longitudinal sect ion of chain grate furnace . dumping pl ate for cl inkers . ash retai n er . flat...
TRANSCRIPT
THE DEVELOPMENT AND USE OF THE
CHAIN GRATE STOKER
THOMAS ALFRED MARSH
B S Universxty of Illmms , 1904
THE SIS
Subm i tted m Partlal Fulfillment of the Requ l rem ents for the
Degree of
MECHANICAL ENGINEER
THE GRADUATE SCHOOL
OF THE
UNIVERSITY OF ILLINOIS i
1 9 09
U N I V E R S IT Y O F IL L I N O I S
THE GRADUATE SCHOOL
May 1 ,
I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDERMY SUPERVIS ION BY
THOMAS ALFRED MARSH, B . S . , 1 9 04
ENTITLED THE DEVELOPMENT AI’ D USE OF THE CHAI N GRATE STOKER
BE ACCEPTED AS FULFILLING THIS PART O F THE REQUIREMENTS FOR THE
DEGREE OF LECHANI CAL ENGINEER
ad of Department
Recommendationconcurred m
Commlttee
THE DEVELOPMENT AND USE OF THE CHAIN GRATE STOKER
BY’
THOMAS MARSH ,BACHELOR OF SCIENCE , 1 904
THESI S
FOR THE OF MECHANICAL ENGINEER
IN THE
GRADUATE SCHOOL
OF THE
UNIVERSITY OF ILLINO IS
PRESENTED APRIL 1 , 1 90 9 .
CONTENTS
Li st of Illu st rat i on s
Int roduct i on
Hi s t or ical
Defin it i on of Terms and Phrase s-
Des ign of the Stoker
Ash Pi t s
The Fi e l d of Chain Gr at e In st allat i on.
De s ign i ngo f B o i l e r Room Layout s and Chain
Gr at e h e 0 . b u c fi fl r ' v o u o o h a u m h m w m m g w g c p- g
Des ign of the
Annual ma intenance Expense of Chain
Const ruct ion
Chimney Dr af t
Induced Dr af t
Forced Dr af t
Chimney
S ize of
Prep aring fo r a Commerc i al Te s t
St oker Troub l e s
Chain Running Ho t -
High Fl ue Gas
LOW'
Fur nace
Low
Low A
Undul y‘
High. Tempe r at ur e of Furnac e wal l s and gr at e s
Coke in
Low"
CC~ 2 with High
iMOd i f i ed Type s of chain
Lit erature Bearing on the sub"ect
ILLUSTRATIONS
Long itudinal Sect ion of Chain Grat e Furnace .
Dump ing Pl ate for Cl inkers .
Ash Retai n er .
Flat susPende d . Arch.
Flat Sprung Arch .
‘
Wat erbeck in C i rculat ion o f the Bo il er .
Plain St e el Pipe Wat erbeck .
cast I r on‘
Wat e rb ack with Pipe cast In .
The Harringt on Aut omat ic'wat e rb ack .
The Junge Automat ic wat erbe ck .
Hor i zont al'wat e r-Tub e Bo il er Vert i cal Pas s
Equipped with Chain Grat e St oker .
St irl ing Bo iler Equipped with Chain Grat e St oker .
Wi cke s Bo iler Equipped with chain Grat e St oker .
Ho r izont al ly B af f l e d. Bo i l er Equipped with Chain cr at e
St oker .
Ho rizont al Return Tubular Bo il er Equipped with
Cha in grate St oker.
st e el Breeching Serv ing Four 550 H . P . Bo il ers .
Diagram o f ve rt i c al pas s Bo iler .
Diagram of Ho r izont al pass Bo il er .
Diagram of St i rl ing Bo ile r .
Di agr am. of Return Tubular Bo ile r.
Diagram of Cahal l Vert ical Bo iler .
Diagram o f Wi cke s vert i cal Bo il er .
Return Tubular Bo ile r Equipped with Incl ine d Typ e
o f Chain Grate .
Chain grat e for Caking Co als .
Diagram Showing Chain Grat e Perfo rmance with
Fluctuat ing Lo ad .
No rmal Draft Condit i on Obt aine d with Vert ically
Baf f l e d. Bo i l er .
No rmal Draft Condit i ons obt ained with Ho rizont ally
Baffled Bo iler Equ ipped with Chain Grat e .
No rmal Draft Condi t i ons Obt ained with St irl ing
Bo il er Equipped with Chain Grat e .
No rmal Draft Cond it i ons Obt aine d with Return Tubular
Bo iler Equipped with Chain Grat e .
Norma 1 . Dr af t condi t io ns Obt ain ed with canal l Vert i cal"
Bo il er Equipped with Chain Grat e .
No rmal Draft Condit i ons Obt ained with Wicke s Vert ic al
B o iler Equipped with chain Grat e St oker .
Diagram Showing Improved Condi t i ons Obt aine d by
Inc reas ing the Area o f the Opening s f or Case s on a
ver t ical l y'
B af f l ed. B o i l er .
Diagram showing Imp r oved Condit ions Obt aine d by
Increas ingthe Are a of the Op ening s fo r Case s on
Hor i zont al l y'
B af f l ed. B oi l e r .
Diagram showing Rat e o f Combu st i on with vari ou s
Draft pre s sure s in Furnace.
Di agram Showing Effect on Furnace condit ions o f
Inc reased Ai r pe r Pound o f Co al .
Di agr am. Showi ngthe Relat i on o f Draft Pre s sure
5
in the Furnac e t o
Plate T2 T3
Bo il er and Engine Room. LogShe et Adapt ed
an Elect r ic Light and Powe r Plant .
D iagram Showing the Hor se Power Devel op ed in a
Wat erbe ck .
-
THE DEVELOPMENT AND USE OF THE CHAIN GRATE STOKER
INTRODUCTION
Wi th the rap idly increas ing numb er o f inst allat i ons o f
the variou s typ e s of Mechan i c al St okers,spe c i fi c l it erature
regarding each typ e i s in demand . The bulk of the present
l it erature regarding Chain Grat es i s academi c in nature,and
the writ er has fo r somet ime felt the need of a p ap er v iewing
the subj ect from a commerc ial st andpo int ,famil i ar iz ing the
reader with the ground that has heret ofo re been c ove red by
re s earch and p ract i ce,ent ering int o the p roblems confront ing
the engine er in thi s f i eld,and set t ing fo rth p re sent-day
p ract i ce bo th from the theo ret ical and op erat ive standpo int .
HISTORICAL
The earl ie st Mechani cal St oker fo r st eam bo ilers was
p robably des igned by Jame s Watt i n the year 1 785 . The
mechani sm was s imply a dev ice t o Push the coal.aft e r i t was
coked at the fro n t o f the grat e.back toward the bridgewall .
The sugge st i on o f Watt was followed by numerous pat ent s in
mrope fo r Mechan i cal St okers.but none o f the se have be en
adopted t o any c ons iderable ext ent in thi s c ountry.b ecau se
o f the i r suppo sed lack o f adapt ab il ity t o Ame ri can bo iler
p ract i ce.
The ir non-adopt i on here was partly becaus e the
mechan i sm. was o f t o o compl icat ed a nat ure t o b e ent rust ed t o
the average f i reman .o r the rat e of spe ed at whi ch. the maohr
ine would be re qu i red t o run was such. that it would be want-
ing in durab il ity . Ano ther ob j ect i on was,that in many case s
the grat e s were s o placed as t o be almo st inacce s s ible e ither
fo r examin ing o r alte ring the condit i on o f the fi re by hand ,
o r fo r renewing wo rn-out p art s .
The Cha in Grat e was one o f the typ e s o rig inat ing in
Emgl and f r om. wat t 's exp eriment s . In it s ear ly st age s it was
exce edingly unme chan ical.having part s no t readily renewable ,
exp o sed t o the heat,and very po o r mechan i sm for driv ing an d
adj u st ing .
The earl i e st reco rd in thi s count ry of a me chan i cal St ok-
er of the progr e s s i ve-f eed typ e o f which we have any reco rd.
i s o ne o f the t ravel ing gr at e-b ar typ e de s igned by Royal F .
