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f?T ft
STATE OF ILLINOIS
DWIGHT H. GREEN, GovernorDEPARTMENT OF REGISTRATION AND
EDUCATION
FRANK G. THOMPSON, Director
DIVISION OF THE
STATE GEOLOGICAL SURVEYM. M. LEIGHTON, CkUf
URBANA
REPORT OF INVESTIGATIONS — NO. 78
CORRELATION OF DOMESTIC STOKER COMBUSTIONWITH LABORATORY TESTS
AND TYPES OF FUELS
I. PRELIMINARY STUDIES
BY
L. C. McCABE, S. KONZO, AND O. W. REES
In Cooperation With the University of Illinois
Engineering Experiment Station
PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS
URBANA, ILLINOIS
1942
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ORGANIZATION
STATE OF ILLINOISHON. DWIGHT H. GREEN, Governor
DEPARTMENT OF REGISTRATION AND EDUCATIONHON. FRANK G. THOMPSON,
Director
BOARD OF NATURAL RESOURCES AND CONSERVATIONHON. FRANK G.
THOMPSON, ChairmanEDSON S. BASTIN, Ph.D., D.Sc, GeologyROGER ADAMS,
Ph.D., D.Sc, ChemistryLOUIS R. HOWSON, C.E., Engineering
WILLIAM TRELEASE, D.Sc, LL.D., BiologyEZRA JACOB KRAUS, Ph.D.,
D.Sc, ForestryARTHUR CUTTS WILLARD, D.Engr., LL.D.,
President of the University of Illinois
GEOLOGICAL SURVEY DIVISIONM. M. LEIGHTON, Chief
(22289)
14
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SCIENTIFIC AND TECHNICAL STAFF OF THE
STATE GEOLOGICAL SURVEY DIVISION100 Natural Resources Building,
Urbana
M. M. LEIGHTON, Ph.D., Chief
Enid Town-ley, M.S., Assistant to the Chief
Jane Titcomb, M.A., Geological Assistant
GEOLOGICAL RESOURCES GEOCHEMISTRY
Coal
G. H. Cady, Ph D., Senior Geologist and HeadL. C. McCabe. Ph.D.,
Geologist (on leave)R. J. Helfinstine, M.S., Assoc. Mech. Eng.James
M. Schopf, Ph.D., Asst. GeologistJ. Norman Payne, Ph.D., Asst.
GeologistCharles C. Boley, M.S., Asst. Mining Eng.Bryan Parks,
M.S., Asst. Geologist
Industrial Minerals
J. E. Lamar, B.S., Geologist and HeadH. B. Willman, Ph.D.,
Assoc. GeologistDouglas F. Stevens, M.E., Research AssociateRobert
M. Grogan, Ph.D., Asst. GeologistRobert R. Reynolds, B.S., Research
Assistant
Oil and GasA. H. Bell, Ph.D., Geologist and HeadG. V. Cohee,
Ph.D., Asst. GeologistFrederick Squires, B.S., Assoc. Petr.
Eng.Charles W. Carter, Ph.D., Asst. GeologistWilliam H. Easton,
Ph.D., Asst. GeologistPaul G. Luckhardt, M.S., Research
AssistantWayne F. Meents, Research Assistant
Areal and Engineering GeologyGeorge E. Ekblavv, Ph.D., Geologist
and HeadRichard F. Fisher, M.S., Asst. Geologist
Subsurface Geology
L. E. Workman, M.S., Geologist and HeadTracy Gillette, Ph.D.,
Asst. GeologistArnold C. Mason, B.S., Asst. GeologistKenneth O.
Emery, Ph.D., Asst. GeologistMerlyn B. Buhle, M.S., Asst.
GeologistFrank E. Tippie, B.S., Asst. GeologistRuth E. Roth, B.S.,
Research Assistant
Stratigraphy and Paleontology
J. Marvin Weller, Ph.D., Geologist and HeadChalmer L. Cooper,
M.S., Assoc. Geologist
Petrography
Ralph E. Grim, Ph.D., PetrographerRichards A. Rowland, Ph.D.,
Asst. Petrographer
Physics
R. J. Piersol, Ph.D., PhysicistB. J. Greenwood, B.S., Mech.
EngineerDonald O. Holland, M.S., Asst. Physicist (on leave)
Frank H. Reed, Ph.D., Chief ChemistH. W. Jackman, M.S.E., Chem.
Eng.Roberta M. Langenstein, B.S., Chemical AssistantMelville A.
