FR2913761A1 - Device for drying thick products containing organic matter such as sludge from urban or industrial wastewater purification stations, comprises an enclosure defined by bottom wall, side walls and roof, a ventilator, and a dehumidifier - Google Patents

Abstract

The device for drying thick products (1) containing organic matter such as sludge from urban or industrial wastewater purification stations, comprises an enclosure defined by a bottom wall (2), side walls (3a, 3b) and a roof (4) with an adjustable air entrance, a ventilator (6) for assuring renewal of air in the enclosure, a dehumidifier, and a unit for controlling the ventilation and humidification according to climatic conditions and/or internal conditions of the drying device. The products to be dried are distributed in the bottom wall of the enclosure. The device for drying thick products (1) containing organic matter such as sludge from urban or industrial wastewater purification stations, comprises an enclosure defined by a bottom wall (2), side walls (3a, 3b) and a roof (4) with an adjustable air entrance, a ventilator (6) for assuring renewal of air in the enclosure, a dehumidifier, and a unit for controlling the ventilation and humidification according to climatic conditions and/or internal conditions of the drying device. The products to be dried are distributed in the bottom wall of the enclosure. The enclosure has a coefficient of thermal inertia of higher than 400 kg/m2> and an average thermal insulation coefficient of lower than 2 W/m2> so that heat is brought to certain moments of the day by solar energy and are stored and restored with certain shift in cold period such as night. The enclosure is immersed with a depth of 0.4 m so that the thermal insulation increases during winter, or covered at ground. The walls other than the roof of the enclosure are made of a concrete layer with strong thermal inertia and a layer of thermal insulation material, and are covered with black paint. The roof consists of a translucent material that allows to pass the solar radiations and has thermal insulating properties. Faces of the translucent material are equipped with a cover used in night period to reduce the thermal losses. Solar energy sensors are situated at outside in communication with the enclosure for air circulation thus transferring the hot air to the enclosure when the temperature of this hot air is higher than a given limit. A conduit is placed in the walls of the enclosure for the circulation of hot fluid. A sludge transport system is equipped with the drying device.

Description

DEVICE FOR DRYING PRODUCTS IN A PASTA CONDITION, IN PARTICULAR SLUDGE

PURIFICATION STATIONS.

  The invention relates to a product drying device in the pasty state, containing organic material, in particular sludge from wastewater treatment plants, urban or industrial, designed to recover solar energy for drying. Drying devices of the kind in question comprise an enclosure delimited by a bottom wall on which are spread the products to be dried, side walls and a roof, with at least one adjustable air inlet, and at least one fan to ensure a renewal of the air in the enclosure. Such drying devices, for example according to FR-A-2 843 958, make it possible to carry out the drying of the products with a reduced energy consumption thanks to the solar-generated recovery. Known devices generally use greenhouses of the horticultural type, the size of which must be carried out taking into account the winter period, so that the greenhouses occupy a large surface area on the ground. They have a large volume, requiring a large flow of sweeping air so that the sweeping flow loses efficiency because it is removed from the surface of the products to be dried, because of the relatively large height of the greenhouses. In addition, greenhouses have a high heat loss and a significant proportion of the heat accumulated during the day is lost at night. In addition, there is condensation on the cold walls, which is not conducive to drying. In general, the drying kinetics is strongly related to the meteorological conditions of the site. A major disadvantage of greenhouses is the bad drying of the products during the night period and during the winter period. In these unfavorable conditions, it happens that the water contained in the sludge can not be evacuated by the ventilation, and the greenhouse then acts as simple place of storage. It is important to reduce the drying time during such adverse weather conditions to limit problems related to the management of pasty products and the formation of odors. To limit these disadvantages, some builders have proposed external heat input in winter, for example by the floor in the form of a heated floor, or by preheating the ventilation air.

