INDUSTtZIAL A N D ENGINEERING CHEMIXI’RY
June, 1931
flow hd/k has, in general, been expressed as a function of two groups of variables: Dv/Z and cZ/k, where Z is the viscosity. There has been some evidence that L / D should also be used, even in those cases where entrance turbulence effects
631
Equation 18 can be written as (6) : hD
= \LT
?,$)
(Pe.
(20)
Equation 20 corresponds to Equation 8 if 2 drops out as a variable and if the effects of Pe and LID are the same. Turbulent flow heat transfer data can be correlated by Equation 20 as well as by Equation 18,and Equation 20 can be used as a general type equation for heat transfer under both viscous and turbulent flow conditions. Acknowledgment
The authors are much indebted to Carl C. Monrad, of the Standard Oil Company of Indiana, for suggestions during this investigation and for his valuable bibliographic work in connection with the problem. Figure 4-Experimental
Average Coefficient Curve
are absent (1, 6). If this is 80, the turbulent flow equation takes the form: hD
Dv CZ L Z k D
(18)
Also, since (19)
Literature Cited
(1) Burbach, “Stromungswiderstand und WArmedbergang in Rohren.” Akad. Verlag, Leipzig, 1930. (2) Colburn and Hougen, IND. ENG.CHBM.,92, 522 (1930). (8) Dittus, University of California, Bull. 9, No. 11 (1929). (4) Graber, “Die Grundgesetze der Wirmeleitung und des Warmetiber ganges,” pp, 1 7 9 4 7 , Springer, Berlin, 1921. (a) Reevil and McAdams, Chem. Met. Eng., 86, 464 (1929). (6) Latzko, 2. angew. Math. Mech., p. 268 (1921). (7) Merkel, “Die Grundlagen der Warmeubertragubg,” p. 16, Steinkopff, Dresden and Leipzig. (8) Morris and Whitman, IND. ENG.CHEM.,90, 234 (1928). (9) Nusselt, Z. Ver. deuf. Ing., 64, 1154 (1910).
Manufacture of Charcoal in Japan‘ With Special Reference to Its Properties Ihachiro Miura Toxvo IMPERIAL UNIVBRSITY, KOMABA, TOKYO, JAPAN
I
N JAPAN about 80 per cent of the total forest production is now being used for firewood, and about 40 per cent of this is converted into charcoal. I n contrast with this only 40 per cent is said to be used for firewood in America and Germany, the remainder being manufactured into lumber. It is therefore obvious that the study of charcoal, which is the principal domestic fuel in Japan, is an important problem from the point of view of both the forest industry and the economies of daily life. For these reasons Japan has made significant progress in charcoal manufacture and is a t present producing several varieties, of which black or soft charcoal and white or hard charcoal are most common. Charcoal burning in Japan is usually accomplished by the use of various types of ovens characteristic of the Orient. Since Japanese charcoal, especially the white charcoal, is made in a special manner a t a very high temperature, the meiler is very seldom employed and the American brick kiln not a t all. Using more than ten kinds of ovens currently employed in Japan the writer has conducted experiments on the tempera* Received December 16, 1930.
ture of carbonization, the selection of materials for the construction of the ovens, the yield, and the properties of the charcoal produced. Charcoal is usually made by ovens of two general types: (1) earthen ovens, in which the materials remain within during the entire process, the combustion being stopped by closing all vents; and ( 2 ) stone ovens, from which the w h i t e hot contents are withdrawn and covered with a slightly moistened mixture of earth, ashes, and charcoal powder in order to extinguish the fire promptly. The charcoal made in the earthen ovens is black and of moderate hardness; hence it is called black or soft charcoal. This kind of charcoal is generally used for domestic purposes, but if made from coniferous wood it can be used in forges. The product of the stone ovens is white on account of the ash powder on its surface, is very hard and of the best quality, and a cross section has a metallic luster. It is called white or hard charcoal and is fitted not only for domestic use but also for other purposes, such as making confectionery and special cooking.
