CN111486662A - Method and device for low-temperature separation of synthesis gas and preparation of ammonia synthesis gas - Google Patents

Method and device for low-temperature separation of synthesis gas and preparation of ammonia synthesis gas Download PDF

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CN111486662A
CN111486662A CN202010245175.4A CN202010245175A CN111486662A CN 111486662 A CN111486662 A CN 111486662A CN 202010245175 A CN202010245175 A CN 202010245175A CN 111486662 A CN111486662 A CN 111486662A
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李红凯
薛天祥
葛雄
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Beijing Santai Tianjie Gas Purification Technology Co ltd
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    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/0252Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of hydrogen
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    • C01B3/50Separation of hydrogen or hydrogen containing gases from gaseous mixtures, e.g. purification
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    • C01B2203/00Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
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    • C01B2203/04Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
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    • C01B2203/068Ammonia synthesis

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Abstract

The invention discloses a method and a device for separating synthesis gas at low temperature and preparing ammonia synthesis gas. The method for separating the synthesis gas at low temperature comprises the steps of firstly precooling and partially condensing raw material purified gas to form low-temperature condensate and noncondensable gas, and then sequentially processing the low-temperature condensate and noncondensable gas to obtain a first gas phase and a first liquid phase by separating the noncondensable gas under the conditions that the pressure is 2.4-5.9 MPa and the temperature is not lower than-182 ℃; separating a second gas phase and a second liquid phase from the low-temperature condensate and the first liquid phase under the conditions of 1-2 MPa and the temperature of-168-175 ℃; step three, distilling the third gas phase rich in CO and rich in CH by the second liquid phase4A third liquid phase of (a); and the third liquid phase part returns to the first step and the second step. The invention can effectively improve the purity and the hydrogen yield of the separated hydrogen and simultaneously recover useful components of CO and CH4And other inert components are removed to meet the synthesis requirement of subsequent products.

Description

Method and device for low-temperature separation of synthesis gas and preparation of ammonia synthesis gas
Technical Field
The invention relates to the field of chemical industry, in particular to a device and a method for separating synthesis gas at low temperature, and a method for preparing ammonia synthesis gas by separating synthesis gas at low temperature.
Background
The synthesis gas uses carbon monoxide and hydrogen as main components and is mostly used as chemical raw material gas. Selection of raw materials for synthesis gas productionWidely, the fuel can be produced by gasifying solid fuels such as coal or coke, can be prepared from light hydrocarbons such as natural gas and naphtha, and can be produced from heavy oil by a partial oxidation method; in terms of synthesis gas production, the composition (in vol%) of the finally obtained synthesis gas differs greatly with respect to the above different feedstocks and processes, but essentially falls within the following ranges: h232~67%、CO 10~57%、CO22~28%、CH40.1~28%、N20.6~23%。
The synthesis gas has many uses, such as synthesis of ammonia, and can also be used for producing methanol, glycol, formic acid, oxalic acid, acetic acid, phosgene and the like. However, no matter what kind of substance is used for synthesis, the composition purity and the proportion of the synthesis gas directly prepared from the raw materials cannot meet the requirements of subsequent synthesis products, and therefore, the synthesis gas needs to be further adjusted. The prior art discloses the use of shift reactions to adjust the hydrogen to carbon ratio and then the purification of the gas to remove sulfur (H)2S, COS), decarburization (CO)2) And further high concentrations of H are obtained respectively2Gas, CO gas, CH4Gas or liquid or high-purity synthetic gas with a certain hydrogen-carbon ratio, and finally, the prepared various gases are respectively utilized to synthesize subsequent products.
At present, there are many methods for separating purified synthesis gas, and physical absorption decarburization technology is generally adopted, which includes methods such as low-temperature separation, membrane separation, pressure swing adsorption and the like. Among them, the cryogenic separation method is most commonly used, and usually employs a plurality of separation towers, and different pressure and temperature conditions are set to separate each main gas component in the synthesis gas.
However, when a plurality of separation towers are adopted for low-temperature separation in the prior art, H-containing gas separated in the conventional condensation separation process2The hydrogen purity of the gas is not high, and the H is separated by adopting the conventional condensation separation procedure2When the gas is directly used as ammonia synthesis gas, the ammonia synthesis catalyst is poisoned, and the ammonia synthesis efficiency is greatly reduced. Thus, the conventional condensation separation procedure disclosed in the prior art results in H-containing2The gas must be treated by a pressure swing adsorption (SPA) unit before it can enterThe H, N ratio is adjusted to be 3: the raw material gas of 1 is added into an ammonia synthesizer, thereby meeting the requirements of the ammonia preparation process.
