Heat transfer is effected by utilizing the reflectivity properties and thermal conductivity properties of a metal constituting the drum wall.

More specifically, this invention relates to a method of claim 1 and an apparatus of claim 22 for heating a material to a high temperature in a heating drum. The improvement is directed to upgrading thermal economy and/or reducing waste gas discharges and/or enhancing heat transfer in a drum from radiation heat to a material to be heated, and/or to reducing the own weight of the drum by means of several optional metals, even in a mobile hollow elongated heating drum, which is horizontal or rotatable about an inclined axis and has one end thereof provided with a supply (A) for a material to be heated and one or more of the drum ends provided with a discharge (B, Bl) for a thermally treated material, and with a burner or an electric heater (C) for generating heat and producing thermal radiation for the heating drum. According to the invention, the improvement is achieved in such a way that the rotary heating drum, manufactured from a refractory and thermal radiation reflecting metal, for example nickel chromium steel, or plated with an alloy thereof or some other reflecting metal, is cooled and ground or abraded for polishing or cleaning the same over its internal surface or external surface with a medium or a heatable material sliding or tumbling along the metal surface of the heating drum, at the same time as the metal- frame heating drum defining a heating space is used for equalizing temperatures, increasing temperatures and transferring thermal energy effectively from radiation heat to a material to be heated.

In this specification, the term"a high temperature"refers to a temperature of at least 200... above 2000°C. In this specification, the term"heating a material to a high temperature"may refer also to the incineration of a material, regarding e. g. the disposal of hazardous wastes, but in primary applications of the invention it refers to the heating of a material to a desired process temperature.

The properties and composition of nickel chromium steel, used as an example, have been described in our earlier International patent application WO 02/088613, which also discloses a general description of the prior art.

Nickel chromium steel is highly durable chemically and also resistant to abrasion and heat.

The reflectance properties of various metals are presented for example in Internet publication http ://www. glacierbay. com/Heat Properties. htm. Even with one and the same material, the reflection of infrared radiation or thermal radiation is subject to major fluctuation according to conditions. With polished nickel, for example, the reflectance is 95%, while with oxidized nickel it is merely 5%. With polished steel the reflectance is 45% and with oxidized steel it is 15%. The best infrared radiation reflection values are usually provided by smooth and polished undoped metals of various types.

The quality of a reflection surface can multiply the reflectance of thermal radiation. A fine-grained material, for example clay or lime sludge, is capable of abrading and cleaning a metal surface to a highly reflective condition.

Desorption cleaning effected by indirect heating is described in Patent publication US-5514286. Some reference publications suggest that rotation be prevented in desorption devices, as it creates undesired intra-drum flows.

One example of this is disclosed in Patent publication US-6143136. The completion of many chemical reactions requires a long residence time, even

in sealed vacuum heating vessels. This topic is discussed also in US Patent publication 5904904.

The thermal energy necessary for sustaining the temperature of a heating drum can be partially obtained from calcium oxide by slaking with water and carbon dioxide in one and the same hollow burner pipe at the downstream end of the heating drum. The large amount of thermal energy released at that point proceeds into a metal barrel and is conducted further therealong.

Consequently, a lot of energy is released upon the formation of calcium carbonate. Carbon dioxide is already present in a hot post-combustion flue gas. Assistance can be provided by using for example barrier feeders between various reaction steps, which can establish an energy, heat or phase barrier between various stages of the process. Various process steps can also be carried out in nested, mutually insulated metal drums. The energy can be conducted along a metal drum barrel longitudinally to where energy is needed, for example to the preheating of a material to be heated.

Bringing down the nitrogen fraction (about 78%) of free air in combustion reduces the unnecessary and environmentally harmful heating of nitrogen and consumption of energy. Nitrogen does not participate in the production of heat but, instead, consumes heat upon warming up as part of the air in a firing process. Nitrogen and oxygen are present in the same air and warm up at the same time. On the other hand, oxygen-enriched air or pure oxygen can induce intense combustion and a rapid increase of heat in combustion, as nitrogen and argon are not there to slow down the burning operation and to consume valuable thermal energy for heating themselves. These gases are merely coolants in the burning process without any useful effect in heating. For example, the burning of acetylene with pure oxygen provides readily a temperature of about 3000 centigrades. Some of the energy used for heating nitrogen can be reclaimed from the hot combustion gas.

When using ordinary nitrogen-rich air in combustion with current technology, a large amount of energy is required just for heating the nitrogen. That in turn requires the use of even more fuel, i. e. plenty of carbon dioxide is produced in added burning, which is another major environmental hazard in modern industry.

The same combustion result is achieved in such a way that a small amount of neat oxygen needed by the reaction is added directly to the point of combustion. Consequently, the creation of nitrogen oxides is largely avoided in heating. The amount of pure oxygen needed for the combustion result is only 20% as compared to ordinary nitrogen-containing air. Only this fraction needs to be heated to a combustion temperature. All the rest of the heating, i. e. up to about 80% of air, only represents the waste of energy in the unnecessary heating of nitrogen and argon unless energy can be efficiently reclaimed from combustion gases. The transfer of heat from metal directly e. g. to particles of calcium carbonate in lime burning or in a lime sludge reburning kiln enhances the process in terms of thermal engineering. In particular, the reflection of thermal radiation from the surface of a metal drum reduces heat losses in the furnace, if use is no longer made of a traditional heat-radiation absorbing ceramic lining but heat radiation is reflected away instead.

The heat stresses of currently used ceramic bricks constitute a problem in combustion, e. g. in the breakdown of calcium carbonate, when temperature rises to about 1100 centigrades, whereby e. g. calcium carbonate breaks down effectively.

An essential improvement is also the elimination of ceramic bricks and the resulting reduction of energy consumption. The thermal energy usually wasted by conduction through the furnace or kiln wall can now be utilized by reflection. The metal drum is maintained in a highly reflective condition by

abrading or polishing it clean and smooth, for example by increasing the rotating speed of a lime sludge reburning kiln.

Another drawback resulting from the use of nitrogen-rich free air in combustion is that, in addition to the cooling and diluting effect of nitrogen, the combustion produces environmentally harmful nitrogen polyoxides, so- called NOX compounds, at high temperatures. The reduction of these gas discharges is a common international objective. The same applies to carbon dioxide discharges, which result from unnecessary burning of coal in many processes. With insufficient oxygen such combustion results in the production of carbon monoxide, which is still a valuable fuel when subsequently supplied with more oxygen, e. g. in an afterburner. It can be provided with oxygen or air inlets for combustion. The oxygen or air inlets can be for example slide gates in a combustion drum, which open up at some point during rotation of the drum allowing the passage of oxygen or air into the drum, but are otherwise closed. The burning of solid fuel usually creates ash on the bottom of the drum. Oxygen or air can be supplied therethrough, whereby the ash undergoes slow burning by smouldering with insufficient oxygen.

The use of electrical heating instead of combustion heating makes it possible to completely eliminate the heating of atmospheric nitrogen in combustion and the creation of nitrogen oxides. The highest heat developed by a heat source transfers in the form of radiation, which propagates in wave motion rectilinearly in every direction without a medium. Some of the radiation energy reconverts to heat upon re-contacting matter, some of it reflects and continues its propagation by radiation. Being in the form of radiation, heat can be reflected the same way as a mirror effectively for example by means of a clean, smooth and reflective metal plate, the infrared radiation not being able to penetrate or absorb into the drum but reflects back from the barrier layer.

Regarding thermal treatment, a heavy-duty ceramic thermal shield lining is useless, yet makes up most of the weight of a furnace or kiln and absorbs plenty of heating energy in itself. However, a ceramic thermal blanket, for example a brick lining, is not generally capable of delivering thermal energy effectively to a material to be heated. The abundant thermal energy absorbed in the brick remains useless, unless it transfers to a material to be heated.

The novel drum itself functions as a thermal equalizer relative to hot and cold drum sections, as the heat transfers by direct conduction along metal. The thermal conductivity of chromium and nickel is better than that of steel. The proportion of chromium and nickel, for example, in the novel raw material for a drum is often significantly high. The exemplified refractory nickel chromium steel material is capable of withstanding the required mechanical, chemical and thermal stresses.

The radiation heat emitting from a burner makes an easy contact with a metal surface, which has been made clean and slick by abrasion or smooth by polishing. The cleaning of a smooth metal surface is easily effected for example by means of acoustic vibrations, when there is no ceramics to form a barrier and to absorb energy in itself. A heated continuous elongated metal drum is able to deliver the thermal energy effectively to a material in contact therewith. The objective is to transfer the energy efficiently to a material to be heated. The novel drum solution is not generally fitted with expensive and heavy thermal insulations. Thermal insulation for the drum and the preheating of air can be readily implemented with an intermediate air layer 3 or with a vacant interspace in the drum structure, as shown for example in the figures, for example 2,2a, 5,9, 10,12, 13 and 16.

