I
M. B. DELL Alcoa Research Laboratories, Aluminum Co. of America, New Kensington, Pa.
Delayed Coking of lignite Tar
LARGE
deposits of lignite occur in Arkansas, North Dakota, South Dakota, and Texas. I n Texas it is used as a boiler fuel for power generation a t an aluminum smelter. Economics of utilization could be considerably enhanced if the lignite were first carbonized at low temperatures to produce tar, with only residual char used as boiler fuel. However, the economics ( 2 , 3 )depend on successful utilization of the tar. Most coke used in aluminum smelting is prepared from petroleum residuals by delayed coking between 400 and 550 C. under moderate pressure. The green coke is calcined before use in carbon electrodes. This process seemed appropriate for coking lignite tar, and apparatus was built to permit determination of yields and evaluation of coke and by-products.
tube of the thermocouple controlling the preheaters extended up through the No. 2 and 3 preheaters, leaving only an annular space for flow of liquid. Feed a t the coking temperature entered an electrically heated drum made from 8-inch schedule 80 steel pipe 7 feet long, mounted vertically and supported at its center so that it could be rotated to the horizontal position for cleanout. About 1 foot of coke formed, the extra height of the drum being provided to take care of foam. Vapors from the drum after passing through condensers were reduced to
Apparatus
atmospheric pressure and passed through a glass wool filter, a sample collection tube, and finally a wet-test gas meter. Condensate was reduced to atmospheric pressure and collected in a receiver or sent to the recycle system. For recycle, condensate was forced upward by drum pressure to a surge flask and then flowed by gravity through
Feed passed from a tank at 170' into a Hills-McCanna UM-2F pump fitted with an alumina ceramic plunger with a working range of 15 to 30 ml. per minute, then through heated lines into three preheaters. To accelerate the feed and prevent deposition of coke and plugging of feed lines, the protection
a decanter to remove water, a glass wool filter, a rotameter, a preheater, a heater, and then into the center of a I-inch Oldershaw column. Bottoms from the column were pumped back to the coke drum feed lines through another HillsMcCanna pump. A sight glass allowed maintaining of constant liquid level in the flask under the column by adjusting column feed temperature. Procedure
Feeds were prepared by topping crude tar made by carbonizing Sandow lignite Distillate, %
Residue,
-235'
Feed B C
Vac. Dist. Flash Batch
Yield
tar acids
3.8 21.4
0.9 3.4
Causticwashed
Yield
2.9 18.0
95.6 78.6
%
at 500" C. The aim was to remove all the low-boiling phenols ( - 235 C.), this was not achieved for feed B (Table I). Feed C was prepared by distillation to a vapor temperature of 130' C. at 10 mm. of mercury in a batch still equipped with a Vigreux head.
Table 1. I.
Properties of Distillates and Residues (Coker Feeds)
Distillate Sp. gr. 25/25
Tar residues were coked in a laboratory delayed coker
Diitillation, Vigrem, wt. % 1st drop, O C. 10 20 30 40 50 60 70 80 90
Feed E
Feed C
0.902
0.892
92 180 187 191 194 199 200 211 213 229 3.5 22.9 4.0 73.1 9 52 39
Residue Tar acids, vol. % Tar bases Neutral oil" Paraffins Olefins Aromatics 11. Residue 1.03 Ash, % 3.44 c-I, % 1.027 Sp. gr. Conradson C, 12.50 Distillation Vigrem, wt. yo 1st drop, O C. 112 10 20 30 a
Coke from petroleum feed, run J-41
22 1 250 263
82
157 173 186 196 206 214 223 237 250 3.9 17.2 3.3 79.5
0.50 1.028
90 267 2 93 300
Hydrocarbon types by silica gel method.
Coke from lignite food, run J-51 VOL. 51, NO. 10
OCTOBER 1959
1297
Table II.