Based on this, the low-temperature separation processes disclosed in the prior art all have the defect that the purity of the separated hydrogen is not high. Especially, when the separated hydrogen-containing gas is used for preparing ammonia synthesis gas, the purity of the hydrogen-containing gas cannot meet the requirement of ammonia synthesis. Therefore, the existing condensation separation process disclosed at present has a problem that the separated hydrogen cannot be directly used in the subsequent ammonia synthesis process.
Disclosure of Invention
The invention aims to solve the problems that the hydrogen purity in the hydrogen-containing gas separated by the existing condensation technology is low and the requirement of the subsequent ammonia synthesis process cannot be directly met; the invention provides a device and a method which can effectively improve the hydrogen purity of separated hydrogen-containing gas and can be directly used for meeting the synthesis requirement of subsequent products, and discloses a method and a device which can directly use the hydrogen-containing gas separated by the method for the subsequent ammonia synthesis process.
A method of cryogenic separation of syngas, comprising:
step one, separating a first gas phase and a first liquid phase from a feed gas under the conditions that the pressure is 2.4-5.9 MPa and the temperature is not lower than-182 ℃;
flashing a second gas phase and a second liquid phase from the first liquid phase under the conditions of 1-2 MPa and the temperature of-168-180 ℃;
step three, distilling the third gas phase rich in CO and rich in CH by the second liquid phase4A third liquid phase of (a); the third liquid phase portion is returned to the first and second steps. The third liquid phase in the above step is high purity CH4
When the third liquid phase part returns to the first step and the second step, the residual third liquid phase is supercooled to-160 ℃ and is output as L NG, and the product output as L NG can also enter a fuel gas system after being reheated.
And in the first step, a hydrogen separation tower is adopted for separation, non-condensable gas enters from the bottom, a quantitative third liquid phase enters from the top of the tower, and high-purity hydrogen is obtained from the top of the tower. The temperature of the tower top is-179 to-182 ℃.
The low-temperature condensate and the first liquid phase are subjected to light component separation by adopting a flash tower (the main component is H)2) And a quantitative third liquid phase enters from the top of the tower. The pressure in the flash tower is 1.2 MPa-1.8 MPa, the pressure is generally one third of the pressure of the raw material gas, and the temperature at the top of the tower is-170 ℃ to-175 ℃.
The second liquid phase adopts CH4The separation is carried out in a/CO separation tower, the separation pressure is 0.2-0.5 MPa, and the tower top temperature is-174 to-185 ℃; the column top temperature is preferably from-174 to-180 ℃.
The CH4The temperature of the top of the CO separation tower is-175 to-177 ℃, and the temperature of CH is4The temperature of the bottom of the tower in the/CO separation tower is 20-40 ℃ higher than that of the top of the tower.
The second gas phase is returned to the feed gas after being pressurized so as to increase H2Yield of the components.
CH in the feed gas4Is higher than 1.3 percent by volume. The temperature at which the third liquid phase is returned to the first and second steps is not less than-181.0 ℃ and preferably not less than-180 ℃.
The synthesis gas obtained by the method is applicable to various raw materials and methods, such as synthesis gas prepared by fixed bed gasification technology, fluidized bed gasification technology, dry powder entrained flow water wall gasification technology, coal water slurry entrained flow hot wall gasification technology, coal water slurry entrained flow gasification technology and the like, and comprises but is not limited to coke oven gas and unconverted purified gas. When the raw material gas contains H2、CO、CH4The coke oven gas comprises the following components in percentage by volume: 50 to 62 percent of hydrogen, 20 to 28 percent of methane, 3 to 9 percent of carbon monoxide, 1 to 5 percent of unsaturated hydrocarbon above C2, 0.5 to 5 percent of carbon dioxide, 0.1 to 1.0 percent of oxygen and 2 to 8 percent of nitrogen.
The device for the method for separating the synthesis gas at the low temperature comprises a hydrogen separation tower, a flash tower and CH which are communicated in sequence4A CO separation column; the CH4The outlet at the bottom of the/CO separation tower is communicated with the hydrogen separation tower and the flash tower through a return pipeline, and high-purity CH is utilized4Is washed with respect to the first and second gas phases. The gas outlet of the flash tower is communicated with the feed gas inlet of the hydrogen separation tower after passing through the hydrogen compressor, so that the second gas phase is returned to the feed gas after being boosted by the hydrogen-rich compressor to improve H2Yield of the components.
A method for directly preparing ammonia synthesis gas in the same cold environment comprises the following steps: and washing the first gas phase by using liquid nitrogen, and adjusting the hydrogen-nitrogen ratio, wherein the gas after the hydrogen-nitrogen ratio is adjusted is the ammonia synthesis gas. The ammonia synthesis gas may be directly fed to a subsequent ammonia synthesis unit for ammonia synthesis.
