DRYING GOODS

The present invention concerns drying devices and working methods for drying goods, especially drying devices and working methods that have been adjusted to recover heat energy from a thermally insulated container included in the drying device.

Aspects of this invention could, for example, be used in the field of cyclic drying of a product, for instance wood, paper, etc., in a thermally insulated chamber. Drying wood or other products is a common practice in the industry. For this purpose, typically large quantities of wood will repeatedly be added to a specially adapted container that is thermally insulated and includes further means for heating the container properly. The wood is heated inside, after which the container is opened, emptied, and filled up with the next load of wood. A lot of energy, especially heat energy, is lost during this process.

This invention aims to provide drying devices and working methods that are more energy-efficient in operation, in particular by recovery of energy available for later use and its re-use. This is achieved by a device in accordance with the features of the characterising portion of conclusion 1 , and by a corresponding working method in accordance with the features of the characterising portion of conclusion 9.

The term "comprising" should be interpreted in a manner that does not exclude any other elements or steps.

Furthermore, it should be noted that the features that are present in the description of different aspects of the invention, are also applicable to the other aspects, as will be understood by a skilled person.

In the first aspect of the present invention, a drying device is described including: - a thermally insulated container for receiving goods which should be dried, such as wood;

- a heating device, for example at least partially placed inside the thermally insulated container, to (also) heat the internal volume of the container to a predetermined temperature, after which the drying process of the goods to be dried can be initiated,

- a condensation device that is at least partially placed inside the thermally insulated container, which has been adapted to dehumidify the thermally insulated container using a condensation process during the drying process; for which the drying device further comprises drainage means to drain the water that is extracted from the thermally insulated container by the condensation device during the drying process, to a thermally insulated water storage medium. This medium is preferably implemented externally to the thermally insulated container.

The use of such a drying device allows recovery of available energy and the reuse of this energy. This provides more energy efficiency than drying devices that are currently used.

Heating water requires a relatively high investment of energy. Recovery of heat during the drying process, by draining condensation water from the thermally insulated chamber to a thermally insulated water storage medium, allows this energy to be stored. On the contrary, this energy can be reused, as will be discussed in more detail later.

In certain preferred working methods, the drying device is adapted to operate at temperatures higher than 60 °C, more preferably higher than 70 °C, more preferably higher than 80 X, more preferably higher than 85 °C, more preferably higher than 90 °C, more preferably higher than 95 °C, and more preferably higher than 99 °C. Typical wood drying devices that are based on a condensation process / include a condensation device, operate at relatively low temperatures, for example at temperatures lower than 45 °C, due to the very high amount of energy that would be needed to reach higher temperatures, amongst other reasons. Wood drying devices that make use of condensation drying techniques that are currently used, heat wood using the residual heat of the fans and/or refrigerating circuit of the condensation device and/or with heat that is added through a heat pump, which makes use of heat from the external surroundings. This obstructs the energy-efficient operation at higher temperatures. An advantage of embodiments of the present invention is that the condensation- drying device operating temperature can be much higher, that is higher than 60°C, and is therefore used.

Drying at these temperatures in a condensation drying chamber is made possible, or also made possible, by the recovery and reuse of the heat energy from the previous drying cycles. For example, by recovery of the heat energy from condensation water, according to embodiments of the present invention.

The operation at such high temperatures also creates other thermodynamic conditions in the drying chamber (thermally insulated container), which balance the condensation and heat recovery in a manner that is very economic, and much more economic than a similar system that would be used at a lower temperature. It should be noted that the system, for example the heating device, should be dimensioned appropriately in a manner recognised by the skilled person.

