[0046] Example 1:
[0047] The embodiment of the present invention provides a water circulation method for improving the surface quality of hot-rolled steel strip. The method is implemented based on an indirect cooling circulating water system, a laminar cooling circulating water system, and a direct cooling circulating water system. The indirect cooling circulating water system, also known as the clean circulating water system (abbreviated as A system), mainly processes the cooling water of the furnace door and beam of the heating furnace, the cooling water of electrical equipment, hydraulic systems, air compressors, instruments and other equipment; laminar flow Cooling circulating water system, also known as laminar water system (abbreviated as B system), mainly deals with laminar strip top spray, bottom spray cooling and side spray water; direct cooling circulating water system, also known as turbid circulating water system (abbreviated as C system) , It mainly treats the roll cooling water of the roughing and finishing mills, and the direct cooling water of all equipment and steel plates of the main rolling line.
[0048] See figure 1 The specific process of the water circulation method for improving the surface quality of hot rolled strip steel is as follows:
[0049] The indirect cooling circulating water of the indirect cooling circulating water system (system A) is filtered and cooled for the users of the indirect cooling circulating water system to recycle; the supplementary water of the indirect cooling circulating water system is new water; the indirect cooling circulating water system is discharged and drained Direct cooling circulating water system.
[0050] Specifically, in this embodiment, the indirect cooling circulating water system includes two circulating systems, one for processing heating furnace cooling water, and the other for processing electrical equipment, hydraulic systems, air compressors, meters and other equipment. In the two circulation systems, the cooling water circulates in the pipeline and performs indirect heat exchange with the outside, so the water temperature only rises after use. However, some suspended impurities will still appear in the water after a period of use, which needs to be filtered.
[0051] In the first set of circulation system, the water used after the heating furnace is cooled by the residual pressure enters the cooling tower through the pipeline for cooling, the cooled water enters the cold pool, and after cooling, it is pressurized by the water pump for the cooling of the heating furnace. In the second set of circulation system, the cooling circulating water uses the residual pressure to enter the cooling tower through the pipeline for cooling. The cooled water from the cooling tower enters the cold pool, and then is pressurized by the water pump for the rolling line users. In the process of supplying rolling line users, a side filter is introduced to filter to remove suspended solids entering the water during the cooling process. After filtering for a certain period of time, the by-pass filter uses residual pressure to backwash, and the backwash drain is discharged into the sewage treatment system.
[0052] In the indirect cooling circulating water process, the salt in the water will be continuously concentrated. In order to maintain the normal operation of the system, new water needs to be added to the system from time to time. In this embodiment, the new water used in the indirect cooling circulating water system is soft water And/or purified water. In the circulation process, it is also necessary to add a water quality stabilizer to the indirect cooling circulating water, and the sewage is discharged into the muddy circulating water system from time to time to ensure the normal operation of the system.
[0053] Specifically, the purified circulating water is continuously circulated, and the concentration of electrolytes continues to increase after evaporation and concentration. During the circulation process, it is necessary to detect the water quality indicators of the indirect cooling circulating water, such as conductivity, chloride ion, sulfate and other indicators, to ensure that the water quality indicators are in Within the standard value range, when it reaches the discharge standard value, the system discharges sewage. Since the water quality of the clean circulating water system when it reaches the discharge standard value is still better than the incoming water requirements of the turbid circulating water system, the sewage will enter the turbid circulating water system.
[0054] The laminar cooling circulating water of the laminar cooling circulating water system (system B) is filtered and cooled, and is used for the laminar cooling system to be recycled; the supplementary water of the laminar cooling circulating water system is new water; the laminar cooling circulating water system discharges sewage and drains Enter the direct cooling circulating water system.
[0055] Specifically, the water after use of the laminar flow cooling system flows into the laminar iron pit by itself, and a part of it is filtered by the pump pressure to send the filter to remove the suspended particles and oil in the water. The filtered water is directly cooled by the cooling tower by using the residual pressure. After cooling, the water enters the suction well, and the other part directly enters the suction well, mixes with the filtered and cooled water, and then pressurized by the water pump for the laminar flow strip top and bottom spray cooling and side spray use.
[0056] In general, about 70% of the upper liquid in the laminar iron pit enters the suction well directly, and this part is the upper water of the laminar iron pit; about 30% is sent to the filter and then the upper cooling tower enters the suction well. This part is the layer Flowing the lower water of the iron pit. The filter uses the residual pressure to backwash after filtering for a certain period of time, and the backwash drain is discharged into the sewage treatment system.
