Studying the Melting Behavior of Coal, Biomass, and Coal/Biomass Ash Using Viscosity and Heated Stage XRD Data

Abstract

The use of biomass for power generation can result in significant economical and environmental benefits. The greenhouse emissions can be reduced as well as the cost of the produced electricity. However, ash-related problems, including slagging, agglomeration, and corrosion, can cause frequent unscheduled shutdowns, decreasing the availability and increasing the cost of the produced power. In addition, the fouling of the heat exchange surfaces reduces the system efficiency. In this work the melting and rheological properties of various biomass and biomass/coal ash samples were studied by using a high-temperature rotational viscometer and a hot stage XRD. The produced data were used to calculate the operating temperature of a pilot-scale entrained flow reactor during the cocombustion of biomass/coal samples in order to ensure the slag flow and to avoid corrosion of the walls due to liquid slag/metal interaction. Biomass ash proved to have significantly different melting behavior compared to that of the coal ash. Furthermore, the addition of biomass to coal ash led to lower viscosity and subsequently to higher stickiness of the produced ash particles. The melting behavior of the slag generated by the cocombustion tests appeared to be somewhat different compared to that of the laboratory-prepared ash samples. The heated stage XRD data provide useful information regarding the reactions among the various ash compounds and the phase transformations during the heating and cooling of the ash samples and helped the explanation of the produced viscosity curves.

A Comparative Study of Fouling and Bottom Ash from Woody Biomass Combustion in a Fixed-Bed Small-Scale Boiler and Evaluation of the Analytical Techniques Used

“…[6,7,9,12,[14][15][16][17][18]. Many researches have focused on minimizing or removing these problems using methods such as co-firing with other types of fuel, such as different coals [9][10][11]13,[19][20][21] or blends of various biomass species [14,22], and the use of additives such as phosphoric acid [3], ammonium sulfate [19], kaolin [14], halloysite [23], titanium oxide [24], Ca-based additives [25] and others [26][27][28]. Therefore, the knowledge on the composition of the ash and fouling material is crucial to understand the mechanisms behind fouling formation and to provide a method to combat it.…”

Research on the slagging characteristics of blended coals in a pilot-scale furnace

“…Blending of coals can be used to satisfy the requirements of given utilities. Possible advantages for power plants include reducing fuel costs, using more acceptable coals, and improving operational performance (Richards et al, 1993;Wang and Harb, 1997;Arvelakis et al, 2006;Ma et al, 2007;Kostakis, 2011).…”

Measurement and simulation of flow properties of coal ash slag in coal gasification

“…There have been a number of studies on the viscosity prediction for coal ash slag at different temperatures. [16][17][18][19][20] As it can be assumed that the viscosity of the fully liquid phase of coal ash slag is of homogeneous liquid silicate slag, a number of silicate slag viscosity models have been developed over the years to predict the viscosity of fully liquid phase of coal ash slag. [21][22][23][24] One group of models uses a simplified expression based on the Weymann-Frenkel equation.…”