1、 Overview of Dehumidification Blowing Project

Blast furnace smelting requires stable furnace conditions, avoiding fluctuations, in order to ensure stable and smooth operation of the blast furnace. Blows (air) contain moisture and vary with seasons, climate, and temperature changes. The moisture brought into the blast furnace by the blower undergoes decomposition reaction in the swirling zone of the blast furnace tuyere and absorbs heat. Decomposing 1g of water requires a wind temperature compensation of about 6 ℃. The fluctuation of moisture content in the wind sent into the blast furnace causes fluctuations in the combustion temperature in front of the tuyere, so the fluctuation of moisture content will inevitably cause unstable furnace conditions.

Dehumidification, as a smelting energy-saving technology, has been adopted in blast furnaces by countries such as the United States, Japan, and Britain since the beginning of the last century, and has achieved the effect of increasing pig iron production and reducing coke ratio. In the past decade, with the development and promotion of domestic blast dehumidification technology, dehumidification, as one of the three recognized energy-saving technologies in the international ironmaking industry (coal injection, oxygen enrichment, and dehumidification), has gradually been adopted by a large number of steel mills in China, and is also a key energy-saving and emission reduction project recommended by national steel enterprises during the 12th Five Year Plan period.

According to the technical report of the "National Key Energy saving and Low carbon Technology Promotion Catalogue" (2015 edition, energy-saving section) released by the National Development and Reform Commission in December 2015, the steel industry should focus on promoting "blast furnace blast dehumidification energy-saving technology". The main indicators of this technology are as follows:

1. For every 1g/m3 decrease in the moisture content of blast furnace air, the comprehensive coke ratio decreases by 0.8kg/tFe-1kg/tFe;

2. For every 1g/m3 decrease in the moisture content of blast furnace air, an increase of 2.23kg/tFe in coal injection is required;

3. For every 1g/m3 decrease in the moisture content of blast furnace air, the production capacity increases by about 0.1% to 0.5% due to the smooth operation of the blast furnace;

4. Reduce the power of the blower by 5-17%.

(1) Reduce the comprehensive coke ratio

The air contains moisture, which changes with seasons, climate, and temperature. As water decomposition is an endothermic reaction, the decomposition of 1g of water requires a wind temperature compensation of~6 ℃. The fluctuation of moisture content in the wind sent into the blast furnace causes fluctuations in the combustion temperature in front of the tuyere, so the fluctuation of moisture content will inevitably cause unstable furnace conditions. Due to dehumidification, it can reduce the heat of decomposition of moisture in the wind, save coke, increase the inlet air temperature, raise the furnace chamber temperature, increase the injection volume, reduce the coke ratio, and facilitate smooth furnace operation.

(2) Increasing the coal injection ratio and replacing the coke ratio to reduce energy costs

Reducing the comprehensive coke ratio is reflected in two aspects: on the one hand, by dehumidifying the moisture in the blast furnace and burning the same amount of fuel through the heating furnace, the hot air temperature can be increased and the coke ratio can be reduced. On the other hand, the chemical reaction heat in the blast furnace can save energy. For every 1g/m3 decrease in moisture content, the theoretical combustion temperature decreases by 7.6 ℃ (based on Shougang's experience), further reducing the coke ratio.

The impact of wind pressure on coal injection is also significant. Due to the moisture content, the combustion temperature at the tuyere decreases, directly affecting the combustion of coal powder and limiting the increase in coal injection rate. Considering only the factor of maintaining the theoretical combustion temperature constant, the moisture content decreases and the coal injection increases.

(3) Save energy consumption of blower

Due to the increase in air density and blowing capacity at the inlet of the blast furnace after dehumidification and blowing, the energy consumption of blowing will decrease without increasing production.

(4) Stable furnace condition

In the production of blast furnace ironmaking, the practical use of blast dehumidification technology has greatly improved the understanding of its significance in stabilizing furnace conditions. Some people even propose that the blast dehumidification technology should be adopted from the perspective of stabilizing furnace conditions alone. After the furnace conditions are stabilized, its output will inevitably be further guaranteed, and the blast furnace humidity is not affected by day, night, and rainy weather. The blast furnace can produce stably and smoothly, and its output is relatively significantly increased, resulting in considerable economic benefits.

