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Mechanisms of conversion of heavy hydrocarbons in biogas initiated by pulsed corona discharges

Mechanisms of conversion of heavy hydrocarbons in biogas initiated by pulsed corona discharges. V.A. Bityurin, E.A. Filimonova , G.V. Naidis Institute for High Temperatures of Russian Academy of Sciences, Moscow, Russia e-mail: helfil@mail.ru. ACKNOWLEDGMENT.

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Mechanisms of conversion of heavy hydrocarbons in biogas initiated by pulsed corona discharges

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  1. Mechanismsof conversion of heavy hydrocarbons in biogas initiated by pulsed corona discharges V.A. Bityurin, E.A. Filimonova, G.V. Naidis Institute for High Temperatures of Russian Academy of Sciences, Moscow, Russia e-mail: helfil@mail.ru ACKNOWLEDGMENT The work was partially supported by NWO-RFBR Grant No 04-02-89006 and RFBR Grant No 05-02-16590.

  2. The contribution of biomass to the world’s energy supply is ranging from 10-14%. Biogas can be used in power generation and production of synthetic fuels as methanol, hydrogen or bio-diesel. Gasification of biomass produces significant amounts of heavy hydrocarbons (TAR). TAR tends to condense in the downstream equipment leading to several operational problems. Main problem is to remove TAR from biogas and reduce the energy consumption in cleaning process. The modeling of removal process of TAR is a difficult task because of absence of many data for simulation of plasma-chemical kinetics at intermediate temperatures. Urgency of problem

  3. Composition of biogas TAR specification Main components: 15-21% H2, 10-22% CO, 11-13%CO2, 1-5%CH4, andN2 C10H8=~ 800-1000 ppm Naphthalene Structure

  4. consideration of several gas compositions without O2, gas temperature is close to 500 K; simulation of positive streamer propagation in biogas; consideration of primary plasma-chemical processes at the discharge stage; consideration of naphthalene removal as a one of the most stable component; using the chemical kinetics code taking into account non-uniform distribution of components in the discharge reactor; comparison with experimental results obtained at the pilot setup. The goal of work is to reveal the main mechanisms governing naphthalene cleaning process Characteristic properties of the work

  5. Experimental setupEindhoven University of Technology, Eindhoven, The Netherlands U = 40-100 kV Vsyst = 300 L VR= 150 L f = 50 Hz Q = 240 Nm3/hr T ~ 500 K Ep= 1-1.4 J/pulse

  6. 2D streamer model Chemical kinetics modeling Cleaning process One pulse Discharge stage: ~10-8 s Afterglow stage: 4*10-2 s N2, CO2, CO, H2O, CH4, H2, N4+, N2+, CO2+, H2O+, e, N2(A3Σ), N, N(2D), O, O(1D), OH, H, CH3 79 components and 350 reactions G-values Initial concentrations Number of pulses is 400-1000 and more

  7. Simulation of positive streamer propagationThe ionization coefficient (α/n) and mean energy(<ε>) of electrons versus E/N. p = 1 bar T = 600 K Solid red lineis 51% N2+20% CO + 12% CO2+17% H2 mixture Blue dashed line is 80% N2+20% O2mixture Cyan dash dotted lineis N2.

  8. Simulation of positive streamer propagation Electric field at the streamer axis Gas composition: 50% N2 + 20% CO + 12% CO2 + 17% H2 + 1% CH4 p = 1 bar T = 600 K

  9. Simulation of positive streamer propagation G-values Gas composition: 50% N2 + 20% CO + 12% CO2 + 17% H2 + 1% CH4 p = 1 bar T = 600 K

  10. Reaction mechanisms for pureN2 Processes by direct electron impact N2+e —> N2(A)+e N2+e —> N2(B)+e N2+e —> N2(C)+e N2+e —> N2(a)+e N2+e —> N2(a’)+e N2+e —> N(2D)+N+e N2+e —> N2++2e Ion – molecule reactions and dissociative recombination N2+ + N2 + M —> N4+ + M,τ ~ 10-10 s N4+ +e —> N2 + N2(A),τ ~ 10-7 s

  11. Comparison of experimental and calculation results in pure N2 Chemical kinetics N2(A) + C10H8—> products N(2D) + C10H8—> products N2(A) + N2(A)—> N2 + N2(A) diffusion —> C10H8

  12. Reaction mechanisms for90%N2+10%CO2mixture Processes by direct electron impact N2+e —> N2(A)+e N2+e —> N2(B)+e N2+e —> N2(C)+e N2+e —> N2(a)+e N2+e —> N2(a’)+e N2+e —> N(2D)+N+e N2+e —> N2++2e CO2+e —> CO+O+e Ion – molecule reactions and dissociative recombination N2+ + N2 + M —> N4+ + M,τ ~ 10-10 s N4+ +e —> N2 + N2(A),τ ~ 10-7 s N4+ + CO2 —> N2 + N2 + CO2+,τ ~ 10-9 s CO2+ +e —> CO + O(1D),τ ~ 10-7 s Processes by direct electron impact N2+e —> N2(A)+e N2+e —> N2(B)+e N2+e —> N2(C)+e N2+e —> N2(a)+e N2+e —> N2(a’)+e N2+e —> N(2D)+N+e N2+e —> N2++2e CO2+e —> CO+O+e

