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.

The compression units installed on sales gas network face wide range of operating modes owing to the varying supply & demand scenarios and the associated network dynamics. It is very challenging to ascertain the real performance in such applications due to changing specific energy consumption. The paper presents development of a novel and robust monitoring system, enabling realtime energy performance monitoring of dynamic compression and revealing realistic opportunities for energy savings. The methodology comprised review of design and OEM data for the compression units, followed by review of operating envelope. Subsequently, developed a thermodynamic model of compression units encompassing all the operating modes. Then embedded the actual performance curves from OEM in the thermodynamic digital twin and validated the model with actual operating data. Carried out site visits and held discussions with technical teams as part of the comprehensive approach. A mathematical model additionally developed, in addition to the thermodynamic model, to enable operators for off-line monitoring of the compressors performance during unavailability of thermodynamic digital twin. Detailed performance analysis of centrifugal compressors is essential to ascertain their condition and functioning. A decrease in performance can be an indication of internal wear or fouling, which if allowed to continue, may result in reduced throughput or excessive energy consumption or even unscheduled outages. Thus, the performance is not just an indication of energy or operating cost but also reflects other vital aspects like reliability. The integrated thermodynamic digital twin developed for large sales gas compression units, with total throughput capacity of more than 500 MMSCFD, has enabled and demonstrated effective energy performance monitoring even with changing operating scenarios. It facilitated real-time comparison of actual performance (specific energy consumption) with model based expected performance. It also aided real-time trending of polytropic efficiency as well as real-time display of potential energy savings opportunities. The digital twin has proven to be a reliable and low cost tool to predict compressor performance for various operating modes on real time basis. The data from the compression digital twin can be tied into process simulation models for process optimization. The model can complement supervisory capabilities, diagnostics, control capabilities and even facilitate in predicting failures ahead of time.