Preheater system for preparation of industrial use aggregate materials

Field of the Invention

The present invention relates to a preheater system for preparation of industrial use aggregate material. The invention concerns a system comprising a preheater and interfaced with a dryer configured with a heater or a burner.

Background of the Invention

Preparation of aggregate materials for industrial use may involve a heating and drying process of the aggregate materials through evaporation of the water contained in the materials. The evaporation of the contained water may involve that the aggregate material is heated to the point or above the point at which water starts to boil resulting in an exhaust from the drying process partly comprising overheated steam. The energy contained in the exhaust has traditionally been released along with the exhaust to the atmosphere.

This results in a great energy loss as a great part of the energy used for the heating and drying process is bound in the overheated steam. Recovering the energy from the overheated steam may cut expenses both in an economic sense and in an environmental perspective.

Drying systems for preparing material aggregates for industrial use have been suggested wherein a preheating process is comprised and wherein the preheating may be achieved by recovering energy from the exhaust from the drying process of the material aggregate. The systems are generally based on an indirect heating wherein the heat energy contained in the exhaust is recovered through the use of heat transfer elements. US 6340240 Bl is one example in which preheating of aggregates is performed through harnessing of indirect heat.

In general, preheating of aggregates are harnessed by utilizing sensible heat through indirect heating or in few cases by direct heating as in WO 8100296 in which a heating system for aggregates is disclosed, which system has the objectives of utilizing the off-gases for fuel and which system reduces the mechanical wear parts to be affected by the high process temperatures of up to 1100°C. The preheating may be carried oul in a process involving aggregate material being led across a surface of the heat transfer elements to obtain heat transmission to the materials. The aggregate materials may be hard, sharp and with edges and expose the heat transfer elements to rugged conditions with a distinct abrasion to the surface.

The energy contained in the exhaust may be released in the heat transfer elements through condensation of the steam contained in the exhaust. The exhaust may carry small particles and contain gases or oil released from the materials during the heating and drying process which may cause abrasion or residue build up within the heat transfer elements.

The aggregate materials for industrial use is generally stockpiled uncovered until it is needed and may be exposed to ambient moist atmosphere, rain and snow. The moisture content in aggregate material may vary but can often be at a high level.

Object of the Invention

It is an objective to overcome one or more of the aforementioned shortcomings of the prior art.

Description of the Invention

The aforementioned aspects may be achieved by a preheater system for preparation of industrial use aggregate material. The preheater system comprises a preheater and a dryer configured with a heater. The dryer is configured to conduct dryer exhaust to the preheater. The preheater is configured with transport means to transport the aggregate material in a first direction. The preheater is configured with exhaust conduction means to conduct exhaust in a second direction and configured to expose the aggregate material to the dryer exhaust comprising superheated steam.

In a further embodiment of the preheater system the preheater may be a preheat- condenser configured to expose the aggregate material to the dryer exhaust comprising superheated steam to preheat the aggregate material. The dryer comprised in the preheater system may be an existing dryer or more existing dryers in a plant to which the preheater is retrofitted through integration or adapted interfaces between the preheater and the dryer.

The preheater system may comprise one or more dryers combined with one or more preheaters. The effect of this embodiment may be that the capacities of the dryers and preheaters are balanced. The advantage of this is an optimized system in regard to capacity or energy consumption or both. Another advantage is that the aggregate materials can be prepared in the preheater system in separate portions, depending on the kind of materials, so that mixture of the aggregate materials may be avoided.

Aggregate materials may comprise the materials or part of the materials to be used for the production. This may include virgin raw materials or recycled materials or a combination of both. The aggregate materials may include construction materials like stone, rock, gravel, sand, minerals. Also included may be raw materials like wood, clay, plant parts or other materials for industrial use which enter a production process requiring drying and heating of the aggregate materials.

The industrial use may be in the construction industry for producing concrete, cement, asphalt, or refining of construction materials. Also included but not limited to may be the timber industry or refineries of wood or wooden chips and productions refining plant parts or productions comprising plant fibres as part of the aggregate materials.

