Economizer for waste heat recovery boiler
Economizer (English name Economizer) is a device installed at the lower part of the flue at the tail of the boiler to recover the waste heat of the exhaust gas. It heats the boiler feed water into a heating surface of saturated water under the drum pressure. Because it absorbs the heat of high-temperature flue gas, it reduces the exhaust temperature of the flue gas, saves energy and improves efficiency, so it is called an economizer.
Economizers using H-type finned tubes are easier to remove dust than spiral finned tubes, extending their service life.
There are many ways to classify economizers, which can be classified as follows:
1. According to the degree of heating of the feed water: it can be divided into non-boiling type and boiling type.
2. According to the manufacturing material: there are two types of cast iron and steel pipe economizers.
Non-boiling economizers are mostly made of cast iron, but they are also made of steel pipes, while boiling economizers can only be made of steel pipes. Cast iron economizers are mostly used in boilers with a pressure of ≤2.5MPa. If the pressure exceeds 2.5MPa, an economizer made of steel pipes should be used.
3. According to the form of the device: there are two types: vertical and horizontal.
4. According to the relative flow direction of exhaust gas and feed water, there are three types: downstream, countercurrent and mixed.
5. According to the structural form, there are light tube economizer and fin economizer. Fin economizers include: H-type economizer (more commonly used) and spiral fin economizer.
6. According to the form of heat conduction, there are direct conduction and indirect conduction;
The role of economizer
1. Absorb the heat of low-temperature flue gas, reduce the exhaust temperature, reduce exhaust loss, and save fuel.
2. Since the feed water is heated in the economizer before entering the drum, the heat absorption of the feed water on the heating surface is reduced, and the economizer can be used to replace part of the evaporation heating surface with a higher cost.
3. When the feed water temperature is increased, the wall temperature difference will be reduced when entering the drum, and the thermal stress will be reduced accordingly, extending the service life of the drum.
Economizer fault inspection and maintenance
The main fault of large-capacity boiler economizer is leakage of the serpentine tube. Most leaks are caused by the following three reasons:
(1) pipe wall wear,
(2) poor welding quality,
(3) inner wall corrosion.
In a few cases, there are other reasons, such as poor pipe material, cracks in the pipe wall in the heat affected zone of the weld, etc. The maintenance work should aim to eliminate these factors, understand the internal laws, and take preventive measures.
