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One of the key requirements related to successful utilization of plasma technology as an oil-free backup system for coal ignition and combustion stabilization in power plant boilers is provision of properly regulated pulverized coal distribution to the feed ducts leading the fuel mixture to a burner. Proper regulation of coal distribution is deemed essential for achieving an adequate pulverized coal concentration in the zone where thermal plasma is being introduced. The said can be efficiently achieved by installation of stationary louver in the coal-air mixing duct ahead of the feed ducts of a burner. The paper addresses numerical simulation of a two-phase flow of air-pulverized coal mixture in the mixing ducts, analyzing the effects of particle size distribution on pulverized coal distribution to the burner feed ducts. Numerical simulation was performed using the FLUENT 6.3 commercial code and related poly-dispersed flow module, based on the PSI-CELL approach. Numerical experiments have been performed assuming a mono-dispersed solid phase with particle diameter ranging from 45 mm to 1200 mm. Distance between the louver blades and the resulting effect on the flow profile was analyzed as well. Results obtained indicate that the size of coal particles considerably influence the overall solid phase distribution. While fine particles, with diameters at the lower end of the above specified range, almost fully follow the streamlines of the continuous phase, coarser particles, which hit the louver blades, deflect towards the thermal plasma zone. In this manner, a desired phase concentration in the considered zone can be reached. For the said reason, installation of stationary louver have been deemed a very efficient way to induce phase separation, primarily due to more pronounced impact of the installed louver on discrete phase flow then the impact on the flow of the continuous phase.

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The paper presents new experimental method developed and new measuring system developed and installed into flame-gas tract of utility boiler. Investigations have been performed at the steam boiler of unit 2 at TPP 'Ptolemais', Ptolemais, Greece, which suffered from very unstable combustion and great pressure oscillations. Experimental method, based on high-speed acquisition system, was developed and used for detection of pressure oscillations and determination of the origin of boiler unstable operation. Signals were obtained from piezoelectric pressure sensors located along the flame-gas tract of the steam boiler and time and frequency domain analysis were used for post processing of collected data. Investigations of the pressure oscillations in boiler gas tract have contributed to reveal origin of the boiler unstable operation, and have been of the great help in establishing proper boiler operation.