Development of a Micro-electromechanical Photoacoustic Spectrometer for Industrial Applications and the Study of SO2 at High Temperatures

This proposal aims to develop a highly sensitive gas sensor, combining photo-acoustic spectroscopy with micro-electromechanical (MEMS) technology. In conjunction with the sensor development, a new high temperature gas spectrometer will be developed to measure the spectral parameters of gas species, such as linestrength and collisional broadening coefficients, and their temperature dependence in the mid infra-red region of the electromagnetic spectrum.

The sensor development will initially target a specific application, the measurement of sulphide gas species during the desulphurisation of natural gas and gas obtained from coal gasification. Coal gasification and natural gas are the likely fuel for large-scale Solid Oxide Fuel Cells, one of the many distributed power generation strategies being considered to reduce carbon dioxide emissions. Without the desulphurisation process, the sulphide species gases present in the fuel source will poison the electrodes of the fuel cell, initially reducing efficiency but ultimately leading to system failure. Monitoring the sulphide species content of the gas entering the fuel cell using an in-situ optical technique will provide a fail-safe solution and reduce the risk of failure.

In standard laser spectroscopy optical detectors are needed, however, in the mid-IR these detectors are expensive and need to temperature stabilised. The use of photoacoustic spectroscopy eliminates the necessity for an optical detector, allowing the gas sensor to be easily adapted to monitor a wide-range of gas species, with the major limitation of the sensor being the availability of an appropriate optical source. The use of a MEMS device to detect the acoustic signal, induced by the laser-gas interaction, provides further advantages as it is robust, cheap to develop with a resonant frequency and high Q-factor, making ideal for operation in industrial environments. This will allow a number of future applications to be targeted including explosives detection, gas leak detection, medical diagnostics, atmospheric monitoring and combustion product analysis.

This work combines fundamental scientific research with a complex engineering challenge to produce a solution for a much needed practical application. A number of scientific fields of research are being applied to develop a low cost, miniaturised optical trace gas detection system for use in harsh environments. Advances will be made in the field of high temperature spectroscopy, in the miniaturisation of photo-acoustic gas sensors through the application of micro-electromechanical (MEMS) structures as microphones and the construction of gas sampling systems using state of the art three-dimensional printing technology.

The prototype optical sensor will be tested by measuring gas concentrations on an operational solid oxide fuel cell (SOFC). Providing a valuable new tool for diagnostics and process control on large scale SOFC's that are to be used as distributed power generation systems with reduced carbon emissions. However, the prototype sensor can be applied to a number of different research fields and industrial applications simply by changing the optical source. This allows future work to be carried out in environmental monitoring, natural gas leak monitoring, explosives detection, carbon dioxide leakage from carbon capture, medical diagnostics through breath analysis and combustion diagnostics. A number of these applications are concerned with current policies in energy efficiency and reduced carbon dioxide emissions or health and safety, making this an ideal time for miniaturised gas sensor development with suitable industrial partners.

The continuation of this research in the future will provide opportunities for new PhD students and post-doctoral research fellows to develop skills in growing research fields, such as micro-electromechanical systems (MEMS), and combine these skills with new physical understanding of high temperature spectroscopy and optical sensor development.

This work therefore provides an industrial partner with a new sensor capable of carrying out essential measurements for process control and a sensor that can be easily modified and developed to match the gas sensing requirements of a number of other industrial applications. It begins to integrate a number of research fields, MEMS, combustion diagnostics and high temperature spectroscopy to provide a platform for future growth and development of research and student training and is applicable to a number of key strategic areas of research including energy, healthcare technologies, physical science, global uncertainties and engineering.