Abstract: A liquid fuel fired apparatus and method for the efficient distribution and utilization of heat in the melting of a particulate feedstock. The feedstock is preheated to an incipient softening point temperature in a vertically disposed shaft. The column of feedstock in the shaft is supported on the top of a freestanding pile of feedstock disposed on the floor of a surrounding melting chamber having downwardly diverging sidewalls. Liquid fuel burners direct hot combustion products towards and around the base and intermediate portions of the feedstock pile causing the outside of the pile to be melted. Gas at a temperature below the softening point temperature of the feedstock is introduced around the top of the pile to prevent the hot gases in the lower portion of the melting chamber from prematurely melting the feedstock.

Abstract: A process for changing the color of partial surface areas of pigmented, hydraulically bonded construction elements by application of high temperatures thereon, wherein the said partial surface areas are subjected to temperatures of at least 1,000.degree. C., until the desired change in coloration has been achieved.

Abstract: A method and apparatus for calcining limestone to produce lime wherein coal is combusted to provide heat for the calcination. The coal is combusted in a two stage combustion unit, with at least seventy-five percent of the slag formed by the coal combustion removed from the first stage of the combustion unit. Residual gases and fuel are further combusted in the second stage of the two stage combustor, with hot combustion gases therefrom, having the molten slag removed, fed directly to the calcining chamber of a rotary lime kiln. The coal may be carbonized to form a char and a fuel gas for use in the two stage combustor.

Abstract: Apparatus and method for removing volatile and semi-volatile organic contaminants from natural soil containing moisture by sealing the soil in a stripping conveyor against contact with air and vapor stripping the contaminants at a temperature below the boiling temperatures of the contaminants.

Abstract: A method for the pyrolytic destruction of microfilm products by utilizing hot silicon oil heated to a temperature of about 250.degree. C. Destruction of the various types of microfilm is accomplished within a five minute time frame.

Abstract: A system to prevent, retard or reverse the decomposition of silicon carbide articles during high temperature plasma sintering. Preferably, the system comprises sintering a silicon carbide refractory or ceramic green body in a closed sintering environment, such as a closed tube, with strategic placement of the plasma torch or torches, exhaust outlet and tube. As sintering proceeds, a silicon vapor pressure builds up within the tube, retarding the decomposition of the silicon carbide body. The plasma torch, exhaust outlet, and tubes are positioned so that buoyant convective flow is maximized to increase the heat transfer and energy efficiency. In another embodiment, a "sacrificial" source of silicon carbide is placed into the sintering furnace. The silicon carbide in the sacrificial source starts to decompose before the silicon carbide refractory or ceramic article, creating a supersaturated atmosphere of silicon vapor species in the furnace.

Abstract: A process for the sintering of silicon carbide refractory or ceramic articles using plasma arc gases. In the process of the invention, a formed silicon carbide article is heated in a plasma fired furnace to a sintering temperature of between 2000.degree. C.-2500.degree. C. at a heating rate of 300.degree. C./hr-2000.degree. C./hr, and held at the sintering temperature for 0.1-2 hours. The enthalpy of the plasma gas is 2000 BTU/lb-4000 BTU/lb, when nitrogen is used as the plasma gas. The total cycle time for the process of the invention, including cooling and loading, is 1.5-20 hours. Silicon carbide articles, produced in accordance with the invention, have high strength, high density, high corrosion resistance and high dimensional stability.

Abstract: A multi-outlet burner for heating material. Nozzles are positioned along a longitudinally extending portion of the burner that generally parallels the material surface. Combustion gas and fuel are combined at each nozzle to produce a plurality of flames that are directed in a sweeping direction over the surface.

Abstract: In the thermal process for treating swellable granulates of clay or the like, the granulates are entered in heaps (4) with free intervals between them into a shaft (1) and traverse said shaft (1) by stages from top to bottom. The heaps (4) are supported by grates (2) of which the bars may be temporarily and at least taken out from the plane of the grate (2) so that the various heaps (4) are fed in the form of a temporarily regulated trickling flow to the next stage, so that a constant thickness with respect to the cross-section is maintained. In the various stages, the heaps (4) are traversed by hot gases introduced sideways into the shaft (1) and exhausted on the other side according to a direction perpendicular to the plane of the layer.

Abstract: Method for sintering blanks into fuel pellets, in which the blanks are moved through the muffle of a tunnel furnace by pushing the blanks through the muffle on a guiding device which goes through the muffle and protrudes therefrom at least on the input side, in the form of a single-layer column of abutting blanks.

