This paper presents the details of a mathematical model for fluid flow, combustion, and heat transfer in cement kilns. The model is based on the finite-volume technique for the solution of the gas-phase equations. The k-ε model is used to represent the turbulence effects. A two-step kinetics scheme is employed to simulate the gas-phase combustion. The Lagrangian formulation is employed for the particle phase, and the coupling between the particle and gas phases is handled by introducing appropriate source terms in the gas-phase equations. The particle reaction model includes coal devolatilization and char oxidation. The radiation heat transfer in the kiln is modeled using the six-flux model. The feed bed is represented as a solid region that is moving in the axial direction with a uniform velocity, which is calculated from the feed rate, feed density, and the fill area. The effect of chemical reactions in the feed bed is modeled by including temperature-dependent heat release/absorption rates in the energy equation.
The model has been applied to a cement kiln in operation. The predicted results agree with the observations and experience for the kiln.
Industrial turbines fired on medium heating value (MHV) gas (nominally 300 Btu/scf) synthesized from coal offer an attractive alternative means of producing electrical power in the future. Peak flame temperatures resulting from combustion of this MHV gas in conventional diffusion flame combustors may be comparable to those of natural gas, yielding undesirably high concentrations of NOx. This paper describes an EPRI-sponsored program conducted to demonstrate a MHV gas turbine combustor capable of meeting EPA NOx requirements without water injection. Program objectives were to design, fabricate, and test three MHV combustor configurations and to demonstrate NOx emissions concentrations of 15 ppmv (dry basis) or less at a burner inlet pressure of 1.27 atm: Design of the combustors was based on a lean-premix fuel metering concept. Tests were conducted in a single-can combustor rig at simulated engine conditions ranging from 40 to 125 percent of engine baseload (74 MW).
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