Acid removal system for coal glycol

Abstract

The acid removal system comprises a shift gas washing tower, a medium-pressure flash tower, a CO2 desorption tower, an H2S concentration tower, an N2 gas stripping tower, a thermal regeneration tower, a methanol-water separation tower and a tail gas washing tower which are sequentially communicated through a first pipeline, the lower end of the shift gas washing tower is communicated with a shift gas pipe which is communicated with the top of the medium-pressure flash tower through a second pipeline, and the top of the shift gas washing tower is communicated with a PSA hydrogen production device through a third pipeline; the CO2 desorption tower is sequentially communicated with the compressor and the urea production part through a fourth pipeline; the comprehensive automation level of the acid removal device can be improved, and the operation labor intensity is reduced; the operation stability of the acid removal device is improved, and the standard deviation of each key process parameter is reduced.

Description

Technical Field

[0001] The utility model relates to an acid removal system for coal-to-ethylene glycol production. Background Art

[0002] The acid removal device includes absorption of raw gas, medium-pressure flashing of effective gas, low-pressure desorption of CO2 and nitrogen stripping, thermal regeneration, methanol-water separation, etc. Its production purposes are as follows: (1) Remove impurities such as CO2 and H2S in the shifted gas, and at the same time remove the saturated water brought in by the shifted gas to obtain qualified purified gas, which is sent to the liquid nitrogen washing and PSA hydrogen production devices. (2) Remove impurities such as CO2 and H2S in the unshifted gas, and at the same time remove the saturated water brought in by the shifted gas to obtain qualified purified gas, which is sent to the cryogenic separation device. (3) Concentrate the H2S fraction and provide a gas rich in H2S to the sulfur recovery process. (4) Analyze and provide qualified CO2 product gas for use in the urea process. (5) Recover methanol and return it to the system for reuse, and the wastewater is discharged after being treated qualified.

[0003] Controlling temperature, pressure, methanol circulation volume, and circulating methanol quality is crucial for the stable, efficient, and low-energy operation of acid stripping units, and represents a significant control challenge. Acid stripping is a physical absorption process. Increasing operating pressure increases the partial pressures of acid gases CO2 and H2S, enhancing absorption driving force and improving gas purity. It also enhances the absorption capacity of the methanol solution and reduces solution circulation volume. However, excessively high pressure increases dissolution losses of active gases such as CO and H2. The partial pressures of both acid gases and methanol vapor are functions of temperature. Decreasing temperature reduces the partial pressures, and low temperatures favor methanol absorption and reduce methanol losses. Under constant operating pressure and temperature, the solubility of acid gases remains essentially constant, increasing the liquid-to-gas ratio and facilitating component absorption. However, increasing the methanol circulation volume increases circulation power consumption and regeneration energy consumption, leading to increased methanol consumption. Therefore, the key control challenge for acid stripping units lies in optimizing the methanol circulation volume within the control system. While ensuring gas purity, selecting an appropriate liquid-to-gas ratio and properly matching the methanol circulation volume ensures solution absorption efficiency without excessively increasing energy consumption. Furthermore, each tower primarily utilizes a conventional PID control system. However, some PID parameters for liquid level and pressure are improperly set, leading to unstable control when material flow is disturbed. Manual adjustments are still primarily dependent on this control. Due to untimely or inappropriate adjustments, these adjustments result in significant fluctuations in indicators such as liquid level, temperature, and pressure, making it more difficult to adjust the associated towers, impacting the smooth operation of the unit and the effectiveness of gas purification. PID adjustments experience significant hysteresis and fluctuations, requiring operators to manually ensure relative system stability, resulting in high frequency and labor intensity. The entire unit and its associated units are multivariable coupled systems. During production operations, the strong coupling between variables must be overcome to maintain material and energy balances across units and within each unit. Process control based on manual experience is difficult to ensure smooth operation and energy conservation, and is therefore challenging to operate. Furthermore, due to varying operating habits among various work teams, control quality also varies. Utility Model Content

[0004] The technical problem to be solved by the utility model is to improve the comprehensive automation level of the acid desorption device and reduce the operating labor intensity; improve the operation stability of the acid desorption device and reduce the standard deviation of each key process parameter; on the basis of stable control of the acid desorption device, through "card edge" optimization, improve the energy utilization rate as much as possible, and reduce the unit product energy consumption of the device under the premise that the device has optimization space; realize the refined control of the acid desorption device, overcome the interference of load fluctuations, and ensure product quality.

