阅读说明：本技术 用于湿基质的干燥设备及湿基质的相关干燥方法 (Drying apparatus for wet substrates and related drying method for wet substrates ) 是由 保罗·弗朗切斯凯蒂 于 2019-06-28 设计创作，主要内容包括：湿基质(8)的干燥设备(6),包括：空气吹入/抽吸装置(24),其适于产生至少一个指向至少一个干燥室(12)内的湿基质(8)的干燥流,以便于除去所述湿基质(8)中的水；及在干燥设备(6)内输送湿基质(8)的装置(28),包括沿纵向方向(X-X)输送湿基质(8)的输送带(32)。有利地,所述干燥设备(6)包括至少一个热交换器(80),其被冷却至露点温度以下,以冷凝来自于湿基质(8)的空气中的水汽。(Drying apparatus (6) for a wet substrate (8), comprising: -air blowing/suction means (24) adapted to generate at least one drying flow directed towards the wet substrate (8) inside at least one drying chamber (12) in order to remove the water from said wet substrate (8); and means (28) for conveying the wet substrate (8) inside the drying device (6), comprising a conveyor belt (32) for conveying the wet substrate (8) along a longitudinal direction (X-X). Advantageously, the drying device (6) comprises at least one heat exchanger (80) cooled below the dew point temperature to condense the water vapour in the air coming from the wet substrate (8).)

1. Drying apparatus (6) for a wet substrate (8), comprising:

-air blowing/suction means (24) adapted to generate at least one drying flow directed towards the wet substrate (8) inside at least one drying chamber, so as to remove the water in said wet substrate (8);

-means (28) for conveying the wet substrate (8) inside the drying apparatus (6), comprising a conveyor belt (32) for conveying the wet substrate (8) along a longitudinal direction (X-X);

the method is characterized in that:

the drying apparatus (6) comprises at least one heat exchanger (80) cooled below the dew point temperature to condense water vapour from the air of the wet substrate (8).

2. Drying apparatus (6) according to any of the preceding claims, wherein the drying stream is recirculated through two heat exchangers (80), one being a cooled heat exchanger (82) and the other being a superheating heat exchanger (84), in order to first dehumidify and then superheat/dry the recirculated air.

3. Drying apparatus (6) according to claim 2, characterised in that the heat exchangers (80,82,84) are integrated in the same heat pump (88) to condense water vapour from the air originating from the wet substrate (8) being dried by means of the cooled heat exchanger (82) and then to superheat the same air by means of the superheating heat exchanger (84).

4. Drying apparatus (6) according to claim 2 or 3, wherein the heat exchangers (82,84) are connected to each other in series by at least one fan (86), the fan (86) generating an air flow through the heat exchangers (82,84) connected to each other in series.

5. Drying apparatus (6) according to any of claims 2-4, characterized in that the drying apparatus (6) comprises a closed air circuit through the heat pump (88) and the heat exchanger (80,82, 84).

6. Drying apparatus (6) according to any of claims 2-5, characterized in that the air circuit is made so as to ensure its airtightness and the continuous recirculation of only air inside it and inside the drying chamber (12).

7. Drying apparatus (6) according to any of claims 2-6, wherein the superheating heat exchanger (84) has a series-connected double circuit comprising a coolant supply circuit (92) and a coolant return circuit (94).

8. Drying apparatus (6) according to claim 7, characterized in that a cooling heat exchanger (96) is interposed between the coolant supply and return circuits (92,94), which is adapted to reduce the excess heat originating from the drying apparatus (6) and to prevent thermal shock within the superheating heat exchanger (84).

9. Drying apparatus (6) according to claim 8, wherein the cooling heat exchanger (96) has two streams, one being a coolant liquid and the other being a cold liquid or air.

10. Drying apparatus (6) according to any of claims 2-9, characterized in that the air flow delivered to the drying chamber (12) is divided into two separate circuits, whereas the coolant circuit is unique, divided in parallel over two cooled heat exchangers (82) and two superheated heat exchangers (84).

11. Drying apparatus (6) according to any of claims 2-10, characterized in that the cooled heat exchanger (82) is provided with a cleaning system (100) adapted to remove solid residues of the wet substrate entrained by the air.

