CN111718769A - Comprehensive utilization synthetic ammonia tail gas preparation PNG system - Google Patents
Comprehensive utilization synthetic ammonia tail gas preparation PNG system Download PDFInfo
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- CN111718769A CN111718769A CN202010603671.2A CN202010603671A CN111718769A CN 111718769 A CN111718769 A CN 111718769A CN 202010603671 A CN202010603671 A CN 202010603671A CN 111718769 A CN111718769 A CN 111718769A
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- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
- C10L3/00—Gaseous fuels; Natural gas; Synthetic natural gas obtained by processes not covered by subclass C10G, C10K; Liquefied petroleum gas
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Abstract
The invention relates to the field of comprehensive utilization of synthetic ammonia tail gas, in particular to a system for preparing PNG (pneumatic network generator) by comprehensively utilizing the synthetic ammonia tail gas. The device comprises a molecular sieve dryer, a first heat exchanger, a second heat exchanger, a third heat exchanger, a rectifying tower and a condensation separator. The system for preparing PNG by comprehensively utilizing the synthetic ammonia tail gas has the advantages that the methane content in the product gas is high, the impurity content is low, and the high-purity PNG can be prepared by simple and direct process treatment. The process fully recycles the effective components of the synthetic ammonia tail gas, and has obvious social environmental benefit and economic benefit.
Description
Technical Field
The invention relates to the field of comprehensive utilization of synthetic ammonia tail gas, in particular to a system for preparing PNG (pneumatic network generator) by comprehensively utilizing the synthetic ammonia tail gas.
Background
Methane is a clean fuel with high calorific value, and with the continuous development of national natural gas projects, the natural gas market is wider and wider, the price is continuously increased, and the market prospect is very optimistic. Pipeline Natural Gas (PNG) refers to gaseous Natural Gas transported by Pipeline. The pipeline pressure is lower than that of compressed natural gas CNG.
In the process of ammonia synthesis production, synthesis gas is recycled, but the concentration of methane cannot be too high, so that part of waste gas containing ammonia, methane and the like, namely purge gas, must be discharged to control the concentration of methane, thereby ensuring the normal operation of ammonia synthesis reaction. Part of the ammonia synthesis system adopts Kazali low-pressure synthesis, about 1.25 percent of methane gas in the semi-water gas and part of converted methane in a double-adding refining section are enriched in the ammonia synthesis system and discharged out of the synthesis system when reaching a certain concentration, wherein CH4The concentration reaches about 12 percent, and part of hydrogen, nitrogen and ammonia gas are entrained, and the process is called as 'purge gas'. After the purge gas is washed by water and the hydrogen in the purge gas is recycled by membrane separation, the synthetic ammonia tail gas is merged into a fuel gas pipe network and is mainly used for combustion of blowing gas and three-waste furnaces. However, because the fuel gas has high methane content and high heat value, and environmental protection indexes are easy to fluctuate after the fuel gas enters the blowing gas and the three-waste furnace for combustion, partial emptying phenomenon exists, and the economic value of the methane gas cannot be fully utilized.
Meanwhile, methane is a greenhouse gas, and the capacity of causing global greenhouse effect per ton of methane is 25 times higher than that of carbon dioxide. If the purge gas is discharged directly, environmental pollution and resource waste are caused, and the consumption of synthetic ammonia is increased. Therefore, the method makes full use of the tail gas of the synthetic ammonia, and is an effective way for solving the environmental pollution, making full use of resources and reducing the cost of the synthetic ammonia.
Disclosure of Invention
The invention provides a system for preparing PNG (pneumatic network group) by comprehensively utilizing synthetic ammonia tail gas in order to fully utilize the synthetic ammonia tail gas.
