Novel system for adjusting hydrogen-carbon ratio in coal-to-methanol synthesis

Abstract

The invention provides a novel system for adjusting the hydrogen-carbon ratio of coal-to-methanol synthesis, and belongs to the technical field of methanol synthesis. The system comprises a CO2 gas flow leading-out pipeline, an inlet end of which is connected to an outlet pipeline of a CO2 compressor in the coal-to-methanol device and is used for leading out a stream of CO2 product gas; an inlet of the desulfurization purification unit is connected with an outlet of the CO2 gas flow leading-out pipeline, and the desulfurization purification unit is used for carrying out desulfurization treatment on the led-out CO2 product gas; the flow regulation and control unit is arranged on a downstream pipeline of the desulfurization purification unit and is used for regulating and controlling the flow of the CO2 gas; and the CO2 injection pipeline is used for injecting the adjusted CO2 gas into the main purified synthesis gas flow. According to the invention, accurate control of the CO2 content is realized through arrangement of an independent CO2 supplementing system and closed-loop regulation, the hydrogen-carbon ratio can be effectively optimized, the methanol synthesis reaction is carried out under the optimal thermodynamic condition, the methanol selectivity and yield are improved, side reactions are reduced, the generation of carbon deposits is inhibited, the service life of the catalyst is prolonged, and the replacement frequency and cost are reduced.

Description

Technical Field

[0001] This invention relates to the field of methanol synthesis technology, specifically a new system for adjusting the hydrogen-to-carbon ratio in coal-based methanol synthesis. Background Technology

[0002] Coal-to-methanol is a key industrial chain in modern coal chemical industry. Its typical process includes gasification, purification, methanol synthesis, and distillation. In the methanol synthesis section, the molar ratio of hydrogen (H2) to carbon oxides (CO+CO2) in the feed gas entering the synthesis tower (i.e., the hydrogen-to-carbon ratio) is a critical parameter affecting reaction efficiency and system stability. Studies have shown that controlling the hydrogen-to-carbon ratio at 2.05–2.10, while maintaining a CO2 content of 2%–3%, can effectively inhibit catalyst coking, optimize reaction thermodynamic equilibrium, and improve methanol selectivity and single-pass conversion. Currently, industrial methanol synthesis almost exclusively uses carbon monoxide and pressurized catalytic hydrogenation. A typical process includes feed gas production, feed gas purification, methanol synthesis, and crude methanol distillation. To ensure stable operation of the methanol synthesis system, there are specific requirements for the hydrogen-to-carbon ratio in the feed gas entering the system. Controlling the hydrogen-to-carbon ratio within a suitable range can improve the methanol synthesis efficiency and yield, reduce feed gas loss, and lower system energy consumption. In actual production, after using low-temperature methanol washing to remove acidic gas for coal gas purification, the CO2 content in the coal gas does not reach the optimal intake ratio.

[0003] Low-temperature methanol washing is a widely used gas purification technology in the coal chemical industry, primarily used to remove acidic gases (such as CO2 and H2S) from syngas. However, in actual operation, it has been found that while the total sulfur content of the purified gas is within acceptable limits, the CO2 content cannot reach the 2%-3% required for methanol synthesis. This leads to increased side reactions in the methanol synthesis reaction and limited product quality. The closest existing technology directly adjusts the CO2 content in the purified gas through the low-temperature methanol washing process, but due to process limitations, the CO2 content is difficult to precisely control within the required range, affecting the efficiency of methanol synthesis and product quality.

[0004] The specific details are as follows:

[0005] 1. Technical problem: The CO2 content in the gas purified by low-temperature methanol washing cannot be stably reached to the 2%-3% required for methanol synthesis, which leads to an increase in side reactions and affects the purity and yield of methanol products.

[0006] 2. Efficiency issues: Due to insufficient CO2 content, the chemical equilibrium of the methanol synthesis reaction is limited, reducing the overall production efficiency.

