Modeling study on the dynamic characteristics in the full-loop of a 350 MW supercritical CFB boiler under load regulation

Abstract

To improve the load regulation ability of the circulating fluidized bed (CFB) unit, investigating the hydrodynamic characteristics of the gas-solid flow in the CFB loop during such processes is of vital importance. In this work, based on the mass and pressure balance in the whole loop, a one-dimensional dynamic model on the gas-solid flow in the full-loop of an industrial CFB was established. In particular, the solid mass flow rate at the dust exit was correlated with the total inventory of the cyclone, and the re-circulating rate to the furnace was depicted by the pressure drop in the loop seal. The model was validated by the field test data of a 350 MW supercritical CFB boiler during a load increasing process. Subsequently, the impact of the load change rate and operating bed pressure on the hydrodynamic performance in the whole loop of the CFB boiler during the load reduction process were analyzed. The results show that the bed pressure in the furnace will fluctuate more violently when the load change rate increases, while the operating bed pressure has a weak effect on the load regulation process. These conclusions can provide theoretical guidance to the variable load operation of the CFB boiler.