October, 1926
INDUSTRIAL AND ENGINEERING CHEMISTRY
1015
Future Trends in Low-Temperature Carbonization By S. W. Parr TJNIVERSITY
OF
ILLINOIS, URBANA, ILL.
H E carbonization of coal at low temperatures first came forward as a topic for discussion in the scientific and technical press about the year 1906, appearing simultaneously in England and America. Xotwithstanding that these discussions were somewhat fantastic and profoundly superficial in so far as fundamental knowledge of underlying principles was concerned, the fact remains that fuel investigators and the public were alike thoroughly committed t o the idea, and this condition has not only prevailed during the intervening twenty years but has gained in momentum with every succeeding year. This feature of virility alone would be sufficient justification for making a brief survey of the field, with the added argument that possibly we may now ha\-e reached a stage where reasonably safe prognostications for the future may be made.
T
Pros and Cons of Low-Temperature Carbonization
The early conceptions as to the advantages of low-temperature carbonization might be briefly stated somewhat as follows: The use of lower temperatures would result in less heat and lower cost of production. Less expensive installations would contribute toward the same end. Higher yields of tar and a richer gas would also be factors of advantage. As offsetting these propositions, which look so attractive on paper, we are forced to a consideration of certain counter factors. The application of lower temperatures for accomplishing the desired end is not so easy a matter as might be imagined. It invol.ires the problem of the transmission of heat to a mass of nonconducting material without the condition of high heat head, and this a t once seems to prescribe the condition that only a thin layer or a narrow cross section of the material can be successfully handled if low-temperature conditions are to be maintained. This suggests the necessity of an elaboration of appliances g i t h its attending requirement of expense of installation, deterioration of plant, and high overhead in the way of labor costs. I n the matter of high yields of tar, the attractiveness of that feature is not so significant in this country as it might be in Europe. for we seem t o have an abundance of liquid fuels here. Moreover, the low-temperature tars for which the virtue of high yield is claimed have the disadvantage that the material is of unknown value. not demonstrated to have any special adaptation in the arts other than that of a liquid fuel. To all these adverse factors should be mentioned the fact that in this country the abundance of cheap fuel in the form of coal screenings, what might be termed the by-products from the preparation of coals of all types, stands as a competitive factor in the development of any of these processed fuels. so that from the standpoint of the operating returns it is a question whether the optimistic predictions a t the outset have found a very good basis for working out a hopeful industry along low-temperature lines. However, it is interesting to note that in the present trend of developments those methods of procedure which seem to be progressing in a hopeful manner towards an industrial status are thoqe which take account of these deterring factors and have inherent properties which would seem to avoid being subject to their influence. It may be said further in this connection that certain other factors are entering into the account aside from the mere
matter of profit, including such matters as health. comfort, and convenience. It has been very well established, for example, that the smoke nuisance from which we suffer so severely in all congested centers is chargeable a t least to the extent of more than 50 per cent of its source to domestic chimneys; hence, the hopeful point is being reached where the domestic smoke producers and the smoke nuisance are looking each other in the face. so to speak, and asking each other, what are you going to do about it? The matter of health is beginning to receive consideration and study for other reasons than the mere accentuation of dirt and grime, especially in the matter of the necessity of free access of the rays of the sun, as opposed to the filtering process which goes on when a pall of smoke intervenes between the sunlight and the earth. Another circumstance bearing upon this entire problem is the fact now somewhat dimly coming to be recognized that the ideal and ultimate fuel is gas, for the reason that fuel in this form is not only convenient but adds very materially to our comfort and health; furthermore, in household appliances especially, fuel gas has a very great advantage from the standpoint of economic combustion where the basis of reference is the heat values involved and not their cost. Lines of Development
From these general considerations as they relate to lowtemperature carbonization, we may formulate in somewhat more specific terms the present status and from that as a basis forecast the future trend of development in this field. Let us observe in the first place that conditions and necessities in this country are radically different from those which prevail in Europe. For example, we are not concerned in the volume of the liquid products so much as we are in their value. I n this country also the limitations in the cost of processing are more pronounced by reason of the competition the product must meet in the almost unlimited amount of cheap fuel available without processing. The development of low-temperature carbonization with us, therefore, in order to meet such competition must proceed along lines involving conditions of large-volume production with minimum cost for labor, fixed charges for investment and depreciation and upkeep expense, and high value factors in the various products which will meet in the highest degree these adverse charges against the process employed. The early argument of lower cost as an accompaniment of lower temperatures used in carbonization has been more than offset by the elaboration of mechanical features, which because of manufacturing and maintenance cost, deterioration, and fixed charges have more than counterbalanced the possible advantage in heat conservation. One other feature of the case should be mentionednamely, the available market. Manifestly a product which competes with anthracite a t from $16 to $20 per ton has a greater leeway in the matter of expense of production than a product which must compete with cheaper fuels selling on the market for less than $10 per ton. Processes Having or Approaching Commercial Status
There are a t the present time about four processes in this country which are in or just entering the commercial stage and whose fundamental principles or environment meet
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IXDCSII'RI-IL A-F-D ENGI,VEERING CHEJIISTRY
the conditions thus outlined to an extent that would seem to forecast successful operation. It is sincerely to be hoped that this will be the outcome, not only because of the improved type of fuel thus to be made available, but also because the successful carbonization of the widely divergent and extensive quantities of coal thus processed is an exceedingly important step in the ultimate production of the ideal fuel-gas. It is of interest to note a few type examples of those processes which are now in or just entering the status of commercial production, making use of that fact as evidence that they have a t least passed through the stage of preliminary experimentation. The Smith Carbo-coal process, as modified by C. V. hIcIntire, engineer in charge, is a three-stage process: first, low-temperature carbonization at 450" C.; second, briquetting; and third, a final carbonization. It is operating within range of a market accustomed to an anthracite standard of cost. The final product for domestic use approaches the ideal, and has reached a stage where operations have been substantially continuous for six months. The McEwen-Runge process, now being installed as an adjunct to one of the large power plants of the country using pulverized coal, operates in a manner to remove the volatile matter by allowing the pulverized coal to drop through a heated vertical tower about 6 feet in diameter by 30 feet in height. The minute granules of low-temperature coke are in suitable condition for burning directly as pulverized fuel in the power plant or for briquetting and carbonizing for the production of a domestic fuel. A throughput is possib:e of 210 tons per unit per day.
