Description

According to a first aspect, the present invention relates to a method for thermal treatment of a flowable material.

Flowable material, such as loose press cake, for example, which can be obtained after the production of paper or sludge, can be thermally treated for the purpose of obtaining a dry material. After drying, the material can subsequently be incinerated, for example, after which the residual ash can be used as a raw material, for example for the production of cement.

From GB 952,735 a method and device are known for drying grain, granular material, peas, beans, seeds or the like. The device comprises a number of air chambers located directly above each other, each having a perforated horizontal upper side. Grane is transported in a zigzag pattern from the top to the bottom over successive perforated upper sides. During said transport, the grain falls as a falling curtain between the perforated upper sides located above each other. To dry the grain, cool or cold air is introduced into the lowermost chamber and heated air is introduced in the chambers located thereabove. Said air flows through the perforations of the associated upper sides and through the layer of grain that is present thereon. Subsequently the air is exhausted. Part of the air flows through a falling curtain upon being exhausted.

A device and method for drying finely distributed materials, in particular for drying small grains consisting of coal or minerals is known from GB 839,535.

A drawback of the above methods is the relatively low process intensity, so that a relatively large device is needed for obtaining the desired processing capacity.

Accordingly it is an object of the present invention, according to a first aspect thereof, to provide a method as described in the introduction which has a higher process intensity, making it possible to use a compact, efficient and less costly device.

This object is achieved by the present invention by providing a method for thermal treatment of a flowable material as defined in claim 1 . Because the heated gas is directly supplied to the material falling as a curtain, relatively little energy is lost between the moment the gas exits the treatment means and the treatment of the material. The invention is based on the perception that by bringing the heated gas into direct contact with the falling curtain, the heated air will still possess a maximum amount of energy, as a result of which a relatively large part of the thermal and kinetic energy generated by the burner can be utilised for thermal treatment, so that a high degree of efficiency can be achieved. In this way a relatively high process intensity can be realised, which can result in a desired processing capacity using a relatively small device suitable for drying a wide range of flowable materials, such as residual waste. The dried residual waste can subsequently serve as fuel, for example in the form of pellets. An additional surprising effect that can be achieved with the method according to the invention is that the thermally treated material is practically odourless.

It may also be advantageous if the method comprises the step c) of conveying the material in the treatment chamber in a direction away from the gas inlet opening once the falling curtain has landed on a bottom of the treatment chamber. Such carrying off of the material is advantageous with a view to discharging the material whilst the thermal treatment can be continued to some extent. In addition, the device can thus be continuously operated for a prolonged period of time.

It is advantageous in that case if the material is swirled up in the treatment chamber during step c), wherein the gas flow thermally treats the swirled- up material downstream of the falling curtain and at least in part contributes toward conveying the material in the treatment chamber in the direction away from the gas inlet opening. Swirling up material in the treatment chamber is advantageous with a view to the further thermal treatment of the material after said initial thermal treatment in step b). During said step, part of the residual heat that remains in the gas after step b) is utilised.

It is advantageous if the gas of the gas flow directly in front of the falling curtain has a temperature in the range of 750 to 1700 degrees Celsius, preferably in the range of 900 to 1200 degrees Celsius. Temperatures in the range of 750 to 1700 degrees are advantageous with a view to realising an efficient thermal treatment of the material being supplied, with higher temperatures making it possible to realise a higher processing capacity. Temperatures in the range of 900 to 1200 degrees Celsius are advantageous with a view to realising a relatively simple device on account of the materials that can be used. Higher temperatures would make it necessary to use costlier and more-difficult-to-process materials at locations near the hot gases.

It is advantageous if the material is supplied continuously to the treatment chamber during step a). Supplying material in this way is advantageous for obtaining a relatively high processing capacity. Such a manner of supplying is furthermore advantageous with a view to realising a relatively stable thermal process in the device, in order to thus obtain in a relative constant way comparable thermally treated material, as well as a very efficient energy consumption. Within the scope of the present preferred embodiment, the term "continuous" refers to the situation in which material is supplied to the treatment chamber without any interruptions for at least a few minutes, but in practice also for a few hours or even days.

It is advantageous if the falling curtain has a thickness of at most 10 cm, preferably at most 7 cm, more preferably at most 4 cm during step a). A thickness of the falling curtain of at most 10 cm is advantageous with a view to drying the falling material over the entire thickness of the curtain during step b). If a curtain thickness of at most 4 cm is used, an even more uniform thermal treatment will be obtained during step b).

