EFFECT OF AUTO COMPRESSION ON VENTILATION SYSTEM OF DEEP SHAFT COAL MINES IN JHARIA COAL FIELD – A CASE STUDY

Abstract

1.0 ABSTRACT The future prospect of underground coal mining in Indian mines is either from extensive mines or at depth (> 300 m). In this situation the intake air is expected to be influenced by various parameters, viz. auto-compression, surface air temperature (seasonal temperature variation), heat due to explosive detonation, heat from mechanized equipments, metabolic heat, heat from broken rock, wall rock heat flow, heat from other sources etc. Many mines in our country are receding towards lower horizon by taking the liability and responsibility of upper seams. In order to address the problem of oppressive climatic conditions at the workings, behavior of various parameters affecting the quality of intake are required to be studied for realistic ventilation planning of deep mines. The effect of auto compression is one of them. The paper deals with realistic estimation of heat addition to the intake air due to auto compression. 2.0 INTRODUCTION Many Indian coal mines have become extensive or receding towards greater depth. As a result in many mines work place environment has become oppressive and affecting the productivity and safety. The importance of ventilation has been realized since beginning of mining operation. It has been established that it has got direct relation with production, productivity and safety of the mines. In a study [1] the relation of wet bulb temperature at workplace environment and efficiency of the workers has been established. On the basis of literature, in US metal mines maximum efficiency is at or below 27 0c and economical efficiency is between 27 0 C to 29 0 C. In addition, the inspectorates of different coal producing countries have also stipulated the value of maximum permissible wet bulb temperature as per their climatic condition considering the miners health. These values are for coal mines India [2] , USA [3] , UK [4] are 33.5 0

Full text

1
EFFECT OF AUTO COMPRESSION ON VENTILATION SYSTEM OF DEEP
SHAFT COAL MINES IN JHARIA COAL FIELD – A CASE STUDY
D. Mishra* and Dr. N. Sahay**
* Trainee Scientist, ACSIR, CSIR-CIMFR, Dhanbad
**Sr. Principal Scientist & Head, Mine Ventilation Discipline, CSIR-CIMFR, Dhanbad
1.0 ABSTRACT
The future prospect of underground coal mining in Indian mines is either from extensive mines or at depth (> 300
m). In this situation the intake air is expected to be influenced by various parameters, viz. auto- compression, surface
air temperature (seasonal temperature variation), heat due to explosive detonation, heat from mechanized equipments,
metabolic heat, heat from broken rock, wall rock heat flow, heat from other sources etc. Many mines in our country
are receding towards lower horizon by taking the liability and responsibility of upper seams. In order to address the
problem of oppressive climatic conditions at the workings, behavior of various parameters affecting the quality of
intake are required to be studied for realistic ventilation planning of deep mines. The effect of auto compression is
one of them. The paper deals with realistic estimation of heat addition to the intake air due to auto compression.
2.0 INTRODUCTION
Many Indian coal mines have become extensive or receding towards greater depth. As a result in many mines work
place environment has become oppressive and affecting the productivity and safety. The importance of ventilation
has been realized since beginning of mining operation. It has been established that it has got direct relation with
production, productivity and safety of the mines. In a study [1] the relation of wet bulb temperature at workplace
environment and efficiency of the workers has been established. On the basis of literature, in US metal mines
maximum efficiency is at or below 270c and economical efficiency is between 270C to 290C. In addition, the
inspectorates of different coal producing countries have also stipulated the value of maximum permissible wet bulb
temperature as per their climatic condition considering the miners health. These values are for coal mines India [2],
USA [3], UK [4] are 33.50C, 300 c, 330C respectively. It has also been established that the temperature of the
environment can be diluted by increasing the air quantity at the workings. For determination of optimum value of air
quantity at particular workings depend on physical parameters of the openings and thermal properties of the virgin
rock etc. For deep shaft mine heat due to auto compression plays an important role in adding enthalpy to the air
flowing in the mine. Auto compression [5] is considered as a source of heat which can’t be diluted by increasing air
circulation in mine. In case of shallow depth mines effect of heat due to auto compression is considered negligible.
However in case of deep shaft mines auto compression of intake air in shaft raises the temperature affecting the
workplace environment. This subject gets more complicated day by day as the Indian coal mines are receding
towards a greater depth i.e. (>300m depth). Therefore consideration of auto compression on air current in deep shaft
mines is necessary. The paper discusses the effect of auto compression on air in one of the mines in Jharia coal field
of Tata Steel Ltd.
3.0 History of auto compression in Indian mines
Value of [6] rise in dry-bulb temperature of air due to auto compression is 0.976 K per 100 m depth. The wet-bulb
temperature of air also rises due to auto compression but its rate depends upon surface dry-bulb and wet-bulb
temperature. For prevalent summer conditions in India the wet-bulb rises at the rate of 0.3-0.25 K for every 100 m
depth in dry air, but as soon as the evaporation in shaft occurs then the dry-bulb temperature decreases sharply and
wet-bulb temperature rises at a faster rate. In this condition the adiabatic index of the intake air can be represented by

