Cost-optimized activated carbon filter replacements in biogas operations

Having no reliable access to continuous H₂S data in the biogas production process, many biogas operations are still left in the dark fighting an uphill battle against the various challenges posed by hydrogen sulfide gas. One of these challenges concern the unknown and often fluctuating concentration of hydrogen sulfide coming in to and out of active carbon filters for H₂S scrubbing, which leads to premature replacements of the expensive filters.

Challenge:
With no solid H₂S data available, activated carbon filters are often replaced at fixed service intervals or when the characteristic smell of rotten eggs occurs. While these replacement indicators function, they are not optimal and often result in a premature and expensive replacement of working filters. The odor-based replacement intervals are particularly inaccurate as H₂S gas has a very low odor threshold as the smell can be detected at extremely low concentrations.

Solution:
As part of the Eurostars project, Unisense and our Dutch project partner Gastreatment Services have demonstrated the SulfiLogger^TM H₂S sensor’s ability to accurately measure H₂S in real-time at one of Gastreatment Service’s biogas installations in The Netherlands. The graph below shows a continuous signal of the H₂S presence at the installation during a 16-hour time period with 1-minute intervals between the individual data points on the graph. A single SulfiLogger^TM H₂S sensor was installed at the plant and used for measuring H₂S at two locations, both before the filter (high points) and after the filter (low points), using a multiplex gas sampler to switch between the two side streams at fixed intervals.

By measuring H₂S passing in to the activated carbon filter, biogas plants can optimize filter replacement intervals based on input volume, while continuous monitoring of the gas after the filter can validate the H₂S removal effectiveness of the filter and the quality of the gas over time.