N itrogen Stabilization
f^A F T H E m any mergers, com binations, and consolidations
^ which characterize our tim e, none has been more u n expected th a n the sales agreem ent recently enacted between the m ajor producers of fixed nitrogen.
Originally th e new international cartel, initiated as usual by the I. G. F arbenindustrie, included the Im perial Chemical Industries of G reat B ritain, th e producers of by-product sulfate of am m onia in th a t country, the Norwegian synthetic plants in w hich the I. G. holds large interests, and th e Chilean producers of n itra te of soda. I t is now sta te d th a t the Com ptoir de l’Azote, representing th e French, and th e M onte- catini com pany, representing th e Italian nitrogen interests, are negotiating for entry. T he to ta l represents 70 per cent of world nitrogen production. So far as has been disclosed, the cartel proposes prim arily to stabilize th e prices of nitro
gen th roughout th e world—w ith th e exception of th e U nited States. T he use of n itra tes is to be prom oted by an exten
sive cam paign of education and propaganda. Experim ents in th e use of the cartel’s products in agriculture are to be carried on cooperatively, and there is to be other coordi
nation am ong th e several groups. A lthough nothing has been said w ith respect to th e control of production, it will naturally follow th a t this will be a p a rt of th e program, if for no other reason th a n to serve as a factor in m arket stabili
zation. I t is also apparent th a t th e cartel intends to estab
lish sales q uotas for all im p o rtan t export m arkets. An
nouncem ents of new prices m ay be expected, and we are inform ed th a t already th e G erm an nitrogen syndicate, which is a p a rt of th e I. G., has announced prices for th e Germ an m arket for th e fiscal year sta rtin g Ju ly 1. These are about 6 per cent lower th a n those which have prevailed during the past year. T he negotiations so far as th e Chilean producers are concerned were carried on by th e Chilean finance com
missioner.
I t will be noted th a t all th e arrangem ents have had to do w ith m arkets and producing u nits outside the U nited States.
This is subject to several interpretations. Chemical Age (London), com m enting editorially on th e developm ent, points out th a t the rapid increase in th e production of fixed nitro
gen by th e I. C. I., which is expected to reach 750,000 tons per annum by th e end of 1929, enabled it to conduct its share of negotiations on equal term s w ith th e I. G. and with the Chilean n itra te producers. Perhaps th e American efforts are regarded as too feeble to w arra n t consideration on th e p a rt of th e new com bination, or it m ay be th a t th e rest of th e world intends to d ictate to America w h at she shall pay for such fixed nitrogen as she m ay im port. Again, th e Ameri
can producers m ay have been approached, b u t for good reasons preferred to go their own way.
In any event it would seem to be highly desirable to go forward w ith a large program for nitrogen production in the U nited States, both through th e synthesis of am m onia and th e expansion of by-product production. W ith th e rest of th e world in an international cartel, sufficient supplies
September 1, 1929
a t satisfactory prices m ay n o t be possible unless we are pre
pared to supply a very substantial p a rt of our needs from our own resources. T he great developm ents of Lazote a t Belle, W. Va., and of th e Allied a t Hopewell are easily capable of any expansion which th e m arket justifies. T he American Cyanam id, w ith nearly a generation of success to its credit, is another factor of im portance. O ther plants can expand, while additional units can easily engage in th e fixation of nitrogen if there is dem and for the product.
M uch th a t has been forecast w ith regard to trends in nitro
gen fixation and the m arket for these m anufactured products will be upset by this unexpected alliance between th e pro
ducers of synthetic am monia, etc., and the Chilean industry, which it once threatened to annihilate. W hile the agree
m ent appears to have as a prim ary object the reduction of selling costs and experim entation and th e prevention of too great an overproduction before th e world is ready for the increase, it is capable of m any other activities. Its course, no d oubt already charted, will have a profound influence upon th e fixed nitrogen industry of th e U nited States.
T o x ic ity of Organic Compounds
A
N IN Q U IR Y recently conducted b y the N ational Safety Council has served to bring o u t th e lack of definite inform ation relative to th e toxic properties of common organic substances. T he introduction alm ost d ay b y d ay of new organic compounds, m any of which have decided com
mercial im portance, m akes it im perative th a t exact inform a
tion be obtained on th e com parative toxicity of all organic chemicals which today find wide application. M ore th a n this, those introducing new reagents and industrial chemicals should be required to subm it a t th e same tim e this ty p e of knowledge for th e guidance of those who m ay be called upon to use th eir m aterial.
W h at is needed is for some one or some group to m ake an exhaustive stu d y of th e whole question. We need d a ta on th e com parative toxic effect of closely related compounds, and th e m inim um q u an tity which can be absorbed b y th e hum an system w ithout causing tem porary or perm anent effects should be established. In th e case of some products which m ay be present in th e air, we should know the con
centration below th a t which will cause toxic sym ptom s and w hether or n o t one can continue to work in such an atm os
phere for either long or short periods w ithout injury to health.
W hich of th e organic compounds possess cum ulative effects so th a t, if present in quantities too sm all to produce tem porary sym ptom s of poisoning th eir presence m ay nevertheless be a real hazard? M ethods of trea tm e n t are obviously im portant, and should be prescribed as definitely as experience and in
form ation will perm it.
T he Chemical Section of th e N ational S afety Council, as well as th e In d ustrial H ealth Division, is deeply interested and will cooperate w ith any research investigation or inquiry relative to this im p o rtan t subject. I t is believed th a t th e
806 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 Vol. 21, No. 9 m a jo rity o f th e h ealth hazards in industry to d a y are of chemi
cal origin, an d m uch of th e fu tu re research in th is field will doubtless be conducted w ithin th e realm of industrial chem
istry . H ere is a definite call for service, and th e chemical in d u stry owes it to itself and its public to ta k e th e lead w ith o u t delay in organizing and forwarding those thorough-going investigations w ithout which th e necessary d a ta for th e avoidance of hazards cannot be secured.
T h e Insects
l \ / f A E T E R L IN C K said th a t insects are so incom parably b etter arm ed and b etter equipped th a n ourselves th a t they are perhaps our successors. T he recent invasion of one more insect—th e M editerranean fru it fly—serves again to call our atten tio n to th e never-ceasing w arfare between m an and these tin y com petitors of his. W e confess th a t there is alm ost enough in th e situation to m ake us pessimistic.