Furthermore, complementary energy recovery could be accomplished, for example by the use of a buffer tank system and corresponding working method as is described in detail in the unpublished Belgian patent application

BE2013/0570 (filing date 2 September 2013), and a further Belgian patent application that was filed on 16 October 2013, entitled "Een buffervat en buffervatsysteem voor warmterecuperatie en werkwijze om energie uit te wisselen" ("A buffer tank and buffer tank system for heat recovery and working method to exchange energy"). These will be fully incorporated, both in the name of the same applicant as the present invention. This buffer tank system comprises, for example, a buffer tank, comprising a container for fluid storage, the container comprising a top end and bottom end, an internal separation element that is arranged for separating a top part of the container liquid tight from a bottom part, the internal separation element being arranged so as to be able to move throughout the container, remaining liquid tight between the upper and bottom part, thereby varying the relative volumes of the upper and bottom part . Furthermore, the buffer tank system can comprise an external circuit device, which connects the first end to the second end and defines a further closed-off liquid cycle. The buffer tank system can be completely or almost completely filled with a liquid, for example water. The closed liquid cycle can comprise an exchange section that is arranged to be able to exchange heat with the thermally insulated chamber or container. The separation element is preferably thermally insulating, comprising an upper side and a bottom side and the buffer tank system further comprises a pressure means, for example one or more pumps, to generate a difference in pressure of the liquid between the top side and bottom side of the separation element, over the closed liquid cycle. Furthermore, this buffer tank system preferably includes a means for determining the temperature of the liquid near to the exchange section, a means for determining the internal chamber temperature, and a control unit that is adapted for receiving information from these means, so as to direct the pressure means such that the temperature of the provided liquid near the exchange section is controlled as a function of the chamber temperature.

In preferred embodiments, the draining means is adapted to lead the water that has been extracted by the condensation device from the thermally insulated chamber to a water storage medium, which is preferably thermally insulated.

In preferred embodiments, the drying device is adapted for use in a cyclic drying process, for which consecutive amounts of goods are consecutively dried in the drying device, and the drying device comprises control means, a piping system and a heat exchange system, which are together adapted for leading heat, previously discharged and stored with the water during previous drying cycles, back to the container from the water storage medium, when bringing the internal volume of the container to a predetermined temperature in a subsequent cycle.

This makes effective reuse of the heat, discharged with the water possible. In preferred embodiments, the water storage medium comprises at least two thermally insulated storage tanks that are connected with the drainage device and, comprise pumping means (e.g. one or more pumps or pressure means) to move water between the drainage means and respective thermally insulated storage tanks. In preferred embodiments, the water storage medium comprises three, four, or more thermally insulated storage tanks. This allows the use of levelled energy recycling and levelled reuse, as will be described in detail later.

In preferred embodiments, the drainage means and the at least two thermally insulated storage tanks are connected in a linear chain, and the pumping means are adapted and arranged to be able to move water between every two consecutive entities selected from the drainage means, the respective thermally insulated tanks, and a device drainage that is implemented at the end of the linear chain of storage tanks.

In the preferred embodiments, the drying device is adapted for use in a cyclic drying process for which consecutive amounts of goods are dried consecutively in the drying device. Furthermore, it includes a piping system, a heat exchange system, and control means that are together adapted to control the drying device in such a way, that respective amounts of water drained by the drainage means during respective, consecutive drying processes are moved during each cycle to respectively following thermally insulated storage tank in the linear chain of storage tanks, or to the device drainage if the end of the linear chain has been reached. For this, an exchange of energy is allowed to take place between the respective amounts of water and thermally insulated container each time during the next process of heating the internal volume of the container to a predetermined temperature.

In preferred embodiments, the drying device is adjusted for use in a cyclic drying process for which consecutive amounts of goods are dried by the drying device consecutively. The piping system, heat exchange system and control means are adapted and arranged to allow a consecutive exchange of energy between the respective amounts of water and the thermally insulated container during the next process of heating the internal volume of the container to a predetermined temperature. This takes place in an order so that the amounts of water with a relatively lower temperature are used first, followed by amounts of water with a relatively higher temperature, and for which the temperature of the respective amounts of water with which the exchange of energy takes place are always close to the temperature of the thermally insulated container at that moment.

In order to be able to work energy efficiently, the skilled person will agree that other parts of the drying device should also be thermally insulated. This is why the piping system that is used to drain condensation water and for recycling this water towards the container to exchange energy, is also preferably completely or largely thermally insulated.

