Decarbonisation of residual waste infrastructure: report

4.6 Heat Networks

The majority of incineration plants in Scotland use the heat from combustion to create steam that then drives a turbine to generate electricity. This process is not hugely efficient, with efficiency percentages in the low twenties being considered normal. As the ratio of fossil carbon to biogenic carbon increases, greater efficiency is required for the process to be better in GHG emission terms than landfill.

The most common and practicable method to improve efficiency is to use the steam to provide heat to another user, such as a district heat network or a large industrial facility. In this mode, efficiency can be doubled or more, reaching 55-65%.

Currently, only one operational incinerator in Scotland is connected to an operational heat network, Gremista in Lerwick, Shetland, which is owned and operated by Shetland Council. This was constructed alongside the heat network for the town of Lerwick and the plant does not generate electricity. Its operation is as a waste solution for the Shetland Islands due to limited available options for recycling and as a source of heat for the heat network. As such its indicative efficiency is greater than other incinerators in Scotland (see Table 4, Annex B – Recovery Status (R1 value)).

The Millerhill incinerator operated by FCC in partnership with the City of Edinburgh and Midlothian Councils has plans to connect to a heat network in the Shawfair development in Southeast Edinburgh. Construction of the initial district heating network, supplying around 3,000 homes, education and retail properties at Shawfair Town in the north of Midlothian Council area is expected to begin soon and deliver heat to homes by 2024. This initial phase is expected to save over 2,500 tonnes of CO₂ per year. The project will benefit from up to £7.3m from the Scottish Government’s Low Carbon Infrastructure Transformation Project (LCITP)^[54].

The Ness incinerator which is currently under construction in Aberdeen is planning to connect to a heat network providing heat to Local Authority buildings and houses in the Torry area of Aberdeen providing up to 10MWth of heat energy from 2025^[55].

Heat networks can therefore be a viable method to allow the sector to support wider decarbonisation. However the examples above show how close collaboration with developers, local authorities and plant operators is required to ensure heat networks can be utilised for new developments and existing infrastructure. This can be difficult to achieve. For example, the incinerator operated by MVV MEB in Baldovie, Dundee has not been able to find a customer for its excess heat. The plant is located adjacent to the former Michelin tyre factory, which was a potential customer before its closure. Finding a viable alternative since then has not been successful.

Incineration facilities are subject to minimum efficiency requirements. SEPA’s ‘Thermal Treatment of Waste Guidelines’^[56] (TTWG) updated in 2014 sets a 20% energy efficiency target for municipal waste incinerators, over 25kt annual capacity, at start-up (generally achievable as electricity only) and require a credible Heat and Power Plan showing how the facility could meet a minimum of 30-35% efficiency.

As per the TTWG, all SEPA permits for incineration plants contain a requirement stating:

Within 7 years from the date of First Operation of the Permitted Installation, the total quantity of energy recovered in the form of electrical or heat energy or a mix of electrical and heat energy shall exceed the amount of energy equivalent to a Combined Heat and Power Quality Assurance (CHPQA^[57]) Quality Index value of 93 or an indicative efficiency of 35%.

Every incineration plant in Scotland in operation or in the planning pipeline is required to prepare a Heat and Power Plan to ensure compliance with the TTWG to demonstrate how they can connect to a heat network or how they demonstrate being ‘CHP ready’ should the option to connect to a heat network become a viable option. Although the TTWG places an obligation on incinerator operators to provide heat and/or steam to a heat network, the availability of a heat network is not within their control and they are reliant on local authorities, developers and other outside stakeholders to develop a viable network.

Plants that cannot meet the TTWG requirements due to circumstances outside of the plant’s control, must submit to SEPA in writing the details of those circumstances and the reasons for the likely non-compliance, with reference to the provisions of the TTWG and the most recently agreed Heat & Power Plan, together with information on the Operator’s proposals on how and when the requirements of said guidelines will be met.

Where this occurs the CHPQA and indicative efficiency requirements are dis-applied from the plant’s permit until such time as the Operator has received written confirmation from SEPA that either the requirements of TTWG continue to apply, or the requirements of the TTWG are varied by issue of a variation notice by SEPA.

