IXDUXTRIAL AND ENGINEERING CHEMlSTR Y
January, 1927
slip after fourteen days of continuous grinding. One of the first linings attached by the Vulcalock process was installed in a 3 x 3 feet batch mill used for grinding white glaze.
141
After eighteen months of continuous service, inspection showed that the wear from the original 3/4-inch thickness was too slight to be measurable.
Reactions in the Fuel Bed of a Gas Producer' 111-Effect of Steam-Coal Ratio By R. T. Haslam, J. T. Ward, and R. F. Mackie DEPARTMENT OF CHEMICAL ENGINEE:RING, MASSACHUSETTS INSTITCTE OF TECHNOLOGY, CAMBRIDGE, MASS.
With the same experimental technic as in the previous work of this series, a study was made of the effect of increasing the amount of steam admitted with the air blast (pounds of steam per pound of coal) on the reactions in the fuel bed of a gas producer. Runs were made using from 0.366 t o 1.03 pounds of steam per pound of coal with constant depth of fuel bed (3.0 feet) and constant rate of firing (40 pounds of coal per square foot of grate area per hour). I t was found t h a t the heating value of the final gas and the cold gas efficiency increased to a maximum and then decreased. The optimum steam-coal ratio for efficient producer operation lay between 0.7 and 0.8 pound of steam per pound of coal. This value is higher t h a n any found by other workers and is explained by the high rate
of firing employed. Apparently, the most desirable steam-
coal ratio increases as the ratio of firing increases. The percentage steam decomposition decreased with higher values of steam-coal ratio, as a result of the lower temperature in the primary reduction zone (where steam is decomposed by carbon) lowering the rate of reaction constant for steam decomposition. The thickness of the primary reduction zone and the thickness of the oxidation zone remained constant. As in the previous work, steam went through the oxidation zone undecomposed. This work indicates the value of operating gas producers a t a high rate of firing with a steam-coal ratio t h a t increases as the rate of Bring increases.
.. .... . .
I
N GAS-PRODUCER operation it is possible to vary three conditions-viz., depth of fuel bed, rate of firing, and amount of steam admitted with the air blast. Each of these primary variables has a definite effect on the results obtained from the producer. The effects of the first two are described in the previous article of this group.2 The work described herein is a continuation of the previous work and shows the effect of the steam-coal ratio (pounds of steam per pound of coal) on the composition of the gases progressively up through the fuel bed. T o tie in with results reported previously, a run was made a t Constant depth of fuel bed (3.0 feet) and constant rate of firing (40 pounds of coal per square foot of grate area per hour), these being the conditions of run 4 of the previous series. Run 4 was repeated and checked by run 201. I n all these runs the same apparatus was used and the same experimental procedure followed as reported p r e v i ~ u s l y . ~A carefully screened anthracite pea coal was used (Table I). T a b l e I-Analysis of Coals as Fired (Coal C was used for runs 4 and 103; coal D for run 105; coal E for runs 201, 202, 203, and 204) COALC COALD COALE Per cent Per cent Per cent Moisture 2.35 3.64 0.92 Volatile combustible matter 7.70 7.95 10.16 Fixed carbon 76.55 75,24 74.34 Ash 13.40 13,17 14,58
78.84
Total carbon Higher heating value (dry basis), B. t. u. per Ib.
77.18
76.17
k', are plotted against the steam-coal ratio in Figures 1 to 4. Figures 5 to 11 show the changes in gas composition and temperature through the fuel bed, and Figures 12 to 18 show the change in the gas ratios through the fuel bed. Discussion of Results The accuracy of the results is controlled by the nearness to which the snap gas samples represent average conditions of operation under the external conditions imposed. The external conditions were held constant for a period of 15 minutes before the run was started. Nevertheless, variations in the coal and its combustion caused the final results to vary to an unavoidable extent.
.
..
.. LSS. STfAM PER LB. C O A L
Figure 1
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0
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13,690
12,630
13,220
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40 0.I
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0.5
The results of this series of experiments are tabulated against pounds of steam per pound of coal in Table 11. Some of the more important results, such as heating values of the final gas, cold gas efficiency, per cent of entering steam decomposed in the bed, and reaction rate constant, Received August 17, 1926.
* Haslam, Mackie, and Reed, page 119, this issue.
* Haslam, Entwistle, and Gladding, THIS J O U R N A L17,,
a1
586 (1925).
0,s
LB C ~ A L
Figure 3
Results
Figure 2
- 0
100
l B 5 . S T E A M PER
1
.
