CN109157944B - Fractional cryogenic recovery system for VOCs (volatile organic compounds) of throttling expansion refrigeration - Google Patents
Fractional cryogenic recovery system for VOCs (volatile organic compounds) of throttling expansion refrigeration Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/002—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by condensation
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2257/00—Components to be removed
- B01D2257/70—Organic compounds not provided for in groups B01D2257/00 - B01D2257/602
- B01D2257/708—Volatile organic compounds V.O.C.'s
Abstract
The invention discloses a throttling expansion refrigeration VOCs grading cryogenic recovery system which comprises a refrigeration system, a primary precooling system, a secondary precooling defrosting system and a VOCs main heat exchange system. The cold energy of the process is comprehensively utilized to liquefy the circulating refrigeration working medium at normal temperature and medium pressure, and the circulating refrigeration working medium exchanges heat with the gas containing the VOCs after throttling expansion reaches cryogenic low temperature, so that the VOCs components are condensed and discharged. And the waste gas with low temperature and low VOCs content obtained after heat exchange is returned to the primary precooling system and the secondary precooling defrosting system, and the input gas is subjected to graded precooling by using cold energy. The treated gas containing VOCs meets the national emission standard and can be directly discharged into the atmosphere. Compared with the traditional condensation method, the method can greatly improve the energy utilization efficiency by cooling different components in the VOCs in a grading way, and has high efficiency, stability and low cost. Meanwhile, the method is not limited by the components and concentration of the source gas, and has wider application range and higher operation stability.
Description
Technical Field
The invention belongs to the field of volatile organic gas purification and separation, and particularly relates to a VOCs (volatile organic compounds) graded cryogenic recovery system for high-efficiency, stable and low-cost multi-stage separation and recovery of volatile organic gases.
Background
VOCs refer to Volatile Organic gases (Volatile Organic Compounds), which are common harmful waste gas sources in life and production processes and have non-negligible influence on human health and ecological environment. In the tail gas emission of industrial production, most of the tail gas contains VOCs components, the problems of low concentration, complex composition and the like generally exist, and how to treat the VOCs with energy conservation and high efficiency is an important research direction of the national energy conservation and emission reduction career.
At present, VOCs treatment technologies used in China mainly comprise a condensation method, an adsorption method, an absorption method, a combustion method, a membrane separation method, a biological treatment method and the like. Although some technologies such as adsorption, condensation, absorption, etc. have been widely applied and developed, there still exists some limitations, such as adsorption and absorption, although it has the advantages of good treatment effect, convenient operation, etc., most of the used collection media have the limit of repeated use and need to be replaced regularly; although the condensation method is not limited by the types of the VOCs components, the recovery cost is greatly increased if the condensation temperature is simply reduced or the adsorption times are increased for improving the recovery rate; the combustion method has higher requirements on gas component flammability, combustion environment, tail gas treatment and the like; the membrane separation method and the biological treatment technology are not completely mature, and are limited by conditions such as VOCs components and the like, so that the large-scale popularization and implementation are difficult. Therefore, in the face of the expanding industrial production scale, increasing VOCs treatment demand and increasing ecological and environmental requirements, improvements and optimizations must be made to increase the VOCs recovery efficiency based on the conventional recovery treatment method. Recently disclosed patents CN201812399160.6, CN201812324258.5, a VOC gas adsorber secondary heat return primary energy-saving system and method, all improve the technology of removing VOCs by adsorption method, and propose optimization from the perspective of dust removal separation and waste heat utilization, but still need to control the adsorption medium; CN201812399234.6 VOC organic waste gas treatment equipment combines a plasma technology and a spray absorption technology, greatly improves the removal effect, but still needs waste liquid treatment and VOCs recovery in the later period; CN 201812337298.3A catalytic combustion adsorption method and device, which adopts combustion method to have higher removal efficiency, but requires higher concentration of VOCs components; CN201812273279.9VOC biological gas purifier and purification method, no secondary pollution, high treatment efficiency, but can only remove part of VOCs components. The new open patents make optimization and innovation on the basis of the principle of the traditional treatment process, and the treatment efficiency of the VOCs is improved to a certain extent. Although the principle of the methods is simple, the technology is greatly improved compared with the prior art, the method still has the problems of limited application range and the like, and the processing technology still has a large optimization space.
