CN217092779U - Liquid nitrogen washing system of by-product nitrogen and methane - Google Patents
Liquid nitrogen washing system of by-product nitrogen and methane Download PDFInfo
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- CN217092779U CN217092779U CN202220615027.1U CN202220615027U CN217092779U CN 217092779 U CN217092779 U CN 217092779U CN 202220615027 U CN202220615027 U CN 202220615027U CN 217092779 U CN217092779 U CN 217092779U
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Abstract
The utility model provides a system is washed to liquid nitrogen of byproduct nitrogen and methane, this system is washed to liquid nitrogen separates and liquefies the nitrogen component in with the nitrogenous feed gas, causes washing tower top and dehydrogenation tower top with this liquid nitrogen for the low carbon hydrocarbon is absorbed in the washing, prepares and satisfies the required raw materials synthetic gas of low reaches synthetic ammonia technology. This system can be with the whole recovery of hydrogen in the raw materials synthetic gas, by-product nitrogen gas or liquid nitrogen, rich methane gas or liquefied natural gas simultaneously, it is more reasonable to make whole liquid nitrogen wash big flow, methane component height in the raw materials synthetic gas can not appear, excessive nitrogen component (exceed the 3/1 requirement of hydrogen/nitrogen mole ratio, especially higher ratio, if 3/2 or 3/3 time) and cause the washing tower bottom to produce the fuel gas calorific value low, the problem that a large amount of big components got into fuel gas system, the rich methane gas of recoverable high added value, but a large amount of low pressure nitrogen gas of by-product again, just the utility model discloses the equipment of system is small in quantity, it is higher to deviate from efficiency, the flow is simpler, the operation is more stable.
Description
Technical Field
The utility model belongs to the separation field of synthetic gas cryrogenic, concretely relates to liquid nitrogen of by-product nitrogen and methane washes system.
Background
Currently, the conventional liquid nitrogen scrubbing process is used to produce raw syngas, i.e., syngas for ammonia synthesis, a mixture of hydrogen and nitrogen in which the molar ratio of hydrogen to nitrogen is 3/1, required by downstream ammonia plants. Usually, the synthesis gas from the liquid nitrogen washing device contains hydrogen as the main component, and also contains a small amount of nitrogen, argon, methane and carbon monoxide, but the impurity components are low and low compared with the hydrogen, and the hydrogen occupies most proportion.
High-pressure nitrogen from an air separation device which is matched with a chemical plant and built in the chemical plant is generally used as a detergent for liquid nitrogen washing, the high-pressure nitrogen enters a low-temperature plate-fin heat exchanger of a liquid nitrogen washing and cooling box and is cooled and liquefied to be changed into liquid nitrogen, the liquid nitrogen enters the top of a washing tower in the liquid nitrogen washing and cooling box and is used as reflux liquid to be in countercurrent contact with ascending gas entering the bottom of the washing tower, in the process of countercurrent contact mass transfer and heat transfer, impurity components in the ascending gas at the bottom of the washing tower, such as argon, methane, carbon monoxide and the like, are washed and absorbed into a liquid phase by the liquid nitrogen flowing down from the top of the washing tower, the separation of the main component hydrogen is completed, finally, a mixture of the low-temperature hydrogen and the nitrogen is obtained at the top of the washing tower, the mixture is reheated by the plate-fin heat exchanger and then mixed with a stream of nitrogen with a stream of which is adjusted in the molar ratio of the hydrogen to the nitrogen, and is sent to a downstream ammonia synthesis device, and the nitrogen is finally formed at the bottom of the washing tower, Liquid mixtures of methane, carbon monoxide, etc., usually this liquid can be reheated to serve as fuel gas.
According to the difference of raw material composition in upstream synthesis gas, such as the difference of pure oxygen and air adopted in the gas preparation stage of coal gasification or natural gas autothermal reforming, and whether an alkylation reactor is arranged after the synthesis gas conversion, but when the pure oxygen oxidation process is adopted, the nitrogen component contained in the synthesis gas is very limited, high-pressure nitrogen is directly introduced from an air separation device to be used as washing liquid nitrogen of a liquid nitrogen washing and cooling box, if the air oxidation process is adopted, the separation of raw material synthesis gas (64.36 v% hydrogen, 33.01 v% nitrogen, 2.24 v% methane and 0.4 v% argon) can be realized without introducing the high-pressure nitrogen into the washing and cooling box, the separation of inert and harmful components and hydrogen and nitrogen can be completed by reducing pressure of liquid at the bottom of a washing tower in the liquid nitrogen washing and cooling box to be provided into a cold source at the top of the washing tower to provide a cold source for the top of the washing tower, the liquid in the top of the washing tower is gasified and then sent to a low-temperature fin heat exchanger to be reheated to be used as fuel gas to be discharged (the fuel gas contains About 15 v% methane, about 5 v% hydrogen, about 2 v% argon, about 78 v% nitrogen), and a mixture of hydrogen and nitrogen (74.84 v% hydrogen, 24.96 v% nitrogen, 0.19 v% argon) is sent out from a single channel of a heat exchanger of a condensed gas (immersed in a heat exchange kettle at the top of a washing tower) at the top of the washing tower, and is reheated by a low-temperature plate-fin heat exchanger (a main heat exchanger) and then sent to a downstream ammonia synthesis device.