The invention is realized by the following technical scheme: a system for preparing PNG by comprehensively utilizing synthetic ammonia tail gas comprises a molecular sieve dryer, a first heat exchanger, a second heat exchanger, a third heat exchanger, a rectifying tower and a condensation separator,
the molecular sieve dryer is provided with a top gas inlet and a bottom gas inlet, the top gas inlet and the bottom gas outlet of the molecular sieve dryer are connected with a first raw material gas inlet of a first heat exchanger through a pipeline, a first raw material gas outlet of the first heat exchanger is connected with a first raw material gas inlet of a second heat exchanger through a pipeline, a first raw material gas outlet of the second heat exchanger is connected with a first raw material gas inlet of a third heat exchanger through a pipeline, a first raw material gas outlet of the third heat exchanger is connected with an upper feed inlet of a rectifying tower through a pipeline, a tower bottom heavy component outlet of the rectifying tower is connected with a first LNG inlet of the third heat exchanger through a pipeline, a first LNG outlet of the third heat exchanger is connected with an upper feed inlet of a condensation separator through a pipeline, a top gas phase outlet of the condensation separator is connected with a first LNG inlet of the second heat exchanger through a pipeline, and a first LNG outlet of the second heat exchanger is connected with a first PNG inlet of the first heat, and a first PNG outlet of the first heat exchanger is connected to a PNG product gas pipe network.
As a further improvement of the technical scheme of the invention, the device also comprises an expander, wherein a condenser is arranged at the top of the rectifying tower, a tower top light component outlet of the rectifying tower is connected with a first tail gas inlet of a third heat exchanger through a pipeline, a first tail gas outlet of the third heat exchanger is connected with an inlet of an expansion end of the expander through a pipeline, an outlet of the expansion end of the expander is connected with an inlet of the condenser through a pipeline, an outlet of the condenser is connected with a second tail gas inlet of the third heat exchanger through a pipeline, a second tail gas outlet of the third heat exchanger is connected with a first tail gas inlet of a second heat exchanger through a pipeline, a first tail gas outlet of the second heat exchanger is connected with a first tail gas inlet of the first heat exchanger through a pipeline, a pipe pass outlet of the heater is connected to a pipe pass inlet of a molecular sieve dryer through a pipeline, and a gas inlet and a gas outlet at the bottom of the molecular sieve dryer are connected to a fuel gas pipe network through pipelines.
As a further improvement of the technical scheme of the invention, the system further comprises a methane evaporator, wherein a reboiler is arranged at the bottom of the rectifying tower, a first raw material gas outlet of the first heat exchanger is connected to a top raw material gas inlet of the methane evaporator in parallel, a bottom raw material gas outlet of the methane evaporator is connected to an inlet of the reboiler through a pipeline, an outlet of the reboiler is connected to a pipeline between a first raw material gas outlet of the second heat exchanger and a first raw material gas inlet of the third heat exchanger through a pipeline, a lower LNG inlet of the methane evaporator is connected with a bottom liquid phase outlet of the condensation separator through a pipeline, and an upper PNG outlet of the methane evaporator is connected to a first PNG inlet of the first heat exchanger through a pipeline.
As a further improvement of the technical scheme of the invention, a dust filter is connected in series on a pipeline between a top gas inlet and a top gas outlet of the molecular sieve dryer and a first raw material gas inlet of the first heat exchanger.
As a further improvement of the technical scheme of the invention, a raw material gas outlet of the dust filter is connected to an inlet of a bearing gas end of the expansion machine through a pipeline, and an outlet of the bearing gas end of the expansion machine is connected to a fuel gas pipe network.
As a further improvement of the technical scheme of the invention, a first branch line is connected in parallel on the PNG product air pipe network, the first branch line is connected to an inlet of a pressurization end of an expansion machine, an outlet of the pressurization end of the expansion machine is connected to a tube pass inlet of a water cooler, and a tube pass outlet of the water cooler is connected to the PNG product air pipe network.
As a further improvement of the technical scheme of the invention, the third heat exchanger is provided with a second raw material gas inlet and a second raw material gas outlet, a first raw material gas inlet of the third heat exchanger is communicated with a second raw material gas outlet of the third heat exchanger, a first raw material gas outlet of the third heat exchanger is communicated with a second raw material gas inlet of the third heat exchanger, a second raw material gas outlet of the third heat exchanger is connected with an inlet of the first buffer tank through a pipeline, and an outlet of the first buffer tank is connected with a second raw material gas inlet of the third heat exchanger through a pipeline.
As a further improvement of the technical scheme of the invention, an organic front buffer tank is connected in parallel on a pipeline between a first PNG outlet of the first heat exchanger and a PNG product gas pipe network.
