Observations on the release of gas-phase potassium during the combustion of single particles of biomass

Patrick E Mason,Leilani I Darvell,Jenny M Jones,Alan Williams

doi:10.1016/j.fuel.2016.05.077

Abstract

One of the more significant characteristics of solid biomass fuels as compared to coal is the quantity of potassium that they contain. Potassium content influences ash deposition and corrosion mechanisms in furnaces, the effects of which may differ depending on phase transformations of potassium species in the gas phase and condensed phase. The fate of potassium from the fuel during the combustion process is therefore an important concern. To investigate this, an experimental method is presented in which the release patterns from single particles of various biomass fuels are measured by use of flame emission spectroscopy implemented using a custom-built photo-detector device. Single particles of fuel are combusted in a methane flame with a gas temperature of ∼1800K. The observed potassium release patterns for thirteen solid biomass materials are presented. The data are analyzed to examine the relationships between: the level of potassium in the fuel particle; the fraction of potassium released at each stage of combustion and the peak rate of release of potassium to gas-phase during combustion. Correlations between these quantities are identified with key trends, patterns and differences highlighted. The analyses provide useful information for the development and validation of modelling of potassium release during combustion of biomass.

Highlights

Many large scale power plants use pulverized fuel furnaces with combustion temperatures above 1600 K
The derived signal in this period shows a low level of potassium release compared with the subsequent period
In pulverized fuel fired large scale power generation plant, this is of concern since high potassium ash and high levels of gas phase potassium in the flue gases can lead to deposition and corrosion problems on heat exchange surfaces

Summary

Introduction

Many large scale power plants use pulverized fuel furnaces with combustion temperatures above 1600 K. Such temperatures affect the partitioning of inorganic components through phase transformations. In biomass fuel in particular, potassium, which may be present as various species in solid fuel, is released to the gas phase during combustion at such elevated temperatures. As combustion gases are cooled at furnace surfaces, potassium chloride and hydroxide condense out and lead to increased corrosive deposits and adhesion of ash. Gas-phase potassium can lead to the formation of sulfate aerosols and re-combine with other. The ability to determine the degree to which potassium is released from the char during combustion is useful. In order to model this and predict the likely fate of potassium during the combustion process, it is necessary to understand the release mechanisms and patterns of release

Results

Discussion

Conclusion