A second aspect of this invention concerns a method for drying goods with a drying device, including a thermally insulated container for collecting the amounts of goods to be dried, including: a moving the goods to be dried into the thermally insulated container; b heating the internal volume of the container, and therefore the

goods to be dried, to a predetermined temperature, starting the drying process;

c extracting liquid from the thermally insulated container through a condensation process with a condensation device during the drying process; In the method, the water extracted by the condensation device from the thermally insulated container is drained to a water storage medium, which is implemented externally of the thermally insulated container.

Preferably, the predetermined temperature is higher than 60°C, more preferably higher than 70°C, more preferably higher than 80°C, more preferably higher than 90°C, more preferably higher than 95°C, more preferably higher than 99°C.

A third aspect of this invention concerns a method for use in a cyclic drying process, for which consecutive amounts of goods are consecutively dried by the drying device, comprising repeating a method according to one of the

embodiments of the second aspect, comprising providing heat that was drained and stored previously with water from the previous drying cycles, to the container from the water storage medium, when bringing the internal volume of the container to a predetermined temperature in a subsequent cycle.

In preferred embodiments the water storage medium includes at least two thermally insulated storage tanks, and these are connected in a linear chain with a drainage device implemented at the end of the linear chain. The working method includes moving the respective amounts of water during every drying cycle, by draining these using the drainage means during the drying process, to the next thermally insulated storage tank in the linear chain of storage tanks. In the case in which the end of the linear chain has been reached, the water is moved to the device drainage. During this process, exchange of energy is allowed between the respective amounts of water and the thermally insulated container on the next occasion that the internal volume of the container is heated up to a predetermined temperature. For preferred embodiments, the consecutive exchange of energy between the respective amounts of water and the thermally insulated container takes place during the next occasion that the internal volume of the container is heated up to a predetermined temperature, in an order so that the amounts of water with a relatively low temperature are used first, followed by amounts of water with a relatively higher temperature. This is done to make sure that the temperature of the respective amount of water with which the exchange of energy takes place, always has a temperature close to the temperature of the thermally insulated container at that moment. For example, within an absolute temperature difference, which is below 20°C or below 10°C.

A first representation of this invention is schematically depicted in figure 1. A drying device 1 , comprising a thermally insulated container 2, in which a product P to be dried, for example wood, is added. This could be effected, for example through door 21 of container 2. The product is moist. A heating device 3 is added to heat the internal volume of the container 2 to a predetermined temperature, or a predetermined temperature range. The predetermined temperature, or minimum temperature of the range, is preferably higher than 60°C, for example 85°C. The container can include one or more fan devices that also generate residual heat, and can therefore be considered as part of the heating device 3. This is also applicable to further described embodiments.

Heating device 3 can consist of one or several heating devices. A heating device can, for example be or comprise a heat exchanger that provides external energy. The heating device can also be or comprise the condenser of the condensation device (the refrigeration circuit of), and can make use of recovered heat from previous drying cycles and/or heat derived from an external heat source. In use, a drying process of a product that is added to the thermally insulated container can start when the predetermined temperature is reached. Even if there can/will be a very limited drying process during the systematic increase of the

temperature inside the container, this description defines the drying process as the drying of the product after reaching a certain minimum or predetermined temperature.

Heating the container (also called a drying chamber) happens relatively quickly (typically between 2 and 24 hours, for example), and at the same time the product drying process in loads, for example a load of wood, is a relatively slow process taking longer (typically between 24 and 96 hours, depending on the type of wood).

The drying device further comprises a drainage device 4, adapted to remove condensation water from the drying chamber to an external water storage medium 6 during the drying process. This could, for instance be a thermally insulated container 6, such as a storage tank 6. This water has the right temperature, and will have the same temperature, or a temperature close to, that of the drying chamber, which is 85°C for example. Heating these amounts of water to certain high temperatures requires a lot of energy, and disposing of it would represent huge energy loss.