Weller , o f Albany , N . Y . , in 1 871 . As an. improvament on
thi s type o f grat e ,S imon Regan
,in 1 877 , de s igned the fi r st
Chain Grat e on reco rd,the de s ign hav ing much. in common with
the Chai n Grat e of the present t ime . Dur ing the ensu ing
fift een years many improvement s were made i n. mechanical de-
t ails,part i cular att ent ion be ing called t o the wo rk of
Eckley B . Coxe, of
'
Dref t on , Pa . ,who d i d. much. pi oneer work in
de s igns o f Chain Grat e det ail s b etwe en the years 1 892 and 1 895 .
ur . Coxe de s igned the remo vable feature of st oke rs mounted o n
t ruck shaft s , and al so i s largely re sp ons ible fo r the develop-
DEFINIT ION OF TERMS AND PHRASES
In o rder t o fac il it at e the unde rst anding of the ensu ing
page s t o the read er unac quaint ed with the commerc ial t erms ,
the following definit i on s o f wo rds and phrase s are p resent ed ,
t o gether with a s ide elevat i on o f a Chain Grat e ( Fig . 1 ) the
name s o f many p art s o f Which are indicat ed thereo n .
CHAI N : The as sembly o f l inks on b ar e fo rming the grate on
whi ch. the fuel re st s .
LINKS The component par t s of which the cha in i s c ompo s ed .
COAL HOPPER : The recept acle o r re servo ir cont ain ing the
fre sh fuel be ing fed int o the furnace .
FURNACE : The chamb er in whi ch. combu st i on of the gase s i s
complet ed .
'
GATE The mechan i sm. by Whi ch the thicknes s of fuel bed o n
the grate i s regulat ed .
LEDGE PLATE’
FLANGES Cast iron plat e s j amb ing clo sely
against the s ide s of the chain throughout i t s length
in o rde r t o shut o ff the ai r leak .
BRIDGEWALL A wall at the b ack end of the grat e t o di rect
the current o f the draft .
BRIDGEWALL OVERHANG The proj ect ing p o rt ion o f the bri dg e-
wall ext ending over the chain .
WATERBACK A p ip e placed at the ext reme end o f the bridge-
wall overhang thr ough. whi chwater c irculat e s . I t s
funct i on i s t o make an ai r s eal eas ily ma int ained ,
1 2
and t o which cl inker will no t adhere .
AL DAMPER : An arrangement ins ide o f the chain me et ing
both. the upper and lower leads,and making
,with a
wall below and the wat erbe ck above,a complete ai r
seal through the machine .
COKING AND IGNIT ING ARCH : An arch o f fire b r ick o r f i re
t ile ext end ing from the front o f the furnac e back-
ward fo r from. 5 t o 6 feet .
ARCH T ILE Sp ec ial f i re bri ck t ile o f which. some arches
are construct ed .
INSPECTION DOOR The doo r through. the si de wall of the
furnac e through Whi ch the f i re i s in spe ct ed.
ASH HOPPER : A recept acle below the flo o r at t he rear of the
grat e t o rece ive the ashand refu se .
DROPPAGE Unburne d coal whi ch p ass e s thr ough the int er-
at i c e s of the chain t o the recept acle below.
BAFFLE : A wall o r part it i on erect ed t o di rect the p as sage
o f the ho t gase s through the b o iler .
1 5
DESIGN OF THE STOKER
The fundament al purpo se of the st oker i s to c onvey an
even bed of fuel int o the furnace within c ertain l imit s o f
thickne s s o f fuel bed and rat e of t ravel .
The f uel thickne s s mu st vary from O t o 1 0 i n . and the
rat e o f t ravel from O t o 6 in . p e r minut e .
The chain i s de s igned of sho rt l inks from 8 t o 1 2 inche s
in length,from 1 t o l i inche s in wi dth
,and we ighing approx-
imat e l y 1 0 lb s . ,st rung in st aggered fo rmat i on up on t ran sverse
bar s , the whole creat ing a web which t ravel s over set s o f
sp ro cket s,thus fo rming a ho rizont al grat e surfac e .
The thicknes s of fuel bed i s regulat ed by a gate which
i s rai s ed and lowered by some su i t able mechani sm, u sual ly a
wo rm and sec to r . Different he ight s o f gat e p e rmit different
thi ckne s se s o f fuel bed t o pas s the reunder . Gate s are mad e
o f cast i ron,o r preferably st e el , I beam frame s int o which
fi re bri ck t ile are f it t ed,pre sent ing a fac e o f f ire bri ck
to the f urnace . The Playford St oker i s e qu ipped with a gat e
hav ing a wat er c i rculat i on therethrough,but the heat re qu i re-
ment s are no t suffic i ently severe t o demand such precaut io n
with all the mechan ical t rouble s inc ident t o a c ont r ivance of
thi s natu re in o rdinary pract i c e . However,when burn ing
such highly inflamable fuels as s i sal from twine mi ll s some
such devi ce i s impe rat ive ,as the fuel igni te s back int o the
hopp er , burning the u sual type of gat e in a sho rt t ime .
It i s of mat er ial as s i st ance in Op erat ing t o have accurate
1 5
1 0 lb s . of coal at lb s . of ai r p er pound , r e qui r e s
lb s . of air .
Volume of ai r pe r lb . 1 5 cu . ft .
Hourly air a 2550 cu . ft .
With 20 p er c ent o f air space and combu st i on rat e o f 1 0 lb s
p er s quare fo o t o f grat e surface p er hour,the veloc ity o f the
air feet per s econd . iB as ed on 50 lb s . o f coal per
s quare fo o t of grat e surface p e r hour,the velo c ity of t he
air feet per s econd .
Links having 20 per cent air sp ace do no t p ermit an
exce s s o f f in e co al t o pas s the rethrough,the average port i on
o f droppage o f slack c oal thr ough grate s o f such de s ign be ing
1 0 per c ent o f the amount f ired .
The writ er has expe rimented with a larger pe r cent o f
air sp ac e but has be en unable t o no t e any change in c ondit i ons
o ther than a. marked increase in the per cent o f dr oppage .
Ade quat e air supply through the fuel bed,o f course
,
impl i e s that no ai r shall ent e r f r omt other sourc es . Thi s
nece s s it ate s that su it able flange s p ro j ect from the furnace
wall s t o the s i de s of the chain,thus cut t ing off air l eaks
from that source,and that the re shall be a sys t em. of t rans-
vers e baffl ing at the re ar o f the st oker p revent ing ai r from
sho rt-c ircui t i ng around the end o f the grat e and thus ent e r-
ing the furnace . Thi s i s ac compl i shed by mean s o f an int e r-
nal dampe r ( Fig . 1 ) which,wi ththe wat erb e ck ab ove the grat e
and a. su i t ab l e dampe r plat e o r wall below,effect s a complet e
air baffle , thus caus ing all air e nt ering the furnace to pas s
1 6
thr ough the fuel bed . Carefully de s igne d st oker chains no w
have flange s on the l inks whi ch p revent the ho rizont al pas s-
age o f ai r . Thi s it em o f ai r leaks at the re ar end o f the
Chain Grat e i s one o f great impo rt ance,al though. unt i l rec ent-
l y it has been given but l it tle at t ent i on . Con side rab le
economi e s are be ing effect ed in old in st allat ion s by int ro-
duci ngeffect ive damp ers , cut t ing off the inru sh o f c old air
at the rail o f the grat e .
A typ e of air s eal that has been ext ens ively t ri ed during
the past two ye ars i s the dump ing plat e at the end of the
grat e ( Fig Thi s dev ic e has me t with l it tle suc ce s s for
the reason that unle s s gene rou sly vent ilat ed it will soo n
burn,and if vent ilat ed suffi c i ently t o p revent burning
,i t
defeat s it s own purp o se o f excluding fre e ai r .
Ash r et ai ne r s x (Fig. 5 ) have been t r ied wi th l i t tle
suc ce s s,the princ iple b e ing t o hold suffic i ent ash at the
rear of the grat e t o make an effect ive ai r seal . The main
diffi culty ari s e s f r om. hot ash ac cumulat ing and burning o ff
the p ro j e ct i ons o f the l inks of the chain .
F . H . Ri char d s , of Hart fo rd,Conn
. , secur ed. pat ent s in
1 895 on a wat er seal at the end of the grat e,emb odying the
idea that the lower lead o f the st oker chain be imme rsed in
wat er . Thi s was so on abandoned as unme chan i cal .
