Application of the hottest regenerative high tempe

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Application of regenerative high temperature air combustion technology in heating furnace of medium-sized plant of Tangshan Iron and Steel Company Abstract: This paper mainly introduces the structure, performance and control system characteristics of blast furnace gas regenerative heating furnace in medium-sized plant of Tangshan Iron and steel company, and analyzes the transformation effect

key words: heating furnace; Blast furnace gas; Regenerative burner

1 preface

in the iron and steel industry, heating furnace is one of the main energy consuming equipment. Reasonably solving the fuel problem of heating furnace and improving the fuel utilization rate is of great significance to reduce energy consumption, reduce the oxidation and burning loss of billet, improve the heating quality, and further improve the economic benefits of the whole rolling line production process

Tangshan Iron and steel medium-sized plant is a medium-sized steel rolling plant that produces 9 varieties of mining support steel, mining I-beam, angle steel, light rail, channel steel, round steel, square billet and more than 70 specifications, with an annual output of more than 500000 tons. There are two original pusher type heating furnaces, with a design heating capacity of 62t/h, and the mixture of heavy oil and blast furnace gas is used. In 2001, the unit consumption of heavy oil was 38.43kg/t and blast furnace gas was 167m3/T. Mixed combustion of oil and gas makes it difficult to control the oil-gas ratio and air-fuel ratio, which not only wastes energy, but also pollutes the environment, resulting in double losses of economic and social benefits, but also increases the difficulty of workers' operation

because the two reheating furnaces in medium-sized plants need to complete the billet heating task of 16 steel types and more than 70 steel specifications, the heating steel types are miscellaneous and there are many specifications, so the output of the reheating furnace fluctuates greatly. With the fluctuation of output, its heat load also fluctuates. The lower the output, the higher the heat consumption per ton of steel. And because the two furnaces cross tapping, it is often in the state of waiting for rolling and waiting for temperature, the heating time is long, and the oxidation burning loss increases

with the elimination of two heat finished products by the company, the billet opening task of medium-sized plants is gradually cancelled, and the annual output is reduced from the previous total billet of 550000 ~ 600000 tons to 400000 tons of all profile steel. The heating capacity of one heating furnace is insufficient, and the fuel waste of two heating furnaces is serious. Therefore, it is necessary to change the heating furnace of medium-sized plants into a heating furnace with strong adaptability and low energy consumption

2 theoretical basis for transforming regenerative heating furnace

regenerative high temperature air combustion technology has been used in blast furnace hot blast furnaces, open hearth furnaces, coke ovens, glass furnaces and other large-scale and high-temperature furnaces since the mid-19th century. The principle is to use the residual heat recovery device of the regenerator to switch the flue gas and air alternately, so that they can flow through the regenerator, so as to recover the sensible heat of the high-temperature flue gas to the greatest extent and improve the temperature of the combustion supporting air. However, the traditional regenerator uses lattice bricks as the heat storage body, which has low heat transfer efficiency, large volume and long commutation cycle, which limits its application in other industrial furnaces. The new regenerator uses ceramic balls or honeycomb as the heat storage body, with a specific surface area of 200 ~ 1000m2/m3, which is dozens to hundreds of times larger than the old lattice brick. Therefore, the heat transfer coefficient is greatly improved, and the volume of the regenerator can be greatly reduced. In addition, due to the improvement of the reversing device and control technology, the reversing time is greatly shortened. The reversing time of the traditional regenerator is generally 20 ~ 30min, while the reversing time of the new regenerator is only 0.5 ~ 3min. The new regenerator has high heat transfer efficiency and short reversing time. The effect is that the exhaust gas temperature is low (below 200 ℃), and the preheating temperature of the preheated medium is high (only 100 ~ 150 ℃ lower than the furnace temperature). Therefore, the waste heat of waste gas is recovered close to the limit, and the temperature efficiency of the regenerator can reach more than 85%, and the heat recovery rate can reach more than 80%

because the calorific value of blast furnace gas in the first iron plant of Tangshan Iron and Steel Co., Ltd. is only 725 × 4.18kj/m3, the theoretical combustion temperature is only about 1100 ℃, and the actual combustion temperature is lower. The conventional combustion technology can not meet the temperature needs of steel rolling heating furnace. High temperature air combustion technology preheat the air and gas to more than 1000 ℃, and the theoretical combustion temperature of blast furnace gas reaches more than 2000 ℃, so that the combustion temperature of pure blast furnace gas can meet the requirements of steel rolling heating furnace temperature of more than 1200 ℃

