Mine Planning and Equipment Selection 2002
MEASUREMENTS OF GASEOUS NITROGEN VOLUMETRIC FLOW RATE IN
PIPELINES
A. Adamus
alois.adamus@vsb.cz; http://www.vsb.cz/nitrogen; Institute of Mining Engineering and Safety, VSB-Technical
University Ostrava, Czech Republic
ABSTRACT: Pure nitrogen has been used for repression and prevention of mine fires for more than fifty years. In
several mines individual mobile sources of nitrogen have been replaced with central gas pipelines, which provide
nitrogen volumes necessary for repression and prevention of mine fires. Measurement of volumetric flow rate in
pipelines is required by optimisation of this inert-medium supply, especially for prevention purposes; the more so if pipe
branches distribute nitrogen to several workplaces. This article deals with measurements of nitrogen volumetric flow rate
in the area of mining safety.
1 INTRODUCTION
France (H.B.L), Bulgaria (Bobov Dol) and the Czech
Republic (the OKR Coal Basin) are among countries with
sophisticated mining systems in which gaseous nitrogen is
brought to mines via centralised pipeline distribution
systems. Such systems usually work in one of the two
basic modes: continuous preventive flow rate of 0.55 –
1.94 m3.s-1 and emergency (fire-extinguishing) volumetric
flow rate of up to 5.0 m3.s-1 and time intervals up to 10
hours. Photographs of and more detailed information
concerning nitrogen-distribution systems can be found at
the website [1]. Volumetric flow rates in emergency
modes usually depend on the capacity of liquid nitrogen
evaporators and technical conditions of nitrogen
transportation through pipelines. Measurements of
volumetric flow rates are required by nitrogen suppliers
for invoicing purposes. Moreover, measurements of
volumetric flow rates in pipe branches operated in
preventive modes provide source information for
regulation and optimisation of inert-medium supply to
working faces. Such optimisation is described in the
literature, e.g. [2, 3, 4, 5].
Volumetric flow rate in mines can be measured by
centric orifice gauges, free-float flowmeters, turbine gas
gauges, vortex-sensor measurement stations and
temperature and pressure sensors. The free-float
flowmeters are mostly used as parts of larger
technological units, such as PSA (Pressure Swing
Adsorption) molecular sieves. The centric orifice gauges,
free-float flowmeters, turbine gas gauges and vortexsensor measurement stations are used in pipelines both
under and above ground. The vortex-sensor measurement
stations are, in the Ostrava-Karviná Mining District (in the
Czech part of the Upper Silesia Coal Basin), mainly used
in aboveground distribution points of centralised gaseousnitrogen networks; and also underground in recent years.
Volumetric flow rates of gases in pipes are often recalculated to the international reference status values, i.e.,
temperature of 0°C and pressure of 101.325 kPa. The
devices measuring volumetric flow rates of gaseous
nitrogen in the Ostrava-Karviná Mining District in the
Czech part of the Upper Silesia Coal Basin are set to
reference values for re-calculating the volumetric flow
rate of gaseous nitrogen to a temperature of 15°C and
pressure of 101.325 kPa. Units different from the SI base
units are also used in practice: volumetric flow rates of
gaseous nitrogen for preventive supply of inert medium
are usually expressed in m3.h-1; and m3.min-1 is often used
in fire repression. Calculations in the present paper are
derived for international standard SI units.
2. CENTRIC ORIFICE GAUGES
Centric orifice gauges are mainly used for degasation
in mines. Accuracy of measurements with the aid of the
centric orifice gauges is affected by moisture and
contamination present in degasation pipes. Nitrogen
measurements are different in this aspect: nitrogen used in
mines is relatively clean and dry. Centric orifice
measurements are based on evaluation of the pressure
difference created by the orifice installed in the gas flow.
