Computational Methods and Experimental Measurements XVI 207

Experimental study on a compact
methanol-fueled reformer with heat
regeneration using ceramic honeycomb(third report: observation of reaction structure
and its effect on reforming characteristics)
Y. Rai1, H. Kogame1, K. Tatsumi1,2 & K. Nakabe1,2
1

Department of Mechanical Engineering and Science,
Kyoto University, Japan
2
Advanced Research Institute of Fluid Science and Engineering,
Kyoto University, Japan

Abstract
A ceramic honeycomb is applied to a 1-kW class compact tubular-type fuelreformer based on non-catalytic partial oxidation (POX) of methanol. Liquidmethanol was used due to its easy handling characteristics. It is confirmed that
POX in a super-rich condition can be sustained within the reactor. In mostconditions, the reaction was stabilized near the outlet surface of the ceramichoneycomb where the maximum temperature is observed. The maximum
temperature reaches approximately the adiabatic flame temperature, therefore,
the ceramic honeycomb works as an adiabatic layer and a reaction stabilizer
which can sustain the reaction at a certain location. The location of the reaction
varies with regard to the thermal load conditions. Stable and high conversion rate
was obtained when the reaction is stabilized on the outlet surface of the ceramichoneycomb. This robust feature of reaction stabilization is a significant
characteristic of the ceramic honeycomb. The reaction characteristic and its
effect on the reforming performance are investigated in this study using detailed
measurements of temperature distributions and gas components.
Keywords: fuel reformer, methanol, non-catalytic partial oxidation, heat
regeneration, porous material.

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208 Computational Methods and Experimental Measurements XVI

1 Introduction
Due to the recent serious environmental crisis and fossil fuel depletion, hydrogenas an energy carrier has gained more attention as a key to alternative energy
supplying system. Hydrogen can be used as a fuel for highly-efficient devices
such as fuel cells and hydrogen engines, which emit only water, provided thatpure hydrogen is introduced. Moreover, in terms of energy security, hydrogen isa candidate fuel for a secure future energy system since it can be derived from avariety of fuels. However, hydrogen must be artificially synthesized from othermaterials. Furthermore, due to its low energy density, its highly-efficientdelivery and storage systems need technological innovations, which still requireconsiderable time and cost. Therefore, at the transition stage to the futurehydrogen society, using conventional infrastructure to deliver hydrocarbon fueland reforming it at the site of use is the only way to build a highly-efficienthydrogen energy system. The primary motivation of the present study is toconstruct a compact and simple fuel reformer with a power output of about
1 kW.
Methanol was chosen as the reforming agent in the present study, due to its
high energy density and wide availability. Methanol is widely available in theindustry and can be synthesized from a variety of hydrocarbon fuels including
the abundant coal resources. In addition, methanol can also be derived frombiomass materials, yet it need not conflict with the food supply because it can besynthesized from sources such as wood chips or animal wastes [1, 2].
To construct a simple and compact reforming system, partial oxidation (POX;
also known as fuel-rich combustion) was chosen. POX is an exothermic reactionthat allows a thermally self-sustainable system without a catalyst, which
contributes to a compact and low-cost system. Moreover, POX can work withvarious fuels including low quality fuels, or heavy fuels.
However, due to its fuel-rich condition, flame temperature and heat release
rate are markedly lower than for complete oxidation reaction, which prevents astable reaction with a high reaction rate from being sustained within the reactor.
Porous material (e.g. ceramic honeycomb) is often introduced in the reactor tostabilize flame by its flow straightening and highly convective nature. The flamestabilizing effect of porous material is well discussed in terms of the flame
location, temperature, and exhaust characteristics [3–5]. In this study, therefore,
the role and its effectiveness of ceramic honeycomb to methanol POX will be
discussed based on the various thermal load conditions.
Furthermore, heat regeneration effect of ceramic honeycomb will be added tothe present reformer by placing the secondary honeycomb in the downstream of
the reaction region. Echigo [6] proposed the concept of the radiation converter
wherein the enthalpy of the working gas is efficiently converted into radiation
emission through highly convective heat transfer between the gas and the solid
surface. Okuyama et al. [7] also reported that by adding a porous material, whichworks as a radiation converter and regenerates the energy from the exhaust gas tothe unburned mixture, it was possible to stabilize a super-rich flame beyond the

