Guidance

Hydrogen production by electrolysis of water: emerging techniques

Emerging techniques on how to prevent or minimise the environmental impacts of hydrogen production by electrolysis of water.

From:
Environment Agency
Published
28 March 2024

Emerging techniques are novel techniques for an industrial activity that, if commercially developed, could provide one of the following:

  • a higher general level of protection of the environment
  • at least the same level of protection of the environment and higher cost savings than existing best available techniques

This guidance is for production of hydrogen by electrolysis of water. This is an emerging technique.

You may need to prepare the hydrogen for:

  • use on site
  • export as a product

These activities are outside the scope of the guidance and you should discuss other permitting requirements with your regulator.

These environmental regulators (referred to as ‘the regulators’) worked with industry and other stakeholders to develop a review of emerging techniques which informs this guidance:

  • Environment Agency
  • Natural Resources Wales
  • Scottish Environment Protection Agency
  • Northern Ireland Environment Agency (an executive agency of the Department of Agriculture, Environment and Rural Affairs)

Except where regulations apply, this guidance on emerging techniques is not a regulatory requirement but identifies best practice to address important environmental issues.

The regulators expect operators to follow this guidance, or to propose an alternative approach to provide the same or greater level of protection for the environment.

1. Who this guidance is for 

This guidance is for:

  • operators when designing and operating their plants and preparing their application for an environmental permit
  • regulatory staff when determining environmental permit applications
  • any other organisation or members of the public who want to understand how the environmental regulations and standards are being applied

This guidance covers all sizes of industrial plant (installations) producing hydrogen by electrolysis of water.

The guidance covers both new plants and variations (changes) to existing plants.

When you apply for an environmental permit for this activity, you must tell your regulator whether you are going to follow this guidance. If not, you must propose an alternative approach which will provide the same or greater level of protection for the environment.

In the UK, these installations are permitted under the:

  • Environmental Permitting (England and Wales) Regulations 2016
  • Pollution Prevention and Control (Scotland) Regulations 2012
  • Pollution Prevention and Control (Industrial Emissions) Regulations (NI) 2013

For environmental permitting purposes, the hydrogen production plant is a:

  • Part A (1) 4.2 (a)(i) inorganic chemicals activity in England and Wales
  • Schedule 1, Part A 4.2 (a)(i) inorganic chemicals activity in Scotland and Northern Ireland

Some plant may be eligible for a simplified permitting process, a low impact installation or standard rules permit, where available. You can check with the environmental regulator for your plant location. For relevant guidance:

There are no existing best available techniques (BAT) reference documents (BREFs) or guidance which specifically cover the production of hydrogen from water by electrolysis.

Where BAT for an activity is not covered in existing BREFs or where all the potential environmental effects are not addressed, the regulator must follow Article 14(6) of the Industrial Emissions Directive (IED).

This means that the regulator must set permit conditions including emission limit values (ELVs) for direct emissions to the environment, together with other permit conditions. These conditions must be based on the regulator’s own assessment of emerging techniques using the criteria listed in Annex III of the IED. They should also consult with operators before setting these conditions. The regulators consulted industry and other stakeholders when developing the review of emerging techniques on which this guidance is based.

Permits must protect the environment by setting conditions to make sure operators do not breach any environmental quality standards (Article 18 of the IED).

Your regulator may grant a temporary derogation of BAT-associated emission levels (BAT AELs) for up to 9 months, on the basis that hydrogen production by electrolysis of water is using an emerging technique (see Article 15(5) of IED). (Derogation means having less strict emission limit values in the permit than the emission levels associated with the best available techniques.) You should discuss this with your regulator if this is likely to apply. 

Your regulator will decide on the emission limits and other permit conditions that will apply on a case-by-case basis. They will do this based on the elements outlined in this guidance and the most appropriate source of reference. This is unless you can show that you can comply with an appropriate standard rules permit, where available.

The review of emerging techniques summarises the available evidence used to inform this guidance. We refer to the relevant sections of the review in this guidance. 

2. Technique selection

When designing a hydrogen production plant and its associated activities, you should consider its overall environmental performance.

You should justify your choice of technology at each stage using the principles of ‘best available techniques’ throughout your permit application including:

  • energy demand and efficiency
  • water demand, efficiency and evaluation for re-use
  • emissions to the environment

These are the hydrogen production by electrolysis methods the regulators considered when producing this guidance:

  • alkaline electrolysis (ALK)
  • polymer or proton electrolyte membrane (PEM)
  • solid oxide electrolyser cell (SOEC)

The guidance may also be generally applicable to other types of electrolysers using water for hydrogen production. Consider it where appropriate.

The choice of technology will determine, for example, the energy required for compression. The selection will depend on the difference between the electrolyser system operating pressure and the pressure required by the user.

