SMART POLYMER INJECTION TECH
Professor Veena Sahajwalla, an alumnus of the Indian Institute of Technology Kanpur, which recently conferred its Distinguished Alumnus Award on her, is a globally respected scientist, inventor and engineer. Her research focuses on the sustainability of materials and processes. One of her most celebrated achievements is the invention of a process of recycling rubber tyres in steelmaking, now known around the world as green steel. She obtained her BTech in metallurgical engineering from IIT Kanpur in 1986, MASc (1988) in metals and materials engineering from University of British Columbia, Canada, and Ph.D. (1992) in materials science and engineering from University of Michigan, USA. She founded the Centre for Sustainable Materials Research and Technology (SMaRT) at UNSW Australia and is heading its research activities in collaboration with the industry. She has published over 250 papers in leading scientific journals and won innumerable honours and awards. In this interview she explains her work on sustainability and innovation in recycling end-of-life plastics/rubber tyre in producing green steel. Excerpts
By TA News Bureau:
Can you please explain your concept of green steel as a product of end-of-life tyre recycling?
Steelmaking is one of the world’s most important industries; steel is ubiquitous, it is the backbone of our built environment, our transport systems and our industries. However, steelmaking is also one of the most carbon- intensive industries, and many steel makers understand the need to reduce their carbon footprints. My background is in process metallurgy, so I have always been very interested in how we can improve steelmaking and other metals processing operations, to deliver both economic and environmental benefits.
Our so-called ‘green steel’ process is used to reduce the costs and the environmental impact of electric arc furnace steelmaking; which makes up about 30% per cent of total global steel production. In EAF steel making, energy efficiency is critical for productivity and is optimised by injecting oxygen and carbon into the molten mix.
Non-renewable coke is generally used as the carbon injectant. However, I knew waste tyres and plastics were an increasingly serious global burden; as well as a waste of potential resources. We already have some four billion waste tyres stockpiled around the world; by 2030 the global automobile fleet is expected to expand to some 1.7 billion cars, from about one billion today; generating billions of waste tyres every year. Due to their composition and high calorific value – a typical tyre has a carbon content of 84.4 wt% and a hydrogen content of 7.2% – waste tyres have long been of interest for resource recovery. But, tyres are also a complex mix of materials and despite considerable research and numerous technological developments; there are few ideal processes for the cost-effective recycling of waste tyres.
In landfills, waste tyres are not readily biodegradable and risk leaching toxic chemicals into the surrounding environment. Waste tyre stockpiles are also significant fire risks, as they are long burning and emit hazardous fumes.
This is where ‘green steel’ comes in. I wondered whether waste tyres and/or waste plastics, which are also good sources of carbon, could be used as an alternative carbon source; I thought we could clean up a global waste problem while at the same time reducing costs to the EAF steel industry.
Please elaborate on your invention Polymer Injection Technology for processing discarded tyres?
The key to the success of ‘green steelmaking’ is the substitution of coke with an alternative source of carbon, for use as a carbon injectant. Specifically, our polymer injection technology (PIT), or ‘green steel’ process leverages steelmaking temperatures of 1550 -1650°C to enable steelmakers to utilise carbon-bearing waste streams, such as waste tyres and plastics, instead of virgin resources. The result is a novel recycling solution that requires only minimal modifications to the manufacturing process and retains the quality and performance of the end product. PIT introduces precisely calibrated mix of crumbed waste into the furnace to optimise outcomes. We spent a number of years researching and understanding the high temperature reactions that take place when waste tyres partially replace coke, enabling us to optimize the operating parameters of the furnaces. As the new polymer (waste) -coke mix improves the foaminess of the slag, it improves furnace efficiency, while absorbing an otherwise problematic waste streams destined for landfill. Worldwide we have absorbed millions of waste tyres, reduced coke usage significantly, achieved savings in electricity and reduced toxic gases, as the polymers are completely consumed at the high temperatures used.
Our patented PIT ‘green steelmaking’ technology has been already integrated into commercial steelmaking operations in Australia, Thailand, South Korea, and the United Kingdom with discussions in process for other locations. Our plans are to continue to promote its implementation worldwide due to its dual economic and environmental benefits. At the same time, we are exploring other options for EAF steelmaking using waste resources, as other waste streams are potentially good carbon sources, such as agricultural waste. The waste shell of the macadamia nut (an indigenous Australian crop), for example, is a particularly good carbon source; and is mostly thrown away.
What are the technologies that you are developing for electric arch furnace for steelmaking that would eliminate non-renewable fossil fuels entirely?
We are currently replacing a large percentage of non-renewable coke in ‘green steel’ making; this is important. However, we are not yet replacing coke entirely. We are, however, working on many research projects investigating how to move away from the use of conventional virgin raw materials, such as coke and coal, towards sourcing industrial inputs from waste. We are fortunate to be working in partnership with a number of innovative businesses who are keen to reduce their environmental impact and their production costs. What’s important is to investigate how we can source the important elements needed in manufacturing from waste; as these elements have to be able to react with other elements to create the materials we need. We have, for example, been successful in using waste automotive glass and waste plastics in the production of valuable ferrosilicon alloys. As automotive glass is laminated it can’t be conventionally recycled. By reacting iron oxide with widely available waste plastics (Bakelite, as a carbon source) and automotive glass at high temperatures, we have shown it is possible to synthesize ferrosilicon alloys using waste. Industries currently use relatively expensive virgin raw materials such as quartz as a source of silicon and coke as a source of carbon, so this process offers both environmental and economic benefits. We have also reported on our success in synthesising various high performance advanced materials from waste tyres, such as nano-composites. For example, we have used waste tyres as a carbon source in the synthesis of silicon carbide-silicon nitride nano-composites; these materials are very promising for numerous applications as they can withstand extreme operating conditions.