The Eighteenth International Symposium on Transport Phenomena,27-30 August, 2007, Daejeon, KOREAHEAT AND REACTION CHARACTERISTICS OF MULTI-STAGE ALCOHOLIC-FUEL REFORMER
K. Tatsumi1, K. Kuwabara1, Y. Rai1 and K. Nakabe1
1

Department of Mechanical Engineering and Science,
Kyoto University, Kyoto, 606-8501 JAPANABSTRACT
A compact multi-stage alcoholic fuel reformer, which iscomposed of multiple ports of reactant supply, is
proposed and examined. The temperature, flow velocity
and exhaust gas components of the multi-stage reformer
were measured, and the effects of stage number,equivalence ratios, fuel flow rate and load change on thereforming characteristics were discussed. Particularly, byincreasing the stage number, H2 concentration increasedby 10%, and a significant increase of the local
temperature in the reformer was also avoided.
INTRODUCTION
Hydrogen is considered to be one of the essential fuels
to be used in the next-generation power supplies; suchas fuel cells, micro gas turbines and internal combustion
engines. However, during the transition period until theinfrastructure of hydrogen supply is developed, an onsite hydrogen fuel production system should be provided
as the alternative. This requires the development of ahigh-efficiency and compact fuel reforming system, bywhich hydrocarbon fuels are converted to hydrogen richsynthesis gas. To put this system into practical use,
however, we must tackle the problems such as load
fluctuation, variation of fuel aspect and low conversion
efficiency [1, 2].
From these motivations, a multi-stage fuel reformer,
which is composed of multiple ports of reactant supply, is
proposed and examined in the present study. By
multiplying the reaction stages, the local heat balance
and temperature inside this reformer can effectively andquickly be controlled, resulting in quick response to loadchange, enhancement of the reforming effectiveness andreduction of the undesired exhausts such as soot or CO[1, 3-5]. The multi-stage fuel and air supply also enables
the temperature control of the reformer, which isimportant in the meanings of the thermal durability of thedevice itself.
In this paper, results of a prototype multi-stage tube
type reformer are reported. Methanol was used as fuel inthe present experiment. Alcohol is relatively easy totransport and storage since it is chemically stable and isin liquid phase under atmospheric temperature andpressure. It is, therefore, considered to be suitable tocompact energy supply systems with an output of several
kilo watts [6]. No catalyst was mounted on the reformer
in this study. It is reported that the thermal condition of
the reformer largely affects the reforming performance ineither case: with and without the catalyst [7, 8]. As theinitial step of evaluating the multi-stage reformer,
therefore, the experiment was conducted without
inserting the catalyst to separate the effects of thecatalyst characteristics from those of multiplying thereaction stages.
The reformer temperature and exhaust gas
components were measured, and the effects of stage

⑪

②

⑬
⑮
⑭

④
⑫
Fuel
②

③

⑨

⑤
⑥

Air

②

Exhaust gas⑦⑯⑩ to Gas analyzer

Air ⑧① Air compressor③ Pressure regulator② Flowmeter⑥ Evaporator⑧ Electric heater⑩ Silica gel⑫ Driving circuit⑭ Computer⑯ Multi-stage air inlet
port⑦ Reactor⑨ Thermocouples⑪ Power supply⑬ Function generator⑮ Multi-port digital
thermometer①

Fig. 1. Schematic view of the experimental setup.
② Fuel injection port ④ Stainless tube bundle⑤ Thermocouples③ Baffle plate① Primary air port

Evaporator

Reactor⑥ Electric heater⑦ Second-stage air port

15mm
100mm

200mm
130mm

65mm 50mm

r
28mm

e

O

xi

ⅱ

ⅲ

ⅳ

ⅴ

ⅵ

ⅶ

ⅷ

ⅸ

(a) Evaporator and reactor(b) Baffle plate(c) Tube bundle

Fig. 2. Schematic view of reformer.
number, equivalence ratios, fuel flow rate, load change,on the reforming characteristics are discussed, mainly
focusing on the partial oxidation reaction (POR).
EXPERIMENTAL PROCEDURE
Figure 1 shows the present experimental apparatus toevaluate the multi-stage methanol fuel reformer. Figure2(a) illustrates the schematic and cross-sectional viewsof the reformer. As shown in the figure, the reformer wascomposed of two parts, i.e., the evaporator and reactor.

