the coking properties of coal at elevated pressures. - Argonne ...

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to the devolatilization of the coal and the time at every one-quarter revolution of
the wet test meter (0.0125 cu ft, 354 cm3) was recorded. After five minutes, the
volume reading of the wet test meter was recorded at 3-minute intervals. Discrete
values of the concentration of each gas were also read from a digital display and
recorded by the operator at intervals of 2.5 minutes, beginning at 5 minutes.
The length of time of each experiment varied. In the experiments conducted
at 800°C and 900°C, the 10 g coal sample was usually allowed to react until 80-
90% conversion of carbon had been achieved. At 7OO0C, the experiments were termi-
nated after approximately two hours.
At the end of the experiment, flow of water to the steam vaporizer and flow
of gases were terminated. All heaters were shut down, and the reactor furnace was
opened. When the apparatus was cool, the reactor was depressurized and opened.
The char and ash were withdrawn and weighed. All condensate was drained from the
trap and the volume of water recorded.
mediately.
The tar filter was removed and weighed im-
Results
In this study, the influence of the following parameters on the steam gasification
rate of Illinois No. 6 coal was investigated: the presence of K2CO3 as a catalyst;
the partial pressures of steam, CO and H2; and reaction temperature.
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The
total pressure of the system was held at a constant value of 2.17 MPa (21.4 atm)
throughout the study. The total flowrate of gases into the reaction zone was also
kept fixed in each experiment at some value between 980 and 1020 sccm. Variation
of the reactant gas composition was accomplished by increasing the mass flowrate
of steam, C02 or H2 and simultaneously decreasing the mass flowrate of the inert
carrier gas, nitrogen. Nitrogen was both a diluent and a carrier gas for product
removal.
Runs were made at 700, 800 and 9OO0C with the pretreated coal and coal imp--*mated
with 10 wt.% K2CO3. The effect of C02 concentration on the gasification rate of
K2C03-impregnated coal was studied at a constant steam partial pressure in a series
of 6 runs. An additional 6 runs were made with a mixture of steam, N2, and H2 of
constant composition to evaluate the magnitude of hydrogen inhibition of the steam
gasification rates. Runs were made at each of the three temperatures, 700, 800 and
9OO0C, with both the pretreated coal and coal impregnated with 10 wt.% K2CO3.
Using the data of each experiment, a number of calculations were performed.
The gasification rate and carbon conversion were calculated from a balance of
carbon-containing reaction products. The extent of reaction of the steam was
determined from a balance of hydrogen-containing or oxygen-containing products.
Reactant and product gas partial pressures were computed at the reactor inlet
and outlet. From these partial pressures, the apparent equilibrium constants of
the water-gas shift, carbon-steam, and carbon-HZ reactions were calculated. Finnllv.
product gas sums and overall material balances were determined for each experiment.
Gasification rate
The carbon gasification rate was generally high initially, decreased rapidly
and then slowly decreased throughout the remainder of the run. Fig. 2 shows
typical results obtained at 70OoC with a catalyzed coal sample. The initial peal:
in the curve seemed to be caused by devolatilization of the coal, which was €01.-
lowed by gasification of the base carbon in the sample.
TO obtain a quantitative measure of the reaction rate, the shrinking, unreacted-
core model for the case of complete gasification of a spherical, solid particle
under conditions of chemical reaction rate control was used to describe the carbon
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