| 摘要 |
A block of refractory material has extending therethrough a throughflow opening, preferably including a funnel-shaped inlet converging inwardly to a throughflow duct. An annular gas collecting space is provided within the block at a position surrounding the throughflow opening radially outwardly thereof. A gas feed duct extends through the block from the exterior thereof to the gas collecting space. At least one annular duct extends radially inwardly from the gas collecting space to the throughflow opening. The annular duct opens into and forms with the throughflow opening at least one narrow slit which extends around the entire periphery of the throughflow opening.
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