3 transformation plan and technical characteristics

according to the characteristics of large production fluctuations in medium-sized plants and narrow heating furnace area, and combined with the size of the external gas supply of the first iron (30000 ~ 35000m3/h). Based on the principle of safety and feasibility, the adjustment is flexible. Based on the principle of outstanding energy-saving effect, we finally chose to cooperate with Beijing Shenwu Technology Co., Ltd. and adopt the "regenerative burner" technology of Beijing Shenwu Technology Co., Ltd. According to the annual output of 400000 tons of section steel in medium-sized plants, the production capacity of different varieties of rolling mills is between 45 ~ 80t/h, and the maximum heating capacity of the heating furnace is designed to be 85t/h

3.1 main parameters and technical performance of heating furnace

heating steel: carbon structural steel, low alloy steel, alloy steel

billet specification: Section 140mm × 140mm、165mm × 165mm、165mm × 225mm、165rnm × 280mm

length: the minimum is 2600 mm, and the maximum impact is applied to the normal deviation of the battery surface 3200mm

billet entry and exit temperature: normal temperature entry, exit 1050 ~ 1220 ℃

billet heating temperature difference: ≤ 50 ℃

furnace type: end entry and end exit pusher continuous heating furnace, Double row charging

furnace heating capacity (maximum): 85t/h

main size of furnace:

effective length of furnace: 22820mm

total length of furnace (masonry length): 24792mm

inner width of furnace: 7300mm

total width of furnace (masonry width): 8348mm

fuel: low calorific value of blast furnace gas (standard state) 725 × 4.18 kj/m3

gas consumption (standard state): 33650m3/h

air consumption (standard state): 22120m3/h

flue gas generation (standard state): 48795m3/h

air preheating temperature: ≥ 1000 ℃

gas preheating temperature: ≥ 1000 ℃

unit heat consumption per ton of billet: 1.20gj

furnace bottom tube cooling mode: vaporization cooling

3.2 technical and structural characteristics

3.2 L regenerative burner

17 gas regenerative burners and 19 air regenerative burners are installed outside each side of the heating furnace. Each air accumulator is arranged adjacent to the gas accumulator. The regenerative burner is divided into single nozzle and double nozzle to adapt to the arrangement of regenerative burners in different positions. An air nozzle and a gas nozzle form a combustion unit. The regenerator in the regenerator adopts the composite heat storage structure of ceramic ball and ceramic honeycomb, which has the advantages of moderate reversing time (the reversing time designed by medium-sized plants is 2min), good quench and heat resistance, and good thermal conductivity; A manual control valve is installed on the gas and air connecting pipe in front of each burner, so that the capacity of each burner, especially the upper and lower burners, can be adjusted as required; The maintenance is convenient, and the heat storage body can be replaced by routine maintenance without affecting the normal production of the furnace

3.2.2 pilot burner

some alloy steels are produced in medium-sized plants, and these varieties have upper limit requirements for the heating furnace temperature in the preheating section. For example, 09cup requires the furnace temperature in the preheating section to be lower than 800 ℃, while the safe combustion temperature of blast furnace gas needs to be higher than 800 ℃. In order to solve this contradiction, 12 pilot burners using converter gas are added in the preheating section to ensure the safe and stable combustion of blast furnace gas below 800 ℃. The hourly gas consumption of 12 ignition burners is 500m3/h low, and they are ignited by electronic ignition, which is safe and reliable