632
INDUSTRIAL A N D ENGINEERING CHEMISTRY Production of Black Charcoal
T’ol. 23, N o . 6
Production of White Charcoal
About 60 per cent of the charcoal produced in Japan is black charcoal. After the wood has been placed in a perpendicular position within an earthen oven, a fire is lighted in front of it and the air supply regulated by means of an air vent
The characteristic feature of the production of white charcoal is the gradual carbonization which follows the combustion of a part of the material (bark) due to a sufficient air supply, which in turn results in a high temperature and hardening of the material. The oven is built by piling up stones and filling the spaces with clay. The interior is sled with wood placed vertically, which is carbonized gradually a t a lower temperature than that employed in making black charcoal. When the carbonization is found to be satisfactory, plenty of air is allowed to enter the oven, resulting in the combustion of the bark of the material, the temperature rising until the contents are almost white hot. At this stage they are drawn out and covered with Figure 1-Vertical Sections of Black Charcoal Ovens a moist mixture of earth, ashes, and charcoal powder to extinguish the fire. As alsufficiently large to allow the materials to become gradually ready mentioned, the stones to be used for building the oven carbonized. When a satisfactory degree of carbonization is in- must be highly resistant to heat. Tuff is the best material. dicated by the color and odor of the smoke, the interior of the Sandstone can also be used, but limestone, mica granite, and oven is ventilated so as to enable the temperature to rise, after clay slate are not suitable. which the fire is extinguished by making the oven air-tight. Charcoal f r o m Ovens of Different ConstrucEarth is usually employed for building such an oven, but Table I-Yield of Black tion, Using Moist Materials one must choose earth that is adhesive, of resistant material, HANAnot melting a t high temperatures, and not contracting on OE WooD ~GAMA T A K B YANA GAMA GAMA RUSA NAGANO GAMA TGA A MIAS H ~ AVERAGE drying or heating. For this reason the use of earth contain% % % % % % ing much combined water or carbonates is to be avoided. Quercus glandulifera 16.86 17.44 16.54 15.20 1 8 . 0 0 16.82 Likewise, earth composed of too fine particles, or containing aculissima 18.05 17.00 20.49 17.56 Carr. 17.31 14.93 sulfur or too much sand and volcanic sand or slag, is not suitable. There are more than ten different varieties of these ovens There are a number of forms of the oven. Five of the in Japan. Figure 3 shows the most common ones. most common ones are shown in Figure 1. It is well known that the temperature of carbonization exerts a remarkable inloo0 fluence upon the quality and yield of Naqano gama charcoal. Experience teaches us that the carbon content of charcoal increases with the temperature elevation, in consequence tJ of which the calorific value becomes x9 greater, the ignition point rises, and the $ specific gravity increases. On the other Qloo hand, we know that if woody materials F are carbonized rapidly a t a high tem- ‘200 perature there is a remarkable decrease i n t h e yieldof charcoaldue to gasification 0 20 30 40 so 60 70 80 so 100 110 of the greater part of the material. For Time Hours Figure 2-Temperature of Carbonization in Production of Black Charcoal this reason, most of the charcoal burners t r y to conduct a gradual carbonization The carbonization temperatures are shown in Figure 4, at a low temperaturefor instance, a t approximately 275’ C., the minimum temperature for exothermic reacfion. They the materials being gradually carbonized a t a lower temperathen raise the temperature for a short time toward the end of ture than in the case of black charcoal. They are, however, carbonization in order to improve the properties of the char- hardened a t the end of the carbonization by raising the temcoal. Curves of carbonization temperature for black char- perature. The yield of white charcoal is not large since, besides the coal are shown in Figure 2 . The yield of black charcoal is not high, because a part of the combustion of a part of the material during carbonization, material burns in the oven. But in cases where carboniza- the loss due to combustion of the bark and of a part of the tion takes place without free combustion, SO that the full interior of the material occasioned by the final increase in form of the woody material is noticeable after carbonization, temperature is considerable. the yield is more than 20 per cent when wood containing Table 11-Shrinkage of Woody Material during Carbonization about 40 per cent of water (green wood) has been carbonized DI.4METER LENGTH VOLUME (Table I). SPECIES or WOOD % 5% % 15.23 52.20 24 98 QueYcus aculissima Carr. The volume-weight of the charcoal also depends largely 14.37 52.74 25.88 Qucrcus glandulifera Blume. upon the contraction of the woody material during carboniza12.40 50.90 25.21 Castanea publineruis S. e l Z . 16.83 50.99 24.66 Alnus japonica S.et Z. tion. I n other words, heavy, hard, good charcoal can be 14.37 55.36 28.29 Albieeia julibrissin Durras. 53 13 14.43 26.10 obtained if the yield is large, in spite of great contraction. Styrax jagonicus S. et Z.