B u t for our implicit faith in w h at can be accomplished through science when th e urge is great enough, we should be inclined to wager on th e side of th e insects. L. 0 . H oward, who for so m any years was chief of th e B ureau of Entom ology, has quoted proved estim ates to th e effect th a t, under favoring conditions and in th e absence of all enemies, th e p la n t lice descended from one individual of one species in a single season would weigh more th a n five tim es as m uch as all th e people of th e world. Some insects have as high as 70 per cent females in their offspring, and th e fecundity of these crea
tures is nothing short of amazing.
T he insects have m ost of th e odds in their favor. T hey were here eons before we were. T heir distribution has been greatly aided b y m odern transportation, which makes it m ore difficult to enforce q uarantines, and they th riv e in new locations from which th e ir n a tu ra l enemies are absent.
T heir powers of flight, their color protection, th eir a d a p ta
tion, their sh o rt period of infancy, th e security enjoyed by th e eggs and larvae, as in th e case of th e cotton boll weevil and the M editerranean fruit fly, th eir h a b it of occupying th e u nder side of leaves as do th e M exican bean beetles, th e protection afforded in hibernation like th a t enjoyed by th e corn borer, and th e com plete change in th e m ethod of re
production which characterizes some of th e aphids are b u t a few instances of w hat we have in mind. Some of our w orst pests combine great flexibility of m ovem ent w ith an arm or
like shell—and one m ight continue alm ost indefinitely.
So far in this com bat m an has had to use m aterials m any of which are poisonous to him, as well as to th e insect he seeks to destroy. T here is m uch agitation concerning arseni
cal residues on apples and other fruit. Some find cause for alarm in th e steadily increasing am ounts of lead and arsenic which are p u t upon our soils. E ven such m aterials as we apply to growing plants need to be renewed a t considerable expense, following rains and other unfavorable w eather.
M any of th e insects are n o t affected or are n o t reached by th e m aterials and our present m ethods of applying them .
I t is evident to us th a t the am ount of research devoted to th e control of insects is far from adequate. Y ou note we refer to control and not to exterm ination, for to th e best of our knowledge th e n a tu ra l enemies, plus th e best th a t science has so far been able to do, have in no case exterm i
nated a pest. T he m ost th a t is hoped for is such a control th a t we are able to secure for hum an use th e m ajor p a rt of th e harvest. As we have pointed out before, there is a real need for other types of insecticides, fungicides, and germi
cides po ten t in destroying our enemies, y et less dangerous to the hum an being.
We are n o t unm indful of w h at has been accomplished, and we have a profound respect for th e research th a t is al
ready in progress. T he ta sk is great, however, and to our m inds th e workers are far too few.
Pygm ies
T T W OULD be u nfair n o t to share w ith our readers th e smile which was ours upon reading in Chemical Markets the fol
lowing quotation from th e Manchester Guardian Commercial:
The chemistry of today remains almost wholly the product of British and German research, while the chemical trade of the world is dominated by two firms—one British and the other German. These two— Imperial Chemical Industries and the I. G. Farbenindustrie— might almost be called the nationalized chemical industries of their respective countries; beside them a representative American firm such as du Pont de Nemours &
Co., despite its growth last year, is a mere pygmy.
So m uch has been published concerning the size of th e I. G.
and the I. C. I. th a t our readers m u st be fam iliar w ith such statistics as invested capital, acres of floor space, num ber of employees, annual profits, p artial lists of products, and the other yardsticks by which concerns are ordinarily measured.
T he same m ust be tru e w ith respect to such a representative firm as E. I. du P o n t de Nem ours & Co., Inc., th e Allied Chemical and D ye Corporation, and those other American firms, to list which would require more space th a n is a t our disposal, which m ay be considered fairly representative of industrial chem istry in this country.
We do not know who w rote th e paragraph in th e M an
chester Guardian Commercial, and of course in describing our feeble efforts as having produced “ a mere pygm y” he uses a relative term , justified or n o t depending upon your point of view. B u t we would like th e opportunity to tak e a little stroll with him about certain American plants w ith which we are familiar, and then compare n o t th e m aterial size of various enterprises as much as actual accom plishment. W e believe, all things considered, he m ight desire to use some other figure of speech th e next tim e he undertakes to w rite of th e chem istry of today. In this we would by all m eans include th e research of our educational, industrial, and federal laboratories as a p a rt of w h at America has to offer, n o t only to industry b u t as a contribution to world science.
Investm ent in Research
T N O U T L IN IN G th e benefits of research to agriculture, -*■ A. F. Woods, of th e D ep a rtm en t of Agriculture, in a radio address sta te d th a t for every dollar invested in agricultural research there has been an annual retu rn to th e nation of five hundred dollars. A fter calling atten tio n to th e extended agricultural college and experim ental work in th e direction of more fundam ental research m ade possible b y legislative acts in th e last few years, he pointed o u t th a t each station now receives S90,000 annually from th e F ederal G overnm ent and th a t, in m ost states, ab o u t three tim es this sum in addi
tion is provided b y th e sta te for operating expenses and re
search. All of his figures were based upon statistical studies, and it developed th a t th e states and th e U nited S tates now spend ab o u t tw enty-five million dollars a year in th e develop
m en t of agricultural industries valued a t sixty billion dollars and w ith a gross income of te n billion dollars. O ther in
dustries of th e country, according to th e statistics of D octor Woods, now invest approxim ately one hundred and eighty mil
lion dollars a year for research and developm ent. T his is con
siderably more in proportion th a n is invested b y agriculture.
These figures are interesting as giving us th e la test esti
m ates of th e extent to which industrial America has come through experience to believe in pure and applied research.
September, 1929 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 807 I t would be surprising if, in th e expenditure of so large an
am ount, a great deal of waste did n o t occur, b u t it can be shown th a t th e present prosperous sta te of th e nation is in no small degree due to th e willingness to m ake such invest
m ents in scientific work and in th e developm ent of th e ideas and d a ta which come from th e laboratories. To estim ate th e retu rn on this great investm ent would be merely guesswork.
T he increase in sum s devoted to scientific work is th e best evidence th a t those responsible for such funds are convinced of th e earning power of research and, b u t for th e occasional u n im p o rtan t exception, there appears to be no inclination to abandon th e scientific m ethod and re tu rn to th e days of chance and empiricism. T he more forward-looking business organizations have determ ined th e percentage upon capital or gross sales which th e y th in k th e y should spend upon re
search and development, and have m ade this as m uch a policy as percentages of profits set aside for surplus and re
serves. In one great industry, when a special problem arose for which no provision h ad been m ade in th e research budget and th e directors were n o t disposed to m ake further com
m itm ents, th e advertising departm ent came forward and offered to release some of th e funds assigned to it th a t this new piece of research m ight go forward—an unusual trib u te to th e earning power of research.
