1 Status of waste heat recovery technology for flushing water

Type and trend furnace INBA waste water energy-saving technology of the present plate heat exchanger plate heat exchanger blast furnace take wood cinder tank Tangshan Stainless Steel Company blast furnace slag water waste heat recovery and utilization process process Jingtang blast furnace slag water for seawater desalination process thermal process Desalination subject Zhou Yong, Li Likun, Huang Jianyang, Zhang Lei, Wang Lina, Fu Benquan (Wugang Research Institute, Wuhan, Hubei, The process flow, the energy consumption and production cost of the ironmaking system accounted for 70% and 73% of the total flow, and the pollutant discharge accounted for more than 75%. In order to reduce costs and realize the environmental friendly responsibility of the production process, advanced energy-saving technologies such as CDQ, blast furnace top gas power generation technology (TR gas combustion technology, removal of CO2 recycling technology from blast furnace gas, etc.) Through the application of various types of thrifty waste heat recovery, a number of gratifying achievements have been achieved, and even so, the exploration of new water quality with high quality of waste heat resources, especially the application of this part of waste heat power generation In recent years, technology has become an urgent problem that needs to be solved in the entire industry.This paper will discuss the blast furnace slag in combination with the experience of many domestic steel companies. The development trend of waste heat recovery technology, with a view to high iron and steel enterprises slag is a by-product of blast furnace ironmaking, its main components are calcium oxide, magnesium oxide, aluminum oxide, silica, accounting for about 95% of the total slag, discharge temperature In the production of blast furnace ironmaking between 1450 C1650C, the treatment of slag was mainly carried out by hydraulic slag-flushing method, and the dry slag treatment method was only used in accident emergency treatment.With the continuous development and improvement of the blast furnace process, water quenching was applied. The treatment of blast furnace slag can be further divided into five methods: INBA, TYNA, RASA, COCP, and MTC. In terms of the above methods, these methods usually lead to a large amount of heat loss, and emit a large amount of dust-laden steam and dangerous toxic gases such as sulfur dioxide, hydrogen sulfide, etc. It can be said that both waste energy and pollute the environment, so how to achieve waste heat recovery of blast furnace slag water The use of steel has become a major issue in the energy-saving and emission reduction of the steel industry.

The iron and steel conglomerate in northern China, combined with the heating time in the region for nearly four months in winter, has tried to use the waste heat of the blast furnace slag water to heat the living area of ​​the plant and surrounding workers in winter, such as Angang, Shougang, Handan, and Ji. In this way, steel and Tangshan Iron and Steel Co., Ltd. can save a lot of heating costs each winter, and also effectively reduce the use of coal and natural gas and reduce the emission of greenhouse gases.

Baosteel continues to track the development and application of energy-saving technologies, actively promote the rapid application of mature technologies, appropriately increase the research difficulty, and continuously improve the utilization of low-grade residual heat resources in the region. Currently, it is supplying hot water, low-temperature power generation and residual heat refrigeration from the blast furnace slag water. In terms of each aspect, the three-joint hot-cold supply plan for low-grade waste heat resources in the blast furnace region was gradually realized.

As a super large iron and steel conglomerate in Central China, WISCO is responding to the call for “Rise of Central China” in response to China’s short winter heating time, large fluctuations in the quality of blast furnace slag water, and tight land for the blast furnace area. How to scientifically use this part of the low-grade waste heat, energy-saving transformation, and conduct more in-depth exploration.

With the development of technology, the idea of ​​using the heat recovery of blast furnace slag water for heating will only become a mature and convenient method through simpler heat exchange methods, and through more advanced processes and equipment such as heat pumps. , Screw expanders, etc., will be the low-grade heat of the blast furnace slag water in the energy saving efforts. Throughout the entire steel production iron system, we must bear the energy-saving, emission reduction and reduction T) of iron and steel conglomerates, sensible heat recovery technology of blast furnace slag, and low calorific value energy technology for blast furnaces, and domestic iron and steel enterprises recover the waste heat of high-quality blast furnace slag water in the blast furnace area. The need to do a lot of entrepreneurship is important in carrying out this work.