2
a variable polytropic index (n). In dry shaft (n) approaches, in wet shafts (n) can be equal to 1.0 (isothermal
compression) or even less than 1.0 because of evaporation of water in the downcast shaft which lowers the dry-bulb
temperature.
3.1 AUTO COMPRESSION IN MINES
3.1.1 The air while descending gets compressed by the columns of air and subsequently gains heat. In dry shaft the
air gains heat due to adiabatic compression resulting in addition of sigma heat to the air current. It is calculated using
formula [7].
Temperature rise (0c) = 

= 
 ----- (1)
3.1.2 The another approach for calculating the temperature of the air in the shaft, considering potential energy of the
air in the shaft gets converted to heat energy provided no work is done by the air descending the shaft, (i.e. the flow is
frictionless and non –accelerative) and no heat or moisture is lost or gained by the air, then the compression of the air
in the downcast shaft will be reversible adiabatic [8].

       -------- (2)
Where T = temperature, K
 = Cp/Cv = 1.404 for dry air (it varies slightly with the moisture content of air, but for mining purpose it
can be taken as equal to 1.4), V= specific volume (volume of unit mass of air), P = barometric
pressure, kPa, Subscripts 1and 2 indicates the state of air at shaft top and bottom respectively.
By finding barometric pressure at shaft top the temperature rise due to auto compression can easily be calculated.
The temperature rise due to auto compression can also be calculated by equating the potential energy with the
enthalpy change in the downcast shaft. This follows the relation given below:
 dQ – dW = dH + dPE + dKE ------- (3)
Where dQ = heat added to or removed from the section (from outside the system), dW = external work done on or by
the fluid in the section, dH = change in enthalpy of the fluid across the section = gdh, dKE = change in kinetic
energy of the fluid across the section = d (v2/2) = vdv, dPE = change in potential energy of the fluid across the
section, g = acceleration due to gravity, h = elevation of the fluid, v = velocity of the fluid. Under the assumptions
made dQ = 0, as no heat is transferred, dW =0, as no work is done on or by the fluid, dKE = 0, as the flow is non-
accelerative. So that the equation becomes = dH = - dPE. Now from the above relation it can be concluded that the
heat source due to auto compression is = H = mgh = m.Cp.T
=  T = H/ m.Cp ----- (4)
Where T = rise in temperature, K, H = change in enthalpy, J/kg, h = depth of the shaft, m, Cp = specific heat of
air, J/kg.K, m = mass of the air column descending in the shaft, kg
3.1.3 Further it is explained [9] that apart from geothermal effect; air in underground mines is also heated due to effect
auto compression.
As the air goes down a shaft or incline gets compressed by the column of air above, its enthalpy is increased due to
conversion of potential energy (I) to heat energy. For enthalpy change energy balance equation is H2 – H1 between
top and bottom of a shaft at Z1 and Z2 (m) above datum per Kg of dry air is given by;
H2 – H1 = g (Z1 – Z2) -------- (5)
The theoretical rise of temperature is-
      
   
 ------------ (6)
Where CP is in j/kg.0C.

