A method and system for producing a nitrogen-rich hydrogen-rich gas product from coal gas co-production of lng

Abstract

The present application relates to a kind of coal gas production nitrogen-rich hydrogen-containing gas product of LNG cogeneration method and system, system includes raw material gas purification unit, heat exchange unit and nitrogen washing tower, raw material gas purification unit is equipped with main adsorber, the bottom of nitrogen washing tower is connected with first gas-liquid separator, first gas-liquid separator is equipped with tail gas pipe, the upstream of main adsorber is connected with pre-adsorber, pre-adsorber is equipped with raw material gas inlet and outlet;The pre-adsorber includes tank body, the middle part of tank body is equipped with sieve plate, raw material gas inlet and outlet are located above sieve plate, sieve plate is filled with molecular sieve, sieve plate below is equipped with liquid accumulation chamber, the bottom of liquid accumulation chamber is equipped with drain port;The middle part of liquid accumulation chamber is equipped with venturi tube, the tail gas pipe is equipped with bypass pipe connected with venturi tube.The present application is by setting pre-adsorber on the upstream of main adsorber, prolongs the regeneration cycle of main adsorber, extends the service life of molecular sieve, while reducing molecular sieve regeneration operation difficulty.

Description

Technical Field

[0001] This invention belongs to the field of coal gasification technology, specifically relating to a method for producing nitrogen-containing hydrogen-rich gas products by co-producing LNG from coal gasification. Background Technology

[0002] In the coal-to-gas ammonia synthesis process, the feed gas purified by low-temperature methanol washing needs to pass through a molecular sieve adsorber to remove residual carbon dioxide and methanol, preventing freezing blockage in the cold box. The molecular sieve adsorber requires periodic regeneration, a process involving adsorber switching, depressurization, preheating, heating, cooling, pressurization, detemperature reduction, and waiting. Completing these procedures relies on medium- and low-pressure nitrogen production, regeneration gas heating, and regeneration gas cooling. A failure in any of these stages will cause the molecular sieve adsorber to malfunction, leading to the shutdown of the nitrogen scrubbing tower. Furthermore, after regeneration, a portion of the feed gas is diverted to the molecular sieve adsorber for pressurization and cooling. However, the molecular sieve has not reached optimal adsorption conditions at this point, resulting in this portion of feed gas having substandard temperature and purity after passing through the adsorber. If two adsors are used in parallel, the mixed feed gas may contain excessive carbon dioxide, easily causing freezing blockage in the cold box. Moreover, the temperature of the mixed gas may be too high, failing to meet the temperature requirements for entering the nitrogen scrubbing tower after cooling, thus increasing the difficulty of process control. Alternatively, the raw gas generated in this stage can be directed to a flare for combustion, resulting in significant waste of raw gas.

[0003] Furthermore, the current regeneration cycle of molecular sieve adsorbers is 24 hours. During the regeneration process, the molecular sieve needs to undergo changes between low temperature and high temperature and low temperature, and high pressure and low pressure, which is quite destructive to the molecular sieve. After a period of use, the molecular sieve is prone to pulverization, resulting in reduced adsorption performance. Moreover, the pulverized dust enters the plate-fin heat exchanger and causes blockage. In addition, completing a series of temperature and pressure adjustments within 24 hours makes the process operation quite difficult.

[0004] In addition, in the existing technology, regeneration gas heating is all done by steam heating. In the article [1] Gai Yunhe. Handling the problem of internal leakage of gas cooler and steam heater in air separation unit [J]. (China New Technology and New Products, No. 18, 2012), it is mentioned that when steam heating is used for regeneration gas, due to the internal leakage of steam heater, some moisture in nitrogen is carried into the molecular sieve, which will reduce the activation performance of the molecular sieve. In this field, the molecular sieve regeneration system used for raw material gas purification also has this problem. Summary of the Invention

[0005] To address the aforementioned deficiencies in existing technologies, this invention provides a method for producing nitrogen-rich hydrogen gas from coal-to-gas and LNG co-production, the specific solution of which is as follows:

