Emissions from combined heat and power couplings and means of reduction

Combined heat and power couplings of agricultural biogas plants are mostly operated with gas-Otto-engines. Those engines should have low emissions and low biogas consumption. Emissions and biogas consumption can be influenced by the air-to-biogas ratio. Experiments have so far been carried out with two engines under field conditions. Emissions of NOx and CO and biogas consumption were measured in dependency on the air-to-biogas ratio (lambda). With lambda about 1.1 - 1.2 NOx emissions reach their maximum, whereas with lambda 1.05 - 1.1 CO emissions reach their maximum. With increasing lambda they decrease. At lambda about 1.3 - 1.5 NOx emissions fell below the limiting value given by the Austrian order concerning the prevention of air pollution. However with growing lambda the biogas consumption also increased. Therefore the operation of the engine has to be a compromise between low emission and low biogas consumption to meet the best environmental control. Regulating the air-to-biogas ratio is a simple means to control air polluting emissions.