Air Preheater
An air preheater is a device used to heat air before another process with the primary objective of increasing the thermal efficiency of the process. They may be used to preheat air, with combustible fuel, prior to combustion in other units, and to preheat process air fed to an incinerator, a boiler or an industrial furnace, thereby reducing the energy required to heat the air.
Heat energy can be extracted from a variety of sources, including exhaust streams from furnaces, engines, and other processes, as well as hot fluids such as water, steam, glycol and thermal oils. By using an air preheater, much of the energy contained in these fluids or exhaust streams can be recovered and put to useful work, such as preheating air for combustion or drying systems.
Air preheaters are far more efficient than direct gas-to-air heating systems such as gas burners or electric strip heaters because they transfer the heat from a much hotter medium—typically the flue gases from an industrial process—to the preheated air. Heat transfer typically takes place over a number of small-diameter pipes to ensure maximum surface contact area, boosting the heat transfer coefficient.
The most common type of air preheater is the regenerative air preheater. In this type of air preheater, exhaust gasses pass through a series of small diameter pipes, surrounded by a rotating drum filled with baffles. These will capture some of the energy contained in the exhaust gasses and transfer it to the air passing through the unit.
The baffles will also help to achieve a uniform velocity of the exhaust gasses, improving the overall efficiency of the unit. As the baffles rotate, they will heat one side of the drum while cooling the other side. This cycling of heating/cooling will increase the efficiency of the preheater by allowing the heated side of the drum to compact against the air being preheated, allowing better energy transference.
Air preheaters can also be used to help reduce emissions from processes by decreasing the flue gas temperature, meaning that further processing such as fabric filters, gas scrubbers, and grey water filtrations can be used. As a result, emissions from processes such as boilers and furnaces can be reduced, thus improving air quality.
Air preheaters also reduce fuel consumption compared to direct-fired systems, as the combustion efficiency increases with the preheating of the air, meaning that less fuel is needed to heat the air. This can lead to improved operations costs, as well as a reduction in greenhouse gas emissions.
Due to their energy-saving and pollution-reducing benefits, air preheaters are an increasingly popular choice for a variety of industrial processes. Not only can they improve efficiency, but they can also reduce costs associated with fuel consumption and pollution control.
