Numerical study on the LNG application for start-up fuel in the commercial scale CFBC boiler

Abstract

We evaluated the applicability of liquid natural gas (LNG) as a start-up fuel in the circulating fluidized bed combustion (CFBC) boiler. A 250 ton/hr scale CFBC boiler, which adopts four LNG over bed burners for the operation at start-up procedure, was investigated through the commercial computational fluid dynamics (CFD) analysis. The complex LNG reactions were simplified and the Eulerian-Granular multiphase model was used to consider the behavior of bed materials and gas-solid interaction. The model reliability was obtained by comparing with design values. The simulation results showed that the bed materials have a significant impact on the internal temperature distribution of boiler despite the cold start-up condition which contains a small amount of bed material. With the consideration of two representative particle size distributions in the modeling, the calculated maximum gas temperature near the refractory was below the allowable temperature of refractory material. Further, it was predicted that the application of the actual particle size distribution on the simulation leads to a decrease of maximum gas temperature adjacent to the refractory wall. Based on the present results, LNG fuel could be acceptable for the start-up operation of CFBC boilers.