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Oct. 15, 1946. ‘
Filed Aug. 18, 1942
, \w
John PrIQQ, @QS
(Eng/‘4 WI;
Patented Oct. 15, 1946
John Price Rees, Johannesburg, Transvaal,
Union of South Africa
Application August 18, 1942, Serial No. 455,268
'In the Union of South Africa July 4, 1942
6 Claims. >(Cl. 98--50)
This invention relates to conditioning the at
mosphere of subterranean excavations and par
ticularly deep mines. Essential requisites of such
depth of downcast travel. It is moreover inde
pendent of the kind of gases of which the Ven
tilating current is composed.
an atmosphere are that it be maintained in re
Some limitation of the temperature rise at the
lower termination of the downcast system has
in practice been attained by pre-cooling the ven
tilating air at the surface where the extracted
heat can readily be disposed of to the earth’s at
mosphere; but it seems that the limit of-tem
perature reduction that can economically be at
tained in this way amounts to about 10 degrees
spirable condition in the sense of preserving the
proper pro-portion of its physiologically active
constituents to its diluent and physiologically
inert constituents, and ensuring the removal of
deleterious substances such as phthisical dust and
gaseous products of blasting; and further that its
temperature, with regard to its cooling e?ect
upon human beings working in it, be kept from
rising to a level at which persons cannot work
with a reasonable degree of, efficiency and may
Fahrenheit; su?icient, when the temperature
gradient is ‘of the order of l‘degree Fahrenheit
per 200 feet of depth, to extend the feasible
depth oimining by about 4,000 feet.
The present invention attacks the autocom
pression problem in a different manner, by tak
ing account of the fact that whilst the quantity
of heat developed by autocompression is virtual
even be in danger of physical collapse.
The maintenance of the atmosphere in the
respirable condition mentioned above can ‘ be
effectively carried out by ventilating currents of
su?icient volume drawn. from and returned to the
earth’s atmosphere.
As regards the heat‘ problemrthe ventilating
air undergoes ariseof temperature due to acquir
ing heat from two principal sources, viz. (a)
heat inflowing from the rock, which is at atem
perature higher than that of the earth’s atmos
phere from which the ventilating current is de
rived; and (b) the heat due to the autocompres
sion of the ventilating air. In ‘the process of
ly~beyond control, the‘temperature rise clue to
the heat of autoco'mpression can be lessened by
increasing the‘ speci?c heat of the ventilating
current. ~ For this purpose there is substituted
‘ for the normal air that is passed vintothe mine
and forms the mine atmosphere, a respirable gas
mixture having a higher speci?c heat than that
of normal air; so that with a given quantity of
. heat added to such substitute atmosphere‘ the‘
autocompression, the air descending the down
temperature rise is less, in correspondence with
cast shaft moves towards the centre of the earth 30 the greater ‘capacitay for heat of the substitute
and is thereby made denser by the -correspond—
atmosphere.‘ More speci?cally, since any‘ respir
ing increase of the mass of air lying above it;
ableatmosphere must contain oxygen and car
the energy which thus appears as increased
bon dioxide in invariable proportions within
denseness of the air and heat being the poten
small limits diluted with a physiologically inert
tial energy that the air has parted with during
gas, the change made by the invention consists
its descent.
in substituting the nitrogen of the normal at
Rise of temperature of the mine atmosphere
mosphere partly or completely by a similarly
due to cause (a) can be and is being kept within
physiologically inert gas, but one which has a
control by such means as making the split ven
higher speci?c heat than nitrogen. Hydrogen
tilating currents ample enough to sweep away 40 for instance which has a specific heat about
the heated air as it is formed; and to some‘ex
fourteen times that of nitrogen, and which is
tent by employing heat pumps to extract‘the heat
physiologically inert, could be used under condi
from small local areas of the mine where work is
tions that would preclude chemical combination
actually going on and conveying away the ex
of the hydrogen with the necessary quota of
tracted heat in a manner that avoids re-heating 45 oxygen. But under present circumstances the
of the downcast air.
