PLASMA PROCESS AND REACTOR FOR PRODUCING SYNTHESIS GAS

Abstract

The present invention describes a plasma reactor for processing natural gas and/or light hydrocarbons, including biomethane and biogas, with a plasma torch that does not require the use of cathode shielding gas (shielding gas), as well as a process for reforming using a plasma reactor for the production of synthesis gas and carbonaceous materials from natural gas and/or light hydrocarbons.

Claims

1.-8. (canceled)

9. Plasma reactor for the production of synthesis gas, characterized by comprising: a torch comprising straight or step anode, tube for the passage of gas, which can be housed in the anode in the case of non-transferred arc, gas inlet chamber, arc stabilization system, arc rotation system and system for cooling the electrodes; anode and/or cathode diameter in the range between 2 mm and 100 mm, plasma power between 1 and 6,000 kW.

10. Reactor, according to claim 9, characterized by having gas outlet flow rates in the range between 2 e 60,000 mole/hr.

11. Reactor, according to claim 9, characterized by comprising electrodes selected from the group consisting of copper and zirconia.

12. Reactor according to claim 11, characterized by comprising zirconia cathode.

13. Reactor, according to claim 9, characterized in that it allows the injection of gases in the region of the anode and/or cathode.

14. Process for the production of synthesis gas, characterized by comprising the reform of natural gas and/or light hydrocarbons through the following steps: injecting CO.sub.2 in the region of cathode, and CH.sub.4 at the anode outlet of a reactor as defined in claim 9 with a gas flow rate, in which the gas outlet flow rate is in the range between 2 and 60,000 mole/h where the power is in the range between 1 to 6,000 kW.

15. Process, according to claim 14, characterized in that the conversion of CO.sub.2 is in the range between 50 and 100%.

16. Process, according to claim 14, characterized by using electric arc current in the range between 20 and 250 A.

17. Reactor, according to claim 10, characterized by comprising electrodes selected from the group consisting of copper and zirconia.

18. Reactor, according to claim 10, characterized in that it allows the injection of gases in the region of the anode and/or cathode.

19. Reactor, according to claim 11, characterized in that it allows the injection of gases in the region of the anode and/or cathode.

20. Reactor, according to claim 12, characterized in that it allows the injection of gases in the region of the anode and/or cathode.

21. Process, according to claim 15, characterized by using electric arc current in the range between 20 and 250 A.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0027] The detailed description presented below refers to the attached figures, which:

[0028] FIG. 1 depicts the electric arc torch used, according to the present invention.

[0029] FIG. 2 depicts the internal dimensions of the plasma torch according to the present invention.

[0030] FIG. 3 depicts a graph with the output flow rates for the several gases resulting from the reaction of VNG with a CO.sub.2 plasma in the HZR11 test, where, mainly, the flow rate remained fixed the flow rates of CO.sub.2 varied and the VNG flow rate varied.

[0031] FIG. 4 depicts a graph of selectivity for dry reform products in the HZR11 test, where the CO.sub.2 flow rate was kept fixed and the VNG flow rate was varied.

[0032] FIG. 5 represents a graph with the output flow rates for the several gases resulting from HZR13 test, where the electric arc current and the CO2 flow rate was fixed and the VNG flow rate was varied.

[0033] FIG. 6 depicts a graph with the results of conversion of VNG into H.sub.2 and abatement of CO.sub.2 from initial gas, which refers to the formation of carbon in solid phase and which was extracted from the VNG, for the HZR13 test, where the current of the electric arc, the flow of CO.sub.2 were kept fixes and the flow of VNG was varied.

[0034] FIG. 7 depicts a graph with the results of energy yields for H.sub.2, CO and C.sub.2H.sub.2 of HZR13 test, where the electric arc current, the flow rate of CO.sub.2 was kept fixes and the flow rate of VNG was varied.

[0035] FIG. 8 depicts a graph of selectivity for the reform products in the HZR13 test, where the electric arc current, the flow rate of CO.sub.2 was fixed and the VNG flow rate was varied.

[0036] FIG. 9 depicts a graph with the electrical consumption, electrical energy consumed in the plasma per mol of H.sub.2 and CO generated in the HZR13 test, where the electric arc current and the CO.sub.2 flow rate were fixed and the flow of VNG was fixed.

[0037] FIG. 10 depicts a graph of the percent conversion of the reagents (CNG and CO2) in CO, H.sub.2 and carbon for the HZR13 test, where the current of the electric arc and flow rate of CO.sub.2 were fixed and the flow of VNG was varied.

