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The release of critical ash-forming elements during the pyrolysis and combustion of corn stover has been investigated through controlled lab-scale experiments supported by multicomponent and multiphase thermodynamic equilibrium calculations. Fuel samples were treated under isothermal conditions ranging from 500 to 1150 °C, under both pyrolysis and combustion atmospheres. The volatilized material was quantified by means of mass balances based on char and ash elemental analysis, compared to a corresponding feedstock fuel analysis. Close relations between the observed K and Cl release are found, suggesting that Cl is the main facilitator for K release through sublimation of KCl, determined to begin as the reaction temperature approaches 700À800 °C. K is present in abundance relative to Cl, and the K release is found to cease as the fuel reaches complete dechlorination. In addition, around 50 wt % of the Cl is released at temperatures below 500 °C, presumably as HCl formed through ion-exchange reactions with functional groups in the organic matrix. Complete dechlorination was achieved under combustion conditions as the temperature exceeded 800 °C. Approximately 50 wt % of the feedstock S is released at temperatures below 500 °C. This low-temperature release is related to the decomposition of the organic matrix, releasing the organically associated S. Under combustion conditions, the S release increases gradually at temperatures exceeding 800 °C, eventually reaching complete desulfurization at 1150 °C. The silicate/ alumina chemistry is found to play a significant role in the alkali retention. The Si-rich sample is capable of retaining all excess K not released as KCl.

Combustion of wood for heat and power production may cause problems such as ash deposition, corrosion, and harmful emissions of gases and particulate matter. These problems are all directly related to the release of inorganic elements (in particular Cl, S, K, Na, Zn, and Pb) from the fuel to the gas phase. The aims of this study are to obtain quantitative data on the release of inorganic elements during wood combustion and to investigate the influence of fuel composition. Quantitative release data were obtained by pyrolyzing and subsequently combusting small samples of wood (∼30 g) at various temperatures in the range of 500–1150 °C in a laboratory-scale tube reactor and by performing mass balance calculations based on the weight measurements and chemical analyses of the wood fuels and the residual ash samples. Four wood fuels with different ash contents and inorganic compositions were investigated, including wood chips from spruce and beech, bark, and fiber board. The results showed a high release of Cl (∼85–100%) and S (∼50–70%) already at 500 °C, so that only small variations in the release trends of Cl and S were seen between the different fuels in the range of 500–1150 °C. The release of the alkali metals K and Na was, however, strongly dependent on both the temperature and the fuel composition under the investigated conditions. The release of the heavy metals Zn and Pb started around 500 °C and increased sharply to more than 85% at 850 °C in the case of spruce, beech, and bark, and was therefore mainly dependent on the temperature. By comparing the data to literature data, and by using tools such as scanning electron microscopy, chemical fractionation analysis, and equilibrium calculations, a better understanding of the release mechanisms was obtained. Mechanisms for the release of Cl, S, K, Na, Zn, and Pb during wood combustion are proposed.

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One of the remaining issues in our understanding of nitrogen chemistry in combustion is the chemistry of NNH. This species is known as a key intermediate in Thermal DeNO x , where NH 3 is used as a reducing agent for selective non-catalytic reduction of NO. In addition, NNH has been proposed to facilitate formation of NO from thermal fixation of molecular nitrogen through the socalled NNH mechanism. The importance of NNH for formation and reduction of NO depends on its thermal stability and its major consumption channels. In the present work, we study reactions on the NNH + O, NNH + O 2 , and NH 2 + O 2 potential energy surfaces using methods previously developed by Miller, Klippenstein, Harding, and their co-workers. Their impact on Thermal DeNO x and the NNH mechanism for NO formation is investigated in detail.