1. Field of the Invention
The present invention relates to a plasma reactor and process for the production of hydrogen-rich gas from light hydrocarbons.
2. Description of the Related Technology
Improving the efficiency of energy production remains an important technological goal, owing to the significant economic benefits that result in almost every sector of the economy. One potential method for improving the efficiency of energy production is to provide an energy efficient method of converting light hydrocarbons to hydrogen-rich gas, to thereby increase energy production from natural gas.
Plasma fuel converters such as plasmatrons are known to reform hydrocarbons to produce hydrogen-rich gas. DC arc plasmatrons, for example, are disclosed in U.S. Pat. Nos. 5,425,332 and 5,437,250. DC arc plasmatrons generally operate at low voltage and high current. As a result, these plasmatrons are particularly susceptible to electrode erosion and/or melting. DC arc plasmatrons also require relatively high power inputs of 1 kW or more and relatively high flow rates of coolant to keep the temperature in check.
Other conventional methods for the conversion of light hydrocarbons to hydrogen-rich gas are generally energy inefficient and, as a result, in many small-scale applications, such as the production of hydrogen for fuel cells, the cost of hydrogen gas made by these methods is not competitive. Thus, there is a need in the art for a more energy efficient process for the conversion of light hydrocarbons to hydrogen-rich gas.
U.S. Pat. Nos. 5,993,761 and 6,007,742 (Czernichowski et al.) describe processes for the conversion of light hydrocarbons to hydrogen-rich gas using gliding arc electric discharges in the presence of oxygen and, optionally, water. In the process, two electrodes having flat sheet geometry are arranged for arc ignition and subsequent gliding of the arc. The distance between the cathode and anode gradually increases to a point that no longer supports the gliding arc. As a result, the gliding arc disappears at one end of the electrodes, creating pulsed plasma wherein the properties of the plasma change with time. Due to the use of pulsed plasma, the process is relatively unstable over time. Reagents and oxygen are preheated using an external heat source. As a result of the preheating of the reagents and oxygen using an external heat source, the process suffers from poor energy efficiency. A premixed feed gas including hydrocarbons and oxygen is introduced to the reactor located at the central axis of the reactor.
U.S. Pat. No. 5,887,554 (Cohn et al.) also discloses a system for the production of hydrogen-rich gas from light hydrocarbons. The system includes a plasma fuel converter for receiving hydrocarbon fuel and reforming it into hydrogen-rich gas. The plasma fuel converter can be operated using either pulsed or non-pulsed plasma and can utilize arc or high frequency discharges for plasma generation. Products from the plasma fuel converter are employed to preheat air input to the fuel converter. In one embodiment shown in FIG. 6, residence time in the reactor is increased by providing a centralized anode and a plurality of radial cathodes to thereby cause the arc to glide towards the center of the reactor under the influence of gas flowing in the same direction as the gliding arc.
U.S. Pat. No. 6,322,757 (Cohn et al.) discloses a plasma fuel converter which employs a centralized electrode and a conductive reactor structure which acts as the second electrode for creation of a plasma discharge. Reagents are fed to the reactor just below the smallest gap between the electrodes and flow in the same direction as the gliding arc to thereby produce hydrogen-rich gas. In alternative embodiments, air and/or fuel are preheated by counter-flow heat exchange with the products of the reforming reaction and fed to the reactor either above or just below the smallest gap between the electrodes.
Although some improvements in the energy efficiency of plasma fuel converters have been achieved, there remains a need for higher energy efficiencies for use of non-equilibrium low temperature plasma.