Retrofit Design for Gas Sweetening Processes

Gas sweetening using amines is an important gas treatment process. Existing gas sweetening units may be revamped to achieve a variety of aims, for example to expand processing capacity, to reduce operating costs, to accommodate a different feed, to reduce emissions levels, etc. Current practice for retrofit design is to use engineering judgement and experience and simulation studies to identify process modifications, but this approach can overlook beneficial options. Instead, a systematic approach for retrofit of gas sweetening units is proposed. The approach involves process simulation, using simplified models, and optimisation of both flowsheet configuration and operating conditions using stochastic optimisation, namely simulated annealing. The optimisation objective considers operating costs, and constraints in the problem formulation guide the solution towards retrofit designs that are practical and have low capital costs. The method is applied to an industrial case study where the CO2 content in a natural gas feed has increased. Modifications that allow the sales gas specifications to be met are identified and evaluated.