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The Eighteenth International Symposium on Transport Phenomena,27-30 August, 2007, Daejeon, KOREA

The evaporator was made of a galvanized steel pipewith the inner diameter and length of 28mm and 200mm,
respectively. A fuel supply port was located at the sidesurface, into which an injector with electric valve wasmounted. An electric signal was sent from a function
generator (Yokogawa; WE500, WE7281) to this injector
to control the valve opening. The flow rate of the fuel jet
was, therefore, controlled by adjusting the frequency andduty ratio of the signal to a certain value. An air supply
port was set at the upstream end of the evaporator. Air
supplied to this port was provided from a compressor,
and the flow rate was controlled by flow meter and valve(Kofloc; RK1250). At the upstream and downstream
areas in adjacent to the fuel supply port, electric bandheaters (Sakaguchi E.H. Voc.; BH3430) were wrappedaround the pipe. This heater was powered by a voltage
slider (Yamabishi; V-130-3) and heated the evaporator
wall up to a specified temperature. Thus, the fuel injectedfrom the fuel supply port impinged the pipe inner wall,
and was vaporized. The vaporized fuel joining the air
flowing from the upstream of the pipe, was then supplied
to the reactor through a baffle plate.
As shown in Fig. 2(a), this baffle plate was locatedbetween the evaporator and reactor, and multiple holes
were drilled in the plate. The configuration of the holes isshown in Fig. 2(b), i.e., a 5.5mm hole was located at thecenter and 6 holes with 2mm diameter surrounded thecenter one. This multi-hole baffle plate was expected toenhance the mixing between the vaporized fuel and air,and to prevent backfire from the reactor to the evaporator.
The reactor was made of a stainless steel pipe 28mm
in diameter and 500mm in length. In the areas of70≤x≤110mm and 120≤x≤160mm, bundles of stainlesstubes (tube diameter=4mm, length=40mm; see Fig.2(c))
were inserted. These tubes were expected to enhance
the reaction efficiency and also produce a stable reaction
under high equivalent ratio by enhancing the heattransfer at the tube walls. Band heaters (Watlow;
MB01E1AB3005) were attached to the pipe sidewall ateach location identical to that where the tube bundles
were inserted. These heaters were powered by a voltage
slider in the same way as those in the evaporator, andthe pipe wall was preheated before the experimentstarted.
Several loading ports were applied to the sidewalls of
the evaporator and reactor at the locations shown in Fig.
2(a). Probes for temperature measurement made of K
type thermocouples were inserted into the pipe throughthese ports. This probe was a two-hole ceramic tube
(tube diameter=3mm) having the weld spot of thethermocouples exposed at the tip. To protect the
exposed parts of the thermocouples from the flame andreactive gas, and also to prevent any catalysis effects,
the thermocouples were coated by silica-particles byburning
them
with
town
gas
into
which
Hexamethyldisiloxane was mixed. The signals from thethermocouples were recorded by a personal computer
through a digital multi-thermometer (Keyence; NR-1000).
The sampling rate and accuracy of the temperature
measurement was 1s and ±1°C, respectively.
Gas sampling for gas analysis was conducted byinserting a sampling probe into one of the loading ports.
The probe was made of stainless tube 2mm in diameter,

BSA

PC

Ar - ion LASER

Photomultiplier
Air Flow
Probe
Optical System

Test Section

Power Supply

Air Compressor

Pressure Flowmeter Particle Generator
Regulator

Fig. 3. Schematic view of LDV measurement.
r

Air
flow

O

2 . 32

1 . 62

1 . 96x / D = 1 . 25

B
x

φ28
A'

A

B'

