This study assesses the socioeconomic feasibility of an integrated waste tyre pyrolysis and electricity generation system in the Gauteng region of South Africa. The primary aim of the research is to address two of South Africa’s challenges, waste tyre management and electricity generation shortages, by integrating waste tyre pyrolysis with a gas turbine. This research is in direct response to the call for further research into the applicability of pyrolysis from the South African government. Gauteng is a highly populated and economically significant province, which provides a crucial case study for this system due to its substantial waste tyre stockpiles, built-up infrastructure, dense population, and high electricity demand.

The designed system involves the pyrolysis of waste tyres to produce char and oils, which are then used to generate electricity through an external gas turbine. This integrated approach highlights the applicability of using pyrolysis outputs for electricity generation, bypassing the need for uncertain secondary markets for pyrolysis products. The system design relies on the availability of waste tyres, regulatory considerations, and market demands for electricity, sizing the system first for the desired electricity generation capacity and fitting the pyrolysis size to meet the demands for electricity generation.

The economic analysis shows that the combined system is a highly feasible solution, with a Net Present Value (NPV) of approximately R4.85 billion and a payback time of 5.4 years, building a solid investment case. The Levelised Cost of Electricity (LCOE) is calculated at 0.12 R/kWh, making the system more cost-effective than current electricity generation methods in South Africa under the national generation company. The economic model’s outlook and results are supported by sensitivity analyses, which indicate the system remains feasible under changing waste tyre and electricity prices, even without government subsidies, a critical condition to eligibility for the support schemes.

The Social Cost-Benefit Analysis (SCBA) reveals a range of significant societal benefits that the integrated system provides. These include job creation, improved power quality, and increased national economic output through reduced load shedding. The system’s Social Net Present Value (SNPV) is strongly positive at R8.56 billion, with significant social benefits across various different sectors. Further, the results highlight the benefits of pyrolysis for waste tyre management over the direct use of tyres in coal power plants, making a clear case to the government regarding the processing method to pursue. Significantly, these benefits outweigh the additional carbon emissions from the increased electricity generation capacity and the increased tax burden of the subsidies to the processing system. Not all of the societal benefits are evident in the SCBA; the system also plays a role in public health improvements and a reduction in road accidents by addressing the waste tyre stockpile issue. These benefits further highlight the potentially significant gains for society following implementation.

The study concludes that the proposed system is a socio-economically feasible solution for Gauteng’s waste tyre and electricity challenges. And a potential driving force for South Africa’s energy landscape transition, paving the way for renewable energy systems to connect to the grid en masse through the added grid stability. Its positive economic indicators and net societal benefits make it a promising candidate for addressing South Africa’s energy transition and waste tyre management goals, meeting all of the government’s objectives of the Industry Waste Management Plan and fitting into the Renewable Energy Independent Power Producer Role. The study paves the way for future research to focus on environmental impacts, changing system assumptions and long-term electricity grid impacts.

Goal and Scope. The decarbonization challenge is especially dire for the energy-intensive industries which worldwide account for a large sum of carbon dioxide emissions. Heat is an essential product demanded by the energy-intensive industries and is currently produced through extensive use of carbon-based fuels including coal, natural gas and oil. Considering the need to meet (inter)national climate targets, these carbon-based fuels must be replaced by cleaner (i.e. less greenhouse gas emitting) alternatives. Biomass, when sourced sustainably, is one such mature alternative yet is still carbon based. For the energy-intensive industries, three of the main non-carbon-based options are: electrification, hydrogen and Iron Fuel Technology™. This research explores the environmental performance of these three alternatives in comparison to natural gas, biomass and each other in two potential future scenarios when implemented in an energy-intensive industry. It also proposes potential ways to reduce environmental impacts and highlights any foreseen (environmental) implications that may occur before large-scale implementation takes place.

Method. The use of ex-ante life cycle assessment allows for the prospective exploration of an upscaled electrification, hydrogen and Iron Fuel Technology™ product system. The life cycle inventory database ecoinvent version 3.9.1 forms the basis for this research in which technology specific processes are modelled by data collected through the inclusion of domain experts and technology developers as well as the completion of desk research. The life cycle impact assessment is based on the European Commission’s proposed Product Environmental Footprint and the subsequent standardized set of impact categories included in this research are climate change; ozone depletion; human toxicity, cancer; human toxicity, non-cancer; particulate matter; ionizing radiation; photochemical oxidant formation; acidification; eutrophication, terrestrial; eutrophication, freshwater; eutrophication, marine; ecotoxicity, freshwater; land use; water use; resource use, minerals and metals; and resource use, fossils. Following the life cycle impact assessment, a contribution analysis was completed which highlighted multiple key parameters within processes that were subsequently tested in sensitivity analyses.

