An Eulerian-Eulerian multifluid simulation for co-combustion of coal and sawdust in industrial scale circulating fluidized bed boiler

Abstract

Co-combustion of coal and biomass reduced the net Carbon di-oxide emissions. The fluidized bed technology is best suited to burn biomass and coal combinations without major modifications to the combustion systems. Experimentation of large-scale CFBC boilers is uneconomical and time-consuming. Mathematical modelling has gained visibility in the last several decades and allows researchers to explore different circumstances and design optimization. The current research presents mathematical modelling of an industrial scale CFBC boiler (165 TPH CFBC Boiler for 100 MWe CPP) functioning in Hindalco Industries, Odisha, India, using co-combustion of coal and sawdust biomass (90 % coal + 10 % sawdust). The simulation is performed using the Eulerian-Eulerian multifluid model by considering the four different Eulerian phases (coal, sawdust, sand, and mixture gas). The kinetic theory of granular (KTGF) flows is used to model the collisions between bed material and fuel particles. User-defined functions (written in C programming language) are employed to model the reaction kinetics of heterogeneous chemical reactions. The numerical methodology is validated with the onsite industrial data of pressure drop, fluidized bed height, suspension density, bed voidage, and temperature variations. The comparison of pressure drop, fluidized bed height, axial velocity profiles, sand and mixture gas temperature variations, gas compositions, and pollutant emissions (Sulfur di-oxide and nitrous oxide) using solo coal and blended fuel are presented in the result section. Hydrodynamics steady reveals the recirculation of sand particles in the fluidized bed region of the boiler. The comparison of solo coal and blended fuel combustion study reveals an 11.42 % reduction in pressure drop, 13.17 % increase in oxygen mass fraction, 10.63 % reduction in carbon mono oxide mass fraction, 16.26 % reduction in Sulfur di-oxide mass fraction, and 7.17 % reduction in nitrous oxide mass fraction is observed at the boiler outlet while using the 10 % sawdust blends with 90 % coal.