The invention provides a method for separating and recycling VOCs by deep cooling in a grading way by using a throttling expansion process to achieve cryogenic low temperature based on a VOCs condensation collection principle in order to meet the waste gas treatment requirement in an industrial large-scale continuous production process and improve the recycling efficiency while reducing the recycling cost. Compared with the patent of invention previously granted by applicant (CN201512068202.4, a high-efficiency and low-cost VOC recovery system and method), the invention provides a plurality of innovation points: the former uses the process of cryogenic cooling by direct expansion of liquid nitrogen, and needs to be continuously input into the liquid nitrogen for refrigeration by a liquid nitrogen tank; the invention uses the cold quantity of the gaseous refrigerant obtained after expansion of the expander and throttling expansion of the expansion valve for precooling, and then uses the throttling expansion process to achieve cryogenic low temperature, thereby reducing the required power of devices such as a compressor and an expander, miniaturizing the devices, improving the space utilization rate, avoiding the need of continuously supplying the cooling refrigerant and reducing the production and operation cost of the system. In addition, the invention has a great difference with the earlier patent (CN128452632A, a VOCs recovery system using air deep cooling) of the applicant, and compared with the former patent, the flow design of the staged cooling provided by the invention can greatly improve the energy utilization rate and reduce the recovery cost of the process. The invention overcomes the defects and problems of the existing condensation collection technology, provides great innovation in principle, flow, equipment and operation method, improves the stability and high efficiency of system operation, can carry out condensation removal on most kinds of VOCs in the cryogenic low-temperature condensation process, and has wide application range.
Disclosure of Invention
The present invention has been compared with the prior art in the above background art. Aiming at the defects in the prior art, the invention aims to design a high-efficiency, stable and low-cost VOCs grading and deep-cooling recovery system and method. The refrigeration principle is that two compressors are respectively compressed to obtain high-pressure working medium, one part of the high-pressure working medium is used for direct expansion and precooling, and the other part of the high-pressure working medium is used for throttling expansion after precooling to obtain cryogenic low temperature: the second compressor compresses the refrigerant to raise the temperature, cools the refrigerant to about 20 ℃ after water cooling, enters a second precooling heat exchanger in the cold box to precool and cool the refrigerant, then expands the refrigerant by an expander to obtain low-temperature low-pressure gaseous refrigerant, and returns the refrigerant to the second precooling heat exchanger to provide cold energy for the heat exchange process; and the low-pressure normal-temperature refrigeration working medium after heat exchange is primarily compressed by a third compressor and then is introduced into a second storage tank, and the flow rate is controlled and then enters a second compressor for recycling. The first compressor compresses a refrigeration working medium for heating, cools the refrigeration working medium to about 12 ℃ after water cooling and precooling heat exchange, enters a second precooling heat exchanger in a cold box for precooling and cooling, the cooled low-temperature high-pressure liquid refrigeration working medium is throttled and expanded by an expansion valve to obtain a low-temperature low-pressure gaseous refrigeration working medium, the low-temperature low-pressure gaseous refrigeration working medium returns to the second precooling heat exchanger to provide cold energy for a heat exchange process, and the liquid refrigeration working medium enters a main heat exchanger to exchange heat with the gas containing VOCs; the low-temperature gaseous refrigerant at the outlet of the main heat exchanger enters the first precooling heat exchanger, the refrigerant is precooled by using the residual cold energy, the normal-temperature refrigerant after precooling and heat exchange and the gaseous refrigerant after throttling expansion and heat exchange are converged in the mixer and introduced into the first storage tank, and the flow is controlled and then enters the first compressor to start the refrigeration cycle again. The gas containing VOCs exchanges heat with the liquid refrigeration working medium in the main heat exchanger and can be deeply cooled to reach a lower temperature, so that the VOCs components in the gas are condensed and separated. And the low-temperature gas obtained after heat exchange and gas-liquid separation is returned to the primary precooling system and the secondary precooling defrosting system, and the newly input gas containing the VOCs is subjected to graded precooling by using cold energy. The treated gas containing VOCs meets the national emission standard and can be directly discharged into the atmosphere. Compared with the traditional condensation method, the method can greatly improve the energy utilization efficiency by carrying out graded cooling on different components in the gas containing the VOCs; the cold quantity of the gaseous refrigeration working medium obtained after expansion of the expansion machine and throttling expansion of the expansion valve is utilized for precooling, and the throttling expansion process is utilized to achieve cryogenic low temperature, so that the required power of equipment such as a compressor-expander is reduced, the space utilization rate is improved, and the production and operation cost is reduced; meanwhile, the method is not limited by the concentration and components of the source gas, and has wider application range and higher operation stability.
