Computer Controlled Scanning Electron Microscopy (CCSEM) Analysis of Straw Ash

Abstract

One of the main problems involved in straw combustion is related to the behaviour and fate of the ash forming inorganic species contained in the fuel. These elements can end up in fly ash‚ bottom ash or may be incorporated in various types of deposits. The inorganic species in straw either occur disseminated or ionically bound in the organic structure‚ are located in inorganic straw constituents or they are constituents of terrigeneuos dirt that is incorporated in the straw during harvesting and handling. Clearly the fate of the inorganic species during combustion depends on their mode of occurence in the straw. Knowledge of straw ash composition and melting behaviour is important to be able to predict‚ at least to some extent‚ the fate of the inorganic elements in terms of practical operation of boilers. The aim is to be able to predict and possibly avoid formation of troublesome deposits and potential corrosion. Additionally‚ knowledge of straw ash compositions and morphology is useful in terms of possible utilization or disposal of the ash. This paper presents part of a project that aims to acquire knowledge about the formation‚ composition and physical-chemical behaviour of ash from combustion of straw and co-combustion of straw and coal. One of the goals is to develop or modify useful analysis techniques for straw ash characterization. The techniques utilized in the project involves Computer Controlled Scanning Electron Microscopy (CCSEM)‚ High Temperature Light Microscopy (HTLM) (Hjuler‚ 1997) and Simultaneous Thermal Analysis (STA) (Hansen‚ 1997). The CCSEM analysis provides information of the composition and morphology of the ash whereas HTLM and STA provides information about melting temperatures and melting behaviour. The combined data on composition and melting