Minimizing Gas Flaring During Plant Depressurization

Abstract During plant depressurization, valuable gases are burned through a flare system in preparation for maintenance. Plant modifications (such as transferring high-pressure gases to the fuel gas system using pressure regulators) should be conducted to minimize the flared gases. Liquified petroleum gas (LPG) storage tanks may also be depressurized through gas compressors to move the gas from tank to tank to reduce the flaring of LPG products. The plant piping and instrumentation diagram (P&ID) study is crucial for allocating the gas transfer ways from high-pressure to low-pressure sections like fuel gas package and building a low-emission system which will be used before plant depressurization for the planned maintenance activity. This paper suggests a new technique to minimize gas flaring during planned plant maintenance. The plant P&ID is studied in deep through a multidiscipline team to ensure plant safety during depressurizing and to minimize the total depressurizing time as much as possible. Adding some small connections with positive isolation is used to connect high-pressure and low-pressure sections which will be used only during plant depressurization and positively isolated during plant depressurizing. The results show that a total of 175 tons from 4 tanks and 3 small pullet tanks was saved using a vapor recovery unit (VRU) to transfer the LPG vapor from the tank under maintenance to the running tanks. In addition, 1.5 MMSCFD of mixed gases from the onshore plant was saved by applying the staged depressurizing technique. The suggested modifications may be applied to other gas plants to reduce emissions and save the environment.