Recycling waste polymers from automotive shredder residue (ASR); application in iron making

Abstract

An investigation was performed on characterisation of automotive shredder residue which resulted in application of its polymeric fraction as a substitute for coke, as reducing agent, in magnetite iron-ore composite pellets. In Australia aloan, nearly 200,000 tonnes of automotive shredder residue is landfilled every year. This thesis aims to characterise this waste stream and come up with an idea to apply it in proper way and prevent it to go to the land. On the other hand iron making industry specifically blast furnace and its feed stock consumes a huge amount of world s energy and resources. It was anticipated that shredder residues could be reused for its energy and composition aspect in iron making process. Samples were collected from an Australian shredder and were analysed for their composition and size distribution. Initial visual inspection confirmed the ASR as a very heterogeneous stream of waste and due to this heterogeneity application based on specific composition seemed to be out of prospect as it needs rigorous and costly separation processes. As result, the simple approach of size distribution, energy value and carbon content was considered as the bases for this study. It was realized that this waste consist of majorly high heat content materials with high carbon and hydrogen, metals and inorganics. The high energy content portion were analysed for their level of calorific value to come up with a representative range with purpose of nominating an effective re-application process. Charring process for analysis of carbon content was done based on standard ASTM E1755-01. This was followed by burning the carbon content to derive the ash. Composition of ash was studied for oxide and element content using XRF. Calorific value analysis was done to determine the right fraction of ASR for the application of heat recovery and the source of carbon. These characterisations led to the understanding of the heat value and carbon content of each size fraction of ASR. This high heat and carbon content of the ASR were realised to be majorly due to the polymeric content. As result it was selected for further application. It was realised that the palletisation of iron oxide with this polymeric portion of ASR, as the source of carbon and energy, would be an attractive choice due to the versatility of palletisation process. Pellets were then made from concentrated magnetite provided by the OneSteel Whyalla. The source of carbon in the pellet was set to be 100% metallurgical coke, 50% ASR, 70% ASR and 100% ASR. The concentrated magnetite is the major source of iron-ore used in the OneSteel s pellet plants. This magnetite was mixed with metallurgical coke, and flux, which basically is the milled limestone, before formed in to pellets and heat treated. These pellets are then fed into the blast furnace for iron extraction. Flux was not used in this project to minimise the effect of other oxides on the overall process. To make the pellets, the raw were mixed together and formed in to the ball-shape pellets and dried in 1050C for 24hrs in the oven. The reduction process was then performed in horizontal tube furnace in 12000C under argon gas flow for 20 min. Various qualitative and quantitative analyses were performed to determine the level of reduction in pellets. Gas products were captured and in-situ infrared gas analyser was applied to measure the concentration of generated CO, CO2 and CH4 gases. The reduction was then calculated based on the weight reduction of the pellets by measuring the weight of pellets before and after process. Oxygen and carbon content of pellets were measured by means of LECO oxygen and carbon analyser to be compare with weight reduction and IR analyses. Analysis of reduced pellets was also performed physically and chemically with help of optical and electron microscopy (SEM-EDS) and XRD analysis. Compressive strength of pellets then was performed on two sets of pellets before and after high temperature reaction. The result for reduced pellets was compared with the standards pellets provided by OneSteel Whyalla blast furnace. This feasibility study has shown that there is possibility for the ASR to be used in the iron reduction process and specially blast furnace process application.