In recent years, China's steel industry has developed greatly. Due to the adjustment of product structure, large steel companies are mostly tropical, medium and heavy plates, cold rolled, galvanized, and painted. Local small and medium-sized private steel enterprises are mostly engaged in the construction and production of rod and wire, narrow medium-bandwidth and section steel.
In the small and medium-sized steel mills built in recent years, the development of “snowball†has grown from small to medium to further develop into large enterprises with annual output of several million tons of steel products. Most of these companies do not build coke ovens and have problems with fuel selection in rolling mills. The small-volume heating furnace can also burn coal or coal powder, but it is limited due to extremely poor working conditions and serious environmental pollution. The new rolling steel production line is an annual output of several hundred thousand tons, or even one million tons, the pursuit of large volume, high yield; heating furnace hourly output of hundreds of tons, the length of heated billet is as short as 6m, generally 9m, 12m, the longest Up to 16m; high heating quality requirements, the temperature difference of the billet is controlled at 30 °C. Therefore, reheating the coal in the furnace is technically completely infeasible. Hot and dirty gas is also limited due to process difficulties; it can be burned with heavy oil, but the operating cost is high. The excess gas produced by the small and medium-sized blast furnaces built by these enterprises is forced to be released if not used, polluting the environment and wasting energy. At this time, the regenerative furnace technology for burning blast furnace gas appeared. This heat exchange combustion technology with Chinese characteristics has been rapidly promoted and applied in small and medium-sized steel enterprises. Since the successful application of this technology in July 1997, the regenerative heating furnace has been built in the hundreds of hundreds of steel enterprises, and the application of regenerative heat transfer technology in the field of heating furnace has been gradually improved and matured.
Application overview
The application of regenerative heat transfer technology in the steel rolling field of iron and steel enterprises, from the furnace type: push steel heating furnace; walking beam heating furnace; vehicle bottom furnace; soaking furnace; hood furnace; strip continuous Baking equipment in the field of heat treatment furnaces and smelting and continuous casting.
From matching mills: bars, high-speed wire, plate, tropical, H-beam, and section steel. Among them, the walking beam furnace is the main one.
From heated steel grades, carbon, low and gold and special steel furnaces. (No performance of heating silicon steel billet temporarily)
From the furnace output: hourly output of several tens of tons to several hundred tons from the heating billet specifications: billet up to 16m, section maximum 300 × 400mm; slab up to 15.6m; slab thickness: 250mm ~ 300mm.
It can be seen from the above that the application range of the regenerative heating furnace has covered various fields of rolling steel production.
The enterprises adopting this technology are mainly concentrated in local small and medium-sized private steel enterprises, and most of them are regenerative heating furnaces that burn pure blast furnace gas. Therefore, the burning cost of these steel slabs is low, and the price of steel products is competitive. Strong, high profit margins. The earliest use of regenerative technology, heating furnace burning blast furnace gas is Pingxiang Iron and Steel Company, they have five regenerative heating furnaces with an hourly output of 60~150t, and the heat consumption index of the heating furnace has reached the "special furnace". Its fuel cost is less than half that of heavy oil. Among the private or joint ventures, it is represented by Tangshan Guofeng, Qianxijinxi, Shanxi Haixin, Tianjin Rongcheng, Shandong Rizhao and the fast-growing Jianlong system. The rolling mills of these steel companies are all regenerative furnaces that burn blast furnace gas. Special steel enterprises are represented by Jiangyin Xingcheng Special Steel. Phase I and Phase II rolling steel walking beam furnaces are all regenerative furnaces for blast furnace gas. Another example is Shagang Group of Zhangjiagang City. In the early stage, it was a “short-flow†steel plant. The walking beam furnace and the push-steel furnace built in more than a dozen rolling mills were all burning heavy oil. In the later stage, a blast furnace was built. After the blast furnace gas, the oil-fired heating furnace was successively changed to a regenerative heating furnace for burning blast furnace gas. According to Shagang's responsible responsible for the renovation of the heating furnace, this technical reform can save the company fuel costs in billions of dollars. For example, more than a dozen heating furnaces of Zhangjiagang Yonglian Iron and Steel Group are also regenerative heating furnaces for burning blast furnace gas.