3
3.1.4 The auto- compression can also be treated as adiabatic compression in the shaft [10]. When there is no heat
exchange in the shaft and no evaporation of moisture takes place.
Heat due to auto- compression in vertical shaft is calculated by the formula
q QpE T
--------------------- (7)
Where q = theoretical heat of auto compression (W), Q = airflow in shaft (m3/s),  = air density (kg/m3) and ∆d =
elevation change (m)
3.1.5 Air auto compression in inclined raise layout
Auto compression process occurs during the air descend through the underground openings and due to its own
compression. The mathematical model [11] is deduced considering the equilibrium condition, air properties and the
influence by the vertical forces as situation presented in Figure (1) In this case depth h can be expressed as a function
of underground opening length L (m) and inclination α (0), and can be written as h = Lsinα and finally the
temperature increased in underground opening due to auto – compression is ∆ta (0).diagram.
.
Figure- 1- air auto compression in inclined raise layout
g.dh – dp/a = 0 ---------- (8)
Where, g is gravity, dh is depth differential, and dp is pressure differential,  is air density.
dh=dp/=vdp ------------ (9)
Where  is specific gravity, v is specific volume
v.dp + k.p.dp = 0 ------------- (10)
Where in adiabatic process p.vk =constant, k is air adiabatic coefficient. According to Clapeyron equation p.v = R.t2,
R is universal gas constant and t2 is the compressed air temperature.
p.dv = R.dt2 – v.dp ------------ (11)
using equations (10), (11) and(12) the following equation is obtained
dh + k(Rdt2 - dh) = 0 ------------ (12)
(1-k)
.R 2dh k dt

= (1-k)h + k.R.t2 + C = 0 ------------ (13)
Where C is constant. Rearranging equation (14) we get the temperature t2 as
 t2 = (k-1)h/ k.R – C ---------- (14)
 ta = t2 –t1 = (k-1) h/k.R ----------- (15)
Figure-1


4
No.2 ,3&4 PITs JAMADOBA COLLIERY, TISCO
NO. 3 PIT
X VA
X VI
X VIA
X VII
X VIII
XV
NO. 2PIT
X VII
X VIII
NO. 4 PIT
X VI
X VIA
X VII
X VIII
RR
[DC] [UC]
XIV
No.2 ,3&4 PITs JAMADOBA COLLIERY, TISCO
NO. 3 PIT
X VA
X VI
X VIA
X VII
X VIII
XV
NO. 2PIT
X VII
X VIII
NO. 4 PIT
X VI
X VIA
X VII
X VIII
RR
[DC] [UC]
XIV
No.2 ,3&4 PITs JAMADOBA COLLIERY, TISCO
NO. 3 PIT
X VA
X VI
X VIA
X VII
X VIII
XV
NO. 2PIT
X VII
X VIII
X VII
X VIII
NO. 4 PIT
X VI
X VIA
X VII
X VIII
RR
[DC] [UC]
XIV
Figure-2: showing the seam wise entry and exit of the mines
Now putting the values of (R = 29.7 kgf-m/kg.0k) and average air adiabatic index (1.302) the final equation is
obtained as follows:
 t2 –t1 = 0.0098h ------------ (16)
 ∆t a = t2 –t1 = 0.0098Lsinα ------------ (17)
3.1.6 In case of moist air, the specific heat per Kg of dry air is slightly more and dependent on moisture content of air,
provided there is no increase in moisture content from water evaporation. Rate of increase of WBT with depth is
independent of the initial WBT of air. For Indian coal fields the rate of rise of wbt is 0.25-0.3 0C/100 m depth.
Hence due to the above reason the rise of DBT due to auto compression effect becomes less and on the other hand the
WBT rises more than the above rate. There is another derivation [12] for calculation of heat source added in the mine
environment due to auto compression of air in the shaft the following procedure is followed;
 T2/T1 = (P2/P1) (γ-1/γ) ----------------------- (18)
Where T = absolute temperature (0K), P = atmospheric pressure (kPa), γ= ratio of specific heats of air at constant
volume and pressure, and subscripts 1 and 2 refers to the initial and final conditions respectively. Values of γ are
1.402 for dry air and 1.362 for saturated air.
Hence in actual mining condition there may be both dry and wet conditions. The contribution of auto compression in
rise of temperature in mine airways as calculated by the formula [13] is about 40-60% of the total.
4.0 INVESTIGATION
About the experimental site
NO.2 Pit Jamadoba Colliery belongs to Jharia group of mines of
Tata Steel Ltd is located on the west side of Jharia- Sindri Road
and about 5 Kms from Jharia Township. The position of the
colliery as per geological map is latitude 23 41’40” to 23 43’00” N
and longitude 87 24’30E. The Mine is surrounded on the North:
Jitpur colliery Keduadih colliery and Bhutgoria colliery on the
South: Bhowrah colliery, on the East Digwadih colliery:and on the
West Amlabad colliery. It is captive mine having very bright future
prospect as mine able coal reserve about 25 million tonnes. The
estimate life of the mine may be more than 50 years with existing
production rate [@500 tons/day]. In the mine there are three Pits,
viz. No.2, No 3 and No 4 . Among them Pits No. 2 and 4 are
acting as downcast while Pit No. 3 Pit acting as upcast. Intake air
from Pit No-2 is utilized for the ventilation of main workings of XI
seam. Hence, Pit No-2 (Depth: 374.8m, Cross sectional area 21.7
m2] is considered for the study. Layout of the shaft with seam
entries is shown in Figure 2. Air enters through Pit No.2 travels
along 3 -X-cut up to 10L- air crossing at 14L- drift mouth - XI
seam intake to 1st rise (1L) –working at22L in XI seam. The
ventilation system in the mine is exhaust with homotropal transportation system. The ventilation is achieved by axial
flow fan (Make: Voltas, Model: VF-300) handling air quantity about 116 m3/s at pressure of 106 mmwg. Air quantity
flowing through Pit no. 2 was of the order of 74.08 m3/s. A schematic diagram of ventilation network of the mine is
shown in Figure 3.
Figure-2

