화학공학소재연구정보센터
Fuel Processing Technology, Vol.40, No.1, 15-48, 1994
THE INORGANIC GEOCHEMISTRY OF COAL, PETROLEUM, AND THEIR GASIFICATION/COMBUSTION PRODUCTS
The inorganic makeup of coal and petroleum differ in several crucial ways. The origins of these differences include the disparate geologic environments of formation, the contrasting parent materials (plant versus planktonic) and hence distinct organic species, and the physical state of the fuels (solid versus liquid). The inorganic chemistry of petroleum is usually controlled by the type and abundance of its organic compounds (i.e., V, Ni, +/- Fe-bearing porphyrins and S-bearing thiols, sulfides, disulfides, thiophenic derivatives, resins, and asphaltenes), with significant, though often smaller contributions from entrained mineral phases. This near balance of inorganic compositional control causes petroleum to form combustion/gasification (pyrochemical) slag and ash with a large number of elements (i.e., V, Ni, S, Fe, Ca, Na, K, Mg, Si, and Al) in significant relative concentrations. This balance provides also opportunities for large departures from any given ''norm''. The inorganic chemistry of coal, on the other hand, is dominantly controlled by its contained detrital and authigenic mineral matter, with relatively small contributions from organically carried elements other than sulfur. Detrital minerals are those that survive the geological processes of weathering and transport, and hence are a small group of physically resistant and chemically stable minerals including quartz, clay minerals, and oxides of Fe and Ti. The most abundant authigenic minerals in coal include clay minerals, pyrite/marcasite, carbonates, Ca- and Fe-sulfates, and Fe-oxides and hydroxides. Pyrochemical slag and ash from coal are therefore primarily enriched in Si, Al, Ca, Fe, and S. From a processing standpoint, the behavior of slag and fly ash is largely a function of the complexity of the fuel's inorganic chemistry (including the original mode of occurrence of the various elements), and the observed oxygen fugacity. Pyrochemical environments vary from reducing to oxidizing as a result of proximity to the flame and operational mode (combustion versus gasification). Consequently, multivalent elements further contribute to the complexity of slag/ash behavior by essentially behaving as separately unique elements when in their various valence states. In coal, the two abundant, multivalent inorganic elements are Fe(O, + 2, and + 3) and S(- 2, 0, + 2, + 4, and + 6). In petroleum there are four abundant, multivalent inorganic elements: Ni (0 or + 2), Fe (0, + 2, and + 3), V (+ 2, + 3, + 4, and + 5), and S ( - 2, 0, + 2, + 4, and + 6). The larger number of abundant inorganic elements in petroleum than coal, as well as the broader range of associated valence states, leads to more diverse slag/ash species formed during petroleum combustion/gasification, and consequently less predictable slag/ash behavior. A phase characterization of slags produced by the gasification of petroleum coke (a petroleum refining byproduct) illustrates their increased complexity with respect to typical coal slags.