On ac count o f the rough. usage due t o lo cat ion and at t end-
ant s, i t i s very e s sent i al that all p ar t s o f the st oke r b e
of a. very sol id and permanent nature . No frail mechan i sm
can exi st under the c ond it i ons .
1 7
All compl icat ed de s igns mus t be avo ided,as the op erat o r
i s o ft en c alled upon t o make rep airs,and s impl ic ity may pre-
vent a shut-down .
All expo sed part s mu st b e ade quat ely p rot ect ed from the
heat . Thi s i s u sually done by making such. par t s o f f ire
brick o r s imi lar mat eri al s . However,should it be ne ce s sary
t o have met al part s in ex p o sed po s i t i ons,an ai r c i rculat i on
should be fo rc ed around such p art s by the draft in the fur-
nac e . If p o ss ible,such p art s should have small readily-
removable plat e s thereon .
Al l p art s that re qu i re fre quen t replac ing , such as chain
l inks,should be made readily r epl acab l e ,
and all large part s ,
so far as p o ss ible , should b e made o f st andard rolled s ec t i ons
in o rder that in eme rgenc ie s they may be purchased lo cally ,
thus s av i ng, t ime and t ran sp ort at i on charge s .
The more readily the ope rat iv e part s of the st oker and
furnace may be in spe ct ed,the bett e r will be the suc ce s s o f
the inst allat ion . To thi s end all gears and mechan i sms
should be expo sed,and ade quat e do o rs put in the furnace fo r
the inspe ct i on and repai r of br ickwo rk .
In the p resent day compet i t i on i s so keen that low shop
co st s are ab solut ely e s sent ial . St okers have be en de s igned
and rede s igned wi th the idea o f minimiz ing the amount o f
machine work,and thus reduc ing shop c o st s . Cast ings must
replac e small st eel part s,and the se c ast ing s must be so de-
s igned as t o readily lend thems elve s t o moulding machine wo rk .
1 8
Part s mu st be so de s igned and fini shed as t o go t ogethe r
eas ily in the‘
fi eld,fo r any delay on thi s end run s int o large
it ems . It o ft en o c curs that c ert ain part s may be mo difi ed in
some manne r , thus min imiz ing the wo rk in the f ield . To thi s
end sugge st i ons f r om. e r ect or s are co ns ide red and d i scus sed ,
and many good . poi nt s o f de s ign have sp rung therefrom,
ARCHES
The fre sh c oal ent ering the furnace is igni t ed by radi a-
t ion,or rather by the refle ct i on of the heat from. the hot t er
cent ral part of the furnace t o the front thereo f . Thi s i s
accompl i shed'
by means o f an arch set app roxi mat ely 1 2" above
the grate surface in front, and . ex t end i ngback ov er the grat e .
Wi th coal s cont aining sozo f volat ile i t i s cu st omary t o g ive
a length of three fe et and a slop e of 2 inche s p er fo o t t o
thi s ar ch . Wi th co al s cont aining a smaller pe rcent o f
volat ile and higher ash, and fo r that reason b e ing mo re
inert,a st ronger ignit i on effec t i s re quired . To accomp
pl i shthi s it i s ne ce s sary t o increase the l ength. of
the arch,se t i t more ne arly ho rizon ta l
,o r both . The var-
i ou s typ e s of bo iler set t ing s re qui re spec ial de s ign s,which
will be mo re tho roughly d i s cus sed in a suc ce eding chapt er .
Arche s are o f two styles : - ( a ) Sprung Arche s : ( b )
Su sp ended Arche s.
Sprung Arche s are suc ce s sful in narrow se tt ing s ( not
exceeding s ix feet in width) . Beyon d thi s width there i s
s o large a differenc e b etween the maximum and min imum di st anc e
1 9
o f the ar ch from. the grat e as t o affect the ignit i on when
cert ain co als are used . Beyon d the width of e ight fe et the
sprung ar ch ,unle ss g iven a ve ry ample r i se
,i s very impr act ic-
able as a maintenanc e propo s i t i on,as the thrust up on the s i de
walls i s very exce s s ive .
suspended Arche s are made o f sp ec ial shaped t ile suppo rt-
ed on a framing f rom. ebove . Figure 4 shows the susp ended
arch u sed by the Green Eng ineer ing Company . Thi s type of
arch has the advantage o f having e qual he ight from. the grat e
and every po int in a t ransverse se ct i on,which g ive s unifo rm
ignit i on and c ombust i on at all such p o int s .
Another typ e o f arch is the Jack Arch recently de s igne d
and shown in Figure 5 . Thi s ar ch embo di e s ce rt ain feature s
o f the susp ended and of the sprung arch. It do e s not over-
c ome the thrust e ffect o f the ordinary sprung arch,but it
p re s ent s a plane surfac e t o the f i re,and avo ids the ns os so-
i ty o f met al framing fo r it s supp o rt .
WATERBACKS
The funct i on of the waterbeck i s t o prevent the inrush
o f cold ai r around the end of the grat e,
and t o pre sent t o
the fire a co ol metal surface t o which cl inker will no t
adhere . It is al so an exc ellent feature fo r maint enance
of bridgewall overhang .
There are two general clas se s o f wat erbacks in us e at
thi s t ime , tho se in the c irculat ion o f the bo iler,and tho se
hav ing a sep arat e water c i rculat i on . The fo rmer type i s
20
u sually de s igned as a ste el b ox rect angular in s ect ion , be ing
connect ed on one end t o t he front header of the b o iler , and
on the other end to the re ar header ( Fig . Thi s clas s of
wat erbeck re quire s fre quent and regular blowing down t o r e-
move mud and se ttlement ,and it i s adv i sable only in plant s
where the p rop er care will be t aken thereo f . The Commo n-
weal th. Ed i son plant,at Fi sk St reet
,Chicago , have many of
thi s typ e ,g iv ing excellent serv ice
,as have al so the C ity
o f Chicago Pump ing st at i ons,but it mu st be b o rne in mind
that thi s type of waterbeck inv it es al l of the t rouble s l n-
herent t o p res sure p art s under the mo st seve re condit i ons,
and for thi s reas on di scret i on should b e u s ed in recommending
such de s ign. In inst all ing the se wat erb acks valve s mu st
be so loc ated as t o p ermi t the prop er blowing out of the p i pe,
and al so the cut t ing out o f the same from the b o il er c i rcular
t i on , in c as e of burn ing out .
Of the clas s o f wat erbeck hav ing separat e c irculat i on,
there are several typ e s
1 ; Plain 4 " ste el p ipe wi th. l " c i rculat ing p ip e ( Fig .
2 . Cast iron waterb eck wi th c irculat ing p ip e s cast
there in ( Fig .
The plain st eel p ipe i s the more preferable unde r
o rdinary condi t i ons , it be ing a readily renewable p art,easy
o f acce s s fo r clean ing,and if sl ightly warped may b e turned
90 degree s in the b rickwo rk without remov ing it from the
furnace . The and conne ct ions are made revers ible fo r thi s
shown in Figure 1 0 .
The i deal po s i t i on for a wat erbe ck i s to have i t set s o
the laye r of ash caus ed by the complet e combu s t ion o f the
fuel will ju st pas s unde r the wat erb eck,but no more . Under
these cond i t i ons e the refuse i s permi tt ed t o e scape,but the
inflow of cold air unde r the wat erbe ck,o r e s capement o f un-
consumed c o al on t op o f the ash b ed,i s prevent ed . If one
grade o f coal were t o b e us ed,and one rat ing o f bo il er main-
t a i ned , thi s condi t i on could b e ve ry nearly secured . Whi le
under pract ical condi t i on s thi s i s imp o s s ible , it shoul d. b e
the a im t o get thi s re sult as nearly as po s sible . As sumi ng
normal draft s and no rmal rat ing o f bo iler,whi ch. i n tu rn
nece s s it at e s no rmal thicknes s of fuel be d,the fo llowing i s
go od pract i ce .
Wi th coal s having f rom. l O pe r cent t o 1 5 p er cent of ash,
in whi ch i s p robably include d the maj o r po rt i on o f Ohi o,
Indiana and Ill ino i s s cre en ings,the wat erbe ck should b e 5
t o 4 inche s ab ove the grat e surfac e .