O ther industries m ay n o t have equaled th e 50,000 per cent realized by agriculture on its research investm ent, b u t we d o u b t if any expenditures have earned more th a n those upon scientific work well chosen and properly directed.
T h e Lord Helps T hose W ho Help T hem selves
"D U T would you th in k of th a t old saying in connection w ith
^ th e P a te n t Office? M r. M cElroy, in his le tte r to th e E d ito r concerning the injustice which we do th e P a te n t Office in complaining, suggests th a t “ concerns aggrieved by th e ap
pearance of w h at th e y th in k are new p aten ts on old things would display an intelligent self-interest by sharing their tabloided inform ation w ith th e P a te n t Office.” T his is n o t p u t fo rth as a novel idea, b u t one which deserved more publicity and upon which it would appear som ething con
structive m ight be erected. W e are indebted to Bruce K . Brown for the further th o u g h t th a t the Am e r i c a n Ch e m i c a l
So c i e t y, probably through th e Division of In d u strial and
Engineering Chem istry, m ight appoint a special com mittee to assist th e P a te n t Office b y providing it w ith th e bibliog
raphies and digests of the ty p e th a t are constantly prepared in th e inform ation departm ents of large industries.
T he Commissioner of P a te n ts would fare badly if he a t
tem pted to absorb such inform ation as m ight be sent to him from all sources w ithout proper organization, b u t we believe th a t if he cared to do so he could profit greatly from such an organized effort to provide him w ith “ tabloided inform a
tion.”
A com m ittee such as M r. Brown has suggested m ight have, am ong others, tw o functions: first, to encourage the coopera
tion needed; and second, which is more im portant, to examine th e d a ta and approve or disapprove them before they are subm itted to th e examining divisions of th e P a te n t Office. In th e past, assistance has been offered th e commissioner by various individuals, and probably one reason w hy he has n o t openly invited it is th a t m uch of th e m aterial subm itted to the examiners has been highly flavored w ith p artisan ideas, if indeed it has n o t been deceptive in some instances.
A com m ittee of th e Am e r i c a n Ch e m i c a l So c i e t y could be set u p and could elim inate th is difficulty. I t could forward to th e commissioner bibliographies and indexes upon which
it could place its stam p of approval. These could be accepted by th e commissioner as legitim ate, authoritative, and u n biased.
If those in au th o rity thin k well of the suggestion, we believe no group will be found more willing to cooperate th a n will the American chemists, for th e y have suffered as m uch as any from th e conditions which have been allowed to develop. A constructive piece of work of this character is one which th e
So c i e t y could carry on w ith a great deal of pride and profit,
knowing th a t in helping th e P a te n t Office n o t only individual chem ists b u t th e public as well would be served.
Fire! Fire!
n n W O m ethods are presented under this heading in a circular of th e Crop P rotection In stitu te, w ith th e in
quiry as to which of them m ost closely resembles our general procedure in dealing w ith a disease or an insect emergency.
There is a little wisp of smoke. A man runs out of the house to a nearby comer and breaks a glass. Immediately the bell rings, the streets clear, and in a matter of minutes a young army of men is on the spot, trained, equipped, and ready to deal with the incipient blaze.
The householder wakes up smelling smoke and finds a fire beyond his control. He calls up the fire department. He is told that the regular fire force will not be available until after next pay day—the day after tomorrow. The Chief promises to send some one to look into the matter, and scurries out and collects a newsboy, a policeman, a tramp, a reporter, and two nightbirds. They finally arrive at the spot to find a helpless crowd and the whole block in flames.
T here are still industries which carefully organize against fire and carry insurance to protect against property dam age b u t which give no thou g h t to th e opportunities science offers.
P roperty which burns is replaceable, b u t a position lost through failure to know m ay never be regained. To rem ain unorganized to cope w ith emergencies, to m eet which th a t type of inform ation gained only through research is needed, is to invite ultim ate em barrassm ent or disaster. T he execu
tiv e who looks to th e fu tu re w ith confidence is th e one who knows he can place dependence in his scientific staff and technical organization to com bat th e incipient blaze or the prairie fire should one appear.
Skill
r P H E continued m echanization of industry, th e increase in autom atic devices, and th e perfection of rem ote control have seemed to some to constitute factors leading to u n em ploym ent. Instead, th e y indicate th e growing need for skilled, and a lessening dem and for unskilled, labor. T he ra te a t which autom atic devices become installed is de
term ined n o t so much by th e devices themselves as by a scarcity of skilled men able to install and m aintain them in satisfactory condition. M uch of th e labor perform ed in th e p a st b y th e unskilled m ay now be done in large p a rt by machines, b u t these create jobs ra th e r th a n destroy them , place a prem ium on skill, and open up new possibilities for those who would im prove them selves and increase their own capacities.
T he same m ay be said for th e profession of chemistry.
We, too, have our tasks which m ay be perform ed b y those com parable to the common laborers of other fields. M any of them are performed b y men w'ho, strictly speaking, are n o t chemists, b u t there is a greater dem and for skill th a n a t a n y other tim e in our history, and th e rewards for those w'ho will m ake themselves skilful are great.
808 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 Vol. 21, N o. 9
SYM POSIUM O N B O IL E R R O O M C H E M IS T R Y
Presented before the joint m eeting of the Divisions of Industrial and Engineering Chemistry, Gas and Fuel Chemistry, and Water, Sewage, and Sanitation Chemistry at the 77th M eeting of the American Chemical Society. Columbus, Ohio, April 20 to M ay 3, 1929. The paper by
Edm und Taylor and H. F. Johnstone, entitled “ D eterm ination of the Sulfur Content of Gases from Boiler Furnaces,” which was presented as a part of this Sym posium , will appear in the October 15 issue of the A nalytical Edition.
Rate of Burning of Individual Particles of Solid Fuel1
H . K. G riffin, J. R . A d a m s,2 an d D avid F. S m ith
Pi t t s b u r g h Ex p e r i m e n t St a t i o n, U . S . Bu r e a u o p Mi n e s, Pi t t s b u r g h, Pa.
A n ap p aratu s an d m e th o d have been d escribed for d e te r m in in g th e ra te o f b u rn in g of in d iv id u a l p a rticles of so lid fu els u n d er co n tro lla b le c o n d itio n s o f fu rn a ce t e m p eratu re, p a rticle size, and oxygen c o n c e n tr a tio n .
