Emission Limit Values for Hydrogen and Non-Conventional Fuels

Emission Limit Values (ELV) for combustion plants burning Hydrogen

The EA and other regulators (NRW, SEPA, NIEA) are working on a project to set some guidance for operators who wish to burn hydrogen in a combustion plant and who will require a permit to do so. The current legislation that applies under the umbrella of the IED, the MCPD and BAT material makes scant reference to Hydrogen as a fuel.

The current project which is scheduled to be completed by the end of March is to provide users and manufacturers with some definitive ELV guidance and some technical assistance when assessing hydrogen combustion projects or retrofits.  The overriding principle is that there should be no more NOx emitted from Hydrogen burning compared to an equivalent combustion process using natural gas.

The Regulators recognise that many such guidance notes are provided as Best Available Techniques (BAT) but in this instance there is little or no availability of data to say what is ‘best’, so the published document will be GET, Guidance on Emerging Techniques.

There are many detailed technical discussions still to be had relating to the way hydrogen burns, the precise pollutants that are created, the concentrations of NOx produced, and the methods of measurement, as examples, but early indications are that a set of ELVs in bands will be provided.   This may yet prove problematical as issues such as the percentage of hydrogen planned to be introduced into the UK Gas grid, the non-linear relationship between %H₂ and NOx emissions (peak NOx at 90%H₂ approx.), and that 100% H₂ as a gas is probably unachievable in practice are some of the sticking points.

Dynamic ELVs are not favoured – they lead to excessive cost in measurement, possibly needing fuel mix analysis, and add a layer of unnecessary complexity.  The proposed bands on a volume basis are therefore

0 – 20% H₂;   20 – 50% H₂;   50 – 80%H₂;   80 – 100% H₂,

The baseline ELVs for specific plant items burning nominally 100%H₂ are proposed as “current gas firing ELV x 1.37” – other blends are to be calculated.

Proposed NOx ELVs mg/Nm3 blend % hydrogen

	100% nat gas	75% gas 25% H2	50% gas 50% H2	25% gas 75% H2	100% H2
Existing plant
Boiler >50MWth	100	109	118	128	137
Boiler 5-50MWth	200	219	237	255	274
Boiler 1-5MWth	250	273	296	319	343
New plant
Boiler >50MWth	100	109	118	128	137
Boiler 5-50MWth	100	109	118	128	137
Boiler 1-5MWth	100	109	118	128	137

Proposed Emission Limit Values for Hydrogen and Non-Conventional Fuels

Comments on these proposals raised at recent consultation included:

• For new boilers, FGR would be important, but ELVs should be achievable.
• For existing boilers, fuel input and physical size of the furnace is fundamental to NOx generation.
• Burner design is important but likely that replacing the entire boiler or derating would be the only means to meet proposed ELVs.
• Where physically possible FGR will likely be required
• Likely that new burners would be required
• In all likelihood replacing boilers might be more feasible
• Cross-sensitivity of CO monitors with H₂ may mean that CEMS may need to be replaced where fuel blends are used.
• Flue gas water vapour will increase with H₂ combustion, but is believed to remain within the design range for extractive CEMS
• Consideration for other greenhouse gases produced
• Early adopters may need to maintain the ability to operate on backup fuel
• Older equipment may need analysis on suitability of combustion chamber, weld design etc.
• Wider considerations to site, e.g. pipework, skids, flange/gasket designs and valves
• Fuel gas flow meters might be required
• Safety systems, e.g. fugitive gas detection, exclusion zones

In summary:

• New boilers are likely to be able to comply with proposed ELVs
• Existing plant are likely to rely on abatement and modifications to meet proposed ELVs
• There are decisions to be made regarding what is to be considered ‘existing’ plant – the clock may be reset to start again at the time the guidance is confirmed

This an important piece of work that will be discussed again at the next Hydrogen ELV Working Group in early March.  Any burner or boiler maker, or any potential user of Hydrogen in their combustion processes, should be contributing to this debate urgently so that the final outcome is understood and agreed – you get what you negotiate!

Further information from [email protected] and [email protected] – they will be pleased to hear your comments and will add you to the list of participants for the next meeting if you wish to contribute.