Abstract: Method and apparatus for high temperature heating, melting, refining and superheating of materials, such a steel scrap, metals, ceramics or glass. The invention provides an economizing method of hydrocarbon fluid fuel combustion in an ongoing flame in a liquid cooled combustion chamber by separately supplying streams of fuel and at least two oxidizing gases wherein a first oxidizing gas reacts with the fuel, and a second oxidizing gas is directed about the flame core to further react with the fuel, while controlling the flow of the fuel, the oxidizing gases and cooling liquid to provide the required heat input, combustion product chemistry, temperature, velocity, emissivity and combustion block temperature. Also disclosed are burners for carrying out the invention.

Abstract: Apparatus for mounting a tungsten electrode in acute relation to the flame of an oxy-fuel cutting torch and permitting the rotation of the electrode during heating, such that the material is vaporized and removed as the electrode is shaped to a needle-like profile. A bearing containing clamp member secures the torch and electrode holder in proper relation to one another and permits the rotation of the electrode holder therein.

Abstract: An apparatus for calcining a granular or powdered mineral, more specifically hydrated calcium sulphate, comprising a vessel the side wall or walls of which slope inwardly toward a bottom of small cross-sectional area, as compared with an upper region of the vessel, and provided with a downwardly extending heating tube connectable in an upper portion to a gas source and an opening in a lower portion into the interior of the vessel adjacent to the bottom thereof, the arrangement being such that, in use, hot gases issuing from the lower portion of the heating tube will mix and heat substantially all the contents of the vessel.

Abstract: An improved process and apparatus for producing sintered material such as dead burned clay, dolomite, magnesite or periclase with the highest particle specific gravity capable from each material. A grinding mill produces raw material which is 100% minus 20 mesh. The ground raw material is supplied to a suspension type preheater and then to a stationary flash calcining system where the material is soft burned at temperatures in the range of 1000.degree. to 1200.degree. C. From the calcining system, the calcined material is immediately supplied to hot briquetting machine where briquettes or nodules are formed. The hot nodules at a temperature of approximately 800.degree. C. are then immediately supplied to a rotary kiln which serves as a sintering furnace where the soft burned material is dead burnt at a temperature in the range of 1650.degree. to 1850.degree. C. Hot spent combustion gas from the sintering furnace is supplied to the calcining furnace to serve as preheated secondary air for combustion.

Abstract: Method and apparatus for high temperature heating, melting, refining and superheating of materials, such as steel scrap, metals, ceramics or glass. The invention provides an economizing method of hydrocarbon fluid fuel combustion in an ongoing flame in a liquid cooled combustion chamber by separately supplying streams of fuel and at least two oxidizing gases wherein a first oxidizing gas reacts with the fuel, and a second oxidizing gas is directed about the flame core to further react with the fuel, while controlling the flow of the fuel, the oxidizing gases and cooling liquid to provide the required heat input, combustion product chemistry, temperature, velocity, emissivity and combustion block temperature. Also disclosed are burners for carrying out the invention.

Abstract: A combination direct/indirect fire drum heating and mixing apparatus includes a frame having an inner cylindrical drum rotatably supported thereto and having an aggregate input in one end thereof and an aggregate output at the other end thereof. A concentric outer drum is mounted around the inner drum and has an aggregate input from the material output of the inner drum and an aggregate output therefrom at the other end thereof, so that aggregate materials can pass through the inner drum and then pass between the inner and outer drums. A burner is mounted to one end of the inner cylindrical drum for directing a flame thereinto and includes a burner blower for blowing atmospheric air under pressure into the burner. An exhaust gas outlet duct operatively connects the exhaust gas from the inner cylindrical drum to the atmosphere or particulate-removing apparatus, while an exhaust gas feedback siphons vapors and gases emitted in the space between the two drums for incineration through the system burner.

Abstract: A method and apparatus for expanding particles of a lightweight aggregate material are disclosed. The apparatus comprises a housing having an upper chamber separated from a lower chamber by a partition having a plurality of openings. Hot air is introduced into the lower chamber and flows through the partition to fluidize particles introduced into the upper chamber. Means are provided for independently regulating the velocity of air through separate sections of the partition. Particles are introduced at the inlet end of the upper chamber. The particles are fluidized and transported toward the outlet end of the upper chamber by the air flow. The temperature of the air flow causes the particles to expand and become lighter. The velocity of the air flow through separate sections of the partition is adjusted to maintain uniform fluidization of the particle bed in the upper chamber.

