T H E J O U R N A L O F I N D U S T R I A L AiVD E , V G I N E E R I N G C H E M I S T R Y
Mar., 191;
leads us t o suppose t h a t a large portion of t h e primary products of t h e decomposition of coal are high molecular weight paraffins. These decompose into olefines which in turn form t h e decomposition products for t h e formation of benzene a n d its homologues. T h e course of the reactions may be indicated as follows: SoLn
+
COAL
I{
High weipht molecular paraffins
{ ;;;:;:::y+ ' Acetylenes
-
Low moleculdr weight
1
J
+
o i ~ $ ~ ~ .
Btsnzene Higher Homo~ogues a n d its of Benzene Homologues compounds --+ Xylene ---3 Toluene ----f Benzene, etc.
269
more efficient yields of t h e aromatics (or possibly of t h e lower boiling paraffins) could be obtained. However, until t h e oil cracking processes prove more fully their industrial worth, this phase of by-product recovery will not be entitled t o serious consideration. T h e authors wish t o express their thanks t o Professor Floyd J . Netzger, Mr. R . J. hloore and Mr. John R . Suydam for their help and suggestions. They desire also t o t h a n k Dr. Gustav Egloff for his interest and valuable help in t h e study of t h e hydrocarbon oils. D E P A R T M E U T OF C H E M I C A L ENLINEERIhG C O L U X B I A L-KIVhRSITY, N E W Y O R K C I T Y
I\--Diminishing t h e duration of t h e carbonization reaction:; by recirculation tends t o increase t h e INFLAMMABILITY OF CARBONACEOUS DUSTS By H. H. BROWN actual yields of total. llght and heavy oils as well as Received November 13, 1916 t h e yields of t h e total benzene, toluene a n d xylene T h e fact t h a t coal dust is explosive is very generally fractions. known to-day. T h e large loss of life t h a t often acV-Recirculation tends t o increase t h e percentage yields of t h e paraffins and t o decrease t h e percentage companies a mine disaster has forcibly called attenyields of aromatics a n d unsaturated bodies thus offer- tion t o this. As early as 1844, Faraday recognized ing further evidence t h a t t h e aromatics are formed a t t h a t coal dust was a n important factor in explosions in mines. But only within t h e last thirty years has t h e expense of t h e other two. VI-Although t h e percentage yields of t h e individual i t been fully recognized t h a t coal dust alone was exaromatics, benzene, toluene a n d xylene, are favored plosive without t h e presence of gas. To-day nearly by increasing the duration of t h e carbonizing reactions every large country has its experiment station t o study by non-circulation, in t h e zones of maximum aromatic causes and means of prevention of mine explosions. It must not be concluded, however, t h a t coal dust formation-usually between 7 0 0 and 900' C.-the is t h e only dust t h a t will explode, as experiments have n c t z d yields are favored by recirculation. VII-Recirculation tends t o increase both t h e clearly shown t h a t many other carbonaceous dusts a c t u a l a n d the percentage yields of t a r acids in t h e light are a t least as easily ignited and as capable of propagaoil. This would t e n d t o confirm t h e conclusions of ting a n explosion as is coal dust. While most of t h e other investigators t h a t t h e t a r acids are products dust explosions reported in surface plants occur in. mills and elevators handling wheat, oats and corn, of t h e primary decomposition of coal. VIII-The results as a whole emphasize t h e neces- and their products, i t appears t h a t no mill handling sity of temperature control in coal carbonization if carbonaceous material is immune froin the possibility t h e yields of t h e important aromatics are t o be con- of an explosion. The list of known explosions in other sidered. Under t h e conditions usually maintained kinds of mills includes those handling dextrine, sugar, in standard practice, it is evident t h a t for actual starch, malt, wood, linseed meal, cottonseed meal, efficient combined yields of benzene, toluene and paper, cork, fertilizer, sulfur, cocoa, and spice dusts. T h a t flour dust miill explode was clearly demonxylene, t h e carbonizing temperatures should not greatly exceed 800' C., nor should they lie much strated in 1878 by a tremendous explosion in t h e Washlower t h a n 700' C. The fact t h a t such good yields burn Flour Mills in Minneapolis. An investigation of t h e aromatics are obtained at t h e gas and coke was made b y Professors Peck and Peckhaml in conworks where very high temperatures are employed is, nection with which they tested t h e explosibility of a no doubt, due t o t h e protection offered by t h e cooler variety of dusts by blowing t h e m as a cloud into a central core of coal which does not reach t h e cracking closed box containing a small flame. They concluded temperatures, and t o t h e cooling effect on t h e hotter t h a t practically all finely divided, highly