12. Drying apparatus (6) according to claim 11, wherein the cleaning system (100) comprises a plurality of nozzles supplied with water at such a pressure as to ensure the shedding of wet matrix material (8) adhering to the surface of the cooled heat exchanger (82).

13. Drying apparatus (6) according to any one of claims 1-12, wherein the conveying means (28) comprise at least one input roller (36), the input roller (36) being arranged so as to intercept the wet substrate (8) carried by the conveyor belt (32), and the input roller (36) being arranged along a transverse direction (T-T) perpendicular to the longitudinal direction (X-X), wherein between the input roller (36) and the conveyor belt (32) a slit (40) is defined which constitutes an inlet filter with a thickness of the wet substrate (8) which is at most equal to the height of the slit (40).

14. Drying apparatus (6) according to claim 13, wherein the shape of the slit (40) is such that the wet substrate (8) constitutes an obstacle to the input of air from the outside into the drying apparatus (6).

15. Drying apparatus (6) according to any of claims 1-14, wherein the conveyor belt (32) is inclined at an angle between 20 ° -30 ° with respect to the horizontal.

16. Drying apparatus (6) according to any one of the preceding claims, wherein the conveyor belt (32) is inclined with respect to the horizontal plane by an angle related to the transverse width of the conveyor belt (32) and to the physical properties of the wet substrate (8) being treated, this angle being represented by the following formula: a θ L/2, where a is equal to the angle of inclination of the inclined conveyor belt (32), L is equal to the width of the conveyor belt (32), and θ is equal to the typical angle of repose of the wet substrate to be treated.

17. Method for drying a wet substrate (8), comprising the step of conveying at least one wet substrate (8) within a drying apparatus (6) according to any one of the preceding claims.

18. Drying method according to claim 17, characterised in that the main drying force is not at the temperature of the incoming air, but at the vapour pressure difference between the wet substrate (8) and the relative humidity of the air.

19. Drying method according to claim 17 or 18, characterised in that the air circulation and its dehumidification are carried out by means of a heat exchanger (80) cooled below the dew point temperature to condense the water vapour from the air coming from the wet substrate (8).

20. Drying method according to any one of claims 17 to 19, characterised in that it provides the step of introducing air at a temperature of between 50 ℃ and 75 ℃ into the drying device (6) in order to reduce as far as possible the relative humidity of the drying air and to thermally promote the drying of the wet substrate (8) itself.

21. Drying method according to any one of claims 17 to 20, characterised in that it provides the step of recirculating the same air inside the drying apparatus (6) in order to obtain a closed system, so as not to be vented to the atmosphere, while maintaining the uniform performance of the drying apparatus (6).

Technical Field

The present invention relates to an apparatus for treating and drying wet substrates and related methods of treating and drying wet substrates.

Background

First of all, the invention can be applied, in particular but not exclusively, in the field of the treatment and drying of wet materials or substrates (for example, food products) and/or in the field of sludges of various origins, in order to reduce the water content and/or other volatile compounds thereof and moisture of different nature.

As is well known, there are various systems for drying wet substrates on an industrial and technical level. Worldwide, there are systems aimed at optimizing the process of removing the water present in the substrate one wishes to dehydrate. Over the years, various techniques have been developed, including the use of Microwave Systems (MADs), Radio Frequency (RFDs), or infrared drying devices (IRDs). The most cost effective, reliable and global method is the drying chamber, where the temperature is raised, waiting for the water to evaporate from the solid matrix. In recent decades, ventilation of the drying chamber by hot air injection (AD) has been added to simple superheating. Indeed, it has been shown that the aeration contributes to a significant reduction in drying time and to an increase in drying efficiency. The ventilation mainly affects the formation of a dry environment inside the drying apparatus, removing the water vapor generated by the evaporation of the wet substrate, thereby forming a dry environment stimulating its evaporation.