(5) Efficiency increase through natural production

Stable and smooth operation of blast furnaces and improved blast capacity can increase iron production capacity and improve enterprise efficiency. The application of the blast dehumidification system at Zhongtian Iron and Steel in similar regions has significantly increased production.

(6) Adjust furnace temperature

Through the practical application of blast furnace dehumidification technology in recent years, various effective adjustment schemes have emerged based on their own blast furnace operation conditions, not limited to methods such as increasing the coal injection ratio and reducing the coke ratio. For example, the adjustment method of Shaogang fully utilizes the effect of reducing moisture content to increase furnace temperature. In the use of blast dehumidification in Shaogang's 7 # and 8 # blast furnaces, the method of adjusting blast furnace humidity to adjust furnace temperature is adopted. This method has a fast adjustment response speed, constant wind temperature and air volume, small changes in furnace conditions, and is relatively stable, with fewer variables and faster speed compared to the adjustment methods in the old process manual. It is a very good furnace temperature adjustment process method.

(7) Reduce CO2 emissions

According to the carbon balance diagram, the gasification carbon amount Cg=Cf+C melting+C volatilization - C infiltration - C dust, where Cf is the carbon amount brought in by fuel (coke ratio and coal ratio) per ton of pig iron, C seat is the carbon amount brought in by limestone (including natural ore) into CO2, C volatilization is the carbon amount taken away by coke volatilization, C infiltration is the carburizing amount per ton of pig iron, and C dust is the carbon amount brought into furnace dust per ton of pig iron. When there is not much limestone used in the blast furnace, the amount of carbon brought in by the flux and coke volatiles is not much, and the amount of carbon entering the furnace dust is also not much, which can roughly offset each other. Therefore, the amount of gasification carbon at this time is Cg=Cf-C infiltration.

For example, the dehydration project of Chongqing Iron and Steel's 2500 blast furnace: From April to October 2018, the pig iron production of blast furnaces 1 and 2 (only blast furnace 1 in April and October) was 2009013 tons. Compared with the same period in 2017, the pig iron production increased by 48255 tons and the coke ratio decreased by 9.78355kg/t. If the carbon content of coke and coal powder is calculated at 84%, and the carbon content of pig iron is calculated at 4%, the CO2 emissions will be reduced by 53500 tons.

(8) Raise the temperature of the furnace top gas

2、 Introduction to dehumidification and air blowing process

This technology uses a dual effect steam type lithium bromide absorption refrigeration method to manufacture low-temperature cooling water. A cooling heat exchanger is installed between the air filter and the blower, and the low-temperature chilled water provided by the refrigeration machine is used to exchange heat with the air, reducing the air temperature to the saturation temperature corresponding to the air pressure and humidity (generally 8 ℃ -10 ℃). The moisture in the air is condensed out, and the relative humidity of the air is 100%. It enters the blower in a low-temperature state, thereby achieving the purpose of air dehumidification.

3、 Dehumidification process flow

A. Air system process: The external atmosphere enters the self-cleaning filter to remove dust, and then enters the surface cooler. The external atmosphere is high in temperature and humidity, and after heat exchange with the cooler in the surface cooler, it is cooled and dehumidified before entering the blower.

B. Cold water system process: The low-temperature water from the refrigeration unit enters the cold water cooler of the surface cooler and exchanges heat with the external atmosphere entering the surface cooler. The air is cooled to 10 ℃, and the air is cooled to remove some moisture. The cold water, on the other hand, increases in temperature due to the extraction of heat from the air. The high-temperature cold water is pumped out by the cold water pump and sent into the refrigeration unit. After refrigeration, the low-temperature cold water is sent out for recycling.

C. Process of circulating cooling water system (the entire circulating water system is not within the scope of this bidding document): The cooling water is sucked out from the water tank by the circulating water pump and sent to the refrigeration unit. After heat exchange in the refrigeration unit, it is heated and then returned to the cooling tower to release heat and cool down, flowing back to the cooling water tank for recycling.

D. Schematic diagram of blast furnace dehumidification process

4、 Main equipment supply content and requirements

The dehumidifier system includes: refrigeration unit, heat exchanger (surface cooler), chilled water system, cooling water system, condensate water system, inspection ladder platform railing, rain shelter facilities, etc. The self-cleaning air filter system includes: filter cartridge, pulse valve, frame steel structure, inspection ladder platform railing, rain shelter facilities, etc., supporting high and low voltage electrical equipment, and automatic control system.