Smart instrumentation: meeting the challenges of hydrogen production

ABB Australia Pty Ltd

By Cornelia Huber, Marketing Manager, ABB Instrumentation
Tuesday, 26 July, 2022


Smart instrumentation: meeting the challenges of hydrogen production

Using green hydrogen as a sustainable fuel source is generating great interest as companies and governments look for new ways to cut reliance on fossil fuels.

As the world undergoes geopolitical, security and environmental pressures that are driving countries worldwide to accelerate the development of alternatives to polluting fossil fuels, many companies and governments are looking for new options.

Hydrogen offers many of the advantages of both renewable generation and fossil fuels — it can be produced with low or zero emissions and can be readily stored and transported. It is also clean-burning, producing only water as a by-product, and can be used in chemical processing or production.

There are several ways to produce hydrogen and the key to gaining the most environmental benefit is to use a method that has the fewest emissions or harmful by-products.

Hydrogen production is generally classified as green, grey, blue, brown or white, depending on the production method used. For example, grey hydrogen is currently the most prevalent form of hydrogen production. It is derived from natural gas using steam methane reforming (SMR). This does not use carbon capture methods and for every kilogram of hydrogen produced by SMR, 10 kg of CO2 is also produced.

Green hydrogen, on the other hand, is the most ecologically friendly type, produced by electrolysis using renewables or nuclear energy. The EU Hydrogen Strategy of 2020 places a strong emphasis on green hydrogen, with some tolerance for low-carbon hydrogen.

The potential of green hydrogen is particularly important for Australia. The government is investing $1.4 billion in building a hydrogen industry, with plans to position Australia as a major player by 2030.1

Producing green hydrogen

Electrolysers are the chief way of producing green hydrogen, as they use renewable electricity from wind, solar or hydroelectric power.

There are three main electrolysis methods used today. The first is alkaline electrolysis. A mature, commercial technology, this largely avoids the use of precious metals, and so has relatively low capital costs compared to other electrolysis methods. However, the process is difficult to start up or shut down and output cannot be quickly ramped up.

The PEM (proton exchange membrane) electrolyser uses pure water as an electrolyte solution. This avoids the need to recover and recycle the potassium hydroxide electrolyte solution used in alkaline electrolysers. The method can produce highly compressed hydrogen for decentralised production and storage.

The third and least developed method utilises solid oxide electrolysis cells (SOECs). Based on high temperatures, they use steam for the electrolysis process and so require a heat source.

Instrumentation requirements

The process of electrolysis involves several challenges and risk factors, not least of which is ensuring safe operation, achieving efficient power-to-hydrogen conversion, and controlling the hydrogen and oxygen gas purity.

ISO22734:2019, Hydrogen generators using water electrolysis — Industrial, commercial, and residential applications, is a standard that identifies many parameters that can be measured to ensure safe and reliable operation of hydrogen electrolysers. Some of the proposed parameters are specific to the electrolyser technology. An example is the detection of the leakage of hazardous liquids. This is more relevant for handling highly concentrated potassium hydroxide solutions on an AEC electrolyser, whereas it would not be so critical on a PEM system, which uses pure water.

Conversely, many of the measured parameters are common to all electrolysers, such as the need to avoid the risk of overheating in the electrolyser stack and the requirement to analyse gas purities.

Figure 1: Process flow diagram of an AEC electrolyser with water treatment, phase separation, electrolyte recycling and cooling systems.

Figure 1: Process flow diagram of an AEC electrolyser with water treatment, phase separation, electrolyte recycling and cooling systems. For a larger image click here.

Gas quality requires close monitoring

Hydrogen production needs close analysis to monitor gas quality and relative volumes. 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 stream. This is defined by ISO22734 as a fault condition and so must be detected by appropriate instrumentation.

This application requires a thermal conductivity detector gas analyser, which can measure traces of hydrogen in the oxygen stream and traces of oxygen in the hydrogen stream.

Liquid level monitoring in the phase separator

Another critical measurement task is monitoring the electrolyte vapours that are carried over from the electrolyser cell. After the electrolyser, an initial knock-down phase separator is used to force gas and liquid separation. Hydrogen is then cooled, and a second separation stage removes the condensate and maximises the effectiveness of the physical phase separation.

