Heat pump system of low-temperature methanol washing heat regeneration tower

Abstract

The invention discloses a heat pump system of a low-temperature methanol washing heat regeneration tower. The cost can be reduced. A tower kettle liquid pump sends tower kettle liquid into a high-temperature flash tank, the saturation temperature in the tower kettle liquid flash process is reduced to be lower than the tower top gas temperature, after flash evaporation, a gas phase enters a high-temperature compression stage front demister, a liquid phase enters a high-temperature evaporator, the tower kettle liquid passing through the high-temperature evaporator absorbs heat to form a gas phase and a liquid phase, the gas phase part enters the high-temperature compression stage front demister, and the liquid phase part enters the high-temperature compression stage front demister. The liquid phase enters a low-temperature flash tank, the saturation temperature of the tower kettle liquid in the low-temperature flash tank is reduced again, the gas phase enters a low-temperature compression demister after flash evaporation, the liquid phase enters a spraying pump, and the material entering the spraying pump enters a sprayer after being pressurized; methanol steam demisted by the low-temperature compression stage front demister is compressed by the low-temperature compression stage, the saturation pressure is increased, the methanol steam is overheated and then enters the high-temperature compression demister, and a gas phase of the high-temperature compression stage front demister enters the high-temperature compression stage, is compressed and then converges with liquid of the spray thrower to return to the tower kettle.

Description

Technical Field

[0001] This invention relates to the field of low-temperature methanol washing process technology, and in particular to a low-temperature methanol washing thermal regeneration tower heat pump system. Background Technology

[0002] In the low-temperature methanol washing process, a thermal regeneration tower is used to recover methanol. Specifically, fresh steam is used as a heat source to heat the tower bottom to generate a gas phase. A multi-component mixture of methanol and acidic gas is discharged at the top of the tower, while a saturated liquid phase with a methanol mass fraction exceeding 99% is enriched in the tower bottom. To ensure the normal operation of the thermal regeneration tower, the gas mixture at the top of the tower needs to be exothermized, with most of the liquid condensed and returned to the tower, while the acidic gas and a small portion of the liquid are discharged.

[0003] Because the temperature at the bottom of the column is higher than that at the top, the heat at the top cannot spontaneously transfer to the bottom due to the second law of thermodynamics. The gas at the top needs to be cooled by cooling media such as cooling water, chilled water, or air. At the same time, fresh steam is continuously supplied to the bottom, and most of the heat of the fresh steam is indirectly carried away by the cooling media. This results in high energy consumption, and the column consumes a large amount of fresh steam. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a heat pump system for a low-temperature methanol washing and regeneration tower, which reduces the amount of fresh steam used in the low-temperature methanol washing and regeneration tower, reduces the amount of cooling water consumed, and reduces the power consumption of compression, thereby reducing costs.

[0005] The objective of this invention is achieved as follows: A low-temperature methanol washing and regeneration tower heat pump system includes a heat regeneration tower. The top material of the thermal regeneration tower is output in gas phase. The top material passes through a high-temperature evaporator and a low-temperature evaporator in sequence to extract part of the latent heat and part of the sensible heat of the top material. During this process, the gas phase top material releases heat and cools down, and part of it condenses. The top material flowing out of the low-temperature evaporator is in a gas-liquid two-phase state, and then enters the cooler together. The liquid in the bottom of the thermal regeneration tower is pumped into a high-temperature flash tank for flash evaporation to reduce temperature and pressure. After flash evaporation, the resulting saturated cryogenic liquid enters a high-temperature evaporator to absorb heat from the gaseous material at the top of the tower and evaporate. The resulting saturated cryogenic gas enters a high-temperature compression stage, the output of which is connected to a sprayer. The bottom material exiting the high-temperature evaporator is in a gas-liquid two-phase state and enters a high-temperature compression demister. The saturated gas obtained from the demister enters the high-temperature compression stage, and the resulting saturated liquid enters a cryogenic flash tank for flash evaporation to reduce pressure and temperature. After flash evaporation in the cryogenic flash tank, the resulting saturated cryogenic liquid enters a high-temperature compression stage. The low-temperature evaporator continues to absorb heat from the top material and evaporate it, resulting in saturated low-temperature gas that enters the low-temperature compression stage. The bottom material exiting the low-temperature evaporator is in a gas-liquid two-phase state. This bottom material passes through a low-temperature compression demister. The saturated gas obtained from the low-temperature compression demister enters the low-temperature compression stage, while the saturated liquid obtained from the low-temperature compression demister enters a spray pump for pressurization. The pressurized gas from the low-temperature compression stage then enters a high-temperature compression demister for further processing. The liquid exiting the spray pump flows into a sprayer, where it sprays and cools the gas exiting the high-temperature compression stage to eliminate overheating. The material after spraying is in a gas-liquid two-phase state and flows back to the bottom of the tower.