  The calories are produced by various conventional methods, such as air heaters, geothermal energy, or by energy recovery of water treated by a wastewater treatment plant, or by energy recovery of hot air extracted from the greenhouse or that extracted from a local booster, or through heat pumps or different exchangers. The invention aims to provide a drying device which, while recovering solar energy, no longer has, or to a lesser degree, the disadvantages mentioned above. In particular, it is desirable that the drying device remains effective, with a minimum of external heat input, when the weather conditions are not favorable, in particular during the winter period or during the nocturnal periods. According to the invention, a device for drying pasty products, containing organic material, in particular sludge from urban or industrial wastewater treatment plants of the kind defined above, is characterized in that the thermal insulation and the thermal inertia of the enclosure are large enough that the calories brought at certain times of the day, by solar energy in particular, are stored and restored with a shift in the colder period, especially at night.

  According to the invention, this result is obtained if the average insulation coefficient k (maximum heat loss) of the whole enclosure is less than 2 W / m2. C and if the thermal coefficient of inertia is greater than 400 kg / m 2, these two coefficients being specified below and in the example below. The average insulation coefficient k is calculated by summing the coefficients k of each face of the enclosure, taking into account the openings and thermal bridges, divided by the total area. The coefficient of thermal inertia is the sum of the masses of the side walls and the floor, divided by the surface of the enclosure The enclosure can be buried at least partially, or covered with earth. The depth to which the chamber is buried is preferably at least 0.4 meters, so that the insulation is increased, especially in winter. Advantageously, the device comprises at least one dehumidifier. The device preferably comprises means for controlling the operation of ventilation and dehumidification depending on the climatic conditions and / or conditions internal to the drying device. The device can be equipped with at least one sludge advance system.

  The walls of the enclosure other than the roof may be made of a material providing the dual function of thermal inertia and thermal insulation. According to another possibility, the walls of the enclosure other than the roof consist of a layer of material with high thermal inertia, in particular concrete, and a layer of a thermal insulating material. In a more general way, it will be possible to use walls composed of several juxtaposed materials, some ensuring the thermal inertia, the others the thermal insulation. The internal faces of the walls of the enclosure other than the roof are advantageously covered with a dark paint, preferably black, in order to best capture the solar energy that passes through the translucent material. Inside these walls, it is advantageous to circulate a hot fluid to provide additional calories. The device may comprise at least one duct housed in the walls for the circulation of the hot fluid. The roof of the enclosure can be out of the ground and be made of a translucent material permitting solar radiation, while having a thermal insulating power. The translucent material is advantageously constituted by polycarbonate. The faces in translucent material can be equipped with a cover used during the night period or in a cold period not sunny to reduce heat loss. The roof can also be made of several translucent materials, separated by air knives. The enclosure can be completely buried, the roof being covered by the ground and made of a thermal insulating material and high thermal inertia like the other walls of the enclosure. Preferably, solar energy sensors are located outside and placed in communication with the enclosure to transfer the heat captured to it when the external conditions allow it.

  The solar energy sensors may be circulating air and produce hot air that is sent into the drying chamber when the temperature of this hot air is above a certain limit. The invention consists, apart from the arrangements described above, in a certain number of other arrangements which will be more explicitly discussed hereinafter with regard to exemplary embodiments described with reference to the appended drawings, but which are not in no way limiting. On these drawings:

  Fig. 1 is a schematic vertical section of a drying device according to the invention. Fig 2 is a vertical section of a wall made of a material with high thermal inertia and an insulating material.

