Plenary Lecture
An Integrated Multidisciplinary Approach for the Development of Novel
Catalytic/Biocatalytic Processes for the Efficient Production of Clean Fuels
Said Salah Eldin Elnashaie
Chemical Engineering Department, Auburn University, Auburn, Alabama, USA
nashaie@eng.auburn.edu
ABSTRACT
A multidisciplinary integrated system approach is presented and discussed for the development of novel
configurations/operating modes for catalytic and bio-catalytic processes. The approach is illustrated for the development
of a novel reformer for the efficient/clean production of the ultra clean fuel hydrogen. The development utilizes an
optimal blend of theoretical and experimental research and development techniques. Extensive use of rigorous
mathematical modeling is shown to be not only the ultimate aim for developing design and control methodologies and
computer design packages but also the optimal mean of directing an efficient experimental program. Preliminary results
show that the novel configuration is far superior compared to the previous two generation of steam reformers (fixed and
bubbling fluidized beds). The approach adopted can be used for other processes such as the efficient production of fuel
ethanol from cellolusic waste. The approach seems to be useful in closing the gap between empirical/experimental based
research and development in one hand and fundamental and theoretical research on the other hand.
1.0 INTRODUCTION
Major environmental problems result from the use of hydrocarbons as fuel and for industrial applications. There is a
tremendous current interest in the development of alternative sources of energy, referred to as “ultra clean” fuels. Recently,
there has been a general recognition that hydrogen offers significant advantages as the ultra clean fuel of the future when
burned directly or processed through fuel cells. Ethanol is another member of the “ultra clean” fuels club, provided it is
produced economically from renewable resources (such as cellulosic waste). In this paper we will focus on novel approaches
to the catalytic production of hydrogen. The multidisciplinary approaches presented will combine in one package:
fundamental, theoretical and practically oriented research. This approach will satisfy industrial needs without sacrificing the
academicians and strategic need for continuous fundamental and theoretical research and will exploit the synergy between
different disciplines. Extensive use of reliable rigorous models is extensively utilized and advanced non-linear dynamics
concepts are practically exploited (Elnashaie and Elshishini, 1993, 1996; Elnashaie and Garhyan, 2002).
Hydrogen Production: Hydrogen is rightly often called the perfect fuel. Its major reserve on earth (water) is inexhaustible
(Ogden, 1998a,b; 1993; 1999, Ogden, 1993). Steam reforming extracts the hydrogen from both hydrocarbon and the water.
Hydrogen can be used directly by fuel cells to produce electricity very efficiently (>50%) and with zero emissions. Ultralow emissions are also achievable when hydrogen is combusted with air to power an engine. The present fixed bed steam
reforming technology suffers from a number of inherent inefficiencies and limitations, which result in oversized units with
inefficient operation. Because of such inefficiencies, the current reforming technologies lead to the production of hydrogen
at prices (per KJ) that are 50 - 70% more expensive than the highly polluting hydrocarbon fuels. Moreover, current systems
have limited flexibility with regard to the range of feedstocks that can be processed. Therefore, the current state of affairs
calls for advancing the state of the art by developing a new technology that can handle a wide variety of feedstocks,
overcomes thermodynamic and other limitations, delivers pure hydrogen economically and with minimum impact on the
environment.
Ethanol Production: In this paper we will concentrate on novel reformers for the hydrogen production. The efficient
production of fuel ethanol from the difficult to ferment sugars (e.g. Xylose, resulting from the hydrolysis of cellulosic
waste) requires not only a novel configuration (membrane packed bed immobilized fermentor) but also a novel mode of
operation (periodic/chaotic) in addition to the use of mutated microorganisms suitable for the fermentation of these
difficulty sugars A preliminary discussion of this process and novel mode of operation is discussed in a paper in this
conference (Garhyan, et.al., 2002).
2.0 Steam Reforming Technology: From Fixed Bed to Circulating Fluidized Bed (CFB)
Since 1989(Elnashaie and Adris, 1989; Adris, et.al., 1991) , we have been involved in the development of novel efficient
technologies for the catalytic steam reforming of natural gas and higher hydrocarbons to produce pure hydrogen and/or
syngas( Adris et. al. , 1994). Some of these technologies( Membrane Bubbling Fluidized Bed Reformers, MBFBR) have
passed the pilot plant testing stage( Adris et.al., 1994, Adris 1994). and others ( Circulating Fluidized Bed CFB reformers)
are still in the research stage (e.g.: Chen and Elnashaie, 2002; Chen, et.al., 2002; Parsad and Elnashaie, 2002). In the
following sections we will present the principles of the steam reforming process, its limitations and the innovative
techniques to overcome these limitations.