  13. Comparison of experimental and calculation results in 90%N2+10%CO2mixture Chemical kinetics N2(A) + C10H8—> products N(2D) + C10H8—> products N2(A) + N2(A)—> N2 + N2(A) CO + N2(A)—> N2 + CO O + C10H8—> H + C10H7O CO2 + N —> CO + NO CO2 + N(2D) —> CO + NO CO2 + N2(A) —> CO+O+N2 NO + N —> O +N2 NO + NH —> H + N2O NO + NH —> OH + N2 NO + NH —> O + N2H diffusion —> C10H8

  14. Comparison of experimental and calculation results in 80% N2+10% CO2+10% COmixture Processes by direct electron impact N2+e —> N2(A)+e N2+e —> N2(B)+e N2+e —> N2(C)+e N2+e —> N2(a)+e N2+e —> N2(a’)+e N2+e —> N(2D)+N+e N2+e —> N2++2e CO2+e —> CO+O+e CO +e —> C+O+e

  15. Reaction mechanisms for50% N2+20% CO+12% CO2+17% H2+1% CH4mixture Processes by direct electron impact N2+e —> N2(A)+e N2+e —> N2(B)+e N2+e —> N2(C)+e N2+e —> N2(a)+e N2+e —> N2(a’)+e N2+e —> N(2D)+N+e N2+e —> N2++2e CO2+e —> CO+O+e CO +e —> C +O+e H2+e —> H +H +e Ion – molecule reactions and dissociative recombination N2+ + N2 + M —> N4+ + M,τ ~ 10-10 s N4+ +e —> N2 + N2(A),τ ~ 10-7 s N4+ + CO2 —> N2 + N2 + CO2+,τ ~ 10-9 s CO2+ +e —> CO + O(1D),τ ~ 10-7s Processes by direct electron impact N2+e —> N2(A)+e N2+e —> N2(B)+e N2+e —> N2(C)+e N2+e —> N2(a)+e N2+e —> N2(a’)+e N2+e —> N(2D)+N+e N2+e —> N2++2e CO2+e —> CO+O+e CO +e —> C +O+e H2+e —> H +H +e Processes by direct electron impact N2+e —> N2(A)+e N2+e —> N2(B)+e N2+e —> N2(C)+e N2+e —> N2(a)+e N2+e —> N2(a’)+e N2+e —> N(2D)+N+e N2+e —> N2++2e CO2+e —> CO+O+e CO +e —> C +O+e H2+e —> H +H +e Processes by direct electron impact N2+e —> N2(A)+e N2+e —> N2(B)+e N2+e —> N2(C)+e N2+e —> N2(a)+e N2+e —> N2(a’)+e N2+e —> N(2D)+N+e N2+e —> N2++2e CO2+e —> CO+O+e CO +e —> C +O+e H2+e —> H +H +e

  16. Comparison of experimental and calculation results in 50% N2+20% CO+12% CO2+17% H2+1% CH4mixture Chemical kinetics N2(A) + C10H8—> products N(2D) + C10H8—> products N2(A) + N2(A)—> N2 + N2(A) CO + N2(A)—> N2 + CO O + C10H8—> H + C10H7O CO2 + N —> CO + NO CO2 + N(2D) —> CO + NO NO + N —> O +N2 NO + NH —> H + N2O NO + NH —> OH + N2 NO + NH —> O + N2H O + H2—> H + OH O(1D) + H2—>H + OH OH + C10H8—> H2O +C10H7 H2 + C10H7—> H + C10H8 diffusion —> C10H8

  17. The results of simulation on naphthalene removal in biogas, pure nitrogen and mixtures of N2 with CO, CO2and H2 agree with the experimental data rather well. A original multifactor self-consistent approach for modeling of cleaning process on the base of pulse corona discharge has been presented. It has been found that the reaction of naphthalene with exited nitrogen molecules plays a key role in the removal process. Addition to N2 of such gases as CO, CO2 and H2 worsens the removal efficiency. It is necessary to take into account the ion-molecule, electron-molecule reactions and dissotiative recombination under the high electric filed because of an appreciable N2(A) influence on the removal C10H8. N2(A) is the best component for destruction of TAR because its energy is enough to destroy TAR. For this reason a streamer type of discharges is very suitable for TAR decomposition in biogas. The knowledge of products and the channels of reactions with participation of TAR is open problem today. Without the decision of this problem we cannot talk about a toxicity level of cleaning. Conclusions

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