[0007] 3. Cost issues: Increased side reactions lead to shorter catalyst life and increased energy consumption, indirectly increasing production costs. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a novel system for adjusting the hydrogen-to-carbon ratio in coal-to-methanol synthesis. The core of this system lies in controlling the CO2 content to stabilize the hydrogen-to-carbon ratio within a suitable range, thereby effectively suppressing side reactions, improving methanol synthesis efficiency and product yield, extending catalyst lifespan, reducing energy consumption, and ultimately enhancing overall production economics.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a novel system for adjusting the hydrogen-to-carbon ratio in coal-to-methanol synthesis, comprising a CO2 gas outlet pipeline, the inlet of which is connected to the outlet pipeline of the CO2 compressor in the coal-to-methanol unit, for outleting a stream of CO2 product gas; a desulfurization and purification unit, the inlet of which is connected to the outlet of the CO2 gas outlet pipeline, for desulfurizing the outlet CO2 product gas; a flow regulation and control unit, located on the downstream pipeline of the desulfurization and purification unit, for regulating and controlling the flow rate of CO2 gas; and a CO2 supplementary injection pipeline, the inlet of which is connected to the pipeline downstream of the flow regulation and control unit, and the outlet of which is connected to the inlet pipeline of the synthesis gas compressor of the methanol synthesis system, for injecting the regulated CO2 gas into the main purified synthesis gas stream.

[0010] As a preferred embodiment of the present invention, the desulfurization purification unit includes at least one desulfurization tank filled with desulfurizing agent, and is preferably a switchable A / B dual-tank structure.

[0011] As a preferred embodiment of the present invention, the desulfurization purification unit is further provided with a steam introduction pipeline for introducing steam into the desulfurization tank to promote the conversion and removal of sulfur.

[0012] As a preferred embodiment of the present invention, the inlet of the desulfurization purification unit is provided with a nitrogen replacement pipeline, and the outlet is provided with a safety discharge pipeline leading to the flare system.

[0013] As a preferred embodiment of the present invention, the method includes the following steps:

[0014] S1: A certain flow rate of high-pressure, high-purity CO2 product gas is diverted from the outlet pipeline of the CO2 compressor. The diverted flow rate is calculated and determined based on the target CO2 content in the syngas after mixing being 2%~3%.

[0015] S2: The diverted CO2 gas stream is passed through the desulfurization and purification unit for deep desulfurization to ensure that its total sulfur content meets the requirements of the methanol synthesis catalyst (usually much lower than 1 ppm).

[0016] S3: The flow rate of CO2 gas after desulfurization is precisely controlled through the flow regulation and control unit.

[0017] S4: The CO2 gas, after desulfurization and flow control, is injected into the inlet pipeline of the methanol synthesis compressor and fully mixed with the main purified synthesis gas. The CO2 content in the raw gas entering the methanol synthesis tower after mixing is measured by an online analyzer to ensure that it is stable within the ideal range of 2.0%-3.0%, and the hydrogen-to-carbon ratio (H2 / (CO+CO2)) is correspondingly stable between 2.05-2.10.

[0018] As a preferred embodiment of the present invention, the flow rate of the diverted CO2 product gas accounts for 1.5%-4.0% of the total flow rate at the inlet of the syngas compressor.

[0019] As a preferred embodiment of the present invention, the online analyzer monitors the composition of the mixed raw gas and uses the flow regulation and control unit to provide feedback control, thereby achieving closed-loop automatic adjustment of CO2 content.

[0020] In some embodiments of the present invention, in step S1, when the total gas flow rate at the inlet of the syngas compressor is approximately 183,000 Nm³ / h, the diverted CO2 gas flow rate is controlled to be approximately 5,000 Nm³ / h (approximately 2.7%).

[0021] As a preferred technical solution of the present invention, the flow rate of the diverted CO2 product gas accounts for 1.5%-4.0% of the total gas flow rate at the inlet of the syngas compressor. After supplementing CO2 gas, the hydrogen-to-carbon ratio (H2 / (CO+CO2)) of the feed gas entering the methanol synthesis system is adjusted to the range of 2.05-2.10. Based on the monitoring results of the mixed feed gas components by the online analysis instrument, the flow regulation and control unit is fed back to achieve closed-loop automatic adjustment of CO2 content. The desulfurizing agent of the desulfurization purification unit needs to be replaced or regenerated regularly. Nitrogen purging and safe discharge are performed before and after the replacement or regeneration operation.