most‘ suitable gas is helium, which has been
The control of temperature rise due to auto
V proved‘ to be physiologically suitable, and even
compression is however a problem of a different
bene?cial as compared with nitrogen‘; is available
kind. The heat developed inthis way cannot
in large quantities; is inert chemically in regard
for instance be swept out by increasing the ven
to oxygenand carbon dioxide; and is obtainable
tilating current since the heat is developed in
‘at a cost that renders its use an economic pos
the ventilating air itself and each unit mass of‘
sibility; Its speci?c heat is favourable; the
air that descends the shaft develops its own
specific heat of helium air—viz. air ‘in which
quota of heat; the only variable factor that in
nitrogen has been wholly replaced by helium-be
?uences the ‘amount of heat being the vertical 55 ing 0.57 as compared with 0.24 for normal nitro
gen air, at the same pressure. The temperature
of helium air would therefore rise about 2.2 de
grees Fahrenheit per 1,000 foot depth; apart from
the cooling effect of evaporation from Wet sur
faces. Such evaporation would cool helium air
rather more than it cools an equal volume of
ordinary air and the rise in wet bulb tempera
ture would be less than with ordinary air. For
is preferred in the present case to ensure its ab
sence by using an innocuous explosive such as
liquid oxygen for the purpose of breaking rock.
Further plant that may advantageously be in
cluded in the duct I5 is that indicated by 2!, the
function of which is to effect the known surface
cooling of the ingoing ventilating current with
the object of lowering the temperature of the
atmosphere in the mine workings. Without the
instance at 12,000 feet the wet bulb temperature
would be about 60° F. the surface wet bulb tem 10 reduction of temperature by means of the present
invention it is not-as mentioned above-feasible
perature being 50° F.
. M
to effect much reduction of underground temper
Experience gained in connection with the Wit
atures by surface cooling without the great ex
watersrand mines suggests the addition of about
pense involved in providing a cooling plant using
10° F. for uncontrolled heating in the shaft 1. e.,
brine as the cooling medium; but the cooling
a little from the rockwalls and the rock being
brought about by the invention, added to the sur
hoisted, from hoists, from water being pumped
face cooling which can be cheaply effected when
out etc., giving an estimated temperature of 70°
the cooling medium is kept above the freezing
F. wet bulb on the shaft station on the average
temperature of water, enables a substantial cool
for the year.
ing effect to be produced underground at moder
The above calculation indicates that in order
ate expense. to extend the depth of mining to about 12,000
In the operation of the ventilating system, us
feet vertically below the surface, it would not be
ing helium air in which all the nitrogen is re
necessary to replace all the nitrogen in the air
placed by helium, the helium air would reach
by ‘helium. In practice the amount of helium
the surface at a higher temperature than ordi
may be adjusted to give comfortable conditions
nary upcast air due to the reversal in the upcast
for mining with minimum outlay on helium. For
l2 of the autocompression occurring in
example, gas mixture consisting of approximate
shaft H. For example, for a certain mine depth
ly 40% helium by volume, 40% nitrogen, 20%
at which ordinary upcast air would be expected
oxgen', together with a small proportion of car
bon ‘dioxide would have a speci?c heat of ‘0.32.
The wet bulb temperature would be, therefore,
about 80° F. at 12,000 feet on the shaft station.
'In view of the monetary value of the helium it
is important that the mine ventilating system be
constructed as a closed circuit that retains the
v to arrive with a temperature of 70 to 75° F., the
helium air would arrive with a temperature of
about 80° F. This excess over about 70° is how
ever easily dealt with at low cost by sprays and
cooling towers and without refrigeration. If the
cooler 2! is arranged to cool the current from
about 70° saturated to about 50° saturated, the
resulting gas temperature at 12,000 feet would
helium with a minimum of loss whilst providing
for there-conditioning of the gas mixture coming
as a consequence be reduced by about 30° F. in
from the'upcast to render it suitable for return
the case of helium air as compared with about
to the mine. In particular, it is necessary to dis
charge from the exhaust current the heat it has 40 10° F. in the case of ordinary air.