Recycled materials are becoming more and more interesting to include as aggregate material. As one example, but not limited to this, is the construction industry which has a high interest in recycling asphalt pavement.

The heater may be dependent on the industry and aggregate materials. The heater may comprise a direct combustion burner, an indirect combustion burner, other burner types, or heat sources. The efficiency of combustion burners for example may be reduced due to a large amount of air in the dryer.

An effect of the embodiment may be to expose the aggregate material to the dryer exhaust comprising overheated steam. The advantage is that heat energy is trans- ferred directly from the overheated steam to the material. The aggregate material fed to the preheater may be at ambient storage temperatures, and due to the temperature difference of the overheated steam and the aggregate material, the energy transferred to the material may comprise two contributions: temperature change and phase transition from vapour phase to liquid phase. The two contributions may also be referred to as sensible heat and latent heat.

An effect of the embodiment may be to expose the aggregate material directly to the dryer exhaust. The advantage is that the preheating may be conducted by condensing directly on or in the close vicinity of the aggregate material and thus utilizing latent heat (condensation) for preheating the aggregate material. Thus, the aggregate material may be used as a medium for the condensation process.

The above-mentioned effect of steam from the exhaust being condensed through energy transfer in the preheated has the further advantage that smell, small particles, gases or oil released from the materials, which may be carried by the exhaust during the heating and drying process, may be bound in the condensate and thus emission of these is reduced.

A further effect of energy transfer by condensation of dryer exhaust to the aggregate materials is that the aggregate material at the preheater outfeed may contain a larger portion of water than the portion of water at the preheater infeed. The advantage of the condensation process is that the water contained in the aggregate material leaving the preheater has a higher temperature entering the dryer infeed and thus the preheated aggregate material will contribute heat energy to the drying and heating process in the dryer compared to non-preheated aggregate material.

A further effect of this embodiment is that heat transfer elements are not comprised in the preheater. This is advantageous in a more simple construction of the preheater as it reduces costs for spare parts and maintenance of heat transfer elements. These advantages are based heat transfer elements being dimensioned in accordance with temperature differences, material load, and the heat transfer rate from the heat transfer elements to the material to be heated, and therefore heat transfer elements should be dimensioned according to a pre-described capacity of the preheater. Furthermore the exhaust may carry small particles and contain gases or oil released from the materials during the heating and drying process which may cause abrasion or residue build up within the heat transfer elements. Additional aggregate material being lead across a surface of the heat transfer elements to obtain heat transmission may result in distinct abrasion of the surface.

In a further embodiment a dryer outfeed may be connected to transport means which leads the dried and heated materials to the next production step or to storage means.

The effect of this embodiment is that the preheater system can be retrofitted to existing production plant or comprised in construction of new plants comprising dryer means which generates dryer exhaust comprising superheated steam. The advantage of retrofitting the preheater system to existing production plants is that with limited construction changes, existing plants may reuse the waste heat from the drying and heating process and thus reduce costs for drying and heating the aggregate materials.

One embodiment of the preheater system may comprise a first aggregate material transport means, a second aggregate transport means, a dryer exhaust duct, a preheater exhaust duct, and an air inlet. The first aggregate material transport means is configured to transport the aggregate material at a controlled rate from an aggregate material source to the preheater infeed. The second aggregate transport means is configured to transport the aggregate material from a preheater outfeed to a dryer in- feed. The dryer exhaust duct is configured to conduct the dryer exhaust from a dryer exhaust outlet to a preheater exhaust inlet. The preheater exhaust duct is configured to conduct preheater exhaust from a preheater exhaust outlet to a plant stack inlet, and the air inlet is configured to allow outside air to enter the preheater exhaust duct or alternatively a plant stack at a controlled rate.

