Application survey and energy saving benefit of do

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Recent years are a period of great development of China's iron and steel industry. Due to the adjustment of product structure, most of the new or reconstruction projects of large iron and steel enterprises are tropical, medium and heavy plate, cold rolling, galvanizing, color coating, etc. Local small and medium-sized and private steel enterprises mostly build and produce rod and wire rod, narrow, medium and wide band, section steel and other products

small and medium-sized steel plants built in recent years have developed in a "snowball" manner, from small to medium-sized, and further developed into large enterprises with an annual output of millions of tons of steel products. Most of these enterprises do not build coke ovens, and they encounter problems in the fuel selection of steel rolling heating furnaces. Small output heating furnaces can also burn coal or pulverized coal, but they are limited due to poor working conditions and serious environmental pollution. New steel rolling production lines often produce hundreds of thousands or even millions of tons per year, pursuing large coil weight and high yield; The hourly output of the heating furnace is hundreds of tons, and the length of the heated billet is the shortest 6m, generally 9m, 12M, and the longest is 16m; The heating quality is required to be high, and the temperature difference of billet is controlled at 30 ℃. Therefore, it is completely infeasible technically to burn coal again in the heating furnace. Burning dirty gas is also limited due to the difficulty of process layout; Heavy oil can be burned, but the operation cost is high. The surplus gas produced by small and medium blast furnaces built by these enterprises, if not used, will be forced to be released, which will not only pollute the environment, but also waste energy. At this time, regenerative heating furnace technology burning blast furnace gas appeared. This heat exchange combustion technology with Chinese characteristics was soon popularized and applied in small and medium-sized iron and steel enterprises. Since the successful application of this technology in July 1997, there have been no less than hundreds of regenerative heating furnaces built in iron and steel enterprises, and the application of regenerative heat exchange technology in the field of heating furnaces has gradually been improved and matured

application overview

the application of regenerative heat exchange technology in the steel rolling field of iron and steel enterprises is divided from the furnace type: there are pusher heating furnaces; Walking beam heating furnace; Car bottom furnace; Soaking pit; Bell type furnace; Strip continuous heat treatment furnace and baking equipment in the field of smelting and continuous casting

from the matching rolling mill, it can be divided into bar, high-speed wire rod, medium and heavy plate, hot strip, H-beam, and section steel heating furnace. The walking beam furnace is the main one

from the heated steel types, ordinary carbon, low alloy and special steel heating furnaces. (there is no performance of heating silicon steel billets for the time being)

from the furnace output point: the hourly output is dozens of tons to hundreds of tons

from the heating steel billet specification point: the square billet is up to 16m, and the section is up to 300 × 400mm; The slab is up to 15.6m long; Slab thickness: 250mm~300mm

it can be seen from the above situation that the application scope of regenerative heating furnace has covered all fields of steel rolling production

the enterprises adopting this technology are mainly concentrated in local small and medium-sized and private steel enterprises, and most of them are regenerative heating furnaces burning pure blast furnace gas. Therefore, these enterprises have low combustion costs for heating billets, strong price competitiveness of steel products and high profit margin. Pingxiang Iron and steel company was the first to use the regenerative technology to burn blast furnace gas in the heating furnace. They have five regenerative heating furnaces with an hourly output of 60~150t put into use. The heat consumption index of the heating furnace has reached the "special furnace", and its fuel cost is less than half of that of burning heavy oil. Among private or joint ventures, Tangshan Guofeng, Qianxi Jinxi, Shanxi Haixin, Tianjin Rongcheng, Shandong Rizhao and Jianlong series, which have developed rapidly, should be represented. The rolling mills of these iron and steel enterprises are regenerative heating furnaces that burn blast furnace gas. Special steel enterprises are represented by Jiangyin Xingcheng Special Steel. The walking beam furnaces for phase I and phase II steel rolling are regenerative furnaces of blast furnace gas. Another example is Zhangjiagang shagang group. In the early stage, it was a "short process" steel plant. The walking beam furnaces and pusher furnaces of more than a dozen steel rolling plants were all fired with heavy oil. In the later stage, a blast furnace was built. After having blast furnace gas, the oil fired heating furnace was successively changed to a regenerative heating furnace burning blast furnace gas. According to the person in charge of heating furnace transformation of Shagang, this technical reform can save hundreds of millions of yuan of fuel costs for enterprises. For another example, more than a dozen heating furnaces of Zhangjiagang Yonglian iron and Steel Group are regenerative heating furnaces that burn blast furnace gas