Details concerning design of orifices and evaluation of
measurements can be found in literature [6, 7]. The
volumetric flow rate in a pipe can be calculated as
follows:
Q  1,108778  D 2  m  α 
V
where:
QV
D
m

p

p

,
(1)
– volumetric flow rate of gas, m3.s-1;
– orifice's outer diameter
(bore diameter of pipe), m;
– contraction coefficient (d/D)2,
(d – orifice's inner diameter , m), – ;
– flow coefficient depending on the contraction
coefficient m, [6], Fig. 1, – ;
– pressure difference on orifice, Pa;
– density of gas in pipe, kg.m-3.
The gas density depends on temperature and pressure at
the measurement point, hence it must be adjusted to the
STP standard conditions:
Mine Planning and Equipment Selection 2002

n

p
T
m  n 1
p
T
k
n
m
,
(2)
Graph of the flow coeffcient 

0,82
0,78
where: 
n
pn
pm
Tn
Tm
k
– density of gas in pipe, kg.m-3;
– normed density of gas
(1.2505 kg.m-3 for nitrogen);
– normed (STP) pressure, 101325 Pa;
– absolute pressure of gas on orifice's
input side, Pa;
– normed absolute temperature
(273.15 K);
– absolute temperature at the
measurement point, K;
– coefficient characterising deviation
of the particular gas from ideal gas, – .
The k coefficient, characterising deviation of the particular
gas from the ideal gas is close to 1 under the relevant
temperature and pressure conditions and can be ignored
[6]. Substituting in (1) according to (2) we get the
following formula for gaseous nitrogen:
Q
VN 2
 19,097  D 2  m  α 
p  (273,15  t )
p
m
,
(3)
where: QVN2 – volumetric flow rate of gaseous
nitrogen, m3.s-1;
t
– temperature of gaseous nitrogen
at the measurement point, °C.
0,74
0,70
0,66
0,62
0,58
0,05
0,15
0,25
0,35
0,45
0,55
0,65
m
Fig. 1. Flow coefficient  according to [7]
Experience with measurements of gaseous nitrogen
volumetric flow rate with the aid of centric orifice gauges
has been gathered in the "Důl Darkov" Colliery, OKD,
a.s. in Karviná, in the Ostrava-Karviná Mining District in
the Czech part of the Upper Silesia Coal Basin. The
100/80 centric orifices have been used for such
measurements in two to three pipe branches since 1993.
The measured values were checked by the Colliery's
rescue service workers with the aid of "U" tubes. Remote
registration of pressure values from an electronic pressure
sensor has also been used. The 100/80 centric orifices
have been established as reliable up to volumetric flow
rate maximum values of 1500 m3.h-1 with accuracy up to
10% (as compared with Rombach turbine-flow rate-meter
readings). A 100/80 mm centric orifice is shown in Fig. 2.
Formula (3) can be adjusted to the conditions of
particular measurements: For example, we can measure
the volumetric flow rate in a pipe bringing nitrogen to a
goaf space underground with the aid of a centric orifice
whose outer diameter is 100 mm and inner diameter is 80
mm (Fig. 2). The contraction coefficient value is m = 0.64
and the flow coefficient value is = 0.765, [7], cf. the
graph in Fig. 1. Adjusting (3) to the said conditions we
get:
Q
VN 2
 0,093498 
p  (273,15  t )
p
m
,
(4)
Temperature and pressure gauges are installed at a
distance of at least 5D and 7D from the centric orifice. If
the underground temperature is stable, temperature
measurement can be omitted and the constants
temperature can be substituted in the formula.
Fig. 2. Centric orifice, 100/80 mm
One of the coal mining districts abroad in which
nitrogen supplies within a centralised system take place is
(Houilleres du Bassin de Lorraine) in France. An
"Azoduct" nitrogen-supply centralised system has been
operated there since 1983. The total length of the system's
pipelines is 70 km. The nitrogen comes from the Air
Liquide plant in Richemond. The maximum volumetric
Mine Planning and Equipment Selection 2002
flow rate is 3.33 m3.s-1 and is applicable to repression of
mine fires. Preventive-inertisation flow rate is 0.55 – 0.83
m3h-1 per longwall face. A 200 m3 liquefied nitrogen tank
is installed on the route (at St. Fontaine) to cover H.B..'s
needs in case of stoppage. Volumetric flow rate values are
measured at the central point and in individual branches
with the aid of centric orifices, and temperature and
pressure measurements are taken as well. The measured
values are electronically transmitted to the control centres.