Known hot air drying devices usually have two energy supply sources, one being a heat source and the other being a power source, the latter being used for drying the movement of the room air. The higher cost of managing the drying apparatus results from the large consumption of energy (fuel or electricity) required to raise the temperature of the air introduced into the system. Currently, the operating costs of extracting one ton of water from a wet substrate vary from 20 to 60 euro, values which vary according to the type of material treated and the optimization of the drying equipment used and the fuel used to generate the heat. To overcome these management costs, research is being conducted to allow the finding of alternative economical energy sources (e.g., solar radiation or renewable resources) and methods of managing the efficiency of the superheated air stream.

For the air streams, they have to perform various functions to achieve maximum efficiency of extracting water from the wet substrate during drying. These requirements are as follows:

the drying chamber is ventilated uniformly to ensure uniform treatment of the entire product to be dried;

-removing steam from the material being dried quickly and efficiently to assist in quick drying;

lower ventilation and lower thrust pressure to reduce the electrical consumption of the moving parts (fans) and the energy consumption for heating the air mass.

Then, there are specific technical problems related to the type of wet substrate to be treated.

The density and physical shape of a wet substrate, particularly of biological origin, varies according to its water content. Typically, the moisture content of the wet substrate in the scoopable state is 86% to 70% by weight. These matrices tend to form aggregates due to the physical and chemical characteristics that constitute them, which can create difficulties in their management and handling by mechanical means. For this purpose, a wet substrate loading system is installed inside the drying oven for the purpose of maintaining a constant particle size, distribution over the entire width of the worktable and preventing the formation of "bridges" inside the hopper and inside the entrance of the drying oven.

Another problem found was the reduction in the volume of wet matrix during the drying step. When the water in the wet matrix is removed, it undergoes a granulation agglomeration process and a significant volume reduction (up to 60% of the initial volume). The reduction in volume can lead to empty spaces within the conveyor belt within the drying apparatus, resulting in a loss of efficiency ("useful air" loss) during the drying process. This loss is even more pronounced if the process takes place in a closed loop air drying plant (the air mass is cooled and superheated by heat exchangers that are cooled or heated by heat pumps (but not just heat pumps, but also others) respectively by fluids or vapours of different temperatures). This loss of "useful air" can lead to thermal drift of the system itself, particularly of the heat pump, leading to excessive temperatures and reduced efficiency.

In order to improve the energy efficiency of the treatment and drying equipment of the wet substrate, heat pump systems are introduced.

These heat pump systems significantly reduce energy consumption, but are extremely sensitive to the type/particle size of the wet substrate to be treated: in other words, the efficiency obtainable by using a heat exchanger, wherein the main drying force of the drying is not at the temperature of the incoming air, but at the vapour pressure difference between the relative humidity of the sludge and the air. In fact, in these systems, the efficiency is closely related to the degree of fragmentation or particle size of the wet matrix, which must be carefully controlled to exploit all the energy saving advantages associated with the use of the heat pump. In the prior art, current heat pump systems do not allow to fully exploit the advantages obtainable by using heat pumps, in which case the main drying force is not at the temperature of the incoming air, but at the vapor pressure difference between the relative humidity of the sludge and the air.

Disclosure of Invention

In view of the foregoing, it is clear that the solutions of the prior art do not allow to realize drying apparatuses that can extract water in a wet matrix efficiently during drying, while ensuring a low energy consumption.

Accordingly, there is a need to provide an apparatus or device that can dry wet materials in a drying chamber efficiently and at low cost. These needs are met by a drying apparatus for wet substrates as claimed in claim 1 and a method of drying wet substrates as claimed in claim 17.

Brief description of the drawings

Further characteristics and advantages of the invention will become better apparent from the following description of a preferred but not limiting embodiment thereof, in which:

fig. 1 is a perspective view of a system for loading wet substrate or sludge of a drying apparatus according to an embodiment of the present invention;

FIG. 2 is a side view of the sludge loading system of FIG. 1 from the side of arrow II in FIG. 1;

FIG. 3 is a plan view of the sludge loading system of the drying apparatus of FIG. 1, as seen from the side of arrow III in FIG. 1;

FIG. 4 is a partial side cross-sectional view of the apparatus for loading wet substrate (sludge) of the drying apparatus of FIG. 1, as seen from the side of arrow IV in FIG. 1;

