Impact of Oxy-fuel Combustion on Ash Properties and Sintering Strength Development

Abstract

For a successful implementation of the oxy-fuel combustion technology, a good understanding of ash-related issues has to be achieved. Knowledge is still lacking on how oxy-fuel combustion can affect ash properties and its sintering behavior. These are the focus of the present work. Combustion experiments of a sub-bituminous coal were carried out in a drop-tube furnace at 1573 K and under air and different oxy-fuel conditions (i.e., OXY21, 21 vol % O2/79 vol % CO2; OXY27, 27 vol % O2/73 vol % CO2; and OXY32, 32 vol % O2/68 vol % CO2). The bulk ash samples were collected and subjected to analyses by techniques such as computer-controlled scanning electron microscopy, X-ray diffraction, and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy. Sintering tests of the bulk ashes were performed at temperatures ranging from 1023 to 1223 K. The compressive strength of sintered ash was characterized. The results show that oxy-fuel combustion has significant impacts on ash speciation rather than its elemental composition. Ash particle size distributions are also affected, which is mainly attributed to changes in char burning temperatures. Oxy-fuel combustion seems to have insignificant effects on the temperature at which the ash pellet starts to sinter but apparently affects the ash sintering strength. In comparison to the ash from air combustion (AIR ash), the OXY21 ash has a much higher sintering strength. Nevertheless, a decrease of the sintering strength is observed for the OXY27 and OXY32 ashes compared to the OXY21 ash. Such differences are attributed to changes in ash chemical properties.

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

“…They found that the ash deposition under oxyfuel combustion was basically similar to air combustion based on the SEM images of the deposits, the deposit chemistry and the visual observations of the deposit build-up. The discrepancies in the effect of oxyfuel combustion on the ash deposit formation can be found in these experimental findings and it can be concluded that: (i) the effects mainly result from the aerodynamic changes in the small scale furnaces, rather than the chemical changes in the fly ash/deposit [6][7][8][9]; (ii) the effect of the oxyfuel combustion condition on the fly ash formation could be decreased when the flame temperature/char temperature are close to those in the air combustion [12]. Therefore, it is important to undertake a CFD analysis on the effect of the aerodynamics on the ash deposition in order to understand the detailed effect of oxyfuel combustion on the particle impaction and sticking behaviours.…”

Application of the Mechanical and Pressure Drop Tests to Determine the Sintering Temperature of Coal and Biomass Ash

“…That observation shows that the breaking stress is very sensitive at the beginning stage of the ash sintering process. In turn, the study of the initial stage of the ash sintering process is very important in identifying the mechanisms of transformation of the mineral substance of solid fuels during combustion under different conditions [22,30].…”

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

“…Gao et al () employ an optically accessible flat-flame burner to reveal the effect of CO 2 and H 2 O on the formation of incipient ultrafine particulate matter (PM) from the combustion of a high-sodium lignite under oxy-fuel conditions. Wu et al () study the impacts of oxy-fuel conditions on ash properties and sintering behavior from the combustion of a pulverized sub-bituminous coal at 1300 °C in a drop-tube furnace. Chen et al () simulate the vaporization of inorganic matter from the combustion of a single coal char particle under oxy-fuel conditions.…”

“…Wu et al(10.1021/acs. energyfuels.7b03161)29 study the impacts of oxy-fuel conditions on ash properties and sintering behavior from the combustion of a pulverized sub-bituminous coal at 1300 °C in a drop-tube furnace. Chen et al (10.1021/acs.energyfuels.…”