Behavior of Slagging Deposits during Coal and Biomass Co-combustion in a 300 kW Down-Fired Furnace

Abstract

Coal and biomass co-combustion in existing utility boilers is a promising option of mitigating the fossil energy crisis and reducing the gaseous emissions of NO x , SO x , and CO2. However, ash-related problems, including fouling, slagging, and corrosion cause damage to the heat exchange tube and reduce boiler efficiency. In an attempt to give better insights into the slagging behavior during coal/biomass combustion, an experimental investigation was conducted to study the growth of slag when coal was co-fired with wood and corn stalk in a 300 kW pilot-scale furnace. For comparison, combustion of pure coal was also conducted. During the experiments, biomass proportions of 5 and 10% by weight were examined. Slags formed on an oil-cooled deposition probe were collected, sampled, and analyzed using scanning electron microscopy and X-ray diffraction (XRD). The change in slag thickness with time was obtained by a charge-coupled device monitoring system. With two thermocouples in the probe, the heat flux through the slag could be measured. The slag from pure coal combustion showed a layered structure with different levels of compactness and hardness. The heat flux decreased by 31.7% as the slag grew to 5.19 mm. The results showed that co-firing wood significantly inhibited the slagging behavior. Especially in the 10% wood case, hardly any slag was collected from the probe. Nevertheless, co-firing corn stalk resulted in severe slagging, with a slag thickness of 5.5 and 6.1 mm for two blend ratios. The formation of bubbles in the deposits together with greater deposit thickness caused heat transfer deterioration. XRD results revealed that the influence of co-firing biomass and corn stalk caused quite different changes to mineral species from wood. It was observed that fly ash under different biomass co-firing conditions differed little on mineral compositions.

Experimental Study on the Bubble Formation Mechanism during the Sintering of Coal and Biomass Ash Blends

“…In our previous work, bubbles forming (left) and bursting to form pores were observed during co-combustion of coal and corn stalk, as shown in Figure 1, and the final deposit thickness can reach 6.1 mm during the co-firing of Shen Hua coal and 10% corn stalk; for Shen Hua coal with 5% corn stalk, the maximum ash layer thickness is 5.19 mm. 23 In conclusion, the formation of bubbles is normal during ash sintering. Gaseous matter in the enclosed space of molten slag forms bubbles.…”

6th Sino-Australian Symposium on Advanced Coal and Biomass Utilisation Technologies

“…Wang et al () investigate the formation mechanisms of ash aerosol and deposition from the co-combustion of rice husks and natural gas under both air and oxy-fuel conditions. Ma et al () report the behavior of slagging deposits during the co-combustion of coal and biomass (wood and corn stalk) in a 300 kW down-fired furnace. Cui et al () conduct field measurements on the emission characteristics of chlorine (Cl) from 410 t/h circulating fluidized bed boilers that co-fire petroleum coke and coal.…”

“…Ma et al ( 10.1021/acs.energyfuels. 7b03050) 39 report the behavior of slagging deposits during the co-combustion of coal and biomass (wood and corn stalk) in a 300 kW down-fired furnace. Cui et al ( 10.1021/acs.energyfuels.…”

Experiments and Simulation on Co-Combustion of Semicoke and Coal in a Full-Scale Tangentially Fired Utility Boiler

“…Based on the characteristics, co-firing semicoke and coal in a coal-fired boiler can be a promising strategy to utilize semicoke cleanly and efficiently. The co-combustion of multiple fuels has been numerously investigated in a laboratory-scale, ,− pilot-scale, , and full-scale furnace. − However, few studies are specific to the semicoke produced by coal upgrading, especially the research on a full-scale coal-fired boiler. The specific study on a full-scale coal-fired boiler is necessary to provide engineering guidance for co-combustion.…”