2.1.Catalytic Steam Reforming of Hydrocarbons:
Steam reforming of natural gas and higher hydrocarbons produces several important components ( Elnashaie, et.al., 1990 ;
Elnashaie and Elshishini, 1993). For natural gas (primarily methane), the main reforming reactions are:
CH4 + H2O  CO + 3H2
(ΔH1 = 206 kJ/mol, 68.7 KJ/ moleH2);
CO + H2O  CO2 + H2
(ΔH2 = -40 kJ/mol, - 13.3 KJ/mol H2) ;
CH4 + 2H2O  CO2 + 4H2
(ΔH3 = 196 kJ/mol, 49 KJ/mol H2);
CH4  C+ 2H2
(ΔH = 75 kJ/mol, 37.5 KJ/mol H2) ;
2CO  C + CO2
(ΔH = -171 kJ/mol).
The rate of steam reforming is non-monotonic with respect to steam ( Elnashaie, et. al., 1990), the reactions have a strong
tendency towards carbon formation ( the tendency increases with the increase in temperature and the percentage of higher
hydrocarbons in the feed, and it decreases with the increase in steam/hydrocarbon ratio), causing catalyst deactivation in
fixed bed and MBFBR . It is important to notice that the lowest energy requirement per mole of H2 ( other than the
exothermic shift reaction) is the methane cracking to C and H2, and for a configuration allowing continuous carbon burning
the energy consumption per mol H2 will be negative ( energy production) as shown later.
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The First Generation of Reformers: Fixed Bed Reformers :It has the following characteristics:
Hundreds of catalyst tubes (e.g.:100 – 900) with diameters in the range 7 – 12 cm and length in the range 10 – 15 m.
Large catalyst particles to avoid excessive pressure drop. Rashig rings with dimensions 1.6 x 0.6 x1.6 cm are employed.
It requires the use of high steam/methane (S/M) ratio (3-6 for natural gas feed) to avoid carbon formation and catalyst
deactivation. This S/M ratio needed increases as the % of higher hydrocarbons in the feed increases.
The typical feed flow rate per catalyst tube ranges from 3.5 – 4.5 kmol/hr. catalyst tube.
Typical natural gas feed composition includes 70 – 80% CH4, 20 – 25 % higher hydrocarbons + H2 + CO2 + N2.
Feed temperature to the catalyst tubes range from 730 to 770 K , while typical feed pressure range from 2400 to 2900 kPa.
To provide the needed heat a furnace with typical dimensions of 21.8x35.5x13.7 m3 is used
Attempts to improve steam reformers: These trials include, fixed bed with hydrogen permselective membranes (Sammels et.
al., 2000a,b, Dyer and Chen, 2000), fixed bed with/without hydrogen permselective membranes using methanol feed
(Amphlett et. al, 1996), microchannel reformer for hydrogen production (Makel, 1999), catalytic oxidative steam reforming
(Hayakawa et. al., 1993, Theron et. al., 1997) and bubbling fluidized bed reformer with/without hydrogen permselective
membranes (Elnashaie and Adris, 1989,Adris et al, 1991, Adris et al, 1994). The most successful milestone to-date involves
the bubbling fluidized bed membrane reformer (BFBMR) for natural gas (Adris et al, 1994), which is more efficient than the
classical fixed bed configuration. The Basic Characteristics of BFBMR(, second generation reformers) are:
1-Using powdered catalyst with η = 1.0 (100 –1000 times higher rate of reaction than conventional fixed bed reformers).
2-Hydrogen selective membranes “break” the thermodynamic barrier giving higher conversions at lower temperatures and also
produce pure hydrogen suitable for fuel cells.
3-In-situ burning of natural gas achieving efficient heat transfer with no large furnace.
However the configuration suffers from fluid dynamic limitations as discussed later preventing the full exploitation of these
fundamental advancements. The rationale for these advancement is next discussed as the basis for further improvement.
