A hydrogen-rich gas containing carbon, methane and nitrogen is used to produce ammonia synthesis gas

Abstract

The utility model relates to the field of gas recovery treatment of raw material gas of ammonia synthetic gas in preparation of ammonia synthetic gas, disclose a kind of rich hydrogen gas preparation ammonia synthetic gas device containing carbon, methane, nitrogen, including methanation device, still including variable temperature dehydration device, pressure demethanizing device and cold box, the gas import of variable temperature dehydration device is connected to the synthetic gas outlet of methanation device, the gas import of pressure demethanizing device is connected to the gas outlet of variable temperature dehydration device, the first gas outlet of pressure demethanizing device is connected to ammonia synthetic gas import, the gas import of cold box is connected to the gas outlet of pressure demethanizing device by the pipeline of being provided with compressor, the gas import of pressure demethanizing device or fuel gas outlet is alternatively connected to the gas outlet of cold box, the LNG outlet of cold box is connected to storage tank.Hydrogen and LNG yield are high, and economy is good.

Description

Technical Field

[0001] This utility model relates to an apparatus for preparing ammonia synthesis gas using hydrogen-rich gas containing carbon, methane, and nitrogen as a feed gas. Background Technology

[0002] Chemical production processes often generate hydrogen-rich off-gas containing carbon, methane, and nitrogen, such as methanol off-gas, refinery off-gas, and ethanol off-gas. These hydrogen-rich off-gas are generally used as feedstock for ammonia synthesis, but purification and hydrogen-nitrogen ratio adjustments are necessary. Currently, conventional processes first methanate this hydrogen-rich gas to convert both CO and CO2 into CH4, eliminating the poisoning effects of CO and CO2 on the ammonia synthesis catalyst. Methane, being an inert gas in ammonia synthesis, is then recovered from the ammonia synthesis off-gas. For example, CN220588974U discloses a system for recovering methane from ammonia synthesis tail gas.

[0003] The typical main components of hydrogen-rich purge gas (by volume) are: H2: 67.15%, CO: 2.79%, CO2: 1.4%, CH4: 3.4%, N2: 25.14%. The disadvantages of using conventional processes to produce ammonia synthesis gas are:

[0004] (1) The introduction of methane gas leads to high energy consumption of the syngas compressor and the circulating machine;

[0005] (2) Because methane was not separated from the synthesis gas in advance, the methane content in the ammonia synthesis gas was high, which had an adverse effect on the conversion rate of hydrogen and nitrogen in ammonia synthesis, thus increasing the amount of ammonia synthesis catalyst used and the investment was large.

[0006] (3) Due to the emission of methane in the ammonia synthesis purge gas, additional hydrogen and nitrogen are lost.

[0007] In addition, since this type of process gas often already contains a certain amount of nitrogen, it is not possible to use another ammonia synthesis gas purification technology—liquid nitrogen washing process. Liquid nitrogen washing process uses nitrogen to diffuse and cool hydrogen, which can separate CO and CH4 from the synthesis gas, such as the method described in CN106568298A.

[0008] Furthermore, although cryogenic separation can be used to directly liquefy and separate methane from the feed gas in ammonia synthesis, current practices often involve introducing all process gas into a cold box, with external cooling provided for methane liquefaction and syngas separation. However, because the methane content is relatively low and the majority is syngas, the temperature difference between the syngas entering and exiting the cold box is approximately 15°C, resulting in significant separation energy consumption and an unreasonable return on investment. For example, the purge gas volume of a typical component in a certain plant is 50171 Nm³. 3The energy consumption for methane liquefaction and syngas separation is approximately 7500 kWh per hour. Therefore, further improvements are needed for the rational utilization of this type of hydrogen-rich gas resource. Utility Model Content

[0009] The technical problem to be solved by this utility model is to provide a more economical hydrogen-rich ammonia synthesis gas device containing carbon, methane, and nitrogen.

