Method for directly coupling production of low-temperature methanol washing carbon removal gas and associated alkali

Abstract

The present application belongs to the technical field of synthetic ammonia associated alkali production, and specifically discloses a method for directly coupling associated alkali production by low-temperature methanol washing carbon removal gas, which comprises the following steps: a deep decarbonization concentration tower is additionally arranged between a low-methanol 8 tower and a low-methanol 2 tower of a low-temperature methanol washing section, low-pressure CO2 flashing gas at the outlet of the low-methanol 8 tower is introduced into the tower, and is reversely contacted with low-temperature semi-lean methanol solution from the low-methanol 2 tower, and synchronous CO2 deep purification and pressure increase are realized by relying on the inherent pressure gradient of methanol absorption-desorption; the outlet pressure of the decarbonization tower is stably controlled to 0.6 MPa, the CO2 purity is greater than or equal to 95 vol%, and the directly sent carbonization tower of associated alkali is directly sent to participate in the reaction. The present application is stably operated within 70% to 100% production load, reduces the comprehensive energy consumption and annual operation cost of the system, deeply embeds the original methanol circulation system of the low-temperature methanol washing, has high energy integration degree, small equipment modification amount, short investment recovery period, and is suitable for the transformation of various synthetic ammonia associated pure alkali devices.

Description

Technical Field

[0001] This invention relates to the field of synthetic ammonia and alkali production technology, and in particular to a method for the direct coupling of carbon gas with low-temperature methanol washing to produce alkali. Background Technology

[0002] In the process of co-producing ammonia and soda ash, the carbonization step of the co-alkali process requires the CO2 feed gas pressure to reach 0.3–0.6 MPa and the purity to meet the carbonization reaction requirements. The CO2 flash vapor produced by the traditional low-temperature methanol washing process has a pressure of only 0.02–0.05 MPa, which cannot be directly used for carbonization. The industry standard solution is to add a CO2 compressor to pressurize it to the process pressure. Industrial compressors are divided into two types: motor-driven and turbine-driven, and both have multiple drawbacks: high investment costs: the compressor main unit, cooling, lubrication, and electrical supporting equipment are purchased in one go, and civil engineering investment is large, requiring backup units; high operating energy consumption: motor-driven compressors consume more than 40 kWh of electricity per ton of soda ash, while turbine-driven compressors consume a large amount of medium-pressure steam per hour, resulting in persistently high energy costs; heavy maintenance burden: compressor impellers, seals, and valves are prone to wear, requiring frequent periodic maintenance and easily causing unplanned shutdowns of the co-alkali process; low system integration: adding a compression unit extends the process flow, increases the number of pipelines and instruments, and results in poor energy cascade utilization.

[0003] Existing technologies have significant limitations: some technologies reduce the compression load by mixing flash vapor with concentrated gas during intake, but still retain small booster compressors, making it impossible to completely eliminate pressurization equipment; another low-methanol CO2 purification technology only optimizes the gas recovery rate and does not match the pressure requirements of soda ash, so CO2 still requires subsequent pressurization. Currently, there is no solution that can fully utilize the methanol cycle and pressure gradient of low-methanol systems to completely eliminate all compression equipment, indicating a huge potential for energy-saving retrofits. Summary of the Invention

[0004] The purpose of this invention is to provide a method for the direct coupling of low-temperature methanol washing decarbonization gas with soda ash production, overcoming the shortcomings of existing soda ash processes that rely on CO2 compressors, such as high investment, high energy consumption, cumbersome operation and maintenance, and low energy utilization. This invention provides a coupling process embedded within the low-temperature methanol washing process, which relies on the methanol absorption-desorption pressure gradient to simultaneously complete CO2 purification and self-pressurization, completely eliminating the need for compression equipment, reducing one-time investment and long-term operating costs, and improving the system's energy integration and the quality of the finished soda ash product.

