Chemistry of inorganic compounds – Carbon or compound thereof – Elemental carbon
Reexamination Certificate
2001-08-22
2003-06-10
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Elemental carbon
C423SDIG001
Reexamination Certificate
active
06576210
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a method for destroying carbon carryover created in high temperature plasma waste treatment systems. More specifically, the present invention relates to a method for capturing carbon carryover produced in a high temperature plasma waste treatment system in a slurry, and directing the slurry back into the high temperature plasma waste treatment system to convert the carbon into a synthesis gas.
BACKGROUND OF THE INVENTION
A variety of schemes exist for the treatment, or conversion, of organic materials into useful gasses such as carbon monoxide and hydrogen. In certain plasma waste treatment systems, a high electrical potential is generated across a pair of electrodes, or a single electrode and the organic material, to create an ionized gas, or a plasma. A plasma generated in this manner will exhibit high temperatures, ranging from approximately 3,500 C. to over 10,000 C. Heat from the plasma is then radiated to the surrounding organic materials. In these arrangements, organic compounds are destroyed by pyrolysis, wherein the high temperatures of the plasma break the chemical bonds of the organic molecules. Oxygen contained within the waste materials is often augmented by the introduction of a supplemental oxygen source, such as steam, into process chamber, and these pyrolyzed organic constituents are then converted into a clean burning synthesis gas consisting primarily of CO, CO
2
and H
2
. An example of a plasma system of this type is shown In U.S. Pat. No. 5,666,891, titled “Arc Plasma-Melter Electro Conversion System for Waste Treatment and Resource Recovery” to Titus et al. the entire contents of which are incorporated herein by reference.
Unfortunately, it is often the case that a portion of the organic materials will not experience complete conversion into this desirable synthesis gas. Instead, a portion of the organic materials will be converted into carbon in a particulate form (hereinafter carbon carryover) and various other hydrocarbons. As used herein, these other various hydrocarbons include, but are not limited to, polyaromatic hydrocarbons (PAHs), polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), volatile organic compounds such as benzene, dichlorobenzene, and toluene, and reformed products made from the foregoing.
Known methods for disposing of carbon carryover, hydrocarbons and reformed hydrocarbon products created by high temperature plasma waste treatment systems have proven to be both labor intensive and expensive. Typically, these materials must be separated from the desirable synthesis gas, and then disposed of. The operations required to separate carbon carryover and hydrocarbons can often add significant expense to the overall cost of operating these high temperature plasma waste treatment systems. Requirements for physical handling of these materials can also create safety concerns, as workers may require special protective clothing and equipment to prevent exposure to potentially harmful effects.
Carbon carryover is also typically produced in a form that is difficult to handle with automated equipment. Dry carbon carryover has a tendency to clog conventional equipment designed to transport materials, such as auger feeders. In the parent application, U.S. patent application Ser. No. 09/575,485, filed May 19, 2000, “SIMULTANEOUS DESTRUCTION OF CARBON AND HYDROCARBON CARRYOVER” now abandoned, one solution to the problems these materials create was introduced with the concept of reintroducing carbon carryover back into the processing chamber of a high temperature plasma waste treatment system to effect the complete conversion of the carbon carryover into synthesis gas. However, carbon carryover in a dry form has been shown to resist efficient processing in high temperature plasma waste treatment systems. Dry carbon carryover introduced directly into the process chamber has a tendency to billow, thus causing the particles to become entrained in the exhaust gas and escape the processing chamber before the required reactions takes place that would convert the carbon carryover into synthesis gas.
These and other drawbacks of the prior art have created a need for an improved methods for separating the carbon carryover and hydrocarbons from the synthesis gas streams produced in high temperature plasma waste processing systems, and converting them to useful products such as synthesis gas once they are separated.
SUMMARY OF THE INVENTION
Accordingly, the present invention is a method for separating carbon carryover and hydrocarbons from the gas streams produced in high temperature plasma waste processing systems, and converting them to useful products such as synthesis gas once they are separated. In one aspect of the present invention, the carbon carryover is removed from the gas stream and is then mixed with a wetting agent to form a slurry. The slurry is then reintroduced back into the high temperature plasma waste processing system to allow further processing, and eventually the destruction of the carbon, preferably through a partial oxidation and steam reforming reactions, thereby producing a synthesis gas consisting mainly of carbon monoxide and hydrogen. By mixing the carbon carryover as a slurry, the carbon carryover may be held more effectively in the plasma heating zone, thereby promoting the desired reactions more effectively than is typically accomplished with dry particulate.
As practiced by the present invention, the carbon is first mixed with an appropriate wetting agent to transform the carbon carryover into a good slurry that may be readily handled with automated equipment. As used herein, a “good slurry” is one in which a minimal amount of the carbon carryover is phase separated with the wetting agent. Typically, this type of phase separation is observed as carbon floating on the surface of the wetting agent.
Several considerations are simultaneously relevant in the selection of an appropriate wetting agent. First, an appropriate wetting agent preferably contains oxygen to assist in the partial oxidation reaction with the carbon carryover. Second, to improve the overall operating cost of the high temperature plasma waste processing system, it is preferred that the wetting agent be inexpensive and readily available. Finally, an appropriate wetting agent should wet the carbon carryover to allow it to be readily and inexpensively handled with automated equipment, for example, with pumps, and to prevent the carbon carryover from billowing within the processing chamber of the high temperature plasma waste treatment system.
Preferably, while not meant to be limiting, the wetting agent is a mixture of a short chain alcohol, such as methanol, and water. Other good wetting agents, either as a mixture with water or alone, include, but are not limited to, ethyl alcohol, propyl alcohol, butyl alcohol, pentyl alcohol, hexyl alcohol, heptyl alcohol, octyl alcohol, decyl alcohol, dodecyl alcohol, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, linoleic acid, linolienic acid, and combinations thereof. In general, any oxygenated organic liquids, including but not limited to aldehydes, carboxylates, carboxylic acids, and long chain alcohols, either as a mixture with water or alone, may also be used as the wetting agent. The present invention should be broadly construed to include any such wetting agent that, when mixed with the carbon carryover, will form a slurry with the carbon carryover. Also, while it is preferred to have water as a component of the wetting agent, or as an additive after mixing the wetting agent and the carbon carryover, it is possible (although typically more expensive) to slurry the carbon carryover without the presence of water. The use of wetting agents with no water present should therefore be construed as included within the scope of the present invention.
Some wetting agents will be less effective in wetting the carbon carryover if they are pre
Integrated Environmental Technologies LLC
Johnson Edward M.
McKinley, Jr. Douglas E.
Silverman Stanley S.
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