Vol. 18, No. 10
The Green-Lauks plant of the Old Ben Coal Corporation, Chicago, which has been operating on a 24-ton-per-day schedule, is being rebuilt for large-scale production. This method employs a spiral movement upward between heated walls approximately 5 inches apart and heated to about 600' C. The process is continuous and delivers solid, irregular lumps averaging about 2 to 3 inches in diameter. This is an ideal domestic fuel, smokeless in combustion and with every desirable quality, since it lends itself to use in ordinary household appliances, including the open grate. The Knowles Sole-flue oven has made upwards of 100 tons of low-temperature coke and is preparing to enter upon regular industrial production. I n the process the floor only of the oven is heated. The layer of coal--8 or 10 inches d e e p receives a considerable amount of heat from the floor but also from the hot gases ascending through the mass. The arch above the floor is not heated; hence the gas after leaving the coal is not subject to secondary decomposition. Both the oven and its operation have the advantage of simplicity and the product is of exceptionally high grade. Indeed, there is a well-founded rumor that one of our large industrial centers stands ready, provided this fuel can be produced at a cost equivalent to other fuels in their market, to require by municipal ordinance that no raw coal be burned in that municipality. These examples, which might doubtless be extended,' are sufficient to afford a general idea of the present trend in the field of low-temperature carbonization. 1 Chapman, F u e l , carbonization.
August,
1926, describes Parr-Layng low-temperature
Future Developments in the Light Metals By Francis C. Frary ALUMINUMC O M P A N Y
OF A M E R I C A ,
T IS especially appropriate for us as chemists to consider
I
this subject since, although broadly speaking the whole subject of metallurgy may be considered a division of industrial chemistry, the production of the light metals has only been rendered possible by the comparatively recent work of chemists and chemical engineers Moreover, it involves relatively complicated chemical changes as compared with the simple reduction processes which generally characterize the metallurgy of the heavy metals. The metals to be considered are those of the alkalies and alkaline earths, together with aluminum and beryllium. With the exception of aluminum, magnesium, and beryllium, these metals are all far too readily attacked by air to be useful in the pure state for any except chemical purposes. Small amounts of them, however, often impart improved properties to the more stable metals and their alloys. With the increasing tendency of nonferrous metallurgists to study the effect of the presence of relatively small amounts of alloying ingredients, it is probable that some of these elements will come into increasing prominence as minor constituents of alloys. Their intrinsic value in this field will probably be all out of proportion to their quantity. While it is also probable that there will be a certain demand for some or all of these metals for chemical purposes, the trend of invention seems to be away from their use in the chemical industry, and it is doubtful whether this market for them will grow much. Magnesium
On the other hand, magnesium is relatively stable when properly purified. Its physical properties can be consider-
N E W KENSINGTOX, PA
ably improved by alloying it with a few per cent of certain other metals, so that its use for the production of metal parts where extreme lightness is required becomes entirely practical. It is particularly sensitive to the presence of a few tenths of a per cent of certain other metals. The development of magnesium has been and will continue to be slower than that of aluminum. for two reasons. When aluminum was introduced it offered a saving of two-thirds the weight of competing metals. Magnesium or magnesiumbase metals have a weight advantage of roughly four-fifths over the same metals, but only one-third over aluminum, with the weight-strength factor somewhat less when the comparison is made with modern high-strength aluminum alloys. The factor of weight saving is therefore less important in the use of magnesium than it was in the introduction of aluminum. More important is the greater difficulty of fabricating it and its alloys. Magnesium hardens under cold work much more rapidly than aluminum, and the great affinity of the molten metal for oxygen has rendered the production of satisfactory castings on a commercial basis extremely difficult. Patient and painstaking research has, however, gone far in the solution of fabricating difficulties, and alloys have been developed and are now being marketed which have excellent mechanical properties and are commercially stable under normal conditions. Naturally, such alloys are finding their first demand in aviation structures, where the slightest saving in the weight of a part is of great importance. On one airplane engine made in this country, for example, there are seventeen different parts made of magnesium castings. The forged aluminum