[0006] Preferably, the saturated cryogenic liquid and saturated cryogenic gas obtained from the high-temperature flash tank have the same temperature and are 3 to 7°C lower than the temperature of the material flowing out of the high-temperature evaporator at the top of the tower. The saturated cryogenic liquid and saturated cryogenic gas obtained from the cryogenic flash tank have the same temperature, and are 3 to 7°C lower than the temperature of the material flowing out of the cryogenic evaporator at the top of the tower.

[0007] Preferably, the saturation temperature corresponding to the gas pressure after being pressurized by the low-temperature compression stage is the same as the saturation temperature of the gas flowing out of the high-temperature evaporator.

[0008] Preferably, the saturation temperature corresponding to the gas pressure after compression in the high-temperature compression stage is 0.3 to 1.5°C higher than the temperature of the liquid in the bottom of the column, and the actual temperature of the pressurized gas is higher than the saturation temperature corresponding to the gas pressure, exhibiting a superheated state, with a superheat of 10 to 40 degrees Celsius.

[0009] Preferably, the ratio of heat release power of the top material in the high-temperature evaporator to that in the low-temperature evaporator is between 4:1 and 1:1.

[0010] Due to the adoption of the above technical solution, the present invention has the following beneficial effects: By utilizing the principle of heat pumps to supply heat from the top gas to the bottom gas, the amount of fresh steam used in the low-temperature methanol washing and regeneration tower is reduced, as is the amount of cooling water consumed. Two-stage evaporation and flash evaporation are used, which reduces the power consumption of compression. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the device in this patent. Attached Figure

[0012] In the attached diagram, 1 is the bottom liquid pump, 2 is the high-temperature flash tank, 3 is the high-temperature evaporator, 4 is the high-temperature compression demister, 5 is the high-temperature compression stage, 6 is the low-temperature flash tank, 7 is the low-temperature evaporator, 8 is the low-temperature compression demister, 9 is the low-temperature compression stage, 10 is the spray pump, and 11 is the sprayer. Detailed Implementation

[0013] This invention primarily addresses the problem that, due to the lower temperature at the top of the thermal regeneration tower compared to the bottom, the heat from the gas mixture at the top cannot be spontaneously transferred to the highly concentrated saturated methanol liquid accumulated in the bottom, thereby reducing the energy consumption of the thermal regeneration tower. A heat pump is a device that transfers heat energy from a low-temperature environment to a high-temperature environment. This problem can be solved using a heat pump device for a low-temperature methanol washing thermal regeneration tower. Aside from reducing steam and cooling water usage, no adjustments are needed to the existing thermal regeneration tower equipment and process.

[0014] This invention relates to a low-temperature methanol washing and regeneration tower heat pump system. The main equipment includes a tower bottom liquid pump, a high-temperature flash tank, a high-temperature evaporator, a high-temperature compression demister, a high-temperature compression stage, a low-temperature flash tank, a low-temperature evaporator, a low-temperature compression demister, a low-temperature compression stage, a spray pump, and a sprayer.

[0015] The bottom liquid pump delivers the bottom liquid to the high-temperature flash tank. During flash evaporation, the saturation temperature of the bottom liquid decreases below the temperature of the overhead gas. After flash evaporation, the gas phase enters the demister before the high-temperature compression stage, and the liquid phase enters the high-temperature evaporator. After passing through the high-temperature evaporator, the bottom liquid absorbs heat and forms a two-phase gas-liquid mixture. The gas phase enters the demister before the high-temperature compression stage, and the liquid phase enters the low-temperature flash tank. In the low-temperature flash tank, the saturation temperature of the bottom liquid decreases again. After flash evaporation, the gas phase enters the low-temperature compression demister, and the liquid phase enters the spray pump. Preferably, the material entering the spray pump is pressurized before entering the sprayer. The methanol vapor, after being demisted by the demister before the low-temperature compression stage, is compressed in the low-temperature compression stage, increasing its saturation pressure and carrying superheat, before entering the high-temperature compression demister. The gas phase from the demister before the high-temperature compression stage enters the high-temperature compression stage, is compressed, and then merges with the liquid from the sprayer back to the bottom of the column.