Rogers, B.S., Research Assistant
Coal
G. R. Yohe, Ph.D., Assoc. ChemistMyron H. Wilt, B.S., Research
Assistant
Industrial Minerals
J. S. Machin. Ph.D., Chemist and HeadDelbert L. Hanna, A.M.,
Research Assistant
Fluorspar
G. C. Finger, Ph.D., Assoc. ChemistEverett W. Maynert, B.S.,
Research Assistant
X-ray and SpectrographyW. F. Bradley, Ph.D., Assoc. Chemist
Analytical
O. W. Rees, Ph.D., Chemist and HeadL. D. McVicker, B.S., Asst.
ChemistP. W. Henline. M.S.. Asst. Chemical EngineerWilliam F.
Wagner, M.S., Asst. ChemistK. F. Bursack, B.A., Research
AssistantMarion Lund Dickman, B.S., Research Assistant
MINERAL ECONOMICSW. H. Voskuil, Ph.D.,Grace N. Oliver, A.B.
Mineral EconomistAssistant in Mineral Economics
EDUCATIONAL EXTENSIONDon L. Carroll, B.S., Assoc. Geologist
PUBLICATIONS AND RECORDSGeorge E. Ekblaw, Ph.D., Geologic
EditorChalmer L. Cooper, M.S., Geologic EditorDorothy E. Rose,
B.S., Technical EditorKathryn K. Dedman, M.A., Asst. Technical
EditorAlma R. Sweeny. A.B., Technical Files ClerkPortia Allyn
Smith, Research AssistantMeredith M. Calkins, Geologic
DraftsmanLeslie D. Vaughan, Asst. PhotographerDolores Thomas Sims,
B.A., Geologic Clerk
Special Staff to Aid in the War Effort
Oil and Gas ResourcesEarle F. Taylor, M.S., Asst.
GeologistArnold Brokaw, M.S., Spec. Asst. GeologistM. W. Pullen,
Jr., M.S., Spec. Asst. GeologistPaul K. Sims, M.S., Spec. Asst.
GeologistJohn A. Harrison, B.S., Spec. Research Assistant
Underground Water Geology
Carl A. Bays, Ph.D., Spec. GeologistC. Leland Horberg, Ph.D.,
Spec. Asst. GeologistStewart Folk, M.S., Spec. Asst.
GeologistErnest P. DuBois, B.S., Spec. Asst. GeologistRobert R.
Storm, A.B., Spec. Asst. GeologistPaul Herbert, Jr., B.S., Spec.
Asst. GeologistCharles G. Johnson, A.B., Spec. Asst. Geologist
Consultants: Ceramics, Cullen W. Parmelee, M.S., D.Sc, and Ralph
K. Hursh, B.S., University of Illinois;Pleistocene Invertebrate
Paleontology, Frank Collins Baker, B.S., University of
Illinois;Mechanical Engineering, Seichi Konzo, M.S., University of
Illinois.
Topographic Mapping in Cooperation with the United States
Geological Survey.
April 1, 1942
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CONTENTS
Page
Introduction 7
Description of the coals studied . . . ." 7
Description of stoker and furnace 11
Laboratory tests 12
British Standards Swelling Index Number 12
Agglutinating value 13
Agde Damm test 13
Photographic procedure 14
Results of tests 14
Discussion of results 15
Summary 19
TABLES
1 Analyses of coals used in tests
2 Comparison of laboratory test values with stoker operation
ILLUSTRATIONS
Figure
1 Block of banded coal from southern Illinois showing fusain,
vitrain, and
clarain 10
2 Block of banded coal from southern Illinois showing clarain
and durain 10
3 Diagram of conversion stoker installation 12
4 View of the furnace 14
5 British swelling index buttons for hand-picked banded
ingredients 15
6 British swelling index buttons for certain stoker fuels
studied 16
7 Photographs of stoker fires with various fuels 17
8 Photographs of stoker fires with various fuels 18
9 Clinkers from vitrain- and clarain-rich fuels 19
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Digitized by the Internet Archive
in 2012 with funding from
University of Illinois Urbana-Champaign
http://archive.org/details/correlationofdom78mcca
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CORRELATION OF DOMESTIC STOKER COMBUSTION WITHLABORATORY TESTS
AND TYPES OF FUELS
I. PRELIMINARY STUDIESBy
L. C. McCabe,* S. Konzo,t and 0. W. Rees %
INTRODUCTION
I n 1937 the Illinois Geological Sur-* vey made exploratory
stoker tests ofcoals from Franklin Comity, Illinois. 1
which demonstrated that in these coalsconcentration of vitrain
causes excessive
swelling and coke-tree formation where-as clarain is more
free-burning and hasconsiderably less tendency to form coketrees.
The behavior of these two typesof coal or mixtures of them could
bedemonstrated in stokers but no exacttests short of combustion
were availablefor determining their suitability. Theneed for such
test methods to evaluatecoals for stoker use is generally
recog-
nized.