[0010] The technical solution adopted by this utility model to solve its technical problem is: a hydrogen-rich gas-to-ammonia synthesis gas device containing carbon, methane, and nitrogen, including a methanation device, a temperature-switching dehydration device, a pressure-switching demethanizing device, and a cold box. The synthesis gas outlet of the methanation device is connected to the gas inlet of the temperature-switching dehydration device, the gas outlet of the temperature-switching dehydration device is connected to the gas inlet of the pressure-switching demethanizing device, the first gas outlet of the pressure-switching demethanizing device is connected to the ammonia synthesis gas inlet, the second gas outlet of the pressure-switching demethanizing device is connected to the gas inlet of the cold box through a pipeline equipped with a compressor, and the gas outlet of the cold box can be selectively connected to the gas inlet of the pressure-switching demethanizing device or the fuel gas outlet. The LNG outlet of the cold box is connected to a storage tank.

[0011] In the aforementioned apparatus, the methanation unit is used to react CO, CO2, and H2 in hydrogen-rich gas containing carbon, methane, and nitrogen to convert them into CH4, and to separate the process water produced during methanation; the temperature-switching dehydration unit is used to further dry the syngas from the methanation unit and separate moisture from it; the pressure-switching demethanizing unit is used to enrich methane gas from the further dried syngas, and the enriched methane gas is compressed by a compressor and sent to a cold box. After demethanization, the gas is adjusted to a hydrogen-nitrogen ratio and can then be used as ammonia synthesis gas; the cold box is used to liquefy the enriched methane gas into LNG and enrich hydrogen gas. The hydrogen-rich gas extracted from the cold box at a higher pressure is returned to the inlet of the pressure-switching demethanizing unit, while the nitrogen-rich gas extracted from the cold box at a lower pressure is used as fuel gas.

[0012] The adsorbent in the variable temperature dehydration device is 3A molecular sieve, in order to thoroughly dry the gas-phase saturated water.

[0013] The demethanizing molecular sieve of the pressure swing demethanizer uses a carbon molecular sieve with a pore size of 0.3 to 0.4 nm, and the nitrogen and methane selectivity can reach close to 10 with low nitrogen loss rate.

[0014] When the composition of the feed gas entering the methanation unit is different, the composition of the syngas generated in the methanation unit will also be different. For example, if the hydrogen to nitrogen ratio in the syngas is greater than 3:1, nitrogen can be added to the syngas after demethanation to adjust the hydrogen to nitrogen ratio to 3:1. If the hydrogen to nitrogen ratio in the syngas is less than 3:1, 5A molecular sieves are packed into the adsorption bed of the pressure swing demethanation unit to remove some nitrogen, so that the hydrogen to nitrogen ratio can still be adjusted to 3:1 as ammonia syngas by adding nitrogen in the subsequent process.

[0015] The adsorption bed of the pressure swing demethanizer can also use copper-based activated carbon adsorbent or zeolite activated carbon adsorbent, which can further improve the methane separation rate, but the cost will increase slightly. Since the hydrogen and nitrogen contained in the methane gas enriched in the subsequent cold box can still be efficiently recovered, the adsorption bed of the pressure swing demethanizer can also use only activated carbon adsorbent as mentioned above.

[0016] The beneficial effects of this invention are as follows: After methanating the hydrogen-rich gas containing carbon, methane, and nitrogen, it undergoes thorough drying to remove moisture. Then, a pressure swing demethanizer (PSD) is used to enrich the methane before sending it to the cold box to produce LNG as a byproduct. The resulting syngas contains H2 and N2, with a methane content below 10 ppm. By adjusting the hydrogen-to-nitrogen ratio, it can be used as ammonia synthesis gas. The methane-rich gas delivered to the cold box by the compressor contains only small amounts of H2 and N2, with the methane liquefied to form LNG. The hydrogen-rich gas (with H2 preferentially separated from the cold box) exiting the cold box is returned to the gas inlet of the PSD to recover H2, while the nitrogen-rich gas is used as fuel gas. Using this invention, the hydrogen yield can reach over 95%, and the LNG yield can reach over 99%. Furthermore, the energy consumption of the cold box unit is mainly for CH4 liquefaction, with very little H2 and N2, resulting in lower separation power consumption and better economic efficiency. The resulting ammonia synthesis gas contains very little methane, which helps improve the conversion rate of the ammonia synthesis process and saves on catalyst usage, resulting in good overall economic benefits. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the composition of a hydrogen-rich ammonia synthesis gas device containing carbon, methane, and nitrogen, according to Embodiment 1 of this utility model.