The effect of this embodiment is that the aggregate material may be transported through the system from the aggregate material source to the dryer and the dryer exhaust is led through the system from the dryer to the plant stack. Both the aggregate materiel and the dryer exhaust are led through the system in a controlled way, direction and rate. This is advantageous in regard to achieving a balanced flow of dryer exhaust and aggregate material to optimize the energy transfer from dryer exhaust to aggregate material, adjusting the heating and drying process according to the material end- temperature at the dryer outfeed and the material feed rate to the dryer, and to adjusting exhaust flow and pressure through the system to avoid air leakage in the system. This may influence the heater efficiency, thereby achieving reduced energy consumption, adjustment of the production to a continuous production flow and adjustment to the relevant production capacity needed within the limits of the maximum capacity of the plant and the system.

A person skilled in the art will know that in the dryer, the heat from the heater is primarily used for heating the product and evaporating the water in the aggregate material. The process is a boiling process which means that most of the exhaust from the dryer is superheated steam. A small part of the heat energy from the heater may be used for heating of combustion air, or air in the dryer due to leaks.

As the evaporated water from the dryer is used to preheat the raw- and recycled material by condensing the superheated steam, the temperature change of the aggregate material through the preheater from the preheater infeed to the preheater outfeed depends on the amount of water in the aggregate material entering the preheater. The higher the water content, the higher is the temperature that can be achieved from the preheater, due to the steam-to-material-ratio. Furthermore, if the water contents in the aggregate material increases, more steam is generated in the dryer and contained in the dryer exhaust resulting in an increased temperature in the preheater.

Thereby, the process may be controlled according to a set-point determined on the basis of the material temperature at the dryer outfeed (in the following referred to as the material end-temperature). To achieve the right end-temperature of the material at the dryer outfeed, the rate of material fed to the dryer may be changed (in the following referred to as the dryer material rate). And the dryer material rate may even be increased in existing plants compared to the previous maximum rate.

At a material end-temperature below the set-point the dryer material rate may be lowered, and a material end-temperature above the set-point may increase the dryer mate- rial rate. If the dryer material rate has not been sufficiently changed to obtain the material end-temperature, the heat source capacity may be adjusted accordingly.

Thus in addition to the above, the effect of the embodiment is that a too high product temperature may be avoided. The advantage is that the materials leaving the dryer is not burned, charred or in other way damaged due to too high temperatures.

A further advantage of the embodiment is that the production may be run as continuous production, semi-continuous production or batch production and with an adjustable throughput production level.

In case that the preheater exhaust is passed through a filter before being emitted to the atmosphere the embodiment of the air inlet has the further effect that the condensation in the filter may be reduced. The preheater exhaust is mainly moist air due to the filtration effect of the condensation process in the preheater. The humidity of the exhaust may be controlled by the air inlet providing outside air to the exhaust before reaching the filter. The advantage of this is that the exhaust humidity may be lowered before reaching the filter, thereby improving the lifetime of the filter, and furthermore, condensation in the plant stack may be decreased, thereby lowering the risk of damage to the plant stack.

One embodiment of the preheater system comprises a condensate trap and a separator. The condensate trap comprises a condensate inlet and a condensate outlet and is arranged with the condensate inlet in communication with the preheater condensate outlet and with a condensate trap outlet. The separator comprises means for separating residue from the condensate, a water outlet, and a residue outlet.

The effect is that the condensate is collected and separated in residue and waste water. Residue may include sludge, sediment or other deposits from the process which are contained in the condensate entering the separator. The residue may comprise small particles, gases and oil released from the aggregate materials during the heating and drying process but may also comprise small particles, gases and oil released in the preheater process or bound in the condensate due to the condensation process in the preheater. One advantage of the separation is that the residue may contain important materials used in the production and thus may re-enter the production process. Another advantage is that the residue may be useable in other productions or industries and may be resold as a by-product. Furthermore the separation process has environmental advantages in regard to decontamination of either residue, waste water or both.

In one embodiment of the preheater system, the preheater transport means may comprise a rotary drum configured to agitate or lift the aggregate materials during transport in a first direction and to expose the aggregate materials to the dryer exhaust in a second direction. The lifting or agitation of aggregate materials in the drum may be achieved by lifting flights or shovels within the rotary drum.