Thermal insulation takes place for example in wool-contained air, in other gases, or voids included in the drum. The primary function of wool is to maintain the immobility of a gas in the intermediate layer. Because of a brittle and heavy ceramic heat protection, the rotational speed of a kiln must currently be kept low, e. g. 2... 7 revolutions per minute. The inner diameters of major industrial mass-production kilns are most often 1, 0... 5,0 meters.

The current lengths of industrial heating drums are commonly more than 5... 150 meters. The current material thicknesses of steel-frame drums are generally 5... 50 mm for steel, which results in a major own weight for the structure.

According to the invention, by making a heating drum surprisingly for example from expensive fireproof or stainless nickel chromium sheet steel, which, being polished or otherwise provided with a smooth finish, is highly reflective of heat radiation and highly conductive of heat, the heating drum's own weight in the structure can be substantially reduced. The heat can be returned by reflection and conducted to a material to be heated.

Temperature of a rotary drum kiln can be raised by virtue of a material, which is refractory and reflective of heat ration and at the same time also corrosion and abrasion resistant, as well as generally resistant to chemical stresses.

The novel inventive kiln or furnace is substantially lighter and heating, as well as cooling, is faster. Even in a continuous process, it is occasionally possible to avoid nighttime work and to settle with less expensive daytime work.

If, for example, an excessive amount of heat is conducting through the wall of a nickel chromium steel drum, the condition can be improved by means of additional thermal insulations. However, the best heat insulation is a vacuum or void, which does not conduct heat. The voids can be provided with

cooling, e. g. by means of a high-pressure water jet to disperse into small droplets, to vaporize and evaporate within abundant air or gas. A high- pressure water jet is also preferred whenever it is desirable to keep the liquid water as far away as possible from the point of spraying. The cooling functions even from the downstream end of a furnace by conduction along metal. The various sections of a furnace in longitudinal or radial direction can be made to function in different ways even in different parts of the process.

By virtue of the novel method, chemical reactions become faster at high temperatures as a result of effective heat transfer to a material to be heated.

Even supertoxins are destroyed at a temperature of about 1000 degrees provided that the dwell time at this temperature is sufficiently long, for example 1... 2 seconds. The cooling of a nickel chromium steel plate with a medium, for retaining strength even at high temperatures, is preferred also for improving reflectivity of the surface.

If fuel and oxygen are fed tangentially onto the outer periphery far away from the centre axis, a long flame vortex can be developed, as shown e. g. in fig. 11 in the form of a burning concentric double vortex, deflecting in the cone to form an inner vortex 52. The resulting outer vortex is ignited downstream of supply vanes by electric sparking, whereby the combustion chamber develops a burning outer vortex 51 containing larger particles. The dispersion of fuel in a high-pressure jet into minute droplets provides efficient combustion with the presence of an oxygen-containing gas. In response to a centrifugal force created by the vortex, the heavier particles, even small particles which contain for example solid matter, end up in the outer vortex and in a direct contact with a hot metal surface. Even the small particles take up thermal energy efficiently from the metal and are thus heated to a desired heating temperature.

Barrier feeders can also be used for maintaining a high or low pressure or temperature in the combustion chamber, for example in the slaking of lime, regardless of other chemical processes in the heating furnace. A plurality of successive barrier feeders are able to enhance a gradual change of temperature or pressure between various chemical functions in the process.

Chemical effects can be created in a heat treatment drum by feeding active additives into the kiln. One such additive can be for example limestone or calcium carbonate. It breaks down into calcium oxide and carbon dioxide at a temperature of about 825... 850. If desired, the elongated heating drum can be maintained roughly at this temperature almost over its entire length. This simplifies the operation of a heating drum, especially if the raw stock is preheated in the same elongated hot barrel. The innermost burner pipe, adjacent to the burner itself, can even be in red heat.

Clay is dredged in many passage and harbour projects from the bottom of a waterway. The contaminants and toxins present in dredged material burn away in the intense heat of the drum. Clay is generally a waste material which is not properly exploitable. Production for light expanded clay aggregate can be implemented preferably for example by burning cheap waste oil with all its impurities. Waste oil can be sprayed, even with its solid waste particles and other contaminants, at a high pressure, for example 1... 10 bars, into highly turbulent air for easier ignition. Air pressure can be relatively low, for example 1... 3 bars. Turbulence is created by blasting air through a multitude of small or slightly larger parallel holes in a metal plate, developing behind the plate a powerful turbulence including minor counter- vortices. The mixture can be ignited electrically by sparking, whereby even poorly ignitable and burning ingredients ignite easily and burn effectively with oxygen nearby and even in motion. This enables manufacture of a new type of burner, especially for waste oils or other hard-to-ignite flowing fuels.

A normal burner also develops a certain amount of infrared or thermal radiation.

Smaller fine-grained solid particles melt and expand readily on the surface of a hot and heat delivering and heat conducting elongated metal barrel. The drum has a high heat capacity in view of providing the drum with a heat storage for delivering energy to a material to be heated. Particles containing a solid matter in the vortex end up generally in contact with a hot metal drum and receive energy therefrom. Hard quartz crystals present on the surface are highly abrasive or grinding ingredients. In this invention, this quality is desirable as the drum material is resistant to abrasion and heat.

The hot drum delivers thermal energy to a matter to be dry distilled, e. g. waste, which does not burn with a limited supply of oxygen. Dry distilled carbonaceous matter can also be burned without major environmental hazards, for example in the production of electric power. A typical dry distillation product, as an intermediate from organic and other wastes, is carbon monoxide.

Fig. 17 visualizes the sorting of components in a single pellet in various parts of the pellet in the process of making light expanded clay aggregate. Thus, the surface layer of a pellet contains plenty of silica crystals or quartz, which is generally hard to melt. Calcium oxide may form eutectic mixtures with other melt oxides, whereby the melting point of hard-to-melt compound oxides becomes lower and melting occurs at a relatively low temperature. In order to preserve eutectic mixtures, the heating temperature must not become too high. Readily evaporable are for example oxides of alkali metals.

Therefore, the temperature of lime sludge reburning kilns is maintained comparatively low, for example at 300... 800 centigrades.

The transfer of heat quickly and directly and by reflection from radiation heat to a material to be heated facilitates the process. In addition, the metal- structured kiln lining is able to take up, to transfer by conduction, and to deliver thermal energy to a material to be heated in areas where the temperature of the metallic kiln wall exceeds that of the material to be heated. The powerful effect of the invention develops as a combined effect of thermal energy reflection and direct radiation heat as the reflection surfaces are kept clean and smooth by abrading with a fine-grained material.

Depending on the metal material, generally 5... 97% of the radiation energy is reflected. Therefore, the cleanliness and gentle abrasion of the surface with large circular movements, e. g. with a material to be heated, is absolutely necessary.

For example, in a firing kiln made of nickel chromium steel and intended for cement clinker, the radiation heat provides a general temperature of about 1100°C in the surface stock of the cement kiln, while the hottest spot in the kiln is presently about 1300... 1400 centigrades. At present, this is primarily a result of the high heating capacity of radiation heat. By the inclusion of additional effects created by the radiation reflection of a metal drum, by the delivery of heat, as well as by the conduction of heat, and also by the contact of centrifugal force with metal, the drum's performance will be enhanced. In such intense heat, most minerals melt to produce Portland cement clinker, including all its hard-to-melt aluminium and silicon oxides and silicates.

The invention finds an extensive application, for example as a cement making kiln and a lime sludge reburning kiln used in pulp industry for burning lime usually off of white or green liquor. Eventual applications are found in the majority of modern industries.

The accompanying figures are only intended as examples and for visualizing the mode of operation of the invention.

Fig. 1 shows a traditional, ceramically brick-lines kiln in a partial cross- section; Fig. 2 shows a metal-clad kiln according to one embodiment of the invention in a longitudinal section; Fig. 2a shows an alternative section for a long metal-clad heating drum in a longitudinal section; Fig. 3 shows a drum provided with a void or cavity 3 in cross-section along a line I-I in fig. 2, the internal surface of a drum 1 being smooth and slick ; Fig. 4 shows an alternative cross-section for a drum provided with a void and lifters ; Fig. 5 shows a cross-section in principle for a heating drum of the invention, wherein the void intermediate layer 3 uses air as thermal insulation ; Fig. 6 shows a longitudinal section in principle for a heating drum of the invention; Fig. 6a shows a temperature distribution in the heating drum of fig. 6; Fig. 7 is a view in principle, partially transparent for the sake of clarity, for a cyclone vortex chamber which functions as a heating drum of the invention;

Fig. 8 shows a longitudinal section for a heating drum ac cording to one embodiment of the invention, which is provided with a cone; Fig. 9 shows a cross-section along a line IV-IV in fig. 8; Fig. 10 shows a cross-section along a line V-V in fig. 8; Fig. 11 visualizes a principle of telescopic or nested twin vortices in a cone-equipped vortex chamber; Fig. 12 shows an alternative cross-section for a segment of the drum wall, wherein voids 18 and 19 constitute a heat exchanger; Fig. 13 shows a cross-section for a segment of the drum wall, visualizing a double-decker zigzag panel structure, wherein sub-voids 18 and 19 may function as a heat exchanger on either side of diagonal panels 35.

