Decarbonisation of End Uses

Malcolm Wilkinson and members of the Sustainability Special Interest Group discuss the technologies available to decarbonise non-power sectors

ACHIEVING zero-carbon is a challenge and an opportunity to the engineering community in general, and chemical engineers in particular. Chemical engineers will play a crucial role in the design of pathways to decarbonise processes in energy-intensive sectors, notably power, heavy industry and transport, and to a lesser extent in buildings and agriculture. The Sustainability Special Interest Group (SSIG) has prepared a series of thought pieces on achieving zero-carbon; this is the third in the series following two entitled The Future of the Oil & Gas Industry¹ and Zero-Carbon Electricity². This latest piece focuses on the end uses of fossil fuels outside the power sector, and the technologies available to decarbonise them. The final contribution in the series will cover materials efficiency and the circular economy.

Global industry contributes 21% of greenhouse gas emissions³. Cement manufacture, iron and steel production and chemicals represent the principal emitters. Agriculture contributes 24% of global emissions, transportation 14%, and gas heating/cooling in domestic and business buildings a further 6% (see Figure 1).

Heavy Industry

Decarbonising cement, steel and chemicals production requires solutions which go beyond electrification of the energy inputs, and necessitates amending the chemical and physical processes employed. To reduce emissions, these sectors will need to replace fossil fuel-based energy inputs with zero-emission electricity or other low or zero-carbon fuels, improve heat integration and energy efficiency, and take advantage of new process routes and methods of working. These industries will also need to develop new products and business models which reduce demand for their carbon-intensive products and services, meet sustainable development goals and promote the circular economy by recycling material at the end of product life.

The emissions from cement production result from the fossil fuels used to generate heat for cement formation, as well as from the chemical process in the kiln that transforms limestone into clinker, which is then ground and combined with other materials to make cement. The clinker formation in the cement manufacturing process accounts for 60–70% of the total carbon emissions. Innovative approaches to reducing emissions are focussing on reducing the limestone content by substituting clay in cement production and injecting recycled CO₂ into concrete, producing in-situ nano-sized mineral carbonates which improve strength. Ultimately though, carbon capture and storage (CCS) will be an essential feature of cement production.

The main contributor to CO₂ emissions in iron and steel production is from the dominant blast furnace/basic oxygen furnace production route which relies on the use of coking coal. There are two principal options for low-emission steelmaking.

First, continued use of fossil fuels but with CCS, and second the use of renewable electricity for producing hydrogen to replace coking coal as the reducing agent or directly in as yet-undeveloped electrolytic processes. The direct reduced iron is then converted to steel in a conventional electric arc furnace.

The chemicals industry accounts for 12% of global industrial energy use using fossil energy such as natural gas and products from oil refining for both heat and feedstock. Carbon is the essential component of many key products and is potentially emitted at the end of the product life cycle. Moving to biomass or biomass-based synthetic feedstocks reduces the use of fossil fuels, and coupled with process chemistry innovations, which improve atom efficiency and lower reaction temperatures, can reduce carbon emissions. However, CCS will ultimately be required.

Industry interdependence in the context of decarbonisation is very important and is an area ripe for technological development. An interconnected systems approach is required, rather than viewing industries and their technologies in silos. An example of this approach is the Kalundborg Symbiosis in Denmark where 12 companies are co-located and a residue from one company becomes a resource to another, benefiting both the environment and the economy. Widely implemented, this approach should accelerate decarbonisation and reduce overall investment costs. However, this will require significant changes to legal and commercial arrangements, balancing co-operation whilst maintaining competition between manufacturers. The global chemicals industry will need to consider many such fundamental changes in its drive towards net negative emissions.

Transport

The transport sector has four main segments, namely road, rail, aviation and shipping (see Figure 2). Within the segments, different strategies will need to be deployed.

Short-to-medium range road transport, cars, vans and light trucks can be decarbonised by battery-powered electric vehicles (EVs) or fuel cell electric vehicles (FCEVs). Decarbonisation of the electricity generation system is a necessary precursor for electric vehicles to impact on carbon emissions. Battery range and rapidity of recharge together with the deployment of recharge infrastructure are issues undergoing major development.