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flammability limit. This concept of porous radiation converter has been applied
to the present reformer to enhance the reforming reaction.
In our study, a compact methanol fuel reformer based on non-catalytic POX
has been investigated in terms of equivalence ratio and the configuration ofceramic honeycomb within the reactor [8, 9]. Then the optimum experimental
condition was obtained in a slight fuel rich condition rather than the
stoichiometric condition of POX. The increase of methanol conversion wasobserved by inserting the secondary honeycomb. However, the specific role andits thermal effect were not clearly explained in the previous reports. Therefore,
the thermal effect of a ceramic honeycomb on the reforming reaction will be
discussed in the present report with regard to the exhaust gas component andreformer performance, correlating the flame stability and its location. We thenapply the radiation converter to the present reformer and discussed the energy
regeneration effect by the secondary honeycomb.

2 Experimental setup and procedure
2.1 Fuel reformer
Figure 1(a) shows the schematic view of the present compact fuel reformer. The
reformer was composed of the evaporator and the reactor. The evaporator was in
the upstream part and was made of a steel pipe with an inner diameter and alength of 28 and 200 mm, respectively. The evaporator was wrapped in twoplaces with electric band heaters for fuel evaporation. Methanol as a fuel was
injected through the injector mounted on the surface of the evaporator. The
electric valve of the injector was driven by the rectangular signal generated by
the function generator for the desired flow rate. Air, on the other hand, wassupplied from the air port located at the upstream end of the evaporator. Air flowrate was controlled by a mass flow controller. Electric band heaters were

Figure 1:

Fuel reformer.

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210 Computational Methods and Experimental Measurements XVI
wrapped around the evaporator and the temperature inside the evaporator was set
to 427K by adjusting the power supply to the heaters during the experiment sothat the fuel injected from the injector was vaporized instantly after impinging on
the high temperature inner wall of the evaporator. The vaporized fuel and air
were mixed in the evaporator and then supplied to the reactor through a baffle
plate shown in Fig. 1(b). This baffle plate was a 12mm-thick stainless steel disk
with multiple holes drilled on it. Due to its multi-hole configuration, it was
expected to enhance the mixing of fuel and air, and to prevent the flame frombackfiring to the evaporator.
The reactor was made of a stainless steel pipe with inner diameter D =36.7mm and 300mm in length. Several ports were opened on the surface of thereactor. These ports could be used to insert probes for temperature measurement
and gas sampling. Another electric band heater was twined around the reactor at
the location of 3.1≤ x/D ≤ 4.3. This heater was attached to preheat the reactor
prior to the experiment so that the reaction starts smoothly once reactants aresupplied to the reactor.
2.2 Ceramic honeycomb
In this fuel reformer, a cylindrical honeycomb ceramic of 34mm in diameter and
40 mm in length was inserted in the reactor in order to obtain a wide range ofreaction stability. The configuration and dimensions are shown in Fig. 1(c). This
honeycomb was made of cordierite ceramic, having mesh of cell number 300 cpi(square cells per square inch). A hydraulic diameter of a unit cell was 1.25mm
and the fraction of the open frontal area was 69%.
2.3 Measurement procedures
The local gas temperature distribution was obtained by two types ofthermocouple probes: radial-type and transversal-type. The radial-type probe wascomposed of two-holed ceramic tube (O.D. 3 mm) and 0.1mm K-type
thermocouple wires. The thermocouple wires were welded together at theceramic tube tip. This probe was radially inserted into the reactor at each port
located on the reactor side-wall so that the gas temperatures at multiple locations
could be measured simultaneously during the experiment. The transversal-typeprobe, on the other hand, was composed of 0.1mm K-type thermocouple wires
inserted from the uppermost port of the evaporator and stretched along the center
axis of the reformer. By using the transversal-type probe, it was possible tomeasure detailed gas temperature distributions along with the center axis of thereactor. All of the welded junctions of the thermocouple probes were coated withsilica particles by which the probe was prevented from both deteriorating andworking as a catalyst for the reaction. Signals from all the probes were recorded
by a personal computer through a digital multi-thermometer (Keyence; NR1000). The sampling rate and accuracy of the temperature measurement was 1Hz
and ±1K, respectively.

