hydrogen production in a thermal plasma hydrogen reformer using

Journal of the Chinese Institute of Engineers, Vol. 31, No. 3, pp. 417-425 (2008)

417

HYDROGEN PRODUCTION IN A THERMAL PLASMA HYDROGEN REFORMER USING ETHANOL STEAM REFORMING

Huan-Liang Tsai*, Chi-Sheng Wang, and Chien-Hsiung Lee

ABSTRACT This paper presents both analytical thermodynamic analysis and experimental results of ethanol steam reforming in a thermal plasma reformer at various working conditions. Since our thermal plasma reformer can work well at atmospheric pressure, a thermodynamic equilibrium prediction is first performed at temperatures in the range from 500 to 1000°C and at mole flow ratios of ethanol to water from 1:1 to 1:6. And then the experiment for ethanol steam reforming of a fabricated thermal plasma reformer is performed and the reformate stream is immediately analyzed using GC/MS, GC/FID/TCD, and pre-concentrator. Comparing predicted data with experimental data, an optimal working condition is determined at the temperature of 750°C and at mole flow ratio of ethanol to water of 1:3. In the future, an optimal temperature control system will be designed to maintain the thermal plasma reformer at the temperature of 750°C under the inlet mole flow ratio of ethanol to water of 1:3. Key Words: thermodynamic equilibrium prediction, ethanol steam reforming, thermal plasma reformer.

I. INTRODUCTION Ever-increasing reliance on current fossil fuels poses some serious challenges in environmental pollution, greenhouse gas emission, and energy supply security. Direct combustion of fossil fuels for vehicles accounts for a significant fraction of greenhouse emission and air pollution. For the purposes of lower pollution, higher efficiency of energy transformation, and producing more environmentally-friendly fuel resources, the conversion of various fuels into hydrogen as a preferred fuel for fuel cell systems (FCSs) and/or fuel-cell-based auxiliary power units (APUs) has been considered feasible for power supply applications. In the coming hydrogen (H2) economy, H2 will be considered as an important clean fuel carrier, especially hydrogen produced from renewable and sustainable fuel resources. Direct combustion or *Corresponding author. (Tel: 886-4-8511888 ext. 2204; Email: [email protected]) H. L. Tsai is with the Department of Electrical Engineering, DaYeh University, Chang-Hwa, 51505, Taiwan, R.O.C. C. S. Wang is with the Clean Energy R&D Center, Da-Yeh University, Chang-Hwa 51505, Taiwan, R.O.C. C. H. Lee is with the Institute of Nuclear Energy Research, Atomic Energy Council, Taoyuan 32546, Taiwan, R.O.C.

electrochemical energy conversion of H 2 can offer energy for engineering applications. Not naturally available, H 2 production can be accomplished using hydrogen reforming of various fuels such as fossil or biomass fuels. A practical FCS generally utilizes a fuel processing system (FPS) to produce H2 from whatever fuel resources are locally available. Ethanol is a clean and renewable fuel source which is a kind of oxygenated hydrocarbon derived from biomass and free from sulfur. The fuel processing system can locally provide gaseous fuel for fuel cell systems after appropriate fuel transformation. It is well known that the common methods for hydrogen reforming of hydrocarbons and oxygenated hydrocarbons are steam reforming (SR), catalytic partial oxidation (CPO), and autothermal reforming (ATR). The SR method can offer the highest concentration of hydrogen from hydrocarbon fuels (Ahmed and Krumpelt, 2001; Brown, 2001). Therefore, steam reforming is a very common and efficient process for hydrogen generation on an industrial scale. Since ethanol is safe to handle, transport, and store, it is a good alternative energy carrier for the growing development of renewable and sustainable energy. On the other hand, Tsiakaras and Demin (2001) demonstrated that the steam reforming of ethanol, which is a kind of oxygenated hydrocarbon fuel, can