This guidance covers activities to prepare hydrogen ready for:

  • use of hydrogen on site
  • export of hydrogen as a product

These activities are outside the scope of the guidance and you should discuss other permitting requirements with your regulator.

Other associated activities may include:

  • feed water treatment
  • hydrogen purification and compression
  • storage of hydrogen
  • electrolyte treatment and recovery (where ALK technology employed)
  • effluent treatment
  • flaring and venting
  • cooling and heat recovery
  • steam systems (where SOEC technology employed)

For more information, see the review of emerging techniques section 4.2 on overall system design and integration. 

3. Plant design and operation

3.1 Operation

You must consider whether your hydrogen production plant may need to operate in steady state or on a flexible basis to balance variations in, for example:

  • supply of power to the plant
  • demand from hydrogen users

You should consider whether this need for flexibility will affect the design, operation and maintenance of the plant.

You should identify all operating scenarios. Include those due to providing flexible operations where environmental performance could be affected, or where additional emissions are expected. For example, these could be because of changes in demand, or start-up and shutdown.

You should describe measures you would take to minimise the environmental impact of these scenarios. These could result in, for example:

  • reduced energy efficiency
  • reduced water efficiency
  • increased emissions to air, including venting and flaring
  • increased effluent or wastes produced
  • increased risk of accidents in non-steady state conditions

3.2 Reliability and availability

You will need to identify the equipment and systems, and their associated operating and maintenance techniques, that are critical in avoiding emissions or minimising environmental impact. You will need to design, operate and maintain these to make sure they are reliable and available. This should include providing installed back-up equipment, where necessary.

You should implement a risk-based other than normal operating conditions (OTNOC) management plan. This should identify potential scenarios, mitigation measures, monitoring and periodic assessment of the OTNOC management plan. This should be part of your environmental management system.

3.3 Energy efficiency, process efficiency, cooling

You should design, operate and maintain your hydrogen production plant to maximise:

  • energy efficiency (minimise the energy needed to produce each tonne of hydrogen)
  • process efficiency (minimise the raw materials needed to produce each tonne of hydrogen)

You should consider the use or recovery of oxygen by-product when this is commercially and technically viable.

To decide on best available techniques for your plant, you will have to balance how you achieve these efficiencies to optimise the environmental and economic requirements. You must explain how you have done this and what your considerations were.

Main energy users will include:

  • electrolysers
  • hydrogen compressors
  • hydrogen purification
  • pumping or fan systems

You should consider:

  • electrical power needs and whether you will import or generate on site
  • high pressure steam need and availability (SOEC)
  • maximising any residual waste heat recovery
  • cooling needs
  • cooling type and medium
  • energy recovery devices on high pressure fluids, for example, reverse osmosis effluent, where applicable

For more on this, see section 3.4 on water supply and use.

You should also consider heat integration optimisation. For example, heat recovery at higher temperatures from hydrogen compression systems for power generation or drives, where this is feasible.

You should reference the BREF documents, where appropriate:

For more information, see the review of emerging techniques:

  • section 4.8.1 on electrolyser operation and performance
  • section 4.9 on heat recovery and cooling systems

3.4 Water supply and use

Water supply and its efficient use is a fundamental aspect of hydrogen production by electrolysis of water.

The quality of the water supply will determine the treatment needed before it can be used as a:

  • raw material in hydrogen production by electrolysis
  • heating medium (such as steam)
  • cooling medium

Water is consumed in the process to make hydrogen in a minimum ratio of 9kg of pure water per 1kg of hydrogen gas produced. The remaining 8kg is oxygen as a gas.

However, the gross quantity of water you bring into the installation needed per kg of hydrogen will be dependent on:

  • your choice of electrolysis method
  • the quality of the water which you use as your supply for the electrolysis process
  • the quantity of water you recover, recycle and re-use
  • the quantity of water which is discharged as a liquid effluent or gaseous emission to atmosphere
  • the cooling technique you use

You should:

  • minimise the quantity of water you use
  • segregate, treat and re-use water where possible
  • identify how much contaminant needs to be removed to maintain the water quality necessary for effective operation
  • determine the quantity of water to be purged, the characteristics of that purged water, and design the treatment process accordingly
  • eliminate, minimise or treat any emissions to air or wastes that may result from the water treatment process
  • choose a cooling method that takes account of the impact of temperature on process performance, energy efficiency and environmental impact on the receiving medium

For more on this, see section 5 on emissions to water.

The review of emerging techniques also has more information on this in section 4.3 on water.

3.5 Electricity supply

The source of power supply is not within the scope of this guidance. However, supply issues can affect the environmental performance of the hydrogen production process, such as through availability and variability. You should take this into account when you design and operate the hydrogen plant to eliminate or mitigate any environmental impact. 