5
Figure -3: A schematic diagram of the ventilation network of Jamadoba colliery
Experimental design
Ventilation circuit extended from surface - Pit No.2 bottom – XI seam via XIV seam was divided into seven
segments. Details of the segments are furnished in the Table-1..
TABLE- 1: Details of the segments
Segment-
no
Location
Length(m)
Area(m2)
Perimeter
(m)
Depth of
inlet (m)
Depth of
out let (m)
Angle of
Inclination
( O)
1
Surface to pit bottom
375
21.07
16.27
0
374.8
90
2
Pit bottom to 3-X(10L)
650
9.81
13.55
374.8
442.3
6
3
3-X(10L) to air crossing at 14L
180
9.93
12.94
442.3
458.2
14
4
air crossing at 14L to drift mouth
50
9.46
13.39
458.2
460
5
5
Drift mouth to intake to XI seam
275
10.75
13.76
460
523.9
2
6
XI seam intake to 1st rise ( 1L)
50
12.24
14.36
523.9
525.3
13.5
7
1st rise ( 1L) to XI seam workings
450
11.81
15.00
525.3
542.2
2
4 P IT
2 P IT
S towing
dri ft
R
18 S ea m
E twar i
S ing h
dri ft 4
4A
4B
3 P IT FAN HOUSE
250
A-2
18 S ea m
14 Seam/2 Pit
R
16A
S eam
C -5
B elt
B
Dip
C -2
28 L
4th XC
160
9th L/B -dip
125
H
Drift-II
5th XC
Drift-I
18th L
-1s t di p
0 R is e
3rd R is e
R
17
S eam
200
A-1
B-2
17 S ea m
RRR
R
16 Seam /2 Pit
Da m 16
S eam/Dip
14
S e am /P attia
1120
Di g wad ih
160
H
3rd C ros s C ut
S ump
dri ft
2 P it d raina ge drift
1401
16 L 26 L
27 L
31s t L P um p
6L 3
P um p
R
1s t
Dip
B-1
15th L
10th L
12th L
S tapl e
S ha ft
1s t X C ut
2nd X C ut
6th L
4th Ris e
5th Ris e
Ve ntilation Ne two rk J am dob a
C ollie ry
( N ot to s c ale)
4 P IT
2 P IT
S towing
dri ft
R
18 S ea m
E twar i
S ing h
dri ft 4
4A
4B
3 P IT FAN HOUSE
250
A-2
18 S ea m
14 Seam/2 Pit
S towing
dri ft
R
18 S ea m
E twar i
S ing h
dri ft 4
4A
4B
3 P IT FAN HOUSE
250
A-2
18 S ea m
14 Seam/2 Pit
R
16A
S eam
C -5
B elt
B
Dip
C -2
28 L
4th XC
160
9th L/B -dip
125
H
Drift-II
5th XC
Drift-I
18th L
-1s t di p
0 R is e
3rd R is e
R
17
S eam
200
A-1
B-2
17 S ea m
RRR
R
16 Seam /2 Pit
Da m 16
S eam/Dip
14
S e am /P attia
1120
Di g wad ih
160
H
3rd C ros s C ut
S ump
dri ft
2 P it d raina ge drift
1401
16 L 26 L
27 L
31s t L P um p
6L 3
P um p
R
1s t
Dip
B-1
15th L
10th L
12th L
S tapl e
S ha ft
1s t X C ut
2nd X C ut
6th L
4th Ris e
5th Ris e
Ve ntilation Ne two rk J am dob a
C ollie ry
( N ot to s c ale)
R
16A
S eam
C -5
B elt
B
Dip
C -2
28 L
4th XC
160
9th L/B -dip
125
H
Drift-II
5th XC
Drift-I
18th L
-1s t di p
0 R is e
3rd R is e
R
17
S eam
200
A-1
B-2
17 S ea m
RRR
R
16 Seam /2 Pit
Da m 16
S eam/Dip
14
S e am /P attia
1120
Di g wad ih
160
H
3rd C ros s C ut
S ump
dri ft
2 P it d raina ge drift
1401
16 L 26 L
27 L
31s t L P um p
6L 3
P um p
R
1s t
Dip
B-1
15th L
10th L
12th L
S tapl e
S ha ft
1s t X C ut
2nd X C ut
6th L
4th Ris e
5th Ris e
Ve ntilation Ne two rk J am dob a
C ollie ry
( N ot to s c ale)
Ventilation network jamadoba
colliery(not to scale)

