Control of the adhesion properties of fly ash represents a considerable challenge for the maintenance and operation of a wide range of combustion plants throughout the world. This is especially true for biomass combustion, which has seen growing interest as a renewable energy production source given that biomass usually contains a significant amount of chlorine, sulfur and alkali metals. These elements are known to cause severe fly ash adhesion in combustion plants and are also responsible for plant corrosion. However, an understanding of the mechanistic aspects of the adhesion process remains challenging, partly due to the chemical complexity of fly ash and the lack of analytical methods that can directly measure adhesion force at high temperatures. In the present study, a novel testing system was developed to provide direct measurement of the shear strength of fly ash powder beds. It is believed that the shear strength of these powder beds is closely linked to the adhesion force acting between the fly ash particles and the containment surfaces. Our experiments indicated that the shear strength of biomass fly ash powder beds that exhibit high shrinkage can be measured directly with the new testing system, which had not been previously possible with a tensile strength testing system.

In thermal power plants, deposition of fly ash on the surfaces of the heat exchanger causes a significant drop in the heattransfer efficiency and this inhibits effective fuel utilization. It is widely accepted that alkali metals such as sodium and potassium are the trigger for fly ash deposition given that the alkali metals potentially form low-melting-point materials which have adhesive properties and can be deposited on the surface of the exchanger. However, detailed mechanistic studies of this process are challenging due to the chemical complexity and diversity of fly ash samples collected from commercial thermal plants. Herein, it is demonstrated that fly ash deposition triggered by alkali metals can have different mechanisms due to the effects of interparticle and/or surface adhesions. A key enabler for facilitating detailed mechanistic studies is the combined use of tensile and shear strength testers linked to a synthetic ash strategy that utilizes chemically synthesized inorganic particles.

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