carbonaceous gases due t o dilution with t h e cooler gases emerging material would explode under t h e conditions tried. More recently R. V. Wheeler,2 chief chemist for t h e from t h e center of t h e charge. IX-By t h e use of a n y device whereby t h e duration Explosion in Mines Committee, England, carried o u t of t h e carbonizing reactions is shortened, i t seems possi- some systematic tests for t h e purpose of discriminable both t o increase t h e yields of t h e paraffin oils a t ting between harmless a n d dangerous dusts, and t o t h e lower temperatures and t h e yields of t h e aromatics determine t h e temperatures a t which inflammation of at t h e higher temperatures. It is also possible t o t h e dangerous dusts takes place readily. As a result of these tests he divided t h e dusts into three classes, operate a t higher carbonizing temperatures. X-The similarity of t h e coal carbonizing reac- v i z . : I-Dusts which ignite and propagate flame readily, tions t o those undergone during oil cracking suggests t h e possibilities of carbonization a t low temperatures t h e source of heat required for ignition being comparaa n d a treatment of t h e low temperature tars by t h e tively small, for example, a lighted match. 1 M i n e s and MineraLs, 29 (1908), 5 5 . cracking processes used on t h e petroleum oils. I n * Report o n the Inflammability and Capacity for Transmitting Exthis way t h e valuable t a r acids could be conserved plosions of Carbonaceous Dust Liable t o be Generated on Premises, undei by removing t h e m before t h e cracking treatment, a n d the Factory and Workshop Acts, 1913. R. V Wheeler, D.Sc.
T H E J O U R N A L OF I R D U S T R I A L A N D ENGINEERING CHEMISTRY
270
11-Dusts which are readily ignited but which, for t h e propagation of flame, require a source of heat of large size a n d high temperature, such as a n electric arc, or of long duration, such as t h e flame of a Bunsen burner. 111-Dusts which do not appear t o be capable of propagating flame under a n y conditions likely t o obtain in a factory, because ( a ) they do not readily form a cloud in air, or ( b ) they are contaminated with a large quantity of incombustible matter, or (c) t h e material of which they are composed does not burn rapidly enough. Certain dusts of interest in t h e present investigation were classified b y Wheeler as follows:
1
Sugar Starch meal and sugar refuse flour
~~c~~~~ I Rice
CLASSI1
I i
Oat husk Rice milling Castor oil meal Offal grinding (bran) Spice milling
CLASSI11 Cottonseed
Cottonseed and soya bean
Grain (flour mill) Maize Grain (grain storage) Rape seed Corn flour Flour (flour mill) Grist milling Horn meal Mustard Sack cleaning Rape seed (Russian) Grain cleaning”
T h e Minneapolis explosion aroused milling men to t h e danger of existing conditions a n d caused many t o t a k e precautions immediately t o guard against repetition of similar occurrences. T h e impression was not lasting a n d although a large number of grain dust explosions occurred after t h a t time, general interest was not awakened again until June 24, 1 9 1 3 , when a n explosion occurred in a feed grinding plant a t Buffalo in which 3 3 men lost their lives, a n d over 7 0 men were injured. This explosion, which occurred during t h e ordinary process of operation, completely destroyed t h e milling plant a n d did considerable damage t o surrounding property. -4s a result of this disaster t h e millers in a n d around Buffalo were very desirous of obtaining a n y possible information relating t o t h e inflammability of grain dust which would help t h e m in taking effective safety precautions in addition t o t h e measures already adopted. An agitation was started which resulted in a cooperation between t h e millers and t h e Bureau of Mines for t h e investigation of questions relating t o explosions of grain dusts. This was later taken u p by t h e Government a n d is being continued as a cooperation between t h e Bureau of Chemistry a n d t h e Bureau of Mines. The laboratory investigations, originally carried on in t h e laboratories of t h e Bureau of Mines a t Pittsburgh, have recently been transferred t o t h e laboratories of t h e Bureau of Chemistry a t Washington. SIUILARITY B E T W E E N
GAS AKD DUST E X P L O S I O X S
Although t h e investigations of dust explosions have not been as complete or conclusive as those made on gas explosions-probably because of t h e great difficulties encountered in maintaining or even obtaining a uniform dust cloud of any desired density-the available d a t a show quite conclusively t h a t t h e phenomena exhibited b y t h e two types of explosions are very similar. A statement of a few pressures and flame velocities measured in explosions of coal dust a n d of gases will serve t o indicate this fact. T h e United States Bureau of Mines’ reports having 1 U.