Handan Iron and Steel is a state-owned large-scale steel enterprise and the first to adopt this technology. The regenerative furnace for burning blast furnace gas, which was put into operation in July 1997 in Handan Iron and Steel Co., was the first blast furnace gas and air double preheating in China. Regenerative furnace. Pingxiang Iron and Steel Company and Jiyuan Iron and Steel Company followed closely. The medium-plate heating furnaces of Handan Iron and Steel and Maanshan Iron and Steel Co., Ltd. are the first large-scale steel enterprises in China to use the regenerative heating furnace for burning blast furnace gas. Nangang Medium Plate and WISCO use large-scale regenerative heating furnaces that only preheat the air. So far, according to incomplete statistics, there are no less than 200 types of regenerative furnaces of various types.
Among them, the regenerative walking beam type heating furnace for burning blast furnace gas includes: one is Tangshan Guofeng's 1450mm continuous casting and rolling project, the heated slab is 15.6m long, and the hourly output reaches 290t. The furnace is also a regenerative walking beam type heating furnace that burns blast furnace gas, and the furnace has been put into production smoothly. Heating quality, output, and heat consumption all achieved the desired results, and recently signed a contract for 2# furnace. Tanggang continuous casting and rolling, slab length 15m, output 250t / h, is also a regenerative walking beam furnace burning blast furnace gas, has also been put into production. The second is the walking beam type heating furnace supporting the Shagang rod and wire rod rolling mill. The heating billet is 150×150×16000mm, the original burning heavy oil, the regenerative furnace that has been reformed to burn the blast furnace gas, the production is normal, this is the world. The widest regenerative furnace on the top. Thirdly, the regenerative walking beam furnace of the blast furnace gas of the 300×400×12000mm bearing billet of Jiangyin Xingcheng Special Steel was reconstructed and built, which not only satisfies the process requirements of heating special steel, but also proves that the furnace is more suitable for bearings. Thermal diffusion of steel. The new large and small rod lines of Xingcheng Special Steel also use regenerative walking beam furnaces that burn blast furnace gas.
Estimation of economic benefits of regenerative heating furnace
To analyze the economic benefits of the regenerative heating furnace, this paper estimates and analyzes the regenerative heating furnace based on the blast furnace gas.
The so-called economic benefits can be analyzed from three levels.
First, the blast furnace gas is rationally utilized.
Previously, the iron and steel complex used to mix blast furnace gas and coke oven gas into a mixed gas with a calorific value of 7500~9200kJ/Nm3. As the main fuel of the rolling steel heating furnace, the whole company will balance the gas according to the gas users. If there is excess blast furnace Gas, a conditional enterprise used as a fuel for power generation, is not a waste.
More companies are still being released, which wastes energy and pollutes the environment. Now blast furnace gas can be used as a single fuel for the heating furnace. The blast furnace gas should not be released again. For some steel joint enterprises, the high calorific value coke oven gas replaced by blast furnace gas, or used as chemical raw materials or for urban civilian use, Make the best use of it and increase the benefits for the company. According to the data of the previous two years, the domestic blast furnace gas discharge rate is 9~12%. Converting the standard coal to more than 2.5 million tons, the release rate is reduced, which is to save energy.
Second, after the original furnace for burning heavy oil was changed to blast furnace gas, it brought huge economic benefits to the enterprise. Taking the bar plant with an annual output of 800,000 as an example, the output of the heating furnace is 150t/h, and the heavy oil is calculated according to the advanced fuel consumption index of 32Kg/t. The annual heating billet is 825,000 tons, and the annual total fuel consumption is 26,400 tons. The price is 2,500 yuan / t, the fuel cost of the furnace is 66 million yuan. Change the burning of blast furnace gas, heating 400Nm3 of blast furnace gas per ton of cold billet (heat value 800 × 4.18KJ / m3), the company's internal price of one cubic meter of blast furnace gas 7 cents. Heating one ton of cold billet is 28 yuan / t. The fuel cost for burning blast furnace gas is 23.1 million yuan. This funding is fully in the business profits of the company. This is just the internal accounting of the company. Otherwise, it will spend an additional 66 million yuan each year. Therefore, its benefits are considerable. It is roughly estimated that there are 200 regenerative heating furnaces with a capacity of more than 100h/t in China. According to the above data, the energy-saving cost can reach more than 800 million yuan.