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Gas sampling for gas component analysis was conducted by inserting asampling probe into the gas sampling port located at x/D = 7.08. The samplingprobe was made of stainless steel tube with 3mm in outer diameter. The positionof the tip end was set at the reactor centerline, and the reforming gas wascollected by connecting the probe outlet to a one litter vacuum-collecting
chamber. On the way to the vacuum bottle, sampling gas flew through a 0.2mmhole nozzle which froze the gaseous reactions. The collected gas was thensupplied to a gas chromatograph (Shimadzu; GC-8A) through a filteringchamber packed with silica gel, by which water and unburned methanol were
removed from the gas. A gas component detector on the basis of TCD (Thermal
Conductivity Detection) method was applied to the gas chromatograph. The
column (Shinwa chem.; Shincarbon ST) mounted in the gas chromatograph ovenwas calibrated for H2, N2, O2, CO, and CO2 using external standard method.
Argon was used as the carrier gas.
2.4 Experimental conditions
In this study, two cases of experiments were conducted. In Case 1, a ceramichoneycomb, called Honeycomb A was introduced at a single location(1.74 ≤x/D≤ 2.83). Honeycomb A worked as a reaction stabilizer which avoided
the reaction from blowoff or backfiring in wide range of thermal load, qload.
In Case 1,therefore, the thermal characteristic and the role of honeycomb
ceramic in the fuel reformer were investigated. In Case 2, on the other hand, thesecondary honeycomb called Honeycomb B was added in the downstream of
Honeycomb, 4.47 ≤x/D≤ 5.56. Honeycomb B worked as an adiabatic layer which
increased the temperature level of the reaction and enhanced the reforming
reaction. The adiabatic characteristic of Honeycomb B in terms of heat
regeneration was discussed comparing the temperature profiles of Cases 1 and 2.
In the present study, thermal and reaction characteristics of the methanol fuelreformer in terms of thermal load, qload, were investigated for both Cases 1 and 2.
Experiments were conducted at a fixed equivalence ratio φ = 3.5. The value ofequivalence ratio is based on the complete combustion reaction. The
stoichiometric equivalence ratio of POX, therefore, is φst = 3. Table 1 shows thefuel and the air flow rates corresponding to each thermal load condition. The
value of qload was determined by the fuel flow rate, Qfuel, based on the lower
heating value, LHV, of methanol.
Table 1:

Fuel and air flow rate (φ = 3.5).

qload [kW]
Qfuel [mL/min]
Qair [L/min]
0.37
1.40
1.65
0.64
2.43
2.87
1.04
4.00
4.71
1.45
5.56
6.56
1.76
6.73
7.94
2.12
8.10
9.56
*Flow rate ratio based on qload = 0.37 kW.
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Ratio *
1
1.74
2.85
3.97
4.81
5.79

212 Computational Methods and Experimental Measurements XVI
The procedure applied in the experiment is described as follows. Prior to theexperiment, the evaporator and the reactor were heated by the electric bandheaters up to about 470 K and 820 K, respectively. Then, the fuel and the air
were supplied to the evaporator at the desired flow rates. After the reactants were
supplied, the power supplied to the electric heaters was adjusted to keep thetemperature inside the evaporator about 420 K. On the other hand, the heaters
attached to the reactor were turned off since the exothermic POX reaction
sustains by itself in the reactor.