It is advantageous in this regard if the falling curtain is at least substantially flat. A flat falling curtain is advantageous for obtaining a maximum processing area between the gas flow and the material being supplied. Moreover, a flat falling curtain can be realised with relatively simple means.

It may furthermore be advantageous in this regard if the gas flow in step b), at least directly in front of the falling curtain, has a width and the curtain in step a) has a width, wherein the width of the gas flow is at least substantially the same as the width of the falling curtain. Using the same width for the falling curtain and the gas flow is advantageous with a view to realising a uniform thermal treatment over the width of the falling curtain. Moreover, the gas flow realised by the treatment means is thus substantially fully utilised for the thermal treatment during step b).

Preferably, the falling curtain is uninterrupted in the direction of the width so as to prevent the gas flow from flowing through a possible interruption, which would result in a decreased process intensity. It may be advantageous if the gas flow used in step b) is generated by means of a pulsating burner, so that the heated gas flow is a pulsed heated gas flow. A pulsating burner is advantageous with a view to disturbing the boundary layer of the falling curtain and material present in the falling curtain. By disturbing the boundary layer, a better heat transfer is obtained, thereby realising a better drying result.

Preferably, the gas of the gas flow directly after the falling curtain has a temperature of at most 800 degrees Celsius, preferably at most 300 degrees Celsius. Such gas temperatures are advantageous for the further thermal treatment of the material, wherein combustion of already thermally treated material in the treatment chamber is prevented.

Preferably, the method comprises a step d) of discharging the material that has been subjected to the action of the heated gas flow from the treatment chamber and supplying at least part of said material as fuel to a burner by which the gas is heated. Supplying the material as fuel is advantageous with a view to reducing the amount of residual material and the consumption of energy and fuel.

In a practical embodiment of the method, flowable material is made up of loose press cake. Within the scope of the present invention, the term "loose press cake" is understood to mean a press cake that has been reduced to individual pellets, fragments, grains and/or fibres, wherein the size of the individual pellets, fragments, grains and/or fibres ranges between 1 mm and 2 cm. Moisture present in the loose press cake can be removed from the press cake in an efficient manner, so that this material will be suitable for use as a fuel. It is for example conceivable for the fraction of solid matter to increase from 30 - 50% to 70 - 90%.

According to a second aspect, the invention relates to a device for thermal treatment of a flowable material, for example using a method according to the invention as described in the foregoing, comprising a treatment chamber provided with material supplying means for supplying material to the treatment chamber as a falling curtain via a material inlet opening thereof, heating means for generating a heated gas flow, a gas inlet opening for supplying the heated gas flow to the treatment chamber via the gas inlet opening, wherein the gas flow is directed directly at the falling curtain and also horizontally or at most 45 degrees downwardly, and at least one outlet opening for discharging the material subjected to the action of the heated gas flow and the gas of the gas flow from the treatment chamber, wherein the material supplying means are configured to supply the material to the treatment chamber in the form of a, preferably flat, falling curtain via the material inlet opening. An advantage of such a device is that it can be made relatively compact for obtaining a desired processing capacity. Further advantages are analogous to those of the present method.

For the aforesaid reasons, it may be very advantageous if the material supplying means are configured to continuously supply the material to the treatment chamber.

Preferably, the gas inlet opening is at least substantially rectangular in shape. Using a substantially rectangular gas inlet opening is advantageous with a view to realising a relatively uniform thermal treatment of the falling material over the width of the falling curtain.

Preferably, conveying means are provided in the treatment chamber for conveying material away from the gas inlet opening once the falling curtain has landed on the bottom of the treatment chamber. The presence of such conveying means in the treatment chamber is advantageous with a view to being able to operate the device continuously for a prolonged period of time, which can be realised by continuously discharging thermally treated material.

It is advantageous in that regard if the conveying means comprise a shaft provided with blades, which is rotatable about a horizontal axis of rotation, for swirling up the material in the treatment chamber. In use, a rotating shaft provided with blades is useful for spreading the material in the treatment chamber, so that the gas present in the treatment chamber can subject the material to further thermal treatment.

It is advantageous if treatment means are provided for heating, in use, a gas that is supplied to the treatment chamber via the gas inlet opening. Providing the device with treatment means makes it possible to realise a simpler device in that a connection with external treatment means is not needed for obtaining a heated gas flow.

It may be advantageous if the treatment means comprise a burner.

Using a burner, it is possible to obtain a high heating capacity using a relatively small construction.

