Conversion of Diesel oil, aviation fuel, Rapeseed oil, and Soybean biodiesel into a Reformate gas Albin Czernichowski1, Piotr Czernichowski2 , Mieczyslaw Czernichowski1 and Krystyna Wesolowska 1 1
ECP - GlidArc Technologies, 45240 La Ferté St Aubin, France,
[email protected] 2 presently with Ceramatec Inc.
Abstract--Power generation can be advantageously done using Solid Oxide Fuel Cells that are capable of operating with CO, light Hydrocarbons and even some H2S. The SOFC operating at high temperatures allow also a heat recycling for the fuel processing. Conversion of liquid fuels into gaseous reformate for SOFC feeding is however quite difficult. The high Sulphur and aromatic content of fuels deactivate classical catalytic processors or create a significant soot problem. We avoid these problems using our High-Voltage discharge (called GlidArc) for the coldstart of such plasma processors. Then the discharge assists the Partial Oxidation of various fuels with atmospheric air. Such assistance concerns the feed pre-reforming in the plasma zone as well as the process achievement in the post-plasma zone packed with activated refractory granules. Such an electrically assisted process accepts almost any feed at up to 4% of Sulphur content. The feed conversion is total and the process is very simple. No soot, coke or tars are produced even from such fuels as fossil Diesel oil, JP-8 military aviation fuel, Rapeseed oil or Soybean biodiesel. Atmospheric pressure reforming is proposed but higher pressures can also be applied. The output reformate gas reaches presently 75 kW (accounted as the LHV power). Roughly 1% of assistant electric power is necessary to drive our processors. Up to 46 vol.% of H2 + CO mixture is produced (the balance being mostly the N2) in long runs. An 82% thermal efficiency of the process is obtained and a large part of remaining heat can be further reused. Index Terms —Diesel oil, GlidArc, JP-8 aviation fuel, Rapeseed oil, Soybean biodiesel, reforming. INTRODUCTION
Electric power generation for various applications can be advantageously done using Solid Oxide Fuel Cells (SOFC) that do not require electrolyte management and are capable of operating with high concentrations of Carbon Monoxide (CO) as well as some content of light Hydrocarbons (HC). High temperature operation of these cells allows also a residual heat recycling. For many applications, the ability of SOFC systems to operate with liquid carbonaceous fuels rather than pure Hydrogen is perhaps their greatest strength. However, such fuels as JP-8, Diesel oil and other fossil or renewable liquids must be reformed prior to their introduction to the SOFC. The high Sulphur and aromatics content of such fuels deactivate however the classical catalytic fu el reformers and/or create a significant soot problem with Partial Oxidation (POX) fuel processing that is the simplest reforming way. Moreover, conventional reforming technologies require for careful liquid
feed injection (atomisation or vaporisation) for soot avoidance, noble-metal catalysts as well as the combustion know-how. Instead of removing thousands of Sulphur-organic molecules from the logistic fuels to avoid the reformer's catalyst poisoning we rather propose a very simple coldplasma assisted conversion of almost any logistic or renewable fuels into a mixture of mostly Hydrogen and Carbon Monoxide (syngas) containing all initial Sulphur converted into the Hydrogen Sulphide (H2S). Such Reformate gas can be then very easily cleaned from H2S, if necessary. Roughly 1% of electric energy recycled from a SOFC electric output is sufficient to generate a very active plasma discharge that assists the reforming. Such electric discharge allows us a: • quick cold start of the reformer (plasma as igniter), • pre-reforming process of the fuel initially mixed with air (plasma as primary catalyst), and • control of the post-plasma polishing zone of reformer where the total fuel conversion is achieved without any soot or residual tars production (plasma as stabiliser). Our preliminary tests with natural gas, cyclohexane, heptane, toluene, gasoline and Diesel oil (DO) were first published in [1]. Then we have presented a study on propane (LPG) [2] and natural gas [3] reforming. The Rapeseed oil conversion to syngas was also successfully tested [4] as an example of various renewable fuels processing. New experiments are now presented on the processing of JP-8 aviation fuel. We return also to our previous studies on the DO reforming and show here our recent results at up to 75 kW output Reformate gas power (Lower Heating Value LHV). Finally we show some brand-new results of the Soybean biodiesel POX reforming at 1 kg/h output Hydrogen flow rate. I. EXPERIMENTAL A. Reformers The reformers of various feeds are based on so-called Gliding Arc (GlidArc) - a part of our Gas-to-Liquid (GTL) technology. Here-presented tests are performed in various reactors devoted to small or large syngas outputs. A 0.6-L (internal volume) reformer is shown on the Fig. 1.
