Peripheral processes

Peripheral processes

Besides its classical Amine and Membrane upgrading technologies to produce biomethane Arol Energy offers several other processes which can be implemented as standalone units or integrated in a total biogas upgrading solution. These processes are especially relevant for the upgrading of biogas from landfills as the raw biogas usually has a complex composition requiring more extended cleaning as compared to biogas from agricultural and wastewater sources. In particular, in addition to CO2, landfill gas usually contains non-neglectable concentrations of oxygen and nitrogen as a result of the specific biogas extraction process used in landfill management.

Oxygen removal

To eliminate the oxygen present in the raw landfill gas Arol Energy uses a non-redox (reduction-oxidation) catalytic design based on a precious metal catalyst.

The approach is a true ‘classical’ catalytic oxidation and thus can operate for many years without catalyst replacement or regeneration. The fuel can come from the methane present in the biogas itself or from the addition of a secondary fuel such as hydrogen or propane. The only products of the reaction are water and CO2.

 A schematic overview of the process and a 3D-view of a typical skid are shown below. Heat recovery has been optimized within the process and further heat integration with the entire biogas upgrading process is possible to reduce overall energy costs.             

    

Nitrogen removal

The concentration of nitrogen in landfill gas is usually significantly higher than the one of oxygen as a result of its higher concentration in air. To remove this nitrogen Arol Energy proposes a unique pressure swing adsorption (PSA) technology based on a specifically designed molecular sieve adsorbant material to reject the nitrogen. The media used is completely regenerable and periodic media replacement is thus not required.

Moreover, besides the nitrogen a part of the carbon dioxide is removed simultaneously reducing the required load on the CO2 removal unit. The tail gas rich in nitrogen usually contains enough methane to be able to be used as fuel in a gas engine or turbine normally present at a landfill site. This ensures a 100% valorization of your biogas without any methane losses. 

The process principle is schematically depicted below :