Release of K from the system: K-Ca(-Si)-P – The Effects of the Ca/Si- and Ca/P-ratios
Sustainable process-product development & green chemistry
Environmental Engineering & Management (T1-3P)
Keywords: Ash, biomass, combustion, release, potassium
In biomass-fired grate boilers, ash formation is strongly influenced by the release of volatile alkali metals. Ash from biomass may cause a number of different operating problems, such as deposition and corrosion. This is due to the high content of alkali metals, causing a low melting point of the ash. Release studies on annual biomass have shown that a Ca-Si – chemistry is responsible for controlling the release of potassium to the gas phase. In the case of wood biomass, a matrix rich in Ca and P is left behind in the residual ash after pyrolysis and char burnout. Thus, these elements may also influence the release of potassium from wood fuels.
A reliable method for studying the alkali release from model species was developed and tested. The effect of Ca on the release of K- species from a mixture of K-, Si- and Ca-species was studied. Two K-sources, KCl and K2CO3, have been investigated, while Quartz has been applied as Si-source, and CaO and Ca(OH)2 have been applied as Ca-sources. The release of K- species from the mixtures was quantified in a fixed-bed reactor. The experiments were done in N2 with 2%(v/v) H2O, at 900°C and 1000 °C. The residue left in the crucible was investigated by scanning electron microscopy and energy dispersive X-ray mapping. The results showed that in the ternary system K-Ca-Si, mixing between the compounds occur, causing a higher K-species release rate, while the presence of Ca alone does not influence the K-release.
Further experiments will be performed in order to investigate the system: K-Ca-P, i.e. the new aspect is the effect of different amounts of Ca and effect of different Ca-species on the release of K-species from mixtures of K-, P- and Ca-species. KCl and K2CO3 will again be used as K-sources, Ca(H2PO4)2 will be used as P-source, while CaCO3 and Ca(COO)2 will be applied as additional Ca-sources. A few experiments will be conducted in which a certain amount of Mg or Mn will be added to the system K-Ca-P, in order to investigate the effect of Mg and Mn on the release of K. Experimental conditions will be the same as stated above.
In order to find out which compounds are formed in this systems during heating, X-ray diffraction will be applied. The residue left in the crucible after the heat treatment will be investigated by scanning electron microscopy and energy dispersive X-ray analysis. These experimental techniques will provide information on sample morphology and mixing of different species in the sample.
Presented Monday 17, 13:30 to 15:00, in session Environmental Engineering & Management (T1-3P).