Considering that the heat value of the liquid at the bottom of the liquid nitrogen washing tower is not high, and when the content of the methane component in the raw material synthesis gas is high, such as more than 5 v% or even about 10 v%, the content of the nitrogen component is far higher than the normal H required by downstream ammonia synthesis 2 /N 2 The nitrogen content (hydrogen/nitrogen molar ratio: 3/x) in the molar ratio of 3/1, when x in the molar ratio of hydrogen/nitrogen corresponding to the nitrogen content in the raw material gas is 1<When x is more than or equal to 1.5 and less than or equal to 3, if the nitrogen quantity sent to a fuel gas pipe network is too large, the liquid at the bottom of a liquid nitrogen washing tower contains more dissolved hydrogen, the temperature at the top of a downstream denitrification tower is too low, the required cold quantity is also very large, and the common separation tower cannot simply separate the three components.
Based on the above factors, it is necessary to design a novel liquid nitrogen washing system, the utility model discloses a method of cryogenic rectification utilizes liquid nitrogen washing raw materials synthetic gas and dehydrogenation top of the tower to send out gas, washes the dissolved hydrogen in the washing tower bottom of the tower liquid with the liquid nitrogen and flashes out in the dehydrogenation tower, separates nitrogen and methane at last again, obtains synthetic ammonia device feed gas, nitrogen gas and rich methane gas promptly. The advantages of this process are particularly apparent when the raw syngas is high in methane and nitrogen components.
SUMMERY OF THE UTILITY MODEL
An object of the utility model is to provide a liquid nitrogen of by-product nitrogen and methane washes system adopts cryrogenic separation, sets up scrubbing tower, dehydrogenation tower and denitrogenation tower, with the H in the raw materials synthetic gas 2 、N 2 The components are directly enriched in the top of washing tower and dehydrogenation tower, and used as raw material gas (H) for synthesizing ammonia after reheating 2 +N 2 Mixture) is sent out, and the raw material is CH in the synthesis gas 4 Excess N 2 The components are separated in a denitrification tower, nitrogen or liquid nitrogen is obtained at the top of the tower, and liquid CH is obtained at the bottom of the tower 4 The liquefied natural gas can be pumped or directly sent to the main heat exchanger for reheating and then sent out as fuel gas, and if a byproduct liquefied natural gas is needed, the liquefied natural gas is extracted from the bottom of the denitrification tower and directly sent to a liquefied natural gas product storage tank.
In order to realize the above purpose, the utility model adopts the following technical scheme:
a liquid nitrogen washing system for by-producing nitrogen and methane comprises a main heat exchanger, a gas-liquid separation tank, a washing tower, a dehydrogenation tower, a denitrification tower, a raw material synthesis gas pipeline, a synthetic ammonia synthesis gas pipeline, a flash evaporation hydrogen pipeline, a low-pressure nitrogen pipeline, a liquid nitrogen pipeline and a methane-rich gas pipeline;
the raw material synthesis gas pipeline passes through a hot channel of the main heat exchanger and then is connected with an inlet of the gas-liquid separation tank; a gas phase outlet of the gas-liquid separation tank is connected with the bottom of the washing tower, and a liquid phase outlet of the gas-liquid separation tank is connected with the middle lower part of the dehydrogenation tower; a top gas phase outlet of the scrubber is connected to the synthesis ammonia synthesis gas line, which passes through the cold path of the main heat exchanger; the bottom liquid phase outlet of the washing tower is connected with the middle upper part of the dehydrogenation tower; the top gas phase outlet of the dehydrogenation tower is connected with the flash hydrogen pipeline, and the flash hydrogen pipeline passes through the cold channel of the main heat exchanger; the bottom liquid phase outlet of the dehydrogenation tower is connected with the middle part of the denitrification tower; the top gas phase outlet of the denitrification tower is connected with the low-pressure nitrogen pipeline, and the low-pressure nitrogen pipeline passes through the cold channel of the main heat exchanger; the bottom liquid phase outlet of the denitrification tower is connected with the methane-rich gas pipeline to output liquefied natural gas, and the methane-rich gas pipeline can also pass through a cold channel of the main heat exchanger to reheat the output liquid phase methane-rich gas and send the reheated gas as fuel gas;
the top of the denitrification tower is also provided with a liquid phase outlet which is connected with the liquid nitrogen pipeline, and the liquid nitrogen pipeline is divided into two paths after passing through the hot channel of the main heat exchanger and is respectively connected with the tops of the washing tower and the dehydrogenation tower.
Preferably, the flash hydrogen line is provided with a compressor after passing through the cold pass of the main heat exchanger, and merges with the synthesis ammonia synthesis gas line after the compressor passing through the cold pass of the main heat exchanger.
