City Research Online

Abstract

A multi-variable optimization program has been developed to investigate the performance of Organic Rankine Cycles (ORCs) for low temperature heat recovery applications. This cycle model contains detailed thermodynamic models of the system components, and the methods used to match the operation of the expander to the requirements of the cycle are described. Two types of ORC system are considered; one containing a turbine to expand dry saturated or superheated vapour, and one with a twin-screw machine allowing expansion of partially evaporated fluid.

Modelling of the ORC system with a twin-screw expander has been described previously (Read et al. 2014a, 2014b). The performance of the turbine in the superheated ORC has been modelled using available operational data for single stage, reaction turbines, where correlations have been used to estimate the efficiency of the turbine at ‘off-design’ conditions using either fixed or variable nozzle geometries.

The capability of the cycle model has been demonstrated for the case of heat recovery from a source fluid at 120°C. The system parameters are optimised for a typical operating condition, which determines the required size of heat exchangers and the expander characteristics. Performance at offdesign conditions can then be optimized within these constraints. This allows a rigorous investigation of the effect of air temperature variation on the system performance, and the seasonal variation in net power output for the turbine and twin-screw ORC systems is estimated.

Publication Type:	Conference or Workshop Item (Paper)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Departments:	School of Science & Technology > Engineering

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