In order to achieve the purpose, the invention provides the following technical scheme:
a throttling expansion refrigeration VOCs grading cryogenic recovery system comprises a refrigeration system, a primary precooling system, a secondary precooling defrosting system, a VOCs main heat exchange system and a cold box. The primary precooling system, the secondary precooling defrosting system and the VOCs main heat exchange system are sequentially connected through a VOCs gas channel, and the airflow is precooled by using the cold energy of the airflow after the VOCs are removed by cooling.
The refrigeration system comprises a first compressor, a first cooler, a first precooling heat exchanger, a second precooling heat exchanger, an expansion valve, a first gas-liquid separator, a mixer, a first storage tank, a second compressor, a second cooler, an expander, a third compressor, a second storage tank, corresponding pipeline valves, monitoring instruments and other auxiliary devices. The first compressor and the second compressor are used for raising the temperature and the pressure of the refrigeration working medium; the first cooler and the second cooler are used for discharging heat of the high-temperature refrigeration working medium and cooling the high-temperature refrigeration working medium to normal temperature; the first precooling heat exchanger precools by using the cold energy of the low-temperature refrigerant at the outlet of the main heat exchanger; the second precooling heat exchanger precools the two strands of high-pressure normal-temperature refrigerant by utilizing the cold energy of the gaseous refrigerant after the expansion machine outlet and the expansion valve throttle expansion; the expansion valve is used for throttling and expanding the precooled low-temperature high-pressure liquid refrigerant to reach the required cryogenic low temperature; the first gas-liquid separator is used for separating gas and liquid of the throttled and expanded low-temperature and low-pressure mixed refrigerant, the gas is used for precooling the refrigerant, and the liquid is used for deeply cooling the VOCs components; the expansion machine is used for expanding and cooling the refrigeration working medium to provide precooling cold energy; the third compressor is used for recycling shaft work output by the expander and improving airflow pressure; the mixer is used for mixing the two strands of refrigeration working media and then conveying the mixture to a first storage tank; the first storage tank and the second storage tank are used for controlling circulation pressure and flow of a circulating refrigerant in the system, and are provided with a working medium supplementing pipeline used for supplementing a refrigerating working medium into the system according to needs.
The primary precooling system comprises a fan, a third precooling heat exchanger, a second gas-liquid separator, corresponding pipeline valves, monitoring instruments and other accessory devices. And the gas containing the VOCs is pumped by a fan and then enters a third precooling heat exchanger, exchanges heat with low-temperature return gas and then enters a second gas-liquid separator, water in gas components is condensed, separated and discharged, and the rest gas is input into a second-stage precooling defrosting system. In particular, the fan should be selected to meet the pressure drop requirement required by the stable operation of the system.
The secondary precooling defrosting system comprises two precooling heat exchangers, an electric three-way valve, corresponding pipelines, monitoring instruments and other auxiliary devices. The electric three-way valve is used for controlling a flow channel containing VOCs gas, switching the precooling heat exchangers when the frosting pressure drop in the channel is increased to reach a set critical pressure, controlling the air input and output processes at two ends of the two precooling heat exchangers, controlling the electric three-way valve to input hot air into the precooling heat exchangers after the VOCs gas is frosted in the precooling heat exchangers and stops being input, and purging and defrosting the equipment channel.
The VOCs main heat exchange system comprises a main heat exchanger, a third gas-liquid separator, a cryogenic pump, corresponding pipeline valves, monitoring instruments and other accessory devices. Particularly, the VOCs-containing gas is subjected to heat exchange and temperature reduction, and VOCs components are separated and removed, and then the gas is returned to a primary precooling system and a secondary precooling system, and the newly input VOCs gas is precooled by using airflow cold energy. Particularly, in a precooling heat exchanger and a main heat exchanger related in the VOCs grading recovery system, the VOCs-containing gas and the heat exchange working medium flow in a countercurrent manner.
The interior of the cold box comprises an expansion machine, a second precooling heat exchanger, an expansion valve, a first gas-liquid separator in a refrigeration system, a main heat exchanger, a third gas-liquid separator and a low-temperature pump in a VOCs main heat exchange system; particularly, the interlayer of the shell of the cold box is filled with pearly-lustre sand and vacuumized to reduce cold loss.
