General Process Description of Gas Plant
The Qadirpur gas processing plant gathers and treats for sale the gas from the Qadirpur gas field. The facilities will produce 400 – 500 MMSCFD of treated gas for export to SNGPL.
The raw gas produced from the wells, through two main gathering headers named as northern and eastern, is collected in a vessel called as “Slug Catcher”. The slug catcher functions as a two phase separator and the raw gas get free from maximum quantity of well liquids. The gas obtained from the top of the slug catcher is pass through inlet separators (two, each 50 %, vertical two phase separator) for further removal of entrained contaminants like sand, pipe scale, water and liquid hydrocarbons. In order to decrease the temperature of gas stream, it is passed through Feed Pre-cooler (two, each 50 %) which use the sale gas from the combined first membrane trains to cool the gas. The regeneration gas exiting the Regeneration Gas Air Cooler is combined with the feed gas just prior to the inlet of the Feed Pre-coolers.
The feed gas then passes through the Chiller Economizer, which provide heat recovery and lower the required chilling duty. Cooled gas stream is passed through Feed Gas Chiller which cools the gas to 600F, which drops out water and heavy hydrocarbons from the combined feed / spent Mem Guard regeneration gas. The chiller package uses propane as refrigerant. The chiller section serves two main purposes: First, as the feed is relatively hot and saturated with water, the chiller significantly reduces the load on the Mem Guard system. Second, UOP’s high performance membranes achieve significantly higher selectivity at lower temperature. In order to ensure further removal of liquid contaminants to a required specific level, the process gas from the Feed Gas Chiller is passed through a vessel named as “Filter Coalescer”. Filter Coalescer is a high efficiency coalescing filter for the removal of entrained liquid droplets not stopped by the inlet separators. Its elements are also suitable to remove all liquid aerosols larger than 0.3 micron. Before passing the gas stream through primary membrane skids, it is passed through the Mem Guard vessels, which is a thermally regeneration adsorption unit consisting of absorber vessels (five), a gas fired Regeneration Gas Heater, Regeneration Gas Air Cooler, a Regeneration Gas Scrubber and a Regeneration Gas Blower. The Mem Guard removes all the water and traces of heavy hydrocarbons. The system also provides dew point control. Treated gas is then passes through a Particle Filter, which removes any entrained fines, dust or other particles from the gas.
The preheated gas processed from outlet of Particle Filter is collected in a Common Feed Header from which it is further distributed to three trains of “Primary Membrane Skids” in parallel arrangement. The existing skids (30 tube skids, five skids per train, two trains, 3rd consists two skids, each has 49 tubes) are to be loaded with high performance CAP membrane elements. Membrane elements selectively separate H2S, CO2 and water traces from the “Feed Gas” stream as in the form of “Permeate Gas” stream. The gas stream after extraction of CO2 and H2S is called as “Residual Gas” which is then sent to SNGPL metering system.
In Permeate gas stream, a considerable portion of hydrocarbon gases is also present. To recover the remaining hydrocarbons the low pressure permeate gas stream is 1st pass through Permeate Gas Compression (to increase its pressure) and then cooled prior to entering the 2nd membrane stage using the Recycle Feed Gas Cooler-cross exchanging with the 2nd stage membrane residual gas-and Recycle Feed Gas Chiller. The gas is then sent to the “Recycle Membrane Skids”. The Residual gas stream is mixed with the Primary process stream, while the Permeate gas stream is discharged as a Recycle Permeate into the exhaust stack of the gas turbine.
The condensate, which gets separated at the separator, is brought to condensate treatment unit where decreasing pressure and increasing temperature strip off all the volatile hydrocarbons along with H2S. The stabilized crude is then sent to storage tanks.