S. Bureau of Mines, Bull 66 (1913).
1‘01. 9, NO. 3
measured in a coal dust explosion an average velocity of 2273 f t . per sec. over a distance of I O O ft. I n experiments a t t h e British Experiment Station,’ Altofts, England, a n average velocity of 2014 ft. per sec. has been obtained. Taffane12 obtained a velocity of 3300 ft. per sec. A pressure of 103 lbs. per sq. in. is reported by t h e Bureau of Mines. The British authorities report pressure u p t o I O O lbs. per sq. in., with a n estimated pressure in one test of 1 2 0 lbs. Taffanel reports having measured pressures of 2 2 7 t o 270 lbs. per sq. in., while in one test t h e steel gallery, with a n estimated breaking strength of 5 7 0 Ibs. per sq. in., gave way, pieces of t h e sheet steel being thrown distances u p to 1 5 0 meters (472 ft.). The maximum velocities of propagation of flame in many gas mixtures have been determined with accuracy by Dix01-1,~ B e r t h e l ~ t , E ~ m i ~ h , Nernst,6 ~ a n d others.’ For certain of these mixtures the following results were obtained: GASEOUSMIXTURES
VELOCITYPER Meters 2820 2700 2364 2322
+ + ............. ++ .................................. + ....................................
2H2 0 2 .................................... 4 parts coal gas 5 parts oxygen.. CzH4 302 202. .................................. CHI 2CO 0 2
1680
SECOND Feet 9250 8876 7724 7616 5510
Mallard a n d LeChatelier* obtained a pressure of 6 . 5 atmospheres (97.5 lbs. per sq. in.) for a mixture of I vol. CHI 2 vol. 0 2 g vol. air. Leau a n d Bone9 found a pressure of 20.7 atmospheres (310. 5 lbs. per sq. in.) developed in a mixture of 2H2 02. It will be noted t h a t as high pressures have been observed in coal dust explosions as in gas explosions. However, t h e extremely high velocities attained b y t h e flame in certain gas mixtures have not been reported as observed in dust explosions. Such high velocities could not be expected, for even t h e finest dust particles are many times larger than gas molecules, a n d so, even in t h e most dense dust clouds t h e particles could not be as close together nor as intimately mixed with t h e oxygen as are gas molecules. Therefore, t h e heat of combustion of one dust particle cannot be as readily transmitted t o t h e next particle as i t can in a mixture of gases. But t h e finer t h e dust t h e more nearly will i t approach the size of a gas molecule. Therefore, i t might be expected t h a t t h e velocity of t h e flame through a cloud of very fine dust would more nearly approach t h e velocity attained in gas explosions. As a matter of fact, this is true. Taffanello has brought this out in tests made a t t h e French Experiment Station. Results obtained by t h e Bureau of Mines11 lead t o t h e same conclusion. T h e rate a t which inflammation travels through a
+
+
+
1 Report of Committee on British Coal Dust Experiments. Record of first series, 1910. 2 “Les experiences fransaises sur les poussieres de houille.” Internationaler Kongress, Diisselford, 1910. Berichte der Abteilung fur Bergbau. a H. Dixon, Phil, Trans., 184, 9 7 , 161; 200, 328; Chem. News, 46, 70. I M. Berthelot, “Sur la Force des Matieres Explosives,” 1 (i883), 159. 6 Emich, Ber., 44, 2462. e Nernst, “Theoretische Chemie,” Dritte Aufluge, p. 628. 7 Notably Vieille; Mallard and LeChatelier. 8 E. Mallrrd and H. LeChatelier, .4nn. Mines, [SI 4 (1883). 379. 9 B. Leau and W. A. Bone, Chem. News, 66 (1882). 101. 10 Taffanel, Fourth Serles of Tests. 11 G. S. Rice, “Investigations of Coal-Dust Explosions,” Bull. A m @ I n s t . Mining Eng., 1914, p. 2476.