Electrodes GlidArc
Post -plasma zone
Syngas
Thermocouples
Fig. 1. Small (0.6-L) GlidArc-assisted reformer of carbonaceous matter.
The plasma zone of the reactor contains two flat electrodes that delimit a space filled with the gliding discharges. A slightly preheated feed + preheated air are mixed and blown into that space through a tube and flows along the diverging steel electrodes. The gliding discharges ionise the air + partially vaporised fuel mix. Given the moderate temperature of the electrodes (not cooled) and a very short contact time of the discharge roots with the electrodes, we do not observe any deterioration (even at a high Sulphur presence) that may prevent the gliding of these current-limited discharges. The plasma zone communicates directly with a postplasma zone filled with activated refractory packing. Noble, rare or exotic elements are not used for activation! The flow of partially converted reactants containing long-living active radicals enters the zone where the conversion is completed by deactivation of all excited species. A 10-kV power supply provides both ionisation of the air/fuel mix and then a transfer of the electric energy into the plasma. The time -averaged electric power is measured at the mains; it is less than 0.1 kW for small reformers or up to 0.4 kW for large ones. The reformer is thermally insulated to keep it as hot as possible. Its total inside volume is 0.6 L (1.8 L for a 20-kW or 5 L for 75 kW processors). No part of reactors is cooled in a forced manner. Some thermocouples measure the post-plasma zone temperatures. The output gas sample crosses white wool for soot presence checking. Other sample is analysed using a two-channel µ-GC dedicated to H2 , O2 , N2 , CH4 , and CO for one channel, and CO 2 , C2 H4 , C2 H6 , C2 H2, C3 H8+C3 H6 , and residual moisture for the second one. B. JP-8 reforming This US military aviation fuel can be considered as a logistic support for SOFC-based auxiliary power supply. The fuel has the following characteristics: relative density 0.800,
average formula CH1.94, aromatics 15.3 vol.%, total Sulphur 433 ppm wt., initial BP 150°C, final BP 252°C, net heat of combustion (LHV) 43.2 MJ/kg. The explored ranges of inputs were: JP-8 @ 4.4 – 8.3 g/min and air @ 23 – 41 L(n)/min. The post-plasma zone of the processor was dumped by 0.34 L of activated refractory granules. The temperature of exiting gas reaches 725°C. As the result of various runs we have always observed the absence of soot, tar or non-reacted feed in the Reformate gas. The dry gaseous output (in vol.%) is: H2 10 – 16 CO 15 – 20 H2 + CO 26 – 35 N2 + Ar 55 – 68 CO2 2.2 – 4.8 CH4 0.7 – 2.8 C2H4 0.01 – 2.8 C2H6 0.00 – 0.19 C2H2 , O2, C3+, others absent From the mass and enthalpy balances we deduce the output Reformate gas power (based on the LHV of all combustible components acceptable for SOFC); it can reach 4.4 kW. Knowing the net heat of combustion (LHV) of the JP-8 we calculate the thermal efficiency of the JP-8 conversion into Reformate gas in our processor. This efficiency (defined as the ratio of the LHV of H2 + CO + light hydrocarbons at 25°C to the LHV of the entering JP-8 fuel) is up to 78% for the explored range of input parameters. Remaining energy content of the initial fuel is converted into the heat – but it is a compromise that we propose to accept for such a simple GlidArc-assisted soot -free and Sulphur-resistant POX technology. Further improvements can be done through a better heat management (heat exchange and/or integration of our reformer to a SOFC stack structure). The total GlidArc assistance power varied from 0.13 kW at the cold -start of the process to some 0.05 kW at the stabilised reforming conditions. The process power consumption related to the output Reformate gas power presents therefore only 1%. Fig. 2 and 3 show a typical composition of the Reformate gas (dry) and give an idea on the reformer output dynamics and its thermal efficiency. A 12-hours run at the constant air flow rate of 29 L(n)/min and the constant fuel flow rate of 6 g/min of JP-8 in 0.6-L processor at 3 kW (LHV) output Reformate gas power and 0.06 kW GlidArc assistance was successfully preformed. No structural changes of the processor and its post-plasma zone after the run were found. Neither soot nor tars were produced. We installed therefore this reformer for online feeding of a SOFC stack in a test laboratory dealing with the SOFC. Four series of tests were performed in December 2003 and February 2004. No problems appeared after long runs during which several litres of this high Sulphur fuel crossed the reformer. Our gas analyses showed a stable Re formate gas composition and the mass balance closure was typically 1%.
