Acid Gas Treating Facility Management by Utilizing Inherent Plant Advantages
Authors: Sitawati Siti , Azwar Noezran , Nugroho Setiya M. , Ardianto M. Nurdin 
Published: May 2012

Combining membrane and solvent technology type of acid gas removal or ‘hybrid’ system, either in series or parallel, is often selected to increase the advantages of each technology and reduce the disadvantages of each technology. Specific for parallel hybrid system, independent operation in parallel does not only provide luxuries for operating the plant under specific circumstances but can also be viewed as implementation of acid gas treating management.

One of the world's unique hybrid combinations of acid gas removal units (AGRU) exists in Singa Gas Plant, located in South Sumatra, Indonesia. The plant is designed to process 93 MMSCFD of sour natural gas, reducing CO2 from 38% to 4% mole and H2S from 350 ppmv to 4 ppmv. Singa plant becomes the unique hybrid configuration for AGRU as it consists of Membrane Unit and Amine Unit operating in parallel. Each unit is designed for 45 and 48 MMscfd of feed gas, respectively, to produce 55 MMscfd sales gas of pipeline gas specification.

Singa Gas Plant was firstly designed to use 100% Amine Unit for AGRU based on initial subsurface analysis. During the project construction, due to HPHT reservoir nature of Singa wells, it was lately found that there was limitation to produce the gas at the expected amount. After series of process optimization scenarios with the constraint of project completion schedule, it was found that installing 50% Membrane and 50% Amine system was the optimum solution.

During gas-in period, the actual gas composition was found different from original design basis in terms of heavier feed gas composition with 0.08 % mole C5+. As a result, more condensation on membrane surface during gas permeation is observed, which eventually leads to degradation. Moreover, due to economic reason and gas availability, Membrane Unit is continuously operated with standard pre-treatment facility only that leads to higher operating vulnerability of Membrane Unit compared to Amine Unit.

To manage such constraints, Membrane Unit operating configuration and performance are analyzed to define the most optimum operating scenarios. Amine Unit production load is maximized, while Membrane Unit will only be loaded for the balance of the gas. In order to meet final sales gas specification, product gas specification from Amine Unit has to be altered to compensate product gas quality from Membrane Unit.

This paper emphasizes that good management of facilities operation of acid gas treating can be achieved through utilizing inherent advantages of plant configuration and capability and by managing existing design capacity to maintain on spec sales gas production without additional capital expenditure. Technical contributions which can be shared for technical knowledge base of petroleum industry are: ■Parallel hybrid system of sweetening technology can also be viewed as implementation of acid gas treating management besides providing flexibility for operating the plant under specific circumstances■Based on assessment of acid gas treating unit performance production scenarios can be established to achieve targeted sales gas specification and delivery■Proper facility management of acid gas treating unit is essential and can be maximized without any additional significant capital expenditure