LB5. STEAM PER LB. COAL
1.1
9 0 0.1
0.3 0.5 0.7 0.0 L8S. S 1 f A W P f R L 0 . C O A L
1.1
Figure 4
(B. t. u. in Figure 1, gross, 30 in. Hg, 60° F., H20 saturated)
A glance a t Figure 1 shows that the cold gas efficiency increases to a maximum and then decreases as the pounds of steam per pound of coal is increased from 0.366 to 1.03. The maximum efficiency which can be obtained with this rate of firing (40 pounds of coal per square foot per hour) is found to lie a t a steam-coal ratio of from 0.7 to 0.8 pound of steam per pound of coal. This value is higher than any
Vol. 19, No. 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
142 SALIPLL HOLE NO.
I
2
3
4
5
6
7
4
Figure % R u n 201 0.366 lb. steam per Ib. coal: 2.88-ft. fuel bed; 40.6 Ibs. coal per sq. ft. per hr. 5AWP.L
Figure (--Run 4 38 3 Ibs coal per sq. ft. per hr ; 3 2-ft. fuel bed, 0.378 Ib. steam per Ib coal IAUDLL
"OLE NO.
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15
28
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2r
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600
200
800
e
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Figure 7-Run
203 0.577 Ib. steam per Ib. coal; 3.08-ft. fuel bed; 38.6 lhs. coal per sq. ft. per hr. SAMPLE
6 20 N C i C S ABOVC
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8
1
2. 28 CilLTL eAR5
1e
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40
44
411
Figure & R u n
204 0.824 Ib. steam per lb. coal; 3.12 ft. fuel bed, 39.0 Ibs. coal per sq. ft. per hr.
MOLL NO
Figure 9-Run 105 0.679 lb. steam per lb. coal; 3.12-ft. fuel bed; 39.8 Ibs. coal per sq. f t . per hr.
Figure 10-Run 202 0.890 Ib. steam per Ib. coal; 3.0-ft. fuel bed; 36.3 Ibs. coal per sq. ft. per hr. 6
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I 1 1 1 1 1
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Figure 11-Run 103 1.03 Ibs. steam per lb. coal; 2.88-ft. fuel bed; 36.1 Ibs. coal per sq. f t . per hr.
2
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Figure 12-Run 201 0.366 Ib. steam per Ib. coal; 2.88-ft. fuel bed; 40.6 Ibs. coal per sq. ft. per hr.
;
l
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1927
Figure 13-Run 4 38.3 Ibs. coal per sq. ft. per hr.; 3.2-ft. fuel bed; 0.378 lb. steam per lb. coal
143
Figure 14-Run 203 0.577 lb. steam per lb. coal: 3.08-ft. fuel bed; 38 6 Ibs coal per sq. ft. per hr. 5AVP.i
,
2
3
4
5
6
r : 1 1 1 1
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Figure 15-Run 204 0.624 Ib. steam per Ib. coal; 3.12-ft. fuel bed; 39.0 lbs. coal per s q . ft. per hr.
Figure 16-Run 105 0.679 Ib. steam per Ib. coal; 3.12-ft. fuel bed; 39.8 lbs. coal per sq. ft. per hr.
Figure 17-Run 202 0 896 Ih. steam per lb coal; 3 0-ft fuel bed; 36.3 lbs coal per sq ft. per hr.
Figure 18-Run 103 1.03 lbs. steam per Ib. coal; 2.88-ft. fuel bed; 36.1 lbs. coal per sq. f t . per hr.
which have appeared in the literature. Table I11 shows the results of previous work done to obtain the optimum steam-coal ratio. These results are all lower than the ones here reported, as a result of the lower rate of firing. The present runs were made a t a firing rate of 40 pounds coal per square foot. per hour, and an optimum steam-coal ratio of 0.7 to 0.8 was found. Previous workers, using a rate of 15 to 20 pounds, obtained an optimum value of 0.4. Increased rate of firing will allow the use of more steam in the air blast. As the rate is increased, more sensible heat must be absorbed by an endothermic reaction. Steam in increasing quantities can be admitted, which upon decomposing will absorb usefully this sensible heat. The decomposition of this steam adds CO and Hz to the gas. The more steam which can be decomposed the richer the gas will
be. Steam admitted in the blast and decomposed in the bed does not bring any diluent nitrogen with it so that the heating value is increased. If too much steam is admitted the bed is cooled off and the COz which is formed in the oxidation zone is not reduced to CO by the carbon in the reduction zones. This leads to poor gas and low efficiency. Therefore, it appears that to get best results from a producer i t should be forced to a high rate, using a large amount of steam to prevent clinkering of the ash by keeping the maximum bed temperature down to a reasonable figure. The authors plan to try, in the near future, even higher rates of firing with increased amounts of steam. The reaction rate constant, decreases as the amount of steam admitted in the blast is increased. This follows naturally from the decrease in the average temperature of the primary reduction zone, the time of contact being con-
Vol. 19, No. 1
INDUSTRIAL A N D ENGINEERING CHEMISTRY
144
Table 11-Experimental 0.366
Lbs. steam per lb. coal Coal used B. t. u. per cu. f t . , gross, 30 in. Hg, 60' F., Hz0 saturated Cold gas efficiency, per cent K, (COn)(Hz) (CO)(HiO) 'k (reaction) Per cent H i 0 decomposed Lbs. coal per sq. ft. per hr. Cu. f t . gas per lb. coal Cu. f t . air per Ib. coal Actual depth, f t . T o p bed temperature, F. Primary reducing zone depth (in.) Primary reducing zone temperature, F. Oxidation zone thickness (in.)