Abstract: A method of removing coatings from scrap glass is disclosed. The scrap glass is milled in the presence of particulate batch, preheated and fed to a glass melting furnace. The particulate batch aids in the milling of the scrap glass. The process removes the coatings from the scrap during preheating and provides clean material for melting.

Abstract: This invention is directed to a method and an apparatus to heat certain particles. These certain particles are heated to make them more desirable. In the heating of these particles, it is often desirable to expand the particles to make a light-weight aggregate. The light-weight aggregate may be used in making a building material or the like. In carrying out the process of heating these particles, there is used air for combustion of the combustible fuel and only a mimimum of air for carrying of the particles or expansion of the particles.

Abstract: A method of producing cement from raw material containing a harmful substance such as sulphur, alkali and/or chlorine. In order to reduce the circulation of harmful substances a proportion of the gas or material stream is extracted from a zone in the cyclone preheater at which the desired reduction in the content of the harmful substance is achieved with minimum heat loss.

Abstract: Apparatus and method for effecting thermal reclamation of granular materials, particularly foundry sand and contaminated soil. In a first embodiment, a sand calciner system (10) includes a refractory-lined drum (12) mounted for oscillation about its longitudinal axis (14). An arrangement of plows (76) are provided along the bottom inside of the drum (12) for mixing the sand received through an inlet (54) and advancing it toward a discharge outlet (56) responsive to oscillation of the drum over a predetermined arc about the axis (14). The plows (76) are arranged in staggered rows with each plow having a transverse front surface facing the inlet (54), an inclined top surface, and an angled back surface facing the outlet (56). An aerator pipe (78) is provided in conjunction with the plows (76) to fluidize the sand and thereby effect more thorough mixing and exposure to burners (58) positioned along the upper side of the drum (12) for complete calcining.

Abstract: A method of polishing the surface of a glass article consists in exposing the surface of the said article to a flame produced by oxygen and by a fuel. In order to obtain a perfect surface quality, whatever the thickness and configuration of the article processed, while preventing any premature collapse of the article in question, use is made of a flame such that the thermal energy originating from the transfer of heat by convection exceeds the thermal energy originating from the transfer of heat by radiation, and preferably of a flame of the oxygen-hydrogen type.

Abstract: An apparatus and method is disclosed for greatly increasing the efficiency of heater treater units, such as those used in heavy oil recovery, wherein exhaust air from the heater treater is circulated around incoming heavy oil lines from a freewater knockout unit to preheat the heavy oil reducing the required temperature increment provided by the heater treater to achieve a predetermined temperature for water/oil separation.

Abstract: A waste liquid is dripped down into a shaft chamber 1 of a shaft furnace 2 t the bottom of which chamber is a rotating conical grate 3 on which is an incandescent bed of carbon-rich material 6 than can be supplied from the top of the shaft. Oxygen is supplied through holes 17 of a raised head 15 of the grate. The liquid, vaporized as it reaches the incandescent bed, is drawn through the bed 6 where it is gasified and where high molecular weight components are cracked, forming a gas mixture that is drawn off through the duct 18 at the bottom of the shaft while solid residues of the liquid collect in the bed 6 from which ashes pass through a peripheral gap 5 and drop down through the duct 18 to a collecting hopper 21. The gas mixture then flows upward through a second incandescent bed 24 of carbon-rich material, such as coke or wood charcoal, where the oxygen, exhausted along with the gas mixture from the shaft 1, maintains a temperature between 900.degree. and 1000.degree. C.

Abstract: Apparatus and method for incinerating toxic and non-toxic waste using a modified preheater-type lime kiln is disclosed wherein the kiln is modified to incinerate waste and the preheater section is modified to provide an incineration processing aid such as limestone and also to more efficiently utilize and conserve heat values.

Abstract: Particulate material is heated by directing a flame downwardly along the central axis of a vertically disposed furnace. The particulate material is introduced at a number of locations distributed radially around the flame at the upper end of the furnace. The particulate material is directed downwardly and toward the central axis of the furnace placing the particulate material within the flame as it passes downwardly through the furnace.

