How Smart Instruments are Opening the Way for Green Hydrogen Production
Published on : Thursday 04-08-2022
Digital instruments can help ensure the hydrogen production process is safe, efficient and productive, says Cornelia Huber, Head of Global Communications and Marketing for ABB Instrumentation.
The concept of using green hydrogen as a sustainable fuel source is finding increased favour as companies and governments look for new ways to transition away from conventional fossil fuels. In this article, Cornelia Huber, Marketing Manager, ABB Instrumentation, looks at some of the key stages in the green hydrogen production process, and the role that measurement instruments and analysers can play in helping to address some of the challenges that can occur.
A combination of geopolitical, security and environmental factors are driving countries worldwide to accelerate the development of alternative fuel sources such as hydrogen as they seek ways to reduce their reliance on polluting fossil fuels. Offering many of the advantages of both – renewable energy and fossil fuels – hydrogen can be produced with low or zero emissions using wind, solar or hydropower and can be readily stored and transported. As a clean burning fuel, it produces only water as a by-product.
Developments in electrolysis technology and the falling cost of renewable energy resources are seeing a rising interest in the potential of ‘green hydrogen’ as a clean and sustainable form of fuel production. The Indian government for example plans to add 175GW of green hydrogen-based energy over the next decade to help sustainably meet the energy demands of its growing population [1].
Producing green hydrogen
Basically defined, green hydrogen production relies on electrolysis to split water into hydrogen and oxygen, with the necessary electricity for the electrolysis process provided by renewable sources such as wind, solar or hydroelectric power.
Carrying out electrolysis, especially on an industrial scale, presents several challenges that need to be addressed throughout the hydrogen production process, including ensuring and maintaining safe operation, achieving efficient power to hydrogen conversion, and controlling the hydrogen gas purity to achieve the highest end quality.
Smart measurement makes the difference
As in any industrial process, measuring multiple parameters as extensively as possible throughout the production of green hydrogen will provide the data needed to achieve safe and efficient performance.
Today’s smart digital measurement technologies enable greater accuracy, range and depth of information that can provide a highly detailed picture both of operating conditions and the status of the measurement devices themselves, especially important in preventing unexpected problems such as faults or failures in safety-critical applications.
Key benefits include remote connectivity, which make diagnostics information more usable, and enable actions such as fault tracing or changes to an instrument’s configuration without an engineer having to be physically present. Greater predictivity also facilitates proactive maintenance and allows process problems to be resolved before they escalate, avoiding unnecessary downtime and minimising the risk of potential damage to key process plants.
Digital instruments also offer enhanced simplicity, making it easier for operators at any level of experience to access or relay key operational and maintenance-related data. An example is the use of QR codes, which can be scanned using a smartphone or tablet to enable data to be sent about the instrument to its manufacturer who can then offer remote assistance to change a setting or fix a fault.
Optimising performance
Green hydrogen production processes feature several stages, each requiring accurate measurement of a variety of parameters to ensure safe and efficient operation. The following covers some of the key measurements that need to be carried out and the options available to help measure them.
Gas quality requires close monitoring
Essentially, electrolysers produce oxygen at the anode and hydrogen at the cathode – however, many reactions in the electrolyser can cause small concentrations of oxygen to build up in the hydrogen stream and hydrogen to build up in the oxygen. This is a fault condition and must be detected by appropriate instruments.
This can be solved by using a gas analyser with the sensitivity needed to detect quantities of hydrogen and oxygen to very low levels. ABB’s EasyLine EL3060 gas analyser for hazardous area applications, for example, incorporates different options for accurately measuring hydrogen down to 0–1 vol.-% and oxygen to 0–10 vol.-%. As such, it can be used to measure both traces of hydrogen in the oxygen stream and traces of oxygen in the hydrogen stream.
The analyser also features QR code displays for easy checking of the system configuration and the health of the analyser, a useful attribute for CEMS instruments which need constant availability.
Liquid level monitoring in the phase separator
Another critical task is monitoring the electrolyte vapours which are carried over from the electrolyser cell. Hydrogen is then cooled, and a second separation removes the condensate.