Thirdly, from the technical point of view, the regenerative heating furnace can preheat the gas and the combustion air to only about 100 ° C lower than the furnace gas temperature. The exhaust gas temperature is only about 150 °C. The physical heat of the flue gas is fully recovered. This heat recovery method is unmatched by the conventional furnace using a metal heat exchanger to recover the physical heat of the flue gas. Therefore, although the low-calorific value of the blast furnace gas is burned, the heat consumption index is not higher than that of the conventional heating furnace that burns the high calorific value gas. The advanced nature of the regenerative furnace technology is fully demonstrated. In the "Energy Saving Rules for Rolling Process (Heating Furnace)", it is clearly stated that heating different steel grades and using different fuels may have different heat consumption rates. The furnace for burning crude oil and natural gas is Ki=1, and the blast furnace gas is changed to Ki=1.4. In fact, the heat consumption index of the blast furnace gas regenerative furnace does not need to be high. At present, the thermal efficiency of conventional heating furnaces (including walking beam furnaces) is up to 55~59%, while the thermal efficiency of regenerative heating furnaces has reached 65~70%, which is 5~10 higher than that of conventional heating furnaces. %.
It should be specially noted that these walking beam type heating furnaces which are matched by different rolling mills have the same conveying method as the conventional furnace except that the combustion system is different from the conventional walking beam type heating furnace. Feeding gantry, feeding roller, cantilever feeding roller, pusher or billet loading machine for step beam furnace, stepping machine, water beam and hydraulic system at the bottom of the furnace; cantilever roller or feeder The electric control system, material tracking system and information transmission system that control the movement of these equipments, etc., are the current high level in China and the world. The regenerative heat exchange technology can save the concrete chimney and flue up to 60~80m high. This will save the investment in the furnace. The regenerative walking beam furnace also uses vaporization cooling to save water and energy. Some manufacturers are using the steam generated by multiple furnaces to generate electricity.
Exploring questions and opinions
The regenerative heat transfer technology is applied to the continuous heating furnace. It has been in China for ten years. China's regenerative heating furnace has Chinese characteristics. The main performance is the use of low calorific value blast furnace gas as the heating furnace. The fuel uses the regenerative heat exchange technology to preheat the blast furnace gas and the combustion air to about 1000 °C, which meets the requirements of the furnace temperature of the furnace. Therefore, this technology has been welcomed by small and medium-sized steel companies as soon as it emerged. It has played an important role in the development of small and medium-sized steel companies. But why are large steel companies not paying attention to this technology? Although WISCO large-scale plants, Nanjing Zhongban Plant, and Panzhihua large-scale plants also use regenerative technology, these furnaces burn mixed gas, and only use heat storage technology to preheat the air, which is technically unreasonable. Therefore, compared with similar conventional furnaces, the advantages of technical and economic indicators are not obvious. For example, Baosteel's tropical walking beam furnace is a regenerative burner imported from the United States. It is in trial use and the effect is still unclear. Only the Maanshan Iron and Steel Group, Handan Iron and Steel, Lingang Medium Plate Heating Furnace use the blast furnace gas and air double regenerative heating furnace to achieve significant economic benefits. The reason why large steel companies have not adopted this technology, I believe there may be two reasons. The original gas pipeline system of large steel company has been formed, the blast furnace gas has been changed, the gas pipeline network has to be reconstructed, and the amount of engineering is very large. Second, there are some unsatisfactory applications of regenerative heat transfer technology in China, such as The furnace pressure control of the regenerative furnace is different from that of the conventional furnace. If there is a problem in the design, the furnace pressure fluctuates greatly and the fire phenomenon is common. Some burners are designed to have a large amount of maintenance in use and the service life is not ideal. These factors have affected the promotion and application of regenerative furnaces.
This paper summarizes the application of regenerative furnaces for blast furnace gas in order to attract the attention of relevant departments and enterprises, especially those enterprises that have not used blast furnace gas and choose natural gas or heavy oil as heating furnace fuel. Some steel companies spend huge sums of money to build gas turbines that build blast furnace gas. This may be reasonable from the perspective of energy recovery when blast furnace gas is not fully utilized. But now the blast furnace gas can be used as a single fuel for various types of heating furnaces. The thermal efficiency of the heating furnace can reach about 70%, and the use of blast furnace gas as a fuel for power generation is economically unreasonable.