Fig. 14 shows a wheel-mounted mobile heating apparatus of the invention in a side view; Fig. 15 shows a side view of a lightweight mobile apparatus of the invention in production, parked by a natural water supply; Fig. 16 shows a segment of the drum wall in cross-section, visualizing a bracing by diagonal panels for two drums 1 and 20 at different temperatures; Fig. 17 shows a kiln-produced pellet in cross-section;

Fig. 18 shows pellets of fig. 17 fused and agglutinated together at a high temperature, which, after cooling, may constitute e. g. a finished lightweight foundation block ; Fig. 19 shows a section of a road structure, which is made with a method and apparatus of the invention.

Fig. 1 shows a cross-sectional piece as an example of a traditional steel- constructed rotary heating drum 16, which is lined with ceramic wedge- shaped thick and heavy bricks or tiles 17, bearing against each other from two directions over four sides thereof and reflecting thermal radiation only to a slight degree. The bricks are intended for protecting the steel-frame drum from powerful radiation heat generated by a flame burning in the kiln. The structure is heavy and awkward to build. Due to manufacturing technique, there is a small heat insulating gap 15 between the bricks for preventing the conduction of heat in longitudinal and lateral direction in the drum structure.

The heavy brick lining of fig. 1 is unnecessary and detrimental as it absorbs nearly all of the heating energy in its slightly porous ceramic refractory brick structure, which is non-homogeneous.

As much as 50... 80% of the total weight of a traditional heating furnace or kiln is made up by a ceramic lining material, which absorbs energy inside itself and converts it to heat and warms up, being unable to reflect it away.

However, being an insulation, the brick is not able to properly deliver that energy to a material to be heated. It is calculated that, in the available rotary heating or firing kilns lined with ceramic bricks, about 10% of the heating energy is spent for a heat flow through the ceramic layers and steel sheet of the drum. Thus, the entire ceramic material is at a heating temperature and the heat is gradually and irrevocably conducted through the metal drum to waste. This ceramic mass is approximately equal to the mass of a heated material in the drum. In reality, this thermal energy would be needed for

heating the material to be heated. Thus, the heating performance of a currently available, ceramic-lined kiln is very poor considering the amount of energy that is used. At least 10% of the energy costs of a furnace are futile in brick-lined furnaces. No use is made of energy benefits provided by infrared reflections combined directly with thermal radiation emanating from a heat source.

Heavy ceramic mass is heated to a high temperature without actual benefit.

A hot ceramic lining blanket as such does not contribute to the heating of a material, as heat does not transfer to a sufficient degree from ceramics to a presently heated material. Thermal radiation reflects poorly from irregular and rough bricks. These develop generally a diffuse reflection, i. e. the energy is distributed unevenly in reflection from brick.

The drum is generally also forced to carry the weight of a major rotating ceramic brick mass, which is usually tens or hundreds of tons and thus stressful e. g. for bearings. The great mass of ceramic linings is uselessly heated to a high temperature, although the intention is to heat up a presently heated material inside. The energy is often spent for a futile purpose. By removing the heavy ceramic lining blanket, it would be possible to gain a major enhancement of heating performance just as a result of a reduced mass to be heated.

Fig. 2 shows in a longitudinal section one elongated, tubular and infrared radiation reflecting metal constructed heating drum of the invention, which is cooled with a cool feedstock, e. g. for making cement. A similar heating drum can also be used as a lime sludge reburning kiln in pulp industry or as a furnace for making light expanded clay aggregate. The drum is constructed for example from nickel chromium steel which, being smooth, provides a good reflection of infrared radiation back to the heating drum, when polished or abraded with a fine-grained heating stock, e. g. lime sludge or clay. The

metal structure is a homogeneous alloy as a result of melting, uniform even in terms of molecular level, whereby reflections are identical. Thus, the smooth metal surface functions the way of a mirror and the method provides a high thermal energy reflection effect, for example from a plate which can be linear or curved. In the most common kiln version, the cylindrical wall of a kiln constitutes a concave mirror, if a heat source, for example a burner, is placed in the middle.

A presently heated material 12 warms up in a natural way as it is in motion in a hot rotating drum 1, while the heat, produced for example by a burner 6, is conveyed by conduction along a continuous metal pipe. The thermal rays reflected from various sides provide a sort of extra burner in the drum without another application of energy. Efficiency improves according to reflections, being about 5... 95% of the infrared radiation, depending on a material. In the infrared radiation of a long radiation source or a reflection surface, such as in a long powerful burning flame, there will be lots of reflections from a clean polished or abraded metal pipe.

This is generally provided at the inlet by a large-radius long burning vortex or an electric source of infrared radiation, which can be for example an electric arc at the end of a heating drum. Electric arc does not burn coal, alleviating in its part the global carbon dioxide problem. Neither is it necessary to heat much nitrogen-containing air for supplying oxygen to the reaction. Hence, by means of infrared radiation, the electric arc reduces both nitrogen and carbon dioxide emissions in many processes, particularly when assisted by using reflections of radiation reflecting metal surfaces, which often interfere with original radiation. Behind the electric arc can be installed a radiation reflecting reflector, e. g. one made of or coated with nickel chromium steel or an alloy thereof or some other reflective metal. It is also possible to cool the reflector whenever necessary, e. g. by means of thermal capacity of other metal structures or cooling currents. The infrared radiation absorbing or

impregnating in an absorbent, generally porous material converts to thermal energy and heats a material encountered thereby. A powerful reflector may have e. g. a bowl-shaped contour for directing the reflections of an electric arc into an elongated reflection pipe sort of like an optical fiber and reflective over its internal surface, wherein the infrared radiation keeps reflecting for example from one slick pipe wall to another unless it comes to contact with a material to be heated. Infrared radiation releases its energy precisely for the intended purpose without creating harmful gas emissions.

In fig. 2, the zone of maximum radiation heat applied to a nickel chromium steel drum and emanating from a stationary burner 6 mounted on a wall 2 is depicted as a range defined by lines 7 without a reflector in the process of burning in nitrogenous air. In reality, the flame or infrared radiation emerging from the burner 6 is long and supplies heat to the drum 1 over a long range and also to a material to be heated, which is generally present on the bottom. Especially the thermal rays, which have collided with the drum 1 at a low angle, reflect back into the drum. This applies particularly to a long heating barrel, having one of its ends provided with the heat source 6 which is often a burner or an infrared-radiation evolving electric heater, for example an electric arc.

The burner or electric heater 6 is mounted at the end of the drum opposite to an inlet end A, at least partially inside the drum 1, in this exemplary embodiment on the centre axis of the drum 1. When the heat source 6 is located at the end of the drum, which is opposite to the inlet end of a material to be heated, the material to be heated is gradually heated as progresses from the material inlet end A towards the heat source 6.

Infrared radiation has a particularly pronounced effect on the bare upper portion of the metal drum 1, which has no material 11 to be heated in between and blocking the effect of radiation heat on the metal drum 1.

Infrared radiation reflects from a clean and bare dressed heating drum surface as long as there is no material to be heated on the drum surface.

When powerful radiation heat comes to contact with the long and smooth drum 1, polished and abraded slick and smooth and made e. g. from nickel chromium steel, the radiation reflects from the metal surface the same way as light back into the heating drum and to the material to be heated. If a material to be heated comes to contact with infrared radiation, it will heat up, i. e. the objective is fulfilled, Excess thermal energy can be converted by means of condensation water to electric power which can be used, for example, for the production of infrared radiation.

Radiation heat remains inside the long heating drum to perform multiple reflections from a slick and smooth metal wall to another within the smooth and clean tubular heating drum. Consequently, the polished, highly reflective heating drum functions the way of an optical fiber as the infrared radiation cannot escape from the heating barrel but keeps reflecting back from a boundary surface of the drum. The efficiency of heating energy is improved by virtue of reflections in a heating process because no energy goes to waste. The heating drum's efficiency becomes extremely high when the material to be heated functions primarily as a polishing and grinding agent.

Regarding its operation, the heating drum becomes a long heating barre or pipe, in which the infrared radiation or thermal radiation, performing multiple reflections, carries out a desired process. The material to be treated is supplied from the inlet end of the pipe and a desired product is obtained from the outlet end, at which a heat source is generally located. Because of multiple reflections within the pipe, the traditional heating drum can be made shorter. The weight of a kiln is reduced and its reflectivity improved by excluding ceramic bricks.

Reflection of radiation occurs the way of a mirror everywhere both in top and bottom portions of the drum. The drum contains material 11 to be

heated usually in its bottom portion, as it is generally heavier than gas. The drum then receives the energy required in heating directly for example from a long burning flame, in which oxygen and fuel come together to provide an energy-releasing reaction, i. e. infrared radiation or thermal radiation. For example, a long burning flame emerging from the burner 6 distributes radiation energy over a long range in the longitudinal direction of the drum.