FCEVs currently depend on clean hydrogen production and refuelling infrastructure. Though hydrogen-powered FCEVs offer a weight advantage over comparable EVs, hydrogen production itself carries an energy penalty. Hydrogen production and accompanying filling procedures consume between two and three times more primary renewable electricity than direct electricity charging⁴. Nonetheless, these technologies are likely to be deployed for long-haul road transport. Truck manufacturer Scania expects electric long-haul trucks to be cost competitive with diesel by 2027 in Sweden⁵, whilst the Hydrogen Council predicts fuel cell vehicles to be cost competitive in the EU by the early 2030s⁶.

EVs and FCEVs in urban areas play a major role in improving air quality and reducing noise pollution, and public transport has been an early adopter of this technology. Innovative battery charging systems (such as by induction) on trams have been installed in Stockholm and Bordeaux.

Due to the projected fast growth of the EV market, there are risks associated with the sustainable supply of battery materials. These include supply issues associated with both the size and location of cobalt and lithium reserves and the required upscaling of supply chains to meet demand. Closed-loop battery recycling will gain importance. Batteries may experience a second use for less demanding applications such as stationary energy storage, as they often have remaining capacities of around 70–80%. Technical and economic barriers exist depending on battery chemistry, their state-of-health, and the intended second use.

EVs and FCEVs in urban areas play a major role in improving air quality and reducing noise pollution, and public transport has been an early adopter of this technology

There are several fuel options which can be used in existing internal combustion engines resulting in varying degrees of decarbonisation. Examples are hydrogenated vegetable oils from used cooking oil, animal fats and vegetable oils, but also fuels from algal oil and ligno-cellulosic material; bio-methane from sewage, landfill, food waste or distillery waste; and so-called “e-fuel” using recycled CO₂ water and electricity usually via Fischer-Tropsch synthesis. When considering such fuels it is vital to verify (eg by LCA) that they do in fact provide a low-carbon option. Replacing fossil fuels, at scale, by biofuels also has consequences for agriculture and biodiversity. This remains an area requiring careful development.

Decarbonising rail transport is by fuel shift from diesel to electricity or potentially hydrogen fuel cells on remote routes, though with the same energy penalties as for vehicles. For aviation, advanced jet fuels – such as synthetic fuels derived from the gasification of biomass or even waste material followed by Fischer-Tropsch synthesis – are the only way to decarbonise the current fleet and also the only option for the near future.

Several prototype electrically-powered aircraft and hybrid versions for low load and short-range applications are under development, with one Slovenian single seater already certified as airworthy by the US Federal Aviation Authority. Commercial flights are tantalisingly close and UBS estimates that by 2035 the aviation industry will be 25% hybrid or fully electric. The airlines are targetting the 500-mile range business to compete with high or ultra-high speed trains which represent a modal shift from flight to rail.

 

Behavioural change towards a lower-energy consuming lifestyle, together with innovation in both technology and business models, is essential as the transition away from the era of cheap fossil fuels is made

Options for short-haul sea transport currently being investigated are battery-electric or hydrogen either combusted directly or in fuel cells with the challenge of the charging infrastructure at ports. For long-haul shipping the possibilities are direct combustion of hydrogen or alternatively ammonia, produced from hydrogen using the Haber-Bosch process, which has a higher volumetric energy density than hydrogen and is a safer and easier storage option. Nuclear power based on current sea-going systems is also an option.

Behavioural change towards a lower-energy consuming lifestyle, together with innovation in both technology and business models, is essential as the transition away from the era of cheap fossil fuels is made.

Buildings

Decarbonising buildings is a major problem, requiring the construction of new buildings and whole districts with zero energy consumption from fossil fuels (zero-carbon buildings) as well as the renovation of existing buildings to meet the same net-zero carbon standards. Direct electrical systems, heat pumps and large-scale fuel cells for large buildings and district heating systems can be solutions, as can hydrogen supplementing and ultimately replacing natural gas in the gas grid. But heating a standard UK house by burning hydrogen will consume up to six times more primary renewable electricity than using a heat pump⁷.