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Journal of the Chinese Institute of Engineers, Vol. 31, No. 3 (2008)

produce the highest concentration of hydrogen yield with a catalytic reforming process. The steam reforming technique using thermal plasma is adopted to achieve a good hydrogen yield in our hydrogen reformer. Most traditional hydrogen reforming is a kind of catalytic reforming reaction on a catalytic bed reactor. Recently, most studies have focused on the catalyst search to improve the concentration of hydrogen production and efficiency of reforming transformation. Liguras et al. (2003) found that some catalysts for steam reforming at temperatures from 560 to 800°C can increase selectivity toward hydrogen with increasing temperature. In addition, the ratio of water to ethanol is an important factor in the steam reforming of ethanol (Batista et al., 2003; Batista et al., 2004; Sun et al., 2004; Yang et al., 2006). Yang et al. (2006) pointed out that there is some carbon formation on the catalysts for these catalytic reforming processes. The degradation of catalyst performance caused by carbon deposition is an important problem for catalytic reforming techniques. On the other hand, we have progressively developed (Wang and Huang, 2003; Tsai and Wang, 2006; Wang et al., 2006) a thermal plasma reforming system without catalysts. The thermal plasma reformer combines flameless pyrolysis, nonequilibrium thermal plasma, and gas-phase superheated steam reforming technologies. Without catalyst in the reformer, there is no problem of sulfur poison and carbon formation in the reactor. For reforming fossil fuels with sulfur content in our reformer, the sulfur compound (H2S) formed in a high-temperature reformate stream can be easily removed using exchangeable columns of metal oxides. Using a traditional catalytic reforming technique, the sulfur compounds in the fuels must be removed before entering into the catalyst bed in order to avoid sulfur poisoning of the catalyst. Therefore, with no sulfur-poison issue we can focus on prevention of carbon formation and high hydrogen yield by choosing an optimal operating temperature and a ratio of water to ethanol. To the best of our knowledge, the thermodynamic analysis of ethanol steam reforming with a catalyst has been studied since 1991 (García and Laborde, 1991; Vasudeva et al., 1991; Comas et al., 2004; Mas et al., 2006). In this paper we first use commercial softwave to perform the thermodynamic equilibrium prediction of ethanol steam reforming in a thermal plasma reformer. The experiments for ethanol steam reforming in a real thermal plasma reformer are then conducted and the reformate stream is immediately analyzed using gas chromatographs/ Mass Sieve (GC/MS), GC/ Flame Ionization Detector/ Thermal Conductivity Detector (GC/FID/TCD), and pre-concentrator at the Clean Energy R&D Center, Da-Yeh University, R.O.C. The experimental data are compared with the predicted data. The main contribution of this paper is to perform

a theoretical thermodynamic analysis of ethanol steam reforming using thermodynamic equilibrium prediction and to experimentally verify the predictions in a real thermal plasma reformer. An optimal working condition is chosen at a temperature of 750°C and mole flow ratio of ethanol to water of 1:3. For easy understanding, theoretical analyses, including both thermal equilibrium prediction using computer code and possible chemical reactions in a thermal plasma reformer, are first briefed in Section II. Section III demonstrates some experimental results obtained at the Clean Energy R&D Center. In addition, there is some discussion of various operation conditions. Finally, brief conclusions are drawn and directions for future vesearch are indicated in Section IV. II. THEORETICAL ANALYSIS Ethanol steam reforming for hydrogen production involves many complex reactions. There are some possible chemical reactions with undesirable reaction species affecting the yield and purity of hydrogen. Hydrogen selectivity strongly depends on process variables such as temperature, pressure, and reactants ratio. In order to optimize the hydrogen yield and minimize the carbon formation, it is necessary and indispensable to perform a thermodynamic equilibrium prediction of the reforming process in order to have better understanding of the optimal operational conditions and possible reformate compositions. 1. Thermodynamic Equilibrium Prediction Without exact knowledge of the possible reactions of ethanol steam reforming in a thermal plasma reformer, we have followed the minimization of Gibbs free energy to calculate the thermal equilibrium of ethanol steam reforming reactions (Tsai and Wang, 2006). We adopted commercial software, HSC Chemistry® 5.1, to calculate the mole fractions of equilibrium compounds for a given operating condition. The main operating parameters are the temperature and pressure of thermal plasma reformer, inlet temperature of ethanol and water, and mass flow ratio of ethanol to water. The ethanol and water are, respectively, pumped into the atomizer/vaporizer where the mixed fuels are heated and evaporated. The temperature of inlet fuels was measured at about 110°C before entering the reformer. Since our thermal plasma reformer can work well at atmospheric pressure the working pressure chosen is 1 atm (14.7 psi). We performed the thermodynamic equilibrium predictions at temperatures in the range of 500 to 1000°C and mole flow ratio of ethanol to water from 1:1 to 1:6. The main compounds of the final reformate steam are H2, H2O,