Abstract: A method of bloating a granular material residing in that a flow of rising gases heated to a temperature of 800.degree.-1000.degree. C. is formed, and a flow of raw granular material is formed to be introduced directly into said flow of rising gases at a velocity 1.5 to 9 times the velocity of rising gases, whereafter said material is roasted to obtain completely or partially bloated granules which are carried by the flow of exit gases away from the zone of roasting. The partially bloated granules of said material are returned to the zone of roasting to roast further until they are completely bloated.

Abstract: Liquefying of pulverulent batch materials (e.g., glass batch) is carried out in two stages. The first stage utilizes extended gas/solid contact to heat the materials to an intermediate temperature, and may recover waste heat. The second stage rapidly liquefies the material in a cavity lined with the batch material, and may employ substantially nitrogen-free heat sources. Another aspect involves maintaining a wet condition in the first stage to entrap particulates.

Abstract: A sand calciner system (10) includes a refractory lined drum (12) mounted for oscillation about its longitudinal axis (14). An arrangement of plows (76) are provided along the bottom inside of the drum (12) for mixing the sand received through an inlet (54) and advancing it toward a discharge outlet (56) responsive to oscillation of the drum over a predetermined arc about the axis (14). The plows (76) are arranged in staggered rows with each plow having a transverse front surface facing the inlet (54), an inclined top surface, and an angled back surface facing the outlet (56). An aerator pipe (78) is provided in conjunction with the plows (76) to fluidize the sand and thereby effect more thorough mixing and exposure to burners (58) positioned along the upper side of the drum (12) for complete calcining.

Abstract: Oil shale, coal, inert heat transfer material and other carbon-containing solids of varying sizes are preheated with a gas in a transfer line by first separating the solids into a plurality of size fractions and then separately introducing the size fractions into the transfer line at predetermined distances from the transfer line inlet. The predetermined distances are inversely related to the size of the particles comprising each fraction of solids so that the fraction of solids containing the largest particles is introduced nearest to the gas inlet and the fraction of solids containing the smallest particles is introduced at a point furthest away from the transfer line inlet. Normally, solids withdrawn from the transfer line will have been heated to a temperature below which any liquids or gases evolve and are ready for further processing in downstream conversion units such as oil shale retorts, coal gasifiers and the like.

Abstract: Perlite and vermiculite are blown by injecting the particles, entrained in a carrier gas, through a burner at the bottom of a fluidized bed furnace, into the latter with, within and codirectionally with the flame to ensure uniformity of the product.

Abstract: A method and apparatus for burning fine grained products, such as in the manufacture of cement clinker from raw cement meal wherein preheated, calcined meal is heated in a separate heating assembly to a temperature from approximately 900.degree. C. to approximately 1250.degree. C. and is then sintered into clinker in a burning assembly such as a rotary tubular kiln. The present invention provides a means for achieving a fast and uniform continuous heating in the heating assembly without reaching the critical temperature of melt phase formation and without danger of encrustations, the heat required for rapid heating being released in controlled amounts in the heating assembly, where it is immediately absorbed by the product, the heat being provided by a plurality of points of fuel introduction and/or combustion air introduction distributed over the heating assembly.

Abstract: For liquefying hot melt adhesive, a hopper is provided at its lower region with one or more discrete upwards projections (for example a single, fluted cone), with means for heating the projection(s). In use, a unitary mass of hot melt adhesive is lowered into the hopper to become supported on the projection(s), as a result of which the unitary mass is progressively melted and the melted adhesive flows from the bottom of the hopper.

Abstract: A method and apparatus for burning cement clinker from differing mineral base materials. One of the base materials has a relatively high proportion of components which form melt phases at a predetermined temperature and another base material has a relatively slight proportion of such components. The two base materials are separately thermally pretreated. The base material higher in melt phases is at least partially melted after thermal pretreatment and is introduced into a clinker reactor in its molten state together with the thermally pretreated base material which is lower in melt phases and still exists in the solid phase. The mixture is heat treated and finish-burned into clinker in the clinker reactor. The invention also comprehends apparatus for performing the method of the invention.

Abstract: A method and apparatus for burning fine grained products, such as raw cement meal, wherein the product is preheated in a preheating stage, calcined in a calcining stage, and is burned into clinker in a clinker stage followed by cooling in a cooling stage. The heating of the largely calcined product in the temperature range of about 900.degree. C. to the beginning of alite formation which occurs at approximately 1250.degree. C. is carried out under the fastest possible temperature rise conditions and the clinker reaction is carried out in concurrent flow with the gas stream in the burning stage. The clinker is then graded into a coarse grained fraction and a fine grained fraction which are then cooled in separate coolers after separation from the gas stream.