The system for preparing PNG by comprehensively utilizing the synthetic ammonia tail gas has the advantages that the methane content in the product gas is high, the impurity content is low, and the high-purity PNG can be prepared by simple and direct process treatment. The process fully recycles the effective components of the synthetic ammonia tail gas, and has obvious social environmental benefit and economic benefit.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic structural diagram of a system for comprehensively utilizing synthetic ammonia tail gas to prepare PNG according to the invention.
In the figure: 1-molecular sieve dryer, 2-first heat exchanger, 3-second heat exchanger, 4-third heat exchanger, 5-rectifying tower, 6-condenser, 7-condensation separator, 8-PNG product gas pipe network, 9-expansion end, 10-heater, 11-fuel gas pipe network, 12-methane evaporator, 13-reboiler, 14-dust filter, 15-bearing gas end, 16-first branch line, 17-water cooler, 18-supercharging end, 19-first buffer tank and 20-front buffer tank.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the examples given herein without any inventive step, are within the scope of the present invention.
As shown in fig. 1, the embodiment provides a system for preparing PNG by comprehensively utilizing ammonia synthesis tail gas, which comprises a molecular sieve dryer 1, a first heat exchanger 2, a second heat exchanger 3, a third heat exchanger 4, a rectifying tower 5 and a condensation separator 7,
the molecular sieve dryer 1 is provided with a top gas inlet and a bottom gas inlet, the top gas inlet and the bottom gas outlet of the molecular sieve dryer 1 are connected with a first raw material gas inlet of a first heat exchanger 2 through pipelines, a first raw material gas outlet of the first heat exchanger 2 is connected with a first raw material gas inlet of a second heat exchanger 3 through pipelines, a first raw material gas outlet of the second heat exchanger 3 is connected with a first raw material gas inlet of a third heat exchanger 4 through pipelines, a first raw material gas outlet of the third heat exchanger 4 is connected with an upper feed inlet of a rectifying tower 5 through pipelines, a tower bottom heavy component outlet of the rectifying tower 5 is connected with a first LNG inlet of the third heat exchanger 4 through pipelines, a first LNG outlet of the third heat exchanger 4 is connected with an upper feed inlet of a condensation separator 7 through pipelines, a top gas phase outlet of the condensation separator 7 is connected with a first LNG inlet of the second heat exchanger 3 through pipelines, the first LNG outlet of the second heat exchanger 3 is connected with the first PNG inlet of the first heat exchanger 2 through a pipeline, and the first PNG outlet of the first heat exchanger 2 is connected to the PNG product gas network 8.
The raw material gas is decompressed from 9-10MPa to 6.5MPa and then enters a gas inlet and outlet at the bottom of the molecular sieve dryer 1, the molecular sieve dryer 1 adsorbs a small amount of water, the dew point temperature of the raw material gas reaches-68 ℃, and the dried raw material gas is discharged from the gas inlet and outlet at the top of the molecular sieve dryer 1 and then enters a cold box.
The methane-rich gas from the molecular sieve dryer 1 firstly enters a first heat exchanger 2 in a cold box to be cooled to-90 ℃, then enters a second heat exchanger 3 to be further cooled to-125 ℃, and then enters a third heat exchanger 4 to be cooled to-160 ℃. The liquefied methane-rich gas enters the upper part of the rectifying tower 5, then flows downwards along the packing in the rectifying tower 5, and performs mass and heat transfer with the hot gas rising at the bottom. Along the gradual rise of liquid along rectifying column 5 decline with the temperature, methane content in the liquid is concentrated gradually, when reaching rectifying column 5 bottom, methane content in the liquid reaches more than 94%, then discharge from the tower bottom heavy ends export of rectifying column 5, the first LNG import that gets into third heat exchanger 4 is heated, then get into condensation separator 7, gaseous methane gets into first heat exchanger 2 after getting into second heat exchanger 3 and is further heated, the gaseous methane that goes out first heat exchanger 2 is retrieved to PNG product air pipe network 8. The product gas has high methane content and low impurity content.