The effect of this embodiment is that the dryer exhaust is led through the rotary drum filling the inside of the drum while the aggregate material is agitated or lifted causing a large surface of the aggregate material to be exposed to the exhaust. The advantage is that heat transfer is to a larger surface, and thus a larger amount of the heat energy may be utilized. This embodiment is also advantageous in relation to draining the aggregate material during the preheater process as the water contained in the cavities between the materials may be drained from the material due to the agitation or lifting.

In one embodiment the preheater system is comprised in an industrial plant further comprising a dryer configured with a heater and production device or storage means for heated and dried aggregate material. The industrial plant is configured such that the dryer configured with a dryer exhaust outlet and the preheater configured with preheater exhaust inlet are interfaced by a dryer exhaust duct. Further, the dryer is configured with a dryer infeed and the preheater is configured with a preheater outfeed which are interfaced by a second aggregate transport means. Furthermore, the dryer is configured with a dryer outfeed, and production device or storage means configured with infeed means are interfaced by transport means for heated and dried aggregate material.

In another embodiment, the preheater system is comprised in an asphalt plant comprising a dryer configured with a heater and at least one mixing device for asphalt production. The asphalt plant is configured such that the dryer configured with a dryer exhaust outlet and the preheater configured with a preheater exhaust inlet are interfaced by a dryer exhaust duct. Further, the dryer configured with a dryer infeed and the preheater configured with a preheater outfeed are interfaced by a second aggregate transport means. Furthermore, the dryer is configured with a dryer outfeed and mixing device configured with infeed are interfaced by transport means for heated and dried aggregate material.

In yet another embodiment, the preheater system is comprised in a wood processing plant comprising a dryer configured to heat and dry the aggregate materials, production device or storage means for heated and dried aggregate materials. The wood processing plant is configured such that the dryer configured with a dryer exhaust outlet and the preheater configured with a preheater exhaust inlet are interfaced by a dryer exhaust duct. Further, the dryer configured with a dryer infeed and the preheater configured with a preheater outfeed are interfaced by a second aggregate transport means. Furthermore, the dryer is configured with a dryer outfeed, and production device or storage means configured with infeed means are interfaced by transport means for heated and dried aggregate material.

The scope of the invention is by no means limited to the above-mentioned three embodiments. Other embodiments may include plants for production of fabrics using plant fibres, plants preparing plant fibres for other uses, plants using plastic clay for the construction industry, which further embodiments by no means are exhaustive. Rather a person skilled in the art facing similar problems in different fields will be able to appreciate the disclosed workings and implement those and thereby make use of the invention in other fields than those here recited.

The effect of the above-mentioned embodiments is that the preheater system may be used in various industries with the advantage that the preheater system can be implemented in existing or new plants by establishing the described interfaces.

Particularly in the construction industry, attempts have been made to improve energy and production efficiency. In conventional plants for making asphaltic concrete paving materials, a stone raw material, recycled raw material and bitumen are mixed, dried and heated to produce the final product. The raw materials and recycled materials typically have moisture content of 5%, and depending on the ambient conditions, the energy consumption in the heating and drying process may reach levels around 100 kWh/ton. Typically 30%-50% of the energy is used for evaporation of water from the aggregate material. The remaining energy is mainly used to raise material temperature.

Conventional direct-fired prior art drum hot mix asphalt (HMA) plants often utilize a mixture of virgin aggregate material and recycled asphalt products (RAP). Increasing the percentage of RAP in the end product is especially interesting. To recover RAP in the production, the virgin aggregate material must be heated to a point far above the boiling point of water during the asphalt production process. The increased temperature of the virgin aggregate material is required because the virgin aggregate material must comprise sufficient heat energy for heating and drying the RAP in the mixing process. This heating to above the vaporization point in the drying and heating process consumes a large amount of energy.

The effect of this embodiment, if for example used in HMA plants, is that the RAP may be added already in the preheater, thereby achieving the advantage of reducing the energy consumption in the heating and drying process as the virgin aggregate material is not transported from the dryer to the mixer at a high temperature with a high heat loss as a consequence.