6
Experimentation
The results of investigation comprising measurement of air quantity, wet and dry bulb temperatures are furnished in
Table -2.
Table2-Results of measurement of air quantity, wet and dry bulb temperatures segment wise
Sl no
Segment no
Air quantity(m3/s)
WBT
(0C)
DBT
(0C)
Wetness in
(%)
1
Segment-1
74.08
32.50
27.50
70
2
Segment -2
30.89
31.70
28.90
30
3
Segment- 3
30.33
31.60
31.40
20
4
Segment- 4
30.03
31.60
31.40
20
5
Segment -5
30.01
32.20
31.90
30
6
Segment- 6
29.98
32.70
31.80
60
7
Segment- 7
18.21
33.40
32.60
70
For determination of effect of auto compression the segment -1 ( Pit No.2) was divided into four sub segments. , viz,
surface - 100m depth, 100m - 200m depth, 200m -300m depth and 300m – 374.8 m depth. Results of measurements
of air quantity flowing in Pit No.2 and wet bulb & Dry bulb temperatures at the end of sub segments are furnished in
table -3
Sl-no
Location
Air Quantity
(m3/s)
DBT (0C)
WBT (0C)
1
Pit- top(0 m)
74.08
28.5
25.5
2
100 m
28.0
26.0
3
200 m
28.0
26.5
4
300 m
27.5
27.0
5
Pit-bottom(374.8 m)
29.0
28.5
25
26
27
28
29
30
31
32
33
34
375
1025
1205
1255
1530
1580
2030
TEMPERATURE(0C)
DISTANCE,(m)
VARIATION OF TEMPERATURE IN U/G WITH DISTANCE
DBT(0C)
WBT(0C)

