Experience With High Load M.E.A. Solutions For Acid Gas Removal
Authors: Deetz J.A. , Wehmeyer C.L. 
Published: December 2007

Removing acid gas from sour natural gas streams by contacting with monoethanolamine solutions is a tried and proven process. The process as used by Sui Gas Transmission Co. for removal of H2S and CO2 at their gas purification plant at Sui, Pakistan is different because they design for total amine solution loadings of .64 mols acid gas/mol M.E.A. This paper analyzes the system as designed and operated paper analyzes the system as designed and operated and determines if the high loading of M.E.A. is an economical approach to gas treating problems.

Introduction

The Sui Gas Purification Plant is located approximately 300 miles (500 km) north of Karachi in the providence of Baluchistan. Access to the plant is limited due to the remoteness of the area. Land access via dirt roads is poor at best. The majority of personnel axe flown to the site. During rare but heavy rainfall the entire area has been cut off from outside communication except for radio telephone messages. The earthen runway of the airstrip becomes a mire of mud such that airlift is impossible. Fortunately for the plant and personnel at Sui, eight to ten months a year the average rainfall is zero.

C-E Natco contracted in 1976 with Sui Northern Gas Pipeline Ltd. to procure and manufacture equipment, and supervise installation and start-up of two 120 MMscfd (3.4 MM Nm3) natural gas treating facilities. These units were to be an addition to the existing facilities located at the plant operated by Sui Gas Transmission.

Because of its importance to the economy of Pakistan (the Sui Field supplies over 50% of the Pakistan (the Sui Field supplies over 50% of the country's natural gas) the plant at Sui must operate with few if any interruptions. Because of somewhat limited chemicals and the production cutback necessary to convert to another process, Sui Gas elected to utilize the existing M.E.A. process with the M.E.A. loaded to unusually high ratios of acid gas.

The existing facilities, which had been constructed in steps of one and two trains per unit since 1955, had a daily average production of 450 MMscfd (12.7 MM Nm3). The addition increased the number of parallel trains to nine and the average production of gas to 675 MMscfd (19MM Nm3). Two of production of gas to 675 MMscfd (19MM Nm3). Two of the existing trains had been initially designed for high loaded M.E.A. and were commissioned in 1971 by Fluor Ltd., U.K. The remaining five trains had been converted from normal M.E.A. treating to the high loaded process, and specifications for the expansion units were drawn up based on past operating experience.

PROCESS DESCRIPTION PROCESS DESCRIPTION The process for treating gas at Sui is similar to many amine type gas treating facilities except for the M.E.A. solution loading. Figure 1 is a simplified process flow scheme. 120 MMscfd of 1100 psig, 140 degrees F gas, containing 7% CO2 and 0.14% psig, 140 degrees F gas, containing 7% CO2 and 0.14% H2S enters the plant through a flow control valve and is cooled by E-260 to 100 degrees F (38 degrees C). Condensed water and hydrocarbon are scrubbed out of the feed stream prior to entering the absorber V-120.

1264 gpm of 20% lean M.E.A. is pumped from the surge tank V-180 to the top tray of the absorber and flows countercurrent to the gas flow. The resulting rich amine exits the bottom of the absorber through a level control valve and flows to the flash tank V-140 where entrained hydrocarbons are flashed off. The purified gas exits the absorber and flows to downstream dehydration facilities,

The rich amine flows from the flash tank through the rich/lean heat exchanger and to the reactivator still column V-160. Steam from the still reboiler strips the acid gas from the rich amine and the acid gas is separated and pumped back to the still as reflux.

The reactivated amine exits the still bottom, is cooled to 100 degrees F (30 degrees C) by heat exchange, air cooling and amine/water trim exchange.