MOTORTECH developed the new NOx emission controller VariSCR to satisfy the increasing immission protection requirements in the future from the amendment to the emission values in TA-Luft (Technical Instructions on Air QualityControl). In addition to the exhaust gas aftertreatment the VariSCR can also control the air/fuel ratio.
After a transition time up to 2018, NOx reduction from a current 500 mg/m³ to 100 mg/m³ for natural gas CHP applications (based on a reference oxygen content of 5% by volume) will become obligatory for new and existing CHP plants. To bring about constant reduction of NOx-emissions in the SCR (Selective Catalytic Reduction) system, AdBlue®, a solution of 32.5% urea in water, will be injected into the exhaust gas flow in front of the SCR catalysts. The urea is converted into ammonia through thermolysis and hydrolysis. In the SCR catalysts, the ammonia then reduces the nitrogen oxides to water and nitrogen.
Besides the algorithms for NOx reduction, the software also contains controllers for controlling the pump module to maintain constant delivery pressure, the heating controller for the dosing unit as well as optionally the fill-level monitoring in the AdBlue®-storage tank.