This effectively means that the regulatory pressure on an incinerator operator to connect to a heat network is not great, and in many cases will not be strong enough to overcome the problems identified above.

Operational facilities are required to update their Heat and Power Plan annually^[17]. Table 4: Current estimated efficiency values, CHPQA and R1 values for Energy from Waste plants in Scotland (Annex B – Recovery Status (R1 value)) summarises the efficiency levels and CHPQA quality index reported up to 2022 by existing and proposed sites in Scotland. Plants operational before 2014 are not required to calculate these values.

The Eunomia report noted that the addition of heat recovery resulted in a modest reduction of net emissions (around 27 – 35 ktCO₂e per annum), compared to CCUS and advanced sorting. This is in part due to assuming that only five additional facilities (Millerhill, GRREC, Aberdeen, Dundee and Earls Gate) will implement heat recovery and connect to heat networks by 2035 given the issues outlined above.

In addition, while increasing the efficiency of a plant results in avoided emissions by displacing other sources of energy, it doesn’t reduce direct emissions. As the wider energy sector decarbonises, there will be less of a displacement effect. So, while heat networks can be an effective way of capturing excess heat from an incineration plant, this is not a reason to construct a new one.

Nonetheless, as heat networks have a wider role to play in decarbonisation, whatever energy source is used, their connection to incineration plants, where possible, is beneficial. Therefore, this Second Report confirms the First Report’s provisional position that:

Recommendation 14: The Scottish Government and local authorities should continue to work with industry to deploy combined heat and power for as many existing incineration facilities as possible.

4.7 Carbon Capture, Use, or Storage (CCUS)

Several technologies^[58] have been proposed to capture the carbon dioxide emitted from combustion processes so that it can either be used elsewhere or sent for long term storage underground. For now, the most suitable capture technology for incineration is likely to be post-combustion removal of CO₂ from the flue gases, which is expected to be carried out by carbon scrubbing with amines, as this is the only capture technology that has been used industrially^[59]. Amine-based carbon capture is a regenerative process using an amine solvent to remove CO₂ from flue gas post combustion. Reversing the reaction releases pure CO₂ for capture and frees up the solvent for re-use. Amine-based post-combustion capture (PCC) is a well-proven and commercially available technology, having been used in the petroleum sector since 1996 and in the coal-fired power industry since 2014^[60].

Less well-developed approaches include membrane separation and chemical looping. Increasingly, technologies that convert the carbon dioxide on site into a useful material^[61] are being developed.

The capture and compression of CO₂ incurs an energy loss (parasitic load) in the form of the provision of steam and/or power. The size of this loss will depend on the efficiency of the capture process but can be as much as 20% of the energy output from the facility. This will impact on the efficiency values stated previously but will improve a plant’s R1 status (see Annex B – Recovery Status (R1 value)). Typically, within an incinerator, CO₂ represents 10-12% of the flue gases; higher concentrations of CO₂ make the capture of CO₂ more efficient. The absorber tower can be made smaller, and the solvent used to capture the CO₂ in the flue gas can be used more efficiently.

CCUS technologies have the potential to capture emissions from both fossil carbon and biogenic carbon released from the incineration of residual waste. The additional work undertaken by Eunomia, following discussion with the CCC, therefore included emissions reductions due to the capture and storage of biogenic carbon emissions. This modelling suggests that the deployment of CCUS in Scotland could have a marked impact on decarbonisation, noting that the addition of CCUS (Pathway 3) would reduce annual net GHG emissions from waste treatment by around 80% (79 – 82% depending on the scenario) compared to the modelled Pathway 1 (Advanced sorting only) in all scenarios (64-68% reduction in direct emissions). The scenarios that examined increased food waste avoidance compared to increased plastics recycling had little impact on the modelled results since CCUS was assumed to capture both biogenic and fossil carbon. In this modelling the sequestration of biogenic carbon in landfill is also included as an assumption, however, emissions from the incineration of biogenic carbon are not included in the baseline (2020) scenario. While this is in line with wider carbon accounting practices, it may be beneficial to consider whether reporting biogenic carbon in all aspects of future modelling for the waste sector could be beneficial (see Section 3.2.1 and Recommendation 15).