It is likely that transformers and rectifiers, where needed as associated activities, would be considered part of the installation.

For more information, see the review of emerging techniques section 4.5 on electricity.

3.6 Hydrogen purification

Your hydrogen purification requirements will depend on:

  • the hydrogen product quality specification
  • the production technique chosen
  • residual impurities in the hydrogen

The impurities may include:

  • oxygen
  • water
  • other trace gases

You should consider which other purification processes are appropriate, depending on the specification of hydrogen required. These may include:

  • deoxidiser system
  • dehydration system
  • other purification processes

You should describe and justify your choice of techniques and the relevant aspects which will affect environmental criteria. For example:

  • consequential wastes and emissions
  • any recovery or treatment required

For more information, see the review of emerging techniques section 4.7 on hydrogen product specification.

4. Emissions to air

You should identify, eliminate, minimise or reduce any emissions to air that could cause pollution.

You should carry out a risk assessment, including detailed air quality modelling where appropriate, to assess the impact of these emissions.

You should refer to the guidance relevant to the location of your plant in the UK through the information on air emissions risk assessment for your environmental permit.

4.1 Emissions of hydrogen

Hydrogen has been identified as an indirect greenhouse gas and so is considered a pollutant.

You should design and operate your plant to achieve the following, which are listed in priority order. (Where technically and economically viable, and ensuring safety is not compromised.)

  1. Prevent or avoid emissions of hydrogen.
  2. Recover or recycle hydrogen.
  3. Avoid or minimise continuous or intermittent flaring of hydrogen.
  4. Avoid or minimise continuous or intermittent venting of hydrogen, whether for operational or safety reasons.

You should consider using these techniques to achieve this:

  • designing and operating your plant to maximise equipment availability and reliability
  • designing and operating your plant to minimise the frequency of and amount of hydrogen purged, including during change of production rate, start-up and shutdown, abnormal operations and preparation for maintenance
  • use of buffer storage of out of specification hydrogen or hydrogen product during start-up and shutdown to minimise intermittent operation
  • recovery of hydrogen
  • treatment of hydrogen, for example, by recombination with oxygen or storage and purification of purged hydrogen
  • flaring rather than venting of hydrogen, where emissions cannot be eliminated and where practicable
  • designing flaring devices to ensure efficient combustion of hydrogen
  • venting hydrogen safely, where the above techniques are not practicable

You should explain your design and operational considerations behind your proposed techniques, including how you have considered overall environmental impact of their use.

4.2 Other emissions from venting or purging

You should quantify and assess other venting and purging requirements, identifying any pollutants that are expected to be present.

Requirements for other continuous venting during normal operations may include, for example:

  • waste oxygen (which may contain hydrogen)
  • water vapour
  • deaeration of steam condensate
  • gases from processing wastewater streams
  • purge of tanks, vent or flare headers

Requirements for intermittent venting may include, for example, venting needed as part of the process of purging equipment for maintenance activities. Such as nitrogen purges which may contain hydrogen.

4.3 Other pollutants

You should identify, quantify and assess other pollutants. These may include, for example, nitrogen oxides (NOx) and hydrogen from flaring of hydrogen.

For more information, see the review of emerging techniques:

  • section 4.4 on flaring and venting
  • section 4.8.2 on lifetime, reliability and availability

5. Emissions to water

You must identify and eliminate, minimise, recycle or treat any emissions to water that could cause pollution.

You should carry out a risk assessment, including detailed modelling where appropriate, to assess the impact of these emissions.

For emissions to surface water, you should refer to the guidance relevant to the location of your plant in UK through the information on surface water pollution: risk assessment for your environmental permit.

5.1 Wastewater treatment

You should identify continuous and periodic effluent streams from the process and determine whether effluent treatment is required. These streams may include waste streams from water pre-treatment processes, cooling and steam systems, including:

  • effluent from reverse osmosis containing ions from the feed water
  • effluent from continuous deionisation
  • effluent from desalination
  • purges from cooling water systems
  • purges from condensed water from steam systems

These will contain contaminants, which may need treatment or removal before discharge, for example:

  • high salinity effluents
  • metal ions

You should decide how much water to treat and how to treat it before it is:

  • re-used
  • discharged to surface water or sewage undertaker
  • disposed of

You should identify how much contaminant can be removed to comply with discharge requirements and design the treatment process accordingly.

You should identify any unavoidable emissions to air or wastes that may result from the water treatment process. Ensure they are minimised or treated appropriately.

You should treat water for re-use, where practicable.

You should refer to the appropriate BREF, BATC and guidance:

6. Emissions to ground and groundwater

You must design your process to avoid emissions to ground and groundwater.