H. L. Tsai et al.: Hydrogen Production in a Thermal Plasma Hydrogen Reformer Using Ethanol Steam Reforming

70

35

65

30

55 50 45 . . MC2H5OH : MH2O = 1 : 1 . . MC2H5OH : MH2O = 1 : 2 . . MC2H5OH : MH2O = 1 : 3 . . MC2H5OH : MH2O = 1 : 4 . . MC2H5OH : MH2O = 1 : 5 . . MC2H5OH : MH2O = 1 : 6

40 35 30 25 500 550 600 650

Fig. 1

700 750 800 850 Temperature (°C)

45

. . MC2H5OH : MH2O = 1 : 1 . . MC2H5OH : MH2O = 1 : 2 . . MC2H5OH : MH2O = 1 : 3

25

. . MC2H5OH : MH2O = 1 : 1 . . MC2H5OH : MH2O = 1 : 2 . . MC2H5OH : MH2O = 1 : 3 . . MC2H5OH : MH2O = 1 : 4 . . MC2H5OH : MH2O = 1 : 5 . . MC2H5OH : MH2O = 1 : 6

20 15 10 5 0 500 550 600 650 700 750 800 850 900 950 1000 Temperature (°C)

900 950 1000

H2 mole fractions at different mole flow ratios of ethanol to water

50

CO Mole fraction (%)

H2 Mole fraction (%)

60

Fig. 3

CO mole fractions at different mole flow ratios of ethanol to water

15

. . MC2H5OH : MH2O = 1 : 4 . . MC2H5OH : MH2O = 1 : 5 . . MC2H5OH : MH2O = 1 : 6


CO2 Mole fraction (%)

H2O Mole fraction (%)

40 35 30 25 20

419

10

5

15 10 5 0 500 550 600 650 700 750 800 850 900 950 1000 Temperature (°C)

Fig. 2

H 2O mole fractions at different mole flow ratios of ethanol to water

CO, CO 2 , and CH 4 . The corresponding mole fractions are depicted in Figs. 1-5. There is some carbon formation shown in Fig. 6 at mole flow ratios of 1:1 and 1:2. It means that insufficient water reacts with ethanol in the form of steam reforming. Without enough superheated steam, the superfluous ethanol directly reacts in the form of thermal decomposition C2 H5 OH → 2C + H 2O + 4H 2

(1)

Therefore, the mole flow ratio of ethanol to water should be greater than 1:2 to prevent the carbon formation

0 500 550 600 650

Fig. 4

700 750 800 850 Temperature (°C)

900 950 1000

CO 2 mole fractions at different mole flow ratios of ethanol to water

in the chamber of the thermal plasma reformer. We also came up with the proper steps for start-up and turn-down processes in the thermal plasma reformer. The hydrocarbon or oxygenated hydrocarbon fuel must be input after water in the start-up process and be closed off before the water in the turn-down process. Fig. 1 shows H2 mole fractions at different mole flow ratios of ethanol to water. At mole flow rate of 1:1, H2 mole fractions increase with temperature owing to thermal decomposition of ethanol. In order to avoid coke deposition, we just pay much attention to H 2 mole fractions at mole flow ratios greater than 1:2. From

420



18

CH4 Mole fraction (%)

16 14 12 10 8 6

100 90 Total Mole fraction (%)

20

80 70 60 50

4

40 2 0 500 550 600 650

Fig. 5

700 750 800 850 Temperature (°C)

900 950 1000

CH 4 mole fractions at different mole flow ratios of ethanol to water

18

. . MC2H5OH : MH2O = 1 : 1 . . MC2H5OH : MH2O = 1 : 2

16

C Mole fraction (%)

14 12 10 8 6 4 2 0 500 550 600 650

Fig. 6

700 750 800 850 Temperature (°C)

900 950 1000

C(s) mole fractions at different mole flow ratios of ethanol to water

Fig. 1, we know that the mole fraction of hydrogen reaches 56.4% (on a wet basis) at mole flow ratio of ethanol to water of 1:3 and at temperature of 750°C. For a proton exchange membrane fuel cell (PEMFC) application, the more hydrogen selectivity, the better reforming efficiency. On the other hand, the mole fractions of the total fuels (H 2, CO, and CH 4 ) for a solid oxide fuel cell (SOFC) are shown in Fig. 7. The total fuels mole fractions approach 75% at temperatures in the range of 750 to 1000°C. Higher operating temperatures, over 750°C, can not effectively