M a r , 1917
T H E J O 1 7 K S . 4 L O F I-\-Ill-STRIAL
gas mixture is dependent upon a t least two factors, the inflammability of t h e gas a n d t h e percentage of t h e gases in t h e mixture. The rate a t which inflanimation travels through a dust cloud seems t o be depende n t upon two similar factors, namely, t h e inflammability of t h e dust a n d t h e amount of dust in suspension. A third important factor is t h e fineness of t h e dust. It mill be seen, therefore, t h a t gas a n d dust explosions are similar in many ways a n d t h a t a gas explosion is only a limited case of a dust explosion. -4 thorough knowledge of t h e nature of dust explosions a n d of t h e accompanying phenomena is necessary in order t o devise means for t h e prevention of such explosions a n d for t h e stoppage of explosions if by mischance they should start. I t is, therefore, necessary t o know how dust ignites, t h e various means by v-hich i t may be ignited, or inflamed, a n d t h e chemical processes t h a t t a k e place. Another important factor t o know is t h e ease with which t h e dust ignites and propagates a flame. This property we may call t h e “inflammability” of t h e dust. T h e term “esplosibility” has also been applied in this connection. D E V E L O P M E S T O F METHOD F O R T E S T I N G I N F L A M M A B I L I T Y
A N D ESGILVEERING C H E M I S T R Y
Bureau of Mines. Preliminary tests showed t h a t it could be adapted. Several kinds of dusts were tested a n d t h e results published by t h e hlillers’ Committee of Buffalo, New York, as a “Preliminary Report on t h e Explosibility of Grain Dusts.”1 Further tests were made with t h e same a n d other dusts, a t t h e same and a t lower temperatures. The results are given in Fig. I. The temperatures were measured by a thermocouple with its hot junction on the inside of t h e igniting coil. The pressures given for temperatures from 1000 t o 1200’ C. are t h e average of all results given b y each dust at these temperatures. But a t t h e lower temperatures ignitions were not obtained in every test, so t h a t t h e points given are t h e average of only those where the dust ignited. The results given a t 1 1 0 0and 1200’ C. were referred t o Pittsburgh Coal Dust as a standard, but t h e results a t all lower temperatures are those actually obtained. Also, as in t h e early tests, all t h e dusts except 61, 1 1 2 , a n d malt, were dried a t 105’ C. in a current of dry air. Tests were also made on a few other undried dusts a t two temperatures only. The results a t 1200’ C. were referred t o t h e coal dust standard.
O F DCSTS
When t h e present investigation was started t o determine t h e causes and means of prevention of grain dust explosions, one of t h e first problems undertaken was t o devise a method for testing t h e inflammability of the various dusts, or t o adapt some method a t present used for testing t h e same property of coal dusts. The method of Wheeler was tried, b u t t h e tests were unsatisfactory. A method for testing coal dusts had been developed by t h e United States
271
SO.
13 A 4A 7 A 6A 11 A 1A 3 A 12 -4 9 A
Pressure a t SAMPLE 1200° C Wheat s m u t . , . . . . . . . . . . . . . . . 21.4 15.5 White dextrin.. Dark canary dextrin.. . . . . . . . . 15.1 Canary dextrin, . . . . . . . . . . . . . 14.9 Wheat s t a r c h . , . . . . . . . . . . . . . . 14.1 S u g a r . . ..................... 13 .O Corn starch.. . . . . . . . . . . . . . . . 1 2 . 6 Rice starch . . . . . . . . . . . . . . . . . 12.3 Potato 0 o u r . . . . . . . . . . . . . . . . . 10.4
..............
Pressure a t 800° C. 0.6 7.6 7.3 7.9 8.5 7.5 6.7 5.3
6.2
These results are given as a basis of comparison of the dusts by t h e method used in testing them a n d t h e 1
Ahstruct THISJOURNAL, 6 (1914), 934.
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHE,MISTRY method t o be described. T h e y are given also to show how low a temperature is required to ignite these dusts-a temperature of 700' C. on t h e inside of t h e igniting coil showing only a very dull redness at t h e surface t h a t is scarcely visible in daylight. VARIABLES AFFECTISG RESULTS-The method as used a t this time was not a t all satisfactory for either coal or grain dusts, as t h e results were less uniform and reproducible t h a n m-as desired. There were too many variables. The igniter, with its means of temperature measurement, was unsatisfactory since i t did not give t h e actual temperature a t t h e point of ignition, a n d did not compensate for the deposition of ash on t h e coil, or t h e wearing away of t h e alundum coating. Probably t h e most important variable was the manner in which t h e dust was inserted into t h e globe a n d against t h e coil. This, i t appeared, was controlled not only by t h e amount of air used t o force in t h e dust and b y its r a t e of flow, b u t also b y t h e size a n d shape of t h e funnel which holds t h e dust, Other variables were t h e amount of dust used, t h e temperature used t o ignite t h e dust, and whether or not a screen was used over t h e funnel through which t h e dust would be forced. MEASURING T E M P E R A T U R E OF