Understanding the effects of oxyfuel combustion and furnace scale on biomass ash deposition

Abstract

Recycled wood oxyfuel combustion is attractive for the advantages of reusing the waste bioenergy and reducing the carbon emissions. However, the changes in the fuel properties and combustion conditions can lead to uncertainties in the ash deposition. In addition, the understanding of the differences in the ash deposition between the pilot-scale and full-scale furnaces is very limited. We have performed ash deposition experiments on a 250 kW pilot-scale furnace for recycled wood air and oxyfuel combustion along with the EI Cerrejon coal combustion as a reference. A CFD-based ash deposition model, which uses the excess energy based particle sticking model, has been developed and the predictions are in qualitative agreement with the measurement data. The results suggest that, besides furnace temperature, the aerodynamics and ash physicochemical properties dictate the ash deposition. The recycled wood has a much higher deposition rate than the coal in the pilot-scale furnace; however, the biomass can numerically have a lower deposition rate under high velocities close to the full-scale boilers. This is mainly due to the biomass having a much lower sticking efficiency since it has high calcium and silicon concentrations and low potassium concentration. Although the effect of oxyfuel combustion is small and within the experimental uncertainties, it is found that oxyfuel combustion can affect the particle impaction and sticking behaviours depending on the fly ash properties and these effects occur in different ways in the pilot-scale and full-scale conditions. Great care should be taken to perform the transfer of the deposition observations from the pilot scale to the full scale and this is because the furnace scale has an effect on the selective deposition behaviour. In this paper a relationship between the fly ash properties (ash composition, size, etc.) and ash deposition for the woody biomass has been proposed.

Experimental Studies on Combustion Characteristics of Oil-Palm Biomass in Fluidized-Bed: A Heat Energy Alternative

“…However, the results were obtained at air flow rates of 0.9375 m 3 /s compared to the others. Measurements regarding the combustion temperature using biomass fuels have also been analyzed by [55,56]. This is similar to the results of research conducted by [23,57,58].…”

Ash Formation and Deposition in Oxy-fuel Combustion of Rice Husk, Coal, and Their Blend with 70% Inlet O2

“…The variation of capture efficiency in different combustion cases may due to different ash fusibility, particle size, and/or deposit shedding. , Ash with less liquid phase and a coarser PSD will, after impaction, more easily bounce off the coupon . Ash rebounding and deposit shedding will decrease ash capture efficiency and lead to less ash retained on the coupon.…”

“…28,36 Ash with less liquid phase and a coarser PSD will, after impaction, more easily bounce off the coupon. 36 Ash rebounding and deposit shedding will decrease ash capture efficiency and lead to less ash retained on the coupon. To give insight into the effect of rice husks co-firing and an OXY70 combustion atmosphere on ash bounce-off behavior, ash PSD and percentage of liquid phase in ash were investigated, as shown in Figures 1 and 3.…”

Modeling and Evaluation of Ash-Forming Element Fate and Occurrence in Woody Biomass Combustion in an Entrained-Flow Burner

“…The 250 kW entrained-flow combustion unit (Figure ) at the PACT facility in Sheffield was used to experimentally investigate the fate and occurrence of various elements during solid fuel combustion. − Gas heaters consisting of primary, secondary, tertiary, and overfire heaters preheat the oxidizer before it enters the burner and combustion chamber. The oxidizer from the primary heater outlet is mixed with the solid pulverized fuel fed via the feeder, which is sent to the burner, with the flows from the tertiary and overfire heater outlets providing additional oxygen staged throughout the burner and reactor to encourage complete fuel burnout and minimize emissions.…”