Washing in a liquid nitrogen washing tower, wherein the pressure of the liquid nitrogen washing tower is 2.4-5.4 MPa, and the temperature is-188 to-192 ℃.
A device for directly preparing ammonia synthesis gas comprises a hydrogen separation tower, a flash tower and CH which are communicated in sequence4A CO separation column; the CH4The liquid outlet of the/CO separation tower is communicated with the hydrogen separation tower and the flash tower through a return pipeline; and a gas outlet at the top of the hydrogen separation tower is directly communicated with the liquid nitrogen washing tower. Thereby obtaining qualified ammonia synthesis raw material gas.
The gas outlet of the flash tower is communicated with the feed gas inlet of the hydrogen separation tower through a hydrogen-rich compressor; the CH4The liquid outlet of the/CO separation column can also be connected to the flash column via a return line, in which case CH is introduced into the flash column4The third liquid phase separated in the/CO separation column can be returned to the hydrogen separation column as well as to the flash column.
The technical scheme of the invention has the following advantages:
1. the invention discloses a method for separating synthesis gas at low temperature, which adopts a hydrogen separation tower, a flash tower and CH4The combined arrangement of the/CO separation tower separates a first gas phase with high-purity hydrogen and a first liquid phase with dissolved hydrogen from the hydrogen separation tower by setting the pressure and temperature in different reaction towers, separates a second gas phase rich in hydrogen from the flash tower and concentrates CO and CH4A second liquid phase of the component and from CH4Separating a third gas phase rich in CO (or high-purity CO) and high-purity CH in a CO separation column4The third liquid phase realizes the main gas component H in the raw material gas2、CO、CH4The separation is carried out efficiently to the maximum extent. Most importantly, the third liquid phase part is quantitatively returned to the hydrogen separation tower for reverse mass transfer separation by ingenious arrangement, so that H obtained by separation2The purity is further improved, and the method can be directly applied to the direct utilization of subsequent products, such as the prepared high-purity H2Can be directly used for preparing ammonia synthesis gas, and tests show that H in the first gas phase2The purity of the components can be not less than 99.0%. The method disclosed by the invention can be suitable for separating various synthesis gases, and the application range is wider.
According to the invention, through the arrangement, the cold quantity input and output of three levels are realized, and the cold balance of the whole system is ensured.
2. The invention further discloses a corresponding device which realizes the production of high-purity hydrogen (H) in the same cold box environment2Concentration greater than 98.8%), high purity L NG, high purity CO gas, and qualified ammonia syngas, and increases the yield to over 99% with high purity.
3. The invention also provides a method and a device for preparing ammonia synthesis gas, and the high-purity H is prepared by the technology2The gas obtained after the raw material gas is separated can be directly used for the subsequent ammonia synthesis process, only a liquid ammonia washing tower is needed, the use of an SPA device is omitted, the cost is saved, the process is greatly simplified, and the production efficiency is greatly improved. Simultaneously eliminates CO and H richly produced in the PSA desorption process2The tail gas recycling system further simplifies the overall equipment investment of the factory.
Detailed Description
The following examples are provided to further understand the present invention, not to limit the scope of the present invention, but to provide the best mode, not to limit the content and the protection scope of the present invention, and any product similar or similar to the present invention, which is obtained by combining the present invention with other prior art features, falls within the protection scope of the present invention.
Example 1
A method for low temperature separation of high purity hydrogen from coke oven gas or direct production of ammonia synthesis gas comprising:
step one, the flow rate is 74874.6NM3The feed gas of the hydrogen/H is added from the bottom of the hydrogen separation tower, the pressure of the hydrogen separation tower is controlled to be 3.33MPa, the temperature of the top of the hydrogen separation tower is controlled to be-180 ℃, and the temperature of the bottom of the hydrogen separation tower is controlled to be 1-3 ℃ higher than that of the top of the hydrogen separation tower. Thereby separating a first gas phase of high-purity hydrogen and a first liquid phase in which hydrogen is dissolved from the hydrogen separation column; wherein, the raw gas introduced into the hydrogen separation tower is purified coke oven gas, and the specific composition comprises: h261.7% v, 8.5% v CO, CH424.6 v%, N22.4 v% C2H6The concentration was 2.8 v%. The composition of the first gaseous phase discharged is shown in Table 1. This first gaseous phase of exhaust can directly discharge for use, also can directly prepare into ammonia synthesis gas and be used for subsequent ammonia synthesis, adopts in this embodiment to directly let in to carry out the mode that liquid nitrogen washed and made ammonia synthesis gas in the liquid nitrogen scrubber, specifically is: directly introducing the first gas phase into a liquid nitrogen washing tower for washing, wherein the pressure of the liquid nitrogen washing tower is 3.31 MPa; the temperature in the liquid nitrogen washing tower is-189 ℃, and the gas treated in the liquid nitrogen washing tower is mixed with high-pressure nitrogen according to the molar ratio of 3:1, and the mixed gas is the ammonia synthesis gas prepared by the method. When preparing synthetic ammonia, only ammonia synthesis gas needs to be introduced into ammonia synthesis equipment for ammonia synthesis, and the process steps and parameters for ammonia synthesis in the ammonia synthesis equipment are the prior art, and are not described in detail in this embodiment. The flow rate of the ammonia synthesis gas obtained by the first gas phase preparation in the present example was 61519.0NM3/H。
Step two, introducing the first liquid phase into a flash tower, and separating a second gas phase rich in hydrogen and main components of CO and CH from the flash tower4A second liquid phase of N2, etc.; the flow rate of the second gas phase was 737.0M3and/HR. In the step, the pressure in the flash tower is controlled to be 1.03MPa, the temperature of the top of the flash tower is controlled to be-178.6 ℃, and the temperature of the bottom of the flash tower is controlled to be 25 ℃ higher than that of the top of the flash tower. Wherein the second gas phase is returned to the feed gas of step one.
