Air preheater classification
Air preheater can be divided into air preheater thermal and regenerative two categories by air preheater heat transfer method. The most common type of thermal air preheater is the tubular air preheater. With the increase of boiler parameters and capacity, the heating surface of tubular air preheater also increases, which makes it difficult to arrange the heating surface of tail. Therefore, the compact, lightweight rotary air preheater is most widely used in large capacity units. Air preheaters are generally divided into plate, rotary and tube three kinds.
Plate air preheater
This air preheater is usually made of 1.5-4mm thin steel. Weld the steel plate into a rectangular box. Spell a number of boxes together. The entire air preheater consists of 2-4 boxes. The flue gas passes from the top to the bottom through the outside of the box, while the air traverses through the inside of the box laterally, turns upward at the bottom, and transfers energy twice through the flue gas to reverse the flow of the flue gas to the air and achieve better heat transfer efficiency.
Plate air preheater due to the consumption of much steel, the structure is not compact; weld more and easy to leak, is now rarely used.
Tubular air preheater
The main heat transfer components of tubular air preheateris thin-walled steel pipe. Tubular air preheater is mostly cubic. Steel pipes are vertically staggered with each other column, both ends welded to the upper and lower tube plate. Tubular air preheater in the tube box with an intermediate tube plate, flue gas up and down along the pipe through the preheater, the air is transverse through the preheater to complete the heat conduction.
Tubular air preheater has the advantage of good sealing, heat transfer efficiency, easy to manufacture and process. It is more used in power plant boilers and industrial boilers. The disadvantage of the tubular air preheater is that it is bulky and easy to block ash in the steel pipe, which is not easy to clean and the flue gas inlet is easy to wear.
Rotary air preheater
Rotary air preheaters are the most common form of regenerative air preheaters that use air and flue gas alternately to heat the air through metal heating surfaces. Rotary air preheater can be divided into heated surface rotation and wind hood rotation two different kinds by movement. The two air preheaters for the furnace are three-point heated rotary air preheaters.
Rotor rotary air preheater consists of cylindrical rotor and fixed cylindrical housing and drive.
Rotary air preheater can be divided into two types: one is the rotation of the rotor rotating rotor rotary type, the other is the air duct rotating air duct rotary.
Rotary rotary air preheater is composed of a rotating circular rotor and a fixed shell, rotor-type heating surface, which is divided into many compartments and is equipped with a regenerative plate. The regenerator absorbs the gas heat and accumulates, waiting until it is transferred to the air side, and then release the attack heat to the air, reducing its own temperature. Heating surface constantly rotating, the heat will continue to be sent to the air from the flue gas, the air is heated, flue gas cooling, which is the working principle of rotary air preheater.
The main advantages of rotary air preheater are small size, light weight, heat transfer element allows greater wear and therefore particularly suitable for large boiler use. The disadvantage is the complex structure, and consumes electricity, air leakage larger.
Rotary preheater mainly has fire alarm (hot spot detection), clearance adjustment, frequency control, lubricating oil system, rotor stall alarm system, soot blowing and cleaning systems.
The key issues affecting the performance of rotary air preheaters are air leakage, corrosion and plugging.
When design the tubular air preheater, the air flow rate and the size of the tube should be selected properly, or the anti-vibration baffle should be installed along the air flow to prevent cavity resonance. Anti-vibration diaphragm also eliminate the noise effect. Leakage of the rotary air preheater is an important issue and measures should be taken in terms of design, manufacture, installation and operation to maintain a reasonable seal clearance between the moving and the moving components under thermal conditions. When high-sulfur fuel is burning , tubular and rotary preheaters are prone to corrosion and ash blocking. Preventive measures include: install air heaters at the air inlet or hot air recirculation; Use the low-oxygen combustion or blending additives to reduce the amount of SO2 gas generated in the flue gas; Soot regularly to keep the heated surfaces clean; Heating surface use corrosion-resistant materials.