Carbon monoxide (CO) emissions

In order to enable comparison of CO from all tests were converted to CO emitted 6% flue gas oxygen. Figure 4, it is evident that there are significant fluctuations in CO emissions, which between 200 and 900 ppm under the same conditions. The orders of fluctuation were similar to those observed by Abelha et al. (2003) and W. A.W. A.K. Ghani et al. (2009). The fluctuations are caused by slight variations in feed composition and this effect is reflected in the temperature profiles. It is noted that the addition of coal has no significant influence on CO emissions during all co-combustion cases, except at coal (50%) / rice husk (50%) where emissions tend to be lower than expected in reference to the other rice husk fractions. This phenomenon is due to the synergistic nature of the coal and rice husk mixture, which en­hances the fuel reactivity and lowers the CO emissions [10]. In most cases the emission of CO seems relatively insensitive to changes in excess and fluidising air. This insensitivity is due to increased segregation of fuels in the combustor between the feed point and the bed. If the combustor receives a batch with a relatively high amount of fuel pellets, then as burning COj is produced since the pellets need to be heated and dried first. While this occurs, oxy­gen is not consumed and results in high CO emissions. The decrease in CO levels at low per­centages of excess air, not below than 50%, can be attributed to low excess air, relatively high bed temperatures (about 900°C) causing rapid enhances and ignition of volatiles from rice husk. Thus, higher CO to CO2 conversion rates was observed which enhanced the reac­tivity of the mixture [13].