Investigation and simulation of replacement of propane as refrigerant in NGL plant

Extensive processing of the gas produced at the well is sometimes required. In every case, the specific processing needed is determined by the flow rate, composition, temperature, and pressure of the produced gas and by the components/impurities that must be removed to meet delivery specifications. Processing may vary from simple separation plus dehydration all the way up to compression, sweetening, natural gas liquids (NGL) recovery, and dehydration. Gas containing considerable amounts of liquefiable HC (ethane, propane and heavier) produces condensate upon cooling or compressing and cooling. If condensation would occur in the transportation, processing, or use of the gas, it may be better to remove the condensate at or near the wellhead. In some cases the potential NGL are sufficiently valuable to justify their recovery, quite apart from other considerations. Normally, condensate is fractionated into the NGL products in a central facility rather than in the field. Recovered condensate may have to be stabilized by partial removal of dissolved gaseous components to obtain a liquid product with low-enough vapor pressure to be transported safely. Obviously any cooling will induce condensation and yield NGL. Most common liquid recovery processes are compression refrigeration, expansion across a turbine and expansion across a valve. In this article five case studies are investigated. The technology that was used to perform the calculations was the process simulation programs HYSIS 3.01, licensed by HYPROTECH, Inc. Other simulation programs with similar capabilities could have been used to perform the calculations. We simulate a compression refrigeration cycle with propane as fluid work to decrease gas temperature, which gathering from the wells near the Ahvaz (south oil region), from ) 130 ( 5 . 54 F C o o to ) 30 ( 5 . 34 F C o o − − . Then change propane to ethane, n-butane, ibutane and mixture of isobutene and normal butane and evaluate results of these replacements. With comparing required rate of refrigerant, heat loads of compressors and heat exchangers, operating pressure can deduce propane is the best refrigerant to recovery of natural gas liquids in gas industry.

Keywords:

recovery of natural gas liquids , compression refrigeration cycle , NGL