‘
Wi th co al s hav ing 1 5
p er cent t o 25 pe r c ent ash,the wat erbe ck shoul d . b e s et 4 t o
4% inche s ab ove the grate surfac e . With c o al s hav ing 5 per
cent t o 1 0 per cent ash,whi ch. i ncl udes the washed co als o f
Ill ino i s , the wat erb eck will op erat e sat i sfact o r ily 2 inche s
t o 2# inche s above the grat e surface .
It will be no t ed that the he ight of the wat erbe ck i s
not in p rop o rt i on t o the per c ent ash fo r the follo wing
reason . With a given draft int ens ity,the cleaner the c o al
,
the thicker i s the fuel b ed . that may be e conomi cally burned .
25
While the p er c ent of refus e may b e doubled o r t r ipled in the
coal,thi s fi gure i s part ially o ffset by the fact that with
such coal the thickne s s of the fuel b ed ent ering the furnac e
is reduced probably one-half .
In all c as e s the heat ent ering the wat er that p as se s
through the wat erbeck should be ut il ized . Thi s may usually
be done by p ip ing the di scharge t o the ho t well .
Plate x illu st rat e s by means of a curve the p er c ent
o f heat re qui red t o maintain a wat erbe ck .
‘
The data fo r thi s
curve were compi l ed . by Mr . Henry B . Dirks, M; E. ,
from te st s
made at the Experimental St at i on of the Univer si ty o f Ill in-
o i s .
The difference betwe en the t emperat ure o f the supply and
di scharge should be approximat ely 1 0 0 ° under which condit i ons
the amount o f wat er re quired t o ma i ntain a wat erbe ck vari e s
f r om t t o 20 p er c ent of the amount re qui red t o fe ed the
bo il er under whi ch the wat erbe ck i s installed .
As regards maint enance o f wat erb acks ,the writ er
recommends the u se of the rmomet ers on the di s charge l ine,and
the ke ep ing o f the di scharge at a f ixed po int ab out 1 80 degrees .
The use o f a thermo stat i c valve t o accompl i sh thi s end would
s eem. t o b e very feas ible,if a pos i t i ve , r e l i ab l e inst rume nt
could b e found .
ASH PIT S
The ash pi t mu st b e de s igned t o ac commo dat e at l east s ix
hours dep o s it o f ash at max i mum. rat i ng, and one of doubl e
THE FIELD OF CHAIN GRATE INSTALLAT ION .
Because of the part i cular adaptab il ity o f the high vol at ile
low carbon co al s of the We st t o thi s metho d of f i ring,the di s-
t r i ct o f Chain cr at e inst allat i ons may b e broadly te rme d as
‘
We st o f Pi tt sburgh . The coking and cakin g c oal s of the Eas t-
ern sect ion g ive ri se t o compl ic at ions,and re qui re t reatment
o ther than that embo died in the st andard Chain Grat e p ract i ce
o f the present t ime . The analys i s o f the no rmal Chain cr at e
co al i s as follows
Volat ile 50 pe r centFixed Carb on 55 p er c entAsh 1 0 pe r c entE20 5 pe r centT o t al 1 0 0 pe r c ent
B o To Us by RObt . We Kl i nt'e f °m 1 3)1 1 429
B . T. U. ( 14 50 0 x F . c. ) ( 1 651 5 x vol . ) 1 00 00
ash H20 )
Thi s analys i s may vary t o the ext ent of the pe r cent o f
ash reaching 50 per cent,anx i the vo lat ile bec oming as low as
20 p er cent,but such a c oal ign it e s very slowly
,which fact
,
comb ined with the low heat ing val ue of the co al,pe rmit s each
unit of grate surface t o del iver only a very low amount of
heat , and ne ce s s i tate s addit i onal grat e surface .
Wi th. e qual l y well p roport i oned furnac e s and s imilar
loads , Chain Grat e s show an in creased comb ined effi c iency
( It em. 75 A . S . M; E . co de ) o f 5 p er cent ove r the be st hand
fired result s . Thi s f igure i s f r om. exhaust i ve t e s t s made
befo re and af t er e quipp ing a large hand-f i r ed p lant wi th
26
Chain grat e s . The 5 pe r cent i s ne ce s sarily accredit ed t o the
unifo rmi ty o f f iring,the evennes s of the fuel bed
,and the
p revent ion o f cold air int o the furnac e . Ho wever ,such a
compar i s on i s unfai r t o the st oker,ina smuch a s b o th te st s
were carefully and skillfully f ired,
and in Chain Grat e f i r-
ing skill i s no t so po t ent a fact o r as in hand-f i r i ng. Due
t o c ar ele s sne s s o r the lack o f skill o f the f i reman ,it i s s afe
t o say that in the average hand-f i r ed . pl ant t here i s a. pos s i b i l -
i ty o f lo p er cent increase in eff i c i ency by the installat i on
o f Chain Grat e s . In addit i on t o thi s actual the rmal s av ing,
there oft en o ccurs a reduct ion in the c oal b ill s,due t o the
fact that the c o st o f low grade fuel i s much. l ower t han that
of the high grades , the variat ion no t always b e ing in d irect
rat i o t o the heat ing value of the c oal s,but oft en very much
in favo r of the lower grade s :
Mbch. ha s been writ t en about the adapt ab il i ty o f the
st oker t o fluctuat ing lo ads . It ha s be en the wri t er's
ob s ervat ion that st okers hav ing ade quat e draft and p roperly
hand l ed . can b e made t o re spond t o fluctuat ing loads and
sud d en. peaks as readily as hand f ire s,in p ro of of whi ch
the re sult s of a t e st with a fluctuat ing lo ad t e st are sub-
mi t t ed .
Plat e A i s a graphical rep re sent at ion of the hourly
ho rse p ower develop ed during a 24 hour ec onomy t e st,the condi-
t i ons under Whi ch the t e st was ma de be ing that the fluctuat ing
heat , l ight and power lo ad o f the st at i on b e carri ed through-
out the t e st . The he ight o f the wat er in the gauge glas s di d
at the mercy o f the i r fi remen . Wi th mechanical st oke rs thi s
condit i on cease s t o exi st,as the number o f f iremen re qu ired
i s le s s,and f iremen can b e b roken i n in a few hour s .
The p as s ing and enfo rcement of smoke o rdinance s cause s
the co al consumers t o seek s ome fo rm o f furnace that will
fulf ill the re qu i rement s of smokeles s combu st i on . The chain
Grat e sat i sf ied the re qu irement o f ”unifo rm di st ill at ion of
vo lat ile from c o al " b ette r than any other form o f mechani cal
st oker yet de s igned,
and lends it self very readily t o the
typ e s of sett ing nec e s sary t o fulf ill the oth er requ irement s .
DESI GN ING OF BOILER LAYOUT S AND CHAIN GRATE SETT INGS .
The b o iler room arrangement i s on ee of f ir st impo rtance
in power st at i on economy .Bo il er sett ings may be de s igned
that will g ive excell ent indi vidual e conomy ,but if the
arrangement i s such that the f ireman canno t g ive the p rop e r
att ent ion t o the f i re s , o r such that the bo ilers cannot be
properly cleaned and so o t blown from. the tube s at regular
in terval s , the economy of the plant under op erat ive condi-
t i on s will be low,
and the labo r c o st o f operat i on will be
high . Wherever po s s ibl e the following it ems shoul d. b e p ro-
vi ded fo r :
Four foo t alley ways between b o ilers,providing space
fo r removal of cl inker and s oot .
Twenty fo ot fro nt sp ace f rom. b oi l e r front t o bu il ding
wall .
Ample head ro ome
Large and well de s igned b r eachi nghaving few turns and
no shar p bends .
L ight al leys b ehi ndt b oi l er s ,permi t t ing fre e ac ce s s
t o b l oWb of f c ocks .
Ample room for a sh removal .
Fre quently it i s imp o s s ible t o obtain one or mo re of
the se it ems , and as a re sult some det ail s of'
ope r at i on are
neglect ed with c orre sp onding l o s se s .
50
DESI GN OF THE FURNACE .
As mr . Bement has expre s sed it,there are thr ee l ink s t o
the st eam generat o r,v iz . ,
the f ire grat e , the furnace , and
the b o iler . we have dealt with t he f ire grat e in our di s-
ous s i on o f the st oke r it self . Combust i on , if comple t e , mu st
o c cur in a furnace wi th wall s and ro o f const ruct ed o f refract-
o ry mat er ial and of ample propo rt ion t o p e rmi t o f compl et e
mixing and uni on of the gase s . When su ch c ondit i ons exi st
no smoke is generat ed .
