Air separation waste nitrogen recovery device

Abstract

The utility model relates to an air separation waste nitrogen recovery device, which adopts low-temperature rectification and expansion machine refrigeration modes to produce nitrogen, a waste nitrogen compressor is sequentially connected with a plate heat exchanger, a main tower and a main cooling evaporator through pipelines, an auxiliary tower is arranged above the main cooling evaporator, and the top of the auxiliary tower is sequentially communicated with the plate heat exchanger and a secondary high-pressure nitrogen pipeline through pipelines. The middle part of the main tower is sequentially communicated with a plate heat exchanger, an expansion machine, an expansion machine aftercooler and a low-pressure nitrogen pipeline through pipelines. High-purity nitrogen with the purity of 99.999%, low-pressure nitrogen with the purity smaller than or equal to 5 ppmO2 and the outlet pressure of 0.9 MPA and medium-pressure nitrogen with the purity smaller than or equal to 5 ppmO2 and the purity smaller than or equal to 100 ppmAr and the pressure of 6.6 MPA are separated from waste nitrogen with the air separation purity of 98%, wherein the high-purity nitrogen meets the GB / T8979-2008 pure nitrogen, high-purity nitrogen and ultra-pure nitrogen requirements, and the purity of the low-pressure nitrogen is smaller than or equal to 5 ppmO2 and the purity of the medium-pressure nitrogen is smaller than or equal to 100 ppmAr.

Description

Technical Field

[0001] The utility model relates to the technical field of chemical industry, in particular to a device for recovering polluted nitrogen from air separation. Background Art

[0002] The air separation unit uses air as raw material, and after precooling and purification system, the air with qualified dew point is sent to the distillation unit, and oxygen, nitrogen and argon products are produced by low-temperature distillation and expansion mechanism refrigeration. Due to the continuous expansion of synthetic ammonia production capacity, the demand for oxygen and nitrogen is increasing, and the design capacity of air separation units at home and abroad is also increasing.

[0003] The air separation unit has a large amount of 98% pure polluted nitrogen gas discharged during production. The 98% polluted nitrogen gas contains 97.2% nitrogen, 1.8% oxygen, and 1% argon. The polluted nitrogen gas from the top outlet of the air separation unit distillation tower is divided into two streams. One stream is transferred to the water cooling tower through the low-pressure plate. The total amount of this polluted nitrogen gas is 155,000 Nm 3 / h, pressure: 10kpa, temperature: 10℃, using the principle of dirty nitrogen hygroscopicity to cool the water; one stream passes through the high-pressure plate to switch the molecular sieve of the purification system, and then goes to the water cooling tower and the muffler to be emptied. This part of the cooling capacity is not fully utilized, and the utilization value of the dirty nitrogen is not realized. Utility Model Content

[0004] In view of the problems existing in the prior art, the utility model provides a device for recovering polluted nitrogen from air separation.

[0005] The utility model is realized by the following technical solutions:

[0006] A device for recovering contaminated nitrogen from air separation comprises a contaminated nitrogen compressor, which is connected to a heat exchanger, a main tower and a main cooling evaporator in sequence through a pipeline; an auxiliary tower is arranged above the main cooling evaporator; the top of the auxiliary tower is connected to a heat exchanger and a secondary high-pressure nitrogen pipeline in sequence through a pipeline; the middle of the main tower is connected to a plate heat exchanger, an expander, an expander aftercooler and a low-pressure nitrogen pipeline in sequence through a pipeline.

[0007] Preferably, the top of the auxiliary tower is connected to an auxiliary condenser evaporator, the auxiliary condenser evaporator is connected to a heat exchanger and an expander through a pipeline, and the expander is connected to a heat exchanger and a dirty nitrogen return pipeline to the owner's air separation through a loop pipeline.

[0008] Preferably, the main cooling evaporator is connected to a liquid nitrogen buffer tank through a pipeline, and the liquid nitrogen buffer tank is connected to the auxiliary tower and the top of the main tower through pipelines respectively.