  Fig. 3 is a vertical section, a device similar to that of Fig.1, partially buried. Fig. 4 is a vertical section, on a larger scale, of a device similar to that of Fig.1., With a single or double slope roof. Fig. 5 is a vertical section of an alternative embodiment of the drying device with a completely buried enclosure. Fig. 6 is a schematic diagram in vertical section of solar collectors with air circulation. 7 is a schematic vertical section of a drying device with solar collector. Fig. 8 is a schematic vertical section with a device for circulating a hot fluid in the walls. Referring to Fig. 1 of the drawings, there can be seen a drying device D of dough-like products 1 containing organic material, in particular sludge from urban or industrial wastewater treatment plants. The device D comprises an enclosure E delimited by a bottom wall 2 on which the products 1 to be dried are spread out in layers, the generally vertical side walls 3a, 3b, and a roof 4. At least one adjustable air inlet 5 and at least one fan 6 are provided to ensure a renewal of the air in the enclosure. The walls 2, 3a, 3b, as illustrated in FIG. 2, consist of a layer 3-1 of high thermal inertia material, especially concrete, and a layer 3-2 of a thermic insulation material. The layer 3-2 of thermal insulating material is located against the layer 3-1 on the outer side relative to the enclosure E. The drying device D of FIG. 1 is of the "veranda" type. The walls 3a, 3b consist of a concrete wall 25 cm thick, on which is reported a layer of thermal insulation of 10 cm; the coefficient k of thermal insulation of such a wall is 0.48 W / m2. C. The floor 2 consists of a 25 cm thick concrete slab with thermal insulation under a 10 cm thick slab; the coefficient k of thermal insulation of such a wall is 0.5 W / m2. C. As the insulating materials are often different on the walls and under the floor slab, the coefficients k of thermal insulation can be different.

  The walls 3c and 3d of the enclosure E parallel to the plane of Fig.1 and located in front and rear of this plane are made of a material identical to the walls 3a and 3b, but have two large openings; the average coefficient k of thermal insulation of the surface is then 1.2 W / m2. C. Finally roof 4 consists of a multilayer polycarbonate having a k-value of 2.5 W / m2. C. So we see that the average coefficient k of all surfaces is less than 2 W / m2. The fan 6 and the adjustable air inlet 5 can be provided in these opposite walls, in an area above ground level S. According to the representation of FIG. 1 the fan 6 is provided in the wall located behind the plane of Fig.1 while the adjustable air opening is located in front of this plane. In the exemplary embodiment of FIG. 1, the roof 4 is out of the ground S and consists of a translucent material passing solar radiation and stopping the infrared radiation from the enclosure. The roof 4 can be made of double or triple-thickness translucent material, with or without an air gap, depending on the case, which makes it possible to capture the solar energy and to keep it inside to promote the drying of the products 1 by night period or in winter. The translucent material may be made of polycarbonate. The roof 4, according to FIG. 1, is plane, inclined at an angle to the horizontal and oriented towards the sun when it is noon at the place considered. Fig.3 shows a drying device similar to that of Fig.1, but partially buried. The depth to which the walls 3a, 3b are buried in the ground is at least 0.4 meters (40 centimeters). Roof 4 is out of the ground. The wall 3a is substantially adjacent to its height at an embankment 7. FIG. 4 shows, in more detail, an embodiment similar to that of FIG. 1 in which is provided a device 8 for advancing the pasty product 1 with, if necessary, a scarification system such as that of the patent FR 2874605.

  The same numerical references are used to denote similar elements of FIG. 4 and FIG. 1. A variant of roof with double slope 4a is shown schematically in phantom in FIG. 4. to promote the capture and conservation of solar energy, according to the orientations. The drying device is equipped, inside the enclosure E, with at least one dehumidifier 9 of the air, and a control cabinet 10 of the dehumidifier 9, the fan or fans 6 and the opening of the adjustable air inlet 5. Sensors (not shown) of the outside temperature, the inside temperature of the enclosure, as well as the sensors (not shown)

  the hygrometry of the outside air and the air in the enclosure are provided and connected to the control cabinet 10. This cabinet 10 constitutes a control system designed to operate in an optimized manner ventilation and dehumidification .

