JOURNAL OF APPLIED ENGINEERING SCIENCES VOL. 1(14), issue 4_2011
ISSN 2247- 3769 ISSN-L 2247- 3769 (Print) / e-ISSN:2284-7197
CONSIDERATIONS REGARDING THE PIPELINE TRANSPORT OF NATURAL GAS-HYDROGEN MIXTURE
HOłUPAN Anca*, DOMNIłA Florin, BORZAN Marian, Technical University of Cluj-Napoca, *e-mail: [email protected]
(correponding adress)
A B S T R A C T The problem of transition to a hydrogen based energy system is a high tech problem whose solution calls for multiple disciplines
covering several areas, not only of engineering sciences, but social sciences also. For this reason the transition to a hydrogen
based energy system must be thought in a way that the substitution of natural gas by hydrogen to be gradual, by exploiting
existing resources of natural gas and filling their deficit with hydrogen.
Keywords: natural gas, hydrogen, pressure, flow rate, density, gas compresibility,pipelines
Received: October 2011
Accepted: October 2011 Revised: November 2011 Available online: November 2011
INTRODUCTION The problems with the supply of natural gas for the consumers are strictly topical, because all
existing stocks are increasingly lower. Implementation of hydrogen in the economic cycle is the
ideal solution both in relation to fuel depletion and environmental protection [1]. The conversion of
natural gas transport systems to hydrogen is a solution that can save a precarious energy system,
based on large natural gas imports [2]. Because the transition from one energy system to another
involves social, economic and policy issues, this can not be achieved only gradually. The ensuring
of conditions for sustainable energy systems development involve the promotion of fundamental
and applied science research, to open new horizons, solutions and technologies. In terms of
structure, the existing natural gas pipelines allow a circulation of a gas mixture of 80% natural gas
and up to 20% hydrogen, without any change in the geometric characteristics of the network [3].
The pipelines used in hydrogen transport and distribution are made of high quality steel and allow
natural gas circulation, too. The study propose a pipeline network through which circulate
successively: 100% natural gas, gas mixture of 80% natural gas - 20% hydrogen, and 100%
hydrogen.
MATERIALS AND METHODS
1. Determination of hydraulic parameters for the gas mixture The relationship which is the base to carry out the calculations in natural gas transport and
distribution networks is the flow rate calculus relationship [4, 5, 6]:
λ⋅⋅⋅ρ⋅
⋅−=
LzT
D)PP(306,4Q
522
21 (m3/h) (1)
in which:
P1 - absolute pressure at the beginning of the pipe, in bara;
P2 – absolute pressure at the end of the pipe, in bara;
D – inner diameter of the pipe, in cm;
T – gas temperature, in K;
CONSIDERATIONS REGARDING THE PIPELINE TRANSPORT OF NATURAL GAS-
HYDROGEN MIXTURE
HOTUPAN A. et all., pp. 23-26
L – length of pipe, in km;
ρ – relative density of hydrogen with respect to air;
λ – linear head losses coefficient, determined with Moody diagram, according to the
report k/D, for the quadratic turbulent flow domain;
k – absolute roughtness;
z – compressibility factor.
Because of the fact that the geometric parameters of gas pipeline remain unchanged at the
variations of transported gas physical parameters, the study continues with the determination of gas
mixture flow rate, in the hypothesis in which the gas mixture must provide the same calorific value
like natural gas; the establishing of the gas mixture relative density and the pressure variation study.
2. Determination of gas mixture flow rate Natural gas flow rate is determined in accordance with „Technical rules for the design,
execution and exploitation of natural gas systems/2008”.
The necessary hydrogen flow rate is determined based on calorific loads for the two gases by
the relationship:
NGNG3
3
NGHCi
NGCiH Q313Q
mMJ7910
mMJ7935Q
P
PQ ⋅=⋅=⋅= ,
/,
/,
)(
)( (2)
in which:
)NG(CiP and )H(CiP are the lower calorific loads of the combustible natural gas,
respectively hydrogen;
QNG and QH are the combustible natural gas volumetric flow rates, respectively hydrogen.