Thus, as many as possible of the material particles to be heated receive effective thermal radiation. The metal drum, heated with thermal radiation in the upper drum position, is brought by a rotating motion to the proximity of or underneath the material to be heated, where it is capable of delivering the thermal energy quickly and effectively to the material to be heated. This mode of heat transfer can be utilized in a material preheating zone, wherein the temperature of a material to be heated is still lower than that of the drum wall. The drum length is beneficial, as the material to be heated therein travels a long distance in a hot metal drum. For example, the length of lime sludge reburning kilns or cement kilns can be made considerably shorter than what it is at present, by virtue of energy delivered by metal. In preheating or drying, water vaporizes quickly in response to hot metal.

In cement making and in a lime sludge reburning kiln and possibly in other applications as well, it is preferred that the kiln or furnace be provided with one or more constrictions with a narrower inner diameter for delaying progression of the mass, whereby the mass has time to mature in desired temperature zones. Thus, the raw stock, which has heated and melted in direct and reflected infrared radiation, is confined behind a threshold to mature, i. e. to have more time in the heating drum.

At high capacities, it is possible to use one or more electric arcs. The maximum benefit offered by an electric arc is that radiation is applied to a material to be heated, not e. g. for heating air, including its nitrogen content.

At least in its hottest section, the inner drum surface has a reflection coefficient higher than 0,5, preferably higher than 0,8, or even higher than 0, 9. As the reflection coefficient of a material to be heated is substantially lower, typically lower than 0,3 or 0,2, a most effective absorption of thermal radiation into the material to be heated is achieved without unnecessarily heating the drum wall. Thus, it is easy to reach a preferred condition, wherein the material to be heated and presently located in the hottest zone of a heating chamber has a temperature higher than 1000°C and the hottest spot of the heating drum's metal wall has a temperature lower than 700°C, preferably about 450-650°C.

When progressing from the hottest drum spot towards the inlet or supply end A, the material of a material to be heated becomes gradually lower than that of the drum wall. In this preheating zone it is feasible to make use of the direct conduction of heat in metal longitudinally and laterally of the drum.

The transfer of heat from the metal drum surface to a material to be heated and coming to contact therewith can be effected by using the direct conduction of heat along metal. In this preheating zone the inner drum surface may have a reflection coefficient substantially lower than that of the hottest drum section, because the drum cools down as heat is transferred to a material to be heated by way of a direct contact therewith. Regarding the hottest drum section, on the other hand, the high reflection coefficient of the inner drum wall contributes to preventing the drum wall from overheating and the material to be heated can be heated by means of direct and reflected radiation heat to a temperature substantially higher than that of the drum wall. The temperature difference can be more than 300°C, preferably more than 400°C.

Some of the radiation heat conducts, for example, through a nickel chromium steel blanket according to the principle illustrated by arrows 8 in fig. 2. The maximum radiation heat applied to the drum lies roughly within the zone

indicated by the arrows 8, from which the heat begins its conduction through the drum and longitudinally, as indicated by an arrow 10, towards the cold end of the drum where the heat comes to contact with the material 11 to be heated and presently entering the drum. Thermal radiation reflected from the walls of the drum 1 further increases the intensity of heating. In its cold condition, the material 11 to be heated can function as the principal coolant for the entire drum 1 after entering the drum.

In its simplest form, the heating drum of fig. 2 comprises a continuous, elongated and often smooth or slick metal pipe, which is supplied with a cold or cool feed stock from its cold end. It cools the pipe from one end at the same time as the feed stock gradually warms up in the elongated metal pipe or barrel while advancing towards the hot end and simultaneously warming up. The transfer of heat between metal and feed stock occurs mainly by direct contact without a normal, gas-involving intermediate step. At present, the heat ends up largely in a combustion gas, for example along with carbon dioxide and nitrogen oxides.

Above and alongside a supply chute 12 can be mounted a fixed or detachable thermal protection wall 2 for conserving the thermal energy presently in the kiln. Thus, the movable light thermal protection wall is naturally made e. g. of a material reflective of thermal radiation. The entry and exit from the kiln are provided by leaving just small openings, usually at the bottom edge A and B1. From the hottest drum section some of the heat conducts also in the direction of an arrow 9 or 10. Outside the nickel chromium steel cylinder can be fitted yet another cylindrical metal drum 4 made of a light or heavier material, e. g. aluminium, or constructed from a previously used heavier heating drum of e. g. reasonably thick steel. A space 3 left therebetween can function e. g. as an air space which is almost non- conductive of heat. The interspace can also be filled with ceramic wool, but that constitutes an addition to the thermally conductive medium. The wool

blocks the movements of air, but that can be done by other means as well.

Fig. 2 shows also a reheater 37 of the heated material for heating e. g. a thermally treated light expanded clay aggregate material for improved plasticity or for fusing pellets slightly melted at the surface. For example a product, in the form of ceramics or light expanded clay aggregate, the maintenance of which in a hot or ductile condition is desirable for an upcoming coating process, must be kept warm. The same objective is accomplished by extending the length of the metal drum 1 beyond the burner 6, such that the hot metal drum 1 maintains the material 11 in a hot state by conduction along a metal, even downstream of the burner 6. The same can be done at both ends of the drum.

In this case, thermal insulation is enhanced by a heat insulation cavity 3, which is a void interspace in the drum. It can be supplied with a cooling air injection or within the generally turbulent air can be injected, even at quite a high pressure, for example 1... 1000 bars, a liquid water jet which disperses into tiny droplets. After leaving the nozzle and upon vaporization in the heat it absorbs heat and provides cooling for the entire drum. The spraying of water need not be done until towards the end of the process downstream of a possibly employed barrier feeder in order not to interfere with the operation of a combustion chamber and the process step performed therein.

The thermally insulated, hot and elongated heating drum 1 can be used as a preheater for a feed stock, for example at a dredging site, if it is desirable to convert the removed mud immediately e. g. to light expanded clay aggregate.

The dredged, fine, water-logged material dries easily upon coming to contact with a hot metal surface, from which heat transfers to the dredged material for heating and drying the same, for example at flood protection sites and harbour construction sites. Wet slurry can be turned into dry. firm soil material for various purposes or ceramic artificial cement stone by heating in a long pipe or barrel. Detrimental substances encapsulate in the ceramic

product, e. g. light expanded clay aggregate, instead of dissolving in water.

The elongated, continuous and externally heat insulated heating pipe functions efficiently by using infrared radiation and by applying the reflected rays, i. e. thermal radiation, to a material to be heated.

The employed fuel may even be cheap waste oil with all its contaminants, since even supertoxins are destroyed within I... 2 seconds when incinerated in the heat of more than 1000 centigrades. A shorter burning time may create supertoxins in the atmosphere. Mobility of the inventive apparatus means that the shipping of feedstock material e. g. to a hazardous waste treatment facility, with its inherently high expenses, can be avoided.

Similarly, the product can be unloaded at a site of use once the heating apparatus has been brought to the vicinity of the site of use.

The inbound feed stock 11 to be heated is in the form of a cool or cold intermediate material and flows, after heating, along the chute 12 into the drum at one end thereof, using its mass for a cooling effect on the entire drum structure. The material to be heated advances in the drum towards the other end, which is provided, if necessary, with the end wall 2 or has no end wall at all. It is preferred that the hot, ceramic feed stock 11 be immediately used for further processing while still hot. For example, it can be coated with another material layer prior to cooling for providing a new product.

The reheater 37 can be used, for example, for maintaining the surface of light expanded clay aggregate pellets in a hot state and for having such pellets agglutinate to each other, for example for foundation blocks.

Fig. 2a shows a piece of an alternative longitudinal section for a heating drum, which is long or functions like a long drum from the aspect of thermal engineering. There, the drum 1 has its clean dressed or polished upper portion reflecting thermal rays as dictated by the laws of wave motion.

Eventually, the reflections of radiation heat generally end up in the material 11 to be heated and use their energy to warm it up. Abrasion of a drum can be readily effected for example throughout the drum 1 by increasing its rotational speed. Heat conducts along the metal drum 1 lengthwise, tangential or through the drum, unless it reflects from the drum.

If desired, very large pieces, for example boulders, may travel through the drum with heating applied to the surface only, i. e. with a moderate application of energy. In anticipation of the thermal treatment of large pieces, the apparatus is preferably designed to be mobile on wheels or tracks.

Fig. 3 shows a cross-section along a line I-I in fig. 2. If necessary, the heat insulation 3 or the cavity can be provided with an external protection blanket of a metal material. A cylindrical outer drum, indicated by reference numeral 4 in fig. 2, may establish an air layer 3 between the drums 1 and 4. In this intermediate layer 3, the combustion air can be preheated by the contacting action of the hot, inner, metallic firing drum 1 readily for example to 300... 1250 centigrades. Thermal energy transfers through the metal layer by conducting efficiently for example in the firing drum 1. After this, there is no longer much need for burning a fuel, generally coal or a carbonaceous substance, to carbon dioxide or for electrical heating in order to reach a desired heating temperature. The same effect is achieved by direct infrared radiation, yet without carbon dioxide and nitrogen emissions. The heating temperature can also be increased by using oxygen-enriched air in the burner.

