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Session: Poster session & Sponsor Exhibition
Session starts: Monday 07 October, 14:00

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Henrik Ohman (KTH)
Per Lundqvist (KTH)

Abstract:
The task of reducing global carbon dioxide emissions leads to a need to reduce the average CO2-emission in power generation. A more energy efficient mix of power generation on national, or regional level, will require the re-use of waste heat and use of primary, low temperature heat for power generation purposes. Modified Rankine Cycles (MRC), such as Organic Rankine Cycles, Trilateral Flash Cycles, Kalina Cycles are types of Low Temperature Power Cycles (LTPC,s) offering a large degree of freedom in finding technical solutions for such power generation. Theoretical understanding of MRC’s advance rapidly though practical achievements in the field show very humble improvements at a first glance. Cost of applying the new knowledge in real applications seems to be an important reason for the discrepancy. As LTPC’s generally are small scale power plants, less than 3MWe, an obvious cost driver is size itself. However, another strong reason for the high cost level is the diversity of process fluids required and consequently the lack of standardization and industrialization. Uses of supercritical power cycle technology tend to cause the same dilemma. New, upcoming regulations prohibiting the use of several process fluids could also lead to remedies increasing plant cost. By using 2-phase turbine inlet conditions in MRC’s the need to use many different process fluids is believed to be reduced, allowing simpler and more cost efficient LTPC’s by simplified matching of heat source temperature characteristics. This article explains the opportunities accordingly. Definitions of different sample applications for LTPC’s have been made in order to simulate the different power generation opportunities using fundamentally different process fluids in the particular applications. The methodology is suitable for optimization in specific cost, Net Power Out or efficiency. The results indicate a potential to design LTPC’s with good efficiency in significantly wider thermal conditions than previously, without changing the fluid. Conclusions are made that cost optimization of LTPC’s is possible through the use of 2-phase turbine inlet fluid conditions, allowing cheaper process fluids and standardization of the power plant architecture. Sensitivity to choice of fluid is reduced to 10% in cost and <5% in FractionOfCarnot and Net Power Out when optimization of 2-phase turbine inlet conditions is allowed. Consequences of the conclusions are that LTPC’s can be made more commercially attractive and thereby contribute in decreasing the average carbon emissions from power generation.