CN102895843A - System for recycling waste heat produced by methyl-diethanolamine (MDEA) decarburization process by using ultra high temperature heat pump - Google Patents

Abstract

The invention discloses a system for recovering the waste heat of the decarburization process by adopting an ultra-high temperature heat pump. In this system, the evaporator of the ultra-high temperature heat pump unit replaces the original cooling water to reduce the temperature of the lean liquid in the decarburization process to the required temperature, and the cooled lean liquid absorbs CO ₂ of the process gas; the condenser of the ultra-high temperature heat pump unit Replace the original high temperature steam. The ultra-high-temperature heat pump technology adopted in the present invention breaks through the technical bottleneck of the original high-temperature heat pump temperature limitation, and greatly expands the reuse range of low-temperature waste heat. The ultra-high temperature mixed working fluid is used, and the waste heat generated by the MDEA decarburization process is used to improve the energy quality, so as to meet the high temperature heat required for the regeneration of the MDEA decarburization solution. This system not only improves the energy utilization rate of the process, but also has good energy saving and economic effects.

Description

A system for recovering and utilizing waste heat of MDEA decarbonization process by using ultra-high temperature heat pump

technical field

The invention belongs to the technical field of heat pumps and decarbonization chemical processes, and in particular relates to a technology and a device for combined utilization of ultra-high temperature heat pumps and MDEA decarbonization processes.

Background technique

The energy consumption of synthetic ammonia accounts for 40% of the total chemical industry, and it is one of the five high-energy-consuming industries in my country's chemical industry. In the production of synthetic ammonia, the energy consumption of the decarbonization process is about 10% to 15% of the total energy consumption. Therefore, there is a lot of room for energy saving in the decarbonization process. Activated MDEA decarburization is a technology developed and industrialized by BASF abroad in the 1970s. This decarbonization process technology has the advantages of high purification, simultaneous desulfurization and decarburization, less loss of nitrogen and hydrogen, high purity of regenerated CO ₂ gas, less loss of solvent, and not easy to degrade. However, the MDEA decarbonization process is a high energy consumption process among many decarbonization processes. Compared with PSA, PC and other processes, the steam consumption and power consumption are all at a disadvantage. Under the background of energy saving and emission reduction, the energy consumption problem of MDEA decarbonization process needs to be solved urgently.

MDEA decarburization is realized by using the principle of MDEA solution to adsorb CO ₂ at low temperature and desorb CO ₂ at high temperature. Under low temperature conditions, the activated MDEA solution absorbs CO ₂ in the process gas, and the MDEA solution that absorbs CO ₂ is called rich liquid. Under the condition of high temperature, CO ₂ is separated from the MDEA solution, and the solution is regenerated at the same time, and the MDEA solution that releases CO ₂ is called lean solution. In order to achieve the required environmental conditions in the traditional process flow, cooling water is used to reduce the high-temperature rich liquid to the required temperature (about 80°C to 50°C-65°C), and the cooled MDEA solution absorbs CO ₂ of the process gas, Use high-temperature steam to heat the MDEA solution (from about 75°C to about 105°C) to regenerate it. In the original process, the cooling tower dissipates the heat in the cooling water to the air. Not only does it need to configure corresponding equipment, but it also needs to consume high-quality electric energy to realize the operation of the equipment. This part of the waste heat is not used, but it also needs to consume a lot of energy. ; In addition, in the process of regeneration of the MDEA solution, it is necessary to consume a large amount of primary energy to generate steam for heating the MDEA solution. This means that the MDEA decarbonization process not only consumes a lot of energy, but also the remaining heat has not been used reasonably and effectively.

How to make full and reasonable use of the waste heat in the MDEA decarbonization process, improve the energy quality, and reuse the high-quality heat generated in the MDEA decarbonization process is one of the ways that the MDEA decarbonization process should be actively explored. This not only greatly reduces the energy consumption of MDEA decarbonization, but also reduces environmental pollution and heat pollution. Heat pump technology is one of the effective technical means to achieve this purpose. The heat pump technology converts the waste heat of the MDEA decarbonization process into high-level energy, and the generated high-level energy heats the MDEA solution in the regeneration process, at the expense of consuming a small amount of high-grade energy (electrical energy, mechanical energy, etc.). This can not only replace the cooling tower and other equipment in the original process, make full use of the waste heat in the process, but also replace the original steam, reduce the consumption of fossil fuels such as coal, and indirectly improve the energy utilization rate of industrial processes. Generally speaking, the heat production temperature of high-temperature heat pumps is above 65°C but below 100°C. However, the high temperature required in the regeneration process of MDEA solution in this process is 105°C. Therefore, it is difficult for high-temperature heat pumps in the traditional sense to meet the requirements of this process.