[0009] Preferably, the auxiliary tower forms a loop with the auxiliary condenser evaporator through a pipeline, and the main cooling evaporator is connected with the auxiliary condenser evaporator through a pipeline;

[0010] The bottom of the main tower is connected to the auxiliary tower through a pipeline;

[0011] The sub-high pressure nitrogen pipeline is provided with a nitrogen booster which is connected to a muffler through a pipeline, and the muffler is also connected to an expander through a pipeline;

[0012] The low-pressure nitrogen pipeline is also connected to the expander, and the expander aftercooler also forms a loop with the expander through the pipeline;

[0013] The pipeline of the device is provided with valves, and the tower is provided with a liquid level meter.

[0014] Preferably, there are several heat exchangers.

[0015] The device performs a process for recovering polluted nitrogen from air separation, and the process comprises the following steps:

[0016] S1: The dirty nitrogen is drawn out from the outlet of the low-pressure plate heat exchanger of the original air separation cold box to the dirty nitrogen pipeline of the water-cooling tower, and is connected to the dirty nitrogen compressor through a pipeline, compressed into raw dirty nitrogen, and enters two plate heat exchangers for cooling. It exchanges heat with the low-pressure nitrogen from the main tower, the low-pressure nitrogen from the auxiliary tower, and the dirty nitrogen from the auxiliary condenser evaporator to obtain dirty nitrogen close to the liquefaction point, and then enters the main tower, passes through the four-stage packed tower, contacts with liquid nitrogen and participates in distillation;

[0017] S2: The nitrogen obtained after distillation in the main tower is reheated by the plate heat exchanger and then flows out of the cold box, and enters the booster end of the expander. The booster is sent out as a low-pressure nitrogen product. The remaining nitrogen enters the nitrogen side of the main condenser evaporator from the top of the main tower, exchanges heat with the liquid nitrogen at the bottom of the auxiliary tower, and becomes liquid nitrogen after condensation and flows back into the auxiliary tower to participate in distillation and supplement part of the cooling capacity.

[0018] S3: The nitrogen evaporated by heat exchange of liquid nitrogen at the bottom of the auxiliary tower is rectified with the liquid nitrogen from the top. The reflux ratio is controlled by the auxiliary tower liquid level regulating valve. Qualified nitrogen is obtained at the top of the auxiliary tower. After reheating through the plate heat exchanger, it leaves the cold box and enters the nitrogen booster. It is pressurized and sent out as sub-high pressure product nitrogen.

[0019] S4: The liquid nitrogen obtained at the bottom of the main tower is throttled by the main tower liquid level regulating valve and then sent to the main condenser evaporator for evaporation, and then enters the auxiliary tower for further distillation;

[0020] S5: The nitrogen obtained from the auxiliary tower is condensed into liquid nitrogen in the main condenser evaporator, part of which returns to the top of the auxiliary tower as reflux liquid, and the other part is sent back to the top of the main tower through a liquid nitrogen pump for reflux, thereby increasing the nitrogen extraction rate of the system;

[0021] S6: The concentrated liquid nitrogen is obtained at the bottom of the auxiliary tower, and is throttled through the auxiliary cooling liquid level regulating valve and sent to the auxiliary condensing evaporator to evaporate into concentrated nitrogen gas;

[0022] S7: The concentrated dirty nitrogen is reheated in the plate heat exchanger, then expanded in the expander, then reheated in the heat exchanger, and sent back to the water cooling tower of the air separation unit.

[0023] Preferably, in step S1, the temperature of the dirty nitrogen compressor is 8-12°C, the pressure is 8-12KPA, the purity of the dirty nitrogen is 96-99%, and the outlet temperature of the dirty nitrogen compressor is 35-45°C, the pressure is 0.6-0.9 MPA of the raw dirty nitrogen.

[0024] Preferably, in step S1, the temperature of the low-pressure nitrogen out of the main tower, the low-pressure nitrogen out of the auxiliary tower, and the auxiliary condenser evaporator is -174°C~-178°C, the temperature of the heat exchange outlets of the two plate heat exchangers is -171~--173°C, the pressure is 0.6-0.9MPA, and the dirty nitrogen gas close to the liquefaction point with a purity of 96-99% enters the main tower, passes through four-stage packed towers, and contacts with -190~-200°C liquid nitrogen to participate in distillation.

