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dc.contributor.advisorBunt, J.R.
dc.contributor.authorStokes, Wilden Graham
dc.date.accessioned2022-07-20T07:19:04Z
dc.date.available2022-07-20T07:19:04Z
dc.date.issued2022
dc.identifier.urihttps://orcid.org/0000-0001-7533-6009
dc.identifier.urihttp://hdl.handle.net/10394/39384
dc.descriptionMEng (Chemical Engineering), North-West University, Potchefstroom Campusen_US
dc.description.abstractThe global population is ever increasing resulting in an ever-increasing energy demand and reliance of fossil fuels which has increased over the past few decades. The production of coke relies on the availability, cost and the quality of coking coals. Environmental pressure together with depleting coking coal resources has forced the metallurgical industry to search for alternative methods/resources to produce coke to be used as a reductant. Studies have shown biomass to be an attractive alternative to coking coal when producing metallurgical coke, especially woody biomass. In this study, the use of thermally treated wet oxidized biomass as feedstock for the production of a metallurgical coke substitute was investigated. The soft wood chips sample was collected from Sappi Ngodwana (Nelspruit) and washed and dried to remove extraneous debris before further utilisation. The biomass sample was subjected to severe torrefaction at 280 °C under an inert atmosphere (nitrogen). This was done as a pre-treatment method to improve the energy density of the biomass. The torrefied biomass was then subjected to wet oxidation at 80 °C for a residence time of 30 minutes. The wet oxidized biomass was pelletized into 0.5 g 10 mm pellets and subjected to thermal treatment at 900 °C at a heating rate of 10 °C/min for a residence time of 2 hours under N2 at atmospheric pressure in order to obtain a metallurgical coke substitute. Characterisation of the raw biomass, torrefied biomass, wet oxidized biomass, thermally treated torrefied biomass, thermally treated wet oxidized biomass was conducted using: Free swelling index (FSI), Fourier-transform infrared spectroscopy (FTIR), ultimate and proximate analysis, gross calorific value (CV), compositional analysis (ADF, ADL & NDF), compressive strength, surface area (BET), coke reactivity index (CRI) and the coke strength after reaction (CSR). These obtained values were then compared to those of metallurgical coke used in the industry (ArcelorMittal). In addition to these characterisations, an economic evaluation has also been conducted. The results concluded that the final reactivity of the prepared coke substitute was significantly higher than that of the metallurgical coke, i.e. the thermally treated wet oxidized torrefied biomass having a reactivity towards CO2 of 132.4 x104 min-1 and 21.2 x 104 min-1 of coke, respectively. This result is confirmed by the BET analysis which showed the thermally treated wet oxidized torrefied biomass has a significantly larger surface area than the metallurgical coke at 327.1 m2/g and 8.8 m2/g, respectively. Degradation of coke can be prevented by using a coke with a higher reactivity forcing the gasification reactions to be limited to the surface layer of the coke structure and thus leaving the stability of the coke intact. The coke substitute had an ash yield of 4.3 wt.% compared with 16.1 wt. % for metallurgical coke, which is advantageous as it will increase the productivity of the blast furnace. Observations indicated that when the ash yield increases by 1 wt. %, the metal production reduces by 2 to 3 wt. %. When taking the low ash yield of the substitute coke into account, the productivity of the blast furnace was four times higher than when using coke. The sulphur content of the coke substitute was <0.1 wt.% compared with 0.7 wt. % for the metallurgical coke. This is advantageous due to an increase in sulphur content leading to a decrease in blast furnace reactivity. The economic evaluation showed that when 50 % of the coke is replaced with biomass, there is a 6.8 % change in the production cost of one ton of liquid iron; 50 % is also considered to be the most economical option. A sensitivity analysis revealed that when using 7.7 % biomass and 92.3 % coke the plant will break even, and when using 88.2 % coke, the plant will start to make a profit. The most economical option explored in this study was to replace the coke with 50 % biomass. Keywords: coke production,en_US
dc.language.isoenen_US
dc.publisherNorth-West University (South Africa).en_US
dc.subjectCoke productionen_US
dc.subjectWoody biomassen_US
dc.subjectEconomic evaluationen_US
dc.subjectReactivityen_US
dc.subjectWet oxidationen_US
dc.subjectBiomass torrefactionen_US
dc.titleA metallurgical coke replacement derived from torrefied wood chips pre-treated by wet oxidationen_US
dc.typeThesisen_US
dc.description.thesistypeMastersen_US
dc.contributor.researchID20164200 - Bunt, John Reginald (Supervisor)


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