Acid Gas Recovery Units (AGRUs) are one of the core and energy intensive units in gas processing. In solvent based AGRUs, the rich solvent leaving absorber column is letdown across control valve before being sent to flash vessel. This pressure letdown indicates opportunity to recover energy by utilizing hydraulic turbine. In this context, an in-house study has been carried out to evaluate techno-economic feasibility of recovering energy from four (04) amine based AGRUs at one of the gas processing sites. Pressure letdown, across amine absorber control valves at selected AGRUs, from 60 to 7 barg indicated significant potential for energy recovery. A comprehensive review of existing design and current operation of AGRUs was carried out by technical team in close co-ordination with site personnel. Design inputs were prepared after discussions with Operations and Technical Services teams to evaluate modifications needed to implement the Hydraulic Power Recovery Turbine (HPRT). Internal estimation of potential power recovery was prepared and modifications needed to develop scope definition were identified. The team consulted potential suppliers for new equipment and technical proposals were evaluated for technical feasibility after discussions with multidisciplinary engineering teams.
The key challenges relate to the feasibility of modification given the brownfield modifications, as the piping routing with existing arrangement of equipment like HP absorber, lean gas circulating pump and rich amine flash vessel etc., could lead to potential constraints of space availability and pipe-rack adequacy. In addition, competent contractors are required to implement modifications to existing lean amine circulating pump as shaft modifications are needed. Efficiency of hydraulic power recovery turbine and performance guarantees signifies the successful implementation. Overall cost, economic feasibility over its lifecycle and schedule for implementation are few of the the major factors governing the management decision.
Based on current operation, preliminary estimates indicated power recovery potential of the order of around 5MW, from the four (04) AGRUs considered in the study, duly considering the overall efficiency of HPRT. The study ascertained significant reduction in power consumption of lean amine circulating pumps by utilization of recovered hydraulic power from respective AGRUs. Economic feasibility observed sensitive to applicable power tariff and other financial basis. However, on overall basis, study established that HPRT technology represent reliable, economically feasible solutions to reduce power consumption and emissions, thereby improving energy efficiency of gas processing industry.