[0005] In order to solve the above problems, the technical solution of the utility model is:

[0006] A glycolic acid removal system for coal - to - ethylene glycol production, comprising a shift gas scrubber, a medium - pressure flash tower, a CO₂ desorption tower, an H₂S concentration tower, an N₂ stripping tower, a thermal regeneration tower, a methanol - water separation tower, and a tail gas scrubber, which are connected in sequence through a first pipeline;

[0007] The lower end of the shift gas scrubber is connected to a shift gas pipe, and the shift gas pipe is connected to the top of the medium - pressure flash tower through a second pipeline. The top of the shift gas scrubber is connected to a PSA hydrogen production unit through a third pipeline;

[0008] The CO₂ desorption tower is connected to a compressor and a urea production section in sequence through a fourth pipeline;

[0009] The lower end of the H₂S concentration tower is connected to a liquid nitrogen wash unit and a cryogenic unit respectively through a fifth pipeline and a sixth pipeline. The top of the H₂S concentration tower is connected to the tail gas scrubber through a seventh pipeline, and the lower part of the top of the H₂S concentration tower is connected to the top of the N₂ stripping tower through an eighth pipeline;

[0010] The top of the thermal regeneration tower is connected to an acid gas desulfurization recovery unit through a ninth pipeline, and the lower end of the thermal regeneration tower is connected to the top of the methanol - water separation tower through a tenth pipeline;

[0011] The top and bottom of the tail gas scrubber are connected to a flare and a sewage treatment station respectively through a tenth pipeline and an eleventh pipeline.

[0012] It also includes an unshifted gas scrubber and a lean methanol tank; the bottom of the thermal regeneration tower is connected to the lean methanol tank and the unshifted gas scrubber in sequence through a twelfth pipeline. The unshifted gas pipe is connected to the lower end of the unshifted gas scrubber. The bottom of the unshifted gas scrubber is connected to the lower end of the shift gas scrubber through a thirteenth pipeline, and the top of the unshifted gas scrubber is connected to a purified gas cryogenic unit through a fourteenth pipeline.

[0013] It also includes a liquid delivery pump and a flowmeter installed on the first pipeline, the twelfth pipeline, and the thirteenth pipeline; a PID regulating valve and a pressure or flow sensor are installed on the second pipeline, the third pipeline, the fourth pipeline, the fifth pipeline, the sixth pipeline, the seventh pipeline, the eighth pipeline, and the tenth pipeline; the liquid delivery pump, the flowmeter, the PID regulating valve, and the pressure or flow sensor are connected to a DCS system.

[0014] The beneficial effects of the present utility model are as follows:

[0015] (1) Controlling the methanol circulation rate: Under the condition of changing production loads of shift gas and unshifted gas, matching an appropriate liquid - gas ratio to ensure that the qualities of purified gas, desorbed gas, and tail gas are qualified, and realizing the marginal consumption of methanol circulation rate.

[0016] (2)Control the temperature of the recycled methanol: By stably controlling the liquid level of the ammonia cooler, the stable evaporation refrigeration of the external cold source is achieved. By stably controlling the pressures of the medium-pressure flash tower and the CO2 desorption tower, the pressure-reducing desorption refrigeration of the rich methanol is achieved. By matching the conversion gas volume, the methanol circulation volume, and the stripping nitrogen gas volume, when the gas volume of the nitrogen gas from the liquid nitrogen wash increases sharply after adsorption regeneration, the deep-cooled nitrogen gas volume is adjusted to stably control the total nitrogen gas volume stripped in the H2S concentration tower, ensuring less H2S desorption, reducing the cold loss discharged to the tail gas scrubbing tower, enabling the thermal regeneration tower to desorb with less heat, simultaneously balancing the cold quantity exchange between the rich methanol and the lean methanol, reducing the temperature of the recycled methanol, and improving the absorption efficiency. In addition, by reasonably distributing the heat exchange of the tail gas, the cold quantity of the tail gas is recovered, the temperatures of the converted gas and the unconverted gas at the inlet of the scrubbing tower are stably controlled, and the condensation recovery of the methanol vapor in the tail gas of the thermal regeneration tower is improved.

[0017] (3)Control the purity and water content of the recovered methanol: When the water content of the methanol increases, the solubility of the acidic gas in the methanol decreases. To meet the purification purity requirements, increasing the circulation volume or reducing the temperature of the lean methanol causes an increase in energy consumption, and the increase in water also increases equipment corrosion. Under the conditions of feed fluctuations and steam pressure fluctuations, the bottom steam valve and the top reflux valve are adjusted to stably control the temperature of the methanol-water separation tower, forming a certain temperature gradient distribution from top to bottom in the tower, achieving high-quality recovery of methanol, reducing the methanol content in the discharged water, and achieving environmental protection emissions.

[0018] (4)Control the methanol content in the acid gas: By adjusting the pressure regulating valve for the acid gas to sulfur recovery, the pressure of the methanol thermal regeneration tower is stably controlled, and the bottom heating steam volume is optimized and adjusted. The temperatures of the top and bottom of the tower are stably controlled, reducing the entrainment of methanol vapor in the acid gas, reducing methanol losses, achieving stable control of the acid gas flow for sulfur recovery, and ensuring stable combustion of the incinerator. Brief Description of the Drawings

[0019] The following further describes the present utility model with reference to the drawings:

[0020] Figure 1 It is a structural schematic diagram of the present utility model.

