Dynamic measurements and analysis of fuel reactivity in a laboratory scale circulating fluidized bed combustor

Fuel reactivity and dynamic behavior strongly affect the design of control logic at power plants. The changes in fuel feeding and in fuel quality, which are ordinary in multi-fuel operation, call for high requirements for control systems. On the other hand, e.g. for the development of high efficiency CFB power plant with once-through system cycle needs advanced methods of steam cycle control and automation. The development of control systems of this kind requires additional information on boiler and combustion dynamics. A laboratory scale circulating fluidized bed combustor is applied to characterize the combustion reactivity of solid fuels in CFB boilers. The test program consists of measurements of different gas components in steady state and transient states. The transient response of oxygen concentration to an impulse in the fuel feed is used in the analysis. A simplified one-dimensional time-dependent numerical model for the transient behavior of the CFB combustor is developed for the interpretation of the transient data. An analytical approximate model is also presented. The most important fuel properties affecting the transient response are the amount of volatile matter, density, particle size and chemical reactivity of char. The ratio between the reactivity and process conditions as also investigated. Temperature, inlet oxygen concentration, amount of fuel in the impulse feed and the ratio of primary and secondary air are varied in the measurements