Abstract: A method and apparatus for producing expanded clay or expanded shale finished product in a straight-line continuous rotary tube kiln provided with charging and discharge ends at respectively opposite ends of the kiln, the kiln being divided into a preheating zone and an expansion zone following one another in the direction from the charging end to the discharge end, the preheating zone being more proximate to the charging end and the expansion zone being more proximate to the discharge end, a stationary burner disposed in the vicinity of the discharge end and a mantle burner which rotates together with the kiln and which is located to heat the preheating zone.

Abstract: The invention relates to plant (1) and to a method for regenerating sand from foundry cores and moulds by calcination in a fluidized-bed furnace (2), the main characteristic of which lies in the fact that the fumes leaving the calcining furnace are used to heat a current of air which is then used, in its turn, to heat the sand to be treated at its inlet to the calcining furnace, and in that the current of air cooled by the sand to be treated is then heated by means of the purified sand leaving the calcining furnace and is then used as combustion air in the calcining furnace.

Abstract: A process and apparatus for producing hydraulic cements such as portland cement utilizing electrical energy as the heat source is described. The electrical heat source includes a plasma arc torch operating in the transferred mode. A feature of the apparatus and process is in utilizing a liner within the furnace composed of a material having substantially the same chemical composition of the cement that is to be produced in the furnace. Preferably the feed materials properly proportioned to have the desired constituency of cement are fed below the melt of the furnace. The process is compact and efficient relative to the conventional rotary kiln used for producing cement.

Abstract: The invention pertains to the manufacture of articles of thermosetting plastics and other materials. In a first stage, a solid article is formed from a particulate material by introducing such material into a first chamber defined partially by the backing surface of a backing member and partially by the opposed pressing surface of a pressing member. The backing member is frangible and is removably mounted on a support. The first chamber is then closed and the pressing member advanced toward the backing surface to contract the first chamber and compress the particulate material between the pressing and backing surfaces to form the solid article. The pressing member is then retracted, the first chamber is opened, and the backing member and solid article are removed from the support as a unit. Finally, the backing member is fractured and the fragments are removed from the solid article. In a second stage, the convoluted article, or any other similar body is supported in a chamber structure.

Abstract: This invention is directed to a method and an apparatus to heat certain particles. These certain particles are heated to make them more desirable. In the heating of these particles, it is often desirable to expand the particles to make a light-weight aggregate. The light-weight aggregate may be used in making a building material or the like. In carrying out the process of heating these particles, there is used air for combustion of the combustible fuel and only a minimum of air for carrying of the particles or expansion of the particles.

Abstract: A process for the removal of volatile liquid from particulate material employing indirect heating of the particulate material by means of combustion gases resulting from the combustion of sulfur-containing fuel, and further employing purging of the thus heated particulate material by means of combustion gases produced by the combustion of low sulfur fuel to remove vaporized volatile liquid from the particulate material. Also disclosed is a system for performing such removal of volatile liquid from particulate material.

Abstract: A unit for heating initially solid asphaltic material to provide asphaltic concrete in a condition suitable for application. The unit is operated to heat initially cold material to a temperature between 275.degree. and 300.degree. F. and to maintain it at that temperature until it is used. A thermostatic control system produces heated air intermittently in accordance with a predetermined schedule, and the heated air is used to heat the asphaltic material.

Abstract: The subject of the invention is a process for igniting a sinter mix composed of a solid fuel and sintering material on a sintering machine in which the sinter mix is passed underneath an ignition kiln with closed end and side walls and a closed hood, whereby hot flue gases are generated in the ignition kiln above the sintering material and these hot flue gases heat and ignite the surface of the sintering material by radiation and convection. A rapid, uniform and economical ignition is thereby attained in that flue gases from one or more approximately stoichiometrically operated burners are introduced into the upper region of the igniting kiln and that gases with an increased oxygen content are introduced into the lower region in such a manner that a kiln atmosphere results which, in the upper region of the igniting hood, is hotter and relatively impoverished in oxygen, while in the lower region it is cooler and relatively oxygen enriched.