The structure of fig. 3 has a heavy appearance but is actually lightweight if, for example, the heat insulation 3 consists of ceramic wool or just air or water vapour miscible therewith. The structure of fig. 3 can be implemented for example by drilling long holes through the nested inner and outer drums

approximately in the direction of a bending radius and by fitting the same with long pins (not shown in the figure), made for example of stainless steel, which are welded at both ends thereof securely to the drums. Excess length of the pins can then be cut off of the pin ends and inside the drum 1. After this, the void interspace 3 in the drum can function as an air flow duct or a water vaporization space. The resulting pressure of water vapour evolved in the interspace is taken up for example by means of the long pins solidly secured at both ends and by means of sturdy drum panels. If desired, the part of a pin remaining inside the smooth drum 1 can be removed from the combustion chamber 1 as the pins are welded securely and tightly at their ends to various drums. Thus, the pins do not interfere with the operation of the smooth and slick combustion chamber 1. The pins may consist of solid metal or lighter metal tubing. In the interspace 3 between the drums, upon the vaporization of water, the pins are generally exposed to a high tensile stress, which is why the pins must be highly resistant to tension. The number of pins sustaining the steam pressure and the thicknesses of panels are dimensioned in accordance with pressure safety regulations. Welding work can also be facilitated by using expanded pins of a rivet type, which engage in a drilled hole or the edges of a panel the same way as a rivet. In that case, one of the pin ends can often go unwelded. By virtue of a tapering shape or the extension, the amount of welding work can also be reduced e. g. in a pressure vessel. A tapering or wedge-shaped pin can be secured in a drill hole, for example by a powerful strike. Thus, welding work may be limited for example to just one end of the pin and can be performed even in a cramped space inside the drum.

The protection blanket can also be reconstructed from the previously used, heavier and thicker metal frame of a heating drum, which is capable of conducting even major heat flows along the drum. The inner drum 1 can be brought to a high temperature, even to so-called red heat. The hot metal drum may in turn deliver its thermal energy and thermal capacity to a

presently heated material often by a direct contact without intermediate steps and losses. A thick or heavy-duty metal pipe enables the transfer of a major heat flow quickly and effectively without major losses. A rather thick metal pipe has also a large mass and a high thermal capacity in addition to heat conduction properties. For example, the rather thick, long pipe 1 heated to red heat is capable of delivering a large amount of thermal energy from its metal mass quickly to a material to be heated.

The hot inner pipe in red heat can be thermally insulated from outside or inside with the intermediate air space 3 or with ceramic wool for conserving energy. The wool can be injected or pumped into the void interspace 3 of the drum for example in a flowing state, which sets in the void for thermally insulating wool a little later. By providing the metal drum 1 with a separate ceramic layer or by combining it for a composite structure, the drum's mass and thermal capacity can be increased as desired e. g. with a ceramic paste by reinforcing the heating drum from outside e. g. by injecting into a mesh resistant to intense heat and corrosion. The thick pipe is rigid and resistant to heat as well as mechanical stresses.

A thin metal drum warms up by the lesser application of energy. It is assisted also by thermal insulations, e. g. ceramic wool, whereby the conduction of thermal energy to waste is not possible even in intense heat.

In many applications it is possible that the temperatures of a long drum rotating in its rotating direction or in the direction opposite thereto can be equalized in a longitudinal direction. This enables bringing the temperatures sufficiently high, even with a rather thin panel which is highly conductive of heat in an annular fashion. The metal mass of a pipe functioning as thermal capacity for the inner pipe can be generally made sufficient in terms of its total thermal capacity. Similarly, in the long, rather thick metal drum of a lime sludge reburning kiln, the valuable thermal energy created in the slaking

of lime can be conducted directly along the metal inner drum 1 from the downstream section of the kiln efficiently in the longitudinal direction to the preheating of cool lime sludge, generally to upstream end of the drum 1.

There, the cold lime sludge functions at first as a coolant for the drum. Thus, the considerable slaking energy can be exploited as desired by conduction along metal in the form of heat in all lime processes, e. g. in a time sludge reburning kiln or in the production of lime, iron, steel or cement. The thick metal drum 1, being made e. g. from nickel chromium steel, is capable of transferring plenty of thermal energy in the longitudinal direction from the site of lime slaking to the site of preheating lime sludge or other presently heated material efficiently without intermediate steps and major losses.

A void interspace in the drum is alone an effective heat insulation provided that a gas present between the drum barrels is not highly motional.

Therefore, as far as the weight is concerned, the drum's rotational speed can be increased as desired. Thus, even a small drum can provide a high production capacity as temperatures can be raised up to high figures. In addition, the reflection of thermal radiation improves the transfer of heat to a presently heated material after the reflection, often on the opposite side of the drum.

The abrasion resistance of a metal, for example nickel chromium steel, enhances the effect of polishing or abrasion. Metal 1 is highly heat resistant as such and, thus, can be placed close to a flame. If necessary, the material to be heated can be supplemented with abrasive ingredients for abrasion and polishing. Centrifugal force presses even small particles against the metal drum 1, which delivers thermal energy effectively to the particles. The inner drum I heats up in response to combustion and tends to expand in such a way that the bending radius tends to increase. Thus, connecting the drums together is not advisable. The inner drum can even be loose inside the outer drum, as shown in the model of fig. 7. For example, the smaller drum can be

freely rotating inside the larger one, as long as the guide vanes for a fire vortex are attached to the inner drum. As a result of this, temperature differences do not cause problems, even if the drums had different temperatures.

The drum 1 has an inner surface which is generally slick and smooth. As the drum's metal material is abrasion resistant, it is possible to place even abrasive material in the drum. A conventional fine-grained material to be heated proceeds to polish the inside metal surface even smoother and slicker than it was before. Abrasion will be more effective when the feedstock composition includes quartz-and alumina-containing ingredients. Therefore, the reflection of thermal radiation becomes highly favourable and effective from the abraded, slick metal surface. Abrasion can be further enhanced by increasing the drum's rotational speed, for example to 2... 100 rpm even with a large kiln. Small kilns may have a much higher rotational speed.

The same way, the drum's interspace 3 can be used for abrading the drum surfaces to make the same slick and smooth. Coating the drum 1 with a wear resistant material over its outer surface as well is favourable in terms of abrasive grinding.

Fig. 4 shows an alternative cross-section for a drum of the invention, made for example from nickel chromium steel, which is provided with wear- resistant ribs 23 for disengaging a presently heated material temporarily from the surface of a drum 1. Material is kicked by the rib for example in the direction of arrows 24, especially when the drum is rotating at a high speed.

The ribs 23 can be hollow, as shown in the figure, or provided with heat conductors extending lengthwise of the drum and made, for example, from ordinary steel or nickel chromium steel. Inclinations on different sides of the ribs can be unequal. Thus, the drum's rotating direction can be reversed for varying the force of a kicking action. Within the zone between the ribs 23,

the smooth metal surface 1 or the slick drum in fig. 3 delivers thermal energy efficiently to a presently heated material.

With large pieces, the lifters or ribs create sudden lift and drop movements in a heating drum, whereby large pieces easily break up in the rotating kiln during heating. A heating furnace provided with lifters or lifting bars can also be set to function as a crusher for large single pieces, as described in Patent application WO 02/088613. The thermal stresses of heating, along with lift and drop vibrations, break up large pieces even to small fragments as long as the temperature difference in pieces is sufficiently high. The lifting bars pick up and place large pieces between the drum and the lifting bar and then drop the pieces onto the bottom of the drum for breaking the same upon impact against the hard bottom of the drum. The inner drum 1 must have a sufficient thickness for this purpose, as large pieces are falling off the lifters while still hot at least at the surface.

The apparatus of fig. 4 can be used for example as a reel oven for burning a fuel. The ribs 23 may function for example as ejectors or lifters for fuel, whereby the burning of wood or coal, for example, can be made efficient as even the heat of ashes can be associated with exhaust gases. With a small addition of oxygen, even smouldering in the furnace can be sustained without producing smoke. In this respect as well, a long furnace or kiln is preferred as heat conducts rapidly a long distance along the furnace metal.

In a heating facility, the heating capacity is increased by the reflection of slick wall thermal radiation from a slick metal surface. Thus, the middle sections of a kiln develop a major concentration of heat. The reflection of thermal radiation e. g. by 92... 95 percent, in the case of polished nickel chromium steel at a standard temperature, is realistic in a heating furnace.

With bright brass, it is possible to achieve the reflection of thermal radiation as high as 97 percent. By increasing the rotational speed of a kiln to a high velocity, the polishing action can be enhanced without scratching. A heating facility no longer requires unnecessary heating of air and nitrogen. The solids

content of lime sludge can be increased to almost a hundred percent.

Centrifugal force functions at the same time the way of a washing machine spinning action. Heat can be conducted along metal members to other parts of the structure as well. Thence, heat can be conducted for example to water vaporizing pipelines for the production of thermal power, for example. In a way the kiln wall constitutes an extra reflection burner without actually consuming energy.

