Research into the removal of siloxanes from biogas at Cranfield University has been recognised by the Worshipful Company of Engineers for excellence in engineering that benefits the environment.
It is hoped that the PhD research project, which is looking at the most effective methods for removing synthetic chemicals, known as siloxanes, from biogas produced by the decomposition of waste materials, will help improve the cost effectiveness of facilities used for generating energy from waste.
Siloxanes are widely used to soften, smooth, and moisten in products such as shampoos and moisturisers and in medical implants, building sealants and lubricants.
However, siloxanes that end up in organic wastes and wastewater do not decompose. They then turn into silicon dioxide, or sand, which blocks engines and causes costly damage to facilities.
The Worshipful Company of Engineers, which aims to promote the development and advancement of the science, art and practice of engineering for the benefit of the public, awarded PhD student Caroline Hepburn the Hawley Award in recognition of the project’s excellence in engineering that is helping to improve the environment.
Benefits of remote monitoring
According to Hepburn, siloxanes in biogas are usually measured by taking a sample in a gas bag or impinger train and sending it away for analysis using Gas Chromatography- Mass Spectrometry (GC-MS).
However, this is expensive and there is a delay in receiving the results, meaning that if a carbon bed is saturated and siloxanes are breaking through into the gas engines, it won’t be detected for several days, by which time a lot of damage may well have occurred.
However, Severn Trent Water, which funded the project, has installed a Fourier Transform Infrared spectrometer at one of its largest sewage treatment works to measure siloxanes in biogas. This instrument provides frequent sampling and immediate results.
Hepburn explained that she won the award for her validation work in comparing the spectrometer’s results to gas bag samples analysed by GC-MS, and plotting breakthrough curves from the data.
According to Hepburn the data demonstrates that online analysis is very beneficial for monitoring siloxane removal, as breakthrough happens so fast it is impossible to capture using bag sampling, but it is critical to engine protection.
“I’m now working with the manufacturer of the FTIR spectrometer to improve the accuracy at low concentrations, but even as it is the instrument is of great value because of the speed at which it can detect breakthrough,” Hepburn told WMW.
The researcher said that moving on in her project she will be looking at the design of carbon beds for siloxane removal in terms of shape and size, as well as the effects of humidity and competition from volatile organic carbons (VOCs) present in biogas on the capacity of carbon to adsorb siloxanes.
“I’ll also compare the capacities of some different media including silica gel, molecular sieves and hopefully some proprietary media,” she added.
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