Aug-2024

Catalytic detectors for monitoring hydrogen in combustion flue gas

Around the world, nations and corporations are looking for ways to adjust to continually evolving regulations and emission control requirements. Many industrial operators are seeking fresh, innovative solutions to decarbonise their heated processes.

AMETEK Process Instruments

Article Summary

Although some equipment can be electrified, there remain many industrial processes still requiring the high temperatures that can only be achieved by using a combustion process.

One possible strategy recently emerged is to substitute carbon-based fossil fuels with hydrogen, either partially or completely. Hydrogen does not produce CO2 emissions when combusted, making it a much cleaner-burning fuel.

As a result, industrial combustion processes are increasingly likely to transition towards the use of hydrogen and high-hydrogen fuels. This move will make the technology around combustion control and safety monitoring systems an important area of focus. In particular, monitoring the exhaust gas, often referred to as flue gas analysis, will be a crucial consideration.

Flue gas analysis is already widely used across fired equipment in the hydrocarbon processing, chemical, and power industries. It typically consists of monitoring excess oxygen, unburnt fuel, and combustibles (the parts-per-million [ppm] levels of products of incomplete combustion and partially combusted fuel, such as CO+H2). By doing so, this analysis provides the essential post-combustion data needed to ensure safe and efficient operation.

As operators look to replace or supplement their fuels with hydrogen, the need to monitor for the presence of hydrogen in the flue gas increases significantly as well. While a wide range of technologies are used across flue gas analysis, only a select few are capable of detecting hydrogen in any capacity. Notably, several catalytic detectors can be tuned to monitor for hydrogen at ppm levels (caused by incomplete combustion) or even per cent levels (which could arise from an unburnt fuel release).

For ppm-level measurements of hydrogen, there are two main catalytic detector types – catalytic bead (hot-wire) and resistance temperature detector (RTD) thick-film – which can monitor for hydrogen as part of a ppm-level combustibles measurement.

Although they are catalytic in nature and unspeciated to a single analyte, these detectors can be tuned to a specific zone of reactivity using calibration gas to ensure sensitivity to a particular range of analytes, including the range between hydrogen and carbon monoxide.

In order to accurately reflect incomplete combustion, these catalytic detectors are typically calibrated with ppm levels of CO and H2. Together these provide the basis for a single, combined ‘combustibles’ measurement, benefitting those combustion processes that use high-hydrogen fuels, pure hydrogen, or both at the burner.

For per cent-level measurements of hydrogen, only the catalytic bead (hot-wire) type can be controlled to operate at a high enough temperature to crack methane and monitor for smaller hydrocarbons and unburnt fuel, including hydrogen.

If greater sensitivity is required, the most advisable method is to calibrate these detectors with per cent-level hydrogen, along with any other hydrocarbon of interest in the fuel. This type of calibration ensures that the per cent-level hydrogen is measured accurately, and it provides a valuable monitor for detecting potential fuel leaks and loss of flame at the burner.

While the use of hydrogen remains outside the mainstream at present, it is widely regarded as a clean-burning fuel source, and it continues to be evaluated as a possible solution to decarbonise the future of many industrial combustion processes.

Anticipating this energy transition towards hydrogen fuels, catalytic detectors provide a viable solution for detecting hydrogen at ppm and per cent levels in flue gas analysis, ensuring safe and efficient combustion control in the processes of tomorrow.

This short case study originally appeared in Decarbonisation Technologies Decarbonisation through innovation Feature - August 2024 Issue