. . M. C2H5OH : M. H2O = 1 : 1 MC2H5OH : MH2O = 1 : 2 . . MC2H5OH : MH2O = 1 : 3 . . MC2H5OH : MH2O = 1 : 4 . . MC2H5OH : MH2O = 1 : 5 . . MC2H5OH : MH2O = 1 : 6

30 500 550 600 650 700 750 800 850 900 950 1000 Temperature (°C) Fig. 7

Total mole fractions of SOFC fuels at different mole flow ratios of ethanol to water

increase the mole fraction of total SOFC fuels. The higher operating temperature, the higher power consumption and the less energy conversion as well. Therefore, from mole flow control point of view, an optimal operation condition of thermal plasma can be chosen at mole flow ratio of ethanol to water of 1: 3 and at temperature of 750°C for both PEMFC and SOFC applications, although Sun et al. (2004) have shown that the selectivity of H 2 reaches higher values at mole ratios of ethanol to water of 1:3 and 1:8. The ethanol steam reforming at mole ratio of 1:8 will lead to much excess water. This corresponds with the increase in water with higher mole ratio of water to ethanol as shown in Fig. 2. To avoid carbon deposition, only mole flow ratios of ethanol to water over 1:3 should be taken into consideration. It should be pointed out that methane explicitly decreases with increasing working temperature. Methane is directly produced by ethanol decomposition not by the methanation reaction at temperatures over 530°C because the standard free-energy change ∆G° of the methanation reaction becomes positive at a temperature of 530°C (Vasudeva et al., 1991). We conclude that the best hydrogen selectivity and the highest total mole fraction of SOFC fuels take place at a temperature of 750°C and at a mole flow rate ratio of ethanol to water of 1: 3 according to the thermodynamic equilibrium predictions. Figs. 8-9 show the mole fractions of reformate stream on wet and dry bases at mole flow rate ratio of ethanol to water of 1:3 and at various temperatures. The mole fractions of H 2, H 2 O, CO, CO2, and CH4 on both wet and dry bases are also listed in Table 1.


421

Table 1 Mole fractions of H 2, H 2O, CO, CO 2, and CH 4 on both wet and dry bases Mole fraction (%)

H2

H2O

CO

CO 2

CH 4

Wet basis Dry basis

56.4142 69.0290

18.2746 —

17.4954 21.4075

7.4538 9.1206

0.3620 0.4429

80

Mole fraction of reformate stream (%)

70 60 50

: H2 : H2O : CO : CO2 : CH4 : SOFC Fuels

40 30 20

80 70 : H2 : H2O : CO : CO2 : CH4 : SOFC Fuels

60 50 40 30

10

0 400

500

600 700 800 Temperature (°C)

900

1000

Mole fractions of reformate stream on a wet basis at different working temperatures

The mole fractions of methane in the reformate compounds significantly decrease with increasing working temperatures. The following reactions, including steam reforming and direct thermal decomposition of ethanol, can be postulated C2 H5 OH + 3H 2O → 6H 2 + 2CO2

(2)

C2 H5OH → CH 4 + H2 + CO

(3)

and

The enthalpies of ethanol steam reforming (ESR) and ethanol direct decomposition (EDD) reactions at temperature of 298 K are ∆ H ESR = 173.4 kJ/mole and ∆ H EDD = 49.5 kJ/mole, respectively. Another two reactions, which are water gas shift (WGS) reaction and steam reforming of methane, must be considered in the formation of final products. CO + H2 O → CO 2 + H 2

0 400

Fig. 9

500


900

(4)

1000

Mole fractions of reformate stream on a dry basis at different working temperatures

CH 4 + H2 O → CO + 3H 2

2. Analysis of Possible Chemical Reactions

and

90

20

10

Fig. 8

Mole fraction of reformate stream (%)

100

(5)

The enthalpies of WGS and methane steam reforming (MSR) reactions at a temperature of 298 K are ∆ H WGS = 41.2 kJ/mole and ∆ H MSR = 206.3 kJ/mole, respectively, The steam reforming of ethanol is assumed to be stoichiometrically completed. With the predicted mole fractions of thermodynamic equilibrium at mole flow rate ratio of ethanol to water of 1:3 and at temperature of 750°C, the overall reaction of ethanol steam reforming in the thermal plasma reformer can be rewritten as C 2H 5OH + 3H 2O→ 4.46H 2 + 1.43H 2O +1.37CO + 0.60CO 2 + 0.03CH 4