A further effect of this embodiment, if for example used in HMA plants, is that when adding the RAP already in the preheater, the temperature of the material when leaving the dryer may be lower than the temperature at the time when RAP is being added in the mixer. This is advantageous as pyrolysis and gasification in the dryer will be reduced, and additionally the production rate may be increased.

An object of the invention may be achieved by a method of preparing industrial use aggregate material comprising the acts of preheating aggregate materials in the preheater, drying aggregate materials in the dryer, and exposing aggregate materials in the preheater to the dryer exhaust from the drying process, while the aggregate mate- rial is moved in said first direction, and the dryer exhaust is conducted in a second direction.

An effect of this method is to expose the aggregate material to the dryer exhaust comprising overheated steam. The advantage is that heat energy is transferred directly from the overheated steam to the aggregate material due to a temperature difference of the overheated steam and the aggregate material. The energy transferred to the material may comprise two contributions: temperature change and phase transition from vapour phase to liquid phase.

A further effect is that steam from the exhaust is condensed through energy transfer in the preheater which has the further advantage of reducing the content of smell, small particles, gases or oil released from the materials during the heating and drying process in the preheater exhaust.

A further advantage of the heat energy transfer due to condensation is that the waste heat previously emitted with the dryer exhaust may be recovered within the preheater system.

A further effect is that the method can be implemented to existing production plant or comprised in construction of new plants comprising dryer means which generates dryer exhaust comprising superheated steam. The advantage of implementing the method is that waste heat from the drying and heating process may be recovered by preheating material entering the production.

Yet another effect of the method is the that heated and dried aggregate material are output with the advantage that the materials are prepared for further production requiring that the materials have been dried, heated or both.

An object of the invention may be achieved by a method of preparing industrial use aggregate material comprising the acts of transporting the aggregate materials at a controlled rate from said aggregate material source to the preheater infeed, transporting the aggregate materials from the preheater outfeed to the dryer infeed, conducting the dryer exhaust from the dryer exhaust outlet to the preheater exhaust inlet, con- ducting the preheater exhaust from the preheater exhaust outlet to a plant stack inlet, and regulating the air inlet to allow outside air to enter the preheater exhaust duct or alternatively the plant stack at a controlled rate.

The effect of this method may be to transport aggregate materials through the system from the aggregate material source to the dryer and to lead the dryer exhaust through the system from the dryer to the plant stack. This has the additional effect that both the aggregate materials and the dryer exhaust may be led through the system in a controlled way, direction and rate.

This is advantageous in regard to regulating the flow of dryer exhaust and aggregate material to optimize the energy transfer from dryer exhaust to aggregate material, to adjust the heating and drying process according to the material end-temperature at the dryer outfeed and the material feed rate to the dryer, and to adjust for exhaust flow and pressure through the system to avoid air leakage in the system. This may influence the heater efficiency, thereby achieving reduced energy consumption, adjustment of the production to a continuous production flow, and adjustment to the relevant production capacity needed within the limits of the maximum capacity of the plant and the system.

The further advantage is that only the acts comprised in the method are used to regulate the rate and direction of the dryer exhaust and aggregate materials to be balanced. The regulation may thus be further optimized through input from existing measuring points in existing plants, by implementing new measuring points in existing plants or by implementing measuring points in new plants.

An object of the invention may be achieved by a method according to the above- mentioned method comprising the further acts of collecting condensate from the preheater condensate outlet in the condensate trap and to separate the condensate from the condensate trap in a separator which comprises means for separating residue from a condensate. The effect is that the condensate is retained and may be separated in residue and waste water. One advantage may be to recycle material either for the actual production or for other industrial use.

An object of the invention may be achieved by use of the preheater system in an industrial plant comprising the acts of preheating aggregate materials in the preheater, drying aggregate materials in the dryer, and exposing aggregate materials in the preheater to the dryer exhaust from the drying process, while the aggregate material is moved in said first direction, and the dryer exhaust is conducted in a second direction.

Further objects of the invention may be achieved by use of the preheater system in an asphalt plant or a wood processing plant comprising the above-mentioned acts.