[0018] Figure 2 yes Figure 1 A schematic diagram of a typical structure that can be used in a medium-pressure demethanizing unit.

[0019] The diagram is labeled as follows: 1-Methanation unit, 2-Temperature-switching dehydration unit, 3-Pressure-switching demethanizing unit, 4-Compressor, 5-Cold box, 6-Two-position three-way valve, 7-Nitrogen replenishment unit, 8-Ammonia synthesis gas inlet, 9-Fuel gas outlet, 10-Storage tank, 30-Gas inlet of pressure-switching demethanizing unit, 31-First gas outlet, 32-Second gas outlet, 33-Adsorber, 51-Gas inlet of cold box, 52-Gas outlet, 53-LNG outlet. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] like Figure 1As shown, this utility model discloses a hydrogen-rich gas synthesis gas device for producing ammonia from carbon, methane, and nitrogen, comprising a methanation unit 1, a temperature-switching dehydration unit 2, a pressure-switching demethanizing unit 3, and a cold box 5. The synthesis gas outlet of the methanation unit 1 is connected to the gas inlet of the temperature-switching dehydration unit 2. The temperature-switching dehydration unit (i.e., Figure 1 The gas outlet of the TSA2 is connected to the pressure swing demethanizer 3 (i.e., Figure 1 The gas inlet 30 of the PSA (Pressure Swing Demethanizer) unit is connected to the first gas outlet 31 of the PSA unit 3, which is connected to the ammonia synthesis gas inlet 8. The second gas outlet 32 ​​of the PSA unit 3 is connected to the gas inlet 51 of the cold box through a pipeline equipped with a compressor 4. The gas outlet 52 of the cold box 5 can be selectively connected to the gas inlet or the fuel gas outlet 9 of the PSA unit 3. The LNG outlet 53 of the cold box 5 is connected to the storage tank 10.

[0022] In methanation unit 1, CO, CO2, and H2 undergo a methanation reaction to convert into CH4, and the process water produced by methanation is separated, which avoids poisoning the ammonia synthesis catalyst in the subsequent process and increases LNG production. The temperature-switched dehydration unit can further dry the gas phase saturated water to remove moisture. Then, the pressure-switched demethanizing unit 3 separates methane from the synthesis gas. After being enriched, the methane is sent to the cold box for cryogenic liquefaction by a compressor. During this process, by adjusting the pressure, hydrogen is preferentially enriched and reused in the pressure-switched demethanizing unit 3, and the remaining gas can be used as fuel gas. The gas after demethanization in the pressure-switched demethanizing unit 3 is then sent to the subsequent process as ammonia synthesis gas after adjusting its hydrogen-nitrogen ratio to 3:1.

[0023] Example 1:

[0024] like Figure 1 and Figure 2 As shown, this utility model discloses a hydrogen-rich ammonia synthesis gas production device containing carbon, methane, and nitrogen, comprising a methanation unit 1, a temperature-switched dehydration unit 2, a pressure-switched demethanizing unit 3, and a cold box 5. The synthesis gas outlet of the methanation unit 1 is connected to the gas inlet of the temperature-switched dehydration unit 2, and the gas outlet of the temperature-switched dehydration unit 2 is connected to the gas inlet 30 of the pressure-switched demethanizing unit. The first gas outlet 31 of the pressure-switched demethanizing unit 3 is connected to the ammonia synthesis gas inlet 8 via a pipeline equipped with a nitrogen replenishment device interface. The second gas outlet 32 ​​of the pressure-switched demethanizing unit 3 is connected to the gas inlet 51 of the cold box via a pipeline equipped with a compressor 4. The gas outlet 52 of the cold box 5 can be selectively connected to the gas inlet of the pressure-switched demethanizing unit 3 or the fuel gas outlet 9 via a two-position three-way valve 6. The LNG outlet 53 of the cold box 5 is connected to a storage tank 10.

