Theoretical and experimental metals flow calculations during biomass combustion

Abstract All creature of nature needs metals for subsistence. The plants and trees contain this element in a different amount. During biomass combustion and energy production this element could cause environmental and health problems, thus, the cognition of burning and determination of material flow is a very important question. The high amount of metals steps out from the combustion chamber in gaseous form. To determine the metal distribution inside the burning equipment system, we have to get samples from the solid combustion remains and flue gas, and we have to measure the material flows. At the first stage, we made a biomass combustion experiment using ligneous plants with high metal content. The experiment was carried out with a Binder RRK 500 type wood chips-, briquette- and bark-fueled heating system. The fuel was wood chips, and the operational parameters were automatically set by the temperature control so that the circulating water was kept at a constant temperature. The amount of flue gas was calculated based on the theoretical estimate. The analysed metals were Zn, Cu, Cd, Pb, Cr, Ni, Co, and Fe. The metal content of the wood chips, ash and fly ash was determined by ICP spectrometry, and the ash content and fly ash concentration in the flue gas was measured. The material flow was calculated in the matter of metals. The results show that under the experimental circumstances, the solid burning residues (bottom ash, fly ash) contain the following percent of metals referred to the fuel metal concentration: Zn - 17–18%, Cu - 2–7%, Cd - 4–20%, Pb - 14–15%, Cr - 0.5%, Ni - 2%, Co - 10–11%, and Fe - 5–7%. The results proved that the metals are very volatile in the combustion temperature (800 °C) and flue gas temperature (250–300 °C).