  Referring to Fig. 5, we can see the diagram of a variant Dl type "tunnel" of the drying device which is completely buried. The roof 4b is constituted by a slab of thermally insulating material similar to that of the side walls 3a, 3b and bottom 2. The roof 4b is covered with a layer of earth 11 or equivalent material. The free height h in the El tunnel is sufficient to allow an operator to stand up. This height h is preferably substantially equal to or greater than 2 m and the device D1 is buried to a depth greater than h. The width I of the bed of pasty products may be of the order of ten meters, for example 12 m, while the length L, in a direction orthogonal to the plane of FIG. 5, is several tens of meters. Solar collectors 12 (Figures 6 and 7) are provided to provide solar energy recovery and heat the air inside the device D1. The sensors 12 are located outside the device D1 and have passages through which a flow of air to be heated from the solar radiation. The hot air thus produced is sent into the enclosure El. As illustrated in FIG. 6, the sensors 12 are inclined about 60 relative to the horizontal and are turned towards the sun at noon. The length B of the sensors can be of the order of 2 m and the distance G between the sensors is about 4 to 5 m. Fig. 7 shows a drying device D1 semi buried tunnel type whose roof consists of a slab 4b, thermally insulating material and opaque, which is not covered by the ground. At least one solar collector 12 is installed on the roof 4b and communicates with the inside of the enclosure E1 through a duct 13 for the passage of air from the enclosure to the sensor 12 and through a return duct 14 allowing to return the heated air in the enclosure El. A fan 15 is advantageously provided at the outlet of the duct 14 to accelerate exchanges between the enclosure El and the sensor 12. There is at least one dehumidifier 9, a control cabinet 10 to operate the various devices, including dehumidifier, extractor fan 6, adjustable opening 5 and 15 fan, depending on the values of indoor and outdoor temperatures, and indoor and outdoor hygrometric conditions. The preheating of the air, in particular for the embodiments in buried or semi buried tunnel of FIGS. 5 and 7, may be supplemented or augmented by

  conventional means such as wood boilers, biogas, gas, heat exchanger, heat pump. In the case of embodiments according to FIG. 1, 3 and 4, the roof 4 of translucent material can be advantageously equipped with a thermally insulating blanket, used during the night to limit heat loss. Fig.8 shows a drying device D having, in its walls 3a, 3b and in the floor 12, one or more ducts 16 recessed for circulating a hot fluid. The duct 16 enters horizontally into the wall 3a, rises vertically to the vicinity of the top of this wall 3a, then descends towards the floor 2 which it crosses substantially horizontally, to go up and down in the wall 3b and go out horizontally. The internal faces of the walls of the enclosure other than the roof are advantageously covered with a dark paint, preferably black, in order to best capture the solar energy that passes through the translucent material. The operation of a drying device according to the invention results from the foregoing explanations. The strong thermal inertia of the enclosure makes it possible to store the calories brought at certain times of the day, by the solar energy or any other energy supplied to the enclosure, and to restore them in colder period, in particular at night. The at least partially buried configuration of the drying device makes it possible to benefit from the thermal regulating effect of the soil, making it possible to limit thermal losses during cold periods.

  In addition, solar energy is captured through a roof made of translucent material or sensors 12. The strong thermal insulation of the walls of the enclosure, and the soil around them, allows to keep inside of the enclosure the heat captured in favorable times. The drying device of the invention makes it possible to obtain a dryness of the pasty products 1 greater than 70% throughout the year, while reducing the surface area on the ground. Drying is controlled and the risk of fermentation and odor production is reduced. The volume of air to be evacuated from the device is also reduced. By way of nonlimiting example, consider an enclosure whose dimensions are L = 100 m, I = 14 m and h = 4.47 m (for wall 3a), h = 2 m (for wall 3b) : Calculation of the average k-factor: Wall 3a: k1S1 = 0.48 x 447 = 215 W / C