[0005] To achieve the above objectives, the present invention provides a method for the direct coupling of low-temperature methanol washing and carbon gas production with soda ash production, comprising the following steps: Step 1: Add a deep decarbonization tower between the low-temperature methanol washing section's low-methanol 8 tower and low-methanol 2 tower. Step 2: The low-pressure CO2 flash vapor from the top outlet of the low-pressure methanol tower 8 is introduced from the bottom of the decarbonization tower, and the low-temperature semi-lean methanol solution drawn from the top of the low-pressure methanol tower 2 is sprayed into the tower from the top of the decarbonization tower; the CO2 gas and the methanol solution come into countercurrent contact in the tower, and the deep purification of CO2 and the pressure increase are completed simultaneously through the inherent pressure gradient of the methanol absorption-desorption process. Step 3: Control the outlet pressure at the top of the decarbonization tower to be stable at 0.6 MPa, and ensure that the purity of the CO2 gas at the outlet is not less than 95 vol; the treated CO2 gas is directly sent to the bottom of the carbonization tower in the alkali treatment section through the connecting pipeline to participate in the carbonization reaction, without the installation of a CO2 compressor or booster throughout the process.

[0006] Preferably, in step 1, the decarbonization tower adopts a packed tower or a plate tower structure; the packed tower is equipped with two sections of packing, each section having a height of 6.0m, and a liquid collection and redistribution device is installed between the two sections; the plate tower is equipped with 32 layers of single overflow floating valve tower plates with a plate spacing of 500mm; a demister is installed at the top of the tower, and a tubular gas distributor is installed at the bottom of the tower.

[0007] Preferably, in step 1, the decarbonization tower is equipped with a matching automatic control system, which includes a tower top pressure control loop, a tower bottom liquid level control loop, a three-point temperature monitoring loop, a methanol mass metering loop, a CO2 flow metering loop, an ESD emergency shut-off loop, and a DCS system.

[0008] Preferably, in step 2, the operating temperature range of the decarbonization tower is: top temperature -20 to -5℃, bottom temperature -10 to +10℃, and the temperature gradient of the entire tower does not exceed 30℃; the purity of the methanol solution entering the decarbonization tower is ≥98.5wt%, and the temperature entering the decarbonization tower is controlled at -25 to -15℃.

[0009] Preferably, in step 2, the methanol spray liquid-to-gas ratio in the decarbonization tower is controlled between 0.008 and 0.015 m³ / s. 3 / m 3 Under low-load conditions of 70%–90%, the liquid-to-gas ratio is adjusted to 0.011–0.015m. 3 / m 3 To ensure the depth of decarbonization.

[0010] Preferably, in step 3, the liquid level at the bottom of the decarbonization tower is maintained within the range of 30% to 60% of the volume, and the normal operating liquid level is 40% to 50%; the allowable fluctuation range of the outlet pressure at the top of the decarbonization tower is ±0.03 MPa.

[0011] Preferably, in step 3, the purity of the CO2 gas fed into the carbonization tower of the soda ash section is normally maintained at 95.0%–98.5 vol%, with a minimum fluctuation of 93.0 vol allowed for short periods of ≤30 minutes; under 100% full load, the CO2 gas volumetric flow rate at the decarbonization tower inlet is 15000–18000 Nm³. 3 / h.

[0012] Preferably, in step 3, the connecting pipeline between the decarbonization tower and the carbonization tower of the soda ash plant is sequentially equipped with a pneumatic emergency shut-off valve, a spring-loaded safety valve, a check valve, and a manual shut-off valve.

[0013] The advantages and beneficial effects of the above-mentioned method for direct coupling of low-temperature methanol washing and carbon gas production with soda ash are as follows: 1. This invention completely eliminates compression equipment, resulting in a significant reduction in investment: It completely eliminates the need for CO2 compressors and their supporting cooling, lubrication, and electrical systems, reducing investment by approximately 78% compared to motor-driven compression equipment and by approximately 83% compared to turbine-driven equipment; it also eliminates the need for backup compressor units, reducing equipment footprint and maintenance workload.

[0014] 2. This invention significantly reduces operating energy consumption and has outstanding energy-saving benefits: compared with the motor-driven process, it saves 33.8 kWh of electricity per ton of alkali, and the annual electricity saving benefits of a 300,000 t / a synthetic ammonia plant with a 200,000 t / a soda ash plant exceed 4.5 million yuan; the steam turbine route completely eliminates the consumption of 30t / h compressed steam, saving more than 37 million yuan in steam costs annually; the overall energy consumption of the system decreases by 17.4% to 21.4%.