The first separation takes place in a vertical vessel. Here, hydrogen is vented from the top, while liquid from the base is pumped and recirculated to the electrolyser. The risk is that the pump will run dry, causing hydrogen to enter the pump then flow to the wrong part of the electrolyser. This makes it crucial to monitor the water level in the knock-down phase separator.

A typical solution for level monitoring in the phase separator uses a magnetically actuated double pole double throw switch. When mounted on a magnetic liquid level gauge, the switch can sense high or low levels within the phase separator.

Cutting the risk of overheating

Using renewable electricity from a solar park or wind farm, there is a risk that hydrogen production may ramp up as the electricity available varies. This in turn causes the current drawn by the electrolyser to increase, raising the stack temperature. As a consequence, temperature measurement and cooling are required to eliminate the risk of overheating.

It is critical to monitor the temperature in the de-oxo unit to keep the reaction under control and ensure that the temperature does not reach a hazardous level. The most advanced temperature sensor solutions will offer continuous sensor monitoring and self-monitoring, including supply voltage and the possibility of wire breaks or corrosion.

Pressure measurement

Some types of electrolysers operate at elevated pressures. This is because feed water is sometimes pumped at high pressure to avoid the cost of compressing the produced hydrogen. It is therefore necessary to use instrumentation to continuously monitor the water feed pressure, as well as that of the hydrogen and oxygen, using instruments that provide for shielding against hydrogen permeation.

Pressure instruments are also needed to ensure that the generated hydrogen and oxygen are flowing away without obstruction, as over-pressurisation of the equipment could lead to unsafe conditions.

Digitalising hydrogen production

As with most industrial processes, digital instrumentation is making its presence felt, bringing major benefits to the production and control of hydrogen electrolysis. Digital instrumentation offers significant benefits over older analog-based units. Among these are greater accuracy, range and depth of information, meaning that digital technology offers operators and process engineers a highly detailed picture both of operating conditions and the status of their measurement equipment.

They also offer great flexibility — rather than being restricted to sending a single measurement to work on, digital instrumentation allows additional measurements to be sent along with the primary measurement, such as density, temperature or pressure.

Advances in digital techniques mean that much more diagnostics information is available remotely, while an instrument’s configuration can also be changed this way. Getting status updates cuts maintenance time and costs, ensuring engineers are only deployed as needed. It also means any problems in the process being measured can be resolved before they escalate. This can be critical in electrolysis as parts of the electrolysis stack can be damaged if conditions veer away from nominal.

With digital data, trends in the electrolysis process are much easier to access and analyse as it can be interpreted and turned into easily readable graphs. Using these, engineers can tell when an event such as oxygen entering the hydrogen stream occurred, as well as how changes in parameters could have caused it.

Process instrumentation that can provide analysis as well as detailed readings can also mitigate the endemic skills shortage, helping young or inexperienced plant personnel. In many cases, familiar everyday technologies such as QR codes are being used to display device maintenance and operating conditions. By scanning the QR code with a smartphone, an engineer can send data about the instrument to its manufacturer to access remote assistance.

Remote support is a major theme in today’s instrumentation. Condition monitoring tools are often used to confirm the health of measurement devices and streamline their servicing. Automated device testing improves the quality and consistency of measurements, giving better results, while sending data to a manufacturer’s service experts can ensure maximum availability. This is critical in electrolysis where the constituents of the gas stream are a critical safety issue and demand constant monitoring.

When used to their full extent, the expanded capabilities offered by digital instruments can bring real benefits to green hydrogen production. They enable maximum productivity through ensuring high reliability and availability of instrumentation, while also providing a wealth of actionable data to keep the process parameters in check.

By keeping the electrolysis process safe, efficient and productive, digital instruments ensure that green hydrogen is on a firm footing to become a sustainable energy source for the future.

Reference
  1. Department of Industry, Science and Resources, Growing Australia’s hydrogen industry, Australian Government, <<https://www.industry.gov.au/policies-and-initiatives/growing-australias-hydrogen-industry>>

Top image credit: ©stock.adobe.com/au/AA+W

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