Fig. 5 shows a cross-section in principle for a metal-constructed smooth and slick multi-barrel heating drum of the invention. The nested drums, e. g. reference numerals 1, 4,36 or 20 (e. g. in figs. 12 and 16), are insulated from each other and thus capable of performing various functions even at the same time. The nested drums can be assembled for ready-to-use cylinder barrels and set within each other. The intermediate layer 3 can sized as desired, for example by means of metal pins fitted in holes and welded securely and tightly to the nested cylinder barrels or drums. Distances between the pins are determined on the basis of anticipated pressure. After this, there is no explosion hazard even in the case of a major pressure developing between the separate drum barrels, for example by heating water the way of a traditional steam engine.

Various process steps, e. g. chemically, can also be implemented in separate barrels. If necessary, barrier feeders can be fitted between the barrels to separate various process steps from each other. Heat can readily travel through a metal-constructed drum by conducting over a short distance from one barrel to another without major losses. There can be a plurality of nested drums and void spaces therebetween. If desired, the process steps can continue from one intermediate layer to another as long as there is provided at least a partial communication between said layers, for example by way of a possibly open end of the drum. The barrier feeders can be used

for regulating a chemical process as the communication between drum barrels or drum sections is kept either open or closed.

The heat source comprises for example a burner 6 at a centre of rotation 13.

Most of the material to be heated lies in a bottom part 56 of the heating drum as a result of gravity. The drum's top portion is principally bare and clean for reflecting the burner's thermal radiation by its curved contour towards the centre of rotation. The reflection effect is enhanced by the polishing or abrasion of a metal surface with a fine-grained material 56, for example a feed stock. It provides a slight wearing of the inner drum's 1 internal surface. By virtue of an abrasion resistant metal, however, there will be no significant wearing. A benefit gained by the abrasive grinding is the excellent thermal radiation reflectivity of a slick and smooth drum surface.

The hot metal drum 1 conducts thermal energy along the metal drum by effective and rapid conduction laterally in both directions on the principle represented by arrows 9, even underneath the material to be heated.

The cool or cold material 56 functions as a drum coolant by a direct contact prior to its warming. This is further enhanced by rotating motion of the drum 1, whereby heated metal ends up even underneath the material 56 releasing some of its thermal energy thereto by a direct contact and conduction. Thus, for example moist lime sludge can be dried and preheated on top of a hot metal drum. Fresh energy of radiation heat is conducting all the time from the drum's 1 top portion to the vicinity of and contact with the presently heated material. Regarding the conduction of heat, it is preferred that the drums, e. g. 1 and 4, be capable of conducting even a large amount of heat, for example in an annular or circular fashion, on the principle represented by the double arrow 9 in both directions, as well as also axially, without major losses. Therefore, the drums can be constructed from a metal stock of considerable thickness.

As described in this example, the heat source can be set at the centre of rotation 13, the radiation heat emitting therefrom in all directions at a high speed. Reflections from a clean ceiling are not shown in the figure. An intermediate layer 3 between the drums 1 and 4 may just be full of air functioning as a heat insulation or it can be used for preheating cold or cool combustion air.

The intermediate layer 3 can also be sprayed with liquid water, which vaporizes in heat and absorbs thermal energy from the drum while cooling the same. The resulting vapour pressure of water in the intermediate layer 3 is convertible by means of low-pressure or high-pressure turbines to useful electric power. The tensile forces of an often low-height pressure vessel can be taken up for example by pins fitted between the drums 1 and 4, which are welded tightly and carefully to both drum panels on either of the void interspace 3. The pins are cooled as water vaporizes in the pressure vessel, thus lowering the temperature.

The pin functions in pressure vessel as a tension rod, which is maintained at a reasonably low temperature by means of vaporizing water, for example at 100... 1000 centigrades. Thus, the metal rod preserves generally quite well its tensile strength and welded joints will also hold up. At one end the rod can be given an extended shape the way of a traditional rivet for taking up and conveying tensile forces to the drum panel. Welding is also used for sealing and reinforcing, whenever necessary. At the other end of a tension rod it is easy to apply welding to the drum panel. Pushing an extended or widened rod through a drill hole is not easy. A necessary number of tension rods will be provided for taking up major tensile forces, e. g. in a lime sludge reburning kiln or a cement kiln. The most preferred form for a pressure vessel is generally spherical, wherein the entire structure is generally governed by tensile forces. That can also be designed according to the invention as a

cooled interspace 3 between two cylinder barrels 1 and 4 and encircling a hot drum as shown in fig. 5.

In order to secure the drums, it is sufficient to use even short, securely fixed pins capable of taking up even major tensile forces between the drums, which are created in the interspace 3 for example by the pressure of water vapour. Automated drills and welding robots reduce the amount of expensive manual labour. The pins can be positioned for example approximately in the direction of the radius of curvature of the panel. Being thin, the pins do not substantially block the flow of vapour or gas in the interspace 3. The number of pins can be reduced by using stronger or thicker panels 1 and 4 as well as pins.

The smooth and slick inner drum 1 allows the passage of even large pieces in the drum, with only their surface warming up. In the absence of lifters, large pieces only roll or slide in the drum, with only their surface warming up in the absence of sudden lifts and drops. The drops would break large pieces by the combined effect of thermal stresses and impacts.

If it is desirable to avoid the problems associated with a pressure vessel, that can be done with a safety valve which is capable of eliminating excessive pressure, when using e. g. a low-pressure turbine.

Fig. 6 shows a longitudinal section in principle for a heating furnace or kiln of the invention, the thermal radiation reflecting from a clean metal surface back into the drum and to a material to be heated. The area of maximum thermal radiation is darkened in the figure. The drum's upper part is usually uncoated and can be abraded to a slick and highly reflective condition while said drum's upper part receives plenty of thermal radiation energy and reflects it downwards to a material to be heated, for example on the bottom.

Fig. 6a shows in principle a temperature distribution in a material to be heated, such as shown in fig. 6. The point of maximum thermal energy generally coincides with the point of maximum radiation heat.

Fig. 7 shows a view in principle, partially transparent for the sake of clarity, for a cyclone vortex chamber. A flat cover around a pipe 21 for deflecting an air flow 66 is omitted from the figure for the sake of clarity. First the cool air applies a cooling effect on a hot kiln 1 from outside but, on the other hand, there is effected at the same time the preheating of the combustion air 66, along with its nitrogen oxides, which is a potential environmental hazard when created at high temperatures.

The central pipe 21 of the cyclone may even function as a support shaft or trunnion for the entire structure, if inclined guide vanes 30 are securely attached, for example by welding, to both or one of the drums 1 or 20.

Alternatively, the vanes 30 and the central pipe 21 can be set in sliding motion within a long barrel 1 after removing the cover. However, the mounting is preferably made slightly flexible because of temperature differences and thermal movements.

Alternatively, the smaller firing drum 1 can be loose inside a larger rotary drum. The drums rotate at an equal pace as a result of mutual contact friction, the smaller drum bearing against the larger one. Rotation of the outer drum sets also the smaller cylinder thereinside in rotation. The air gap 3 constitutes an annular space encircling the cyclone for preheating.

The supply of a material to be heated can be effected into the pipe 1, movable for example in a planetary fashion, by way of a flexible tube and a slidably mounted inlet pipe.

Another supporting point for the apparatus can be provided at the apex element of a cone 28 for external bracing. However, the most convenient arrangement is to maintain the cylinder drums stationary and to allow a freedom of movement for gases only.

At the same time, the cyclone may function as a grader for product pellets, on the basis of either grain size or density. The heaviest large pieces are removed upstream of the cone through a separate slot from the outer periphery (not shown in the figure). The heated air flow is deflected by means of a flat baffle or cover (not shown in the figure) around the central pipe 21 towards the guide vanes to create a burning outer vortex 51. As it advances, the vortex comes to contact with the cone, which uses its friction to generate a small-radius inner vortex 52 advancing towards the central pipe 21 of the cyclone.

The feed stock 11 to be heated can be passed inside the long barrel 1, where it first functions with its mass as a coolant for the hot barrel 1. The metal- constructed heating barrel 1 or heating drum, which is hot at one of its ends, preheats the cold feedstock directly by conduction in the same hollow, rather thick heating barrel. The inlet end of the long barrel or pipe 1 is not shown in the figure. For the passage of feed material, it is possible to leave a suitable vacant space between the vanes 30 and the drum 1, as shown for example in fig. 9.

Fig. 8 shows a longitudinal section for a heating drum of the invention fitted with a cone 28, which can concurrently function as a grader and a separator for thermally treated material. Oxygen or supply air and a fuel 31 are guided by the vanes 30 tangentially into a cylindrical vortex chamber to first create an outer vortex. A small-radius inner vortex, reflecting from the cone 28, contains the very lightest particles and gases urging to enter the central pipe 21. In a top separator, the gas flow is generally intensely turbulent and,

thus, the mixing of air or oxygen with fuel occurs easily. In a cyclone separator, a powerful turbulence is created by the action of continued rotary motion, surface friction, and shearing forces.