E 107.4 67.4 1.112 3.69 80.4 40.6 76.0 56.8 2.88 1450 7.0 2200 2.0
stant. The decrease in the reaction constant explains the decrease in the percentage steam decomposed in the bed (Figures 3 and 4). Table 111-Previous WORKERS Bone and Wheelero Clementsb Clementsb Osannc
20.6 16.8 15.5 16.7
0.4 0.35 0.4 0.4
J . Iron Steel Insl. (London), 73, 126 (1907).
* I b i d . , 107, 97 (1923).
Siahl Eisen, 46, 1566 (1925).
I n these runs, as in the previous ones, the steam goes through the oxidation zone unchanged. I t s decomposition does not start until it reaches the primary reduction zone. The thickness of the primary reduction zone, as well as the thickness of the oxidation zone, is constant and is not affected by the amount of steam passing through. The apparent equilibrium constant,
remains substantially constant. This is in accord with previous w ~ r kbecause , ~ ~ ~the depth of the fuel bed has been kept constant in these runs so that the equilibrium constant, 4
Run203
Run 204
0.577
0.624
106.8 69.5 0.921 2.09 68.3 38.6 78.3 56.7 3.08 1260 9.0 1900 4.0
115.2 75.6 1.980 2.05 80.2 39.0 79.5 54.5 3.12 1200 11.0 1800 3.0
E
E
Run 105 0.679 D
116.8
73.0 0.839 1.43 69.0 39.8 76.2 52.2 3.12 1100 13.0 1900 3.0
Run 202
R u n 103
0.896 E 118.8 71.0 0.921 1.21 58.7 36.3 79.1 54.2 3.00 1400 10.0 1950 3.0
1.03 C 114.4 74.1 0.765 1.96 59.1 36.1 80.1 52.8 2.88 1300 7.5 1900 4.5
which was found to be a function of the fuel bed depth, varies only to the extent of 12 per cent average deviation, leaving out run 204. Conclusions
FUELBED FIRING COLDGASEFFICIENCY Ft. Lbs. coal/sq. ft./hr. Lbs. steam/lb. coal 7.0 5.0 3.5 2.5
0.378 C 104.8 65.2 0.72 4.34 73.4 38.3 77.4 59.0 3.20 1450 5.8 2200 2.5
Results
RATEOF STEAM-COAL RATIOFOR MAX.
DEFTH O F
Data
Run4
Run 201
1-The optimum value of steam-coal ratio for efficient producer operation at 40 pounds of coal per square foot per hour lies between 0.7 and 0.8 pound of steam per pound of coal. 2-This optimum value is a function of rate of firing, increasing with increased rates of firing, it being possible to decompose more steam with the excess heat evolved a t high rates. 3-It appears that the most desirable method of operation of a gas producer is a t high rates of firing with thick fuel beds and with steam-coal ratios that increase as the rate of firing increases. 4-The thickness of the oxidation zone and the thickness of the primary reduction zone are constant. 5-The reaction rate constant, k', decreases with increasing amounts of steam in the air blast. 6-The average temperature of the primary reduction zone decreases with increasing steam-coal ratio. Acknowledgment
The authors wish to express their sincere thanks to W. H. Emerson, J. T. McCoy, and John Buss for their helpfulness in the experimental work.
Haslam, THIS JOURNAL, 16,782 (1924)
Volumetric Determination of Alumina in Aluminum Salts' By Frederick G. Germuth DEPARTMENT OF PUBLIC W O R K S , BUREAUOF
T
HE method described herein is as accurate as the gravimetric method so universally employed, and has the advantage of requiring less time to accomplish. Method
Dissolve a 1-gram sample of the aluminum salt in 100 cc. of distilled water contained in a 250-cc. beaker. This process is hastened by gentle heating over a Bunsen burner. After dissolution is complete add several drops of methyl red indicator, concentrated ammonium hydroxide (sp. gr. 0.90), and finally 10 per cent ammonium hydroxide as the indicator shows a tendency to change color. Heat the solution containing the precipitated aluminum hydroxide slowly on the hot plate until the excess ammonia is removed, as indicated by the change of color of the methyl red to a faint 1
Received October 27, 1926.
STANDARDS,
BALTIMORE, MD
pink. Filter, while still warm, on an asbestos mat in a Gooch crucible, and wash three times with a warm 2.5per cent solution of ammonium chloride in distilled water. Discard the filtrate, add slowly to the precipitate on the filter 50 cc. of standard sulfuric acid solution (measured from a 50-cc. buret, into a 250-cc. beaker), and then heat to 80" C. After the aluminum hydroxide is dissolved, add 25 cc. of boiling distilled water. Add another 25 cc. of boiling distilled water to filter, and after this has passed into the filter flask, wash again thoroughly with hot water. Pour the filtrate from the flask into a 400-cc. beaker, add one drop of methyl orange (indicator solution), and then run in from a buret standard solution of potassium hydroxide, to determine excess of standard sulfuric acid. Deduct the number of cubic centimeters of standard sulfuric acid employed in excess of that amount required for
