Tar Removal from Biomass Derived Fuel Gas by Pulsed Corona

W F L M Hoeben , F J C M Beckers , A J M Pemen , E J M van Heesch , W L Kling. Journal of Physics D: ... Chemical Engineering Journal 2007 132 (1-3), ...
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Ind. Eng. Chem. Res. 2005, 44, 1734-1741

Tar Removal from Biomass Derived Fuel Gas by Pulsed Corona Discharges: Chemical Kinetic Study II S. A. Nair,*,† K. Yan,† A. J. M. Pemen,† E. J. M. van Heesch,† K. J. Ptasinski,‡ and A. A. H. Drinkenburg‡ Faculty of Electrical Engineering and Faculty of Chemical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands

Tar (heavy hydrocarbon or poly aromatic hydrocarbon (PAH)) removal from biomass derived fuel gas is one of the biggest obstacles in its utilization for power generation. We have investigated pulsed corona as a method for tar removal. Our previous experimental results indicate the energy consumption of 400 J/L for naphthalene removal (model tar compound) from synthetic fuel gas (CO, CO2, H2, CH4, N2) at a temperature of 200 °C. The present study extends our work on experimental and kinetic calculations for temperatures up to 500 °C. Radical yields are evaluated at various temperatures. According to the kinetic model and experimental results we concluded that the optimum temperature for tar removal is around 400 °C. The energy consumption for tar removal at 400 °C is about 200-250 J/L, whereas at 200 °C, this is about 400-600 J/L. 1. Introduction In principle, nonthermal plasma via its generation of radicals should reduce the need for higher temperatures of the existing processes. Hence the majority of the investigated applications are studied at normal temperature and pressure conditions. The eventual reduction in operating temperature is perceived as an advantage with respect to conventional processes. However, from a processing point of view and depending on application, certain investigations are done at higher temperatures to achieve favorable chemistry. Some of these are cited below: (a) Simultaneous NOx, SOx Removal Processes Which Are Optimized around 60 °C.1 Combined NOx and SOx removal from flue gas of power plants by nonthermal plasma techniques is a combination of removal by plasma as well as by physical methods. Plasma promotes conversion of NO to NO2, which thereafter is absorbed in the aqueous phase. Similar processing is done for SOx removal, for which a liquid phase oxidation is preferred. The operating temperature is therefore close to the dew point of the flue gas, where the cleaning is most efficient. (b) CH4 Partial Oxidation and CH4 Reforming at Varying Temperatures with Catalysts.2 Reactions of CO2 reforming of methane have been performed up to temperatures of 900 °C. At 5 kJ/mol of plasma energy, which is equivalent to 10% of the thermal energy required for heating to 900 °C, resulted in higher conversion levels (approximately two times) of methane. (c) DeSOx up to 800 °C with TiO2 Catalyst.3 The investigation focuses on a dry desulfurization process and also for study of surface reactions on a catalytic surface. An increase in the oxidized fraction (about 10% from a value of 5% at lower temperatures) at higher temperatures (from 200 °C to 800 °C) was observed, when a combined plasma-catalytic configuration was used. (d) VOC Removal. At room temperatures, several investigations related to VOC removal by nonthermal * To whom correspondence should be addressed. Tel.: +31 40 247 4494. Fax: +31 40 245 0735. E-mail: [email protected]. † Faculty of Electrical Engineering. ‡ Faculty of Chemical Engineering.

plasma have reported formation of polymeric substances.1 Wet reactors have been envisaged for purposes where functional groups are attached to these molecules and scrubbed.4 plasma

R-X98R-OH(gas) f R-OH(liquid phase) At higher temperatures, oxidation processes dominate the processing conditions with air as the gas medium. Penetrante has reported a reduction in the energy requirements with increase in temperature (up to 300 °C) for the case of removal of benzene, acetone, and ethylene from airlike mixtures by pulsed corona plasma.5 This has been attributed to an increase in reaction rates of O radicals with the molecules. Higher temperatures can lead to two contradicting effects: (1) a decrease in bulk gas density thereby causing a possible decrease in radical density; (2) favorable kinetics for the desired process. The effect of higher temperatures on streamer corona generation itself is not known. Thus experimental data is needed for estimating the radical yields at higher temperatures. 2. Experimental Setup The experimental setup has the same concept as described in the earlier study.6 However, a different reactor and second pulse power source are used for high temperature experiments. The configurations of the two setups are compared in Table 1. The setup has been described in detail elsewhere.7 The chemical and electrical diagnostics remain the same. For calculations, it is essential to first investigate the effects of these parameters on the energy consumption of the process or the radical yields. With respect to the two setups the following parameters are different: (1) output impedance of the power source; (2) reactor diameters and reactor length; (3) internal flow velocities or the residence time in the reactor. Naphthalene removal is carried out under dry reforming conditions as well as in the presence of terminating species to compare the energy consumption in