3 Results and discussion
3.1 Temperature profiles
In the present fuel reformer, a steady-state, super-rich flame of methanol could
be stabilized due to the preheating and adiabatic characteristics of the ceramichoneycomb. As described in the previous section, the reactor was preheated up
to 820K prior to the experiment so that the premixed gas supplied was ignited byitself due to the high temperature environment in the reactor. Once the reaction
started, the reaction was able to sustain by itself without the heat supply from theelectric band heater in the reactor. In this section, the heat transfer characteristics
in terms of temperature profiles within the reactor are discussed forunderstanding the thermal structure of the reformer.
Figure 2 shows the representative temperature profiles in Case 1 for several
qload conditions varying from 0.37 kW to 2.12 kW at a constant φ = 3.5. A
hatched region corresponds to Honeycomb A, and a horizontal broken line
indicates the calculated value of the adiabatic flame temperature, Taf, based on
the initial temperature condition of 420 K in the evaporator.
1400

φ = 3.5

Taf

Temperature [K]

1200
1000
800
qload

600

0.37 kW1.04 kW2.12 kW

400
1

2

3

4

5

6

7

8

x/D

Figure 2:

Temperature profiles (Case 1, φ = 3.5).

In all the cases, the reaction region was stabilized at the outlet of Honeycomb
A, where the maximum temperature was observed. The value of the maximum
temperature Tmax reached close to Taf, which indicates the reaction occurs almost

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in an adiabatic condition. The temperature in the downstream region of thereactor, x/D> 4.0, on the other hand, increased with the increase of qload. This isbecause the net heat amount of the reaction increased under larger qload
conditions, lessening the effect of heat loss, and causing the temperature gradientat the downstream region of the reactor to become gentle in the larger qload
conditions.
Figures 3(a) and (b) show the location of the maximum temperature,(x/D)Tmax, and the value of Tmax with respect to qload, respectively. In both figures,the square symbols correspond to the raw data obtained by the respective
experiments, and the solid lines represent the averaged values of the experimentsin the middle range conditions of qload, 0.64 ≤ qload≤ 1.76 kW. The broken line in
Fig. 3(b) shows the adiabatic flame temperature of φ = 3.5. As shown in
Fig. 3(a), for the conditions of 0.64 ≤ qload≤ 1.76 kW, the reaction region stayedat around x/D= 3.2, indicating that the stable reaction occurred at an almostidentical location even in the wide range of qload. The values of Tmax
corresponding to these qload conditions shown in Fig. 3(b) stayed around Taf. In
the smaller qload condition (qload≤ 0.64 kW),the value of Tmax observed a slightdecrease which is believed to be the effect of its relatively small reaction heatrelease rate.
1600

4.5

Case 1Case 1

φ = 3.5

4.0

1400

Tmax [K](x/D)Tmax

3.5
1200

3.0
2.5

1000

Honeycomb A

2.0
1.5

0.5

1.0

1.5

2.0

φ = 3.5
800

0.5

1.0

qload [kW](a) The location of maximum
temperature, (x/D)Tmax.
Figure 3:

1.5

2.0

qload [kW](b) Maximum measured temperature,
Tmax.

Effects of qload, on the reaction region and its temperature(Case 1, φ = 3.5).

In the higher qload conditions, on the other hand, the reaction location moved
downstream, while the value of Tmax did not change markedly. This phenomenon
can be explained as “liftoff” of the reaction from Honeycomb A. The reaction
region moved downstream due to its large mixture gas velocity, although thereaction itself kept on at the same level as for the stable conditions. Liftoff may
cause unstable reaction within the reactor which is not suitable in a compact fuelreformer. It can also be estimated that “blowoff” of the reaction will occur whenqload is increased beyond the stable limitation.

