Comparison of Direct Combustion in a Circulating Fluidized Bed System and Decoupling Combustion in a Dual Fluidized Bed System for Distilled Spirit Lees

At present in China, a fluidized bed combustor is not suitable to treat a high-water-containing (30-60 wt %) industrial biomass residue, such as distilled spirit lees (DSL), which can cause a low bed temperature and inflammation retardation. Our previous fundamental studies showed that the so-called dual fluidized bed gasification decoupling combustion technology (or decoupling combustion for short) can ensure the highly efficient and stable combustion for high-water-containing biomass fuel and lower NO emission as well. In this study, the combustion characteristics of DSL in a circulating fluidized bed (CFB) system and a dual fluidized bed (DFB) system will be examined and compared systematically. For direct combustion of DSL in a CFB system, the high moisture of 30 wt % decreased the bottom temperature of the combustor significantly and brought in unstable combustion, thus leading to s large amount of auxiliary fuel (such as coal) needed to raise the temperature to reach an adiabatic flame temperature and ensure normal bed combustion. Besides, the slag formed in the loop seal also affected the stable run of the DFB combustion system. For decoupling combustion of DSL in a DFB system, both the temperatures in the gasifier and combustor were kept stable and a uniform temperature distribution in the combustor was also observed. In terms of gas emission, the average NO contents in a CFB system and a DFB system were about 160 ppm (369 mg/m(3)) and 50 ppm, respectively, which fully verified the property of low NO emission by decoupling combustion. The direct combustion of DSL in a CFB system and decoupling combustion in a DFB system were compared in an industrial demonstration plant for demonstrating technical features of decoupling combustion.