FR3027378A1 - DEVICE FOR DRYING MATERIALS AND ASSOCIATED METHOD - Google Patents

Abstract

The present invention relates to a material drying device comprising a structure (11) comprising: - a floor (12) receiving the materials to be dried, - a first hot water circulation circuit placed under at least a part of the outer surface of said soil (12) for heating thereof, and - a second hot water circulation circuit and a cooling assembly (17) of said second hot water circulation circuit, - said cooling assembly (17) generating air flows directed to the interior volume of said structure so as to heat said materials after said air flows have achieved heat exchange with said second hot water circulation circuit.

Description

FIELD OF THE INVENTION The present invention relates to a device for drying materials. The invention also relates to the associated method. The invention has applications in many fields and can, for example, be used to dry wood logs or wood chips resulting from the grinding of wood.

State of the art For decades, firewood has traditionally been dried in the form of ridges, usually 2.5m long. These ridges are exposed to wind and sun in order to evacuate moisture. In addition, they are watered regularly to eliminate attacks of fungi and insects. This drying period is between fourteen and eighteen months and drying under shelter can only be done under good ventilation conditions. It is only after this drying period that the wood can be cut to a desired length and split. This storage has of course a cost, and produces a relatively wet wood (around 35% humidity) which ignites badly but which has the advantage of burning slowly. The wood thus cut and split must then be put under shelter to limit the resumption of moisture.

The major drawbacks of this traditional drying are based on the multiple manipulations that the wood must undergo between the cutting of the trees and the delivery of the dry wood, cut to the desired length and split. The drying time of the wood depends on the position of the moon at the time of cutting inducing a rise or descent of sap. Thus, the drying time is between fifteen and twenty-four months.

In order to reduce drying times, covered, ventilated and heated drying devices have been developed. These drying devices comprise a structure provided with ventilation. The wood is arranged in the structure and the ventilation is provided by air-coolers that push heated air through the cells of the structure. The air is heated either by gas or oil or by solar energy combined with heat pumps. The length of the cells of the structure is limited in size because the first products to dry capture a lot of calories, and reject all their moisture to the following. The latest products therefore receive a much less hot and very humid air. In an attempt to overcome this problem, a known solution is to use a high temperature, minimum 90 ° C, to reduce heat losses. With these known drying devices, the drying time is of the order of one month, to obtain an average humidity of 35%.

These drying devices have several disadvantages. At first, these devices impose a high energy consumption to obtain a minimum temperature of 90 ° C. Then, depending on the position of the products to dry their hydrometry is different at the end of the drying cycle. Indeed, the proximity or distance of the heating source and the position in the structure at the bottom or top of the wood pile are important sources of differentiation of the hydrometry obtained. In addition, these drying devices limit the positioning possibilities of the products to be dried in the structure because the products to be dried easily burn if they are placed too close to the heat source or dry very badly if they are located too far from the source of heat. These drying devices also generate significant condensation in the structure due to temperature differences. DISCLOSURE OF THE INVENTION The present invention intends to respond to the problems of drying devices of the prior art by proposing, in a first aspect, a device for drying materials.

For this purpose, the present invention relates to a material drying device comprising a structure comprising a floor receiving the materials to be dried, a first hot water circulation circuit placed under at least a portion of the external surface of said floor to heat the floor. and a second hot water circulation circuit and a cooling assembly of said second hot water circulation circuit, said cooling assembly generating air flows directed towards the interior volume of said structure so as to heat said materials after said air flows have achieved heat exchange with said second hot water circulation circuit.

The invention thus makes it possible to improve the homogeneity and the control of the moisture content of the materials during drying. Indeed, the floor heating provides a vertical flow of calories ensuring a better temperature homogeneity than conventional devices. In addition, the combination of underfloor heating and ventilated heating considerably reduces the heterogeneity of the materials to be dried. According to one embodiment, said cooling assembly generates air flows parallel or substantially parallel to the surface of said floor. According to one embodiment, said cooling assembly comprises air-cooling devices. According to one embodiment, said cooling assembly being placed at a first end of said structure, said device comprises at its end opposite said first end at least one air extractor for extracting air from the interior volume of said structure . This embodiment makes it possible to propel the calories of the air coolers and to evacuate the humidity. The extractors thus provide ventilation through the materials to be dried. According to one embodiment, said first and second hot water circuits are connected to a single hot water supply circuit.

According to one embodiment, the temperature of the hot water of the single hot water supply circuit is between 40 ° C and 50 ° C. This embodiment makes it possible to limit energy consumption by using a lower temperature than the devices of the prior art. In addition, the water can be recovered from a conventional cooling circuit, for example a nearby plant. According to one embodiment, the device comprises a transparent or translucent cover. Advantageously, said cover is made of glass. This embodiment makes it possible to obtain good capture of the sun's rays. According to one embodiment, the structure is divided into several cells and in that the device comprises a control member adapted to vary the heat of the cells. This embodiment makes it possible to control the temperature and humidity of the products to be treated per cell.