[0006] A system for producing nitrogen-rich hydrogen gas from coal-to-gas and co-production of LNG includes a feed gas purification unit, a heat exchange unit, and a nitrogen scrubbing tower. The feed gas purification unit is equipped with a main adsorber, and the heat exchange unit is equipped with a main heat exchanger. The feed gas pipe is sequentially connected to the main adsorber, the main heat exchanger, and the nitrogen scrubbing tower. The bottom of the nitrogen scrubbing tower is connected to a first gas-liquid separator, which is equipped with a tail gas pipe. An upstream pre-adsorber is connected to the main adsorber, and the pre-adsorber is equipped with a feed gas inlet and outlet. The pre-adsorber includes a tank with a sieve plate in the middle. The feed gas inlet and outlet are located above the sieve plate. Molecular sieves are filled above the sieve plate, and a liquid accumulation chamber is located below the sieve plate. A drain outlet is located at the bottom of the liquid accumulation chamber. A Venturi tube is located in the middle of the liquid accumulation chamber, and the tail gas pipe is equipped with a bypass pipe connected to the Venturi tube.

[0007] This invention adds a pre-adsorbent before the existing feed gas adsorber. The pre-adsorbent performs coarse adsorption to pre-remove impurities such as carbon dioxide and methanol from the feed gas. The feed gas then enters the main adsorber for secondary adsorption, further removing impurities.

[0008] The pre-adsorber is designed to perform continuous adsorption and desorption, transferring the adsorbed impurity gases from the molecular sieve and thus initially reducing the impurity gas content in the feed gas, significantly reducing the workload of the main adsorber. This improvement extends the regeneration cycle of the main adsorber from 24 hours to over 48 hours. This reduces the regeneration frequency of the molecular sieve, extends its service life, and simplifies the regeneration process.

[0009] Furthermore, both the main adsorber and the pre-adsorber are connected in parallel in two sets. The parallel connection of the two sets of adsorbers allows for easy switching without affecting the continuous operation of the nitrogen washing process.

[0010] In one improved embodiment of the present invention, the main adsorber is connected to a molecular sieve regeneration gas path, the molecular sieve regeneration gas path is provided with a regeneration gas thermal control mechanism, including a vortex cooling tube, the inlet of the vortex cooling tube is connected to a medium-pressure nitrogen system, the vortex cooling tube is provided with a cold flow tube and a hot flow tube, both the cold flow tube and the hot flow tube are provided with a main gas path and a branch gas path, the main gas path is connected to the molecular sieve regeneration gas path, the branch gas path of the cold flow tube is connected to a first heat exchanger, the branch gas path of the hot flow tube is connected to a second heat exchanger, the high-pressure nitrogen inlet pipe of the nitrogen scrubbing tower is connected to the first heat exchanger, and the tail gas pipe of the first gas-liquid separator is connected to the second heat exchanger.

[0011] Based on the significantly extended molecular sieve regeneration cycle, this solution considers using eddy current cooling elements to generate the heat or cold required for the regeneration gas, and using a stream of cold nitrogen to replace the feed gas for cooling the molecular sieve. This solves the technical problem of moisture being introduced into the regeneration gas due to internal leakage in the steam heater. It also addresses issues such as substandard or wasted feed gas caused by using feed gas for molecular sieve cooling.

[0012] Eddy current cooling tubes have relatively low cooling and heating efficiency. Taking a large eddy current cooling tube with a length of 326mm as an example, with an inlet pressure of 0.8MPa and a cold air flow rate of 20% of the inlet volume, the cold flow end temperature can reach -50℃, but the flow rate is only 100m³ / h. 3 With a flow rate of around 3000 m³ / h, even using multiple vortex refrigeration tubes in traditional regeneration processes, it is difficult to achieve this. 3 If the regeneration gas flow rate requirement is higher than / h, the predetermined cooling curve cannot be achieved.