[0016] The invention will now be described clearly and completely with reference to the accompanying drawings.

[0017] like Figure 1As shown, this diagram illustrates the airflow direction, showing the chambers or channels formed by various components to accommodate the gas. The top material exits the thermal regeneration tower in a gaseous phase, referred to as top gas. This gas primarily consists of methanol, followed by acidic gases and non-condensable gases. The acidic gases are mainly H2S, CO2, and SO2, while the non-condensable gases are mainly N2. Due to its strong corrosiveness, it is not suitable for direct compression in the compressor. Part of the latent heat and sensible heat of the top gas are extracted through the high-temperature evaporator 3 and the low-temperature evaporator 7. The top material, acting as a heat source, flows sequentially through the high-temperature evaporator 3 and the low-temperature evaporator 7, releasing heat and cooling down during this process, with partial condensation. The top material exiting the low-temperature evaporator 7 is in a gas-liquid two-phase state, and then enters the original cooler (the existing technology cooler has been modified). The original process's reflux and acidic gas separation parameters remain unchanged. The ratio of heat release power of the top material in the high-temperature evaporator 3 to the low-temperature evaporator 7 is between 4:1 and 1:1. Because methanol is concentrated in the bottom of the column, with a methanol mass fraction generally greater than 99% and low corrosiveness, the bottom liquid is used as a cold source to absorb the latent and sensible heat of the overhead material. The bottom liquid is pumped by pump 1 into a high-temperature flash tank 2 for flash evaporation to cool and depressurize. After flash evaporation, the resulting saturated low-temperature liquid enters a high-temperature evaporator 3 to absorb heat from the overhead material and evaporate. The resulting saturated gas enters a high-temperature compression stage 5. Due to the single component, the saturated gas and saturated liquid have the same temperature during flash evaporation, which is 3 to 7°C lower than the temperature of the overhead material exiting the high-temperature evaporator 3. A portion of the total pumped liquid flow is used for evaporation and heat absorption, while the other portion is used to spray the compressed gas from the high-temperature compression stage 5. The spray volume ensures that the material remains in a vapor-liquid two-phase state after spraying. The principle of this stage of the process is that, since the original bottom liquid temperature is higher than the overhead gas temperature, flash evaporation lowers the bottom liquid temperature to the overhead gas temperature, allowing heat transfer to occur. The heat from the overhead gas is transferred to the bottom liquid, causing it to evaporate. The liquid material flowing out of the high-temperature evaporator 3 is in a gas-liquid two-phase state. This material passes through the high-temperature compression demister 4, and the saturated gas enters the high-temperature compression stage 5. The resulting saturated liquid enters the low-temperature flash tank 6 for flash evaporation to reduce pressure and temperature. After flash evaporation in the low-temperature flash tank 6, the resulting saturated low-temperature liquid enters the low-temperature evaporator 7 to absorb heat from the overhead material and evaporate. The resulting saturated gas enters the low-temperature compression stage 9. During flash evaporation, the saturated gas and saturated liquid have the same temperature, which is 3 to 7°C lower than the temperature of the overhead material exiting the low-temperature evaporator 7. The principle of this stage of the process is that, since the temperature of the bottom liquid is higher than the temperature of the overhead gas, flash evaporation lowers the temperature of the bottom liquid to the temperature of the overhead gas, allowing heat transfer to occur. The heat from the overhead gas is transferred to the bottom liquid, causing it to evaporate. The liquid material flowing out of the bottom of the low-temperature evaporator 7 is in a gas-liquid two-phase state. This material passes through the low-temperature compression demister 8, and the saturated gas enters the low-temperature compression stage 9. The resulting saturated liquid enters the spray pump 10 for pressurization. The saturation temperature corresponding to the gas pressure after pressurization by the low-temperature compression stage 9 is the same as the saturated gas temperature flowing out of the high-temperature evaporator 3. After being pressurized by the low-temperature compression stage 9, the gas enters the high-temperature compression demister 4 and merges with the gas flowing out of the high-temperature flash tank 2. It then enters the high-temperature compression stage 5 for further compression. The saturation temperature corresponding to the compressed gas pressure is 0.3 to 1.5°C higher than the bottom liquid temperature. The actual temperature of the pressurized gas is higher than the saturation temperature corresponding to the gas pressure, indicating a superheated state with a superheat of 10 to 40 degrees Celsius. The liquid flowing out of the spray pump 10 flows into the sprayer 11 to spray and cool the gas flowing out of the high-temperature compression stage 5, eliminating overheating. Due to the large amount of liquid sprayed, the material after spraying is in a gas-liquid two-phase state and flows back to the bottom of the tower. During implementation, the bottom liquid of the tower is used as a medium. The saturation temperature of the bottom liquid is lowered to below the temperature of the top gas to absorb the heat energy of the low-temperature top gas. The heat energy is transferred to the low-temperature bottom steam. The saturation temperature of the steam is then increased by a compressor and sent to the bottom, so that the heat energy of the original top gas is used for the high-temperature operation of the bottom. This process does not change the original reflux ratio of the regeneration tower, the composition of the top gas and bottom liquid, or the separation of the original acidic gas. By using a heat pump to use the heat energy of the low-temperature top gas for the high-temperature operation, the amount of fresh steam used is reduced, thus achieving energy saving.

