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Preheating air and fuel with regenerators was an early technology that was applied to large, high-temperature furnaces such as blast furnaces, hot blast stoves, and coke ovens in the mid-19th century, but traditional regenerators used The lattice brick is a heat storage body, the heat transfer efficiency is low, and the regenerator is bulky. The reversing valve has a complicated structure, low efficiency, and long commutation period, so it has not received much attention. Since the energy crisis in the 1970s, energy conservation has received the attention of various countries. In addition, the continuous advancement of science and technology has resulted in a reversing system with simple structure, convenient control and high reliability. In 1982, the British Hot Work Development Company and the Brit2ish Gas Research Institute successfully developed the first new regenerative heating furnace using ceramic pellets as a regenerator, which has significant energy saving effects. In the past 10 years, regenerative combustion technology has been greatly developed. Many countries are studying various regenerative burners and high-efficiency regenerative combustion technology as well as high-temperature combustion technology.
2 Regenerative combustion technology
In 1998, Dalian Beidao Energy Technology Co., Ltd. took the lead in using the regenerative combustion technology to burn pure blast furnace gas on the rolling steel heating furnace of Pinggang Bar Co., Ltd., and realized the first regenerative technology burning blast furnace gas in the continuous rolling steel heating furnace in China. Applications. Since then, a number of companies in China have carried out research on regenerative combustion technology and its promotion and application in China, and the regenerative combustion technology has gradually matured. In the aspect of regenerative combustion technology, a set of more perfect design ideas and methods have been formed. The application of regenerative technology in industrial furnaces has achieved high yield, low consumption, less pollution and high automation level, reaching the combustion industrial furnace. The development direction of high and low (high furnace temperature, high smoke temperature, high waste heat recovery, low inertia). Since the 1990s, domestic regenerative combustion technology has evolved into the following two series:
(1) The built-in channel type heating furnace represented by Beijing Beidao is characterized by: 1 The organic regenerator and the furnace body are organically integrated into one, the structure is compact, the floor space is small, and the furnace appearance is neat. 2 The regenerator uses ceramic balls, which are inexpensive and centrally commutated. The commutation time is about 180 s, and the running cost is low. 3 The furnace body has small heat loss and high thermal efficiency. It is easy to double preheat the air and gas, the combustion nozzle is densely distributed, the furnace temperature uniformity is good, and the billet oxidation loss is low. 4 furnace type structure is more complicated, the furnace wall thickness is up to lm, the physical and chemical properties of refractory materials are required to be high, and the technical level and experience of design and construction are high. 5 If there is a problem with the furnace wall, the maintenance time is long.
(2) A regenerative burner type furnace represented by Beijing Shenwu. An integrated regenerative combustion technology that combines a regenerator and a burner in one body with a reliable commutation system. In 2000, Beijing Shenwu Thermal Energy Technology Co., Ltd. successfully developed a series of regenerative burners adapted to domestic industrial furnaces, forming the Beijing Shenwu regenerative burner technology system, the first domestic application of this technology. It is a medium-plate heating furnace transformed by the Medium Plate Plant of Handan Iron and Steel Company in 2000, and has achieved remarkable economic and social benefits. Since then, the company has developed a variety of regenerative burners, each using different fuels and industries.
It can be seen from the above analysis that although the two types of regenerative heating furnaces have their own advantages and disadvantages, and have practical application examples in the domestic metallurgical industry, the general development trend is toward the burner type regenerative heating furnace. Development, the specific performance has the following aspects: 1) Compared with the original ordinary heating furnace, the regenerative burner heating furnace adjusts the furnace temperature by adjusting the heat load of the burner, which is easy for the operator to accept. (2) Each burner can be adjusted separately. The ability to heat the burner up and down is reasonable. The adjustment of the heating temperature of each section is very convenient. (3) There are manhole doors and slag gates on both sides of the furnace wall for easy maintenance. This is the biggest advantage of the burner structure. (4) For high calorific value gas fuels, it can be directly ignited by a cold furnace, and a separate ignition burner is not required. (5) The burner type structure can adopt the centralized commutation and the distributed reversing mode. When the reversing valve is close to the burner, the connecting pipe between the reversing valve and the burner is short and small, and the combustion interruption time is short. Therefore, there is less residual gas loss in the pipeline during commutation, which is more conducive to energy conservation. (6) The maintenance workload is slightly larger, but the inspection time is short and the shutdown time is short.