[0015] 3. This invention deeply couples with the original low-methanol cycle, resulting in high energy utilization: The decarbonization tower is located in the middle of the methanol cycle loop of the low-methanol tower 8 and the low-methanol tower 2, reusing the original low-temperature refrigeration and methanol regeneration system. It relies on the natural pressure gradient of methanol absorption and desorption to complete the self-pressurization of CO2 without additional pressurization power input.

[0016] 4. This invention can stably output qualified CO2 within the 70%–100% load range of the device, with pressure fluctuations ≤ ±0.015MPa; the CO2 purity is higher than that of the traditional compression process, and the rate of high-quality soda ash is increased by 5 percentage points; only one decarbonization tower and supporting piping and instrumentation are added, and the original low-methane and combined alkali main units do not need to be modified; the total investment for the modification is about RMB 4.8 million, and the entire modification cost can be recovered in 1–2 years under normal operating conditions; the regular maintenance and spare parts replacement procedures of the compressor are eliminated, and the annual operation and maintenance cost is reduced by 82.5% compared with the electric motor compression process and by 87.3% compared with the steam turbine process.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 This is a flowchart of a method for producing alkali by direct coupling of carbon gas with low-temperature methanol washing according to the present invention. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0021] The following examples are not intended to limit the invention, but are only for illustration. Unless otherwise specified, the experimental methods used in the following examples are generally performed under conventional conditions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0022] Benchmark unit conditions: Ammonia synthesis capacity of 300,000 t / a, co-production of soda ash of 200,000 t / a; low-temperature methanol washing section at full load processing 80,000 Nm³ of feed gas. 3 / h, annual operating time 8000h. Two types of traditional compression processes were set up for comparison.

[0023] Comparative Example 1: Electric motor driven CO2 compressor process.

[0024] Equipment configuration: 2 centrifugal CO2 compressors (1 in use, 1 on standby), each with an operating power of 1000kW and a total installed power of 2000kW; inlet pressure 0.02~0.05MPa, outlet pressure 0.60MPa.

[0025] Energy consumption cost: 1000 kWh per hour, 8 million kWh per year; electricity price: 0.68 yuan / kWh, annual electricity cost: 5.44 million yuan; electricity consumption for alkali compression: 40 kWh / t-alkali.

[0026] Investment and maintenance: The one-time investment in equipment is approximately RMB 22 million; the annual maintenance cost is approximately RMB 1.6 million.

[0027] Quality indicators: CO2 purity in the carbonation tower is 96.0%~98.0 vol; the rate of superior grade soda ash is 82%~88%; the overall energy consumption of the system is 385 kgce / t-alkali.

[0028] Comparative Example 2: Steam Turbine Driven CO2 Compressor Process.

[0029] Equipment configuration: 2 steam turbines drive centrifugal CO2 compressors (1 in use, 1 on standby), with inlet and outlet pressures the same as comparative example 1.

[0030] Energy consumption cost: 30t of steam per hour, 240,000t of steam per year; steam price of 170 yuan / t, annual steam cost of 40.8 million yuan; steam consumption per ton of alkali is 1.2t / t-alkali.

[0031] Investment and operation and maintenance: The one-time investment in equipment is approximately RMB 28 million; the annual operation and maintenance cost is approximately RMB 2.2 million (including maintenance of the steam turbine and condensate system).

[0032] Quality indicators: CO2 purity in the carbonation tower is 96.0%~98.0 vol; the rate of superior grade soda ash is 82%~88%; the overall energy consumption of the system is 392 kgce / t-alkali.

[0033] Example 1 On the aforementioned benchmark unit: the original CO2 compression system was removed, and a packed deep decarbonization and concentration tower and supporting instrumentation and piping were added between the low-carbon alkali tower 8 and the low-carbon alkali tower 2; the unit scale, low-carbon alkali processing capacity, and soda ash production remained unchanged.

[0034] A method for the direct coupling of low-temperature methanol washing and carbon gas removal with sodium hydroxide production, such as... Figure 1 As shown, it includes the following steps: Step 1: Add a deep decarbonization tower between the low-temperature methanol washing tower 8 and the low-temperature methanol washing tower 2 in the low-temperature methanol washing section. The decarbonization tower adopts a packed tower or plate tower structure; the packed tower has two sections of packing, each section with a height of 6.0m, and a liquid collection and redistribution device is installed between the two sections; the plate tower has 32 layers of single overflow floating valve tower plates with a plate spacing of 500mm; a demister is installed at the top of the tower, and a tubular gas distributor is installed at the bottom of the tower.