Construction materials represent almost a third of building-related emissions and the development of new low carbon materials is essential. As buildings become more efficient and the grid decarbonises, the proportion of embodied carbon (ie carbon associated with the extraction, transport and manufacture of construction materials) increases significantly. By 2050, accounting for all new constructions between 2020-2050, embodied carbon emissions and operational carbon emissions will be roughly equivalent. In this context, the construction industry must radically change its manufacturing processes to abate the increasing proportion of embodied energy.

Demand-side management is vital and in recent years, energy management systems in buildings have become smarter, integrating external data sources, such as weather conditions, traffic patterns, and more. Using artificial intelligence, these advanced systems can forecast energy demand and improve response capabilities. Digitalisation can be especially beneficial in the world’s rapidly-growing cities where dense populations, increasingly high concentrations of electric vehicles, and innovative district energy, heating, and cooling systems can work to optimise demand and consumption and aid decarbonisation.

Construction materials represent almost a third of building-related emissions and the development of new low carbon materials is essential

For hard-to-abate, typically remote, sectors a wide range of potential synthetic fuels is available, including hydrogen and methane, methanol and other liquid hydrocarbons generated from biomass or waste.

Current building renovation rates account for about 1% of existing building stock each year whilst a higher than 3% rate is required to achieve the zero-carbon goal by 2050. Fostering higher renovation activities requires the stimulation of the financial market for energy renovations and mandatory standards for better energy performance. New builds must be zero-carbon and the construction sector workforce – from property developers through designers to operatives – need training to build competence and awareness of innovative solutions. Inefficient technologies (eg gas/oil boilers, window air conditioners etc) must be quickly phased out, guiding building owners and designers towards more efficient and renewable choices.

Agriculture

The agriculture sector contributes up to a quarter of all greenhouse gas emissions from deforestation, the use of industrial fertilisers, livestock farming, and direct and indirect fossil fuel uses. Intensive farming which produced the post-war “green revolution” was based on fossil fuel energy and has resulted in extensive soil loss and degradation.

Achieving net-zero agriculture is a complex issue involving the whole supply chain from farm to plate with many tradeoffs with other zero-carbon activities. Globally, the available land must provide food for a growing population and crops for biomass production for synthetic fuels and chemicals, living space, amenities and industrial infrastructure to support the population, space for carbon off-setting activities such as tree planting, and natural habitats to maintain bio-diversity.

Chemical engineering may seem peripheral to agriculture but in a systems approach it is important to be aware of the potential for cross-sector impacts

The necessary deep emissions cuts require a high uptake of low-carbon farming practices coupled with releasing land out of traditional agricultural production for long-term carbon sequestration, particularly in high GDP per capita economies, improving sustainable productivity, shifting diets away from livestock-derived food products, and changes in the distribution, sale and consumption of food products to reduce food waste.

Chemical engineering may seem peripheral to agriculture but in a systems approach it is important to be aware of the potential for cross-sector impacts. For example, the use of biofuels and the sustainability of biomass used for biofuels must be carefully assessed to avoid competition with food production, deforestation or loss of biodiversity and also to avoid competition with industries that currently use the biomass for higher-value products or uses. As sustainable biofuels will only be available in limited volumes, their use should be prioritised in hard-to-abate modes such as aviation.

Conclusion

Achieving zero-carbon within 30 years is vital to address climate change, and it demands the urgent attention of governments and businesses and societal acceptance of the necessary changes. We have highlighted the challenges and some potential avenues for achieving zero-carbon in the principal carbon emitters in the non-power sectors. The necessity for a systems approach to take into account cross-sector interfaces is clear. Chemical engineering and chemical engineers must play a major role in applying their systems skills to address these urgent issues, and it must be the principal focus of our activities.

References

1. The Chemical Engineer, May 2021, Issue 959, pp54-57.
2. The Chemical Engineer, June 2021, Issue 960, pp42–45.
3. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, IPCC 2014.
4. “Roadmap to Decarbonising European Cars”, Transport & Environment, August 2019, https://bit.ly/3zToXDl.
5. Scania, “The Pathways Study: Achieving Fossil-Free Commercial Transport by 2050”, August 2019, https://bit.ly/3AUtt54
6. Hydrogen Council, “Path to Hydrogen Competitiveness – A cost perspective”, January 2020.
7. Ground Source Heat Pump Association, “Hydrogen Fuelled Heating”, https://bit.ly/3vN889X.