[0025] Among them, such as Figure 2 As shown, the pressure swing demethanizing unit includes multiple ( Figure 2(Example 4) Adsorbers 33 are equipped with alkali-modified activated carbon adsorbent. Each adsorber 33 is connected to the gas inlet 30, the first gas outlet 31, and the second gas outlet 32 ​​of the pressure swing demethanizing unit via pipelines equipped with valves. In this unit, the crude syngas from the preceding TSA process enters the gas inlet 30 of the pressure swing demethanizing unit and then enters the adsorber 33 through the corresponding valves. The crude syngas adsorbs and removes methane in the adsorber 33. The valves control the product syngas after the methane adsorption to go to the ammonia synthesis process through the first gas outlet 31. The "pressure equalization-adsorption-regeneration" of each adsorber is controlled in sequence. The valves control the methane-rich gas released by the desorption process to be sent to the compressor 4 through the second gas outlet 32 ​​and then to the cold box 5 to produce LNG.

[0026] Alkali-modified activated carbon adsorbents utilize activated carbon treated with alkaline substances, allowing the functional groups on the activated carbon surface to be adjusted to the desired quantity according to actual needs. NaOH / KOH treatment increases the number of hydroxyl groups and alkaline sites on the activated carbon surface, enhancing its affinity for methane; the locally negative charge polarizes the CH bonds of CH4, forming a transient dipole-induced dipole interaction, thus increasing the adsorption enthalpy; the alkaline sites generate electrostatic attraction with the weakly positively charged hydrogen atoms of CH4, with particularly significant effects under high pressure (>5 bar). Treatment with KOH or NaOH increases the specific surface area and micropore distribution of activated carbon. To the applicant's knowledge, activated carbon modified with 8% KOH (i.e., 8 parts KOH and 92 parts activated carbon out of a total of 100 parts by mass) exhibits the highest methane adsorption efficiency.

[0027] Among them, the adsorption bed of the pressure swing demethanizer can be made of copper-based activated carbon adsorbent or zeolite activated carbon adsorbent, or carbon molecular sieve with a pore size of 0.3 to 0.4 nm.

[0028] In addition, the connecting pipelines between the various devices should be equipped with necessary control valves, which is common knowledge in the field and will not be described in detail.

[0029] Using the aforementioned apparatus to produce ammonia synthesis gas from hydrogen-rich gas containing carbon, methane, and nitrogen reduces energy consumption in the synthesis gas compressor and recycle gas compressor. The ammonia synthesis gas after methane removal has a low inert component content, requiring less ammonia synthesis catalyst compared to traditional processes, thus reducing investment. It also boasts a high hydrogen yield and produces LNG as a byproduct, improving economic efficiency. With the aforementioned apparatus, the purge gas volume with the above typical components is 50171 Nm³. 3 Based on / h, the energy consumption for obtaining the same process gas can be reduced to approximately 5500kWh, demonstrating a significant energy-saving effect.

[0030] The aforementioned apparatus produces ammonia synthesis gas from hydrogen-rich gas containing carbon, methane, and nitrogen, reducing energy consumption in the synthesis gas compressor and recycle gas compressor. The ammonia synthesis gas after methane removal has a low inert component content, requiring less ammonia synthesis catalyst compared to traditional processes, thus reducing investment. It also boasts a high hydrogen yield and produces LNG as a byproduct, improving economic efficiency. With this apparatus, the purge gas volume of the typical components is 50171 Nm³. 3 Based on / h, the energy consumption for obtaining the same process gas can be reduced to approximately 5500kWh, demonstrating a significant energy-saving effect.

[0031] Table 1 lists four typical feedstock gases. Tables 2 and 3 show the composition of the synthesis gas in each step when these four typical feedstock gases are prepared into ammonia synthesis gas using the apparatus of this invention, along with information on the corresponding product yield and energy-saving effect.

