Control of Hazardous Air Pollutant Emissions from Crude Oil and Condensate Storage Tanks Using Thermal-Swing Adsorption

摘要

This study focuses on the design, set up and testing of a bench scale thermal-swing adsorption (TSA) technology to capture and recover hazardous air pollutants emitted from crude oil and condensate storage tanks. Benzene, toluene, ethylbenzene, and xylene isomers (BTEX) are examples of hazardous air pollutants emitted from storage tanks and are selected for this study. Commercially available granular activated carbon is used as the adsorbent. The operation of the bench scale TSA unit occurs in four steps including 1) offline to enable the generation of the BTEX mixture at steady state conditions; 2) online when the BTEX gas stream is sent to the adsorption vessel; 3) regeneration, in which N_2 is passed through the adsorber to purge O_2 to ensure safe desorption conditions; and 4) liquid recovery of BTEX through cooling and condensation. Experimental and adsorption model results were used to explain the effects of gas flow rate and BTEX concentration on the adsorption and desorption processes and to assess the efficiency of the bench scale TSA system. Overall, BTEX removal efficiencies were over 92% for gas flow rates ranging from 1 to 6 sLpm at 77℉. Desorption and liquid recoveries of the condensate were 98 % and 30-35%, respectively. Competitive adsorption among the BTEX components was more apparent between benzene and toluene. Toluene and benzene vapors were more easily adsorbed on the granular activated carbon than ethylbenzene and xylene probably due to a combination of the highest gas concentration, molecular weights and boiling points for benzene and toluene.