Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
  • F26B21/06—Controlling, e.g. regulating, parameters of gas supply
  • F26B21/08—Humidity
  • F26B21/086—Humidity by condensing the moisture in the drying medium, which may be recycled, e.g. using a heat pump cycle
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B23/00—Heating arrangements
  • F26B23/02—Heating arrangements using combustion heating
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B25/00—Details of general application not covered by group F26B21/00 or F26B23/00
  • F26B25/005—Treatment of dryer exhaust gases
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B2210/00—Drying processes and machines for solid objects characterised by the specific requirements of the drying good
  • F26B2210/16—Wood, e.g. lumber, timber

Definitions

• the technical field of the invention is that of heat treatment processes of a material in an oven, and more particularly that of processes for treating an organic material such as wood.
• the known methods use the combustion gases of a boiler operating with gas, fuel oil or wood.
• flue gases carry unburnt and hot dusts that can lead to an inflammation of the wood and permeate the wood and adversely affect its quality and subsequent market value.
• dust and solid residues are particularly abundant when the fuel itself is wood.
• Patent WO81 / 00147 also discloses a process in which the solvents contained in the gases leaving a drying oven are removed by condensation. However, this method is associated with a drying oven for printing in which the gas temperatures are much lower than those required for the treatment of wood.
• the patent WO2005 / 116551 proposes a wood treatment device in which the gas leaving a furnace is condensed to remove the water present.
• the condensation is here carried out downstream of a heat exchanger. The level of condensation obtained does not therefore ensure the cleaning of the combustion gases that is necessary to perform the wood treatments.
• the object of the invention is to propose a heat treatment process that makes it possible, on the one hand, to eliminate the particles carried by the combustion gases and, on the other hand, to also control the oxygen content of the gases used.
• the method according to the invention also makes it possible to optimize the use of the energy used. It can operate in a continuous way and allows the processing of large volumes of wood.
• Thermal energy is used optimally.
• the residues are recovered and can be reused or recovered.
• the subject of the invention is a method of heat treatment of a material in an oven, and in particular of an organic material such as wood, a process using the combustion gases supplied by at least one burner associated with a furnace, a process characterized in that there is provided a first step of condensing the combustion gases between their outlet from the furnace and the furnace, which condensation makes it possible to eliminate part of the dust contained in the combustion gases, the first condensation step being carried out using an absorption refrigerating means and being followed by a step of superheating the combustion gases to obtain the desired temperature for the heat treatment.
• Overheating can be achieved using gases supplied by a hot gas generator which is itself heated by the burner.
• Overheating can be achieved through an exchanger heated by the burner.
• the second condensation step may be followed by a separation step between the solid and / or liquid fraction and the combustion gases themselves.
• the combustion gases can be redirected at the exit of the separation step to the burner and / or the hearth, via a mixer stage ensuring a mixture of the gases with air, mixture which will be dosed according to the measurement of the level of at least one combustible compound included in the combustion gases.
• the invention also relates to a heat treatment unit of a material, and in particular an organic material such as wood, unit for implementing the method according to the invention.
• This unit comprises at least one furnace, heated from the combustion gases from at least one burner associated with a furnace, it is characterized in that it comprises at least a first condenser which is arranged to cool the gases.
• the condensation for removing with water a portion of the dust contained in the combustion gases, dust that is recovered in a settling means, unit comprising at least one superheater connected to a means of heating and for heating the combustion gases at their outlet from the first condenser, and also comprising at least one absorption refrigeration means which uses as a hot source the hearth and which comprises at least one refrigerant circuit which is coupled to the first condenser.
• the heating means may be connected to the superheater via a means for regulating the temperature of the combustion gases.
• the heating means may be connected to a hot gas generator which will itself be heated by the burner or burners.
• the superheater may comprise at least two hot gas circulation circuits arranged in an enclosure through which the combustion gases circulate, the circuits being arranged in such a way that the combustion gases flow in a direction opposite to that of the hot gases supplied. by the gas generator, each circuit being further provided with a gas flow control valve, the opening of which is controlled by the temperature control means.
• the superheater may be constituted by an exchanger heated by the burner itself.