[0038] FIG. 11 depicts a graph with the output flow rates for the several gases resulting from the reaction of VNG with a CO.sub.2 plasma in the HZR13 test, where the flow rates of VNG and CO.sub.2 were fixed, and the plasma current was varied.

[0039] FIG. 12 depicts a Graph with the results of the conversion of VNG into H.sub.2 and CO.sub.2 abatement in the HZR13 test, which refers to the formation of carbon in solid phase and which was extracted from VNG, where the flow rates of VNG and CO.sub.2 were fixed, and the plasma current was varied.

[0040] FIG. 13 depicts a graph with the results of energy yields for H.sub.2, CO and C.sub.2H.sub.2 of HZR13 test, where the flow rates of VNG and CO.sub.2 were fixed, and the plasma current was varied.

[0041] FIG. 14 depicts a graph of selectivity for the products in the HZR13 test, where the flow rates of VNG and CO.sub.2 were fixed, and the plasma current was varied.

[0042] FIG. 15 depicts a graph with the electrical consumption, electrical energy consumed in the plasma mol of H.sub.2 of CO and carbon generated in the HZR13 test, where the flow rates of VNG and CO.sub.2 were fixed, and the plasma current was varied.

[0043] FIG. 16 depicts a graph of the percent conversion of reagents into CO, H.sub.2 and carbon for the HZR13 test, where the flow rates of CNG and CO.sub.2 were fixed, and the plasma current was varied.

DETAILED DESCRIPTION OF PRESENT INVENTION

[0044] The present invention refers to a reactor powered by carbon dioxide plasma and a plasma torch containing electrodes for processing natural gas and/or light hydrocarbons.

[0045] The present invention also refers to a reform process utilizing a carbon dioxide plasma reactor and plasma torch containing electrodes for processing natural gas and/or light hydrocarbons, including biogas, aiming the production of synthesis gas and solid carbon, preferably nanostructured, from natural gas and/or light hydrocarbons.

[0046] Within the scope of the present invention, plasma torches have the following construction elements [0047] Electrodes: cathode and anode; [0048] A tube for the passage of gas, which can be housed in the anode in the case of a not transferred arc; [0049] A gas inlet chamber (vortex chamber); [0050] Arc stabilization system (usually in a vortex); [0051] Arc rotation system (magnetic or vortex); [0052] Cooling system of the electrodes.

[0053] According to present invention, the torches show an anode selected from the group consisting of straight anode, conical anode or step anode. In a preferred mode, the torches have a straight or step anode.

[0054] According to present invention, gas injection can occur in the cathode or anode region. Preferably, CO.sub.2 is injected into the cathode region, which first causes CO.sub.2 ionization. Also, preferably, CH.sub.4 is injected at the anode outlet, which allows: [0055] injecting any flow of CH.sub.4 without affecting the stability of the electric arc; [0056] obtaining high percent conversion of CO.sub.2 (from 75% to 100%, preferably between 90 and 100%), regardless of the CH.sub.4 flow rate applied in the process; [0057] obtaining conversion from 75% to 100%, preferably between 90 and 100% of CO.sub.2+CH.sub.4 into 2H.sub.2+2CO.

[0058] In one embodiment of present invention, the diameter of the anode and/or cathode can be in the range between 2 mm and 100 mm, preferably between 5 and 50 mm.

[0059] Within the scope of present invention, cathode as described in the prior art can be used. Preferably, cathodes selected from the group consisting of copper and zirconia are used.

[0060] According to present invention, the power to be used in the plasma can vary between 1 to 6,000 kW, preferably between 20 and 200 kW.

[0061] To carry out the process according to present invention, gas flow rates in the range between 2 and 60,000 mol/hr are used, preferably between 10 and 2000 mol/hr are used.

[0062] The following description will start from preferred embodiments of present invention. As will be apparent to any person skilled in the art, the present invention is not limited to those particular embodiments.

EXAMPLES

[0063] For a better understanding of the processes that took place inside the plasma torches, the Computational Fluid Dynamics (CFD—Computational Fluid Dynamics) simulation resource was used. The rendered showed a good energy efficiency in the production of hydrogen, however, with low conversion of CO.sub.2. The electric arc thermal plasma torch achieved superior results in converting natural gas into CO.sub.2 plasma, in terms of efficiency and scale.

HZR11 Test

[0064] In order to observe the effects of gas confinement, the second anode had its internal diameter reduced. In this test, the fixed flow rate of 131 mol/hr for CO.sub.2 was kept, while the flow rate of VNG was varied from 112 to 639 mol/hr. The current of the electric arc was kept constant at 103 A, but the power decreased with the increase in the flow rate of VNG, due to the small diameter of the second anode that caused an increase in pressure at the output of the first anode. The decrease in the diameter of the second anode, in addition to causing a greater pressure drop, increases the temperature of the gases passing through it. This fact is reflected in the CO flow rate that decreases with the increase in VNG flow rate. This behavior can be seen in the selectivity graph shown in FIG. 4.