a2::r
’
-
INDUSTRIAL A N D ENGINEERING CHEMISTRY
June, 1931
Table 111-Yield of White Charcoal from Different Kinds of Ovens, a n d Using Green Material Which Contained About 40 Per Cent Water YOSHIOA B I N C H ~ HIUGA KINDOF WOOD GAMA GAMA GAMA % % % .._ 12.43 ll'.i4 13.60 Evergreen oaks 1 2 . 3 5 1 1 .83 12.09 Other hardwoods
The contraction of material due to carbonization is very striking, but thereby hard and compact charcoal is obtained. The amount of contraction is, in the case of evergreen oaks, about 45 per cent in diameter, 20 per cent in length, and 76 per cent in volume, and in the case of other hard wood (deciduous and broad-leaved trees) about 40 per cent in diameter, about 21 per cent in length, and 67 per cent in volume.
Figure 3-Vertical
633
and not upon its calorific value, it may be reasonable to attach importance to the former properties when judging the quality of charcoal for domestic use or for the production of confectionery. IGNITION PorNT-The ignition point of charcoal is from 300" to 500' C. Hard charcoal prepared a t SI high temperature has a high ignition point, while soft charcoal ignites a t a lower temperature.
Sections of White Charcoal Ovens
Properties of Charcoal
HYGROSCOPICITy-Tests made on black charcoal indicate that about 5 per cent of moisture will be adsorbed within 24 hours after drawing the material from the oven in winter. Following this the amount fluctuates with the temperature and atmospheric humidity (Figure 5). SPECIFIC GRAVITYAND VOLUME-WEIGHT-The Specific gravity of charcoal prepared a t a high temperature is high. The volume-weight of charcoal from wood of the same species prepared a t a high temperature is also high and is proportional to its hardness. The volume-weight of the best charcoal is above 1, so that the charcoal sinks in water. This fact is not in agreement with the belief of Europeans that "good charcoal floats." (Table IV) Table IV-Specific
Gravity a n d Volume-Weight of Charcoal SPECIFIC VOLUMESPECIES OF WOOD GRAVITYWEIGHT WHITE CHAXCOAL
Quercus ilex, L. war. Pkyllireozdes Franch. Quercus stenophylla M a k Quercus acuta Thunb. Vuercus glauca Thunb. Queri,us glandulifera Alume. Pasania cuspidata OersJ. Acer japonicum, ThunE. var. T y p i c u m G s . et Schw. Mallotus japonicus ddUell. A l g . BLACK
1.76 1.75 1.76 1.76 1.76 1.73 1.74 1.35
1.07 0.89 0.85 0.86 0.65 0.61 0.51 0.39
1.42 1.39 1.28 1.39 1.43 1.13
0.70 0.61 0.48 0.42 0.47 0.45
i4
4 '4s k 4'7 i o iz62 h j 2 ;I iz 30 b 48 48 49 44 44,4544 42 42 43 Temperature, F. Figure 5-Hygroscopicity
of Charcoals
HARDmss-The hardness of charcoal varies almost in proportion to its volume-weight and bears a close relation to the duration of combustion. It may therefore be regarded as an important factor in judging charcoal. Moreover, since hardness can be measured more easily than volume-weight, most investigators in Japan are now inclined to judge charcoal by its hardness. Table V-Amount
of Metals Used t o Form Alloys i n Miura's Charcoal Meter
DECREE OF HARDNESSLEAD ANTIMONYTIN Grams Grams Grams 1 100 .. ..