IGNITER-TO overcome t h e variables in t h e igniter, a coil of similar construction was used, except t h a t it had, outside t h e alundum coating, platinum foil fastened tightly around t h e coil. T h e temperature at t h e surface of t h e coil is measured b y a thermocouple. The wires of t h e thermocouple are not fused together in t h e usual manner t o form t h e hot junction, b u t are attached separately t o t h e platinum foil. T h e platinum rhodi u m wire is fastened around t h e coil at t h e center and t h e platinum wire about 3 mm. t o one side. These were fastened t o t h e foil by means of heat a n d pressure. T h e hot junction is then a t t h e immediate surface of t h e coil a n d t h e temperature registered is t h a t of t h e point of contact between t h e small To platinum rhodium wire a n d t h e platinum foil. reduce t o a minimum t h e loss of heat from t h e surface of t h e igniter by conduction along t h e wires, t h e ends in contact with t h e foil are drawn down t o a diameter of 0.15 mm. With this arrangement t h e coil can always be kept clean and t h e actual temperature a t t h e point of ignition known. M E T H O D O F I N S E R T I N G DUST-It Was early observed t h a t b y grading t h e releasing of t h e air used t o force in t h e dust, t h a t is, b y opening t h e pinchcock a t various rates, a great variation in results could be obtained with a n y dust. T o obviate this a mechanical releasing device was made which would always release a t t h e same rate and very rapidly. With cert a i n dusts this rapid forcing of t h e dust against t h e igniting element was found t o be too rapid t o obtain t h e highest pressures possible. Therefore, t h e r a t e of flow of t h e air was controlled by a short piece of capillary tubing placed between t h e releasing device a n d t h e funnel. This method gave much more satisfactory results t h a n h a d previously been obtained. However, it was observed t h a t t h e results could be varied b y in-
Vol. 9 , No. 3
serting t h e dust into t h e funnel in different ways, t h a t is, whether i t was compact or loose, partly around t h e bend in t h e funnel, or entirely in the upright portion, or partially in t h e bowl. Concordant results were very difficult t o obtain with the original funnel. Therefore, a n extensive series of tests was started t o develop a funnel t h a t would be suitable for all types of dusts, and also a size of capillary which would give consistent results. I n these series of tests seven different types of funnels were tested before one was obtained which was satisfactory. Tests with several different types of dusts were made with each funnel. Capillaries of from I . o t o 2 . 5 mm. bore were used in the tests. The two extreme sizes were used in only a few tests as the one of 0 .I mm. bore was found to be too small t o allow passage of sufficient air t o raise t h e dust, a n d t h e one of 2 . 5 mm. bore gave results only slightly higher in some cases t h a n were given with t h e next size smaller. Therefore, only the following sizes were used in most of the tests: I . j, 2 . 0 5 , a n d 2.35 mm. bore, respectively. The pressure of t h e air used t o force the dust into t h e globe also affected t h e results very appreciably. Tests were made with t h e air under I j cm. and 2 0 cm. of mercury. The latter pressure was found t h e more satisfactory. The manner in which t h e dust was inserted was also affected by a 14-mesh screen placed over t h e funnel. This served t o break u p t h e dust and make a more uniform cloud. However, some of t h e grain dusts were very fibrous, a n d so did not pass readily through t h e screen. This gave irregular and low resuIts with some of these dusts so t h a t tests were made using t h e screen a n d without it. A M O U N T O F DUST-In all the early work j0 mg. Of t h e dusts were used i n each test except where curves were run with varying amounts of material. These results indicated t h a t a larger amount of material would give more uniform results, therefore series of tests were run with both j o a n d 7 5 mg. of t h e dusts. The results with 7 5 mg. were much higher in every case, fully as uniform, a n d in some cases more uniform t h a n with 50 mg. As 7 5 mg. was a convenient'amount to handle, giving sufficiently high results with t h e less inflammable materials, a n d not too high for safe handling of t h e apparatus with t h e more inflammable, this amount was used in all later experiments. E F F E C T O F LARGE A M O U N T S O F DUST-The tests With 7 5 mg. of dusts suggested a study of t h e effect of large amounts of material. Therefore, a short series of tests was made with four different dusts. T h a t size capillary was used which previous tests h a d indicated would give highest results. T h e results of these tests are given in Fig. 11. It will be observed t h a t for Samples 4 7 a n d 33 t h e curve h a d nearly reached its maximum a t 150 mg. of material, while t h e pressures for sugar a n d starch were still increasing a t this point. Higher points were not run because pressures might be obtained beyond t h e safe working limits of t h e apparatus.