The subj ect o f the de s ign o f Chain cr at e furnace s has
been very tho roughly c overed in the papers of the we st ern
So ci ety o fWMechanical Eng ine ers , here inbefore ment ioned ,and
the writ er will do no mo re than t o indicat e a suitable furnace
fo r each type o f b o iler .
Furnace s in which. comp1 e t e c ombust i on o c cur when burning
Ill ino i s s creen ing s o f high volat ile c ont ent ar e be ing obtain-
ed. under Babcook a Wi lcox bo ilers,hav ing e ight fe et s ix
inche s ( Fig . 1 1 ) under the front header,and a furnac e pro-
J ect i on o f s ix feet . With the se di mensi on s it i s p o ss ible
t o ob tain an arch p ro j ect ing ent irely over the grat e surface
and hav ing a p o s it ive mi xing effect pro duc ed by the differ-
ence in elevat i on b etwe en the ign i t i on and se condary arch .
The flame s penet rat e amon g the tub e s p robably t hree o r four
fe et befo re the combust ion has reached a st age whe re the
chill ing effect of t he tube i s no t suffi c i ent t o p ro duc e
smoke , when operat ed at no rmal rat ing s . Thi s s et t ing is
app roved by the smoke depar tment s o f the large c i t ie s .
With a St i rl ing bo il er ( Fig . 1 2 ) the comb ine d ignit ing
and St i rl ing arch,e qual t o the length o f ac t ive grat e surface ,
prov ide ample furnace,with excell ent mixing c ondi t i on s at
the de s i red p o int . Such s et t ing s always g ive c omplet e come
bust i on and smokeles sne s s up t o ve ry hi gh rat ing s . In thi s
case the travel o f the gase s i s along the tube s , and it i s p ro-
bable that the gase s are no t as :much. b roken up as in the Bab-
cook Wi lc ox type .
The ‘
Wi cke s ( Fig . 1 5 ) and cahall Ve rt i cal Bo il er , bo th
have the same type o f dut ch oven furnac e,and g ive pe rfect
condi t i on s as regards c ombu st ion and smokeles sne s s .
The type o f b o i le r pro vi ded wi th. t ub e t ile on the lowe r
row of tube s , as in the He ine, Hur r ay I ron or O'B r i en Bo ile rs
( Fig . 1 4 ) naturally ext end the incande sc ent f i re br ick chamb er
just that much mo re ,and t he arch prov ided with. the st oker
need no t be as long,t herefore
,as with the type of
‘
b oi l er
hav ing the p as sage of the gase s acro s s the tube s . In thi s
type of s et t ing it i s usual for the flame t o be c omplet ely
c on sumed befo re the heat ing surface of the bo ile r i s reached .
Becau se of the st rong arch effect,t hi s sett ing has a st rong-
er ign it i on than the other typ e s he re in ment ioned .
With the Ret urn-Tub e type of bo iler,such a s the B enson ,
the Soderholm, o r the Sco t ch mar ine b o iler,the flame mus t b e
ent i rely ex t i ngu i shed . b ef or e reachi ng the f ire tub e s,as
in st ant ext inct i on o ccurs at the moment the gas e s ente r the
tube s . However , in the ordinary Return-Tub e typ e of bo ilers,
52
the shell may be c on s ide red as an exten si on of t he fu rnace
ro o f,inasmuch as it s chill ing effec t i s not suffi c i ent t o ex-
t i ngu i shthe flames . An excellent Chain Grate set t ing under a
Return-Tub e bo iler i s shown in Fig . 1 5 .
Thi s set t ing i s smokeles s wi thin the Chicago o rdinance up
t o 50 p er c ent above the rat ing of the b o iler .
In general it may be said of furnace cons t ruct ion , that
t o produce pe rfect combust i on the furnac e roo f should extend
over the ent i re length o f the grat e surface,and be o f suff ie-
isnt he ight t o p ermit of the mixing o f the gase s .
chain Grat e pract i c e do e s no t re qui re as much i ncande s-
cent b rickwork ihconjunct i on therewith as hand-f i r ed pract -
i ce,i nasmuch. ss the gradual int roduc t ion of the fuel re sult s
in the gradual evolut i on o f the volat ile c ombust ible,and the
t e rminat ion o f the flame s at approximat ely the same p o int at
al l t ime s . The sudden introduct i on of sev eral shovel sful l
o f co al int o the furnace in the pe r io d of a few sec onds ,
re sult s in the sudden evolut i on o f a bo dy of vol at il e gas
which. cannot b e c onsume d wi thin the t ime of it s pas sage
thr ough the ordinary combu st i on chamber .
It may be he re no t ed that the l ong-f l ami ngwe st e rn c o al s,
e sp ec i ally if washed,re qu i re greate r l ength. of c ombu st ion
chamb er t o produc e smokeles sne s s,than the shor t -f l ami ngsemi-
b i t umi noue c o al s o f the Pitt sburgh di st ri ct .
The mo st de s irable sett ings with the st andar d. b o i l e r s
har e be en di s cus sed . However,it i s c omp ar at ively seldom
that it i s po s s ible t o c on st ruct sett ings of su ch p ropo rt i on s .
54
The maint enance c ondi t i on s may b e cons i de red very seve re,inas-
much as s ixt een o f the furnace s are of the dutch-oven de s ign ,
hav ing arche s thirt e en fe et long . The it em o f great e st int e r-
e st i s p e rhap s the t ot al annual maintenance of st okers and
furnace s per 1 0 0 horse p ower,whi ch i s
Tabl e No . 1
ANNUAL MAINTENANCE E"PENSE OF CHAIN
Annual‘
Mat er i al Co s t
mat e r ial
Tot al I ns t al l at i on l
;$5727 .951 4 80 0 H . P .
1 0 0 H. P .
1 H. P .
grat e width
NOTE Installat i on under cons iderat i on con s i st s
20 600 H . P . bo il ers,
7 4 0 0 H . P . bo il er s,
1 6 o f Whi ch. have 1 3 ft . long arche s,
ll o f Which have 5 ft . long arche s .
56
purpo se of keep ing the se suppo rt s c ool . Thi s i s done by cau s-
ing an ai r current t o p ass over the t op of the ar ch , the
current b e ingcreat ed by the furnac e draft , and duct s be ing
left through the out s i de wall and curt ain wall o f the furnace
t o p ermi t o f thi s syst em.
The const ruct ion o f the b ridgewall ove rhang i s no t so
diffi cult,as it i s cust omary t o have spe c ial shap ed t ile ,
and thu s avo id exce s s ive co rbel ing out , and the se t il e re st
on the wat erb eck ,making a st rong and s imple de s ign .
The red or common br ick fo rming the out s ide of the furnace
wall should b e well burned and un ifo rm in s iz e . The mort ar
in whi ch these ar e laid should b e c ompo sed of one part o f l ime
t o thre e part s o f cl e an , sharpsand . The longer the l ime
has been slacked the b ett er . Every f ifth c ourse should be a
header,and extreme care should be exerc i se d in f ill ing al l
int e rst ice s in o rde r t o p revent the infilt rat io n of ai r ,
whi ch reduc e s the draft and lowers the b o iler e conomy .
The mo st advant ageou s manner of erect ing a Chain Grat e
i ns t al l at i on , i s t o s et the st oker rails at the t ime o f laying
the b o iler foundat ions ; then erect the bo il er t o the po int at
which it i s ready for b ri ckwo rk . At thi s t ime the st oke r
shoul d. b e e re ct ed and set in it s c o rrect p o sit i on . The
br ickwork of the furnace can then b e bu ilt very clo se and
t ight t o the st oker,cut t ing off all undue air l eaks and pr e-
vent ing the p o s s ible mi stake s o f t o o wi de o r t o o narrow f ur -
nace . Thi s p rocedure al so p ermi t s the b rick masons t o ut il ize
the grat e surfac e on whi ch t o c onst ruct the cent e rs fo r the
58
H"
: he ight o f t op o f st ack ab ove the grat e surface
in fe et .
PM: atmospheri c p re s sure in pounds p er s quare inch .