Preparation of Cokes by Delayed Coking 5-41 J-56 J-51 Lig. B
Lig. R
,743' Lip. (I
450 16.8 0
400 19.9 0
400 18.7 0.62
400 14.4 0.64
14.7 13.3 1.41 69.4
31.4 24.9 0.99 60.7
35.5 27.7 1.12 46.3
39.7 27.7 1.22 41.7
23.8 0.95 54.6 3.4
26.6 1.08 40.5 3.7
21.8 0.96 30.2 2.6
Pet. Temp. C. Fced rate, g J m i n . Recycle ratio Actual coker yields Green coke, wt. 5 Calcined coke, wt. % Gas, cu. ft. Ib. Condensate, wt. Yc Yields based on crude tar Calcined coke, wt. 70 Gas, cu. ft. {lb. Caustic-washed condensate, wt. % Tar acids (-235' C.), wt. V,,
C'oinmercial petroleuni w k e r feed
btoi
li.
For a coking run, the heated coke drum was flushed and pressurized to 50 p.s.i. with nitrogen and the pumps Lvere primed; Lvhen the feed pressure built up to the drum pressure, the valve leading to the drum was opened and the feed preheaters Irere turned on for about 20 minutes. At the end of a run, the drum \vas maintained at temperature for
Table 111.
Calcined Coke Properties Rotmy C':drlnPd
Feed Temp. of run, Revycle i n t i 0
J-dl Per. 450
' C'.
0
Analysis Ash Fe S Si Vol. matter Real density X-ray parameters
L,, d. rl, -1. Microstrength Resistivity
Table IV.
13 400 I1 6.2
0.45 0.06 1.58 0.04 0.14 2.04
0.24 0.06 1.27 0.02 0.00 2.10
3.20 0.12 0.62 0.62 0.00 2.03
35.6 3.474 9 51 0.005
39.5 3.465 10 '49 0.038
28.5 3.484 25 56 0.051
Analysis of Liquid Products ,J-41 J-51 Petriileuiii 13
1~1111
Feed Tenili., C. ller~y-rleratio S,), . E.-, 2 5 / 2 5 \.ipreur tlist, wt. % 1st drop C. 10 20 30 40 50 60 70 80 90 Decomp. Decomo.. - . '3 .Residue Tar acids, vol. R Tar bases Paraffins Olefins Aromatics
1 298
.J-51
450 0
o.s2:3
400 0.621 0 hSS
.1-03 ('
400 0.04
0 SGY
57 108 143 178 215 248 280 310 343 373 368 91. 7.5
62 164 195 213 220 229 249 255 270 280 280 94.8 4.1
52 138 168 200 220 228 243 253 265 269 272 93. 4.7
2.4 0.8 47 18 35
15.6 3.2 35 26 39
13.9 3.4 38 19 43
a
li.6-hour
ri111.
4 hours.
A gas sample \vas taken half-
ivay through the run and analyzed by a
combination of gas chromatography and mass spectrometry. .After cooling. the bottom flange \vas removed lrom the drum, and the green coke removed and weighed. Cokes ivere calcined i n a nitrogen atmosphere at a heating rate of 1 O per minute Ivith a 12-hour soak period at 1200 C . For recycle runs the normal start-up procedure \vas followed. \ W e n the surge rank contained enough condrnsate, it was fed into the Oldersha\v column as produced. the heatertrmperarure bring adjusted to rake as ov-rrhrad all material not required by the rec!-cle pump. For run 63, because the coke feed \vas heavier than usual and tended t o coke in the preheater, recycle was started using condensate from a previous run: and once the preht,atcr lines \vcre fillcd, the reed p u m p \vas started. Discussion
In runs 5-51 and 5-56, lignite tar partially topprd before feeding to the coker (Table 11). .A deeper cut \vas taken to prepare feed C for run ,J-63. By this procedure, a greatcr total yield of -235" tar acids \vas obtained, 6.0 2's. 4,.5Yc. Presumably, this \vas due to greater thermal cracking or hiyh-boiling tar acids unhindred by the presence of lo\