It was with this need in mind thatthe exploratory stoker tests
were con-tinued and were supported by a varietyof laboratory
procedures in 1939 and1940 by the Illinois Geological Surveyin
cooperation with the Department ofMechanical Engineering of the
Univer-
sity of Illinois. These tests and the sup-porting laboratory
data are described
in this report.
The coals were collected and preparedunder Dr. McCabe 's
supervision. Dr.Rees directed the routine analyses andthe special
laboratory tests. The com-bustion tests were made in a
domesticunderfeed stoker in the Warm Air Re-search Residence at the
University of
Illinois under Professor Konzo's super-vision.
The writers gratefully acknowledgethe helpful suggestions of Dr.
G. H.
Cady, Head of the Coal Division of theSurvey, and of Professor
A. P. Kratz
of the Engineering Experiment Stationof the University of
Illinois.
DESCRIPTION* OF THECOALS STUDIED
The investigation was primarily con-cerned with Illinois coals
and the differ-ences inherent in them. However inorder to inquire
more adequately intothe problems met in burning bituminouscoals in
stokers and better to test thelaboratory procedures, a few coals
thatoriginated outside the State were in-cluded. The origin and the
proximateand ultimate analyses of the coals usedin the tests are
given in table 1.
The banded character of coals, insouthern Illinois particularly,
has animportant bearing on their preparationand utilization. The
three most commoncomponents, fusain. vitrain, and clarain,are
illustrated in figure 1. The fourth.durain or splint ('fig. 2),
occurs infre-
quently in Xo. 6 coal in Franklin Countyand more abundantly in
the splint coalsof the Appalachian fields.
Fusain, the most friable of the fourcomponents, breaks down
during themining and preparation until the greaterpart of it will
pass a 100-mesh screen. 2, 3
Little of it is found, therefore, in well
prepared stoker coals.Vitrain does not break as easily as
fusain but it is much more friable thanclarain. Clarain is
closelv knit and
* Geologist, Illinois Geological Survey.t Special Research
Associate Professor of Mechanical
Engineering, University of Illinois.% Chemist, Illinois
Geological Survey.1 McCabe, L. C, Illinois coals; Constitution
important
with reference to their utilization: Mech. Engr.. p. 217,March
1933 ; Illinois Geol. Survey Cir. 26, 1938.
2 Parks, B. C, and McCabe. L. C Fusain content offine sizes of
Illinois coal : Trans. Illinois Acad. Sci.vol. 33, no. 2, Dec. 1940
; Illinois Geol. Survev Cir. 68,1940.
3 Thiessen, Gilbert, Fusain content of coal dust froman Illinois
dedusting plant : Am. Inst. Mining and MetEngr. Tech. Pub. 664,
1936.
[7]
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Location
DOMESTIC STOKER COMBUSTION
TABLE 1.
—
Analyses of
Fixedcarbon
Illinois
Franklin Co
Franklin Co
Franklin Co
St. Clair Co.
St. Clair Co,
Gallatin Co.
West VirginiaRaleigh Co.
Raleigh Co.
Labor- Vola-Coal atory Condi- Mois- tilebed Sample number tion*
ture matter
6 A C-2204 12
5.7 42.845.4
6 E C-2212 12
7.9 35.038.0
6 B C-1988 12
6.5 34.436.8
6 C C-2133 12
9.2 41.846.1
6 D C-2134 12
10.2 36.941.1
5 G C-2132 12
3.6 36.638.0
Eagle F C-2252 12
1.5 29.930.3
Poca- H C-2135 1 0.8 18.3hontas 3 2 18.4
46.649.448.152.252.255.943.247.542.247.048.049.8
63.464.475.275.9
TABLE 2.
—
Comparison of Laboratory
Coking tendency British Standard Agglutinating Softening
Temp.observed in the fuel bed Swelling Index No. Value (15:1) Agde
Damm
Sample 1 Indication Sample 1 Value Sample Value Sample 1
Value
A None A 3 A 2.5 G 324 °CB None B 3 F 2.02 C 330C None C 4 E 4.1
D 331D Slight D \y2 H 6.3 E 348E Slight E 4H C 6.6 F 353F Positive
F 5 G 8.0 A 361G Very positive g iy2 D 8.1 B 366H Very positive H 9
H 412
( 1. As received ; 2. Moisture-free.
A—Franklin County, 111. Durain-rich No. 6B—Franklin Countv, 111.
Clarain-rich No. CC—St. Clair Countv, 111. Top coal No. 6D—St.
Clair County, 111. Bottom coal No. 6E—Franklin County, 111.
Vitrain-rich No. 6F—Raleigh County, West Virginia. Eagle
seamG—Gallatin County, 111. No. 5H—Raleigh County, West Virginia.
