the nozzle 10 in fig1 has a tube 11 , having a ncg / steam inlet 15 and outlet 16 , surrounded by a cooling jacket 12 . between the tube 11 and the jacket 12 is a thermally insulating plenum 13 that extends essentially along the length of the tube 11 . the nozzle 10 extends through the wall of a lime kiln 14 so that nozzle outlet 16 is disposed within said kiln 14 . cooling jacket 12 has a cooling fluid inlet 17 and outlet 18 located near inlet 15 outside of the kiln 14 . plenum 13 has an air inlet 19 and outlet 20 also located near inlet 15 and outside of the kiln 14 . in operation a mixture of ncg and steam at a temperature of 120 ° c . is fed to nozzle inlet 15 and passes through tube 11 . the mixture exits via tube outlet 16 at a temperature of 120 ° c . which temperature substantially prevents steam from condensing in the tube . nozzle 10 extends into kiln 14 to a sufficient depth to ensure combustion of the ncg . in order to protect the nozzle from failure caused by the extreme heat of 1150 ° c . in the kiln , cooling water at 10 ° c . is fed to cooling jacket inlet 17 . the water passes through jacket 12 and exits via water jacket outlet 18 at 60 ° c . cooling jacket 12 is thermally separated from tube 11 by air filled plenum 13 . although not required , air can be circulated through plenum 13 via air inlet 19 and outlet 20 . alternatively , air inlet 19 and outlet 20 can be capped to provide stationary air insulation . in fig2 it can be seen that plenum 13 completely surrounds tube 11 and is itself surrounded by cooling jacket 12 . cooling jacket 12 is divided into an upper compartment 21 and a lower compartment 22 . in operation , cooling water travels from cooling fluid inlet 17 along the length of the nozzle assembly in the lower cooling jacket compartment 22 before passing to the upper cooling jacket compartment 23 . the cooling water then travels back along the length of the nozzle assembly in upper cooling jacket compartment 23 before exiting via cooling fluid outlet 18 . this embodiment allows direct cooling of the tube 11 only near the tube exit 16 , thus substantially eliminating the area of potential steam - condensing surface of tube 11 , while cooling and protecting the outer surface of the nozzle 10 from the high temperatures of the kiln . in general , the dimensions of the injection nozzle will be dictated by design considerations which include volume of ncg , ncg composition , type of incinerator , etc . a typical lime kiln nozzle would have an inner tube through which the steam motivated ncg stream passes with a diameter of between 4 and 8 inches . the insulating gap typically would be between 1 / 4 and 1 inch and the cooling jacket would have a thickness of about 1 inch . the overall length of the tube assembly would typically be 6 to 10 feet in the case of a ncg injection nozzle for lime kiln applications . the degree of outer surface cooling can be controlled by adjustment of the flow rate of the cooling water in accordance with the temperature of the water . the water feed would preferably be low pressure . alternative insulating materials with different heat insulating capacities could be used in place of air circulation in the plenum . for example , a vacuum could be incorporated in the plenum as the thermal insulator . solid insulators such as fiberglass could also be used . a continuous flow of steam would be suitable as well . it will be clear to one skilled in the art that modifications in dimensions , insulating materials and cooling media may be made to the apparatus within the scope of the present invention . numerous variations of such details can be employed while still achieving the benefits of the invention .