A hot potash striping device and method

Abstract

This invention provides a hot potassium alkali desorption device and method. The method involves passing a hot potassium alkali solution that has absorbed CO2 gas through a desorption tower, where it is heated by steam to desorb the CO2. The device includes a hot potassium alkali desorption tower, a reboiler at the bottom of the tower, an evaporator at the top of the tower, a steam compressor, and a steam / condensate flash tank. This application uses water as a medium to recover heat from the top of the tower in the evaporator. The generated steam is compressed, and the high-temperature, high-pressure steam is either directly fed into the bottom of the tower for stripping or indirectly fed into the reboiler for heating. Simultaneously, an acidic catalyst is used as packing material inside the tower to catalyze and accelerate CO2 desorption, reducing the energy consumption of hot potassium alkali desorption and decreasing the consumption of refrigerant at the top of the tower and the heat source consumption of the reboiler at the bottom of the tower.

Description

Technical Field

[0001] This invention belongs to the fields of coal chemical and petrochemical technology, and specifically relates to a thermal potassium alkali desorption device and method. Background Technology

[0002] Industrial production facilities such as coal chemical, ammonia synthesis, and conversion processes all involve CO2 absorption and purification of raw gas. Recovering CO2 from flue gas requires separating it from the flue gas through absorption and desorption. CO2 is generated during ethylene oxide production and needs to be separated from the recycle gas. Among various CO2 separation methods, solvent absorption is currently the most mature and cost-effective CO2 absorption and capture technology. The hot potassium carbonate decarbonation process uses a hot potassium carbonate solution as the absorbent to absorb carbon dioxide from the mixed gas and convert it into bicarbonate. The absorbed solution, under normal pressure, desorbs CO2 gas from the carbonate solvent through heating and stripping, regenerating the carbonate for recycling. Because the hot potassium carbonate decarbonation process is an inorganic absorption system, it is suitable for many applications, including flue gas CO2 capture, ammonia synthesis purification, and carbon dioxide removal from ethylene oxide reaction recycle gas, offering advantages such as stable solution properties and minimal solvent loss. CO2 desorption from the hot potassium carbonate solution requires high temperature and low pressure, necessitating a continuous input of heat. Currently, the main method involves passing hot potassium bicarbonate solution through a desorption tower under slightly negative or slightly positive pressure conditions for steam heating and desorption. The heat provided during desorption not only removes CO2 from the potassium bicarbonate solution but also heats some water, generating steam. The top of the tower contains not only CO2 but also a large amount of water vapor, altering the water balance within the tower and increasing desorption energy consumption.

[0003] In the prior art, CN108434995B discloses a membrane desorption scheme: adding nano-inorganic material particles, an active crosslinking agent, and a catalyst to a polydimethylsiloxane solution to carry out a crosslinking reaction to obtain a membrane solution; coating the membrane solution onto a substrate, and forming a membrane after solvent evaporation. This membrane is suitable for aqueous solution systems, achieving a reduction in desorption temperature to 70℃-90℃. This scheme still requires additional heat, but the heat level can be reduced, achieving a certain degree of energy consumption reduction. CN117531337A discloses an absorption and desorption device and method for producing ethylene oxide using the ethylene process. This method uses a heat pump in conjunction with an EO stripping tower and a carbonate desorption tower. However, it still suffers from the disadvantages of different operating pressures and reboiler temperatures between the two towers, requiring the heating steam to be compressed according to the highest steam level required by the reboilers in both towers. Therefore, the compressed steam is high, resulting in high energy consumption. Furthermore, it requires adding water to the carbonate desorption tower to maintain water balance, which also increases wastewater discharge.

[0004] Potassium bicarbonate desorption of CO2 is a physicochemical process that separates CO2 into a gaseous form by altering gas-liquid equilibrium conditions such as temperature and pressure. The industry commonly employs heating desorption by increasing temperature and decreasing pressure, using physical methods to enhance the desorption rate.

[0005] Therefore, the existing hot potassium alkali desorption system still suffers from high desorption energy consumption and poor desorption effect. A more energy-efficient solution is needed to address the problems of high energy consumption, water balance in the tower, and wastewater discharge in the existing technology. Summary of the Invention

[0006] To achieve the above objectives, the present invention provides a hot potassium alkali desorption method, which can better desorb carbon dioxide, improve the desorption rate, and improve the utilization rate of hot potassium alkali.

[0007] The present invention also provides a hot potassium alkali desorption device, which can make reasonable use of heat and reduce energy consumption.