Pocahontas No.
1 Silicon carbide to coal ratio, 20 to 1
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Coals Used in Tests
COALS STUDIED
Ash Sulphur Hydrogen Carbon Nitrogen Oxygen B. t. u.
Description
4.9 1.37 5.99 73.66 1.58 12.50 13,260 Durain-rich5.2 1.46 5.69
78.13 1.68 7.84 14,0649.0 1.75 5.43 67.29 1.49 15.00 11.941
Vitrain-rich9.8 1.90 4.94 73.08 1.62 8.64 12,9716.9 1.09 12,532
Clarain-rich7.3 1.16 13.4055.8 3.03 5.94 67.05 1.68 16.48 12.212
Top coal6.4 3.34 5.43 73.84 1.85 9.14 13.44910.7 3.71 5.53 61.77
1.19 17.06 11.131 Bottom coal11.9 4.13 4.89 68.79 1.32 8.91
12.39511.8 3.85 5.19 70.02 1.42 7.76 12,719 2x1 in. screen12.2 3.99
4.97 72.60 1.48 4.76 13,189
5.2 0.59 5.14 81.57 1.54 5.96 14,468 Lump5.3 0.60 5.06 82.81
1.57 4.68 14,6885.7 0.77 4.59 84.24 1.59 3.13 14,576 Lump5.7 0.78
4.54 84.92 1.60 2.43 14,693
Test Values With Stoker Operation
Decomposition Setting Temp. Initial Contraction Plastic
IntervalTemp. Agde Damm Agde Damm Interval. Agde Damm Agde Damm
Sample1 Value Sample 1 Value Sample 1 Value Sample 1 Value
G 384°C D 414°C H 38°C H 58°CC 392 C 416 B 49 B 67D 401 B 433 A
58 A 73F 415 F 434 C 62 F 81B 415 E 436 F 62 D 83E 417 A 438 G 64 C
86A 419 G >444 E 69 E 88H 450 H 470 D 70 G >120
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10 DOMESTIC STOKER COMBUSTIOX
Fig. 1.—Block of banded coal from southernIllinois showing
fusain (F), vitrain (V),
and clarain (C).
withstands breaking when mechanicallyhandled. Durain is the
toughest andmost resistant component. The follow-ing excerpt from a
recent U. S. Bureauof Mines publication 4 describes theenergy
consumed in pulverizing thefour coal constituents
:
" Contrary to general belief the ash-bearing constituents are
not always mostresistant to crushing, as was shown intests of coal
constituents, that is vitrain,
clarain, durain, and fusain—from theSouthern Illinois field. The
net powerconsumed in crushing the constituentsfrom minus 20-mesh to
minus 150-mesh,with their ash content is given in the
following table
:
CoalConstituent Fusain Vitrain Clarain Durain
Net horsepower—hours perton ofminus150-meshproduct.
.
1.8 3.8 5.1 13.6Ash, per-
cent 15.6 22 8.3 5.2
Fig. 2.—Block of banded coal from southernIllinois showing
clarain (C), and
durain (D).
It is shown that the durain, the hardestconstituent, contains
less ash than the
clarain, although comparison of thevalues for fusain with any of
the othersis even more startling. It has beenrecognized that fusain
is the most easily
crushed constituent, in spite of its rela-
tively large percentage of ash."Study of production has shown
that
the breakage characteristics of the con-
stituents in commercial coal are reflected
by the energy necessary to pulverizethem. Both vitrain and
clarain can befound in lump sizes, and the partingsurfaces may have
a thin layer of fusainon them. Most of the fusain will havebeen
broken off, however, and can befound in the screenings ; or if the
coalsare dedusted, it will be in the deduster
dust. In wet-washing most of the fusain
is carried to the settling pond. For thisreason, it is not
considered in the stoker
tests.
The 3- by 2-inch egg contains some ofthe smaller vitrain bands,
but for the
most part is clarain. The No. 2 nut (2- byl^-inch) is still
richer in clarain. The
4 Fieldner, A. C, and Rice, W. E., Annual report ofresearch and
technologic work on coal, fiscal year 1940:U. S. Bur. Mines I. C.
7143, pd. 23-24. 1940.
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STOKER AND FURNACE 11
No. 3 nut (1U- by %-inch) of well-banded coals has eight to ten
percentmore vitrain than the coal bed fromwhich it is mined. This
concentrationprevails down to the 100- or 200-meshsize, but fusain
is the predominant com-ponent in smaller sizes.