The underground measurements of volumetric flow rate
sum up to a value that is about 10% lower than that
measured on the surface – the difference is due to nitrogen
losses caused by leaking pipes. The Merlebach Colliery in
Freiming-Merlebach is equipped with remote control of
servo-operated valves, which enable regulation of
nitrogen volumetric flow rate in the underground pipe
branches. Fig. 3 shows a distribution measurement station
of the Reumax Colliery; the station is equipped with
centric-orifice gauges and remote transmission of
measured values. The station has two parallel
measurement branches, suitable for measuring both low
flow rate values for prevention and high flow rate values
for fire repression.
Fig. 3. Gaseous nitrogen measurement station on the
surface, at the Reumax Colliery in H.B.L.
3. TURBINE GAS METERS
In the Ostrava-Karviná Mining District in the Czech
part of the Upper Silesia Coal Basin, the centralised
nitrogen-supply system was put into operation in April
1993; the surface distribution stations were equipped with
TZ Rombach (J. B. ROMBACH GmbH & Co. KG of
Karlsruhe, Germany) turbine gas meters then. However,
their operation was often faulty due to freezing and
mechanical damages caused by contamination which
remained in pipes after commencement of operation. The
turbine gas meters at surface measurement points were
replaced with Vortex sensors made by the Japanese
company Yokogawa. A TZ 80/G 250 Rombach turbine
gas meter remained in operation underground, in a branch
interconnecting two mines. It is used for measuring
nitrogen flow rate in preventive mode – a bypass pipe
branch is used if the fire-repression mode is activated. On
the gas meter input there is a safety ball valve (the type
usually used in degasation), protecting the gas meter from
contamination.
Fig. 4 TZ 80/G250 Rombach turbine gas meter in the
underground of the "Důl Darkov" Colliery in Karviná, the
Ostrava-Karviná Mining District in the Czech part of the
Upper Silesia Coal Basin
The TZ 80/G250 gas meter is equipped with an 80mm-diameter axial runner turbine. Rotation of the runner
wheel is transmitted via a worm-gear drive to an
evaluation unit with remote transmission of measured
values. The gas meter's pipe body is a pressure unit,
whose length is three times the nominal diameter; the
unit's input goes via flanges equipped with an
aerodynamic rectifier. The rectifier's design is such that it
ensures, from the aerodynamic point of view, optimum
gas supply to the runner wheel even under difficult
installation conditions. The nominal range of the
TZ 80/G250 gas meter's measurements is 0.0055 –
0.11 m3.s-1. The measurement station is further equipped
with temperature and pressure measurement points, from
which the values are transmitted to control centres on the
surface. The distribution equipment includes a remotely
servo-controlled valve, regulating the volumetric flow
rate; this valve is installed after the gas meter. Under the
current conditions, the turbine gas meter has worked
reliably to date – there has been only a single defect in the
entire period from 1993 to 2001.
The Rombach Company supplies the TZ gas meters in
diameters ranging from 50 to 600 mm, to which the range
of the measured pressures from 0.0022 to 4.44 m3.s-1
corresponds.
4. VORTEX SENSORS
Vortex flow rate meters have no moving parts. They
are based on evaluation of turbulent vortices that
alternately occur on both sides of a body immersed in a
fluid flow (the so-called Karman vortices). Vibrationgenerating turbulent vortices are transformed to electrical
quantities (voltage, current, or frequency) on the basis of
Mine Planning and Equipment Selection 2002
the piezoelectric principle or ultrasound; from these the
flow rate is derived. The vortex flow rate meters are used
to measure volumetric flow rate in combination with
temperature and pressure measurements.