FIG. 5 is a side view of the apparatus for loading wet substrate (sludge) of the drying apparatus of FIG. 1, as seen from the side of arrow V in FIG. 1;

6-7 are side views of the input roll of the apparatus for loading wet substrate (sludge) of the drying apparatus of FIG. 1 at different angles according to one embodiment of the present invention;

fig. 8-10 are a perspective view and two side views, respectively, of an intermediate crusher system of a drying apparatus of the invention according to a possible embodiment of the invention;

FIGS. 11-12 are perspective views of internal components of a drying apparatus according to an embodiment of the present invention;

the same elements or parts of elements as those of the embodiments described below are denoted by the same reference numerals;

fig. 13 is a perspective view of a system for loading wet substrate or sludge of a drying apparatus according to another embodiment of the present invention;

FIG. 14 is an enlarged perspective view of detail XIV shown in FIG. 13;

FIGS. 15-16 are views of the detail shown in FIG. 14 at different angles;

fig. 17 is an enlarged perspective view of detail XVII shown in fig. 14;

FIG. 18 is a schematic diagram of the operation of the apparatus of the present invention.

Detailed Description

With reference to the above figures, the reference numeral 4 generally designates the device for loading wet substrate (sludge) of the drying device 6 for wet substrate 8 of the present invention.

It should be noted that the particular type of wet substrate is not critical for the purposes of protecting the present invention. For example, while the apparatus is primarily intended for use with loose wet substrates, it may also be suitable for use with wet materials of connectivity, such as surfaces or fabrics, which require drying.

The wet substrate may also be food grade.

The drying device 6 of the wet substrate (sludge) 8 comprises a container body 10, the container body 10 delimiting a drying chamber 12 suitable for containing at least one wet substrate to be dried according to a predetermined degree of dryness. The predetermined degree of drying means that the wet substrate may have a residual moisture content at the end of the drying process, according to the user's requirements. The degree of dryness may be determined by the user in accordance with suitable parameters of the apparatus, as described in detail below.

The drying chamber 12 is of a suitable insulating material so as not to disperse the flow of fluid heat (preferably hot air) blown therein, and the drying chamber 12 is of an airtight seal.

The container body 10 or hopper extends from an inlet 16 for introducing the wet substrate 8 to be dried to an outlet 20 for defining a layer of material into a drying chamber of a drying apparatus for the wet substrate. The outlet 20 is constituted by a baffle (bulkhead) able to isolate the interior of the drying chamber from the external environment in cooperation with the wet material 8.

The drying device 6 comprises air blowing/suction means 24 adapted to generate and send a flow of drying fluid (for example, air) on the wet substrate 8 inside said drying chamber 12 to remove the water vapour and/or water from said wet substrate 8. It is of course preferred to use air as the drying medium; however, in any case, other gaseous drying media may be used.

The blowing/suctioning device 24 may include a forced draft device (e.g., a fan (not shown)) and a natural draft device (e.g., a chimney (not shown)) to produce a desired fluid flow rate.

The invention is particularly advantageous and is synergistically associated with the inherent features of the belt dryer apparatus 6 with low temperature air recirculation, for which the main drying power is given by the vapour pressure difference of the air humidity.

In particular, from a fluid-dynamic and thermodynamic point of view, as mentioned above, the drying device 6 comprises an air blowing/suction device 24 suitable for generating and sending a flow of drying fluid (for example, air) on the wet substrate 8 inside said drying chamber 12, so as to remove the water vapour and/or water from said wet substrate 8.

According to a possible embodiment, the drying device 6 comprises at least one heat exchanger 80 cooled below the dew point temperature in order to condense the water vapour in the air coming from the humid substrate 8.

Preferably, the drying stream is recirculated through two heat exchangers, a cooling heat exchanger or evaporator element 82 and a superheating heat exchanger or condenser element 84, to first dehumidify and then superheat/dry the recirculated air.

The heat exchangers 82,84 may be integrated into a single heat pump 88. The heat pump 88 finds its essential application in the present invention, allowing the condensation of moisture from air derived from the dried wet substrate 8 by the cooled heat exchanger 82, followed by heating of the air by the superheated heat exchanger 84.

