What You Need to Know to Reliably Handle Waste Coal

Many power producers have been designing for, or switching to waste coal. A major consideration when dealing with waste coal is the design of the fuel handling system. Since waste coal is typically finer and more cohesive and therefore harder to handle in silos, bunkers, chutes and feeders, design of the handling system for reliable, non-stagnant flow is essential. This paper describes a systematic approach to designing and retrofitting handling systems to avoid bulk solids flow problems. Potential trouble areas such as coal hoppers, silos, bunkers, and transfer chutes are discussed. Mass flow and funnel flow patterns that develop in silos and bunkers are presented. Funnel flow results in large stagnant regions, which are a major problem for coals that combust easily and are prone to problems such as arching and ratholing. Mass flow patterns, which eliminate the stagnant coal regions, are also explained. Coal properties and bunker designs that result in mass flow and funnel flow are described. Transfer chute design techniques to avoid pluggages, reduce dusting, and minimize chute wear are discussed. The Panther Creek Energy facility in Nesquehoning, Pennsylvania is used as an example where solids flow handling methodologies were used to solve handling problems with anthracite culm. The modifications presented were required for reliable, stagnant-free coal flow, which prevented belt slippage and high belt loading on gravimetric feeders.

Exergetic, Thermal, and Externalities Analyses of a Cogeneration Plant

A thermodynamic study of an 88 MW cogeneration plant located in the United States is presented. The plant is singled out for consideration since the feedstock consists of waste anthracite culm banks. The culm banks remain on the ground surface after decades of active coal mining in the region. Before combustion, usable coal within the culm is separated from the indigenous rock and conveyed to circulating fluidized bed (CFB) boilers. The indigenous rock and ashes from combustion are used as fill in adjacent land previously scared by strip mining. Trees and grass are planted in these areas as part of a land reclamation program. The research reported here includes the results of thermodynamic analyses of the cogeneration plant cycle and processes. Analyses based on the First and Second Laws of Thermodynamics are first presented to acquaint the reader with the plant’s components and operation. Data used in the calculations are based on actual operating data obtained at the cogeneration plant during a mass and energy balance study conducted in the late 1990’s. The data are average values and indicative of the plant’s base load operating state. Using emission and other relevant environmental data from the plant, an externalities study is outlined that estimates the plant’s effect on the local population.

Industrial AFB-Fired Gas Turbine Systems With Topping Combustors

An Atmospheric Fluidized Bed (AFB) combustor providing thermal input to gas turbines is a promising near-term means of decreasing national premium fuel consumption, in an AFB many solid fuels, including marginal fuels such as anthracite culm, bituminous gob, high sulfur coals, lignite, and petroleum coke, can be used effectively providing both very low emission levels and acceptable return-on-investment. This paper discusses the state of AFB/gas turbine cogeneration technology with reference to typical industrial plant applications. Design considerations and design limits for both the AFB heat exchangers and the topping combustor are discussed and compared. An example based on plant process data and commercially available components is also presented. Both the heat exchangers and the combustors are viewed with reference to state-of-the-art technology.