In 1994 the above-described turbine gas meters at the
surface measurement points were replaced with Vortexsensor gauges supplied by the Yokagava Company
(www.yokogawa.com). Fig. 5 shows one of the five
Yokagava measurement stations of gaseous nitrogen
installed in the Ostrava-Karviná Mining District.
Fig. 5 Yokogawa nitrogen measurement gauge on the
surface at the “Doubrava" Colliery in Doubrava, the
Ostrava-Karviná Mining District in the Czech part of the
Upper Silesia Coal Basin
The station contains a YF 100 Vortex sensor, a YA 53
pressure sensor, a PT 100 temperature sensor, and an
evaluation unit YFCT (Yokogawa Flow Computing
Totalizer). The YF 100 sensor puts a vortex-generating
trapezoidal body in the way of the flow; vibrations of the
trapezoidal body are registered by two piezoelectric
sensors integrated in the body. The maximum measured
velocity is 80 m.s-1; the minimum measured velocity is
given by the Reynolds number, which equals 5000. For
normal operational conditions (i.e., pipe diameter of 100 –
200 mm and pressure at the measurement point of 0.3 –0.6
Mpa), the lower bound of measurable velocity is 3 –
6 m.s-1. Measurement accuracy is, for the impulse output,
at ± 1.0% of the actual value up to 35 m.s-1 and ± 1.5% for
the actual velocity from 35 to 80 m.s-1. If the output is
analog, the deviation must be increased by ± 0.1% of the
total range. The temperature bounds are from – 40°C to +
80°C for the basic design. By the manufacturer's
recommendation, a vortex sensor should be installed at a
distance of 10 D from a change-point of the flow profile
in the input side and at least 5D on the output side. The
temperature and pressure measurement points should be
on the output side, 2 – 7 D from the vortex senor for
pressure measurements and 6 – 8 D for temperature
measurements. The YFCT evaluation unit has a number of
parameters that can be adjusted, including volumetric
units. The gaseous nitrogen volumetric flow rate
calculation can be set to the STP normed values, or
selected reference values of temperature, pressure and
relative humidity. A dimensionless coefficient can be set
which characterises deviation from the ideal gas (called
"deviation coefficient"). The reference values for
distribution and measurements of volumetric flow rate in
the Ostrava-Karviná Mining District in the Czech part of
the Upper Silesia Coal Basin are determined as follows:
temperature 15°C, STP absolute pressure 101.325 kPa,
and 0% relative humidity. The deviation coefficient is set
to 1. The Yokogawa flowmeters have been found very
reliable and accurate; five such measurement stations have
been operated without any defects in the Ostrava-Karviná
Mining District at the end of 2001. (Collierys: "Důl
Dukla" in Havířov, "Důl Lazy" in Orlová , "Důl
Doubrava" in Doubrava, "Důl ČSA" in Karviná, and "Důl
Darkov" in Karviná.) The Yokogawa Company is now
supplying a new type of flowmeter, which is more
resistant to vibrations and has a higher measurement range
and smaller length. The new features make use of spectral
analysis of the flowmeter's frequency signal. Yokogawa is
the only company that has applied this sophisticated
technology; such flowmeters have been available since
2001.
For measurements of gaseous nitrogen volumetric
flow rate underground with the aid of Vortex type
flowmeters in the Ostrava-Karviná Mining District in the
Czech part of the Upper Silesia Coal Basin, sensors made
by the British Trolex Company have been used
(www.trolex.com). The Trolex Vortex flowmeters
evaluate the quantity of vortices generated on passage
over an obstacle, which quantity is measured by an
ultrasound sensor. First such sensors were used in the
Collierys "Důl Lazy" in Orlová and "Důl Darkov" in
Karviná. The first measurement in the "Důl Darkov"
Colliery in Karviná used a Trolex TX 1321 flowmeter (a
model without a display). The measurement range was
from 0.5 to 30 m.s-1. The Trolex Company currently offers
the TX 5920 series flowmeters, based on the same
principle. TX 5921 and TX 5922 models have compact
workmanship and a 17-digit alphanumeric LCD display.