[0013] However, based on the significant extension of the regeneration cycle achieved by this invention, the requirements for the heating and cooling rates of the molecular sieve are greatly reduced, and the demand for regeneration gas flow rate is also reduced. Therefore, even with a less efficient vortex cooling tube, the heat or cold flow required for regeneration can still be provided.

[0014] Furthermore, the heat flux tube is equipped with an electric auxiliary heating mechanism. The hot end temperature of the eddy current cooling tube can only reach a maximum of 110°C, but by using electric auxiliary heating, the heat flux temperature can be further increased to the regeneration requirement of 220°C.

[0015] Furthermore, a second gas-liquid separator is connected downstream of the main heat exchanger via the feed gas pipeline. Functioning the same as the first gas-liquid separator, the second gas-liquid separator can separate LNG from the exhaust gas.

[0016] According to the system disclosed in this invention, this invention also claims a method for producing nitrogen-rich hydrogen-containing gas products from coal-to-gas and LNG co-production, using the system for producing nitrogen-rich hydrogen-containing gas products from coal-to-gas and LNG co-production disclosed in this invention, and including the following steps:

[0017] During system operation, at each cycle, the feed gas inlet and outlet of the pre-adsorber are closed, the bypass pipe of the tail gas pipe is opened, and the Venturi tube generates negative pressure. This causes desorption of the molecular sieve in the pre-adsorber, and the desorbed material is drawn into the lower liquid accumulation chamber. After the feed gas inlet and outlet are closed, the pre-adsorber maintains high pressure. At this time, the bypass pipe of the tail gas pipe is opened, connecting through the Venturi tube. This reduces the pressure in the pre-adsorber, causing the molecular sieve to desorb to some extent, and the released impurity gas enters the lower liquid accumulation chamber. In later stages, the negative pressure generated by the Venturi tube promotes the migration of impurity gas desorbed by the upper molecular sieve downwards. Due to the low temperature of the tail gas, it has a cooling effect on the liquid accumulation chamber, causing the impurity gas to condense into liquid, forming a liquid that can be periodically discharged through the drain port.

[0018] Another method for producing nitrogen-rich hydrogen gas from coal-to-gas and LNG co-production uses the improved system described in this invention and includes the following steps:

[0019] 1) During system operation, one of the main adsorbers undergoes regeneration, with a regeneration cycle of 48–96 hours;

[0020] 2) During regeneration, the main adsorber is first preheated with room temperature nitrogen provided by the low-pressure nitrogen system. After preheating, the main adsorber is heated by the hot nitrogen flow generated by the eddy current cooling tube. After heating, the main adsorber is precooled with room temperature nitrogen and cooled by the cold nitrogen flow generated by the eddy current cooling tube.

[0021] Furthermore, in step 2), when the main adsorber is heated by the hot nitrogen gas flow, the cold nitrogen gas flow generated by the eddy current cooling tube precools the high-pressure nitrogen gas used in the nitrogen scrubbing tower. Since the hot and cold ends of the eddy current cooling tube generate both heat flow and cold flow simultaneously during operation, the cooling capacity of the cold flow is utilized while the heat flow is used to heat the main adsorber.

[0022] Furthermore, in step 2), when the main adsorber is cooled by a cold nitrogen stream, the hot nitrogen stream generated by the vortex cooling tube reheats the exhaust gas from the first gas-liquid separator. Similarly, when the main adsorber is cooled by a cold stream, the heat from the hot stream is utilized.

[0023] This invention extends the regeneration cycle of the main adsorber and the service life of the molecular sieve by setting a pre-adsorber upstream of the main adsorber, while reducing the difficulty of molecular sieve regeneration operations. The improved design utilizes a hot airflow generated by a vortex cooling tube to heat the molecular sieve. The vortex cooling tube is stable and reliable with a low failure rate. Combined with electric auxiliary heating, temperature control is simple, and it can replace steam heating systems, reducing the failure rate. Attached Figure Description

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] Figure 1 This is a system schematic diagram of the present invention;

[0026] Figure 2 This is a schematic diagram of the pre-adsorber in this invention. Detailed Implementation

[0027] The present invention will now be clearly described with reference to the accompanying drawings and specific embodiments. This description is merely illustrative and is not intended to limit the scope of the invention. Any modifications, equivalent substitutions, or improvements made by those skilled in the art based on the embodiments of the present invention without inventive effort to obtain all other embodiments should be included within the scope of protection of the present invention.