It is furthermore advantageous in that regard if the burner is a pulsating burner. A pulsating burner is advantageous with a view to disturbing the boundary layer of the falling curtain and material present in the falling curtain. By disturbing the boundary layer, a better heat transfer is obtained, thereby realising a better drying result.

It may also be advantageous if the heating means comprise a burn- off chamber, which burn-off chamber is provided between the burner and the gas inlet opening and which comprises an air inlet opening for supplying air to the burn- off chamber. The use of a burn-off chamber is advantageous with a view to being able to control the temperature of the hot gas.

Preferably, the treatment chamber comprises a gas outlet opening for discharging the gas from the treatment chamber and a material outlet opening for discharging the material that has been subjected to the action of the heated gas flow from the treatment chamber. The use of an opening configured for discharging gas is advantageous with a view to making it possible to clean and discharge the gas in a relatively simple manner, whilst an opening for discharging the thermally treated material makes it easier to realise a continuous process.

Preferably, the material outlet opening is connected to the heating means for supplying the material to the heating means as fuel. Such a connection is advantageous with a view to making it possible to supply thermally treated material to the treatment means in a simple manner.

The present invention will now be explained by means of a description of a preferred embodiment of a method and devices according to the invention for thermal treatment of flowable material, in which reference is made to the following schematic figures, in which:

Figure 1 is a perspective view of a device according to the present invention;

Figure 2 is a schematic, cross-sectional side view of a device according to the present invention;

Figure 3 is a cross-sectional view along the line E-E in figure 2; Figure 4 is a schematic cross-sectional side view of supply means according to the present invention;

Figure 5 is a schematic view of an embodiment of the heating means;

Figure 6 is a schematic side view of another embodiment of a device according to the present invention. The device 1 is a possible embodiment of a device according to the present invention for thermal treatment of a flowable material 17, such as loose press cake that is obtained after the production of paper or sludge. Loose press cake can be obtained from press cake in ways that are known, for example by crumbling or hammering the press cake, wherein the press cake is reduced to individual pellets, fragments, grains and/or fibres. The device 1 has a treatment chamber 2, which is provided with legs on the underside, near the corners, for supporting the device 1 on the ground. The treatment chamber 2 has a length of 275 cm, a width of 80 cm and a height of 120 cm. Preferably, the treatment chamber has a width of at least 60 cm in order to obtain a processing capacity of at least 1000 kg/h. It is conceivable, however, to make the treatment chamber larger or smaller so as to obtain a device having a different processing capacity. The treatment chamber 2 is provided with a material inlet opening 3 for supplying material 17, such as sewage sludge and/or paper sludge, in direction A to the treatment chamber 2 as a falling curtain. The treatment chamber 2 is further provided with a gas inlet opening 4. The material inlet opening 3 is provided above, i.e. at a higher level than, the gas inlet opening 4. The gas inlet opening 4 is in communication with heating means. In the present embodiment, the heating means are made up of a burner 5 and a burn-off chamber 21 . The burn-off chamber 21 has an opening 24 for supplying air to the burn-off chamber 21 . The burn-off chamber has a downward bend near the gas inlet opening 4. Said bend in the burn-off chamber 21 is provided for reducing a possible flow of material 17 to the burn-off chamber 21. Such a flow in the burn-off chamber can lead to accumulation of material 17, for example due to caking, resulting in a less efficient operation of the device. The treatment chamber 2 is further provided with two outlet openings, a gas outlet opening 6 and a material outlet opening 7. The material outlet opening 7 can be connected, by means of a pipe 22 which is partially shown in figure 1 , to the burner 5 via a connecting opening (not shown) of the burner 5. A screw wheel 28 is provided in the pipe 22 for conveying thermally treated material through the pipe 22.

In the treatment chamber 2, conveying means are further provided.

The conveying means comprise rotary shafts 10, to which blades 11 are connected (shown in a sectional view part of the side view of the device 1 in figure 2). The shafts 10 are driven by electric motors 12. In use, the shafts 10 rotate about the longitudinal axis. The direction of rotation of the shafts 10 is indicated by arrows F and G in figure 3. It is noted that rotation opposite the direction of rotation F and G is also possible, although this is less advantageous for obtaining a good drying result of the material that is swirled up by the blades in use. The bottom side of the treatment chamber 2 is made up of two gutters located beside each other, the diameter of which gutters is larger than the diameter of the combination of a respective shaft 10 and the blades 1 1 attached thereto. A gutter-shaped bottom side of the treatment chamber is advantageous with a view to preventing accumulation of material near corners of the treatment chamber. In the treatment chamber, walls 23a, 23b, 23c and 23d are provided. The walls divide the treatment chamber 2 into several compartments, in which compartments formed by the walls 23a, 23b, 23c, 23d and the sidewall 27 the material is swirled up by the conveying means.

