Produced using renewable power, Green Hydrogen is presenting an increasingly attractive alternative to conventional energy sources. In this article, Cornelia Huber, Head of Global Communications and Marketing for ABB Instrumentation looks at key aspects of Green Hydrogen production, and how measurement instruments and analyzers can help address some of the operational challenges that can occur during the production process.
Interest is growing in the production of Green Hydrogen as a clean and sustainable source of fuel as countries worldwide become aware of the need to reduce their reliability upon fossil fuels and seek out alternative sources of energy.
Produced using wind, solar or hydropower, Green Hydrogen is made with low or zero emissions and offers many of the same advantages as other renewable energy sources and fossil fuels, with the added benefit that it is easy to store and transport.
In simple terms, Green Hydrogen uses electrolysis to split water into hydrogen and oxygen with the electricity used in the production process being produced by renewable sources of energy such as wind, solar or hydroelectric power. This production process presents several challenges. For example, it is important to ensure operations are safe, that efficient power to hydrogen conversion is achieved and that hydrogen purity is controlled to ensure the end product is of the highest quality.
Using smart digital measurement technologies during the production process of Green Hydrogen can help to achieve this. The latest generation of measurement devices offer high accurancy and an extensive range and depth of information, providing a highly detailed picture of operating conditions. This is especially important in preventing unexpected problems such as faults or failures in safety-critical applications.
Smart digital measurement technologies offer many benefits. Connecting remotely, these devices allow easy access to diagnostic information, enabling actions such as fault tracing and changes to an instrument‘s configuration without the need for an engineer to be present. They also offer greater predictivity, making proactive maintenance easier and allowing for problems to be resolved in the early stages without escalation, avoiding unnecessary downtime and minimizing the risk of potential damage to key process plant. With their intuitive interfaces, digital instruments are also easy to use, making it possible for even the most inexperienced operators to access and view key operational and maintence data.
Monitoring gas quality
Electrolyzers produce oxygen at the anode and hydrogen at the cathode. However, many reactions in the electrolyzer 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. These issues can be resolved by the use of a gas analyser with the required sensitivity to detect quantities of hydrogen and oxygen at very low levels. ABB‘s EasyLine EL3060 gas analyser for hazardous area applications incorporates different options for accurately measuring hydrogen down to -0-1 vol.-% to 0-10 vol.%. As such, iIt can be used to measure both traces of hydrogen in the oxygen stream and traces of oxygen in the hydrogen stream.
Liquid level monitoring
In addition to gas monitoring, monitoring electrolyte vapors from the electrolyzer cell is another critical task. Hydrogen is then cooled and a second sepaaration removes the condensate. In a vertical vessel, hydrogen is vented from the top, while liquid from the base is pumped and recirculated to the electrolyzer. There is a risk that hydrogen can enter the pump and flow to the wrong part of the electrolyzer and so it is crucial that the water level is monitored in the knock-down phase separator.
It is important that any device used can safely measure the level while also being able to withstand high pressures, temperatures and the risk of corrosion, all three of which can occur in hydrogen applications. Using magnetic level instruments such as magnetic switches and sensors to measure low and high levels in the phase separator is ideal for this application. By isolating the device from the process medium, magnetic level meaurement provides a non-contact solution for measuring levels in the phase separator. The use of magnetic devices also eliminates 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 can be quickly deployed, readily adjusted and easily maintained.
Electrolyzers are powered by sustainable sources of electricity from solar parks and wind farms. The variability of renewable power sources can increase the risk of the conversion process ramping up to produce more hydrogen as more electricity becomes available. In this situation, the current drawn by the electrolyzer can increase, causing the stack temperature to rise and leading to overheating. To prevent this, it is important to continously measure stack temperature so that effective cooling can take place, ensuring that temperatures remain within safe parameters. This can be achieved by combining a platinum resistance thermometer with an transmitter, which provides a reliable temperature measurement and alarm solution. The latest generation of transmitters contain additional continuous self-monitoring features which can provide additional information on supply voltage and issues such as wire breaks or corrosion.
The same solution can also be applied to monitor and control temperatures in 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. Here it is essential to monitor the temperature to make sure that the reaction remains under control and that conditions remain within safe limits.
Maintaining safe, efficient electrolyzer pressure control
Some types of electrolyzers 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 electrolyzer at an elevated pressure such as 30 bar is less costly and much less energy intensive than compressing the hydrogen gas from atmospheric pressure to 30 bar after the electrolyzer. Installing a device such as ABB’s 261GS digital pressure transmitter in the water circuit can help to ensure that pumping pressures are maintained.
It is also important to obtain accurate and reliable measurements of pressure. To maintain the safety of the process, over-pressurization of the electrolyzer must be prevented and hydrogen and oxygen gases generated must be able to flow away without obstruction. For pressure measurement of the oxygen and hydrogen gases, ABB’s 266GST and PGS100 series are an ideal solution. Both are certified by TUV NORD for use in process safety control systems according and meet the IEC61508 standards series on functional safety, as well as 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 pressurized electrolyzers.
Hydrogen permeation is another issue that can impact pressure transmitters in hydrogen applications. 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 behavior and impairing transmitter performance until failure occurs.
Certain types of processes carry a greater risk of hydrogen permeation, such as those involving pressures above 1000psi (68.95 bar) or temperatures exceeding 176°C (350°F), which can
increase the dissociation of hydrogen molecules from a harmless diatomic state into an atomic condition. There is also a risk in applications where pipeline equipment is made from dissimilar
materials, which can increase the formation of atomic hydrogen through galvanic corrosion.
A solution to this problem is ABB’s ‘H-Shield’ titanium-based binary nano coating. H-Shield forms a protective coating at a uniform thickness across the surface of the diaphragm. With its tight molecular structure, it provides the highest resistance against the permeation of hydrogen ions, whilst still offering the flexibility for the diaphragm to move in response to changing pressure conditions.
Digitizing hydrogen production
When used to their full extent, the expanded capabilities offered by digital instruments can bring real benefits to Green Hydrogen production, maximizing productivity and providing fast access to detailed data to inform decision making.
By keeping the hydrogen production process safe, efficient and productive, digital instruments have a major role to play in helping to ensure that Green Hydrogen can become a major sustainable energy source for the future.
For more information, visit https://bit.ly/ABBMeas_Hydrogen.