Melter Life/Keeping Melters Hot/Not Cycling

DOE-HDBK-1132-99

feed material is supplied from the top. This feed material usually forms a " old

cap"on top of the molten glass, melting into the glass pool as it is heated by

convective currents rising from below. The melter feed will off-gas as the cold

cap dries out and heats and as volatile elements are driven out of the glass

itself. Off-gas will vary depending on the makeup of the feed material; it

should be accommodated and treated in some type of off-gas system. The

second chamber is a heated discharge cavity through which the molten glass

can flow into a canister.

Melter Life/Keeping Melters Hot/Not Cycling . Melter life is dependent

2.14.11

largely on how the melter is operated during its productive life. Operating

temperatures of vitrification melters range between 1050 and 1250 EC. These

temperatures present special design considerations for any metals used in

melter fabrication.

The melter is usually heated through infrared heaters in both melter

chambers. The heaters in the glass " ool"chamber are for startup only and

are shut down once the glass becomes molten and joule heating can be

activated. Melters should be brought up to operating temperature in a

controlled manner at an average heat-up rate of approximately 10 EC per hour.

Exact heat-up rates are a function of the materials used and will vary

accordingly. Refractories can be heated at much faster rates than the metals

(50EC per hour). Heat-up rates should be developed around stress/strain

curves plotted as a function of temperature for the specific metal used. Once

the operating temperature is reached, it is good operating practice to keep the

melter at temperature and eliminate thermal cycling. For maintenance or

other considerations that cannot be avoided, it will become necessary during

the melter operating life to reduce the temperature of the melter. Design

planning should accommodate these instances to minimize the number of

occurrences and the amount of cool down and reheat required. When

reheating, a slow, controlled reheat is recommended.

Glass Pouring is usually accomplished by air lift over a weir into a heated

discharge chamber with a pour trough that directs the flow into the top of a

canister.

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