There is no doubt that Energy from Waste (EfW) is a much-needed addition to processing municipal solid waste. There is still a vast quantity of refuse material that cannot be recycled due to there being no local separate collection mechanism in place for organic (kitchen) wastes, or because there are limitations in recycling technology both financial and practical, for such things as certain plastics, metals, glass etc.
Recently there has been a significant focus on carbon emissions from industrial facilities, including the EfWs, given the prospect of the introduction of a carbon tax.
Before talking about carbon capture it is important to distinguish between “biogenic” carbon and “non-biogenic”. The uptake of carbon dioxide (CO2) from the atmosphere during photosynthesis is a natural process and this “capture” of CO2 results in a removal of CO2 and storage in plant biomass (biogenic carbon). For greenhouse gas (GHG) accounting purposes, biogenic carbon capture can be considered as a reduction or a “negative emission”. All residual waste contains biogenic carbon and it will be possible for the EfWs to achieve negative CO2 emissions by incorporating carbon capture technology on site. Thus, neutralising other emissions which are difficult to reduce/remove and providing cities with a necessary mitigation of climate change from waste generation and processing.
Proactive innovation is required in the near future if we are to achieve net-zero carbon emissions in the UK and this is why the development of carbon capture solutions has drawn considerable attention in the past two years. One of the most popular methods of carbon capture are catalytic systems, as they produce products which can be utilised in transport fuels or the chemical industry, whilst reducing GHG emissions. Typically, in such systems, a stream of gas containing CO2 passes through water (or another liquid medium, such as amines) to deliver CO2 for the electrochemical reaction. The challenges of such systems are energy consumption and catalysts usage, which all result in substantial costs. However, these can be offset by converting CO2 into carbon-based products which have industrial applications (such as ethylene, for example). One of the advantages of such post-combustion process capture CO2 systems is that they can be fitted retrospectively at the operational facilities. Such systems are now being explored by leading waste management companies like Veolia and Suez.
There are two very important elements of the carbon capture technologies which need to be considered along the capital costs:
- Need to ensure that all of the solvent is recovered and not emitted with the flue gasses to minimise operation costs and reducing environmental impact
- Energy efficiency, as carbon capture can be an energy-intensive process, thus increasing parasitic load of the EfW
- Absorption area which will lead to a more effective utilisation of the system
- Technology based on resistant materials, as amine-based solvents, CO2 can corrode the system
There are a number of captured CO2 uses which have been already used in the industry, such as injecting CO2 into depleted oil fields to enhance oil recovery and greenhouses to boost plant growth. But other uses are also being developed: building materials (converting CO2 gas into a solid aggregate for concrete and thus sequestering it for hundreds of years); organic chemicals (soaps, detergent, fertilizer, bioplastic, synthetic fuels, textile dying industry).
Carbon Capture Technologies
It is worth having a look at some of the emerging Carbon Capture technologies such as:
Compact Carbon Capture technology (http://compactcarbon.no/) offers a modular, compact solution capable of capturing CO2 in the range of 10k to 1m tonnes per year. This technology uses rotating beds instead of the usual gravity-based columns to bring the flue gases in contact with the solvent, thus reducing the footprint and capital costs. The company can reduce the carbon capture costs below $120 per tonne now and work on improvements that will halve the cost.
Carbon Clean (https://www.carbonclean.com/ ) also offers a modular solution, suitable for retrofitting as its installation allows minimal site disruption time. It also offers semi-modular systems, which can be incorporated during the design of the facility and is fully scalable. The technology utilises a patented process, involving a proprietary solvent (absorber) that extracts CO2 gas. Carbon Clean is targeting to reduce the cost to $30 pet tonne making decarbonisation more affordable.
Aker Carbon Capture (https://www.akercarboncapture.com/ ) is a provider of another cost-effective technology, which uses a mixture of water and organic amine solvents to absorb CO2. Aker has already signed an agreement to deliver their system with one of the EfWs to capture 100,000 tonnes of CO2 per annum.
O.C.O. Technology (https://oco.co.uk/waste-treatment/ ) provides a great solution for capturing significant volumes of CO2 from the residues (ash) produced by the EfWs by producing a carbon-negative artificial aggregate, known as Manufacture Lime Stone. It has three UK operations in Leeds, Avonmouth and Suffolk, where c.310,000 tonnes of carbon-negative aggregate was produced in 2020.