[0021] In the figure: converted gas scrubbing tower 1, medium-pressure flash tower 2, CO2 desorption tower 3, H2S concentration tower 4, N2 stripping tower 5, thermal regeneration tower 6, methanol-water separation tower 7, tail gas scrubbing tower 8, unconverted gas scrubbing tower 9, lean methanol tank 10. Detailed Embodiment

[0022] The technical solutions in the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present utility model without creative efforts shall fall within the protection scope of the present utility model.

[0023] A glycol acid removal system for coal-to-ethylene glycol production includes a shift gas scrubber 1, a medium-pressure flash tower 2, a CO2 desorption tower 3, an H2S concentration tower 4, an N2 stripping tower 5, a thermal regeneration tower 6, a methanol-water separation tower 7, and a tail gas scrubber 8, which are connected in sequence through a first pipeline; the lower end of the shift gas scrubber 1 is connected to a shift gas pipe, and the shift gas pipe is connected to the top of the medium-pressure flash tower 2 through a second pipeline. The top of the shift gas scrubber 1 is connected to a PSA hydrogen production device through a third pipeline; the CO2 desorption tower 3 is connected to a compressor and a urea production section in sequence through a fourth pipeline; the lower end of the H2S concentration tower 4 is connected to a liquid nitrogen washing device and a cryogenic device respectively through a fifth pipeline and a sixth pipeline. The top of the H2S concentration tower 4 is connected to the tail gas scrubber 8 through a seventh pipeline, and the lower end of the top of the H2S concentration tower 4 is connected to the top of the N2 stripping tower 5 through an eighth pipeline; the top of the thermal regeneration tower 6 is connected to an acid gas desulfurization recovery device through a ninth pipeline, and the lower end of the thermal regeneration tower 6 is connected to the top of the methanol-water separation tower 7 through a tenth pipeline; the top and bottom of the tail gas scrubber 8 are connected to a flare and a sewage treatment station respectively through a tenth pipeline and an eleventh pipeline. It also includes an unchanged gas scrubber 9 and a lean methanol tank 10; the bottom of the thermal regeneration tower 6 is connected to the lean methanol tank 10 and the unchanged gas scrubber 9 in sequence through a twelfth pipeline. The unchanged gas pipe is connected to the lower end of the unchanged gas scrubber 9. The bottom of the unchanged gas scrubber 9 is connected to the lower end of the shift gas scrubber 1 through a thirteenth pipeline, and the top of the unchanged gas scrubber 9 is connected to a purified gas cryogenic device through a fourteenth pipeline. It also includes a liquid delivery pump and a flow meter installed on the first pipeline, the twelfth pipeline, and the thirteenth pipeline; a PID regulating valve and a pressure or flow sensor are installed on the second pipeline, the third pipeline, the fourth pipeline, the fifth pipeline, the sixth pipeline, the seventh pipeline, the eighth pipeline, and the tenth pipeline; the liquid delivery pump, the flow meter, the PID regulating valve, and the pressure or flow sensor are connected to a DCS system.