7
Psychometric properties, viz. density, specific enthalpy, total enthalpy, total sigma heat and dew point of air quantity
flowing through the above segments were calculated by using software based on the formula[14] given below:
The results are furnished in Table -3
(i) True density of air-water vapour mixture(wt, kg of air –water vapour mixture/m3):
wt = 1/vt ------------------------ (19)
(ii) Enthalpy of air-water vapour mixture(H,Kj/kg of air):
H = 1.005tdb + r(2.5016 + 0.0018tdb) ---------------- (20)
Where tdb = dry-bulb temperature (0C);
r = moisture content (g of vapour/kg of air)
(iii) Sigma heat(S, Kj/kg of air)
S = H – 0.004187rtwb ---------------- (21)
Where H = enthalpy of air-water vapour mixture (H, Kj/kg of air);
r = moisture content(g of vapour/kg of air);
twb = wet-bulb temperature(0C).
During any adiabatic saturation process, the sigma heat remains constant (but not the enthalpy) and
the use of sigma heat in calculations involving wet heat transfer is more accurate than when the
enthalpy is used.
(iv) Dew point temperature(tdew,0C):
tdew = 237.3 loge (e/610.5)  17.27 – loge(e/610.5) ---------------- (22)
Where e = vapour pressure (Pa)
Table-4: Psychometric properties of air flowing through different segments
S.No
Segments
Sub segment
Mass flow
(kg/s)
Sp. Enthalpy
(kJ/kg)
Relative humidity
(%)
1.
Surface
78.74
2.
1
I
87.717
79.54
85.42
3.
II
87.674
81.65
88.96
4.
III
87.765
83.92
96.21
5.
IV
87.225
90.89
96.22
6.
2
I
37.917
93.19
97.03
7.
3
1
37.279
93.58
96.31
8.
4
I
37.294
94.13
96.31
9.
5
I
36.960
94.23
96.34
10.
6
1
36.907
95.46
96.34
11.
7
I
22.111
108.56
94.54

8
4.2 Calculation of temperature due to auto compression
The value of actual temperature rise due to auto compression in the air descending through Pit No. 2 was calculated
using formulae given by different researchers at different depths. The results are furnished in the table-5.
Table -5- Temperature (t) of air descending through Pit No.2 at different depth due to auto compression ( OC).
Equation No.
formula used
100 m
200 m
300 m
374.8 m
1
(t)=m.g.h/cp
0.98494
1.96988
2.954819
3.691554
2
(t)=g.(h2 - h1)/cp
0.976119
1.952239
2.928358
3.658496
3
(t)= h/m.cp
0.9801
1.98209
2.973134
3.76597
4
(t)= 0.0098Lsin
0.98
1.96
2.94
3.67304
Calculation of Enthalpy from measured values and calculated values (Table -4)
The value of change in enthalpy (∆H) sub segment wise calculated from measured data (Table-4) and enthalpy
(∆Ha ) due to auto compression considering rise in temperature wet condition of shaft ( Table-5). The results are
compared and percentage enthalpy due to auto compression are furnished in Table- (6)
Table -6: Depicts auto compression effect in the shaft
Sl-no
Location
Air mass
flow
(Kg/s)/ 100
m
∆H= change
in Specific
enthalpy
(kJ/kg)/ 100m
] ∆Ha= Heat due
to auto
compression
(kJ/kg)
Effect of auto
compression in
(%) on each
section
Relative
Humidity (%)
2
100 m
87.717
2.17
1.029
47
85.42
3
200 m
87.674
2.2
1.029
46
88.96
4
300 m
87.765
2.27
1.029
45
96.21
5
374.8 m
(Pit No.2 –
bottom)
87.225
6.97
1.16
17
96.22
The results from table (6) reveal that the effect of auto compression in the shaft at 100m, 200m, 300, and 374.8 m is
47 %, 46%,45% and17% respectively.. The corresponding value of relative humidity in sub segments are of the
order of 85.42%, 88.96%, 96.21% and 96.22% respectively. The change in enthalpy due to auto compression is less
in sub segment from 300m – 374.8m. This may be due to the seepage of water followed by conversation of heat to
latent heat. Hence the results are corroborated with findings of other researcher [15].