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214 Computational Methods and Experimental Measurements XVI
Figures 4(a) and (b) show the locations of the maximum temperature and its
values with respect to the qload conditions for both Cases 1 and 2. As shown in
Fig. 4(a), the reaction region moved upstream by the effect of Honeycomb B in
the cases of qload< 1.45 kW. For larger qload conditions, the effect of Honeycomb
B on (x/D)Tmax was not noticeable. Moreover, as the value of qload was decreased
less than 0.64 kW in Case 2, the reaction region moved into Honeycomb A. Thiseffect deteriorated the reaction efficiency, which will be discussed in thefollowing section.
1600

4.5
4.0

Case 1Case 2

Case 1Case 2

φ = 3.5
1400

Tmax [K](x/D)Tmax

3.5
1200

3.0
2.5

1000

Honeycomb A

2.0
1.5

0.5

1.0

1.5

2.0

φ = 3.5
800

0.5

1.0

(a) The location of maximum
temperature, (x/D)Tmax.
Figure 4:

1.5

2.0

qload [kW]qload [kW](b) Maximum measured temperature,
Tmax.

Effects of secondary honeycomb on the reaction region and its
temperature (φ = 3.5).

Figure 4(b) shows the Tmax distributions for Cases 1 and 2. Comparing with
Case 1, a slight increase of Tmax was observed in most qload conditions for Case 2.
This temperature increase was caused by the energy regeneration brought by
Honeycomb B. Honeycomb B absorbed a portion of enthalpy of the exhaust gas
flowing through, and the solid surface of the honeycomb emitted radiation to the
upstream region. By the rough calculation of the shape factor within the reactor,
the radiation emitted from the upstream surface of Honeycomb B reaches to thereactor inner-wall surface by the ratio of 77%, and the outlet surface of
Honeycomb A by 23%. Therefore, the energy regenerated from Honeycomb B
was used mostly to warm up the reactor wall, which decreased the heat release to
the wall from the exhaust gas. The remainder of the radiation contributed towarm up the vicinity of Honeycomb A and enhanced the preheating of the
mixture gas. By both of these effects, the temperatures of the reaction and postreaction region were increased.
3.2 Reforming characteristics
Methanol conversion, α, is defined in order to evaluate the efficiency of thepresent reformer:

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where MX and YX are the mole flow rate and the concentration of species X,
respectively.
Figure 5 shows the dependence of α on qload for Cases 1 and 2. In Case 1, thevalue of α did not change remarkably. It is estimated from this result that thereaction efficiency is not affected by qload condition as long as the reaction isstabilized at the outlet of Honeycomb A. For Case 2, on the other hand, αenhanced in conditions of 0.64 ≤qload≤ 1.74 kW. This enhancement was causedby the heat regeneration effect by Honeycomb B. Radiation emission from
Honeycomb B caused a slight temperature rise of the reaction region (see Fig.
4(b)), and decrease of the heat loss through the reactor wall surface. By theseeffects, the methanol decomposition was enhanced and resulted in higher
methanol conversion.

Methanol conversion, α

1.0
0.9
0.8
0.7

0.5

Case 1Case 2

φ = 3.5

0.6

0.5

1.0

1.5

2.0

qload [kW]Figure 5:

Dependence of α on qload (Cases 1 and 2).

In the condition of qload = 0.37 kW in Case 2, the value of α decreased
compared with qload = 0.64 kW. This deterioration of α was an effect of thereaction region moving into Honeycomb A. If a solid surface exists adjacent to
the reaction region, the reaction heat is used to heat up not only the combustiongas, but also the solid phase of the honeycomb. This effect decreased the
maximum temperature of the reaction region. Moreover, the high temperaturesolid surface emits radiation to the open space in the downstream region of thehoneycomb, which causes an additional heat loss from the reaction region. By
these effects, the temperature at the reaction region dropped and the reaction wasdeteriorated.
In the case of qload = 2.12 kW for Case 2, the value of α also decreased
drastically. This was also caused by the existence of the solid phase of, in thiscase, Honeycomb B. In large qload conditions, the reaction region will liftoff andapproaches to Honeycomb B. In this case Honeycomb B will quench the reaction
and reduces the value of α. From this effect, the radiation emitter should beplaced in a certain distance from the reaction region in order to avoid undesired
temperature drop, which deteriorate the reforming efficiency drastically.

