Experience gained in the design and optimisation of gas-cleaning equipment for sugar-mill boilers

Design experience in gas-cleaning equipment between the boiler, air heater and economiser is highlighted. Having multicyclones fitted into the horizontal ducting before the air heater and economiser is extremely important to protect both from erosion and build-up and improve heat- transfer efficiency, thereby reducing operating costs. Depending on the boiler fuel, specific gas-cleaning equipment is designed to meet specific environmental legislation. Bagasse firing requires a medium-efficiency wet scrubber, whereas dual-fired bagasse-coal firing requires a higher-efficiency venturi scrubber. For dual-firing, it is important to note the two duty points for design, and design for suitable turndown. Overall, it is important to custom design the capacities of the gas-cleaning equipment to closely match the boiler’s maximum continuous rating, maximum load and turndown requirements. The water quality and requirements for the effects are highlighted for the wet-scrubber operations. Experience in designing and operating boiler off-gas fans has led to innovations in fan designs, linings and coatings. Case studies highlighting the efficiencies are presented. Key words Gas cleaning, cyclone, cyclonic scrubber, venturi scrubber, vane scrubber