10.1021/ie049292t CCC: $30.25 © 2005 American Chemical Society Published on Web 02/08/2005

Ind. Eng. Chem. Res., Vol. 44, No. 6, 2005 1735 Table 1. Comparison of the Configurations of the Experimental Setup Used in the Study pulse power source characteristics

reactor

diagnostics

triggered spark gap switch 200 Ω output impedance 80-85 kV 350-375 A 1-1.2 J/pulse 50-100 pulses/s CL ) 18 µF Ch ) 5 nF transformer ratio ) 60

closed loop circulation system max operating temp ) 200 °C dimensions: 25 cm diameter, 3 m length internal flow velocity: 1.3-1.5 m/s (within reactor) internal flow rate: 240 Nm3/h total system volume: 300 L

chemical measurements: online FTIR analysis & GC analysis GC-MS (for condensates) electrical measurements: D/I system for voltage and current measurements

laboratory investigations (setup I) (well-matched reactor and pulse power source system)6

triggered spark gap switch 100 Ω output impedance 50-60 kV 200-220 A 0.2-0.5 J/pulse 50-100 pulses/sec CL ) 7 µF Ch ) 2 nF transformer ratio ) 60

closed loop circulation system max operating temp ) 800 °C dimensions: 15 cm diameter, 1 m length internal flow velocity: 8-9 m/s (within reactor) internal flow rate: 650 Nm3/h total system volume: 56 L

chemical measurements: online FTIR analysis GC-MS (for condensates) electrical measurements: D/I system for voltage and current measurements

laboratory investigations (setup II) (unmatched reactor and pulse power system for temperatures less than 400 °C)

for all experiments: “synthetic fuel gas” composition

N2 (50%) + CO2 (12%) + CO (20%) + H2 (17%) + CH4 (1%)

the two setups. Figure 1a indicates naphthalene removal in N2 + CO2 mixture and Figure 1b in the presence of a terminating species (N2 + CO2 + CO) at 200 °C with both configurations, i.e., setup I (low temperature, up to 200 °C,matched reactor and pulse source) and setup II (high temperature setup, up to 800 °C, unmatched reactor and pulsed source at 200 °C).

The energy consumption (J/nL) is expressed as the energy required per volume of the treated gas at STP conditions. Although for setup II perfect matching conditions do not exist, the pulse width (200 °C) naphtha-

Figure 4. (a) Naphthalene removal (Ci ) 4-5 g/Nm3) in N2 + CO2 (10%) at 400 °C: comparison between removal by thermal effects and by corona. (b) Naphthalene removal (Ci ) 4-5 g/Nm3) by thermal effects in N2 + CO2 (10%) at 500 °C: a comparison between removal by thermal effects alone and removal by plasma. The experiment indicates that thermal effects do not influence the data significantly on removal efficiencies by plasma.

lene removal can occur via two pathways: (a) by thermal decomposition; (b) by streamer corona plasma. Hence to obtain naphthalene removal due to streamer corona alone, thermal decomposition or “blank runs” are performed at various temperatures. A typical case at 400 °C is depicted in Figure 4a. Thermal decomposition is a first order process, hence dependent on the initial concentration. The initial removal (50%) at high concentration of naphthalene occurs within a period of 10 min. For further decrease of concentration to 20% an additional residence time of 10 min is needed (Figure 4a). The corresponding removal (50%) with plasma occurs with an energy density of less than 40 J/L, which is equivalent to a total experiment time of 3 min. This includes the measurement time between two successive corona runs. Thus, the plots shown in Figure 3 are removal due to streamer corona with a small fraction (10%) removed by thermal effects. Thermal effects do not significantly influence the measurements. However, for higher temperatures, e.g., for 500 °C, the power source is continuously run with simultaneous FTIR measurements. The spectrometer is programmed to take a sample with a delay of 1 s. The total experimentation time in this case is about 30 s whereas the thermal effects are seen over a period of 5 min (Figure 4b). The time axis in Figure 4a is the overall experimentation time. For the case of corona, each measurement

