An Analysis of LNG(Liquefied Natural Gas)-fired Combined Cycle Power Plants with a Waste Heat Recovery System

Presented was a waste heat recovery system,which fully recovers two kinds of low-temperature waste heat in a LNG(Liq-uefied Natural Gas)-fired combined cycle power plant,i. e. the latent heat of the exhaust steam from a steam turbine and the vapor latent heat of flue gases from a waste heat recovery boiler. A thermodynamic analysis shows that relative to a 240 MW conventional combined cycle power plant,the net electric efficiency and exergy one of the system in question can in-crease by 1.6% and 2.84% respectively. The fuel utilization rate can hit 62.88%.This means that a heat quantity of 86.27 kJ/s can be recovered from each kilogram of the flue gases. Hot water at a mass flow rate of about 46.1 kg/s,with a temperature of 167.45℃ and a pressure of 0.84 MPa,can be extracted from the outlet of a low-pressure economizer,which can be fed into a waste heat utilization sub-system. A cost-effectiveness analysis indicates that the payback period of the investment for the heat recovery system is 0.117 years. All these features attest to an extremely strong attractiveness inherent to newly-built LNG-fired combined cycle power plants and the retrofitting of the existing ones.