Abstract: An inlet for a rotary kiln comprises a plurality of arcuate segments supported adjacent the inlet opening of the kiln to form a trough protruding through the inlet opening. Each of the segments is hollow and has an opening through which a cooling medium may be introduced.

Abstract: The invention relates to apparatus and to a method for the heat treatment of fine-grained material using a multi-stage cyclone preheater and a combustion chamber supplied with tertiary air from the cooler, in which the branched part of the tertiary air pipe extends upwards and the material discharged from the second-lowest stage of the cyclone preheater is introduced into one branch pipe at a point which lies lower than the point at which this branch pipe is connected to the combustion chamber. In this way good dispersal of the material which is delivered pneumatically to the combusion chamber and excellent combustion conditions are achieved at the same time as a considerable reduction in the overall height of the entire cyclone preheater.

Abstract: The heat treatment of fine-grained material wherein two quantities of fuel are delivered to a precalcination zone at two different levels. The first quantity of fuel is delivered at a lower level nearer the combustion zone and the oxygen content of the gases passing through this region of the precalcination zone are such that in this region a substoichiometric combustion takes place and a CO content between 0.05% and 1% is established. As a result a reducing decomposition of the NO.sub.x content of the exhaust gases from the combustion zone takes place.

Abstract: Apparatus for the heat treatment of fine material comprises a multi-stage cyclone preheater, a rotary kiln and a calciner supplied with tertiary air from a cooler for precalcination of the preheated fine material. The tertiary air pipe is narrowed at the point where it joins into the calciner. In this way an intensification of the mixing together of material, fuel and gas is achieved as well as an improved combustion, particularly fuels which are slow to react.

Abstract: Apparatus for heat treatment of fine-grained material has a multi-stage cyclone preheater, a rotary kiln, and a gas pipe extending between the kiln and the preheater and forming a calcination zone for precalcining materials entrained in the gas stream. The gas pipe has an upwardly extending pipe section that communicates with an arcuate deflector section and a downward pipe section which extends downwards to and communicates with the lowest cyclone stage. The downwardly extending pipe section of the gas pipe has an extension constructed as a coarse separator so that relatively coarse material particles contained in the mixed gas-material stream are kept away from the lowest cyclone stage of the preheater.

Abstract: A rotary tubular kiln and a preheater for material supplied to the kiln are connected by a duct leading from one end of the kiln, for conducting waste gases from the kiln to the preheater. A bypass conduit is connected to said duct for diverting part of said waste gases and extends from the duct in such a direction as to divert a stream of waste gases at an angle of at least 90.degree. to the stream of gases flowing through the duct. An upright mixing chamber is connected at its bottom to said bypass conduit to cause said diverted stream of gases to flow upward through said mixing chamber. The mixing chamber has in its lower portion at least one lateral inlet for introducing cooling air into said diverted stream of gases, and the distance between the axis of said duct and a point on the axis of said mixing chamber at the level of said inlet is from 1.5 to 3 times the square root of the quotient of the cross-sectional area of the duct divided by pi.

Abstract: Fine-grained material adapted to be fired in a furnace is discharged from a preheater into a gas conduit extending from the furnace to the preheater and through which a stream of hot gases pass. The conduit is shaped to deflect the gas stream and concentrate it along one side of the conduit in the area of introduction of the material to the conduit. Below the area of introduction of material to the conduit fuel burners provide a heating zone through which the material falls. The concentration of the gas stream along one side of the conduit assures entrainment of the material in the gas stream and passage of the material again through the heating zone. Above the area of introduction of material to the conduit the latter is shaped to deconcentrate the gas stream and permit some of the material entrained therein again to fall downwardly through the heating zone, following which such material is reentrained in the gas stream.

Abstract: Fine-grained material such as raw ground cement adapted to be fired in a rotary tube furnace is introduced to a vertical preheater and falls through a heating zone located at a level below the level at which the material enters the preheater. A stream of air enters the preheater at a level below the heating zone and passes upwardly at sufficient velocity to entrain the material that has passed through the heating zone, thereby causing such material to pass again through the heating zone. From the preheater the material is delivered to the furnace for final firing.

Abstract: Fine-grained material such as raw ground cement adapted to be fired in a rotary tube furnace is introduced to a vertical perheater and falls through a heating zone located at a level below the level at which the material enters the preheater. A stream of air enters the preheater at a level below the heating zone and passes upwardly at sufficient velocity to entrain the material that has passed through the heating zone, thereby causing such material to pass again through the heating zone. From the preheater the material is delivered to the furnace for final firing.