Carbon is a necessary reductant in steel production to convert iron ore to metallic iron. The use of coal and coke causes CO2 emissions to be released into the environment. Using bio-based carbon sources has the potential to offset these emissions and reduce cokemaking overall carbon footprint. The use of biomaterial in coal blends reduces the fossil fuel requirements but to what capacity and type of biocarbon can replace coal is unknown. The full effects of coal and coke characterization from the addition of biomaterial are unknown. In this work, raw biomaterials available to industrial users were evaluated for substitution at low amounts in operational coal blends. Physically, the optical properties of carbon coke forms can provide insight into the strength, reactivity, and performance in the blast furnace, resulting from coal rank and type. The interaction of the biomaterial substitutions with coal during the coking process is evaluated to better understand the reduction in coke strength after reaction (CSR). For this purpose, a series of the pilot oven and sole heated oven tests were performed. When coal was substituted with low amounts of raw biomaterials, the most notable changes in coke texture analysis were to incipient and circular textures. In this work, data from a series of pilot oven and sole heated oven tests showed that fine coke textures and overall inerts increased. The changes in coke textures can be linked to decreases in coke strength after reaction (CSR). / Thesis / Master of Applied Science (MASc) / Metallurgical coke remains the main fuel and reductant source for ironmaking by blast furnace operation. Quality metallurgical coal, a fossil fuel, is required to produce coke. This work continues ongoing steel industry research investigating biomaterial substitution of coal as a more sustainable option. Coal is considered a new release of greenhouse gas (GHG) emissions when used in the steelmaking process compared to a biomaterial which is regarded as a GHG neutral replacement. Three raw biomaterials, available to industrial users, were evaluated for substitution at low amounts and compared to an operational coal blend. The substitution could allow for GHG emissions of the cokemaking processes to be reduced if quality coke can be produced. The interaction of the biomaterial substitutions with coal during the coking process is evaluated in this work to better understand the resultant coke textures related to reduction in coke strength from the substitution.

Thesis (MBA)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: It was found that the hot metal cost of ISCOR Newcastle's single blast furnace can significantly be reduced by the correct use of an integrated model to predict reductant cost based mainly on coal blend. The model uses coal ash chemistry, fluiidity, vitrinite rank and volatile matter to predict coke strength after reaction (CSR), coke ash and coking yield. CSR is used to predict maximum allowable coke nut- and pea consumption in the furnace as well as hot blast temperature. Pitch injection levels are predicted using CSR and blast furnace production rates. Coke ash, pitch injection and hot blast temperature is used to predict the coke rate. The above is used with imported Chinese coke cost to accurately predict reductant cost. It was found that the current optimum blends should include Australian en Nieu Zeeland coals because of price and quality conciderations. Because of its low cost of production and low quality the optimum percentage of Grootegeluk in the blend is determined largely by its transfer price. / AFRIKAANSE OPSOMMING: Die vloeiyster koste van ISCOR Newcastle se enigste hoogoond kan drasties verlaag word deur die korrekte gebruik van 'n geïntegreerde model wat reduktant koste voorspel op grond van steenkoolmengsel. Die model gebruik die chemiese samestelling van steenkool-as, fluiiditeit, vitriniet rang en vlugstof om kooks warmsterkte (SNR), kooks-as en verkooksingsopbrengs te voorspel. SNR is gebruik om die maksimum kooksneute- en -erteverbruik in die hoogoond sowel as blaastemperatuur te voorspel. Pikinspuiting is bereken met SNR en hoogoond produksietempo's. Pikinspuiting en blaastemperatuur word saam met kooks-as gebruik om kookskoers te voorspel. Bogenoemde is saam met die koste van ingevoerde Chinese kooks gebruik om reduktant koste akkuraat te voorspel. Daar was bevind dat die huidige optimum mengsels Australiese en Nieu Zeelandse steenkool moet bevat as gevolg van huidige prys- en kwaliteitsoorwegings. As gevolg van sy lae produksiekoste en lae kwaliteit word die optimum hoeveelheid Grootegeluk bepaal deur sy oordragprys.