The process of using the liquid nitrogen washing system of the utility model comprises the following processes:
and the raw material synthesis gas enters the gas-liquid separation tank for gas-liquid separation after passing through the raw material synthesis gas pipeline and being cooled, cooled and partially liquefied through a hot channel of the main heat exchanger, the gas-phase synthesis gas enters the bottom of the washing tower, and the liquid-phase synthesis gas enters the middle lower part of the dehydrogenation tower to participate in rectification. The gas-phase synthesis gas is used as ascending gas at the bottom of the washing tower to be in countercurrent contact with liquid nitrogen entering from the top of the tower (about-185 ℃), argon, methane and ethane components in the gas-phase synthesis gas are washed by the liquid nitrogen and absorbed in the liquid nitrogen flowing in the countercurrent direction in the process of mass and heat transfer, most of hydrogen and most of nitrogen which are not absorbed enter a synthesis ammonia synthesis gas pipeline from a gas-phase outlet at the top of the washing tower, and are reheated by a cold channel of a main heat exchanger to be sent to a downstream synthesis ammonia device as synthesis ammonia synthesis gas; the excessive nitrogen in the gas rising from the bottom of the washing tower can be condensed, and the nitrogen, the argon, the methane, the ethane and a small amount of dissolved hydrogen are enriched at the bottom of the washing tower and are sent to the middle upper part of the dehydrogenation tower through a pipeline to participate in rectification.
In order to remove the hydrogen component in the tower bottom liquid of the dehydrogenation tower to the maximum extent and ensure the minimum methane carrying rate of the tower top gas phase of the dehydrogenation tower, liquid nitrogen (about 185 ℃) is introduced on the uppermost tower plate or filler of the dehydrogenation tower to wash high boiling point components such as methane in the tower bottom ascending gas before leaving the tower, the minimum carrying rate is ensured, such as not more than 10ppmv or stricter 1ppmv, then the components are sent to a cold channel of a main heat exchanger through a flash evaporation hydrogen pipeline connected with the tower top for reheating, and then the components are mixed with the synthetic ammonia synthetic gas sent from the tower top of the washing tower and then sent to a raw gas pipeline of a synthetic ammonia device. And (3) sending the liquid phase at the bottom of the tower after dehydrogenation to the middle part of a denitrification tower for separating nitrogen and methane components, obtaining pure nitrogen at the top of the tower, obtaining a methane-rich liquid at the bottom of the tower, and controlling the content of nitrogen in the methane-rich liquid at the bottom of the tower to be less than 1 v%. Part of liquid nitrogen extracted from the top of the denitrification tower is sent to a hot channel of a main heat exchanger through a liquid nitrogen pipeline for supercooling, and then is divided into two streams of liquid nitrogen, one stream of liquid nitrogen enters the top of the washing tower, the other stream of liquid nitrogen enters the top of the dehydrogenation tower, and a liquid nitrogen washing cycle is respectively completed; the redundant nitrogen is pumped out from the top of the denitrification tower and is sent to a cold channel of the main heat exchanger for reheating through a low-pressure nitrogen pipeline, and the reheated nitrogen is sent to a low-pressure nitrogen pipe network; the tower bottom methane-rich liquid of the denitrification tower is output through a methane-rich gas pipeline to be liquefied natural gas, and can also be sent to a cold channel of the main heat exchanger for reheating, and then sent to a methane-rich gas pipe network after reheating, and can be used as fuel gas or natural gas conversion feed gas and the like.
The utility model discloses the system adopts cryogenic separation to separate blue charcoal tail gas, and blue charcoal tail gas carries out cryogenic separation through transform, decarbonization, alkylation and molecular sieve absorption back, obtains synthetic gas, nitrogen gas and the rich methane gas that is used for synthetic ammonia technology, also can direct by-product liquefied natural gas, still can obtain the liquid nitrogen product as required. The utility model discloses the system is particularly useful for the synthetic ammonia synthetic gas that the feed gas is used for preparing low reaches synthetic ammonia device, and nitrogen component when containing in the feed gas is higher than the required synthetic gas medium nitrogen volume of synthetic ammonia technology, when hydrogen/nitrogen component ratio is less than 3/1 in the feed gas promptly, especially when hydrogen/nitrogen ratio is low to 3/3 or even lower, the utility model discloses the system can be more advantageous.
The utility model discloses a liquid nitrogen washing system sets up scrubbing tower, dehydrogenation tower and denitrogenation tower, with the H in the raw materials synthetic gas 2 、N 2 The components are directly enriched in the top of the washing tower and the dehydrogenation tower and used as raw material gas (H) for synthesizing ammonia after being reheated 2 +N 2 Mixture) is sent out, and the raw material is CH in the synthesis gas 4 Excess N 2 The components are separated in a denitrification tower, nitrogen or liquid nitrogen is obtained at the top of the tower, and liquid CH is obtained at the bottom of the tower 4 The liquefied natural gas can be pumped or directly sent to the main heat exchanger for reheating and then sent out as fuel gas, and if a byproduct liquefied natural gas is needed, the liquefied natural gas is extracted from the bottom of the denitrification tower and directly sent to a liquefied natural gas product storage tank.
According to the utility model discloses a liquid nitrogen system of washing, preferably, the dehydrogenation tower is provided with dehydrogenation tower bottom of the tower reboiler. The dissolved hydrogen in the liquid phase at the bottom of the tower (the main component is the mixture of liquid nitrogen, liquid methane, liquid ethane and a small amount of liquid argon) is thoroughly removed, and the hydrogen component at the bottom of the tower is ensured not to exceed 1 ppmv. Or a liquid phase pipeline is led out from the bottom of the dehydrogenation tower, and the liquid phase pipeline returns to the bottom of the dehydrogenation tower after being partially gasified through a cold channel of the main heat exchanger. The main heat exchanger is coupled with the reboiler at the bottom of the dehydrogenation tower, so that the number of the heat exchangers can be reduced, and the cold box can be more compact.