[0028] Example 1

[0029] like Figure 1 and Figure 2As shown, a system for producing nitrogen-rich hydrogen gas from coal-to-gas and co-production of LNG includes a feed gas purification unit, a heat exchange unit, and a nitrogen scrubbing tower. The feed gas purification unit is equipped with a main adsorber, and the heat exchange unit is equipped with a main heat exchanger. The feed gas pipe is sequentially connected to the main adsorber, the main heat exchanger, and the nitrogen scrubbing tower. The bottom of the nitrogen scrubbing tower is connected to a first gas-liquid separator, which is equipped with a tail gas pipe. A pre-adsorber is connected upstream of the main adsorber, and the pre-adsorber has a feed gas inlet and outlet. The pre-adsorber includes a tank body with a sieve plate 4 in the middle. The feed gas inlet and outlet are located above the sieve plate, and molecular sieves are filled above the sieve plate. A liquid accumulation chamber 5 is located below the sieve plate, and a drain port 6 is located at the bottom of the liquid accumulation chamber. A Venturi tube 7 is located in the middle of the liquid accumulation chamber, and a bypass pipe 8 connected to the Venturi tube is located on the tail gas pipe. The Venturi tube is horizontally arranged, with both ends penetrating the sidewalls of the liquid accumulation chamber and connecting to the bypass pipe. When the drain port and the bypass pipe are closed, the liquid accumulation chamber and the tank body together form a sealed state.

[0030] The top of the nitrogen scrubbing tower is equipped with a hydrogen-rich product outlet pipe, which is connected to the main heat exchanger. The high-pressure nitrogen gas pipe used for nitrogen scrubbing is connected to the main heat exchanger. At the same time, the raw material gas pipe is connected to the main heat exchanger after being connected to the main adsorber, so that the cooling capacity of the product gas is used to cool the high-pressure nitrogen gas and the raw material gas.

[0031] The molecular sieve loading of the pre-adsorber can be selected as 1 / 2 to 2 / 3 of the main adsorber loading. The molecular sieve of the pre-adsorber does not need to be regenerated in the short term, but can be replaced after a longer period of operation.

[0032] The feed gas, washed from low-temperature methanol, first enters the pre-adsorber, where most of the carbon dioxide and methanol are adsorbed. The pre-adsorber's function is not to directly purify the feed gas to the requirements for entering the cold box, but rather to intercept and transfer most of the carbon dioxide and methanol in the feed gas, reducing the load on the main adsorber. After treatment by the main adsorber, the carbon dioxide in the feed gas is reduced to below 5 ppm.

[0033] Both the main adsorber and the pre-adsorber are connected in parallel in two sets. The parallel connection of the two sets of adsorbers allows for easy switching without affecting the continuous operation of the nitrogen washing process.

[0034] During normal operation of the system in this embodiment, after each cycle, the feed gas inlet and outlet of the pre-adsorber are closed, the bypass pipe of the tail gas pipe is opened, and the Venturi tube generates negative pressure. This causes desorption of the molecular sieve in the pre-adsorber, and the desorbed material is drawn into the lower liquid accumulation chamber. After the feed gas inlet and outlet are closed, the pre-adsorber maintains high pressure. At this time, the bypass pipe of the tail gas pipe is opened, connecting through the Venturi tube. This reduces the pressure in the pre-adsorber, causing the molecular sieve to desorb to a certain extent, and the separated impurity gas enters the lower liquid accumulation chamber. In the later stages, the negative pressure generated by the Venturi tube promotes the migration of the impurity gas desorbed by the upper molecular sieve downwards. Due to the low temperature of the tail gas, it has a cooling effect on the liquid accumulation chamber, causing the impurity gas to condense into liquid, forming a liquid that can be periodically discharged through the drain port.