The heat exchangers 82,84 are connected to one another in series by at least one fan 86, the fan 86 generating an air flow that can flow through the heat exchangers 82,84 connected to one another in series, as described below.

Condensing the moisture and possible contaminants allows the drying device 6 to recirculate the same air, avoiding the emission outside the drying device 6. Drying apparatus 6 with closed air circuit by heat pump 88, preferably but not exclusively CO, in order to improve its performance₂As the refrigerant gas, thereby ensuring a higher air superheat temperature than other refrigerant gases.

The production of drying apparatuses 6 for wet substrates 8 with a closed air circuit involves a problem known as "thermal drift", which leads to an increase in the internal temperature of the drying apparatus 6 over the course of the treatment time.

For this purpose, a suitable circuit of coolant liquid and superheating heat exchanger 84 configuration is necessary. In this description, the superheating heat exchanger 84 has a dual circuit in series, including a coolant supply circuit 92 and a coolant return circuit 94.

Preferably, between said coolant supply and return circuits 92,94, a further heat exchanger is interposed, i.e. a cooling heat exchanger 96 adapted to reduce the excess heat originating from the drying apparatus 6.

The cooling heat exchanger 96 has two streams, one being a coolant liquid and the other being a cold liquid or air.

The combination of the superheating heat exchanger 84 and the cooling heat exchanger 96 allows the drying apparatus 6 to be kept at a constant heat balance and to obtain optimum performance in order to dry the wet substrate 8 present therein. In other words, the presence of a closed circuit of air inside the drying apparatus 6 necessarily requires a controlled heat diffusion (interposed cooling heat exchanger 96).

The process of extracting the water contained in the wet matrix 8 is ensured by using the heat pump(s) 88, according to an embodiment, the heat pump 88 may provide a supply of CO₂The use of a coolant.

Specifically, the air flow passing over/in contact with the moist substrate 8 is collected and sent to the cooled heat exchanger 82, which dehumidifies and cools the air, which is drawn in by the fan element 86, which fan element 86 pushes the air through the superheating heat exchanger 84, and the heat exchanger 84 raises the temperature and lowers the relative humidity. According to a possible embodiment, the air flow delivered to the drying chamber 12 is divided into two separate circuits; while the coolant circuit is unique and split in parallel (one for each air circuit) over the two cooled heat exchangers 82 and the two superheated heat exchangers 84 to better control the exchange efficiency between the air and wet substrate 8 that cross/overlap at two different areas: the first air circuit treatment involves a flow of a first portion of the wet substrate 8, the arrangement of which on the conveyor belt 32 is given by the hopper loading system 10 and contains a large amount of water; while the second air circuit handles a flow involving a second portion of the wet substrate 8, which is disposed on the conveyor belt 32 as a result of the intermediate moving element 64 material or substrate tumbling (inverting), and which has a lower average moisture content than the first portion of the wet substrate 8. The air circuits are made to ensure their airtightness and the continuous circulation of only air inside them and inside the drying chamber.

The cooling and superheating heat exchangers 82,84 and 96 are in communication on the coolant side, preferably but not exclusively, through a thermostatic expansion valve, a liquid receiver, a heat recovery unit and a compressor.

The coolant loop of the superheating heat exchanger 84 may, for example, be interrupted to ensure that the heat accumulated by the system is handled as necessary to minimize the adverse impact on the overall efficiency of the thermodynamic process.

According to a possible embodiment, the cooled heat exchanger 82 is provided with a cleaning system 100 capable of removing solid residues entrained by the air that may get stuck between the surfaces of the heat exchanger 82 itself. Preferably, but not exclusively, the cleaning system 100 comprises a series of nozzles supplied with water at a pressure that ensures the shedding of wet matrix material 8 adhering to the surface of the cooled heat exchanger 82.

The drying apparatus 6 further comprises means 28 for conveying the wet substrate 8 within the drying apparatus 6.

For example, the conveying device 28 comprises a hopper 30 into which the wet substrate 8 to be treated can be poured and a conveyor belt 32 arranged along an inclined surface 34, the conveyor belt 32 carrying the wet substrate 8 along a longitudinal direction X-X.