A 1.8-L GlidArc-assisted processor is shown on Fig. 4. It is very similar to the previously described reactor. The plasma compartment (0.6 L) contains two electrodes powered through a 10-kV supply. The same activated granules dump the postplasma zone of 1.2 L volume.
20
vol.% (dry)
15 CO H2 CO2 CH4 C2H4
10
5
0 4
5
6 7 JP-8 input g/min
8
9
80
8
60
6
40
4
20
2
kW
%
Fig. 2. Composition of the Reformate gas as a function of JP-8 fuel input rate.
thermal efficiency output kW LHV
0
0 4
6
8
JP-8 input g/min Fig. 3. Reformate output power and the thermal efficiency of the reforming as a function of JP -8 fuel input rate.
The SOFC stacks were composed of a single 10-cell and then a dual 11-cell systems. The stacks worked perfectly. Their performance were comparable to the Hydrogen baseline and the electric power output difference correlated well with higher steam content in our reformate gas. No soot was found in manifolds or electrodes after the stacks dismantling. Similar stacks have previously shown their high Sulphur tolerance during >1500 hours at 1000 ppm level of H2 S at 900°C. C. Diesel oil reforming Already in 2001-2 our feasibility tests with various road DO were successful [1] and further tests with a highly Sulphur-polluted heavy oil showed us that practically no harm is observed up to 4% Sulphur content. We performed then more detailed studies and long tests expanding the output Reformate gas power to >20 kW scale.
Fig. 4. GlidArc assisted 1.8-L processor of fuels; >20-kW LHV Reformate gas output.
French road DO (from Total) was processed. Its average Carbon number is 15.6 (ranging from C8 to C29 ); an averaged formula can be written as CH 1.83, and the molecular mass is in the range of 210–220. This fuel has a quite high relative density of 0.826 and surprisingly high Sulphur content of 310 ppm by weight. The DO (dosed by a metering pump) and compressed air (controlled by a mass flow meter) are simply mixed in a "T" connector and preheated up to 140-200°C before their injection to the GlidArc zone by an 8-mm (inner diameter) tube centred on the electrode axis. Through a porthole one can see the plasma discharge in the stream of the air + DO droplets. The droplets do not however affect our electric discharge. Explored inputs were: Compressed air 48 – 146 L(n)/min Diesel Oil 11 – 30 g/min Preheat 140 – 200°C GlidArc power 0.3 – 0.4 kW As result we observe the following outputs at no sooting conditions and at total fuel conversion: Bottom reformer temperature: ≤870°C Reformate gas content (dry basis): H2 16 – 20 vol.% CO 19 – 22 H2 + CO 38 – 41 CO2 2.4 – 4.8 CH4 0.8 – 3.3 C2 H4 0.0 – 2.1 N2 + Ar 52 – 58 C2 H2 , O2 absent Reformate gas LHV power: 7 - 22 kW.
Fig. 5 and 6 show the LHV power output of all combustibles that a SOFC accepts as fuel (H2 , CO, CH4 , and C2H4 ) as a function of the DO input flow rate. They also illustrate the specific LHV energy output (in kWh per kg of DO) and the dry Reformate gas composition as a function of O2/C molar ratio at the input (reflecting the air/fuel ratio).
blower, is used as oxidant at various flow rates that we set using a variables frequency power supplying the blower's electric motor. The air flow rate can vary between 150 and 520 L(n)/min. This flow of air at variable rates is set in a function of the variable fuel flow rates that define a wanted output Reformate gas flow rate and its LHV power.
25
kW otput
20 15 10 5 0 10
20
30
40
g/min DO input
Fig. 5. LHV power output of 1.8 L processor as a function of the input flow rate of Diesel oil.