[0008] This invention provides the following technical solution:

[0009] A hot potassium alkali desorption method involves passing a hot potassium alkali solution that has absorbed CO2 gas through a desorption tower, where the solution is heated with steam to desorb the CO2.

[0010] The hot potassium alkali solution, after desorbing CO2, is returned to the absorption unit to absorb CO2 gas again.

[0011] Preferably, the hot potassium alkali desorption tower is equipped with a catalyst in its bottom, the catalyst being a molecular sieve, specifically a silica-alumina molecular sieve. The silica-alumina molecular sieve can be one or more of type A, type X, type Y, ZSM-5, etc., with ZSM-5 type molecular sieve being preferred.

[0012] Preferably, the silica-alumina molecular sieve has been filtered through alkali metal ions (such as Na+). + K + Modified silica-alumina molecular sieves, removing H from them + Replaced with alkali metal ions (such as Na) + K + Alkali metal ion-modified silica-alumina molecular sieves can alter the acidic sites of molecular sieve catalysts, thereby enhancing the catalytic desorption capacity of CO2.

[0013] Preferably, the silica-alumina molecular sieve has been filtered through alkali metal ions (such as Na+). + K + Modified HZSM type silica-alumina molecular sieve.

[0014] Preferably, the hot potassium alkali desorption tower is also provided with packing material, preferably acidic packing material, such as silica-alumina molecular sieve packing.

[0015] The silica-aluminum molecular sieve can be placed in the gaps between plate packing materials, bundled into a package, and installed in the reboiler; alternatively, it can be fixed or installed using other methods. Ideally, the packing material should be completely submerged below the surface of the carbon dioxide absorbent solution in the reboiler. The packing height is preferably 1-2m, and the diameter of the packing package is slightly smaller than the diameter of the reboiler, with a cross-sectional area accounting for approximately 50%-80% of the reboiler's cross-sectional area.

[0016] Preferably, the operating pressure of the hot potassium alkali desorption tower is between -10kPa and 30kPa (gauge pressure), the temperature at the top of the tower is between 90℃ and 120℃, and the temperature difference between the top and bottom of the tower is between 5℃ and 20℃.

[0017] Preferably, the hot potassium alkali solution of the present invention is potassium carbonate and sodium carbonate containing some additives. Preferably, the hot potassium alkali solution may also contain additives, namely potassium vanadate or potassium borate, which are used to adjust the activity of the absorbent solvent.

[0018] The hot potassium alkali solution can be used for CO2 absorption during urea production, CO2 absorption during syngas conversion, and CO2 absorption in ethylene oxide plants.

[0019] The present invention also provides a hot potassium alkali desorption device, including a hot potassium alkali desorption tower, a reboiler at the bottom of the tower, an evaporator at the top of the tower, a steam compressor, and a steam / condensate flash tank.

[0020] The hot potassium alkali desorption tower is connected to a top evaporator, and a reboiler is connected to the bottom. The gas phase from the top of the hot potassium alkali desorption tower is cooled by the top evaporator and then separated into gas and liquid phases in a gas-liquid separator. The separated gas phase is sent to the tail gas treatment unit, while the liquid phase enters a steam / condensate flash tank as makeup water to regulate the system's water balance; the remaining liquid is discharged as wastewater. Steam from the top evaporator outlet enters the steam / condensate flash tank, and steam from the top of the flash tank enters a steam compressor. After compression, a portion enters the reboiler at the bottom of the hot potassium alkali desorption tower to provide heat, while the remaining portion directly enters the hot potassium alkali desorption tower to provide heat. The condensate at the bottom of the flash tank returns to the top evaporator for heat exchange with the gas phase from the top of the hot potassium alkali tower. The reboiler outlet is connected to the flash tank; the condensed compressed steam returns to the original system for circulation.

[0021] The gas phase at the top of the hot potassium alkali desorption tower enters the top evaporator and exchanges heat with the condensate in the steam / condensate flash tank. In the evaporator, the condensate is vaporized into steam. The steam compressor operates at a steam pressure between -60 kPa and 10 kPa, and the evaporation temperature is between 80°C and 105°C.

[0022] Steam from the evaporator outlet at the top of the tower enters the steam / condensate flash tank, where the pressure is between -60 kPa and 10 kPa and the flash temperature is between 50 and 90°C.

