Research On Control Of Dual-fuel System Of Chemically Recuperated Gas Turbine Test-bed

Chemically recuperated cycle of gas turbine is an advanced cycle to improve efficiency and reduce emissions. Dual-fuel system is a key component of chemically recuperated gas turbine, and making the combustor outlet temperature stay at the set value of temperature is the primary control requirement of such system. The combustor outlet temperature is not allowed overheat no matter it is in the course of burning fuel, mixing gas, or switching fuels.In this paper, the mathematical model of the main parts of dual-fuel system is established, and the diesel cracking reaction under certain temperature and pressure is analyzed. Besides, the mixture calorific value under different cracking rate is calculated, and the control system with burning fuel and the mixture gas is also designed. The control simulation shows that cascade PID control is better than single-loop PID control, and the cascade PID control's adjusting time is 42.9% shorten than single-loop PID control's under certain combustor outlet temperature.The combustion mixture control is different from the ordinary dual-fuel system. In order to make the combustor outlet temperature invariable, the fuel flow of chemical regenerator should fluctuate within certain borders in a system which burns gaseous fuels. For example, when the setting combustor outlet temperature is 1250℃, the fuel flow of chemical regenerator fluctuates between 0.174kg/s and 0.140kg/s.Dual-fuel exchange is the key to a dual fuel system control for the fact that there often appear fluctuations of speed, power and temperature during the course of dual fuel exchange. The combustor outlet temperature is an important index of gas turbine, and the sharp fluctuation is not allowed in a running project. So on the basis of the detailed analysis of fuel exchange, subsection approximating methods is adopted as a good way to solve such a problem. The control simulation shows that it is not over-temperature with subsection approximating methods while no basically change in response time.On the basis of establishing control strategy of dual-fuel system and exchange, hardware and software with Siemens PLC are designed, and HMI with convenient parameter settings and control is built.