Baffleplate

Stainlesstube bundle

Fig. 4. Cross-sectional view of the measuring region.
to which a 0.3mm hole was applied at the end. The
position of the tip end was set at the reactor centerline,
and the gas was collected by connecting the tube to a
vacuum-collecting chamber. The collected gas was thensupplied to a gas chromatograph (Shimadzu; GC-8A)
through a filtering chamber packed with silica gel, by
which water and unburned methanol were collected. A
component detector on the basis of TCD (Thermal
Conductivity Detector) method was applied to the gas
chromatography.
Thecolumn(Shinwachem.;
Shincarbon ST) mounted in the chromatograph wascalibrated for H2, N2, O2, CO, CO2 gases. Ar gas wasused as the carrier gas.
Additional air was also supplied through these ports
to the reactor operated in the way of multi-stage
reforming. The end of the air-feed tube was located at
the central axis of the reactor, and two holes were madeat the sidewall of the tube tip, from which air was injectedto the reactor in the radial direction.
Measurements
using
LDV
(LaserDoppler
Velocimetry) were also conducted to evaluate thevelocity field in the reactor. The experimental apparatus
is shown in Fig. 3. In this case, a test section different
from that used in the aforementioned experimentaccompanying reactions and temperature measurements
was applied. An acrylic pipe of the same size with thereactor shown in Fig. 2 was made where an opticalmeasurement from the sidewall was available. This pipe
was attached to the same evaporator and baffle plateshown in Fig. 2. Air with the flow rate equal to the total
value of the air and fuel supplied to the evaporator in thereaction experiment was provided to the upstream end of
the evaporator. In the upstream of the evaporator, aparticle generator (TSI; six-jet atomizer 9306) was
attached and tracing particles of oil mist (DEHS: Di-EthylHexyl-Sebacate C26H50O4, nominal diameter 1μm) was
mixed in the air. In the optical system of the LDV, thelaser produced by an argon-ion laser system (Spectra

848

The Eighteenth International Symposium on Transport Phenomena,27-30 August, 2007, Daejeon, KOREA

Physics; model 2017L-AR) having a wavelength of
514.5nm was used together with a beam splitter coupledwith a Bragg cell to detect backward flows. The Doppler
burst signals from the back-scattering light of theparticles were recorded and analyzed by a signal
processor (DANTEC; BSA F50), which was linked to andcontrolled by a personal computer.
The procedure applied in the reaction experiment is
described in the following. In the steady stateexperiments, the evaporator and reactor pipes were firstheated by the electric heater bands so that thetemperatures measured at the locations of 4.6D
upstream of the baffle rear surface and x/D=4.11
reached 200°C and 600°C, respectively. Then, theheaters attached to the reactor were turned off and thefuel and air were supplied to the reformer. Note that theheaters of the evaporator were powered during theexperiment and the temperature inside the pipe was kept
at 200°C.
In the unsteady experiment, same as the steady stateexperiment, the fuel and air were supplied after theevaporator and reactor were heated up to 200°C and
600°C, respectively. The reactor was operated under the
initial condition until the temperature characteristics wereconfirmed to be in steady state (approximately 3000s
later). The flow rates of the fuel and air were, then,changed to the secondary condition.

Table 1. Flow rate conditions in singe-stage case.
case
Qfuel [cm3/s]
qe [W]
φ1
ss_f1
0.066
112
3.0, 3.5, 4.0, 4.5,
ss_f2
0.092
151
5.0, 5.5, 6.0, 6.5,
ss_f3
0.122
201
7.0
ss_f4
0.145
270
Table 2. Flow rate conditions in double-stage case.
case
Qfuel [cm3/s] φtotal
φ1
ds_f1
0.066
4.0,
4.0
4.5, 5.0, 5.5,
ds_f2
0.092
6.0, 6.5, 7.0
ds_f3
0.145

γ =Qair2/Qair1
0.0,0.125,0.25,0.375,
0.50, 0.625, 0.75

qe [W]
112
151
270

Table 3. Flow rate conditions in unsteady operation
case.
identical case
case
Qfuel [cm3/s]
φ1
→
uo_ss
0.066
= ss_f1
4.0
uo_ds
0.066
= ss_f1→

