Trilateral Cycle Research Articles

Efficiencies of power flash cycles

Power flash cycles (PFC) are a generalization of trilateral cycles (TLC) in which the compressed liquid is heated up to its boiling point and then performs a flash expansion during which it delivers power. The end point of the expansion may be in the wet vapour region (TLC) or in the dry vapour region. Here model results are presented for PFC-systems including the heat transfer to and from the cycles with aromates, siloxanes, and alkanes as working fluids. Optimization criterion is the exergy efficiency for power production at different pairs of heat carrier and cooling agent inlet temperatures ranging from (350 °C, 62 °C) to (150 °C, 15 °C). Comparisons with TLC for water, organic Rankine cycles (ORC) and water Clausius-Rankine cycles are made. General findings are that PFC has higher power production efficiencies than ORC but larger volume flows at the expander outlet. Moreover, TLC with water have in all cases the highest or nearly highest power production efficiencies. The disadvantage of water are the large outlet volume flows at low temperatures. For these cases alkanes like cyclopentane are to be preferred in PFC which can have significantly smaller outlet volume flows and rather high power production efficiencies.

Comparison of trilateral cycles and organic Rankine cycles

A comparison of optimized trilateral cycle (TLC) - systems with water as working fluid and optimized organic Rankine cycle (ORC) – systems with pure organic working fluids is presented. The study includes the heat transfer to and from the cycles. The TLC - systems were optimized by the selection of the maximum water temperature, the ORC - systems by the selection of the working fluid and the process parameters. The optimization criterion is the exergy efficiency for power production being the ratio of the net power output to the incoming exergy flow of the heat carrier. Results will be presented for five different cases specified by the inlet temperature of the heat carrier and the inlet temperature of the cooling agent. The inlet temperature pairs are (350 °C, 62 °C), (280 °C, 62 °C), (280 °C, 15 °C), (220 °C, 15 °C) and (150 °C, 15 °C). It is found that the exergy efficiency for power production is larger by 14%–29% for the TLC than for the ORC. On the other hand, the outgoing volume flows from the expander are larger for the TLC than for the ORC by a factor ranging from 2.8 for the first case to 70 for the last case.

Development of the Trilateral Flash Cycle System: Part 1: Fundamental Considerations

The world market for systems for power recovery from low-grade heat sources is of the order of £1 billion per annum. Many of these sources are hot liquids or gases from which conventional power systems convert less than 2.5 per cent of the available heat into useful power when the fluid is initially at a temperature of 100° C rising to 8–9 per cent at an initial temperature of 200°C. Consideration of the maximum work recoverable from such single-phase heat sources leads to the concept of an ideal trilateral cycle as the optimum means of power recovery. The trilateral flash cycle (TFC) system is one means of approaching this ideal which involves liquid heating only and two-phase expansion of vapour. Previous work related to this is reviewed and details of analytical studies are given which compare such a system with various types of simple Rankine cycle. It is shown that provided two-phase expanders can be made to attain adiabatic efficiencies of more than 75 per cent, the TFC system can produce outputs of up to 80 per cent more than simple Rankine cycle systems in the recovery of power from hot liquid streams in the 100–200°C temperature range. The estimated cost per unit net output is approximately equal to that of Rankine cycle systems. The preferred working fluids for TFC power plants are light hydrocarbons.