Removing pollutants from landfill biogas
Landfill sites contain a potential source of power: the biogas that is naturally emitted by decomposing waste.
However, biogas contains not only usable methane (CH4), but also pollutants which must be removed to avoid damaging the engines used to power electric generators. Learn more on how we help landfills throughout Europe convert waste into power.
A major power supplier in France is developing greener forms of energy, namely solar, wind, water, and biogas.
It operates at several former landfill sites, producing biomethane to power engines to generate electricity.
Closed landfill sites produce lower levels of biogas and pollution than functioning landfills, as much of the waste has already biodegraded. However, treatment can still be required for 10-20 years or more after closure.
Upgrading the biogas to biomethane quality also requires the removal of hydrogen sulphide (H2S) and volatile organic compounds (VOCs). Siloxanes are an especially damaging group of VOCs, which can cause abrasion damage to engines.
Concentrations of pollutants vary depending on the composition of the waste, for H2S concentrations are often in the range 100-2000 ppm and VOC concentration in the range 500-2 000 mg/m³
Engine manufacturers set advisory levels for these pollutants. Exceeding these limits can damage the engine, and invalidate the manufacturer’s warranty.
DESOTEC has a framework contract with this energy supplier. At one site in north-eastern France, we had already installed a solution in place: two small filters in series, the first to remove the H2S and the second the VOCs.
As H2S is best treated in humid conditions and VOCs in dry, the VOC filter was installed downstream of a cooler, a demister and a booster.
However, the site is operated by one lone-working technician who found the process of changing the 2,3 m-high filters somewhat risky as it involves climbing a ladder to reach connectors at the top, which can become wet or even icy in winter.
The company wanted to ensure a safe working environment, and therefore asked DESOTEC for an alternative solution.
DESOTEC proposed replacing the two small filters with one larger one.
Although these larger models are around 8 m high, the inlet and outlet connections are below head height, making it simple for one person to manage without the risk of climbing a ladder.
This single unit comprises two layers of activated carbon. The first removes the H2S and the second the VOCs.
It is not possible to change the humidity levels between the layers, which can affect adsorption capacity on VOCs as the relative humidity is not in the optimal range. However, the company is satisfied with this trade-off in order to improve workplace safety.
Furthermore, while the smaller models must be unloaded by the site technician, the larger filter units are delivered by DESOTEC truck and unloaded by our staff. That means the site technician no longer needs to hire and operate a forklift himself.
The new filter is successfully reducing pollutants to below the required levels.
Together with the client, we are monitoring consumption of carbon, which is expected to be slightly higher than under the previous dual filter system, and will make a comparative analysis at the end of the year.
They can then make tweaks to further optimise the system, for example by changing the composition of the carbon layers or the flowrate of the gas.
So far, the filter has been exchanged once. Although it’s now a very large unit, the on-site technician found it simple and safe to install.
As with all DESOTEC filters, there is no need for technicians to empty spent carbon, store it on site, or refill with fresh carbon. All units are sealed and transported off-site for reactivation in DESOTEC’s furnaces.
This makes the process clean, dust-free and safe, which has prompted the client to switch their fixed filter at another site to a DESOTEC mobile alternative. A third site is considering following suit.
Contact DESOTEC today
To find out how DESOTEC mobile filters could solve contamination issues at your sites, or if you have any questions, please contact our experts to discuss.
At DESOTEC’s facilities, all used carbon is analysed so the right measures can be taken for handling and removing the saturated carbon out of the mobile filters. All molecules that were adsorbed on the activated carbon at the customers’ site, are desorbed inside DESOTEC’s reactivation furnaces. These contaminants are then fully destroyed, in accordance with National and European legislation, by an incineration and neutralisation setup. The entire installation and it's emissions are under continuous on-line monitoring, which guarantees that only harmless water vapour is seen exiting the chimney.