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216 Computational Methods and Experimental Measurements XVI

4 Conclusions
In the present study, the thermal and reaction characteristics of a several
kilowatt-class compact methanol fuel reformer were investigated in terms ofreaction location and temperature. The conclusions obtained from the discussion
are summarized as follows:
-

-

-

-

In the present conditions, the maximum measured temperature almost
reached the adiabatic flame temperature in the downstream region close to
the outlet surface of Honeycomb A.
Stable reaction could be held at an almost-identical location at the outlet of
Honeycomb A under a wide range of thermal loads. However, more increaseof thermal load eventually caused “blowoff” of the reaction.
In Case 2, the reaction region moved upstream and the temperature becameslightly higher, which led to higher methanol conversion? This was caused by
the energy regeneration effect by Honeycomb B.
For the smallest and largest qload conditions in Case 2, the deterioration inmethanol conversion was observed. This is due to the existence of the solid
surface (i.e. ceramic honeycomb) within the reaction region.

References[1] Demirbas, A. (2007) Progress and Recent Trends in Biofuels. Prog. Energy
and Combust. Sci., 33, 1–18.
[2] Cantrell, K.B., Ducey, T., Ro, K.S., and Hunt, P.G. (2008) Livestock Wasteto-Bioenergy Generation Opportunities. Bioresour. Technol., 99, 7941–
7953.
[3] Min, D.K., and Shin, H.D. (1991) Laminar Premixed Flame Stabilized
inside a Honeycomb Ceramic. Int. J. Heat Mass Transf., 34(2), 341–356.
[4] Lammers, F.A., and Goey, L.P.H. (2003) A Numerical Study of Flash Backof Laminar Premixed Flames in Ceramic-Foam Surface Burners. Combust.
Flame, 133, 47–61.
[5] Mendes, M.A.A., Pereira, J.M.C., and Pereira, J.C.F. (2008) A Numerical
Study of the Stability of One-Dimensional Laminar Premixed Flames inInert Porous Media. Combust. Flame, 153, 525–539.
[6] Echigo, R. (1982) Effective Conversion Method between Gas Enthalpy and
Thermal Radiation and Its Application to Industrial Furnaces. Trans. Japan
Soc. Mech. Eng., Ser. B (in Japanese), 4(435), 2315–2323.
[7] Okuyama, M., Echigo, R., Yoshida, H., Koda, M., and Hanamura, K. (1994)
Spectral Radiation Properties of Super Fuel-Rich Premixed Flame. Trans.
Japan Soc. Mech. Eng., Ser. B (in Japanese), 60(577), 3145–3152.
[8] Rai, Y., Tatsumi, K., and Nakabe, K. (2010) Experimental Study on a
Compact Methanol-Fueled Reformer with Heat Regeneration Using
Ceramic Honeycomb. Proc. Int. Heat Transf. Conf. 14, IHTC14-22742.

WIT Transactions on Modelling and Simulation, Vol 55, © 2013 WIT Press
www.witpress.com, ISSN 1743-355X (on-line)Computational Methods and Experimental Measurements XVI 217[9] Rai, Y., Kogame, H., Tatsumi, K., and Nakabe, K. (2011) Experimental
Study on a Compact Methanol-Fueled Reformer with Heat Regeneration
Using Ceramic Honeycomb (2nd Report: Reaction Region Detection by aPositive Ion Current Probe). Proc. Int. Conf. on Power Eng. 2011,
POWER2011-55377.

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