In this study, coke oven tar addition over a range of 0 – 8 wt.% was evaluated as a possible substitute for imported coals fractions. Coke oven tar used was collected from coke oven tar decanters of the by-products section of the coke making plant. Moisture content in coke oven tar varied depending on the residence time and water carryover from coke oven tar separators to storage tanks. Therefore, various moisture ranges were considered in order to observe its effect on coal blend, carbonization and coke properties. The optimum moisture content in coke oven tar was found to be 3% with a coke oven tar addition of 6 wt.% in the coal blend. At the same coke oven tar addition of 6 wt.% in the coal blend but with 6% moisture content in coke oven tar, coke properties improved, coke yield showed up to 4% decrease. On the other hand, with 1% moisture content in coke oven tar of 6 wt.% in the coal blend, coke yield increased by 1% and low coke properties such as I40 of 42.9 and Stability of 50.3 were achieved. The latter process was characterized by excessive increased in wall pressure and pushing energy. Both wall pressure and pushing energy increase are less desirable due to their detrimental effect on the physical condition of the oven walls. Furthermore, addition of coke oven tar with 1% moisture content to coal blend can be prohibited by its high viscosity. At 3% moisture content in coke oven tar addition of 6 wt.% in the coal blend, coke properties improved. When the amount of coke oven tar was increased to 8 wt.% at the optimum coke oven addition, coke yield was not affected but low CSR of 57.8 against a target of ³60 was achieved as opposed to CSR of 65.4 at 6 wt.%. Also, coke stability of 52.2 at 8 wt.% as opposed to 56.1 at 6 wt.% was achieved. Moreover, the highest I40 of 50.9 was achieved at 6 wt.% whereas with 8 wt.% coke oven tar, I40 of 47.9 was achieved. However, up to 2% decrease in coke yield was observed. Despite this 2% decrease in coke yield, coke oven tar addition is a positive and viable option based upon economic factors (i.e. this reduces the quantity and cost of imported coals and still achieves improved coke quality which result in improved blast furnace operation and better hot metal quality).

Carbon dioxide emissions to the atmosphere today cause problems around the world. In Sweden, the steel production contributes significantly to carbon dioxide emissions. The steel industry challenge is to improve the metallurgical processes to decrease the carbon dioxide emissions. One way to reduce the emissions is to use renewable carbon sources. The blast furnace process is a counter current reduction process for ironmaking. Raw materials such as iron ore agglomerates, coke and slag formers are charged at the top of the furnace while oxygen-rich blast air and powdered coal are injected in the bottom. The gases produced by combustion rise through the burden on the top of the furnace. The combustion of carbon produces carbon monoxide which is the reducing gas used for the reduction of iron oxides to pig iron. The process is the highest producer of CO2 emissions in Sweden; biomass can partially replace fossil carbon in coal blends for cokemaking, coal powder for coal injection and coke in self-reducing briquettes.  The purpose of this project was to maximize the addition of biomass in coal blends for cokemaking and the addition in briquettes produced for the recovery of iron bearing rest products. The challenge with biomass in cokemaking is its low density and high reactivity which decrease the coke yield and coke strength at the same time that it increases the coke reactivity. The coke quality has to be kept at sufficient quality in order to avoid effects on productivity and process stability in the blast furnace. The addition of biomass in briquettes is limited due to the low density of the biomass which may affect the strength of the briquettes. The effect of the addition of sawdust in coke and briquettes has been studied to understand the effect on reaction behaviour of bio-coal. Heat-treatment of sawdust with high volatile coal was performed in order to achieve a coating of coal on the sawdust surface and get less reactive sawdust. Torrefied sawdust contained 23 wt. % fixed carbon while the pre-treatment of sawdust with high volatile coal increased the content to about 60 wt. %. Pre-treated sawdust was added to coal blend for coke making and briquettes containing iron oxide. The pre-treated sawdust was added to five coal blends for coke production, the contents were 5, 10 and 20 wt. %, and a base blend was used as reference. Coke reactivity, chemical composition and cold compression strength in coke were studied. This work resulted in an improved bulk density; up to 20 wt. % pre-treated