[0035] The shut-off interval of the feed gas inlet and outlet of the pre-adsorber can be set to 4 to 8 hours, and the bypass opening duration can be set to 2 to 4 hours.

[0036] Example 2

[0037] like Figure 1 Based on Example 1, this example improves the regeneration gas unit of the main adsorber. The main adsorber is connected to a molecular sieve regeneration gas path, which is equipped with a regeneration gas thermal control mechanism, including a vortex cooling tube 1. The inlet of the vortex cooling tube is connected to a medium-pressure nitrogen system. The vortex cooling tube has a cold flow tube 3 and a hot flow tube 2. Both the cold flow tube and the hot flow tube have a main gas path and a branch gas path. The main gas path is connected to the molecular sieve regeneration gas path. The branch gas path of the cold flow tube is connected to the first heat exchanger, and the branch gas path of the hot flow tube is connected to the second heat exchanger. The high-pressure nitrogen inlet pipe of the nitrogen scrubbing tower is connected to the first heat exchanger, and the tail gas pipe of the first gas-liquid separator is connected to the second heat exchanger. Multiple vortex cooling tubes can be connected in parallel to provide sufficient regeneration gas flow.

[0038] The hot flow tube is equipped with an electric auxiliary heating mechanism, specifically an electric heater that can be connected to the hot flow tube. The hot end temperature of the eddy current cooling tube can only reach a maximum of 110°C, but by using electric auxiliary heating, the hot flow temperature can be further increased to the regeneration requirement of 220°C.

[0039] A second gas-liquid separator is connected downstream of the main heat exchanger via a feed gas pipeline. Similar in function to the first gas-liquid separator, the second gas-liquid separator can separate LNG from the exhaust gas.

[0040] In this embodiment, during system operation, one of the main adsorbers undergoes regeneration, with a regeneration cycle of 48–96 hours. First, the main adsorber is preheated with ambient temperature nitrogen supplied by a low-pressure nitrogen system. After preheating, the main adsorber is heated further with a hot nitrogen stream generated by a vortex cooling tube. After heating, the main adsorber is precooled with ambient temperature nitrogen, and then cooled with a cold nitrogen stream generated by the vortex cooling tube.

[0041] When the main adsorber is heated by a hot nitrogen stream, the cold nitrogen stream generated by the vortex refrigeration tube pre-cools the high-pressure nitrogen gas used in the nitrogen scrubbing tower. When the main adsorber is cooled by a cold nitrogen stream, the hot nitrogen stream generated by the vortex refrigeration tube reheats the tail gas from the first gas-liquid separator.

[0042] Taking a 48-hour regeneration cycle as an example, the regeneration operation can be performed according to the following steps:

[0043] a. Main adsorber switching; b. Pressure reduction for 0.5 hours; c. Preheating for 1 hour; d. Heating for 18 hours; e. Precooling for 8 hours; f. Cooling for 19 hours; g. Parallel pressure increase for 0.5 hours; h. Waiting for 1 hour. The heating and cooling rates are set to half of the original process. The regeneration gas flow rate requirement can be reduced to more than half of the original, significantly reducing the requirements for the regeneration gas's cooling and heating efficiency.