[0024] The working process of the present utility model is as follows: The acid removal process includes chemical operation units such as absorption of shift gas and unshifted gas, medium-pressure desorption of effective gas, low-pressure desorption, nitrogen stripping, and thermal regeneration. The shift feed gas contacts the sprayed lean methanol solution countercurrently in the shift gas scrubber 1, selectively removing acidic gases such as H2S, COS, and CO2 in the shift gas. The purified gas obtained at the top of the tower is sent to the downstream liquid nitrogen wash and PSA hydrogen production units after heat exchange. The rich methanol liquid obtained at the bottom of the tower is regenerated through a pressure reduction flash tower 2, a low-pressure nitrogen stripping tower 5, a thermal regeneration tower 6, a methanol-water separation tower 7, etc., and then stored in the lean methanol tank 10 and recycled. The gas separated by flashing in the medium-pressure flash tower 2 and the liquid nitrogen wash recycle hydrogen are pressurized by a recycle gas compressor and returned to the shift gas to recover useful gases. The flashed methanol enters the CO2 desorption tower 3. The CO2 product gas is desorbed at the top of the CO2 desorption tower 3 and sent to the urea production section after being compressed by a CO2 compressor. The rich methanol at the bottom of the CO2 desorption tower 3 enters the H2S concentration tower 4 and is stripped with molecular sieve nitrogen from the liquid nitrogen wash unit and the cryogenic unit to complete the concentration of H2S and COS and the regeneration of CO2 gas in the rich methanol liquid. The tail gas at the top of the tower goes to the tail gas scrubber 8, is washed with sewage and then sent to the flare. The rich methanol at the bottom of the tower enters the N2 stripping tower 5 after filtration and heat exchange, and is stripped with medium-pressure nitrogen to further desorb CO2 in the solution. The tail gas after stripping in the N2 stripping tower 5 enters the H2S concentration tower 4. The rich methanol liquid at the bottom of the tower enters the thermal regeneration tower 6 after being pressurized, filtered, and heat exchanged. The thermal regeneration tower 6 performs thermal regeneration of H2S and COS with steam. The higher-concentration acidic gas obtained at the top of the tower is sent to sulfur recovery and incineration after cooling. The lean methanol liquid obtained at the bottom of the tower enters the lean methanol tank 10 after heat exchange and temperature reduction, and then enters the scrubber 1 as an absorbent after further heat exchange and cooling to complete the methanol cycle. The methanol-water solution obtained from the acidic gas separation tank enters the middle of the methanol-water separation tower 7. A small amount of lean methanol coming out from the bottom of the thermal regeneration tower 6 is used as reflux liquid. The methanol-water separation tower 7 is heated with steam. The methanol vapor obtained at the top of the tower returns to the middle of the thermal regeneration tower 6. The methanol sewage obtained at the bottom of the tower meets the discharge standards and is used as the washing liquid for the tail gas scrubber 8 after heat exchange and temperature reduction. The unshifted feed gas contacts the sprayed lean methanol solution countercurrently in the unshifted gas scrubber 10, selectively removing acidic gases such as H2S, COS, and CO2 in the unshifted gas. The purified gas obtained at the top of the tower is sent to the downstream CO cryogenic separation unit after heat exchange. The rich methanol liquid obtained at the bottom of the tower is pressurized and sent to the lower tower of the shift gas scrubber 1. In the acid removal device, a heat exchange network composed of multiple heat exchangers is set up to ensure cold quantity balance.

[0025] The content described in the embodiments of this specification is only a list of the implementation forms of the utility model concept. The protection scope of the present utility model should not be regarded as limited to the specific forms stated in the embodiments. The protection scope of the present utility model also extends to equivalent technical means that can be conceived by those skilled in the art based on the utility model concept.

Claims

1. A glycolic acid removal system for coal-to-ethylene glycol, characterized in that: It includes a shift gas scrubber, a medium-pressure flash tower, a CO2 desorption tower, an H2S enrichment tower, an N2 stripping tower, a thermal regeneration tower, a methanol-water separation tower, and a tail gas scrubber that are connected in sequence through a first pipeline; The lower end of the shift gas scrubber is connected to a shift gas pipe, the shift gas pipe passes through the top of the medium-pressure flash tower through a second pipeline, and the top of the shift gas scrubber is connected to a PSA hydrogen production unit through a third pipeline; The CO2 desorption tower is connected to a compressor and a urea production section in sequence through a fourth pipeline; The lower end of the H2S enrichment tower is connected to a liquid nitrogen washing unit and a cryogenic unit respectively through a fifth pipeline and a sixth pipeline. The top of the H2S enrichment tower is connected to the tail gas scrubber through a seventh pipeline, and the lower end of the top of the H2S enrichment tower is connected to the top of the N2 stripping tower through an eighth pipeline; The top of the thermal regeneration tower is connected to an acid gas desulfurization recovery unit through a ninth pipeline, and the lower end of the thermal regeneration tower is connected to the top of the methanol-water separation tower through a tenth pipeline; The top and bottom of the tail gas scrubber are connected to a flare and a sewage treatment station through a tenth pipeline and an eleventh pipeline respectively.

2. The glycolic acid removal system for coal-to-ethylene glycol according to claim 1, characterized in that: It also includes a non-shift gas scrubber and a lean methanol tank; the bottom of the thermal regeneration tower is connected to the lean methanol tank and the non-shift gas scrubber in sequence through a twelfth pipeline. The non-shift gas pipe is connected to the lower end of the non-shift gas scrubber. The bottom of the non-shift gas scrubber is connected to the lower end of the shift gas scrubber through a thirteenth pipeline, and the top of the non-shift gas scrubber is connected to a purified gas to a cryogenic unit through a fourteenth pipeline.

3. A glycolic acid removal system for coal-to-ethylene glycol according to claim 2, characterized in that: It also includes that infusion pumps and flow meters are installed on the first pipeline, the twelfth pipeline, and the thirteenth pipeline; PID regulating valves and pressure or flow sensors are installed on the second pipeline, the third pipeline, the fourth pipeline, the fifth pipeline, the sixth pipeline, the seventh pipeline, the eighth pipeline, and the tenth pipeline; the infusion pumps, the flow meters, the PID regulating valves, and the pressure or flow sensors are connected to a DCS system.

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