9
5.1 FIELD OBSERVATION OF AUTO-COMPRESSION IN INCLINE OPENINGS:
The value of temperature of intake air from Pit no.2 bottom to XI seam working, divided into six segments was
calculated using equation (18). The results are furnished in table-7.
TABLE – 7: Temperature rise in all the segments due to auto compression of air in inclined airways
Sl.
No
Segment-no
sin 
Temp rise
due to auto
compression
Addition of
heat due to
auto
compression
(kJ/kg)
Specific
enthalpy
(kJ/kg)
Effect of
heat due to
auto
compression
(%)
Relative
Humidity
( %)
1.
Segment-2
0.1031
0.656747
0.689
2.3
30
97.03
2.
Segment -3
0.0397
0.106915
0.11
0.39
28
96.31
3.
Segment 4
0.087
0.153468
0.162
0.55
29
96.31
4.
Segment -5
0.0378
0.018522
0.02
0.1
20
96.34
5.
Segment-6
0.03752
0.1654632
0.173
1.23
15
96.34
6.
Segment -7
0.2323
0.6260405
0.658
13.1
5
94.54
Figure -4: Gradient of specific enthalpy & heat due to auto compression and relative humidity from Pit No. 2
bottom to XI seam working with distance
Figure depicts that total specific enthalpy due to addition of heat of auto compression is almost equal to the specific
enthalpy as calculated by the formulas. In this case the specific sigma heat i.e. the dry heat obtained from the
simulation of the field data is less than that of the specific enthalpy. This may be due to the evaporation of water.
5.2 Computer simulation of climatic condition of ventilation circuit
The climatic condition of intake airways was simulated using software“PREDCLIM based on radial variation in
temperature around the incremental length of airway[16] . In the software input parameters are: (i) area of cross-
section, m2 , (ii) perimeter, m, (iii) airway length, m, (iv) depth from any assumed datum of inlet of airway, m, (v)
depth from any assumed datum of outlet of airway(m), (vi) distance interval at which results are required, m, (vii)
94
94.5
95
95.5
96
96.5
97
97.5
0
2
4
6
8
10
12
14
0500 1000 1500 2000 2500
Relative humidity (%)
Heat(kJ/kg)
Underground length(m)
Graph showing the variation of relative humidity with specific enthalpy and heat due to
auto compression in inclined roadways
Addition of heat
due to auto
compression
(kJ/kg)
Specific enthalpy
(kJ/kg)
reiative humidity
%

10
thermal conductivity of the rock, W/mK, (viii) thermal diffusivity of the rock, m2/hr, (ix) friction factor in SI units,
(x) average wetness of the airway in fraction , (xi) geothermic gradient, m/K, (xii) virgin rock temperature, deg .0C,
(xiii) dry bulb temperature of air, deg . 0C, (xiv) wet bulb temperature of air, deg. 0C, (xv) barometric pressure, kPa,
(xvi) airflow rate, m3/s, (xvii) distance of heat source from airway inlet, m, (xviii) starting distance of linear heat
source from airway inlet, m, (xix) running length of linear heat source, m, (xx) total sensible heat load, kW, (xxi)
total latent heat load, kW. The values of parameter s segment wise were taken from table (1-3). The wet and dry
bulb temperatures of air at the entry of the working ( XI seam by increasing overall air quantity in each segments by
40%. were predicted. The results are furnished in Table-9. Similarly, wet and dry bulb temperatures of air at the
entry of the working ( XI seam by increasing overall air quantity in each segments by 40% with the value of heat due
to auto compression as an additional heat source ( kW) in each segment ( table-5&6) were also predicted The results
are furnished in Table-9. The required air quantity in the ventilation circuit was achieved by introducing Booster fan
in main return. The result of investigation after installation of booster fan are also furnished in table-9
Table – 9: Result of simulation of ventilation circuit without considering auto compression
The following points are emerged from field investigation and computer simulation studies:
1. The ventilation circuit of length 2405 m comprising seven segments from surface to XI seam
working at depth of 542.2m is taken into consideration in this study.
2. The addition of specific enthalpy due to auto compression in segment -1(Pit No.2; depth 374,8m)
is measured of the order of 4.24 kJ/kg. This is about 31% of the total enthalpy (i.e. of the order of
13.61 kJ/kg).
3. The wet & dry bulb temperatures with air quantity 26.2 m3/s predicted by computer simulation
studies without considering the effect of auto compression is of the order of 30.030c % 30.50c
respectively.
4. The wet & dry bulb temperatures with air quantity 26.2 m3/s predicted by computer simulation
studies considering the effect of auto compression is of the order of 30.420c % 31.380c
respectively.
5. The wet & dry bulb temperatures with air quantity 26.0 m3/s measured is of the order of 30.50c %
31.50c respectively.
6. Hence the result of measurement of wet & dry bulb temperatures and the values predicted by
computer simulation studies considering the effect of auto compression are almost same.
Segment-
No
Predicted
Measured
Without considering Auto
compression
Considering Auto compression
Air
quantity
(m3/s)
dbt(0C)
wbt(0C)
Air
quantity
(m3/s)
dbt(0C)
wbt(0C)
Air
quantity
(m3/s)
dbt(0C)
wbt(0C)
Segment-2
44.5
29.01
28.77
44.5
30.61
29.97
44
30.5
29.5
Segment-3
43.7
29.17
28.85
43.7
30.91
30.51
44
31
30.5
Segment-4
43.2
29.18
28.88
43.2
30.94
30.62
42
31.5
30.5
Segment-5
43.2
29.65
29.20
43.2
31.04
30.73
41
0.5
31
Segment-6
43
29.55
29.22
43
31.24
30.8
40
31.5
31
Segment-7
26.2
30.50
30.03
26.2
31.38
30.42
26
31.5
30.5