According to the utility model discloses a liquid nitrogen system of washing, preferably, the denitrogenation tower is provided with denitrogenation tower bottom of the tower reboiler. Or a liquid phase pipeline is led out from the bottom of the denitrification tower, returns to the bottom of the denitrification tower after being reheated by the cold channel of the main heat exchanger, and provides tower bottom ascending gas for the denitrification tower.
According to the utility model discloses a liquid nitrogen system of washing, preferably, the denitrogenation tower still is provided with denitrogenation tower top of the tower condenser. Or a gas phase pipeline is led out from the top of the denitrogenation tower, and the gas phase at the top of the denitrogenation tower is cooled and partially condensed by the gas phase pipeline through a heat channel of the main heat exchanger and then returns to the top of the denitrogenation tower to provide top reflux liquid for the denitrogenation tower.
According to the liquid nitrogen washing system of the utility model, preferably, the methane-rich gas pipeline is provided with a liquid methane pump; and the tower bottom methane-rich liquid of the denitrification tower is pumped out to a liquid methane pump through the methane-rich gas pipeline, is sent to a cold channel of the main heat exchanger for reheating after being pressurized, is sent to a methane-rich gas pipe network after reheating, and can be used as fuel gas or natural gas conversion feed gas and the like.
According to the utility model discloses a system is washed to liquid nitrogen, preferably, be provided with the liquid nitrogen pump on the liquid nitrogen pipeline. And pumping part of liquid nitrogen from the top of the denitrification tower, conveying the liquid nitrogen to a liquid nitrogen pump for pressurization through the liquid nitrogen pipeline, conveying the liquid nitrogen to a hot channel of the main heat exchanger for supercooling, and then dividing the liquid nitrogen into two strands of liquid nitrogen which are respectively used as tower top washing liquid of the washing tower and the dehydrogenation tower.
According to the liquid nitrogen washing system of the utility model, preferably, a throttle valve is arranged on a connecting pipeline between the liquid phase outlet of the gas-liquid separation tank and the middle lower part of the dehydrogenation tower; and the liquid-phase synthesis gas separated by the gas-liquid separation tank is decompressed by the throttle valve and then enters the middle lower part of the dehydrogenation tower to participate in rectification.
A pressure reducing valve is arranged on a connecting pipeline between the bottom liquid phase outlet of the washing tower and the middle upper part of the dehydrogenation tower; the tower bottom liquid of the washing tower is decompressed by a pressure reducing valve and then is sent to the middle upper part of the dehydrogenation tower to participate in rectification.
A pressure reducing valve is arranged on a connecting pipeline between a liquid phase outlet at the bottom of the dehydrogenation tower and the middle part of the denitrification tower; and the liquid phase at the bottom of the dehydrogenation tower after dehydrogenation is decompressed by a pressure reducing valve and then is sent to the middle part of the denitrification tower for separation of nitrogen and methane components.
Two branches of the liquid nitrogen (LIN) pipeline are respectively provided with a throttle valve, one branch of liquid nitrogen enters the top of the washing tower after being decompressed by the throttle valve, and the other branch of liquid nitrogen enters the top of the dehydrogenation tower after being decompressed by the throttle valve, so that liquid nitrogen washing circulation is respectively completed.
According to the utility model discloses a system is washed to liquid nitrogen, preferably, the cold volume balance of main heat exchanger is provided by nitrogen cycle refrigerating system. The nitrogen circulating refrigerating system comprises a nitrogen compressor, an expander, a liquid nitrogen separation tank, corresponding valves, pipelines and the like. The refrigeration cycle can also adopt other media, such as mixed refrigerant and the like, and can also adopt single cycle or double cycle and the like.
The liquid nitrogen washing system of the utility model can be used in a newly-built synthetic ammonia plant, can also be used for improving the yield of the synthetic ammonia by the transformation of the prior synthetic ammonia process, and can realize the yield increase of the synthetic ammonia by about 10 percent by adopting the cryogenic separation and the traditional non-cryogenic separation.
The system of the utility model can enrich the hydrogen components in the synthetic ammonia synthesis gas, the top of the washing tower is provided with the gas and the top of the dehydrogenation tower is provided with the gas, the recovery rate of the hydrogen is 100 percent, and the nitrogen-containing components of the methane-rich gas or the liquefied natural gas produced by the denitrification tower<1 v% safety threshold, nitrogen content of produced nitrogen or liquid nitrogen>99.99v％(N 2 + Ar). As the liquid phase at the bottom of the denitrification tower requires that the nitrogen component is less than 1 v% (based on the liquefied natural gas storage safety consideration), the liquid rolling vaporization phenomenon caused by the density difference of the liquefied natural gas in the large liquefied natural gas storage tank can be greatly reduced, and the safety accident of the large liquefied natural gas storage tank can be avoided.
