MODELLING AND SIMULATION OF THE STEAM REFORM PROCESS IN THE TRANSFORMATION OF METHAN IN SYNGAS IN THE GTL TECHNOLOGY

Student: Rodrigo Farias

Federal University of AlagoasTechnology Center

Chemical Engineering Course

Maceio, 2013

INDEX

INTRODUCTION OBJECTIVES METHODOLOGY RESULTS CONCLUSIONS REFERENCES

INTRODUCTION

GTL Technology

Big sources of natural gas (oil) Offshore plants

INTRODUCTION

GTL Technology:

Steam reformingNatural gas

Steam (H2O)

Syngas (CO + H2) Fischer-Tropsch’s

reactions

Cracking

Liquid hydrocarbons

Diesel, Naphta etc.

Process’ part to be modelled

INTRODUCTION

Phenomenological Modelling:

Figure 1 – Example of a phenomenological model

Using of computer to solve them.

AdvantagensBetter comprehension of the phenomena involved;Usually allows better results in extrapolations;It can be adaptated to any programming language;

INTRODUCTION

Models regarding the time

Steady state Dynamic StateDisturbing

Project ControlReactor length (m)

Time (h)

To develop a phenomenological model to a reactor for the steam reforming process in MATLAB in the steady and dynamic states.

OBJECTIVES

METHODOLOGY

+

Dimensional model, which only takes into account interfacial gradients.

Fast reactions

Distinction between the fluid and the conditions in the catalytic surface or even inside the catalyst

It was observed that the steam reforming reactions are strongly controlled by the diffusion[6] [10].

Important thermal effects

Choosing the model:

Mass and energy balances to the fluid and solid phases (steady state):

METHODOLOGY

)( ssvgs yyak

dzdyu

)(4)( rt

ssvfpgs TT

dUTTah

dzdTcu

Flui phase:

For a cross section of the bed including solid and gas:

)( ssvgAB yyakr

)()( ssvfAB TTahrH

Initial conditions

y = y0

eT = T0

para z = 0

Conservation equations of mass and energy for the fluid and solid phases (dynamic state):

METHODOLOGY

)( ppaktp

pMzp

pMu s

svgtm

g

tm

gs

)(4)( rt

ssvfpgpgs TT

dUTTah

tTc

zTcu

For the fluid phase:

For a cross section of the bed including solid and gas:

tp

pCppakr

ss

st

tssvgAB

)1()(

tTcTTahrH

ss

Bpss

svfAB

)()(

Initial conditions:

00

zt

0

s

rs

ppTTT

00

zt

0

0

ppTT

Data for the reactor design

METHODOLOGY

Temperature in the feed 793.15 KTotal pressure 29 barNatural gas flow 135.0 Nm³/hSteam flow 399.17 Nm³/h

Natural gas composition ( volumetric base)

CH4: 81.4 % N2: 14.1 %C2H6: 2.8 % CO2: 1.0 %C3H8: 0.4 % C4H10: 0.1 %C5H12: 0.2 %

Intern diameter of the reactor 0.1016 mExtern diameter of the reactor 0.1322 mLength of the reactor 12 m

Table 1 - Data for the reactor design [10]

Sketch do reactor:

METHODOLOGY

Figure 2 – General Sketch fot the reactor

Reaction’s kinetic [19]

METHODOLOGY

2

1

3

5.21

1 )(

24

DEN

Kpp

pppk

r

COHOHCH

H

s

s

22

2

2 )(

2

2

2

DEN

Kpp

pppk

r

COHOHCO

H

s

23

42

5.33

3 )(

22

24

DENKpp

pppk

r

COHOHCH

H s

2

22

44221

H

OHOHCHCHHHCOCO p

pKpKpKpKDEN

OHCH3HCOHCOOHCO

3HCOOHCH

242

222

224

I. Steam reforming:

II. Water-gas shift:III.Metanation:

Properties of the catalyst and the bed

METHODOLOGY

Dep 0.0173 mDip 0.0084 mH 0.010 mρs 2355.2 kg/m³

Table 2 - Properties of the catalyst and the bed [10]

epipepepip

ip

epp DDDH

DDHD

DHd

)2(

21

23 3

1

2

1

2

1 2

1073,038,0

p

p

dD

dD

pc d

a 16tt

ts PA

RTFu )1( SB

The catalyst used in the model : rings Ni/Al2O3

METHODOLOGY

Phenomenological model

Phisical and chemical properties

Propriedades físico-químicas e termodinâmica

Kinetic constants

Flow propertiesThemodynamic properties

METHODOLOGY

Solution of ODE’s systems:- Runge-Kutta Method (4th e 5th order) - ode45 in MATLAB. Solution of PDE’s system:- Method of lines;- Discretization by finite differences:

zzfzf

zzf iii

)()()( 1

zzfzf

zzf iii

)()()( 1

System of PDEs → System of ODEs

METHODOLOGY

Figure 3 – Sketch of the reactor and of its spatial discretization

Sketch of the reactor with spatial discretization:

METHODOLOGY

Simplifications

Use temperature’s behavior from ALVES (2005); Ideal gas; Superficial mass velocity (us) constant; Constant pressure;