Mar., 1917
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
273
Pittsburgh coal dust, gave higher results with the 2 . o ja n d 2.3j mm.-bore capillaries, and in some cases with t h e I . 5 mm. capillary t h a n were given a t t h e highest temperature in t h e earlier tests. The 2 . 0 5 mm. capillary gave t h e most concordant results. O T H E R VARIABLES-However, t h e results a t this point were not entirely satisfactory. The only other variables t h a t had not been thoroughly tested were t h e effect of higher temperature a n d t h e action of t h e valve between t h e air reservoir and explosion flask. A slight change in capillary was also considered. E F F E C T OF vaLvE-Tests were made t o determine t h e effect of t h e valve. The results obtained without t h e valves were appreciably lower t h a n when the valve was used. This was expected as t h e volume of air affected by t h e ignition was thereby increased by t h e volume of t h e air reservoir. However, t h e valve 6
/5u
200
I
250
3m
Wejyhf of Dust- Mi//iyrams FIG. I1
'
The results indicate t h a t large amounts of the more inflammable materials could not be used in t h e present t y p e of apparatus, and also t h a t only a certain pressure will be developed even though more material is used. It is possible t h a t these curves would behave as gas curves and begin t o decrease if sufficiently large amounts of materials were used. I n running this series of tests i t was observed t h a t a slight amount of charring resulted in each test with I O O mg. of Sample 47, while with Ijo mg. of material a considerable amount of charred material was found in t h e flask after ignition. Only very slight charring was noticed with t h e starch a n d flour. When I jo mg. of sugar were used, a perceptible odor of formaldehyde came from t h e flask, while with zoo mg. the odor was quite strong. These observations would indicate incomplete combustion with these amounts of material, a n d also t h a t t h e heat of t h e reaction caused some decomposition of t h e dust. INDICATIVE RESULTS-For comparison with previous a n d later results there is given in Fig. I11 t h e results obtained with a few typical dusts, using three different sized capillaries, with a n d without a screen over t h e funnel. These results were obtained with t h e funnel t h a t was found t o be most satisfactory. Seventy-five milligrams of material were used a n d ignited a t a temperature of 1100" C., a temperature approximately t h e same as I Z O O " C. on t h e inside of t h e coil, which had been used quite satisfactorily in t h e early work. The results are those actually given, a n d are not referred t o a n y standard dust. I n these tests i t will be observed t h a t t h e results with dextrin, sugar, a n d Samples 1 3 a n d 47 are higher a t certain or all points when no screen was used over the funnel. N o reason can be assigned t o t h e two former, b u t t h e latter two contained fibrous material which was held back by t h e screen. With t h e other dusts t h e screen served t o break u p t h e dust a n d form a more uniform cloud. All these dusts except wheat flour ( N o . 33), a n d
\
T I I E J O C K N . 4 L OF I N D U S T R I A L
274
resuits ;it ail these temperatures were quitc iiniforni a n d concordant. O n account of these facts, and because t h e results at 7 2 0 0 ' C. were not much different from those obtained at 1 1 joO C., which would mean t h a t a slight variat.ion of this tempcrature would not make any appreciable difference in the rcsults, and since 1 2 0 0 ' C. was more convenient t o use than a higher temperatur?: i t was taken as a standard temperature. EFFECT c-\iw~T.mi-. to determine the most satisfactory size of capillary for aii types of dusts, a series of tests was m x l e at 1200' C., using four differe n t capillaries, 6 cm. long and varying in hore by 0 . 1 rnm. from s . 9 min. to 2 . z mm. These rcsiilts are given in Fig. T'. It will be ohser capiilary had no mark suits. This was due, probably, to the high igniting temperature, and l o t h e fact that t h e differences in diameter of the capillaries wcre no1 large enough t o affect greatly the rate of florv of tlic air. However, there was a ditierence in t h e iiniformity of t h e results obtained. T h e 2 . o mm. capillary gave t h e more uniform and concordant resuits, and these !viere ncarly as high or higher than thc results given with other capillaries. So this capillary was chosen as t,he liest for future work. COMPABISON
UP
\13:1110135
POli
CVhi.
:AS11
GUAIN
uusl's--During t h e development oi this method, t h e Biireau of Mines was also perfecting their met.hod for testing c o d dusts. A s the properties of the two y (Iissiniilar, i i duplication of tests could not he avoided. Ho\wever, it was thought advisable
I
I
I
.
.
1'10.
. ..
.. . . ..