[0023] Steam from the top of the tank enters the steam compressor, which is either a centrifugal or screw compressor, preferably a screw compressor. The steam compression ratio is between 2 and 6, and the compressor outlet pressure is between 150 kPaG and 300 kPaG. The compressor compression ratio can be adjusted according to the reboiler temperature to ensure that the reboiler cycle has sufficient thermal driving force.

[0024] The steam from the compressor outlet is split into two streams. One stream enters the reboiler at the bottom of the column, indirectly supplying heat to the desorption column to promote CO2 desorption. The other stream enters the column bottom directly, directly supplying heat to the desorption column to promote CO2 desorption, while simultaneously introducing steam into the column to regulate the concentration of hot potassium alkali and the water balance of the desorption system. The distribution of the two steam streams is adjusted according to the liquid level at the bottom of the column and the concentration of hot potassium alkali. The reboiler outlet is connected to the inlet of the steam flash tank, and a condensate circulation pump is connected to the outlet pipeline of the steam / condensate flash tank.

[0025] Preferably, the reboiler return port is located above the packing material inside the hot potassium alkali desorption tower. After passing through the packing material, the liquid phase flows out from the tower bottom and into the reboiler. After passing through the packing material, the CO2 desorption temperature of the carbon dioxide absorbent decreases, and then it enters the reboiler to raise the temperature. The reboiler provides the heat required for desorption.

[0026] The beneficial effects of this invention are as follows:

[0027] First, by utilizing the characteristic that a large amount of steam evaporates at the top of the desorption tower, the heat of this steam is recovered and directly or indirectly input back into the desorption tower through a heat pump compressor to raise the temperature and pressure, thereby significantly reducing the energy consumption of the entire desorption process.

[0028] Second, by returning the condensate from the vapor buffer tank at the top of the tower to the steam buffer tank, where it is vaporized and compressed, and then directly inputting the compressed steam, the water balance inside the tower is regulated. This changes the way industrial production processes replenish the tower with demineralized water to regulate the water balance, thus reducing wastewater discharge.

[0029] Third, by adopting a catalytic desorption mode and adding a desorption catalyst to the bottom of the tower to change the desorption equilibrium, it can promote the desorption of CO2 by hot potassium alkali. The energy consumption for desorbing the same amount of hot potassium alkali solution is reduced by more than 10%. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the hot potassium alkali desorption device provided by the present invention.

[0031] The components include: ① hot potassium alkali desorption tower; ② steam compressor; ③ tower top evaporator; ④ steam / condensate flash tank; ⑤ condensate circulation pump; ⑥ reboiler; ⑧ desorption tower packing; ⑨ desorption catalyst; and ⑩ gas-liquid separator. Detailed Implementation

[0032] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0033] After Na + The modified HZSM-type molecular sieve catalyst is prepared by soaking HZSM-5 molecular sieve in sodium chloride, allowing sodium ions to exchange with hydrogen ions. Then, through washing, drying, and calcination, all hydrogen ions on the molecular sieve framework are replaced by sodium ions, thereby altering its catalytic performance. Other modified molecular sieves are prepared using the same method, only requiring the replacement of the type of molecular sieve or alkali metal salt to be modified.

[0034] A hot potassium alkali desorption device includes a hot potassium alkali desorption tower 1, a reboiler 6, a tower top evaporator 3, a steam compressor 2, and a steam / condensate flash tank 4.

[0035] The hot potassium alkali desorption tower 1 is connected to a top evaporator 3, and a reboiler 6 is connected to the bottom of the tower. The gas phase from the top of the hot potassium alkali desorption tower 1 is cooled by the top evaporator 3 and then undergoes gas-liquid separation in the gas-liquid separator 6. The gas phase obtained after separation is sent to the tail gas treatment unit, while the liquid phase enters a steam / condensate flash tank as makeup water to regulate the water balance in the system, and is partially discharged as wastewater. The steam from the top evaporator outlet enters a steam / condensate flash tank 4. The steam from the top of the steam / condensate flash tank enters a steam compressor. After compression, part of the steam enters the reboiler at the bottom of the hot potassium alkali desorption tower to provide heat, and the other part directly enters the hot potassium alkali desorption tower to provide heat. The condensate at the bottom of the steam / condensate flash tank returns to the top evaporator for heat exchange with the gas phase from the top of the hot potassium alkali tower. The reboiler bottom outlet is connected to the steam / condensate flash tank; the condensed compressed steam returns to the original system for circulation after becoming condensate.

