Release and Transformation of Inorganic Elements in Combustion of a High-Phosphorus Fuel

Abstract

The release and transformation of inorganic elements during grate-firing of bran was studied via experiments in a laboratory-scale reactor, analysis of fly ash from a grate-fired plant, and equilibrium modeling. It was found that K, P, S, and to a lesser extent Cl and Na were released to the gas phase during bran combustion. Laboratory-scale experiments showed that S was almost fully vaporized during pyrolysis below 700°C. Sixty to seventy percent of the K and P in bran was released during combustion, in the temperature range 900À1100°C. The release of K and P was presumably attributed to the vaporization of KPO 3 generated from thermal decomposition of inositol phosphates, which were considered to be a major source of P and K in bran. The influence of additives such as CaCO 3 , Ca(OH) 2 , and kaolinite on the release was also investigated. Ca-based additives generally increased the molar ratio of the released K/P, whereas kaolinite showed an opposite effect. Thermodynamic modeling indicated that the fly ash chemistry was sensitive to the molar ratio of the released K/P. When the molar ratio of the released K/P was below 1, KPO 3 and P 4 O 10 (g) were the main stable K and P species at temperatures higher than 500°C. Below 500°C, the KPO 3 and P 4 O 10 (g) may be converted to H 3 PO 4 (l), which may cause severe deposit build-up in the economizers of a grate-fired boiler. By increasing the molar ratio of the released K/P to above 2, the equilibrium distribution of the K and P species was significantly changed and the formation of H 3 PO 4 (l) was not predicted by thermodynamic modeling.

A new class of electroactive Fe- and P-functionalized graphene for oxygen reduction

“…26,53 In the case of GPFe, P can react with Fe to form phosphate complexes such as iron phosphate. 54 As can be seen in Fig. 3c, the deconvolution of O 1s spectrum of pristine RGO resulted in only 3 peaks, which can be assigned to double oxygen bond in carbonyl (O2): C]O (531.7 eV), 10 (O3): single oxygen bond in C-O (533.2 eV), 10 and (O4): CO 3 À group at 534.5 eV.…”

KOH capture by coal fly ash

“…One option to deal with these alkali-induced problems is to inject additives that can react with volatile alkali species to form less problematic compounds with higher melting points. Various additives have been investigated, and they can largely be categorized into four groups: Al-Si based [3,[15][16][17][18], S-based [19][20][21], P-based [22] and Ca-based [23], according to the major elements that are present in the additives [3,24]. Among the different additives, coal fly ash was the only one that has been commercially utilized in full-scale suspension-fired boilers due to its low cost and high effectiveness [1,2,25].…”

Impact of coal fly ash addition on ash transformation and deposition in a full-scale wood suspension-firing boiler

“…Due to the very different physical and chemical properties of biomass, a conversion from coal to biomass on existing suspension-firing power plants involves a range of major technical constraints for the boiler and the flue gas treatment units [2]. The majority of these constraints are related to the content of the critical ash forming elements present in biomass, such as K and Cl, which are highly volatile during combustion [3][4][5][6][7][8][9][10]. These elements can cause severe ash deposition and corrosion in the convective section of the boiler [2,, forcing the plant to operate at lower superheater temperatures and thereby jeopardizing the high electrical efficiency of suspension-fired units.…”