T yp ical d a ta for th ree siz e s o f coal an d tw o sizes of se m i-c o k e an d a ctiv e ch arcoal have b een p resen ted and d iscu ssed a s follow s: (a) U nder th e ex p erim en ta l c o n d i
tio n s, fu e ls c o n ta in in g h ig h p ercen ta g es o f v o la tile m a tte r sh o w a p ro n ou n ced in crea se in b u rn in g tim e w ith in crea s
in g fu rn a ce tem p era tu re; (b) fu e ls c o n ta in in g p ractically n o v o la tile m a tte r sh o w a m u c h sm a lle r tem p era tu re co efficien t over th e tem p era tu re range covered in th e ex
p e r im e n ts; and (c) a ctiv e ch arcoal req u ires a con sid erab ly lon ger period to bu rn th a n coal or se m i-c o k e o f th e sa m e siz e (w eig h t per p a rticle).
P
U L V E R IZ E D fuels, which, in th e U nited S tates usually m ean bitum inous coals, are finding a steadily increasing use in power plants. T he boiler furnace burning pulverized fuels m ay also serve as an o u tle t for th e semi-coke produced in increasing q u antities by low -tem perature car
bonization processes; this condition would be of im portance in conservation and smoke abatem ent. T o a tta in it, how
ever, th e greater cost of th e coke, arising from th e expense of m anufacture and from its lower heating value, will have to be offset either by th e sale of by-products or by a greater u tility of th e coke in th e boiler room, or by both.
F undam ental d a ta on th e burning characteristics of powr- dered fuels are meager, although th e y are obviously essential to th e rational design of furnaces intended for th eir use.
F u rth e r, although powdered coal is successfully and ad
vantageously used in m any installations, th e burning char
acteristics of powdered semi-coke are largely known.
As a first approxim ation, th e ra te of liberation of h eat energy in a given boiler installation, other things being equal, will depend on two m ain factors: (1) th e ra te of propagation of th e flame through th e cloud of powdered fuel and air, because this determ ines th e num ber of fuel particles ignited per u n it tim e; and (2) th e tim e of burning of th e individual particles of th e fuel, because this determ ines th e ra te of libera
tion of energy from th e particle, once i t is ignited. B oth factors probably are functions of other variables, some of th e la tte r undoubtedly being common to both factors.
A stu d y of th e fundam ental phenom ena occurring in th e com bustion of powdered fuels has been conducted during the p a st tw o years by th e P ittsb u rg h E xperim ent S tation of th e U. S. B ureau of M ines jointly w ith th e Carnegie In stitu te of Technology and th e M ining A dvisory Board. A lthough the d a ta obtained during th e first year did n o t perm it evalu-
1 R eceived April 2, 1929. Published by permission^of the Director, U . S. Bureau of M ines, Carnegie Institute of Technology and the M ining A dvisory Board. (N o t subject to copyright.)
J Research fellow, 1928-29, Carnegie Institute of Technology.
ating th e absolute ra te of flame propagation, app aren tly th e flame propagates more rapidly through a suspension of pow
dered coal in air th a n through a sim ilar “ cloud” of powdered semi-coke of th e same fuel concentration and particle size.3
As a fu rth e r step in th e fundam ental stu d y of this problem , during th e college year 1928-29 th e ra te of burning of th e individual particles of certain solid fuels u nder known con
ditions of furnace tem perature, particle size, and oxygen concentration was determ ined.
A p p aratu s an d M eth od
Figures 1 and 2 illu strate th e experim ental m ethod of determ ining th e ra te of burning of th e individual particles of solid fuels. T h ey show, respectively, th e furnace in which th e particles were burned and th e revolving-drum cam era for determ ining th e period during which each particle was in process of com bustion.
T he essential p arts of th e furnace are th e six nichrom e ribbons th a t serve both as th e heating elem ent and as th e walls of th e furnace proper; th e silica glass windows; and th e feeder b y w hich th e particles, which have been previously sized, are dropped into th e furnace. T he nichrom e ribbons are each 34 inches (86.4 cm.) long and 0.01 inch (0.25 mm.) (No. 30 B. & S. gage) thick. Two strips are each 1 inch (2.5 cm.) wide, and th e other four strip s are each 3/< inch (1.9 cm.) wide. T he six ribbons are disposed (Figure 1, A A ) ab o u t th e periphery of a hexagon, 1 inch (2.5 cm.) on a side, held in such arrangem ent prim arily b y a ttac h m e n t a t th e ends to hexagonal stu d s on th e furnace term inals. T he two 1-inch (2.5-cm.) ribbons are placed opposite each other, and th e other four are disposed as indicated in Figure 1. T his arrangem ent leaves tw o opposite vertices of th e heating ele
m en t open to form th e windows.
T he u pper furnace term inal carries th e w eight of th e heating elem ent and th e lower term inal. T he la tte r is free to move through th e hole in th e tra n site board furnace end, as th e heating elem ent expands w ith tem perature. Springs a t th e b ottom of th e furnace p u t a slight tension on th e heating elem ent and aid in keeping th e elem ent in align
m ent.
Slots are cu t in th e furnace shell or exterior (m ade of 6-inch (15-cm.) Shelby seamless steel tubing), which align w ith the window's in th e heating element. N arrow ties, on 6-inch (15-cm.) centers, are left w hen milling such slots; otherwise th e tu b e would n o t reta in its cylindrical shape. T he sectional slots in th e furnace shell m ake necessary fused and polished silica-glass windows, which are placed directly against th e
“ edge” of th e heating elem ent in 6-inch (15-cm.) sections.
Likewise, th e pieces of tran site board th a t provide a clear passage for th e light from th e interior to th e exterior of the
* Thesis subm itted b y D . L. Reed as part requirement for an M .S.
degree, Carnegie Institute of Technology, 1927-28.
Septem ber, 1929 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 SO 9
Terminal- Dust feeder. §0j
Vcntv I
F ig u r e 1— F u r n a c e f o r D e t e r m in in g T im e o f B u r n in g o f I n d iv id u a l P a r t ic le s o f P o w d er e d F u e ls
furnace are m ade in sections 6 inches (15 cm.) long. B oth silica windows and tran site board pieces are supported from special brackets attach ed by screws to th e furnace shell. The slots on th e outside of th e furnace shell are covered w ith tra n sp a ren t mica. Space between heating elem ent and shell is filled w ith short-fiber asbestos.
Slow and uniform feeding of th e fuel particles, as well as keeping them 'cool until they en ter th e furnace a t th e end of th e funnel stem , is essential. T he form er is accomplished by sifting them , as previously sized, through a screen placed in a long-stemmed m etal funnel. T he funnel is vibrated, w ith some control over period and am plitude, by m eans of a large electric buzzer. T he particles are k ep t cool u n til th e y enter the furnace by sheathing th e steam of th e funnel w ith a w ater ja ck e t formed of concentric tubes, as shown in th e enlarged section of th e feeder in Figure 1.