Contents of the invention

In order to solve the problems existing in the prior art, the present invention provides a system that uses an ultra-high temperature heat pump to recover and utilize the waste heat of the MDEA decarbonization process, so as to solve the problem that the low-grade waste heat in the MDEA decarbonization process cannot be utilized and consumes a large amount of primary energy The resource waste problem of generating steam for heating MDEA solution.

Technical scheme of the present invention is as follows:

A system that uses ultra-high temperature heat pumps to recover and utilize waste heat from the MDEA decarburization process. It is mainly composed of two processes coupled with MDEA decarburization and ultra-high temperature heat pump working fluid:

(1) MDEA decarbonization process

The MDEA decarbonization process sequentially includes a circulation system composed of regeneration tower, condenser, evaporator, lean liquid pump, absorption tower, flash tower, and solution heat exchanger; the lean liquid regenerated in the regeneration tower (about 105°C) After entering the solution heat exchanger, part of the heat is released, and the cooled lean liquid (about 80°C) enters the evaporator again to release heat, and the lean liquid whose temperature has dropped to 50°C to 65°C is pressurized by the lean liquid pump and then enters the absorption tower. In the upper part, the lean liquid in the absorption tower absorbs CO ₂ in the process gas, and the MDEA solution that absorbs CO ₂ becomes a rich liquid; the rich liquid at the bottom of the absorption tower enters the upper part of the flash tower after decompression, and the liquid is mixed with the regeneration tower from top to bottom The steam and CO ₂ mixed gas are in countercurrent contact, absorbing the heat of the steam and CO ₂ mixed gas, and after passing through the packing layer, part of the CO ₂ in the rich liquid is decomposed, and the rich liquid becomes semi-lean liquid; the semi-lean liquid coming out of the flash tower The liquid is divided into two parts, most of the semi-poor liquid is pressurized and sent to the middle of the absorption tower, and the other part of the semi-poor liquid is pressurized and then enters the solution heat exchanger to recover the heat of part of the lean liquid; the heated semi-poor liquid enters the The upper part of the regeneration tower enters the condenser together with the bottom-up steam and CO ₂ mixed gas through the packing layer, absorbs heat in the condenser, and the temperature of the semi-lean liquid rises from about 75°C to about 105°C. The semi-poor solution is returned to the regeneration tower, and the CO ₂ in the solution is desorbed to become a poor solution for recycling;

(2) Ultra-high temperature heat pump working fluid process

The ultra-high temperature heat pump working fluid process mainly includes compressor, expansion valve, condenser, evaporator and ultra-high temperature heat pump working fluid; the high-temperature gaseous refrigerant expands through the expansion valve to reduce the pressure and temperature, and the low-temperature and low-pressure refrigerant enters the evaporator and absorbs The waste heat of the poor liquid is gasified, and the gasified low-pressure refrigerant enters the compressor to be compressed, and the refrigerant at the exhaust port of the compressor becomes a state of high temperature and high pressure. The MDEA decarburization solution in the regeneration process makes it meet the process requirements, and the liquefied refrigerant enters the expansion valve for cycle operation.

The high-temperature working medium is a mixed refrigerant BY-4. The product name is Beiyang 4# Refrigerant, and the manufacturer is Refrigerant Factory of Tianjin University.

In this system, the evaporator of the ultra-high temperature heat pump unit replaces the original cooling water to reduce the temperature of the lean liquid in the decarburization process to the required temperature, and the cooled lean liquid absorbs CO ₂ of the process gas; the condenser of the ultra-high temperature heat pump unit Replace the original high-temperature steam to meet the demand for high-quality heat in the regeneration process of MDEA solution.

