Char reactivity factor

Here f is a char reactivity factor equal to one unless otherwise stated, while a represents the relative activity of HjO and C02 a typical value would be 3 [7]. Little is known about the kinetics of the reactions involving the CaO and CaS crystallites. Rates of CaS formation in calcined dolomite and limestone have been measured [8,9], but they are likely to be much slower than those possible on the crystallites. Therefore, we use ... 

PH2 = hydrogen partial pressure, atm /r = relative reactivity factor for rapid-rate methane formation dependent on the particular carbonaceous solid (defined as unity for air-pretreated Ireland mine coal char) a = kinetic parameter dependent on gas composition and pressure... 

The char is also quite reactive as is shown in Figure 5.4, the kinetics of switchgrass char oxidation. The activation energy associated with switchgrass char oxidation is considerably lower than that associated with any of the coals. This reactivity is pronounced at lower temperatures. Because the pre-exponential constant or fiequency factor is also low, switchgrass char reactivity can be lower than that for some coals at the high temperatures. 

The reactivity of the residual char is the rate-controlling factor for brown coal hydrogasification (16). 

Fig. 1 shows a comparison of the reference profiles normalised to the reactivity at X = 0.2. This reveals a pronounced difference in the development of the overall reactivity as a function of conversion. For the spruce char the overall reactivity increases with a factor of 2.8 between X = 0.2 and 0.8, while wheat straw char and Longyear coke gives 1.0 and 1.2 respectively. 

Most of the literature of pyrotechnics available in English is unenlightening on the subject of charcoal. Most of the commercial producers of charcoals in the United States have no appreciation for the needs of pyrotechnists. The commercial producers seem to feel that if it is black and about the proper mesh size then it is suitable for pyrotechnics. In the author s experience no two species of wood or other plants produce charcoal with identical properties. Many pyrotechnists seem to think that particle size controls the reactivity of the charcoal. They have only to examine a fast burning composition from the Orient to realize this is not always the case. Gross particle size does have a marked effect on the reactivity, but not to the same degree that species factors and charring conditions do. 

The reactivity data presented in this section document the high autoignition temperatme for petroleum coke, along with its relatively slow burning characteristics. The dominant combustion mechanism is the heterogeneous char oxidation mechanism. These factors become significant in the utilization methods that have been successful for this opportunity fuel. 

---