I t w as found necessary to introduce th e sm aller particles farth er down in the furnace, because when introduced near th e to p th e relatively violent convection currents in th e neighborhood of th e water-cooled term inal m ade it difficult to ta k e photographs. T he feeder for this purpose was identi
cal in principle w ith th e top one. Differences in construction details included passing the stem of th e funnel through one of th e furnace window spaces a t an angle of 45 degrees w ith th e vertical and producing th e vibration by m eans of an eccentric, of variable am plitude, driven b y a variable speed m otor.
T he cam era used (Figure 2) is an ordinary 8 by 10 inch view cam era modified as required for th e purpose. T he regular cam era back is replaced by an alum inum plate, containing an opening, w ith rabbeted edges, ab o u t 4 by 10 inches (10 by 25 cm .). A rem ovable drum box, w ith slide and cover as indicated in th e figure, fits into th e rabbets, where it is held b y special thum bnuts. T he box w ith drum is th u s readily removed and transported to th e d ark room.
The drum proper is a piece of 33/v in c h (9.5-cm.) brass tubing, which is ju st th e correct size to tak e a 10 by 12 inch (25.4 b y 30 cm.) photographic film or paper w ith a slight lap.
T he geometrical arrangem ent of th e drum assembly is such as to bring th e surface of th e drum in th e plane norm ally occupied by th e ground glass of th e camera. I t is th u s possi
ble to focus sharply on th e burning particles by placing th e regular cam era back in position. T he lens used is an anas- tig m at of speed F 3.5, fitted w ith a front sh u tter. P eriph
eral speed of th e drum is obtained b y means of a spark gap, focused on th e drum surface and controlled by a 50- cycle tuning fork.
I n m aking an experim ent th e drum is sta rted and allowed to ru n an in sta n t to a tta in constant speed. T he drum -box slide is then removed and th e spark plug allowed to function for ab o u t one revolution of th e drum . T he vib rato r of th e feeder is then sta rted ; and a t ab o u t th e same in sta n t the sh u tte r of th e cam era is opened. A fter enough particles—
usually ab o u t 50—have been fed into th e furnace and burned the cam era sh u tter and drum -box slide are closed. T he drum box is then rem oved and carried to th e dark room for developm ent of th e film or paper.
D escrip tio n o f F u els and M eth od o f P reparation T he fuels used were as follows: (1) a powdered coal from th e Cabin Creek d istrict of W est Virginia, described as K anaw ha gas coal; (2) a semi-coke produced from this coal by th e M cEw en-Itunge process of low -tem perature carbonization; (3) a beehive coke; and (4) an activated charcoal. T able I gives th e proxim ate chemical analyses of th e first three of these fuels.
810 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 Vol. 21, No. 9
T a b le I— P r o x im a te A n a ly s is o f F u e ls T e s te d Co n s t i t u e n t Co a l Se m i- Co k e Be e h i v e Co k e
P er cent Per cent Per cent
Moisture 1 .4 2 .1 0 .5
V olatile m atter 3 2 .5 1 3 .8 1 .6
Fixed carbon . 5 6 . 3 7 1 .6 8 6 .8
Ash ' 9 .8 1 2 .5 11.2
Sulfur 1 .0 1.1 0 .8
B. t. u. 13,260 12.760
As th e coal and semi-coke were re
ceived in pulverized form, preparation of t h e s a m p le s con
sisted in screening th e fuels t h r o u g h screens of th e de
s i r e d mesh. T he s a m p l e s w e r e s c r e e n e d twice to aid in elim inating fines which have a tendency to adhere to th e larger p a rti
cles and m ight be
c o m e s e p a r a t e d w hen th e fuel is introduced into th e f u r n a c e . O t h e r wise, these would introduce an error in th e tim e of burn-
Flfturc 3—M in u s 45 + 50 M esh C o a l. X 16 i n g f o r t h e g i v e n particle size. A fter screening, th e samples v’ere placed in stoppered bottles until needed.
T he beehive coke and active charcoal available were of such sizes as to require grinding before screening. The charcoal was of a size commonly used in gas masks. T he coke sam ple was prepared from a piece of coke of m etallurgical size. T he grinding was done by hand, using an iron m ortar and pestle. T re atm en t after grinding wras th e same as for th e coal and semi-coke.
Figures 3 to 6 are photom icrographs of th e coal, semi-coke, beehive coke, and active charcoal, respectively, — 45 + 50 mesh size. T he sizing appears to be very satisfactory.
T he ap parently highly porous and rough surface of the semi-coke and very irregular shapes of th e particles are notew orthy. Several particles, evidently of uncoked coal, appear in the semi-coke, as m ight have been anticipated and would have been predicted from photographs of the burning semi-coke. T he high friability of th e semi-coke is indicated by th e presence of fines which were produced in spreading th e coke on th e slide for m aking th e photom icro
graph.
T he usual cratered surface is clearly seen in th e photo
graph of th e particles of beehive coke. In th e photograph of active charcoal variation in th e character of th e m aterial from particle to particle is evident. T his likewise could have been predicted from w atching th e charcoal while it was burning in th e furnace, as will become evident la ter in the description of th e experim ental results. I t is notew orthy also th a t th e charcoal particles appear larger, a t least in
“ plan,” th a n th e corresponding screen size of particles of the other fuels. T his probably indicates greater angularity of th e charcoal particles, because they m ust have been closely th e same in minim um dimension as particles of th e other fuels. T he surface of m ost of th e charcoal particles appears to be porous, as would be expected.
w h at lower tem pera
tures, the tra c k for FiSure 45x+,56° Mesh SemI' Coke-
coal has tw o por- '
tions, each of different character; th e earlier portion suggests th a t th e volatile m a tte r is driven off and burned during such period. A fter such ap p aren t distillation of th e volatile, th e particle burns more like one of coke. D uring th e early portion of th e burning a t th e higher tem peratures th e particle travels downward a t relatively high and nearly uniform velocity, as indicated b y th e nearly vertical straig h t line form ing this portion of th e trace. E vidently, th e volatile m a tte r burns
E xp erim en tal R e su lts
Figures 7 to 14 are typical photographs of burning particles, as obtained w ith th e revolving-drum camera, of th e various fuels of different sizes and a t different tem peratures. In explanation of th e photographs (see Figure 7), ro tatio n of th e cam era drum moves th e film from left to right. T he tim ing dots by which th e drum speed is determ ined are visible a t th e u pper edge of th e picture.