VI
1200' C., capillary 6 cni. long mid 2 . 0 m m . bure: air under 2 0 cm. pressure; no one-way valve between air reservoir a n d explosion flask, but a pinchcocli back of the air reservoir; 7 j mg. of material; a coarse screen ovcr t h e funnel except when very fibrous dust is tested; and a funnel 4 . 0 min. internal diamercr, with a bowl in. deep and in. across at t h e top, and t h e bend in the funnel beitlg a right-angle 6 j s in. below t h e bowl and having a sinali wire screen inside and just back of t h e bend. T h e same type of apparatus is used in testing the inflammability of both t h e coal and t h e grain dusts. I t is shown in Figs. V I a n d VI1. T h e only difference in construction is in the funnel. T h c methods of
\,.
-,
I
i Cu,i//ary C u r v e /zuo "C 10 cm A i r
2 IDDO Temperohre NO0
Cent9Yrade ;zoo
Fie. IV
19 Dium-2.0 uf CopiNory z/ 2.2
v
FlG~
to have its few differences iii !.he methods as possible. i t was partly for this reasoi,, to conform more closely t o Bureau of Mines practices. t h a t the valve was discarded, a n d t h a t a temperature ai 1200' C . mid a 2.0 mni. capillary was adopted. These conditions gave the best results with coal dust, and pr;ictically the same results with grain dusts as slightly different conditions would give. T h e method as adopted for testing grain dusts is as follows: Temperatiire,
Frc. VI1
operatiun are ditierent, honeyer, in t h a t jj ins. of grain dust are uscd as against 100 mg. lor tiic more inflammable coals, and 300 mg. for t h e less inflanimable. T h e vital difference is that osygen under I j cm. of mercury pressure is used t o insert t h e 100 mg. of coal dust, while air at 2 0 cni. of mercury pressure is used t o insert the grain dusts. RY.SUL'TS WITII C A R B O N A C X O U S U T ~ S T S - -The method as developed and standiirdized has been used in tesi-
Mar., 1917
T H E J O U R N A L OF,I N D U S T R I A L A N D ENGINEERING CHEMISTRY
ing t h e inflammability of a large variety of dusts. T h e results are given in Table I in t h e order of inflammability : TABLE I-INFLAMMARILITY
Sample No. 51 A 13 A 61
CARBOXACEOUS DUST6 Pressure Generated Lbs. per KIND O F DUST Sq. In. OF
Stinking smut o Yellow corn d u
Dextrin dust from i n............ 18 A Stinking smut of w 47 A Powdered wheat s t 20 A USt . . . 46 A White dextrin. ......................... 4 A Starch dust (corn) from dry starch kilns. , 21 A Canary dextrin, , , 6A 43 A (200 mesh) Powdered corn starch. . . . . . . . . . . . . . . . . . . SA Wheat starch.. . . . . . . . . . . . . . . . . . . . . . . . . . 11 A 17 A Starch and dextri Y . filler. .......... . 35 (200) Wheat elevat . Dextrin dust 19 A . Wood dust fr 36 A (200) Corn starch ................ 3A Oat and cor nloading station. . 37 (200) Lump corn starch pulverized t o pass 200 2A mesh. ............................... 112 White corn dust, top of eleva Wheat elevator d u s t . . 13 (200) Oat and corn dust, top of ele 43 57 (100) Oat dust from ground oat h Sugar, lump pulverized t o pass 200 mesh. . 1A Gluten feed dust, from beams, etc., in cur23 A
14.6 13.9 13.9 13.8 13.2 13.1 13.0 13.0 12.8 12.8 12.i 12.6 12.5
.......
47 (200) 7A 65 (200) 9A 31 A 12 A 33 (200) 14 A 24 A (200) 50 A 103 48 A (200) 26 A 34 A x13 C 43 A 29 A 32 A 97 33 42 A SA 41 A 44 A 49 A 30 A 25 A (200) 15 A 37 A
.................. llector..
...........
12.2
11.8 11 , 8
Wheat flour from packing room.. . . . . . . . . . 11.2 Powdered wheat starch. . . . . . . . . . . . . . . . . . 1 1 . 0 . . . . . . . . . . . . . . . . 11.0 Malt dust from rge of collecting 10.6 system .............................. 10.5 Wheat flour dust, rolls and purifiers..
.....
.....
Sugar dust, co Pittsburgh Standard Coal D u s t . . . . . . . . . . . T a n bark d u s t , . . . . . . . . . . . . . . . . . . . . . . . . . Reduction middlings.
10.4 10.1 IO. 0
......
Cocoa dust from cocoa cooling room.. ..... Rice starch.. ........................... Extra fine sulfur flour.. . . . Wheat smut and field dust Ground cork d u s t . , . . . . . . . Arrowroot pow Potato starch Gelatin dust from elevator..
.............