Furthermore, the embodiment further includes an expander, a condenser 6 is disposed at the top of the rectifying tower 5, an outlet of the light components at the top of the rectifying tower 5 is connected to a first tail gas inlet of the third heat exchanger 4 through a pipeline, a first tail gas outlet of the third heat exchanger 4 is connected to an inlet of an expansion end 9 of the expander through a pipeline, an outlet of the expansion end 9 of the expander is connected to an inlet of the condenser 6 through a pipeline, an outlet of the condenser 6 is connected to a second tail gas inlet of the third heat exchanger 4 through a pipeline, a second tail gas outlet of the third heat exchanger 4 is connected to a first tail gas inlet of the second heat exchanger 3 through a pipeline, a first tail gas outlet of the second heat exchanger 3 is connected to a first tail gas inlet of the first heat exchanger 2, a first tail gas outlet of the first heat exchanger 2 is connected to a tube pass inlet of the heater 10 through a pipeline, a tube pass outlet of the heater 10 is connected to a top gas inlet and outlet of the molecular sieve dryer, the bottom gas inlet and outlet of the molecular sieve dryer 1 are connected to a fuel gas pipe network 11 through pipelines.
Specifically, the liquefied methane-rich gas flows downwards along with the filler in the rectifying tower 5, the gas which is not condensed is discharged from a light component outlet at the top of the rectifying tower 5, the liquefied methane-rich gas firstly enters the third heat exchanger 4 for reheating and then enters the expansion end 9 of the expansion machine, the expansion end 9 of the expansion machine is refrigerated to obtain low-temperature gas and then enters the condenser 6 for heat exchange, a low-temperature environment is provided for the rectifying tower 5, and then the low-temperature gas sequentially enters the third heat exchanger 4, the second heat exchanger 3 and the first heat exchanger 2, heat exchange is carried out in the third heat exchanger 4, the second heat exchanger 3 and the first heat exchanger 2 respectively, and the cold energy of the tail gas is further recovered. A part of the gas discharged from the first heat exchanger 2 is used as regeneration gas when the molecular sieve dryer 1 is regenerated, and then is sent to a fuel gas pipe network 11 for combustion; the other part is directly sent to the fuel gas pipe network 11 for combustion.
Further, this embodiment still includes methane evaporator 12, rectifying column 5 bottom is equipped with reboiler 13, the first raw material gas export of first heat exchanger 2 is connected to the top raw material gas import of methane evaporator 12 in parallel, the bottom raw material gas export of methane evaporator 12 is connected to the import of reboiler 13 through the pipeline, the export of reboiler 13 is connected to the pipeline between the first raw material gas export of second heat exchanger 3 and the first raw material gas import of third heat exchanger 4 through the pipeline, the lower part LNG import of methane evaporator 12 is connected with the bottom liquid phase export of condensation separator 7 through the pipeline, the upper portion PNG export of methane evaporator 12 is connected to the first PNG import of first heat exchanger 2 through the pipeline.
In this embodiment, the reboiler 13 can provide a heat source for the bottom of the rectifying tower 5, so as to separate liquid methane and gaseous tail gas inside the rectifying tower 5, and the hot gas source of the reboiler 13 can be a raw material gas. In specific implementation, the raw gas exiting the first heat exchanger 2 is divided into two streams, and enters the second heat exchanger 3 and the methane evaporator 12 respectively, the methane-rich gas exiting the tube pass of the methane evaporator 12 is cooled to-100 ℃, and then enters the reboiler 13 to be continuously cooled, the temperature of the methane-rich gas exiting the reboiler 13 is further reduced to about-125 ℃, and then enters the third heat exchanger 4. The methane-rich gas which is discharged from the second heat exchanger 3 is mixed with the methane-rich gas from the reboiler 13, and then enters the third heat exchanger 4 for further temperature reduction. Liquid methane at the bottom of the rectifying tower 5 enters the third heat exchanger 4 and the condensation separator 7, gaseous methane in the condensation separator 7 enters the first heat exchanger 2 after entering the second heat exchanger 3, and after the liquid methane in the condensation separator 7 enters the methane evaporator 12 to be evaporated, absorbed and gasified, the gaseous methane enters the first heat exchanger 2 and is further sent to the PNG product gas pipe network 8.
In this embodiment, in order to promote the cooling efficiency of third heat exchanger 4, third heat exchanger 4 is equipped with second raw material gas import and second raw material gas export, the first raw material gas import of third heat exchanger 4 is linked together with the second raw material gas export of third heat exchanger 4, and the first raw material gas export of third heat exchanger 4 is linked together with the second raw material gas import of third heat exchanger 4, and the second raw material gas export of third heat exchanger 4 passes through the pipe connection with the import of first buffer tank 19, and the export of first buffer tank 19 passes through the pipe connection with the second raw material gas import of third heat exchanger 4. After entering the third heat exchanger 4, the methane-rich gas passing through the first raw material gas inlet of the third heat exchanger 4 reaches a temperature of-160 ℃, is discharged from the second raw material gas outlet, enters the first buffer tank 19, then enters the third heat exchanger 4 through the second raw material gas inlet, and finally is conveyed to the rectifying tower 5 through the first raw material gas outlet.