Abstract: An apparatus and method for drying organic and other waste materials such as industrial by products, agricultural and animal wastes, blood and manure. A round, flat bottom substantially closed pan with a double-wall bottom and side forming a jacket and having a paddle-type agitator receives the material to be dried. Heat is provided by a gas-fired incinerator which preheats air that is admitted to the pan and then drawn into and combusted in the incinerator together with gases and moisture evolved from the material being dried. The incinerator's combustion products are passed through the pan jacket to heat the material being dried and are then vented through a chimney.

Abstract: A method is disclosed for heat treating raw material components of a cement clinker prior to admitting the components to a reactor for sintering the components to form the clinker. A calcareous component of the raw material is preheated with a hot gas flow and admitted to a furnace in a calcioning stage. Fuel combusted in the furnace heats the calcareous component to a calcination reaction temperature and calcines the component. The calcined component is transferred to a furnace in a superheating stage where a fuel is combusted to further heat the component beyond a sintering temperature at which a calcined component and an argillaceous component sinter to form cement clinker. The superheated calcareous component is transferred to a sintering reactor. Hot gas from the furnace in the sintering stage is flowed to a second heat exchanger to preheat and dehydrate an argillaceous component of the raw material.

Abstract: A method is disclosed for heat treating raw material components of a cement clinker prior to admitting the components to a reactor for sintering the components to form the clinker. A calcareous component of the raw material is preheated with a hot gas flow and admitted to a furnace in a calcining stage. Fuel combusted in the furnace heats the calcareous component to a calcination reaction temperature and calcines the component. The calcined component is transferred to a furnace in a superheating stage where a fuel is combusted to further heat the component beyond a sintering temperature at which a calcined component and an argillaceous component sinter to form cement clinker. The superheated calcareous component is transferred to a sintering reactor. Hot gas from the furnace in the sintering stage is passed to the furnace in the calcining stage to augment the heat in the calcining stage furnace.

Abstract: The invention relates to a method for converting metal-containing waste material having substantial quantities of organic constituents, such as plastics, rubber, paper and greases, to a product from which metal can readily be recovered. The waste material is introduced into a reactor vessel arranged for rotation about its longitudinal axis, the vessel being provided with a bottom and a common charge and discharge opening, whereafter the reactor vessel is rotated with its axis inclined to the horizontal plane at an angle of less than 90.degree.. The reactor vessel is maintained during this rotation at a temperature which is sufficiently high to expel organic constituents in the form of a combustible gas for as long as such a gas continues to be generated. The combustible gas is combusted continuously at a location external of the reactor vessel, and the residual content of the reactor vessel is taken out in a molten and/or non-molten state.

Abstract: In a process for decontaminating contaminated metallic scrap, an oxygen bearing hot gas stream is passed into the inlet end of a container and is discharged from an exit end of the same container. The decontaminated scrap is loaded in the container at the inlet end. Concurrently the scrap is (a) moved from the inlet end to the exit end, (b) mixed and agitated within the interior of the container, and (c) during the mixing and agitation contacted with the hot gas stream moving through the interior of the container. The contact of the scrap with the hot gas stream is under conditions essentially capable of inhibiting flaming. By virtue of the contact with the hot gas stream, heat from the hot gas stream is transferred to the scrap, which lowers the temperature of the hot gas stream while raising the temperature of the scrap.

Abstract: A method is disclosed for fixing certain dangerous substances into recyclable waste foundry sand so that they are less likely to leach out into the environment. The method uses a roasting process which causes the dangerous substances to form insoluble compounds with the sand. One example is shown where hazardous waste foundry sand which contains acetic acid soluble lead contamination is treated by this method. In this example the lead is believed to react with the sand during the roasting process forming compounds such as lead silicate which are insoluble to acetic acid. The amount of lead which may be leached out into the environment is reduced to a safe level according to the currently accepted test methods promulgated by the U.S. Environmental Protection Agency. The method may be applied to the conversion of waste foundry sand into reusable sand or landfill which are less likely to leach dangerous substances into the environment.

Abstract: Cement clinker is produced from cold, dry, finely divided raw material by causing hot flue gases to flow in a first direction out of a rotary kiln and suspending a major portion of the finely divided raw material in the hot flue gases until the raw material has been preheated and at least partially decarbonized. The preheated and at least partially decarbonized raw material is introduced into the kiln. A fraction of the cold, dry, finely divided raw material is pneumatically injected into an end of the kiln to flow countercurrently to said first direction approximately parallel to the axis of the kiln to form a dust cloud of the raw material occupying substantially the entire cross section of the kiln at said end, the end being upstream with respect to a second direction of flow of the raw material into the kiln.