Application analysis of Baosteel's waste heat recovery technology

The three annealing furnaces of Baosteel No. 4 Cold Rolling adopt different types of waste heat recovery technology, namely pure heat exchanger type low pressure heat recovery technology

Technology, waste heat boiler recovery technology, superheated water recovery technology, which are also three popular waste heat recovery technologies today. After the high-temperature flue gas generated by the annealing furnace is recovered by waste heat, the heat recovery rate is basically 10% to 14%.

1. Low-pressure heat exchanger type waste heat recovery technology

The low-pressure heat exchanger type waste heat recovery technology is characterized by the use of flue gas heat to heat water or gas through the heat exchanger. It is applied to other processes of this unit. Its biggest advantage is that the heat exchange system has a low pressure and does not constitute a pressure vessel. It is easy to maintain and has no hidden dangers. The disadvantage is low heat recovery efficiency and relatively large investment. The exhaust fan has a heat-resisting temperature of 400. To ensure that the exhaust fan operates normally, a cooling air intake is provided in the system. That is, if the exhaust gas discharge temperature is too high, the valve of the cooling air intake will automatically open to draw cold air from the outside. To reduce the final exhaust gas temperature. After the recovery system, about 10% of the heat energy is recovered.

The heat energy recovered by the waste heat recovery system has basically met the energy requirements of the cleaning process, but when the capacity is large, the flue gas temperature is very high. Sometimes in order to ensure that the heat exchanger is not damaged by overheating, a large amount of pure Water is used to cool the heat exchanger. The hot water passing through the heat exchanger is greater than the amount of hot water used in other processes of the unit. Therefore, the excess hot water is only discharged in vain, which causes waste of water resources.

2. Waste heat boiler recovery technology

The heat recovery system of the 1CGL unit uses a waste heat boiler to more efficiently recover flue gas waste heat. The temperature of the flue gas discharged from the burner of the heating section (RTF) of the annealing furnace is about 675. First, the protective gas is heated by the preheating furnace heat exchanger, and the strip steel can be preheated from 35 to 200. The temperature of the flue gas after heat exchange is 515, and after being recovered by the waste heat boiler, the temperature of the flue gas generally does not exceed 200 At the maximum working capacity of the burner, the amount of steam produced by the waste heat boiler is 8.2 t / h, and the maximum steam consumption requirement of the production line is 4.8 t / h. When the steam consumption of the production line is lower than the maximum consumption The rich steam will be added to the steam pipe network, so there is no problem of insufficient heat recovery due to high production capacity. The production capacity of the waste heat boiler decreases as the processing capacity of the annealing furnace decreases. A waste heat boiler recovery system is adopted, and the heat energy recovery rate can reach 14%; however, the investment of the waste heat boiler is relatively large, which is a pressure vessel, and the management is more troublesome. The safety valve needs to be checked every year, and regular inspection and inspection are required. .

3 Superheated water recovery technology

2CGL's annealing furnace also uses a similar heat recovery system, the main equipment of which is the superheated water system. The superheated water system is a closed high-pressure circulation system with a design pressure of 1.2 MPa. Under this pressure condition, the flue gas waste heat is used to exchange heat with the high-pressure water. The temperature of the circulating water before entering the heat exchanger is 90. The water temperature after heat exchange is 140. Because the pressure of the pipeline is relatively high, the superheated water cannot form steam, but exists in the pipeline in a gas-liquid mixed state to circulate. The hot water passes through the heat exchanger, and the heated air is used for hot water rinsing and hot air drying in the cleaning section. This method of recovering flue gas heat energy is similar to a waste heat boiler, but the equipment structure is simple, the investment is small, and maintenance is relatively easy.

The superheated water system is a closed circulation system. If there is no leakage, it is not necessary to make up water frequently. The waste heat boiler actually consumes a lot of pure water in order to generate steam, so the superheated water system is much better than the waste heat boiler.

From the comparison of the three types of waste heat recovery, the waste heat boiler has the best effect, but the investment is large and the maintenance cost is high. Superheated water system is the best choice with small investment and high heat recovery efficiency.

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