The utility model discloses can retrieve the hydrogen in the raw materials synthetic gas is whole, simultaneously can by-product nitrogen gas or liquid nitrogen, rich methane gas or liquefied natural gas, it is more reasonable to make whole liquid nitrogen wash big flow, methane component height in the raw materials synthetic gas can not appear, excessive nitrogen component (exceed the 3/1 requirement of hydrogen/nitrogen mole ratio) and cause the fuel gas calorific value that produces in the bottom of the washing tower to be low, a large amount of big components get into fuel gas system's problem, the rich methane gas of recoverable high added value, but a large amount of low pressure nitrogen gas of by-product again, just the utility model discloses the equipment of system is small in quantity, deviates from efficiently, and the flow is simpler, and the operation is more stable.
Drawings
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. In addition, the shapes, the proportional sizes, and the like of the respective members in the drawings are merely schematic for helping the understanding of the present invention, and do not specifically limit the shapes, the proportional sizes, and the like of the respective members of the present invention. The skilled person in the art can, under the teaching of the present invention, choose various possible shapes and proportional dimensions to implement the invention according to the specific situation.
FIG. 1 is a schematic diagram of a liquid nitrogen scrubbing system and process for by-producing nitrogen and methane (by-producing nitrogen + methane-rich gas) in a preferred embodiment.
FIG. 2 is a schematic diagram of a liquid nitrogen scrubbing system and process for by-producing nitrogen and methane in another preferred embodiment (by-producing liquid nitrogen + liquefied natural gas).
Description of reference numerals:
e100 a primary heat exchanger;
EH110 to EH140 thermal vias;
EC 110-EC 170 cold channels;
101-166 pipelines;
a V100 gas-liquid separation tank;
a C100 washing tower;
a C200 dehydrogenation tower;
c300, a denitrification tower;
e200, E200' dehydrogenation tower bottom reboilers;
e300, E300' denitrification tower bottom reboiler;
e400, E400' denitrogenation tower overhead condenser;
a P100 methane pump;
a P200 liquid nitrogen pump;
a K100 nitrogen press;
a V200 liquid nitrogen separation tank;
a T100 expander;
SCOG Semi-Coke Offgas (raw syngas);
LIN Liquid Nitrogen/Liquid Nitrogen;
ASG Ammonia Synthesis Gas/synthetic Ammonia Synthesis Gas;
HFG Hydrogen Flash Gas/Flash Hydrogen (dehydrogenation overhead Gas);
LPN Low Pressure Nitrogen/Low Pressure Nitrogen;
MRG Methane Rich Gas;
HPN High Pressure Nitrogen/High Pressure Nitrogen;
LNG Liquefied Natural Gas/Liquefied Natural Gas;
RFN Refrigerant N 2 refrigerant N 2 。
Detailed Description
In order to explain the present invention more clearly, the present invention will be further described with reference to the preferred embodiments and the accompanying drawings. Similar parts in the figures are denoted by the same reference numerals. It is to be understood by persons skilled in the art that the following detailed description is illustrative and not restrictive, and is not to be taken as limiting the scope of the invention.
As shown in fig. 1 and 2, the present invention is applied to a liquid nitrogen washing system combined with an ammonia synthesis plant. Wherein FIG. 1 differs from FIG. 2 in whether the by-product gas is a liquid: fig. 1 shows the by-production of low-pressure nitrogen gas and methane-rich gas, while the dashed line labeled parts in fig. 2 show the by-production of liquid nitrogen LIN and liquefied natural gas LNG, which are described in detail below.
The processes corresponding to the systems in fig. 1 and fig. 2 require that the liquid at the bottom of the dehydrogenation tower does not contain hydrogen components, so long as the hydrogen components are all enriched in the gas at the top of the washing tower and the top of the dehydrogenation tower, high-purity nitrogen or liquid nitrogen can be obtained at the top of the denitrification tower, and the load of the condensed gas at the top of the denitrification tower is not too large.
Before raw material synthesis gas from an upstream synthesis gas production device enters a liquid nitrogen washing device, carbon monoxide components in the synthesis gas are generally subjected to water vapor conversion through a conversion device to generate carbon dioxide and hydrogen, then the carbon dioxide components enter an amine carbon elution device to be separated to about 30ppmv, then the carbon monoxide components and the carbon dioxide components enter an alkylation reactor to react with hydrogen to generate methane, the two components are removed, and then the two components are dried through a molecular sieve absorber arranged at an inlet of the liquid nitrogen washing device and the trace carbon dioxide components are completely removed (less than 1ppmv) so as to prevent the trace moisture and the carbon dioxide from freezing and blocking equipment or pipelines and the like in the cryogenic separation process.
Raw material synthesis gas (semi-coke tail gas SCOG) enters a main heat exchanger E100 (a low-temperature plate-fin heat exchanger) through a pipeline 101, the temperature can fluctuate within the temperature range of 0-15 ℃, the raw material synthesis gas enters a raw material synthesis gas-liquid separation tank V100 for gas-liquid separation through a pipeline 102 after being cooled, cooled and partially liquefied through a hot channel EH110 (about 180 ℃), the gas-phase synthesis gas enters the bottom of a washing tower C100 through a pipeline 103, and the liquid-phase synthesis gas enters the middle lower part of a dehydrogenation tower C200 through a pipeline 107 after being decompressed through a pipeline 106 to a throttle valve to participate in rectification.