The nested or concentric burning vortices 51 and 52 of a cone-equipped top separator are shown in principle in fig. 11. The sorting of a tangential supply 53 is effected in the vortices by a centrifugal force.

The supply of a material to be heated can be effected by way of a gap 26 between the cone 28 and the cylinder barrel 1. Another alternative is to supply the feed stock from the opposite end of the long barrel 1 by means of supply vanes 30, as shown in fig. 7. The supply of feed stock applies a cooling effect on the cone 28 from outside. In this case, the cone is connected to the heating drum by means of flexible rods. As the drum 1 is rotating, feed stock deflectors 33 rotate along with the drum and deliver material into the drum in the direction of an arrow. Thin rods 26 transmit cooling from drum to cone. An arrow 31 represents a general direction of flow in axial direction for the supply vortex of combustion air/oxygen and fuel. During rotation, the baffle 33 may deflect a presently heated feed material 32 into the cylindrical firing or vortex drum 1. A blanket 20 can be a light-material constructed flow pipe around the drum 1 for a coolant, e. g. water or air.

It is possible to use several casing blankets 1,4, 36,20 and a cooling medium flowing therebetween, such as air and possibly a water jet, which mix and vaporize to water vapour, thus absorbing thermal energy. The nested casing blankets can be set to gradually cool down, such that desired temperatures are reached for various blankets. In a lime sludge reburning kiln, the outermost blanket has a temperature which is as low as less than 100°C, even though the inner drum has a high temperature, for example 300... 600 centigrades. Excessive heat should be avoided to prevent the

vaporization of alkali metals. In a lime sludge reburning kiln, this means the loss of an eutectic mixture as a combination of several oxides, whereby the melting point becomes a little lower. By virtue of cooling the drum 1 and its inner surface reflecting thermal rays the way of a mirror, the heating and cooling can be balanced in such a way that the temperature difference between the heating drum and the hottest spot of a heating chamber defined thereby is more than 300°C, preferably more than 400°C. The hottest spot of a heating chamber has a temperature which is typically higher than 1000°C and the hottest spot in a metal-frame heating drum has a temperature which is lower than 700°C, preferably about 450°C-650°C.

Fig. 9 shows a cross-section along a line IV-IV in fig. 8. The supply vanes 30 can be adjusted to a desired angle of deflection for providing a desired vortex in the drum. The distance of the vanes 30 from the drum 1 may vary as necessary. The pitch angle can be adjustable according to material or capacity. The ignition of a fuel is effected by means of a continuous spark ignition immediately downstream of the vanes 30. The central pipe 21 can be coated or cooled, for example with water, for making it resistant to intense heat. Against the drum 1 can be provided an interspace for preventing the drum from heating. The drum 1 can be thermally insulated with air cavities or water vapour cavities 18,19, which are provided on either side of zigzag folded panels.

Fig. 10 shows a cross-section along a line V-V in fig. 8. Fine material is collected by a free vortex from the cone 28 in an opening 34 at the cone end. The fine material can be passed to a further treatment, for example to a desorption apparatus, a multicyclone or a fabric filter, for separating particles from gas.

Fig. 11 shows a principle regarding concentric twin vortices in a cone- equipped vortex chamber. A tangential feed 53 develops first a larger-radius

outer vortex 51. As a result of friction caused by the cone, the vortex dies away and deflects for a smaller-radius inner vortex 52 directed towards the central pipe. The finest-grained material discharges through B3. A slightly coarser fraction discharges through the cone apex by way of an outlet B2.

Fig. 12 shows a heat insulation, which is implemented by bending a nickel chromium steel plate 35 inside a drum 20 in a zigzag pattern for providing voids 18 and 19 for the passage of a coolant. The bent panel 35 is only welded to the drum at a single spot of each piece. This type of well cooled furnace can function for example as a cement kiln or a lime sludge reburning kiln, wherein intense heat is isolated by an air layer between the panels and the heat is conducted along the metal by direct conduction for preheating a material to be heated. The structure of fig. 12 can be applied as a heat exchanger by passing e. g. hot exhaust gases into the channels 18 and combustion air to be heated into the channels 19. As a result, heat transfers readily through a rather thin metal layer, but clean and dirty gases remain apart. The structure of fig. 12 can be implemented by making holes in the diagonal panels 35 for connecting the channels 18 and 19 to establish for example an air insulation layer, in which air is hardly movable.

Fig. 13 shows a double-decker zigzag panel assembly, which provides a multitude of thermally insulating voids and which has a long heat conduction distance in the metal structure. Thus, the propagation of heat in the structure becomes more difficult. The voids 18 and 19 can be sprayed with water in liquid form, which upon vaporization absorbs heat from the drum.

Temperature can be regulated by means of the amount of vaporizing water.

The structural strength can also be enhanced by means of an intermediate drum 36. The demand for cooling may be high, for example in petrochemical or metallurgical and mining engineering related applications.

Fig. 14 shows a side view of a heating apparatus of the invention mobile on wheels 57, which can be used for spreading a hot material directly at a construction site, for example for a road bed 44. An element 41 represents a feed hopper for a material to be heated and an element 42 represents a multicyclone, a fabric filter, a desorption apparatus, or a receiver for fine fraction.

An element 43 represents a combustion gas discharge pipe or a gas collector, from which the gas can be removed for example by burning in an afterburner, whereby the hazardous, e. g. toxic gases burn and become harmless. The after burner may also produce energy, e. g. by burning carbon monoxide to carbon dioxide by means of extra air or pure oxygen. The after burner may also burn combustion gas, when supplemented even with a small amount of pure oxygen or oxygen-rich air. The reflection of thermal radiation from metal promotes a rise of temperature at a desired stage of the reaction.

A curved reflector shape is preferred, as it concentrates thermal radiation in the vicinity of a focal point, at which the temperature may rise even to a very high level. The pyrolysis reaction takes place in a sort of self-sustained manner in response to concentrated thermal radiation, when the metal surface has been polished or abraded to a slick, smooth and clean, i. e. a highly reflective condition.

The required high temperature is obtained by supplementing ordinary air with pure oxygen. The light fraction of a top separator or cyclone separator can also be absorbed from the central pipe 21 in fig. 8 by means of a vacuum pump for further processing or for example to combustion in the way of desorption. At the same time it is also possible to provide a pressure difference required by a cyclone separator.

A quantity of mixed soil of varying granularity can be heated in the drum in its entirety at a high temperature, such that the smallest particles flux by the

combined effect of powerful thermal radiation and reflection of thermal radiation. Subsequently, such particles function as a flux adhesive between larger pieces. Large pieces do not generally flux or melt, which conserves plenty of heating energy. Organic substances burn during a heating process.

Fine-grained mineral matter behaves like clay, i. e. loses at least some of its crystal water. Thus, the fine matter swells in response to released gases to produce a porous light material similar to the core of light expanded clay aggregate. The resulting material is in the form of a lightweight and thermally insulating new builder, which can be used for many applications as such. Production is facilitated by the fact that the novel heating drum has a high thermal conductivity in longitudinal and lateral directions, as well as tangentially in the drum rotating direction. The fact that the largest pieces are only heated over their surface with radiation heat represents a huge saving of heating energy, as opposed to heating the entire mass. The central bracing of a drum in line with the wheels, as shown in fig. 14, is more generally applicable to the adjustment of longitudinal inclination in the furnace 1 of fig. 2 or 2a, when there is no tractor vehicle interfering with the work. Mobility can be provided by a separate engine on wheels 57 or on tracks.

Fig. 15 shows a side view of a mobile apparatus of the invention, which is parked at waterfront. If desired, the produced material can be laid directly on water after heating and cooling, for example as a pontoon, a bridge, or a floating raft 45. It can function, for example, as a section of a large floating airfield. The material to be heated can be preheated for promoting expansion or swelling and improving buoyancy in a separate drum 55, as well as coated with a waterproof vitreous silicate substance. Preheating of the material can be performed for example in a multilayer drum as shown in fig. 2 or 5. The void interspace 3 can also be used for the preheating of combustion air, when the other side of a metal drum comprises a hot combustion chamber. A long bridge may first float on water as a pontoon, which is subsequently

lifted by means of jacks for example upon in-situ piles propped on the bottom. Ships are thus provided with a passageway.

Fig. 16 shows a bracing for two drums 1 and 20 at different temperatures by means of adjacent diagonal panels 35, such that the structure does not break down during a heating process. The hotter drum barrel 1, which is generally the inner one, has a tendency to stretch or elongate in response to heat to an extended length, but that is not possible due to an annular structure, whereby the frame is left with tension. The cooler, outer metal pipe 20 experiences the same effect to a lesser degree. The elongated, hot, annular metal pipe 1 or 20 can be left in a stress state of thermal expansion caused by heat, such as a long rail track in hot state, which is welded to become continuous and whose lateral deflections are prevented mechanically. In a cylindrical heating drum, thermal stress is taken up and lateral deflections are prevented by the annular tubular contour, which constitutes at the same time also a closed frame structure. It holds thermal stresses within itself. Its thickness can be chosen arbitrarily. Flexural stiffness in a metal pipe is also better than in a ceramic, generally more discontinuous pipe. With regard to the equalization of temperature and wearing, a thick structure is preferred. However, with regard to mobility of the apparatus, a thinner and lighter metal panel is preferable.