Further, in the primary precooling system and the secondary precooling defrosting system, the upper parts in the two gas-liquid separators are gas circulation layers, and the gas circulation layers are communicated with the next-stage heat exchange system through pipelines; the lower part is a condensate storage layer which is communicated with a pipeline and the output flow of the condensate is regulated by a control valve. According to the difference of the components and the content of VOCs processed by the system, a wire mesh can be additionally arranged near a gas outlet in the gas-liquid separator according to actual needs, so that the situation that liquid drops are taken away by gas flow or condensed liquid in the gas flow cannot be separated in time is prevented; particularly, if the boiling point of the VOCs components processed by the system is high, the situation that the VOCs gas components and water are condensed simultaneously in the second gas-liquid separator in the first-stage precooling system can occur, at the moment, the outlet of the second gas-liquid separator can be connected to a rough processing recovery point, and the condensate components are separated and recovered again.
Compared with the prior art, the invention has the beneficial effects that:
1. the refrigerating medium in the refrigerating system is recycled, continuous input of a cooling medium is not needed, the cryogenic low temperature is achieved by throttling expansion in the refrigerating process, the power of a required compressor and an required expander is small, the size of equipment is small, and the investment cost is low.
2. The cold energy of each link is comprehensively utilized in a multistage manner in the system flow, the low-temperature heat exchange process is completed in the cold box, the system has small cold loss, energy conservation and high efficiency, and the operation cost is greatly reduced.
3. The design of the two-stage precooling defrosting system can not only precool the gas containing the VOCs, improve the energy utilization rate of the system, but also carry out secondary cooling separation on residual moisture in the components of the gas flow, ensure that the influence of the moisture in the gas flow introduced into the next-stage heat exchange system is not required to be considered, and improve the recovery precision of the VOCs gas. And the two precooling heat exchangers defrost alternately, so that the safety and the stability of the system operation can be improved, and the equipment debugging and the maintenance are facilitated.
4. The recovery process and the recovery method are not limited by the conditions of concentration, components, flow and the like of the source gas, and are generally applicable to the waste gas recovery treatment link of industrial production.
Drawings
FIG. 1 is a flow chart of example 1 of the present invention.
Fig. 2 is a schematic flow diagram of a two-stage pre-cooling defrost system according to the present invention.
Detailed Description
The invention is described in detail below with reference to the drawings and specific examples. It is to be understood that the described embodiments are only a few, and not all, embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Fig. 1 is a schematic flow chart of a graded cryogenic recovery system for VOCs in embodiment 1, which includes a refrigeration system, a primary precooling system, a secondary precooling defrosting system, a primary heat exchange system for VOCs, and a cold box 22. The refrigerating system comprises a first compressor 1, a first cooler 2, a first precooling heat exchanger 3, a second precooling heat exchanger 4, an expansion valve 5, a first gas-liquid separator 6, a mixer 7, a first storage tank 8, a second compressor 9, a second cooler 10, an expansion machine 11, a third compressor 12 and a second storage tank 13; the primary precooling system comprises a fan 14, a third precooling heat exchanger 15 and a second gas-liquid separator 16; the secondary precooling defrosting system comprises a fourth precooling heat exchanger 17, a fifth precooling heat exchanger 18 and corresponding switching valves; the primary heat exchange system of the VOCs comprises a primary heat exchanger 19, a third gas-liquid separator 20 and a low-temperature pump 21.
