Brandt, Warren2023-01-192023-01-192022https://hdl.handle.net/10539/34164A dissertation submitted in partial fulfilment of the requirements for the degree of Master of Science in Engineering to the Faculty of Engineering and Built Environment, School of Mechanical, Industrial and Aeronautical Engineering, University of the Witwatersrand, Johannesburg, 2021Regenerative rotary air heaters are usually one of the large contributors to the reduction of boiler efficiency, due to high leakage rates and insufficient heat transfer. Dew point related fouling of air heater element packs is one of the factors that causes insufficient heat transfer. Coal fired power station air heaters can experience excessive dew point related fouling, which commonly causes high pressure differences over the air heater steel matrix, increasing FD (Forced Draught) and ID (Induced Draught) fan loading, along with elevated air heater leakage rates. Additional consequences are premature failure of element packs, due to inflated fly ash erosion rates that occur on localised areas of the air heater steel matrix, air heater hoods, dampers and ducts. It also contributes to exaggerated levels of dust emissions due to an augmented flow and velocity of flue gas. Excessively fouled element packs can only be rectified by either applying frequent high pressure washing or replacement of element packs. Both of these are costly activities which can be avoided through applying the correct operating conditions and maintenance strategies. Through modelling of dew point operating conditions of a rotary regenerative air heater, the onset of dew point related fouling was predicted. This modelling tool was developed using mass and energy balance methods applied to element volumes in the steel matrix to estimate the gas temperature, element surface metal temperature, and dew point temperatures (water, sulphuric acid and sulphurous acid) of the flue gas. The tool provides a platform to predict the temperature profiles and to identify where the onset of dew point related fouling exist. If the element surfaces and the flue gas experience temperatures less than the dew point temperatures, the onset of dew point related fouling is expected. The modelling tool was validated through plant experiments and historical test results from previous research projects. The plant experiments were conducted for three different load conditions, namely 99% MCR (Maximum Continuous Rating), 80% MCR and 68% MCR. The results indicated that the fouling region is located mostly in the cold end layer of packs, as predicted by the simulation model. The prediction of dew point related fouling regions correlated best for the full load condition, where the metal temperatures were below the 134˚C to 152˚C range (1% to 5% SO2 to SO3 conversion respectively) of sulphuric acid dew point temperatures. (Sulphurous acid and moisture dew point temperatures are mostly encountered during boiler shut-downs or light-ups, where transient states are experienced.) During sulphuric acid condensation in normal operation, ash particles start to adhere to each other and to the surrounding metal surfaces operating below the sulphuric acid temperature band mentioned above. For all three load conditions the simulated cold end metal temperatures compared quite well to the measured metal temperatures. The measured values were influenced by factors such as thermal inertia and contact resistance, which was caused by the selected method of installation. The modelling tool was developed to equip system engineers with the means to improve operating conditions and maintenance strategies in order to prevent the onset of dew point related fouling. This study contributes to the possibility of increasing the life expectancy of air heater element packs and draught group components. It provides a platform to improve boiler efficiency, reduce maintenance costs and production losses.enDissertation