In this embodiment, in order to reduce the impurity content of the product gas and also to reduce the influence of impurities on the pipeline, a dust filter 14 is connected in series on the pipeline between the top gas inlet and outlet of the molecular sieve dryer 1 and the first raw material gas inlet of the first heat exchanger 2.
Further, a first branch line 16 is connected to the PNG product gas pipe network 8 in parallel, the first branch line 16 is connected to an inlet of a pressurizing end 18 of the expansion machine, an outlet of the pressurizing end 18 of the expansion machine is connected to a tube pass inlet of a water cooler 17, and a tube pass outlet of the water cooler 17 is connected to the PNG product gas pipe network 8. In this embodiment, the methane in the PNG product gas pipe network 8 may be a gas source at the pressurization end 18 of the expander, and the pressurization end 18 of the expander may pressurize the gas in the pipe network, and the water cooler 17 may reduce the temperature of the gas in the pipe network, so that the temperature and the pressure of the gas in the pipe network meet the requirements of the pipe network. In a specific application, a seventh branch line 27 is connected in parallel between the first branch line 16 and the inlet line of the bearing gas end 15 of the expander. When the supercharging end 18 of the expander normally operates, the seventh branch 27 is closed, and when the PNG product gas pipe network 8 cannot provide a gas source for the supercharging end 18 of the expander or the gas source is insufficient, the seventh branch 27 can be opened, and the raw gas is used for supplying gas to the supercharging end 18 of the expander, so that the abnormality of the supercharging end 18 of the expander is avoided.
Furthermore, the raw gas outlet of the dust filter 14 is connected to the inlet of the bearing gas end 15 of the expander through a pipeline, and the outlet of the bearing gas end 15 of the expander is connected to the fuel gas pipe network 11. The raw gas outlet of the dust filter 14 may further branch out a pipeline to be connected to the inlet of the bearing gas end 15 of the expander, the methane-rich gas pressure in the bearing gas end 15 is controlled to be 0.7-0.8MPa by a pressure reducing valve on the pipeline, and the methane-rich gas is used as the bearing gas, and then the gas is sent to the fuel gas pipe network 11 through the outlet of the bearing gas end 15.
Further, an organic front buffer tank 20 is connected in parallel on a pipeline between the first PNG outlet of the first heat exchanger 2 and the PNG product gas pipeline network 8. In this embodiment, the front buffer tank 20 is mainly used to protect the stability of the air intake at the supercharging end 18 of the expander.
The PNG system provided by the present embodiment can complete product sales locally in the form of PNG. The natural gas is not required to be converted into CNG or LNG for long-distance transportation, so that the final natural gas liquefaction rate, refrigeration power, compression power and the like are not required to be used as main economic and technical indexes when a refrigeration process is designed.
Because the pressure of the raw material gas of the PNG system is higher and the pressure of the methane gas is lower, the system pressure difference and the nitrogen and methane in the raw material gas can be directly utilized for indirect expansion refrigeration. The gas source pressure of the tail gas from hydrogen extraction of the synthesis post membrane in the embodiment is higher (11.2MPaG), the PNG pressure is lower (0.50MPaG), and the system pressure difference and the medium nitrogen and methane in the raw material gas can be directly utilized for indirect expansion refrigeration. The system has the advantages of less required equipment, no power consumption, simple operation and convenient start and stop.
The following table is a table of raw material gas content data in specific application of this example, and specific data are shown in table 1.
Table 1 feed gas content data table
As can be seen from the above table, the raw material gas pressure is high, the methane content is high, the gas composition is simple, and the impurity content is low. In the prior art, after being conveyed to a fuel gas cabinet through a fuel gas pipe network 11, the fuel gas is respectively conveyed to a three-waste furnace and a blowing gas boiler to be combusted and recycled, and combustible components of the fuel gas are recycled. However, because of high methane content, improper control of the blending combustion amount easily causes environmental protection index fluctuation of the three-waste furnace and the air blowing device, and partial emptying phenomenon exists.
