THE JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
3 40
THE DECARBONATION OF DOLOMITE LIMESTONE IN THE ROTARY KILN B y E. E. EAKINS Received October 16, 1918
T o determine if possible t h e points a t which decarbonation of our stone commences and t h e point a t which i t is complete, it was decided t o investigate t h e contents of our rotary kiln during a recent shutdown. This work was undertaken with no intention of making a scientific research, b u t merely as a matter of general plant information. Results alone are given, and these are published only as a matter of general information for those who may be calcining limestone in a rotary kiln. The limestone used in our kiln is t h e well known Cedar Hollow stone crushed t o pass a I in. screen, All fine material (screenings) is removed. T h e rotary kiln is of t h e usual type used in cement practice, 150 ft. long b y 6 ft. 6 in. inside t h e lining, which is of clay brick well grouted with cement. T h e inclination is 3/4 in. per ft.l The kiln rotates normally at t h e rate of one revolution in I min. 40 sec. T h e feed is continuous, and t h e output of t h e kiln averages 100 tons of burned lime per 24 hrs. Firing is b y producer gas from two Chapman producers rated t o gasify 18 tons of coal each per 24 hrs. T h e fuel used is a low sulfur semi-gas coal, averaging about 30 per cent volatile combustible matter. It has been impossible t o secure accurate temperat u r e measurements inside t h e kiln proper. The temperature of t h e gas taken a t t h e port just before its entrance t o t h e kiln varies from 1500' F. t o 1600' F., while t h e temperature of t h e stack gases, taken in t h e dust chamber at a point where they are undiluted b y cold air, varies from 1100' F. t o 1300' F. The stone was present in t h e kiln t o a depth of 1 2 or 14 in., and samples were taken from a point about 3 in. below t h e surface t o t h e bottom of t h e mass. Only clean lumps in. or larger were taken for t h e sample. Samples were taken a t t h e intervals specified below, starting a t t h e discharge end of t h e kiln. Each sample was analyzed for carbon dioxide, and was examined macroscopically and microscopically. qistance Ft. 0 10 20 30 40
coz
Per cent 1.02 2.35 4.68 21.46 37.12
CHEMICAL ANALYSIS Distance Ft. 50 75 100 125
COS
Per cent 42.20 42.92 42.96 43.09
MACROSCOPIC E X A Y I i S A T I O N
T h e sample taken a t o f t . (discharge end) showed no evidence of core when t h e lumps were broken open. The carbon dioxide content is apparently due t o recarbonation from t h e air. T h e sample taken a t I O f t . showed slight evidence of core. T h e quantity of core increased in each sample u p t o t h e sample taken a t 40 f t . , which was hard, like stone, b u t lacked t h e full crystalline character of limestone. From 40 f t . t o 7 5 f t . t h e similarity in appearance of t h e samples t o limestone progressively increased, and a t t h e latter point t h e material was apparently unchanged limestone. 1
This is greater than is usual in cement practice.
Vol.
11,
No. 4
MICROSCOPIC EXAMINATION I N POLARIZED LIGHT
I n addition t o t h e chemical analysis recorded above, all samples were examined under t h e microscope, with, very interesting results. The sample taken a t 1 2 5 f t . was completely crystalline in character, excepting a small amount of impurities, and corresponded in all respects t o our raw stone. At 100 f t . t h e quantity of non-crystalline amorphous matter showed a slight increase, due t o the decomposition of some magnesium carbonate. From I O O ft. t o 3 0 f t . t h e amorphous material progressively increased in quantity, and a t 30 f t . t h e first evidence of free calcium oxide was obtained.' T h e quantity of free calcium oxide then increased rapidly t o t h e o f t . mark where it reached its maximum. At I O f t . there was very slight evidence of crystalline calcium carbonate. At o f t . there was no evidence of crystalline calcium carbonate. '
I
COMPARISON
O F RESULTS
The results of t h e microscopic examination and chemical analysis check reasonably closely. An average analysis of t h e stone supplied t h e rotary kiln would be as follows: CaO ......................................... MgO
........................................
co*.........................................
