The present study is concerned with thermal decomposition of ten kinds of coal in different ranks of which fuel ratio ranges relatively widely from 0.9 to 6.6. The pyrolysis characteristics of coal were investigated by TGA (Thermo-gravimetric Analy-sis) in an atmosphere of nitrogen under the following conditions: the coal particle size 37-2000μm, the heating rate 2-200K/min, and such thermal decomposition parameters as the reaction order, the frequency factor and the activation energy were determined. The effects of particle size and also heating rate on the pyrolysis rate were examined. Then, the thermal decomposition parameters thus determined were correlated with the fuel ratio. As a result, it was recognized that the experimental data were well reproduced with respect to TG curves by using these parameters determined in the present study. The validity of the obtained parameters was then demonstrated.
Wandoan coal was liquefied with a fraction of FCC residual oil (FHO) as a solvent in the presence of synthetic pyrite as catalyst, at 400-500°C of reac-tion temperature under 20°C120kg/cm2G of initial hydrogen pressure for 1-4h of reaction time in a 50l autoclave. After reaction of FHO itself with synthetic pyrite at 400°C and 500°C, 100kg/cm2G initial hydrogen pressure for 1h, the product was completely soluble in nhexane. At any reaction temperature from 400 to 500°C, the total yield of the reaction products was obtained more than 85% based on the sample (coal+FHO). The maximum yield attained to 98% at 450°C. The oil yield showed maximum at 475°C. Preasphaltene and asphaltene decomposed to oil and gas, resulting in the increase of oil and gas yield. Hydrogen consumption tended to increase from 1.5% at 400°C to 4.1% at 500°C, with the reaction temperature. With varying the reaction time at 475°C, 100kg/cm2G of initial hydrogen pressure, there were not so much difference in the total product yield, but preasphaltene tended to disappear and asphaltene decreased, while oil yield was almost constant and gas increased. With the increase in hydrogen pressure at 475°C for 1h, under the higher hydrogen pressure than 60kg/cm2G the total product yield showed not so much difference. The increase in oil corresponded to decreasing preasphaltene and asphaltene. The increase in coal conversion supposed to be due to increase in asphaltene. With increasing hydrogen partial pressure (100kg/cm2G of initial pressure balanced with nitrogen), oil produced became lighter. In the case of hydrogen pressure only, oil contained a little bit heavier fractions with increasing hydrogen pressure. The increase in total product yield was supposed to come from preasphaltene and asphaltene produced from coal. Increasing oil was considered to be due to decomposition of preasphaltene and asphaltene. The lighter oil was obtained at the higher reaction temperature, under the higher hydrogen partial pressure and for the longer the reaction time.
To evaluate the effects of catalyst concentration on liquefaction, concentration distributions of the catalyst particles in a slurry reactor were estimated and autoclave experiments were carried out under various gasliquid mass transfer conditions. The estimation showed following results. The concentration distributions of catalyst particles became more uniform with smaller iron particles. And when dp<dpap=min, ap (surface area of catalyst particles in a slurry) increased with decreasing dp (diameter of catalyst particle). The autoclave experiments showed following results. Coal conversions increased with increasing of catalyst concentration under the good mass tranpfer condition. On the other hand, under the poor mass transfer condition, the conversions decrease at high catalyst concentration. The results which used hydrogenated anthracene oil as a solvent showed higher oil yields with lower hydrogen consumption. Yields of methane under the poor mass transfer condition were higher than those of under the good mass transfer condition, it shows that production of methan reflect the mass transfer condition in the reactor. These results suggest that using of smaller iron particle catalyst and better donor solvent under the condition of better gasliquid mass transfer lead to higher coal conversion.
We tried to estimate the amount of hydrogen radical transferred from gas phase to coal fragments during flash hydropyrolysis of coal. A known amount of hydrogen was supplied to the reactor only while the coal particles were heated to a reaction temperature. The hydrogen unreacted and the product gases were all collected in a gas holder. Then the amount of hydrogen transferred from gas phase to coal radicals were successfully measured from the hydrogen balance. Its value reached over 12mol/kg-coal at 920°C for the pyrolysis of Morwell (MW) brown coal under 5MPa of H2. Next, the flash pyrolysis of coal swollen by tetralin, which was effective to increase the conversion and the tar yield in an atmospheric pressure of He, was performed under high pressure. This pyrolysis method was also effective in 5MPa of He, and was more effective in 5MPa of H2, indicating the presence of combined effect of hydrogen and tetralin. Comparing the product distribution during the flash pyrolysis of the MW coal and the tetralin swollen MW coal in He and H2 atmospheres, the mechanism of hydrogen transfer from the additives to coal was clarified. The hydrogen radical from high pressure hydrogen is utilized only to stabilize hydrocarbon gases at high temperatures. On the other hand, the hydrogen radical deriving from tetralin is mainly transferred to tar fragments at rather low temperatures. The combined effect of hydrogen and tetralin was found to be realized by a rapid hydrogen transfer from gaseous hydrogen to coal fragments via tetralin.
In order to get information on liquefaction reactivity of coal, effect of pretreatment on transferable hydrogen in coal was studied. The amount of transferable hydrogen in coal was estimated by the method of formation of hydroanthracenes through heattreatment with anthracene. Deashing pretreatment and CO2/H2O treatment increased transferable hydrogen for Taiheiyo and Illinois No.6 coals. From IR measurements the bulk structure of coal was found to be hardly changed by these pretreatments. It can be said that transferable hydrogen is sensitive to the slight change of coal structure. On the other hand, transferable hydrogen was decreased with preheating for Wyoming and Morwell coals. Transferable hydrogen is an evaluating parameter of the pretreatment.