New low-cost method
for determination of heating value of natural gas
Rybitskyi Ihor, Karpash Oleg, Darvay
Iryna, Karpash Maksym
Ivano-Frankivsk National Technical University of Oil and Gas
Karpatska St.,15, Ivano-Frankivsk, Ukraine 76018
(e-mail: mkarpash@nung.edu.ua,
rybitsky@nung.edu.ua )
Natural gas quality determination as
primary energy resource for our country can be assigned to energy security from
the point of view of its limited resources in Ukraine and the dynamics of the
continuous growth of prices for natural gas. Just so, since 1999, the price for
natural gas has increased at an average almost in 3 times for the population
and in 10 times for enterprises.
Heat, released by the natural gas
burning (heating value) is the main indicator of natural gas quality, the
indicator of its application.
The heating value of natural gas can
be determines in two ways:
- by the calculation method (for
component composition) [1];
- by the experimental method (using
the water calorimeter) [2].
Both methods for natural
gas heating value determination have a number of significant drawbacks
[8, 9], the main of which are:
- significant time and cost expenses for the research;
- inability of the heating value continuous
measurement (in real time) directly to the consumer.
For solving the above mentioned problems new method
have been developed and proved theoretically for natural gas heating value determination,
which is compatible to measuring of ultrasound velocity in a gas, carbon
dioxide content and to the usage of artificial neural networks as heating value
nonlinear approximates as the function of the complex specified parameters. These informative parameters were selected by
correlation analysis of natural gas heating value with a number of standard physical and chemical parameters of natural
gas, namely: hydrocarbons content (methane, ethane, propane, butane and higher
hydrocarbons), density, molar mass, ultrasound velocity in gas, carbon
dioxide content and nitrogen content [3].
Adequacy of a new express-method for gas heating value
measuring was tested with the usage of artificial neural network (SHNM) with
reference values of gas physical and chemical parameters [4] and real values of
natural gas parameters from the natural gas quality certificates, as defined in
one of the companies of Ivano-Frankivsk region.
The purpose of this article is to conduct experimental
investigation to establish the possibility of practical application of the
proposed method directly to the consumers of natural gas.
The essence of experimental investigation was in the
following: two identical samples of natural gas were selected simultaneously
from gas network. Thereafter one of the samples was analyzed by means of
specially developed experimental unit for heating value determination by the
proposed method. Another gas sample was put into the chromatograph serial type
KCH (industrial No. 3875) for component composition measuring and natural gas heating
value calculation. After the above-mentioned investigations were performed,
their results were compared. To reduce the influence of ambient temperature
readings for research measuring results, the investigations were conducted
simultaneously in same room.
The experimental unit for gas heating value
determination has the following main blocks (Figure 1): gas preparation block
1, which includes water segregator, and flow-metering tube that is designed to
clean the samples of dust and moisture; sensors for measuring the sound
dispersion speed in gas 2; CO2
concentration in natural gas measuring unit, which consists of carbon dioxide
sensor serial-type IP 3-CO2 (industrial No. 1 / 3002) and gas analyzer 4
"DOZOR-C (industrial No. 3002).
1 – gas
preparation block, 2 - measuring chamber, 3 - CO2 feeding for natural gas, 4 -
block for measuring the sound dispersion speed in gas, 5 - pressure gauge;
6 - thermal
hygrometer 7 - thermometer, 8 - ultrasound stethoscope
Figure 1 -
Experimental unit for natural gas calorific value determination
The specifically designed and manufactured block for measuring the sound
dispersion speed in gas 2 (Figures 2, 3) is of particular interest. Block is a
tight construction made of stainless steel in cylindrical form, into which the
natural gas is supplied. The initial ultrasonic transducer of own production is
set up in the block. Its frequency is at up to 1 MHz, which works in couple
mode as emitter-receiver. At the calculated and clearly set distance of 57.7 mm upon condition of maximum energy
value of reflected signal receiving, the reflector, made of stainless steel
with diameter of 22 mm and a surface roughness Rz = 20, is set.
Also, the unit consists of 5 pressure gauges of type MT-2H (TR 33.2-33884768.001-2006)
thermal hygrometer of type OVT-6-7302 (industrial No. 08,082,341);
ultrasonic defectoscope DIO 562 (industrial No. 138).
1 –
generation-receiving circuit 2 - primary ultrasound transducer;
3
- reflector, 4 - processing results device, 5 – device output;
6 -
humidity sensor, 7 - temperature sensor, 8 - pressure sensor
Figure 2 -
Functional diagram of block for measuring the sound dispersion speed in gas
1 - tap 2 -
fitting, 3 - reflector, 4 - measuring chamber;
5 - piezoelectric
ultrasonic transducer, 6 – pressure gauge, 7 - connector;
8 - captivating
plate, 9 - temperature and humidity sensor
Figure 3 - Block
determining velocity of sound in gas
Technology for natural gas heating value determination
by means of the experimental unit is the next. Sample gas enters the measuring
chamber 2, where sound dispersion velocity is determined. To measure the carbon dioxide content in natural gas,
sample gas is needed to be additionally cleaned from mechanical impurities and
dried with the preparing samples block. The carbon dioxide content of
determined in the carbon dioxide determination block (3,4). Also the pressure,
temperature and humidity of gas sample are measured.
