A complementary VOCs recovery system based on cryogenic condensation and low-temperature adsorption

The control of volatile organic compounds (VOCs) emission has a significant influence on the environment and human health. Liquid nitrogen (LN2) condensation is a highly efficient method for VOCs recovery with a wide range of applications, but it is poor in the treatment of light hydrocarbons, especially methane and ethane, and has some shortcomings such as high emission concentration and large carbon emissions. In this paper, a novel cryogenic condensation system combined with low-temperature adsorption was proposed. The low-temperature exhaust gas treated by cryogenic condensation equipment is introduced into an adsorption bed, resulting in lower temperature and higher adsorption capacity of the adsorption bed, which not only effectively improves the recovery rate of VOCs, but also solves the spontaneous combustion problem caused by the adsorptive heat effect of traditional room-temperature adsorption method. A thermodynamic calculation model was established, and related experimental verifications were carried out. The results show that the economic value of the recovered VOCs condensate is 1.24 times of the cost of consumed LN2 and the carbon emission reduction is 1683 t per year, achieving an acceptable breakthrough time of 16,971 s at an adsorption temperature of 198.15 K exceeding that at 238.15 K by a factor of 16 when the cryogenic condensation temperature is 138.15 K with a 600 m3/h of waste gas. The effects of cryogenic condensation temperature, adsorption temperature, inlet gas concentration, flow rate, and the proportion of components on the system performance are analyzed in detail.