Feasibility Study On Gas-steam Combined Cycle Flue Gas Latent Heat Utilization

The performance thermal of Gas-steam combined cycle is good, but the energy efficiency is far from the maximum, and it’s still has the potential to increase. The flue gas due to combustion of natural has large proportion of water vapor and substantially free SO2, so reducing the temperature of cycle heat and recycling the latent heat of flue gas can effectively improve energy efficiency. Aiming gas-steam combined cycle latent heat recovery problem theoretically conducted systematic research.First, according to Hebei fueled with natural gas components, we can conduct combustion calculations, and then analysis the flue gas produced by combustion. Through comparing the recycled flue gas sensible heat and latent heat relationship we can analyze the trends in different exhaust gas temperature and analysis the condensation characteristic of flue gas under equilibrium conditions.Second, investigating the condensation heat transfer mechanism of mixed convection gas in which containing a small amount of water vapor, which focusing on the volume fraction of water vapor in the range of6%to15%of the heat transfer case. Analyzing transfer characteristics of mass, heat and momentum inside diffusion film near the Phase boundary by using film model.If using the analogy relations about heat and mass transfer and taking into account the impact of additional speed caused by the mass transfer, then we can propose convective sensible heat exchanger of flue gas which contents moisture and latent heat of condensation heat transfer model. Export describing the phenomenon of differential equations and solve to get gas film speed, concentration and temperature distribution and velocity distribution within the film. Of the convective heat and mass transfer process dimensionless analysis, the dimensionless number-condensing heat factor associated guidelines, the use of relational seeking condensation heat transfer film coefficient.According to the Endothermic balance of the heat recovery boiler feed water, exhaust temperature cannot reduce to a temperature below the dew point by using boiler feed water as cryogenic medium, which resulting in water vapor condensation takes very small proportion in heat exchanger and the quantity of flue gas heat recovering is very limited. For this problem, put forward a new idea of recovering flue gas latent heat. It is said that combining the condensing heat exchanger and double-effect absorption heat pump to use the low-temperature circulating water (backwater25℃) of heat absorption heat pump as cryogenic medium of condensing heat exchanger to design a heating hot water cogeneration system which utilizing the waste heat to heat network water. Analysis the economic and environmental benefits of the new system, the results show that the new system can effectively recycle flue gas latent heat. The new system can reduce by30%the amount of extraction steam turbine, the steam turbine power generation improved11.32%in rated extraction conditions, heating capacity increased by53.66%, which shows that the utilization of natural gas significantly improved. For system problems, exploring feasibility and strengthening effect of different means of condensation heat transfer enhancement.