In general, 800 to 1000 pounds of coalwere prepared for the
stoker tests, andabout 50 pounds were riffled from thissample for
the proximate and ultimateanalyses and special tests. The
high-vitrain sample (70 percent vitrain, 30percent clarain) from
Franklin County,Illinois, was taken directly from the7/16-inch by
10-mesh stoker coal-load-ing chute at the mine. The
high-clarainsample (84 percent clarain, 16 percentvitrain) from the
same mine was pre-pared by crushing 3- by 2-inch egg-coalto stoker
size. The durain sample wasprepared by crushing to stoker size 6-
by3-inch egg-coal from which the otherconstituents had been
removed.
In the Belleville district near Darm-stadt in St. Clair County
the upper twofeet of Xo. 6 coal is a bright micro-bandedclarain
with silky luster, low ash andhigh volatile content, and a
relativelyhigh B.t.u. value. The lower four feetof the bed consists
of alternating bandsof clarain, vitrain. and fusain. The ashof the
bottom coal is higher and thevolatile matter and B.t.u. values are
con-siderably lower than in the top coal(table 1). When coals of
this type arepoorly prepared, lack of uniformity dueto segregation
and other factors maycause difficulties in stoker operation.
Because the rocks of Gallatin Countyhave been folded and
faulted, the Xo. 5coal bed of that region is of higher rankthan the
same bed in Saline County. Al-though clarain predominates in this
bed,the coal has been so increased in rankthat it is all strongly
swelling.
The Eagle Seam and Pocahontas coalsof Raleigh County, West
Virginia, arehigh-rank coals not represented in Illi-
nois but were tested in order to have awider range of coals in
the stoker andlaboratory tests. Run-of-mine wascrushed in both
instances to make thestoker coals used in the tests.
DESCRIPTION OF ST< >KERAND FURNACE
A complete description of the WarmAir Research Residence and the
forcedwarm-air heating system, together withthe automatic control
system used tooperate the stoker and the circulatingfan, has been
reported in two papers. 5,
6
The heating plant consisted of a warm-air furnace used in
connection with theforced-air heating system. The furnacewas of the
cast-iron circulator-radiatortype having a 27-inch firepot and
23-inchgrate. As shown in figure 3. the stokerwas of the underfeed
type, and the coalwas delivered from the hopper to the re-tort by
means of a rotating screw. The re-tort was located in the center of
thehearth. Both the rate of fuel input andthe rate at which air was
supplied tothe tuyeres could be independently regu-lated. Xo
cut-off damper was providedin the air tube to prevent air being
drawn through the blower and into thefuel bed during the off
periods of thestoker. The overfire damper in the fir-ing door was
left open prior to thephotographing of the fuel bed. Thepyrex plate
glass door which was placedin position just prior to the photo-
graphic study was fitted loosely on thefurnace front to give a
total overfire air
opening approximately equivalent to
that provided by the regular firing doorand the overfire damper
opening. Abalanced check damper was installed inthe clean-out of
the chimney and wasregulated to maintain a constant draft
of approximately 0.05 inches of water
in the smoke pipe.
After a new batch of coal had beenadded to the hopper the plant
was al-lowed to operate intermittently underthermostatic control
for two or threedays, at the end of which time the fuelbed had
assumed the characteristics ofthe coal under test. During this
pre-liminary period of adjustment approxi-
mately 300 to 600 pounds of coal were
5 Kratz, A. P., Konzo, S., and Engdahl, R. B., Per-formance of
stoker-fired and hand-fired warm-air fur-naces in the research
residence: A.S.H.V.E. Journalsection. Heating, Piping, and Air
Conditioning, pp.732-742, Nov. 1933.
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12 DOMESTIC STOKER COMBUSTION
PLAN VIEW
22'
18" 6f
BALANCED DRAFTDAMPER IN CLEANOUT
ELEVATIONVIEW
77
POT
BRICK
OVERFIREDAMPER 300- LB. j HP.
-""' HOPPER MOTOR
29^
Fig. 3.—Diagram of conversion stoker installation in furnace in
research residence.
burned. The feed rate maintained dur-ing the tests was about 26
pounds perhour. The setting for air-rate to thestoker was
maintained the same in alleases. The resulting burning rate6
varied somewhat depending upon thecoal used, but averaged about
13 poundsper hour. It is possible that the rate at
which air is supplied to the fuel bedmay affect the coking
characteristics ofthe fuel. Hence the results obtained inthis
preliminary survey may not be en-tirely representative of the
coking action
of the coal over a wide range of air ratesand feed rates. It
would be advisablein any later studies to investigate thisphase of
the problem.
LABORATORY TESTSProximate and ultimate analyses were
made on all samples tested according tostandard procedures of
the AmericanSociety for Testing Materials. 7
British Standards SwellingIndex Number
Swelling index numbers were deter-mined according to the British
Standardmethod 8 with the following modifica-tions :
1. Instead of the B.S. 72-mesh test
sieve specified by the British Standardmethod for preparation of
the testsample a No. 60 U. S. Standard sieve
was used.