In the small and medium-sized steel mills built in recent years, the development of “snowball†has grown from small to medium to further develop into large enterprises with annual output of several million tons of steel products. Most of these companies do not build coke ovens and have problems with fuel selection in rolling mills. The small-volume heating furnace can also burn coal or coal powder, but it is limited due to extremely poor working conditions and serious environmental pollution. The new rolling steel production line is an annual output of several hundred thousand tons, or even one million tons, the pursuit of large volume, high yield; heating furnace hourly output of hundreds of tons, the length of heated billet is as short as 6m, generally 9m, 12m, the longest Up to 16m; high heating quality requirements, the temperature difference of the billet is controlled at 30 °C. Therefore, reheating the coal in the furnace is technically completely infeasible. Hot and dirty gas is also limited due to process difficulties; it can be burned with heavy oil, but the operating cost is high. The excess gas produced by the small and medium-sized blast furnaces built by these enterprises is forced to be released if not used, polluting the environment and wasting energy. At this time, the regenerative furnace technology for burning blast furnace gas appeared. This heat exchange combustion technology with Chinese characteristics has been rapidly promoted and applied in small and medium-sized steel enterprises. Since the successful application of this technology in July 1997, the regenerative heating furnace has been built in the hundreds of hundreds of steel enterprises, and the application of regenerative heat transfer technology in the field of heating furnace has been gradually improved and matured.
Application overview
The application of regenerative heat transfer technology in the steel rolling field of iron and steel enterprises, from the furnace type: push steel heating furnace; walking beam heating furnace; vehicle bottom furnace; soaking furnace; hood furnace; strip continuous Baking equipment in the field of heat treatment furnaces and smelting and continuous casting.
From matching mills: bars, high-speed wire, plate, tropical, H-beam, and section steel. Among them, the walking beam furnace is the main one.
From heated steel grades, carbon, low and gold and special steel furnaces. (No performance of heating silicon steel billet temporarily)
From the furnace output: hourly output of several tens of tons to several hundred tons from the heating billet specifications: billet up to 16m, section maximum 300 × 400mm; slab up to 15.6m; slab thickness: 250mm ~ 300mm.
It can be seen from the above that the application range of the regenerative heating furnace has covered various fields of rolling steel production.
The enterprises adopting this technology are mainly concentrated in local small and medium-sized private steel enterprises, and most of them are regenerative heating furnaces that burn pure blast furnace gas. Therefore, the burning cost of these steel slabs is low, and the price of steel products is competitive. Strong, high profit margins. The earliest use of regenerative technology, heating furnace burning blast furnace gas is Pingxiang Iron and Steel Company, they have five regenerative heating furnaces with an hourly output of 60~150t, and the heat consumption index of the heating furnace has reached the "special furnace". Its fuel cost is less than half that of heavy oil. Among the private or joint ventures, it is represented by Tangshan Guofeng, Qianxijinxi, Shanxi Haixin, Tianjin Rongcheng, Shandong Rizhao and the fast-growing Jianlong system. The rolling mills of these steel companies are all regenerative furnaces that burn blast furnace gas. Special steel enterprises are represented by Jiangyin Xingcheng Special Steel. Phase I and Phase II rolling steel walking beam furnaces are all regenerative furnaces for blast furnace gas. Another example is Shagang Group of Zhangjiagang City. In the early stage, it was a “short-flow†steel plant. The walking beam furnace and the push-steel furnace built in more than a dozen rolling mills were all burning heavy oil. In the later stage, a blast furnace was built. After the blast furnace gas, the oil-fired heating furnace was successively changed to a regenerative heating furnace for burning blast furnace gas. According to Shagang's responsible responsible for the renovation of the heating furnace, this technical reform can save the company fuel costs in billions of dollars. For example, more than a dozen heating furnaces of Zhangjiagang Yonglian Iron and Steel Group are also regenerative heating furnaces for burning blast furnace gas.