(6)

Here the main compounds of the reformate steam considered on a wet basis are H2, H 2O, CO, CO2, and CH 4, respectively. The carbon formation is assumed to be well controlled to zero with an optimal mole flow ratio of ethanol and water. The total enthalpy of outlet flow H outlet is the summation of the heat flow of all compounds in the reformate stream, i.e.,

422


Table 2 Coefficients for molar heat capacities of gas in the ideal gas state C2 H 5 OH H 2O H2 CO CO 2 CH 4

a

b × 10 2

c × 10 5

d × 10 9

4.75 7.700 6.952 6.726 5.316 4.750

5.006 0.04594 –0.04576 0.04001 1.4285 1.200

–2.4779 0.2521 0.09563 0.1283 –0.8362 0.3030

4.790 –0.8587 –0.2079 –0.5307 1.784 –2.630

Temperature range 273-1500 273-1800 273-1800 273-1800 273-1800 273-1500

K K K K K K

Table 3 Thermodynamic molar enthalpies of reactants (∆ H specied : kJ/mole) Temp. 25°C

110°C

650°C

750°C

–234.87 –241.826 0 –110.5 –393.5 –74.87

–227.56 –238.911 2.456 –108.0 –390.1 –71.44

–146.99 –216.730 18.778 –90.18 –360.1 –32.14

–128.25 –211.828 22.029 –86.51 –353.8 –22.14

Substance

∆H C 2H 5OH(g) ∆H H 2O(g) ∆H H2 ∆H CO ∆H CO2 ∆H CH4

H outlet =

Σ m. SpeciesCSpecies(TTPR – TREF)

(7)

. where m Species are the mass flow rate of species in the reformate stream, CSpecies are the specific heat of these compounds. The specific heat of all species at temperature of T(K) can either be roughly considered to be a constant or be approximately written in the form [Sandler, 1989] CSpecies = a + bT + cT 2 + dT 3

(8)

where the coefficients a, b, c, and d for all possible species in the plasma reformer are listed in Table 2. The associated thermodynamic molar enthalpies of reactants at various temperatures are calculated and listed in Table 3. III. EXPERIMENTAL RESULTS AND DISCUSSIONS 1. System Description A hydrogen reforming process in the form of steam reforming is the most efficient process of all current hydrogen production methods to produce hydrogen from hydrocarbon or oxygenated hydrocarbon fuels mixed with superheated steam at high temperature. Fig. 10 shows the system schematic of a 1kWe thermal plasma reformer implemented at the Clean Energy R&D Center, Da-Yeh University in Taiwan, R.O.C. The acronyms, LI, PI, TI, SW, LC, TC, and NC shown in the diagram stand for level input, pressure input, temperature input, switch, level

control, temperature control, and nozzle control, respectively. The fuel processing system includes tanks of fuel/water storage, pumps, injectors, atomizer/evaporator, thermal plasma reformer, heat exchanger, and electronic control unit (ECU). The level sensors of storage tanks, as well as pressure and temperature sensors are installed at critical locations within the system and provide measurable output variables. Since the thermal plasma reformer can work well under atmospheric pressure, the working reformer pressure chosen is 1 atm (14.7 psi). The temperatures of components, as well as mass flow rates of fuel and water were controlled by ECU via the associated control units and switches. Fuel and water were proportionally mixed before injecting into atomizer/evaporator, and then entering the chamber of thermal plasma reformer. Heat exchanger is a critical component for the transformation efficiency which effectively recovers heat energy, efficaciously reduces electricity input, and significantly increases energy and fuel conversion efficiencies. The key subsystems are described as follows. (i) Fuel Supply System Ethanol fuel and water are, respectively, stored in the tanks and pumped through injectors into the atomizer/evaporator according to the flow diagram shown in Fig. 10. They are controlled by an ECU. Since the inlet flow rates of ethanol and water are small, a nozzle generally used in a scooter or motorcycle is adopted as an atomizer/evaporator. The amount of flow is based on a special design using a