Step three, introducing the second liquid phase into CH4CO separationTower from CH4Separating CO-rich third gas phase and high-purity CH in CO separation column4The third liquid phase is partially returned to the hydrogen separation tower in the first step and the flash tower in the second step to respectively wash the first gas phase and the second gas phase, the rest part is subcooled to-160 ℃ to be used as L NG products, and the flow rate of the third liquid phase serving as L NG products is 20539.5NM3H, CH in the third liquid phase4Has a molar purity of 89.4% (CH)4+C2H6Greater than 99.0% molar purity). Control CH in the third step4The pressure of the/CO separation column was 0.25MPa, CH4The temperature of the top of the CO separation column is-182 deg.C, and CH is controlled4The temperature at the bottom of the column in the CO separation column is 25 ℃ higher than that at the top of the column. Also, the temperature of the third liquid phase returned to the hydrogen separation column and the flash column in this step was controlled to-178 ℃. Wherein the flow rate of the third gas phase is 11525.6M3/HR。
As a result of the detection, the compositions (mole percentages) of the components detected to be discharged after returning the third liquid phase to the hydrogen separation column and the flash column are shown in table 1.
TABLE 1
First gas phase Second gaseous phase Third gas phase
H2 98.8417 98.2002 0.7526
N2 0.1735 0.0410 44.6421
CO 0.0227 0.0852 54.3980
CH4 0.9621 1.6736 0.2067
The effective component H in the product of this example was calculated2、CH4Wherein the hydrogen yield (%) (75% ammonia synthesis gas flow rate)/(feed gas flow rate of feed gas hydrogen concentration in feed gas) 100%, and the methane yield (%) (concentration of methane in the third liquid phase as flow rate of the third liquid phase of L NG product)/(feed gas flow rate of feed gas methane concentration in feed gas) 100%.
Through calculation, H in this embodiment2The yield was 99.81% CH4The yield thereof was found to be 99.87%.
Example 2
A method for separating high-hydrogen-out-of-hundred degrees from purified coke oven gas and directly preparing ammonia synthesis gas by a low-temperature method comprises the following steps:
step one, the flow is 74874.6NM3The feed gas of the hydrogen/H is added from the bottom of the hydrogen separation tower, the pressure of the hydrogen separation tower is controlled to be 3.33MPa, the temperature of the top of the hydrogen separation tower is controlled to be-182 ℃, and the temperature of the bottom of the hydrogen separation tower is controlled to be 1-3 ℃ higher than that of the top of the hydrogen separation tower. Thereby separating a first gas phase of high-purity hydrogen and a first liquid phase in which hydrogen is dissolved from the hydrogen separation column; wherein the raw material gas introduced into the hydrogen separation tower is purified coke oven gasThe method comprises the following steps: h261.7% v, 8.5% v CO, CH424.6 v%, N22.4 v% C2H6The concentration was 2.8 v%. The composition of the first gaseous phase discharged is shown in Table 2. This first gaseous phase of exhaust can directly discharge for use, also can directly prepare into ammonia synthesis gas and be used for subsequent ammonia synthesis, adopts in this embodiment to directly let in to carry out the mode that liquid nitrogen washed and made ammonia synthesis gas in the liquid nitrogen scrubber, specifically is: directly introducing the first gas phase into a liquid nitrogen washing tower for washing, wherein the pressure of the liquid nitrogen washing tower is 3.31 MPa; the temperature in the liquid nitrogen washing tower is-189 ℃, and the gas treated in the liquid nitrogen washing tower is mixed with high-pressure nitrogen according to the molar ratio of 3:1, and the mixed gas is the ammonia synthesis gas. When ammonia gas is prepared, only ammonia synthesis gas needs to be introduced into ammonia synthesis equipment for ammonia synthesis, and the process steps and parameters for ammonia synthesis in the ammonia synthesis equipment are the prior art, and are not described in detail in this embodiment. The flow rate of the ammonia synthesis gas obtained by the first gas phase preparation in the present example was 61493.5NM3/H。
Step two, the first liquid phase is introduced into a flash tower, and a second gas phase rich in hydrogen and CO and CH are separated from the flash tower4A second liquid phase of (a); the flow rate of the second gas phase was 750.8M3and/HR. In the step, the pressure in the flash tower is controlled to be 1.03MPa, the temperature of the top of the flash tower is controlled to be-178.6 ℃, and the temperature of the bottom of the flash tower is controlled to be 20 ℃ higher than that of the top of the flash tower. Wherein the second gas phase is returned to the feed gas of step one.