According to a second aspect, the invention relates to a drying method by means of a drying device according to the invention, the method comprising the following steps: storage of the materials to be dried in the structure, control of the first circulation circuit of hot water and the at least one cooling assembly for heating the structure, recovering the materials to be dried when a predetermined drying time has been reached. According to one embodiment, the predetermined drying time is between two and four weeks. According to one embodiment, the materials to be dried being green wood, the predetermined drying time is determined according to the position of the moon when the wood is cut. According to one embodiment, the method comprises a step of stirring or turning the materials to be dried. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood by means of the following description, given purely for explanatory purposes, of the embodiments of the invention, with reference to the figures in which: Figure 1 illustrates a schematic top view of a drying device according to one embodiment of the invention; - Figure 2 illustrates a cell of the device of Figure 1 in a front view; and Figure 3 illustrates a flow chart of the drying steps of the materials according to one embodiment of the invention. DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION FIGS. 1 and 2 illustrate a drying device 10 having a structure 11 of at least fifty cubic meters placed on a floor 12. For example, in the case of FIGS. 1 and 2 , the structure 11 comprises a base of 5632 square meters made of hot-galvanized steel sections. The structure 11 is supported in length by 8 cells 35a-35h of 3 m by 4.26 m for a total length of 102.4 m and width by 11 crosspieces 5 m long for a total width of 55 m. The structure 11 has a height of 7 m. Alternatively, the dimensions of the structure 11 can be modified without changing the invention. The cover 25 is made of sliding aluminum profiles supporting a transparent and translucent sunlight capturing element. Preferably, the element for capturing sunlight is made of glass. The glass cover 25 thus makes it possible to heat the interior of the structure 11. The drying device 10 also comprises two other heating sources. First, the floor 12 is provided with a floor heating 20 30 having a heat-transfer water circuit 21 incorporated in a concrete slab forming the soil 12 of the device. Secondly, the water of the heat-conducting water circuit is used to supply hot air coolers 17 via a water / air heat exchanger. The heat transport circuit 21 and the air coolers 17 use water at medium temperature, for example water in the temperature is between forty and fifty degrees Celsius. This water comes from the cooling circuit of a plant 9 close to the drying device 10. In the case of Figure 1, the plant 9 corresponds to a power plant generating 12 MWe of electricity from the gasification of 50 000 tonnes waste and agricultural biomass. In parallel with the production of electricity, the plant also generates heat in the form of hot water at low temperature, that is to say between forty-five and fifty degrees Celsius, with a flow rate of 1400 m 3 / h, that is 16MWth. This heat is, in general, very difficult to value. Hot water from the gasification process is delivered by a go pipe 22a at a temperature of about fifty degrees Celsius. After the passage of this water and the recovery of its heat in drying device 10, via the heating planchant 20 and the air-cooling 17, it returns to the factory 9 by a return pipe at a temperature of about forty degrees Celsius. This cooled water can thus be reused by the plant 9. The drying device is heated by sixteen air-coolers 17 of 20 unit power 1.2MWth composed of 288 fans and radiators delivering a flow of air at 50 ° C. The air coolers 17 are arranged vertically on the front face 30 so as to heat an upper portion 16 of the structure 11. The air coolers 17 are associated with extractors 27 disposed on the rear face 31 of the structure 11, visible on the front of the Figure 2. The drying device 10 of Figures 1 and 2 comprises six extractors 27 per cell 35a-35h, ie 48 extractors 27 in total. The extractors 27 are stacked on two blocks of three extractors 27 around a removable metal curtain. The metal curtain of the first cell 35a is fully open in FIG. 2. Conventionally, the metal curtains of the eight cells 35a-35h are motorized.

The upper part 16 is also heated by the cover 22 glazed in good weather using the energy of the sun. Solar energy can heat from thirty-five to forty degrees Celsius. A lower portion 15 of the structure 11 is heated by the heating floor 15 substantially uniformly by a network of serpentine or snail pipes of the heat-exchange circuit 21. Figure 3 depicts the steps of a drying process by means of a drying device 10 of the invention. In a first step 40, the materials to be dried are layered on the heating floor 20. In the case of Figure 2, the materials to be dried are wet wood chips and wood strips 37. In a second step 41, the drying device 10 is controlled to circulate hot water in the heating floor 20 and in the drycoolers 17. With the floor heating 20 and conduction, the heat is propagated from the pipes of the heat transfer circuit 21 buried to the slab then towards the wood. The other part of the hot water is conveyed to the air coolers 17, it circulates through tubes which are cooled by a ventilation system. The pulsed air heats up in contact with its tubes and feeds the structure 11. In fact, the air coolers 17 are normally laid horizontally, but in the drying device 10 of the invention, the arrangement of the air coolers 17 is an innovation because its vertical installation that allows to introduce the forced air to the structure 11. This hot air helps maintain a certain temperature of the ambient air of the structure 11 promoting the drying of materials. Subsequently, the ventilation located at the rear of the structure 11 makes it possible to draw the moist air outwards and to extract moisture from the materials. Given the low temperature of the coolant, ventilation is important. In the case where the heaters 17 operate at idle, for example in winter, the extractors 27 evacuate the ambient humidity and manage to "pump" calories to the heaters of the heaters 17, while the underfloor heating 12 still works.

