Waste heat boiler is a boiler that uses the calorific value of sensible heat or (and) its combustible substances in industrial waste gas, waste or sewage in a variety of industrial production processes. Or in the four kinds of oil (or gas) cycle machine equipment, using the heat value of the high temperature flue gas discharged from the small turbine boiler.

Basic principle of waste heat boiler

Green waste heat boiler scheme design is a complex and complex, reliability and rationalization requirements of large, medium and small processes, there is a common problem of dependence on designers with work experience, long design time, poor recognition of professional skills and other problems, whether the rapid development of consumers must develop new products, related to the survival and development trend of enterprises.

Waste heat boilers are divided into fire tube heat exchangers and water pipe type. Its structure is similar to that of industrial boilers. The waste heat boiler of fire tube heat exchanger has large water output and small steam pressure fluctuation under the condition of smoke volume and used gas volume fluctuation, but its water surface evaporation and steam pressure are limited by the diameter of the pot drum and operation specifications.

In addition, the exhaust system hydraulic pipe and head due to poor cooling and temperature thermal stress is relatively large, in the case of high smoke temperature (higher than 600℃), thick head is not suitable for this type of boiler, and it is appropriate to use water pipe waste heat boiler. There are two kinds of circulation system of water tube waste heat boiler: help circulation and natural circulation.

Waste heat boiler A boiler that uses the gas or industrial waste gas, sewage in the industrial production operation process, and the calorific value of the exhaust steam pipe of some motor equipment to create steam or boiling water. Waste heat boiler is a very important energy-saving equipment. The exhaust system temperature of various melting furnaces and cultivation kilns is 650 ~ 1250℃; The exhaust pipe temperature of small steam turbine and diesel engine and other motor equipment is 370 ~ 540℃.

By installing waste heat boilers to digest part of the calorific value of such exhaust systems, the thermal engineering utilization of the whole management system can be significantly improved. For example, after the waste heat boiler is installed in the rolling steel heating furnace, the utilization rate of the thermal energy engineering of the whole operating system can even be increased by about 1 times.

The flue gas temperature entering the waste heat boiler is one of the most important factors in the management decision on the rational layout of the waste heat boiler heating surface. If the foreign flue gas temperature is 400 ~ 900℃, the boiler is important to set the convection tube bundle, do not set the furnace chamber; However, when the soot melting point is low, the cooling furnace room should be set up to control the temperature of the smoke entering the safe passage into the convection heat transfer kitchen flue, so as to avoid the coal ash bridging between the convection heat pipe rows.

In the cracking production process of chemical enterprises, in order to avoid the re-polymerization of high temperature cracking gas, it is necessary to rapidly cool the high temperature cracking gas to the temperature at which the cracking reflects the stop, and then the waste heat boiler becomes an indispensable chill production process.

After the high-temperature dust industrial waste gas is based on the waste heat boiler, in addition to reducing the temperature, a part of the concrete crack can be inhaled particles, which is beneficial to reducing environmental pollution and selecting dust collector equipment. In the production process of chemical enterprises, the exhaust steam pipe of waste heat boiler depends on the requirements of the next production process.

Waste heat boilers used in industrial furnaces generally use centrifugal fans to exhaust steam pipes to gas; The waste heat boiler used in the production process of motor equipment and chemical enterprises relies on the pressure of the air inlet itself to make it go to the gas or enter the next production and processing technology.

When the imported flue gas temperature or industrial waste gas ignition temperature is above 1100 ° C, its reasonable layout method is not much different from the general industrial production boiler. When the high-temperature industrial waste gas contains a lot of accumulative fine ash, the tube row of the boiler should be vertically and reasonably arranged, and the flue gas should be longitudinally cleaned at a higher smoke speed (about 20 m/s).

For high temperature industrial waste gas containing etched soot, the flow rate should be low (about 8 m/s) and uniform, and other corrosion prevention measures should be selected for high temperature industrial waste gas containing sulfur dioxide (SO2), usually the exhaust system temperature should be higher, rather than the use of heating water supply and drainage boiler household appliances, the purpose is to improve the wall temperature of metal composite materials. Protect metal composites from sulfuric acid attack. Second, waste heat boiler classification

Important waste heat boiler types are: Waste heat boiler of continuous casting, waste mixed combustion furnace and blowing style waste heat boiler, cement kiln waste heat boiler, stainless steel plate waste heat boiler, hazardous waste heat boiler, waste heat boiler of waste incineration power generation, waste heat boiler of coking, waste heat boiler of metal product industry, sulfuric acid waste heat boiler, waste heat boiler of mineral heat furnace industry, waste heat boiler of glass kiln, waste heat boiler of iron blast furnace, waste heat boiler of carbon plant kiln Furnace, gas steam turbine waste heat boiler, steelmaking waste heat boiler, etc.