In a vertical vessel, hydrogen is vented from the top, while liquid from the base is pumped and recirculated to the electrolyser. The risk is that hydrogen can enter the pump then flow to the wrong part of the electrolyser, making it crucial to monitor the water level in the knock-down phase separator.
It is important to use a device that can safely measure level whilst also being able to withstand obstacles including high pressures and temperatures as well as the risk of corrosion, all three of which can occur in hydrogen applications. One solution is to use magnetic level instruments, including magnetic switches and sensors to measure low and high levels in the phase separator. By isolating the device from the process medium, magnetic level measurement offers an ideal non-contact solution for measuring levels in the phase separator, while also eliminating the need for costly seals, diaphragms, and process connections commonly associated with point level switch technology. Set points can be adjusted without any changes to process piping, resulting in level switches that are quickly deployed, readily adjustable and easy to maintain.
Preventing overheating at the electrolyser
Where an electrolyser is fed with variable renewable electricity from a solar park or wind farm, there is the risk that the conversion process may ramp up with the electricity availability to produce more hydrogen. As this happens, the current drawn by the electrolyser increases, causing the stack temperature to rise. To prevent this, it is necessary to continuously measure stack temperature to enable effective control of cooling to maintain levels within safe limits. This can be achieved by combining a platinum resistance thermometer with an appropriate transmitter to give a reliable temperature measurement and alarm solution. This can be augmented by the additional continuous sensor monitoring and self-monitoring features included in the latest generation of transmitters, which can be used to provide information about supply voltage and issues such as wire breaks or corrosion.
The same solution can also be applied to monitor and control temperatures at the de-oxo stage, where traces of oxygen in the hydrogen are converted to water in an exothermic catalytic reaction to create the final hydrogen product. At this stage, it is essential to monitor the temperature to ensure that the reaction remains under control and that conditions remain within safe limits.
Safe, efficient electrolyser pressure control
Some types of electrolysers are designed to operate at elevated pressure. This is especially important if the gas is to be used at high pressure because pumping the liquid water feed to the electrolyser to an elevated pressure such as 30 bar is both less costly and much less energy intensive than compressing the hydrogen gas from atmospheric pressure to 30 bar after the electrolyser. Installing a device such as ABB's 261GS digital pressure transmitter in the water circuit can help to ensure that pumping pressures are maintained.
Accurate and reliable pressure measurement is also important in maintaining process safety by preventing over-pressurisation of the electrolyser and ensuring that hydrogen and oxygen gases generated by the electrolyser are flowing away without obstruction. For pressure measurement of the oxygen and hydrogen gases, ABB’s 266GST and PGS100 series can provide a solution. Both are certified by TUV NORD for use in process safety control systems according to the IEC61508 standards series on functional safety and meet the requirements for SIL2 applications when specified with a single transmitter configuration and for SIL3 applications when a redundant configuration is chosen, making them ideally suited for protecting pressurised electrolysers.
Another issue that can affect pressure transmitters in hydrogen applications is the problem of hydrogen permeation. In certain conditions, hydrogen molecules can pass through the pressure transmitter diaphragm. As the hydrogen accumulates, it slowly diffuses into the pressure transmitter’s fill fluid, changing its behaviour and impairing transmitter performance until failure occurs.
A solution is ABB’s ‘H-Shield’ titanium-based binary nano coating. With its tight molecular structure, H-Shield provides the highest resistance against hydrogen ion permeation, whilst still enabling the diaphragm to respond to changing pressure conditions.
Digitising hydrogen production
When used to their full extent, the expanded capabilities offered by digital instruments can bring real benefits to green hydrogen production, maximising productivity and providing fast access to detailed data to inform decision making.
By keeping the hydrogen production process safe, efficient and productive, digital instruments ensure that green hydrogen can become a major sustainable energy source for the future.
References:
[1] https://www.livemint.com/industry/energy/india-to-launch-national-green-hydrogen-mission-in-2-months-11653418598894.html
