Waste heat resources are ubiquitous, especially in the production process of steel, chemical, petroleum, building materials, light industry and food industries, so making full use of waste heat resources is one of the main contents of energy conservation in enterprises. Plate heat exchangers play an important role in industrial waste heat recovery technology.
The potential for waste heat utilization is huge and plays an important role in current energy conservation. Waste heat resources can be divided into six categories according to their sources:
1. Waste heat from high temperature flue gas
2. Waste heat from high temperature products and slag
3. Waste heat of cooling medium
4. Waste heat from combustible waste gas, waste liquid and waste materials
5. Waste steam and waste water waste heat
6. Waste heat from chemical reactions
Waste heat resources can be divided into three categories according to their temperature:
1. High-temperature waste heat (waste heat resources with a temperature higher than 500°C)
2. Medium temperature waste heat (waste heat resources with a temperature of 200-500℃)
3. Low temperature waste heat (flue gas with a temperature below 200°C and liquid with a temperature below 100°C)
| Low temperature waste heat (flue gas with a temperature below 200°C and liquid with a temperature below 100°C) | Sources of industry waste heat resources | Proportion of fuel consumption |
| Metallurgy | Steel rolling heating furnace, soaking furnace, open hearth furnace, converter blast furnace, roasting kiln, etc. | 33% or more |
| Chemicals | Chemical reaction heat, such as physical sensible heat of gasification, shift gas, synthesis gas, etc.; Combustible chemical heat, such as fuel heat of carbon black tail gas, calcium carbide gas, etc. | 15% or more |
| Building Materials | High temperature flue gas, kiln top cooling, high temperature products, etc. about 40% Glass-lined melting furnace, enamel kiln, crucible kiln, etc. | About 20% |
| papermaking | Drying cylinder, steamer, waste gas, black liquor, etc. | About 15% |
| Textile | Dryer, sizing machine, cooking pot, etc. | About 15% |
| mechanical | Forging heating furnace, cupola, heat treatment furnace and steam hammer exhaust, etc. | About 15% |
There are various ways to recover industrial waste heat, but they are generally divided into two categories: heat recovery (direct use of heat energy) and power recovery (converted into power or electricity for reuse). When recovering waste heat, the first thing to consider is that the recovered waste heat must be useful and economically viable. If the equipment investment consumed in order to recover waste heat is too much, and the benefits after recovery are not great, then the gains will outweigh the losses. The principles for waste heat recovery are:
1. For various thermal equipment that discharge high-temperature flue gas, the remaining heat should be used by the equipment or system first, such as preheating combustion air, preheating fuel, etc., to improve the thermal efficiency of the equipment and reduce fuel consumption.
2. When waste heat and waste energy cannot be recovered for heating the equipment itself, or when part of it can still be recovered after use, it should be used to produce steam or hot water, as well as to produce power, etc.
3. Based on the type of waste heat, discharge conditions, medium temperature, quantity and possibility of utilization, the enterprise's comprehensive thermal efficiency and economic feasibility analysis should be conducted to determine the type and scale of waste heat recovery equipment.
4. Develop specific management standards for the temperature, quantity and range of condensed water, high and low temperature liquids, solid high temperature objects, combustibles and gases and liquids with residual pressure that must recover waste heat.
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