Claims

1. A system for producing nitrogen-rich hydrogen gas from coal-to-gas and LNG co-production, comprising a feed gas purification unit, a heat exchange unit, and a nitrogen scrubbing tower, wherein the feed gas purification unit is equipped with a main adsorber, the heat exchange unit is equipped with a main heat exchanger, and the feed gas pipe is sequentially connected to the main adsorber, the main heat exchanger, and the nitrogen scrubbing tower, the bottom of the nitrogen scrubbing tower is connected to a first gas-liquid separator, and the first gas-liquid separator is equipped with a tail gas pipe, characterized in that: An upstream pre-adsorber is connected to the main adsorber, which has a feed gas inlet and outlet. The pre-adsorber includes a tank with a sieve plate in the middle. The feed gas inlet and outlet are located above the sieve plate, and molecular sieves are filled above the sieve plate. A liquid accumulation chamber is located below the sieve plate, and a drain port is located at the bottom of the liquid accumulation chamber. A Venturi tube is located in the middle of the liquid accumulation chamber, and a bypass pipe connected to the Venturi tube is provided in the tail gas pipe. During system operation, after each cycle, the feed gas inlet and outlet of the pre-adsorber are closed, the bypass pipe of the tail gas pipe is opened, and the Venturi tube generates negative pressure. The molecular sieves of the pre-adsorber undergo desorption, and the desorbed material is drawn into the liquid accumulation chamber below. Because the tail gas temperature is low, it can cool the liquid accumulation chamber, causing impurities to condense into liquid and form a liquid, which can be periodically discharged through the drain port.

2. The system for producing nitrogen-rich hydrogen-containing gas from coal-to-gas and LNG as described in claim 1, characterized in that: The main adsorber and the pre-adsorber are both connected in parallel in two sets.

3. The system for producing nitrogen-containing hydrogen-rich gas from coal-to-gas and LNG co-production according to claim 2, characterized in that: The main adsorber is connected to a molecular sieve regeneration gas path, which is equipped with a regeneration gas thermal control mechanism, including a vortex refrigeration tube. The inlet of the vortex refrigeration tube is connected to a medium-pressure nitrogen system. The vortex refrigeration tube is equipped with a cold flow tube and a hot flow tube. Both the cold flow tube and the hot flow tube are equipped with a main gas path and a branch gas path. The main gas path is connected to the molecular sieve regeneration gas path. The branch gas path of the cold flow tube is connected to the first heat exchanger, and the branch gas path of the hot flow tube is connected to the second heat exchanger. The high-pressure nitrogen inlet pipe of the nitrogen scrubbing tower is connected to the first heat exchanger, and the tail gas pipe of the first gas-liquid separator is connected to the second heat exchanger.

4. The system for producing nitrogen-containing hydrogen-rich gas by co-producing LNG from coal gasification according to claim 3, characterized in that: The heat flow pipe is equipped with an electric auxiliary heating mechanism.

5. The system for producing nitrogen-rich hydrogen-containing gas by co-producing LNG from coal gas as described in claim 1, characterized in that: A second gas-liquid separator is connected downstream of the main heat exchanger via a raw material gas pipe.

6. A method for producing nitrogen-containing hydrogen-rich gas by co-producing LNG from coal gasification, characterized in that, It is a system for producing nitrogen-containing hydrogen-rich gas products using coal-to-gas co-production LNG as described in claim 4, and includes the following steps: 1) During system operation, one of the main adsorbers undergoes regeneration, with a regeneration cycle of 48~96 hours; 2) During regeneration, the main adsorber is first preheated with room temperature nitrogen provided by the low-pressure nitrogen system. After preheating, the main adsorber is heated by the hot nitrogen flow generated by the vortex cooling tube. After heating, the main adsorber is precooled with room temperature nitrogen and cooled by the cold nitrogen flow generated by the vortex cooling tube.

7. The method for producing nitrogen-containing hydrogen-rich gas from coal-to-gas and LNG co-production according to claim 6, characterized in that: In step 2), when the main adsorber is heated by hot nitrogen gas flow, the cold nitrogen gas flow generated by the vortex cooling tube precools the high-pressure nitrogen gas used in the nitrogen scrubbing tower.

8. The method for producing nitrogen-containing hydrogen-rich gas by co-producing LNG from coal gasification according to claim 6, characterized in that: In step 2), when the main adsorber is cooled by a cold nitrogen gas flow, the hot nitrogen gas flow generated by the vortex cooling tube reheats the tail gas coming out of the first gas-liquid separator.

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