The diagonal panels 35 can be fitted in a heating drum sparsely further from each other, whereby the drums become bound to each other provided that the mountings of both ends are rigid. If a rigid mounting is only provided at one end, for example for the outer drum 20, the other drum can be temporarily left with a slice-shaped opening of a desired size for welding, which opening can be subsequently filled with a panel, if desired. The structure will be extremely rigid after welding. At the same time, a tension cable or belt can be readily disengaged, whereby the panels 35 press against the other drum.

The drum's hottest spot can be provided with a thermal shield in the form of a ceramic coating material, which can be injected, if necessary, to an engageable, hard-to-melt expanded metal mesh. Underneath the dense expanded metal mesh can be another more durable and more robust expanded metal or diamond mesh. In a diamond mesh cutting or expanding process, the metal strands usually deflect upwards for a good attachment of the ceramic bonding agent to the mesh. The mesh apertures provide natural attachment point for ceramics between various layers for bonding the same together. The separate ceramic layers or linings provide a beneficial and heat resistant structure. The void space remaining between the panels 1 and 20, as designated for example with reference numerals 3,18 or 19, can be utilized as a thermal insulation layer when filled, for example, with mobile or immobile air or wool.

The air or water jet layer 3 left underneath may function as a drum cooling blanket involving the use of liquid water. Cooling can be provided for example by means of water jets vaporizing from the other side of the metal pane 1 by applying for example fig. 5. Discharge nozzles directed to the void intermediate layer 3 are not shown in the figure. Thus, for example in cement production for making Portland cement, it is possible to avoid lime slaking by cooling the separate closed interspace 3 through the metal panel 1 with abundant water jets vaporizing e. g. in air. Cooling can be effected also by a high-pressure water jet, whereby water flies in a partially liquid state far away from the nozzle prior to vaporization.

The void space 3 becomes in vaporization a pressure vessel, whose energy can be exploited for example in low-pressure turbines for producing electricity. From the safety aspect it is important to provide the apparatus with a relief valve for releasing excess pressure.

The purpose of diagonal intermediate panels 35 (also in fig. 12) is to increase the conduction distance of heat by means of a diagonal or inclined structure. The intermediate panels 35 are often attached just by one end thereof for ensuring flexibility and for allowing minor relative movements between the drums 1 and 20. In order to facilitate the work, the intermediate panels 35 are often securely fastened to just one of the pipes, for example to pipe number 1.

By contracting the diagonal panels 35 by means of a cable or belt, the structure can be made more compact in size and tensioned against the other drum, e. g. with a springback factor. Subsequently, the diagonal panels 35 are held in place or secured to the drum 1 or 20 by tension or light welding, so-called stitch welding. The primary purpose of diagonal panels 35 is to keep the drums 1 and 20 apart and at different temperatures by utilizing air or vacuum heat insulation in the drum's void spaces. The diagonal panels 35 can be positioned even at a fair distance from each other, when the drums 1 or 20 are robust in their own right. The welding of panels 35 to the drum barrels can be carried out by welding even with a powerful electric current. A previously used drum, e. g. 20, can be covered with a new drum, e. g. 1. The diagonal panels 35 are first welded securely to the new drum. The contracted structure can be fitted inside the previously used drum, where the contracting clamp belt or cable is released for providing the final structure.

For example, a previously used or old lime sludge reburning kiln can be lined on the inside with a thin sheet of stainless nickel chromium steel, which is chemically capable of withstanding a multitude of process demands.

The panels 1,4, 36 and 20 may have a wide range of thicknesses. If there is a cold and a hot zone on opposite sides, the temperature will change across the thickness of a drum panel 1 or 20. In addition, a diagonal panel 35 shall effectively increase the distance between the drums.

As a rule, the inner panel 1 is hot and the outer one can be cooled, e. g. with a vaporizing water jet, or it is possible to employ a single thick panel capable of withstanding stresses of a temperature difference. The thickness of a heat resistant and highly heat conductive metal plate or panel can be for example 5... 50 mm for equalizing a heat flow, but a thinner plate is also functional. A thinner panel conserves drum heating energy and reduces thermal capacity in proportion to masses.

The plate or panel can be manufactured from various types of metal stocks, which are jointed for a single unitary composite structure. The jointing can be done e. g. by spot welding or by milling various layers together in hot state. One of the panels to be jointed can be provided with depressions or recesses, grooves or holes, such that the other hot metal is milled thereon to fill the depressions, recesses or holes with its metal material in response to the milling pressure. One of the components of a composite structure can be shipped in hot state even over long distances enclosed in a material reflective of thermal rays, for example a blanket of nickel chromium steel.

After a cooling process, the various layers are strongly bonded together.

Thus, for example, a sheet made of black and cheap ordinary steel can be coated with more expensive stainless or acid-proof steel which is more resistant to chemical stresses. A milling slab can be transported in hot state even over long distances to a milling site. The milling temperature can be increased or sustained for example by means of a heating tunnel or a reheater, for example at 600... 1100 centigrades.

The inventive composite-structured heating tunnel highly reflective of infrared radiation can also be used in the production of light expanded clay aggregate, such that the heating takes place at a correct temperature precisely in the clay to be heated as the regulation is easy by means of an electric arc. Thus, production can be automated for reducing human labour.

The same applies also for example to a cement and lime sludge reburning kiln.

A laid-open and detached metal panel cools down relatively quickly even in air, but cooling can also be assisted by the use of vaporizing water. After a cooling process, the bond is strong, preventing all relative movements between the layers. When hot or warm, the composite panel can still be bent to a desired curvature for manufacturing a heating drum or sections thereof.

The manufacture of stainless and acid-proof pipes from the composite panel by bending the same in hot state is also possible. The bending temperature can be for example 800... 1200 centigrades. Temperature can be raised by local heaters prior to bending. The heating drum can be assembled for example from bent elements. The composite or joint panel can be a novel product in metal industry, which facilitates the manufacture of revolving rotary kilns or curved structures in large series, saving expensive human labour. A stainless or chemically resistant metal component may be inevitable in some processes, but making the entire structure stainless could be too expensive because of high consumption of raw stock. Coating a cheap metal plate with rather thin, chemically more resistant metal for a composite structure may be economically highly attractive for many applications.

A sheet of stainless nickel chromium steel can be bonded for example to hot black iron. That can be further bonded to another chemically resistant sheet of nickel chromium steel, which can even be rather thin. The stainless surface sheet is capable of withstanding chemical effects in many applications Such a bilaterally corrosion-proofed product is suitable for use e. g. in salty seawater. The sheet material can also be bilaterally corrosion protected.

In cement making, the panel thickness can be increased by fluxed feed stock, which produces cement clinker by layers on the hot inside surface of

the panel, increasing the kiln weight. Thus, the total blanket thickness increases and temperature differences equalize.

A clear and slick-polished metal surface of the kiln does not accumulate fluxed cement feedstock, the kiln weight remaining low. Dynamic stresses remain also low, even at high rotational rates of the drum. This simplifies, among other things, a bearing system for the drum.

The heat insulating air layer or water jet cooling space 3,18, 19 blocks the spreading of heat to unnecessary places.

Fig. 17 shows a principle regarding the disposition of pellet stock particles in a kiln during exothermal foam production. Larger size particles do not melt or flux easily, thus ending up in the surface of a pellet to form a dense and hard glass-like fluxed shell layer 39. In the middle of a grain remains a porous and light fraction 40, for example as a thermal insulation. The outermost layer will be a vitreous strong and dense shell layer 38, produced in sintering and generally impervious to water.

Fig. 18 shows pellets of fig. 17, fluxed and cemented together at a high temperature. Pellets 38 can also be replaced with such a structural design that large natural stones are agglutinated together by means of melted fine fraction. Only the surface layer of large pieces is heated, the core portion remaining cooler. The resulting body may have a high compression and tensile strength by virtue of the strength of fluxed and hardened soil or natural hard stone. The material of varying gain sizes, for example moraine, can be processed for form artificial cement stone, wherein the fluxed fine matter functions as an adhesive-like bonding agent. Spreading is most conveniently effected in hot state from a mobile heating furnace, whose own weight is low.

Fig, 19 shows a section of a road structure made according to the invention, wherein on top of porous and light bottom layers 48 is laid a stronger surface layer 47 and asphalt 46. The bottom layers 48 can be made from all types of in situ mineral waste materials by stuffing those in a mobile pipe or drum 1 reflective of infrared radiation, which is placed near the ground level. The layer 48 can have fluxed therein also large stones and large fractions of moraine by heating the same only at the surface. This way, the fluxed fine fraction constitutes a sort of agglutinant in a resulting rigid slab. Thus, the finished product will also be at a suitable height after cooling and setting.