2.2 Limitations of Fixed Bed Technology, Advantages of BFBMR and the Possibility of Further Improvement:
Catalytic Steam Reforming and Diffusional Limitations: The effectiveness factor η of the catalyst pellets, expressing the
fraction of the intrinsic rate of reaction being exploited in the fixed bed configuration, is extremely small (η = 10-2 – 10-3) due
to the large catalyst pellet sizes used (Soliman et al, 1988, Elnashaie et al, 1992, Alhabdan et al, 1992). This severe limitation
is “broken” in the BFBMR by using fine catalyst particles (η = 1.0), thus the full intrinsic activity of the catalyst is utilized.
The “Breaking” of Thermodynamic equilibrium barrier for the reversible steam reforming(Collins and Way, 1993, Sammels et
al, 2000a,b) : The reversible, endothermic steam reforming reactions are thermodynamically limited, dictating very high
temperature for high conversion. This barrier can be “broken” through the continuous removal of one (or more) of the products.
In the BFBMR hydrogen is removed using hydrogen permselective membranes. Nowadays there are many techniques to
produce such membranes, examples include: Sputter deposition, chemical vapor deposition (CVD), electrodeposition,
electroless plating and spray pyrolysis (e.g.: Yeung, et. al., 1999) It is recognized that the key to prepare a membrane of high
flux is a composite type structure composed of a thin selective layer of palladium alloy, on porous supports such as glass,
ceramic, stainless steel and other metals in porous form. Kikuchi’s group has invented a 100 % hydrogen selective composite
membrane consisting of a thin palladium layer deposited on the outer surface of porous ceramics by electroless plating and
based on the use of this membrane, Tokyo Gas and Mitsubishi Heavy Industries have developed a membrane reformer
applicable to the polymer electrolyte fuel cell system. (Kikuchi, E., 2000; Kikushi,et.al.,2000) Porous stainless steel is also a
good choice for support due to its similar thermal expansion coefficient to Pd-based films, ease of fabrication and processing,
corrosion resistance, anti-cracking resistance and low cost (Nam, et.al., 1999; Nam and Lee,2001). A detailed review of the
current research on supported metal membranes for hydrogen separation including membrane materials, methods of fabrication
and transport mechanisms has been published by Uemiya (Uemiya, 1999). Many researchers have also developed hydrogen
selective ceramic membranes. A modified ceramic membrane called ‘Nanosil’ membrane has been developed and it shows
hydrogen selectivity of 100 % it was also found to be stable to hydrothermal stresses (Prabhu and Oyama ; Prabhu, et.al.,
2000). Hydrogen permeable membranes are also commercially available from several companies ( e.g.:REB Research’
(http://www.rebresearch.com/)). Russian scientists at the Russian Academy of Sciences (Topchiev Institute of Petrochemical
Synthesis, 2002) have developed very durable hydrogen selective membranes and used it in both petrochemical and nuclear
applications. They are also developing more advanced hydrogen selective membranes in co-operation with European and
American scientists.
Further improvement in the reformer performance is possible through continuous removal of the product CO 2 (Han and
Harrison, 1994, 1997) using CaO ( or any other CO2 acceptor) according to the exothermic reaction, which will also supply a
part of the heat,
CaO (s)+CO2(g)  CaCO3(s)
.The CaO acceptor can be recovered through the reaction endothermic reaction :
CaCO3(s)  CaO(s)+CO2(g)
This use of CO2 acceptor requires a configuration allowing for the continuous regeneration of the acceptor. The use of this
CO2 acceptor raises a number of interesting optimization problems, for although it is obvious that smaller particle sizes of
CaO ( or any other adsorbent we find better) will be favorable to the rate of its reaction with CO2 ( avoidance of diffusional
limitations , specially through the CaCO3 layer formed during the reaction), however the small particle size have
disadvantages regarding ease of fluidization and attrition( e.g.: Cook et.al., 1996 Khinast et.al., 1996 ; Ding and Alpay,
2000a,b) which certainly requires a fundamental optimization approach to find the optimal CaO particle size distribution and
its relation to the design and operating parameters. It is important in this respect to remember the well known fact ( e.g.:
Oakeson and Cutler, 1979) that this non-catalytic gas-solid reaction has two stages: an initial rapid surface reaction rate and a
slow diffusion-controlled stage, and that the transition from surface reaction to diffusion control takes place upon the formation
of the carbonate layer. This fact supports the need to use smaller particles for higher reaction rates, however this should be
achieved without violating the fluid dynamics limitations associated with the smooth operation of the CFB. Relatively recently
(Ding and Alpay, 2000a,b) demonstrated experimentally in a fixed bed reformer the advantages of using CO 2 adsorbent to
“break” the thermodynamic barrier of the reversible steam reforming catalytic reaction on Ni-based catalyst. Lobachyov
et.al.,1997 utilized
MagO.CaO as the CO2 acceptor successfully in novel coal fueled power plant. Han and
Harrison(1994,1997)have achieved 0.995( 99.5%) fractional removal of the CO2 produced from the shift reaction using CaO as
the CO2 sorbent.