  Wall 313: k2S2 = 0.48 x 200 = 96 W / C Wall 2: k3S3 = 0.5 x 1400 = 700 W / C Wall 3c: k4S4 = 1.2 x 45 = 54 W / C Wall 3d: k5S5 = 1.2 x 45 = 54 W / C Roof 4: k6S6 = 2.5 x 1421 = 3553 W / C average k = Sum (kS) / StotaIe = 4672/3358 = 1.39 W / m2. VS

  Calculation of the coefficient of inertia (density of concrete: 2300 kg / m3 Wall 3a: mass = 2300 x 0.25 x 447 = 257025 kg Wall 3b: mass = 2300 x 0.25 x 200 = 115000 kg Wall 2: mass = 2300 x 0.25 x 1400 = 805000 kg Wall 3c: mass = 2300 x 0.25 x 42 = 24150 kg Wall 3d: mass = 2300 x 0.25 x 42 = 24150 kg Coefficient of inertia = Sum (mass) / Splancher = 1225325/1400 = 875 kg / rn2

Claims (16)

  1. Device for drying pasty products containing organic material, in particular sludge from urban or industrial wastewater treatment plants, comprising an enclosure defined by a bottom wall on which the products to be dried are spread, sidewalls and a roof, with at least one adjustable air inlet, and at least one fan to provide a renewal of the air in the enclosure. characterized in that the enclosure (E, E1) has a thermal coefficient of inertia greater than 400 kg / m2 and an average thermal insulation coefficient of less than 2 W / m2. C so that the calories brought at certain times of the day, by solar energy in particular, are stored and restored with a certain lag in the colder period, especially at night.   2. Device according to claim 1, characterized in that the enclosure is buried at least partially, or covered with earth.   3. Device according to claim 2, characterized in that the depth at which the chamber is buried, is at least equal to 0.4 meters, so that the insulation is increased, especially in winter.   4. Device according to any one of the preceding claims, characterized in that it comprises at least one dehumidifier (9).   5. Device according to claim 4, characterized in that it comprises means (10) for controlling the operation of ventilation and dehumidification depending on the climatic conditions and / or conditions internal to the drying device.   6. Device according to any one of the preceding claims, characterized in that it is equipped with at least one system (8) for advancing the sludge.   7. Device according to any one of the preceding claims, characterized in that the walls (2,3a, 3b, 3c, 3d) of the enclosure other than the roof (4) are made of a material providing the dual function of thermal inertia and thermal insulation   8. Device according to any one of claims 1 to 6, characterized in that the walls (2,3a, 3b, 3c, 3d) of the enclosure other than the roof (4) consist of a layer (3 -1) of high thermal inertia material, in particular concrete, and a layer (3-2) of a thermal insulating material.   9. Device according to any one of the preceding claims, characterized in that the walls (2,3a, 3b, 3c, 3d) of the enclosure other than the roof (4) are covered with a dark paint, preferably black. 10   10. Device according to any one of the preceding claims, characterized in that the roof (4) of the enclosure (E) is out of the ground and is made of a translucent material permitting solar radiation, while having a thermal insulating power. 15   11. Device according to claim 10, characterized in that the translucent material consists of polycarbonate.   12. Device according to claim 10 or 11, characterized in that the translucent material faces are equipped with a cover used in the night period to reduce heat losses.   13. Device according to any one of claims 1 to 8, characterized in that the enclosure (El) is completely buried, the roof (4b) being covered by the ground (11) and made of a thermal insulating material and strong thermal inertia like the other walls of the enclosure.   14. Apparatus according to any one of the preceding claims, characterized in that solar energy sensors (12) are located outside and placed in communication with the enclosure (El) to transfer the captured heat to it. when external conditions permit.   15. Device according to claim 14, characterized in that the solar energy sensors (12) are circulating air and produce hot air which is sent into the drying chamber when the temperature of this air warm is above a certain limit.   16. Device according to any one of the preceding claims, characterized in that it comprises at least one conduit (16) housed in the walls (3a, 3b, 3c, 3d) for the circulation of a hot fluid.