of the equipment commonly referred to as a firebox generally this is accomplished by igniting a suitable fuel in presence of air with one or more burners materials other than conventional fuels can however be combusted in the firebox portion of the equipment which is generally the case when combustion is effected in an incinerator in any event the principle combustion products are carbon dioxide and steam and those products along with the other combustion products such as carbon monoxide and the various oxides of nitrogen and sulfur combined with any excess oxygen and unconverted nitrogen to form what is referred to herein a combustion effluent usually the combustion effluent also contains about 0 1 20 volume percent oxygen preferably 0 1 to 11 volume percent the temperature of the combustion effluent is usually at a maximum near the point of combustion i e firebox and decreases axially along the flow path and radically outwardly as the effluent moves along its flow path from the point of combustion until its is emitted to the atmosphere in this regard it should be appreciated that the maximum change in temperature will occur along the path of flow of the effluent when the effluent is contacted with heat exchange equipment i e cooling means which usually occurs in the convection section of the combustion apparatus it.