[0035] Packed tower design: tower diameter DN1400mm, total height 22m; two sections of 250Y type metal saddle packing, each section height 6.0m; liquid collection and redistribution device between the two sections; DN1400mm×200mm wire mesh demister at the top of the tower; tower body material is Q345R+316L composite plate.

[0036] Plate tower design: tower diameter DN1600mm, total effective height 18m; 32-layer F1 type floating valve tower plates, single overflow structure, plate spacing 500mm; baffle plate demister installed at the top of the tower; design pressure 0.8MPa, design temperature -40℃.

[0037] The decarbonization tower is equipped with a matching automatic control system. The signals of the automatic control system are connected to the DCS (Distributed Control System) system for centralized monitoring. The automatic control system includes: tower top pressure control loop, tower bottom liquid level control loop, three-point temperature monitoring loop, methanol mass metering loop, CO2 flow metering loop, ESD (Emergency Shutdown System) emergency cut-off loop, and DCS system. All instrument signals are connected to the DCS system for centralized monitoring.

[0038] Step 2: The low-pressure CO2 flash vapor from the top outlet of the low-pressure methanol tower 8 is introduced from the bottom of the decarbonization tower, and the low-temperature semi-lean methanol solution drawn from the top of the low-pressure methanol tower 2 is sprayed into the tower from the top of the decarbonization tower; the CO2 gas and the methanol solution come into countercurrent contact in the tower, and the CO2 deep purification and pressure increase are completed simultaneously through the inherent pressure gradient of the methanol absorption-desorption process.

[0039] The operating temperature range of the decarbonization tower is: top temperature -20~-5℃, bottom temperature -10~+10℃, with a total temperature gradient not exceeding 30℃. The purity of the methanol solution entering the tower is ≥98.5wt%, and the inlet temperature is controlled between -25~-15℃. This avoids excessively high temperatures leading to decreased absorption efficiency or excessively low temperatures causing pipeline freezing. The methanol spray liquid-to-gas ratio within the decarbonization tower is controlled between 0.008 and 0.015m³. 3 / m 3 (Standard condition volume ratio); Recommended operating value: 0.010–0.012 m³ 3 / m 3 Under low-load conditions, the liquid-to-gas ratio should be appropriately increased to ensure decarbonization depth. Under 70%–90% low-load conditions, the liquid-to-gas ratio should be adjusted to 0.011–0.015m. 3 / m 3 To ensure the depth of decarbonization.

[0040] Step 3: Control the outlet pressure at the top of the decarbonization tower to be stable at 0.6 MPa, and ensure that the purity of the CO2 gas at the outlet is not less than 95 vol. The treated CO2 gas is directly sent to the bottom of the carbonization tower in the alkali treatment section through the connecting pipeline to participate in the carbonization reaction, and reacts countercurrently with ammonia brine to generate sodium bicarbonate slurry. No CO2 compressor or booster is installed throughout the process.

[0041] The bottom liquid level of the decarbonization tower is maintained within the range of 30% to 60%, and the normal operating liquid level is 40% to 50%. The allowable fluctuation range of the top outlet pressure is ±0.03MPa. Closed-loop control is achieved by using an outlet regulating valve in conjunction with a pressure transmitter, with a response time ≤10s.

[0042] The purity of CO2 gas fed into the carbonization tower of the soda ash plant is normally maintained between 95.0% and 98.5 vol, with a minimum allowable fluctuation of 93.0 vol for ≤30 minutes; under 100% full load, the CO2 gas volumetric flow rate at the decarbonization tower inlet is 15000–18000 Nm³. 3 / h, 10500~12600Nm at 70% load 3 / h.

[0043] The connecting pipeline between the decarbonization tower and the carbonization tower of the soda ash plant is equipped with a pneumatic emergency shut-off valve, a spring-loaded safety valve, a check valve, and a manual shut-off valve in sequence.

[0044] Step 4: The material discharged from the carbonation tower undergoes solid-liquid separation and calcination to obtain soda ash product, while the mother liquor is sent to the subsequent ammonium processing step.