Each flowmeter is equipped with programmable setting of
parameters, including calibration. The LCD display shows
the currently measured value in the selected units, and
other data. The measurement range can be selected as 0.5
– 5 m.s-1, or 0.5 – 30 m.s-1, with ± 2% accuracy and ± 1%
linearity; in the basic design, the operational temperature
range is form –15°C to + 50°C.
The Trolex Company also offers programmable
analog pressure sensors for system applications, equipped
with a TX 6140 display. A TX 8141 absolute pressure
gauge with the measurement range of 0 – 0.5 MPa is
suitable for pressure measurements in secondary pipe
branches. Its parameters are: ± 0.25% overall
measurement accuracy ,
± 0.5% long-term annual
stability, ± 0.25% linearity, ± 0.06%°C-1 temperature
stability, environment temperature limits from –10°C to
+50°C, relative humidity 0 – 95% non-condensing, 17digit alphanumeric LCD display; the gauge is
microprocessor-controlled.
Mine Planning and Equipment Selection 2002
The sensors are situated in compliance with the above
layout. The velocity sensor's head must be centred with
respect to the flow direction at one-third of the pipe
diameter. The sensors can be operated with a logicalparent microprocessor system, e.g., data concentrator
Transmitton HB-2, HD, Venturon VAL, Trolex TX 9042,
or a Czech-made MTA-PNS measurement exchange. Fig.
6 shows the TX 5922 flow velocity and TX 6141 absolute
pressure sensors.
Fig. 7 Gaseous nitrogen measurement pipe segment on
the 8th floor of the "Důl Lazy" Colliery in Orlová, the
Ostrava-Karviná Mining District in the Czech part of the
Upper Silesia Coal Basin
Fig. 6 Trolex sensors – TX 5922 type for flow velocity
measurements (on the left), TX 6141 type for absolute
pressure measurements (on the right)
Fig. 8. Venturon VAL 101 concentrator installed on the
8th floor of the "Důl Lazy" Colliery in Orlová, the
Ostrava-Karviná Mining District in the Czech part of the
Upper Silesia Coal Basin
Qvn2 [m 3h-1]
1400
1200
1000
800
600
400
200
21.5.01
19.5.01
17.5.01
15.5.01
13.5.01
11.5.01
9.5.01
7.5.01
5.5.01
0
3.5.01
The described Trolex sensors were used in May 2001,
for experimental monitoring of goaf inertisation by
gaseous nitrogen of longwall face no. 138 202 in the the
"Důl Lazy" Colliery in Orlová, the Ostrava-Karviná
Mining District in the Czech part of the Upper Silesia
Coal Basin. The sensors were installed in the 100-mm
diameter pipe segment recommended by the
manufacturer. The segment was installed on the 8th floor,
in a nitrogen distribution pipe branch to longwall face
no. 138 202, near the hoisting step of the first pit (Fig. 7).
Temperature of flowing nitrogen was not measured and
was taken for constant (20°C). On the 8th floor, the sensors
were connected to a local Venturon concentrator, type
VAL 101 (Fig. 8). The concentrator was equipped with
evaluation system of electrical quantities, and derived
velocity and pressure readings from such quantities. The
measured data were transferred by the monitoring system
to the central control room on the surface and
continuously recorded.
The Venturon system recorded the measured data in
electronic form once per minute. The time evolution is
depicted in Fig. 9.