sawdust could be added to the coal blend and still keep a bulk density of 800 kg/m3. The coke yields in cokes with pre-treated sawdust were comparable to the coke reference. The temperature at which carbon in coke began to be consumed was slightly higher in coke containing sawdust treated with 50 wt. % high volatile coal. It was estimated that the CO2 emission from fossil coal could be reduced with 8.6 % per ton hot metal (THM) with the addition of 10 wt. % pre-treated sawdust to coal blends for cokemaking. The addition of 20 wt. % pre-treated sawdust could reduce the CO2 emission with 10% per THM. In addition, two different mixes of briquettes were produced, one with torrefied sawdust and one with pre-treated sawdust. The chemical composition and reduction of iron oxides in briquettes was also studied and evaluated. Briquettes with treated sawdust were more compact, i.e. had a higher density than briquettes containing torrefied sawdust. The amount of hematite that could be added to the briquette mixes was 0.107 moles in briquettes with torrefied sawdust and 0.112 moles in briquettes with pre-treated torrefied sawdust. / Koldioxidutsläppet till atmosfären orsakar idag problem runt om i världen. I Sverige bidrar stålproduktionen avsevärt till koldioxidutsläppet. Stålindustrin har som en utmaning att förbättra de metallurgiska processerna för att sänka utsläppet av koldioxid. Ett sätt att sänka koldioxidutsläppen är att minska påverkan genom att använda förnybara kolkällor. Masugnsprocessen är en kontinuerlig reduktionsprocess för råjärnframställning och en av processerna där det används reduktionsmedel från fossila kolkällor. Råmaterial som järnmalm, koks och slaggformare chargeras på toppen av ugnen medan syrgasberikad blästerluft och pulveriserat kol injiceras i botten av ugnen genom masugnens formor. De gaser som produceras vid förbränning stiger upp genom beskickningen upp till ugnens topp. Vid förgasning av kol bildas kolmonoxid som är den reducerande gasen, den möjliggör reduktionen av järnoxider vid framställning av råjärn. Torrefierad biomassa kan delvis ersätta fossilt kol i kolblandningarna för kokstillverkning, i kolinjektionen och i briketter. Syftet med detta projekt var att maximera mängden tillsatt biomassa i kolblandningarna för kokstillverkning och i briketter för återvinning av järnbärande restprodukter. Utmaningen med biomassa i kokstillverkningen är den höga reaktiviteten och den låga densiteten av kol, vilket resulterar i låg koksutbyte när den tillsätts i kolblandningar. Biomassa innehåller också en högt halt flyktiga ämnen vilket resulterar i koks med låg hållfasthet och hög reaktivitet. Kokskvalitén måste behållas för att undvika processvariationer i masugnen. Tillsatsen av biomassa i briketter, är begränsat då biomassa kan påverka briketternas hållfasthet. Effekten av tillsatsen av biomassa i koks och briketter har studerats för att kunna förstå reaktionsbeteendet i dessa när torrefied sågspån och förbehandlat sågspån med hög fluiditetskol har tillsatts till blandningarna. Värmebehandling av torrifierat sågspån med en hög fluiditeteskol gjordes för att uppnå en mindre reaktiv biomassa. Torrifierat sågspån innehöll 22.9 viktsprocent kol, förbehandlingen av sågspån med hög fluiditetskol ökade halten till cirka 60 viktsprocent. Den behandlade sågspånen tillsattes till fem kolblandningar för koksframställning, 5, 10 och 20 viktprocent tillsattes till en bas blandning som användes referens. Koksreaktiviteten, kemisk sammansättning och hållfasthet i koks studerades. Arbetet resulterade i en förbättrad bulkdensitet då upp till 20 viktprocent förbehandlad biomassa kunde tillsättas i kolblandningen och fortfarande behålla en bulkdensitet på 800 kg/m3. Koksutbytet i alla koks med förbehandlat sågspån var jämförbart med koksreferensen. Temperaturen där kemisk kol i koks började förbrukas, var något högre i koks som innehöll sågspån med 50 viktsprocent hög fluiditetskol. Koldioxidutsläppen från fossilt kol per ton råjärn (THM) uppskattades att vara 8,6 % lägre med tillsatsen av 10 viktprocent förbehandlat sågspån i kolblandningar för kokstillverkning. Tillsatsen av 20 viktprocent skulle innebära en minskning på 10 % per ton råjärn. Briketter med två olika blandningar framställdes, en blandning med torrifierat sågspån och en blandning med behandlat sågspån. Briketterna karakteriserades genom att analysera den kemiska sammansättningen och reduktionen av järnoxider i termisk reducerade briketter. Briketter med behandlat sågspån var mer kompakta, d.v.s. hade en högre densitet än briketter som innehöll torrifierad sågspån. Mängden hematit som kunde tillsättas i mixen med torrifierad sågspån var 0.107 mol, medan i mixen med förbehandlat sågspån 0.112 mol kunde tillsättas. / Bio4metals / CAMM