CHARCOAL
Quercus acutissima Carr. Quercus glandulifera Blume. Castanea publinenis Schneid Styrax japonicus S. et 2. Alnusjaponica S. et Z. rllbizzia julibrissin Durraz.
oays
Hours
Tl'me after Charcoalwithdrawn from Oven +5 io g8 6s ji i7 +4 +I j , j7 77 70 i o is js 7k8bi1'5 +5 Hum/ d i t y I I I I f I I I I
COPPER Grams , .
~~
19 25 20
.. ..
.. ..
59 65 6
.. ..
4 8 12 16 20 30
..
IO
20
30
40
50
60
70
80
90
/#
110
/20
/30
140
7im e , Hours Figure &Temperature of Carbonization in Production of White Charcoal
CALORIFIC VALm-The calorific value of Japanese charcoal is from 6000 to 7500 calories and, in spite of variations in hardness or volume-weight, no large deviation due to species of wood is noticeable. Since the duration of combustion depends largely upon hardness and volume-weight of charcoal
8 10 20 100 90 86 82 78 74 70 65
..
ZINC
%BEL
Grams
Grams
.. ..
.. ..
..
.... 10
10 10 10 10 10 5
..
..
.. .. .. .. .. .. ..
..
100
The range of hardness of Japanese charcoal is usually measured by means of Mohs' scale of hardness for minerals, from below talc to above fluorite. The writer has, however, devised a meter to determine this property quickly. This meter consists of twenty pieces of metal ranging in hardness between lead (assumed hardness 1) and steel used for making saws (hardness 20), the intermediate pieces being of alloys containing varying proportions of lead, tin, zinc, copper, and antimony, as indicated in Table V. This meter is now being
INDUSTRIAL A N D ENGINEERING CHEMISTRY
634
widely used in Japan, especially for use in inspections and sometimes in commercial transactions. I n order to compensate for the loss due to oxidation, 3 per cent of tin and 5 per cent of zinc should be added to the percentages of the metals shown in this table.
Table VII-Average
.
of Miura’s Charcoal Meter with Mohs’ Scale of Hardness M O H S ’ SCALE M I U R A ’ S CHARCOAL OF HARDNESS METER T~IC 1 Under 1 Gypsum 2 4 Calcite 3 13 Fluorite 4 18
Table VI-Comparison
Vol. 23, No. 6
Hardness of Charcoal by Miura’s Charcoal Meter
S P E C I E S OF U’OOD
HARDNESS
WHITE CHARCOAL
Qucrcus ilcx. L . war. Phyllireoides Pranch. Qucrcus stenophylla M a k . Qucrcus acuta Thunb. Quercus glauca Thunb. Q U C ~ C U Sglandulifera Blume. Pasania c r r p i d a f a Ocrst. Acer japonicurn, Thunb. v a r . Tygicum G s . el. Schw. Mallofus japonicus Mucll. Arg.
20.0 17.0 18.0 18.0 12.0
11.0 9.5
1.0
B L A C K CHARCOAL
Quercus acutissima Carr. Quercus glanduliftra Blume. Ace? piclum Thunb. Castanea publinervis Schneid. Pinus densiflora S.el 2.