The device 1 is provided with supply means 13 comprising a conveyor belt 14 driven by an electric motor 25. In use, the conveyor belt 14 moves in the direction E. An adjustment element 15 is provided above the conveyor belt 14. The spacing between the bottom side of the adjusting element 15 and the upper side of the conveyor belt 14 limits the through-flow of the material 17. The material is supplied to the conveyor belt 14 upon flowing out of the hopper 16. The width of the conveyor belt 14 is the same as the width b of the gas inlet opening 4, which is substantially rectangular in shape. In the hopper 16 a rotary wheel provided with plate fins 19 is provided. In combination with the wall 20 of the hopper, said plate fins provide at least substantially a substantially airtight seal of the interior space of the supply means 13. This seal prevents air from being sucked into the treatment chamber 2 via the material inlet opening 3 whilst also preventing air from escaping from the treatment chamber 2 via the hopper 16.

According to the invention, flowable material can be thermally treated in the following manner by means of the device 1.

Material 17 to be thermally treated is loaded into the hopper 16, after which it is conveyed on the conveyor belt 14 to the material inlet opening 3 of the treatment chamber 2. The material subsequently falls in the direction A from the conveyor belt 14 into the treatment chamber 2 as a falling curtain. Because the hopper 16 is filled with material 17 at all times and the conveyor belt 14 is continuously in operation, the material is supplied to the treatment chamber 2 in a continuous flow. The burner 5 creates a heated gas flow B, which enters the treatment chamber 2 through the gas inlet opening 4 and directly acts on the falling material. Because the gas inlet opening 4 is substantially rectangular in shape, the falling material is subjected to a substantially uniform thermal treatment across the width b of the material. The gas flow is in that case directed horizontally or at most 45° downwardly. The gas flow thus enters the treatment chamber 2 horizontally or at a downward angle. The temperature of the gas flow passing through the gas inlet opening 4 ranges between 750 and 1700 degrees Celsius. Because the hot gas directly acts on the falling material 17, particles present in the material 17 are preferably heated to a temperature of at most 70 degrees Celsius. Higher temperatures may result in combustion of the material. After this first step of the thermal treatment, the material finds its way to the bottom of the treatment chamber 2. The conveying means then convey the material in the direction C, away from the gas inlet opening 4, toward the material outlet opening 7. In doing so, the conveying means cause the material 17 to swirl up in the compartments formed by the walls 23a-d and 27 in the treatment chamber 2, where the material is subjected to further thermal treatment by hot gas present in the treatment chamber 2. The temperature of the gas in the treatment chamber 2 is lower than 800 degrees Celsius so as to prevent combustion of the material. Once the material has passed the material outlet opening 7, the material is carried through the pipe 22 by the screw wheel 28, whereupon it is supplied to the burner 5 as fuel.

Figure 5 shows an embodiment of the heating means comprising a pulsating burner 50. In use, said burner is pulsed at a frequency ranging between 20 Hz and 200 Hz, preferably at 180 Hz. The heating means further comprise an afterburner 51 and an afterburner chamber 52 for increasing the gas temperature. An inlet 54 is provided between the burn-off chamber 53 and the afterburner chamber 52 for supplying thermally treated material to the hot gas flow, which thermally treated material is incinerated in use. The burn-off chamber 53 is provided with an air inlet 55 for supplying air to the burn-off chamber 53. Furthermore, an air inlet 56 is provided for supplying air to the hot gas flow before said gas flow passes the inlet 54.

Figure 6 shows an alternative embodiment of a device 101 according to the present invention. In figure 5, parts corresponding to parts of the device 1 are indicated by the same numerals augmented by 100.

The device 101 comprises a treatment chamber 102 which is provided with a material inlet opening 103 and a gas inlet opening 104. In the treatment chamber 102, conveying means are provided for swirling up and conveying material 1 17. The treatment chamber 102 is further provided with a gas outlet opening 1 16 and a material outlet opening 1 17. Disposing the burner 105 and the heating means 121 above a part of the treatment chamber is advantageous with a view to further reducing the required floor area of the device according to the present invention.