T he fuel particles move downward, a t least initially, so th a t if th e particles continued to fall a t a uniform ra te th e tracks would be straig h t lines sloping downward on th e right. A ctually, while th e particles fall initially, th e y s ta rt to rise soon after ignition, th u s producing th e curved traces shown in th e photographs. Obviously, then, so long as th e particles m ove in a vertical line (otherwise th e particles would pass from view because of th e narrow furnace window), th e tim e of burning is obtainable from th e projection of the trace on the tim e axis, being actually th e length of such projection divided b y th e (linear) speed of th e film. D e
partu re from m otion in a vertical line, while introducing an error in th e tim e th u s com puted, was small. M oreover, th e resu ltan t error obviously tends to be elim inated over a considerable num ber of particles, although if th e particle describes an intricate space curve some error m ay result.
E rro r from such sources, however, was negligible, as evi
denced by th e reproducibility of th e experim ental values, which were surprisingly good for work of th is type.
All th e photographs shown were m ade on regular pan
chrom atic film, which is sensitive, n o t only to th e usual photographic wave lengths, b u t to th e red rays as well. A special paper, known as E astm an No. 1 recording paper, was used in general for obtaining th e photographs, because by so doing more d a ta could be obtained in th e tim e available.
This is a desirable feature w hen covering th e field ra th e r broadly.
Ch a r a c t e r i s t i c s
o f T r a c k s o f
Bu r n i n g Pa r t i c l e s— T h e w id e , dense trac k for coal, as com pared w i t h th a t for th e other f u e l s , particularly for th e cokes, un
doubtedly c a n b e a ttrib u te d t o t h e higher percentage of volatile m a tte r in th e coal. T his ap
pears to form an en- v e l o p e of burning gas of considerable size ab o u t th e coal particle and burns a t a high tem pera
ture. A t 1000° C., as well as a t some-
Septem ber, 1929 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 S i l
T a b le I I —T e m p e r a t u r e s a n d B u r n in g P erio d s o f —4 5 4 -5 0 M esh F u e ls Av e r a g e In d i c a t e d Ti m eo p Bu r n i n g
PKRATURE Coal Semi-coke A ctive charcoal
° C. Milliseconds M illiseconds Milliseconds
7 2 0 2 5 8 2 2 7
7 5 0 3 1 5 3 0 0
7 6 8 3 0 0 2 8 6
8 0 6 3 7 2 3 1 3 5 4 8
8 5 5 4 3 9 3 4 2 5 5 0
9 0 6 4 7 8 3 7 8 5 4 2
9 5 0 5 1 1 4 1 0 6 4 8
9 7 5 4 3 5
1 0 0 0 5 7 8 4 5 5
Fu e l Me s i i
Nu m b e ro f Pa r t i c l e s We i g h e d
We i g h t sp e r
100 Pa r t i c l e s
Mg.
C o a l - 4 5 4 - 5 0 1000 2 .8
Semi-coke - 4 5 4 - 5 0 1000 1.4
Charcoal - 4 5 4 - 5 0 1000 1 .8
Coal - 5 0 4 - 6 0 500 1.9
Coal - 8 0 4 - 9 0 1000 0 .7 3
Beehive coke - 4 5 4 - 5 0 1000 3 .1
T he results on — 45 + 50 and — 80 + 90 mesh fuels are given in Tables I I and III . T he results on — 50 + 60 mesh coal, th e values for — 45 + 50 m esh semi-coke taken from m ostly “ behind” th e particle, probably because of the
initial velocity of fall, th e expanding products of com bustion driving th e particle before them . M any of th e tracks are alm ost perfect corkscrews or spirals. Some such p ath would be expected for particles of these irregular shapes.
T he proportion of th e to ta l num ber of burning coal particles th a t show tracks of th e ty p e found for practically every particle burning a t 1000° C. decreases as th e tem perature is decreased. Some appear even a t 750° C., although th e particular coal photograph a t 806° C. has none. A pparently, in m ost cases, w ith coal a t th e lower tem peratures th e vola
tile m a tte r is distilling thro u g h o u t th e tim e of burning.
T he dense high-velocity spiral tra c k also occurs fairly frequently w ith semi-coke and occasionally w ith beehive coke. A pparently, some of th e particles of beehive coke contained considerable volatile m atter, although th e over-all average was small.
T he active charcoal gives a trac k different in ty p e from an y of th e other fuels in th a t th e particles generally fall much farth er before sta rtin g to ascend. I n fact, some were n o t entirely consumed in th e entire length of th e furnace, as in
dicated b y th e passing of th e tra c k off th e edge of th e film.
T his indicates variation in character of th e charcoal from one particle to another.
Experim ents w ith beehive coke were n o t very satisfactory, as some of th e particles dropped through th e whole furnace w ithout igniting, even a t 1000° C. Accordingly, th e pictures shown probably are tracks of only th e smaller particles or of those containing appreciable volatile or of both. T he w riters
do n o t consider th a t t h e r e is a n y such v a r i a t i o n in t h e burning tim e for — 80 + 90 mesh bee
hive coke from 800°
to 1000° C., as th e photographs would indicate.
Su m m a r y o f Re s u l t s—T he experi
m ental results a r e s u m m a r i z e d i n Tables I I to V and are shown graphi
cally in Figures 15 and 16.
T able I I gives the results on th e — 45 + 50 m e s h f u e ls from 720° to 1000°
C. T he active char
coal, being readily c o m b u s t i b l e and
F ig u r e 5— M in u s 45 + 50 M e sh B ee h iv e Containing no vola-
C o k e. x 16 tile m atter, was in
cluded.
Us i n g To p Fe e d e r Us i n g Si d e Fe e d e r
Furnace tempera
ture
AVERAGE in d i c a t e d
b u r n i n gt i m e Furnace tem pera
ture
a v e r a g ein d i c a t e d BURNING TIME
Coal Semi-coke Coal Semi-coke Charcoal
° C . M illiseconds ° c . M illiseconds
67 1 9 6 7 0 0 8 1 2 4 9
7 3 1 111 8 0 7 2 0 7 4
7 6 8 1 3 8 9 7 7 5 0 8 9 7 9 2 6 5
8 0 6 1 3 7 1 05 8 0 0 104 98 2 8 2
8 5 5 1 8 0 166 8 5 0 133 131 2 9 0
9 0 6 1 6 3 1 4 2 9 0 0 176 1 7 6 286
9 5 0 189 2 1 0 264
1 0 0 0 2 1 5
T a b le IV— W e ig h t o f F u el P a r ticle s
T able I I I gives th e results on th e — 80 + 90 mesh fuels, introduced both a t the top and from th e side of th e furnace.