Therefore, Shaogang is a large state-owned iron and steel enterprise and the first one to adopt this technology. The regenerative furnace burning blast furnace gas, which was put into operation in the third rolling mill of Shaogang in July 1997, is the first regenerative furnace with double preheating of blast furnace gas and air in China. Pingxiang Iron and steel company and Jiyuan Iron and steel company followed. The medium plate reheating furnaces of Shaogang and Masteel are the first large-scale steel enterprises in China to adopt these bottlenecks and prohibit them from being widely used as functional or structural components. They are regenerative reheating furnaces burning blast furnace gas. The large-scale regenerative heating furnace with mixed gas and only preheating air is used in the medium plate and WISCO of Nangang. So far, according to incomplete statistics, there are no less than 200 regenerative heating furnaces of various types

among them, the representative regenerative walking beam heating furnace burning blast furnace gas includes: first, the 1450mm continuous casting and rolling project of Tangshan Guofeng, which heats the walking beam heating furnace with a slab length of 15.6m and an hourly output of 290t. It also uses the regenerative walking beam heating furnace burning blast furnace gas, which has been successfully put into operation. The heating quality, output and heat consumption have achieved the desired results. Recently, a contract for 2 # furnaces has been signed. Tangshan Iron and Steel Co., Ltd. has a slab length of 15m and a production of 250t/h. It is also a regenerative walking beam furnace burning blast furnace gas, which has also been put into production. Second, there are several walking beam heating furnaces supporting Shagang rod and wire mill, and the heating billet is 150 × one hundred and fifty × 16000mm, originally burning heavy oil, has been transformed into a regenerative furnace burning blast furnace gas, and the production is normal. This is the widest regenerative heating furnace in the world at present. Third, Jiangyin Xingcheng Special Steel reconstruction and new construction of two 300 × four hundred × The regenerative walking beam furnace burning blast furnace gas for 12000mm bearing billet not only meets the process requirements of heating special steel, but also has been proved to be more suitable for thermal diffusion heating of bearing steel. Regenerative walking beam furnaces burning blast furnace gas are also used in the new large and small rod lines of Xingcheng Special Steel

estimation of economic benefits of regenerative heating furnace

analysis of the economic benefits of regenerative heating furnace, this paper is still based on the regenerative heating furnace burning blast furnace gas for estimation and analysis

the so-called economic benefits can be analyzed from three levels

first, blast furnace gas is reasonably utilized

previously, the iron and steel complex mixed blast furnace gas and coke oven gas into a mixed gas with a calorific value of 7500~9200kj/nm3, which was used as the main fuel of the steel rolling heating furnace. The whole company balanced the gas according to each gas user. If there was excess blast furnace gas, there was no waste when qualified enterprises used it as power generation fuel. More enterprises are still scattered in vain, which wastes energy and pollutes the environment. Now blast furnace gas can be used as a single fuel for heating furnaces, and blast furnace gas should no longer be dispersed. For some iron and steel complex enterprises, the high calorific value coke oven gas replaced by blast furnace gas can be used as chemical raw materials or for urban civil use, making full use of everything and increasing benefits for enterprises. According to the data of the previous two years, the emission rate of domestic blast furnace gas is 9-12%. Converted to more than 2.5 million tons of standard coal, the emission rate is reduced, which is to save energy

