Injection of substances into high temperature liquids

A method of injecting gas into a high temperature melt via a passage through the wall of a vessel containing the melt, the passage initially having a dislodgeable stopper closing its inner end, comprising the steps of:

• (a) from outside the vessel (10), inserting a delivery pipe (24) into the passage (18) and disposing an inner end of the pipe adjacent the stopper (20), the pipe being smaller transversely than the passage by a predetermined amount;
• (b) cooling the pipe (24) and passage (18) in the vicinity of the stopper (20) by passing gas along the pipe and exhausting the gas to the exterior of the vessel (10);
• (c) immediately before injecting gas into the melt, establishing gas pressure and flow rate in the pipe (24) of sufficient magnitudes that, upon injection, the gas velocity leaving the pipe is great enough to ensure the gas enters the melt as a jet rather than as bubbles;
• (d) forcibly thrusting the pipe (24) at the stopper (20), dislodging the stopper into the melt and thereby commencing injection of gas into the melt;
• (e) maintaining substantially undiminished the gas pressure and flow rate during the ensuing injection;
• and
• (f) when the injection is adjudged complete, reducing the gas pressure/flow rate and allowing the melt to enter and freeze in the pipe (24) thereby closing it,
• the amount by which the pipe (24) is smaller than the passage (18) affording a space therebetween large enough for the melt to intrude for a limited distance, before freezing, as soon as the stopper (20) is dislodged.