Measurement Problems in Gas Plant Operations

In September, 1962, the gas processing plant owned by Edmonton Liquid Gas, located on the southern outskirts of the City of Edmonton, started processinggas delivered to it by Northwestern Utilities for the removal of hydrocarbonliquids. The plant was originally designed to handle 50 MMcf/D of gas coming toEdmonton from the Pembina field and another 20 MMcf/D from the Texaco plant atBonnie Glen. These gas streams were to remain segregated, so two separateabsorption towers were required for processing. The Pembina unit was to operateat 650 psig and the Bonnie Glen at 450 psig. The residue gas was to be returnedto the Northwestern Utilities transmission line system. The reduction in gasvolume through the extraction of approximately 48,000 gal/D of liquid productswas estimated at 3.6% of the inlet gas volume. Payment was to be made for thisreduction on a therm basis. Normally, gas plants of this nature are either subsidiaries of production ortransmission companies or part of an integrated system. As such, anydiscrepancies in a plant balance between the gas shrinkage and the extractedproducts are of no great consequence and can be taken care of in the accountingprocedures. However, in this case with separate ownership of the two companies, metering becomes a major problem to determine an accurate value of the productsextracted or used. The measurement in the reduction of gas volume cannot beused because the inherent inaccuracies in gas orifice metering are too greatfor this purpose. Measurement of the liquid products with positive displacementmeters would be the basis for billing. Gas measurement would be done only forthe purpose of obtaining plant balances. Prior to the selection and installation of the gas measurement equipment, asurvey was made of gas plants operating under similar circumstances in bothCanada and U.S.to determine their experiences and practices.