Halogenated Hydrocarbons

Halogenated hydrocarbons, particularly chloro- and flouro-compounds, are often present in landfill gas. However, they are reported only rarely in the case of biogas from the digestion of sewage sludge or organic waste (Persson et al. 2006) .

These compounds can be oxidized during biogas combustion, generating corrosive products that can cause corrosion in CHP engines, in the combustion chamber, valves, cylinder heads and other equipment. Moreover, during the combustion they can be the precursors for dioxines (PCDDs) and furanes (PCDFs) generation.

The most common fluorinated contaminants are the chlorofluorocarbons (CFCs), which were widely used as refrigerants. Although their use has been completely forbidden since the late 1980s, they are persistent compounds in landfills due to their slow volatilization from old waste. Cleaning technologies normally applied to remove these compounds, are the same as described for carbon dioxide removal.

A special technique based on adsorption, is to pass the biogas through pressurised tube exchangers filled with specific activated carbon. Small molecules like methane and carbon dioxide will pass through the tube, while big molecules will be adsorbed. The system consists of two stages, one vessel will adsorb the halogen compounds from the biogas and at the same time, the other vessel is used for regeneration, desorbing the pollutants by heating, (Wellinger and Lindberg 2000) .

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