14.0 8.0 2.0 1.0 Under 1.0
Preparation of Metal Powders by Electrolysis of Fused Salts 111-Tantalum’ F. H. Driggs and W. C. Lilliendahl WESTINGHOUSE LAMPC O M P A N Y ,
HIS ,paper represents a
BLOOMFIELD,
N. J.
Electrolysis of fused salts has been successfully apt a n t a l u m b y s o m e other plied to the production of tantalum metal of a high means and offer a direct r e continuation of the indegree of purity. The method consists of electrolyzing v e s t i g a t io n dealing duction of a tantalum comtantalum oxide dissolved in potassium fluotantalate pound to pure m e t a l . The with the preparation of the in the presence of other alkali halides. most feasible compound for rare refractory metals by elecThe effect of fluorides and chlorides upon the charthis purpose appeared to be t r o m e t a l l u r g i c a l methods. acter of the deposited metal has been investigated. the double fluoride of potasThe successful preparation of Pressing, sintering, , and degasifying the metal by sium and tantalum, KzTaF,. uranium (1) and thorium (2) heat treatment in vacuo are necessary to obtain ductile The deposition of uranium by electrolysis strengthened metal. and thorium metal from baths the belief that this method The use of this method for obtaining a tantalum plate containing only a small permight have a r a t h e r wide on base metals has been investigated and some results centage of the halide of the a p p l i c a t i o n to metals of a are illustrated. metarmade it seem probable similar nature, such as tanthat a tantalum bath could be talum. The preparation of metallic tantalum by the electrolysis operated in which the proportion of potassium tantalum fluoride of fused salts has been limited, according to the literature, to was very low and thus avoid excessivevolatilization of the salt. The nature of the deposited metal obtained by electrolysis the purification of tantalum. A patent issued to Weintraub (4) describes the purification of tantalum by electrolysis of is especially important in the case of tantalum, because of the fused potassium fluotantalate using an impure tantalum anode subsequent purification, pressing, and heat-treatment steps. and depositing pure tantalum a t the cathode. A tantalum If a dense, coherent deposit is obtained, it must be ground to a powder in order that bars of suitable size may be pressed oxide container was recommended for the fused salt. While the above method might conceivably yield tantalum from the material. If, on the other hand, a very fine powder metal, several factors prevent its practical application. Some is obtained during the electrolysis, the difficulty of washing of the principal objections are: (1) It requires a previously and mechanical removal of insoluble impurities becomes too reduced tantalum metal as one of the raw materials; (2) great. A powder of approximately 200 to 400 mesh seemed the solvent action of potassium fluotantalate upon tantalum the most desirable from all standpoints, and in the following oxide is too pronounced to allow its use as a container; (3) experiments the bath composition and current densities were the high volatility of fused potassium fluotantalate would investigated to obtain a powder approaching this range of involve the use of large quantities of this salt owing to the particle size. high losses from the bath with constant operation; (4) a Preliminary Tests coherent mass of tantalum metal obtained by electrolysis of fused baths is not sufficiently free from combined or abThe first test runs were made in a graphite crucible using sorbed gases to be considered pure enough for subsequent cold- a carbon anode. At the end of the run the salt was dissolved working. out and the metal powder recovered from the sides and bottom I n order that the production of metallic tantalum by of the crucible. When prepared in this manner, the metal electrolysis of fused salts might be carried out on a practical always contained particles of graphite which were difficult scale, all of these objections would have to be avoided. to separate, However, the type of metal powder obtained Previous experience with other metals made it almost certain from various bath mixtures could be determined with a fair that the use of a tantalum anode was not necessary to main- degree of accuracy. tain the concentration of tantalum in a fused bath, since this It was later found that nickel could be substituted for could be accomplished by adding a halide compound of tan- graphite, as it was not attacked by the bath and little if talum to the bath as the tantalum was deposited out. This any alloying took place with the tantalum metal. This would avoid the necessity of a preliminary reduction of made it possible for a number of test runs to be made with a very simple apparatus consisting of a nickel crucible sup1 Received March 20, 1931.
T