HZR13 Test

[0065] As the decrease in the diameter of the second anode reduced the energy yield in the production of H.sub.2, in the HZR13 test, the diameter returned to 25 mm. As a new attempt to increase the plasma temperature, in this test the diameter of the first anode was decreased. The results of this test were divided into two groups. Firstly, the procedure was the same as that of HZR11 test, where the CO.sub.2 flow rate was fixed at 135 mol/hr, making the VNG flow rate vary to a constant current of 103 A. In this case, there was no decrease in power due to the increase in the flow rate of VNG. In the second group, VNG flow rates were set at 312 mol e/hr and CO.sub.2 at 135 mol/hr, making the current vary by 70, 103, 125 and 150 A, consequently, the plasma power and temperature.

Variation of VNG Flow Rate

[0066] The graphs in FIGS. 5 to 11 show the results of the test where the current and the flow rate of CO.sub.2, which is the working gas, were kept constant, while the flow rate of the VNG was varied.

[0067] FIG. 5 shows a graph with the flow rates of gases entering and leaving the plasma torch, as well as the power for each flow rate of VNG. The arc power increases slightly with the increase in the flow of VNG, the opposite behavior to that found in test 11, where the power decreased due to the increase in pressure at the output of the first anode, caused by the loss of pressure due to the small diameter of the second anode. The flow rate of H2 reaches a maximum when the flow rate of VNG is approximately 2.3 times the flow rate of CO.sub.2. The same maximum applies to the energy efficiency in the production of H.sub.2 and its selectivity, as can be seen in FIGS. 8 and 9. FIG. 7 shows that for the highest energy efficiency in the production of H.sub.2; the conversion of VNG into H.sub.2 is around 58% and the CO.sub.2 abutment at 10%. FIG. 10 shows that the electrical consumption for the production of H.sub.2 is much lower than that of CO. For the condition of maximum energy efficiency in the production of H.sub.2, the percentage of conversion of reagents into CO, H.sub.2 and carbon was 60%, and the maximum conversion was 92% for flow rates of VNG lower than the flow rate of CO.sub.2 according to FIG. 11.

Variation of Plasma Power

[0068] The graphs in FIGS. 12 to 17 were the results of tests with the variation of the plasma power, via the variation of the electric arc current, where the ratio between the flow rates of VNG and CO.sub.2 corresponded to the maximum energy efficiency in the production of H.sub.2, for the ratio [flow rate of CO.sub.2/(flow rate of CO.sub.2+flow rate of VNG)]=0.30. The graph in FIG. 12 shows the flow rate of reactant gases and products, where it is observed that the increase in power reduced the residual flow rates of CH.sub.4 and CO.sub.2. As for the products, there was a slight increase in the flow rates of C.sub.2H.sub.2 and CO, with an increase in the H.sub.2 flow rate much greater. FIG. 13 shows that the conversion of VNG into H.sub.2 varied from 40 to 77%, in the range of power explored, and the behavior of the curve indicates that this result may be greater for higher powers. This graph also signals that the CO.sub.2 abutment should increase with the increase in plasma power.

[0069] FIG. 14 shows the energy yield for the products, which decreases for CO, increases continuously for C.sub.2H.sub.2 and goes through a maximum for H.sub.2. This drop in performance may be associated with the characteristic curve of the plasma, which with increasing current, the arc voltage decreases, followed by a decrease in the length of the electric arc, causing the plasma torch to leave the maximum performance point. Thus, for the plasma torch to continue operating at maximum efficiency, it is necessary to increase the flow rate of CO.sub.2, so that the arc voltage returns to the initial value and, consequently, the arc length.

[0070] The selectivity graph, shown in FIG. 15, shows that the increase in power favors the formation of H.sub.2, decreases the formation of CO, with little variation in the flow rate of C.sub.2H.sub.2 and carbon.

[0071] The electrical consumption for H.sub.2, shown in FIG. 16, indicates an almost imperceptible reduction with increasing power, while increasing for CO and going through a maximum for carbon.

[0072] The graph in FIG. 17 shows that the increase in plasma power increases the percentage of conversion of reagents to CO, H.sub.2 and carbon.

[0073] The description that has been made so far of the object of present invention should be considered only as a possible or possible embodiments, and any particular characteristics introduced therein should be understood only as something that has been written to facilitate understanding. Therefore, they cannot in any way be considered as limiting the present invention, which is limited to the scope of the following claims.