[0025] Preferably, in step S2, the nitrogen temperature after distillation in the main tower is -176-172°C, the pressure is 0.61-0.65 MPa(G), the purity is ≤5ppmO2, and the expander is pressurized to 0.6-0.9 MPa(G) low-pressure nitrogen product.

[0026] Preferably, in step S3, the pressure at the top of the auxiliary tower 4 is 0.5-0.53 MPa (G), and the purity is ≤5 ppm. 2 , ≤100ppmAr qualified nitrogen, the sub-high pressure product nitrogen pressure is 6.5-6.8 MPa(G).

[0027] Step S7: The concentrated dirty nitrogen is reheated to -148~-146°C, 0.31-0.34Mpa (G) in a plate heat exchanger, then expanded to -185~-170°C, 25-35kpa (G) in an expander, and then enters a heat exchanger to be reheated to 34-38°C, 8-12kpa (G).

[0028] The utility model has the following beneficial effects:

[0029] The utility model produces 99.999% high-purity nitrogen that meets GB / T8979-2008 "Pure Nitrogen, High-Purity Nitrogen, and Ultra-Purity Nitrogen" from the polluted nitrogen gas with a purity of 98% in the air separation unit, with a pressure of 0.9MPA, a flow rate of 19000Nm3 / h, and a purity of ≤5ppmO2 of low-pressure nitrogen, and a by-product pressure of 6.6MPA, a flow rate of 48000Nm3 / h, a purity of ≤5ppmO2, and ≤100ppmAr of medium-pressure nitrogen, with a unit consumption of 0.17 yuan / Nm3, which is 35% lower than that of the original air separation unit. By making full use of the polluted nitrogen gas produced as a by-product of the air separation unit, 88.9% of the polluted nitrogen gas can be recovered each year, which can save 300,000KW of cooling capacity and play a comprehensive utilization of cooling capacity. Instrument regulating valves, zirconium oxide / electrochemical analyzers, argon chromatographs, etc. are installed in the dirty nitrogen pipeline, medium-pressure nitrogen pipeline, low-pressure nitrogen pipeline, etc. The CCS and DCS control systems can automatically adjust the process indicators and improve the intelligence level of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a diagram showing the connection relationship of the equipment of the present utility model.

[0031] In the figure, there are dirty nitrogen compressor 1, plate heat exchanger 2, main tower 3, auxiliary tower 4, main condenser evaporator 5, auxiliary condenser evaporator 6, liquid nitrogen pump 7, liquid nitrogen buffer tank 8, expander 9, nitrogen booster 10, expander aftercooler 11, muffler 12, raw dirty nitrogen regulating valve 13, reflux dirty nitrogen regulating valve 14, low-pressure nitrogen product reflux regulating valve 15, expander anti-surge valve 16, low-pressure nitrogen pressure regulating valve to expander 17, low-pressure nitrogen pressure regulating valve to nitrogen booster 18, low-pressure nitrogen product delivery regulating valve 19, start-up valve 20, main tower liquid level regulating valve 21, auxiliary tower liquid level regulating valve 22, auxiliary cooling liquid level regulating valve 23. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the present invention and implement it, the present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but the embodiments are not intended to limit the present invention.

[0033] The polluted nitrogen gas with a purity of 98% in the air separation unit is separated into nitrogen with a purity of ≤5ppm 2 , outlet pressure 0.9MPA low pressure nitrogen, separated purity ≤5ppmO 2 , ≤100ppmAr, medium-pressure nitrogen with a pressure of 6.6MPA, and its material balance is shown in Table 1. It will reduce the production cost of nitrogen, reduce the operating pressure of the system, lay the foundation for the expansion and transformation of synthetic ammonia, and generate considerable economic benefits.