8 Kratz, A. P., and Konzo, S., Performance of a stoker-fired
warm-air furnace as affected by burning rate andfeed rate:
A.S.H.V.E. Journal section, Heating, Piping,and Air Conditioning,
pp. 55-60, January 1940.
7 Standard methods of laboratory sampling and analy-sis of coal
and coke: A.S.T.M. designation, D271-37.
8 British standard method for the crucible swellingtest for
coal: British Standards Institution pub. no.
804, 1938.
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LABORATORY TESTS 13
2. In place of the "Teclu" burner aFisher high temperature usual
styleburner with grid top was used. By plac-ing- a thermocouple
inside the crucibleand experimentally adjusting the gasflow to the
burner, it was possible to es-tablish conditions of proper
temperatureand proper rate of heat rise. Naturalgas of
approximately 1000 B.t.u. calo-rific value was used.
3. Transite pipe class F was used forthe draught shield. This
pipe was 4%inches outside diameter and 4 inches in-side diameter.
It was cut according tothe specifications given in the
standardmethod.
4. The crucibles which were usedwere glazed vitreosil of the
followingspecifications
:
External height 26 to 26.6 mmExternal diameter at top. .40 to
41.5 mmInternal diameter at base. .13 to 14 mmCapacity 17 to 17.5
mlWeight 11 to 12 gms.
5. Silica triangles which are suppliedas standard items by most
chemical ap-paratus supply houses were used. Thoseused in this work
were about 63.5 mm inlength of side with a diameter of in-scribed
circle of about 31.75 mm.
Briefly the test consists of heating
one-gram portions of coal in the stand-ard crucibles at a
specified rate of tem-perature rise until all the volatile mat-ter
has been expelled. The buttons arethen removed from the crucibles
andcompared to standard outlines to whichhave been assigned numbers
from 1 to 9.The average of four such tests is thevalue
reported.
Agglutinating Value
Agglutinating value determinations
were made according to the "ProposedMethod of Test for
Agglutinating Valueof Coal" as published by the AmericanSociety for
Testing Materials. A ratio of15 silicon carbide to 1 coal was used
forall samples with the exception of sampleF where a ratio of 20 to
1 was used.
The apparatus used for crushing testbuttons was designed and
built in thislaboratory.
This method is a laboratory test forobtaining information on the
coking andcaking properties of coal. It is an ap-proximate measure
of the material incoal which becomes plastic under theinfluence of
heat. Briefly the procedureconsists of mixing coal with an inert
ma-terial such as silicon carbide, coking themixture as in a
volatile matter deter-mination and determining the compres-sion
strength of the buttons so formed.
Agde Damm Test
The apparatus used in this test wassimilar to that described in
U. S. Bureauof Mines Bulletin 344. 10 This apparatuswas further
described by Thiessen. 11 Itconsists essentially of a cylindrical
cop-
per block three inches in diameter andseven inches long which is
fitted into aspecially built electric furnace. TwoV2-inch holes are
provided in this copperblock for the small sample tubes.
Theapparatus is so arranged that a one-pound rod rests on one
sample while amicrometer distance gauge is mountedon the top of the
rod in such a way as toregister contraction or expansion of the
sample. The other sample is allowed toexpand and contract
freely. Thermo-couples are provided for temperaturereadings. In the
tests the samples of
coal which have been compressed in thesample tubes under a
weight of 5.8 kilo-grams are heated at a specified rate,
anddistance gauge and temperature read-ings are recorded. When
plotted, thesedata show the initial softening tempera-ture, the
decomposition temperature, the
solidification temperature, and the plas-tic interval.
9 Proposed method of test for agglutinating value ofcoal
(proposed draft) : A.S.T.M. Standards on Coal andCoke, p. 96,
1938.
10 Fleldner, A. C, Davis, J. D., Thiessen, R., Kester,E. B., and
Selvig, W. A., Methods and apparatus usedin determining the gas-,
coke-, and by-product-makingproperties of American coals : U. S.
Bur. Mines Bull.344, p. 16, 1931.
11 Thiessen, G., Coke from Illinois coals: IllinoisGeol Survey
Bull. 64, Appendix B, page 22"), 1937.
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14 DOMESTIC STOKER COMBUSTION
Fig. 4.—View of the furnace showing pyrex door, lamps, and
camera in position forphotographing fuel bed.
PHOTOGRAPHIC PROCEDURE
A pyrex glass door replaced the firing-door while the fuel beds
were beingphotographed (fig. 4) so that the normaloperation of the
stoker was not affected.The combustion chamber was illuminat-ed by
two No. 2 Photoflood lamps in re-flectors; this lighting was
necessary toproperly distinguish between coke andclinker
masses.