Step three, introducing the second liquid phase into CH4/CO separation column from CH4Separating a CO-rich third gas phase and a CH-rich gas phase in a CO separation column4The third liquid phase is respectively returned to the hydrogen separation tower of the first step to wash the first gas phase and the second gas phase in the second step to wash the second gas phase, the final part is subcooled to be minus 160 ℃ to be used as L NG product, and the flow rate of the third liquid phase used as L NG product is 20540.4NM3The methane molar purity of the/H, L NG product was 89.4%, the flow rate of the third liquid phase returning to step one was 5617.8M3HR, flow rate of the third liquid phase returned to step two 2670.8M3and/HR. This stepSudden control of CH4The pressure of the/CO separation column was 0.25MPa, CH4The temperature of the top of the CO separation column is-184 ℃, and CH is controlled4The temperature at the bottom of the column in the/CO-separation column is 29 ℃ higher than that at the top of the column. Also, the temperature of the third liquid phase returned to the hydrogen separation column in this step was controlled to-180 ℃. Wherein the flow rate of the third gas phase is 32640.5M3/HR。
As a result of the detection, the compositions (mole percentages) of the respective substances detected as discharged after returning the third liquid phase to the hydrogen separation column are shown in table 2.
TABLE 2
Figure BDA0002433799730000081
Figure BDA0002433799730000091
The hydrogen and methane yields in this example were calculated, wherein the hydrogen yield (%) (75% ammonia synthesis gas flow rate)/(feed gas hydrogen concentration in feed gas) 100%, and the methane yield (%) (methane concentration in third liquid phase as third liquid phase flow rate of L NG product)/(feed gas methane concentration in feed gas) 100%.
The yield of hydrogen in this example was 99.77% and the yield of methane was 99.87% by calculation.
Example 3
Low-temperature method for gasifying unchanged gas (low CH) from medium pressure and high temperature4Content) of hydrogen and CO gas, comprising:
step one, the flow is 140065.0NM3The purified unchanged gas of the/H is added from the bottom of the hydrogen separation tower, the pressure of the hydrogen separation tower is controlled to be 5.71MPa, the temperature of the top of the hydrogen separation tower is-180.8 ℃, and the temperature of the bottom of the hydrogen separation tower is controlled to be about 11 ℃ higher than that of the top of the hydrogen separation tower; thereby separating a first gas phase of high-purity hydrogen and a first liquid phase in which hydrogen is dissolved from the hydrogen separation column; wherein the separated first gas phase is discharged for standby, and the flow rate of the discharged first gas phase is 62525.6NM3/H。The raw material gas adopted in the embodiment is unconverted purified gas, and the specific composition comprises: h244.6 v%, CO 54.3 v%, CH40.2 v%, N20.7 v% and Ar 0.2 v%.
Step two, introducing the first liquid phase into a flash tower, and separating a hydrogen-rich second gas phase and a gas phase containing CO and CH from the flash tower4A second liquid phase of N2; the flow rate of the second gas phase was 14498.4M3and/HR. In the step, the pressure in the flash tower is controlled to be 1.93MPa, the temperature of the top of the flash tower is-169.3 ℃, and the temperature of the bottom of the flash tower is controlled to be 22 ℃ higher than that of the top of the flash tower. Wherein the second gas phase is returned to the feed gas of step one. Since the methane content in this step is less than 1.3%, in this embodiment, the purchased natural gas is supplemented, the purchased natural gas is pretreated to obtain pure methane gas before the supplementation, then the second gas phase is returned to the step one, and simultaneously the pure methane gas and the second gas phase are returned to the step one, and the flow rate of the pure methane gas addition is 1405.4NM3H, methane content in the gas entering the cold box after makeup is 1.4%.
