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An apparatus and method sinters or partially sinters green pellets in a selected temperature range to make proppant particles as the green pellets pass between an electrical arc and a gas flowing in the vortex path and exit an underflow of a vessel. The vessel has an overflow disposed in a first end

An apparatus and method sinters or partially sinters green pellets in a selected temperature range to make proppant particles as the green pellets pass between an electrical arc and a gas flowing in the vortex path and exit an underflow of a vessel. The vessel has an overflow disposed in a first end, an underflow disposed in a second end, a middle portion having a circular cross-section disposed between the first end and the second end, and a tangential inlet proximate to the first end such that a gas from the tangential inlet flows along a vortex path from the first end to the second end of the vessel. A first electrode extends through the overflow and a second electrode extends through the underflow. The electrodes are used to create the open electrical arc. One or more feed tubes extend through the overflow proximate to the first electrode.

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1. An apparatus for sintering green pellets to make proppant particles, the apparatus comprising: a vessel having an overflow disposed in a first end, an underflow disposed in a second end, a middle portion having a circular cross-section disposed between the first end and the second end, and a tang

1. An apparatus for sintering green pellets to make proppant particles, the apparatus comprising: a vessel having an overflow disposed in a first end, an underflow disposed in a second end, a middle portion having a circular cross-section disposed between the first end and the second end, and a tangential inlet proximate to the first end such that a gas from the tangential inlet flows along a vortex path from the first end to the second end of the vessel;a first electrode extending through the overflow and a second electrode extending through the underflow, wherein both electrodes are at least partially disposed within the vessel, spaced apart from one another, and axially aligned with one another along a central axis of the vessel from the first end to the second end;one or more feed tubes extending through the overflow proximate to the first electrode; andwherein the electrodes are used to create an open electrical arc that sinters or partially sinters the green pellets from the one or more feed tubes in a selected temperature range to form the proppant particles as the green pellets pass between the electrical arc and the gas flowing in the vortex path and exit the underflow. 2. The apparatus as recited in claim 1, wherein the one or more feed tubes extend past the first electrode. 3. The apparatus as recited in claim 1, wherein the one or more feed tubes comprise a single tube having a larger diameter than the first electrode such that the first electrode is disposed within the single tube and a gap separates the single tube from the first electrode. 4. The apparatus as recited in claim 1, wherein the one or more feed tubes are made of an electrical insulating material or comprise one or more third electrodes. 5. The apparatus as recited in claim 1, wherein the apparatus is configured to sinter or partially sinter the green pellets in the selected temperature range which is between about 1,200° C. and 3,700° C. 6. The apparatus as recited in claim 1, wherein the apparatus is configured to sinter or partially sinter the green pellets in the selected temperature range which is based on a chemical composition of the green pellets, a size of the green pellets, a resonance time of the green pellets within the vessel, or a combination thereof. 7. The apparatus as recited in claim 1, further comprising a radio frequency source attached to or disposed within the vessel. 8. The apparatus as recited in claim 7, wherein the radio frequency source comprises one or more radio frequency coils, a waveguide, or a combination thereof. 9. The apparatus as recited in claim 1, wherein the gas or the one or more feed tubes contain a material that coats or chemically reacts with the green pellets. 10. The apparatus as recited in claim 1, further comprising a DC power source connected to the first and second electrodes. 11. The apparatus as recited in claim 10, wherein the DC power source comprises one or more batteries or one or more solar powered batteries. 12. The apparatus as recited in claim 1, wherein an interior of the middle portion of the vessel is cylindrical shaped, cone shaped, funnel shaped or a combination thereof. 13. The apparatus as recited in claim 1, wherein the vessel comprises a cyclone separator, a hydrocyclone, or a gas-sparaged hydrocyclone. 14. The apparatus as recited in claim 1, wherein the apparatus is configured such that the gas is mixed with a liquid. 15. The apparatus as recited in claim 1, wherein a portion of the gas exits through the overflow. 16. The apparatus as recited in claim 1, further comprising a heated gas source connected to the one or more feed tubes to pre-heat the green pellets. 17. The apparatus as recited in claim 16, wherein the heated gas source comprises a high temperature blower, a high temperature compressor, an electrical heater or heated gas source, a burner, a thermal oxidizer, a jet exhaust, an oxy-fuel torch, a plasma torch, an internal combustion engine exhaust, or a combination thereof. 18. The apparatus as recited in claim 1, further comprising a gas slide having a first inlet for the green pellets, a second inlet for a feed gas and an outlet connected to the one or more feed tubes. 19. The apparatus as recited in claim 18, further comprising a heater connected to the second inlet to heat the feed gas. 20. The apparatus as recited in claim 18, further comprising: a gas line connecting the overflow to the second inlet of the gas slide such that the feed gas comprises at least a portion of the gas that exits the overflow; anda valve or regulator attached to the gas line to control a pressure of the feed gas. 21. The apparatus as recited in claim 18, further comprising: a feed gas source;a gas line connected to the overflow, wherein a portion of the gas exits the overflow; anda gas-to-gas heat exchanger connected to the feed gas source, the second inlet of the gas slide and the gas line such that heat from the gas is transferred to the feed gas. 22. The apparatus as recited in claim 1, further comprising a gas line connecting the overflow to the tangential inlet, wherein a portion of the gas exits the overflow and recirculates to the tangential inlet. 23. The apparatus as recited in claim 22, further comprising a hot gas clean up device attached to the gas line and the tangential inlet. 24. The apparatus as recited in claim 22, further comprising a gas compressor attached to the gas line and the tangential inlet. 25. The apparatus as recited in claim 1, further comprising a linear actuator connected to the one or more feed tubes or the first electrode or the second electrode that adjusts a position of the one or more feed tubes or the first electrode or the second electrode within the vessel. 26. The apparatus as recited in claim 25, wherein the linear actuator is used to move the first electrode or the second electrode in order to strike the electrical arc between first electrode and the second electrode. 27. The apparatus as recited in claim 1, wherein the apparatus is configured to be mounted on a skid, trailer, truck, rail car, barge or ship. 28. The apparatus as recited in claim 1, wherein the first electrode or the second electrode contain a material that is released by the electrical arc and coats or chemically reacts with the green pellets.