8 54
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
I t must be admitted that to secure a higher efficiency than corresponds to the figure quoted by Mr. Wadman, requires the condensation of the water evaporated and the recovery of the heat given up thereby. This amounts to an application of the principle of multiple-effect evaporation, but this principle can in ‘theory a t least be applied just as effectively in air drying as in ordinary evaporation. Furthermore, the only industrial obstacle t o a realization of these conditions is the low heat conductivity From gas through solid separating wall to gas, a fact which necessitates an enormous heating surface. In the discussion of several years ago a heat consumption resulting from a commercial test of a Ruggles-Coles dryer was quoted as below the figures stated by AIr. m’adman to be the theoretical minimum possible, and it was stated that such a result was impossible. Unlikely such a result may be, but it is not impossible, in the type of dryer employed. That dryer cools the gases to a remarkable extent, and under certain conditions the gases leaving the dryer coming in contact with the cold, wet material entering it are cooled below their dew point. This results in separation of moisture in the Form of fog, which is carried along by the gases. I t is easily possible for the heat given up upon condensation of this moisture to more than compensate for the fact that the gases are still higher in temperature than the air supply. Under such conditions the Ruggles-Coles dryer is effectively utilizing a part of the heat of condensation of the water once evaporated, and in this way is making use to a degree of the multiple-effect principle. While such conditions can arise only under unusual circumstances in that dryer, there is no inherent absurdity in the low heat quotation referred to, and it is readily conceivable that in the future that particular type of dryer may be perfected to the point where such re-utilization of the heat may become industrially practicable. Just because it is possible to lay out a dryer using air under atmospheric pressure which will evaporate water a t practically any heat consumption demanded, it must be admitted that there is no theoretical consumption for such an apparatus and therefore no meaning to the term “efficiency” as applied to air dryers. The writer feels very strongly that it is unfortunate to consider evaporation and air drying as unrelated, and that it is not true “that the two things are quite distinct;” on the contrary, the fundamental factors involved are identical while the differences are scarcely more than superficial, and appreciation of this is necessary to progress in the development of both types of processes. Regarding Mr. Wadman’s misunderstanding of the statement concerning the evaporation of solutions, I evidently failed to make the point clear in my first communication. As a specific illustration, assume a 34 per cent solution of caustic soda, boiling under atmospheric pressure a t 1 2 0 ” C. Mr. Wadman evidently understands that the vapor coming from such a solution is a t 100’C., but such is not the case. The vapor coming from a solution cannot possibly be a t a temperature other than that of the solution itself. It is true that in this case the vapor must cool to 100’before condensation will take place. Furthermore, if a thermometer be inserted into the vapor space, its cooling action will cause condensation of vapor upon it, and i t will therefore register 100’ until that condensation has been re-evaporated. The ‘vapor rising from the solution, being a t 1 2 0 ° , must be compressed isothermaZZy to 14 lbs. gauge in order to condense a t slightly above IZO”, its heat of condensation then being available for evaporation of more water from the original solution, The work consumption necessary t o remove I lb. of water from the 34 per cent solution of caustic soda is therefore
+
I. (1545)(460 -I- 248)bn(14.7 I4)/ I8 1 4 . 7 = 40,600 foot-pounds of energy per pound of water
W = nRTlnp/p,
=
Wol. 8 , No. 9
evaporated. The process involved is truly isothermal throughout-solution, vapor, and condensed steam being a t all times a t 120’. W. K. LGWIS MASSACHUSETTS INSTITUTE OF TECHNOLOGY CAMBRIDGE, August 17, 1916
SIR WILLIAM RAMSAY Editor of the Journal of Industrial and Engzneering Chemistry: In the death notice of Sir William Ramsay, in your August issue, the fact is omitted that he studied for some time under Prof. Rudolph Fittig, in Tuebingen, where he also acquired his degree of Dr. Sci. Nat. He came to Tuebingen while Ira Reinsen was there and he told me that he tried to enter the laboratory through a door seldom used, which was locked; after considerable knocking Remsen opened the door and promptly answered Kamsay’s question in broken German, in English. PITTSBURGH, PA. K. F. STAHL August 23. 1916
ANILJNE OIL POISONING Editor of the Journal of Industrial and Engineering Chemistry: A letter in THISJ O ~ R S A L ,8 (1916), 573, written by Messrs. Fiske and Green on the subject of aniline poisoning, has come to my notice and I commend it to the careful consideration of all manufacturers and users of aniline oil. It is with the hope that I may add a few details thereto, that I am writing this. Soon after the outbreak of hostilities, this company realized that it could no longer depend upon overseas sources for its aniline and by h-ovember I , 1914, we were manufacturing aniline in large quantities; since that date the plant under the writer’s supervision has produced approximately 1500 tons without a single fatality due to aniline poisoning; our good fortune has not been a matter of pure luck but is the result of a persistent campaign to eliminate every possible source of danger and to care promptly for such cases of poisoning as have actually resulted. The premonitory symptoms of aniline poisoning are as described by Fiske and Green, the severe cases showing dizziness, unsteadiness on the feet and finally unconsciousness; however, men who are working constantly in the plant and who have, in a measure, become immune to the effect of aniline vapor, show bluish lips and skin; the poisoning does not seem to go beyond that stage and the men are not inconvenienced in any way; it has been our experience that the severest cases, those most prompt in making themselves manifest, have resulted from the spilling of aniline, nitrobenzol, or aniline hydrochloride liquor directly ’upon the skin and on this point we seem to be a t variance with Fiske and Green. Realizing that poisoning may be caused either by inhalation of rapor or direct contact with liquid, our manufacturing precautions have been based upon these two points; the building is provided with suction ventilating fans in the roof; several 24in. fans located in the exterior sidewall of the building play streams of air directly upon the men while they are a t their operating positions; in clement weather the windows are removed, a t other times satisfactory floor ventilation is provided; suction ventilating ducts are led directly to stuffing boxes and iron-boring feeders where there is always more or less escape vapor; the manufacturing system i s closed so that a t no point is it necessary for a man to handle open aniline; drinking men are excluded from the operating force; regular rations of milk are issued and their consumption insisted upon; showers are provided and a daily bath is compulsory; the company provides two clean working uniforms weekly per man; rubber boots are supplied; pumps, valves, stuffing boxes, etc., are inspected frequently and all leaks taken care of a t once.
