In Australia, the use of plastics has increased tremendously over the last few decades, but less than 20 % of the waste plastics are recycled. The rest is usually landfilled, which poses major environmental problems. The solution to this problem involves the development of novel environmentally-benign technologies that would utilise these waste materials. This work investigates the reduction of EAF slags (47 % FeO) by blends of metallurgical coke with High-Density Polyethylene (HDPE) plastics at 1 550°C. The experiments were conducted in a laboratory-scale horizontal tube furnace, and were coupled with off-gas analysis using an infrared gas analyser and a multiple gas chromatographic analyser. The results indicate that the rate of FeO reduction in slags is significantly higher when the coke/plastics blends were used compared to pure coke, with the maximum rate of reduction (Blend 4) being over twice that of coke. Moreover, the CO 2 content in the off-gas was observed to decrease (by ϳ75 %) with increase in the polymer content of the blend. Additionally, the degree of carburisation and the removal of sulphur from the metal improved considerably when the coke was blended with plastics. The observed improvements in the rates of reduction, carburisation and desulphurisation are attributed to the reactions of hydrogen evolved from the waste plastics at these high temperatures.

Electric Arc Furnace (EAF) steelmaking uses different carbon based materials as foaming agents. Depending on cost and availability, anthracite and metallurgical coke are among the conventional injecting materials. Considering the energy and green house gas emissions requirements, alternative carbon sources are put on the spot to replace, at least partially, the conventional materials, i.e. waste materials such as rubber and high density polyethylene (HDPE) plastics may react with gas and slag phases resulting in devolatilization, combustion and iron oxide reduction reactions. The addition of waste tyres and waste plastics in EAF steelmaking has been studied in detail by our groups at UNSW and OneSteel is developing a method for EAFs to use blends of different proportions of rubber/HDPE plastics and coke as a slag foaming agent. Initially, laboratory investigations were carried out to establish the feasibility of carbon and polymer blends as foaming agents. The enhanced slag foaming performance compared to coke was found to be in good accordance with the results obtained in the laboratory indicating an increased slag volume when using polymeric blends. Following the successful installation of materials handling systems at both plants, the use of a rubber and coke blend is no longer considered a trial and is instead standard practice.

The present study investigates the effect of addition of waste rubber tires on the combustion behavior of its blends with coke for carbon injection in electric arc furnace steelmaking. Waste rubber tires were mixed in different proportions with metallurgical coke (MC) (10:90, 20:80, 30:70) for combustion and pyrolysis at 1473 K in a drop tube furnace (DTF) and thermogravimetric analyzer (TGA), respectively. Under experimental conditions most of the rubber blends indicated higher combustion efficiencies compared to those of the constituent coke. In the early stage of combustion the weight loss rate of the blends is much faster compared to that of the raw coke due to the higher volatile yield of rubber. The presence of rubber in the blends may have had an impact upon the structure during the release and combustion of their high volatile matter (VM) and hence increased char burnout. Measurements of micropore surface area and bulk density of the chars collected after combustion support the higher combustion efficiency of the blends in comparison to coke alone. The surface morphology of the 30% rubber blend revealed pores in the residual char that might be attributed to volatile evolution during high temperature reaction in oxygen atmosphere. Physical properties and VM appear to have a major effect upon the measured combustion efficiency of rubber blends. The study demonstrates that waste rubber tires can be successfully co-injected with metallurgical coke in electric arc furnace steelmaking process to provide additional energy from combustion.

Interactions between blends of metallurgical coke and polymers with EAF slag (30.5% FeO) at 1 550°C have been investigated using a sessile drop arrangement to determine the influence the polymer and its chemical composition on carbon/slag interactions. Two polymers, namely polyethylene terephthalate (PET) and polyurethane (PU), were used in this study. The CO emissions during carbon/slag interactions for PET/Coke and PU/Coke blends were lower as compared to corresponding emissions from metallurgical coke. An improvement in slag foaming, as determined by the dynamic changes in the volume of the slag droplet, was observed when PET/Coke and PU/Coke blends were used compared to the coke alone. Relatively greater number of gas bubbles was found to be entrapped in the slag droplet along with reduced iron droplets. Higher level of H2O formation was also seen in the case of PET/Coke and PU/Coke blends as a result of FeO reduction by H2. These results indicate that volatiles (H2 and CH4) released from the polymer/coke blends can influence the interactions between carbon and slag (in addition to reduction reactions by solid carbon). This study shows that a variety of waste polymers can be utilised as a carbon resource in EAF steelmaking processes.