A Weston meter was used to deter-mine the proper exposure of the
film.Exposures were made at 16 frames persecond with a 15 mm, F 2.7
lens. Fourhundred feet of 16 mm, Type A, Koda-chrome film was used
in making themoving pictures of the fuel beds of theeight coals.
This was supplemented by300 feet of film showing the coals,
speciallaboratory equipment, and titles. Photo-
graphs of the fuel beds were taken atintervals as follows
:
Fuel bed prior to stoker operation
Start of stoker operation
Fuel bed after five minutes of stokeroperation
Beginning of off-period
Photograph of clinkers.
RESULTS OF TESTS
Analyses of the coals used in thisstudy are given in table 1.
Results of
the special tests are given in table 2, andBritish Standards
Swelling Index but-tons are shown in figures 5 and 6. Photo-graphs
of stoker fires for the fuelsstudied are shown in figures 7 and 8,
andclinkers from vitrain- and clarain-richfuels are shown in figure
9.
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RESULTS 15
Fig. 5.—British swelling index buttons for hand-picked banded
ingredients.a. durain; b. clarain; c. vitrain.
DISCUSSION OF RESULTS
The correlations attempted in thisstudy were (1) correlation of
laboratorytests with combustion behavior in theunderfeed stoker,
and (2) correlation oftypes of coal with combustion behavior.There
appeared to be no correlation be-tween agglutinating and AgcleDamm
val-ues and the formation of coke in the firebed, which was the
principal combustionbehavior characteristic observed. How-ever the
authors believe that results of
these tests may be correlated with com-bustion characteristics
other than cokeformation. A study of such correlationsand of
correlations with other chemicaltests is now in progress.
Correlations ofBritish Standards Swelling Index valuesand types of
coal with combustion be-havior were possible and the
discussiondeals mainly with these correlations.
Figure 5 illustrates the swelling but-tons obtained from
hand-picked samplesof durain, clarain, and vitrain from amine in
Franklin County, Illinois. Thedurain sample (figure 5a) showed
no
tendency to swell and is therefore as-signed a swelling index of
one. Clarain
(figure 5b) and vitrain (figure 5c) hadswelling indices of 3 and
5 respectively.Large samples having the purity of
small hand-picked samples could not be
readily prepared. While the 800- to1000-pound samples were not
composedentirely of a single ingredient the con-
centration obtained by the preparationmethods described earlier
in this reportis sufficient to illustrate the characteris-
tics of the predominant ingredient in thesample.
The egg-coal crushed to make thedurain-rich stoker fuel
contained somevitrain and clarain. The standard cokebutton for this
fuel is given the number3 in table 2. The predominant
duraininfluence on the swelling is brought out
by comparing these buttons (figure 6a)with the hand-picked
durain and clarainbuttons (figures 5a and 5b). BritishStandards
Swelling Index buttons forcoals A, F, G and H are shown in
figures6a, b, c, d. Figures 7a and 7b are en-largements from moving
picture film of
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16 DOMESTIC STOKER COMBUSTION
a
Fig. 6.—British swelling index buttons for certain stoker fuels
studied.a. Durain-rich stoker fuel; b. Eagle Seam, West Virginia,
stoker fuelc. Gallatin County No. 5 stoker fuel; d. Pocahontas
stoker fuel.
two stages in burning of the durain-rich coal. The stoker is
just coming onin figure 7a and the fuel bed is readilyseen. Figure
7b, after five minutes ofstoker operation, illustrates the
freedomfrom coking and the uniformity of thefuel bed. There is
somewhat moresmoke at the beginning of the off-periodwith durain
than with the clarain orvitrain.
The clarain-rich fuel ("B", table 2)had a swelling index of 3 as
did thehand-picked sample (figure 5b). Figure7c illustrates the
beginning of stokeroperation and 7d shows the open natureof the
fuel bed after five minutes in theon-period.
The vitrain-rich sample ("E", table2) has a swelling index of 4%
as com-pared with an index of 5 for the care-full}^ hand-picked
sample, which indi-
cates the presence of a small amount ofdurain or clarain.
However, figure 7eillustrates the tendency of the vitrain toform
coke in the off-period. Figure 7fillustrates the behavior of this
friable
coke tree after five minutes of stokeroperation. Only in mild
weather whenthe stoker operates infrequently mightany difficulty be
encountered with avitrain-rich coal of this type.