Advantageously, the conveying means 28 comprise at least one input roller 36 for intercepting the wet substrate 8 carried by the conveyor belt 32.

The input rollers 36 are arranged in a transverse direction T-T perpendicular to the longitudinal direction X-X and rotate about an axis of rotation R-R parallel to the transverse direction T-T.

Between the input rollers 36 and the inclined surface 34 of the conveyor belt 32, a slit 40 is defined, which constitutes an inlet filter with a thickness of the wet substrate 8, which is at most equal to the height of said slit 40.

Said slit 40 in cooperation with the outlet 20 is therefore shaped so that the moist substrate 8 constitutes a cover for introducing air from the outside into the interior of the drying apparatus 6, so as to achieve a closed system which does not introduce air from the outside and which does not receive air from the outside.

Preferably, the shape of the input rollers 36 is such as to distribute the wet substrate 8 across the width of the conveyor belt 32 and to break up wet substrate agglomerates 8 having a diameter or thickness greater than the slits 40.

According to one embodiment, the input roll 36 is a hollow roll having a plurality of screen walls 44 for the wet substrate 8 adapted to comminute agglomerates of the wet substrate 8.

According to one embodiment, the input roller 36 includes a plurality of rods 48, the rods 48 being angularly disposed at a constant spacing to be spaced apart from one another and to define continuous or spaced cavities 52 between the rods 48.

The rods 48 serve as a screen wall 44 for the wet substrate 8.

Preferably, the bar 48 is parallel to the axis of rotation R-R of the input roller 36.

Preferably, the rods 48 are oriented radially with respect to the axis of rotation R-R of the input roller 36.

According to an embodiment, said bar 48 is fixed to a plate or support 56, the plate or support 56 being fixed to the rotation axis R-R of the input roller 36, so as to have no surface to which the wet substrate to be treated adheres, enabling a better management of the quantity of material moving towards the outlet 20 of the drying apparatus 6.

Thus, the support 56 serves to stiffen the structure of the input roll 36, while having as small a thickness/dimension as possible to facilitate passage of the wet substrate.

Preferably, the hollow input roller 36 counter-rotates about the rotation axis R-R with respect to the direction of advance of the conveyor belt 32 carrying the wet substrate 8. In this way, the effect is obtained that the excess wet material falls back due to the effect of gravity to the correct introduction into the loading device 4.

The conveyor belt 32 is provided with a blading 60 preventing slippage of the wet substrate 8 carried by the conveyor belt 32 itself.

Because the conveyor belt 32 is not flat but is inclined at an angle of 20-30 to the horizontal, the blade arrangement 60 can also be used to counteract the effects of gravity. Preferably, said angle of inclination is equal to 24 °. More generally, the conveyor belt 32 is inclined relative to the horizontal by an angle associated with the lateral width of the conveyor belt 32, as shown by the following equation: where α is the angle of the inclined conveyor belt 32, L is the width of the conveyor belt 32, and θ is the typical angle of repose of the wet material 8 to be treated. The latter derives in a known manner from the adhesive properties and the static friction coefficient of the treated wet material.

According to an embodiment, the drying apparatus 6 comprises an intermediate tilting system 64 located inside the container body 10 of the drying apparatus 6, which intermediate tilting system 64 is capable of intercepting and moving the whole piece of material, i.e. the whole piece of material of the wet substrate 8, during the drying step.

Preferably, said intermediate crushing system 64 is located approximately in the middle of the entire path of the conveyor belt 32 inside the container body of the drying apparatus 6, in a position suitable for the wet material 8 to produce a first surface drying step, avoiding the possibility of recondensation of the wet material 8 itself.

In fact, sludge of biological origin will show variable behaviour during the drying step. It has been scientifically proven that biological materials have a transition phase during drying, called "sticky phase", which accounts for 20-60% by weight of dry matter. In this step, the material is particularly sticky, tending to cause the material to block internally, while sticking externally to the contact surface. Once above 60% concentration, internal adhesion and sludge internal to surface adhesion are lost, resulting in a significant reduction in the tendency and volume of the agglomerates to break up.

