ABSTRACT
The paper describes the methodology adopted, and presents some of the test results of the in-flame probing work at Ratcliffe power station, on both circular register and Low NOx axial swirl burners, and on a Low NOx axial swirl burner, identical to that installed at Ratcliffe, in the Large Scale Burner Test Facility at Babcock Energy in Renfrew. The work formed part of the collaborative project 'Minimising the effect of high temperature coal ash deposition in pulverised coal-fired boilers'. At both sites, water-cooled probes, with internal water quench spray, were employed to extract small samples of particulate material from different regions within the flame. Simultaneous measurements of the CO and O2 concentrations at the sampling points, over 15 minute sampling periods, were also taken. Flame temperature profiles were measured using a sheathed thermocouple mounted on a water-cooled probe. All of the in-flame particulate samples have been analysed for C, H, S and loss on ignition, to define the progress of the combustion and ash transformation processes as a function of position within the flame. The in-flame particulate samples are currently being subjected to detailed examination using the computer-controlled SEM, recently installed at Imperial College, London. Four series of tests firing three British power station coals, selected to represent the range of British coal ash chemistry, have been performed. The temperature and gas composition profiles show clearly the differences in flame structure and in the time-temperature-atmospheres to which the burning coal particles are subjected, and this is reflected in the degree of burnout and the rates of release of H, and S from the coal. The results of this testwork will form the basis of both physical and computer models of the ash transformation processes which occur in full-scale, power station flames.