Waste heat boiler type

(A) According to the characteristics of waste heat recovery can be divided into the following:

1. High-temperature flue gas waste heat recovery: it is a commonly used method, which is characterized by a large total output, concentrated production point, strong continuity, conducive to recovery and utilization, and its sent heat value accounts for 40~50% of the total heat, the waste heat boiler recovery heat value, can be used for production and processing or daily life with heat and power generation capacity.
2. High-temperature fly ash waste heat recovery: such as iron blast furnace fly ash, steel furnace coal ash, heat treatment furnace fly ash, etc., the coal ash temperature is above 1000℃, and the calorific value sent by it accounts for 20% of the total calorific value.
3. Waste heat recovery of high-temperature products: such as iron-making blast furnace coke, stainless steel castings, stainless steel plates, high temperature stainless steel castings, etc., it is generally temperature. It is very high and contains a lot of waste heat recovery.
4. Recovery of waste heat from flammable industrial waste gas and sewage: such as blast furnace gas, hydrocracking and remolding industrial waste gas from beneficiation plants, black liquor from paper mills, etc., they can all be used.
5. Chemical reaction waste heat recovery: such as metallurgical industry, sulfuric acid, phosphoric acid, fertilizer, synthetic fiber, paint and other industries, have led to a lot of chemical reaction waste heat recovery.
6. Waste heat recovery of cooling components: Many circulating water systems discharged from a series of cooling towers such as water coolers of industrial furnaces, and the steam produced by various vaporizing and freezing equipment contain a lot of waste heat recovery, and they can all be rationally utilized.
7. Condensate waste heat recovery: The physical sensible heat that the steam used in the production process of various industries should have when the condensation decreases after the entire process of industrial production.

(B) Since waste heat recovery is closely connected with other production equipment and production process, waste heat recovery and utilization has the following characteristics:

1. The heat supply is not stable, and it is important to make management decisions in the production process.
2. The effective composition, concentration value and particle size analysis of smoke and dust are very different. Therefore, the reasonable layout of the heating surface of the boiler is affected, and the corrosion resistance, ash blocking and dust removal are fully considered as far as possible.
3. The multi-dimensional nature of the active components of the smoke makes some smoke corroded. Such as SO2 in flue gas, soot or fly ash in a variety of metal composite materials and non-metallic elements, etc., may lead to low or high temperature erosion and dust on waste heat recovery machinery and equipment.
4. Limited by the original specifications of the installation. If there are restrictions on the building elevation of the boiler inlet and outlet air ports; Some restrictions on the temperature of the boiler exhaust system make it meet the requirements of the production process.

(3) Due to the different characteristics of waste heat recovery flue gas, the types and structural forms of waste heat boilers are different. According to the structural characteristics, it can be divided into two categories: tubular heat exchanger waste heat boiler and kitchen flue waste heat boiler. According to the flue gas dust content and flue gas characteristics imported from waste heat boilers, it can be divided into the following five categories:

1. The waste heat boiler whose dust content in the flue gas cannot exceed 20g/Nm3 is the first-class waste heat boiler;
2. The waste heat boiler whose dust content in the flue gas is 20g/Nm3 and cannot exceed 70g/Nm3 is the second-class waste heat boiler;
3. The waste heat boiler with the dust content in the flue gas * 70g/Nm3 is the third class waste heat boiler;
4. The waste heat boiler containing adhesive dust in the flue gas is the first four types of waste heat boiler;
5. Waste heat boilers that contain strong erosive active components in the flue gas or have harmful flue gas are the * five types of waste heat boilers.

Classified according to the pressure level of the steam produced by the waste heat boiler

At present, the waste heat boiler adopts five categories of steam water operating system, such as single pressure, double pressure, double pressure reheating, and three pressure reheating.

1. Single-pressure waste heat boiler: waste heat boiler only produces and processes steam of one pressure to the turbogenerator.
2. Double pressure or multi-pressure waste heat boiler: waste heat boiler can produce and process two different pressures or a variety of different pressures of steam to turbogenerators.

Classified according to the reasonable layout of heating surface

1. Column type waste heat boiler with reasonable layout
2. Vertical waste heat boiler with reasonable layout

Classification according to the circulation characteristics of steam consumption rate in the evaporation heating surface (basic principle)

1. Natural circulation waste heat boiler: the flue gas passes horizontally over the tube cluster installed vertically. The water composition in the tube cluster and the reduction of the relative density difference of the cool water in the tube are the driving forces to maintain the natural circulation of the water composition in the cooler.
2. Forced circulation waste heat boiler: the flue gas usually passes vertically over the horizontal rational layout of the tube cluster. According to the circulating pump to ensure the uniform movement of circulating flow in the cooler car.
3. Dc power waste heat boiler: The DC electric waste heat boiler relies on the tensile force of the feed pump to turn the water supply and drainage into superheated steam according to each heating surface. In the evaporative heating surface, the circulation of the steam consumption rate is carried out by the tensile force of the feed pump.