[0036] The gas phase at the top of the hot potassium alkali desorption tower enters the top evaporator and exchanges heat with the condensate in the steam / condensate flash tank. In the evaporator, the condensate is vaporized into steam, with a steam pressure between -60 kPa and 10 kPa and an evaporation temperature between 80℃ and 105℃.

[0037] Steam from the evaporator outlet at the top of the tower enters the steam / condensate flash tank, with a pressure between -60 kPa and 10 kPa.

[0038] Steam from the top of the tank enters the steam compressor, which is either a centrifugal or screw compressor, preferably a screw compressor. The steam compression ratio is between 2 and 6, and the compressor outlet pressure is between 150 kPaG and 300 kPaG. The compressor compression ratio can be adjusted according to the reboiler temperature to ensure that the reboiler cycle has sufficient thermal driving force.

[0039] The steam from the compressor outlet is split into two streams. One stream enters the reboiler at the bottom of the column, indirectly supplying heat to the desorption column to promote CO2 desorption. The other stream enters the column bottom directly, directly supplying heat to the desorption column to promote CO2 desorption, while simultaneously introducing steam into the column to regulate the concentration of hot potassium alkali and the water balance of the desorption system. The distribution of the two steam streams is adjusted according to the liquid level at the bottom of the column and the concentration of hot potassium alkali. The reboiler outlet is connected to the inlet of the steam flash tank, and a condensate circulation pump is connected to the outlet pipeline of the steam / condensate flash tank.

[0040] Example 1

[0041] In this embodiment, the operating pressure of the hot potassium alkali desorption tower 1 is 25 kPa, and the temperature at the top of the tower is around 100°C. The gas phase at the top of the tower enters the top evaporator 3 to exchange heat with the condensate. In the top evaporator 3, the condensate is vaporized into steam, with a steam pressure of -80 kPa and an evaporation temperature of around 100°C.

[0042] The top evaporator is a BKM type, with the top vapor phase flowing through the tubes. To reduce the pressure drop of the top vapor phase, the tubes are single-pass. The condensate flows through the shell side, with condensate entering from the bottom and steam exiting from the top. The BKM type heat exchanger facilitates the separation of steam and water phases, preventing water phase from being carried into the steam compressor and affecting its operation. The steam from the evaporator outlet enters a steam / condensate flash tank at a pressure of -30 kPa. A wire mesh demister is installed at the top of the flash tank, and the pipeline connects to the compressor inlet. This pipeline is equipped with high-temperature steam tracing to prevent liquid condensation during transport. The compressor is a screw compressor with a steam compression ratio of 3 and an outlet pressure of 300 kPaG. A portion of the compressed steam is directly fed into the bottom of the column, serving as a direct heat source. This steam not only provides desorption heat but also helps regulate the water balance. The amount of steam directly fed into the bottom of the column can be adjusted according to the liquid level. Another portion of the compressed steam is fed into the reboiler in the tower bottom. After condensation and heat release in the reboiler, the condensate enters the flash tank for secondary flash evaporation.

[0043] The makeup water for the steam / condensate flash tank consists of two parts: one part is the condensate from the reboiler at the bottom of the column, and the other part is the condensate from the overhead steam. Part of this condensate is returned to the steam flash tank as makeup water, while the other part is sent externally. The water balance within the column is achieved through the path: overhead vapor → overhead tank condensate → steam flash tank condensate → steam evaporator → steam compressor → desorption tower bottom. This eliminates the need for the traditional method of adding demineralized water to the column to achieve water balance in industrial plants, thus reducing wastewater discharge.

[0044] In this embodiment, the hot potassium alkali desorption tower is equipped with catalytic desorption packing material in its bottom column. The packing material is treated with Na... + Modified HZSM molecular sieves can provide acidic sites. Under the condition that carbonates are present at these acidic sites, CO2 desorption is accelerated, reducing the energy consumption of desorption.

[0045] Example 2

[0046] The main difference between this embodiment and Embodiment 1 is that the operating pressure of the hot potassium alkali desorption tower 1 is 20 kPa, the top temperature is around 110°C, the process is the same as in Embodiment 1, and the molecular sieve is K... + Modified HZSM molecular sieve. In this embodiment, the same desorption effect is achieved, and the steam used in the reboiler is basically the same as in Example 1.

[0047] Example 3

[0048] The main difference between this embodiment and Example 1 is that the molecular sieve used is an unmodified molecular sieve with different pore sizes and different silica-to-alumina ratios, such as type A, type X, type Y, and type ZSM-5. The main difference from Example 1 is the molecular sieve used in the bottom packing; the bottom temperature remains unchanged, achieving the same hot potassium alkali desorption effect, but the bottom steam consumption is approximately 13% higher than in Example 1. Ordinary silica-alumina molecular sieves do not significantly promote hot potassium alkali desorption.