Tr : atmo spheric t emp erature ab solut e .
t empe rature o f st ack gase s .
The fact o r . 52 t ake s int o ac count the p re s sure p er
s quare inch o f wat e r,and the dec imal po int .
Thi s fo rmul a doe s no t take int o account the dens i ty o f
the flue gase s,it be ing as sumed t o b e pract i c ally e quivalent
t o that o f air .
Thi s fo rmula g ive s the theo ret i cal draft pre s sure . On
ac count of the frict ion o f the gase s against the s ide s of the
st ack,the actual available stack pre s sure i s only about 80
pe r cent of the theo ret i c al value .
Extremely po rou s chimneys o r connect ions theret o decreas e
the draft pres sure o f a g iven stack but it i s an unu sual case
in which the actual value varie s mo re than 5 pe r cent from
the cal culat ed value .
In the di scus s i on thus f ar only chimneys have b een ment i on
ed . The case i s unalt e red if fo r the chimney i s sub st itut-
ed the induced draft fan,o r any of the fo rced draft syst ems .
In each ca se the same fundame nt al c ond it ion exi st s,a c ont in-
uou s difference in pre s sure driving the gas e s through. the
bo iler sett ing .
4 0
cau s ing it t o pas s th er ethrough,on it s way t o the furnace .
Othe rwi se there is no air c irculat ion through the chain , wit h
the re sult of the cha in becoming exce ss ively ho t and rapidly
det e rio rat ing .
From. the chimney t o the ash. p it the difference in pre s s-
ure that i s universally known as draft i s cause d by the d iffe r-
ence in the veloc ity o f the gase s,which i s in turn affect ed
by the re s i stance o ffered t o the i r pas sage , Whether such
re s i st anc e be useful such as that o ffe red by a bank o f b o il er
tube s,or non-us eful such as cau sed by a dep o s it o f s o ot , a
shar p turn in a breeching,o r a re st r ict ed area .
It fre quently o c curs that breeching s are so de s igned
that,becaus e of ~ r e st r ict ed areas o r t o rtuou s p as sage s
,the
amount of air that can be fo rced through a g iven fuel bed i s
greatly def i c ient o f the prope r amount fo r a furnace and b o i ler
o f g iven p rop o rt i on s .
In the de s ign of the b r eachi ngthe following general
rule s should b e bo rne in mind .
1 . The ret arding effect o f a s quare flue i s 1 2 p er cent
great er than a c ircular one of the same area.
2 . Abrupt turns shoul d. b e avo ided whe re p o ss ible,us e
be ing made of long easy sweep s .
5 . With c i rcular s teel flue s o f the s ame s ize as the
stack , o r r educed. pr opor t i onat e l y t o the volume o f gase s,a
c onvenient rule t o follow i s t o all ow on e inch draft lo s s pe r
each hundred fe et length o f flue,
and f ive hundredths inch
fo r each r ight angle turn . Fo r s quare o r rect angular bri ck
4 5
int ers t i ce s of the b ri ckwork const itut ing the b o iler sett ing .
The fri ct ion due t o the re st ric t ed p as sage s through
which the ga se s mu st p as s in the vari ou s type s of bo i lers in
c ommon u se causes a draft ob tainable in the furnac e and avai l-
able fo r fo rc ing air through the fuel bed o f much les s magn i-
tude than that obtainable at the b o iler damp e r ,and fo r any
g iven difference in po t ent ial b etween the ash. p i t and the up-
take there i s a c ert ain "fundamental furnace draft " dependent
thereon . Should the re s i st ance offered t o the p as sage of air
through the fuel bed b e inc reased e i ther by increas ing the
thickn es s of the fuel bed or o therwi s e,the effec t would be
that insuffi c i ent air would b e admi t t ed for c omplet e combu e-
t i on of the fuel , re sult ing in dull f ire s and. ex ce s s c oke in
the ash .
With the con di t i ons obtaining as here inaft e r set fo rth,
thi s furnace condi t i on i s ve ry c los ely ob tain ed wi th. a s ix
inch fuel bed o f i - i n . washed p ea c o al . It i s wi th such a
furnac e condit ion,the b o iler damper
‘
b e i ngwide open and the
grat e complet ely cove red, ( Which are s t andar d ,highl y economi cal
op erat ing condit ions ) that al l the following inve st igat i ons
o f the d ifferenc e in po t ent ial due t o decreas e in velo c ity
o r o the r cause s ,wer e made .
Figure s 1 7 , 1 8 , 1 9 ,20 ,
21 and 22 are diagrams o f the
variou s common typ e s o f bo ilers,the l et t e r s thereon indica-
t ing the p o int s at whi ch inve s t igat i on was mad e . Fo r con-
ven i enca of study the draft re adi ngs obt ained have be en shown
d i agr amat i cal l y on Plate s B,C,D
, E ,F and G referr ing in
4 5
ash cont ained 4 0 p er c ent o f c ombu st ible mat t er .
2 . Increas ed c ap ac ity o f the bo ilers,pe rmi tt i ng the
plant lo ad to be carri ed wi th two bo il er s,whereas thre e had
fo rme rly b een u sed.
Thi s pe rmi tt ed the bo il ers t o be ope rat ed
at a. mo re economic r at i ng, and saved the st and w by lo s se s of a
third set t ing .
Plat e 0 ,wi th reference t o the d i agr am. shown in Fi gure
1 8,shows the no rmal draft curve o f a ho ri zonta l ly baffled
bo iler of the typ e of the He ine, O'B r i en , hurray I ron o r
Eri e city . The mo st severe l o s se s exi st at the sect i on
between the drums ( F G ) and at the front o f the upp er baffle
(E F ) . If thro ttled t o the ext ent of lowering the furnac e
draft t oo much , the s e sect ions may b e rel ieved as was don e in
cas e Shown on Plat e J,in Whi ch the furnac e draft was increased
from . 1 1 inch to . 22 inch,and the capac ity an d economy at
rat ing mat erially imp roved .
The cond it i ons exi st ing in St irl ingbo ilers ar e shown
in Plate D,wi threfe rence t o Figure 1 9 , the greate st lo s s
be ing at the third pas s E . F .
Plat e Ei showe the condit i on ex i st ing throughout the
return tubul ar , s e t t i ng, Figure 20 .
Plat e F , and refe rence Figure 21,rep re sent the draft
condit i on s of t he Cahall vert i cal b o ile r . It will b e no te d
that th ere i s a re st ri ct i on t o the pas sage o f the gase s at
the p o int at whi ch they le ave the b o iler . Thi s typ e b o iler i s
s o de s igned . It b e ing a. one-pas s b o iler,i s thrott led at
thi s sect i on in o rder t o reduce the t emp erature of the e scap-
4 9
Lo s se s o ccurring in 50 feet o f
Lo s se s due t o three r ight -angle b ends
Requ i red net pres sure t o b e exert ed by atmo-
sphere at base of the
He ight o f chimney re qui red ( as suming 50 0 degre es
chimney t emp erat ure )
Diame t er re qu ired ( based on 5 p ounds o f c o al
per ho r se p ower ) -
OPERAT ION
In the ensu ing page s the wr it er de s i re s t o s et fo rth
the co rrect p ro cedure fo r start ing a new ins t allat i on, g iv-
ing fi ring rul es ,and di scus s ing the b e st metho ds o f handl ing
vari ou s typ e s o f bo il er lo ads .
In st ar t ing a new ins tallat i on it i s well t o ope rate
the Chai n grat e s cold for a day o r two ,to in sure their prop er
‘mechan i cal op erat i on . If st eam. i e ob ta inable , thi s i s a
simple mat t e r , o the rwi se i t i s nec es sary t o op erate the
machine by hand . The rep resent at ive in charge should then
inspec t,no t only the furnace
,but al so the b o i ler
,in si de and
out,and the b reeching
,as suring himself that the dampe r f i t s
well and operate s fre ely,and that wat er flows thr ough. the
waterbeck unre st rict ed . Aft er running the machine co ld fo r
a day,a sl ow f ire may be put un der the b o il er . The f ire i s
st art ed in the following manner : -
Clo se the damp e r two thirds,set the st oker gat e at a
he ight of s ix inche s,
and run in twenty four inche s o f c oal .