Per cent 29.12 19.40 44.22
This percentage of calcium oxide requires 22.88 per cent carbon dioxide for conversion into calcium carbonate, while t h e magnesium oxide requires 21.34 per cent carbon dioxide for conversion into magnesium carbonate. At 40 f t . from t h e discharge end, t h e contents of t h e kiln show 37.12 per cent carbon dioxide present, or more t h a n enough t o satisfy all t h e calcium oxide. At 30 ft. from t h e discharge end, t h e contents of t h e kiln show 21.46 per cent carbon dioxide present or less t h a n t h e quantity necessary t o satisfy all t h e calcium oxide. T h e microscope shows t h a t no free lime is prese-nt 40 f t . from t h e discharge, b u t t h a t considerable free lime is present 3 0 f t . from t h e discharge. CONCLUSIONS
I-The first decomposition of t h e stone takes place about I O O f t . from t h e discharge end of t h e kiln. a-This decomposition is entirely of magnesium carbonate, and increases gradually until a point is reached between 30 and 40 f t . from t h e discharge, where t h e calcium carbonate first decomposes and free lime is obtained. . 3-The production of calcium oxide in our rotary kiln takes place entirely in t h e last 30 or 40 f t . of t h e length of t h e kiln, and is not complete until t h e last I O f t . of t h e kiln is reached. CHAELESWARNERCOMPANY DEVAULT, PENNSYLVANIA 1 The presence of free lime was determined by refractive index and also by treatment of sample on the slide with White's solution, and the subsequent production of strongly doublesrefracting needles of calcium phenolate.
Apr.1 1919
T H E J O U R N A L OF I,VDUSTRIAL A N D ENGINEERING C H E M I S T R Y
STANDARD ALKALI FOR MIXED ACID CONTROL By EVELYN HEARSEYAND C. M . JOYCE Received August 15, 1918
S t a n d a r d alkali for t h e titration of mixed acids usually consists of normal sodium hydroxide s t s n d ardiaed through normal sulfuric acid, standardized in t u r n b y sodium carbonate with methyl orange as a n indicator. This procedure has several disadvantages, which are discussed i n t h e (‘Standardization of Alkalimetric Solutions,” b y Francis D. Dodge,l who recommends potassium acid phthalate as a standard. T h e accuracy of this method has been established b y W. S. Hendrixson i n his careful experimental s t u d y of t h e subject.2 T h e advantages of direct standardization with potassium acid phthalate over titration with normal acid which m u s t b e standardized b y a troublesome process, are so obvious t h a t it seems strange t h a t t h e new method has not come into more widespread use. T h e reason may be contained in t h e fact t h a t phenolphthalein, in spite of its sensitiveness, is not a s desirable an indicator as methyl orange when carbonates are present in t h e s t a n d a r d alkali. B y following t h e procedure described in “Preparation of a Solution for Ma,king S t a n d a r d Solutions of Sodium Hydroxide,”3 t h e interference of carbonates with t h e indicator can be easily eliminated. A s t a n d a r d solution prepared in t h i s manner m a y be titrated against potassium acid phthalate in t h e cold using phenolphthalein as a n indicator. A standardization along these lines, performed in 1
THISJOURNAL, 7 (1913,
*
J . A m . Chem. Soc., 37 (1915), 2352. Cowles, I b i d . , 30 (19081, 1192.
29.