[0045] The entire original compression system was dismantled, and a packed-type deep decarbonization tower was added between the No. 8 and No. 2 low-pressure towers, along with supporting piping, instrumentation, and insulation. The net investment for the renovation was 4.4 to 5.2 million yuan. Continuous operation tests were conducted under three load conditions: 100%, 90%, and 70%. The results are as follows: Operating condition 1: 100%.

[0046] Low-profile intake 80000Nm 3 / h, CO2 flow rate at the decarbonization tower inlet: 16500 Nm³ 3 / h; Tower top pressure 0.61MPa, temperature -12℃, methanol-to-gas ratio 0.011m³ / h. 3 / m 3 The liquid level at the bottom of the tower is 45±3%.

[0047] The CO2 purity at the decarbonization tower outlet was 97.3 vol, the CO2 purity at the carbonization tower inlet was 97.1 vol, and the pressure fluctuation was ±0.010 MPa.

[0048] The rate of high-quality soda ash was 91.5%; the newly added cooling capacity converted to electricity consumption was 6.2 kWh / t-soda ash; compared with the motor process, the electricity saving per ton of soda ash was 33.8 kWh, and the comprehensive energy consumption was 318 kgce / t-soda ash, a decrease of 17.4%; compared with the steam turbine process, the energy consumption decreased by 18.9%.

[0049] Operating condition 2: 90% load.

[0050] Low-pressure intake air volume 72000Nm 3 / h, CO2 flow rate at the decarbonization tower inlet: 14850 Nm³ 3 / h; Top pressure 0.60MPa, Top temperature -13℃; Methanol-to-gas ratio 0.011m 3 / m 3 The liquid level at the bottom of the tower is 44±2%.

[0051] Gas parameters: CO2 purity at the decarbonization tower outlet is 97.6 vol, and CO2 purity at the carbonization tower inlet is 97.4 vol; pressure fluctuation is ±0.010 MPa.

[0052] Products and Energy Consumption: The rate of high-quality soda ash was 92.0%; the electricity consumption of the newly added cooling capacity was 6.0 kWh / t-soda ash; the net electricity saving per ton of soda ash was 30.0 kWh compared to the motor process, and the comprehensive energy consumption of the system was 313 kgce / t-soda ash, a decrease of 18.7%; the comprehensive energy consumption of the turbine process decreased by 20.2%.

[0053] Operational verification: The system ran continuously and stably for 120 hours with no abnormalities in any parameters, verifying its stability under medium load.

[0054] Operating condition 3: 70% load.

[0055] Low-pressure intake air volume 56000 Nm 3 / h, CO2 flow rate at the decarbonization tower inlet: 11550 Nm³ 3 / h; Top pressure 0.60MPa, Top temperature -15℃; Methanol-to-gas ratio 0.012m 3 / m 3(Low load to increase volume while maintaining purity); bottom liquid level 40±2%.

[0056] Gas parameters: CO2 purity at the decarbonization tower outlet is 97.8 vol, and CO2 purity at the carbonization tower inlet is 97.6 vol; pressure fluctuation is ±0.015 MPa.

[0057] Products and Energy Consumption: The rate of high-quality soda ash was 92.3%; the electricity consumption of the newly added cooling capacity was 5.8 kWh / t-soda ash; the net electricity saving per ton of soda ash was 22.2 kWh compared to the motor process, and the comprehensive energy consumption of the system was 308 kgce / t-soda ash, a decrease of 20.0%; the comprehensive energy consumption of the turbine process decreased by 21.4%.

[0058] Operational verification: The system operated continuously and stably for more than 72 hours, with liquid level, pressure, and purity all meeting the standards, thus verifying its adaptability to a wide range of operating conditions.

[0059] The operating parameters and costs of Comparative Examples 1-2 and Example 1 are compared, and the comparison results are shown in Tables 1 and 2.

