Abstract
Slags are valuable by-products of iron- and steelmaking processes. Their efficient reutilization and the recuperation of their thermal energy are key for improving the overall efficiency of these processes. With the innovative approach presented in this work, it is possible to recover thermal heat from liquid slags. The process concept consists of a slag tundish and four subsequent heat exchangers. The liquid slag is poured into the slag tundish which homogenizes the slag and guarantees a constant mass flow. The heat exchangers extract thermal energy from the slag and transfer it to water or oil. The first module cools the slag from the tapping temperature of about 1500 °C down to 850 °C. Inside the second module, more thermal energy is gathered from the already solidified slag cooling the slag down to ambient temperature. The captured energy can be used for various processes, such as gas preheating or generation of steam. The solidified slag is volume stable and forms amorphous phases, depending on its basicity. The process was designed, and the concept was tested on lab-scale demonstrators with an overall heat recovery rate of 42%. Some applications of the recovered slag heat are also presented in this work.Graphical Scheme of the process concept with the three heat exchangers and buffer unit.
Highlights
Slags are valuable by-products from iron- and steelmaking processes performed worldwide [1]
Journal of Sustainable Metallurgy (2021) 7:783–793 applications incorporating the recycling of those by-products are common since many decades and include examples like (1) the grinding of water-quenched blast furnace slag (GGBFS) to receive hydraulic properties for their use in cement, (2) using stabilized slags as aggregates in roads and civil installations, (3) using free-lime and phosphorous containing converter slag as fertilizer or (4) recycling of secondary metallurgical slags for re-introduction into the steel desulfurization process like Calexor® Aluminate
The energy loss via the vibrating unit was between 0.7 and 1.2 kWh/t slag for 60–100 s vibration for 6.5 kg of solidifying slag. This corresponds to 2.6–4.3 MJelectric/t slag and to 0.4–0.6% of the recovered slag heat
Summary
Slags are valuable by-products from iron- and steelmaking processes performed worldwide [1]. The first module cools the slag from the respective tapping temperature of about 1450 °C down to around 850 °C in a continuous process while recovering the energy at the same time. The PHE cooling medium system (in this case water was used, in other tests [14] thermal oil) as well as the vibrating unit were turned on with a target frequency of 50 Hz. The tundish sliding gate was partially opened to allow a slag flow ṁ S of 20–26 l/min.
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