Research Of Biomass Slagging Characteristics Based On Ash Composition

Nowadays, while world energy and environmental issues is becoming increasingly prominent, biomass energy is getting more and more attention as a clean and renewable energy, and biomass generation shows a good momentum of development. However, in the actual biomass combustion, gasification process, it is prone to the phenomenon of slagging, which has become a major problem of biomass boilers. Therefore, it is of great importance in raising our level of large-scale use of biomass energy to study the mechanism of biomass ash fusibility in depth, master the slagging characteristics in the process of biomass burning, reduce the likelihood of slagging, and provide a viable solution for safe and efficient operation of biomass boilers.This article mainly did related works focused on the impact of ash composition on biomass ash fusion temprature. With aexperimental methods like dditives and rinsing, complemented by ash melting point measurement, SEM/EDS and other methods, biomass slagging characteristics were studied. Specific contents were as follows:First, the basic properties of 7 kinds of biomass were studied straw, which were grains, furfural, bagasse, corn cob, platane wood and melon-seed shell, and fusibility study of all kinds of biomass using SEM/EDS methods and YX-HRD ash fusion tester was carried out. The results showed that:volatile content of biomass fuel was much more than coal, and hydrogen and oxygen content was higher, while the carbon content was lower, which made it easy to ignite the biomass fuel. But it also made a lower heating value of biomass fuels. Meanwhile the ash content of different biomass varied widely; Significant regional differences existed in different biomass ash, and on the whole, it showed in the form of irregular particles in different morphologies; For most biomass ash, silicon, potassium and calcium were the main inorganic elements, and high levels of alkaline elements is reasons for the low fusion temprature of biomass ash.Second, biomass ash composition were changed, that was, certain components of biomass ash content were increased or decreased through additives and rinsing, and fusion characteristics were studied. Additives study found sodium oxide had always played the role of ash fusion temprature reduction; Potassium oxide, calcium oxide, silica oxide, magnesia oxide, alumina oxide showed a two-sides effect on biomass ash fusion temprature. Quartz sand was inappropriate as bed material for biomass fluidized bed, and according to the fuel, limestone, dolomite, high alumina bauxite were alternative, where limestone and dolomite had inhibitory effect only on slagging of straw fluidized boiler. In biomass, K, Ca, Cl, S, P, etc. existed mainly in soluble phase, while only a small amount of Na was in ionic state, and the rinsing effect was not good. For key elements in the biomass ash components, the order from high to low of rinsing efficiency was:Cl> K> S> Fe> P> Ca> Na> Mg. K element, Cl element were main factors leading to low ash fusion temprature of biomass. With the rinsing temperature going high, the fusion temprature of biomass ash generally increased firstly and then decreased, and the best rinsing temperature was about 60℃～70℃. Biomass ash fusion temprature rose with the increase in liquid to solid ratio, but when the liquid to solid ratio was too high, its impact on the ash fusion temprature would be little, and the best liquid to solid ratio of straw was 25 (ml/g).Finally, the establishment of stepwise regression model of biomass ash composition and ash fusion temperature was carried out, which was tested by the negative correlation coefficient test, t test and F test. Comparison between the predicted ST and the actual one showed that, the relative error of regression model was little, which was suitable for prediction of biomass ash fusion temprature. Study found that coal ash slagging discriminant index did not apply to biomass. The new biomass discriminant slagging index was derived:A= (MgO+Al2O3+Fe2O3)/CaO, which was proven feasible. Fusion temprature of biomass ash, ST value basicly rose with the increase of A, and when the A value was less than 2.0, biomass showed severe slagging.