Auxiliary ventilation

Auxiliary ventilation

3. VENTILATION IN
COAL MINE DEVELOPMENT FACE,
TUNNEL AND DRIFT

4. Tunnelsordriftsareessentiallyblindheadingstillthey
areconnectedtoshaftsoraditsthusposingareal
challengetoventilationengineers.
Theworkplaceenvironmentintunnelsisgreatly
influencedbytheventilationmethod,selectionofproper
fanandductapartfromcostofventilation

5. Ventilationintunnelsanddriftsismainlydonby:
a)Bratticecloths.
b)AuxiliaryFansandducts

6. BRATTICE CLOTH
Thisissimplyasheetorsheetsofcanvascommonlymadeoutoftreatedhessiancloth
nailedontopropsplacedat1to1.5intervalalongtheheadingtopreventtheshort
circuitofairfromintaketoreturn,socausingtheventilationairtoreachthefaces.It
maybeused:
Asascreenacrossanairwaytopreventorreducetheflowofairalongit.
Asapartitionalongtheroadwaytodevideitintotwopartsintakeanreturn
ConditionofusingLineBrattice:
1.BratticeClothcoatedwithP.V.C.isimpermeabletoairflow,andismore
suitableforlinebratticetoventilateaheading.
2.Thiscanbeusedonlyforashortdistance(notmorethan20mlong)
intotheheadingduetoheavyairleakage
3.Theintakesideofabratticeshouldbekeptwiderthanitsreturnside.The
widerintakewillhelptocirculateadequatequantityoffreshandcoolairfor
theminersatfaceaswellaswillfaciateeasymovementofthemenand
machineriesthroughit.

7. Line Brattices Used for Auxiliary Ventilation

9. Auxiliary ventilation can be of following types:
Forcing
Exhausting
Overlapping and
Reversible

12. Reversiblesystemofventilationof
headingswithasingleforcingfanF

13. Ducts for Auxiliary Ventilation
Purpose:
The efficiency of most of the auxiliary ventilation systems depends more on the proper choice
of the duct than the ventilator.
Duct have low co-efficient resistance (0.003-0.005 NS
2
m
-4
)
If length of the is more, the resistance will be more that requires more fan pressure to overcome the
frictional pressure loss.
High pressure leads to excessive leakage
New rigid steel ducts if properly jointed and aligned have a coefficient of friction within limit
P.V.C. coated flexible ducting when properly inflated have a fairly low coefficient of friction (upto
0.002 NS
2
m
-4
)
The resistance can be reduced by having large diameter ducts, but such ducts become costly, more
difficult to carry and install and take up a large space which is undesirable in headings of small cross-
sectional area.
Thus, the choice of proper size of duct, commensurate with the length, is essential.
Ducts for Auxiliary Ventilation
Purpose:
The efficiency of most of the auxiliary ventilation systems depends more on the proper choice
of the duct than the ventilator.
Duct have low co-efficient resistance (0.003-0.005 NS
2
m
-4
)
If length of the is more, the resistance will be more that requires more fan pressure to overcome the
frictional pressure loss.
High pressure leads to excessive leakage
New rigid steel ducts if properly jointed and aligned have a coefficient of friction within limit
P.V.C. coated flexible ducting when properly inflated have a fairly low coefficient of friction (upto
0.002 NS
2
m
-4
)
The resistance can be reduced by having large diameter ducts, but such ducts become costly, more
difficult to carry and install and take up a large space which is undesirable in headings of small cross-
sectional area.
Thus, the choice of proper size of duct, commensurate with the length, is essential.
According to NCB, U.K. 104, the use of 450 mm diameter ducts up to a distance of 900 m, beyond
which the duct should be of 600 mm.
In India, however, a wide range of duct size s varying from 300 mm to 800 mm are used.

14. Ducts for Auxiliary Ventilation
Two types of duct are commonly used, the flexible ducts and the rigid ducts
Flexible Ducts
Flexibleductingismucheasiertostore,transportandinstallthanrigidducting.
Theyarecheaperininitialcost,buthaveshorterlife.
Earlier,flexibleductingwasmadefromrubberizedcottonfabric,butthismaterialwas
inflammableandwaseasilytorn.
Now,flexibleductingmaybemadefromterylene,rayonornyloncoatedwithPVC.
FlexiblecanvasorPVCcoatedductingincorporatingwirearmouringembeddedinthe
fabricisnowavailableforexhaustventilation.
Theyareconvenientlyusedinshorterheadingsuptoadistanceof300m,whereamore
permanentsteelductingbecomeunnecessaryoratthefaceendofrigidductwherethey
canbeeasilyremovedatthetimeofblasting.
Flexibleductsareverysuitableincurvedheadings.
Flexibleductsaremadeinlongersectionsthusreducingthenumberofjointsand
consequentlytheleakage.