[0022] Compared with existing technologies, this invention provides a novel system for adjusting the hydrogen-to-carbon ratio in coal-to-methanol synthesis, which has the following beneficial effects:

[0023] A novel system for adjusting the hydrogen-to-carbon ratio in coal-to-methanol synthesis is proposed. By setting up an independent CO2 replenishment system and implementing closed-loop regulation, the CO2 content can be precisely controlled, effectively optimizing the hydrogen-to-carbon ratio. This allows the methanol synthesis reaction to proceed under optimal thermodynamic conditions, improving methanol selectivity and yield, reducing side reactions, inhibiting carbon deposition, extending catalyst lifespan, and lowering replacement frequency and costs. The A / B design of the desulfurization tank and the safety pipeline ensure continuous production and maintenance safety, and the system has strong adaptability. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example

[0027] Please see Figure 1 In this embodiment, a novel system for adjusting the hydrogen-to-carbon ratio in coal-to-methanol synthesis includes a CO2 gas outlet pipeline, the inlet of which is connected to the outlet pipeline of the CO2 compressor in the coal-to-methanol unit, for outleting a stream of CO2 product gas; a desulfurization and purification unit, the inlet of which is connected to the outlet of the CO2 gas outlet pipeline, for desulfurizing the outleted CO2 product gas; a flow regulation and control unit, located on the downstream pipeline of the desulfurization and purification unit, for regulating and controlling the flow rate of CO2 gas; and a CO2 supplementary injection pipeline, the inlet of which is connected to the pipeline downstream of the flow regulation and control unit. The outlet end is connected to the inlet pipeline of the synthesis gas compressor of the methanol synthesis system, which is used to inject the regulated CO2 gas into the main purified synthesis gas flow. The desulfurization purification unit includes at least one desulfurization tank filled with desulfurizing agent, preferably a switchable A / B dual tank structure. The desulfurization purification unit is also equipped with a steam introduction pipeline, which is used to introduce steam into the desulfurization tank to promote the conversion and removal of sulfur. The inlet of the desulfurization purification unit is equipped with a nitrogen replacement pipeline, and the outlet is equipped with a safety discharge pipeline leading to the flare system. The flow regulation and control unit includes a regulating valve, a flow meter, and pressure and temperature monitoring instruments.

[0028] In this embodiment, approximately 5000 Nm³ / h of CO2 product gas is diverted from the main outlet pipeline of the three-stage CO2 compressor via a newly added lead-out pipeline. The gas parameters are: pressure 6.5 MPa(G), temperature 123°C, CO2 purity ≥98.5%, and total sulfur ≤5vppm. The diverted CO2 gas first enters the desulfurization and purification unit. The desulfurization tank is filled with highly efficient desulfurizing agents such as zinc oxide. An appropriate amount of steam is added through the steam introduction pipeline to promote the hydrolysis and conversion removal of sulfur. Tanks A and B can be operated in parallel, or in series, to ensure the desulfurization effect. After desulfurization, the total sulfur content of the gas should be reduced to a safe level below 0.1vppm.

[0029] In this embodiment, the clean CO2 gas after desulfurization is precisely controlled by a flow regulating valve and a flow meter to stabilize its flow rate at a set value. It is then injected into the purified syngas pipeline from the low-temperature methanol wash through an injection pipeline. It is fully mixed with the main gas flow in the inlet pipeline of the syngas compressor. The CO2 content in the mixed gas is increased from the original 0.5%-1.0% to about 2.49%, and the hydrogen-to-carbon ratio is adjusted accordingly to about 2.07, which meets the optimal requirements of the methanol synthesis catalyst. The DCS system monitors parameters such as flow rate, pressure, and temperature, and finely adjusts the opening of the flow regulating valve in real time based on the feedback of the mixed raw material gas composition from the online chromatograph to achieve closed-loop control of CO2 content and ensure continuous and stable operation. When it is necessary to replace the desulfurizing agent, the nitrogen replacement pipeline can be used for purging, and the residual gas can be safely vented through the flare discharge pipeline.

[0030] The working principle and usage process of this invention are as follows: First, a CO2 gas flow outlet pipeline is connected to the existing CO2 compressor outlet pipeline in the factory (e.g., a pipeline identified as 126CG-002-250-C6A-H2) to draw a high-pressure, high-purity CO2 product gas from the CO2 compressor outlet. Typical parameters of this CO2 product gas are: pressure approximately 6.5 MPa(G), temperature approximately 123°C, CO2 volume concentration ≥98.5%, and total sulfur content ≤5vppm. Next, a desulfurization and purification unit is connected in series with the CO2 gas flow outlet pipeline to perform deep desulfurization treatment on the drawn CO2 gas flow. This unit preferably includes at least one desulfurization tank, more preferably an A / B dual-tank structure arranged in parallel or series, and is equipped with a bypass pipeline. The desulfurization tank is filled with desulfurizing agent and equipped with a steam introduction pipeline (e.g., introduced from the top) to convert inorganic sulfur (such as H2S) into organic sulfur (such as COS) when needed, and to achieve effective sulfur removal through subsequent bed or condition control. The desulfurization tank inlet is also equipped with a nitrogen replacement pipeline, and the outlet is equipped with a safety discharge pipeline leading to the flare system, which facilitates the replacement of the desulfurizing agent and the safe isolation of the system.