Results. This research confirms that electrification, hydrogen and Iron Fuel Technology™ can limit climate change impacts in comparison to natural gas, thereby helping decarbonization efforts and achieve climate targets. From a solely climate change perspective, sustainably sourced biomass is a better alternative to electrification, hydrogen and Iron Fuel Technology™, but it has limited upscaling potential due to the finite availability of sustainable biomass. Considering other impact categories including acidification, freshwater ecotoxicity, marine, terrestrial and freshwater eutrophication, human toxicity cancer and non-cancer, mineral and metal resource use and particulate matter, electrification, hydrogen and Iron Fuel Technology™ all exert more pressure on the environment than steam produced through natural gas. Most of the exerted pressures as seen in the electrification, hydrogen and Iron Fuel Technology™ product systems stem from the assumed electricity mix and the expansion of the electricity network. As a result, some of the impacts, like those associated with expanding the electricity network, are inherently tied to the energy transition.

The comparison between electrification, hydrogen and Iron Fuel Technology™ showed that Iron Fuel Technology™ using scrap iron and waste hydrogen generally performed best except for the impact category human toxicity, cancer. Only when using a fully wind-based electricity mix is Iron Fuel Technology™ outperformed by direct electrification for climate change, fossil resource use, human toxicity cancer, ionizing radiation, land use, and particulate matter. Hydrogen, due to its large electricity demand for water electrolysis, consistently performed the worst throughout all investigated cases and can only be competitive to electrification and Iron Fuel Technology™ based on waste hydrogen when water electrolysis is completed with a fully wind-based electricity mix. The same applies for Iron Fuel Technology™ using green hydrogen.

Discussions. This research has made the first comparison of electrification, hydrogen and Iron Fuel Technology™ considering its implementation in the energy-intensive industries in comparison to natural gas and biomass as well as comparing them among each other. It thereby investigated potential environmental impacts in a possible 2030 and 2050 Dutch future identifying hotspots and key parameters that are highly influential in determining environmental performance through performing ex-ante LCA. It stands out as it investigates a broad range of impact categories when most reviewed studies only focused on a set of impact categories. Consequently, the outcomes of this research can be used to guide research and development, monitor potential problem areas and be used as the basis for evaluation and further research.

However, the limitation of ex-ante life cycle assessment is that it is exploratory in nature and subject to large uncertainties. As “what if” scenarios are examined, this research does not provide any conclusive results and can only be used to provide insights into potential environmental performances of alternatives, to identify environmental hotspots, for debate and to make recommendations for research and development activities. Large uncertainties in the research stem from temporal mismatches in foreground ex-ante data and background dated data, unquantified characterization factors, and slight inconsistencies regarding system boundaries. The largest uncertainty yet may be the development of each product system in time as ex-ante LCA examines and compares a potentially upscaled emergent technology to a mature technology in the present which may also not necessarily be a fair comparison. The underlying availability and quality of the data in this research reflects this. Even though comparison is made at the same assumed technological readiness level, the underlying data of the mature technology is proven to be possible whereas the data of the emerging technologies is assumed based on expected results. The availability and quality of the used data is therefore drastically different and may lead to arbitrary results.

Recommendations. The results of this research suggest reducing material usage, making manufacturing processes of required background products more sustainable (e.g. copper) and decreasing electricity consumption are the most effective ways to limit environmental impacts in the electrification, hydrogen and Iron Fuel Technology™ product systems. Specifically for Iron Fuel Technology™ it is further recommended to source waste hydrogen, produce initial iron fuel from scrap, further improve the circularity of iron fuel and to use ship transport over truck transport whenever possible. For hydrogen, key recommendations include keeping hydrogen losses to a minimum, and technologically improving the electrolyzer and boiler efficiencies. This research also highlighted that differences in case application and assumptions can influence the environmental performances significantly. As a result, it is strongly recommended to further examine electrification, hydrogen and Iron Fuel Technology™ for various end-use applications and under different scenarios.

