Intermittent Energy Source Becomes Reliable Power with Help from INFICON Leak Detector
Significant development time is saved by a Swedish manufacturer of energy storage systems, using the Sentrac Strix® hydrogen leak detector from INFICON.
Azelio manufactures thermal storage units that enable operators of renewable energy installations to provide consistent power to the grid from an energy source that varies in intensity. For instance, operators of solar parks can harvest energy at midday when the sun is strongest and supply electricity in the evening when demand is greatest.
The TES.POD from Azelio stores energy using liquid aluminum and produces electricity with a Stirling engine. Photo courtesy of Azelio.
Azelio's TES.POD unit achieves this by maintaining 4.4 tonnes of molten aluminum at a liquid state, using electricity from the renewable power source. Aluminum melts at around 600°C. Once liquid, the metal stays in this state and maintains its temperature for a long time. The heat is extracted using a heat exchanger containing liquid sodium, which has a low melting point at around 100°C.
The heat drives a Stirling engine. Unlike an internal combustion engine, where heat is produced on the inside, the cylinder of a Stirling engine is heated from the outside. Gas inside the cylinder expands and contracts to move the piston, which turns the crankshaft where a generator is fitted.
Leak-free enclosure a necessity
The Sentrac Strix hydrogen leak detector helps ensure that gas cannot pass into or out of the structure. The working gas inside the Stirling engine is hydrogen gas, which is inherently prone to leaking due to its low viscosity. Meanwhile, air must be prevented from entering into the heat exchanger and the heat storage unit itself, as oxygen causes corrosion and degrades performance. To prevent corrosion, the system is topped off with nitrogen and sealed.
"The unit is expected to have a working life of 30 years. To ensure long and trouble-free service, entry of air into the system must be prevented, as corrosion would lead to blocked passages in the unit and degradation of the ceramic coating on the inside. Eventually, the unit would stop working.
A small amount of hydrogen leakage from the Stirling engine is expected, but the rate needs to be controlled," says Fredrik Edin, test supervisor at Azelio.
The sensor recovers quickly after exposure, enabling the test to continue without delay. Photo courtesy of Azelio.
"In the past, we have used leak detection spray, but INFICON's leak detector is far more effective."
"The range of temperatures is significant here. A leak that is barely noticeable at room temperature can be substantial at 600° C."
The wide range of temperature fluctuations would also make other common leak detection methods with lower sensitivity, such as pressure decay, ineffective.
"INFICON's leak detector is very easy to use," says test operator Marcus Carlsson.
"Any leaks are detected quickly and accurately, even extremely small ones. It is also useful for detecting very large leaks, where leak detection spray would just get blown away."
Easy-to-use hand probe
The Sentrac Strix Edition hydrogen leak detector uses a sensor on a hand probe that fits into intricate geometries to pinpoint any leaks accurately. The leak detector finds any presence of gas quickly and helps locate leaks of widely varying sizes.
The leak detector uses non-flammable forming gas, containing 5% hydrogen and 95% nitrogen, as a tracer gas to find leaks. This is injected into the empty structure before the test is performed. The outline of the structure is then followed by an operator or a robot holding the probe, detecting any escaping gas.
The sensor responds fast and recovers quickly after exposure, enabling the test to continue without delay.
Even very large leaks are identified without the detector becoming over-saturated. In addition, it handles high levels of hydrogen in the background, enabling the operation to continue even if the workstation should become momentarily contaminated with escaped forming gas.
"We use the Sentrac Strix hydrogen leak detectors for quality control, fault finding and product development. We now have three detectors and they certainly help shorten the time for development and manufacture," says Edin.
A TES.POD unit can receive up to 100 kW charge during 6 hours and deliver 13 kW nominal effect for 13 hours or longer, depending on user demand. Several TES.POD units can be combined side-by-side into a system of desired output, up to 100 MW.
While batteries charge slowly at the beginning and are at their most efficient in the middle of the charging cycle, the thermal storage can receive full charge from start to finish.
Unlike batteries, thermal storage does not degrade over time. The core can store as much energy after 30 years of use as it did the when it was new. Nor does it require rare minerals, such as lithium and cobalt, which are needed for battery manufacture. All its active materials – aluminum, sodium and hydrogen – are easily available in large quantities. The core in Azelio's TES.POD is made from recycled aluminum to further minimize environmental impact.
"The first systems have recently been delivered to customers and we are now looking to ramp up production. We see great potential for this product and the Sentrac Strix hydrogen leak detector will be part of our continued journey," Edin concludes.
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