In the embodiment, nitrogen is selected as the refrigeration working medium, when the system works, the second compressor 9 compresses the refrigeration working medium firstly to raise the temperature, the refrigeration working medium is cooled by water through the second cooler 10 to about 20 ℃, the refrigeration working medium enters the second precooling heat exchanger 4 in the cold box 22 to be precooled and cooled, then the expansion machine 11 expands the refrigeration working medium to obtain the low-temperature low-pressure gaseous refrigeration working medium, and the low-temperature low-pressure gaseous refrigeration working medium returns to the second precooling heat exchanger 4 to provide cold energy for the heat exchange process; the low-pressure normal-temperature refrigeration working medium after heat exchange is primarily compressed by a third compressor 12 and then is introduced into a second storage tank 13, and the low-pressure normal-temperature refrigeration working medium enters a second compressor 9 for recycling after flow control. The first compressor 1 pressurizes the refrigeration working medium to 5MPa, the obtained high-temperature high-pressure gaseous refrigeration working medium is introduced into the first cooler 2 to perform water-cooling heat exchange to about 20 ℃, the cooled normal-temperature high-pressure gaseous refrigeration working medium is introduced into the first precooling heat exchanger 3, and preliminary precooling is performed by using the cold energy of the refrigeration working medium at the lower temperature of the outlet of the main heat exchanger 19; the precooled gaseous high-pressure refrigerant is output by the first precooling heat exchanger 3 and then enters the second precooling heat exchanger 4, and the cold energy of the gaseous low-temperature low-pressure refrigerant obtained after the throttling expansion of the outlet of the expansion machine 11 and the expansion valve 5 is utilized for heat exchange and cooling. The high-pressure normal-temperature refrigerating working medium is converted into a high-pressure low-temperature liquid form after being subjected to heat exchange and cooling, is subjected to throttling expansion by an expansion valve 5, is cooled to about minus 170 ℃, and is introduced into a first gas-liquid separator 6. A liquid outlet of the first gas-liquid separator 6 conveys a cryogenic low-temperature liquid refrigerant into a main heat exchanger 19 in a VOCs main heat exchange system, and the cryogenic low-temperature liquid refrigerant exchanges heat with VOCs-containing gas to cool the gas to about minus 160 ℃, so that the VOCs components in the gas-liquid separator are subjected to cryogenic separation; the low-temperature refrigeration working medium which is output by the main heat exchanger 19 and is at the temperature of about minus 30 ℃ is introduced into the first precooling heat exchanger 3 to provide cold energy, and the cold energy is sent into the mixer 7 after heat exchange. And a gas outlet of the first gas-liquid separator 6 introduces the low-temperature gaseous refrigerant of-170 ℃ obtained after throttling expansion into the second precooling heat exchanger 4, provides cold energy for a precooling heat exchange process, and sends the cold energy into the mixer 7 after heat exchange. The mixer 7 mixes the two refrigerating working mediums and then conveys the mixture to the first storage tank 8, and the mixture enters the first compressor 1 for recycling after controlling the flow. A pressure detection device and a flow control device are arranged in the first storage tank 8 and the second storage tank 13, airflow parameters of the first compressor 1 and the second compressor 9 are regulated and controlled, and when the system is started and the pressure of gas circulation in the system is reduced, a refrigerating working medium is supplemented into the system through a supplementing working medium pipeline.
VOCs-containing gas from a production link is pumped by a fan 14, introduced into a third precooling heat exchanger 15, subjected to primary heat exchange with low-temperature return gas, cooled to 2-4 ℃, and introduced into a second gas-liquid separator 16 to condense and remove most of water in gas components. Introducing the separated gas into a No. four precooling heat exchanger 17, exchanging heat with low-temperature return gas, and cooling to about-27 ℃; if there is still residual moisture in the gas stream, frost will be removed from the main stream at this temperature. And introducing the gas containing the VOCs after secondary precooling into a main heat exchanger 19 in a cold box 22, exchanging heat with a low-temperature liquid refrigeration working medium to cool and condense the VOCs in the gas flow, and separating and discharging the gas in a third gas-liquid separator 20 to ensure that the VOCs content of the main gas flow reaches the national organic waste gas emission standard. And the low-temperature gas after heat exchange is output from the third gas-liquid separator 20, flows back and is introduced into the fourth precooling heat exchanger 17 and the third precooling heat exchanger 15, the gas containing VOCs to be treated and input into the recovery system is subjected to heat exchange and precooling by using airflow cold energy, and finally is discharged into the atmosphere from the outlet of the third precooling heat exchanger 15 to finish the heat exchange process.
