Lance for use during combustion

Abstract

A composite lance for use during the injection of gases during combustion, and a method for making such a lance. The lance has a channel through which gas flows, and it includes a core of a metallic material and a ceramic layer outside the core. The outer surface of the core includes a region having a smaller diameter bounded axially by regions each having larger diameters. The ceramic layer is positioned around the core with a gap between the outer surface of the core and the inner surface of the ceramic layer. The gap prevents the ceramic layer from cracking because of differences in thermal expansion between the core and the ceramic layer when temperature changes take place in the lance.

1 . A lance for use during the injection of gases into a combustion region, said lance comprising: a tubular member including a channel within which a gas can flow, wherein the tubular member is a composite lance structure including a tubular core formed from a metallic material and a ceramic layer outside of the core, wherein an outer surface of the core includes a first region having a first diameter, the first region bounded axially by respective second regions each having larger a larger diameter than that of the first region, wherein the ceramic layer is positioned outside of the core with a gap between the outer surface of the core and an inner surface of the ceramic layer, whereby the gap prevents the ceramic layer from cracking because of differences in thermal expansion between the core and the ceramic layer when temperature changes take place in the lance.  
   
   
       2 . A lance in accordance with  claim 1 , wherein the ceramic layer overlies both the first and second regions of the core.  
   
   
       3 . A method for the manufacture of a lance for use during the injection of gases into a combustion region, the lance including an inner channel within through which gases flow, wherein the lance is a composite lance, said method comprising the steps of: providing a tubular core of a metallic material, the core including a channel for gas flow, wherein the core has an outer surface that includes a first region having a first diameter and bounded axially by respective spaced second regions each having a larger diameter than that of the first region; positioning a ceramic layer in overlying relationship with the outer surface of the core; and providing a gap between the outer surface of the core and an inner surface of the ceramic layer, whereby the gap prevents the ceramic layer from cracking because of differences in thermal expansion between the core and the ceramic layer during changes of temperature in the lance.  
   
   
       4 . A method in accordance with  claim 3 , wherein the gap between the core and the ceramic layer is formed by applying between the core and the ceramic layer an intermediate material that disintegrates at a temperature that is lower than the melting temperature of the metallic core.  
   
   
       5 . A method in accordance with  claim 4 , wherein the intermediate material is a polymer-based material.  
   
   
       6 . A method in accordance with  claim 3 , wherein the ceramic layer is sintered after it is positioned over the core.  
   
   
       7 . A method in accordance with  claim 3 , including the steps of: sintering the ceramic layer to a final tubular form; sliding the sintered ceramic layer onto the core; and introducing a glue between the metallic core and the ceramic layer with the gap positioned between the metallic core and the glue.  
   
   
       8 . A method in accordance with  claim 7 , wherein the glue is a ceramic glue, and including the step of sintering the glue after the ceramic layer has been slid onto the core.  
   
   
       9 . A method in accordance with  claim 4 , wherein the intermediate material is a paper-based material.