Analysis of ironmaking water consumption and water saving practice in Angang

　　Abstract: in order to reduce the water consumption of Angang iron and Steel Co., Ltd., the water consumption of sintering process and blast furnace process was analyzed. By taking measures such as overflow control, water point transformation and increasing concentration ratio, the industrial new water consumption and net circulating water consumption per ton of iron in 2018 were reduced by 0.134m3 and 2.174m3 respectively compared with that in 2013, and the cost per ton of iron was reduced by 2.384 yuan. The practical effect of water saving was remarkable.

　　Key words: ironmaking; Blast furnace process; Sintering process; Water consumption; water conservation

　　Ironmaking process is one of the key processes of water consumption in iron and steel enterprises, and its water consumption is an important base affecting the indicators of water consumption per ton of steel. The ironmaking plant of Angang iron and Steel Co., Ltd. (hereinafter referred to as the ironmaking plant) has 4 2580m3 blast furnaces, 4 3200m3 blast furnaces, 2 360m2 Sintering machines, 2 328m2 sintering machines, 2 265m2 sintering machines, 1 pellet roasting machine, and the supporting raw material yard and auxiliary systems. In 2013, the consumption of industrial new water in the general iron making plant was about 9.43 million m3, and the consumption of new water per ton of iron was 0.581m3; The net circulating water consumption is about 113.91 million m3, and the net circulating water consumption per ton of iron is 7.02m3. The common consumption of fresh water per ton of iron and clean circulating water in steel plants at home and abroad are 0.3m3 and 4m3 respectively. In contrast, the consumption of Angang is relatively high. In order to reduce the water consumption in ironmaking process, since 2013, the ironmaking plant has taken a series of water reduction measures to improve the industrial water circulation rate and the reuse rate of fresh water, with good results.
 

　　1. Analysis of ironmaking water

　　In ironmaking process, water system is required for raw material preparation, sintering and blast furnace cooling. Five water supply systems are set up in the sintering process of the general iron making plant to supply water for sintering production and equipment cooling; The blast furnace process is equipped with 10 closed-circuit water station systems to supply water to the blast furnace cooling system. The types of water are industrial new water and clean circulating water.

　　1.1 sintering process

　　There are 6 sintering machines, 1 pellet roaster and 4 sintering ring cooling waste heat boilers in the water sintering process, which are divided into 5 areas. Independent water supply circulating systems are set up in each area to supply water for cooling of equipment in the sintering process and adding water to the sintering mixture and quicklime. The system is made up of clean circulating water in the plant. An independent circulating system is set up for pellet roasting for cooling of each fan. The annular cooling waste heat boiler uses industrial new water to make water. In winter, it supplies waste heat steam in the plant area, and the consumption of new water is large; In summer, the waste heat boiler is used for power generation, and the condensate can be recycled.

　　1.2 water for blast furnace process

　　The cooling water system of blast furnace process can be divided into the following parts: ① soft water system. It mainly includes cooling staves and hearth of blast furnace, hot blast valve of hot blast stove and cooling of top gear box. This system adopts closed-circuit circulation system; ② High pressure clean circulating water system. It includes a small set of circulating system at the tuyere, water supply from the water gun on the furnace top and dust removal and water supply from the gravity dust collector; ③ Low pressure clean ring system. It includes the cooling water system of each fan and hydraulic station, blast furnace slag flushing and make-up water, drum cleaning water, shaft seal water, etc.

　　The water supply system of 8 blast furnaces is as follows:

　　(1) Hearth water station and shaft water station are set up in 2\3\4\and 5\\blast furnace areas to supply water to the corresponding blast furnace shafts and hearth respectively. The water system is shared with the shaft system, and the soft water is cooled by evaporative air cooler. The main cooling mode of evaporative air cooler is spray cooling, and the water quality is generally new industrial water. In production practice, in order to prevent the scaling of the evaporative air cooler tube bundle, the method of continuously adding new water is adopted.

　　(2) Hearth water station and shaft water station are set up in 1\and 11\blast furnace area to supply water for 1\and 11\blast furnace shafts and hearth respectively. The water system is shared with the shaft system, and the soft water is cooled by plate heat exchanger. The plate heat exchanger is cooled by secondary cooling water, and the purified circulating water is used to supplement the evaporation loss. As the cooling method is plate heat exchanger, the evaporation loss is very small, so this cooling method is better than evaporative air cooler.

　　(3) A set of closed-circuit water station system is set up for 7\y blast furnace to supply cooling water for the whole blast furnace hearth and shaft system.

　　(4) A set of cooling system is adopted for the shaft and hearth of 10 \. When the air outlet leaks water, it is converted to high-pressure clean circulating water. Clean circulating water is mainly used for blast furnace slag flushing water. Since blast furnace ditch head water, slag bin mixing water, shaft seal water, dehydrator cleaning water and other water sources continue to enter the slag flushing system during blast furnace slag flushing, the water consumption for slag flushing is evaporation and water content of water slag. The water from the system is greater than the water consumption in the slag flushing process. Therefore, the blast furnace slag flushing water will overflow for a long time.
 

　　2. Measures to reduce water consumption

　　2.1 overflow control

　　The overflow volume of slag flushing water in ironmaking plant is relatively large, 500m3/h. In view of the overflow of slag flushing water, an independent circulating system is established to strengthen the inspection of the system, and the daily periodic repair drainage application system is implemented to control the drainage and water replenishment. In order to thoroughly control the overflow of slag flushing water, the following measures are taken.

