Comparative char combustion kinetics and potential greenhouse gas reductions for alternative fuel-to-energy schemes.

摘要

Apparent agreement has been found amongst a growing majority of scientists in the association of markedly increasing carbon dioxide emissions with anthropogenic origin. The incorporation of renewable solid fuels into our energy program by partially or fully replacing coal, the traditional solid fuel for boilers at power plants, offers one short-term solution to reducing the net release of CO2 to the atmosphere. This work details both experimental and mathematical avenues for progress to that end. Through rigorous pyrolytic, thermogravimetric (TGA), and gas adsorption work with dozens of fossil fuels, renewable solid fuels, solid waste fuels, and model chemical compounds, low-temperature (700°C) chars were found to have intrinsic (Zone 1) reactivities that vary by nearly five orders of magnitude, a variation larger than any reported by other researchers. Chars prepared at a slightly higher temperature (1000°C) were found to also vary significantly, though not to such a great extent. Comparative surface areas for essentially catalyst-free materials versus those with ubiquitous mineral matter, coupled with numerous literature insights, suggest that nearly-pure carbon chars have similar reactivities while the catalytic action of metals, particularly alkali and alkaline, is responsible for the majority of the marked increases in char reactivity. A unique modeling approach was then developed, capable of reasonably predicting char reactivity from a simple chemical characterization of the parent fuel.; These experimental results provide a tool for transitioning from fossil to renewable fuels, via comparative combustion kinetics, but further consideration of renewable solid fuels for energy production reveals that even greater greenhouse gas emission reductions can be achieved through alternate fuel-processing technologies. Investigating combustion (total fuel oxidation), oxidative pyrolysis (volatile gas oxidation alone and char storage), and simple carbonization (no oxidation whatsoever) as variations to current (baseline) energy production via combustion of either coal or natural gas revealed that some innovative treatments of biomass fuels and/or decaying natural wastes are theoretically available for greater carbon dioxide emission reductions. These results, highly variable according to specific fuel chemistry, warrant continued research in an optimal method for fractionation of different fuels into char and volatile portions, particularly for renewable and waste fuels.