The use of the invention is by no means limited to the above-mentioned embodiments. Other uses of the invention may include plants for production of fabrics using plant fibres, plants preparing plant fibres for other uses, plants using plastic clay for the construction industry, which further embodiments by no means are exhaustive. Rather a person skilled in the art facing similar problems in different fields will be able to appreciate the disclosed workings and implement those and thereby make use of the invention in other fields than those here recited.

An effect of the above-mentioned use is that the aggregate material is exposed to the dryer exhaust comprising overheated steam. The advantage is that heat energy is transferred directly from the overheated steam to the aggregate material due to a temperature difference of the overheated steam and the aggregate material. The energy transferred to the material may comprise two contributions: temperature change and phase transition from vapour phase to liquid phase.

A further effect is that steam from the exhaust is condensed through energy transfer in the preheater which has the further advantage of reducing the content of smell, small particles, gases or oil released from the materials during the heating and drying process in the preheater exhaust. A further advantage of the heat energy transfer due to condensation is that the waste heat previously emitted with the dryer exhaust may be recovered within the preheater system.

A further effect is that the use of the preheater system can be implemented to existing productions or incorporated in new productions with the advantage that incorporating the use of a preheater system may require none or small changes in workflow and recipes used in a given production.

Description of the Drawing

Figure 1 illustrates the preheater system for preparation of industrial use aggregate material. The preheater system comprises a preheater and a dryer. A heater is connected to or comprised in the dryer. In the preheater, the aggregate material moves in a first direction, and the dryer exhaust moves in a second direction. Furthermore, the figure illustrates an embodiment of the preheater system comprising a first aggregate material transport means, a second aggregate transport means, a dryer exhaust duct, a preheater exhaust duct, an air inlet, a condensate trap, and a separator.

Figure 2 illustrates one embodiment of the preheater illustrated with aggregate materials infeed and outfeed, preheater exhaust inlet and outlet, and preheater transport means. The transport direction of the aggregate materials and the direction of the dryer exhaust are illustrated relatively to the infeed and outfeed and the inlet and outlet of the illustrated preheater.

Figure 3 illustrates one embodiment of the dryer comprising a heater. Also illustrated is an infeed for aggregate materials, an exhaust outlet, and an outfeed for aggregate materials. The transport direction of the aggregate materials and the direction of the dryer exhaust are illustrated relatively to the infeed and outfeed and the outlet of the illustrated dryer.

Figure 4 illustrates the material flow to and from the preheater system, within the preheater system, and in an embodiment wherein a condensate trap and a separator are connected to the preheater system. Figure 5 illustrates the dryer exhaust flow from the preheater system, within the preheater system, and in an embodiment wherein an air inlet is connected to the preheater system.

Figure 6 illustrates a method of preparing industrial use aggregate material comprising the acts of preheating the materials in a preheater, drying the materials in a dryer, and exposing the materials to dryer exhaust in the preheater.

Detailed Description of the Invention

Figure 1 illustrates the preheater system 10 for preparation of industrial use aggregate material 20. The preheater system 10 comprises a preheater 30 and a dryer 40. The preheater may be a preheat-condenser 32. A heater 50 is connected to or comprised in the dryer. Furthermore, the figure illustrates an embodiment of the preheater system comprising a first aggregate material transport means 100, a second aggregate transport means 110, a dryer exhaust duct 120, a preheater exhaust duct 130, an air inlet 160, a condensate trap 170 with a condensate outlet, and a separator 180.

In the illustrated embodiment the materials entering and leaving the system are also illustrated. Also illustrated are the transport means 70 and exhaust conduction means 80 within the preheater and the transport means within the dryer 90. The industrial use aggregate material 20 to be prepared is fed to the preheater via the first aggregate material transport means 100. The heated and dried aggregate material 24 is output from the dryer through the dryer outfeed 406 prepared for further production or storage. The surplus product from the preheater system may be collected and separated into residue 190 and waste water 194 through a separation process by separation means 182 in the separator 180.