Carbon Formation and Catalyst Deactivation/Regeneration( Trimm, 1977Demicheli et al, 1994, Barbier,J. 1987, Praserthdam
et al, 1992): The reforming reactions have strong tendency to deposit carbon and deactivate the catalyst. Solution of this
problem is usually through increasing the feed steam/hydrocarbon ratio. The use of membranes for the removal of hydrogen
helps to achieve high equilibrium conversion at lower temperatures, which in turn decreases the carbon forming tendency at
lower steam to hydrocarbon ratios. This severe limitation, will turn out to be an advantage in the third generation reformers, as
discussed later in this paper..
The Supply of Heat Necessary for the Endothermic Steam Reforming Reactions: The heat transfer from the furnace to the
catalyst in the tubes of the fixed bed configuration is not very efficient causing an excessive amount of heat dissipation and
environmental pollution. The BFBMR addresses this problem through: Simultaneous oxidative reforming. Further
improvement can be achieved through oxygen selective membranes(Tsai,et.al., 1997; Jin, et.al., 2000a,b ; Ritchie, et.al., 2001)
and continuous catalyst regeneration as shown later in this paper.
Hydrodynamic Limitations (Kunii and Levenspiel, 1997, 2000) : AS diffusional limitation is “broken” the BFBMR, a new
limitation arises related to the fluid dynamics of the system. In bubbling fluidized bed it is not possible to fully exploit the very
high intrinsic kinetics of the powdered catalyst. Fast fluidization (transport) reactor configuration offers excellent potential to
“break” this fluid dynamic limitation. In addition the use of CFB ( Circulating Fluidized Bed) , allows the continuous generation
and recycling of catalyst and CO2 acceptor. The latest CFB conference in Niagara Falls, Canada (2002) has emphasized the
importance of CFB, their practical potential and the most challenging research issues. The first exploratory reactionengineering/permeation model of this novel configuration should be simple enough to assume that the gas and solid are
traveling with the same mean velocity which is varying axially only due to changes accompanying the reactions. In such a
model the effects of secondary flows, boundary layer, viscous effects, rotationally or vorticity of the flow field and turbulence
are neglected. In the recent years the Circulating Fluidized Bed (CFB) has been well studied using different approaches (e.g.
Cook, et.al.,1996 ; Kehlenbeck et al., 2001) Computational fluid dynamic (CFD) models ( e.g.: Cockx, 1996 , 1997). should be
used as tools for design and analysis of the CFB part of this novel configuration in order to relax many of the simplifying fluid
dynamics assumptions included in the model. A multidisciplinary team is to develop a Computational Fluid Dynamics (CFD)
model for this Circulating Fluidized Bed (CFB) and verify it experimentally . This model is be coupled with the reactionengineering model for the design, optimization and process control of this novel configuration.
Catalyst Attrition and Entrainment: Catalytic attrition and entrainment are problems in the BFBMR limiting the range of flow
rate and dictating the use of cyclones. For Fast fluidization (transport) reactors this catalyst attrition problem is not restrictive.
2.3 Principles and Main Processes of the Novel Configuration for the Efficient Production of Hydrogen/ Syngas
The BFBMR overcome the main limitations of the fixed bed , namely : intraparticle diffusion limitation (η = 10 -2 – 10-3) and
the thermodynamic equilibrium limitation. The development of third generation reformer (Integrate Circulated Fluidized Bed
Membrane Reformer, ICFBMR) is based on overcoming the fluid dynamics limitations of the BFBMR and satisfying the need
for continuous generation of the catalyst especially for higher hydrocarbons. The development is further expanded through the
introduction of CO2 acceptor and its regeneration. It is essential to recognize that the use of CO2 acceptor and the allowance for
continuous carbon formation and regeneration of the catalyst are characteristic to the ICFBMR configuration.