[0034] Table 1

[0035] materials Dirty nitrogen Dirty nitrogen Nitrogen Nitrogen Nitrogen Nitrogen Nitrogen Dirty nitrogen state gas gas gas gas gas gas gas gas PressureMpa(A) 0.11 0.80 0.76 0.92 0.90 0.62 6.70 0.11 Temperature ℃ 10 40 36 60 40 36 40 36 Flow rateNm 3 / h 89000 89000 19000 19000 19000 48000 48000 22000 Nitrogen 2 (%) 97.2 97.2 99.8 99.8 99.8 99.99 99.99 88.9 Oxygen 2 1.8% 1.8% <5ppm <5ppm <5ppm <1ppm <1ppm 7.3% Argon 1.0% 1.0% 0.2% 0.2% 0.2% <100ppm <100ppm 3.8%

[0036] Example 1

[0037] A device for recovering waste nitrogen from air separation, the device comprising a waste nitrogen compressor 1, the waste nitrogen compressor 1 being connected to a plate heat exchanger 2, a main tower 3, and a main cooling evaporator 5 in sequence through a pipeline, an auxiliary tower 4 being arranged above the main cooling evaporator 5, the top of the auxiliary tower 4 being connected to the plate heat exchanger 2 and a secondary high-pressure nitrogen pipeline in sequence through a pipeline, and the middle of the main tower 3 being connected to the plate heat exchanger 2, an expander 9, an expander aftercooler 11, and a low-pressure nitrogen pipeline in sequence through a pipeline.

[0038] Preferably, the top of the auxiliary tower 4 is connected to the auxiliary condenser evaporator 6, the auxiliary condenser evaporator 6 is connected to the plate heat exchanger 2 and the expander 9 through a pipeline, and the expander 9 is then connected to the heat exchanger 2 and the dirty nitrogen return to the owner's air separation pipeline through a loop pipeline.

[0039] Preferably, the main cooling evaporator 5 is connected to the liquid nitrogen buffer tank 8 through a pipeline, and the liquid nitrogen buffer tank 8 is connected to the auxiliary tower 4 and the top of the main tower 3 through pipelines respectively.

[0040] Preferably, the auxiliary tower 4 forms a loop with the auxiliary condenser evaporator 6 through a pipeline, and the main cooling evaporator 5 is connected with the auxiliary condenser evaporator 6 through a pipeline.

[0041] Preferably, the bottom of the main tower 3 is connected to the auxiliary tower 4 through a pipeline.

[0042] Preferably, a nitrogen booster 10 is provided on the secondary high-pressure nitrogen pipeline and is connected to a muffler 12 through a pipeline, and the muffler 12 is also connected to an expander 9 through a pipeline.

[0043] Preferably, the low-pressure nitrogen pipeline is also connected to the expander 9, and the expander aftercooler 11 also forms a loop with the expander 9 through the pipeline.

[0044] Preferably, valves are provided on the pipeline and liquid level gauges are provided on the tower.