The dryer exhaust 60 is illustrated entering the preheater through the dryer exhaust duct 120 and the preheater exhaust 62 is illustrated leaving the preheater exhaust duct 130. The preheater exhaust duct 130 may be connected to the plant stack inlet ISO of the plant stack 140. In this embodiment the plant stack inlet is illustrated to be positioned in the close vicinity of the preheater and before the air inlet 160, however, the connection between the preheater exhaust duct 130 and the plant stack inlet 150 is not limited to this illustrated embodiment. The exhaust being emitted from the plant stack has reduced levels of heat energy, humidity, dust particles and other small particles, smell, gases and the like due to the condensation process in the preheater.

Figure 2 illustrates one embodiment of the preheater 30,32. The preheater comprises a preheater infeed end 303, a preheater outfeed end 305, a preheater infeed 302 for receiving aggregate materials 20, a preheater outfeed 304 for discharge of aggregate materials 20, a preheater exhaust inlet 306, a preheater exhaust outlet 308 and a preheater transport means 70 arranged to transport the aggregate materials 20 from the preheater infeed 302 to the preheater outfeed 304, and arranged with the preheater exhaust inlet 306 at the preheater outfeed end 305, the preheater exhaust outlet 308 at the preheater infeed end 303, and a preheater condensate outlet 310 arranged to collect condensate 192 from the preheater 30. Furthermore, the dryer exhaust 60 conducted from the dryer to the preheater is illustrated along with exhaust conduction means within the preheater 80. The exhaust conduction means 80 is here simply illustrated by two dotted lines to indicate that the dryer exhaust 60 is conducted in the direction of the transport means 70 and thus in the direction of the aggregate material to obtain the preheating effect due to condensation on or in the close vicinity of the aggregate material.

However, as illustrated in figure 1 the exhaust conduction 60 may simply be conducted into the preheater 30,32 and thus the preheater chamber, a rotary drum or other unities may constitute the exhaust conduction means 80. The exhaust conduction means 80 are by no means limited to the above-mentioned illustrations and examples.

The dryer exhaust 60 is led into the preheater 30 from the dryer 40 via the preheater exhaust inlet 306, through the preheater 30, and the remaining exhaust is then led out from the preheater 30 via the preheater exhaust outlet 308. As the dryer exhaust 60 moves through the preheater 30, the aggregate material 20 being transported through the preheater is exposed to the exhaust. The exhaust comprises overheated steam which heat energy is partly transferred to the aggregate material 20 through a condensation process by contact to the aggregate material. During condensation the heat energy transferred comprises two energy contributions: the energy released due to temperature change, and the energy released due to phase change from vapour phase to liquid phase. Different effects may result with regard to the condensate 192: The condensate is bound in the material, part of the condensate is bound in the condensate, and part of the condensate is released from the material and is led to the preheater condensate outlet 310, the condensate is not bound in the material and is led to the preheater condensate outlet 310 possibly with an extra part of condensate released from the material in the preheating process. These effects may depend on amongst other things, the type of aggregate material, the water content in the materials, the steam content in the dryer exhaust, temperatures, differences in temperature, and transport rates 16, which is not illustrated.

Figure 3 illustrates one embodiment of the dryer 40. The dryer comprises a heater 50, an infeed for aggregate materials 402, an exhaust outlet 404, outfeed for aggregate materials 406 and dryer transport means 90 arranged to transport the aggregate materials 20 from the dryer infeed 402 to the dryer outfeed 406. In the dryer, the aggregate material 20 moves in a first direction 12, and the heat from the heater moves in a second direction 14. The dryer outfeed 406 may be connected to transport means which leads the dried and heated materials to the next production step or to storage means 210, which are not illustrated. The next production step could involve mixing devices 200 or production devices 220, which are not illustrated.

The choice of heater 50 implemented in the dryer 40 may be dependent on the industry and aggregate materials 20 used. The heater 50 may be configured as a direct combustion burner, an indirect combustion burner, other burner types or heat sources. The heat source 50 may be positioned to achieve a high interaction of heat to the aggregate material 20. The material is subject to a drying and heating process in the dryer.