Then thrust some kindl ing unde r the st oker gat e and on t op
51
a thinner fuel bed i s neces sary,as it re qui re s a great er
difference in p ot ent ial t o fo rce ai r through the thi ck one .
Large . clean c o al re qui re s thicker fi re s than small s i zed c oal
o r slack,the reason be ing that the ai r p as se s thr ough the
fo rme r mo re readily .
In any sett ing with a. speci f i ed coal and draft there i s
a cert ain be st condi t i on o f f ire that re qui res pract i ce t o
obtain . Should the f i re t end t o burn ”sho rt ",1 . e . , t o
leave a b are sp ac e on the rear end o f the grat e,cove red only
by complet ely burned ash When the grat e i s op erat ed at no rmal
speed of two inche s p er minut e , it i s evi dent that the gat e
should b e rai sed,and a thi cker fuel bed should b e t ri ed . The
thickness should b e increased up to a po int where at the slo t h
e st op erat ive sp eed of the ma chine ( approximat ely one inch
per minut e ) the fuel i s no t complet ely burned b efo re reaching
the end of the grat e . The economy o f thick f i re s o c curs on
ac count of the inc reased depth o f fuel bed cut t ing off the
anmunt of free ai r ent ering the furnace during the early
stage s of combus t ion,and al so the increased depth. of ash b ed
at the re ar of the s toker ,maki nga mo re effe ct ive ai r seal at
that sect i on than the thin ash b ed . 1Moreover there i s le s s
danger of ho le s o ccurring in the thick fuel b ed than in the
than . The e conomy o f high however be st obtained i s
shown very clear ly from. the chart shown in plat e R,which has
rec ently come t o the wr it e r's att ent i on . The curve rep re s ent-
i ngthe furnace t emp erature may be c ons i dered as a bo i le r
effi c i ency curve,o r a curve of effi c ienc i e s based on the c omp
52
bus t i b l e in the c oal,the mo s t favo rable condit i ons be ing oh-
t ai ned wi th high furnace t emperat ure s .
SI"E OF COAL
Hr . W. L . Abbot t ,in a.pape r ,
" Some Charact eri st i c s o f
Co al as Affect ing the Pe rfo rmance o f St eam Bo il er s ," W. S . M; E . .
Sept. 1 5 , 1 906 ,
bring s out the p o int s that with the part i cular
in st allat i on under hi s ob servat i on,washed coal o f three-
quart er s ize p ro duced the max i mum. r e su1 t s bo th as regards
effi c iency and capac ity . The wr it e r's exp erienc e has be en
co inc ident wi th. Mr . Abbo t t's regarding thi s it em,maxi mum
result s always b e ing obt ained with washed . pea and nut c oal of
the s ize that pas sed . thr ougha s even- e ighths inch scre en,and
over a ni ne- s i x t e enthinch s creen . Unifo rmi ty in size of
c oal i s ve ry e s sent ial,as lar ge lump s do no t burn with the
same rap i di ty as do the small er p iec es,thus giv ing ri se to
e ither coke in the ash p i t . o r bare spo t s on the grat e .
PREPARING FOR A COMMERCIAL TEST
much. has been writ ten regarding the conduct ion o f
evapo rat ion te st s from. the st andpo int of a Consult ing Engin-
eer . The Ame ri can So c i ety of mechan ical Eng ineers has fully
and c omplet ely st andardized each it em,leav ing no que st i on r e-
garding the manner of conduct ing t est s,ob serving data
,o r
calculat ing re sult s . The wr it er wi she s t o v i ew the t e st fram
the s tandp o int o f a repre sent at ive of the st oker comp any sent
out t o fai rly ob tain a c ertain guarant eed effi c i ency and capac-
i t y .
54
heat ing surfac e,be ing po s i t ive o f it s pe rfect c ondi t ion as
regards ab sence of scale ins ide,
and so o t out s ide .
He may then f i re up and .make a p rel iminar y run , we i ghing
wate r and c oal,hav ing hi s f i reman pre s ent
,if pos s i b l egand
taking f ift een minut e reading s o f 0 and CO,f l ue gas
t emperature and draf t throughout the sett ing .
The purp o se of thi s p rel iminary run i s t o learn the most
e conomi cal condit i ons,and to e st abl i sh cert ain fuel b ed thi ck-
ne s s,rat e of t ravel
, p er cent o f and 0 ,and flue gas
temp erat ure obt ained thereby . When the de s i red c ondit i ons
are obt ained,careful not e should b e made th ereof , and the
repre s ent at ive may i nf orm. the purchaser o r hi s eng ine er that
he i s ready t o make the guarant ee t e st .
During the t e st p rop er inspect ion should be made o f all
i t ems ,as regards we i ghing apparatu s , reco rds
,et c . ,
to in sure
that ev erything i s done in acc ordance with the s tandard code,
but the ma in it aw. i s t o s e e that the e st abl i shed condi t i on s
ar e maintained .
Ob servat ion s o f CO-2 , draft and . f l ue gas t emp eratures
shoul d. b e made at intervals o f f ift een minute s , and the r epr e s-
ent at i ve should let no reading go un insp ect ed.
During the
t e st he should o ccupy no part i cular st at ion,bu t shoul d. keep
a general inspect i on,ke ep ing hourly t ab on the e st imat ed
effi c iency en t o rse power develop ed .
It should b e ev er bo r ne ihmind that the inve st igat i on
and t e st in themselve s have l i t tl e val ue ,s ince the economi e s
obt ain ed with chain grat e s are well known and e st abl i shed
stay-bolt i n the front header .
It was c onclus ively proven that a s ix inch f ire of
prop er cond it i on gave a draft re s i st ance o f .25 inch t o .50
inch,any exce s s of thi s amount always indi cat ing that the
fuel was p il ing up agains t the bri dgewall,e i ther be cause of
the overhang me lt ing o r p art ially cl os i ng, the ap erture , or
b ecause the rat e of t ravel of the grat e was t o o fast,in e i ther
case 6 3 8 1 1 ? remedi ed . Any draft re ad ing below . 25 inch
indi cat ed e ither a'
bare sp o t on the grat e o r a sho rt f ire in
nine case s out o f t en the l at t er .
By making inve st i gat i on of each indiv idual sett ing,it
'was proven that the p e r cent o f vari ed dire ctly as the
length of the f ire,the maximum reading b e im 1 4- t o 1 5 per
cent , with a full fi re,and l o r 2 p er cent with a fi re 2
f eet long . Plate 8 shows a graphical rep re sent at i on of the
draft and relat i ons in bo il ers Nos . 1 and 2 .
The operat ive force was then in st ruct ed by means o f a
t est made on a s et t ing hav ing all inspe ct ion hole s clo sed,
and the furnace condit i ons indi cat ed sol ely by the draft
gauge . The t e s t p roved ve ry suc ce s sful,bo th r egarding
eff ic i ency and capac i ty ,and thereaft er al l
"bl ind sett ings "
were op erat ed in thi s manner with very sat i sfacto ry re sult s .
Peri odi cally all set t ing s are inve st igat ed by means o f an
Great t o det ermine i f ai r leaks exi st,any re ad ings out o f
l ine with draft reading s b e ing indi cat i ons o f such . The
curve s shown in Plat e 8 rep re sent the relat i on o f draft in
furnace t o in the rear of two typ i c al b o il er sett ings,
59
i s fai rly con st ant,with the except i on o f the se sho rt sharp
peaks due t o the open ing of a st eam l ine int o a cooker o r
a brewing vat . In o rder that such. d emand s fo r s t eam. may b e
met succe s sfully,it i s e s sent ial that s ignal s (u sually by
ring ing o f a bell ) be g iven t o the bo il er r oom. thi r t y minut e s ,
and f ive minut e s in advance o f op ening the l ine . At the
fi r s t signal the ope rato r fill s the hoppe rs and st ar t s the
machine . At the f iv e minut e b ell he opens the damp er . The
durat ion o f such peaks i s usual ly constant,and aft er a few
t r ial s the op erato r can dr op the p eak without p opp ing o ff by
carrying low wat er and cu tt ing out the st oker sl ightly in
advance o f the t erminat i on o f the p eak .
machine shop lo ads are fairly constant dur ing wo rking
hours,be ing ent irely off betwe en such . In the se case s it
i s po s sible t o bank the f ire s twent y'
mi nut es befo re the lo ad
come s o ff , carrying the lo ad upon the heat in the wat er and
furnace . When the eng in es ar e st opp ed the wat e r will b e l ow,
the f i re s sho rt , and the set t ings comparat ively co ol . Then
by st art ing the pump s the b o ilers may b e p reve nt ed f rom. pop-
p ing off .
