Patent Number: 054616484
Section: description

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1, a supercritical water oxidation (SCWO) reactor 10 is shown having a corrosion-resistant lining 15 in accordance with the present invention. The SCWO reactor comprises a vessel 20, a first cooling section 30, a heat exchanger 40, a second cooling section 50, an oxygenating section 60, and a trap 80. The vessel 20 has an inner surface which is coated with the corrosion-resistant lining 15. The lining 15 is an artificial ceramic or diamond coating. The artificial diamond coating is thin and crystal-like in structure. This structure is capable of withstanding pressures up to 350 atm and temperatures up to 650.degree. C. Additionally, this coating's structure resists chemically reacting with a mix of water, carbon dioxide, oxygen, ambient air, fluorides, halides, and salts. The diamond coating also resists thermal shock, interaction with radionuclides, and high concentrations of halogens, acids, alkali metals, ammonia, heavy metals, and other hazardous wastes. The vessel 20 has an outer region 22 which includes an opening 24 where an aqueous solution of hazardous and radioactive mixed waste enters. A seal assembly 25 inserts between the end of the vessel 20 and a pump (not shown) for the SCWO system. The seal assembly 25 prevents leakage of hazardous waste between the interface of the pump and the vessel. The seal assembly 25 may include a conventional seal such as an O-ring or a gasket. Alternatively, the seal assembly includes a spring-loaded, graphite-reinforced polytetrafluorethylene seal as shown in FIG. 4. The product polytetrafluorethylene is sold under the trademark TEFLON. Referring again to FIG. 1, a cooling section 30 circumferentially surrounds the vessel 20 at outer region 22. The cooling section 30 includes an inlet 32 for supplying cold-water or any other cooling liquid to the section 30. The liquid exits through outlet 34. The cooling section 30 cools the aqueous mixed waste before it reaches inner region 26 and prevents conditions at the seal assembly 25 from reaching supercritical levels. A heat exchanger 40 circumferentially surrounds the inner region 26 of the vessel. The heat exchanger 40 has an inlet 42 for supplying a hot fluid having a temperature in the range of 300.degree. C. to 700.degree. C. The hot fluid exits through outlets 44 and 46. Alternatively, the heat exchanger 40 comprises an electrical heating coil wrapped around the exterior of vessel 20. The heat exchanger 40 heats the aqueous mixed waste to supercritical values. A second cooling section 50 circumferentially surrounds a second outer region 28 of the vessel. The second cooling section 50 includes an inlet 52 for supplying cold-water to the exchange and an outlet 54. The cooling section 50 also has a pressure release valve 56 for regulating back pressure within the vessel 20. The cooling section 50 cools the aqueous mixed waste below supercritical conditions before the waste reaches outlet 29 of the vessel. This cooling reduces the corrosive environment at the outlet 29 and thereby increases the life of seal assembly 70 located at the outlet. Positioned within the vessel 20 is an oxygenating section 60. Section 60 comprises a porous cylindrical baffle 62 having an inlet 64, an outlet 66, and a plurality of disbursing holes 68. The cylindrical baffle 62 extends axially within the interior of the vessel. Inlet 64 receives an oxygenating agent such as oxygen or hydrogen peroxide. The agent travels within the baffle 62 and exits through the holes 68 into the aqueous mixed waste. The exterior surface of the baffle has an artificial diamond coating 65 along the inner surface of the vessel. The artificial diamond coating is thin and crystal-like in structure. The properties of coating 65 are similar to the lining 15. A seal assembly 70 is located at the outlet 29 of the vessel and the outlet 66 of the baffle. The seal assembly 70 preferably includes spring-loaded, graphite-reinforced polytetrafluorethylene seal. Alternatively, the seal assembly 70 may include an O-ring or gasket held into place by a bolted-down lid. A trap 80 is also located at the outlet 29 of the vessel. The trap has two valves 82 and 84 for removing waste product separated from the aqueous mixture. In accordance with another aspect of the invention, FIG. 2 illustrates a SCWO reactor 110 having a corrosion-resistant lining 115. The SCWO reactor 110 comprises a vessel 120, a first seal assembly 125, a first cooling section 130, a heat exchanger 140, a second cooling section 150, an oxygenating section 160, a second seal assembly 170, a rotating drive 175, and a trap 180. The components of reactor 110 are substantially similar to the components of reactor 10. The reactor 110, however, has a different oxygenating section 160 and a rotating drive 175. The oxygenating section 160 comprises a porous shaft 162 positioned concentrically within the vessel 120. The shaft 162 has a helical extension 163 which wraps axially about the shaft 162. The shaft 162 extends axially within the interior of the vessel and connects to the rotating drive 175. An inlet 164 receives an oxygenating agent such as oxygen or hydrogen peroxide. The oxygenating agent travels within the shaft 162 and exits through disbursing holes 168 into the aqueous mixed waste. The exterior surface of the shaft 162, including the helical extension 163, has an artificial diamond coating 165 to resist