Hydrogen

Hydrogen technology is the rising energy star. The Australian federal government has created a $300 million fund to finance hydrogen projects.

Hydrogen is used in transport and in the manufacture of ammonia.

However, Hydrogen can be dangerous. Hydrogen is invisible and odourless, yet volatile and extremely flammable. A four percent hydrogen to air mix produces the highly flamable gas oxyhydrogen (knallgas).

A correct sensing setup can be used to prevent accidents and to troubleshoot existing problems.

All stages of the hydrogen life cycle requires sensors:

Manufacture & Supply
Storage
Transport
Use
Critical Situation Management

Manufacture & Supply of Hydrogen Sensors

Sensor requirements are dictated by the hydrogen manufacturing method. Common manufacturing methods include:

Natural Gas
Coal
Electrolysis

Natural Gas

1.Identification & Removal of Sulphates from Natural Gas:
A gas chromatograph sensor is used to measure the impurities in the hydrogen recycle stream and a second gas chromatograph sensor is used to monitor the finished petroleum product.

2. Temperature control of the steam reformation reactor:
Closed-loop control systems are used to control the heat input rate based on a temperature measurement.The location of the temperature sensor relative to the heat input location is a choice made during reactor design that can have significant impact on reactor temperature control. Alternatively infred red cameras or a distributed temperature sensor can be used to optimise the system.

3. Water gas shift:
WGS ajusts the scrubbed syngas hydrogen/carbon monoxide (H2/CO) ratio to meet downstream process requirement passing the gas through a multi-stage, fixed-bed reactor containing shift catalysts to convert CO and water into H2 and carbon dioxide (CO2) according to the water-gas shift (WGS) reaction. Temperature and Humidity sensors are required.

4. Pressure Swing Absorption:
Pressure is fluctuated between multiple adsorber vessels containing one or more adsorbent layers where gas molecules selectively physically bind to the adsorbent material, causing a gas separation to take place. Gas leakage and pressure sensors are required.

Coal

1. Gasification:
Coal is mixed with oxygen and steam under high pressures and temperatures to form synthesis gas. Gas leakage, pressure and temperature sensors are also are required.

2. Identification & Removal of Sulphates from Natural Gas:
A gas chromatograph sensor is used to measure the impurities in the hydrogen recycle stream and a second gas chromatograph sensor is used to monitor the finished petroleum product.

3. Water gas shift
WGS ajusts the scrubbed syngas hydrogen/carbon monoxide (H2/CO) ratio to meet downstream process requirement passing the gas through a multi-stage, fixed-bed reactor containing shift catalysts to convert CO and water into H2 and carbon dioxide (CO2) according to the water-gas shift (WGS) reaction. Temperature and Humidity sensors are required.

4. Pressure Swing Absorption
Pressure is fluctuated between multiple adsorber vessels containing one or more adsorbent layers where gas molecules selectively physically bind to the adsorbent material, causing a gas separation to take place. Gas leakage and pressure sensors are required.

Electrolysis

1. Voltage Regulation:
The Anode and Cathode voltage is monitoed with a voltmeter or power (quality) meter.

2. Capture/leak detection:
Hydrogen and an oxygen detector measure output and detect leaks.

3. H azardous byproduct detection
A gas chromatograph sensor or individual gas sensors are used to detect toxic gas.

4. Electrolyzer
Both alkaline or solid oxide (ceramic) electrolysers can dry out, requiring monitoring for replacement. Solid oxide electrolysers have a higher operating temperature, and need to be monitored to maintain efficiency.

Storage

The pressure of a hydrogen tank is 300 times greater than the pressure in car tires. Hydrogen can be unsafe because it is highly flammable. Adsorbent materials enable storage of gas at much lower pressures, reducing storage costs.

The safety of hydrogen storage can be improved through hydrogen or leak sensing.

Tranport

While Hydrogen is amenable to small localised production facilities, sometimes it is more economical or only possible to transport hydrogen to certain locations. Hydrogen is transported via pipeline, over the road in cryogenic liquid tanker trucks, or by rail.

Transport requires compression and freezing making use of pressure sensors and temperature sensors.

Metal hydride compressors use metals that form hydrides via exothermic reactions and then release hydrogen at high pressures when heat is applied.

Use

The pressure of a hydrogen tank is 300 times greater than the pressure in car tires. Because of hydrogen's low density, it is expensive to accomplish this pressure, and it also can be unsafe because the gas is highly flammable. Adsorbent materials enable storage of gas at much lower pressures, reducing storage costs.

The safety of hydrogen storage is improved through hydrogen or leak sensing. In particular hydrogen vehicles, to operate safely, require high speed and high resolution/accurate hydrogen sensors.

Critical Situation Management

Sensors are required when a critical event does occur.

Hydrogen fires are invisible to the naked eye, but can be observed through various sensing. Thermal imaging can be used, but must be placed directly in front of the fire otherwise it won't set off the alarm. UV detectors can also be used, however UV detectors are sensitive to arcs, sparks, welding, lightning, and other UV-rich sources which can cause false alarms. In fixed situations, such as plants, a distributed temperature sensor could provide course resolution imaging either over a greater range, or where imaging is not possible (such as in wells and behind other infrastructure). The three can be used together with software analysis to reduce false alarms.