Continuously extracting and transforming into high-grade electric energy will surely become a development trend and promote the development of energy-saving and environmental protection technologies in China to world-class levels. Therefore, this paper will discuss the status quo and development trend of blast furnace slag water waste heat recovery technology based on the experience of many domestic iron and steel enterprises, in order to provide important for steel companies in the development of this work. At present, domestic and foreign reports on this area and field test data are rarely reported.

1 Current status of waste heat recovery technology for flushing water After comprehensive analysis of the publicly reported information, it is known that the development of blast furnace waste water reclamation technology in domestic steel complexes has undergone the following stages: bath water for winter heating Improve the ultrafiltration water temperature (abbreviated as ultrafiltration warm water) for seawater desalination. As the use of blast furnace slag water for bath water (eg Xuan Gang) and winter heating process (eg: Angang, Shougang, Handan Iron and Steel, Jinan Iron and Steel, Tangshan Iron and Steel, etc.) have been used for more than 20 years, the process is very mature, so this article Introduction is omitted.

1.1 Ultrafiltration warm water The second stage soft water station of Tangshan Iron & Steel Co., Ltd. adopts river water as raw water. After high density clarifier and V-shaped filter process, part of it is used as production water, and the other part is used as soft water preparation. This soft water preparation uses ultrafiltration. + Reverse osmosis water process. Since ultrafiltration requires a water inlet temperature of 20C, the average temperature in winter in Tangshan is about 2C. The temperature of river water in winter cannot meet the demand for ultrafiltration water, resulting in a drastic reduction in water production capacity of the ultrafiltration system, only 25% of design capacity. about. In order to meet the needs of the ultrafiltration system, and taking into account the comprehensive utilization of energy in the plant area, the residual heat of the slag from the blast furnace water is recycled to improve the ultrafiltration water inlet temperature. The blast furnace slag water heat recovery process flow see.

The second phase of the blast furnace water scouring project of Tangshan Iron & Steel Co., Ltd. has been operating for nearly one month, and the heat transfer effect is obvious. The temperature of blast furnace water flushing water is reduced from 60 C to 30 C, and the temperature of ultrafiltration water is increased from 2C to 25C. To meet the requirements of ultrafiltration on water temperature, the water production capacity is restored to the original level, and the water production capacity before heat exchange is increased by nearly 3 times. The utilization of blast furnace waste heat only increased the operating costs of 2 secondary circulating pumps, which is approximately 6% of the boiler's coal-fired costs. It can save 10,000 t of standard coal per year. The economic benefits and environmental benefits of energy conservation and emission reduction are obvious.

1.2 For desalination of seawater Shougang Jingtang Iron and Steel United Co., Ltd. (Jingtang Iron & Steel Co., Ltd.) The ironworks constructs two 5,500m3 blast furnaces, of which the No. 1 blast furnace has been put into operation since May 21, 2009. Chongshui Jingtang Steel Co., Ltd. has constructed the current seawater desalination project with the most scientific and technological information in the country. The scientific and technological information Flash Evaporation System process schematic diagram has a construction scale of 50,000 t/d, of which the first-stage water production scale is 25,000. t/d, and has been put into use, the project selected thermal process, with a hot compress of low-temperature multi-effect (MED-TVC) process is based on the partial evaporation of the input seawater, steam condensation to form a pure product water, non-volatile The lysate was left in brine. According to the current situation, the residual heat of the blast furnace slag water can be recycled to seawater desalination and used in the water production process (see below).

The economic data summarized in the actual operation of this project shows that the amount of steam recovered from the blast furnace waste heat can meet the 114t/h steam consumption required for seawater desalination. When seawater desalination power station extracts water from the power station, the extraction cost of the power station is 100 yuan/t. The annual operating cost of the blast furnace is not less than 7800 h. The annual waste heat savings cost 8,892,200 yuan.

The investment estimate for the thermal energy conversion system is as follows: The construction and installation cost is estimated at 10 million yuan, the hot water circulation pump is 1 million yuan, the heat exchanger is 3 million yuan, the pipeline and bracket is 1 million yuan, and the ancillary facilities is 1 million yuan. Total 16 million yuan.