50 45 40 35 30 25 20 15 10 5 0 0.45
CO2 C2H4 CH4 H2+CO kWh/kg
0.5
0.55
0.6
10 9 8 7 6 5 4 3 2 1 0 0.65
Fig. 7. New 75-kW GlidArc -assisted reformer of various carbonaceous feeds.
kWh per kg DO
vol.% (dry)
Our tests are successful: such quite highly Sulphur polluted Diesel oil is totally POX-reformed at no water or steam added and at no soot or tars production (when checking the gas output with a white wool). To confirm that absence we dismantled several times our processor after its cooling and did not find any soot deposits inside.
O2/C molar ratio
Fig. 6. Specific energy (LHV) output and the Reformate gas composition as a function of O2 /C at the input (right).
New prototype of the GlidArc assisted reformer (see Fig. 7) is presently developed by ECP on the basis of our new French patent application [5]. The prototype has a nominal output power of 75 kW LHV and can process almost any carbonaceous feed. The GlidArc plasma and the post-plasma zones have respectively 0.8 and 4.0 L of volume. Atmospheric air, aspirated/pushed this time by an industrial
In order to maximise the Hydrogen output we admix water to the fuel. This operation enhances the "water shifting" of some amount of CO (a part of the Reformate gas) into H2 : CO + H2 O = CO2 + H2 . (1) The tap water is directly taken from a supplying pipe, it crosses a calibrated rotameter and finally is injected to the reformer through the same 1/8" steel injection pipe used for the fuel injection. The explored water flow rate varies between 21 and 75 g/min. A special no-Sulphur fossil Diesel oil (from Shell) is reformed. It presents the LHV of 42.4 MJ/kg and its average chemical formula is C15.5H28.0 . A gear pump sucks the fuel from a recipient put on a scale. The pump sends the liquid through another rotameter. The explored flow rates of the oil are between 34 and 131 g/min. The tests target is to produce up to 1 kg of H2 for a specific industrial application. At that target level (see Fig. 8) the LHV output power of the Reformate is 75 kW. It contains more than 44 vol.% of CO + H2 (dry basis) with only minor amounts of CH4 (1.4 %), C2 H4 (0.10 %) and C2 H6 (0.04 %). As always in the case of the POX reforming we are loosing some carbon; the CO2 concentration for the target point is 5.3 %. At that point the calculated thermal efficiency of the reforming process reaches 82%.
Fig. 10 presents the composition of the output gas (all successful tests are put into the same graph). In fact, the syngas is always diluted by Nitrogen as we use air for reforming. The N2 concentration at the output is typically in the 55 – 60 vol.% range (dry basis) depending on the air/oil ratio applied for the given test.
1.2 kg H2 per hour
1.0 0.8 0.6 0.4
70
0.2
60 CO2
50 0
50
100
150
Input of Diesel oil, g/min
vol.%
0.0
H2
40
N2
30
CO
20
D. Rapeseed oil reforming We use other 1-L reactor, similar to that shown on the Fig. 1. This processor contains three electrodes connected to 3-phase power supply giving us 0.1 A current to each electrode. No preheat is applied to any stream. Several runs were preformed using French edible oil having the density of 913 kg/m3 . At the accumulated runtime of 6 hours we never changed any part of the reformer. The process was always very stable. When soot was starting to appear at an insufficient air/oil ratio we just added more air (or reduced the oil flow) to establish the non-sooting reforming conditions. During these runs the air flow rate was comprised between 35 and 102 L(n)/min for the oil input flow rate between 11 and 30 mL/min. Fig. 9 shows temperatures T1 (upstream) and T2 (downstream, equal to exiting gas product temperature) such as observed when the thermal equilibrium of the reactor is achieved. Various tests are put together on the same graph showing therefore the explored range of the parameters.
10 0 3000
3200
3400
3600
3800
4000
air/oil L(n)/L
Fig. 10. Concentration of the main components (dry basis) in the output gas as a function of the air/oil ratio for all successful runs. Other gases are at minor concentrations: CH 4 0.5–1.0, C2 H4 0.1–0.5, C2H6 0.01–0.03, and C2H2 0.001–0.005 vol.%.
As results of the mass balances we calculate the output flow rate of 100% syngas (H2 +CO only) in L(n)/min for all runs as shown on the Fig. 11. The H2 + CO flow rate in the output can also be presented as the potential thermal output power. Such a power (in kW also presented on the Fig. 11) is therefore assimilated to the LHV. Our runs and reactor are not yet optimised but they indicate that we already obtain (at atmospheric pressure) as much as 11 kW or 3.5 m3 (n)/h of pure syngas output. Higher outputs are expected for elevated pressures and/or preheat of the air and oil streams.
