Types and characteristics of air preheaters

Air preheaters come in forms such as heat pipe type, tube type, plate type, box type, etc. The specific conditions are determined by the use occasion, and different conditions determine different forms.

I only know about tubular air preheaters, which are used in pulverized coal furnaces. The inside of the air preheater tube is flue gas, and the outside of the tube is wind. There are three main problems that may occur.: 1. Wear problem. This situation mainly occurs at the entrance of the preheater tube 200mm-350mm. The cause of this problem is mainly caused by the disturbance when the flue gas enters the pipe section. The internal flow is basically stable, so the wear problem is not serious. In addition, the wear and tear of the air preheater in the low temperature section is also caused by corrosion. ； Second, corrosion problems mainly occur in the superheater tube section in the low-temperature section due to low exhaust gas temperature. They also occur near the furnace wall due to air leakage in the furnace. ； Third, the clogging problem. Most of the clogging problems are caused by the leakage of the economizer pipe. The phenomenon is that the exhaust gas temperature rises and the fan power consumption increases. In addition, after the air preheater pipe is clogged, due to incomplete cleaning, it will also cause the deviation of the exhaust gas temperature to become larger. This is my little gain, I want to share it. . . .

Our company mainly uses heat pipe type, tube type, and coal-mediated type (heat is transferred through the intermediate medium, and the flue gas and air do not exchange heat directly, which is especially useful for flue gas that is highly corrosive)

It seems that the people above are all small boilers. As we all know, units with a single unit capacity of more than 125,000 (boiler 400T/h) use three-compartment rotary air preheaters. Of course, it is also a type of regenerative heat exchanger.

Introduction to Plate Air Preheater Plate air preheater, as its name implies, is an exchanger made of flat plates for gas heat exchange. It is different from liquid plate heat exchangers in that it can be used as a preheater in flue gases with temperatures up to 580 degrees. Generally, plate air preheaters are divided into two categories:: Flat plate heat exchanger and corrugated plate heat exchanger. The function of the air preheater is to recover heat and reduce consumption. It is mainly used in hydrogen production reformers or cracking furnaces of large chemical companies. It is used in devices that convert raw materials such as natural gas, refinery petroleum gas, and naphtha into hydrogen production. It is used as a heater for combustion air. It has a wide range of applications and has replaced the traditional tube plate air preheater and heat pipe air preheater abroad. Wide range of application fuels: Natural gas, petroleum gas, naphtha, coal, sulfur recovery, etc. Application prospects: Technological breakthroughs in large-scale chemical plants have opened up the application prospects of plate air preheaters. The construction of hydrogen production units with a capacity of more than 100,000M3 has made plate air preheaters an indispensable and preferred equipment (tubular air preheaters are too large to be deployed). The flat plate air preheaters of Dutch APEX Company have good application performance in large-scale projects such as Nanjing Yangba Company, Shanghai BASF Ethylene, CNOOC 800,000 tons of urea, CNOOC 600,000 tons of methanol, Qinghai Zhonghao 600,000 tons of methanol. Advantages of plate air preheater: 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. High heat exchange efficiency,

Used heat pipe type: The resistance is small, a soot blower is added to the flue gas side, and some air blowing outlets are added.

The air preheater is a heat exchange device that uses the flue gas at the rear of the boiler to heat the air. The air preheater has the following functions. 　　 (1) Reduce exhaust smoke temperature, improve boiler efficiency, and save fuel. In modern power plants, due to the use of heat recovery cycles, the temperature of the feed water after passing through the heaters at all levels is relatively high, so the flue temperature at the outlet of the economizer is still relatively high. After installing the air preheater, the exhaust heat is used to heat the cold air so that the exhaust temperature can be reduced. Tests show that every 10°C decrease in exhaust gas temperature can increase boiler efficiency by 1%. 　　 (2) Increase the air temperature, improve combustion conditions, and reduce incomplete combustion losses. The air is heated to a certain temperature and then sent into the furnace, which increases the temperature level of the furnace, improves the ignition and combustion conditions of the fuel, makes the ignition and combustion in the furnace rapid and complete, reduces the mechanical incomplete combustion loss q4 and chemical incomplete combustion loss g3, and improves the boiler efficiency. 　　 (3) Increase the furnace temperature and increase furnace heat transfer. Higher temperature hot air is sent into the furnace, which increases the temperature level of the furnace, thereby increasing the radiant heat in the furnace and increasing the evaporation of the boiler. Under a certain amount of evaporation, the evaporation heating surface in the furnace can be reduced and the metal consumption of the boiler can be reduced. 　　 (4) Improve the working conditions of the induced draft fan. As the exhaust smoke temperature of the boiler decreases, the inlet smoke temperature of the induced draft fan decreases, which improves the working conditions of the induced draft fan and also reduces the power consumption of the induced draft fan. 　　 2. Classification of air preheaters According to the heat transfer method of air preheaters, air preheaters can be divided into two categories: heat conduction type and regenerative type. The most commonly used thermal air preheater is the tubular air preheater. As boiler parameters and capacity increase, the heating surface of the tubular air preheater also increases, which brings difficulties to the layout of the tail heating surface. Therefore, compact and lightweight rotary air preheaters are mostly used in large-capacity units. 　　 Rotary air preheater is the most common form of regenerative air preheater. It uses flue gas and air to alternately pass through a metal heating surface to heat the air. Rotary air preheaters can be divided into two types according to the movement mode: heating surface rotation and wind hood rotation. The two air preheaters of this furnace are three-compartment heating surface rotating air preheaters.