In addition, the cover 22 also captures the heat of solar radiation to provide additional heat for the drying cycle through the greenhouse effect. With the combination of these three heating systems, the moisture content of wet wood chips and wood ridges 37 increases from 48 to 18% in two to four weeks. The drying time may vary depending on the position of the moon when the wood is cut. In addition, during the drying cycle, the materials to be dried can be returned or stirred in a step 43. This step 43 can be repeated several times during the drying cycle.

When the drying cycle is finished, the materials to be dried can be destocked in a step 42 and delivered directly. The invention thus makes it possible to rapidly and efficiently dry materials, for example damp wood chips and wood strips 37.

With regard to the forest chips, it appeared that the fresh forest chips containing 45 to 50% moisture could be dried to 20% moisture with the following provisions: - 12 to 15 days of exposure with 3 reversals or periodic brewing on a thickness of 1m, or - 8 days of exposure without turning over a thickness of 30 centimeters. As regards the wooden ridges 37, when the sawmill is close to the drying device 10, the handling is reduced to their simplest expression; the sawmill cuts, splits and puts the logs in metal cages.

These cages are put in kiln, then loaded after drying for delivery. The use of "green" and split wood becomes possible. This wood then has a brand new feature; it is very dry on the surface (15%) but still a little damp at heart. The result is logs that ignite very well without the help of small wood, but then burn slowly. Regardless of the storage thickness, you just need to have air between each log. The cages can thus be stacked on each other and fill the cell 35a-35h entirely. Cycle times between tree cutting and wood delivery vary between two and four weeks following the position of the moon at the time of cutting.

The invention thus makes it possible to reduce the drying time and to increase the rotation of stocks of materials to be dried. The invention makes it possible to quickly obtain "pre-conditioned" products ready to deliver. In addition, the invention makes it possible to obtain a very high homogeneity of drying between the products and new type of logs, which burn well and slowly. At the energy level, the invention has an "ecological" yield more favorable than existing devices with a very low energy consumption.

Claims (10)

REVENDICATIONS1. Apparatus for drying (10) materials comprising a structure (11) comprising a floor (12) receiving the materials to be dried, characterized in that it also comprises: - a first hot water circulation circuit placed under at least a portion of the outer surface of said floor (12) for heating thereof, and - a second hot water circulation circuit and a cooling assembly (17) of said second hot water circulation circuit, 10 - said set cooling system (17) generating air flows directed to the interior volume of said structure so as to heat said materials after said air flows have achieved heat exchange with said second hot water circulation circuit. 15 2. Device according to claim 1, characterized in that said cooling assembly (17) generates air flows parallel to or substantially parallel to the surface of said floor (12). 3. Device according to claim 1 or 2, characterized in that said cooling assembly (17) comprises air-cooling devices. 4. Device according to any one of claims 1 to 3, characterized in that said cooling assembly (17) being placed at a first end (30) of said structure (11), said device (10) comprises at its 25 end (31) opposite said first end (30) at least one air extractor (27) for extracting air from the interior volume of said structure (11). 5. Device according to any one of claims 1 to 4, characterized in that said first and second hot water circuits are connected to a single circuit (21) for supplying hot water. 6. Device according to claim 5, characterized in that the temperature of the hot water of the single circuit (21) for supplying hot water is between 40 ° C and 50 ° C. 7. Device according to any one of claims 1 to 6, characterized in that it comprises a cover (25) transparent or translucent. 8. Device according to claim 7, characterized in that said cover (25) is made of glass. 9. Device according to any one of claims 1 to 8, characterized in that the structure (11) is divided into several cells (35a-35d) and in that the device (10) comprises a control member (37) able to vary the heat of the cells (35a-35h). 10. Drying process by means of a drying device (10) according to one of claims 1 to 9, characterized in that it comprises the following steps: - storage (40) of the materials to be dried in the structure ( 11), - control (41) of the first hot water circulation circuit and the at least one cooling assembly (17) for heating the structure (11), - recovery (42) of the materials to be dried when a predetermined drying time has been reached.