The exhaust flue gas from natural gas boiler(NGB)contains a lot of sensible heat and latent heat

and recycle and utilization of the heat can significantly improve energy efficiency.Based on the heat features of NGB flue gas

a new heat recovery system was proposed to realize recycle and cascade utilization of both latent and sensible heat in the flue gas.In this system

the high grade sensible heat is converted to electric energy by organic Rankine cycle(ORC)

while the low grade sensible heat and latent heat recovered by condensation of working fluids and absorption of cooling water.A thermodynamic and economic model is established to evaluate the system performance.The results show that

thermal efficiency of natural gas boiler equipped with the heat recover unit increase by 11% under the reference conditions

and payback period of the unit is about 1.2 years

and the net present value is approximately 4.32 million CNY after five years.Based on this performance evaluation

effects of main operating parameters on system thermodynamic and economic performance are analyzed

which can provide a foundation for optimization of the system.