Air preheating coils and air preheaters

Air preheater air preheater is a heating surface where the flue gas in the tail flue of the boiler preheats the air before entering the boiler to a certain temperature through the internal heat sink. Used to improve the heat exchange performance of the boiler and reduce energy consumption. 　　Generally referred to as air preheater. Mostly used in coal-fired boilers. The application in boilers is generally a three-compartment type. 　　The space-time preheater rotates slowly while the flue gas inlet and air inlet remain unchanged. The flue gas enters the flue gas side of the air preheater and is discharged. The radiator fins that have absorbed the heat of the flue gas come to the air side as the air preheater rotates and transfer the heat to the air. 　　The accompanying systems mainly include fire alarm (hot spot detection), gap adjustment, and frequency conversion control. 　　The key issues affecting the performance of air preheaters are: Vibration, noise, air leakage, corrosion and dust blocking. When designing a tubular air preheater, the air flow rate and tube box size should be reasonably selected, or an anti-vibration baffle should be installed along the air flow direction to prevent cavity resonance. Anti-vibration partitions also have the function of eliminating noise. Air leakage of the rotary air preheater is an important issue, and measures should be taken from the aspects of design, manufacturing, installation and operation to maintain a reasonable sealing gap between the dynamic and static components in the hot state. When burning high-sulfur fuel, both tubular and rotary preheaters are prone to corrosion and ash clogging. Preventive measures include: Install a heater at the air inlet or use hot air recirculation ； Use low-oxygen combustion or blending additives to reduce the generation of SO2 gas in the flue gas ； Blow soot regularly to keep heating surfaces clean ； The heating surface is made of corrosion-resistant materials.

The air preheater is a device that uses the waste heat of flue gas to heat the air. It preheats the cold air to a certain temperature as needed, and then assists combustion in various sizes of combustion furnaces to achieve energy saving.

I think the preheating tube is the tube bundle in the air preheater. This is my understanding. The preheater uses the waste heat of the flue gas or uses the flue gas to heat the introduction in the heat pipe. After vaporization, it is condensed by the air on the other side. And this air is heated. The heat transfer medium in the middle is the introduction and heat pipe in the heat pipe.

My understanding is that the concept should be similar. The structural forms are different and the occasions for use are different. If the heat exchange area is small, air preheating coils can be used. However, if the heat exchange area is large, the coil will have to be wound many times, which is not economical. In that case, air preheaters are more suitable.

Theoretically they are the same, but the heat exchange area and structure are different.

Are air preheating coils and air preheaters the same concept? answer: The air preheater coil is an internal component of the tubular air preheater. There are many types of air preheaters. The most commonly used ones are heat pipe type, plain tube type, fin tube type, reinforced tube type, and rotary type. With the need for large-scale chemical engineering projects, the floor space of the tube air preheater is very large and cannot be arranged. Plate air preheaters have been used in large-scale chemical projects constructed in recent years. Plate air preheaters have many advantages. Compact structure, flexible design, wide selection of materials to avoid thermal expansion, carbon steel, stainless steel, cast iron, glass,,, maintenance-free, with a service life of up to 30 years, small size, adaptable to the needs of large-scale installations, it is 1/3 the volume of a tubular air preheater. It has high heat exchange efficiency and a wide range of fuel applications.

Almost the same, just the heat exchange area and usage scenarios are different.

How to choose the heat transfer coefficient of this preheater?