Step three, introducing the second liquid phase into CH4/CO separation column from CH4Separating CO-rich third gas phase and high-purity CH in CO separation column4A third liquid phase of (a); and returning the third liquid phase part to the hydrogen separation tower and the flash tower in the first step and the second step respectively, washing the first gas phase and the second gas phase respectively, and discharging the rest gas serving as methane liquid finally. The third liquid phase flow of the return portion was 26121.0NM3The flow rate of discharged methane gas is 1152.5NM3H (balanced, practically necessary external methane make-up about 253NM3H), the molar purity of methane in the third liquid phase was 99.4%. Control of CH in this step4The pressure of the/CO separation column was 0.43MPa, CH4The temperature of the top of the CO separation column is-176.4 ℃, and CH is controlled4The temperature at the bottom of the column in the CO separation column is 36 ℃ higher than that at the top of the column. Also, the temperature of the returned third liquid phase was controlled at-178.5 ℃ in this step. Wherein the flow rate of the third gas phase is 77869.5M3/HR。
As a result of the examination, the compositions (mole percentages) of the respective substances discharged after returning the third liquid phase to the hydrogen separation column and the flash column were examined as shown in table 3.
First gas phase Second gaseous phase Third gas phase
H2 99.081 95.941 0.6751
N2 0.0495 0.2369 1.2251
CO 0.0007 0.1355 97.762
CH4 0.8685 3.687 0.01
Ar 0 0 0.3275
TABLE 3
Since the methane content in this example was very low and needs to be replenished, only the hydrogen yield was calculated in this example. In this example, the hydrogen yield (%) (concentration of hydrogen in the first gas phase · flow rate of the first gas phase)/(concentration of hydrogen in the feed gas · feed flow rate of the feed gas) · 100%.
The yield of hydrogen in this example was found to be 99.16% by calculation.
Example 4
A method for separating Lurgi gasifier gasification gas and coke oven gas mixed purification gas by a low-temperature method, optimizing FT synthesis raw material gas composition and preparing L NG comprises the following steps:
step one, the flow is 158742.2NM3Pre-cooling and partially condensing the H raw material gas to form non-condensed steam and low-temperature condensed liquid, adding the non-condensed steam from the bottom of a hydrogen separation tower, controlling the pressure of the hydrogen separation tower to be 2.36MPa, the temperature of the top of the hydrogen separation tower to be-181.0 ℃, and controlling the temperature of the bottom of the hydrogen separation tower to be higher than that of the top of the hydrogen separation tower to be 8 ℃. Thereby separating a first gas phase of high-purity hydrogen and a first liquid phase in which hydrogen is dissolved from the hydrogen separation column; wherein the separated first gas phase is discharged for standby, and the flow rate of the discharged first gas phase is 89559.2NM3and/H. The raw material gas adopted in the embodiment is a mixed gas of Lurgi gasifier generation gas and coke oven gas (wherein the coke oven gas accounts for about 15%). The mixed gas is separated from ash, tar, naphthol, sulfur (H)2S, COS), decarburization (CO)2) Dehydration, and the like. The concrete components include: h255.9% v, 27.6% v CO, CH414.8 v% N21.4% by v, Ar 0.2% by v, C2H60.1v%。
Step two, introducing the low-temperature condensate and the first liquid phase into a flash tower, and separating a second gas phase rich in hydrogen and CO and CH from the flash tower4A second liquid phase of N2, etc.; the flow rate of the second gas phase was 4056.0M3and/HR. In the step, the pressure in the flash tower is controlled to be 117MPa, the temperature of the top of the flash tower is-179.2 ℃, and the temperature of the bottom of the flash tower is controlled to be 28 ℃ higher than that of the top of the flash tower. Wherein, the second gas is reheated and pressurized, and then phase is returned to the raw material gas in the first step.
Step three, introducing the second liquid phase into CH4/CO separation column from CH4Separating CO-rich third gas phase and high-purity CH in CO separation column4The third liquid phase is partially returned to the hydrogen separation column and the flash column of steps one and two, the first gas phase and the second liquid phase are washed, the remaining part is discharged as L NG product, and the flow rate of L NG product is 22885.5NM3The molar purity of methane in the third liquid phase was 98.5% (99.49% for C1+ C2). Control of CH in this step4The pressure of the/CO separation column was 0.44MPa, CH4The temperature of the top of the CO separation column was-176.0 deg.C, and CH was controlled4The temperature at the bottom of the column in the CO separation column is 37 ℃ higher than that at the top of the column. Also, the temperature of the third liquid phase returned to the hydrogen separation column and the flash column in this step was controlled to-178.5 ℃. Wherein the flow rate of the third gas phase is 64118.7M3/HR。
And step four, introducing the third gas phase into a CO/N2 separation tower to separate high-purity CO liquid. The high purity CO liquid is gasified and then mixed with the previously inactive first gas phase to synthesize FT synthesis gas. The FT synthesis gas amount is: 131857.32NM3/H。
As a result of the detection, the composition (mole percentage) of each of the substances detected as being discharged after returning the third liquid phase to the hydrogen separation column and the flash column is shown in table 4.
