Patent Number: 054616484
Section: summary

FIELD OF THE INVENTION The present invention relates generally to a corrosion-resistant reactor and more particularly to a supercritical water oxidation reactor with a corrosion-resistant lining. BACKGROUND OF THE INVENTION The Department of Energy has chosen supercritical water oxidation as a promising technique for destroying hazardous and radioactive mixed waste. Supercritical water oxidation (SCWO) occurs by mixing water with hazardous waste and then heating and pressurizing this mixed water to supercritical values in an extraction vessel or reactor. The benefits of SCWO processes include short residence times, nearly complete efficiencies for destruction, and effectiveness for a large number of organic compounds. One of the other advantages of SCWO includes its use of water. Water is inexpensive, non-toxic, and easily separated from many products. Water is also a convenient solvent because the material to be processed may already be in an aqueous solution, thereby eliminating the need to remove water from the final product. Further, the polarity of water can be controlled by temperature and pressure. Water is thus a good solvent for polar materials. Unfortunately, the critical parameters of temperature and pressure for water are much higher than for other solvents. These high temperatures and pressures, plus the presence of oxygen, corrode the surfaces of any metallic pans located in a SCWO reactor. Severe metal corrosion occurs when the hazardous wastes include halogens and nitrates. Current solutions to preventing severe corrosion to the metallic pans located in SCWO reactors include lining or coating these parts with exotic metals. Examples of such exotic metals include nickel, palladium, and alloys consisting mainly of nickel and copper or of nickel and chromium. These metals are expensive, difficult to machine, and cannot be coiled easily to provide a compact reaction chamber. Further, these exotic metal liners last for only a few hours of operation before their corrosion requires replacement. Accordingly, SCWO reactors need a smooth, inert lining for their metallic pans to resist corrosion. Other shortcomings of the prior art include maintenance of the integrity of the seals after repeated use. Design of the sealing arrangement for a high pressure vessel such as an SCWO reactor is important not only to extend the life of the seals but also to prevent loss of hazardous materials, which would result in violations of safety regulations. Related art commonly uses a lid or head with a series of bolts which apply pressure on a seal such as an O-ring or a gasket made of gold or silver. These seals are exposed to the same corrosive environment which destroys the metallic parts within these reactors. Additionally, the bolted-down lids of these reactors are labor intensive to open and close, do not lend themselves to automation, and create considerable down time which all combine to increase overall operating costs. Examples of other related art include U.S. Pat. No. 5,147,597 by Roofthooft et al. Roofthooft et al. disclose a prestablized chromium protective film which retards the build-up of radioactive contaminants on the inside surface of light water reactor systems. The film has a thickness of at least 500 Angstroms. Roofthooft et al. concentrate on reducing the formation of a radioactive isotope, Cobalt 59, and the corrosive products which are created by Cobalt 59 and are retained by steel piping during normal use. Other related art includes U.S. Pat. No. 5,135,709 by Andresen et al. Andresen et al. disclose a method for reducing corrosion exposed to high-temperature water such as steam or water at about 150.degree. C. or greater. The method concentrates on components formed from carbon steel, alloy steel, stainless steel, nickel-based alloys, and cobalt-based alloys. The method includes providing a reducing species, which can combine with the oxidizing species of the water, and forming a catalytic layer of a platinum group metal on the treated component. Andresen et al. do not specifically discuss high-temperature water containing hazardous wastes. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to destroy hazardous and radioactive mixed waste. Another object is to reduce corrosion and degradation of metallic parts and seals caused by high concentrations of halogens, acids, alkali metals, ammonia, heavy metals, and other hazardous wastes in a reactor used for supercritical water oxidation. Yet another object of the invention is to resist thermal shock and interaction with radionuclides present in a reactor used for supercritical water oxidation. A further object is to enable quick, automated opening and closing of a supercritical water oxidation reactor. The present invention attains the foregoing and additional objects by providing a supercritical water oxidation reactor with a corrosion-resistant lining. The supercritical water oxidation (SCWO) reactor comprises a vessel with an interior surface, two cooling sections, a heat exchanger, an oxygenating section, and a trap. The interior surface of the vessel has a corrosion-resistant, artificial ceramic, diamond, or diamond-like coating. The artificial diamond coating is thin and crystal-like in structure. The cooling sections of the vessel are located on the outer ends of the vessel, and each section includes an inlet for cold water or other cooling fluid and an outlet. The heat exchanger, located between the two cooling sections, may also have inlets and outlets for entry and exit of hot fluids. The oxygenating section comprises a porous cylindrical baffle positioned within the vessel. The porous baffle transfers either oxygen or hydrogen peroxide which travels through the cylindrical baffle. The trap has valves for removal of the waste product. A seal is located at each end of the vessel. In accordance with another aspect of the invention, the oxygenating section includes a shaft having a helical extension. The shaft has a corrosion-resistant, artificial diamond or diamond-like coating. The shaft is porous to permit the addition of oxygen or hydrogen peroxide to the hazardous waste. The helical extension increases the removal of solids from the waste. A seal is located at each end of the vessel. In accordance with another aspect of the invention, the SCWO reactor comprises a vessel with an interior surface, a heat exchanger, an oxygenating section, and a trap. The interior surface of the vessel has a corrosion-resistant lining which may be a ceramic or artificial diamond coating. The oxygenating section comprises a porous cylindrical baffle or a shaft positioned within the vessel. A seal is located at each end of the vessel. Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.