Selected theoretical and practical investigations and optimization issues of Organic Rankine Cycle applied for waste heat use
Session: Poster session & Welcome drinks
Session starts: Wednesday 13 September, 17:30
Slawomir Smolen (German)
One of the comprehensive practical application areas of Organic Rankine Cycle is heat recovering from different low and middle temperature “waste heat” sources. The possible waste heat utilization from biogas power plants could be mentioned here as one of the typical relevant examples. Relating to this context, the paper presents some important theoretical optimization issues and selected results of the practical investigation carried out at the test and demonstration ORC plant with screw engine as expansion device.
Selection of suitable organic fluids for application in Organic Rankine Cycle is a crucial step to achieve high thermal efficiency. Within a previous study a special tool has been elaborated in order to compare the influence of different working fluids on the performance of an ORC heat recovery power plant installation. The elaborated tool should create a support by choosing an optimal working fluid for special applications and become a part of a bigger optimization procedure applicable by different boundary conditions. The second optimization issue is minimization of exergy losses between heat source and the cycle by special optimization procedures selecting not only the working fluids but also evaluating the possible types of process (subcritical, overcritical, one or more stages process, internal heat recovery) under consideration of given frame conditions and limitations - mostly temperatures of the heat source and cooling air or water and pressure limitations.
Based on these theoretical considerations and in accordance with practical requirement, a special ORC test and demonstration plant has been developed and installed, especially for “waste heat” utilization from exhaust gas and cooling water of biogas installations. The biggest practical solution and challenge was the application of screw engine as expansion machine. This paper presents some aspects of this, especially a novel lubrication installation adopted from a compressor and modified for the requirements of expansion machine. At the end, some representative measurement results are presented to illustrate some practical possibilities and limits of the tested installation and to compare them with theoretical assumptions.