Gas Transmission and Metering (GT&M) are committed to reducing emissions from the operation of the National Transmission System (NTS) and eliminating emissions by 2050. The transition to hydrogen provides an opportunity to reduce carbon emissions at compressor sites. The use of hydrogen as a fuel gas was investigated in the Hydrogen Fuel Gas project and it was concluded that the use of hydrogen would significantly increase the volume of NOx emissions. This conclusion was based on the temperature of a diesel flame, as no experimental work has been undertaken on a NTS gas turbine. The project will aim to quantify the NOx & CO emissions from an aeroderivative gas turbine fuelled with hydrogen and investigate potential options for emissions abatement.
Benefits
As the benefits of this project will be environmental it is difficult to quantify the benefits. The opportunity to fuel a gas turbine with hydrogen at NTS sites would reduce carbon emissions generated. The project will also inform the hydrogen strategy for the NTS.
Learnings
Outcomes
This project has quantified the NOx emissions from combustion of hydrogen blends and 100% hydrogen in a test rig representative of NGT’s gas turbine fleet. It was found that, in the worst case scenario, that NOx could increase by ~400% compared to natural gas, significantly more than the diesel flame model predicted. For blends of around 25% hydrogen, the NOx remained below the typical site permit limit. However for blends >60% hydrogen the NOx was seen to increase rapidly. Carbon monoxide emissions were measured however were insignificant in all test scenarios primarily due to the high combustion efficiency of the test combustor. With hydrogen being a non-carbon based fuel, it is unlikely that CO will increase with increasing hydrogen blends in the fuel gas.
The project has highlighted several NOx abatement methods which NGT could deploy on the fleet in order to comply with environmental regulations. Steam injection was investigated and showed to decrease NOx by 63% in the worst hydrogen case. Exhaust gas recirculation was also investigated and resulted in a decrease in NOx of 81.5% for the worst hydrogen case. Direct water injection was also trialled but resulted in limited NOx reduction compared to the other abatement solutions. This means NGT can deploy hydrogen as a fuel gas to reduce CO2 emissions whilst remaining compliant with NOx levels.
The exact requirements for NOx abatement technology and deployment will depend on the development of Project Union and blending across the NTS. It is likely that low blends will not require NOx abatement. However for high blends and 100% hydrogen, NOx abatement will be required. Dry Low Emissions technology is a relatively simple solution with minimal additional equipment and ongoing maintenance requirements, and would be the preferred solution for Siemens Energy units. A site-by-site assessment should be undertaken to determine the most suitable solution for a given site.
Value tracking Data Point Data Point Definition
Maturity TRL4 Bench scale testing has been carried out to prove the concept.
Opportunity 100% of single asset class The findings can be applied to all gas turbines on the NTS compressor fleet.
Deployment costs £3,000,000 An indicative cost estimate of £3m per unit was provided, relating to ~£300m if deployed across the NTS.
Innovation cost £192,573 This cost covers experimental preparation, execution of experimental campaign, reporting, desktop review of NOx abatement, and project management activities.
Financial Saving - There may be financial savings associated with the reduction in NOx emissions from the solution however this is not yet known.
Safety - The solution will not improve safety.
Environment 240,000 tonnes CO2 Enabling hydrogen as a fuel gas could result in a CO2 saving of 240,000 tonnes however NOx abatement will be required. Reducing the NOx emitted also has environmental and health benefits.
Compliance Ensures compliance The solution will ensure NGT are compliant with relevant environmental permits for compressor stations.
Skills & Competencies No change There will be no change in skills and competencies from the project solution.
Future proof Must have for business strategy This work supports the use of hydrogen as a fuel gas in NTS compressors which supports the strategy of repurposing the NTS for hydrogen.
Lessons Learnt
Technical learnings
· The average increase in NOx for 25%vol hydrogen blend fuel gas was 18.7%. Although not insignificant, this increase in NOx could be managed by deploying in-combustor abatement solutions or DLE technology.
· The average increase in NOx for 100% hydrogen fuel gas was 404%. This is significantly higher than the 125% increase predicted by the diesel flame model. Steam injection offered significant NOx reduction for 100% hydrogen although it may not be sufficient to meet current site permit levels for NOx. Exhaust gas recirculation was highly effective in reducing NOx for 100% hydrogen, with an indicative reduction to acceptable levels.
· In-combustor abatement solutions such as steam injection and exhaust gas recirculation could be effective NOx reduction solutions, however they require significant upgrades to units and there is potential for increased corrosion due to water present in the combustion system. There is ongoing OPEX associated with these solutions.
· The desktop review presented other post-combustion solutions such as Selective Catalytic Reduction and Selective Non-Catalytic Reduction. These solutions could reduce NOx effectively however they come with increase CAPEX and OPEX and additional complex operation and maintenance and footprints.
· DLE is a simple combustor modification being developed by Siemens Energy and other OEMs for hydrogen duty. With limited installation costs and much lower OPEX, it is the preferred solution for the NGT GT fleet.
· DLE was not investigated experimentally as only in-combustor abatement solutions were tested. DLE should be investigated experimentally, if possible, to validate it’s effectiveness in reducing NOx generation compared to steam injection and exhaust gas recirculation.
Project delivery learnings
· There were significant contracting delays which caused delays to the start of the project. This resulted in added risk for Cardiff and the delivery of the test campaign and managing other projects, given the limited capacity of the test facility and having to be set up for a specific test. Future projects will now ensure the contract template is issued to new suppliers well in advance (at the Request for Quotation stage) and for repeat suppliers, a previous contract should be agreed as the basis of the upcoming project.
· The proposed test plan and methodology was reviewed by Siemens Energy experts, which gave confidence that the results would be representative of NGT’s Siemens Energy gas turbine fleet.
