Application of plate heat exchanger in cooling of medium and small blast furnace body

　　Application of plate heat exchanger in cooling of medium and small blast furnace body

　　Abstract: The cooling effect of air cooler used for soft water cooling of medium and small blast furnace body fluctuates with the seasons, and the highest inlet blast furnace water temperature reaches 70C or more in summer, affecting the safety, high yield and service life of blast furnace. The plate heat exchanger takes the corrugated plate as the heat transfer surface, with high heat transfer coefficient, small size, convenient disassembly and cleaning, high heat exchange intensity, and good heat exchange effect. According to the characteristics of large flow and small temperature difference of the cooling soft water system of the medium and small blast furnace body, it is advisable to select the plate heat exchanger made of 316 or 316L stainless steel, with a short structure, two in operation and one in standby and three in parallel. BR1.1xC (1.0/100) 200.2 water plate heat exchanger is adopted, and the temperature of demineralized water entering the blast furnace is stable at 34~39C throughout the year

　　1. Preface

　　Most of the soft water cooling of medium and small blast furnaces in China uses air coolers. Because air coolers use air as the refrigerant, the temperature of soft water entering the blast furnace fluctuates with the seasons. In summer, the highest water temperature into the blast furnace reaches more than 70 ℃, and the best water supply temperature of far higher temperature is 35~40 ℃. The air cooler tube bundle is prone to corrosion and water leakage. After the "blind" measure is adopted for the corroded tube bundle, the heat exchange area of the air cooler is reduced, and the temperature of the soft water entering the blast furnace is increased. With the improvement of ironmaking process and the improvement of utilization coefficient of blast furnace, the contradiction of insufficient cooling capacity of air cooler has become increasingly prominent, which has seriously affected the safety, high yield and service life of blast furnace.

　　2. Selection of plate heat exchanger

　　2.1 Characteristics of plate heat exchanger

　　Plate heat exchanger is a new and efficient heat exchanger with corrugated plate as the heat transfer surface, which has the following characteristics:

　　(1) High heat transfer coefficient. As the corrugated plates and sheets are reversed, a mesh contact is formed in the flow channel, the flow channel is cross and changes, and the fluid direction is variable. When the critical Reynolds number is about 200, turbulence can be achieved, which greatly improves the film conductivity and enhances heat transfer.

　　Table 1 Selection calculation of plate heat exchanger

　　(2) Small size, small floor area, light weight, especially suitable for occasions with limited space. The plate heat exchanger is compact in structure and small in volume, and its floor area is 1/5~1/10 of that of the tube heat exchanger

　　(3) Flexible assembly, convenient disassembly and cleaning.

　　22 Type of plate heat exchanger

　　As the cooling soft water system of medium and small blast furnace body is characterized by large flow and small temperature difference, the plate heat exchanger is characterized by short and fat structure, that is, large width-height ratio. This structure not only ensures good heat exchange effect, but also minimizes pressure loss.

　　23 Technical parameters of plate heat exchanger

　　2. 3.1 Number of plate heat exchangers According to the characteristics of medium and small blast furnaces, the number of plate heat exchangers used in the cooling soft water system of the furnace body should be 3 in parallel, each with a flow rate of 5O% of the maximum flow rate, and two for normal operation and one for standby.

　　2.3.2 The flow rate of softened water shall be determined according to the reasonable flow rate of water in the cooling stave, and the situation that the heat resistant layer on the inner wall of the blast furnace is thinned and the heat transfer is increased sharply in the later stage shall be considered.

　　2.3.3 The temperature of demineralized water in and out of the heat exchanger is based on the existing experience of the soft water supply of blast furnace. When the soft water supply temperature is between 35 and 40 ℃, it is most beneficial to the stable and high yield and safe production of blast furnace. At the same time, considering the cooling capacity of the cooling water and cooling tower in summer, the temperature of demineralized water entering the blast furnace should be less than 40 ℃ in the most unfavorable working condition in summer, and the temperature of demineralized water leaving the blast furnace should be less than 45 ℃, that is, the temperature of demineralized water entering the heat exchanger should be 45 ℃, The outlet temperature of the heat exchanger should be 40 ℃.

　　2.3.4 Pressure loss at soft water side of heat exchanger

　　As other parts of the soft water system remain unchanged except the air cooler and the plate heat exchanger, the pressure loss at the soft water side of the plate heat exchanger must be less than the pressure loss at the soft water side of the original air cooler. The pressure loss at the soft water side of the original air cooler is less than 0.05MPa, so the pressure loss at the soft water side of the plate heat exchanger must be less than 0.05MPa

　　2.3. 5 Plate material of heat exchanger Plate material of heat exchanger is basically stainless steel and titanium alloy

　　Species. Since the price of titanium material is 4~6 times that of stainless steel, and the plate material of plate heat exchanger of blast furnace cooling system can meet the requirements by using stainless steel, so the plate material of plate heat exchanger is stainless steel.

　　2.3.6 Heat exchanger plate thickness The heat exchanger plate thickness is inversely proportional to the heat transfer coefficient. The smaller the plate thickness is, the better the heat transfer effect is, but it is also easy to corrode and leak. At present, the plate thickness of domestic plate heat exchanger is 0.5~1.0mm. Considering the manufacturer's manufacturing process, on-site operation level, corrosion, scale removal and other factors, the plate thickness of heat exchanger should be 0.7~0.9ram

　　2.3.7 The gasket material should be EPDM rubber, taking into account the actual situation of the site, the working temperature of the plate heat exchanger, the composition of softened water and other factors.

　　2.3.8 The normal working pressure of the heat exchanger shall be based on the characteristics of closed circulation of the soft water system. The minimum value of the normal working pressure of the heat exchanger shall be the sum of the outlet pressure of the circulating water pump of the soft water system and the water level height of the high level expansion tank of the blast furnace.

　　2.3.9 The temperature of cooling water entering and leaving the heat exchanger should be less than 32 ℃, and the temperature of cooling water entering and leaving the heat exchanger should be less than 37 ℃ according to the cooling water supply temperature in summer and the working capacity of the cooling tower.

　　2.3.10 Inlet and outlet pipe diameter The size of inlet and outlet pipe diameter should be determined based on the velocity of the medium in the pipeline is less than 3 m/s, and the maximum velocity should be less than 4 m/s

　　3. Selection calculation of plate heat exchanger

　　See Table 1 for the determination of operation parameters of blast furnace cooling system, type selection of plate heat exchanger and structural parameters

　　4. Application effect

　　The blast furnace replaced the air cooler with plate heat exchanger 2 in July 2004. After two years of operation, the effect is good. It has been successively applied in other blast furnaces. See Table 2 for the comparison of the statistical data of the blast furnace inlet water temperature before and after the use of the plate heat exchanger. After the use of the plate heat exchanger, under the condition that the soft water flow and cooling water are stable at 960~1200m/h, the temperature of the softened water entering the blast furnace is basically stable at 34~39 ℃ throughout the year, which is far lower than the inlet water temperature of the air cooler before July 2004.

　　Table 2 Comparison of inlet water temperature of blast furnace using air cooler and plate heat exchanger ℃

　　5. Conclusion

　　The water-water plate heat exchanger is used in the cooling soft water system of the blast furnace body, which can keep the inlet water temperature of the blast furnace at the optimal temperature of 35~40C~fd], and the water temperature fluctuation is small, which completely solves the problem of insufficient cooling capacity that restricts the high and stable production of the blast furnace and affects the service life of the blast furnace, meets the increasingly progressive smelting strength requirements of the blast furnace, and extends the service life of the blast furnace.