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Figure 5. Experimental and calculated results with modified fit parameter for naphthalene removal at various temperatures. The error bars indicates a deviation of (5%. Table 2. Estimated O Radical Yields at Different Temperatures global radical yield (GO) temp (°C)

(molecules/m3/J)

(mol/100 eV)

200 300 400 500

3.75 × 1017 3.37 × 1018 6.12 × 1018 6.09 × 1018

1.134 1.569 2.429 2.105

is done at 50 pulses per second for a period of a 30 or 60 s. The FTIR measurements follow the corona run. The thermal decomposition studies are therefore significant to indicate removal between corona runs. The data from Figure 4a and Figure 4b therefore indicates that measurements for removal of naphthalene by corona are not significantly affected by thermal effects. 3.2. Comparison of Calculated and Experimental Results: Dry Reforming. The fit parameters need to be recalculated, which is done in a similar way as described for the case of 200 °C in the earlier investigation.6 The respective fit parameters at different temperatures along with the corresponding radical yields are listed in Table 2. Figure 5 depicts the calculated results and compares it with the experimental results. As described earlier6 the model assumes a well-mixed condition for the plasma and bulk gas-phase, i.e. a homogeneous system. The energy density or the energy consumption for the process is determined by the (i) the kinetics of the decomposition process and (ii) the radical utilization. The radical utilization can be best described by the schemes described by K. Yan.1 Accordingly, the competing reactions to the desired process of decomposition can be classified as (i) linear terminations (where radicals are consumed via the bulk gas) and (ii) nonlinear terminations (radical-radical reactions dominate). A process governed by nonlinear terminations is not well described by the kinetic model.6 For such cases, the axial and radial distribution of radicals needs to be incorporated in the model. These processes typically occur at time scales of 10-100 µs, which is close to the diffusion time scale. The calculations thus describe the process, if nonlinear terminations or radical-radical interactions in the local areas of a streamer channel do not influence the process. For the case of 200 °C and 300 °C, termination reactions in gas mixtures containing

CO2 (or for gas compositions such as N2 + CO2) are mainly nonlinear terminations. However, with increase of temperature (T > 400 °C), it tends to be dominated by linear terminations. The fast radical-radical reactions that occur within the local areas of streamer channels decrease due to higher diffusion coefficient with increase in temperature (D ∝ T 1.75) (thus D573 K ) 1.4D473 K). (Gas phase diffusion can be estimated as DAB ) [(1e - 3)T1.75(1/MA + 1/MB)]/{PT[(∑VA)1/3 + (∑VB)1/3]2}, where DAB is in units of cm2/s, T is the absolute temperature (K), PT the total pressure in atmospheres, and VA and VB are the atomic and molecular volume contributions.11) It is this factor that contributes to the higher radical yields. The estimated yields are in fact a global value and a measure of the radical utilization, rather than the actual radical production value by means of the plasma itself. The diffusion effect with the favorable oxidation kinetics thus contributes to the observed decrease in energy requirements. The effects related to the gas dynamics lead to deviations in the calculated results. At 500 °C, the removal can be achieved without significant termination reactions, which is an ideal situation from a plasma processing point of view. The calculated results at 500 °C for the case of dry reforming as shown in Figure 5 also include removal/conversion of naphthalene by thermal effects. The data for the thermal decomposition kinetics is obtained from the experimental results indicated in Figure 4b (thermal decomposition kinetics at 500 °C, obtained from Figure 4b): rnaphthalene removal ) -0.0092Cnaphthalene). 4. Effect of Terminating Species As discussed earlier 6 two termination mechanisms have to be decreased: (1) via CO due to the recombination reaction and (2) via H2, through a series of chain reactions. The key issue in improving energy consumption of the process would be to limit the consumption of O radicals by the above two processes. Increase of temperature was found to have a positive effect on the dry reforming, due to higher radical yields, although it is mainly by increased diffusion of the species from the channel. As discussed below, this is further confirmed in the presence of the terminating components both CO and H2. 4.1. Effect of CO. Earlier experiments under 200 °C have demonstrated that, at these temperatures, the main termination reaction is by CO. Hence, the following linear terminations by CO have to be reduced so as to increase the radical utility for the desired process.