1500
3000
1200
2000
900
L(n)/L T1 T2
1000 0 10
20
600
temperature °C
air/oil ratio L(n)/L
4000
300
30
rapeseed oil input mL/min Fig. 9. Temperatures T1 (upstream) and T 2 (downstream) inside the postplasma zone as a function of the input flow rate of rapeseed oil. The left axis presents the air/oil ratio required for completely non-sooting reforming of the oil.
output LHV power (kW) of SynGas
12
72 kW
10
60
L(n)/min
8
48
6
36
4
24
2
12
0
L(n)/min of SynGas
Fig. 8. Hourly output mass of Hydrogen as a function of the Diesel oil input rate.
0 10
15
20
25
30
oil mL/min
Fig. 11. Output flow rate of 100% syngas (H 2 + CO only) in L(n)/min and in kW units for all runs at close-to the thermal conditions of the reformer.
The thermal efficiency of the reforming process can be estimated from these results. If one takes the LHV of the feed as 35 MJ per kg then for our run at 30.4 mL/min = 0.507 mL/s = 0.463 g/s the thermal input power corresponds to 16 kW. For 11.4 kW thermal power (LHV) output that we obtain as syngas one finds therefore the thermal efficiency of the process at no sooting conditions equal to 70%. This quite high efficiency is based on only standard enthalpy heats (at 25°C) of the output H2 + CO combustion to CO2 and steam (LHV) with respect to the standard heat of combustion (LHV) of entering oil. Such efficiency does not take into account any residual light hydrocarbon gas useful for SOFC or the sensitive heat content in the gas leaving the reformer. A part of that heat can certainly be reused to preheat entering feed and air so the thermal efficiency could be increased. No such heat exchange was used in this study. E. Soybean biodiesel reforming There is a growing interest to use such renewable fuel to feed the SOFC or to produce Hydrogen (and CO) for other applications. For our preliminary tests we took the B100 biooil produced in the USA. It presents the specific gravity of 883 kg/m3 at 15°C, the LHV of 34.7 MJ/kg and an average chemical formula of (CH 1.87O0.11)n . The same 75-kW reformer and its environment is used for the tests. This time the air flow rate vary between 140 and 460 L(n)/min depending on wanted output of the Reformate gas flow rate and its LHV power. The tests target was again to produce up to 1 kg of H2 for a specific industrial application, see Fig. 12. Close to that target level (0.96 kg/h) the LHV output power of the Reformate is 72 kW and it contains more than 43 vol.% of CO + H2 (dry basis) with only minor amounts of CH4 (1.5 %), C2H4 (0.20 %) and C2 H6 (0.05 %). The CO 2 concentration for that point is 6.7 % and the calculated thermal efficiency of the reforming process reaches 68 %.
1.0 0.9
kg H2 per hour
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0
50
100
150
Input Biodiesel in g/min
Fig. 12. Hydrogen output rate as a function of the Biodiesel input rate.