For more information, see section 8.3 on monitoring emissions to ground and groundwater.

7. Waste

Before considering waste disposal, as far as practicable you must follow the waste hierarchy and:

  • prevent
  • minimise
  • re-use
  • recycle
  • recover
  • treat

You should consider how to deal with the following wastes that may be generated and justify your choice following this waste hierarchy.

7.1 Liquid wastes

Liquid wastes such as:

  • waste alkaline solutions, for example, potassium hydroxide
  • any residual liquid wastes from the water treatment processes

7.2 Solid wastes

Solid wastes such as:

  • spent adsorbent materials from gas treatment, dehydration, hydrogen purification
  • spent or damaged membranes
  • catalyst materials
  • other solid consumables, for example, electrolyser components such as seals

8. Monitoring and reporting

The main purpose of monitoring is to:

  • appropriately control the process to ensure compliance with the permit
  • show that emissions to air, water or land from the process are not causing harm to the environment

You must also carry out process monitoring to show that resources are being used efficiently. This may include:

  • energy efficiency
  • water efficiency
  • resource efficiency, for example, electrolyser consumables
  • verifying (when applicable) compliance with low carbon hydrogen standards, including any requirements relating to emissions of hydrogen

Your permit application should include a monitoring plan for:

  • routine operation
  • commissioning, where appropriate

You may need to do more extensive monitoring during the commissioning phase than during routine operation. As these production techniques for hydrogen by electrolysis of water are emerging techniques, you may need to develop monitoring methods and standards.

Where relevant, during the commissioning phase, you will need to assess any monitoring results and optimise the operation of the process. You may need to report on:

  • your commissioning phase monitoring results
  • your assessment of the results
  • any changes you want to make to the operation

You must report on emissions and process monitoring as stated in your permit.

8.1 Monitoring point source emissions to air

You should eliminate or minimise emissions of hydrogen due to their global warming potential.

You should provide a monitoring plan for monitoring emissions to air, based on expected pollutants such as hydrogen.

You should do this using appropriate methods and measuring techniques.

Your monitoring should consider, for example, any other sources of hydrogen emissions, such as venting and fugitive emissions, including vented oxygen.

8.2 Monitoring emissions to water

You must monitor emissions to water based on expected impurities using appropriate methods and measuring techniques.

You should use monitoring standards for discharges to water following BATC for common waste water and waste gas treatment/management system in the chemical sector.

8.3 Monitoring emissions to ground and groundwater

Though the life of the permit, your regulator may require a:

  • site condition and baseline report
  • soil and groundwater monitoring plan

You should seek advice from the appropriate regulator.

8.4 Monitoring standards

The person who carries out your monitoring must be competent and work to recognised standards, such as the monitoring certification scheme (MCERTS).

MCERTS sets the monitoring standards you should meet. You can use another certified monitoring standard, but you must provide evidence that it is equivalent to the MCERTS standards.

You must use a laboratory accredited for the required analysis method by the United Kingdom Accreditation Service (UKAS) to carry out analysis for your monitoring.

You should also refer to the JRC reference report on monitoring for IED installations.

8.5 Monitoring process performance

You should identify the main requirements for monitoring process operations where these ultimately impact on environmental performance. This includes:

  • energy consumption per kg of hydrogen product
  • water consumption per kg of hydrogen product

You should monitor energy efficiency in the hydrogen production by measuring energy consumption per kg of hydrogen produced to calculate overall energy consumption.

You should monitor overall water use by quality of water and purpose of use by carrying out a water balance across the installation. This is to:

  • identify opportunities for reduction in water use, where technically and economically feasible
  • consider other environmental impacts, such as energy efficiency

Requirements for process performance monitoring which relate to environmental performance, either continuous or periodic, may also be a condition of the permit. For example, frequency of operations leading to additional emissions.

9. Unplanned emissions and accidents

You should design your plant to:

  • inherently avoid leaks by good design practice
  • ensure the plant is operated and maintained to appropriate industry standards

You should propose a risk-based leak detection and repair (LDAR) programme that is appropriate for the fluids and their composition. This should use available industry best practice to minimise releases, including from:

  • joints
  • flanges
  • seals
  • glands

You should include how you will use the principles of LDAR to eliminate or reduce fugitive emissions of hydrogen due to its global warming potential.

Your hazard assessment and mitigation for the plant must consider the risks of accidental releases to the environment.

10. Noise

You should consider sources that have potential for noise and vibration. Hydrogen compression, pumps and fans could be significant sources.

Please refer to the guidance on noise and vibration management: environmental permits.

11. For more advice from your regulator

You can request advice before applying for your permit.

For more advice from your regulator, in:

Updates to this page

Published 28 March 2024

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