Effects of Pretreatment of Coal by CO₂ on Nitric Oxide Emission and Unburned Carbon in Various Combustion Environments

Abstract

Polar solvents are known to swell coal, break hydrogen bonds in the macromolecular structure, and enhance coal liquefaction efficiencies. The effects of the pretreatment of coal using supercritical CO2 on its physical structure and combustion properties have been studied at the bench-scale level. Emphasis has been placed on NO reburning, NO emissions during air-fired and oxy-fired combustion, and loss on ignition (LOI). Pretreatment was found to increase porosity and to significantly alter the fuel nitrogen reaction pathways. Consequently, NO reduction during reburning using bituminous coal increased, and NO emissions during oxidation of lignite decreased. These two benefits were achieved without negative impacts on LOI.

Photochemical and acoustic interactions of biochar with CO2 and H2O: Applications in power generation and CO2 capture

“…While the treatments remove roughly 33–43 wt % minerals in biochar, calculations based on ultimate analysis, see Table , show 0.1 to 2.2% weight losses of the organics into the aqueous phase during thermal and photochemical treatments, respectively. This level of loss of organics was also observed in our previous SC CO 2 treatment of coals . Table indicates that organic oxygen is one of the elements contributing to the weight loss during the photochemical treatments.…”

“…About 57% of Si, 92% of K, and at least 61% of Na are removed from biochar during photochemical treatment. We have noted the losses of these minerals earlier in the treatment of lignite by supercritical CO 2 . The technological significance of mineral removal in the process will be discussed in a later section.…”

“…Biochar was produced in an alumina tube of 1.92 cm i.d. identical to that previously used for coal pretreatment . The alumina tube was vertically placed in an electrically heated tube furnace with carrier gas He entering from the top.…”

“…Although, it is known that solvent‐treated coals have higher reactivity in liquefaction and swelled coal has a higher gasification rate, the possible benefit of using solvent‐treatment (such as CO 2 ) as a method of tuning carbon reactivity in combustion and gasification has not been explored. Recently, Gathitu et al found that supercritical CO 2 treatment of coals induces physical structure changes including swelling and increased internal surface area; moreover, it can also be adopted as a method for tuning the evolution of nitrogen from solid fuels and therefore, the NO formation in combustion …”