The conversion of an ordinary mine atmos
acquired from the mine workings: to make up
phere to the atmosphere of the invention offers
oxygen consumed and helium lost; and to remove
no outstanding di?iculty since it involves no
deleterious substances. Such a circuit is shown
change in the respirability of the atmosphere.
in the accompanying drawing which is a diagram
matic section through the mine. Therein ID in 45 It wouldbe necessary to continue the normal
procedure of discharging the upcast ventilating
dicates workings in which persons are engaged in
current to the open air while the helium is being
mining. II is a shaft which gives access to said
introduced into the downcast current. Loss of
working and is also the downcast shaft of the
helium in such exhaust would be vminimized by
ventilating system. I2 is the upcast shaft of the
having large quantities of helium stored atthe
system; and I3 is a ventilating fan which may be
surface and introducing it as rapidly as possible,
positioned at the foot of the upcast shaft with the
so that current-from the upcast shaft can be di
object of setting up a plenum in the latter and
verted as soon as possible into the conduit I5
thereby preventing leakage of normal air into
and the discharge of such current to atmosphere
the ventilating atmosphere.
I4 indicates the surface of the mine, where 55 simultaneously terminated.
I claim:
there isv erected an enclosing structure [5 forming
1. A closed circuit mine ventilating systemin
a duct through which the gas discharge from
cluding mine workings, downcast and upcast
the upcast shaft I2 is passed to the downcast shaft
shafts connected with said workings, means dis
II. Said structure l5 encloses the headgear I6
and is provided with an airlock I‘! through which 60 tant from the workings for discharging heat from
gas in the circuit, and means for injecting into
tra?ic to and from shaft H can pass with mini
the circuit a respirable inert gas which com
mum leakage of gas into or from the closed cir
prises helium in a proportion of at least about
40% by volume.
Said structure l5 also includes means indicated
2. A process of conditioning a mine atmos
generally by [8 by which rock dust, smoke and 65
phere so as to minimize heating of the downcast
soluble gases given off in the mine are removed
ventilating current due to its autocompression,
by water sprays l9, which may also cool the air
to some extent. 20 indicates further means
through which the gas current passes for the
which process comprises the step of passing into
the _mine to provide the atmosphere therein a
addition thereto of make up oxygen and helium, 70 non-explosive respirable gas mixture containing
the substantially normal atmospheric proportion
and for the removal of excess carbon dioxide.
of oxygen and in which the normal nitrogen con
Carbon monoxide is a constitutent of the exhaust
tent of atmospheric air is replaced by a diluent
current from a mine in which nitroglycerin and
gaseous component selected from the group con
similar explosives, are used; but as that gas is
dif?cult to remove from a ventilating current, it 75 sisting of hydrogen, helium, and the nitrogen
helium mixtures containing at least 50% by vol
ume of helium under ‘conditions which preclude
interaction between the components of said re
spirable miXture.
3. A process of conditioning a mine atmos
phere so as to minimize heating of the down
cast ventilating current due to its autocompres
a subterranean excavation having a depth of at’
least about 10,000 feet, which process comprises
the step of passing into the excavation to provide
the atmosphere therein at substantially atmos
pheric pressure at earth surface level a respirable
gas mixture containing the substantially normal
atmospheric proportion of oxygen and in which
the normal nitrogen content of atmospheric air is
sion, which process comprises the step of passing
replaced to at least 50% of its volume by helium.
into the mine to provide the atmosphere therein
6. A process of conditioning the atmosphere of
a non-explosive respirable gas mixture contain 10
a subterranean excavation having a depth of at ,
ing helium to at least about 40% of its volume.
4. A process of conditioning the atmosphere of
least 10,000 feet, which process comprises pass
ing into the excavation to provide the atmos
a subterranean excavation having a depth of at
phere therein at substantially atmospheric pres
least about 10,000 feet, which process comprises
the step of passing into the excavation to provide 15 sure at earth surface level a respirable gas mix
ture containing the substantially atmospheric
the atmosphere therein at substantially atmos
proportion of oxygen and in which the normal
pheric pressure at earth surface level a respirable
nitrogen content of atmospheric air is replaced
gas mixture containing the substantially normal
atmospheric proportion of oxygen and in which
to at least about 50% of its volume by helium,
the normal nitrogen content of atmospheric air 20 circulating said gas mixture through a closed cir
is replaced by a diluent gaseous component se
cuit, cooling said mixture at at least one point of
said closed circuit and removing from said mix
lected from the group consisting of hydrogen,
helium, and the nitrogen-helium mixture con
taining at least 50% by volume of helium whilst
preserving in said excavation conditions which
preclude chemical interaction between the com
ponents of said respirable mixture.
5. A process of conditioning the atmosphere of
ture at at least one point of said closed circuit
such carbon dioxide as may be in excess of the
substantially normal atmospheric proportion of
carbon dioxide.
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