O + CO + M f CO2 + M

(18)

(Reaction numbering as per ref 6). Experiments are therefore performed with a gas composition of N2 + CO2 (10%) + CO (10%) at varying temperatures. Figure 6 indicates the energy requirement for removal of naphthalene at varying gas temperatures (200 to 400 °C). As observed for the case of dry reforming, a decrease in the energy consumption is seen with increase of temperature. At a temperature of 400 °C, the energy consumption for gas mixtures with and without CO is almost the same. Thus, terminations from bulk gas, i.e. CO, are decreased and hence the generated O radicals are utilized efficiently. To further investigate the influence of varying concentrations of CO, calculations are ex-

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Figure 6. Naphthalene removal (2-5 + CO (10%) at varying temperatures.

g/Nm3)

in N2 + CO2 (10%)

Figure 7. (a) Naphthalene removal (3-5 g/Nm3) from N2 + CO2 (10%) + CO (varying composition) at 300 °C: by calculation, GO value ) 1.5695 molecules/100 eV. The error bars indicate a deviation of (5%. (b) Naphthalene removal (3-5 g/Nm3) from N2 + CO2 (10%) + CO (varying composition) at 400 °C: by calculation, GO value ) 2.430 molecules/100 eV. The error bars indicate a deviation of (5%.

tended for the case of varying temperatures and for the mentioned gas composition (Figure 7a and Figure 7b). The GO values estimated from the dry reforming process are used for estimating the effects of higher CO concentration in the gas mixture. At 300 °C, there exists

Figure 8. Naphthalene removal (3-5 g/Nm3) in N2 + CO2 (10%) + CO (10%) + H2 (10%) at 400 °C. The curve indicates a trend line.

some discrepancy between the calculated and experimental results. As was explained, the calculation best describes linear termination dominated reactions. A difference between the calculated and the experimental results is most likely due to additional nonlinear terminations which occur within the areas where the concentration of radicals is high or in the streamer channels before they mix with the bulk gas phase. In the present case, i.e. at 300 °C, a fraction of the O radicals are still lost via the fast reactions due to the local high concentrations of the generated species, CO, via the inefficient nonlinear terminations (reaction 18). As implied from Figure 7a, if the produced O radicals would be well mixed with the bulk gas, then the energy consumption would be the same as seen from the calculations. The experimental result thereby indicates loss of O radicals via the inter-radical reactions within the streamer channel. At temperatures of 400 °C, the differences between the calculated and experimental results (Figure 7b) become smaller. This suggests a better mixing between the plasma and the gas phase in the reactor. Alternatively, the bulk CO gas does not increase the consumption of O radicals as compared to the case with the produced CO via CO2 dissociation. The system thus approaches the case of a perfect linear termination. 4.2. Effect of H2. At 400 °C, the loss reactions of O radicals via bulk CO are the least. For these conditions the effect of H2 is investigated. Calculations suggest that a reaction of O radicals with H2 leads to more radical consumption and therefore increasing the energy requirements. The results from the experiments for naphthalene decomposition in a gas composition of N2 + CO2 (10%) + H2 (10%) + CO (10%) are presented in Figure 8. Contrary to the case at 200 °C, H2 acts as the main terminating species at temperatures of 400 °C. This is most evidently via the combustion reactions between O and H2.

O + H2 f OH + H

(21)

Although reactive OH radicals are created via this mechanism, these are terminated via the fast recombination reactions to form H2O.

OH + H2 f H2O + H

(38)

OH + H + M f H2O + M

(38a)

Apart from these reactions, the major consumer of OH

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Figure 9. Naphthalene removal (3-5 g/Nm3) from synthetic fuel gas composition at 400 °C: calculated (G value ) 2.430 molecules/ 100 eV) and experimental results.

Figure 10. Naphthalene removal (3-5 g/Nm3) at 400 °C in various gas compositions: to compare the situation with H2 and without H2 containing gas. The curve indicates a trend line.

radicals is via the reactions between OH and CO to form CO2.12

OH + CO f CO2 + H

(32)