The gas-phase synthesis gas is used as ascending gas at the bottom of a washing tower C100 (the operation pressure of the washing tower can be selected within the range of 9-35 barA according to the pressure of raw material gas) to be in countercurrent contact with liquid nitrogen (about-185 ℃) entering from the top of the tower through a pipeline 120, in the process of mass and heat transfer, argon, methane and ethane components in the gas-phase synthesis gas are washed by liquid nitrogen and absorbed in the liquid nitrogen flowing down in a counter-current manner, most of hydrogen and most of nitrogen which are not absorbed are sent to a cold channel EC110 of a main heat exchanger E100 from a connecting pipeline 104 at the top of a washing tower for reheating, then are sent to a raw material gas pipeline of a downstream ammonia synthesis device as synthesis ammonia synthesis gas ASG through a heat exchanger outlet pipeline 105, redundant nitrogen in ascending gas at the bottom of the washing tower C100 is also condensed, and argon, methane, ethane and a small amount of dissolved hydrogen components are enriched at the bottom of the washing tower C100 and are sent to the middle upper part of the dehydrogenation tower C200 through a pipeline 108, a pressure reducing valve for pressure reduction and a pipeline 109 to participate in rectification.
In order to remove the hydrogen component in the liquid at the bottom of the dehydrogenation column C200 (the operation pressure of the dehydrogenation column can be selected in the range of 9-15barA according to the pressure of the raw material gas) to the maximum extent and ensure the minimum methane carrying rate of the gas phase at the top of the dehydrogenation column C200, a liquid nitrogen introducing pipeline 122 is required to be arranged at the upper part of the tower inlet position of the liquid phase synthesis gas entering the dehydrogenation column C200 through pipelines 107 and 109, namely the uppermost tower plate or the filler of the dehydrogenation column C200, liquid nitrogen (-185 ℃ or so) is introduced through the pipeline to wash the high boiling point components such as methane and the like in the tower bottom ascending gas before the tower outlet, the minimum carrying rate in the obtained flash evaporation hydrogen HFG is ensured, for example, the minimum carrying rate is not more than 10ppmv or strictly 1ppmv, and then the flash evaporation hydrogen is sent to the cold channel EC120 of the main heat exchanger E100 through the tower top connecting pipeline 110 for reheating, then sent out through the outlet pipeline 111 of the main heat exchanger E100, and then sent to the synthesis gas after being directly mixed with the ammonia synthesis gas sent out from the top of the washing tower after being pressurized by a compressor (omitted in the figure) and then sent to the synthesis gas to the ammonia loading device for synthesis of the ammonia synthesis gas A raw gas pipeline is arranged; a reboiler is arranged at the bottom of the dehydrogenation tower C200, dissolved hydrogen in a tower bottom liquid phase (the main component is a mixture of liquid nitrogen, liquid methane, liquid ethane and a small amount of liquid argon) is thoroughly removed, the tower bottom hydrogen component is ensured not to exceed 1ppmv, and the tower bottom liquid phase after dehydrogenation is sent to the middle part of the denitrification tower C300 through a pipeline 112, a pressure reducing valve for pressure reduction and a pipeline 113 for separation of nitrogen and methane components; the reboiler E200 at the bottom of the dehydrogenation tower can adopt a cold channel EC160 which leads a liquid phase pipeline 161 at the bottom of the tower to send liquid to the main heat exchanger E100 for partial gasification, and then returns to the bottom of the dehydrogenation tower through a pipeline 162, and couples the main heat exchanger E100 and the reboiler E200 at the bottom of the dehydrogenation tower (the corresponding part of the main heat exchanger is named as E200'), so that the number of heat exchangers can be reduced, and a cold box can be more compact.
The cryogenic liquid from line 113 is subjected to separation of nitrogen and methane components in denitrogenation column C300 (the denitrogenation column operating pressure can be selected to be around 5.5barA depending on the downstream low pressure nitrogen or fuel gas operating pressure) to obtain pure nitrogen at the top of the column and a methane-rich liquid at the bottom of the column, the nitrogen content of which is controlled to <1 v%. Part of liquid nitrogen LIN extracted from the top of the denitrogenation tower C300 is sent to a liquid nitrogen pump P200 through a line 116 to be pressurized, and then is sent to a main heat exchanger hot channel EH120 through a line 117 to be subcooled, and then is divided into two liquid nitrogen streams through a heat exchanger outlet line 118, one liquid nitrogen stream enters the inlet at the top of the washing tower C100 through a line 119, a throttling valve for pressure reduction and a line 120, and the other liquid nitrogen stream enters the inlet at the top of the dehydrogenation tower C200 through a line 121, a throttling valve for pressure reduction and a line 122, so that a liquid nitrogen washing cycle is respectively completed; the redundant nitrogen is extracted from the top of the denitrification tower C300 and is sent to a cold channel EC130 of the main heat exchanger E100 for reheating through a pipeline 114, and the reheated nitrogen is sent to a low-pressure nitrogen pipe network as low-pressure nitrogen LPN through an outlet pipeline 115 of the main heat exchanger E100; if liquid nitrogen LIN is required to be produced, a branch line 116A can be branched from the line 116 to produce liquid nitrogen LIN (shown in FIG. 2).