EXPERIMENTAL CONDITIONSAs described above, experiment was carried out withsinge-stage and double-stage reformers under both
steady and unsteady state conditions, in the meanings ofevaluating the fundamental characteristics of the multistage reactor and its performance under load changing
conditions.
Table 1 shows the conditions of the experiment of thesingle-stage reformer. In this case, the fuel and air wereboth supplied to the reactor from the evaporator throughthe baffle plate. Namely, no air was injected from the
sidewall of the reactor in this case. Qair and Qfuel are thevolume flow rates of the air and fuel fed to the evaporator,
respectively. Note that Qfuel represents the flow rate of
the fuel in liquid form. φ1 is the equivalence ratio on thebases of the oxidative reaction. The stoichiometric ratioof the POR, therefore, takes place at φ1=3. qe is theoutput power of the electric heater attached to theevaporator. As shown in Table 1, the fuel flow rate, Qfuel,was changed under four conditions, and with each Qfuel,the air flow rate, Qair, was varied in the range ofequivalence ratios, 3.0≤φ1≤7.0.
In Table 2 is shown the conditions of the experimentcarried out for a double-stage reformer. In this case,additional air was injected to the reactor at the location
between the two tube bundles, x/D=4.11. The
experiment was conducted under three conditions of Qfuel.
In regard to each Qfuel, air was supplied to the evaporator
and reactor at the mass flow rate of Qair1 and Qair2,
respectively. The total amount of air provided to thereactor, Qtotal=Qair1+Qair2, was kept constant in each Qfuelcase, and the ratio of Qair1 and Qair2 (γ =Qair2 /Qair1) waschanged. Therefore, the equivalence ratio at the firststage, to which fuel and air were supplied from the baffle
plate, was varied in the range of 4.5≤φ1≤7.0. Note that

Qfuel [cm3/s]
0.145
0.145

φtotal

φ1

4.0
4.0

4.0
5.0

identical case
= ss_f4= ds_f3

the total equivalence ratio of the whole reformer, φtotal,
calculated from the values of Qtotal and Qfuel , was kept at
4.0.
Table 3 tabulates the conditions of the unsteadyexperiment. The experiment was conducted by firstrunning the reformer in a steady operation under the
initial condition, and then changing the condition to thesecondary one. Two cases were tested. One is bystarting the reformer under an initial condition of
Qfuel=0.066cm3/s and φ1 =4.0 both supplied in a singlestage form, which was identical to that in case ss_f1.
Then Qfuel and Qair were changed to Qfuel=0.145 cm3/s
and Qair=151 cm3/s both supplied again in a singe-stage
fashion. This condition implies a load change fromsingle- to single-stage case keeping φ1 constant at φ1=4.0.
The other is by starting the experiment under the same
initial condition mentioned above, and then supplying thefuel and air in a double-stage fashion. In this case, Qfuel,Qair1 and Qair2, were 0.145, 100 and 51cm3/s, respectively,i.e., the equivalence ratios were φ1=5.0 and φtotal=4.0. In
this experiment, measurements of the instantaneoustemperature distributions and gas sampling at the time
period of 0, 10, 30, 60, 90, 120, 180, 600 and 2000s after
changing the condition were carried out.
RESULTS AND DISCUSSION
Here are discussed the results of the multi-stage
reformer under the conditions of single-stage, doublestage and unsteady state conditions. Before moving onto the discussion, several parameters that are used in
discussing the characteristics of the reformer are
introduced here.

849

The Eighteenth International Symposium on Transport Phenomena,27-30 August, 2007, Daejeon, KOREA

φ=4.0,
φ=7.0

0.5

φ=5.0

x/D = 5.89
0.4

800

r/D

0.3

600

0.2

400

0.1

200
0

Tube bundles

0 2 4 6 8 10 12 14 16 18 0 2 4 6 8 10 12 14 16 18

x/D
o

0.0
200

x/D

(a) case ss_f1
Temperature, T [ C]x/D = 2.32

Tube bundles

400

x/D = 4.11

600 200400

600 200

400

600

o

Temperature, T [ C](b) case ss_f2

Fig. 6. Radial temperature distributions in the reactor
at x/D=2.32, 4.11, 5.89 (case ss_f2, φ1=5.0).

800
600

0.5

400

x/D =1.25

0x/D =1.62

x/D =1.96

3 0 1 2 3

0 1 2 3x/D =2.32

0.4

200

Tube bundles

Tube bundles

0 2 4 6 8 10 12 14 16 18 0 2 4 6 8 10 12 14 16 18

x/D

x/D

(c) case ss_f3

0.3

r/D

o

Temperature, T [ C]

φ=3.0,
φ=6.0,

0.2(d) case ss_f4

0.1

Fig. 5. Streamwise temperature distributions along
reactor centerline (case ss_f1~f4).