This is why an aim of this invention is to collect this stored water inside the external thermally insulated container, so that it may be reused for other purposes. Preferably, this water and the corresponding energy are used to heat the thermally insulated container / drying chamber up to a predetermined temperature for the next drying process, that is, the drying process for the next load of wood.

In a preferred embodiment, schematically depicted in figure 2, the drying device 1 also comprises a condensation device 8, at least partially arranged inside the drying chamber 2, which is implemented and adjusted to actively dehumidify the drying chamber by use of a condensation process. Such a condensation device 8 is known to the skilled person. These condensation devices 8 typically comprise closed liquid/gas circulation with an evaporator and condenser, and a

compressor. At minimum, the condenser and evaporator of such a condensation circulation should be implemented in the drying chamber. The water moved from the container will then almost fully be derived from such a condensation process. The water can be collected by implementing a water collection means, comprised in the water drainage means, close to the evaporator of the condensation device, for example a funnel type device. A skilled person knows that more complex means of collecting the water that results from dehumidification in the drying chamber, and methods how to remove it from the drying chamber exist. The skilled person will appreciate that the thermodynamic conditions of a condensation type drying chamber, which operates at higher temperatures (for example, more than 60°C), are of the nature that energy recovery can be conducted in a very effective manner, as described in detail by use of the embodiments represented in the present invention.

Figure 3 illustrates an embodiment of a drying device 2 for use in a cyclic drying process, for which consecutive amounts of P are consecutively dried by the drying device 1 , with further implemented control means (no figure), a piping system 9, and a heat exchange system 3, 10. All of these adapted to recycle heat that is drained and stored with water from the previous drying cycles, to the thermally insulated container 2 from water storage medium 6, when heating the internal volume of container 2 to the predetermined temperature in the next cycle. In order to do so, the piping system can, for example, include a pressure means, such as one or more pumps, as well as one or more valves or taps. A skilled person could implement the piping system 9 and heat exchange system 3, 10, as well as the monitoring device to ensure that the intended objective is achieved.

The reintroduced water can then be collected and reused for the next heating process, or can be drained to a drain 1 1 by piping system 9 part 91 1 for that purpose. In embodiments, the heating device 3 is useable, at least partially, as the heat exchange system 10. In embodiments of the invention, the heat exchange system 10 is comprised in heat device 3. In embodiments, the condensation device 8 is comprised, or partially comprised, in the heating device 3. In embodiments, the condensation device 8 embodies all or part of the heat exchange system 0 and/or the heating device 3. In embodiments, different heating devices 3 and/or 0 and/or 8, and possibly one or more further heating devices, can cooperate when the internal volume of the container needs to be heated to a predetermined temperature for the next drying cycle. The above- mentioned is also applicable to other embodiments described. Figure 4 shows a more advanced variety of the embodiments that has been discussed in detail in relation to figure 3. In this drying device, the water storage medium 6 comprises thermally insulated storage tanks 61 , 62, which are connected to drainage means 4. It also includes pumping devices to move water between the drainage means 4 and respective thermally insulated storage tanks through a piping system 9.

The drainage means 4 and two thermally insulated storage tanks 61 and 62 are connected in a linear chain, possibly and typically by a suitable chain of valves and/or taps. Piping system 9, the integrated pumping means and possibly valves and any other components integrated in them, and a control system, are adapted and arranged to be able to move water between each two entities that follow one another in the chain, chosen from drainage means 4, the respective thermally insulated storage tanks 61 , 62 and a drainage device 1 that is implemented at the end of the linear chain of storage tanks. Drying device 1 also includes heat exchange system 3, 10, and a control means which are adapted together to control the drying device 1 in such a way, that respective amounts of water drained by means of drainage means 4 during respective consecutive drying processes, during each cycle, are moved to the respective consecutive thermally insulated storage tank 61 , 62 in the linear chain of storage tanks, or to the drain if the end of the linear chain has been reached. During this process, exchange of energy is allowed between the respective amounts of water and thermally insulated container 2 during the next occasion that the internal volume of container 2 is heated to a predetermined temperature.