[0060] Table 1 Comparison of performance indicators between the comparative and example models under full load (100%)

[0061] As shown in Table 1, Example 1 only requires the addition of a deep decarbonization tower, with a one-time equipment investment of only 4.8 million yuan, which is 78.18% lower than the electric motor compression scheme and 82.86% lower than the steam turbine compression scheme. It eliminates the need for the entire set of supporting civil engineering and equipment for the compressor main unit, cooling, lubrication, and standby units, significantly reducing the amount of modification work. The traditional electric motor route consumes 40 kWh of electricity per ton of soda ash pressurization, while Example 1 only requires 6.2 kWh of electricity for cooling, resulting in a saving of 33.8 kWh per ton. The steam turbine route consumes 1.2 tons of medium-pressure steam to produce 1 ton of soda ash, but Example 1 completely eliminates steam consumption.

[0062] The annual energy cost of the electric motor solution is 5.44 million yuan, while that of the steam turbine solution is as high as 40.8 million yuan. Example 1 costs only 840,000 yuan per year, with annual energy costs decreasing by 84.56% and 97.94% respectively, demonstrating a strong long-term economic advantage.

[0063] The compressor suffers from continuous wear of impellers, seals, and valves, resulting in high annual maintenance and spare parts replacement costs. In Example 1, the static tower equipment has no high-speed rotating parts, and the annual maintenance cost is only 280,000 yuan, which is 82.5% and 87.27% lower than the two traditional solutions, respectively.

[0064] CO2 feed gas purity: The purity range of traditional compression process is 96.0-98.0 vol%. In Example 1, the stable measured purity was 97.1 vol. The decarbonization tower removes trace amounts of methanol and sulfide impurities in the gas phase through low-temperature methanol reverse washing, resulting in a higher lower limit of inlet gas purity and lower impurity content.

[0065] The yield of high-quality soda ash is as follows: the highest yield of high-quality soda ash produced by traditional processes is only 88%, while Example 1 shows a stable yield of 91.5%. The reduction of impurities significantly improves the conversion rate of carbonation reaction, and the quality of finished products is steadily upgraded.

[0066] Table 2 Operating parameters for three working conditions in Example 1

[0067] As shown in Table 2, the outlet pressure of the decarbonization tower remains stable at 0.60-0.61 MPa during the 70%-100% full load range of the unit. Only during the 70% low load condition does the pressure fluctuation slightly increase to ±0.015 MPa, and the fluctuation during full and medium loads is only ±0.010 MPa. This fully matches the 0.3-0.6 MPa inlet pressure requirement of the alkali carbonization tower, eliminating the need for frequent manual adjustments.

[0068] As the unit load decreases, the tower top operating temperature is simultaneously lowered to -15℃, while the methanol-to-gas ratio is slightly increased to 0.012m. 3 / m 3 This compensates for the decrease in gas-liquid contact efficiency under low load and ensures purification depth.

[0069] The bottom liquid level of the tower is stably controlled within the range of 40%~45% under full load, with fluctuations controlled within ±3%, avoiding the risk of liquid carrying due to excessively high liquid level and interruption of methanol circulation due to excessively low liquid level. The automatic control system has strong fault tolerance.

[0070] The lower the load, the higher the CO2 outlet purity: the purity at 70% low load reaches 97.8 vol%, corresponding to an increase in the rate of superior grade soda ash to 92.3%. The extended gas-liquid contact residence time under low load conditions allows for more thorough removal of trace sulfur and methanol droplets from the gas phase by low-temperature methanol, reduces interference from impurities in the carbonation reaction, improves the purity of sodium bicarbonate crystals, and results in a slight increase in the rate of superior grade finished products as the load decreases, creating a positive synergistic effect.

[0071] The overall cooling capacity of the low-temperature methanol wash is increased under low load, and the energy consumption per unit product is further reduced by allocating the cooling capacity required for self-pressurization of the decarbonization tower. It has the unique advantage of being more energy-efficient the more production is reduced, and is suitable for low-load intermittent production scenarios in chemical plants.