0.0

M CH OH , consumed
3

M CH OH , supplied=

3

M CO + M CO
YCO + YCO
YN

2

2

×

MN

(

3 0 1 2 3

0 1 2 33

x/D =2.32

0

1

2

0

1

2

3

r/D

U [m/s](b) Cross-section B-B'

Fig. 7. Cross-sectional distributions of thestreamwise velocity in the area downstream thebaffle plate (identical flow condition with case ss_f1).
belonging to the reacted methanol were used ingenerating H2 and H2O. ξ H O is, thus, obtained by the2following equation.
ξ H 2O = 2α − ξ H 2

2

(3)

3

)

Single-stage Reformer
Figure 5 shows the streamwise distributions of thetemperature along the reactor centerline in cases
ss_f1~4. In Fig. 5(a), the temperature at the location of
x/D=4.11 takes its maximum value in the case of φ1=3.0
and decreases as φ1 increases. This tendency is incommon with the temperatures at other locations or inother fuel flow rate cases. This is due to the fact thatwhen φ1 becomes small, the oxygen supply rate to themethanol increases that results in enhancement of theoxidization reaction and increase of the gas

(2)

2

was

x/D =1.96

2

0.3

0.0

In calculating the production rate of H2O, ξ H O , theassumption

x/D =1.62

x/D =1.25

1U [m/s]0.1

M CH OH , supplied

YX / YN 2 M N 2
MX=
M fuel,supplied
M fuel,suppliedfollowing0

0.2

M is the molar flow rate. YX is the concentration of the X
component in the exhaust gas. Thus the conversion
ratio of methanol, α, was defined.
To evaluate the production efficiency of eachcomponent, the production rate of component X against
1mol of methanol, ξX, was defined as Eq. (2).

ξX ≡

2

0.4

(1)

3

=

0.5

2

M CH OH , supplied

1(a) Cross-section A-A'

In the present study, the quantities of the reacted or
unreacted methanol cannot be measured directly due tothe properties of the column applied to the gas
chromatograph and the silica gel chamber, which collects
water and methanol. Therefore, these quantities were
estimated from the concentrations of other gases
included in the exhaust gas.
Since the summation of the concentrations of H2, N2,
O2, CO and CO2 in the exhaust gas was 100±2%, themajor components of the gas was expected to be these5 values plus water and methanol that was collected by
the silica gel chamber. When paying attention on the
carbon atom, the components possessing it among the
aforementioned ones are CO, CO2 and methanol.
Therefore, the quantity of the reacted methanol can becalculated by Eq. (1) using the concentrations of CO and
CO2 in the exhaust gas.

α≡0applied:

all

H

atoms

850

80

YH ,
2

YO ,

YCO,

YCO

YN

2

2

1.0

2

0.8

60

α

0.6

40

0.4

20
0

3

4

5

6

φ1

7

3

(a) case ss_f1
Concentration [%]case ss_f1
case ss_f3

0.2

4

5

6

φ1

7

0.0

3

4

80

5

6

φ1

7

4

5

Fig. 9. Conversion ratios of methanol.

60

ξH ,

ξH O,

2

2

ξCO,

40
20
0

case ss_f2
case ss_f4(b) case ss_f2

3

4

5

6

(c) case ss_f3

φ1

7

3

4

5

6

φ1

7

ξ

Concentration [%]The Eighteenth International Symposium on Transport Phenomena,27-30 August, 2007, Daejeon, KOREA(d) case ss_f4

Fig. 8. Relation between concentrationequivalence ratio (cases ss_f1~4).

