Abstract
Bottom ash from Municipal Waste fired boilers have sufficient heat content and this can be used to pre-heat the boiler feed water or the combustion air. A study of the recent developments in this area is done with a focus on the air based cooling method. Modeling and simulation of the thermal performance of an air cooled ash cooling system is done with the help of Gambit/Fluent software. Among several methods of waste disposal, incineration of Municipal Waste is opted mainly due to its energy potential and specific advantages like high volume reduction ratio and convenience in plant location. However, the inherent fuel qualities that confront this method are its high moisture and ash content and the consequent low calorific values. The fuel bed temperature in stoker fired incineration systems can reach up to 1200K and a considerable part of this heat is wasted by way of ash sensible heat loss. The methods used for ash cooling include the water cooled ash screw system, the rolling cylinder ash cooler, fluidized bed ash cooler and the high strength steel belt ash cooler. In this study, the simulation of the performance of water based and air based ash cooling systems is done for a certain municipal waste fired boiler. The effect of the two methods on the overall boiler efficiency is studied. Comparison of results with that of a working system indicates that air cooling systems can be as efficient as the water cooled systems. With the help of this study, bottom ash heat recovery, especially for waste fired boilers, will be appreciated better and power plant designers will have a better insight into this area.