Energy efficiency improvement in oil refineries through flare gas recovery technique to meet the emission trading targets

Flare gas recovery is one of the most attractive methods to improve energy efficiency in oil refineries to decrease greenhouse gas emissions. The recovered gas is used to feed refinery processes, granting advantages in terms of fuel economy and flare stress. This paper presents the results obtained by a feasibility study of a flare gas recovery system in a real refinery; the work focused on: i) the choice and the design of the flare gas recovery system; ii) the gas treatment and reuse; iii) the economic feasibility, and the payback period. An experimental campaign has been performed to evaluate both the composition and the flow rate of the flare gas. Results showed that the flare gas had a strongly variable flow rate and composition due to the different gas species processed in refinery. A methodology for the system selection is presented: a 400 kg/h liquid ring compression device is chosen; its basic design is described as well as the chemical treatments of inert gases and hydrogen sulphide (H2S). The yearly energy recovery was estimated to be 2900 TOE, corresponding to 6600 tons of CDE (Carbon Dioxide Equivalent). Finally, an economic evaluation was carried out, showing a payback period of about 2.5 years.