OPERATION, TESTING AND MODELLING OF THE ADVANCED SWIRL SPREADER AND SECONDARY AIR SYSTEM INSTALLATION AT PROSERPINE MILL

IN MANY CASES, factory expansion is limited by boiler steam generating capacity. The cost of conventional new boiler plant is high, making it a far more attractive proposition to increase the steam generating capacity of existing boilers. Another issue of concern to sugar factories is combustion instability. This can result in major disruptions to factory operations by causing losses in steam pressure and damage to the boiler structure. The advanced combustion system that has been retrofitted on the No.4 boiler at Proserpine Mill is an attempt to address both these issues. This retrofit consists of advanced swirl spreaders and a novel secondary air configuration. With the swirl spreaders in operation the boiler could generate at above MCR levels with minimal combustion stability problems. Only a small amount of flow was required through the outer two remaining conventional spreaders. With low bagasse moisture there was minimal grate build up and with high bagasse moisture there was localised build up near the front wall and in the rear corners with most of the grate area remaining clean. Furnace performance was found to be relatively unaffected by the settings of the spreaders. Furnace temperature measurements indicated the main flame was adjacent to the furnace rear wall. Efficiency measurements carried out when the boiler was operating above boiler MCR showed that unburnt levels were high but comparable to the unburnt levels measured shortly after the boiler commissioning. With the new front wall secondary air nozzles in operation, the main gas and particle flow was pushed away from the front wall of the furnace. Observations and temperature measurements indicated that the flow from the new front wall secondary air nozzles creates a recirculating flow pattern that causes some of the hot furnace gas to travel down the front wall.