AD ALTA
JOURNAL OF INTERDISCIPLINARY RESEARCH
DESIGN AND COMPARISON OF PURE HYDROGEN PRODUCTION SYSTEM VIA STEAM
METHANE REFORMING COUPLED WITH PSA PROCESS
a
VIDA SANGSEFIDI
Islamic Azad University, Department of Chemical Engineering,
Faculty of Technical & Engineering, Pirozi St. Abozar Blv.-
Ahang St. Tehran, Post code 1777613651, Iran.
Email:
a
vida_s1991@yahoo.com
Abstract: Steam Methane Reforming (SMR) coupled with Pressure Swing Adsorption
(PSA) is the most common process to produce pure hydrogen. This paper presents a
simulation and energy evaluation of hydrogen production system. In this simulation,
the energy released in exothermic adsorption reaction, is recovered to increase the
latent and sensible heat of water. Required energy for desorption reaction is provided
from recovered heat of SMR process. Since the rate of the saved energy is not
significant enough, the temperature of the reformer is being increased. The simulation
results are compared to conventional and heat integrated hydrogen production system.
Generally, the modified design reduces the total energy consumption in 66.2%
compared to conventional process and 14.32% compared to heat integrated process.
Keywords: Steam Reforming, PSA, Hydrogen Production, Energy consumption.
1 Introduction
Hydrogen is a clean and environmental friendly fuel which can
be considered as an alternative for future. Although it is newly
getting started in the market as a transportation fuel, the industry
is working toward clean, economical, and safe hydrogen
production. Hydrogen can be supplied from two sources:
renewable (biomass and water) and non-renewable (natural gas
and heavy hydrocarbons) (Holladay et al. (2009),
Kapdan et al.
(2006)).
The most common technology to produce hydrogen in large
scale is steam reforming, which almost 50% of hydrogen
production is via steam methane reforming (SMR) (R. Soltani et
al. (2014),
Metz et al. (2005)). SMR consists of two stages:
reforming and water gas shift (WGS) reactions (Park et al.
(2008),
Martínez et al. (2014)). Reforming reaction happens in
high temperature (700°C to 900°C) in order to produce syngas.
While, WGS reaction takes place in two stages to have a higher
hydrogen yield. The first WGS stage works at high temperature
(350°C–510°C) and the second one works at lower temperature
(180°C - 310°C). In addition, it is more economically beneficial
to perform SMR process at high pressure (1500 Kpa-3000 Kpa),
despite of its negative effects on the rate of methane conversion
(Rostrup-Nielsen et al. (2002),
Johnsena (2006)). Since there is a
need for pure hydrogen in the industry, CO2 in the syngas needs
to be removed completely. The most common technologies used
to separate impurities from hydrogen with high purity degree,
are membrane and pressure swing adsorption (PSA) (Steven F.
Rice,
Ding (2002)). In the PSA process used in this study, there
are different sorbents available to adsorb carbon dioxide (Fausto
Gallucci et al. (2013),
Liu et al. (2010)). Calcium oxide (CaO) is
the most used CO2 sorbent available in nature. CaO has broadly
attracted the attention due to low cost as well as high capacity of
CO2 adsorption (Barelli et al. (2008), Yancheshmeh (2016)).
Although the SMR coupled with PSA process is the best way to
produce hydrogen, it is not an efficient process due to high
energy consumption (Boyano et al. (2011)). Various studies
were performed on different aspects of SMR process to make it
more efficient. For instance,
in 2012, Hajjaji et al. performed an
analysis on energy consumption in hydrogen production based
on SMR process, in which heat exchangers were used to recover
the waste heat so as to enhance the thermal efficiency. Wu et al.
in 2013 dealt with improvement of heat regeneration using a
heat exchanger network for the hybrid process of steam methane
and dry reforming.
In 2015, Lin Zhu et al. worked on Calcium based sorption
enhanced steam methane reforming (SE-SMR) to reduce the
energy penalty for capturing CO2 from combustion flue gas.
They were able to increase exergy efficiency by 14.39%.
Furthermore, Guoqing Li et al. (2016) proposed a new design of
SMR process which recovers heat and pressure energy via a gas
turbine at the outlet of the reforming furnace. The energy
consumption in this design was reduced by 2.5%.
In this work, both processes are studied to determine the
possibility of reducing the energy consumption further. The
simulation of this process is done via PRO/II v9.4 simulator. In
the simulation, a network of heat exchangers are used to recover
the waste heat of both processes. Also, temperature of reformer
is being increased to obtain better results in energy recovery and
hydrogen production rate. At the end, the energy consumption
of the design will be compared to the design of Chunfeng Song
et al. (2015).
2 The governing equation
Hydrogen production system consists of the following reactions:
1.
Steam Methane Reforming reaction :
4
+
2
↔+3
2
,∆
298.15
=+206 [
] (1)
2.
Water Gas Shift (WGS) reaction:
+
2
↔
2
+
2
,∆
298.15
=−41 [
] (2)
3.
CO2 adsorption and desorption reaction:
()
+
2
↔
3
,∆=−175.7 [
] (3)
Considering the exothermic reaction 1 and endothermic reaction
2, the above processes require a source of energy supply (Liu et
al. (2010)). Reaction rate constants have been proposed by Xu &
Froment and are used to determine the kinetics of these two
equations. Equations 4 to 6 are the Rate equations for reactions
1 and 2 which are based on LHHW (Langmuir–Hinshelwood–
Hougen–Watson Rate Equations) expression.
Rate equation of steam methane reforming reaction:
1
=
2
2.5
�
4
2
−
2
3
,
�
2
[
.ℎ
] (4)
Rate equation of water gas shift reaction:
2
=
2
�
2
−
22
,
�
2
�
.ℎ
� (5)
DEN term is defined as below:
=1+
+
2
2
+
4
4
+
2
2
2
(6)
Where,
are the reaction rates i (i = 1, 2), respectively;
are
the reaction rate constants i, respectively;
are the adsorption
constant of chemical species i (i =
4
,CO,
2
), respectively;
is the partial pressure of the chemical species i in the shell side
(reaction part) (i =
4
,
2
,
2
,CO,
2
) (Silva J.D et al.
(2016), Sánchez et al. (2012), Baek et al. (2014)).
In rate equations, pressure unit is in bars, energy unit in rate
constant equations is in Kj/mole and temperature unit is in
Kelvins. Equilibrium, rate, and adsorption constants are all
included in equations 7 to14 (Baek et al. (2014)).
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