[0057] During the circulation of the laminar cooling circulating water, the salt will be continuously concentrated. In order to maintain the normal operation of the system, it is necessary to discharge sewage to the turbid circulating water system (C system) from time to time. In order to prevent scaling and corrosion of equipment and pipelines, it is necessary to add a water quality stabilizer to the circulating water of the system to ensure the normal operation of the system. During the normal operation of the entire system, due to the splashing, evaporation, and system discharge of the cooling tower, the water volume of the system is reduced, and new water needs to be added to the system from time to time. The new water is purified water (purified water is industrial new water passing through For the filtered water, the filter screen has at least 80 meshes, and some high-end products use 100 mesh or even higher mesh filters.
[0058] Specifically, the laminar flow cooling circulating water system itself is a relatively independent circulating system. The laminar flow water is continuously concentrated during its operation. During the circulation process, the water quality indicators of the laminar cooling circulating water, such as electrical conductivity, chloride ion, and sulfate radical, need to be tested. When the water quality index reaches the standard value, discharge is required to ensure the laminar water quality and thus the surface quality of the steel plate product. However, the water quality when it reaches the discharge standard value is still better than the incoming water requirement of the turbid water system, that is to say When the concentration of laminar water reaches its discharge value, the sewage enters the turbid water system.
[0059] The direct cooling circulating water of the direct cooling circulating water system (C system) is filtered and cooled for the users of the direct cooling circulating water system to recycle. During the normal operation of the entire system, due to the splashing, evaporation, and system discharge of the cooling tower, the water volume of the system is reduced. It is necessary to supply water to the system from time to time. The water supply of the direct cooling circulating water system uses the laminar cooling circulating water system and The drainage of the indirect cooling circulating water system, as well as new water, and the make-up water of the direct cooling circulating water system, the volume ratio of drainage to new water is 5:1 to 20:1, such as 5:1, 7:1, 9:1, 12:1, 15:1, 18:1, 20:1, etc. In this embodiment, purified water is used as fresh water. The direct cooling circulating water system is discharged outside.
[0060] Specifically, the direct cooling water adopts a cyclone to precipitate large particles of oxide scale. The water after precipitation, that is, the supernatant liquid of the cyclone tank, is partly pumped to the rolling line to be used for removing the oxide scale, and the other part of the water is lifted into the advection sedimentation tank by the water pump for treatment. In general, about 70% of the sedimented water directly enters the suction well, which is the upper water of the swirling tank; about 30% is sent to the advection sedimentation tank, which is the lower water of the swirling tank. The iron oxide scale precipitated in the cyclone is grabbed by a crane grab, loaded into the train and transported away.
[0061] Coagulation sedimentation and degreasing are carried out in the advection sedimentation tank. The coagulation sedimentation step uses polyacrylamide (PAM) and polyaluminum chloride (PAC), and the dosage of polyacrylamide is 5-15mg/L. The dosage of polyaluminum chloride is 0.5-5mg/L, and the coagulation precipitation treatment time is 30-60min. A belt-type degreasing machine is used in the advection sedimentation tank to remove oil. Through mechanical transmission, the oil in the advection sedimentation tank is removed with a lipophilic and water-repellent tape. The oil pollution enters the oil drum through the reverse pipe for collection; the water surface in the advection sedimentation tank is floating The oil is collected by an oil skimmer, then pumped into an oil storage tank, and transported away by a car; the oxide scale precipitated in the advection sedimentation tank is grabbed into the slag tank with a grab bucket for draining, and then loaded into a car for transportation.
[0062] After coagulation, sedimentation and degreasing, the supernatant of the advection sedimentation tank is pressurized with a water pump and sent to the filter for filtration to remove suspended particles and oil in the water. The filter medium of the filter is quartz sand and anthracite. The working pressure is 0.3~0.5Mpa, the operating flow rate is 8~10m/h, the filter is backwashed with self-filtered water, the backwash pressure difference is controlled at 0.08Mpa, and the backwash drain is discharged into the sewage treatment system. The filtered water is directly cooled by the cooling tower using residual pressure, and the cooled water enters the cold water pool. Finally, according to the user's demand for water pressure, it is pressurized with a water pump for 0.4MPa and 1.2MPa direct cooling users in the rolling line.
[0063] When the water quality is difficult to meet the requirements for use, or the internal water volume of the C system exceeds the maximum carrying capacity of the C system due to the sewage of the A system and the B system, the direct cooling of the circulating water system is directly discharged, and part of the unusable sewage is discharged, and the sewage enters the sewage treatment System unified processing.