The reduction of FeO-containing slag by blends of metallurgical coke and end-of-life tyres (RT) have been investigated through experiments conducted in a laboratory-scale horizontal tube furnace. Composite pellets of EAF slag (47.1% FeO) with coke, RT, and blends of coke/RT (in four different proportions) were rapidly heated at 15508C under high purity argon gas and the off gas was continuously analyzed for CO and CO 2 using an online infrared (IR) gas analyzer. The extent of reduction after 10 min, level of carburization and desulfurization, and the total amount of CO 2 emissions were determined for each carbonaceous reductant. The results indicate that the extent of reduction, level of carburization and desulfurization of the reduced metal are significantly improved when coke is blended with RT. Blending of coke with RT resulted in a decrease in direct CO 2 emissions from the reduction reactions.

Recycling end of life products, such as waste tires and waste plastics in iron- and steelmaking permits their use as energy and material resources. The current paper discusses the combustion efficiencies of blends of metallurgical coke (MC) with plastics for electric arc furnace (EAF) steelmaking. Laboratory tests involved the combustion in a drop tube furnace (DTF) at 1473 K of MC premixed with different proportions of plastics, polypropylene (PP), and high-density polyethylene (HDPE) (10−30%) under a 20% O2 and 80% N2 gas mixture. In the tested conditions, coke−plastic blends indicated higher combustion efficiencies compared to coke. The gas-phase reactions appear to be influenced by the amount of volatile matter present in the carbonaceous matrix and its subsequent effect on the structural transformation of the particles because of the release of volatiles. The surface area of the coke−polymeric mixtures before and after combustion was found to be higher than the surface area of coke alone. The residual chars collected after the reaction in the DTF were characterized as a function of pore volumes and surface area of the particles. A previous study has demonstrated the possibility of partially replacing conventional coke in EAF steelmaking with end of life rubber tires. The present paper studies the potential replacement of MC with waste materials, such as PP and HDPE, as auxiliary fuels in EAF steelmaking. A comparison to previously reported combustion efficiencies for rubber blends is also provided.

Research on the use of waste polymeric materials is one of the solutions for developing environmentally friendly recycling processes for steelmaking. Different polymeric materials [i.e., rubber, high-density polyethylene (HDPE), polyethylene therephtalate (PET), and Bakelite], which have different chemical structures and compositions, were selected for this study as carbon resources. The rapid heating to high temperatures provided during steelmaking will break down the polymeric chains and reactions with liquid slag, enabling gas formation. The dynamic changes in the volume of the slag droplet while in contact with the coke/polymer substrates are measured. Significant levels of gas generation and entrapment are present, leading to an improved performance over coke. Carbon/metal reactions were studied by measuring carbon and sulfur pick-up by liquid metal as well as the formation of reaction products at the metal/carbon interface. The measured carbon pick-up value after 2 min of reaction for metallurgical coke was approximately 0.08 wt %, whereas 100% polymers, such as PET and HDPE, showed an increased value of >2 wt %. The proportion of sulfur pick-up was very similar. The formation of interfacial products, in the case of Bakelite–coke blends, was studied, and the presence of CaCO3 used as a filler was seen to influence the chemical properties of the carbonaceous substrate. This study has established fundamentals of the interaction of waste polymers with slag and metal in the steelmaking process.

Bakelite is a thermoset plastic commonly found in electronic and automobile components. CaCO 3 is generally found in the polymer as a filler material. Since it cannot be remelted, the disposal of this material has become an environmental issue. The present study investigates a new route to utilize waste bakelite as a source of carbon in EAF steelmaking process. This paper reports the carbon dissolution behaviour of bakelite/ coke blends into liquid steel at 1550 8C. The carbon pick up in the liquid steel after reaction with varying blends of bakelite/coke for 30 minutes ranged between 0.13 wt% to 0.17 wt%; these were generally higher than that observed from coke alone (0.1 wt%). The dissolution rate (K) was also found to improve and the observed trend was BK2 (0.045 Â 10 À3 s À1 ) > BK3 (0.023 Â 10 À3 s À1 ) > BK1 (0.005 Â 10 À3 s À1 ) > coke (0.003 Â 10 À3 s À1 ). The reaction products formed at the interface after 30 minutes of contact between liquid steel and bakelite/coke blends were observed to be a CaS-Al 2 O 3 complex. The presence of CaS in the interfacial layer due to the CaO in the ash, lowered melting temperature of the layer, thereby allowing for increased removal of the ash layer and greater carbon pick-up. The CaO is formed from the decomposition of CaCO 3, and its presence was found to have a positive effect on modifying the properties of the coke, and thereby enhancing the carbon dissolution behaviour.