The beneficial effects of the present invention are: the present invention proposes a system and device for recovering and utilizing waste heat of MDEA decarbonization process by using ultra-high temperature heat pump, and organically combines waste heat utilization and energy grade improvement technology with MDEA decarbonization process. In this system device, not only the low-temperature waste heat generated in the MDEA decarburization process is recovered, but also the energy quality of the waste heat is improved through the ultra-high temperature heat pump, and the high-grade heat generated meets the heat demand of the MDEA solution regeneration in the process. In this process, the ultra-high temperature heat pump has a high energy efficiency ratio (above 3.5). In general, it not only reduces the application of cooling water in the traditional process, but also reduces the heat pollution caused by waste heat discharged into the atmosphere. In addition, the high-temperature heat generated can be used for regeneration of MDEA solution, reducing the high-temperature steam in the original process. Therefore, the consumption of fossil fuels such as coal and the emission of a large amount of harmful gases caused by steam generation are reduced. This system not only improves the energy utilization rate of the process, but also has good energy saving and economic effects.

The ultra-high-temperature heat pump technology adopted in the present invention breaks through the technical bottleneck of the original high-temperature heat pump temperature limitation, and greatly expands the reuse range of low-temperature waste heat. The ultra-high temperature mixed working fluid is used, and the waste heat generated by the MDEA decarburization process is used to improve the energy quality, so as to meet the high temperature heat required for the regeneration of the MDEA decarburization solution.

Description of drawings

Fig. 1 is the process flow diagram of the system that adopts ultra-high temperature heat pump to recycle waste heat of MDEA decarburization process in the present invention;

Among them, 1—absorption tower; 2—flashing tower; 3—solution heat exchanger; 4—regeneration tower; 5—condenser; 6—compressor; 7—expansion valve; 8—evaporation device; 9——poor liquid pump.

Detailed ways

The system and device for recovering and utilizing the waste heat of the MDEA decarbonization process by the ultra-high temperature heat pump are used for an example analysis of the MDEA decarbonization process of an enterprise in Gansu, and combined with the system flow chart 1 for expression.

In this example, the lean liquid (105° C.) regenerated in the regeneration tower 4 enters the solution heat exchanger 3 to release part of the heat, and the temperature drops to 80° C. The lean liquid at 80°C enters the evaporator 8, and the temperature of the lean liquid in the evaporator 8 drops to 60°C, then the lean liquid returns to the inlet of the lean liquid pump 9, and enters the absorption tower 1 to absorb CO ₂ in the process gas, and the lean liquid becomes rich liquid. The rich liquid enters the flash tower 2 and contacts the steam and CO ₂ mixed gas in the regeneration tower 4 countercurrently to absorb heat, and the rich liquid passing through the flash tower 2 desorbs part of CO ₂ , and the rich liquid becomes a semi-poor liquid. The semi-poor liquid is divided into two parts, most of the semi-poor liquid is pressurized and sent to the middle of the absorption tower 1; the other part of the semi-poor liquid is pressurized and enters the solution heat exchanger 3 to absorb heat, and the semi-poor liquid after heating enters the regeneration The upper part of the tower 4 enters the condenser 5 together with the bottom-up steam and CO2 mixture. The semi-lean liquid enters the condenser 5 to absorb the heat of condensation, and the temperature rises from 75°C to 105°C. Then, the heated semi-poor solution is returned to the regeneration tower 4, and the CO ₂ in the solution is desorbed to become a poor solution for recycling. In this example, the ultra-high temperature heat pump unit is used to absorb the waste heat of the lean liquid, which reduces the circulating water volume of the cooling water in the original scheme, reduces the operating cost of the cooling water and equipment costs; the high-temperature heat generated at the condenser end of the unit is used to heat the regenerated MDEA Carbon solution replaces the heating of high-temperature steam in the original scheme.

The high-temperature and high-pressure refrigerant BY-4 enters the condenser 5, and the refrigerant in the condenser 5 liquefies and condenses to release heat to heat the semi-lean liquid in the MDEA decarburization process, and then the refrigerant BY-4 enters the expansion valve 7, where the expansion valve 7 The temperature and pressure of the medium refrigerant are reduced, and the low-temperature and low-pressure refrigerant BY-4 enters the evaporator 8, absorbs the heat of the lean liquid in the MDEA decarbonization process and is vaporized; the vaporized low-pressure refrigerant enters the compressor 6 for compression, The compressed high-pressure refrigerant enters the condenser to circulate.