Conclusions. The results of this research suggest electrification, hydrogen and Iron Fuel Technology™ could all reduce climate change impacts in both 2030 and 2050. However, it is also noted that they are not fully clean alternatives, i.e. that not all environmental impacts are lower in comparison to carbon-based fuels. The completed ex-ante LCA showed higher environmental impacts for multiple impact categories, among others: acidification, freshwater ecotoxicity, freshwater eutrophication, human toxicity cancer and mineral and metal resource use among other impact categories. Some of these impacts are a direct result of the assumed 2030 and 2050 scenarios reflecting the transition away from carbon-based fuels sketched in this research. The environmental impacts related to copper associated with an expansion of the electricity network is an example of this. To limit environmental impacts, this research suggests a multitude of redesign recommendations for electrification, hydrogen and Iron Fuel Technology™, primarily focused on increasing efficiencies, limiting electricity demand and decreasing emissions of background processes. Though implementing a set of these redesign recommendations helped decrease environmental impacts for electrification, hydrogen and Iron Fuel Technology™, it was shown to be insufficient to reduce environmental impacts in all impact categories to below the environmental impacts of carbon-based fuels or generally alter the environmental performance of electrification, hydrogen and Iron Fuel Technology™ in comparison with one another. The results therefore indicate that Iron Fuel Technology™ based on scrap iron and waste hydrogen is most preferable among the clean alternatives in decreasing climate change impacts while limiting other environmental impacts in as far as possible. However, it must still be noted that dependent on the specific case, the assumptions used, and which impact categories are prioritized, which technology is best suited may be subject to change.

Perspectives. This research suggests that electrification, hydrogen and Iron Fuel Technology™ can help alleviate climate change impacts to varying degrees depending on the scenario assumed, but that tradeoffs of other environmental impacts will likely arise in the transition away from carbon-based fuels. It should therefore be cautioned that a sole emphasis on tackling climate change impacts, specifically decreasing CO2 emissions, may result in overlooking potential side effects that may be environmentally harmful. The environmental impacts of any technology must therefore always be holistically examined over multiple impact categories.

The global production of textiles carries a significant share in global greenhouse gas emissions, with a demand projected to grow. Especially for scope 3 emissions, materials play a significant role, with polyethylene terephthalate (PET) as a dominating fibre material with unique properties. Virgin PET based on fossil oil as the conventional option is non-renewable, not aligning with a sustainable future supply route. Alternative drop-in feedstock options for PET are biobased or recycled. Biobased PET has the potential for an emission reduction, but that is not automatically the case. Also there is a trade-off with a worse performance in other impact categories because of the agricultural production. With recycled PET, there are mechanical and chemical recycling options. Mechanical recycling for fibres is feasible and established as open-loop recycling from bottles. For mechanical recycling from textiles, a blend with virgin PET becomes necessary to maintain the required quality. Chemical recycling is more promising for closed-loop recycling from textile waste, but infrastructure and design barriers are current limitations for its expansion. Because these PET sourcing routes come with different trade-offs and barriers, it is reasonable to explore other routes as well, such as basic oxygen furnace (BOF) gas fermentation and compare them with the alternatives.
In this study, Life Cycle Assessment (LCA) was conducted to determine the climate change impact of BOF gas fermentation-based PET compared to mechanically recycled and fossil-based PET. Then, the results were also compared to literature values for biobased and chemically recycled PET, embedding the results in the context of alternative sourcing routes for PET in the textile industry. In the focus technology of this study, feedstock gases rich in carbon are fermented into ethanol by microorganisms. Through several intermediates, monoethylene glycol (MEG) is made as one of the two main components of PET. Together with pure terephthalic acid (PTA), it is polymerised into PET. Several carbon-rich feedstock gases such as syngas from biomass or wastes, but also reformed natural gas have been explored in previous research and development. However, the commercially available option is to use off-gas from the steel industry from the BOF. Therefore, the examined feedstock in this LCA is BOF gas with a composition of 85% CO and 15% CO2.
With a climate change impact of 4.95 CO2eq / kg PET, fermentation-based PET had the highest impact within the LCA model results of this study, followed by virgin PET (2.93 kg CO2 eq per kg PET) and then mechanically recycled PET (1.05 kg CO2 eq per kg PET). Biobased PET literature values ranged between comparable impacts to mechanically recycled PET up to values higher than all other investigated sourcing alternatives. Chemically recycled PET had an impact between mechanically recycled PET and virgin PET. In terms of environmental contributions, for all alternatives the major share of greenhouse gas emissions was from fossil CO2 (around 80%). Technosphere contribution hotspots were the carbon dioxide released during the fermentation and high voltage electricity production, mainly for the conditioning of the feedstock gas (compression and cooling). Also the provision of the virgin PTA component had a considerable contribution (1.11 CO2eq / kg PET).
Under the current global electricity mix, the gas fermentation technology was concluded to not be an advisable alternative to reduce greenhouse gas emissions. A combination of a best-case renewable electricity scenario, a substitution of the missing energy from the BOF gas in the steel process with wind energy instead of natural gas and an orange-peel based PTA sourcing route could reduce the climate change impact down to be comparable to mechanically recycled PET. However, that result is only valid if the emission credit assumption for the avoided emissions in the steel process holds. Otherwise, the gas fermentation technology emits more greenhouse gas emissions than both conventional alternatives, even under the best-case scenario.