and

1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0

3

4

ξCO

2

5

6

φ1

7

3

(a) case ss_f1

ξ

temperature. In addition to this, since φ1 was adjusted
by changing the air flow rate under a constant fuel flowrate condition, increase of φ1 leads to a reduction of thetotal flow rate of the gas supplied to the reactor. In thiscase, the heat loss from the reactor wall increases. Thismight be another reason why the temperature
decreases under larger φ1 condition.
The streamwise distributions of the temperatureshow a common characteristic in all cases, namely, amaximum peak is obtained at the location of x/D=4.11
and decreases in the downstream area. It is, therefore,
expected that the reaction takes place mainly at thelocation where the first tube bundle is inserted.
Cross-sectional temperature distributions were
measured by traversing the thermocouple probe in theradial direction. Figure 6 shows the results obtained incase ss_f2 of φ1=5.0. The measured streamwise
locations were x/D=2.32, 4.11 and 5.89 that correspond
approximately to the inlet of the first tube bundle,
middle of the first and second bundle and the outlet ofthe second bundle, respectively.
Figure 7 shows the spanwise distributions of thestreamwise velocity at the locations of x/D=1.25, 1.62,
1.96 and 2.32, i.e., the area between the baffle plateand first tube bundle, obtained in the LDV
measurements. Figures 7(a) and (b) show the results ofthe cross-sections respectively intersecting the centerand midpoint of the surrounding nozzles of the baffle
plate (see Fig. 4).
In Fig. 6, at the location of x/D=2.32, thetemperature takes a minimum peak at the reactor
centerline and higher temperature is obtained near the
sidewall. In Fig. 7(a), two peaks of U are observed at
the locations of r/D=0 and 2.85. In Fig. 7(b), a maximum
peak is obtained at r/D=0. These peak locations
correspond to the areas in the downstream of thecenter and surrounding jets. Since the center nozzle
has a larger diameter compared with that of the

1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0

3

4

5

6

(c) case ss_f3

φ16(b) case ss_f2

7

3

4

5

6

(d) case ss_f4

φ1

φ1

7

7

Fig. 10. Mole production rates (cases ss_f1~4).
surrounding ones, a jet of large flow rate is produced
from the center nozzle. The lower temperature obtainedat the centerline is, therefore, attributed to this center jet
blowing the mixed gas produced from the evaporator.
On the contrary, the reactor wall temperature isincreased by the heat produced from the downstreamof the reactor. The air near the wall is, hence, heated
and a higher temperature is obtained compared withthe fluid located near the centerline.
As shown in Fig. 7(a), the surrounding jets diffuse in
the downstream, and the velocity decreases as x/Dincrease. In the same area close to the sidewall, flow
with negative velocity is obtained in Fig. 7(b). These
results indicate that a flow of three-dimensional
structure was generated in the downstream area of thebaffle plate, and a circulation might exist near the
sidewalls due to the interaction between the center jet
and surrounding jets. Consequently, most of the fuel-air
mixed gas enters the inlet of the first tube bundle in thearea near the reactor centerline.
On the other hand, at the outlet of the tube bundles,
i.e., x/D=4.11 and 5.89 shown in Fig. 6, the temperaturetakes a maximum peak at the reformer centerline anddecreases as it approaches the reactor wall. The
temperature increase obtained between x/D=2.32 and851

The Eighteenth International Symposium on Transport Phenomena,27-30 August, 2007, Daejeon, KOREA

x/D=4.11 implies that the reaction mainly starts not in
the area between the baffle plate and the first tube
bundle but inside the first tube bundle. Furthermore,since the maximum peaks of U at x/D=2.32 and T at
x/D=4.11 are located at the centerline, the reaction is
expected to occur in this area.
Figure 8 shows the relation between theconcentrations of components in the exhaust gas andequivalence ratio, φ1. The concentration of O2 is lessthan 0.2% in all cases indicating that the supplied O2
were totally consumed in the reaction. The
concentration of H2 increases as φ1 increases in thearea of φ1<5.0. However, at φ1>5.0, the values areconstant or, in some cases, slightly decreases as φ1increases.
The aforementioned gas concentrations are thevalues directly obtained from the gas analysis of theexhaust gas. Therefore, effects of the methanol andwater removed from the gas are not sufficiently
considered. In the following, the characteristics ofparameters α and ξX described in Eqs. (1) and (2) are
discussed.
Figure 9 shows how φ1 affects the conversion ratioof methanol, α. α decreases linearly as φ1 increases.
When φ1 is small, larger reaction heat is produced dueto the increase of the supplied O2 rate. The temperatureinside the reactor, therefore, increases as described inFig. 5, and the decomposition and fully-oxidation
reactions of methanol become more active. On thecontrary, under larger φ1 conditions, the air flow rate is
reduced that incurs a fuel-rich condition in the reactions
including POR and larger heat loss at the reactor walls.
The production ratio, ξ, is shown in Fig. 10. In theregion of φ1<5.0, ξ H is constant or slightly increases ascase ds_f3: γ=0.375, φ1=5.0
case ds_f3: γ=0.75, φ1=7.0800oTemperature, T [ C]case ss_f4: φ =4.0,
case ds_f3: γ=0.50, φ1=6.0,