　　2.1.1 control of external water sources

　　In order to reduce the water from the slag flushing water system, the blast furnace ditch head water was recovered and transformed, and the ditch head water originally entered the slag flushing water system was recovered and discharged to the blast furnace tuyere return tank; Stop mixing water in slag silo and control the amount of shaft seal water and dehydrator cleaning water; At the same time, the shaft seal water and cleaning water are turned on when the blast furnace slag flushing is stopped, and the shaft seal water and cleaning water are turned off when the slag flushing is stopped; In addition, close all water make-up valves and replace the lax valves.

　　2.1.2 improve process flow

　　In the original IMBA system of 1\yao 2\yao 3\yao 4\. The general iron making plant improved the process flow by changing the water in the recovery pool to flow into the flushing tank. After being treated in the flushing tank, the water removed from the dehydrator enters the circulating system again to reduce the slag content in the water and reduce water make-up. The process flow of blast furnace slag flushing and cooling is shown in Figure 1.

　　No cooling facilities are available for the slag flushing process of 10\n\blast furnace. If the water temperature is high, it is necessary to reduce the water temperature by making up water, so that the water volume of the system increases and needs to be discharged. The general iron making plant will add cooling towers to reduce the temperature of slag flushing water, reduce water make-up, and then reduce the external drainage. See Fig. 2 for the technological process of slag flushing and reinbar of the reconstructed 10\.

　　11 \blast furnace slag washing process is the granulation wheel method. The water content in the slag is large. It is transformed from the granulation wheel method to the IMBA method. The granulation pump is changed to frequency conversion to match the water content. A recovery tank is added in the large tank. The settled fine slag is sent to the drum again by the air lift pump for dehydration, so as to reduce the slag content in the water and reduce the slag washing and water replenishment. See Fig. 3 for the slag flushing process of 11\.

　　2.1.3 treatment of equipment hidden dangers

　　Focus on sorting out the missing items of equipment, rectify the equipment problems that affect the overflow of slag flushing water, timely deal with the equipment hidden dangers that affect the overflow, and control the overflow of slag flushing water.

　　2.2 water point transformation

　　The water used in the sintering system of the general iron making plant is relatively independent. Each sintering machine is designed with an independent water supply circulating system. The equipment cooling water is recycled, centrally treated and recycled. Water for sintering process mixture, quicklime digestion and other consumptive water are also supplied from this system. The original make-up water in the sintering process is industrial new water, and after the transformation, industrial clean circulating water is used to meet the water consumption demand of the system, realizing the technical transformation goal of not using industrial new water in the sintering process (except for the annular cooling waste heat boiler). The concentrated water produced in the process of making soft water by waste heat boiler is recycled for adding water as part of the sintering process to reduce the water consumption in the sintering process. The water consumption of blast furnace system is complex, the water consumption points are scattered, and the original cooling water is discharged directly. After the transformation, the cooling water of the gear box on the top of the blast furnace, the cooling water in front of the furnace and the hydraulic station on the top of the furnace will be recycled, and an independent small circulating system will be established. When the system is short of water, it can be supplemented. At the same time, the cooling water system of the dedusting fan in front of the furnace and the dedusting fan in the ore tank was reformed to realize the recovery and recycling of the cooling water.

　　2.3 increase concentration multiple

　　The concentration multiple is an important index in the operation of circulating water. The concentration multiple will determine the reuse rate of water and the level of water saving. The higher the concentration ratio, the more water-saving can be achieved. However, in order to ensure the water quality, the amount of chemicals added to the water will increase, resulting in an increase in the cost of chemicals. The concentration multiple of circulating water in general iron making plant is generally about 2. By controlling water loss, reducing pipeline and valve leakage, reducing air cooler drift, and controlling the sewage discharge of each system, the cascade use and reuse of water are improved, and the concentration multiple of circulating water is increased to about 3. The use of new industrial water and clean circulating water has been effectively controlled.

　　3. Water saving effect

　　After the above measures are taken, the consumption of industrial fresh water in the general iron making plant shows a downward trend year by year, and the consumption of clean circulating water shows an upward trend year by year. See Table 1 for water consumption of ironmaking plant from 2013 to 2018.

　　It can be seen from table 1 that compared with 2013, the consumption of industrial new water in the sintering process decreased by 920800 m3 in 2018. As the sintering process used clean circulating water instead of industrial new water, the consumption of clean circulating water increased; The industrial new water consumption in blast furnace process decreased by 1.5673 million m3, and the clean circulating water consumption decreased by 28.6939 million m3; The industrial new water consumption and net circulating water consumption per ton of iron in the general iron making plant were reduced by 0.134m3 and 2.174m3 respectively, and the cost per ton of iron was reduced by 2.384 yuan.

　　4. Conclusion

　　Since the ironmaking plant of Anshan Iron and Steel Co., Ltd. adopted measures to reduce water consumption, such as overflow control, water point transformation and increasing concentration ratio in 2013, the water consumption of blast furnace process and sintering process has been continuously reduced. Compared with 2013, the industrial new water consumption and net circulating water consumption per ton of iron in 2018 decreased by 0.134m3 and 2.174m3 respectively, and the cost per ton of iron decreased by 2.384 yuan. The water-saving effect is remarkable, and good economic benefits have been achieved, which can be used as a reference for iron and steel enterprises to carry out water-saving and emission reduction.