Characteristics of coke ovens and their technical development with refractory materials

The application of resistant materials affects the technological progress of coke ovens

In modern coke production, coke ovens present the following characteristics: First, they are large, heavy and long-lived; Second, the amount of refractory materials used in a single coke oven is large, and it is the type of furnace with the highest proportion of refractory materials known for high-temperature furnaces, accounting for more than 80% of the overall coke oven weight; the energy consumption of the coking process reaches 13% to 15% of the energy consumption of the steel industry. Therefore, the technical progress of coke ovens cannot be separated from the technical progress of refractory bricks and other resistant materials.

Refractory experts said, coke oven daily maintenance of refractory materials by type, composition and use can be divided into: silica brick, to scale quartz as the main crystalline phase, used for masonry coke oven silica refractory products, also used to repair the furnace wall; cordierite door brick, fired by cordierite, also used to repair the door; grout, the main component of phosphoric acid + clay material + water, used for roof sealing; ceramic fiber rope, the main component of aluminum silicate, used for furnace wall plugging; 901 mud. It is used for plugging the furnace wall; 901 mud, the main component is clay + water, used for pouring furnace cover; asbestos felt, the main component is asbestos, used for coke oven environmental protection plugging; high temperature rubber sheet, the main component is high temperature resistant rubber, used for repairing furnace door.

Grasp the direction of resistant material technology from two aspects

According to reports, the current choice of coke oven resistant material basically uses the following criteria: carbonization chamber / combustion chamber sidewalls, coking process with water discharge, should not use easily hydrated refractory materials, almost all countries in the world now choose silicon resistant material. The bottom of the charring chamber, with the same thermal expansion rate, bears the greater weight of coal and coke and the frictional effect of the coking process, and should be selected with high-strength and wear-resistant refractory materials. The top of the charring chamber is subjected to the static and dynamic load of the covering layer and coal loading car, so it should also be made of high strength and wear resistant material. Charring chamber door lining and charring chamber two ends of the furnace head, because the furnace door often open, the temperature from about 1000 ℃ suddenly dropped to 500 ℃ below, it is desirable to use a good resistance to thermal shock, load softening temperature of high aluminum resistant material. Slanting flue area, not in contact with coal and coke, working temperature is slightly lower than the combustion chamber, it is appropriate to use silicon resistant material. Both sides of the side walls of the heat storage chamber, cold and hot alternating temperature difference is large, it is appropriate to use good clay bricks. Heat storage room lattice brick, non-load-bearing structure, should have high heat storage capacity and thermal shock resistance, should use clay bricks.

In view of the problems in the application of resistant materials, experts believe that: carbonization chamber furnace door is currently commonly used to seal glaze furnace door brick, the door is easy to adhere to heavy tar, difficult to clean, the door is easy to break, at present, Baowu Group Baosteel, Wuhan Iron and Steel and other large iron and steel enterprises are using large cast furnace door brick, cleaning difficulty is greatly reduced. The side walls of the carbonization chamber/combustion chamber are all made of silica bricks, which expand by heat and are seriously damaged when pushing coke, easily causing the furnace wall to wear and leak, which not only affects the quality of coke, but also seriously affects the life of the coke oven and increases the maintenance time and cost of the coke oven. Zero expansion silica bricks can be used in this part, which can significantly reduce the thermal expansion pressure and have higher densities, so it is not easy to cause leakage through the furnace wall.

At present, the overall development of coke oven refractory materials shows the characteristics of individual customization, high purity, dense and precise, the popularization of carbon refractory materials, the compounding of oxide and non-oxide materials, and indefiniteness. The direction of its technological development is considered from the purification and homogenization of mineral processing on the one hand, and from how to use low-grade raw materials to prepare aluminum and silicon refractories on the other.

Coke oven refractories have great potential for energy saving and emission reduction

At present, the configuration of conventional refractory materials for coke ovens is as follows: siliceous materials for roof, bottom, ramp, heat storage chamber, heating wall, coal loading hole and fire observation hole, clay bricks for roof, heat storage chamber, coal loading hole and fire observation hole, and cordierite, mullite, red pillar stone and silica wire stone for furnace door.

The whole coke oven with silicon material accounts for more than 60% of the amount of resistant materials, and the life of the coke oven and the quality of operation are closely related to the quality of silicon material. The product standards of silica bricks for coke ovens have also changed as follows: the Japanese JIS standard was introduced in the early 1980s, the German DIN standard was introduced in the early 21st century, and the Baosteel standard was adopted in the second decade of the 21st century.

It can be seen that, over the years, China’s coke oven technology has been continuously improved. However, the traditional resistant material is still used in the resistant material technology, only the standard is improving, especially in the energy-saving and environmental protection of coke oven, the resistant material does not play the proper technical potential.

In order to meet the development requirements of large coke ovens in the 21st century, the domestic production, academia, research and use departments jointly developed new refractory materials and new technologies such as high-density silica bricks, composite prefabricated parts, composite ceramic materials on the surface of silica bricks, new materials for furnace bottom, homogeneous and homogeneous silica fireclay, electrofused (low expansion) silica bricks for thermal repair, and new technologies for thermal maintenance of coke ovens, and were widely and effectively applied.

For example, the strength of the new coke oven resistant material high dense silica brick is about 1.5 times that of ordinary silica brick. Its low porosity and thermal conductivity can be increased by more than 20% compared with traditional coke oven silica bricks, which can reduce coke oven fuel consumption, reduce NOx and other pollutant emissions, save energy and protect the environment. Under the same conditions, the use of high-density silica bricks can effectively increase the production capacity of coke ovens. Domestic use of nanotechnology makes silica brick products improve brick density, thermal conductivity, anti-wear properties while retaining the basic properties of silica materials. The reason for this is that the dispersion performance of nanoscale mineralizing agent is far better than that of traditional mineralizing agent. Its application makes the main crystalline phase of the resistant material and the matrix more tightly bonded, reducing the porosity of the product, while improving the homogeneity of the product.

The actual application results of this high-density silica brick in the coke ovens of large domestic steel enterprises show that under the same working conditions, the coke ovens using high-density silica brick have better energy-saving effects than those using traditional silica brick. Based on the coking time of 22 hours and the annual production time of 8760 hours, the 50-hole×4 high-density silica brick coke oven can save 124 million cubic meters of mixed gas per year compared with the traditional silica brick coke oven, which is equivalent to 20,682 tons of standard coal, with remarkable energy-saving effect.

Under the same working conditions, when ordinary silica bricks are replaced by high-density silica bricks, the heat transferred to the charring chamber should be the same in one cycle, and the only thing that changes is the temperature of the fire channel in the combustion chamber. Therefore, when the thermal conductivity of high-density silica bricks is 2.33 (w/m-k), the flame temperature inside the combustion chamber can be reduced by 46℃. It can be seen that the use of high-density silica bricks can indeed theoretically reduce the flame temperature of the combustion chamber, which is conducive to reducing fuel consumption and thus the effect of energy saving and emission reduction.

In addition, the flame temperature in the combustion chamber built with high-density silica bricks can be lower under the condition that the temperature inside the coking chamber remains unchanged; lowering the fire escape temperature is conducive to reducing the NOx concentration. Under the same conditions of coking time, the NOx emission of high-density silica brick coke oven is lower than that of traditional silica brick coke oven. According to the calculation of 7 kg NOx per 1 ton of standard coal burned, one high-density silica brick coke oven with an annual output of 2.47 million tons of coke can reduce NOx emission by 430 tons per year compared with the traditional silica brick coke oven, which is a significant effect of emission reduction.