Method for carrying out endothermic processes in a shaft furnace

Claim 1

A process for an endothermic reaction in a furnace or kiln having first and second vertical shafts with each shaft having, from top to bottom, a preheating zone, a combustion zone and a cooling zone, means for joining the two shafts and providing communication therebetween at the lower regions of the combustion zones and fuel gas supply means located in each shaft and in the means for joining the shafts, which process comprises: a. Introducing the materials required to undergo the reaction down into the tops of the shafts, b. preheating the materials in the preheating zones of the shafts, c. introducing a source of primary air down into the top of the first shaft concurrently with the materials being fed therein, d. feeding fuel gas into the combustion zone of the first shaft from the fuel gas supply means located therein such that a portion of the fuel gas is caused to enter into the second shaft through the means joining the two shafts, e. introducing a source of secondary air up into the bottom of at least the second shaft countercurrently against the materials being fed therein such that only the secondary air effects combustion of the portion of the fuel gas entering the second shaft.