[0064] Since in the present invention, the water supplement of the direct cooling circulating water system uses the drainage of the laminar cooling circulating water system and the indirect cooling circulating water system, as well as new water, compared with the existing process using circulating turbid circulating water, the water quality of the laminar water is improved. The surface quality of strip steel has been significantly improved.
[0065] The water supply mode of A and B systems remains unchanged, and the A and B system drainage and purified water are supplemented to the C system. The ratios of the A and B system drainage to the supplemented purified water are 5:1, 10:1, and 20:1. Situation, the surface quality of the strip produced figure 2 As shown, the above three different proportions of replenishment correspond to figure 2 In (a), (b), (c). From figure 2 It can be seen that the water quality of laminar water decreases successively, the uniformity of the steel plate surface decreases successively, and the surface quality successively deteriorates, but they are all within the allowable range of the surface quality of high-end steel grades. On the other hand, with the gradual increase in the proportion of purified water supplementation, the surface quality of the steel plate has been effectively improved.
[0066] A steel mill enterprise previously used the existing technology cascade water process, that is, the circulating water after replenishing new water is first used by the cleaning water system such as the heating furnace, and the sewage from the cleaning water system enters the turbid water system, and the turbid water system is used The back drain sewage enters the laminar flow water system. The existing technology cascade water process water circulation method such as image 3 Shown.
[0067] The prior art cascade utilization of circulating water system has a major problem. After the direct cooling system, the circulating water carries a large amount of iron oxide scale and oily substances, so that the water quality of the subsequent laminar cooling water circulating system cannot be effectively guaranteed. High conductivity, suspended solids, oil and other water quality problems caused by the black and gray surface of the strip steel, seriously affecting the surface quality of the product, unable to meet the production requirements of high-strength structural steel, silicon steel and other high-end products. The above-mentioned water quality problems force the steel plant to increase water treatment facilities to improve water quality, increase water pressure to spray on the upper and lower surfaces of the strip, and increase the drainage volume. This is currently increasing energy conservation and environmental protection requirements and production costs. Both new water consumption and drainage volume With strict requirements, it has been unable to meet market and environmental requirements.
[0068] Later, the steel mill company improved the water circulation process and adopted the water circulation method for improving the surface quality of hot-rolled strip steel in Example 1 (the replacement of the old and new processes was basically completed in the first quarter of the first year of the new process). The water quality indexes of turbid ring water and laminar water are shown in Table 1.
[0069] Table 1 Water quality indicators of clean circulating water, turbid circulating water, and laminar water before and after process improvement
[0070]
[0071] It can be seen from Table 1 that after the process is improved, Cl, which has a greater impact on the surface quality of the strip - Concentration, SO 4 2- Concentration, hardness, and conductivity have been significantly reduced, especially the most influential conductivity has been greatly reduced, so the surface quality of the strip can be improved. In addition, the concentration ratio of the clean circulating water is significantly increased, the recycling utilization rate of the clean circulating water is increased, and the system cost is reduced.
[0072] After the steel mill enterprise adopted the water circulation method for improving the surface quality of hot-rolled strip steel in Example 1, the system cost reduction was mainly reflected in three aspects: new water consumption, water treatment cost (water treatment cost mainly refers to the system supplementary water cost ) And energy consumption. See Table 2 and Table 3 for specific data on new water consumption and water treatment costs.
[0073] Table 2 Comparison of new water consumption before and after process improvement
[0074]
[0075] Table 3 Comparison of new water consumption before and after process improvement
[0076]
[0077]
[0078] Note: The above-mentioned new water includes soft water, purified water, filtered water and other water types, and the price is different, and the water cost is calculated at a comprehensive price.
[0079] It can be seen from Table 2 and Table 3 that the amount of supplemental water or water consumption is significantly lower than before the process improvement, especially in the first year of the replacement of the old and new processes. Taking the first year of the new process as an example, water consumption decreased by 68.7%, and the total output was about 12 million tons. The annual water saving and emission reduction of the whole plant was about 1200* (2.132-0.667) = 17.58 million tons, or about 1.465 million tons per month. . The average total water volume of the whole plant's water treatment is about 75,000 tons/hour, or 1.8 million tons/day, so the electricity consumption of the water treatment system is basically reduced by nearly one day every month. The daily power consumption of the water treatment system of the whole plant is about 660,000 kWh. Therefore, the power consumption of the new process in the first year is about 12*66*0.6* (146.5/180) = 3.87 million yuan (electricity price 0.6 yuan/kW· h). Similarly, in the second year of the new process, the power consumption was reduced by 620,000 yuan compared with the first year of the new process, and then various costs stabilized.