If the gas mixture is composed of 80% gas and 20% hydrogen, the flow rates are determined
by the relationship:
NG3
3
NG
)H(Ci
)NG(CiNGH,NG
NGNG)H(Ci
)NG(CiNGHH,NG
Q463,18,0m/MJ79,10
m/MJ79,352,0Q
8,0P
P2,0QQ
Q8,0QP
P2,0Q8,0Q2,0Q
⋅=
+⋅=
=
+⋅=
⋅+⋅⋅=⋅+⋅=
(3)
3. Determination of relative humidity Starting with the relationship:
HNG
HHNGNGHNG
VV
VV
+ρ⋅+ρ⋅
=ρ , (4)
in which: ρNG=0,554 kg/m3, ρH=0,069 kg/m3, represent the relative humidities of natural gas,
respectively hydrogen [7]. Given the scale of which is composed the gas mixture:
.,
;,
;
,
,
,
HNGH
HNGNG
HNGHNG
V20V
V80V
VVV
⋅=
⋅=
+=
(5)
JOURNAL OF APPLIED ENGINEERING SCIENCES VOL. 1(14), issue 4_2011
ISSN 2247- 3769 ISSN-L 2247- 3769 (Print) / e-ISSN:2284-7197
it result the mixture relative humidity: 3
HNGHNG mkg45600690205540802080 /,,,,,,,, =⋅+⋅=ρ⋅+ρ⋅=ρ (6)
4. Determination of compresibility factor For pure gases, compressibility factor, z, depends on the reduced pressure (Pr) and reduced
temperature (Tr), z = f(Pr,Tr), parameters that have the following calculus relationships [8, 9]:
c
rP
PP =
cr
T
TT = (7)
in which: P, T – pressure, respectively temperature at absolute scale;
Pc, Tc – critical pressure, respectively critical temperature at absolute scale.
If gas mixtures, the pseudo-critical properties are used instead critical properties [8]. The
pseudo-critical pressure and pseudo-critical temperature calculation are presented in Table 1.
Table 1. Pseudo-critical temperature and pseudo-critical
pressure for 80% natural gas - 20% hydrogen gas mixture
Component Molar
fraction x
Tc
K
x· Tc
K
Pc
bar
x· Pc
bar
Natural gas 0,8 190,65 152,52 46,3 37,04
Hydrogen 0,2 374,3 74,86 40,67 8,134
80% natural gas - 20% hydrogen gas mixture 1,0 - 227,38 - 45,174
5. Determination of pressure and pressure loss In accordance with „Technical rules for design, execution and exploitation of the natural gas
systems/2008”, the principle scheme to establish the pressure drop in natural gas distribution
pipelines is shown in Figure 1.
Fig. 1. Principle scheme for determination of pressure drop in natural gas
transport pipelines at medium pressure regime
The principle scheme to establish the pressure drop in hydrogen distribution pipelines is
shown in Figure 2 [9].
Fig. 2. Principle scheme for determination of pressure drop in hydrogen transport
pipelines at medium pressure regime
The starting point for calculating the pressure of gas mixture consists of Dalton’s law:
CONSIDERATIONS REGARDING THE PIPELINE TRANSPORT OF NATURAL GAS-
HYDROGEN MIXTURE
HOTUPAN A. et all., pp. 23-26
.,
;,
;
,
,
,
HNGH
HNGNG
HNGHNG
P20P
P80P
PPP
⋅=
⋅=
+=
(7)
in which: PNG,H – gas mixture pressure;
PNG – partial pressure of natural gas;
PH – partial pressure of hydrogen.
Based on relations (7) and on the two principle schemes shown in Figure 1, respectively
Figure 2, was determined the principle scheme to calculate gas mixture (80% natural gas - 20%
hydrogen) distribution pipelines, shown in Figure 3.
Fig. 3. Principle scheme the determination of pressure drop in gas mixture
(80%natural gas - 20% hydrogen) transport pipeliness at medium pressure regime
CONCLUSIONS The substitution of natural gas transport networks with hydrogen transport network remains a
viable solution for an energetical strategy. It is quite obvious that despite the important financial
effort is still exists concrete technical opportunities, by gradual transition from natural gas to
hydrogen, so by following an intermediate stage, in which is transported a gas mixture consisting of
natural gas and hydrogen in various proportions and their separation from the user, the financial
effort is reduced considerably. Since there is not a law requiring how to calculate the transport
networks of the natural gas-hydrogen mixture, the solution presented in the paper allows the
calculation of transport networks in the version of conversion the transport systems from natural gas
to hydrogen.
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JOURNAL OF APPLIED ENGINEERING SCIENCES VOL. 1(14), issue 4_2011
ISSN 2247- 3769 ISSN-L 2247- 3769 (Print) / e-ISSN:2284-7197
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