Project Summary
The Electrolyser Improvements driven by Waste Heat Recovery project looks to demonstrate efficiency improvements in hydrogen production through the use of waste heat produced in the transportation of network gases.
Innovation Justification
How does your Project demonstrate novel and ambitious innovation in theenergy networks?
Challenge Theme
This project looks to address the challenge of preparing for net zero powersystems using novel ways to reliably support low stability systems. Green hydrogen production is a low stability system in that the production is dependent on the weather (wind/solar) and/or constraints in the electricity network. Thismakes it very hardto predict the alignment of production and use of hydrogen. Improvements in the efficiency of hydrogen production will maximise the hydrogen produced in periods of high renewable energy availability and reduce the overallcost of hydrogen.
Previous innovation projects
We have undertaken several innovation projects looking at the feasibility of deploying electrolysers and utilising hydrogen in gas turbines and other assets to reduce emissions before hydrogen is available in the NTS. Green hydrogen from electrolysis is the best approach for emissions reduction but can be costly, so hydrogen production efficiencies should be maximised.
Working with stakeholders and beyond incremental innovation
The project has engaged with National Gas Transmission internal teams including Subject Matter Experts in Rotating Machinery, Operations and Policy and Regulation to help define the system requirements, as well as other networks to understand their needs. The project has also engaged with other SIF projects to share knowledge and experience, including UKPN's 'Connectrolyser', WWU'sNextGen Electrolysis and NGT's Hybrid Storage System projects.
Project Innovative Aspects
The application of waste heat recovery on gas turbines is not new but the application for National Transmission System (NTS) assets has not previously been investigated. The integration of waste heat recovery with solid-oxideelectrolysers (SOE) has not previously been considered and could provide an optimised hydrogen source for many applications. SOE is a relatively new technology which is looking to demonstrate capability in 2023 alongside theDiscovery and Alpha phase of this project to enable full demonstration of the system in 2024.
State of the Art
PEM and alkaline electrolysers are currently more established technologies but less efficient than SOE, leading to less hydrogen produced for every unit of electricity utilised and increasing the overall cost of hydrogen. Waste heat recovery is not currently deployed on NTS assets and doing so could enable SOE for hydrogen production as well as other applications including hydrogen storageor electricity generation from steam turbines.
TRL, IRL and CRL
The integration of waste heat recovery with solid oxide electrolysers is a novelapplication;
TRL Discovery 2-3, Alpha 4-5 and Beta TRL 6-7
IRL Discovery 1-2, Alpha to 4-5, then up to 7 at the start of Beta
CRL Discovery 1-2, Alpha 4-5
Project Scale
The demonstration will take place on a low utilisation compressor station, reducing the CAPEX on equipment and minimising disruption, whilst allowing the increased efficiencies to be demonstrated on an active site. The project will consider different sites on the NTS to better understand the business case and wider roll out of the solution.
BAU
The proposed system is novel and low in TRL therefore it cannot be deployed as business-as-usual (BAU). The BAU alternative is limited by efficiency and therefore the business case is harder to justify. SIF funding will enable this technology to be accelerated into use across the 24 compressor stations. In the case that hydrogen does not become available in the NTS this solution will enable reduction in emissions whilst providing hydrogen for other users in the local area.
Counterfactuals
We have considered the deployment of PEM/alkaline electrolysers for onsite hydrogen production, however these solutions lack an innovative aspect. The chosen approach will result in increased hydrogen production efficiency as well as capturing waste heat from gas turbines which is currently released to atmosphere.
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Impacts and Benefits
Pre-innovation baseline
Compressors are critical assets on the National Transmission System (NTS), providing pressures and flows to meet demand for gas and provide flexibility on the network, in total 65 of 74 compressor units are driven by gas turbines, burning natural gas from the network, thereby emitting carbon dioxide. As this is the single largest source of emissions on the NTS, National Gas Transmission have an obligation to reduce these compressor emissions and are also required to meet the Medium Combustion Plant (MCP) directive by 2030.
Hydrogen is a potential solution which can be utilised as a fuel gas in most of the gas turbines to reduce emissions, however it is unlikely to be available in the majority of the NTS before 2030. An alternative is to produce hydrogen directly onsite from electrolysers, which can be done more efficiently in combination with waste heat recovery. The deployment of hydrogen as a fuel to our gas turbines by 2030 will enable them to be ready when hydrogen is transported in the network and prevents multiple investments into the assets.
Forecast benefits
The alpha phase will further develop the business case and the cost/benefitanalysis for this project. The benefits that we propose to track are as follows:
Financial - Electrolyser efficiency with waste heat recovery vs alternative commercially available system
From Discovery outputs, the efficiency of solid oxide electrolysers with waste heatrecovery is 40 kWh/kg hydrogen compared to "low temperature" PEM/Alkaline electrolysers at 54 kWh/kg. Therefore, less electricity is required to produce the same amount of hydrogen, leading to a lower levelised cost of hydrogen for solidoxide electrolysers with waste heat recovery. Over time, this would pay back the initial investment and provide lower cost hydrogen with no direct CO2 emissions.