In this scheme, the COP of the high temperature heat pump is conservatively set at 3.5, the flow rate of MDEA decarburization solution is 170m ³ /h, and the specific heat capacity is 1.29kcal/(kg·℃). It can be calculated that the waste heat of lean liquid is 4491.3kW, and the heat required for heating up when the MDEA decarburization solution is regenerated is 3725.17kW. According to the calculation that fully meets the heating heat demand of 3725.17kW for the process, a 1064KW heat pump unit needs to be established, and the heat pump needs to absorb 2660kW of waste heat, which can be obtained from The lean liquid cooling part absorbs about half of the heat. The annual economic benefits can reach more than 1 million yuan. In addition, there are also good environmental benefits and energy-saving effects. After conversion, it can save more than 2,200 tons of standard coal, reduce CO ₂ emissions by more than 4,900 tons, reduce SO ₂ emissions by more than 150 tons, and reduce NO _x emissions by more than 70 tons.

Generally speaking, the total amount of waste heat for cooling the lean liquid is relatively large, as long as part of the waste heat is absorbed from the lean liquid, it can meet the heat required for the process to heat up. Therefore, the unabsorbed lean liquid waste heat still needs to be cooled by cooling water, but the amount of cooling water is much smaller than that in the original process, thereby reducing the power consumption of cooling water circulation and reducing equipment costs such as cooling towers. In addition, the ultra-high temperature heat pump can also be used to utilize all the waste heat of the lean liquid, and part of the high-temperature heat generated is used for the heat demand of the MDEA solution regeneration, and the rich high-quality heat can also be used for heating, domestic hot water or other technological processes, etc. Save a lot of high-quality energy, reduce the emission of a large number of harmful gases and thermal pollution produced by the combustion of primary energy.

Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments, and the above-mentioned specific embodiments are only illustrative, rather than restrictive. Under the enlightenment of the present invention, without departing from the gist of the present invention and the protection scope of the claims, many modifications can be made, and these all belong to the protection of the present invention.

Claims (2)

1. a system that adopts the superhigh temperature heat pump to recycle MDEA decarbonization process waste heat is characterized in that, mainly is coupled to form by MDEA decarburization and two flow processs of superhigh temperature heat pump fluid:

(1) MDEA decarburization flow process

MDEA decarburization flow process comprises the circulatory system that regenerator, condenser, evaporimeter, lean pump, absorption tower, flash column, solution heat exchanger are interconnected and form successively; The lean solution of regenerating in regenerator enters solution heat exchanger, emits the part heat, and the lean solution after the cooling enters evaporimeter again, emits heat, then enters the top on absorption tower after the lean pump pressurization, the CO in the lean solution absorption technique gas in the absorption tower ₂, absorb CO ₂MDEA solution become rich solution; Enter the top of flash column after the rich solution decompression of absorption tower bottom, liquid from top to bottom with steam and the CO of regenerator ₂The gaseous mixture counter current contacting absorbs steam and CO ₂The heat of gaseous mixture, behind packing layer, the CO of part in the rich solution ₂Parse, rich solution becomes semi lean solution; The semi lean solution that goes out flash column is divided into two parts, wherein delivers to the middle part on absorption tower after most of semi lean solution pressurization, enters solution heat exchanger, the heat of recovery section lean solution after the pressurization of another part semi lean solution; Semi lean solution after the intensification enters the top of regenerator, through same steam and the CO from bottom to top of packing layer ₂Gaseous mixture enters into condenser together, absorbs heat in condenser, and the temperature of semi lean solution raises, and the semi lean solution after the intensification returns regenerator, parses the CO in the solution ₂, become lean solution, recycle;

(2) superhigh temperature heat pump fluid flow process

Superhigh temperature heat pump fluid flow process mainly comprises compressor, expansion valve, condenser, evaporimeter and superhigh temperature heat pump fluid; The high-temperature gas cold-producing medium expands and the reduction pressure and temperature through expansion valve, the cold-producing medium of low-temp low-pressure enters evaporimeter, absorb the waste heat of lean solution and gasify, the low pressure refrigerant of gasification enters compressor and compresses, the cold-producing medium of exhaust outlet of compressor becomes high-temperature high-pressure state, and the cold-producing medium of HTHP enters the condenser condenses heat release and liquefies the MDEA decarbonizing solution in the condensation heat thermal regeneration process, make it reach technological requirement, the cold-producing medium of liquefaction enters expansion valve circular flow again.

2. described employing superhigh temperature heat pump is recycled the system of MDEA decarbonization process waste heat according to claim 1, it is characterized in that, described high temperature refrigerant is mix refrigerant BY-4.

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