[0045] A flow of 89000Nm3 / h, temperature of 10℃, pressure of 10KPA and purity of 98% of dirty nitrogen is drawn out from the outlet of the low-pressure plate heat exchanger of the original air separation cold box to the dirty nitrogen pipeline of the water-cooling tower. It is connected to the dirty nitrogen compressor 1 through a DN1400 pipeline, compressed into raw dirty nitrogen with a temperature of 40℃ and a pressure of 0.8MPA, and enters two plate heat exchangers 2 for cooling. It exchanges heat with the -174℃ low-pressure nitrogen out of the main tower, the -176℃ low-pressure nitrogen out of the auxiliary tower, and the -178℃ dirty nitrogen out of the auxiliary cooling tower. The temperature is -172.5℃, the pressure is 0.8MPA, and the purity is 98%. After approaching the liquefaction point, it enters the main tower 3 and passes through the four-stage packed tower to contact with -196℃ liquid nitrogen. After distillation in the main tower, nitrogen with a temperature of -174°C, a pressure of 0.64 MPa (G), a purity of ≤5 ppm O2, and a purity that meets the requirements is obtained. Most of the nitrogen is reheated by the plate heat exchanger 2 and then discharged from the cold box, and enters the boosting end of the expander 9, where it is boosted to 0.8 MPa (G) and delivered as product nitrogen. The remaining nitrogen enters the nitrogen side of the main condenser evaporator 5 from the top of the main tower 3, exchanges heat with the liquid nitrogen at the bottom of the auxiliary tower 4, and becomes liquid nitrogen after condensation and flows back into the auxiliary tower 4. The nitrogen evaporated by the heat exchange of the liquid nitrogen at the bottom of the auxiliary tower 4 is rectified with the liquid nitrogen from the top, and the reflux ratio is controlled by the regulating valve 22. Nitrogen with a pressure of 0.52 MPa (G), a purity of ≤5 ppm O2, and ≤100 ppm Ar is obtained at the top of the auxiliary tower 4. The nitrogen with a purity that meets the requirements is reheated by the plate heat exchanger 2 and then discharged from the cold box, and enters the nitrogen booster 10 where it is boosted to 6.6 MPa (G) is sent out as product nitrogen; the liquid waste nitrogen obtained at the bottom of the main tower 3 is throttled by the main tower liquid level regulating valve 21 and sent to the main condenser evaporator 5 for evaporation, and then enters the auxiliary tower 4 for further distillation. The nitrogen obtained in the auxiliary tower 4 is condensed into liquid nitrogen in the main condenser evaporator 5, and a part of it returns to the top of the auxiliary tower 4 as reflux liquid; the other part is sent back to the top of the main tower 3 through the process liquid nitrogen pump 7 for reflux, thereby increasing the nitrogen extraction rate of the system. The concentrated liquid waste nitrogen obtained at the bottom of the auxiliary tower 4 is throttled by the auxiliary cooling liquid level regulating valve 23 and sent to the auxiliary cooling 6 for evaporation into concentrated waste nitrogen. After the concentrated waste nitrogen is reheated to a certain temperature in the plate heat exchanger 2, it is expanded to normal pressure in the expander 9, and then reheated to normal temperature in the plate heat exchanger 2 and sent back to the water-cooled tower of the air separation unit. Part of the nitrogen product goes to the expander booster end to recover expansion work, providing low-pressure nitrogen of 19,000 Nm3 / h, purity ≤5 ppm O2, and outlet pressure 0.9 MPA for the subsequent process. The remaining 48,000 Nm3 / h, purity ≤5 ppm O2, ≤100 ppm Ar, is compressed to 6.6 MPA in the nitrogen booster and then delivered.

[0046] Preferably, the dirty nitrogen compressor 1 has a rated power of 8800KW, four-stage compression, four-stage cooling, double-layer arrangement, motor drive, and a containerized oil station. It compresses the dirty nitrogen with a flow rate of 89000Nm3 / h, a temperature of 10°C, a pressure of 10KPA, and a purity of 98% to a temperature of 40°C and a pressure of 0.8MPA to provide a gas source for the cold box.

[0047] Preferably, a new low-temperature cold box system is added after the dirty nitrogen compressor, including two plate heat exchangers 2, main tower 3, auxiliary tower 4, main condenser evaporator 5, auxiliary condenser evaporator 6, two liquid nitrogen pumps 7, and a liquid nitrogen buffer tank 8. The dirty nitrogen gas with a temperature of 40°C and a pressure of 0.8MPA after compression by the dirty nitrogen compressor 1 passes through the plate heat exchanger 2 and enters the main tower 3 at a temperature of -173°C. After low-temperature distillation and deep cold separation, nitrogen with a purity of ≤5ppmO2, ≤100ppmAr and a pressure of 0.8MPA can be extracted. The cold box is 4.2*5.8*36 meters, the main tower 3 is filled with four sections, the plate heat exchanger 2 is placed in the cold box, the auxiliary tower 4 is placed on the plate heat exchanger 2, and the plate heat exchanger 2 is arranged symmetrically without bias flow. The liquid nitrogen buffer tank 8 and the liquid nitrogen pump 7 mainly provide cooling capacity for the main tower 3. The outlet of the liquid nitrogen pump 7 has one flow direction, which reduces the difficulty of distributing liquid in process operation and makes the flow into the main tower more stable, which is beneficial to purity.

