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: anca.hotupan@insta.utcluj.ro

(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.

REFERENCES 1. SURIANU D., Economia hidrogenului – de la utopie la realism, (Hydrogen economy - from utopia to

realism), disponible at the following Internet adress: http://www.agir.ro/buletine/292.pdf.

2. TABAK J., ( 2009), Natural gas and hydrogen, USA, ISBN 978-0-8160-7084-8.

3. ADAMS T.M., (2005), Evaluation of Natura Gas Pipeline Materials for Hydrogen Service, disponible at the following Internet adress: http://www1.eere. energy.gov /hydrogenan dfuelcells/pdfs/04_adams_nat_gas.pdf.

4. GHEORGHE G., (1972), DistribuŃia şi utilizarea gazelor naturale, (Distribution and utility of natural

gas), Ed. Tehnică, Bucharest. 5. BADEA GH., HOłUPAN ANCA, CHICINAŞ ADRIANA, (2008), Dimensioning method of

hydrogen/natural gaz transport networks, Acta Technica Napocensis, vol. IV, Cluj-Napoca.

6. BADEA GH., BACOłIU C., HOłUPAN ANCA, (2007), Determinarea relaŃiei de calcul pentru transportul gazelor prin conducte, particularizare pentru transportul hidrogenului (Determining

calculus relations for the gas transporting in pipelines, particularised for the hydrogen), „ŞtiinŃa Modernă şi Energia” Confence Volume, Ed. Risoprint, Cluj-Napoca.

7. CREłU I., ş.a., (1973), Probleme de hidraulică, (Hydraulics applications), Ed. Tehnică Bucureşti.

8. *** (2008), Norme tehnice pentru proiectarea, executarea şi exploatarea sistemelor de alimentare cu

gaze naturale (Technical standards for the design, execution and exploitation of natural gas supply networks).

JOURNAL OF APPLIED ENGINEERING SCIENCES VOL. 1(14), issue 4_2011

ISSN 2247- 3769 ISSN-L 2247- 3769 (Print) / e-ISSN:2284-7197

9. BADEA GH., HOłUPAN ANCA, MOLDOVAN E., (2007), Studiul comparativ privind dimensionarea

reŃelelor pentru transportul hidrogenului şi a gazelor naturale, în varianta substituirii gazelor naturale

cu hidrogen, (Comparative study regarding the dimensioning of hydrogen and natural gas network,

when natural gas will be replaced with hydrogen), „ŞtiinŃa Modernă şi Energia” Conference Volume, Ed. Risoprint, Cluj-Napoca.