000			03680nab a2200205 4500
005			20260520000841.0
008			260224s2009 xxu
245	0	0	_aRelease of potassium from the systems K-Ca-Si and K-Ca-P
260			_a _b _cjul./ago. 2009
270			_a15/06/2010 ; 14/06/2010
300			_a6 p. ; 3423-3428
520			_aTranscripción del resumen del autor. Release of potassium (K) during biomass combustion, may cause significant operating problems in terms of ash deposition and high-temperature corrosion of superheater tubes. Other ash-forming elements, such as calcium (Ca), silicon (Si), and phosphorus (P), may to a certain degree control the K release. The aim of this work was to study the release of K from simple systems, to obtain information on the retaining effects of the elements Ca, Si, and P. Further objectives were to investigate the effects of temperature, the presence of water vapor, the speciation of K and Ca, and the sample size on the release rate of K, from the simple ternary systems K-Ca-Si and K-Ca-P. Well-defined mixtures of K, Ca, and Si (or P) species were heat-treated in a reactor, at constant temperature (900 or 1000 °C), in a gas flow of 4 nL/min N2 containing 2% (v/v) H2O. Average release rates were calculated from weight measurements of the samples after every 15 min of the heat treatment (and subsequent cooling to room temperature). The presence of water in the gas flow was found to significantly enhance the K-release rate, from both the K-Ca-Si system and the K-Ca-P system. For the K-Ca-Si system, a significantly higher release rate was observed at 1000 °C compared to 900 °C. Furthermore, doubling the Ca/Si molar ratio K2CO3-CaO-SiO2 mixture strongly enhanced the K-release rate (by about 2 times) at 1000 °C. This suggests that SiO2 preferentially reacts with CaO, so that more K is being released to the gas phase instead of being incorporated into the silicate structure. For the K-Ca-P system, with K2CO3 as the K source, the Ca/P molar ratio had a strong effect on the K-release rate: a decrease in the Ca/P molar ratio (or increase in the P content) significantly decreased the K-release rate from the K-Ca-P mixtures. As opposed to the K-Ca-Si system, it thus seems that K is preferentially incorporated in (nonvolatile) (K2O)k·(CaO)l·(P2O5)m structures. The effects of temperature and Ca source on the K-release rate from this system were limited but most pronounced for the mixtures with the highest Ca/P ratio (lowest P content). Furthermore, the sample size had a strong influence on the K-release rate. In the case of K-Ca-P mixtures containing KCl as the K source, the K-release rate was significantly higher at 1000 °C compared to 900 °C in the first 15 min of the heat treatment, whereas the Ca/P ratio had no effect on the K-release rate. Selected samples of the K-Ca-Si and K-Ca-P mixtures, before and after the heat treatment, were studied by scanning electron microscopy (SEM) in combination with energy-dispersive X-ray (EDX), to investigate the morphological and compositional changes. Moreover, selected samples of the K-Ca-P mixtures were heated from room temperature to 1400 °C, in a simultaneous thermal analyzer (STA), to investigate the melting and gas-phase release behavior. Both methods confirmed the effects of the Ca/Si and Ca/P ratios and the speciation of K and Ca on the release behavior observed in the heating experiments.
581			_a4
773	0		_tEnergy & fuels _g23
942			_cARTICULO
100	1		_aNovakovic, Aleksandra _942612
100	1		_aVan Lith, Simone C. _942613
100	1		_aFrandsen, Flemming J. _918218
999			_c170988 _d170988