600
400
tube bundles

200
0

0

2

4

6

8

10 12 14 16 18

x/D
Fig. 11. Streamwise temperature distributions(comparison of cases ss_f4 and ds_f3).
ξH ,

ξ

1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0

2

ξH O,
2

ξCO,

ξCO

2

Single-stage

0.0

0.2

0.4

γ

0.6

Single-stage

0.8

0.0

(a) case ds_f1

ξ

1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0

2

0.2

0.4

γ

0.6

0.8

(b) case ds_f2

Single-stage

0.0

0.2

0.4

γ

0.6

0.8

(c) case ds_f3

φ1 increases, and decreases in the area of φ1>5.0.

Fig. 12. Relation between γ and ξ.

Hence, the maximum production ratio of H2 is obtained
approximately under the condition of 4.0<φ1<5.0. When
φ1 is small, a large conversion ratio, α, is obtained asshown in Fig. 9. However, oxidization of H2 to H2O also
becomes active due to the high temperature and theconcentration of H2 decreases as shown in Fig. 8. On
the contrary, under larger φ1 condition, the conversion
rate of methanol becomes small. Thus, a tradeoff
matter exists between α and H2-yield. This is believed
the be the reason why the maximum peak of ξ H is
2

obtained at 4.0<φ1<5.0
Double-stage Reformer
Figure 11 shows the streamwise distributions of thetemperature along the reactor centerline obtained in thecases of a double-stage reformer. The results of case
ss_f4 of φ1=4.0 are included in the figure for comparison.
At x/D=3.97, the temperature decreases as γ
increases, and in the downstream area (x/D≥6), thetemperature increases under larger γ conditions. Since
the total amount of air supplied to the reactor was fixedin cases ds_f1~3, an increase of γ, which is the ratio of
the air flow rate injected to the second and first stages,
implies the increases of φ1 and air flow rate supplied tothe second stage. In the double-stage reformer, the airand fuel were supplied to the first stage in the same852

way as in the single-stage case, and a common
reaction characteristic is expected to take place. The
reaction temperature is, therefore, reduced under larger
φ1 condition due to the fuel rich condition obtained in
the first stage of the reactor as mentioned in theprevious section.
On the other hand, as indicated in Fig. 9, larger
amount of unreacted methanol enters the second stage
in association with the increase of φ1. In combination
with the additional air injected to the second stage, amore active reaction, therefore, takes place in thedownstream. This is believed to be the main reason
why a higher temperature is obtained in case ds_f3 in
the downstream area.
Figure 12 illustrates how γ affects ξ. The results ofthe single-stage case are included in the figure forcomparison. In cases ds_f1 and ds_f2, the variation ofξ H is small against γ . In case ds_f3, a slight increase2of ξ H is obtained as γ increases in the area of γ <0.5,
2

and the difference between the results in cases ss_f4
and ds_f3 is approximately 10%. This implies that the
production ratio of H2 is not largely affected byincreasing the reformer stage from single- to doublestage: at least the performance of double-stage case is

The Eighteenth International Symposium on Transport Phenomena,27-30 August, 2007, Daejeon, KOREA

800
Tx/D=4.11oTemperature, T [ C]

not inferior to that of the single-stage case in thepresent study.
Although a noticeable improvement was notachieved in terms of the reaction efficiency byintroducing the double-stage reforming, the results
obtained in Figs. 11 and 12 indicate the possibility ofcontrolling the temperature of the reformer bymultiplying the reaction stages without incurring aserious deterioration of the reforming efficiency. This isimportant since the reformer can be protected fromthermal fatigue by applying an appropriate gas supply
ratio and preventing the generation of a significant
increase of local temperature.

600

Tx/D=5.89

400

0

Te
0

100

t=30s,

ξH

500

600

Temperature, T [ C]oTx/D=5.89

400

Tx/D=2.32
200

Te
0

100

200

300

400

500

600

Elapsed time, t [s](b) case uo_ds

Fig. 13. Temperature profiles after load change(t=0: load change period).

1.0

ξH

2

0.8
case uo_ss
case uo_ds

0.6
0.0
0

2

At

400

Tx/D=4.11600

2(t=10s).