11
7. CONCLUSION
From the results of investigation and computer simulation studies it may be concluded that for realistic estimation of
air quantity requirement for deep mines (i.e. >300 m) consideration of heat due to auto compression is necessary.
8. Acknowledgements
The authors would like to express their deep gratitude to AcSIR (Academy of Scientific and Innovative research) for
providing the onsite training programme in mines, to the mine officials of no-2 pit of Jamadoba colliery, Tata Steel
Ltd.
9. REFERENCES
1. T.C 9.2 Industrial air conditioner, chapter-27, Mine air conditioning and ventilation, American society of
heating, refrigeration and air conditioning engineers (ASHRAE-handbook), HVAC application,pp-27.2.
2. Ramani R. V. (1992). Personnel Health and Safety, Chapter 11.1 SME Mining Engineering
Hand Book, 2nd Edition Volume 1, H. L. Hartman Senior Editor, pp. 995 -1039.
3. http://books.google.co.in/books/about/Mine_Ventilation_and_Air_Conditioning.
4. Hartman, H L, Mutmansky, J M and Ramani, R V, 1997. Mine ventilation and air conditioning. New York:
John Wiley.
5. Banarjee, S.P, Auto compression of mine air, Chapter- 4, Mine Ventilation, Textbook, Lovely prakashan,
Dhanbad, 1986, page- no- 127.
6. Mishra, G.B, auto compression, chapter-iii, Mine environment and ventilation, textbook, Oxford University
press publication, 1986, Pp-160-162.
7. Vutukuri, V.S, Lama, R.D, Adiabatic compression, Chapter- 7, Environmental engineering in mines,
Textbook, CAMBRIDGE UNIVERSITY PRESS, 1986, page-no- 217-218.
8. Mishra, G.B, auto compression, chapter-iii, Mine environment and ventilation, textbook, Oxford University
press publication, 1986, Pp-160-162.
9. Banarjee, S.P, Auto compression of mine air, Chapter- 4, Mine Ventilation, Textbook, Lovely prakashan,
Dhanbad, 1986, page- no- 127-128.
10. T.C 9.2 Industrial air conditioner, chapter-27, Mine air conditioning and ventilation, American society of
heating, refrigeration and air conditioning engineers (ASHRAE-handbook), HVAC application,pp-27.2.
11. Navarro, Vidal F. Torres, Singh, N. Raghu, 2003, Thermal state and human comfort in underground mining,
intech open publication, pp-592.
12. Hartman .L Howard, Mutmansky, .M Jan, Ramani, R.V, Wang, Y.J Auto compression, Chapter – 16, Mine
Ventilation and Air conditioning, Textbook, John Wiley & sons publication 1997,page-no -587.
13. Navarro, Vidal F. Torres, Singh, N. Raghu, 2003, Thermal state and human comfort in underground mining,
intech open publication, pp-595.
14. Vutukuri, V.S, Lama, R.D, psychometrics of air-water vapour mixtures, appendix iii, Environmental
engineering in mines, Textbook, Cambridge university press, 1986, page-no- 485.
15. Navarro, Vidal F. Torres, Singh, N. Raghu, 2003, Thermal state and human comfort in underground mining,
intech open publication, pp-595.