II. CONCLUSIONS •
Working dozens of hours we never changed any part of the reformer and/or its post-plasma zone loading. The technology is robust. • Reformate gas appears after ~ 15 min from a cold start (small reformer), after ~ 40 min (large reformer) or after ~ 2 min when the reformers are kept hot. At such quite quick starts we do not obtain yet optimal performances – but the Reformate gas flow may be sufficient to start operate an application, for example a SOFC (that also asks for a quite long heating and equilibration period). • Thermal efficiency of the process can reach 82%. An overall efficiency of our fuel processor + SOFC system can be increased thanks to a synergetic effect. • Some methane and ethylene are present in the Reformate gas. They can be kept at quite low concentration, if necessary, by applying a higher O2 /C ratio at the input but it would slightly lower the thermal efficiency of the reforming. These gases are however considered as good fuels for SOFC. • Reformer works also when Sulphur is present in the feed. We proved it when reforming the JP-8 and Diesel oil at respectively 433 ppm and 310 ppm (weight) content. Our previous experiments show that even 4% of Sulphur in a heavy liquid carbonaceous feed (end distillation point of 600°C) is not harmful. In fact, even 100% H2 S can be processed using our GlidArc reactors for Hydrogen recovery from such waste gas [6]. • Conversion of the fuels is total, as we do not find any residual fuel or Oxygen at the exit. We do not produce soot, coke or tar. • Noble, rare or exotic elements are not used for activation of the solid mater present in the post-plasma zone of the reformer. • Process is stable. The Reformate gas output flow and composition can be kept constant or match a required level by regulating the fuel and air flow rates. Drastic changes of the Reformate gas output flow and/or composition can be done in a fraction of minute. • Electric assistance is low, around 1% relative to the LHV of produced Reformate gas flow. • According to our tests a 1-L (inside volume) reformer can produce a flow of Reformate gas that is equivalent to 15 kW LHV power. A higher H2 (syngas) and power output can probably be reached as in the explored range of input parameters we do not see any curving (see Figs. 5, 11, and 12). ECP is presently fabricating a 30-L processor. ***** Here presented results show a simple way for a Reformate gas production from such fossil matter as JP-8 aviation fuel or Diesel Oil, from the plant oils such as the Rapeseed oil, and from a renewable biodiesel. Other fossil and renewable carbonaceous liquids were already studied in our laboratory: gasoline and naphtha [7]. Some new tests with 96% ethanol, glycerol, molasses, and heavy biooil from a flash pyrolysis of wood are also successful: we are getting a soot-free Reformate gas at the total feed conversion. All that
opens opportunities to upgrade some farm-issued products or waste bio-oils from various activities. Our past tests [8] show that pure Oxygen or O2 -enriched air can be used instead of atmospheric air. It opens some opportunities for more efficient GlidArc-assisted reformers and processes if such extra Oxygen is applied to reduce the Nitrogen content in the Reformate gas… One can also reduce the reformer volume or increase its output when working at higher pressures; we have some results at up to 6 bars [8]. Finally, we are starting to add steam to perform, at least partially, some "water shift" of CO into H2 (so approaching so-called Auto-Thermal Reforming). Our expertise in this field [9] starts to be developed… REFERENCES [1] A. Czernichowski, M. Czernichowski, and P. Czernichowski, "Noncatalytical reforming of various fuels into syngas", France-Deutschland Fuel Cell Conf. on "Materials, Engineering, Systems, Applications", Forbach, France, 2002, p. 322-8. [2] A. Czernichowski, M. Czernichowski, and P. Czernichowski, "GlidArcassisted reforming of various carbonaceous feedstocks into synthesis gas. Detailed study of propane reforming", 14-th Annual U.S. Hydrogen Meeting, 2003, Washington, DC, CD-proceeding, 8 pp.
[3] A. Czernichowski and K. Wesolowska, "GlidArc-assisted production of synthesis gas through partial oxidation of natural gas", First International Conference on Fuel Cell Science, Engineering and Technology, Rochester, NY, April 21-23, 2003, p. 181-5. [4] A. Czernichowski, M. Czernichowski, and K. Wesolowska, "GlidArcassisted production of synthesis gas from Rapeseed oil", Hydrogen and Fuel Cells Conf. and Trade Show, Vancouver, Canada, 2003, post conference proceedings (CD), 6 pp. [5] A. Czernichowski, K Wesolowska, J. Czernichowski, Conversion plasma-catalytique de matières carbonées, French application No. 0407054. [6] A. Czernichowski, M. Czernichowski, and K. Wesolowska, "Glidarcplasma reactors for Hydrogen recovery from waste H2S", HYPOTHESIS V, 2003, Porto Conte, Italy, p. 301-309. [7] A. Czernichowski, M. Czernichowski, and P. Czernichowski, "Plasmaassisted reforming of some liquid fuels into synthesis gas", 15th Annual U.S Hydrogen Conf., April 26-30, 2004, Los Angeles, USA, CD Proceedings, 12 pp. [8] A. Czernichowski and P. Czernichowski, "Assistance électrique d'oxydation partielle d'hydrocarbures légers par l'oxygène", French Patent No. 276424, 1997. [9] K. Meguernes, A. Czernichowski, and J. Chapelle, "Oxidization of CH4 by H2 O in a gliding electric arc", 3rd European Congress on Thermal Plasma Processes, Aachen, Germany, 1994; full text in VDI Berichte 1166, 1995, p. 495 -500.