341
this laboratory, differed from t h e result of a titration against N / 5 acid standardized with sodium carbonate b y less t h a n 0 . o 5 per cent. STANDARDIZATION OF N / 5 wit,
KHC8HaOl Grams 1.750 I ,754 1.743 1,741
HYDROXIDE WITH ACID POTASSIUM PHTHhLATE Vol. N / 5 NaOH Equivalent NaOH(a) t o 1 g . KHCeHaO4 X N/5 Grams cc. cc. 42.81 24.49 X 1.750 i42.81 = 1.001 42.95 24.49 X 1.754 + 42.95 = 1,000 42.66 24.49 X 1.753 -+ 42.66 = 1.001 42.61 24.49 X 1.741 -+ 42.61 = 1.001 SODIUM
AVERAGE, 1,001 STANDARDIZATION O F N / S SULFURIC ACID WITH SODIUMCARBONATE Wt. Vol. N / S HzSO~ Equivalent NaaC03 HzSOc(a) t o 1 g . NazCOs x n/s cc. c c. Gram Gram 47.44 94.33 X 0.5000 0.5000 + 47.44 = 0.9942 47.49 94.33 X 0 . 5 0 0 5 + 47.49 = 0.9942 0.5005 47.41 94.33 0.4995 X 0.4995 + 47.41 = 0.9939 47.40
0.4995
94.33
X 0.4995 f 47.40 = 0.9941
-
AVERAGE, 0.9941
N / S SULFURIC ACID vs. N / 5 SODIUMHYDROXIDE N / 5 HzSOa(o) X N/5 N / 5 NaOH cc. Gram cc. N / 5 NaOH X X X X
42.33 42.45 42.34 42.33
0.9941 0.9941 0.9941 0.9941
-:
f
-: -:
42.03 42.15 42.05 42.05
= = = =
1.001 1.001 1.001 1.001
.... 1.001
AVERAGE
( a ) Corrected for calibration, temperature, and run back.
These d a t a were obtained in connection with ordinary control work a n d without unusual precautions, except t h a t all t h e burettes used for alkali were freshly calibrated as t h e y change appreciably every few months from solvent action. T h e potassium acid p h t h a l a t e used was prepared from Merck’s phthalic anhydride b y Dodge’s meth0d.l T h e sodium carbonate used was Kahlbaum’s “for analysis.” LEOMINST~R, MASSACHUSETTS 1
LOG.
cit.
ADDRESSES AND CONTRIBUTED ARTICLES OUR OPPORTUNITY By BERNHARD C. HESSE~
Since the early days of the war, exhortations to cooperation as a remedy-in fact the only remedy-for the then suddenly revealed, although long known, lack of self-containedness and of xndustrial independence in many countries and especially in what have since been grouped as “key” or “pivotal” industries have been numerous, widespread, and persistent. Our own country and our own business and profession have by no means escaped those exhortations. In fact, our profession has been made the special target for unfounded, vehement, and indiscriminate charges of inexcusable backwardness in development and of conspicuous want of courage in operation and expansion; in corresponding measure we have been urged and have ourselves repeatedly promised cooperation as a cure for those alleged conditions. While the war was on, all our industries bent all their energies towards accomplishing the heavy tasks imposed upon them in the shortest possible time, regardless of any and all refinements as to efficiency and exquisiteness of workmanship. Consideration of measures of development or of cooperation to be followed upon the return of peace had to be put to one side until the imniediate and pressing war needs were out of the way. With the signing of the armistice opportunity for such consideration 1
Read before the Lehigh Valley Section, American Chemical Society,
at Easton, P a , , March 14, 1919.
CHEMIcame measurably closer. The Council of the AMERICAN CAL SOCIETY then took immediate steps to formulate a cooperative policy for after-the-war conditions. THE CHEMIST IN THE LIFE O F THE NATION
Before discussing our opportunity it will be serviceable to review what the probable general position of our business and profession is in the national economic life of our country. Those who follow chemical pursuits of whatever kind in this country made up, before the war, I/IOOOO of our population; those of us then engaged in industrial activities, as distinguished from educational and like activities, were engaged in industries which employed 1/6 of the industrial wage-earners of the country, produced 1/4 of the value of all manufactures in the country, created r / 5 of the total value created by manufacture in this country, in their trade with one Eoreign country alone made up 1/20 of our total foreign business and produced 117 of our balance of trade. The forthcoming census will, no doubt, show a decided growth of our importance, both relative and actual, in our national economic life. RECIPROCAL RESPONSIBILITIES
Bulking so large in the economic life of our country as do the industrial activities of this I/IOOOO of the country’s population it is clear on the one hand that the nation owes it to itself to see to it that the activities of this I/IOOOO are interfered with as little as possible and are enhanced to the utmost, and on the
