OCR Text |
Show more molten slag deposit in the vicinity of the near burner region and may be due to the high flame temperatures (see Figure 2) monitored for this high oxygen concentration test. 5. Summary and conclusions • A newly constructed pilot plant to bum fossil fuels in air and 02/C02 mixtures and designed to capture environmental pollutants and greenhouse gases was successfully commissioned and operated at the C A N M E T , Energy Technology Centre, a R & D arm of the Canadian ministry of Natural Resources. • Experimental trials indicate that it is feasible to bum pulverised coal in 02/C02 mixtures and to produce flue gas mixtures with a C 0 2 concentration of up to 9 5 % by volume on a dry basis in the flue gas. The balance of the gases in the combustion stream is determined by the excess 0 2 concentration maintained in the flue, and the SOx and N O x produced by fuel combustion. A s a corollary, it may be expected that higher C 0 2 concentrations for the capture and disposal of the flue gas can be obtained by reducing the excess 0 2 concentration to a minimum level desired to sustain satisfactory fuel combustion in the 02/C02 gas mixtures. • No problems were encountered with fuel ignition and flame stability when burning pulverised coal in the 21/79, 28/72 and 35/65% 0 2/C02 gas mixtures. However, in comparison to the higher oxygen concentration 02/C02 gas mixtures and air, the flame established by the 21/79% 0 2/C02 gas mixture was less luminous and unable to register a signal in the flame scanners used in the burner management system. This property is thought to arise from the lower radiation emissions from the coal flame at this feed gas mixture composition. • Measurements indicate that the flame temperatures, total and radiant heat fluxes increase with the oxygen concentration in the 0 2/C02 gas mixtures. However, in comparison to pulverised coal combustion in air, the flames established at the 21/79 and 28/72% 0 2/C02 mixtures were cooler and less radiant. This behaviour may be attributed to the higher specific heat and mass flux of these combustion gas mixtures relative to air. Although not shown by some of the data due to experimental errors, the 35/65 0 2/C02 gas mixture is expected to b u m hotter and be more radiant than for air. This feature is due to higher anticipated adiabatic flame temperatures and a lower gas heat capacity for coal combustion in this highest oxygen concentration mixture. • Evaluation of in-flame oxygen concentrations show the expected result that the partial pressures of this gas are higher as the oxygen content increases in the 02/C02 feed gas mixture. However, despite a lower inlet concentration, the air blown flame shows the highest measured in-flame oxygen concentrations. 12 |