How many types of air preheaters and Explain its advantages? Types of air preheaters and its advantages

How many types of air preheaters and Explain its advantages?
An air preheater (APH) is a General term to describe any device, the air before another
process is heated (e.g., combustion in a boiler) with the main objective to improve the
thermal efficiency of the process.
Air pre-heating can increase boiler efficiency and reduce chimney loss. They can be used
alone or replace a heat recovery system or replace the Steam coil. An air preheater (APH) is
a device used in steam boilers to transfer heat from the flue gases to the combustion air
before it enters the oven. Air preheater recovers the heat from the boiler flue gas and
increases the thermal efficiency of the boiler . The flue gases are fed into the combustion
gas stack at a lower temperature to control the temperature of the gases.
The combustion air preheaters are used in large boilers in thermal power plants to
generate electricity from such fossil fuels, biomass or waste.
The purpose of the air preheater heat recovered from boiler flue gases that increase the
boiler thermal efficiency by reducing the useful heat lost in flue gases. As a result, the flue
gas is also sent to the stack flue gas(or chimney) at lower temperatures, making simplified
construction of duct and exhaust stack. It also allows control over the temperature of the
gas leaving the stack (to meet emissions regulations, for example,)