[0072] Therefore, the present invention adopts the above-mentioned method of direct coupling of low-temperature methanol washing decarbonization gas with soda ash production, which overcomes the defects of existing soda ash processes that rely on CO2 compressors, such as high investment, high energy consumption, cumbersome operation and maintenance, and low energy utilization. It provides a coupling process embedded in the low-temperature methanol washing process, which relies on the methanol absorption-desorption pressure gradient to simultaneously complete CO2 purification and self-pressurization, completely eliminating the need for compression equipment, reducing one-time investment and long-term operating costs, and improving the system's energy integration and the quality of soda ash products.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for producing soda ash from carbon gas by direct coupling at low temperature during methanol washing, characterized in that, Includes the following steps: Step 1: Add a deep decarbonization tower between the low-temperature methanol washing section's low-methanol 8 tower and low-methanol 2 tower. Step 2: The low-pressure CO2 flash vapor from the top outlet of the low-pressure methanol tower 8 is introduced from the bottom of the decarbonization tower, and the low-temperature semi-lean methanol solution drawn from the top of the low-pressure methanol tower 2 is sprayed into the tower from the top of the decarbonization tower; the CO2 gas and the methanol solution come into countercurrent contact in the tower, and the deep purification of CO2 and the pressure increase are completed simultaneously through the inherent pressure gradient of the methanol absorption-desorption process. Step 3: Control the outlet pressure at the top of the decarbonization tower to be stable at 0.6 MPa, and ensure that the purity of the CO2 gas at the outlet is not less than 95 vol; the treated CO2 gas is directly sent to the bottom of the carbonization tower in the alkali treatment section through the connecting pipeline to participate in the carbonization reaction, without the installation of a CO2 compressor or booster throughout the process.

2. The method for producing soda ash from low-temperature methanol by direct coupling of carbon gas and methanol washing according to claim 1, characterized in that: In step 1, the decarbonization tower adopts a packed tower or plate tower structure; the packed tower is equipped with two sections of packing, each section is 6.0m high, and a liquid collection and redistribution device is installed between the two sections; the plate tower is equipped with 32 layers of single overflow floating valve tower plates with a plate spacing of 500mm; a demister is installed at the top of the tower, and a tubular gas distributor is installed at the bottom of the tower.

3. The method for producing soda ash from low-temperature methanol by direct coupling of carbon gas and methanol washing according to claim 1, characterized in that: In step 1, the decarbonization tower is equipped with a matching automatic control system, which includes a tower top pressure control loop, a tower bottom liquid level control loop, a three-point temperature monitoring loop, a methanol mass metering loop, a CO2 flow metering loop, an ESD emergency shut-off loop, and a DCS system.

4. The method for producing soda ash from low-temperature methanol by direct coupling of carbon gas and methanol washing according to claim 1, characterized in that: In step 2, the operating temperature range of the decarbonization tower is: top temperature -20 to -5℃, bottom temperature -10 to +10℃, and the temperature gradient of the entire tower does not exceed 30℃; the purity of the methanol solution entering the decarbonization tower is ≥98.5wt%, and the temperature entering the decarbonization tower is controlled at -25 to -15℃.

5. The method for producing alkali directly by washing carbon gas at low temperature according to claim 1, characterized in that: In step 2, the methanol spray liquid-to-gas ratio in the decarbonization tower is controlled between 0.008 and 0.015 m³ / s. 3 / m 3 Under low-load conditions of 70%–90%, the liquid-to-gas ratio is adjusted to 0.011–0.015m. 3 / m 3 To ensure the depth of decarbonization.

6. The method for producing alkali by direct coupling of carbon gas from low-temperature methanol washing according to claim 1, characterized in that: In step 3, the liquid level at the bottom of the decarbonization tower is maintained within the range of 30% to 60% of the volume, and the normal operating liquid level is 40% to 50%; the allowable fluctuation range of the outlet pressure at the top of the decarbonization tower is ±0.03MPa.

7. The method for producing soda ash from low-temperature methanol by direct coupling of carbon gas and methanol washing according to claim 1, characterized in that: In step 3, the purity of the CO2 gas fed into the carbonization tower of the soda ash plant is normally maintained between 95.0% and 98.5 vol, with a minimum fluctuation of 93.0 vol% allowed for short periods of ≤30 minutes. At 100% full load, the CO2 gas volumetric flow rate at the inlet of the decarbonization tower is 15,000–18,000 Nm³. 3 / h.

8. The method for producing alkali directly by washing carbon gas at low temperature according to claim 1, characterized in that: In step 3, the connecting pipeline between the decarbonization tower and the carbonization tower of the soda ash plant is sequentially equipped with a pneumatic emergency shut-off valve, a spring-loaded safety valve, a check valve, and a manual shut-off valve.

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