Glass manufacturing – Processes – Devitrifying glass or vitrifying crystalline glass
Reexamination Certificate
2001-01-31
2003-05-27
Colaianni, Michael (Department: 1731)
Glass manufacturing
Processes
Devitrifying glass or vitrifying crystalline glass
C065S033900, C065S066000, C065S082000, C065S134700, C065S134800, C065S135600, C065S144000, C065S355000, C065SDIG004, C219S683000, C588S011000, C373S027000, C373S156000, C373S157000, C264S432000, C264S434000, C264S460000, C264S489000, C264S490000
Reexamination Certificate
active
06568215
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
This invention relates to a melting process for a particulate material in which the main heat source is microwave energy.
2. The Relevant Technology
UK Patent No: 2122859A, UKAEA, discloses the use of microwave energy to heat a material, such as a glass, in a container having a cooled outer surface, the arrangement being such that a layer of melted and re-solidified material, known as a “skull”, is formed in contact with the internal surface of the container. Whilst the skull protects the container wall and avoids reactions between it and the melt, the container cannot easily be cleaned as the material adheres to the walls. Furthermore, start-up may be slow due to poor microwave heating of the materials to be melted at low temperature.
UK Patent No: 2228476 VERT Ltd. discloses a cold-top melter furnace in which a blanket of unmelted glass frit is maintained above the molten glass, the blanket thickness assisting in retaining volatiles. However, infrasound energy is specifically used to prevent the formation of a skull of solidified glass. This ensures that the molten glass is in contact with the furnace wall, and reactions may occur as a result.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to avoid the disadvantages of the two known methods.
According to the invention apparatus for melting a fusible material comprises:
a microwave cavity;
means for cooling the exterior of the cavity;
means for supplying the fusible material to be melted to the interior of the cavity;
a crucible within the cavity and spaced from its walls by a layer of unmelted material, said crucible being formed from melted and re-solidified material; and
means for supplying microwave energy to the cavity of such power that fusible material in the interior of the crucible is melted.
The material to be melted may be in particulate form and/or liquid form. The particles may be between 0.5 and 10 mm and preferably 1 to 5 mm in size and/or have a volume of 1 mm
3
to 100 mm
3
.
The material to be melted may be a preformed material, such as glass particles. The material to be melted may comprise materials to be melted to form a further material. For instance glass forming materials may be added to the cavity. Glass forming materials may include sand, sodium carbonate, lime or calcium carbonate. The sand may be replaced wholly or partially by other acidic oxides, such as B
2
O
3
or P
2
O
5
and/or with potassium, lithium, alkali earth metal or lead oxides.
The material to be melted may be fed to the cavity together with other materials which are not intended to be melted by the cavity. Thus higher temperature materials may be introduced and dispersed in a melt of the melted materials. The materials to be melted may comprise a matrix forming material and a material to be dispersed within that matrix. A glass matrix in which waste material is dispersed may be provided in this way. The material may be calcined or partially calcined prior to feeding.
The cavity may be microwave tunable. The cavity may be at least partially microwave tuned by its physical dimensions. The cavity may have four side walls, a bottom and top wall. The cavity may be provided in substantially spherical configuration. The cavity may have an internal volume of 2 to 500 liters and is preferably 10 to 300 liters.
The material from which the crucible has been formed may be the same as the fusible material to be melted within the crucible, and/or the same as the unmelted material. Different fusible materials may be used Preferably the crucible is formed of the same material as the unmelted material, the crucible being formed from melted and re-solidified such material. Preferably, the unmelted material remains substantially as fed to the cavity. The crucible is preferably liquid impermeable. The layer forming the crucible may be between 0.5 and 10 cm thick and is preferably 1 to 5 cm thick. The thickness of the material forming the crucible may vary between different locations. Preferably the crucible is substantially ovoid in shape. Preferably the crucible is spaced from the walls defining the cavity by the unmelted material over at least 80% of its surface area. Levels of 90 and 95% are to be preferred and most preferably no contact between the crucible and the cavity walls occurs. Preferably the crucible is made of glass.
Preferably the unmelted material is in particulate form with voids between individual particles. Preferably the unmelted material is of the same material as the crucible. The unmelted material may be provided in particles of between 1 and 5 mm. Preferably the unmelted material remains free to move relative to other portions of the unmelted material and most preferably relative to the crucible. Preferably the unmelted material provides a layer between the crucible and the cavity wall. Preferably the layer is at least 1 cm thick and more preferably 3 cm thick over at least 90% of the surface area of the crucible.
The material to be melted may be fed to the cavity by feed means such as a hopper. Preferably the fusible material feed means are provided above the cavity. Gravity feed may be relied upon to convey the fusible material into the cavity. Preferably the material is fed on to the top of the skull. Preferably the material is kept topped up within the cavity, most preferably contact between the top cavity wall and the unmelted material is maintained. Sensing means may be provided in the material feed means to determine the level of feed material. The feed means may introduce the feed into the cavity by means of a passage. Microwaves may also be introduced into the cavity by means of this passage. Preferably a column of feed material is maintained in the feed means, in gaseous contact with the cavity. In this way the column feed material can act as a filter for off gases from the melt.
The means for cooling the exterior of the cavity may comprise radiation and/or convection and/or conduction of energy away from the exterior cavity surface. Additional means may be provided to supplement the natural cooling of the cavity. One or more heat exchangers may therefore be provided in proximity to the exterior of the cavity. Heat exchangers may be provided inside the cavity and/or inside the cavity wall and/or in thermal contact with the exterior of the cavity. The provision of the heat exchanger means in contact with the exterior of the cavity is preferred for simplicity of construction. The heat exchanger may employ forced air or other forced fluid flow, such as water. Preferably the cooling means comprise one or more pipes in contact with the exterior surface of the cavity. Preferably the flow of fluid through the heat exchanger is variable. In this way the cooling extent can be varied as desired.
Preferably the microwave energy source is separated from the cavity by a fluid impermeable barrier, permeable to microwaves. Alumina, quartz, polythene or other barrier materials may be employed.
The microwave source may have a power of between 10 and 50 Kw. Preferably the power output from the microwave source is controllable.
The microwave source and/or cavity may be provided with tuning means. Preferably coarse tuning means are provided for the cavity. The coarse tuning means may be provided in a passage leading from the cavity. The cavity and passage may be separated by a fluid impermeable barrier which is permeable to microwaves. A tuning stub may be employed.
Coarse tuning means for the cavity may be provided, preferably in the form of moveable shutters. Preferably the shutters are presented in the microwave guide leading to the cavity. This microwave guide may also serve as the feed route for the fusible material.
Preferably there is further provided further means for supplying energy to material/particles within said cavity and/or crucible. The further energy means may be used during the crucible formation process and/or during tapping of the molten core. Preferably the further means are located/generated below the cavity. The further means may ex
Lucas James
Schofield John Anthony
British Nuclear Fuels PLC.
Colaianni Michael
Workman & Nydegger & Seeley
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