Comparison of two methods of retrofitting a bagasse boiler: increasing the heating-surface areas and installing a flue-gas dryer

The efficiency of a bagasse boiler increases as the final flue-gas temperature decreases. High flue-gas temperatures may be used to reduce the moisture content of bagasse in a flue-gas dryer. Alternatively, increasing the surface areas of an economizer and air heater can also decrease the flue-gas temperature. In this paper, both methods of retrofitting a low-efficiency bagasse boiler, based on a boiler model and a flue-gas dryer model, are compared. The bagasse boiler in this model consists of a furnace, evaporator, steam drum, superheater, boiler bank, economizer, and air heater. Both models are used to demonstrate that, under the same controlled conditions, both methods of retrofitting can effectively reduce the fuel consumption and increase the boiler efficiency. It is also shown that the cost of the flue-gas dryer must be lower than an upper limit so that the total cost of installing a flue-gas dryer is not higher than the total cost of adding heating-surface areas. Key words Process simulation, heat recovery, flue-gas dryer, heat exchanger