With the vigorous economic development, the pollution of the atmospheric environment has become more and more serious, and energy conservation and environmental protection have become the dominant trend in the 21st century. The problem of volatile organic compounds (VOCs) emissions from the oil refining and petrochemical, chemical raw materials and chemical product manufacturing, chemical raw materials, pharmaceutical manufacturing, synthetic fiber manufacturing, surface coating and printing industries, and the pollution of VOCs must be comprehensively treated. Reducing total emissions and effectively improving the ambient air quality in districts and cities has become the top priority of environmental protection tasks. Therefore, the fully automatic, multi-functional integrated closed-loop liquid ring compressor unit will play an increasingly prominent role in reducing the total emissions of VOCs. EVP vacuum can provide a highly efficient and energy-saving closed-loop liquid ring compressor unit. Become an indispensable focus.
VOCs and liquid ring compressors
1.VOCs is the abbreviation of Volatile Organic Compounds, which refers to volatile organic compounds with a boiling point of 50-260°C and a saturated vapor pressure of> 133.3 Pa at room temperature. The main components are hydrocarbon compounds and sulfur compounds. VOCs react with NO in the atmosphere to generate O3, which can form photochemical smog, accompanied by peculiar smells and malodors, which have a stimulating effect on human perception, nose and respiratory tract, and have a stimulating effect on the heart, lungs, liver and other internal organs and nerves. The system produces harmful effects, and some are the sources of allergies that affect certain organs and organisms of the human body, and even cause acute and chronic poisoning, which can cause cancer and mutation, and can also lead to reduced crop yields. Therefore, the treatment of VOCs has received more and more attention from various countries, and many developed countries have issued corresponding laws and regulations to limit the emission of VOCs.
2.The Liquid ring compressor‘characteristics：The impeller of the liquid ring compressor is eccentrically installed in a close to circular system. When the impeller rotates, the liquid injected into the aggregate forms a rotating liquid ring due to the centrifugal force. A crescent-shaped space is formed between the impeller wheels, and the volume of each crescent-shaped cavity periodically expands and shrinks with the rotation of the impeller, so as to achieve the process of inhaling and compressing gas. When the exhaust port pressure reaches the system back pressure, the gas is discharged. The gas compression process is almost an isothermal compression process, which is especially suitable for pumping flammable and explosive gases. The liquid ring compressor can use different working fluids for pumping different media. , Use different metal materials to meet different media requirements. Liquid ring compressors are divided into cone type and flat disc type. Since the distributor of the cone compressor can only be made into a rigid exhaust port, it cannot meet the requirements of different compression ratios. When the discharge pressure or inlet pressure changes, the compressor’s air volume will be greatly reduced, and the efficiency will therefore be lower. The flat disc compressor is equipped with a flexible valve plate on the exhaust port, which is a flexible exhaust port. When the exhaust pressure or the inlet pressure changes, the exhaust angle of the exhaust port can automatically change, so that the flat disk compressor is When working under different compression ratios, they all have higher efficiency. Because the liquid ring compressor only has impeller and shaft rotating parts, it is easy to assemble and disassemble with fewer parts, simple operation, and basically maintenance-free.
3.Application of liquid ring compressors in the recovery of VOCs. Since liquid ring compressors are almost isothermally compressed during gas compression, different gas media can be manufactured with different working fluids and different materials, so liquid ring compressors are particularly suitable Application in the recovery of VOCs. Since VOCs are flammable, explosive and toxic gases, the use of closed-type circulating liquid ring compressors will be more reliable and safe, while avoiding secondary pollution and meeting environmental protection and energy saving requirements. According to the specific properties of VOCs and the similarity of organic substances The principle of compatibility, diesel and medium oil with higher boiling point and lower vapor pressure can be used as the working fluid for the closed cycle of the liquid ring compressor to transfer VOCs from the gas phase to the liquid phase to recover VOCs. Normally, use Demineralized water is used as a working fluid to compress and liquefy VOCs through a compressor to achieve the effect of recovering VOCs.
Liquid ring compressor for VOCs recovery of selection
We have encountered customer VOCs treatment cases: 93.5mg/L&16.82kg/h cyclohexane, air, benzene, toluene, and acrylic acid content have reached the environmental protection emission requirements. These VOCs contain traces of corrosive Gas, but not highly corrosive, the closed-loop liquid ring compressor is made of 304 stainless steel to meet the requirements of use. The material of the seal should be perfluoro rubber or at least PTFE. Design of closed circulating liquid ring compressor units for VOCs recovery In order to reduce secondary pollution and the consumption of working fluid, most of the VOCs recovery devices use closed circulating liquid ring compressor units. After the gas containing VOCs enters the liquid ring compressor to be pressurized, the condensable VOCs gas is pressurized and liquefied into a liquid and enters the gas-liquid separator together with the working fluid, and settles in the gas-liquid separator, and the non-condensable dry air is discharged from The pipeline is exhausted to the atmosphere. In order to ensure the outlet temperature, the outlet pipe must be equipped with a condenser to condense the outlet gas, so as to ensure the content of cyclohexane at the outlet. The closed cycle liquid ring compressor designed by EVP is as follows:
1, According to the requirements of API681 and petrochemical standards, such working conditions need to use the design of the mechanical seal flushing system to match the PLAN53 system flushing solution. To ensure the reliability of the seal, it is more convenient and safer to use.
2. Tube-and-tube heat exchangers with good air-tightness and few leakage points must be selected. The material is SS316L, and the single-pass heat exchanger recovers VOCs.
3. For the design of high-efficiency gas-liquid separator, if the working Liquid is Water, the liquefied VOCs need to be recovered.
4. The fully automatic and multi-functional integrated design of the closed-cycle liquid ring compressor unit is designed to ensure the normal operation and fully automated control of the liquid ring compressor unit, and the following control points are connected to the user’s DCS or on-site control cabinet.
The EVP liquid ring compressor unit is a positive displacement compressor, which can be flexibly configured according to the composition of the medium contained in the VOCs, and is particularly suitable for use in the recovery of VOCs. The EVP closed-loop liquid ring compressor unit has a high degree of automation, reliable performance, and safety, while avoiding secondary pollution, energy saving and environmental protection; different circulating working fluids can also be selected according to the specific properties of VOCs media and the principle of similar compatibility of organic substances. Reasonable selection of the design parameters of the liquid ring compressor will help reduce the energy consumption and cost of the VOCs recovery device. EVP Vacuum can provide high-performance, safe and reliable liquid ring compressors according to customers’ specific working conditions.
Keywords: VOCs liquid ring compressor, liquid ring compressor closed cycle unit
Editor: Selena of Shanghai Kanter Vacuum Technology Co., Ltd.