RESULTS AND DISCUSSION

0 2 4 6 8 10 120

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Comprimento do reator (m)

Fraç

ão m

olar

dos

com

pone

ntes

CO2CH4C2H6C3H8C4H10C5H12N2H2COH2O

0 2 4 6 8 10 12750

800

850

900

950

1000

1050

Comprimento do reator (m)

Tem

pera

tura

do

reat

or (K

)

Figure 4 - Temperature profile (K) along the reactor length (m)

Figure 5 - Profile mole fraction of components with the reactor length (m)

Steady state

RESULTS AND DISCUSSION

It was observed consistent trend of the variation of the molar fraction of reactants and products;

It was found in the references a behavior similar to that found in this work. It probably differs by operating conditions and characteristics of the model adopted (Mazandarani, 2007);

Steady state

RESULTS AND DISCUSSION

Figure 8 - Profiles of each component partial pressure (bar) and reactor temperature (K) versus time (s) and the reactor length (m).

Dynamic model

RESULTS AND DISCUSSION

Dynamic model Simulation were run using the profiles from the steady state model; The integration of the discretized equations was performed using the Runge-Kutta

fourth order, implemented through own routines; Several experiments were conducted in relation to the number of discretization

points and integration step (trial and error), even though stable results were not obtained;

The results presented in Figure 8 show problems, which can be source of future studies;

CONCLUSIONS

From the simulations performed for the model in steady state and comparing the same with the literature[15], it was noted that the model is suitable for modeling the process of steam reforming;

Simulations for the dynamic state show that despite the numerical integration of the equations was performed, they still have problems. Therefore, they do not have physical meaning;

REFERENCES

• [1] ALVES, S. C. Reforma a vapor do metano para produção de hidrogênio: estudo termodinâmico e protótipo de modelo matemático de reator com membrana. Uberlândia, 2005.

• [2] ANP. Boletim da Produção de Petróleo e Gás Natural. Disponível em: <www.anp.gov.br/?dw=61389>. Acesso em: 10 ago. de 2012 às 14h.  • [3] ARMOR, J.N. The multiple roles for catalysis in the production of H2. Applied Catalysis A: General, v.176, p.159-176, 1999.• [4] ARZAMENDI, G. et al. Methane steam reforming in a microchannel reactor for GTL intensification: A computational fluid dynamics simulation

study. Chemical Engineering Journal, v. 154, p. 168-173, 2009.• [5] BAKKERUD, P. K. Update on synthesis gas production for GTL. Catalysis Today, Lyngby, v. 106, p. 30-33, 2005.•  [6] BIRUEL JÚNIOR, J. Análise comparativa das tecnologias embarcadas de aproveitamento de gás natural. Universidade Federal do Rio de

Janeiro, 2008.•  [7] CALLAGHAN, C. A. Kinetics and catalysis of the water-gas-shift reaction: A microkinetic and graph theoretic approach, 2006. •  [8] DEDEKEN, J. C.; DEVOS, E. F.; FROMENT, G. F. Chemical Reaction Engineering, série 196, 1982.•  [9] DWIDEVI, P. N.; UPADHYAY, S. N.; Industrial & Engineering Chemistry Process Design and Development. v. 16, p. 157, 1977.• [10]  FERNANDES, F. A. N.; SOARES JR, A. B.; Modeling of methane steam reforming in a palladium membrane reactor. Latin America Applied

Research v. 36, p. 155-161, 2006.•  [11] FOGLER, H.S. Elements of Chemical Engineering. 4. ed., 2005.• [12]  FRANCO, T. V. Análise Termodinâmica das Reações de Reforma do Metano e do GLP para a produção de hidrogênio, Uberlândia, 2009.• [13]  FROMENT, G. F.; BISCHOFF, K. B. Chemical Reactor Analysis. 2. ed. Wiley Series in Chemical Engineering, 1990.• [14]  GONÇALVES, G. et al. Modelagem de um reator integral aplicado na reação de reforma a vapor. Acta Scientiarum : Tecnology, Maringá, v.29, n.

2, p. 181-185, 2007.• [15]  MAZANDARANI, M. T.; EBRAHIM, H. Modeling and Simulation of industrial adiabatic fixed-bed reactor for the catalytic reforming of methane to

syngas. European Congress of Chemical Engineering. p. 16 -20, Copenhagem, 2007. • [16]  NEZHAD, M. Z. et al. Autothermal reforming of methane to synthesis gas: Modeling and simulation. Internacinoal Journal of Hydrogen Energy.

v. 34, p. 1292-1300, 2009.• [17]  REICHELT, W.; BLASZ, E.; Chemie Ingenieur Technik, v. 43, p. 949, 1971.• [18]  VASCONCELLOS, N. Reforma a vapor do metano em catalisadores à base de níquel promovidos com nióbia. Niterói, 2006.• [19]  XU, J.; FROMENT, G.F. Methane steam reforming: II. Diffusional limitations and reactor simulation. AIChE Journal, v. 35, n. 1, p. 97-103, 1989.