Through a series of tests carried out on the treated material, it was observed that sludge agglomerates covered with dehumidified air (for example, at temperatures between 50 ℃ and 75 ℃) would form a particularly dry surface layer, which can be defined as "crust" (crust), which slows down the drying of the whole mass inside the agglomerate. It is therefore necessary to locate the intermediate motion system 64 within the drying apparatus 6 in a position to break up the agglomerates after they have formed the first non-tacky outer "crust" to break up these agglomerates and allow the drying air to dry the interior thereof.

If the crushing movement system is placed at the beginning of the drying process, it is observed that the sludge or wet matrix 8 re-agglomerates, thus eliminating the effect of the crushing system itself. On the contrary, the formation of new agglomerates can be avoided, since a dry and no longer tacky surface is formed first.

Preferably, the intermediate movement system 64 is located in a position inside the drying apparatus 6 that is not covered by the air flow, thus avoiding the dispersion of the material moving inside the container body 10. Therefore, the localized area of the intermediate motion system 64 should preferably be free of dry air input to avoid diffusion of the finer material.

The transverse width of the rotating bar 68 is equal to the transverse dimension of the conveyor belt 32.

The operation of the drying apparatus of the present invention and the related drying method will be described below.

Specifically, the wet substrate 8 is introduced through the hopper 30 onto the conveyor belt 32, the conveyor belt 32 being inclined at an appropriate angle with respect to the horizontal.

The conveyor belt 32 is provided with a vane arrangement 60 to prevent "bridging" along the incline or slippage between the sludge and the belt. In front of the top end of the conveyor belt 32, an input roller 36 is placed, the input roller 36 being motorized and rotating in the opposite direction to the advancing direction of the conveyor belt 32. The input roller 36 is constituted by a central rod on which at least two circular plates 56 of the same diameter are hooked and fixed. On these circular plates, the rotating rods 68 are preferably metallic but not exclusively fixed perpendicular to the circular plate 56 and preferably radially fixed with respect to the axis of rotation of the input roller 36.

With this arrangement, the input rollers 36 are able to break up the wet substrate 8 into smaller pieces and also distribute it across the transverse width of the conveyor belt 32.

Meanwhile, since an internal space is formed between the rotating rod 68 and the rotating shaft of the input roller 36, the input roller 36 can prevent the process from being blocked. The combined action of the conveyor belt 32 and the counter-rotation of the input rollers 36, which conveys the sludge material or wet substrate 8 upwards as described above, only results in that the sludge or wet substrate 8, the thickness of which is comprised between the conveyor belt 32 and the input rollers 36, continues to rise along the determined slope of the conveyor belt 32, while the material, the particle size of which is larger than the distance between the above-mentioned input rollers 36 and the conveyor belt 32, falls downwards under the influence of gravity.

The combined action of the two opposing forces (the raising of the belt 32 and the lowering of gravity) creates a zone of swirling downward motion of the wet substrate immediately in front of the input rollers 36. This movement may cause the sludge to move towards its outward opening, thus causing the distribution of the wet substrate 8 over the entire transverse width of the conveyor belt 32 and thus to the inlet of the drying chamber 12. Thus, there is an accurate relationship between the inclination of the conveyor belt 32 and its transverse width. In addition to the distribution of the material, the falling of the material can also lead to the breaking of larger sludge agglomerates. This disruption is facilitated by the structure of the input roll 36 itself, which, together with its rotating shaft 68 (preferably rectangular) disrupts the surface of the agglomerate.

The input rollers are purposely constructed internally empty to prevent structural failure due to the presence of larger solid materials (which are not infrequently present in the operating environment) and mixed with sludge. Without the voids, these solid materials would actually be present between the conveyor belt 32 and the input rollers 36.

Finally, the characteristics of the empty input roller 36 allow for no sludge accumulation points on the input roller itself, given the substantial viscosity of the wet substrate 8. If there is a solid cylinder with an external rod, a layer of sludge material will be formed in a shorter operation time, which will eliminate the presence of the rotating rod 68. The lack of an inner surface allows the sludge material to accumulate only minimally on the rotating rods 68, but in any event does not form a substantial layer of sludge, since excess wet substrate 8 will fall into the input rollers 36 and thus (due to the gaps between the rods) fall onto the underlying conveyor belt.

