Features and technology / Features in general


CO and HC reduction methods


Oxidation catalysts The reduction of CO is also predominantly achieved using catalytic systems. Oxidation catalysts are used for CO reduction, but again the purity of the fuel gas is a major factor.


Using oxidation catalysts for the reduction of unburned hydro- carbons is currently not possible because the required reaction temperature cannot be achieved. Such catalysts are available for


the reduction of formaldehyde (H2CO) only, but again the purity of the fuel gas is a major factor as mentioned above.


Three way catalysts Three way catalysts require a very precise control of the air-fuel ratio at stoichiometric conditions to enable extraordinarily high conversion ratios (NOx app. 99 %, CO app. 95 %). In addition the high exhaust gas temperatures of rich burn engines allow a significant HC reduction and low formaldehyde emissions.


Please note The installation of any catalytic system is only possible when using very clean fuel gases (e.g., natural gas, or other gases if adequately pre-cleaned). The allowance for trace components such as sulfur, halogens, or heavy metals is very low (see fuel specifications). When using fuels such as sewage gas or landfill gas, the removal of Volatile Organic Silicone Compounds (VOSC) is very important, as these VOSCs would otherwise deactivate the surface of the catalyst in a very short period of time. Using activated carbon filters in this system is a very effective means of avoiding this problem.


The higher conversion rate demand of the catalytic system at rich burn engines is an additional hurdle to use this technology for sewage gas, biogas or landfill gas. Three way catalysts are state of the art technology for natural gas only.


Non-catalytic post combustion of CO, HC and Formaldehyde – CL.AIR* Because catalytic systems bear numerous risks in operation with biogases such as landfill gas or sewage gas, the technology team developed a non-catalytic system for the reduction of CO, THC (Total Hydro Carbons) and formaldehyde more than 15 years ago.


This system, called CL.AIR, uses the reaction heat from the post- combustion of these compounds to maintain the required oxidation temperature (above 700°C / 1,300°F). This regenerative system uses a ceramic storage mass to preheat the exhaust gases to the


required temperature for the oxidation of CO, HC and H2CO into CO2 and H2O. The heat from this reaction is then transferred to a second storage mass. By switching the direction of flow using a


four-way valve, the second storage mass then releases heat to the exhaust gas, and the cycle repeats.


Benefits


• Insensitive against impurities in the fuel gas • No problems with build-up of deposits • Very low levels of emission (CO and THC < 200 mg/m³,


H2CO < 20 mg/m³ @ 5 % O2) • Reliable fulfillment of emission levels over life time • Very low maintenance costs. • Additional thermal output (increase of exhaust gas temperate by 20 – 30°C)


Status GE’s Jenbacher CL.AIR* system was developed in 1994 and has been installed in more than 250 landfill gas and biogas installations.


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