Fig. 2 is a schematic flow diagram of a two-stage pre-cooling defrost system. When the system works, the gas containing VOCs after the previous stage of precooling is controlled by the electric three-way valve 23 to be input into the fourth precooling heat exchanger 17, is cooled to about minus 27 ℃ after exchanging heat with the low-temperature return gas, and is controlled by the electric three-way valve 24 to be conveyed to the VOCs main heat exchange system; the low-temperature return gas is controlled by an electric three-way valve 25 to be input into a No. four precooling heat exchanger 17, and is sent to a first-stage precooling system after exchanging heat with the gas containing VOCs. If residual moisture exists in the VOCs airflow, the residual moisture is condensed and attached to a channel of the No. four precooling heat exchanger 17 at the temperature, and when frost is formed, resistance is increased, pressure drop is increased and a design critical value is reached, the electric three- way valves 23, 24 and 25 automatically switch airflow passages: the VOCs-containing gas flow passes through an electric three-way valve 23 and then is introduced into a fifth precooling heat exchanger 18, exchanges heat with return gas and then is introduced into a VOCs main heat exchange system through an electric three-way valve 24; the low-temperature return gas is controlled by an electric three-way valve 25 to be introduced into the fifth precooling heat exchanger 18, exchanges heat with the gas containing VOCs and then is sent to the first-stage precooling system. At this time, no VOCs gas is input into the fourth precooling heat exchanger 17, the electric three- way valves 26 and 27 open a purge gas passage, the heat purger is introduced into the fourth precooling heat exchanger 17 for purging and defrosting, and the valve is closed after the defrosting operation is finished to stop the input of the heat purge gas. When frosting and pressurization in the fifth precooling heat exchanger 18 reach a critical value, the electric three- way valves 23, 24 and 25 switch the VOCs airflow passages again, precooling heat exchange operation is carried out in the fourth precooling heat exchanger 17, the electric three- way valves 26 and 27 are opened to blow and defrost the fifth precooling heat exchanger 18, and the two precooling heat exchangers work alternately in the switching manner, so that continuous and stable production is ensured.
The embodiments described above are to be considered as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein and are therefore intended to be embraced therein.
Claims (9)
1. The utility model provides a hierarchical cryrogenic recovery system of cryogenic VOCs of throttle expansion which characterized in that: comprises a cold box and four subsystems: the system comprises a refrigeration system, a primary precooling system, a secondary precooling defrosting system and a VOCs main heat exchange system;
the refrigeration system comprises a first compressor, a second compressor, a third compressor, an expander, a first cooler, a second cooler, a mixer, a first precooling heat exchanger, a second precooling heat exchanger, an expansion valve, a first gas-liquid separator, a first storage tank and a second storage tank; the outlet channel of the first compressor is sequentially connected with a first cooler, a first precooling heat exchanger, a second precooling heat exchanger, an expansion valve and a first gas-liquid separator; a liquid outlet of the first gas-liquid separator is sequentially connected with a main heat exchanger in the VOCs main heat exchange system, a first precooling heat exchanger of the refrigerating system and a mixer, and a gas outlet enters a second precooling heat exchanger and then is connected to the mixer; the mixer conveys the two flows to a first storage tank after mixing, and the two flows return to a first compressor from the first storage tank; an outlet channel of the second compressor is sequentially connected with a second cooler, a second precooling heat exchanger and an expander; and an outlet of the expansion machine is connected to a third compressor after being introduced into a second precooling heat exchanger, and is conveyed to a second storage tank after being compressed and returned to the second compressor by the second storage tank.
2. The staged cryogenic recovery system for VOCs cooled by throttling expansion according to claim 1, wherein: in the refrigeration system, the low-temperature refrigeration working medium obtained after expansion of the expansion machine and the low-temperature refrigeration working medium obtained after throttling expansion of the expansion valve at the gas outlet of the first gas-liquid separator provide cold energy, so that the high-pressure refrigeration working medium which is output by the first compressor and is cooled to the normal temperature by the first cooler and the high-pressure refrigeration working medium which is output by the second compressor and is cooled to the normal temperature by the second cooler are precooled and cooled in the second precooling heat exchanger; a pressure detection device and a flow control device are arranged in the first storage tank and the second storage tank, airflow parameters of the first compressor and the second compressor are regulated and controlled, and when the system is started and the pressure of gas circulation in the system is reduced, a refrigerating working medium is supplemented into the system through a supplementing working medium pipeline.
3. The staged cryogenic recovery system for VOCs cooled by throttling expansion according to claim 1, wherein: the primary precooling system comprises a fan, a third precooling heat exchanger and a second gas-liquid separator; and the gas containing the VOCs is pumped by a fan and then enters a third precooling heat exchanger, exchanges heat with low-temperature return gas and then enters a second gas-liquid separator, water in gas components is condensed, separated and discharged, and the rest gas is input into a second-stage precooling defrosting system.