Handan Iron and Steel is a state-owned large-scale steel enterprise and the first to adopt this technology. The regenerative furnace for burning blast furnace gas, which was put into operation in July 1997 in Handan Iron and Steel Co., was the first blast furnace gas and air double preheating in China. Regenerative furnace. Pingxiang Iron and Steel Company and Jiyuan Iron and Steel Company followed closely. The medium-plate heating furnaces of Handan Iron and Steel and Maanshan Iron and Steel Co., Ltd. are the first large-scale steel enterprises in China to use the regenerative heating furnace for burning blast furnace gas. Nangang Medium Plate and WISCO use large-scale regenerative heating furnaces that only preheat the air. So far, according to incomplete statistics, there are no less than 200 types of regenerative furnaces of various types.
Among them, the regenerative walking beam type heating furnace for burning blast furnace gas includes: one is Tangshan Guofeng's 1450mm continuous casting and rolling project, the heated slab is 15.6m long, and the hourly output reaches 290t. The furnace is also a regenerative walking beam type heating furnace that burns blast furnace gas, and the furnace has been put into production smoothly. Heating quality, output, and heat consumption all achieved the desired results, and recently signed a contract for 2# furnace. Tanggang continuous casting and rolling, slab length 15m, output 250t / h, is also a regenerative walking beam furnace burning blast furnace gas, has also been put into production. The second is the walking beam type heating furnace supporting the Shagang rod and wire rod rolling mill. The heating billet is 150×150×16000mm, the original burning heavy oil, the regenerative furnace that has been reformed to burn the blast furnace gas, the production is normal, this is the world. The widest regenerative furnace on the top. Thirdly, the regenerative walking beam furnace of the blast furnace gas of the 300×400×12000mm bearing billet of Jiangyin Xingcheng Special Steel was reconstructed and built, which not only satisfies the process requirements of heating special steel, but also proves that the furnace is more suitable for bearings. Thermal diffusion of steel. The new large and small rod lines of Xingcheng Special Steel also use regenerative walking beam furnaces that burn blast furnace gas.
Estimation of economic benefits of regenerative heating furnace
To analyze the economic benefits of the regenerative heating furnace, this paper estimates and analyzes the regenerative heating furnace based on the blast furnace gas.
The so-called economic benefits can be analyzed from three levels.
First, the blast furnace gas is rationally utilized.
Previously, the iron and steel complex used to mix blast furnace gas and coke oven gas into a mixed gas with a calorific value of 7500~9200kJ/Nm3. As the main fuel of the rolling steel heating furnace, the whole company will balance the gas according to the gas users. If there is excess blast furnace Gas, a conditional enterprise used as a fuel for power generation, is not a waste.
More companies are still being released, which wastes energy and pollutes the environment. Now blast furnace gas can be used as a single fuel for the heating furnace. The blast furnace gas should not be released again. For some steel joint enterprises, the high calorific value coke oven gas replaced by blast furnace gas, or used as chemical raw materials or for urban civilian use, Make the best use of it and increase the benefits for the company. According to the data of the previous two years, the domestic blast furnace gas discharge rate is 9~12%. Converting the standard coal to more than 2.5 million tons, the release rate is reduced, which is to save energy.
Second, after the original furnace for burning heavy oil was changed to blast furnace gas, it brought huge economic benefits to the enterprise. Taking the bar plant with an annual output of 800,000 as an example, the output of the heating furnace is 150t/h, and the heavy oil is calculated according to the advanced fuel consumption index of 32Kg/t. The annual heating billet is 825,000 tons, and the annual total fuel consumption is 26,400 tons. The price is 2,500 yuan / t, the fuel cost of the furnace is 66 million yuan. Change the burning of blast furnace gas, heating 400Nm3 of blast furnace gas per ton of cold billet (heat value 800 × 4.18KJ / m3), the company's internal price of one cubic meter of blast furnace gas 7 cents. Heating one ton of cold billet is 28 yuan / t. The fuel cost for burning blast furnace gas is 23.1 million yuan. This funding is fully in the business profits of the company. This is just the internal accounting of the company. Otherwise, it will spend an additional 66 million yuan each year. Therefore, its benefits are considerable. It is roughly estimated that there are 200 regenerative heating furnaces with a capacity of more than 100h/t in China. According to the above data, the energy-saving cost can reach more than 800 million yuan.
