Dynamic Modeling of the Reactive Side in Large-Scale Fluidized Bed Boilers

Abstract

This work presents a dynamic model of the reactive side of large-scale fluidized bed (FB) boilers that describes the infurnace transient operation of both bubbling and circulating FB boilers (BFB and CFB, respectively). The model solves the dynamic mass and energy balances accounting for the bulk solids, several gas species, and the fuel phase. The model uses semiempirical expressions to describe the fluid dynamics, fuel conversion, and heat transfer to the furnace walls, as derived from units other than the studied ones. The model is validated against operational data from two different industrial units: an 80 MW CFB and a 130 MW BFB, both at steady-state and transient conditions. The validated model is used to analyze: (i) the performance of the reactive side of two FB boilers under offdesign, steady-state conditions of operation; and (ii) the open-loop transient response when varying load or fuel moisture. The results underline the key role of heat capacity on the stabilization time. Within a given unit, the differences in heat capacity between the top and bottom of the furnace affect also the stabilization times, with the furnace top (lower heat capacity) being 1−3 times faster in the CFB unit and up to 10 times faster in the BFB unit. Due to the differences in gas velocity, the investigated boilers are found to stabilize more rapidly to input changes when running at full load than at partial load. Lastly, a variable ramping rate analysis shows that the inherent transient responses of the reactive side disappear when disturbances are introduced at (slower) rates, typical of industrial operation. Thus, the reactive side could be modeled as pseudo-static.

Double-Eccentric Design for the Vortex Finder of a Cyclone Separator

“…Most gas–solid fluidized bed systems adopt cyclone separators to collect the particles and maintain the material balance. − As an indispensable component for the CFB boiler, the cyclone separator plays a major role in the stable operation, which is expected with high separation efficiency.…”

Numerical and experimental study of co-combustion of refuse-derived fuels in a circulating fluidized bed during load change

“…In contrast to steady-state modelling, fewer publications have been found regarding dynamic process simulation of the CFBs. Dynamic simulation, an extension of steady-state process simulation with time-dependence, offers an essential tool for the design of energy conversion, prediction of the transient behaviour of the combustion chambers, and process configurations under changing conditions (Alobaid et al, 2017;Castilla et al, 2021). A dynamic simulation model of a 750 MW el coal-fired power plant has been developed to evaluate the operation flexibility (Starkloff et al, 2015).…”

Hydrogen Production by Coal Gasification in a Supercritical Water Fluidized Bed: Dynamic Modeling of an Industrial-Scale Reactor

“…The results showed that the model can predict the load transient response very well. Castilla 28 presented a dynamic model of large-scale fluidized bed boilers to describe the steady-state and transient conditions. The fluidized beds are found to stabilize more rapidly to input changes when running at full load than at partial load.…”