corrosion. This coating is similar to the lining 115 covering the inner surface of the vessel 120 and the lining 15 covering the inner surface of vessel 20 in FIG. 1. The coating is thin and crystal-like in structure. Referring again to FIG. 2, the rotating drive 175 rotates the shaft 162. The helical path through which the aqueous hazardous mixed waste travels in vessel 120 aids in the removal of solids 200 from the aqueous mixed waste. In particular, the helical path increases the mass transfer coefficient of the mixed waste, which in turn increases the rate of reaction. This increase facilitates physical separation and reduces the reaction time. In accordance with another aspect of the invention, FIG. 3 illustrates a SCWO reactor 210 having a corrosion-resistant lining 215. The SCWO reactor 210 comprises a vessel 220, a heat exchanger 240, an oxygenating section 260, and a trap 280. The vessel 220 has an inner surface which is coated with a corrosion-resistant lining 215. The lining 215 is an artificial ceramic or diamond coating. The artificial diamond coating is thin and crystal-like in structure. The properties and structure of lining 215 are similar to lining 15. The vessel 220 has an opening 224 where an aqueous solution of hazardous and radioactive mixed waste enters. A seal assembly 225 inserts between the end of the vessel 220 and a pump (not shown) for the SCWO system. The seal assembly 225 prevents leakage of hazardous waste between the interface of the pump and the vessel. The seal assembly 225 may include a conventional seal such as an O-ring or a gasket or may include a spring-loaded, graphite-reinforced polytetrafluorethylene seal as shown in FIG. 4. Referring again to FIG. 3, the heat exchanger 240 circumferentially surrounds the vessel 220. The heat exchanger has an inlet 242 for supplying hot fluid having a temperature in a range of 300.degree. C. to 700.degree. C. The hot fluid exits through outlets 244 and 246. Alteratively, the heat exchanger 240 comprises an electrical heating coil wrapped around the exterior of vessel 220. The heat exchanger 240 heats the aqueous mixed waste to supercritical values. Positioned within the vessel 220 is an oxygenating section 260. Section 260 comprises a porous cylindrical baffle 262 having an inlet 264, and a plurality of disbursing holes 268. The cylindrical baffle 262 extends axially within the interior of the vessel. Inlet 264 receives an oxygenating agent such as oxygen or hydrogen peroxide. The agent travels within the baffle 262 and exits through the holes 268 into the aqueous mixed waste. The exterior surface of the baffle has an artificial diamond coating 265 similar to the lining 215 along the inner surface of the vessel. The coating 265 is thin and crystal-like in structure. The properties of coating 265 are similar to the lining 15 of FIG. 1. Referring again to FIG. 3, a seal assembly 270 is located near an outlet 229 of the vessel. The seal assembly 270 preferably includes a spring-loaded, graphite-reinforced polytetrafluorethylene seal. Alternatively, the seal assembly 270 may include an O-ring or gasket held into place by a bolted down lid. A trap 280 is also located at the outlet 229 of the vessel. The trap has two valves 282 and 284 for removing waste product separated from the aqueous mixture. FIG. 4 illustrates a seal assembly in accordance with the present invention which includes a spring-loaded, graphite-reinforced polytetrafluorethylene seal 300. This type of seal provides an effective sealing method requiring minimal force and is practically self-sealing. The seal consists of a graphite reinforced body 310 with a spring 315 in the middle. The spring 315 pushes the two sides of the seal outside. One side of the seal touches the body of a vessel 320 and the other side of the seal touches a cap 330. When the pressure inside the vessel increases, it acts against the seal and pushes the lips even further towards the wall. Little force is necessary to maintain a seal. The seal assembly shown in FIG. 4 eliminates the need for bolted-down lids used in a conventional sealing design and enables quick, automated opening and closing of the vessel. Automated opening and closing is achieved by threading both the cap 330 and the vessel body 320 and leaving enough stock to take any axial stresses. A simple motor mechanism can feed the cap into the vessel. This automation provides considerable amount of safety to the operator. The novel features of the present invention include the artificial diamond or diamond-like coating along the inner surface of the vessel and the exterior surface of the cylindrical baffle or the porous shaft of the SCWO reactor. Other novel features include cooling sections near the outlets of the vessel and spring-loaded, graphite-reinforced polytetrafluorethylene seals. Advantages of the present invention include reduced corrosion and degradation of the seals and metallic parts located within a SCWO reactor and increased resistance to thermal shock and to interaction with radionuclides. Other advantages include quick, automated opening and closing of the SCWO reactor and increased resistance to high concentrations of halogens, acids, alkali metals, ammonia, and heavy metals. Although the invention has been described relative to a specific embodiment thereof, numerous variations and modifications will be readily apparent to those skilled in the art in the light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described.