Thirdly, from the technical point of view, the regenerative heating furnace can preheat the gas and the combustion air to only about 100 ° C lower than the furnace gas temperature. The exhaust gas temperature is only about 150 °C. The physical heat of the flue gas is fully recovered. This heat recovery method is unmatched by the conventional furnace using a metal heat exchanger to recover the physical heat of the flue gas. Therefore, although the low-calorific value of the blast furnace gas is burned, the heat consumption index is not higher than that of the conventional heating furnace that burns the high calorific value gas. The advanced nature of the regenerative furnace technology is fully demonstrated. In the "Energy Saving Rules for Rolling Process (Heating Furnace)", it is clearly stated that heating different steel grades and using different fuels may have different heat consumption rates. The furnace for burning crude oil and natural gas is Ki=1, and the blast furnace gas is changed to Ki=1.4. In fact, the heat consumption index of the blast furnace gas regenerative furnace does not need to be high. At present, the thermal efficiency of conventional heating furnaces (including walking beam furnaces) is up to 55~59%, while the thermal efficiency of regenerative heating furnaces has reached 65~70%, which is 5~10 higher than that of conventional heating furnaces. %.
It should be specially noted that these walking beam type heating furnaces which are matched by different rolling mills have the same conveying method as the conventional furnace except that the combustion system is different from the conventional walking beam type heating furnace. Feeding gantry, feeding roller, cantilever feeding roller, pusher or billet loading machine for step beam furnace, stepping machine, water beam and hydraulic system at the bottom of the furnace; cantilever roller or feeder The electric control system, material tracking system and information transmission system that control the movement of these equipments, etc., are the current high level in China and the world. The regenerative heat exchange technology can save the concrete chimney and flue up to 60~80m high. This will save the investment in the furnace. The regenerative walking beam furnace also uses vaporization cooling to save water and energy. Some manufacturers are using the steam generated by multiple furnaces to generate electricity.
Exploring questions and opinions
The regenerative heat transfer technology is applied to the continuous heating furnace. It has been in China for ten years. China's regenerative heating furnace has Chinese characteristics. The main performance is the use of low calorific value blast furnace gas as the heating furnace. The fuel uses the regenerative heat exchange technology to preheat the blast furnace gas and the combustion air to about 1000 °C, which meets the requirements of the furnace temperature of the furnace. Therefore, this technology has been welcomed by small and medium-sized steel companies as soon as it emerged. It has played an important role in the development of small and medium-sized steel companies. But why are large steel companies not paying attention to this technology? Although WISCO large-scale plants, Nanjing Zhongban Plant, and Panzhihua large-scale plants also use regenerative technology, these furnaces burn mixed gas, and only use heat storage technology to preheat the air, which is technically unreasonable. Therefore, compared with similar conventional furnaces, the advantages of technical and economic indicators are not obvious. For example, Baosteel's tropical walking beam furnace is a regenerative burner imported from the United States. It is in trial use and the effect is still unclear. Only the Maanshan Iron and Steel Group, Handan Iron and Steel, Lingang Medium Plate Heating Furnace use the blast furnace gas and air double regenerative heating furnace to achieve significant economic benefits. The reason why large steel companies have not adopted this technology, I believe there may be two reasons. The original gas pipeline system of large steel company has been formed, the blast furnace gas has been changed, the gas pipeline network has to be reconstructed, and the amount of engineering is very large. Second, there are some unsatisfactory applications of regenerative heat transfer technology in China, such as The furnace pressure control of the regenerative furnace is different from that of the conventional furnace. If there is a problem in the design, the furnace pressure fluctuates greatly and the fire phenomenon is common. Some burners are designed to have a large amount of maintenance in use and the service life is not ideal. These factors have affected the promotion and application of regenerative furnaces.
This paper summarizes the application of regenerative furnaces for blast furnace gas in order to attract the attention of relevant departments and enterprises, especially those enterprises that have not used blast furnace gas and choose natural gas or heavy oil as heating furnace fuel. Some steel companies spend huge sums of money to build gas turbines that build blast furnace gas. This may be reasonable from the perspective of energy recovery when blast furnace gas is not fully utilized. But now the blast furnace gas can be used as a single fuel for various types of heating furnaces. The thermal efficiency of the heating furnace can reach about 70%, and the use of blast furnace gas as a fuel for power generation is economically unreasonable.
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