Study of Operation of a Pilot CFB-Reactor in Dynamic Conditions

Abstract

The development of a high efficiency CFB power plant (once-through supercritical CFB technology) and the use of alternative fuels require advanced methods of control and knowledge of the dynamic behavior of the furnace. Dynamic response analysis is needed for design of control algorithms in load changes. The operation of a pilot CFB-reactor in dynamic conditions and in load changes is analyzed experimentally and by modeling at different process conditions. Reactivity parameters for different fuels can be extracted from simple dynamic measurements and then used in computations studying operation in load changes. Dynamic studies are also required to see the necessary requirements for the fuel quality and fuel feed system to maintain stable operation. For high volatile coals the fuel feeding must be steadier to keep the variation in the outlet oxygen concentration at some range than with coals with low reactivity or alternatively greater air coefficient is needed to prevent too low O2 concentrations, which can cause an increase in CO emissions. The fuel quality can be characterized by the fluctuation of oxygen concentration in flue gases in steady operation conditions, which depends on the fluctuations in the combustion and in the fuel feed and on operational conditions. The amplitude of the fluctuations was studied. For advanced controls, it is necessary to know the factors affecting the process dynamics, such as reactivity and the behavior of char inventory in bed. This information is also necessary in developing and optimizing the CFB boiler considering emissions, combustion process and furnace scale up.

Acceleration of Load Changes by Controlling the Operating Parameters in CFB Co-Combustion

“…The carbon inventory inside the bed has a major impact on the load following capabilities of a CFB boiler, as it damps any changes in the fuel feeding rate. Gao et al (Gao et al, 2017) and Tourunen et al (Tourunen et al, 2003) proposed to take into account this carbon inventory as an energy storage to accelerate the boiler response time by a suitable control strategy, e.g., burning the carbon with additional primary air. The carbon inside the bed depends on the combustion conditions and can be adjusted e.g., by co-combustion of coal and biomass (high volatile content).…”