Online Coal Analyzers Bring Benefits to the Utility Industry

Online coal analyzers have been in commercial use for more than two decades now, with coal producers accounting for most of the units purchased. In the past three years or so, coal-fired power plants have shown an increasing share of the analyzers bought. This article explains the most common applications of analyzers at power plants, ranging from boiler optimization to compliance with emission regulations. The article also provides a brief overview of different analyzer types, their principles of operation, and typical performance achieved. INTRODUCTION Online coal analyzers were first introduced to the coal and utility industries in the early 1980’s. Those units were products of research that had begun in the mid 1970’s. As with most new technologies, it took some time for the products to mature and for the industry to embrace them. In the case of online coal analyzers, that wholesale acceptance did not begin until 1990 or so, but even then the usage varied widely. Coal producers bought these analyzers at four times the rate that utilities did. Geographically, the greatest use occurred in the United States, followed by Australia, perhaps owing to the fact that the manufacturers were located primarily in these two countries. Europe by notable exception accounted for less than 1% of the purchases of the elemental coal analyzers; this can be somewhat explained by the declining use of coal throughout the continent. Now that we are in a new century the patterns of use of online coal analyzers are changing, and in fact major change has occurred in the past three years alone. The purpose of this paper is to explain what analyzers exist, how they work, and what changes are occurring within the industry. In particular, given the focus of this conference, the attention will be skewed toward the use of analyzers in power plants. THE EARLY DAYS It is ironic, given that power plants form a distinct minority in the use of analyzers, that the first elemental coal analyzers actually came about from research sponsored by the US utility industry, specifically from the Electric Power Research Institute. The Tennessee Valley Authority’s Paradise plant and Detroit Edison’s Monroe plant were the beta-sites for elemental coal analyzers from SAIC. Another analyzer supplier, MDH Motherwell, emerged in the early 1980’s, with its beta-site at the prep plant at the Penelec Homer City power plant. Despite the early utility interest in coal analyzers, it was the coal producers in the US and Australia that saw the promise and began purchasing these analyzers with some regularity. The analyzer producers who took over the leadership of this fledgling industry were Gamma-Metrics (now known as Thermo Electron) in San Diego, CA, USA, and Mineral Controls Instrumentation (now Scantech) in Adelaide, AUS. Thermo Electron dominated the elemental analyzer segment while Scantech led the way in ash gauges. Today the coal analyzer industry produces annual revenues of about $10 million. THE PRODUCTS There are two types of analyzers which constitute the majority of coal analyzer usage throughout the world. Ash gauges which mount around conveyors account for about 75% of all online coal analyzers. These units are known sometimes as dual-gamma ash gauges, a designation arising from the fact that they use two different gamma isotopes to irradiate the coal. The relative attenuation of the two gamma signals can be used to infer the total ash concentration in the coal. However, these gauges rely on an assumption that the ash constituent composition doesn’t change. Their accuracy is particularly vulnerable to shifts in the iron fraction of the ash, a limitation made worse by high levels of ash. CaO effect 6 % ash sub-bitum inous Fe2O3 effect 0 Error in ash determination Variation in % Fe2O3 in bituminous or % CaO in sub-bituminous 2%