300

800

0

condition was changed. Te in Fig. 13 is the temperatureof the gas in the evaporator. In case uo_ss, thetemperature at x/D=4.11 increases markedly andreaches 750°C at 250s. On the contrary, in case uo_ds,
the temperature difference at the time period of the loadchange is small. This is considered to be owing to theseparation of the air supply into the first and second
stages. By dividing the air, the equivalence ratio in thefirst stage, φ1, was increased and the reaction
temperature was, therefore, decreased. On the other
hand, due to the additional air produced to the second
stage, the temperature at x/D=5.89 was increased,larger in case uo_ds than in case uo_ss.
In Fig. 14, ξ H decreases just after the reformer loadchanged200

Elapsed time, t [s](a) case uo_ss

Experiment of Load Change in Single-/double-stage
Reformers
In this section, the results obtained in the reformer
operating under the condition of load change are
discussed. As the load change condition, the fuel flowrate was increased, and the reformer characteristics
after the load change were monitored in the experiment.
Figures 13 and 14 show the distributions of thetemperature and H2 production rate, ξ H , after theis

Tx/D=2.32

200

continuously

50

100

150
200
250
Elapsed time, t [s]Fig. 14. Time history of H2 production rate after
load change.

2

decreases in case uo_ss, while in case uo_ds, it makesa relatively quick recovery and increase. As the timeproceeds, ξ H in case uo_ds shows a larger value and2

the difference of ξ H between the two cases remains

transfer between the fluid and wall that preserves
high temperature condition.
4. A maximum peak existed in the H2 production rate
per supplied fuel in relation with φ. This is due to thetrade-off between the methanol conversion ratio, α,and H2-yield.
5. In the double-stage case, temperature control of thereformer was possible without deteriorating thereforming efficiency. Moreover, in some cases, anincrease of the H2 production rate by 10% was
obtained in this case compared with the singe-stage
case.
6. A faster recovery from a temporal decrease of the H2
production performance during the load change of thereformer was obtained in the double-stage case,which indicated that a higher response performance
could be achieved in this case than the single-stage
case.

2

almost constant. This result implies the possibility ofobtaining a better response by multiplying the reaction
process in the reformer.
CONCLUSIONSIn the present article, single- and double-stage methanol
fuel reformer was experimentally evaluated particularlyon the basis of the thermal and reaction characteristics.
The major conclusions obtained are listed in the following.
1. A multi-stage reformer consisting of evaporator andreactor was fabricated and operated under theconditions of varying the equivalence ratio, φ, in therange of 3.0≤φ≤7.0. Hydrogen production and asuitable temperature level for practical use wereobtained by the reformer.
2. A better performance was obtained under theconditions of φ=4.5~5.0 than the stoichiometric valueof partial oxidation, φ=3, in the present reformer.
3. Most of the reaction was expected to take place
inside the first tube bundle due to the effective heat

853

The Eighteenth International Symposium on Transport Phenomena,27-30 August, 2007, Daejeon, KOREAREFERENCES
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Problems Identification and Research Needs, Int. J.
of Hdyrogen Energy, 26 (2001), pp. 243-264.
3. H. Marsh and D. Thingarajan, AIChE Ammonia
Safety Symposium, (1992).
4. M. Dunster and J. Korchnak, Production of Synthesis
gas from Hydrocarbonaceous Feedstock, Eur Patent
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5. T. Calcott and T. Deague, US Patent No. 4 042 344(1977).
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Profile of Catalyst Bed during Oxidative Steam
Reforming of Methane over Pt-Ni Bimetallic
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ACKNOWLEDGEMENT
The work is partially supported by the Mazda foundation,
General Sekiyu K.K. research foundation and Japan
Society for the Promotion of Science. The authors
would like to gratefully acknowledge their support.
NOMENCLATURE
D reactor inner diameter, mm
M molar flow rate, mol/s
q heat provided from the heater, W
Q volume flow rate, cm3/s
r radial distance from the reactor centerline, mm
T temperature, °C
x streamwise axis, mm
YX volume concentration of component X, %Greek symbols
α methanol conversion rate
ξX production rate of component X against supplied fuelflow rate
φ1 equivalence ratio at the first stage
φtotal equivalence ratio of the whole reformer
γ ratio between the air flow rates supplied to the firstand second stages

854