[0049] The above embodiments are merely illustrative examples and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom remain within the scope of this invention.

Claims

1. A method for thermal potassium alkali desorption, characterized in that, The hot potassium alkali solution that has absorbed CO2 gas is passed through a desorption tower, where it is heated by steam to desorb the CO2.

2. The desorption method according to claim 1, characterized in that, The hot potassium alkali desorption tower is equipped with a catalyst in its bottom, which is a molecular sieve, specifically a silica-alumina molecular sieve. Preferably, the silica-alumina molecular sieve is one or more of type A, type X, type Y, and ZSM-5, with ZSM-5 molecular sieve being the most preferred. Preferably, the silica-alumina molecular sieve is a silica-alumina molecular sieve modified with alkali metal ions, wherein the H... + Replaced with alkali metal ions; Preferably, the silica-alumina molecular sieve is an HZSM type silica-alumina molecular sieve modified with alkali metal ions; Preferably, the hot potassium alkali desorption tower is further provided with packing material; Preferably, the packing material is an acidic packing material, such as a silica-alumina molecular sieve.

3. The desorption method according to claim 1 or 2, characterized in that, The hot potassium alkali desorption tower operates at a pressure of -10kPa to 30kPa, with a top temperature of 90℃ to 120℃ and a temperature difference of 5℃ to 20℃ between the top and bottom of the tower. Preferably, the hot potassium alkali solution is potassium carbonate; Preferably, the hot potassium alkali solution may also contain additives, namely potassium vanadate or potassium borate; Preferably, the hot potassium alkali solution is used for CO2 absorption during urea production, CO2 absorption during syngas conversion, and CO2 absorption in ethylene oxide plants.

4. A thermal potassium alkali desorption device, characterized in that, This includes a hot potassium alkali desorption tower, a reboiler at the bottom of the tower, an evaporator at the top of the tower, a steam compressor, and a steam / condensate flash tank; The hot potassium alkali desorption tower is connected to a top evaporator, and the bottom of the tower is connected to a reboiler. The gas phase at the top of the hot potassium alkali desorption tower is cooled by the top evaporator and then separated into gas and liquid in a gas-liquid separator. The gas phase obtained after separation in the gas-liquid separator is sent to the tail gas treatment unit, and the liquid phase enters the steam / condensate flash tank as makeup water to adjust the water balance in the system. The liquid phase is sent out as wastewater. Steam from the evaporator outlet at the top of the tower enters the steam / condensate flash tank. Steam from the top of the flash tank then enters the steam compressor. After compression, a portion enters the reboiler at the bottom of the hot potassium alkali desorption tower to provide heat, while the remaining portion directly enters the hot potassium alkali desorption tower to provide heat. Condensate from the bottom of the flash tank returns to the evaporator at the top of the tower for heat exchange with the vapor phase at the top of the hot potassium alkali tower. The reboiler outlet is connected to the flash tank.

5. The apparatus according to claim 4, characterized in that, The gas phase at the top of the hot potassium alkali desorption tower enters the top evaporator and exchanges heat with the condensate in the steam / condensate flash tank. In the evaporator, the condensate is vaporized into steam. The steam compressor has a steam pressure between -60 kPa and 10 kPa and an evaporation temperature between 80℃ and 105℃. Preferably, the steam from the outlet of the evaporator at the top of the tower enters the steam / condensate flash tank, the pressure of the steam / condensate flash tank is between -60kPa and 10kPa, and the flash temperature is between 50 and 90°C; Preferably, the steam at the top of the tank enters a steam compressor, which is a centrifugal or screw compressor, preferably a screw compressor. The steam compression ratio is between 2 and 6, and the compressor outlet pressure is between 150 kPaG and 300 kPaG. The compressor compression ratio can be adjusted according to the reboiler temperature to ensure that the reboiler cycle has sufficient thermal driving force.

6. The apparatus according to claim 4, characterized in that, The reboiler return port is located above the packing material in the hot potassium alkali desorption tower. After passing through the packing material, the liquid phase flows out of the tower bottom and into the reboiler. After the hot potassium alkali solution passes through the packing material, the CO2 desorption temperature decreases, and then it enters the reboiler to raise the temperature. The reboiler provides the heat required for desorption.

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