[0018] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A low temperature methanol wash heat regeneration tower heat pump system, characterized in that: The heat regeneration tower comprises a heat regeneration tower, The tower top material outputting gas phase in the upper part of the heat regeneration tower passes through a high-temperature evaporator and a low-temperature evaporator in sequence to extract part of latent heat and part of sensible heat of the tower top material, in the process, the gas phase tower top material releases heat and cools down, and is partially condensed, and the tower top material flowing out of the low-temperature evaporator is in a gas-liquid two-phase state, and then enters a cooler together; The tower kettle liquid in the heat regeneration tower is sent into a high-temperature flash tank by a tower kettle liquid pump to be flashed to reduce temperature and pressure, the saturated low-temperature liquid obtained after the high-temperature flash tank is flashed enters a high-temperature evaporator to absorb heat of the gas phase tower top material and evaporate, the saturated low-temperature gas obtained enters a high-temperature compression stage, and the output end of the high-temperature compression stage is connected with a sprayer; the tower kettle material flowing out of the high-temperature evaporator is in a gas-liquid two-phase state, the tower kettle material enters a high-temperature compression demister, the saturated gas obtained by the high-temperature compression demister enters the high-temperature compression stage, and the saturated liquid obtained enters a low-temperature flash tank to be flashed to reduce temperature and pressure; the saturated low-temperature liquid obtained after the low-temperature flash tank is flashed enters a low-temperature evaporator to continue to absorb heat of the tower top material and evaporate, the saturated low-temperature gas obtained enters a low-temperature compression stage; the tower kettle material flowing out of the low-temperature evaporator is in a gas-liquid two-phase state, the tower kettle material passes through a low-temperature compression demister, the saturated gas obtained by the low-temperature compression demister enters the low-temperature compression stage, the saturated liquid obtained by the low-temperature compression demister enters a spray pump to be pressurized, the gas pressurized by the low-temperature compression stage enters the high-temperature compression demister to be treated; the liquid flowing out of the spray pump flows into the sprayer, and sprays and cools the gas flowing out of the high-temperature compression stage in the sprayer to eliminate overheating, the material after the spraying is in a gas-liquid two-phase state and returns to the tower kettle.

2. The low temperature methanol wash heat regeneration tower heat pump system according to claim 1, characterized in that: The saturated low-temperature liquid and the saturated low-temperature gas obtained by the high-temperature flash tank have the same temperature and are 3 to 7 ℃ lower than the temperature of the tower top material flowing out of the high-temperature evaporator; The saturated low-temperature liquid and the saturated low-temperature gas obtained by the low-temperature flash tank have the same temperature and are 3 to 7 ℃ lower than the temperature of the tower top material flowing out of the low-temperature evaporator.

3. The low temperature methanol wash heat regeneration tower heat pump system according to claim 1, characterized in that: The saturated temperature corresponding to the pressure of the gas pressurized by the low-temperature compression stage is the same as the saturated temperature of the gas flowing out of the high-temperature evaporator.

4. The low temperature methanol wash heat regeneration tower heat pump system according to claim 1, characterized in that: The saturated temperature corresponding to the pressure of the gas compressed by the high-temperature compression stage is 0.3 to 1.5 ℃ higher than the temperature of the tower kettle liquid, the actual temperature of the pressurized gas is higher than the saturated temperature corresponding to the pressure of the gas, and the pressurized gas is in a superheated state with a superheating degree of 10 to 40 degrees.

5. The low temperature methanol wash heat regeneration tower heat pump system according to claim 1, characterized in that: The ratio of the heat release power of the tower top material in the high-temperature evaporator to the heat release power of the tower top material in the low-temperature evaporator is between 4:1 and 1:1.

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