INNOVATIVE ORC SCHEMES FOR RETROFITTING ORC WITH HIGH PRESSURE RATIO GAS TURBINES

asme-orc2015 Tracking Number 2

Combined cycle mode of power generation is one of the efficient way of generation of power. Combined cycles generally use gas turbine in the toping cycle. Gas turbines with retrofits like intercooling between the compressor stages and regenerator are not suitable for combined cycle operations. Tapping gas turbine exhaust heat to power for a high pressure ratio, recuperative gas turbines needs organic working fluid. This work discusses integration of ORC as a bottoming cycle in a combined cycle mode. Commercially available gas turbine models like small capacity SGT200 and medium capacity GE LM -6000 have been considered for the toping cycle. Toluene, cyclopentane, butane, MM, MDM, MD2M, D4, D5 are studied parametrically for different ORC schemes, to understand energy recovery potential from the gas turbine exhaust. ORC working fluids have been studied for saturated, superheated and supercritical schemes. The working fluid with higher potential for power generation is best suited for ORC integration. The power recovered by toluene cycle at 0.85Pr is highest with a value of 2.723MW and thermal efficiency of 31.09% for cycle with internal regeneration (IHE) amongst saturated schemes for integration with SGT200. The corresponding combined cycle efficiency is 54.11%. While recovering waste heat to power using dry working fluids, the efficiency with internal heat exchange does not actually matter, in the sense of savings in fuel. The advantage of IHE can be understood with reduced condenser loads and enhanced potential for waste heat recovery from the source fluid. It can be either used for thermal applications or power applications depending upon its availability. As siloxanes are deep dry working fluids, their internal regeneration capability is good and hence another bottoming cycle can be thought with lower boiling point organic working fluid in conjunction with primary bottoming cycle. A very innovative scheme with R-245fa and butane bottoming cycles are studied in conjunction with MM saturated cycle at 0.9Pr. The power recovery potential by using both the bottoming cycle schemes is studied. The combined cycle efficiency of 70.82% is obtained by using this arrangement. This scheme increases complexity of the combined cycle. Hence a dual pressure bottoming cycle scheme is developed using MM as the working fluid. Saturated MM is injected with expanding vapor in the turbine (which is in superheated state). Studying the potential of energy recovery in this arrangement is very creative.