In order to fully utilize the raw material gas and maximize environmental benefits and economic benefits, the embodiment adopts the technical scheme of the system and adopts the low-temperature liquefaction rectification technology to extract and process most of methane components in the synthetic ammonia tail gas into PNG, thereby solving the actual situation of insufficient utilization of the synthetic ammonia tail gas. After the device is put into operation, the safe and stable operation of the blowing gas is ensured (combustion)The methane content of the feed gas is more than or equal to 15 percent), and the maximum gas amount of the delivered PNG product is 2400Nm3H, average 1800 Nm/h3And h, the quality of the product gas reaches the national first-class natural gas standard.
TABLE 2 PNG product gas inspection data comparison
Note: the reduced methane low heat value is 35.9MJ/m3And (6) counting.
The detection result of the PNG product gas accords with national industrial policies, energy policies and environmental protection policies, and has good economic benefits and social benefits. The project is also a PNG clean fuel project manufactured by comprehensively utilizing the waste gas of the first approved synthetic post in Shanxi province in cities, and has important demonstration significance. The implementation of the embodiment solves the problem of venting the hydrogen-extracted tail gas of the synthesis post membrane, which is equivalent to extracting and selling methane in the original vented gas; the PNG new product is added, the product chain extension is realized, the sales profits of the new product are increased, and the method has better social environmental benefit and economic benefit.
In this example, as shown in fig. 1, the molecular sieve dryer 1 is divided into two, one being a molecular sieve dryer 1A and the other being a molecular sieve dryer 1B, and the two molecular sieve dryers 1 are alternately adsorbed and regenerated by program control. In specific implementation, besides the pipelines of the bottom gas inlets and outlets of the molecular sieve dryer 1A and the molecular sieve dryer 1B are connected to the raw material gas pipeline 23, a second branch line 21 and a third branch line 22 are connected in parallel between the bottom gas inlets and outlets of the molecular sieve dryer 1A and the molecular sieve dryer 1B, and the middle parts of the second branch line 21 and the third branch line 22 are connected to the fuel gas pipe network 11; a fourth branch line 24, a fifth branch line 25 and a sixth branch line 26 are connected in parallel between pipelines of the top gas inlets and outlets of the molecular sieve dryer 1A and the molecular sieve dryer 1B, the middle part of the fifth branch line 25 is connected to the raw gas inlet of the dust filter 14, and the middle part of the sixth branch line 26 is connected to the tube side outlet of the heater 10. Specifically, a first valve 23A is installed between the bottom gas inlet/outlet of the molecular sieve dryer 1A and the feed gas pipeline 23, a second valve 23B is installed between the bottom gas inlet/outlet of the molecular sieve dryer 1B and the feed gas pipeline 23, a third valve 21A is installed on a second branch line 21 of the bottom gas inlet/outlet of the molecular sieve dryer 1A, a fourth valve 21B is installed on the second branch line 21 of the bottom gas inlet/outlet of the molecular sieve dryer 1B, a fifth valve 22A is installed on a third branch line 22 of the bottom gas inlet/outlet of the molecular sieve dryer 1A, a sixth valve 22B is installed on the third branch line 22 of the bottom gas inlet/outlet of the molecular sieve dryer 1B, a seventh valve 24AB is installed on the fourth branch line 24, an eighth valve 25A is installed on a fifth branch line 25 of the top gas inlet/outlet of the molecular sieve dryer 1A, a ninth valve 25B is installed on the fifth branch 25 of the top gas inlet/outlet of the molecular sieve dryer 1B, a tenth valve 26A is installed on the sixth branch 26 of the top gas inlet/outlet of the molecular sieve dryer 1A, and an eleventh valve 26B is installed on the sixth branch 26 of the top gas inlet/outlet of the molecular sieve dryer 1B.