[0048] Preferably, two expanders 9 are used for refrigeration, and the expansion end medium is polluted nitrogen with a flow rate of 19500 Nm 3 / h, inlet pressure 0.44MPA, outlet pressure 0.3MPA, inlet temperature -160℃, inlet temperature -190℃, used to provide cooling for the cold box; the booster end medium is nitrogen, this low-pressure nitrogen is extracted from the upper part of the main tower 3, with a flow rate of 19000Nm3 / h, inlet pressure 0.76MPA, outlet pressure 0.9MPA, outlet temperature 40℃, providing low-pressure nitrogen with a purity of ≤5ppmO2 for the subsequent process section.

[0049] Preferably, a nitrogen booster 10 is arranged behind the cold box. The rated power of the compressor unit is 6600KW, four-stage compression, four-stage cooling, double-layer layout, motor drive, and container oil station. The low-pressure nitrogen with a flow rate of 48000Nm3 / h, a temperature of 36°C, a pressure of 0.8MPA, a purity of ≤5ppmO2, ≤100ppmAr is compressed to a medium-pressure nitrogen with a temperature of 40°C and a pressure of 6.6MPA for use in the synthetic ammonia device.

[0050] The above embodiments are only preferred technical solutions of the present utility model and should not be regarded as limitations of the present utility model. The embodiments and features in the embodiments of the present application can be arbitrarily combined with each other without conflict. The protection scope of the present utility model shall be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present utility model.

Claims

1. A device for recovering contaminated nitrogen from air separation, the device comprising a contaminated nitrogen compressor (1), characterized in that: The dirty nitrogen compressor (1) is connected to the heat exchanger (2), the main tower (3), and the main cooling evaporator (5) in sequence through pipelines. An auxiliary tower (4) is arranged above the main cooling evaporator (5). The top of the auxiliary tower (4) is connected to the heat exchanger (2) and the secondary high-pressure nitrogen pipeline in sequence through pipelines. The middle of the main tower (3) is connected to the plate heat exchanger (2), the expander (9), the expander aftercooler (11), and the low-pressure nitrogen pipeline in sequence through pipelines. The top of the auxiliary tower (4) is connected to the auxiliary condensing evaporator (6). The auxiliary condensing evaporator (6) is connected to the heat exchanger (2) and the expander (9) through pipelines. The expander (9) is then connected to the heat exchanger (2) and the dirty nitrogen return pipeline of the owner through a loop pipeline.

2. The device for recovering nitrogen from air separation pollution according to claim 1, characterized in that: The main cooling evaporator (5) is connected to the liquid nitrogen buffer tank (8) through a pipeline, and the liquid nitrogen buffer tank (8) is connected to the top of the auxiliary tower (4) and the main tower (3) through pipelines respectively.

3. The device for recovering nitrogen from air separation pollution according to claim 1, characterized in that: The auxiliary tower (4) forms a loop with the auxiliary condensing evaporator (6) through a pipeline, and the main cooling evaporator (5) is connected to the auxiliary condensing evaporator (6) through a pipeline.

4. The device for recovering nitrogen from air separation pollution according to claim 1, characterized in that: The bottom of the main tower (3) is connected to the auxiliary tower (4) through a pipeline.

5. The device for recovering nitrogen from air separation pollution according to claim 1, characterized in that: The secondary high-pressure nitrogen pipeline is provided with a nitrogen booster (10) which is connected to a muffler (12) via a pipeline, and the muffler (12) is also connected to an expander (9) via a pipeline.

6. The device for recovering polluted nitrogen from air separation according to claim 1, characterized in that: The low-pressure nitrogen pipeline is also connected to the expander (9), and the expander aftercooler (11) also forms a loop with the expander (9) through the pipeline.

7. The device for recovering polluted nitrogen from air separation according to claim 1, characterized in that: The pipeline of the device is provided with valves, and the tower is provided with a liquid level meter.

8. The device for recovering polluted nitrogen from air separation according to claim 1, characterized in that: The heat exchangers (2) are provided in plurality.

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