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Improvement of membrane reactor performance in hydrogen production
Desalination 200 (2006) 695–696
Improvement of membrane reactor performance in hydrogen production Giovanni Chiappettaa*, Gabriele Clariziaa, Enrico Driolia,b a
Research Institute on Membrane Technology ITM-CNR c/o University of Calabria, Via P. Bucci Cubo 17/C, 87030, Arcavacata di Rende (CS), Italy email: [email protected] b Department of Chemical Engineering and Materials, University of Calabria, 87036, Arcavacata di Rende (CS), Italy Received 22 October 2005; accepted 4 March 2006
1. Introduction
2. Results and discussion
The increasing demand of energy in both civil and industrial fields requires the environmental friendly carrying out of more efficient production and distribution systems. In this framework, hydrogen is one of the more attractive energy vector for its use in different refinery processes and for its application as clean fuel, specially as it is possible to produce it in-situ and use directly [1]. Membrane reactors hold an important role for their ability to carry out in the same unit the separation and reaction steps and can be successfully used in the hydrogen production by means of the water gas shift reaction [2]. This work sets the guide-lines to pursue in a Pd-based non isothermal membrane reactor design suitable to achieve high reagent (CO) conversion and product (H2) recovery, controlling temperature hot spots in the reaction system as some operating parameters change.
A two-dimensional pseudo-homogeneous model for simulating water gas shift reaction carried out in a membrane reactor (MR) has been developed. The influence of factors such as wall-heat transfer coefficient (hw), effective radial thermal conductivity (keff) and H2 permeation rate on conversion, product recovery and also on temperature hot spot generation has been investigated. By doubling the keff value the disappear of lumen temperature hot spot is combined with a decrease of conversion (–7%), whereas the same change in hw does not produce appreciable differences (see Fig. 1). At a fixed feed pressure, a decrease of sweep gas flow rate causes a lumen temperature increase along the reactor and produces a decrease of the conversion due to a reduced cooling ability. A high lumen pressure, by increasing the reaction rate and the driving force for the permeation, allows to enhance the H2 recovery. In order to control the temperature hot spots without loosing CO conversion at low pressure
*Corresponding author.
Presented at EUROMEMBRANE 2006, 24–28 September 2006, Giardini Naxos, Italy. 0011-9164/06/$– See front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.desal.2006.03.464
696
G. Chiappetta et al. / Desalination 200 (2006) 695–696
720
Reference case (keff, hw) 2*keff, hw Keff, 2*hw
Lumen temperature, K
700
the H2 permeation term becomes important for membrane samples thinner than 1 mm.
680
3. Conclusions
660 640 620 600 0.0
0.2
0.4
0.6
0.8
1.0
Axial length, –
Fig. 1. Lumen temperature vs. axial length as a function of keff and hw changes.
and fixed operating conditions of the sweep gas, the influence of a catalyst amount distribution along the reactor on the MR performance has been also analysed. At a fixed inlet feed temperature, pressure and flow-rate, a higher H2O/CO molar ratio reduces both hydrogen driving force and temperature profile determining a decrease in H2 production and permeation rates. In order to improve the global performance of the membrane reactor, the effect of hydrogen selective membrane thickness has been also analysed. Simulation tests have indicated that
The heat exchange in a membrane reactor is significantly affected by fluid dynamics and working conditions as well as by design parameters. The influence of some heat transfer coefficients on CO conversion and hydrogen recovery has been evaluated. High feed pressure values favour in water gas shift reaction the production and recovery of the hydrogen and limit the temperature hot spot inside the membrane reactor since the net forward reaction rate decreases. An appropriate choice of the sweep gas type and flow-rate, inlet temperature on shell side allows to control the thermal load into the reactor as well as the recovery of the hydrogen. References [1]
[2]
B. Johnston, M.C. Mayo and A. Khare, Hydrogen: the energy source for the 21st century, Technovation, 25 (2005) 569–585. G. Saracco, H.W.J.P. Neomagus, G.F. Versteeg and W.P.M van Swaaij, High temperature membrane reactors: potential and problems, Chem. Eng. Sci., 54(13–14) (1999) 1997–2017.
