14:30 - 15:00
Thursday, 19 September 2019
T3.9 Minimum OPEX and Environmental Friendly LPG Plant
The Bahrain National Gas Company Central Gas Plant (CGP-III) was successfully commissioned in November 2018 to produce LPG and condensate by Bahrain National Gas Company and JGC corporation.
The plant was designed to process 350 MMscfd of sour gas consisting of Associated Gas (AG) and Refinery Off Gas (ROG) to recover approximately 13,800 BPD of C3 and heavier liquid products.
Minimum OPEX and environmental friendly design have been achieved applying the following design considerations.
1.Optimization of Propone Recovery
The original design planned to achieve a target guarantee value of 98.5 % mol for the Propane (C3) recovery rate. However, this requires removing a certain amount of CO2 in the feed gas to a level where CO2 should not solidify in cryogenic streams and the Deethanizer Column in NGL Recovery Unit.
A CO2 removal facility requires extremely high energy consumption for the Amine Regeneration and Acid Gas Compression units, and high initial investment.
We selected the 91.0 % LPG Recovery Rate because of an environmentally friendly facility, lower CAPEX and lower OPEX due to lower energy consumption, and lower CO2 emissions, while maintaining a profitable process flow design.
2.Selection of Optimum AGR Process and Licensor
The type of solvent used in the Acid Gas Removal Unit (AGRU) will affect the degree of H2S and CO2 removal from the feed gas. We selected MDEA-based solvents doping special promoter in order to maximize CO2 slip to the treated gas and to selectively remove H2S from the treated gas.
A maximum CO2 slip helps minimizing utility consumption in the amine reboiler and the acid gas compression unit. However, we have deliberately limited the maximum CO2 slip to 4.5 mol% for the CO2 freezing tolerance of the downstream NGL Recovery Unit in order to meet the target 91.0% propane recovery rate.
3.Elimination of Regeneration Gas Compressor
Regeneration Gas Compressor for Dehydrator and LPG Treater system was eliminated from facility design. To eliminate the Regeneration Gas Compressor, the part of Residue Gas Compressor 1st stage discharge gas is taken as slipstream and this is used as regeneration gas for Dehydrator and LPG Treater system. Spent regeneration gas is re-injected into the Residue Gas Compressor 2nd Stage Suction.
By the elimination of Regeneration Gas Compressor, the availability of regeneration gas is improved, and the maintenance and operating cost & work of Compressor / Driver are reduced.
BAHX（Blazed Aluminum Heat Exchanger）is used in LPG Recovery Unit at downstream of dehydrator system and allowable temperature change rate of BAHX is specified by BAHE supplier to avoid thermal stress on equipment. Dehydrator outlet temperature change would continue to be cyclic and then metal fatigue of aluminum is started. Also, Dehydrator outlet temperature change could make the unstable operation for LPG recovery unit and the LPG recovery rate also drops.
Therefore, JGC develop the innovative sequence logic for dehydrator to minimize the Dehydrator outlet temperature change and this sequence is functioned successfully in the actual operation.