In o rder t o in sure the co rrect handl ing of b o il er s,i t i s
e s sent ial t o keep a log,and the wr it er rec ommends one similar
t o that shown in Plate s TI ,T2 and T5 . Thi s log i s applied t o
an elect ri c l ight and power lo ad , but might eas ily be adapt ed
t o v ari ou s condi t i on s . The upp e r part,Plat e TI ,
o f thi s
l og sheet i s filled out f r om. d at a. submi t t ed o n proper forms
by the b o iler ro om fo reman at the t erminat i on o f each shift .
61
from ash p it t o furnace and i s c ommonly sp oken o f as low draft ,
as di scu s sed in a pr oceed i ngchapt er . The co al consumpt i on ,
and ne ce s sarily the ho rse power ,devel oped are d irectly prop o rt-
i onat e t o the draft in the furnace . The l imit s of op erat ive
draft may generally be st ated as .4 0 inch for a maximum and .20
inch min imum,with the rat io s and p r opo rt ions o f pres ent pr ac-
t i c e .
Mr . Bement in a p aper ”Some Perfo rmance s o f Bo il ers and
Chain grat e s tokers,with suggest ions fo r Imp rovement ,
" W. S .
M. E . ,Feb ruary
,1 904 ,
shows re sult s obt ained from a serie s o f
t rial s t o det e rmine the effec t of furnace draft up on ef f ic-
i ency and c apac i ty . The max imum eff i c i ency was ob tained with
.20 inch draft in the furnace,the econorrwgradually d ecr eas-
i ngwith in creased draft . The maximum capac i ty was obt ained
with .4 0 inch .
There i s cons iderable di scu s s ion at t hi s t ime of highe r
rat e s o f combu st ion p er s quare fo o t o f grat e surface . Thi s
will not apply t o Chain Grat e s as at p re sent de s igned,fo r
the reason that the igni t i on o f the incoming fuel i s induct ive
and dependent on grat e sp e ed and fuel b ed thi ckne s s . It i s
safe t o say that the pre sent de s ign of Chain Grat e s will no t
p ermi t of great er fuel con sumpt i on , r egar dl e s s o f draft,than
fo rty p ounds o f dry co al p er s quare fo ot o f grat e surface p e r
hour .
In all in stance s that have c ome under the writ e r's
ob servat i on,the capac ity reache s the maximum at about .4 0
inch furnace draft . Any addit i onal draft merely fo rce s
65
The effect i s the ret ent i on of the heat in the furnace,cau s-
i ngexce s s ively ho t chains and s ide wall s . In some case s thi s
i s so seve re as t o l imi t the l ife o f the chain t o a few we eks,
and t o burn down the s ide wall s and ign i t ing arch. in as short
an int erval . The cause of thi s t rouble may be lo cat ed by the
u se of a draft gauge,and the c omp ar i s on of the reading s ob t ain-
ed t o the standard curve s d i s cu s sed i n a.pr eced i ngchapt e r .
Following i s a t abulat ion of the t rouble s t hat are en-
count ered l n connect i on with Chain Grat e install at ion s . The
writ er has arranged these under the he ading s of Effe ct ,Cau se
,
and Remedy,hop ing that thi s arrangement may prove u s eful no t e-
bo ok info rmat i on i n v i s it ing plant s t o o thers,as i t has be en
t o the Wr it er .
CHAIN RUNNING HOT
Effect
Burn s l inks .
Cau se
( a ) Ash. p i t full of hot ashes .
( b ) Ho t coal p il ing against wat e rbe ck on br idgewall .
( c ) Ret ent i on of gase s in furnac e .
( d ) T o o long o r low ro of in " dutch oven" s et t ing s .
Remedy °
Cau se Empty ash. p it mo re fre quently ,o r de s ign
larger p i t s .
Run f i re s so as not t o caus e bank at rear.
Op en up baffl ing at po int Where throt tl ing
OC CUI‘
B .
65
Insuff i c i e nt he at ing su rface ab so rb heat .
Sho rt c ircu it in b o il er .
Exce s s ive over rat ing .
Exces s ive draf t in furnace .
Air l eaks through fuel b ed s .
Remedy -
Apparent .
Apparent .
Put in ext ra pas s fo r gase s .
Repai r baffle s .
Det e rmine whether b o ile r i s Op erat ing mo st
economi cal rat ing .
Cau s ing e ither ( 3 ) o r ( b ) o r ( c ) .
iKe epgrat e covered .
LOW FURNACE TEMPERATURE
Effe ct
1 . Po o r ign it ion .
2 . Po or combu st ion .
5 . smoke .
Cau se .
Incomplet e combu st ion .
Grat e surface t o o small fo r he at ing surface .
Furnac e t oo large,t emp erature fall s as ga s
expands .
Low grade co al .
( a) High
( f ) Thin f i re s .
( 8 ) Unburned hydro-carbons .
( a ) Inc rease draft .
( b ) clean tube s.
Look fo r ai r leaks in furnace
and through fuel bed .
( 0 ) Clean tub e s .
( d ) St 0pair leaks .
( e ) imo re ai r,and p rop er mixing at high t emperature .
( f ) Thicker f ire s .
( 8 ) Can only be r emed i ed . by rede s igning furnac e .
UNDULY HIGH TEMPERATURE OF FURNACE WALLS AND GRATES
Effect :
Sho rt l ife o f chain and si de wall s , due t o exce s s-
ive heat .
Caus e
Conf in ing heat in furnace by
( a ) Throt t l ing areas through the b o ile r set t ing .
(b ) Admit t ing cold ai r t o ent er set t ingback o f
furnace s .
( a ) Prop o rt ion areas co rrectly .
(b ) Cut o ff air admi s s ion .
COKE IN ASH
Effect
Low effi c iency .
69
gradual in creas ing area as the gase s t ravel along ,mu st be
prov ided,and the sudden increase in cro s s sect i on mu st be
carefully avo ided if cont inuou s high t emp erature s are de s i red .
It i s somet ime s not ed even with good coal and goo d draft , dull
red flame s and smoky cond it i ons exi st,due t o the sud den
increase in c ro s s sect i on o f the furnace,cau s ing an expan-
si on o f the gase s and a co rre spond ing decre ase of the temp e ra-
ture . It has been not e d in thre e di st inct case s under the
writ er's ob s ervat i on that an increase o f 1 0 0 p er cent in area
p ract i cally prevent ed cont inuous c ombust ion by fail ing t o
generat e suff i c iently high r empe r at ur e s t o su st ain a con-
t i nuous ignit i on . A sudden incre ase of 50 pe r cent in cro s s
se ct i on rendered it imp o s s ible t o get br ight,whit e f ire s
,
but when a furnace area was p rov ided g iv ing an increase of
only 1 5 o r 20 p er c ent in cro s s sect i on at any p o int,high
t emp erat ure s were maint ained ,and sat i sfact o ry c ondi t ions
of ign it i on and combu st i o n exi st ed . Thi s re sult was obt ain-
ed on two s ett ings by merely pro viding a fur nace not hav ing a
sudden inc rease o f cro s s- sect ional area,all o ther condi-
t i ons remain ing const ant .
75
Fo r l it erature b earing on the subj e ct,ref erence i s made
the following papers
Some Perfo rmance s of B o il ers and Chain Grat e St okers
wi th. Sugge st i ons fo r Improvement s .- A .
Howt o Burn Ill ino i s Co al Wdthout Smoke Bullet in
No . 1 5 , Univers ity o f Ill ino i s,L . P . Breckenridge .
The Suppre s s i on of Indu st rial Smoke with Part i cular
Refe rence t o St eam Bo ilers . A . Bement WkS .M; E .
Some Charact er i st i c s o f Coal as Affec t ing Perfo rmance o f
St e am. B oi l er s . W; L . Abbo t t .
The S ign if icance of Draft s in St e am Bo iler Pract i ce .
Bullet in No . 567 ,U . 8 . Ge olog ical survey
‘
Walt er T . Ray and Henry Kr e i s i nger .