From a naphthalene decomposition point of view, a higher concentration of H radicals is both favorable and detrimental as well. As can be seen from its decomposition pathways6, H radicals contribute in both ways, viz., by initiating decomposition as well as enabling oxidized naphthalene to be regenerated. A favorable situation would be an optimum concentration of H radicals where it would be consumed only for decomposition but not for regeneration of naphthalene. However, at 400 °C, bulk H2 acts as a primary source of termination, thus there is room for improvement. At lower temperatures, i.e. for the case of 200 and 300 °C, both simulations and experiments indicate insignificant terminations via H2 for O radicals. 5. Removal in Fuel Gas Similar to the case at 200 °C for CO, at 400 °C, H2 acts as the main terminating component for the O radicals. At these conditions, the influence of gas composition on the energy consumption is investigated. Figure 9 reports the calculated and the experimental results for removal of naphthalene from synthetic fuel gas. From the energy density curves, it is evident that the removal efficiency is not affected by the change in gas composition. Thus, energy requirements are in the order of 200 J/L at 400 °C for the removal of tar components from the fuel gas. Similar observation can also be derived from the calculated results as well. The relative order of consumption of radicals can be seen from Figure 10 where the removal of naphthalene is plotted in varying gas composition at 400 °C. The objective is to obtain a situation where the best removal rates can be obtained. Experiments are further carried out to investigate the effects of the increased reaction rates on terminations at higher temperatures. Results of the experiments for naphthalene removal in a gas composition of N2 + CO2 (10%) + CO (10%) + H2 (10%) are presented in Figure 11. A consequence of increased terminations by H2 is production of H radicals. From the naphthalene decomposition pathway, it is quite evident that a higher H radical concentration is detrimental to the process. Experimental results in Figure 11 thus indicate the fact

Figure 11. Naphthalene removal (3-5 g/Nm3) in N2 + CO2 (10%) + CO (10%) + H2 (10%) at 500 °C: comparison between experimental and calculated results. The error bars indicates a deviation of (5%.

that complete removal of naphthalene at 500 °C requires higher energy densities than at lower temperatures. Apart from this, at these temperatures, experiments at higher energy density would mean longer experimentation time. From the thermal decomposition or the blank runs at 500 °C in a N2 + CO2 (10%) gas mixture, naphthalene should be thermally decomposed at the time scales of the experiments performed. The present experiments therefore demonstrate the need of blank runs in the mentioned gas compositions. Figure 12 thus indicates naphthalene removal by both thermal effects and corona plasma in the gas composition (N2 + CO2 (10%) + CO (10%) + H2 (10%)). Thermal effects are indicated at the corresponding values of energy density, by converting the experimental time into equivalent values. The data thus consists of some fraction removed by thermal effects. Simulations at 500 °C with the radical yield obtained from the dry reforming experiments also show the same observations of incomplete removal of naphthalene as indicated in the experiments. Experiments are also performed with low concentrations of naphthalene (2 g/Nm3) to indicate the sensitivity for removal of last fractions. The experiments further indicated that complete removal demands higher levels

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Figure 12. Naphthalene removal (3-5 g/Nm3) in N2 + CO2 (10%) + CO (10%) + H2 (10%) at 500 °C: comparison between removal by thermal effects alone and by plasma alone. Thermal effects are measured with time, however this is converted into equivalent values of energy density in the figure.

Figure 13. Calculated results for removal of naphthalene in various conditions.

of energy density at 500 °C than at the lower temperatures even with lower initial concentrations. At still higher temperatures, e.g. for the case at 600 °C, calculations are done with the same radical yield at 500 °C, for the case of removal of naphthalene in synthetic fuel gas composition. Figure 13 represents the calculated results in a view to compare the energy consumption in various gas composition and gas temperatures: synthetic fuel gas composition N2 (50%) + CO2 (12%) + CO (20%) + H2 (17%) + CH4 (1%)

500 °C 600 °C

a gas composition of N2 (70%) + CO2 (10%) + CO (10%) + H2 (10%)

500 °C 600 °C

The calculated results indicates two observations: (1) complete removal of naphthalene requires higher energy; (2) with increasing temperatures the influence of gas composition increases. For the case of 400 °C, as seen from Figure 9 and Figure 10 a change in the gas composition of CO2, CO, H2 does not influence the energy consumption. Thus considering the above factors, 400 °C is an optimum temperature for the processing.

Figure 14. Reaction rate constants at varying temperatures (Yaxis is plotted on a log scale).