4.7.1 Development of CCUS

The modelling undertaken by Eunomia is intentionally optimistic about the potential for Scotland to deploy CCUS, presenting what could be considered a best case scenario. CCUS was not modelled on its own without other options (Advanced Sorting or Heat Networks) as it is currently the least feasible option and there are a number of potential barriers to deployment of CCUS.

The development of CCUS is anticipated to occur in a phased manner, led by the location of incineration facilities (and wider industry) which strongly influence technical and economic viability. There is recognition that large CO₂ emitters close to each other and to a transport and storage solution will likely form into a CCUS ‘cluster’. Incineration facilities are suitable candidates to join such clusters and are already aligning themselves with such projects.

Proposals for a CCUS cluster in Scotland are led by the Acorn Project^[62], a consortium of companies backed by the UK & Scottish Governments and the EU. This proposes to use existing and new pipelines, ships and other containers to move CO₂ emissions from projects in Scotland, across the UK and internationally to permanent storage 2.5km (1.5miles) under the North Sea.

Those plants most likely to overcome the barriers, and therefore be able to deploy CCS first are anticipated to be those along the east side of Scotland initially and within 30km of an identified cluster or pipeline. Following this, it is anticipated that facilities that are within 30km of potentially suitable port facilities to be developed next (second phase). This is on the basis that given existing infrastructure, these ports would likely represent the most likely future 'hubs' through which captured carbon would be transported (via ship) to cluster locations.

Transport solutions for the remaining incinerators away from the cluster and port locations are likely to be expensive due to their remote locations. If current CCUS technologies are applied to these, it will require substantial wider learning and cost reductions from earlier phases. For some of these incinerators the costs of applying CCUS may be prohibitive.

The operational sites in Scotland within 30 km of the Acorn cluster are:

• Earls Gate Park, Grangemouth
• MVV Environment Baldovie, Dundee
• FCC Millerhill, Edinburgh

The sites within 30 km of suitable ports are:

• Dunbar ERF - Forth port is well located to access the Acorn Cluster storage site.

Earls Gate Energy Centre in Grangemouth, Westfield Incinerator in Fife, Ness Incinerator in Aberdeen and Inverurie Incinerator are likely to be within 30 km of the Acorn Cluster when operational.

All other sites are considered to be away from suitable clusters or port locations.

We asked incineration operators if they had plans for CCUS on site. Of those that responded, several are actively considering CCUS (e.g. through feasibility studies) and one operator noted that it is likely to depend on the Net Zero strategy of the contractual authority.

The sooner CCUS can be developed on incineration facilities the greater the impact on carbon emissions there will be. It is therefore prudent, when choosing which of the pipeline of incineration facilities to pursue, to opt for those with the greatest opportunity to decarbonise quickly. The Review recommends that:

Recommendation 20: In considering which plants with planning permission to construct, financers, developers and planning authorities should prioritise those plants where deployment of currently available CCUS technology is most feasible.

This Recommendation is not intended to over-rule Recommendation 10^[63], especially if it is possible to use newer technologies to allow carbon capture and use.

Recommendation 21: The Scottish Government should consider support for emerging carbon capture and use technologies that could overcome challenges to deployment for facilities already in operation, or required for more remote facilities.

While there should be a diminishing need for residual waste treatment, for as long as there is a need to burn waste to treat it in a sanitary manner, we should pursue all possible ways to decarbonise the incineration sector, including through CCUS, particularly given the potential to capture biogenic carbon. Current barriers, such as access to the Acorn Pipeline, may be overcome by emerging carbon capture and use technologies, especially those that remove the need for transport of carbon dioxide.

4.8 Recycling More By-Products

The Review has received no new information on this aspect and therefore has nothing to add to the First Report.

4.9 Decarbonising Landfill

Landfill is a significant but declining option for biodegradable waste management in Scotland. It is currently associated with higher GHG emissions in comparison to other forms of residual waste treatment and is a significant source of anthropogenic methane emissions^[64] from the degradation of biodegradable material^[65]. For example, the Eunomia modelling found that sending waste to landfill without pre-treatment was between 381 and 408ktCO₂e per kt of household waste landfilled for the BES-F and BES-P scenarios, respectively.

