Energy & Fuels, Vol.26, No.2, 1044-1053, 2012
Combustion of Predried Brown Coal in a Tangentially Fired Furnace under Different Operating Conditions
A major challenge in the use of brown coal in Victoria, Australia, for power generation is its high moisture content, which results in high greenhouse gas emissions. Predrying technologies for coal are one option being considered for use in brown-coal-fired power plants in Victoria to reduce greenhouse gas emissions. Using a validated computational fluid dynamics (CFD) model, this study investigates the combustion of predried brown coal in a 375 MW tangentially fired furnace that was designed for raw or non-predried brown coal. Different operating arrangements of the fuel gas for the predried coal with various moisture contents are proposed and assessed. When predried brown coal is burned with 55% or lower moisture content, the CFD results indicate that additional gas needs to be added to the fuel gas to maintain the original mass flow rate and reduce the heat flux in the furnace. Arrangements with additional air or recirculated flue gas added to the fuel gas are proposed and tested for predried coal with 55, 45, 35, 25, and 15% moisture contents. The increase in the furnace temperature for the recirculated flue gas arrangement is smaller than that of the additional air arrangement, and stack loss is expected to be smaller than for additional air cases. The temperature distributions and wall heat fluxes in the boiler for the recirculated flue gas cases are similar to that of the raw coal combustion case. Therefore, use of recirculated flue gas is proposed as an option for future operation of the furnace with predried coal. Nevertheless, further studies are essential to understand the technical and financial feasibility of using flue gas to maintain the fuel gas flow rate.