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(Liquefied 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 energy one of the system in question can increase 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°C 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.