Preferably, piping system 9 and heat exchange system 3, 10, and the monitoring device are arranged and adapted to allow the consecutive energy exchange between the respective amounts of water and thermally insulated container 2 during the next occasion of heating internal volume of container 2 to a

predetermined temperature, in an order so that the amounts of water with a relatively lower temperature are used first, followed by amounts of water with a relatively higher temperature, and whereby the temperature of the respective amount of water with which the exchange of energy takes place, is always close to the temperature of the thermally insulated container 2 at that moment.

The drying device, described in relation to Figure 4, and its operation can proceed as in the following example. At the start of the cyclic drying process, both thermally insulated storage tanks are empty. A first quantity of goods to be dried, such as wood, P1 , is added to the thermally insulated container / drying chamber 2 through a closable door 21.

A heating device 3 is used to heat he internal volume of the container to a predetermined temperature, for instance a temperature higher than 80°C. When this predetermined temperature has been reached, the wood (P1) drying process can begin.

In order to do so, the condensation device 8 extracts moisture/water from the internal volume of the thermally insulated container. This water is drained through drainage means 4 to the water storage medium 6, which in this case consists of two storage tanks 61 and 62. These storage tanks are/can be connected to each other and to an energy/heat exchanging device 3, 10 though a liquid circuit or piping system, which means that this process can take place, subject to a suitable arrangement of any valves and/or taps. The water coming from the first load of wood P1 is initially received into the first storage tank 61 , and has a temperature close to that of the drying chamber, for example, 75°C to 80°C. When product P1 has been dried sufficiently, it is removed from drying chamber 2. The next load of wood P2 is then added to the drying chamber, after which the temperature is increased to the predetermined drying temperature of 80°C again. When increasing the temperature, the water that has been collected from the load P1 is firstly reintroduced to a heat-exchanging means 10, which transfers at least part of this corresponding energy to the internal volume of the container 2. This water is then transferred through the liquid circuit to the next tank of the chain of storage tanks 61 , 62, which is tank 62, and has a reduced temperature, for example, a temperature of about 60 to 65°C. The first tank in the chain, tank 6 , is hereby emptied. Other heating devices 3 can cooperate to reach the predetermined temperature. A skilled person will recognise that the reuse of the energy associated with the condensation water of the first load of wood P1 substantially reduces the energy consumption of heating device 3.

Once this temperature has been reached, the second drying process for the load of wood P2 can begin. The condensation water in this second drying process is again drained by drainage means 4 into the first storage tank 61.

When the second load of wood P2 has been dried sufficiently, it will be removed from drying chamber 2 again. A third load of wood P3 is added to drying chamber 2, after which the temperature is again increased to a predetermined temperature to start the third drying process. When increasing the temperature, the water collected from load 1 before is initially transferred back from tank 62 to the heat exchanging device 10, at least part of this energy will be transferred to the internal volume of container 2. This water has a reduced temperature, of about 45°C to 55°C. This makes it difficult to recover any further energy from it so it is sent to drain 1 1 afterwards and the second tank 62 is emptied. In the meantime, the temperature of the drying chamber has increased due to at least the exchange of heat from condensation water from load P1 , and the condensation water from load P2 with a temperature of about 75°C to 80°C, thus having a temperature higher than the termperature of the condensation water of load P1 , is further moved from tank 61 to heat-exchange device 10, that transfers also at least part of the energy to the internal volume of container 2. Other heating devices 3 can hereby cooperate to reach the predetermined temperature inside the container. The load P2 condensation water is then transferred to the next tank number 62 in the chain of storage tanks 61 , 62 through the liquid circuit. This water has a lower temperature of about 60 to 65°C. The first tank of the chain, 61 is emptied again.

The condensation water from the first drying process of the load of wood P3 is moved through the drainage means 4 again to the first storage tank 61 , and the cycle can repeat. The potential energy recovery from condensation water of previous cycles with a device as described above, should be appropriately dimensioned, which the skilled person can do.

