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Iron-Making Processes
Published in Ram Pravesh Bhagat, Agglomeration of Iron Ores, 2019
These constituents make up over 95% of the (slag) mass. The balance is made up of FeO, MnO, MnS, CaS, and alkali silicates. Another product of the iron-making process, in addition to molten iron and slag, is hot gases. These gases exit the top of the blast furnace and proceed through gas-cleaning equipment where particulate matter is removed from the gas and the gas is cooled. This gas has a considerable energy value and therefore is suitable as fuel. It is burned as a fuel in the “hot blast stoves” that are used to preheat the air entering the blast furnace to become “hot blast.” The remaining gases are sent to different units of iron and steel plants to generate heat, including to the sinter plant for ignition.
Introduction
Published in Amit Chatterjee, Beyond the Blast Furnace, 2017
The classical blast furnace is still the principal means of hot metal production. In fact, over 95% of the total iron in the world today is produced using this process, as was the case a century ago. Figure 1.1 presents the percentage contribution of hot metal in steelmaking across the globe in 1990.1 Such a long and sustained track record of blast furnaces arises out of the continuous developments in design, such as increases in capacity; alterations in profile; improved burden distribution systems like movable throat armor and Paul Wurth (PW) top; high top pressure operation, etc.. It also reflects upgrades of the process technology, such as the use of higher hot blast temperature, oxygen enrichment of the blast, auxiliary fuels including coal injection, prepared burdens, automatic measurement and control systems, and artificial intelligence systems, resulting in a significant increase in productivity, a decrease in coke rate, and an improvement in the quality of hot metal in classical blast furnaces. It is interesting to note that, in the year 1990, 527 million tons of hot metal were produced by 541 blast furnaces, which means an average production per furnace of almost 1 million tons of hot metal,1 although many of the new furnaces constructed between 1986 and 1991 were either “very large” or “very small” — the latter comprising the so-called mini blast furnaces (Figure 1.2).1
Refractories and Failures
Published in Debasish Sarkar, Ceramic Processing, 2019
K. Sarath Chandra, Debasish Sarkar
Hot blast stoves are generally cylindrical shaft kilns used for preheating air that is blown into a blast furnace to increase the process efficiency. These stoves constitute two types of chambers: the combustion chamber where the furnace gas is allowed to burn and the checker chamber where high alumina refractories are installed to store the generated heat in a whole volume of checker bricks, which can be further utilized to heat up the cold blast at any particular temperature. Therefore, it is obvious that high alumina refractories (60% class) intimately interact with the blast furnace gas to ensure complete heat transfer. The various steps involved in the failure mechanism of 60% class high alumina refractories are as follows [20, 47]: Blast furnace gas carries dust that contains alkali matter including Fe2O3, SiO2, Al2O3, P2O5, and CaO.The deposition of dust onto the surface of a refractory during the period of interaction leads to clogging of checker bricks holes.The penetration of the fused alkali matter into the open pores of the refractory under service temperatures in the range 1200°C–1250°C leads to different high temperature chemical reactions and the formation of undesirable compounds such as lucite and kaliophilite. These reactions are accompanied by sudden volume changes in the refractory matrix that reduces the creep strength and causes cracking.The failure tendency of blast stove refractories is commonly aggravated by key wear factors including an increase in the hot blast temperature, a prolonged dome temperature of 1250°C, the high dust content of blast furnace gas, and a greater amount of clogging of checker bricks holes.
Experimental Investigation on Performance of Multi-Stage Dehumidification Heat Pump Tower Corn Drying System in High Cold Regions
Published in Heat Transfer Engineering, 2023
Weizhao Li, Juan Wei, Ya Yuan, Luwei Yang, Chong Zhang, Bo Li
The life-cycle cost analysis of the corn heat pump drying system is quantified in comparison with a traditional coal-fired corn drying system, shown in Figure 5. Due to its wide deployment, it is considered reasonable to select a traditional coal-fired corn drying system as a benchmark for the comparison of different corn drying systems. The coal-fired corn drying tower of SFH-300 is a commercial product supplied from Kaiyuantiancheng. It mainly consists of a GDT, a hot blast stove (HBS), a heat exchanger (EH), a HAB, a CAB, and a boiler induced-draft fan (IDF) and relies on the heat generated by burning coal in the HBS to dry corns. During the drying process, the dust-laden air discharged from the GDT and the flue gas discharged from the HBS are directly discharged into the environment. The coal-fired corn drying tower of SFH-300 has a drying rate of 6667 kg/h (dried corn) with wet basis moisture content of corns decreased from 34% to 14%, and a corresponding nominal power supply of 145 kW and coal consumption of 460 kg, respectively.
Comprehensive utilisation of blast furnace slag
Published in Canadian Metallurgical Quarterly, 2023
Jinyu Zou, Zihan Liu, Qiang Guo
A large number of high-temperature molten slag produced in the steel production process, the slag temperature is as high as 1400∼1600°C. The specific heat capacity of slag is about 1.2 kJ/(kg°C), if the average value of the slag temperature is calculated at 1400°C, and the temperature of the recovered heat and the slag discharge is calculated at 400°C, then 1.2GJ of sensible heat can be recovered per ton of slag, which is roughly equivalent to the heat generated by the complete combustion of 41 kg of standard coal, and most of the blast furnaces use water to flush slag, and the slag is used for heating, power generation, etc. But in the past, only about 40%−50% of physical sensible heat recovery was used for heating and power generation in winter, and in summer and places without heating equipment, this part of the energy is wasted. To a certain extent, physical sensible heat recovery of blast furnace slag is the last and biggest goal in the field of blast furnace waste heat recovery. The method of chemical heat recovery of blast furnace slag is usually the direct use of slag and sensible heat to produce high value-added products. As early as the early days of the founding of the People's Republic of China, China realised for the first time that molten blast furnace slag without tempering and temperature control treatment was sprayed into slag cotton fibre [4]. The use of slag cotton can not only reduce the production cost of slag cotton, if the liquid blast furnace slag is directly used, the utilisation rate of the sensible heat of blast furnace slag can be more than 80%. At present, in order to make more efficient use of the physical sensible heat of blast furnace slag, China usually uses air or other gases as a heat exchange medium to absorb and transfer the heat of the molten blast slag to the hot blast furnace, so that the physical sensible heat of the molten blast slag can be recycled in the production process.