T he side feeder was used because of th e difficulty of photo
graphing these smaller burning particles when introduced in th e furnace a t th e top.
I t was interesting to obtain an idea of th e relative burning periods of th e fuels where th e w eight of com bustible per particle was approxim ately th e same, because this (rather th a n a comparison of th e same screen size) would more nearly measure the
relative ra te of en
ergy l i b e r a t i o n in an actual boiler as affected by th e tim e of burning of th e in
dividual particles.
T o t h i s e n d t h e w eight per particles of th e several fuels w as o b t a i n e d b y counting and weigh
ing a large num ber (500 to 1 0 0 0 ) of them . T he p arti
cles were weighed on a balance having a sensitivity of about 0.02 m g ." T able IV and Figures 15 and 16 give th e results.
As it was n o t fea
sible to obtain fuels of th e same weight
n o r n o r t i ’ p l p h v F ig u r e 6 — M in u s 45 + 50 M esh A c tiv e p c i p d i t i c i c * u y C h a r c o a l. X 16
screening, burning
tim es were determ ined for three screen sizes of coal: — 80 + 90, — 50 + 60, and — 45 + 50 mesh. From these d a ta a curve of burning tim e against w eight per particle was plotted.
F rom this curve the burning tim e for coal particles of the same w eight as those for — 45 + 50 mesh semi-coke was obtained, th u s giving a comparison of th e burning tim es of these two fuels where th e w eight per particle was th e same.
T a b le III— T e m p e r a t u r e s a n d B u r n in g P erio d s o f — 8 0 4 -9 0 M csli F u els
812 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 Vol. 21, No. 9
F igu re. 7—T r a c k s o f B u r n in g P a r tic le s o f C o a l, —45. + 50 M esh
a t 1000° C. F ig u r e 8 —T ra c k s o f B u r n in g P a r tic le s o f S e m i- C o k e , —45 + 50 M esh a t 806° C.
F ig u r e 10—T ra c k s o f B u r n in g P a r tic le s o f B ee h iv e C o k e, —80 + 90 M esh a t 806° C.
th e experim ental values were, as already m entioned, sur
prisingly reproducible, particularly for th e coal and semi-coke.
T he charcoal and beehive coke were exceptions, th e beehive coke offering more difficulty th a n th e charcoal. Perhaps th e maximum reproducibility was obtained w ith th e — 80 + 90 mesh fuels introduced from th e side of th e furnace, for tem peratures u p to 900° C. A t 950° and 1000° C. th e results were more erratic.
T he authors attem p ted to cover th e field as com pletely as possible, w ith fair q u an tita tiv e correctness, in th e tim e available. H ad th e experim ents been repeated, introducing all th e refinem ents readily possible in th e m ethod, th e slopes of th e curves m ight have been changed; it is believed, how
ever, th a t th e im p o rta n t conclusions from th e work would have rem ained unchanged.
D isc u ssio n o f R e su lts
T he interesting points b rought o u t by the results are:
(1) th e pronounced negative tem p eratu re coefficient for th e coal and seini-coke as com pared w ith th e much sm aller coefficient for th e non-volatile fuel, active charcoal, and probably for beehive coke; and (2) th e much longer tim e of burning of th e active charcoal as com pared w ith th e o ther fuels.
T he behavior of beehive coke was n o t definitely settled.
R esults obtained on — 80 + 90 mesh fuel a t 850° and 900° C.
indicated a pronounced negative tem p eratu re coefficient;
those obtained for — 45 + 50 mesh fuel a t th e same tem pera-
Fu r n a c e Te m p e r a t u r e
Av e r a g e In d i c a t e d Ti m eo p Bu r n i n g
-5 0 + 60
Coal - 5 0 + 6 0
Semi-coke
Coal, same weight par
ticle as —4 5 + 5 0 sem i
coke
° C.
750 800 850 900 1000950
Milliseconds 282 317 367 386 436 466
M illiseconds 275 308 342 374 410 455
Milliseconds 214 , 240 276 308 336 368
In general, each determ ination represents an average value obtained from 150 to 200 particles. Sometimes m any more were m easured; and, in a few instances, in which conditions were more favorable for obtaining reliable values, fewer particles were used.
T he experim ental difficulties were often formidable, par
ticularly for th e larger particles a t the lower tem peratures and for th e sm aller ones a t th e higher tem peratures. Ac
cordingly, th e corresponding values in such tem perature ranges have n o t th e same degree of reliability as those in th e interm ediate tem perature range. In th e interm ediate region
F ig u r e 9 —T ra c k s o f B u r n in g P a r tic le s o f A c tiv e C h a r c o a l, —45 + 50 M esh a t 806° C.
sm ooth curves, and, for comparison, the values (interpolated from th e curves of burning tim e against weight) for coal particles of th e same weight as — 45 + 50 mesh semi-coke are given in T able V.
T a b le V— T e m p e r a tu r e s a n d I n d ic a te d B u r n in g P erio d s o f C e rta in S iz e s o f F u els
Septem ber, 1929 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 S13
F ig u r e 11—T ra c k s o f B u r n in g P a r tic le s o f G oal, —45 + 50 M esh
a t 1000° G. F ig u r e 12—T ra ck s o f B u r n in g P a r tic le s o f S e m i- C o k e , —45 + 50 M esh a t 1000° G.
F ig u r e 14—T ra ck s o f B u r n in g P a r tic le s o f B e e h iv e C o k e, - 8 0 + 90 M esh a t 1000° G.
from th e burning particles as th e furnace tem perature in
creased, it seemed w orth while to m ake some experim ents using a photographic emulsion having a color sensitivity, and probably an emulsion speed, quite different from those of th e recording paper. To th is end th e — 45 + 50 mesh coal and semi-coke were re-run and photographs taken on panchrom atic film.
T he indicated tim es of burning were, in general, longer on panchrom atic film th a n on paper; but, w ithin th e lim its of experim ental error, th e results were entirely analogous in th a t th e curves (lines) for coal and semi-coke were parallel to those for th e same fuels as determ ined by recording paper.
T he values obtained b y the tw o m ethods were alm ost th e sam e for th e coal particles, while those for th e semi-coke were abo u t 10 per cent higher using th e panchrom atic film.
