Improving bagasse-furnace combustion and modelling

The control of bagasse combustion in the furnace is an important part of boiler operations for sugarcane factories. High bagasse moistures and/or high boiler steam loads can lead to furnace combustion issues. Significant effort has been carried out, for example, in improving boiler operating procedures and equipment interlocks to minimize the probability of such occurrences. This paper has considered options and designs to reduce the likelihood of bagasse deposition on furnace grates and resultant furnace instability. The literature described a modified conventional spreader design that resulted in improved combustion. The computational fluid dynamics (CFD) software code FURNACE, was used to determine the predicted steady-state behaviour of a furnace when fed by conventional spreaders and swirl spreaders, with the swirl spreaders using a significant quantity of the hot air previously going through the grate. The predictions and previous research were used to gain an improved understanding of how swirl spreaders modify the operation of the furnace. With improved combustion stability, a boiler could be operated at lower excess air levels and, therefore, higher efficiency. This should lead to a significant reduction in wear of boiler components such as convection banks, economisers, dust collectors and air heaters. Some current limitations of the FURNACE code are described. Addressing those limitations and subsequent application of the updated code will assist in evaluating improvements to boiler design for improved combustion performance. Key words Furnace combustion, bagasse grate deposition, pressure fluctuations, computational fluid dynamics