Improvement of membrane reactor performance in hydrogen production Giovanni Chiappettaa*, Gabriele Clariziaa, Enrico Driolia,b a
Research Institute on Membrane Technology ITM-CNR c/o University of Calabria, Via P. Bucci Cubo 17/C, 87030, Arcavacata di Rende (CS), Italy email: [email protected] b Department of Chemical Engineering and Materials, University of Calabria, 87036, Arcavacata di Rende (CS), Italy Received 22 October 2005; accepted 4 March 2006
1. Introduction
2. Results and discussion
The increasing demand of energy in both civil and industrial fields requires the environmental friendly carrying out of more efficient production and distribution systems. In this framework, hydrogen is one of the more attractive energy vector for its use in different refinery processes and for its application as clean fuel, specially as it is possible to produce it in-situ and use directly [1]. Membrane reactors hold an important role for their ability to carry out in the same unit the separation and reaction steps and can be successfully used in the hydrogen production by means of the water gas shift reaction [2]. This work sets the guide-lines to pursue in a Pd-based non isothermal membrane reactor design suitable to achieve high reagent (CO) conversion and product (H2) recovery, controlling temperature hot spots in the reaction system as some operating parameters change.
A two-dimensional pseudo-homogeneous model for simulating water gas shift reaction carried out in a membrane reactor (MR) has been developed. The influence of factors such as wall-heat transfer coefficient (hw), effective radial thermal conductivity (keff) and H2 permeation rate on conversion, product recovery and also on temperature hot spot generation has been investigated. By doubling the keff value the disappear of lumen temperature hot spot is combined with a decrease of conversion (–7%), whereas the same change in hw does not produce appreciable differences (see Fig. 1). At a fixed feed pressure, a decrease of sweep gas flow rate causes a lumen temperature increase along the reactor and produces a decrease of the conversion due to a reduced cooling ability. A high lumen pressure, by increasing the reaction rate and the driving force for the permeation, allows to enhance the H2 recovery. In order to control the temperature hot spots without loosing CO conversion at low pressure
*Corresponding author.
Presented at EUROMEMBRANE 2006, 24–28 September 2006, Giardini Naxos, Italy. 0011-9164/06/$– See front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.desal.2006.03.464
696
G. Chiappetta et al. / Desalination 200 (2006) 695–696
720
Reference case (keff, hw) 2*keff, hw Keff, 2*hw
Lumen temperature, K
700
the H2 permeation term becomes important for membrane samples thinner than 1 mm.
680
3. Conclusions
660 640 620 600 0.0
0.2
0.4
0.6
0.8
1.0
Axial length, –
Fig. 1. Lumen temperature vs. axial length as a function of keff and hw changes.
and fixed operating conditions of the sweep gas, the influence of a catalyst amount distribution along the reactor on the MR performance has been also analysed. At a fixed inlet feed temperature, pressure and flow-rate, a higher H2O/CO molar ratio reduces both hydrogen driving force and temperature profile determining a decrease in H2 production and permeation rates. In order to improve the global performance of the membrane reactor, the effect of hydrogen selective membrane thickness has been also analysed. Simulation tests have indicated that
The heat exchange in a membrane reactor is significantly affected by fluid dynamics and working conditions as well as by design parameters. The influence of some heat transfer coefficients on CO conversion and hydrogen recovery has been evaluated. High feed pressure values favour in water gas shift reaction the production and recovery of the hydrogen and limit the temperature hot spot inside the membrane reactor since the net forward reaction rate decreases. An appropriate choice of the sweep gas type and flow-rate, inlet temperature on shell side allows to control the thermal load into the reactor as well as the recovery of the hydrogen. References [1]
[2]
B. Johnston, M.C. Mayo and A. Khare, Hydrogen: the energy source for the 21st century, Technovation, 25 (2005) 569–585. G. Saracco, H.W.J.P. Neomagus, G.F. Versteeg and W.P.M van Swaaij, High temperature membrane reactors: potential and problems, Chem. Eng. Sci., 54(13–14) (1999) 1997–2017.