Processing Sour Natural Gas To Meet Pipeline Quality
Authors: Goar B. Gene , Goar Thomas O. 
Published: December 2007

The processing of sour natural gas is gaining interest and popularity due to the search for additional sources of available energy. The decision to build a sour natural gas processing plant involves many considerations and represents a sizeable investment. Selection of the optimum processing scheme encompasses the areas of:gas cleaning,gas treating,LPG liquids recovery,gas dehydration andpossibly sulfur recovery and tail gas clean-up.

Major factors and various options affecting the selection of an optimum processing scheme are discussed in this paper.

Introduction

The use of fossil fuels in the United States doubles about every 20 years. With the ever increasing demand for more energy, the interest in processing and conditioning of sour natural gas for pipeline sales is growing. The large reserves of sour gas in the Southwest are located in the Permian Basin of West Texas and the Smackover trend running through East and Northeast Texas, Louisiana, Mississippi, Alabama and Western Florida. Huge amounts of sour gas will be produced and processed from the Smackover trend in the produced and processed from the Smackover trend in the future.

When an evaluation to build a "grass-roots" sour natural gas processing plant is conducted, many process considerations and economic factors must be process considerations and economic factors must be reviewed to decide upon the optimum overall scheme. A detailed evaluation must be performed to establish the best combination of processing steps for:gas cleaning,gas treating (sweetening),LPG liquids recovery required for dewpoint control or liquid sales,gas dehydration,sulfur recovery andtail gas clean-up (TGCU), if required.

The major factors affecting the outcome of the evaluation are:the daily volume of sour gas to be processedthe estimated life of the reservoir at this flowthe liquids content of the gas (GPM of C +)the amount of sour components (H2S and CO2) to be removedthe amount of sulfur to be recoveredthe presence and amount of inerts and other comtaminants such as N2, O2, COS, CS2 and mercaptansthe sales gas specifications to be metthe air pollution regulations which will dictate if sulfur recovery and/or TGCU is requiredthe availability of a close market for the plant productsthe price and total revenue obtained for the plant products, i.e., sweet sales gas, liquidsand sulfurthe investment required to construct and operate the plant

Discussion

Best Processing Approach

Once the drilling activity in a sour gas field is nearing completion, the producer must decide upon the best approach to processing the sour gas:Is it more economical to lay a sour gas line to the nearest gas processing plant, which handles similar gas and may have excess capacity, and pay a processing cost (cts/MCF) to have the gas conditioned?Or, is it more economical to lease equipment(skid-mounted plant) for on-site processing?Or, is it most feasible to build a"grassroots" plant to be owned and operated by the producer? The plant can be owned by one company or a group of companies/parties, contributing to the overall investment and operating cost, and sharing in the overall revenue.