Modelling of heat recovery in LKAB's grate-kiln process

Examensarbete för masterexamen
Master Thesis
Sustainable energy systems (MPSES), MSc
Andersson, Hanna
Pedersen, Simon
This master thesis uses process modelling to investigate energy efficiency measures in the grate-kiln process for iron ore production; specifically, how waste heat contained in flue gas could be recirculated in order to achieve a decrease in specific fuel consumption. Consequently, fossil carbon emissions would be reduced as the grate-kiln units are fired with coal or oil. The implementation of flue gas recirculation is simulated with a process model in EBSILON Professional 10.0. Process concepts which make use of available waste heat are developed and their impact on fuel usage, pellet temperature profiles and the magnetite oxidation process is evaluated. Aside from partial flue gas recirculation, a heat recovery concept is investigated. Both concepts are applied to decrease the fuel consumption by increasing the temperature and oxidation on the grate and to recover heat at a high temperature. To minimize the effect of recirculation and heat recovery on the pellet heat treatment process, concepts that use intercooling before the grate are also evaluated. The implementation of heat recovery affects the performance of the pellet cooler. The cooler’s operation is studied in detail with a cooler model developed in MATLAB. The cooler model is evaluated, and a sensitivity analysis is made to determine which parameters have a crucial impact on the pellet cooling. The results indicate that waste heat utilization can reduce the fuel consumption by up to 30% if a heat exchanger is used. It was revealed that increased temperature into the cooler’s hottest section elevates the temperature levels on the grate, which lowers the fuel usage. Direct flue gas recirculation lowers the oxygen content in the air passing the kiln and grate, which has a negative impact on the oxidation process and the overall heat balance. The cooler model showed that to maintain adequate pellet cooling, the mass flow through cooler zones C3 and C4 should be increased by 70 %, or the area of the C3 and C4 sections should be increased by 40% when heat recovery is used. The direct flue gas recirculation concepts requires a 40% and 25% increase for the two measures, respectively. The thesis recommends three process designs, based on indirect heat recovery from the flue gases.
Energi , Hållbar utveckling , Energiteknik , Energy , Sustainable Development , Energy Engineering
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