DEEP-CONDENSATION VOCS RECOVERY SYSTEM USING AIR AS REFRIGERANT

Abstract

A high-efficiency low-cost deep-condensation VOCs recovery system uses air as refrigerant. The recovery system includes a gaseous air purification system, an air liquefaction system and a VOCs recovery cold box. The gaseous air purification system includes an air filter, a cold dryer and an air purifier; the air liquefaction system comprises an air compressor, an air storage tank, a turbo-expander and an air precooler. The VOCs recovery cold box includes a VOCs precooler, a VOCs condenser and a gas-liquid separator.

Claims

1. A deep-condensation VOCs recover system using air as refrigerant, comprising a gaseous air purification system, an air liquefaction system and a VOCs recovery cold box; the gaseous air purification system comprises an air filter, a cold dryer and an air purifier; the air liquefaction system comprises an air compressor, an air storage tank, a turbo-expander and an air precooler; he VOCs recovery cold box comprises a VOCs precooler, a VOCs condenser and a gas-liquid separator, the VOCs recovery cold box is provided with the air precooler and the turbo-expander, and the interlayer of the shell of the VOCs recovery cold box is filled with powder and vacuumized to achieve the purpose of heat insulation; the cooling medium of the VOCs is used as liquefied air to realize deep-condensation recovery of the VOCs gas; firstly, air enters the air filter to remove microparticles and impurities contained in the air; the outlet of the air filter is connected with the inlet of the air compressor, and the outlet of the air compressor is connected with the inlet of the air storage tank; and the preliminarily purified air is compressed by the air compressor and enters the air storage tank for storage.

2-4. (canceled)

5. The VOCs recovery system of claim 1, characterized in that the outlet of the air storage tank is connected with the inlet of the cold dryer, the outlet of the cold dryer is connected with the inlet of the air purifier, and the outlet of the air purifier is connected with the hot air inlet of the air precooler in the VOCs recovery cold box; and further purifying the preliminarily compressed air by the cold dryer and the air purifier to remove water vapor and impurity gas.

6. The VOCs recovery system of claim 5, characterized in that the hot air outlet of the air precooler is connected with the inlet of the turbo-expander, the outlet of the turbo-expander is connected with the air inlet of the VOCs condenser, and the air outlet of the VOCs condenser is connected with the cold air inlet of the air precooler; the precooled air is liquefied by the turbo-expander and then enters the VOCs condenser for heat exchange with VOCs gas, and enters the air precooler for heat exchange with hot air from the air purifier after heat exchange so as to realize cascade utilization of cooling capacity.

7. The VOCs recovery system of claim 1, characterized in that firstly, the VOCs gas enters the VOCs precooler to remove moisture in the VOCs gas; the outlet of the VOCs precooler is connected with the inlet of the VOCs condenser in the VOCs recovery cold box, and the outlet of the VOCs condenser is connected with the inlet of the gas-liquid separator; after removing water vapor, the dried VOCs gas enters the VOCs condenser in the VOCs recovery cold box and exchanges heat with liquid air, wherein the VOCs gas is condensed into a liquid state; and the gas-liquid mixture flows out from the outlet and enters the gas-liquid separator to separate liquid components in the gas-liquid mixture, and the gas enters the next process.

8. The VOCs recovery system of claim 7, characterized in that the gas outlet of the gas-liquid separator is connected with the inlet of the VOCs precooler; and the low-temperature up-to-standard tail gas flowing out from the VOCs recovery cold box is subjected to heat exchange again with the VOCs gas with higher concentration to achieve efficient use of energy, so the recovery cost is further reduced.

9. The VOCs recovery system of claim 7, characterized in that the VOCs precooler is a fin plate VOCs three-stream partition-wall precooler, two streams are VOCs channels, one stream is a liquefied air channel, the liquefied air channel is a microchannel with a diameter smaller than 1 mm, the VOCs channels are wide-size channels, the two streams of the VOCs channels work alternately, when one stream of VOCs is precooled, hot air is introduced into the VOCs channel of the other stream for purging, the two channels are alternately switched to work to ensure the continuous production.

10. The VOCs recovery system of claim 9, characterized in that the VOCs inlet and outlet of the VOCs precooler are symmetrically positioned on the left side and the right side of the precooler, and the liquefied air inlet and outlet are symmetrically distributed at the upper end and the lower end of the precooler; the VOCs gas in the VOCs precooler flows in cross flow with the liquefied air.

11. The VOCs recovery system of claim 1, characterized in that the VOCs recovery system comprises a microchannel mixer, the gas flowing out of the gas-liquid separator enters the microchannel mixer to be directly mixed with liquid air, the separated liquid components enter the storage tank to be stored, and low-temperature gas enters the next process.

12. The VOCs recovery system of claim 11, characterized in that the outlet of the air storage tank is connected with the inlet of the cold dryer, the outlet of the cold dryer is connected with the inlet of the air purifier, and the outlet of the air purifier is connected with the hot air inlet of the air precooler in the VOCs recovery cold box; and further purifying the preliminarily compressed air by the cold dryer and the air purifier to remove water vapor and impurity gas.