[0031] Then, the flow regulation and control unit is located on the pipeline downstream of the desulfurization and purification unit, including regulating valves, flow meters, and possible pressure and temperature monitoring instruments. This unit is used to precisely control the flow rate of CO2 gas supplied to the methanol synthesis system. Finally, the CO2 supply injection pipeline delivers the desulfurized and flow-regulated CO2 gas stream to the inlet pipeline of the synthesis gas compressor in the methanol synthesis system, where it mixes with the purified synthesis gas from the low-temperature methanol wash unit. By introducing an external high-purity CO2 source, the fluctuations and risks that may be caused by directly adjusting the main low-temperature methanol wash system are avoided.

[0032] In the description of this invention, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising a reference structure" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. It should be noted that, herein, relational terms such as "first," "second," etc., are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0033] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A novel system for adjusting the hydrogen-to-carbon ratio in coal-to-methanol synthesis, characterized in that, include: The CO2 gas outlet pipeline is connected at its inlet end to the outlet pipeline of the CO2 compressor in the coal-to-methanol unit, and is used to draw out a stream of CO2 product gas. The desulfurization and purification unit has its inlet connected to the outlet of the CO2 gas flow outlet pipeline, and is used to desulfurize the extracted CO2 product gas. A flow regulation and control unit is installed on the downstream pipeline of the desulfurization and purification unit to regulate and control the flow rate of CO2 gas. The CO2 supplementary injection pipeline has its inlet end connected to the pipeline downstream of the flow regulation and control unit, and its outlet end connected to the inlet pipeline of the synthesis gas compressor of the methanol synthesis system, for injecting the regulated CO2 gas into the main purified synthesis gas flow.

2. A novel system for adjusting the hydrogen-to-carbon ratio in coal-to-methanol synthesis according to claim 1, characterized in that: The desulfurization purification unit includes at least one desulfurization tank filled with desulfurizing agent, and is preferably a switchable A / B dual-tank structure.

3. A novel system for adjusting the hydrogen-to-carbon ratio in coal-to-methanol synthesis according to claim 2, characterized in that: The desulfurization and purification unit is also equipped with a steam introduction pipeline for introducing steam into the desulfurization tank to promote the conversion and removal of sulfur.

4. A novel system for adjusting the hydrogen-to-carbon ratio in coal-to-methanol synthesis according to claim 3, characterized in that: The desulfurization and purification unit is equipped with a nitrogen replacement pipeline at its inlet and a safety discharge pipeline leading to the flare system at its outlet.

5. A novel system for adjusting the hydrogen-to-carbon ratio in coal-to-methanol synthesis as described in claims 1 to 4, characterized in that: S1, a certain flow rate of CO2 product gas is diverted from the outlet pipeline of the CO2 compressor; S2, which causes the diverted CO2 product gas stream to undergo desulfurization treatment in the desulfurization and purification unit; S3 precisely controls the flow rate of CO2 gas after desulfurization through a flow regulation and control unit; S4, CO2 gas with flow control is injected into the main purified syngas in the inlet pipeline of the syngas compressor through the injection pipeline, and the CO2 volume content in the mixed raw gas is measured by online analysis instrument to reach 2.0%–3.0%.

6. A novel system for adjusting the hydrogen-to-carbon ratio in coal-to-methanol synthesis according to claim 5, characterized in that: The flow rate of the diverted CO2 product gas accounts for 1.5%-4.0% of the total gas flow rate at the inlet of the syngas compressor.

7. A novel system for adjusting the hydrogen-to-carbon ratio in coal-to-methanol synthesis according to claim 5, characterized in that: The online analyzer monitors the composition of the mixed feed gas, and the flow regulation and control unit provides feedback control to achieve closed-loop automatic adjustment of CO2 content.

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