4. The staged cryogenic recovery system for VOCs cooled by throttling expansion according to claim 1, wherein: the secondary precooling defrosting system comprises two precooling heat exchangers, and an electric valve controls the switching of the ventilation pipeline, so that one precooling heat exchanger is ensured to be in an operating state; the joints of the two precooling heat exchangers are connected with a hot air input pipeline and an emptying pipeline, so that the defrosting and the maintenance of the equipment are facilitated.
5. The staged cryogenic recovery system for VOCs cooled by throttling expansion according to claim 4, wherein: when the secondary precooling defrosting system normally works, the gas containing VOCs after the primary precooling treatment and the low-temperature return gas exchange heat only in one precooling heat exchanger, and the gas is conveyed to the primary VOCs heat exchange system; when the pressure drop is increased due to frosting in the channel in the running process, the electric valve automatically switches the pipeline channel after the critical pressure is set, the gas containing the VOCs is introduced into another precooling heat exchanger for heat exchange and precooling, and hot air is introduced into the frosting precooling heat exchanger which stops air flow conveying for blowing and defrosting.
6. The staged cryogenic recovery system for VOCs cooled by throttling expansion according to claim 1, wherein: the VOCs main heat exchange system comprises a main heat exchanger, a third gas-liquid separator and a low-temperature pump; the outlet of the main heat exchanger is connected with the inlet of a third gas-liquid separator, the gas outlet of the third gas-liquid separator is connected with the backflow gas inlets of two precooling heat exchangers in the secondary precooling defrosting system, and the liquid outlet of the third gas-liquid separator is connected with a low-temperature pump and outputs VOCs condensate to the outside of the system.
7. The staged cryogenic recovery system for VOCs cooled by throttling expansion according to claim 1, wherein: the interior of the cold box comprises an expansion machine, a second precooling heat exchanger, an expansion valve, a first gas-liquid separator and a main heat exchanger of a VOCs main heat exchange system, a third gas-liquid separator, a low-temperature pump and corresponding heat-preservation pipeline valves in a refrigeration system; the interlayer of the shell of the cold box is filled with pearly-lustre sand and vacuumized to reduce cold loss.
8. The staged cryogenic recovery system for VOCs cooled by throttling expansion according to claim 1, wherein: the primary precooling system, the secondary precooling defrosting system and the VOCs main heat exchange system are sequentially connected through a VOCs gas channel, and the gas is subjected to graded cooling to remove VOCs and then is returned to be sent to the secondary precooling defrosting system and the primary precooling system, so that the gas newly input into the system is precooled by using the cold energy of the gas; in all the precooling heat exchangers and the main heat exchanger, cold and hot fluids flow in a countercurrent mode.
9. A staged cryogenic recovery system for VOCs with throttling expansion refrigeration according to any one of claims 1 to 8, wherein: in the refrigeration system, the primary precooling system and the secondary precooling defrosting system, the upper parts in the three gas-liquid separators are gas circulation layers, and a precooling heat exchanger communicated with the next link through a pipeline is arranged; the lower part is a condensate storage layer which is communicated with a pipeline and the output flow of the condensate is regulated by a control valve; the silk screen is additionally arranged near the gas outlet in the gas-liquid separator, so that the condition that liquid drops are taken away by the gas flow or condensed liquid in the gas flow cannot be separated in time is prevented.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201811221895.6A CN109157944B (en) | 2018-10-19 | 2018-10-19 | Fractional cryogenic recovery system for VOCs (volatile organic compounds) of throttling expansion refrigeration |
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| CN109646984A (en) * | 2019-01-17 | 2019-04-19 | 南京工业大学 | A kind of VOCs multistage cooling recovery system having cold storage function |
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| CN113398903B (en) * | 2021-06-16 | 2022-10-04 | 山东鹏达生态科技股份有限公司 | Desorption-recovery device and process for clean and efficient adsorption material of waste gas |
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| CN115371455B (en) * | 2022-07-21 | 2023-03-10 | 瑞燃(上海)环境工程技术有限公司 | Heat insulation structure and heat insulation method for liquid nitrogen heat exchange equipment |
| CN116571226B (en) * | 2023-07-13 | 2023-10-13 | 山东鹏达生态科技股份有限公司 | Continuous operation device and process for desorbing and recycling VOCs (volatile organic compounds) adsorption material |
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