3.2.3 automatic control

the furnace temperature control system adopts the double cross limiting control mode widely used in industrial furnace control. In order to ensure the controllability of the temperature in each heating area, an independent furnace temperature control circuit with temperature as the main loop and air gas flow regulation as the secondary loop is first set for each area. According to the heat supply distribution of the process, it is divided into three temperature regulating circuits, corresponding to three heating areas: preheating section, heating section and soaking section. Furnace pressure control to reduce the interference of reversing on furnace pressure regulation, manually adjust the exhaust gas regulating valve of gas flue and air flue to ensure that the furnace pressure is stable within the given range

3.2.4 reversing control

the reversing adopts four chamber four-way reversing valve. The reversing combustion control is based on the principle of timing and the specified reversing sequence to control the actions of three gas reversing valves and three air reversing valves, and the reversing can also be manually controlled

3.2.5 safety protection system

the instrument control safety interlock logic protection system automatically stops the boiler in the case of low gas header pressure, low air pressure, low instrument air source pressure and power failure; When automatic boiler shutdown occurs, the system completes the following actions: the gas in the main pipe is cut off immediately, and the induced draft fan is stopped after 10min, and the blower needs to be stopped manually. In addition, there is emergency manual shutdown: the manual shutdown system is a hardware interlocking system independent of PLC control. It is used in special cases, such as control system failure, by the operator through the emergency stop button on the console to complete the boiler shutdown operation

4 heating furnace transformation effect

4.1 operation condition

the heating furnace in medium-sized plants has been in good use since December 3, 2001, which greatly reduces the labor intensity of pyrotechnics. In normal use, the operation of the heating furnace and the control of the furnace temperature can be understood through the TV picture, which is very easy. The firemen of each shift generally reflect that the adjustment is accurate and convenient. The oxidation burning loss is significantly reduced, and the slag removal work of the heating furnace is changed from once per shift in the past to every inspection, which can not be the user's real need to repair the slag once. Due to various alarm records, problems can be found in time. For thermal problems, we can also analyze various records to find out the problem in time and solve it quickly. The establishment of automatic boiler shutdown control system can automatically shut down the boiler in time in case of abnormal conditions, which plays a good protective role in preventing major accidents. Practice has proved that this system operates stably

after 3 months of operation, the operation of the heating furnace is basically stable. At present, the furnace temperature in the soaking section of the heating furnace is controlled between 1200 ~ 1300 ° C, the furnace temperature in the heating section is about 1100 ° C, and the exhaust gas temperature is only 120 ° C. The sensible heat of the combustion products is recovered to the greatest extent. The maximum heating capacity has reached 87T/h, and the average consumption per ton of steel in February 2002 was 494m3/T. The heat consumption per ton of wood decreased by 26.9% compared with that before the transformation

4.2 economic benefits

after the transformation, the medium-sized plant will produce 400000 tons of section steel annually, and the current unit gas consumption is 494m3/T. The price of heavy oil is 1.33 yuan/kg, and the price of blast furnace gas is 0.05 yuan/m3

it can reduce the heavy oil recovery cost for the company every year: 38.43 × one point three three × 40 = 20.4448 million yuan

medium sized plants increase blast furnace gas costs annually: (494-167) × zero point zero five × 40 = 6.54 (ten thousand yuan)

annual economic benefits of medium-sized plants: 2044.48-654 = 13.9048 (ten thousand yuan)

payback period of investment:

the heating electronic tensile testing machine is a furnace that tests the tensile force through sensors. The total investment is 10.8761 million yuan, and the payback period of investment is: (1087.61/1390.48) calculated only based on the annual fuel savings × 12 = 9.4 (months)

the total investment payback period can be recovered in only 9.4 months, and the economic benefit is very obvious

4.3 social benefits

while achieving good economic benefits, it has also achieved good social benefits. Due to the reduction of heat consumption, medium-sized plants reduce CO2 emissions by more than 6000 m3 every year, which will greatly change the environment. At the same time, due to high-efficiency heat storage combustion, the emission temperature of flue gas is lower than 150 ℃, which not only reduces the thermal effect of flue gas, but also the blackness of flue gas emission is invisible to the naked eye, which is a great contribution to environmental protection

due to the high theoretical combustion temperature produced by the mixed combustion of high-temperature gas and air, this blast furnace with low calorific value

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