3 burner type regenerative heating furnace
3. 1 Structure of the regenerative burner
The burner adopts air and gas combination type, which is composed of air heat storage burner and gas heat storage burner. The upper gas nozzle is heated, the air nozzle is on the upper and lower, and the burner is reversed. The upper and lower surfaces of the billet are formed as much as possible. Reducing atmosphere, reducing oxidative burning and surface decarburization. The design of the regenerative burner is to consider the combustion mixing problem of low calorific value gas, and to ensure the complete burning of the gas and the uniformity of the furnace temperature. Therefore, the double-flow regenerative burner is used.
The combustion nozzle is a key part of the combustion system. Reasonable combustion organization depends on this. In the combustion organization, it is necessary to ensure that the gas is fully burned in the furnace, and will not continue to burn in the opposite heat storage body, and at the same time Reasonably promote the realization of low-oxygen combustion, avoid local high-temperature overheating; Enhance the uniformity of furnace temperature, reduce the generation of harmful gases such as NOx, and reduce the occurrence of decarburization at high temperatures. Therefore, the optimum gas outlet velocity and mixing jet angle are chosen for the nozzle design.
The fuel is burned while mixing at the nozzle. The air and gas are entangled in the surrounding furnace gas during the spraying process, diluting the air gas concentration, and the low-oxygen combustion, so that the generation of NOx in the flue gas is greatly reduced, and the emission of harmful gases is reduced. the amount. Due to the centralized ignition oven method, as long as the furnace gas temperature is higher than 700 °C, the blast furnace gas will be burned into the furnace, and the continuous heating furnace will not start the furnace frequently, so the high temperature section regenerative burner will be used. It is not necessary to equip the automatic ignition and flame detection system, which simplifies the structure of the burner, reduces the investment, and reduces the frequent burning of the ignition burner in the high temperature section.
3. 2 regenerator
The regenerator has ceramic pellets and ceramic honeycomb bodies, and the development trend is to use ceramic honeycomb bodies. The high temperature section is made of high-purity aluminum material with high refractoriness and good slag resistance. The middle part is made of mullite material; the low temperature section is made of cordierite, which is characterized by working conditions below 1000 °C. It has good corrosion resistance and rapid cold resistance. The front end of the honeycomb body is increased with corundum bricks to reduce the radiation of the high temperature furnace to the honeycomb body, and at the same time increase the stacking stability of the honeycomb body. 5å€å€, compared with the particulate heat storage body (spherical heat storage body), the honeycomb heat storage body has the following advantages: a large heat exchange area per unit volume, a honeycomb of 100 pores per square inch is 5.6 times the specific surface area of ​​the Φ15 mm sphere, 7 times the Φ20 mm ball. Under the same conditions, the volume of the honeycomb body when the same mass of gas is exchanged to the same temperature is only 1/3 to 1/4 of the spherical regenerator, and the weight is only about 1/10 of the weight of the ball, which means the honeycomb body. The regenerative burner is lighter in construction and more compact in construction. The honeycomb wall is very thin only 0.5 to 1 mm, and the heat penetration depth is small, so the heat storage and heat release rate are fast, the temperature efficiency is high, and the commutation time is only 30 to 45 s, which is more than the reversal of the spherical heat storage body. The time is shortened by 3 min, which is more conducive to uniform temperature field in the furnace and ensures uniform heating of the billet. This is especially beneficial for heating alloy steel and high carbon steel. According to the rules of the airflow passage in the honeycomb body, the resistance loss is only 1/3 to 1/4 of the spherical shape. The airflow resistance loss of the spherical regenerator increases with the increase of the air flow rate, and the change law is a power function relationship. When the ball diameter is large, the resistance becomes smaller, but the structure of the regenerator is correspondingly increased.
Honeycomb
Since the gas with higher pressure frequently reverses, it acts as a blowing passage, so it is less likely to cause dust deposition and blockage. For a furnace with a wide furnace, the corresponding furnace length is short, and the space for the burners on both sides of the furnace is small. When a small ball with a small specific surface area is used, the heat storage capacity is often insufficient due to space constraints. Therefore, in a heating furnace in the form of a regenerative burner, it is an inevitable choice to use a honeycomb having a specific surface area several times larger than the pellet. The use of ceramic pellets is not convenient for online replacement, while the ceramic honeycomb body facilitates on-line replacement of the regenerator, which ensures very good production continuity.