TABLE 4
First of allGas phase Second gaseous phase Third gas phase FT syngas
H2 98.953 98.102 0.1359 67.2104
N2 0.0142 0.1416 3.7367 0.3393
CO 0.0005 0.3633 95.48 31.5307
Ar 0 0.0004 0.6174 0.2085
CH4 1.032 1.3928 0.03 0.7111
The hydrogen and methane yields in this example were calculated, wherein the hydrogen yield (%) (concentration of hydrogen in the FT synthesis gas × (flow rate of FT synthesis gas)/(intake flow rate of feed gas) × 100%, and the methane yield (%) (concentration of methane in the third liquid phase × (flow rate of the third liquid phase used as L NG product)/(intake flow rate of feed gas) × 100%.
The yield of hydrogen in this example was found to be 99.90% and the yield of methane was found to be 96.01% by calculation.
From all the data above, it can be seen that the hydrogen concentration separated by the present invention can be higher than 99%, and the yield of the separated hydrogen is higher than 99%. The methane is entrained somewhat by the first gas phase and therefore the yield of methane is somewhat lower. But the major inert component CH in FT syngas treated by this technique4And N2The removal effect is obvious, wherein 96 percent of methane is removed, and N is2Is removed by 80%.
In the embodiment of the present invention, the raw material gas used includes, but is not limited to, gas generated by gasifying coal or coal water slurry, such as coke oven gas, lurgi furnace gas, and german gas.
Taking coke oven gas as an example, the gas composition of the coke oven gas comprises 50-62% of hydrogen, 20-28% of methane, 3-9% of carbon monoxide and 1-5% of C2The unsaturated hydrocarbon, 0.5 to 5 percent of carbon dioxide, 0.1 to 1.0 percent of oxygen and 2 to 8 percent of nitrogen.
Taking Lurgi furnace gas as an example, the gas composition of the Lurgi furnace gas is 32-43% of hydrogen, 8-15% of methane, 10-20% of carbon monoxide, 0.1-1.3% of hydrocarbons and 29-36% of carbon dioxide.
Taking Texaco gas as an example, the gas composition of the Texaco gas is 33-40% of hydrogen, 42-51% of carbon monoxide, less than 0.2% of methane and 13-23% of carbon dioxide. When the Texaco gas is adopted, because the content of methane is lower, when the method is adopted for separation, the methane can be added into the raw material gas to ensure that the content of the methane is higher than 1.3 percent.
Example 5
This example provides a suitable apparatus for the cryogenic separation of synthesis gas as described in examples 1 to 4 above.
The device for low-temperature separation of the synthesis gas comprises a hydrogen separation tower, a flash tower and CH which are communicated in sequence4a/CO separation column. The apparatus of the present invention is different from the existing apparatus in that the CH4Rich CH flowing out of liquid outlet of CO separation tower4The third liquid phase is communicated with the hydrogen separation tower through a return pipeline and is used for washing the first gas phase separated by the ammonia-hydrogen separation tower; the gas outlet of the flash tower is communicated with the feed gas inlet of the hydrogen separation tower through a compressor; the CH4The liquid outlet of the/CO separation column can also be connected to the flash column via a return line.
Example 6
This example provides a device for directly producing ammonia synthesis gas from a first gas phase suitable for use in examples 1-4 above, i.e., discloses a device for directly producing ammonia synthesis gas.
The device for directly preparing the ammonia synthesis gas comprises a liquid nitrogen washing tower, and a hydrogen separation tower, a flash tower and CH which are communicated in sequence4A CO separation column; the CH4The liquid outlet of the/CO separation tower is communicated to the hydrogen separation tower through a return pipeline; a gas outlet of the hydrogen separation tower is communicated with a raw material synthesis gas inlet of the ammonia synthesizer through a liquid nitrogen washing tower; the gas outlet of the flash tower is communicated with the feed gas inlet of the hydrogen separation tower through a compressor; the CH4The liquid outlet of the/CO separation tower is communicated with the flash tower through a return pipeline. When the ammonia gas is prepared, the ammonia synthesis gas treated by the liquid nitrogen washing tower is directly introduced into an ammonia synthesizer for synthesis.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.

Claims (13)

1. A method for cryogenic separation of syngas, comprising:
step one, separating a first gas phase and a first liquid phase from a feed gas under the conditions that the pressure is 2.4-5.9 MPa and the temperature is not lower than-182 ℃;
step two, separating a second gas phase and a second liquid phase from the first liquid phase under the conditions of 1-2 MPa and the temperature of-168 to-180 ℃;
step three, distilling the third gas phase rich in CO and rich in CH by the second liquid phase4A third liquid phase of (a); the third liquid phase portion is returned to step one.