13. The VOCs recovery system of claim 12, characterized in that the hot air outlet of the air precooler is connected with the inlet of the turbo-expander, the outlet of the turbo-expander is connected with the air inlet of the VOCs condenser, and the air outlet of the VOCs condenser is connected with the cold air inlet of the air precooler; the precooled air is liquefied by the turbo-expander and then enters the VOCs condenser for heat exchange with VOCs gas, and enters the air precooler for heat exchange with hot air from the air purifier after heat exchange so as to realize cascade utilization of cooling capacity.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a flow chart of embodiment 1 of the present invention.

[0016] FIG. 2 is a schematic view showing the structure of the fin plate precooler of the present invention.

[0017] FIG. 3 is a flow chart of embodiment 2 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

[0018] The present invention will now be described in detail with reference to the drawings and specific embodiments. Obviously, the embodiments described are only a few, but not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by a person of ordinary skill in the art without involving any inventive effort are within the scope of the present invention.

[0019] As shown in FIG. 1, a VOCs recover system, comprises a gaseous air purification system, an air liquefaction system and a VOCs recovery cold box. The gaseous air purification system comprises an air filter 1, a cold dryer 4 and an air purifier 5; the air liquefaction system comprises an air compressor 2, an air storage tank 3, a turbo-expander 6 and an air precooler 8; the VOCs recovery cold box comprises a VOCs condenser 7, a VOCs precooler 9 and a gas-liquid separator 10.

[0020] When the system works, air at normal temperature and normal pressure enters the air filter 1 through a pipeline for primary filtration, and most dust and particles in the air are removed. The preliminarily purified air flows out from the outlet of the air filter 1 and enters the air compressor 2 to be preliminarily compressed, and the compressed air is conveyed to the air storage tank 3 to be buffered and stored. The outlet of the air storage tank 3 is connected with the cold dryer 4, compressed air with certain pressure and temperature enters the cold dryer 4 from the outlet of the air storage tank 3, moisture contained in the compressed air is removed, water vapor in the air is prevented from freezing in a subsequent process to cause channel blockage, and to affect the operation of the system. And the dried compressed air continues to enter the air purifier 5 along the pipeline to remove part of impurity gases such as hydrogen sulfide, sulfur dioxide and the like contained in the air and finish the final purification process. One part of the purified air enters an air bearing of the turbo-expander 6, the other part of the purified air enters the air precooler 8 for precooling, and the precooled high-pressure air enters the turbo-expander 6 to expand to be liquefied air. The liquefied air enters the VOCs condenser 7 and exchanges heat with the precooled VOCs gas to liquefy the VOCs gas. The temperature of the heat-exchanged air is still low, and if the heat-exchanged air directly enters the atmosphere, the cooling capacity is wasted. Therefore, the low-temperature air is introduced into the cold fluid channel of the air precooler 8, exchanges heat with the high-temperature and high-pressure air flowing out from the air purifier 5, precools the high-temperature and high-pressure air, and realizes the cascade utilization of the cooling capacity in the liquefied air. The heat-exchanged air can be directly discharged into the atmosphere or returned to the compressor to be compressed and liquefied again and recycled.

[0021] VOCs gas from the production link enters the VOCs precooler 9 firstly, is precooled to about 3° C. to 4° C. in the VOCs precooler 9, and water vapor contained is removed. The dried VOCs gas enters the VOCs condenser 7 along a pipeline and exchanges heat with liquefied air from the turbo-expander 6. In the VOCs condenser 7, the VOCs are cooled to −130° C. to −140° C. by liquefied air, after the non-methane total hydrocarbon content in the VOCs condenser 7 is reduced to 70-120 mg/m.sup.3, enters a gas-liquid separator 10, and the VOCs condensate is separated and conveyed to a storage tank for storage. And the purified low-temperature tail gas enters the precooler through the cold fluid inlet of the VOCs precooler 9 due to low temperature, performs primary heat exchange with the VOCs with high temperature, and then discharges into the atmosphere through the outlet of the VOCs precooler 9.

[0022] FIG. 2 is a schematic view showing the structure of the fin plate type VOCs precooler 9. The three-stream fin plate precooler, wherein the liquefied air channel is a microchannel with the diameter smaller than 1 mm, and the VOCs channel is a wide-size channel. 9-1 and 9-3 are VOCs gas inlets, 9-2 and 9-4 are VOCs outlets, 9-5 are purified air inlets, and 9-6 are air outlets. During operation, VOCs gas and low-temperature purified air enter the precooler from 9-1 and 9-5 respectively, after heat exchange is completed in the precooler, the air flows out from an outlet 9-6 above the precooler and enters the next process, and a VOCs gas-liquid mixture after water vapor removal flows out from an outlet 9-2 at the other end. After a period of operation, the channels between 9-1 and 9-2 need to be purged with hot air to prevent water vapor from freezing and blocking the precooler channels. At this time, the VOCs gas is introduced into the precooler from 9-3, and flows out from the outlet 9-4 after heat exchange. Therefore, switching is carried out, the two channels work alternately, and continuous production is guaranteed.

Example 2

[0023] In addition to the process adopted in embodiment 1, the gas separated by the gas-liquid separator can be further treated to reduce the VOCs content therein. As shown in FIG. 3, gas flowing out of the gas-liquid separator 10 enters the microchannel mixer 11 to be directly mixed with liquid air, separated liquid components enter a storage tank to be stored, and low-temperature gas enters the next process. In the present embodiment, the VOCs precooler and the air precooler may be identical or different in structure, but perform different functions. The other devices are the same as those in Embodiment 1 and will not be described in detail.