The purpose of the air preheater is to recover the heat from the flue gas(exhaust gases) from the boiler to improve boiler efficiency. Incidentally the gases are sent to the chimney or stack at lowered temperature so that the design of the ducting and the stack becomes simplified. Also it controls the temperature of gases coming out of the stack.

Air pre-heater is a device used to improve the heat exchange performance of the boiler and reduce energy consumption. It refers to the flue gas in the tail flue of the boiler which passes through the internal heat sink and preheats the air before entering the boiler to the heating surface with a certain temperature.Air preheater is generally divided into three types: plate type, rotary type and pipe type.The working principle of air preheater is introduced by taking rotary type as an example.A large number of unburned combustibles may deposit on the heat transfer elements and the air preheater may catch fire.The analysis of brake drop and air leakage control are also introduced in detail.

Different types

For the use in Steam Generators (boilers)in Thermal power stations of Utility power stations, there are two types of design of the Airpreheaters. One is a tubular type built into the boiler outlet Flue_gas ducting and another one is of the regenerative type known as Ljungstrom (named after the name of inventor) Regenerative Air Pre Heater(RAPH),a rotating type. This may be horizontal (now very common in power generation utilities) or vertical.

Functions

1. Improve and strengthen combustion
The air after the waste heat enters the furnace, accelerates the fuel drying, ignition and combustion process, ensures the stable combustion in the boiler, and improves the combustion efficiency.
2. Strengthen heat transfer
As the combustion in the furnace has been improved and strengthened, and the temperature of hot air entering the furnace has been increased, the average temperature level in the furnace has also been increased, so as to strengthen the radiation heat transfer in the furnace.
3. Reduce the loss in the furnace, reduce the smoke discharge temperature, and improve the boiler's thermal efficiency
Because the combustion in the furnace is stable and the radiation heat exchange is strengthened, the chemical incomplete combustion loss can be reduced.On the other hand, the air preheater makes use of the waste heat of flue gas to further reduce the loss of smoke exhaust, so as to improve the boiler's thermal efficiency.According to experience, when the air preheater in rise by 1.5 ℃, exhaust temperature can reduce 1 ℃. After installation of air preheater in boiler flue, if we can put the air heat 150-160 ℃, can reduce exhaust temperature 110-120 ℃, the boiler thermal efficiency can be increased by 7% - 7.5%.You can save 11 to 12 percent on fuel.
4, hot air can be used as fuel desiccant
For laminar combustion furnace, hot air can be used as fuel with high moisture and ash content. For power plant boiler, hot air is an important desiccant and coal powder conveying medium in the fat and powder system.

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