Sensitivity analysis at 200 °C6 indicated two primary routes of termination reactions, via CO and via H2. An inspection of the respective reaction rate constants at varying temperatures is done in Figure 14. At temperatures, higher than 200 °C, the rate constant of termination by H2 is greater than that for the case with CO. However the severe terminations are visible at temperatures higher than 400 °C. Thus as is quite evident, apart from the factors related to reaction rates, the species distribution and the global radical yields exert a greater influence on the processing. This has been demonstrated by both experimental and calculated results. Apart from this at very higher temperatures, terminations are as well seen by the presence of CH4 in the synthetic fuel gas (Figure 13). Condensate samples collected at temperatures of 400 °C and 500 °C from the fuel gas do not indicate formation of higher aromatics. Prominent products seen in the spectrum are unconverted naphthalene and alkanes/alkenes. However, the data from the mass spectrum is not good enough to distinguish the type of alkane. Its formation can be because of the ring opening of the aromatic structure formed during the naphthalene decomposition pathway. 6. Conclusions Tar removal by pulsed corona plasma is investigated at various gas temperatures. Radical yields are obtained at these conditions, the increase being mainly from the diffusion of these species from the streamer channel. A gas temperature of 400 °C was found to be optimum for the process. Higher temperatures (to 600 °C) leads to production of more H radicals, which increases the energy consumption for complete removal due to regeneration of the dissociated naphthalene. Acknowledgment The author acknowledges the support of SDE (Dutch foundation for sustainable energy) and the Dutch Energy Research center, ECN. We are grateful to Dr. E. M. van Veldhuizen, Faculty of Applied Physics, Eindhoven University of Technology, and Prof. Bruce Locke, Department of Chemical Engineering, FAMU-

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FSU (Florida State University), for their suggestions during the preparation of the manuscript. Literature Cited (1) Yan, K. Corona Plasma Generation; Eindhoven University of Technology: Eindhoven, The Netherlands, 2001. (2) Mutaf-Yardimci, O.; Saveliev, A. V.; Fridman, A. A.; Kennedy, L. A. Employing plasma as catalyst in hydrogen production. Int. J. Hydrogen Energy 1998, 23 (12), December, 1109-1111. (3) Kim, H.; Mizuno, A.; Sakaguchi, Y.; Lu, G.; Sadakata, M. Development of a New Dry-Desulfurization Process by a NonThermal Plasma Hybrid Reactor. Energy Fuels 2002, 16 (4), 803808. (4) Gustol, A.; Fridman, A.; Kennedy, L.; Saveliev, A. Method for abatement of VOC in exhaust gas by a wet pulsed corona discharge. WO 03/080234. (5) Hsiao, M. C.; Penetrante, B. M.; Merritt, B. T.; Vogtlin, G. E.; Wallman, P. H. Effect of gas temperature on pulsed corona discharge processing of acetone, benzene and ethylene. J. Adv. Oxid. Technol. 2 1997, 306-311. (6) Nair, S. A.; Yan, K.; Pemen, A. J. M.; Heesch, E. J. M. van; Ptasinski, K. J.; Drinkenburg, A. A. H. Tar removal from biomass derived fuel gas by pulsed corona dischargessA chemical kinetic study. Ind. Eng. Chem. Res. 2004, 43 (7), 1649-1658. (7) Nair, S. A.; Yan, K.; Pemen, A. J. M.; Winands, G. J. J.; Van Gompel, F. M.; Van Leuken, H. E. M.; Heesch, E. J. M. van;

Ptasinski, K. J.; Drinkenburg, A. A. H. A high temperature pulsed corona plasma system for fuel gas cleaning. J. Electrost. 2004, 61 (2), 117-127. (8) Nair, S. A.; Pemen, A. J. M.; Yan, K.; Heesch, E. J. M. van; Ptasinski, K. J.; Drinkenburg, A. A. H. Tar removal from biomass derived fuel gas by pulsed corona discharges. Fuel Process. Technol. 2003, 84 (1-3), 161-173. (9) Nair, S. A.; Pemen, A. J. M.; Yan, K.; Heesch, E. J. M. van; Ptasinski, K. J.; Drinkenburg, A. A. H. Chemical processes in tar removal from biomass derived fuel gas by pulsed corona generation. Plasma Chem. Plasma Process. 2003, 23 (4), 665-680. (10) Pemen, A. J. M.; Nair, S. A.; Yan, K.; Heesch, E. J. M. van; Ptasinski, K. J.; Drinkenburg, A. A. H. Pulsed Corona discharges for tar removal from biomass derived fuel gas. Plasma Polym. 2003, 8, 209-224. (11) Basmadjian D. Mass transfer: Principles and applications; ISBN 0-8493-2239-1; CRC Press: Boca Raton, FL, 2004. (12) Westbrook C. K.; Dryer F. L. Chemical kinetic modeling of hydrocarbon combustion. Prog. Energy Combust. Sci. 1984, 10, 1-57.

Received for review August 5, 2004 Revised manuscript received December 4, 2004 Accepted December 18, 2004 IE049292T