Wheat straw and peat for fuel pellets—organic compounds from combustion

Wood pellets are an environmentally friendly biofuel with no net contribution to global warming. Today, the demand for wood pellets for residential heating is rapidly increasing in Sweden and many other countries. Therefore, alternative raw materials for pellet production, such as wheat straw and peat, are of great interest. Before these new fuels are widely used, it is important to study the emissions to air during combustion. The smoke contains a large number of compounds which, to varying degrees, can affect health and the environment. Specific organic compounds from five sequential combustion stages; initial smouldering, early flaming, late flaming, after-flame smouldering and final glowing, were determined for incomplete combustion of straw and peat/wood pellets on a laboratory scale and compared to those from softwood pellets. The emissions from incomplete combustion reflect the chemical composition of the fuel. During initial smouldering of the studied fuels, methoxyphenols from the lignin of the fuels were released at high concentrations. Relatively high concentrations of 1,6-anhydroglucose and furan-related compounds, originating from the polysaccharides of the fuel, were also found during this stage, especially in peat/wood pellet smoke. During flaming burning, wood pellets burned more efficiently and with even lower emissions than the other fuels. After-flame smouldering of the studied pellets, especially straw pellets, released high concentrations of compounds that are hazardous to health and the environment.