3. 3 commutation system
The blast furnace gas reversing system and the air/flue gas reversing system are all in a fully distributed reversing mode. The reversing valves are all pneumatic, with clean compressed air as the power source, and the air source pressure is ≥0.3 MPa. The blast furnace gas/flue gas adopts the quick-disconnecting reversing valve, that is, one gas regenerative burner adopts two quick-disconnecting valves, and the quick-cutting valve adopts a triple eccentric structure, which is flexible, reliable and easy to replace. The air/flue gas is switched by a three-way reversing valve, and the valve drive can be hydraulically operated, and the operation is stable, but the input cost and the running cost are high.
3. 4 working methods
The regenerative burner is operated in pairs and the commutation period is adjustable. During normal operation, the commutation period is around 30 - 45 s, using dual signal control: time and flue gas temperature are used as control parameters. The reversing system adopts PLC programmable controller control, which can complete automatic program reversing control and manual forced reversing control. It has function display and working status display, which enables the operator to see the operation of the regenerative combustion system at a glance, operation and monitoring. Very convenient.
3. 5 full dispersion commutation system technical characteristics
(1) The reasonable combination of each burner's ability to adjust separately and to heat the burner up and down, so that the heating temperature of each section of the furnace is very convenient. (2) On the same side of the same direction, it can realize the staggered combustion of each adjacent two burners. This way optimizes the composition of the furnace gas flow, which is conducive to uniform furnace temperature and improved heating quality. (3) Each set of burners uses a set of reversing system, which can eliminate faults in the case of any set of system failures, and ensure the continuity of operation and production stability without any failure. In the case of centralized commutation, it is necessary to stop all the problems that have occurred. (4) The reversing valve can be placed close to the combustion nozzle, shortening the reversing blind zone between the reversing valve and the spout, and minimizing the unsafe factors caused by cross-contamination. The combustion interruption time is short, so there is less residual gas loss in the pipeline during commutation, which is more conducive to energy conservation. (5) Using the wheel sequence reversing mode, the impact of each set of reversing devices on the furnace pressure is greatly reduced, and the furnace temperature and furnace pressure of each part are precisely controlled, and the control performance of the furnace and the heating quality of the billet are improved. Compared with centralized commutation, the pipeline is complicated and not easy to arrange.
3. 6 digital pulse regenerative combustion technology
Under the premise of conventional segmented proportional combustion control technology, digital pulse regenerative combustion technology can be applied. The heating furnace of Shigang Bar Plant used digital pulse regenerative combustion technology for the first time in China. This technology not only makes the characteristics of regenerative technology itself more powerful, but also adapts to changes in cooling and hot loading and changes in output. Larger and often varying heating requirements for each steel grade. Since the concept of the original “segment†is virtualized, it can be said that this combustion method can meet the heating demand of any steel type and lay a solid foundation for the development and production of new steel. Pulse technology has the following features: 1) Timing heating. There are only two working states of the burner: full-load operation and no-operation, only by adjusting the time ratio of the two states to adjust the temperature, and the low-temperature control can still ensure that the burner works in the optimal combustion state. With the pulse combustion control method, the gas pressure and the air pressure can be adjusted to an appropriate value at one time. After the system is put into operation, it is only necessary to keep the two pressures stable.
Therefore, the burner is always operated with maximum efficiency and with a minimum amount of excess air. (2) Achieve any "virtual" division of the heating zone. Virtual heating section and soaking section (independent control of each pair of burners) With digital control technology, the furnace capacity can be adjusted according to the output while ensuring good uniformity of the product. The computer can set each pair of burners in real time according to the heat data of a series of furnace billets. It can set on or off some burners to accurately control the heating capacity of the furnace. Under any working conditions, the fuel consumption is comprehensive. The amount is reduced throughout the mill's production range.
4 Conclusion
From the perspective of long-term market, the demand for steel varieties and small batches is increasing. From the perspective of short-term billet heating, the situation of billet cold and hot packs often exists. The burner type regenerative heating furnace solution meets the above steel heating requirements. In addition, there are manhole doors and slag doors for easy maintenance on both sides of the regenerative burner type furnace wall, which can only be achieved by using the burner structure; for high calorific value gas fuel, it can be directly cold The furnace is ignited and does not require a separate ignition burner; the maintenance workload is slightly larger, but the inspection time is short and the shutdown time is short. The domestic regenerative heating furnace has developed rapidly. It is still impossible to say which form is the most advanced and mature. There are some problems. The life of the regenerator and the life of the regenerative heating furnace need to be improved. However, the regenerative burner type heating furnace is a development direction.
1 Overview