Early calculations suggest initial savings of up to £36m could be achieved by utilising onsite electrolysis with waste heat recovery across the network whencompared with offsite electrolysis and H2 delivery by tube trailer. Furthermore, savings of up to £56m across the network over 20 years in general could berealised through the lower levelised cost of hydrogen.
More widely, there are currently 30 Avon gas turbines on the NTS which are earmarked for replacement in order to meet the MCP Directive as no alternative low emissions retrofit technology will be ready by 2030. If these units can be repurposed for hydrogen by 2030 (which would also necessitate adequate hydrogen storage and supply), National Gas could avoid replacing these units at a cost of ~£60m each, or £1.8Bn in total.
Environmental - System Emissions
In 2021, Avon gas turbines at compressor stations emitted around 106,000t CO2 from burning natural gas. If the fuel gas contained 20%vol hydrogen this would decrease emissions by ~7%, or alternatively could be eliminated if 100% hydrogen is used as the fuel gas. In the highest utilisation scenarios, using 100% green hydrogen could result in significant CO2 emissions savings of up to 12,000t per year per compressor. Using green hydrogen from electrolysis would mean there would be no indirect CO2 associated with the hydrogen production. Benefits could be seen during the beta phase, once the demonstration is operational, however most benefits will occur once the system has been deployed across multiple operational sites. We believe this could be through the ProjectUnion timeline of between 2026 and the early 2030s for the gas transmission network.
Benefit Synergies
A broader understanding of the wider system benefits will be achieved through working in conjunction with other SIF projects (HyNTS Hybrid Storage, Carnot
Gas Plant & Connectrolyser) to ensure alignment and that synergistic benefits arecaptured.
Impacts and benefits
Continuation outside of SIF
The project has identified a significant opportunity for NGT in terms of energy generation from the normal operation of our assets. Ultimately, the project was successful through SIF however the timelines for Beta did not align with the progress made through Discovery and Alpha. We now plan to take the findings from Discovery and Alpha into a Conceptual Design Study and preFEED to perform detailed optioneering for a demonstrator including defining a suitable location, scale and scope for any demonstrator. Additionally, we will also investigate the site-specific cases for heat recovery across the network in more detail to full define the business case.
Progress towards benefits
One of the initial benefits identified was the emissions savings from generating hydrogen. The project concluded that steam generated from heat recovery could be used to generate electricity and subsequently to produce hydrogen through electrolysis. We learnt that although up to 4.8MW electricity could be generated at maximum turbine load to feed to an electrolyser, this would only equate to around 8% emissions reduction if all of this hydrogen was blended into the fuel gas. Different electrolyser types were investigated to determine which would offer the best option for integration with heat recovery. It was found that this is dependent on the compressor utilization. For higher utilization sites, a solid oxide electrolyser would be more suitable as this offers increased efficiency of hydrogen production, however it benefits from the input of heat from an external source. For lower utilization sites where heat recovery is not as high or consistent, a PEM/alkaline type electrolyser would be more suitable, as keeping the solid oxide system at temperature would require external energy and this has carbon associated with it.
Another key benefit identified was the reduced cost of operating the network. By recovering waste heat and using this for any usecase, we would see an increase in the efficiency of our compressor units as the energy consumed by the compressor unit as fuel would be more fully utilized. The efficiency of the unit could increase by 10-12% compared to current operation. The use of waste heat to generate steam, electricity or hydrogen could result in revenue streams for NGT. We are exploring the different ownership options for the heat recovery system. NGT could own the system but are currently restricted by the Gas Transporters License conditions around generation. A third party could own and operate the heat recovery system and NGT would generate revenue from lease of land etc. Any revenue generation would be passed onto the consumer.
Key figures associated with heat recovery at compressor stations
· The operation of compressor stations produced around 240,000 tonnes CO2 and 3,000 TJ energy was lost as heat in 2021.
· Around 20MW steam can be generated at maximum gas turbine power. Although not explored in Alpha, we are investigating the possibility of feeding this steam to heat networks.
· If fed through a steam turbine generator, the heat could generate up to 4.8 MW electricity.
· A 4.8MW electrolyser could produce around 100kg hydrogen per hour. If fed into the fuel gas stream this hydrogen would equate to a maximum of 20% by volume, or ~8% by energy, resulting in up to ~8% CO2 emissions reduction by feeding the hydrogen directly into the fuel gas system.
· The electricity generated from compressor stations would be more than enough to satisfy the site power demand, reducing NGT’s imported power requirements and subsequently energy bills. This means that any surplus electricity could be exported via local distribution networks or private wires.
Regardless of the usecase, capture of waste heat and generation of energy (steam, electricity, hydrogen) would require NGT to investigate the Gas Transporters License conditions around generation. Currently, production and supply is prohibited for the Gas Transporter however National Gas are now separated from electricity transmission and are therefore independent of electricity transmission and there is no longer any conflict of interest.
