Safe Hydrogen production – the way forward!
Hydrogen is an important energy carrier of the future, and green hydrogen in particular is becoming increasingly effective in this context. The development of electrolysers capable of splitting water into the constituent elements of hydrogen and oxygen is gaining in global significance.
In order to operate electrolysers in a stable, reliable and predictable manner, various analytical techniques of the systems and components are employed, e.g. determining the quality of the chemicals and raw materials used or the continuous monitoring of the energy demands. Cell Voltage Monitoring (CVM) plays a pivotal role when it comes to increasing efficiency and preventing malfunctions or system failures.
Alkaline electrolysis has been tried and tested for many decades. The world’s largest electrolyser is currently working at the Aswan Dam in Egypt. Three tons of hydrogen are produced every hour and the rated electrical output is 156 megawatts (MW). Among the advantages of alkaline electrolysers are their cost-effective design and high long-term stability – up to 90,000 operating hours can be achieved. On the downside, alkaline electrolysers react sluggishly to load changes.
PEM electrolyzers are more suitable to operate with variable power sources like renewables because, unlike alkaline electrolyzers, they’re not affected by gas contamination in partial load operation and have significantly shorter cold start times. However, the operating conditions of the electrolyser are influenced by the fluctuating electricity supply from renewable energies, which can adversely affect an electrolyser‘s operational efficiency and operating life.
For manufacturers of PEM electrolysers, the focus is concentrated on maximizing efficiency, controlling costs, increasing power density (area consumption) and achieving the longest possible lifespan. Fine tuning the production process is essential in order to achieve cost-effective and reliable hydrogen production, so if you want to optimize the process, you have to measure the factors involved. Consequently, it is importantant to monitor the health of the individual cells in the electrolyser stack. This applies particularly during the development and testing phases to be able to identify any unfavorable operating conditions.
During high-performance operation, the primary concern is to minimise production downtimes, particularly unplanned downtimes and to achieve the longest operating life. The operational lifespan can be extended by detecting negative modes of operation or identifying contaminated supplies of water, which are harmful to the system. Unplanned downtimes can be avoided by continuous monitoring of the condition and performance of the electrolyser, which has the added benefit of improving maintenance planning.
Various chemical and physical-electrical parameters are used for process control and allow forward-looking projections about the status of the electrolyser. On the one hand, there are the chemical parameters for the raw materials (water or brine) and returns, the physical parameters of temperature, density, flow and electrical parameters of the total power requirement from the rectifiers.
On the other hand, the voltage values of the individual cells are of significant importance. Through precise monitoring, changes in performance can be detected at an early stage and planned maintenance and repairs executed when necessary or as part of a regular inspection and maintenance plan. This provides greater scope for efficient operaton and responsible use of resources.
Systems for monitoring the individual cell voltages in electrolyser stacks, called CVM systems (Cell Voltage Monitoring), have the ability to monitor the interior of the cell stack, measure the current operating status of individual cells and deliver the real time data via fieldbus protocols to the process management system. Whenever the CVM detects an anomaly or disruption in the stack, operators have the opportunity to immediately intervene, switch off the affected stack, before major damage occurs or plan the corresponding repairs or replacement of components during the next scheduled maintenance.
Although it is possible to assess the overall peformance of the electrolyser by measuring the total voltage of the stack. CVM monitoring of individual cells delivers the most precise electrolyser health information and offers the advantage that maintenance cycles can be better planned and executed efficiently. CVM offers precise information on individual cell conditions in real time, ahead of maintenance schedules, concerning cells that may have problems or where membranes may require replacement. The corresponding spare parts can be sourced in advance, to ensure downtimes are kept to a minimum during repairs and that maintenance stays on schedule.
Less downtime and lower maintenance costs
More predictable maintenance avoids additional downtime, unplanned costs and production losses, or eventual breaches of supply contracts. CVM systems are essential to the analytical oversight that facilitates an efficient, on-budget maintenance strategy.
The ideal location of the installed CVM equipment must fulfill various criteria: the cell voltage monitor should be installed as close as possible to the electrolyser itself, thereby avoiding long connection lines as possible sources of error. The safety requirements increase if CVMs are placed overhead the electrolyser, yet the requirements and risks are lower when placement is to the side of the electrolyser. The CVM itself is a fundamental sensor system that also performs additional functions such as communicating with a control unit. Safety requirement level 2 (SIL level 2) is sufficient here to also be part of the safety chain as a measurement component. Mounting as close as possible to the electrolyser is recommended to keep electromagnetic interference to a minimum.
SMART TESTSOLUTIONS CVM systems are currently available with single, double, triple or so-called quadruple cell scanning. Explosion protection for components and a corresponding ATEX certification is issued by an independent testing and certification institute.
For more info, see www.smart-testsolutions.de.