Figure 5 shows a model similar to that is described in relation to figure 4. This drying device includes the water storage medium 6, four thermally insulated storage tanks 61 , 62, 63, 64 connected to the drainage means 4, and comprises further pumping means to move water between drainage device 4 and respective thermally insulated storage tanks, through piping system 9. The principle of the operation of the drying device is the same as that described in detail in relation to figure 4. However, instead of collecting water from load P1 of heat exchange device 10 to drain 11 , this water, with a decreased temperature, is drained into the third tank 63 in the linear chain of storage tanks 61 , 62, 63, 64. The P3 condensation water is collected in storage tank 61. A new load P4 is added to container 2. The temperature of drying chamber 2 is again increased to a predetermined temperature, consequently making use of the condensation water that has been collected in the first, second and third drying processes, by allowing it to exchange heat with the internal volume of drying chamber 2 in an order of lower to higher temperature (from tank 61 , after tank 62, after tank 63). After exchange of energy with drying chamber 2, the water collected from load P1 is drained from the device heat exchange 10 to the fourth tank 64 in the linear chain of storage tanks 61 , 62, 63, 64. After the exchange of energy with drying chamber 2, the water collected from load P2 is drained from the device heat exchange 10 to the third vessel 63. After the exchange of energy with the drying chamber 2, the water collected from load P3 is drained from the device heat exchangel O to the second vessel 62. The condensed water from P4 is moved to the first tank 61 , during the fourth drying process.

This water collected from load P1 will not be drained to drain 1 until the next cycle, after it has exchanged energy with the drying chamber by means of heat exchange device 0, to increase the temperature of the drying chamber to the predetermined temperature for a fifth load of wood, P5. After this, the condensation water from P2, P3 and P4, with a temperature of condensation water (P1) < temperature condensation water (P2) < temperature condensation water (P3) < condensation water (P4), can exchange energy with the drying chamber by means of heat exchange device 10, and afterwards be moved to the respective storage tank next in the linear chain.

By dimensioning the system differently, the difference in temperature of the condensation water in two consecutive tanks can be kept lower than the example given for the embodiment described in figure 4.

This can lead to more efficient exchange of energy, and more efficient use of energy by the drying machine. It should be noted that the drying device can comprise a chain of three, or a chain of more than four storage tanks, operating based on the same principle. Preferably, the drying device includes four storage tanks.

In certain embodiments, the efficiency of the heat pump could be improved when taking heat out of the condensation water. If the difference in temperature (ΔΤ) between condensation water entering and leaving the heat exchanger is considerably large, that is, larger than 5°C, the efficiency of the heat pump can be improved by working in several steps. For example, by placing two, three, or more heat exchangers in series, and adding / implementing a separate compressor for each heat exchanger. The condensers can preferably be employed as a joint condenser. During the use of a single heat exchanger, the evaporation temperature is lower than the outgoing temperature of the heat exchanger, in order to enable heat exchange. If several heat exchangers are used in series, only the last heat exchanger will work at this evaporation temperature. The preceding heat exchanger(s) work(s) at a higher evaporation temperature, which is closer to the condenser temperature. This will achieve better average efficiency.

For example, if there is a single heat exchanger with an ingoing temperature of 40°C and an outgoing temperature of 20°C, and a ΔΤ of 5°C between the evaporation temperature and outgoing water, the evaporation temperature will be 15°C. If two heat exchangers with separate compressors are placed one after another, the evaporation temperature of the first heat exchanger will be 25°C if the ingoing temperature is 40°C and the outgoing temperature 30°C. The evaporation temperature of the second heat exchanger will then be 15°C with an ingoing temperature of 30°C and an outgoing temperature of 20°C. The average evaporation temperature will then be 20°C, 5°C higher than with a single heat exchanger and compressor.

Different features are sometimes grouped into a single embodiment, figure or description according to the embodiments of this invention, in order to contribute to the concept of one or more of the different inventive aspects of the invention. This should not be interpreted as if all features of the group are necessarily present to solve a specific problem. Whilst the principles of the invention have been described above in relation to specific models, it is to be clearly understood that this description is made only by way of example, and is not limiting the scope of protection that is defined by the appended claims.