production energy supply system according to claim 3, characterized in that: At the combustion-supporting gas inlet end of the heating boiler, the combustion-supporting air intake accounts for C1% of the total combustion-supporting gas intake per unit time, 73≤C1<100, and the combustion-supporting exhaust gas intake accounts for C2% of the total combustion-supporting gas intake, 0<C2≤27.

5. A polyester production energy supply system according to any one of claims 1 to 4, characterized in that: The waste heat boiler is connected to an air heat exchanger through a flue gas duct, and the air heat exchanger is connected to the heating boiler through a combustion-supporting air pipe.

6. A polyester production energy supply system according to claim 5, characterized in that: The air heat exchanger is connected to a cold water heat exchanger through a flue gas pipeline, the cold water heat exchanger is connected to a soft water pipeline, and the soft water pipeline is also connected to a soft water pool.

7. A polyester production energy supply system according to claim 6, characterized in that: The soft water pool is connected to a hot water heat exchanger through a soft water pipe, and the hot water heat exchanger is connected to a steam-using device through a steam pipe; the hot water heat exchanger is connected to a circulation pipe, and the hot water heat exchanger is located downstream of the heat-using device.

8. A polyester production energy supply system according to claim 7, characterized in that: The hot water heat exchanger is connected with a circulation branch pipe, and the other end of the circulation branch pipe is connected with the circulation pipeline upstream of the heat-using equipment.

9. A polyester production energy supply system according to claim 8, characterized in that: A nitrogen oxide detector is provided at the smoke outlet of the smoke duct, and a smoke return pipe is connected to the smoke duct downstream of the cold water heat exchanger, and the other end of the smoke return pipe is connected to the heating boiler.

10. A polyester production energy supply system according to claim 9, characterized in that: The other end of the flue gas return pipe is connected to the heating boiler and the combustion-supporting exhaust gas pipe respectively; and the connecting point between the flue gas return pipe and the combustion-supporting exhaust gas pipe is located on the side close to the exhaust gas tank, and a one-way valve is provided on the combustion-supporting exhaust gas pipe between the connecting point and the combustion-supporting air pipe.

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