Steam expander as a throttling valve replacement in industrial plants: A techno-economic feasibility analysis

This study analyses the replacement of a pressure reduction valve with an expander in those industrial plants that use the steam as a heat transfer fluid at different pressure levels. This replacement can be an effective technique to recover some mechanical energy as the pressure reduction is commonly performed by a throttling valve and thus the pressure work is wasted. Conceptually, it is possible to recover this energy through an expander that converts it in mechanical or electric energy. The substitution of throttling valves in those plants which use steam as heat medium is often not a way to reduce the total consumption of the plant, as the thermal energy is actually extracted from the system and converted with relatively low efficiency. Nonetheless, the economic advantage of such application can be relevant, since thermal and electric energy are commonly priced differently. Therefore, this last application is gaining interest in the industrial world but still it is not thoroughly investigated. This study helps to fill this gap by analysing the replacement of the throttling valve from the thermodynamic and economic point of view. The results showed that the introduction of an expander could lead to substantial economic revenues and that in many of the investigated scenarios the discounted payback time is lower than four years. The economic analysis is carried out for several combination of expander purchasing and installation cost and for several combinations thermal and electric energy prices, to account for most of the economic and operational differences that could characterize the investigated application in the practice.