Reducing temporary H₂S peak from landfill biogas in Belgium

Emissions from waste can be hard to treat, as fluctuations in concentrations and contaminants are common. DESOTEC partners with waste management companies across Europe, designing lasting solutions for biogas issues.

The challenge

A Belgian company manages waste on behalf of businesses and municipalities. Among its operations is a landfill site, which produces biogas for conversion into electricity via a combined heat and power (CHP) plant.

The company already had four DESOTEC filters to treat VOCs and hydrogen sulphide (H₂S) emissions from the site. However, after suddenly noticing sulphurous smells and receiving odour complaints, the company tested H₂S levels and found that concentrations at several spots had risen to 10-30 000 ppm, which is much higher than usual.

The cause of this exceptional spike is still unknown, though sulphur levels in waste have generally risen in recent years.

Combined with water, H₂S turns into highly corrosive sulphuric acid. Therefore, CHP manufacturers set limits for the concentrations that their units can handle: in this case, just 50 ppm.

The increased level of 10 000 ppm was also too much for the existing DESOTEC filters, so as an interim measure, the company used a mobile flare unit to burn off the sulphur.

This process created a double cost for the client. Firstly, it needed to rent a mobile flare unit. However, this also caused sulphur oxide (SOx) emissions for which limits also exist so this wasn’t a long-term solution. Secondly, it reduced the amount of biogas available for conversion into energy as it was simply flared off.

Therefore, the company asked DESOTEC to design a new solution.

The solution

Together with the client, we decided that a caustic scrubber, supplied by a third party, would be the optimal solution to treat around 95% of the H₂S.

However, levels would still be too high for the CHP plant. Therefore, two further DESOTEC filters would be installed as a polishing step, with the second as back-up if the first became saturated.

These AIRCON 2000 C filters are designed for low flow rates (c. 40 m³/h) and high contact times. They have three compartments, which can be filled with layers of different carbon types.

We filled the first compartment with a less reactive type of carbon, R-PURE® 1DS-1. This was chosen as a safety measure to avoid the risk of an excessive exothermic reaction, i.e. if a flaw developed in the scrubber causing H₂S to rise sharply again.

The next layer is AIRPEL ULTRA DS-6, which can adsorb high levels of sulphur.

The results

The results after three months have been excellent: H₂S levels have been below 50 ppm, allowing the biogas to be safely fed into the CHP plant.

It is envisaged that the filters will require exchange after a year, depending on the scrubber’s performance and whether the increased H2S levels will persist or not.

Another DESOTEC client is now considering adopting this solution at its own site. It has been using a flare to treat H₂S, but rising gas prices are prompting it to reconsider its approach.

DESOTEC’s ultimate goal is always to help clients find solutions, even if these involve third party technology rather than our own filters. We always look at the bigger picture, and learn from other technologies.

Biogas is rarely thought of as a source of industrial problems, but issues can arise that require urgent action. DESOTEC filters can be installed within a matter of days, and will start working immediately. In this case, however, the flare provided a temporary solution while we designed a longer term set-up. Our filters are supplied on a monthly rental basis, so if they are no longer required, the contract can simply be ended.

All spent carbon is transported in closed units away from clients’ sites for treatment at DESOTEC’s facilities, where we have the expertise and equipment to handle dangerous waste. All molecules are completely destroyed in our furnaces and, where possible, the carbon is reactivated. Only harmless water vapour exits our chimneys.