15. Ducts for Auxiliary Ventilation
Two types of duct are commonly used, the flexible ducts and the rigid ducts
Rigid Ducts
Rigidductsofroundsectionarecommonlyusedforallpermanentinstallations.
Theycanbemadeofsteel,aluminium,plywood,fibre-glass-reinforcedplasticorhigh-
densitypolythene.
Aluminiumductsarelight,haveasmoothinternalfinishresultinginlowcoefficientof
friction,andaswellaseasytotransport.But,theyhavenotfoundcommonusein
minesastheyarecostlyandareeasilydamagedandD-shaped.
Steelductsarecommonlyusedineveryminesandtunnelsaspermanentbecauseof
theirsturdinessandlonglife.
Fibre-glass-reinforcedplasticorhigh-densitypolytheneductscanalsobeusedinwhere
theairishighlycorrosiveinnature.
Steelductsareusuallymadeofhot-rolledmildsteelsheetsof1.6mmthickness,30to75
cmindiameterand2to4minlength.Differentsectionsarejointedbybolts.

16. Air requirement in drifts, tunnels and development headings in coal mines
ILOrecommendedaquantityof0.175m
3
s
-1
perm
2
ofthedriftface
Inextremelyhotfaces,quantitiesashighas0.75m
3
s
-1
perm
2
ofthedrift
face
Incoalmines,asperCMR1957,
i.Quantityofairshouldbe6m
3
min
-1
permanor2.5m
3
min
-1
perdaily
tonneoutput,whicheverislarger,passesalongthelastventilation
connectioninthedistrict
ii.Ateveryactiveworkingplaceinthemine,airdoesnotcontainless
than19%ofoxygenormorethan0.5%ofcarbondioxideorany
noxiousgasinquantitylikelytoaffectthehealthofanyperson
iii.Thepercentageofinflammablegasdoesnotexceed0.75inthe
generalbodyofthereturnair1.25inanyplaceinthemine
iv.TheWBTinanyworkingplacedoesnotexceed33.5
0
Candifit
exceeds30.5
0
C,arrangementshouldbemadetoventilatethesame
withaairvelocityofnolessthan1m/s

17. Air requirement in drifts, tunnels and development headings in coal mines
Inlongheading,thequantityrequiredtobecirculatediscontrolledchiefly
bytheneedtoquicklyremovetheblastingfumesfromthedriftfaceinorder
tominimizelossofworkingtime.
TheDGMS,Indiarequirestheventilationofdriveexceeding50minlengthto
besuchastodilutethenitrousfumesproducedbyblastingto5p.p.m.andCO
to50p.p.m.withinaperiodoffiveminutes.
Consideringadilutingtimet,therequiredrateofair-flowcanbe
obtainedfromthegasbalanceequationfortimet.
q Mq
/
Q=------ORQ=------ -------Eqn1
ct ct
where,
Q=quantityofairflow(m
3
min
-1
),
q=amountofgasaddedduringtimet=Mq
/
,
M=massofexplosiveblasted,
q
/
=volumeofnoxiousgasproduceperunitmassofexplosive,
c=concentrationattimet.

18. Air requirement in drifts, tunnels and development headings in coal mines
Inlongtunnelshowever,mixinganddilutionoccursoverashortlengthat
thefaceinfrontoftheventilationtube.Insuchcaseitwouldbemore
logicaltousethefollowingrelation:
V
m q V–V
m
t=2.303------log-------+--------- --------Eqn2
Q V
mcQ
where,
Q=quantityofairflow(m
3
min
-1
),
q=totalvolumeofnoxiousgasproducedattimet=Mq
/
,
V=volumeoftunnel
V
m=volumeoftunneloverwhichmixingofgasesproducedattheface
andairdeliveredbythefanoccurs,
c=concentrationattimet.

19. Air requirement in drifts, tunnels and development headings in coal mines
Problem:1
18kgofexplosiveisfiredina2mx2.5mdrivewhichis1000mlong.
Calculatethequantityofairtobecirculatedbyanauxiliaryfantobring
downtheconcentrationofnitrousfumesinthedrivetothetolerablelimit
of5p.p.m.withinaperiodof5minutes.Akgofexplosiveproduces2000
cm
3
ofnitrousfumes.
Problem:2
16kgofexplosiveisfiredina2mx2.5mdrivewhichis1200mlong.
Calculatethequantityofairtobecirculatedbyanauxiliaryfantobring
downtheconcentrationofcarbondioxidefumesinthedrivetothe
tolerablelimitof50p.p.m.withinaperiodof5minutes.Akgofexplosive
produces2500cm
3
ofnitrousfumes.

20. Air requirement in drifts, tunnels and development headings in
coal mines
Solution(Problem1):
Thevolumeofthedrive=2x2.5x1000=5000
Thevolumeofnitrousfumesproduced=18x2000cm
3
=36000cm
3
=0.036m
3
maximumpermissibleconcentrationofgas=5p.p.m.=0.005%
Assumingtheventilationtubetodischargeatapoint10mawayfromtheface.
Therefore,themixingvolumeV
mcanbetakenequalto10x2x2.5=50m
3
Nowusingequation2,
50 0.036 5000–50
5=2.303------log----------------+---------------
Q 50x0.0005 Q
or,Q=993.648m
3
/min=16.56m
3
/s
Therefore,quantityofairrequiredtobecirculatedbyanauxiliaryequalsto16.56m
3
/s