9.1 9 .O
1.1
T h e results in Table I cannot be considered as absolute, as showing t h a t t h e order as given here is t h e exact order of ease with which these will ignite. It is, however, t h e order of inflammability, as given under t h e conditions used in t h e tests. A change of any of t h e conditions might increase t h e pressure given by some, while i t would decrease t h e pressure given b y others. This fact is clearly shown in Fig. 111, where increasing t h e size of capillary caused a n increase in pressure with certain dusts, b u t a decrease with others. However, t h e results indicate t h a t most of t h e dusts have a higher degree of inflammability t h a n Pittsburgh coal dust, but in t h e light of present knowledge i t is difficult t o interpret t h e significance of this higher pressure, except t h a t t h e dust is more easily ignited. Although these results are only relative, t h e y indicate t h a t all t h e dusts tested have a high degree of inflammability, and t h a t a dangerous condition exists where a cloud of any one of t h e m is in suspension, or in a position where i t can be easily thrown into suspension in t h e air. The relative degree of danger is approximately in t h e order of t h e foregoing results. Tests on a larger scale are under may which will aid
27j
in t h e interpretation of these results. These are designed t o demonstrate under what conditions each dust will ignite, whether t h e source can be as small as a static spark, or whether i t must be as large as a gas flame, or something between these limits. A C K ii0 W L E D G LIE i i T S
The author desires t o express his appreciation of t h e assistance a n d helpful suggestions given by Dr. G. A. Hulett, consulting chemist, and D r . J. K. Clement, physicist, U. S.Bureau of Mines. DEPARTMEKT O F ACRICULTURK BUREAUOF CHEMISTRY WASHINGTON, D. C.
A STUDY OF COMMERCIAL BEECHWOOD CREOSOTE By H. K. SMITHA N D S F. ACREE Received December 19, 1916
A sample of beechwood creosote, made b y a commercial process a n d furnished b y t h e manufacturer, has been analyzed at t h e Forest Products Laboratory, Madison, Wisconsin, as a p a r t of t h e studies on hardwood tars, creosotes a n d other related substances. T h e sample was found t o have t h e character istics indicated in Table I. TABLEI-ANALYSIS Fraction Temp. No. = c. 1 205 2 215 3 225 4 235 5 245 6 255 7 265 8 275 9 285 Residue . . .
__ Per centObserved 3.7 10.1 20.8 8.1 5.5 8.4 13.4 2.7 4.8 21.6
Cumulative 3.7 13.8 34.6 42.7 48.2 56.6 20.0 ,2.7 i7.5 99.1
OF
SAMPLE
Sp. Gr. 60' C.
Ind. Ref. 60' C.
1:003 1.009 1.012 1.019 1,021 1.022
1.50i4 1 , SO83 1.5 111 1.5117 1.5123 1.5138 1.5138
...
....
....
CEARACTBR OF
FRACTIOX
Yellow liquid Golden yellow liquid Golden yellow liquid Golden yellow liquid Golden yellow liquid Golden yellow liquid Golden yellow liquid Golden brown liquid Red-brown paste Black solid
.., ... .... I n t h e present investigation i t was desired especially t o determine if any considerable portion of t h e phenolic constituents have boiling points around 2 0 j O C.t h a t of guaiacol. -4s t h e sample contained some t a r a n d pitch it was thought best t o remove these before further studies. The distillation was carried on in a n iron still holding about j liters. On account of frothing, only about z liters could be distilled a t one time. There was a n overflow attachment t o t h e still so arranged t h a t when frothing became so violent as t o cause an overflow, t h e lead t o t h e condenser could be closed and another passing out of t h e window opened t o prevent t h e contamination of t h e distillate with t h e froth. I n t h e first run there were about 2 liters in t h e still. This was heated slowly, about I ~ , hours ' ~ being required for t h e first drops t o come over a t 45 t o j o o C. The temperature rose rapidly t o about 8 j O , then slowly t o goo, where it was constant for a while. The liquid coming over a t this temperature was light brown and a good deal of water was present. Finally, the temperature rose t o 130' and t h e other fractions were TABLE11-DISTILLATION OF BEECHWOOD CREOSOTE pl-0. 1 2 3 4 Amount Distilled 2 liters 2510 g. 2609 g . 2597 K. 130 t o 200; 175 cc. 63 66 64 160 200to215 140 288 286 215 t o 230'. ..... 240 638 48 1 521 230 t o 245'. 390 450 485 459 357 209 177 245 t o 250'. . . . . . . . . 26O0-up., ... 192 267 Pitch.. . . . . . . . . . . . . 584 590
......
...... ..... ........
...
taken. Table I1 gives a summary of t h e fractions obtained in four distillations.
