Characterization of Biomass Ashes

Abstract

Energy production from combustion or gasification of biomass has recently attracted increased interest. These fuels form a valuable indigenous energy resource for some countries. They represent also an attractive way to decrease CO₂ emissions from the energy production. The development of new combustion and gasification techniques, such as atmospheric or pressurized fluidized bed combustion and gasification has also made it possible to utilize biomass in a more feasible way than before. The availability of these new energy conversion systems is, however, still unknown. Among other questions the behavior of ash can be critical.

In this paper we present some initial results from an ash characterization work performed on 10 different types of biomass ashes with the focus on the new energy conversion systems. The characterization methods were the following:

• 1) Ash thermal behavior analyzed with a combined differential thermal, thermogravimetric analyzer (DTA/TGA).

• 2) Ash sintering tendency with the compression strength sintering testing method. Ashes tested in both oxidizing and reducing conditions, in temperatures ranging from 500–1000°C. Selected ashes tested further in 100% CO₂(g).

• 3) Chemical analyses of the ashes and sintering tested samples.

• 4) Standard fuel characterization analyses.

• 5) Reactivity analyses for selected biomasses.

The results showed clear differences in the thermal behavior of the ashes. The sintering tendencies varied significantly. The chemical analyses showed that ashes rich in silicon started to sinter at 800–900^°C both in oxidizing and reducing conditions, while ashes with low silicon content did not. These ashes showed instead an increase in sintering at approximately 700°C and a decrease above 700°C when CO₂(g) was present in the gas atmosphere. In some cases the sintering tendency of the ash also correlated with the gasification reactivity of the corresponding biomass.

The results and their relevance to full scale conversion systems are discussed in the paper.