Seawater desalination station has 4 staff members, and the annual labor cost is about 160,000 yuan. The annual budget for maintenance costs is 100,000 yuan. The electricity cost saved by the cooling fan is about the same as the power consumption of the hot water circulating pump, which is not included in the benefits. The blast furnace slag water is adopted. Turbid water, for the production of wastewater, saving water is temporarily not included in the benefits. Therefore, the blast furnace slag water used for seawater desalination has an annual profit of 8.632 million yuan, and the cost can be recovered in 2 years.

2 Development of slag water waste heat recovery technology At present, large domestic blast furnaces have waste heat recovery of hot blast stove, TRT residual pressure power generation, CDQ and other waste heat recovery measures, but slag sensible heat, which accounts for 5.5% of blast furnace energy consumption, has not been recycled. Many research institutes in the world have intentionally focused on the research of the waste heat recovery of blast furnaces to change the slag treatment process. However, there is currently no complete set of process system for the direct use of power generation after recovery of this part of waste heat. Therefore, in order to reduce the environmental pollution caused by thermal energy emissions and reduce the energy consumption of ironmaking processes, the development of blast furnace slag water waste heat recovery power generation technology has become an urgent task.

After a period of comparative analysis, blast furnace slag water waste heat power generation has two relatively feasible ways: one is to directly flash 90C95C slag hot water, flash steam to promote steam turbine power generation. The slag hot water is pumped into the flash tank. The hot water passes through a small part of the sprinkler to generate flash steam. Most of the water heat returns to the original cooling water system after absorbing and cooling the flash steam. Flash steam is sent from the pipeline to the steam turbine for power generation, and the spent steam is condensed into water in the condenser and returned to the slag water system. The cooling water is provided by the new cooling water system.

Such as blast furnace slag flushing water: 2600t / h, temperature: 90C. The flash steam pressure can be generated: 0.03MPa, temperature: 69C, steam volume: 100t / h, power generation: 4000kL The system's process structure as simple as.

The other is the slag water heating with adjustable boiling point working substance, making it produce steam, the working substance steam promotes the high efficiency turbine or screw expander to generate electricity, and the steam turbine outlet working substance lacks steam into the plate condenser to condense into the working fluid, the liquid Into the tank, the pump hit the flash evaporator heat evaporation, repeat the above process. Cooling water is provided by the new cooling water system. Such as the blast furnace slag flushing water: 2600 t/h, temperature: 90C, power generation: 3200kW. The system's process structure is as simple as.

3 Conclusion The stage of development of blast furnace slag water waste heat recovery technology is as follows: The bath water is heated for a period of one winter to increase the ultrafiltration water inlet temperature (abbreviated as ultrafiltration warm water) for desalination of a waste heat power generation. From the analysis of energy quality, the low-grade waste heat is converted into high-grade electric energy. The economic efficiency of blast furnace slag water waste heat power generation is very obvious. At the same time, the lower the temperature of the scouring water, the higher the cement activity of the slag. Therefore, the industrial technology extracts the residual heat of the slag water, and reduces its recycling temperature. It not only helps to improve the slag quality, but also reduces the load of the original cooling tower, saves the power consumption of the water pump and the fan, and further enhances the development potential of the technology.

However, the application of waste heat recovery power generation technology for blast furnace slag water is still in its infancy. At present, there are still many companies that want to do development in this area, but they all stay in the technical demonstration, and they have not made substantial progress. Whether it can be combined with the blast furnace process There are a large number of technical issues that need to be studied. To this end, we use the advantages of WISCO's familiarity with the ironmaking process, combined with external technical means, to maximize the technical recovery of the high-temperature flushing water residual heat, and the working conditions can be designed according to specific circumstances; On the one hand, the waste heat of the slag water was recovered for power generation, which reduced the energy consumption per ton of iron in the blast furnace.

In summary, the blast furnace slag water waste heat recovery power generation technology has great promotion significance, and it should seize the opportunity of the country to vigorously develop energy-saving emission reduction technologies, and complete the system's independent integrated development through the development and optimization of system configuration, thereby transforming the company into a company. The core technology.

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