For the new method of heating value measuring 20
samples of natural gas were selected. By means of experimental unit the
following informative parameters were determined: ultrasound velocity in gas
and carbon dioxide content. Table 1 presents results of informative parameters
determination. Natural gas heating value was determined in Ivano-Frankivsk
National Technical University of Oil and Gas.
Table 1 - Results of the informative
parameters measuring
|
Gas sample No.
|
Sound dispersion
velocity in gas,
|
Carbon
dioxide content, %
|
Gas heating
value, kkal/m3
|
|
1
|
398,95
|
0,59
|
9086,4
|
|
2
|
410,82
|
0,52
|
8931,0
|
|
3
|
403,67
|
0,47
|
8838,2
|
|
4
|
406,64
|
0,56
|
8822,3
|
|
5
|
395,72
|
0,56
|
8961,6
|
|
6
|
402,66
|
0,55
|
8873,5
|
|
7
|
406,91
|
0,51
|
8879,2
|
|
8
|
409,34
|
0,56
|
8962,8
|
|
9
|
408,03
|
0,58
|
8772,4
|
|
10
|
409,19
|
0,57
|
9071,0
|
|
11
|
401,85
|
0,6
|
9167,6
|
|
12
|
403,9
|
0,62
|
9099,1
|
|
13
|
406,56
|
0,64
|
9042,2
|
|
14
|
399,18
|
0,57
|
9108,2
|
|
15
|
401,64
|
0,59
|
8957,8
|
|
16
|
404,13
|
0,6
|
8983,3
|
|
17
|
394,52
|
0,53
|
8885,5
|
|
18
|
399,63
|
0,56
|
9174,0
|
|
19
|
401,65
|
0,56
|
8825,2
|
|
20
|
403,9
|
0,56
|
8951,7
|
In order to calculate the natural gas
heating value by the results of measurements specially designed artificial
neural networks were used. 16 sets
of 20 informative parameters were selected to train the network and to test it
- 4 that were not used for training. At the entrance of ANN sound dispersion
velocity in gas and carbon dioxide content were given, and at the output - the
natural gas heating value. ANN testing results
are presented in Table 2.
As it is seen from the Table 2, the heating values,
defined by gas chromatograph, are equal to the values obtained by using
artificial neural network of developed method. Absolute error was 39.64 kkal/m3
and given to the range - 4.66 %. These results can be considered acceptable,
since for method control on data taken from the natural gas quality
certificates, the ranges error reached to 56%.
Experimental method of new method for natural gas
heating value measuring proved its adequacy and applicability.
Experimental unit required improvement, because it was
necessary to take into account the effect of humidity and temperature on gas
samples. For this purpose the block of sound dispersion velocity in gas velocity
was updated by the including humidity and temperature sensors directly into the
cylindrical measuring chamber unit. There have been improved the reflector –
the previous one was replaced by the concave reflector, made of stainless steel
with the diameter 20 mm and the curvature surface of 520, allowing to focus
acoustic signal from the primary converter and to increase the energy value of
received acoustic oscillations. In addition, the
block construction of sound dispersion velocity in gas provides the possibility
of distance regulation from the primary reflector to the transducer, that
allows get the maximum energy value of the reflected signal due to the radiated
frequency.
Table 2 - Results
of the natural gas heating value determination by the developed method
|
Sample No.
|
Heating value, received by the usage of ANN, kkal/m3
|
Heating value, received by the usage of gas chromatograph, kkal/m3
|
|
1
|
8815,8
|
8822,3
|
|
2
|
8948,5
|
8961,6
|
|
3
|
8958,8
|
9071,0
|
|
4
|
8924,9
|
8957,7
|
After corrective measures the industrial approval of
proposed method of natural gas heating value determination by the above
mentioned technique and results comparing with the data of gas samples
chromatography analysis was conducted in SE
"Ivano-Frankivskstandardmetrology" and JSC "Ivano-Frankivskgas.
The given measurement error, using the proposed
method, does not exceed 4%.
Currently works on the unit
industrial pattern production are performed.
Literary
1. Natural gas -- Determination of composition
with defined uncertainty by gas chromatography: DSTU ISO 6974 (parts 1-4): 2007 .- [Valid from 2007-01-01]
.- K: Derzhspozhivstandart Ukraine, 2007 .- 62 pp.
2. Natural burning gases. Method for heating value
determation by pressurized water calorimeter: GOST 27193-86 .- [Carried in
1988-01-01] .- M: USSR State Committee on Standards, 1987 .- 14 pp.
3. Karpash O.M. New informative parameters for natural
gas heating value determination / O.M. Karpash, I.Ya. Darvay, M.O. Karpash / /
Oil and Gas industry .-2008 .- № 4.-p.57-60.
4. Morrow Т.B. Development of a
low cost inferential natural gas energy flow rate prototype retrofit module,
Final report, DOE Cooperative Agreement No. DE-FC21-96MC33033, U.S. Department
of Energy, Morgantown, WV. Southwest Research Institute, San Antonio, TX.