423

Electronic Control Unit (ECU) LI#1

LC#1

SW#1

NC#1 TI#1

Water tank

Water pump

TC#1

Injector

SW#3 TI#3 Heat recovery

Atomizer/ Evaporator Fuel tank

Fuel pump

Heat exchanger

TI#2

TC#2

SW#4

Thermal plasma reformer

Injector PI#1

LI#2

LC#2

SW#2

NC#2

TI#4 ECU

Reformate

Fig. 10 Schematic diagram of the 1kWe thermal plasma reformer

time-pulse, duty-cycle control technique with extraflow recirculation to accurately control the valve on a millisecond scale. (ii) Thermal Plasma Hydrogen Reformer Thermal plasma hydrogen reformer is a critical key component for hydrogen production and for any types of fuel-cell-based power generation systems. Thermal plasma technology uses water and renewable fuels to produce hydrogen. It dissociates fuel and water, and utilizes thermal radiation enhancement and high-density insulation to maintain high temperature and increase heat utilization. No catalyst is used; therefore, there is no poison or temperature problem in the reactor. However, there are ions and electrons with high intensity activation inside the reactor’s structures. The reactor has a catalyst function. Sulfur-containing fuel does not require pretreatment before entering the reactor. After reformation, the sulfur becomes H 2 S in an H 2-rich reformate stream and can easily be removed by a commercially available chemical agent like ZnO. (iii) Heat Exchanger Heat exchangers are widely used in various industries to recover waste heat of industrial processes and better system efficiencies. A compact heat exchanger is adopted in the thermal plasma reformer to recover the waste heat of reformate from the reformer. There are two main kinds of compact heat exchangers available in the commercial market. One is a plate heat exchanger (PHE) and the other is a fin tube heat exchanger (FTHE). A compact FTHE is adopted to perform waste heat recovery from the reformate.

(iv) Electronic Control Unit (ECU) A control system of the 1-kWe H 2-Reformer is designed with programmable PID and PID/Fuzzy controllers of ECU. The practical parameters of the control system are observable and controllable, such as pressures, temperatures, and mass flow rates of ethanol and water. The selection and optimal control of these key parameters is important and indispensable to the performance of an H 2 -Reformer. Both hardware and software of the reformer unit are constructed according to the above theoretical analysis. The start-up and shut-down processes of the thermal plasma reformer have been well defined and programmed in the programmable ECU. This ECU includes programmable logic control (PLC), human-machine interface (HMI), fuel/water input control, H 2 purifier control, alarm and surveillance unit, and dual PLC redundancy. Water and ethanol tanks have a level sensor each for measuring the stored amounts of water and ethanol, respectively. Each water and fuel pumps has been provided with an electric switch that is controlled by the controller so that the amounts of water and ethanol fuel can be adjusted. Both evaporator and reformer operate with required electricity input and are simultaneously equipped with pressure and temperature sensors. A compact heat exchanger is also equipped with pressure and temperature sensors. There are 7 sensors, 6 actuators, and 4 electric switches installed in the thermal plasma reformer. 2. Experimental Results Theoretical data are based on thermal equilibrium calculations as mentioned above. The operational pressure was 1 atmosphere. Different ratios of ethanol to

424

2.5

5

7.5

10

12.5

15

17.839 - ETHENE

19.381 - ETHANE

0

16.411 - ACETYLENE

100

14.302 - CARBON DIOXIDE 14.622

200

41.984 - METHANE

300

7.237 - OXYGEN 7.404 - NITROGEN

4.870 HYDROOEN

25 uV TCD1 B. (0600228\001F1601.D) 400

9.421 - CARBON MONOXIDE


17.5

20

min

Fig. 11 TCD graphic results of reformate stream

3. Discussion The current fuel processing system is intended to be integrated with a 1-kWe SOFC power generation system. With ethanol as fuel, there is no need to use a desulfurizer to remove the sulfur compounds in the reformate steam. In addition, no other H2 purifiers are required because H 2, CO, and CH 4 are all feedstocks for the SOFC stack. The experimental conditions are optimized using thermal equilibrium software for the total fuels (includes H2, CO, and CH4). Even for sulfur-containing fuels, our reformer does not require