The top coal of the Belleville Districtof St. Clair County has a
swellingindex of 4; the bottom coal has a swell-ing index of 4%
(table 2, samples C andD). There is practically no coke forma-tion
apparent when the top coal is burn-ed, and only a slight tendency
to formcoke in the bottom coal (figures 8a and8b). The difference
in swelling tendencyis attributed to the presence of a greater
amount of vitrain in the bottom coal. At
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RESULTS 17
Fig. 7.—Photographs of stoker fires with fuels as follows:a.
Stoker fire, durain-rich fuel, stoker just turned onb. Stoker fire,
durain-rich fuel, after 5 minutes of operationc. Stoker fire,
clarain-rich fuel, stoker just turned ond. Stoker fire,
clarain-rich fuel, after 5 minutes of operatione. Stoker fire,
vitrain-rich fuel, stoker just turned onf. Stoker fire,
vitrain-rich fuel, after 5 minutes of operation
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18 DOMESTIC STOKER COMBUSTION
Fig. 8.—Photographs of stoker fires with fuels as follows:a.
Stoker fire, top bench St. Clair County No. 6 coal, after 5 minutes
of operationb. Stoker fire, lower bench St. Clair County No. 6
coal, after 5 minutes of
operationc. Stoker fire, Eagle Seam, West Virginia coal, after 5
minutes of operationd. Stoker fire, Gallatin County No. 5 coal,
after 5 minutes of operatione. Stoker fire, Pocahontas coal, stoker
just turned onf. Stoker fire, Pocahontas coal, after 5 minutes of
operation
-
SI'MMARY 19
Fig. 9.—Clinkers from vitrain- and clarain-rich fuels.
the beginning of the off-period the topcoal has a considerably
greater tendencyto smoke than the bottom coal. This isexplained, in
part at least, by the highervolatile content of the top coal
(46.1and 41.1 per cent respectively on thedry basis).The Eagle Seam
coal (Raleigh Coun-
ty, West Virginia) is assigned a swell-ing number of 5. A
peculiarity of thiscoal is that after heat is removed fromthe
crucible the apexes of the buttonscollapse. This may have some
bearingon the behavior of this coal during com-bustion. In
assigning a swelling num-ber this apex is restored, however.
Fig-ure 8c shows the condition of the fuelbed after the stoker had
operated forfive minutes. Part of the coke ringformed on the hearth
appears in theforeground of the figure and a coke treeappears in
the center. The coke formedin the stoker was dense but in spite
ofthis the response to combustion was notunsatisfactory.
The Gallatin County (Xo. 5) coal,with a swelling index of T 1/^,
had a tend-ency to form flat masses of coke in thefurnace rather
than coke trees (fig. 8d).Such coke masses ignited less readily
than the original coal when the stokercame on after being off
for some time.The Pocahontas fuel bed is shown in
figure 8e and f. Figure e shows theappearance with the stoker
just comingon and f shows the appearance afteroperation for five
minutes. Referenceto this figure and table 2 shows thatthere is
considerable coke formationwith this fuel (swelling index number9)
under the conditions used for thisstudy.
Figure 9 shows a vitrain clinker ascompared to a clarain
clinker. The vit-rain clinker appears to be denser andharder than
the clarain clinker.
SUMMARYThis paper is a preliminary attempt
to correlate behavior of various types ofcoal in an underfeed
stoker with labora-tory tests for the few samples studiedunder one
specific set of conditions.The tests substantiate earlier
findings
in regard to the importance of physicalcomposition of coal, that
is, types offuel, as related to combustion behavior.No correlations
between agglutinating
value and Agde Damm plasticity testsand coke formation were
apparent.
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20 DOMESTIC STOKER COMBUSTION
Correlation between British Stand-ards Swelling Index values and
cokeformation in the stoker fire was appar-ent. This is in accord
with the findings
of Sherman. 12 On the basis of thesestudies it appears that
coals with B. S. I.numbers below 4% or 5 do not form ap-preciable
masses of coke in the fuel bedwhereas coals with B. S. I. numbers
of5 or above may form large amounts ofcoke.
Although coals of high-vitrain contenttend to form more coke
than those ofhigh-clarain and high-durain content,this difference
is not as striking in the
present tests as might be predicted from
the swelling index numbers of the hand-picked constituents of
the FranklinCounty coal.
Laboratory tests described in this re-port measure more or less
specific char-acteristics of coal. On the other hand,behavior of
coal in an underfeed stokeris influenced simultaneously by
manyphysical and chemical properties. Theinfluence of certain
properties maymask that of others. Studies are now inprogress to
clarify some of these rela-tionships.
12 Sherman, Ralph A., The evaluation of coal for usein domestic
stokers : Univ. Illinois Eng. ExperimentSta. Cir. ser. 39, pp.
39-57, 1939.
Illinois State Geological Subvet
Report of Investigations No. 78
1942