2. The process for the cryogenic separation of synthesis gas according to claim 1, wherein the third liquid phase portion is subcooled to-160 ℃ as the product output when the third liquid phase portion is returned to step one and step two, respectively.
3. The method for separating the synthesis gas at low temperature according to claim 1 or 2, wherein the separation is carried out by using a hydrogen separation tower in the first step, the raw material gas enters from the bottom, and the temperature of the top of the tower is-179 to-182 ℃.
4. The method for the cryogenic separation of synthesis gas according to claim 1 or 2, characterised in that the first liquid phase is separated using a flash column, the pressure in the flash column is 1.2MPa to 1.8MPa and the temperature at the top of the column is-170 ℃ to-175 ℃.
5. The process for the cryogenic separation of synthesis gas according to claim 1 or 2, wherein the second liquid phase employs CH4/CO separation column for CH4And CO is separated, the separation pressure is 0.2-0.5 MPa, and the tower top temperature is-174 to-185 ℃.
6. The method of cryogenic separation of syngas according to claim 5, wherein the CH is4The temperature of the top of the tower in the CO separation tower is-175 to-177 ℃, and the temperature of the bottom of the tower is 20 to 40 ℃ higher than that of the top of the tower.
7. A process for the cryogenic separation of synthesis gas according to any of claims 1 to 6, wherein the second gaseous phase is returned to the feed gas after being pressurised.
8. The process for the cryogenic separation of synthesis gas according to claim 7, wherein the temperature of the third liquid phase returned to steps one and two is subcooled to a temperature of not less than-180 ℃.
9. The method for low-temperature separation of synthesis gas according to any one of claims 1 to 8, wherein the feed gas contains CH4Is higher than 1.3 percent by volume.
10. A method for directly producing ammonia synthesis gas, comprising: and washing the first gas phase by using liquid nitrogen, and adjusting the hydrogen-nitrogen ratio, wherein the gas after the hydrogen-nitrogen ratio is adjusted is the ammonia synthesis gas.
11. The method for directly preparing ammonia synthesis gas according to claim 10, characterized in that the washing is carried out in a liquid nitrogen washing tower, the pressure of the liquid nitrogen washing tower is 2.4-5.4 MPa, and the temperature is-188-192 ℃.
12. A device for directly preparing ammonia synthesis gas comprises a hydrogen separation tower, a flash tower and CH which are communicated in sequence4a/CO separation column, and a liquid nitrogen wash column; characterized in that the CH4The liquid outlet of the/CO separation tower is communicated with the hydrogen separation tower through a return pipeline; and a gas outlet of the hydrogen separation tower is communicated with the liquid nitrogen washing tower.
13. The apparatus of claim 12, wherein the gas outlet of the flash column is in communication with the feed gas inlet of the hydrogen separation column via a compressor; CH (CH)4The liquid outlet of the/CO separation tower is communicated with the hydrogen separation tower and the flash tower through a return pipeline.
CN202010245175.4A 2020-03-31 2020-03-31 Method and device for low-temperature separation of synthesis gas and preparation of ammonia synthesis gas Pending CN111486662A (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB832619A (en) * 1955-02-11 1960-04-13 Saint Gobain Improvements in or relating to a method of separating phthalic anhydride entrained in gases
EP0307983A1 (en) * 1987-09-16 1989-03-22 Metallgesellschaft Ag Process for obtaining an ammonia synthesis gas
CN1252517A (en) * 1998-06-26 2000-05-10 液体空气乔治洛德方法利用和研究有限公司 Method for producing CO
CN103940199A (en) * 2014-05-09 2014-07-23 中国石油集团工程设计有限责任公司 Method and device for extracting ethane-mixed hydrocarbon from natural gas
CN107367127A (en) * 2017-08-15 2017-11-21 成都深冷液化设备股份有限公司 A kind of cryogenic separation CO, H2Nitrogen cycle methane wash system and method

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB832619A (en) * 1955-02-11 1960-04-13 Saint Gobain Improvements in or relating to a method of separating phthalic anhydride entrained in gases
EP0307983A1 (en) * 1987-09-16 1989-03-22 Metallgesellschaft Ag Process for obtaining an ammonia synthesis gas
CN1252517A (en) * 1998-06-26 2000-05-10 液体空气乔治洛德方法利用和研究有限公司 Method for producing CO
CN103940199A (en) * 2014-05-09 2014-07-23 中国石油集团工程设计有限责任公司 Method and device for extracting ethane-mixed hydrocarbon from natural gas
CN107367127A (en) * 2017-08-15 2017-11-21 成都深冷液化设备股份有限公司 A kind of cryogenic separation CO, H2Nitrogen cycle methane wash system and method

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