100 90 80

Mol fraction of SOFC fuels (%)

water were used in the experiment. Mass flow rate of ethanol to water was fixed in order to produce the desired amount of reformate steam. For a specific mole flow ratio of ethanol to water, the corresponding mass flow rate was fixed and the operational temperature ranged from 500 to 900°C in 50°C steps. The experiment on ethanol steam reforming was carried out using a 1kWe thermal plasma reformer. The reformate stream specimens for various working conditions were sampled and stored using specially designed stainless canisters. In order to measure the quality of the reformate stream, a modern hydrogen analytical laboratory, which meets the target thresholds of hydrogen fuel quality and provides quick reformate composition results, has been set up. The reformate stream was analyzed in our laboratory. We immediately injected 100 µL reformate with a syringe into the GC/MS and GC/FID/ TCD apparatuses to perform gas analysis. The gas species can be measured at ppb (parts per billion) levels using GC/MS, GC/FID/TCD, and pre-concentrator. The detection limits were within the threshold targets of the California Fuel Cell Partnership (CaFCP). Fig. 11 displays the TCD graphic results of reformate stream. Fig. 12 shows the comparisons between the theoretical and experimental data on a dry basis based on mole flow ratio of ethanol to water of 1:3 and the temperatures ranged from 500 to 900°C. The results reveal that theoretical data have an approximate fit with the experimental data, especially in mole fractions of total SOFC fuels on a dry basis at temperature of 750°C.

70

: Theoretical data : Experimental data

60 50 40 30 20 10 0 500

550

600


800

850

900

Fig. 12 Comparisons between experimental data and theoretical data

pretreatment before fuel enters the reactor. After reforming, all the sulfur compounds become H2S in a H 2-rich reformate stream and are easily removed by commercial available chemical agents like ZnO. Therefore, an optimal design could be achieved by combining ECU for system controls, available software tools (such as a thermal equilibrium computer program) for optimal operational conditions at different operational parameters (such as working temperatures and pressures, flow rate of fuel and water, etc.), and an analytical laboratory capable for quality analysis of the reformate stream. IV. CONCLUSIONS Being non-catalytic reforming, our thermal plasma reforming technique does not pose any problems of sulfur poisoning or carbon formation. Even for sulfur-containing natural gas, the sulfur compounds (in the form of H 2 S) in the high-temperature reformate stream can be easily removed using a column


exchangeable desulfurizer. The desulfurized syngas can be directly introduced into an SOFC system or internal combustion engine (ICE) for power generation, or can further go through a purification system (such as PSA) to produce high purity hydrogen gas for a PEMFC system. From above thermodynamic analysis for the thermal plasma reformer, we have concluded that an optimal operation condition of thermal plasma reformer can be chosen at the temperature of 750°C and mole flow ratio of ethanol to water of 1:3 (mass flow ratio of 1:1.2). With this optimal mole flow ratio, an optimal temperature control system to maintain a temperature of 750°C in the thermal plasma reformer will be designed. ACKNOWLEDGMENT This study, NL950125, was sponsored by the Institute of Nuclear Energy Research, Atomic Energy Council of the Republic of China. REFERENCES Ahmed, S. and Krumpelt, M., 2001, “Hydrogen from Hydrocarbon Fuels for Fuel Cells,” International Journal Hydrogen Energy, Vol. 26, No. 4, pp. 291-301. Batista, M. S., Santos, R. K. S., Assaf, E. M., Assaf, J. M., and Ticianelli, E. A., 2003, “Characterization of the Activity and Stability of Supported Cobalt Catalysts for the Steam Reforming of Ethanol,” Journal of Power Sources, Vol. 124, No. 1, pp. 99-103. Batista, M. S., Santos, R. K. S., Assaf, E. M., Assaf, J. M., and Ticianelli, E. A., 2004, “High Efficiency Steam Reforming of Ethanol by CobaltBased Catalysts,” Journal of Power Sources, Vol. 134, No. 1, pp. 27-32. Brown, L. F., 2001, “A Comparative Study of Fuels for On-Board Hydrogen Production for Fuel-CellPowered Automobiles,” International Journal Hydrogen Energy, Vol. 26, No. 4, pp. 381-397. Comas, J., Laborde, M., and Amadeo, N, 2004, “Thermodynamic Analysis of Hydrogen Production from Ethanol Using CaO as a CO 2 Sorbent,” Journal of Power Sources, Vol. 138, No. 1-2, pp. 61-67. Dolgykh, L., Stolyarchuk, I., Deynega, I., and Strizhak, P., 2006, “The Use of Industrial Dehydrogenation Catalysts for Hydrogen Production from Bioethanol,” International Journal of Hydrogen Energy, Vol. 31, No. 11, pp. 1607-1610. García, E. Y. and Laborde, M. A., 1991, “Hydrogen Production by the Steam Reforming of Ethanol: Thermodynamic Analysis,” International Journal of Hydrogen Energy, Vol. 16, No. 5, pp. 307-312. Liguras, D. K., Kondarides, D. I., and Verykios,

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