After 8 hours of continuous use of the molecular sieve dryer 1A, the molecular sieve must be regenerated. Before regeneration, the molecular sieve dryer 1A needs to be depressurized. Before pressure relief, firstly, the molecular sieve dryer 1B is pressurized by utilizing the outlet gas of the molecular sieve dryer 1A, then the molecular sieve dryer 1B is put into use, and meanwhile, the molecular sieve dryer 1A is isolated. The method comprises the following specific steps:
when the molecular sieve dryer 1B is pressurized, the seventh valve 24AB is opened, the molecular sieve dryer 1B is pressurized to 6.5MPa, which is the same as the pressure of the molecular sieve dryer 1A, and then the seventh valve 24AB is closed. Second valve 23B and fifth valve 25B are then opened and molecular sieve dryer 1A is isolated after one minute of operation has stabilized. When the molecular sieve dryer 1A is isolated, the first valve 23A and the eighth valve 25A are closed. After the isolation is completed, the third valve 21A is opened, and the molecular sieve dryer 1A releases the pressure to the fuel gas pipe network 11. When the pressure of the molecular sieve dryer 1A is reduced to 0.1MPa, the third valve 21A is closed, the steam valve of the heater 10 is opened, the tenth valve 26A and the fifth valve 22A are opened, the nitrogen-rich gas (tail gas) from the first heat exchanger 2 enters the top of the molecular sieve dryer 1A after being heated by the heater 10, the nitrogen-rich gas serving as the regeneration gas enters the fuel gas pipe network 11 through the tenth valve 26A, the molecular sieve dryer 1A and the fifth valve 22A, and the water in the molecular sieve dryer 1A is heated to steam and then is carried to the fuel gas pipe network 11. When the regeneration temperature in the molecular sieve dryer 1A reaches 160-180 ℃, the cooling stage is entered. The steam valve of the heater 10 is shut off, regeneration is completed, and the adsorbent is ready to be used in the adsorption process. When the molecular sieve dryer 1B needs to be regenerated, refer to the isolation, pressure relief, heating, and cooling steps of the molecular sieve dryer 1A.
Of course, a part of the nitrogen-rich gas (tail gas) from the first heat exchanger 2 can be used as a regeneration gas when the molecular sieve dryer 1 is regenerated, and then the nitrogen-rich gas is sent to a fuel gas pipe network 11 for combustion; the other part can be sent directly to the fuel gas pipe network 11 for combustion according to the requirements.
In this embodiment, when the molecular sieve dryer 1 alternately performs adsorption and regeneration, the valves on the top gas inlet and the bottom gas inlet are both closed, unless otherwise specified.
And all the pipelines in the embodiment are provided with valves, and the pipelines are opened in a working state and closed in a non-working state.
Specifically, the PNG product gas pipe network 8 is connected to a fuel gas pipe network 11 through a branch line. When the gas in the PNG product gas pipe network 8 does not meet the standard, the product gas in the pipe network can be conveyed to the fuel gas pipe network 11 for combustion and utilization.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.
Claims (8)
1. A system for preparing PNG by comprehensively utilizing tail gas of synthetic ammonia is characterized by comprising a molecular sieve dryer (1), a first heat exchanger (2), a second heat exchanger (3), a third heat exchanger (4), a rectifying tower (5) and a condensation separator (7),
the molecular sieve dryer (1) is provided with a top gas inlet and a top gas outlet and a bottom gas inlet and a bottom gas outlet, the top gas inlet and the top gas outlet of the molecular sieve dryer (1) are connected with a first raw material gas inlet of a first heat exchanger (2) through a pipeline, a first raw material gas outlet of the first heat exchanger (2) is connected with a first raw material gas inlet of a second heat exchanger (3) through a pipeline, a first raw material gas outlet of the second heat exchanger (3) is connected with a first raw material gas inlet of a third heat exchanger (4) through a pipeline, a first raw material gas outlet of the third heat exchanger (4) is connected with an upper feed inlet of a rectifying tower (5) through a pipeline, a tower bottom heavy component outlet of the rectifying tower (5) is connected with a first LNG inlet of the third heat exchanger (4) through a pipeline, a first LNG outlet of the third heat exchanger (4) is connected with an upper feed inlet of a condensation separator (7, the top gas phase outlet of the condensation separator (7) is connected with the first LNG inlet of the second heat exchanger (3) through a pipeline, the first LNG outlet of the second heat exchanger (3) is connected with the first PNG inlet of the first heat exchanger (2) through a pipeline, and the first PNG outlet of the first heat exchanger (2) is connected to the PNG product gas pipeline network (8).