The methane-rich liquid at the bottom of the denitrogenation tower C300 is pumped out to a liquid methane pump P100 through a pipeline 123, is sent to a cold channel EC140 of the main heat exchanger E100 through a pump outlet pipeline 124 after being pressurized for reheating, and is sent to a methane-rich gas pipe network from an outlet pipeline 125 of the main heat exchanger E100 after being reheated, so that the methane-rich gas MRG can be used as fuel gas or natural gas conversion raw material gas and the like; if the LNG is to be by-produced, a branch line 124A for by-producing LNG is branched from the line 124 (see fig. 2).
The reboiler E300 at the bottom of the denitrogenation tower and the condenser E400 at the top of the denitrogenation tower are also coupled with the cold channel EC170 and the hot channel EH140 of the main heat exchanger E100, similar to E200/E200 ', and are respectively named as E300/E300 ' and E400/E400 ', wherein a bottom liquid is led to the cold channel EC170 of the main heat exchanger E100 from a bottom leading-out pipeline 163 of the denitrogenation tower C300, and is returned to the bottom of the denitrogenation tower from a pipeline 164 after reheating to provide a bottom ascending gas for the rectification tower, a top gas phase is led to the hot channel EH140 of the main heat exchanger E100 from a top leading-out pipeline 165 of the denitrogenation tower C300 for cooling, and a part of the condensed top gas phase is returned to the top of the denitrogenation tower C300 through a pipeline 166 to provide a top reflux liquid for the rectification tower.
The cold quantity balance of the whole cold box is provided by a nitrogen circulating refrigeration system, and the nitrogen circulating refrigeration system comprises: the system comprises a nitrogen compressor K100, an expander T100, a liquid nitrogen separation tank V200, corresponding valves, pipelines and the like. The refrigeration cycle can adopt other media, such as mixed refrigerant and the like, and can also adopt a single cycle or a double cycle and the like, and a conventional nitrogen cycle refrigeration system is taken as an example.
High-pressure nitrogen HPN (the operation pressure is generally not more than 42barA) compressed by a nitrogen compressor K100 enters a hot channel EH130 of a main heat exchanger E100 through a pipeline 130 and is cooled to a certain temperature, for example, after the temperature is about 110 ℃, a strand of high-pressure nitrogen is extracted from the middle part of the hot channel EH130 and is sent to an expander T100 (the outlet operation pressure is generally not lower than 3.5barA) through a pipeline 136 for low-temperature expansion refrigeration, the other strand of high-pressure nitrogen is continuously cooled until the high-pressure nitrogen is liquefied and subcooled and then enters a liquid nitrogen separation tank V200 through an outlet pipeline 131 of the main heat exchanger E100, a throttle valve for pressure reduction (the outlet operation pressure is generally not lower than 1.5barA) and a pipeline 132, the gas phase at the top of the liquid nitrogen separation tank V200 enters a cold channel EC150 of the main heat exchanger through a pipeline 133 for reheating, the liquid nitrogen at the bottom of the liquid nitrogen separation tank V200 enters a cold channel EC152 of the main heat exchanger through a pipeline 134 for reheating phase change and then is merged with the reheated low-temperature nitrogen in the cold channel EC150, the low-temperature section of the reheated nitrogen separation tank V200 and then is merged with the reheated expanded low-temperature-expanded nitrogen entering a cold channel EC151 of the main heat exchanger E100 from the pipeline 137, then sent from the outlet line 135 of the main heat exchanger E100 to the inlet of the nitrogen compressor K100, and a nitrogen refrigeration cycle is completed. The expander T100 may be used to drive a section of the nitrogen compressor K100, and on the premise of ensuring rotor balance and sealing matching of both sides, the two sections with matching shaft power may be paired, which is not described herein.
Table 1 below is a table of material parameters for a specific application using the system of fig. 1. Wherein, the raw material synthesis gas SCOG with higher contents of methane and nitrogen components comprises the following components: hydrogen ═ 41.94 v%; 47.17 v% nitrogen; argon gas 0.56 v%; methane 9.50 v%; ethane-0.83 v%. The raw material synthesis gas is the semi-coke tail gas SCOG after purification, transformation, decarburization, alkylation and molecular sieve purification, and is referred to as the raw material synthesis gas.
Table 1: material parameter table
As can be seen from Table 1, the system of the present invention can enrich all hydrogen components in the synthesis ammonia synthesis gas, and the hydrogen components are sent out from the top of the scrubberThe gas and the gas sent from the top of the dehydrogenation tower have the hydrogen recovery rate of 100 percent, and the nitrogen-containing component of the methane-rich gas or the liquefied natural gas produced by the denitrification tower<1 v% safety threshold, nitrogen content of produced nitrogen or liquid nitrogen>99.99v％(N 2 + Ar). As the liquid phase at the bottom of the denitrification tower requires that the nitrogen component is less than 1 v% (based on the liquefied natural gas storage safety consideration), the liquid rolling vaporization phenomenon caused by the density difference of the liquefied natural gas in the large liquefied natural gas storage tank can be greatly reduced, and the safety accident of the large liquefied natural gas storage tank can be avoided.