Since the ICFBMR will produce a large amount of pure CO2 it is most beneficial to add an auxiliary part consisting of a novel
reactor-regenerator for the efficient dry reforming of natural gas using the produced CO2.
Feedstock pre-processing: The special features of this ICFBMR makes it suitable for a wide range of feedstocks in addition to
natural gas and higher hydrocarbons. These include waste and renewable materials, which are to be pre-processed to produce
hydrocarbons suitable as feedstocks to this novel reformer. All classes of feedstocks are to be desulfurized to prevent catalyst
poisoning in the reformer. Careful analysis shows that available fossil fuels will be the most dominating feedstocks for the short
term, while in the medium/long term renewable energy sources will take over. Wide ranges of fossil fuels (natural gas, diesel,
gasoline, etc) and renewable/waste materials are considered .Examples of the strategic renewable feedstocks include:
i-Biomass (Mann et al, 1998, Katofsky, R.E., 2000): gasification, hydrogasification and pyrolysis produce hydrocarbons suitable
for the ICFBMR
ii-Municipal Wastewater Sludge (Stiegel, 2000): pretreatment of the waste(e.g.: gasification) followed by reforming using the
ICFBMR, offers a cost effective and environmentally friendly alternative to the existing technologies.
iii-Scrap Tires/Municipal Waste (Larson et. al., 1996): treatment produces feedstock for the ICFBMR.
iv-Coal (Breault et al, 1999): coal gasification will produce suitable feedstock for the ICFBMR.
Catalytic Processes: The following three catalytic processes are involved:
a) Steam Reforming( Xu and Froment, 1989; Elnashaie,et.al.,1990): supported Ni catalysts are very efficient for steam
reforming of hydrocarbons to hydrogen/syngas.
b) Dry Reforming( Gadalla, and Sommer, 1989): The main reaction is endothermic,
CO2 + CH4  2CO + 2H2
(ΔH = 247 kJ/mol)
Suitable catalysts include: Ni, Rh, Ru supported catalysts and ZrO2– supported Pt catalysts promoted with Cerium.
c) Oxidative Reforming(Ashcroft, et.al, 1994; Baharadwaj and Schmidt, 1995; DeGroot and Froment,1996, Roy,et.al.,1999 ):
The main reaction is highly exothermic,
CH4 + ½ O2  CO + 2H2
(ΔH = - 208 kJ/mol, exothermic).
Suitable catalysts are Ni based catalysts, Titanates based Perovskite oxides, Cobalt containing catalysts.
d)Carbon Formation: reactions a and b are usually accompanied with carbon formation on the catalyst especially for higher
hydrocarbons and for cases with low steam/hydrocarbon ratios.
Non-catalytic processes: The main non-catalytic reactions involved are :CaO reaction with CO2 ( Silaban, et.al., 1995) and
homogeneous combustion in the riser reformer part of the ICFBMR in addition to the carbon burning for catalyst
regeneration and CaCO3 regeneration in the recycle circulating part of the ICFBMR.
2.4. Main Components of the ICFBMR ( Fig.1)
Circulating Fluidized Bed (CFB): It is formed of the riser where the main reforming reactions take place as well as the
hydrogen and CO2 removal by selective membrane and acceptor( e.g.: CaO) respectively. Oxidative reactions also take place
in this part utilizing directly supplied oxygen and/or oxygen supplied through oxygen selective membranes. The other main
part of the CFB is the downer where at optimum locations of this recycle loop the catalyst and CaCO3 are regenerated and
fed back to the riser reformer part of the CFB. This CFB achieves a number of advantages over the BFBMR :
1. Breaks the fluid dynamic limitation “born” after the break of the diffusional limitations in the BFBMR.
2. Gives near plug flow conditions, which are beneficial for conversion and hydrogen selectivity.
3. Allows the continuous regeneration of the catalyst and its associated possible energy efficient autothermic operation.
4. Distribution of the oxidizing agent along the height of the reformer giving better control over oxidative reforming.
5. Flexibility of using different configuration for the sweep gas in the membrane side.
6. Continuous use and regeneration of CaO for the continuous removal of CO2.
Hydrogen permselective membranes: used in the riser reformer to break the thermodynamic equilibrium barrier of the
reforming reactions and to produce pure hydrogen in the membrane side as discussed earlier
CO2 Acceptors: addition of CaO ( or any other suitable CO2 acceptor) to the catalyst circulating bed to remove CO2 thus
assisting in “breaking” the thermodynamic barrier of the reforming reactions and supply part of the heat as discussed earlier.