second, after the original heating furnace burning heavy oil was replaced by blast furnace gas, it has brought huge economic benefits to the enterprise. Now take the bar mill with an annual output of 800000 as an example, the output of the heating furnace is 150t/h, the burning of heavy oil is calculated according to the advanced oil consumption index of 32kg/t, the annual heating of steel billets is 825000 tons, and the total annual fuel consumption is 26400 tons. Based on the heavy oil price of 2500 yuan/t, the fuel cost of the heating furnace is 66 million yuan. Instead of burning blast furnace gas, 400nm3 blast furnace gas (calorific value 800) is required to heat each ton of cold billet × 4.18kj/m3) 4. The operation of high and low temperature experimental machine is simple. The internal price of the enterprise is 7 cents for a cubic meter of blast furnace gas. Heating a ton of cold billet is 28 yuan/t. The fuel cost for burning blast furnace gas is 23.1 million yuan. This fund is fully included in the operating profits of the enterprise. This is only the internal accounting of the enterprise. Otherwise, 66 million yuan will be spent every year. Therefore, its benefits are very considerable. It is roughly estimated that it can be used to test the mechanical properties of metallic and non-metallic materials, such as stretching, tightening, bending, shearing, stripping, etc. 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 800million yuan

third, technically speaking, the regenerative heating furnace can preheat the gas and combustion supporting air to only about 100 ℃ lower than the furnace gas temperature. The exhaust temperature is only about 150 ℃. The physical heat of flue gas is fully recovered. This heat recovery method is incomparable to the physical heat recovery of flue gas by metal heat exchanger in conventional heating furnace. Therefore, although the blast furnace gas with low calorific value is burned, its heat consumption index is still not higher than that of the conventional heating furnace with high calorific value gas. It fully shows the progressiveness of regenerative heating furnace technology. The regulations on energy conservation in steel rolling process (heating furnace) clearly stipulates that when heating different steel grades and using different fuels, the specific heat consumption is different. The furnace burning crude oil and natural gas ki=1, and the furnace burning blast furnace gas ki=1.4. In fact, the heat consumption index of the regenerative furnace burning blast furnace gas does not need to be high. At present, the thermal efficiency of conventional heating furnace (including walking beam heating furnace) can reach 55~59%, while the thermal efficiency of regenerative heating furnace has reached 65~70%, which is 5~10% higher than that of general conventional heating furnace

it should also be noted that these walking beam reheating furnaces matched with different rolling mills, except that the combustion system is different from the conventional walking beam reheating furnace, the billet conveying mode is no different from the conventional furnace. Feeding platform, feeding roller table, cantilever feeding roller table, steel pusher or billet loader for walking beam furnace, furnace bottom walking machinery, water beam and hydraulic system; The electric control system, material tracking system and information transmission system that control the program action of these equipment, such as the cantilever roller table or the supporting machine of the furnace, the lifting and lowering of the furnace door, are currently at a high level in China and even in the world. The combustion mode of regenerative heat exchange technology can save up to 60~80m high concrete chimneys and flues. Then the investment of heating furnace will be saved. The regenerative walking beam furnace also adopts vaporization cooling, which is both water-saving and energy-saving. Some manufacturers are combining the steam generated by multiple furnaces for power generation

problems and opinions discussed

it has been a decade since the regenerative heat exchange technology was applied to the continuous heating furnace in China. The regenerative heating furnace in China has Chinese characteristics, which is mainly reflected in the fact that at the beginning, the blast furnace gas with low calorific value was used as the heating furnace fuel, and the regenerative heat exchange technology was used to preheat the blast furnace gas and combustion supporting air to about 1000 ℃, meeting the requirements of the heating furnace temperature. Therefore, this technology has been welcomed by small and medium-sized steel enterprises as soon as it appeared. It has played an important role in the development of small and medium-sized steel enterprises. But why have large steel enterprises not paid attention to this technology? Although the large-scale plants of WISCO, Nanjing medium plate plant and Panzhihua large-scale plant also use regenerative technology, these furnaces burn mixed gas and only use regenerative technology to preheat air, which is technically unreasonable. Therefore, compared with similar conventional furnaces, the advantages of technical and economic indicators are not obvious. For example, the walking beam furnace in Baosteel tropical zone is a regenerative burner imported from the United States, which is being tried out, and the effect is not clear. Only the medium plate heating furnaces of Masteel, Shaogang and Lingang adopt the dual storage of blast furnace gas and air

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