When biodegradable waste is deposited in a landfill, biological decomposition can be hastened or delayed depending on the amount of oxygen, temperature, and moisture available. Waste in a landfill can take anywhere between 10 days (eg for a banana) and 800 years (eg for sanitary products) to decompose and is dependent on the waste composition and other factors. This long term emission means that even if no more biodegradable waste is deposited in Scotland’s landfill sites, there will nonetheless be an ongoing need to capture the significant GHG emissions for years to come.

Other impacts associated with landfills include groundwater and surface water risks, odour, noise, dust, litter, and vermin. Furthermore, some active and historical landfill are in coastal and alluvial areas prone to flooding and/or erosion and this is likely to increase in the future because of risks associated with climate change such as increased frequency of extreme rainfall events and sea level rise. These risks need to be better understood and managed in the future.

Therefore, while the environmental risks associated with landfill, including GHG emissions, are most acute during the operational phase, they may persist for many decades, well beyond the operational period. Once landfills are full, capped and restored, active site management is required to mitigate the longer-term environmental risks.

4.9.1 Gas Management

Landfill capping and gas management systems help manage the risks posed by landfill gas, but many older, closed sites in Scotland passively vent landfill gas to the atmosphere with little or no collection infrastructure. As well as methane and carbon dioxide from degradation of biodegradable wastes, landfill gas may include other volatile contaminants. Gas management is required at landfills to mitigate risks to human health and the environment, including to reduce climate change impacts.

The landfill gas capture rate across the UK is estimated to be between 59% and 63%, which is lower than that reported in other countries^[66]. Increasing the proportion of landfill gas captured is, therefore, likely to play a part in decarbonising the residual waste sector^[67].

Gas that is collected can be used to generate electricity or, in a combined heat and power (CHP) system, to provide both electricity and heat, or flared to the atmosphere to convert the methane to carbon dioxide. Though landfill gas production generally reaches a peak in five to seven years, a landfill can continue to produce gases for more than 50 years. Whilst gas generation rates remain sufficient to make energy recovery from the landfill gas commercially viable, the gas risks will usually be actively managed. However, as landfills age, gas generation rates reduce^[68] and consequently the technical and commercial feasibility of generating energy from landfill gas will lessen. Where energy generation is not economically or practically possible, for example due to waste composition changing to less biodegradable waste (less methane produced), it can be flared and where this is not possible, it can be managed passively, for example by an appropriate choice of plant cover.

Recommendation 22: The Scottish Government and landfill owners and operators should ensure maximum capture of landfill gas for open and closed landfill sites, and develop new approaches to do this as methane levels decrease.

Stakeholders have raised concerns around the future incentives to capture landfill gas for energy production or flaring. The Renewables Obligation (RO), covering England and Wales and the Renewables Obligation (Scotland) (ROS), have supported most of the renewable capacity built across the UK since their introduction in 2002. Under these schemes, certificates (ROCs) are issued to operators of accredited renewable generating stations for the eligible renewable electricity they generate, including landfill gas renewable technologies^[69]. However, since April 2017 and the closure of the RO to new entrants, new landfill gas generation capacity has not qualified for any subsidy support, and support for existing landfill gas generation ceases from April 2037.

The RO/ROS withdrawal could result in the potential loss of a significant revenue stream and an increase in the volume of gas being flared. Consideration of the impacts of the removal of the ROS and how to incentivise landfill operators and their renewable technology partners to maximise the efficiency of landfill gas management would seem beneficial^[70].

Recommendation 23: The Scottish Government should consult with landfill owners and operators to address the consequences of the withdrawal of current landfill gas management financial incentives after 2037.

4.9.2 Further Decarbonisation Options

There may also be opportunities for further incentives and opportunities to support decarbonisation of the sector, as the number of Scottish landfills in the restoration phase continues to increase. These include:

• Options to use energy on-site instead of exporting to the grid;
• Opportunities for mobile flaring technology which could be used for flaring on a part-time basis as the gas generation rates fall;
• Opportunities for heat recovery from the landfill;
• Improvements in capture technology such as improved containment liners or using biosolids (containing microorganisms) that convert methane into carbon dioxide.