Oxygen permselective membranes: used in the riser reformer to supply the oxygen along the height of the reformer for the
oxidative reforming reaction as discussed earlier.
Unique catalyst/acceptor mixture in the reformer: A mixture of mainly steam reforming catalyst with an optimum
percentage of oxidative reforming catalyst and CO2 acceptor is to be used in the reformer in order to minimize the
homogeneous combustion, maximize hydrogen production and heat integration, as discussed earlier.
Gas-solid separation unit: The catalyst out from the reformer is to be separated from the gases in a gas/solid separator and the
regenerated solid catalyst recycled to the reformer. The hydrocarbon/steam feed is to be fed in the downer pipe used for recirculating the regenerated catalyst to make use of the residence time in this pipe for the reforming reactions.
Air for
Catalyst
Combustion
Regeneration
Gas+ Solid Catalyst+CaCO3
N2
Feed
Hydrocarbon/Steam
Hydrogen
Permselective
Membranes
Fast Circulating
Fluidized bed
(Transport Reactor)
Oxygen
Permselective
membranes
Sweep Gas
Air
Gas/Solid
Separator
Catalyst circulation+CaO
H2
Gas (Mainly
CO +CO 2)
Solid
Catalyst
External
Source of CO 2
Novel reactor-regenerator dry reformer: The output gas from the separator following the reformer which is will be very poor
in hydrogen and rich in CO2 can be used together with a suitable hydrocarbon in a dry reforming process (e.g.:Gadalla and
Sommer, 1989, Bradford and Vannice, 1999). A promising approach for this reaction is to use a novel fluidized bed reactorregenerator system that utilizes the carbon formed on the catalyst in the reactor to supply the necessary heat for the
endothermic dry reforming reaction through the regeneration of the catalyst in the regenerator and recycling the hot
regenerated catalyst to the reactor (similar in a sense to the FCC process, Elnashaie and Elshishini,1996). This part of the unit
can also be used separately as a stand-alone unit for the sequestration of CO2 produced from different sources (e.g. power
plants), thus contributing to the national/international efforts to control global warming.
Syngas
CO+CO2
Reactor
Regenerator
Dry reforming
Catalyst
Circulation
Hydrocarbon
Source e.g.
Natural Gas
Fig.1 Simplified Schematic Diagram for the ICFBMR
2.4. Preliminary Evaluation of ICFBMR in Comparison to BFBMR and Industrial Fixed Bed Reformers
A comparison of the performance of the non-isothermal CFB part (actually the riser reformer part only) of the ICFBMR
against both, the industrial fixed bed reactor data and the BFBMR pilot plant is shown in table1.
The total hydrogen yield is calculated as the total amount of hydrogen produced( through the reformer and the
hydrogen membranes) per mole of methane fed.
Case A in table 1 is a comparison between CFB Riser Reformer (CFBRR) which is the main part of the novel ICFBMR
and an industrial fixed bed reformer. Even though the molar feed flow rate and the cross-sectional area are the same for both,
the difference in the size of the catalyst particle makes the CFBRR operates in the fast fluidization regime. The comparison
shows the effect of overcoming not only the diffusion resistance of the catalyst pellets in the fixed bed, but also the breaking
of the thermodynamic equilibrium barrier by the use of the hydrogen permselective membranes. A key performance
parameter to note is the hydrogen yield per m3 of the reactor, which is an important indication of the efficiency of the reactor.
It is clear that the CFBRR is much more efficient than the industrial fixed bed reformer although its exit temperature is lower
than that of the industrial fixed bed reformer.
