Achieving efficient recovery of organic solvents - the liquid nitrogen cryogenic organic solvent recovery process

　　The treatment of volatile organic compounds (VOCs) in exhaust gas has always been a difficult problem in industrial production
.
The use of liquid nitrogen as a refrigerant for cryogenic organic solvent recovery can not only solve the problem of VOCs emission, but also save 70% to 80% of the solvent, which greatly saves costs
.
The liquid nitrogen cryogenic organic solvent recovery device developed by Linde (Shanghai) Industrial Gas Co.
, Ltd.
(hereinafter referred to as Linde Gas) was selected into the "Petrochemical Green Process Directory (2021 Edition) for its low cost, high process safety and environmental friendliness.
)"
.

　　Recycling instead of destroying efficient treatment of VOCs

　　There are more than 3,000 types of organic solvents currently in use.
Although the types vary widely, most of them are highly volatile, and the volatilized organic compounds are usually harmful to the human body and the environment
.
Therefore, whether VOCs can be effectively managed in production is an important part of the "health, safety and environment" (HSE) management of industrial production
.

　　In the early stage of VOCs treatment, the destruction technology of gas flame combustion or flameless catalytic combustion was mostly used to reduce the content of volatile organic solvents in the exhaust gas.
However, this type of technology is still not very friendly to the environment, and it also causes waste of raw materials
.
Soon, people began to study how to recycle organic solvents more effectively in production.
Liquid nitrogen cryogenic recycling technology is one of the more effective ones
.

　　The process uses liquid nitrogen to perform cryogenic condensation and freezing of organic waste gas, so that the organic matter to be removed reaches a condensed or frozen state and is separated from the gas
.
The organic solvent separated by condensation can be directly recycled, and the treated tail gas can be discharged up to the standard, which has both economic benefits and environmental protection needs
.
Linde Gas took a fancy to these advantages of this process, and developed and designed a complete set of liquid nitrogen cryogenic organic solvent recovery equipment to achieve efficient treatment of VOCs
.

　　Establish triple protection to solve ice jam problem

　　Liquid nitrogen as a refrigerant can provide a cryogenic temperature as low as -196°C, and can efficiently condense most volatile solvents
.
But at the same time, this feature is also a double-edged sword, which is easy to cause the problem of ice jam of the device during operation
.
In this regard, Linde Gas' liquid nitrogen cryogenic system, combined with process simulation and years of engineering experience, has established a triple defense system through fully automated operation
.

　　The first line of defense is pre-cooling and water removal before the cryogenic system
.
Linde Gas has installed 2 high-efficiency condensers in series, using the treated low-temperature exhaust gas or on-site chilled water for pre-cooling
.
At the same time, a mist eliminator is added to physically remove water through a dense grid to prevent liquid particles from being entrained downstream by the airflow, and completely "keep out" components that are not conducive to deep cooling
.

　　The second line of defense is to set up twin towers to ensure the flexible and continuous operation of the cryogenic system
.
The core of the complete set is 2 cooling towers selected according to the needs.
During the operation, the operation of 1 cooling tower with liquid nitrogen and 1 defrosting is always maintained
.
By monitoring the pressure difference changes in the two towers, the system automatically switches the modes of the two towers before the frost is serious in the cryogenic tower to ensure the continuous operation of the system and is always online
.

　　The third line of defense is the establishment of automatic emergency response devices
.
The system is equipped with two-way self-controlled nitrogen purging.
When a local ice block occurs, the ice can be melted in the shortest time, so that the system can be put into use again
.
At the same time, at the key temperature points of the system, Linde Gas has set up low temperature alarms, and adopts automatic control methods to prevent the system from being overcooled
.

　　Significant cost savings while taking into account environmental protection and safety

　　In addition to solving the ice plug problem of cryogenic devices, the liquid nitrogen cryogenic recovery process designed by Linde Gas also has good economic and ecological benefits
.
According to Linde Gas statistics, using this process can save 70% of the solvent consumption.
If it is used with nitrogen pressure regulation and reuse, the operating cost of the device is only about 100 yuan per day for electricity, which can be recovered in 1 to 2 years.
device cost
.

　　It is worth mentioning that the operating temperature of the cryogenic process of the device is in the range of -160℃~-30℃, which can recover most of the VOCs
.
After on-site testing, the emission concentration of VOCs in the process tail gas can be reduced to below 60 mg/m3, meeting the direct emission standard
.
At the same time, the device uses liquid nitrogen as the single refrigerant, and does not use other refrigerants that may be harmful to the environment, such as fluorine-containing compounds
.

　　In addition, the device belongs to the "unplugged" static equipment, with no noise, no by-products, and no risk of explosion, which can improve the process safety from the setting of the process route
.
At present, the process has taken root in the domestic market, and about 30 sets of devices are operating in chemical, pharmaceutical and other production enterprises.
The project with the longest running time has been in service for more than 10 years and is well recognized by customers
.