The utility model discloses the system can be with the whole recovery of hydrogen component, simultaneously can by-product nitrogen gas or liquid nitrogen, rich methane gas or liquefied natural gas, it is more reasonable to make whole liquid nitrogen wash big flow, can not the raw materials synthetic gas methane component height, excessive nitrogen component (exceed the 3/1 requirement of hydrogen/nitrogen mole ratio, especially higher ratio, if 3/2 or 3/3 time) and cause the fuel gas calorific value that produces in the washing tower bottom low, a large amount of big components get into fuel gas system, the rich methane gas of recoverable high added value, but a large amount of low pressure nitrogen gas of by-product again, just the utility model discloses the required equipment of system is few, and it is higher to deviate from efficiency, and the flow is simpler, and the operation is more stable.
Obviously, the above embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention, and it is obvious for those skilled in the art to make other variations or changes based on the above descriptions, and all the embodiments cannot be exhausted here, and all the obvious variations or changes that belong to the technical solutions of the present invention are still in the protection scope of the present invention.
Claims (10)
1. A liquid nitrogen washing system for by-producing nitrogen and methane is characterized by comprising a main heat exchanger, a gas-liquid separation tank, a washing tower, a dehydrogenation tower, a denitrification tower, a raw material synthesis gas pipeline, a synthesis ammonia synthesis gas pipeline, a flash evaporation hydrogen gas pipeline, a low-pressure nitrogen pipeline, a liquid nitrogen pipeline and a methane-rich gas pipeline;
the raw material synthesis gas pipeline passes through a hot channel of the main heat exchanger and then is connected with an inlet of the gas-liquid separation tank; a gas phase outlet of the gas-liquid separation tank is connected with the bottom of the washing tower, and a liquid phase outlet of the gas-liquid separation tank is connected with the middle lower part of the dehydrogenation tower; a top gas phase outlet of the scrubber is connected to the synthesis ammonia synthesis gas line, which passes through the cold path of the main heat exchanger; the bottom liquid phase outlet of the washing tower is connected with the middle upper part of the dehydrogenation tower; the top gas phase outlet of the dehydrogenation tower is connected with the flash hydrogen pipeline, and the flash hydrogen pipeline passes through the cold channel of the main heat exchanger; the bottom liquid phase outlet of the dehydrogenation tower is connected with the middle part of the denitrification tower; the top gas phase outlet of the denitrification tower is connected with the low-pressure nitrogen pipeline, and the low-pressure nitrogen pipeline passes through the cold channel of the main heat exchanger; the bottom liquid phase outlet of the denitrification tower is connected with the methane-rich gas pipeline;
the top of the denitrification tower is also provided with a liquid phase outlet which is connected with the liquid nitrogen pipeline, and the liquid nitrogen pipeline is divided into two paths after passing through the hot channel of the main heat exchanger and is respectively connected with the tops of the washing tower and the dehydrogenation tower.
2. The liquid nitrogen wash system with byproduct nitrogen and methane according to claim 1, wherein the flash hydrogen line is provided with a compressor after passing through the cold path of the main heat exchanger, and is merged with the synthesis ammonia synthesis gas line after the compressor passing through the cold path of the main heat exchanger.
3. The liquid nitrogen scrubbing system with by-produced nitrogen and methane according to claim 1, wherein the dehydrogenation tower is provided with a dehydrogenation tower bottom reboiler; or
And a liquid phase pipeline is led out from the bottom of the dehydrogenation tower, and returns to the bottom of the dehydrogenation tower after passing through the cold channel of the main heat exchanger.
4. The liquid nitrogen washing system for by-producing nitrogen and methane according to claim 1, wherein the denitrification tower is provided with a denitrification tower bottom reboiler; or
And a liquid phase pipeline is led out from the bottom of the denitrification tower and returns to the bottom of the denitrification tower after passing through the cold channel of the main heat exchanger.
5. The liquid nitrogen washing system for by-producing nitrogen and methane according to claim 1, wherein the denitrification tower is further provided with a denitrification tower overhead condenser; or
And a gas phase pipeline is led out from the top of the denitrification tower, and returns to the top of the denitrification tower after passing through a hot channel of the main heat exchanger.
6. The system for liquid nitrogen scrubbing of byproduct nitrogen and methane according to claim 1, wherein a liquid methane pump is disposed on the methane-rich gas line; and a liquid nitrogen pump is arranged on the liquid nitrogen pipeline.
7. The system for washing by-produced nitrogen and methane with liquid nitrogen according to claim 1, wherein a throttle valve is provided on a connecting line between a liquid phase outlet of the gas-liquid separation tank and a middle-lower portion of the dehydrogenation tower.
8. The system for liquid nitrogen scrubbing of by-produced nitrogen and methane according to claim 1, wherein a pressure reducing valve is provided on a connecting line between a bottom liquid phase outlet of the scrubbing tower and an upper middle portion of the dehydrogenation tower;
and a pressure reducing valve is arranged on a connecting pipeline between the liquid phase outlet at the bottom of the dehydrogenation tower and the middle part of the denitrification tower.
9. The system for washing liquid nitrogen with by-produced nitrogen and methane according to claim 1, wherein two branches of the liquid nitrogen pipeline are each provided with a throttle valve.
10. The system for scrubbing by-product nitrogen and methane according to claim 1, wherein the cold balance of the main heat exchanger is provided by a nitrogen cycle refrigeration system.
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