There are various types of gas preheaters, and the following introduces their common types from different classification methods:
Classified by heat exchange method
Heat exchange preheater
Metal preheater: commonly used forms include tubular, radiant tube, jet type, needle shaped, sheet shaped, etc. It has good thermal conductivity, large heat transfer coefficient, and small volume. Due to welding between metals, it has good airtightness and can preheat high-pressure air or gas. However, the temperature that metals can withstand is limited. When the preheating temperature of gas or air is slightly higher, other materials of preheaters are often considered.
Ceramic preheater: with a small heat transfer coefficient, large volume, poor air tightness, but high fire resistance, it can preheat air to high temperatures of 900-1000 ℃, long service life, suitable for occasions with high preheating temperature requirements and relatively less strict requirements for equipment volume and air tightness.
Heat pipe preheater: a new type of energy-saving equipment that has the characteristics of small volume, light weight, and high efficiency compared to steel pipe preheaters and rotary preheaters. It is composed of a closed tube shell or shell, with a porous capillary wick embedded on the inner surface. The wick is immersed in liquid phase working fluid, while the remaining space of the heat pipe contains gas phase working fluid. The heat transfer efficiency is high through the phase change of the working fluid.
Regenerative preheater (also known as rotary heat exchanger): The flue gas enters the heat exchanger from the inlet and flows downwards through half of the heat storage plate of the rotor. When the flue gas flows through the heat storage plate, it transfers heat to the plate, causing its temperature to rise. Air enters the heat exchanger from below on the other side, flows through the rotating rotor at 120 °, and absorbs heat from the heat storage plate that has been heated by the flue gas, causing its temperature to rise. Its characteristics are compact structure, small volume, steel saving, convenient layout, low risk of smoke corrosion, and long maintenance cycle.
Classified by structural form
Tube preheater: There are various structural forms, including straight pipes, bent pipes, U-shaped pipes, etc. The arrangement of pipes can be in series or staggered, and the installation method can be horizontal or vertical. The preheated air can flow inside or outside the tube, usually outside the tube. For example, straight pipe production and installation are simple, but have a large expansion force; The expansion stress of the bent pipe is relatively small, but it is difficult to produce and replace the pipe; The U-shaped steel pipe preheater tube group has the smallest expansion force after heating, making installation and tube replacement more convenient. However, the bending radius of the tubes is different, making production more complex.
Plate preheater: Using fully welded plate bundles as heat transfer units and stainless steel plates as heat transfer elements, the plates are sealed by welding to ensure high heat transfer efficiency and solve the safety problem of flue gas leakage. Compared with traditional preheaters, it has good heat transfer performance, high heat transfer efficiency, compact structure, and is suitable for low resistance waste heat recovery systems that burn clean fuels. The fully welded structure and inter plate bulging support ensure the overall safety performance of the core, and the operation is stable and reliable.
Combination preheater: combines the advantages of plate and tube types, making it more suitable for high sulfur conditions and resistant to scaling. Preheating is divided into high temperature section and low temperature section according to the inlet and outlet temperature requirements of the flue gas.
Enamel tube air preheater: using enamel tubes as heat transfer elements, preheating low-temperature air with high-temperature flue gas. Smoke flows outside the tube, and inorganic silicates adhere to the outer surface of the enamel tube, which can effectively resist dew point corrosion caused by smoke during the cooling process. Non corrosive air flows inside the tube, forming cross flow heat transfer between cold and hot fluids, effectively solving the corrosion problem in waste heat recovery of smoke and improving the utilization of low-grade heat in smoke.