2. The system for preparing PNG by comprehensively utilizing synthesis ammonia tail gas as claimed in claim 1, further comprising an expander, wherein a condenser (6) is arranged at the top of the rectifying tower (5), the light component outlet at the top of the rectifying tower (5) is connected with the first tail gas inlet of the third heat exchanger (4) through a pipeline, the first tail gas outlet of the third heat exchanger (4) is connected with the inlet of the expansion end (9) of the expander through a pipeline, the outlet of the expansion end (9) of the expander is connected with the inlet of the condenser (6) through a pipeline, the outlet of the condenser (6) is connected with the second tail gas inlet of the third heat exchanger (4) through a pipeline, the second tail gas outlet of the third heat exchanger (4) is connected with the first tail gas inlet of the second heat exchanger (3) through a pipeline, the first tail gas outlet of the second heat exchanger (3) is connected with the first tail gas inlet of the first heat exchanger (2), a first tail gas outlet of the first heat exchanger (2) is connected to a tube pass inlet of the heater (10) through a pipeline, a tube pass outlet of the heater (10) is connected to a top gas inlet and outlet of the molecular sieve dryer (1) through a pipeline, and a bottom gas inlet and outlet of the molecular sieve dryer (1) is connected to a fuel gas pipe network (11) through a pipeline.
3. The system for preparing PNG by comprehensively utilizing the tail gas of synthetic ammonia according to claim 1 or 2, the device is characterized by further comprising a methane evaporator (12), wherein a reboiler (13) is arranged at the bottom of the rectifying tower (5), a first raw material gas outlet of the first heat exchanger (2) is connected to a top raw material gas inlet of the methane evaporator (12) in parallel, a bottom raw material gas outlet of the methane evaporator (12) is connected to an inlet of the reboiler (13) through a pipeline, an outlet of the reboiler (13) is connected to a pipeline between a first raw material gas outlet of the second heat exchanger (3) and a first raw material gas inlet of the third heat exchanger (4) through a pipeline, a lower LNG inlet of the methane evaporator (12) is connected with a bottom liquid phase outlet of the condensation separator (7) through a pipeline, and an upper PNG outlet of the methane evaporator (12) is connected to a first PNG inlet of the first heat exchanger (2) through a pipeline.
4. The system for comprehensively utilizing the tail gas from the synthesis of ammonia for preparing PNG according to claim 1 or 2, wherein a dust filter (14) is connected in series on a pipeline between the top gas inlet and outlet of the molecular sieve dryer (1) and the first raw gas inlet of the first heat exchanger (2).
5. A comprehensive ammonia synthesis tail gas production PNG system according to claim 4, characterized in that the feed gas outlet of the dust filter (14) is connected to the inlet of the bearing gas end (15) of the expander through a pipeline, and the outlet of the bearing gas end (15) of the expander is connected to the fuel gas pipe network (11).
6. The system for comprehensively utilizing the tail gas from the synthesis of ammonia to prepare PNG according to claim 5, characterized in that a first branch line (16) is connected in parallel to the PNG product gas pipe network (8), the first branch line (16) is connected to the inlet of the pressurizing end (18) of the expansion machine, the outlet of the pressurizing end (18) of the expansion machine is connected to the tube side inlet of the water cooler (17), and the tube side outlet of the water cooler (17) is connected to the PNG product gas pipe network (8).
7. The system for comprehensively utilizing the tail gas from the synthesis of ammonia for preparing PNG according to claim 1 or 2, wherein the third heat exchanger (4) is provided with a second raw material gas inlet and a second raw material gas outlet, the first raw material gas inlet of the third heat exchanger (4) is communicated with the second raw material gas outlet of the third heat exchanger (4), the first raw material gas outlet of the third heat exchanger (4) is communicated with the second raw material gas inlet of the third heat exchanger (4), the second raw material gas outlet of the third heat exchanger (4) is connected with the inlet of the first buffer tank (19) through a pipeline, and the outlet of the first buffer tank (19) is connected with the second raw material gas inlet of the third heat exchanger (4) through a pipeline.
8. The system for comprehensively utilizing the tail gas from the synthesis ammonia to prepare PNG according to claim 1 or 2, characterized in that an organic front buffer tank (20) is connected in parallel on a pipeline between the first PNG outlet of the first heat exchanger (2) and the PNG product gas pipeline network (8).
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Application publication date: 20200929 |