Authors: Cyrus Meher-Homji, David Messersmith, Pradeep Pillai
The use of supercritical CO2 (sCO2) as a working fluid for waste heat recovery has several advantages and can be deployed in a LNG facility boosting the overall thermal efficiency and reducing emissions. Supercritical CO2 is inexpensive, nonflammable and easily available. Due to its high working pressure, highly compact systems can be built. The high density and volumetric heat capacity of CO2 with respect to other working fluids make it very effective in capturing waste heat from gas turbines.
This paper examines the feasibility of power generation for a LNG Liquefaction facility and makes a comparison of such a system to traditional simple cycle gas turbines and combined cycle systems. The deployment of this technology for power generation from waste heat can significantly reduce emissions. Steam based combined cycles are thermodynamically weak in performance when coupled with high efficiency aeroderivatives because of their low exhaust temperature and mass flow. This weakness can, to some extent, be offset by the deployment of supplemental firing and multi-pressure level heat recovery, both of which increase complexity. Organic Rankine Cycles have the disadvantage of using a thermodynamically inferior and toxic working fluid.
These issues can be overcome by the use of supercritical CO2. With a supercritical CO2 system, the power attainable at ISO conditions from a LM6000 is at least 10 MW. Due to the properties of supercritical CO2, equipment is much smaller, and will cost less than traditional steam HRSG equipment. Plot space is significantly lower than comparable steam systems. The most advanced packaged equipment currently is being tested in the 7-10 MW size.
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