Case A
Case B
Fixed
CFBRR BFBMR CFBRR
Bed#
Methane Conversion
0.8527
1.0
0.419
0.498
Total Hydrogen Yield
2.812
3.981
1.515
1.926
Methane Feed Rate (mol/hr)
3.953
3.953
0.041
3.953
Total Hydrogen Production(Kmol/hr) 11.12
15.74
0.062
7.61
3
Total Hydrogen Production per m of
107. 86 1992.4
4.46
963.3
Reformer ( Kmol/hr.m3)
Process gas exit temperature (K)
1130 1111.3
814
820.7
Pressure (kPa)
2200
2200
640
640
Length (m)
13.72
1.0
1.14
1.0
3
Reactor Volume (m )
0.1031 0.0079
0.0139 0.0079
Hydrogen Yield per m3 of Reformer
27.3
503.9
109
243.8
Table 1. Comparison Between the Three Reactor Configurations
(# Elnashaie and Elshishini, 1993; * Adris , 1994)
Case B in Table 1 is a comparison between BFBMR and CFBRR, both operating at low temperature/Conversion( for valid
comparison with the pilot plant data of Adris,1994). A clear advantage of the CFBRR is that much higher feed flow rates can
be used leading to higher production rates. The hydrogen yield per m3 of the reactor gives a valid indication of the efficiency
of the reactor. The progression from one generation of reformers to the next is quite obvious and the two cases of comparison
clearly show the superiority of the suggested novel configuration. Table 1 also shows the total hydrogen production (
Kmol/hr) and the total hydrogen production per unit volume of the reformer ( Kmo/hr.m3), the superiority of the CFBRR over
the BFBMR and the Fixed Bed Reformer is obvious.
In addition it is important at this stage to point out to the fact that the CFB and it continuous solid ( catalyst and CaCO3)
regeneration can be designed to be extremely thermally efficient. The steam reforming reactions are highly endothermic, and
the CaO absorption of CO2 is exothermic and will supply part of the heat in the riser of the CFB. Also, partial oxidation
(direct and/or through the O2 permeation membranes) can also supply the rest of the heat. However the most important side
of the thermal efficiency of the CFB reformer is related to the fact that the possible carbon formation in the riser reformer can
be utilized to minimize the external heat needed for the whole process. This carbon will be continuously burned during the
recycling in order to regenerate the catalyst and it will produce heat. To make this point clearer , notice the following very
simple facts for the following reactions:
CH4 + H2O  CO + 3H2
CH4 + 2H2O  CO2 + 4H2
CH4  C+ 2H2
(ΔH1 = 206 kJ/mol, 68.7 KJ/ moleH2);
(ΔH3 = 196 kJ/mol, 49 KJ/mol H2);
(ΔH = 75 kJ/mol, 37.5 KJ/mol H2)
It is clear that the third reaction of carbon formation is characterized by the lowest energy consumption per mole H 2 produced,
however in industrial fixed bed configuration this fact can not be exploited because of the catalyst deactivation associated with
this carbon formation. However in the CFB the carbon formed is continuously burned in the downer, keeping up the catalyst
activity. In addition , the carbon burning produces heat according to the reaction,
C + O2
 CO2
, ΔH = - 393.5 kJ/mol, - 196.75 KJ/ mol H2
Making thus the hydrogen production process a net energy producer rather than consumer with a heat production per mole of
H2 produced equal to 159.25 KJ/mol H2. This is from an energy point of view , however the main advantage of steam
reforming is that it does not only extract hydrogen from the hydrocarbon but also from the steam. Therefore in this
configuration the coke formation on the catalyst should not be avoided using excess steam to hydrocarbon ration since this
carbon formation is beneficial from an energy point of view. This shows that the optimal operat6ion of this CFB is
fundamentally different than the classical fixed bed and bubbling fluidized bed reformers introducing the possibility of
autothermicity without oxidative reforming and at the same time achieving very high hydrogen yields. This will eliminate the
huge furnaces of the industrial reformers . A very important industrial process, which uses in principle a somewhat similar
concept, is the Fluid Catalytic Cracking (FCC) unit for the production of high octane number gasoline from gas oil (Elnashaie
and Elshishini, 1996). The CaO cycle although it provides part of the heat to the reformer , it does not offer the same
advantage from an overall heat balance point of view because the heat produced in the reformer is equal to the heat consumed
during regeneration and recycling.
2.5. Fundamental and Practical Research Challenges for the Development of the ICFBMR
The ICFBMR is more than a novel configuration for the ultra efficient production of Hydrogen/Syngas. It actually
represents a different concept for the radical improvement of processes through addressing not only the design and operating
parameters but also more fundamentally through addressing the configuration utilizing a multidisciplinary approach. This
approach also includes the use of novel operating modes as shown in another paper in this Conference( Garhyan, et.al., 2002).
These new configuration and modes of operations help to build a very sound bridge of co-operation between theoretical and
experimental research. Some of the fundamental challenges associated with the successful development and practical
exploitation of this ICFBMR includes but is not limited to:
1.