The heat is primarily used for heating the product and evaporating water from the aggregate material. The process is primarily a boiling process, which means that the dryer exhaust from the dryer comprises superheated steam. A small part of the heat energy from the heater may be used for heating of combustion air or air in the dryer 40 due to leaks.

The dryer exhaust generated in the dryer is led out from the dryer further on to the preheater via the dryer exhaust outlet 404.

Figure 4 illustrates the material flow to and from the preheater system 10, and within the preheater system 10. The preheater system is illustrated in an embodiment in which a condensate trap 170 and a separator 180 is connected to the preheater system 10. The separator 180 has a water outlet 184 and a residue outlet 186. The aggregate materials 20 enter the preheater system 10 and are transported through the preheater 30,32 in a first direction 12. From the preheater 30,32, the materials are transported further on into the dryer 40. From here the heated and dried materials 24 are led through the dryer outfeed 406 onto subsequent production.

The method acts performed in connection with the material flow through the illustrated embodiment are also indicated in the figure. The aggregate materials are transported 540 from the aggregate material source 22 to the preheater at a controlled rate. After preheating, another act for transporting 540 the aggregate materials is performed; this act is for the materials to enter the dryer 40. The condensate 192 from the preheater is collected 570 in the condensate trap 170 through a condensate inlet 172 and is led into the separator 180 in which the residue 190 is separated 580 from the condensate. The residue 190 may be stored for later use in the production or as a by-product in other products, or may re-enter the production in a continuous manner. The waste water 194 from production is also collected to be further processed in a given way.

Figure 5 illustrates the dryer exhaust flow from the preheater system 10, and within the preheater system. The preheater system is illustrated in an embodiment in which an air inlet 160 and a plant stack 140 are connected to the preheater system.

The dryer exhaust is generated in the dryer 40 and led to the dryer exhaust in a second direction 14 and from the dryer through the dryer exhaust outlet to the preheater 30,32. The dryer exhaust is then led through the preheater in a second direction 14. The remaining dryer exhaust is the led from the preheater to the plant stack 140.

The aggregate material is exposed to the dryer exhaust comprising overheated steam. Hereby heat energy is transferred directly from the overheated steam to the material by condensation. The exhaust amount leaving the preheater is reduced compared to the exhaust amount entering the preheater. Due to the steam from the exhaust being condensed in the preheater, smell, small particles, gases or oil released from the materials, which may be carried by the exhaust during the heating and drying process, may be bound in the condensate and thus emission of these from the preheater to the plant stack may be significantly reduced. The method acl performed in connection with the dryer exhaust flow through the illustrated embodiment is also indicated in the figure. The dryer exhaust is conducted 550 from the dryer to the preheater. The remaining dryer exhaust from the preheating and condensation process is conducted 550 from the exhaust outlet to the plant stack inlet.

By use of the illustrated air inlet, the act of regulating 560 an air flow of ambient air to blend with the remaining dryer exhaust from the preheater after the preheater may be performed. The air flow in the air inlet may be regulated to enter at a controlled rate 18, not illustrated.

Blending ambient air into the remaining exhaust may be used to regulate the humidity in the exhaust to prevent or reduce condensation in the plant stack, or a filter, if such is present in connection with the stack.

Figure 6 illustrates the method 500 of preparing industrial use aggregate material 20 comprising the acts of preheating 510 the materials in a preheater, drying 520 the materials in a dryer and exposing 530 the materials to dryer exhaust in the preheater. The method outputs heated and dried material.

The material is preheated 510 in a preheater and is then led on to a drying process 530 in a dryer 40 in which the material is dried and heated. The drying process releases exhaust comprising overheated steam which is conducted to the preheater 30,32. In the preheater the aggregate material is exposed 530 to the dryer exhaust. This is a continuous process in which the heat energy comprised in the dryer exhaust 60 is transferred to the aggregate material in the preheater through a condensation process of overheated steam comprised in the dryer exhaust.