Once through the screen formed by the input rollers 36, the wet substrate again enters the drying chamber 12 by virtue of the conveyor belt 32, where it is subjected to a flow of drying air within the drying chamber 12. The sludge 8, before entering the drying chamber 12, encounters another slot or outlet 20, the height of which is equal to or slightly less than the distance between the conveyor belt 32 and the input roller 36. In view of the size of this slit or outlet 20, it allows to slightly slow down the speed of the wet substrate 8 and thus to form a plug of the inlet and/or outlet of the outside air inside the drying chamber 12.

Preferably, according to the invention, the sludge or wet substrate 8 is dried at 50-75 ℃ by air recirculation, subjected to a dehumidification step and subsequently to an overheating and relative humidity reduction step.

In particular, it is observed that the main drying force of the evaporation is not at the evaporation temperature of the sludge or wet substrate 8, but at the vapor pressure difference between the sludge or wet substrate 8 and the air relative humidity.

For example, the air is circulated and dehumidified by a heat exchanger 82 cooled below the dew point temperature to condense moisture from the air in the wet substrate.

Preferably, a step of recirculating the same air inside the drying apparatus 6 is provided, so as to obtain a closed system, so as not to be vented to the atmosphere and to maintain the uniform performance of the drying apparatus.

Thus, the drying apparatus 6 does not introduce air at all nor discharge it outside, to avoid unbalances of humidity management and loss of efficiency inside the drying chamber 12.

The at least partially dried material in the drying chamber 12 is further subjected to a crushing action by an intermediate crushing system 64.

Indeed, as can be seen, the sludge of biological origin exhibits a variable behaviour during the drying step: the biomaterial has a transition phase, called the "sticky phase", during drying, which represents 20% to 60% by weight of dry matter. In this step, the material is particularly tacky, causing the material to block internally while allowing the external portion to adhere to the contact surface. Once above 60% concentration, internal adhesion and adhesion to the surface within the sludge is lost, resulting in a significant reduction in the tendency and volume of the agglomerates to break up.

Sludge agglomerates covered with dehumidified air (e.g., at temperatures between 50 ℃ and 75 ℃) can form a particularly dry surface layer, which can be defined as "crust" (crust), which can slow the drying of the entire material within the agglomerate. It is therefore necessary to arrange an intermediate breaker system 64, which is specifically built into the drying apparatus 6, in a suitable position to break up the agglomerates after the first non-sticky outer "crust" has been formed, to break up these agglomerates and to allow the drying air to dry the interior.

As will be appreciated from the description, the present invention overcomes the disadvantages of the prior art.

In fact, the present invention can achieve complete drying at a lower cost.

The present invention therefore provides a loading system in an oven for drying a wet substrate, suitably designed not to create "bridges" of material, while distributing the material evenly over the entire width of the conveyor belt.

Furthermore, the invention consists in an embodiment of a system which is suitable for crushing the material to be dried in order to make the agglomerate size uniform and which is located in a suitable position within the drying apparatus so as not to undergo a new formation of the agglomerate itself.

The apparatus has a condensation and superheating system of the air circulating in the drying oven to remove the moisture from the wet material, which combines, among other things, a reduction in the relative air humidity with the mechanical action of the air itself. The apparatus also comprises a system managed by one or more heat pumps or fluids, capable of generating cold surfaces for condensing the water vapour and overheated surfaces due to the increase of the air temperature and the consequent decrease of its relative humidity.

Since the wet substrate is processed both at the inlet and inside the drying apparatus, the use of the heat pump is optimized: in this way, the energy performance of the drying is maximized, thereby facilitating the dehumidification of the wet material, which combines the reduction of the relative humidity of the air with the mechanical action of the air itself.

A person skilled in the art may apply to the drying apparatus and to the drying method described above many variations and modifications to meet specific and contingent needs, all of which fall within the scope of the invention as defined by the appended claims.