N either th e relative color sensitivity of the panchrom atic film in th e violet and red nor th e relative speeds of th e emul
sions on the film and paper are known. Hence, th e foregoing experim ents cannot be com pletely interpreted. I t would be a strange coincidence, however, if two emulsions so different in essential characteristics yielded th e same result unless th a t result were real. Accordingly, recording paper was used in subsequent experiments, as its use enabled m ore results to be obtained in th e tim e available. ,
Some of th e possible causes of th e above results th a t have been suggested or have occurred to the authors m erit brief mention, although it seems unwise to elaborate th e discussion
F ig u r e 13—T ra c k s o f B u r n in g P a r tic le s o f A c tiv e G h a rco a l, - 4 5 + 50 M e sh a t 950° C.
tures gave th e same value a t both tem peratures. The la tte r coke gave m uch more satisfactory pictures. Accordingly, the authors believe th a t when enough experim ents are made to settle th e question th e beehive coke will show little or no tem perature coefficient over th e range 850° to 1000° C.
T his coke does n o t ignite readily a t lower tem peratures, even in — 80 + 90 mesh size.
A slight increase in burning tim e of th e fuels w ith increase in tem perature was anticipated, because the increased num ber of collisions between th e oxygen molecules and th e fuel particles due to th e increased velocity of th e form er is more than offset b y th e fewer oxygen molecules per u n it volume due to the decreased density of th e air. Theoretically, th e num ber of collisions a t constant pressure varies inversely as th e square ro o t of th e absolute tem perature, or in th e ratio of 1 to 1.14 from 700° to 1000° C. If all of th e oxygen molecules are n o t in a condition to react— th a t is, if an oxygen molecule a t these high tem peratures still requires activation—-the tim e of burning a t th e higher tem peratures will be decreased. Accordingly, th e pronounced increase in th e tim e of burning w ith increased tem p eratu re was som ewhat surprising.
T he first experim ents m ade were on — 45 + 50 mesh coal and semi-coke. As a possible explanation of th e pronounced negative “ tem perature coefficient of burning" th u s disclosed lay in th e insensitivity of th e recording paper to non-actinic light and a possible increase in th e q u a n tity of actinic light
814 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 Vol. 21, No. 9 a t present because th e d a ta appear insufficient to settle the
points definitely. Obvious possible explanations of th e negative tem perature coefficients for coal and semi-coke are:
(1) incom plete com bustion a t th e lower tem peratures; (2) selective burning—as, for example, only th e sm aller particles burning a t the lower tem peratures; and (3) sm aller loss of h eat a t th e higher furnace tem peratures due to sm aller tem p eratu re difference between particle and furnace walls.
F ig u r e 15—T im e s fo r B u r n in g P o w d er e d F u e ls o f T h r e e S iz e s a t V a rio u s F u r n a c e T e m p e r a t u r e s , U sin g t h e T o p F e e d e r
E ith e r of th e first tw o effects m entioned would cause an a p p a ren t increase in burning tim e w ith tem perature. If it be recalled th a t th e particle is a t a tem perature considerably higher th a n th a t of th e furnace in th e th ird instance, such tem perature being determ ined prim arily by th e com bustion processes, it is clear th a t th e particle will a tta in a higher tem p eratu re th e higher the tem perature of the furnace.
Hence, a longer trace m ight be anticipated a t th e higher furnace tem perature because of greater actinic power of the em itted light or because th e particle m ay rem ain luminous for a longer tim e.
A fter observing th e phenom ena th a t occur in the furnace d u ring th e m ajor portion of a year, th e authors feel th a t th e first tw o causes m ay be dismissed from consideration, and com putation shows th a t th e th ird effect is small on th e basis of any ratio n al assum ptions regarding th e tem peratures of th e burning particles.
T he following explanation of th e negative tem perature coefficient for th e coal has been suggested by A. C. Fieldner of th e B ureau of Mines: I t is known th a t the higher the coking tem perature th e less reactive is th e coke. If coking of th e particle takes place before m uch of th e burning has occurred (exclusive of possible tim e lag in th e coking as it can be shown readily th a t th e particles will a tta in practically furnace tem perature in perhaps 10 to 20 milliseconds), one
m ay be recording th e tim e of burning for a less reactive coke a t th e higher furnace tem peratures th a n a t a lower furnace tem perature. T he same effect would be present w ith th e semi-coke, although presum ably less so because this fuel is already p a rtly coked. However, particles of coal and semi-coke of equal screen size do n o t yield th e same am ount of coke, because th e density of th e semi-coke is only abo u t 50 per cent th a t of th e coal. Coal and semi-coke of th e same w eight per particle appear to have th e same tem perature coefficient (Figure 15), although th e am ounts of high-tem perature coke form ed on th e above theory m u st be very different for th e tw o fuels.
According to th e foregoing explanation th e tem perature coefficients for th e charcoal and beehive coke would be expected to be small, as it appears to be, although th e pro
nounced increase in burning tim e for — 45 + 50 mesh char
coal between 900 ° and 950 0 C. is an exception. I t is believed, however, th a t this increase is n o t real. T he charcoal offered considerable difficulties when photographed on paper, because of th e faintness of th e traces obtained. P hotographs of th e sam e fuel on panchrom atic film, which gives m uch denser traces w ith th e charcoal, yielded th e same value of th e burning tim e for tem peratures from 850° to 1000° C.
A nother possible explanation of th e negative tem perature coefficients is th a t th e p articular volatile products produced from both th e coal and semi-coke and th e am ount of cracking are dependent on th e tem perature. T his could be caused, n o t only by th e tem perature a t which distillation occurs, b u t also b y different ra te s of distillation a t th e different tem peratures. T he distillation products m ight be dependent also on th e size of th e particle, owing to v ariation in tem pera
tu re distribution w ithin th e particle w ith variation in particle size a t th e same furnace tem perature. Thus, a t different furnace tem peratures and perhaps w ith particles of different size, one m ay be burning products of different burning char
acteristics. T he phenom ena are obviously so com plicated, p articularly because of th e presence of th e volatile m atter, th a t it appears very difficult to theorize on th is phase of the
F ig u r e 16—T im e s fo r B u r n in g —80 + 90 M esh C o a l, S e m i- C o k e a n d A c tiv e C h a r c o a l P a r tic le s a t V a rio u s T e m p e r a t u r e s , U sin g t h e S id e F e e d e r
problem . I t is seen th a t all reactions commonly considered to occur in com bustion processes have a decided tendency to proceed a t one or another of th e tem peratures w ithin th e range covered; b u t d a ta on th e reaction rates, which are essential to attac k in g th e problem theoretically, are largely lacking. M oreover, in so com plicated a system reactions other th a n th e common com bustion ones are probably occurring.
As a la st explanation of th e negative tem perature coefficient m ay be m entioned th e possibility th a t, under th e expcri-
