YUHONG GROUP - Working Principle and Classification of Waste Heat Boilers

Working Principle of Waste Heat Boiler
Waste heat boiler is a boiler that utilises the sensible heat in the waste gas, waste materials or waste liquids of various industrial processes or the heat generated by the combustion of its combustible materials. Or in the combined cycle unit of oil (or gas), the boiler that uses the heat of high-temperature flue gas discharged from the gas turbine.
Waste heat boilers are divided into two categories: fire tube and water tube. Its structure is similar to industrial boilers. Fire tube type waste heat boiler water storage capacity, in the flue gas volume and steam volume fluctuations in the conditions of steam pressure fluctuation is small, but its evaporation and steam pressure are subject to the diameter of the drum and the limitations of the operating conditions. In addition, the end of the flue pipe and tube plate due to poor cooling and temperature stress is greater, in the smoke temperature is high (higher than 600 ℃), the tube plate thickness of the case is not suitable for such a boiler, it is appropriate to use the water tube waste heat boiler. Water tube waste heat boiler has auxiliary circulation and natural circulation of two kinds of circulation.
Waste heat boiler is an important energy-saving equipment, a variety of smelting furnace and kiln exhaust temperature of 650 ~ 1250 ℃; gas turbines and diesel engines and other power machinery exhaust temperature of 370 ~ 540 ℃. Installation of waste heat boilers to absorb part of the heat in these exhaust fumes, the heat energy utilisation rate of the whole system can be significantly improved.

Classification of waste heat boilers
There are many varieties of waste heat boilers, such as three-waste mixed combustion furnace, cement kiln waste heat boiler, iron and steel waste heat boiler, hazardous waste waste heat boiler, waste incineration waste heat boiler, steelmaking waste heat boiler and so on.

According to the nature of waste heat can be divided into seven categories:
1. High-temperature flue gas waste heat: it is a common form, which is characterised by a large output, production point concentration, continuity, easy to recover and use, the heat taken away from the total heat accounted for 40 to 50% of the heat, the waste heat boiler to recover the heat, which can be used for production or living heat and power generation.
2. High-temperature slag waste heat: such as blast furnace slag, converter slag, electric furnace slag, etc., the slag temperature of more than 1,000 ℃, it takes away 20% of the total heat.
3. Waste heat of high-temperature products: such as coke oven coke, steel ingots and billets, high-temperature forgings, etc., which are generally very high temperature and contain a large amount of waste heat.
4. Waste heat of combustible waste gas and waste liquid: such as blast furnace gas, catalytic cracking regeneration waste gas from refineries, black liquor from paper mills, etc., which can be utilised.
5. Waste heat of chemical reaction: such as metallurgy, sulfuric acid, phosphoric acid, fertiliser, chemical fibre, paint and other industrial sectors, all produce a large amount of waste heat of chemical reaction.
6. Waste heat of cooling medium: such as industrial furnaces and kilns, water jackets and other cooling devices discharged a large number of cooling water, steam output from a variety of vaporised cooling devices contain a large amount of waste heat, they can be reasonably used.
7. Waste heat of condensate: the physical sensible heat of the steam used in the production process of various industrial sectors when it is condensed and reduced after the industrial process.

Classification according to the pressure level of the steam produced by the waste heat boiler
At present, waste heat boilers use five major types of steam systems, including single-pressure, double-pressure, double-pressure reheat, triple-pressure, and triple-pressure reheat.
1. Single-pressure class waste heat boiler: the waste heat boiler produces only one pressure of steam supply to the turbine.
2. Double-pressure or multi-pressure waste heat boiler: the waste heat boiler can produce two different pressures or a variety of different pressures of steam supplied to the turbine.

Classified according to the arrangement of the heating surface
1. Horizontal arrangement of waste heat boiler
2.Vertical arrangement of waste heat boiler

According to the flow characteristics of the mass in the evaporation of the heating surface (principle of operation) classification
1. Natural circulation waste heat boiler
2. Forced circulation waste heat boiler
3.Direct current waste heat boiler