ENVIRONMENT/LOSS PREVENTION HYDROCARBON PROCESSING AUGUST 2010 I 51 E conomic and environmental considerations increase when using flare gas recovery systems (FGRSs) to reclaim gases from flare header systems for other uses. An FGRS reduces flaring noise; thermal radiation; operating and maintenance costs; air pollution and emissions; and fuel gas and steam consumption while increasing process stability and flare tip life without any impact on the existing safety relief system. The article details installing an FGRS at the Khangiran gas refinery in Iran and how the system was involved in the reduction, recovery and reuse of flare gases. The system’s operation, design guidelines and process economics will also be covered. Introduction. Flaring is used to consume waste gases—includ- ing hydrogen sulfide (H 2 S) rich gases and gases burned during emergencies—in a safe and reliable manner through combustion in an open flame. It is used routinely to dispose of flammable gases that are either unusable or uneconomical to recover. Often, gas plant workers must do emergency flaring for safety purposes when equipment is depressurized for maintenance. Worldwide, final product costs for refinery operations are becoming proportionally more dependent on processing fuel costs, particularly in the current market where reduced demand results in disrupting the optimum energy network through slack capacity. Recovering hydrocarbon gases discharged to the flare relief system is probably the most cost-beneficial plant retrofit available to the refinery. Flare gas use to provide fuel for process heaters and steam generation leaves more in fuel processing, thus increasing yields. Advantages are also obtained by reducing flare pollution while extending tip life. In spite of the advantages, suitable projects for flare gas reduc- tion and recovery have not yet been planned. Therefore, there is an essential need to emphasize installing FGRSs into the gas refinery to recover and reuse flare gases. Khangiran gas refinery. Due to the large amount of flare gases produced in the Khangiran gas refinery (21,000 m 3 /hr), operational conditions were investigated, especially in the units that produced flare gases. 1 Based on the existing data, it was found that the methyl diethanolamine (MDEA) flash drum, MDEA regenerator column and MDEA regenerator reflux drum, residue gas filter and inlet gas separator into the gas treating unit (GTU) were the most critical when looking at producing flare gases. Flare gas composition in the flare header during three tests is given in Table 1. Regarding the results of the data analysis—the mean value of the molecular weight of the flare gas is 18.16 and the flow discharge rate modulated between 2,500 m 3 /hr and the maximum of 10,000 m 3 /hr. The average temperature is 30°C and the average pressure is 6 psig. Advised practical methods to reduce, recover and reuse flare gases for the Khangiran gas refinery are presented in Table 2. Gas refineries can benefit from installing a flare gas recovery system Take a look at these environmental and economic paybacks O. ZADAKBAR and A. VATANI, University of Tehran, Iran; and S. MOKHATAB, Consultant, Dartmouth, Nova Scotia, Canada TABLE 1. Flare gas composition in flare header Test No. 1 No. 2 No. 3 composition % mole % mole % mole C1 86.327 75.723 85.682 C2 0.461 0.759 0.58 C3 0.104 0.212 0.076 i-C4 0.03 0.062 0.012 n-C4 0.05 0.124 0.018 i-C5 0.028 0.07 0.028 n-C5 0.022 0.089 0.022 C6+ 0.218 0.212 0.218 CO 2 8.2 14.575 8.713 H 2 S 3.3 5.265 3.393 N 2 1.26 2.909 1.258 Total 100 100 100 TABLE 2. Advised practical methods to reduce, recover and reuse flare gases Objective Advised practical methods Reduce and/or reuse flare gases • Improving structure of MDEA flash drum to reduce CO 2 and H 2 S to send gases to the fuel gas header • Improving equipment with predicted streams to send gases to the fuel gas header • Improving inlet gas separator internals Recover and reuse flare gases • Installing the flare gas recovery system for the MDEA flash drum • Installing the overall flare gas recovery system