The measurement equipment and the gaseous nitrogen
pipe branch were in test operation from May 3, 2001, to
May 16, 2001. Old flushing pipe was used for nitrogen
transportation, whose permeability and tightness required
repairs. In the period from My 16, 2001 to May 21, 2001,
the gaseous nitrogen volumetric flow rate was regulated
between 1,000 and 1,200 m3.h-1. The total consumption of
gaseous nitrogen during the experiment was 191,000 m3.
t
Fig. 9. Time evolution of gaseous nitrogen consumption
during inertisation of goaf space at face no. 138 202, the
"Důl Lazy" Colliery in Orlová, the Ostrava-Karviná
Mining District in the Czech part of the Upper Silesia
Coal Basin
Mine Planning and Equipment Selection 2002
From the graph, the preparation period (May 3 – May
16, 2001) and the goaf inertisation period (May 16 – May
21, 2001) are obvious. When the longwall face no. 138
202 was inertised, the "Důl Lazy" Colliery's total
consumption of nitrogen was 1,800 m3. h-1, divided into
no. 138 202 and no. 138 706 faces. From 07:55 to 08:15
hours on May 21, 2001, the branch of no. 138 706 was
closed and nitrogen was only supplied to no. 138 202. At
that time the volumetric flow rate was checked with the
aid of the "Důl Lazy" Colliery's distribution centre. The
Yokogawa device in the centre showed a volumetric flow
rate of 0.3055 m3.s-1, while the underground measurement
segment, equipped with Trolex flowmeters, showed
0.31977 m3.s-1 at a velocity of i 11.5 m.s-1 and absolute
pressure of 0.385 MPa at that time, as calculated
according to the below-stated formula (6). The Trolex
TX 5922 flowmeter was handed over to a state testing
laboratory for calibration after the end of the experiment.
In the period of May 16 – May 21, 2001, gaseous nitrogen
was brought to the goaf space with a flow rate of 0.3055
m3.s-1, and the flow velocity was measured as 10 – 12 m.s1
. The calibration confirmed an admissible deviation in the
relevant velocity interval (the calibration reference value
was 10.51 m.s-1, the flowmeter's reading was 10.44 m.s-1)
[8].
The measurement segment equipped with Trolex
flowmeters was installed in the gaseous nitrogen branch of
longwall face no. 138 202 near Pit no. 6. The total length
of the pipe route from the measurement to the release
point was 2,100 m. There were four approx. 90° and three
approx. 60° elbows in that route. Calculated pressure loss
for 0.3055 m3.s-1 gaseous nitrogen volumetric flow rate
was, for undamaged pipe, 0.14 MPa. The actual absolute
pressure for the given volumetric flow rate was measured
as 0.35 MPa; the pressure loss with respect to the
barometric pressure therefore was 0.203 MPa. The
difference between the calculated and measured values of
the pressure los can be explained by condition of the pipe
(it had formerly been used as a flushing pipe).
The volumetric flow rate was similarly measured on
the 9th floor of the "Důl Darkov" Colliery in the OstravaKarviná Mining District in the Czech part of the Upper
Silesia Coal Basin. The measurement segment was
installed in the 150-mm diameter gaseous nitrogen pipe
branch of the Colliery's auxiliary plant; the segment was
equipped with a Trolex TX 5922 flowmeter, a Czechmade absolute-pressure gauge made by the MTA Servis
Company in Ostrava (wwww.mta-ostrava.cz) of the
TMAG type, with measurement range from 0 to 0.6 MPa
and a PT 100 temperature sensor. The nominal values of
the TMAG pressure gauge were set as follows: the
measurement range was selected as 10 kPa to 2.5 MPa,
the maximum non-linearity 1%, the maximum hysteresis
0.2%, the maximum temperature drift of zero 0.3%.10°C1
, the maximum temperature drift of range 0.3%.10°C-1,
the operational temperature range from –20°C to + 80°C,
a spark-safe workmanship. The sensors used were
connected to a Czech-made MTA Servis s.r.o. information
system.
If Vortex-type flowmeters are used, the gaseous
nitrogen volumetric flow rate is determined form the
pipe's cross-section area, measured velocity of flow, and
the absolute pressure and temperature at the measurement
point:
p
T
m
Q  S v
 n
V
p
T
n
m
where: QV
S
v
,
(5)
– volumetric flow rate of gas, m3.s-1;
– pipe's cross-section area, m2;
– flow velocity, m.s-1 ;
Substituting the STP normed values, we get:
Q
VN 2
21,173 * 10  4
 d v p
(273,15  t )
where: QVN2
d
p
t
2
,
(6)
– volumetric flow rate, m3.s-1;
– pipe's diameter, m;
– absolute pressure of flowing gas, Pa;
– temperature of flowing gas, °C.