[0032] Table 1. Composition of four typical feed gases (by volume ratio)

[0033] 1 72.57％ 2.63％ 1.67％ 1.71％ 21.42％ 2 62.93％ 2.67％ 1.78％ 1.53％ 31.09％ 3 76.45％ 2.49％ 1.85％ 1.45％ 17.76％ 4 68.78％ 3.01％ 2.26％ 1.97％ 23.98％

[0034] Table 2 shows the composition of intermediate products obtained from the raw gas using the device of this invention.

[0035]

[0036]

[0037] Table 3 shows the effect of the raw gas treated by the device of this utility model in Table 1.

[0038]

[0039] It is evident that the device of this invention can effectively utilize hydrogen-rich gas containing carbon, methane, and nitrogen, with high yields of hydrogen and methane, and significant energy-saving effects.

[0040] Example 2:

[0041] Depending on the composition of the feed gas entering the methanation unit, the ratio of hydrogen to nitrogen in the synthesis gas generated in the methanation unit is less than 3:1. The first gas outlet 31 of the pressure swing demethanizer 3 is connected to the ammonia synthesis gas inlet 8 through a pipeline with a hydrogen replenishment device interface, and the rest is the same as in Example 1.

[0042] Example 3:

[0043] The adsorption bed of the pressure swing demethanizer 3 can be filled with 5A molecular sieve to remove part of the nitrogen gas, and the rest is the same as in Example 1.

[0044] Example 4:

[0045] The first gas outlet 31 of the pressure swing demethanizer 3 is connected to the ammonia synthesis gas inlet 8 via a pipeline with a selective hydrogen or nitrogen supply interface, and the rest is the same as in Example 1.

Claims

1. A hydrogen-rich gas synthesis gas device for producing ammonia from carbon, methane, and nitrogen, comprising a methanation unit (1), characterized in that: It also includes a temperature-switching dehydration unit (2), a pressure-switching demethanizing unit (3), and a cold box (5). The syngas outlet of the methanation unit (1) is connected to the gas inlet of the temperature-switching dehydration unit (2). The gas outlet of the temperature-switching dehydration unit (2) is connected to the gas inlet (30) of the pressure-switching demethanizing unit. The first gas outlet (31) of the pressure-switching demethanizing unit (3) is connected to the ammonia syngas inlet (8). The second gas outlet (32) of the pressure-switching demethanizing unit (3) is connected to the gas inlet (51) of the cold box through a pipeline equipped with a compressor (4). The gas outlet (52) of the cold box (5) can be selectively connected to the gas inlet or the fuel gas outlet (9) of the pressure-switching demethanizing unit (3). The LNG outlet (53) of the cold box (5) is connected to the storage tank (10).

2. The ammonia synthesis gas production apparatus containing carbon, methane, and nitrogen using hydrogen-rich gas as described in claim 1, characterized in that: The adsorbent for the variable temperature dehydration device (2) is 3A molecular sieve.

3. The ammonia synthesis gas production apparatus containing carbon, methane, and nitrogen using hydrogen-rich gas as described in claim 1, characterized in that: The demethanizing molecular sieve of the pressure swing demethanizing unit (3) is a carbon molecular sieve with a pore size of 0.3 to 0.4 nm.

4. The ammonia synthesis gas production apparatus containing carbon, methane, and nitrogen using hydrogen-rich gas as described in claim 1, characterized in that: The adsorption bed of the pressure swing demethanizer (3) is filled with 5A molecular sieve.

5. The ammonia synthesis gas production apparatus containing carbon, methane, and nitrogen using hydrogen-rich gas as described in claim 3, characterized in that: The adsorption bed of the pressure swing demethanizer (3) is filled with copper-based activated carbon adsorbent or zeolite activated carbon adsorbent.

6. A hydrogen-rich gas-to-ammonia synthesis gas apparatus containing carbon, methane, and nitrogen as described in any one of claims 1-5, characterized in that: The pressure swing demethanizing device (3) uses an adsorber (33) filled with alkali-modified activated carbon adsorbent.

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