The integrated synergy and the continuous further development of this configuration through continuous research is
scientifically important to chemical engineering and other disciplines. Classical, old fashioned chemical engineering
thinking concentrates on optimization of the operating and design parameters of processes. However, modern more
advanced methodology (e.g. Process Synthesis and Process Integration) has moved forward, considering not only the
optimization of the design and operating parameters, but also the development of the optimal configuration.
2.
The development of this novel configuration dictates a well-organized interaction between mathematical modeling and
experimental work. Rigorous mathematical models are to be developed and verified against the experimental results.
This will result in a major scientific contribution regarding the development/verification/improvement of rigorous
mathematical models. It will also give a very strong insight into the fundamentals of the non-linear coupling between
the different kinetic/separation processes taking place within the boundaries of this novel integrated configuration. It is
fundamentally important to understand the synergy between these different processes. The rigorous mathematical
modeling of the process is the best way to optimally direct the experimental program and the experimental program is
the best way to verify and improve the predictive power of the mathematical models making them suitable as reliable
design packages.
3.
Important optimization problems that are specific to this configuration ( specially for higher hydrocarbons such as
diesel) are opening the door for almost autothermic operation similar , in a sense, to industrial FCC units. This involves
strong interaction between a number of chemical engineering disciplines including, Process Integration, Process
Synthesis, Advanced Steady State and Dynamic Modeling, Advanced Multi-Objective Optimization.
4.
Rigorous dynamic modeling, stability analysis and optimal control investigation of this novel configuration are essential
for the optimal design and safe operation of this ICFBMR.
5.
The fluid dynamics of this novel configuration is not as simple as earlier configurations . The fluid dynamics under
reaction conditions is to be modeled and the nonlinear interaction between its associated phenomena on one hand and
the reaction/chemisorption and mass transfer phenomena on the other hand is to be rigorously investigated .
6.
This novel configuration is mathematically and practically not simple. It actually involves circulation of the solid
causing the models to be represented by highly nonlinear two point boundary value differential equations with all their
numerical difficulties and physico-chemical implications ( Elnashaie and Elshishini, 1996 ; Elnashaie and Garhyan,
2002).
7.
The suggested novel configuration involves a number of exothermic reactions, which will cause complicated bifurcation
and dynamic instabilities ( Elnashaie and Elshishini, 1993, 1996 ; Elnashaie and Garhyan, 2002). These important
phenomena is to be addressed in full details for the optimal , safe and stable design and operation of this ICFBMR. It is
important to mention that despite the great advances in the theory of bifurcation and chaos, little has been done
regarding its relevance to practical systems( Elnashaie and Elshishini, 1996)
8.
The rigorous fluid dynamic modeling will uncover the bifurcation and chaotic behavior associated with the fluid
dynamics of the system while kinetic/diffusion modeling will uncover the bifurcation/chaotic behavior associated with
the exothermic reactions. The combination of both models will give deeper insight into their nonlinear coupling and the
final behavior of the system. Very little has been done regarding this interaction between fluid dynamic induced and
reaction/diffusion induced chaos.
9.
The educational impact of this approach is also extremely important, fundamentally and scientifically ( Elnashaie and
Garhyan, 2002).
3.0 CONCLUSION:
An ambitious plan is outlined for the development of a novel configuration for the efficient/clean production of the ultra
clean fuel hydrogen. The plan is based on a novel configuration which exploits the main advantages of Circulating Fluidized
beds ( CFB) is order to break the fluid dynamics as well as the thermodynamic equilibrium limitations. It is shown that this
configuration will allow the use of more than one technique for product removal and thus the breaking of the thermodynamic
equilibrium barrier for these highly endothermic reactions is more efficient and flexible. It is shown that he catalyst
deactivation problem due to the carbon deposition can be utilized to achieve higher energy efficiency approaching
autothermic operation while maintaining the high hydrogen productivity of the system. Preliminary results show clearly that
this novel configuration is far superior to the previous two generations of steam reformers ( the fixed bed and the bubbling
fluidized bed). The integrated system also includes a novel reactor regenerator system for the dry reforming of hydrocarbons
utilizing the CO2 produced. A multidisciplinary approached based on the optimal combination of mathematical and
experimental techniques is adopted and the general advantages of this approach are clearly. illustrated . A Preliminary list of
the main fundamental research challenges is presented
4.0 ACKNOWLEDGEMENT
This work is financially supported by Auburn University, Grant Number 2-12085
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