5. PROCESSING OF SENSORS' INPUT SIGNALS
Output electrical signals of flow velocity, temperature
and pressure sensors (Yokogawa or Trolex) are evaluated
with the aid of connection to the corresponding evaluation
unit (Yokogava –YFCT, Trolex – Venturon VAL 101
concentrator), in the required dimensions of the velocity,
temperature and pressure quantities. These devices make
it possible for selection of the time unit and switching
between SI and Imperial units. If different systems with
no presets are used, the electrical variables must be recalculated prior to determination of the volumetric flow
rate. The information systems in mines enable
transmission of the electrical signals to a central control
room on the surface. Here the electrical (and other
physical) variables must be evaluated to determine the
corresponding volumetric flow rate values.
The velocity, temperature and pressure sensors are
used with electric current, voltage, frequency or impulse
output values. Current and voltage types are used most
often. For example, an absolute pressure sensor can be
used with the 0 – 600 kPa range and a current or voltage
output. If a sensor with a 0.4 – 2.0 V linear voltage output
is used, the calculation of the pressure from the voltage is
depicted in Fig. 10. The relationship's graph is a straight
line in the corresponding coordinate system.
Current values of sensors with electric-current output
can be processed in a similar way. If the sensor used has a
non-linear output characteristic curve, the calculation can
use the sensor's calibration values and regression function
of the curve.
Mine Planning and Equipment Selection 2002
References:
Calcualtion of Pressure Sensor's Otuput Voltage
[1] Adamus, A.: Nitrogen Inertization in Mines [online].
VSB-TUO [Ostrava (Czech Republic)]: VSB –
Technical University in Ostrava, May 2001, updated
on an ongoing basis [cit. February 15, 2002].
Available online: <http://www.vsb.cz/nitrogen>.
International topical databases and discussions.
700
600
p [kPa]
500
p  tg * (U  0,4)
400
300
tg 
200

100
600
(2,0  0,4)
 375
0
0,2
0,4
0,6
0,8
1
1,2
1,4
1,6
1,8
2
U [V]
Fig. 10 Graph and calculation of pressure sensor's
output voltage
6. CONCLUSIONS
Measuring gaseous nitrogen volumetric flow rate in
individual branches of nitrogen distribution systems in
deep mines has become a part of the technology of
preventive inertisation with the aid of gaseous nitrogen.
Current technology enables taking measurements in gassy
mines and transmitting them electronically to the surface;
thus regulation and automation can be applied in gaseous
nitrogen distribution and optimisation. Accuracy of
underground measurements is to be improved, since the
measurement deviations often get as high as 10% of the
measured value.
Acknowledgements
The author wishes to express his thanks to the H.B.L.
Mining Safety Department in Fraiming-Merlebach,
management of the "Důl Lazy" Colliery in Orlová, the
Yokogawa Company's representative in Ostrava, DPB
Paskov Company's Gas Department workers in Paskov,
the Trolex Company's representatives in Ostrava, the
MTA Servis Company in Ostrava, the Czech Mining
Authority in Prague, and all the others who provided
source information and consultations on the basis of
which the present paper could be written.
[2] Amartin, J.P. (2001), Optimisation of Nitrogen
Injection for Inertisation of Longwall Face Goaf in
CdF Coal Mines. Proceedings of the 7th
International Mine Ventilation Congress. Krakow,
17-22 June 2001, Poland.
[3] Makarius R.: Inertization of Underground Fires,
SNTL, Praha 1993.
[4] Adamus, A.: Gas Inertization of Gobs, Uhlí rudy
geologický průzkum, 1994, No. 4.
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