• the superheater heat exchanger may comprise tubings which will be incorporated structurally to a hot gas generator.
• the means for regulating the temperature of the combustion gases may comprise two circuits: a cold combustion gas circuit coming from the first condenser and a hot combustion gas circuit coming from the superheater, the temperature of the combustion gases used being regulated. by at least one mixing valve ensuring the mixing of the cold gases with the hot gases.
• Each hot and cold circuit will incorporate a pump, the flow rate of the pumps being regulated so as to ensure equal flow of flue gas upstream and downstream of the superheater.
• Each hot or cold combustion gas circuit preferably comprises a balancing circuit to compensate for the pressure losses generated by the mixing valve, balancing circuit reinjecting a portion of the hot or cold gases upstream of the circuit pump considered.
• the unit may include at least one second condenser which will be disposed at the outlet of the oven.
• the processing unit may advantageously comprise a decanting means for separating the solid and / or liquid fraction and the combustion gases themselves.
• the heat treatment unit may also comprise a mixing stage which will ensure a mixture of the gases leaving the second condenser and the associated decanting means with air, this mixing stage including at least one valve whose opening will be controlled by a control means which will control the degree of opening of the valve according to the measurement of the rate of at least one combustible compound included in the combustion gases, the mixture of air and combustion gases being redirected to the burner and / or the focus.
• At least one refrigerant circuit of the absorption refrigeration means may also be coupled to the second condenser.
• the hot gas generator may be supplied with air through a third condenser connected to a refrigerant circuit of the absorption refrigeration means.
• the heat treatment unit according to the invention When the heat treatment unit according to the invention is more particularly intended to ensure the treatment of wood, it will advantageously comprise at least one oven which will comprise two side walls facing one another and an upper wall, walls which will be realized in the form of caissons in which will circulate the combustion gases, the latter being brought to the level of the upper box which will be divided into two half-boxes, a half-box receiving the combustion gases arriving at the oven and the other half -caisson collecting gases for their evacuation after passing through the furnace, each half-box also communicating with a separate side box, the walls of the side boxes being provided with perforations allowing the passage of the gases of the side box towards the interior of the oven, the gases are thus introduced into the oven at a side box and being removed from the oven through the other caisso n lateral.
• the upper box will be generally parallelepipedal and divided into four compartments by two partitions which extend along diagonals, a first compartment being connected to a flue gas inlet pipe and a second compartment being connected to a pipe of flue gas evacuation, the two other compartments being each connected to one of the side boxes, a median pivoting flap can be optionally positioned in the extension of one or the other of the diagonal partitions, so as to share the box superior in two half-boxes. The pivoting flap will thus direct the combustion gases to the choice towards one or other of the side boxes.
• the side boxes may be provided with perforations which will be distributed over the entire height of each box, each side box being further provided with a sliding panel vertically and allowing, depending on the chosen position, closing all the perforations of an upper half or all those of a lower half of said side box, the panels being also positioned in the up position on a side box and in the lower position on the other side box according to the position, the pivoting flap of the upper box.
• the positioning of the panels will be chosen so as to always ensure a flow of combustion gases passing through the furnace from a lower part of a side box to an upper part of the other side box.
• the furnace comprises two side walls facing one another, walls which are formed in the form of boxes in which the combustion gases circulate, each side wall being divided into two half-boxes , a lower box for receiving the combustion gases arriving in the oven and an upper box collecting the gases for their evacuation after their passage in the oven, a three-way valve being arranged upstream of the lower boxes and another three-way valve being arranged downstream of the upper caissons of to ensure, by the control of the two valves, the control of the direction of passage of gases from one wall to the other partition.
• FIG. 1 is a general block diagram of a processing unit according to the invention
• FIG. 2 is a detailed view of the combustion gas generator of this heat treatment unit
• FIG. 3 is a diagrammatic section of an exemplary embodiment of the superheater
• FIGS. 4a and 4b are two simplified longitudinal sectional views of an oven used in the unit according to the invention, the sections are made. following the plane whose trace BB is marked in FIG. 5a, each figure also shows the oven in a different position for the gas circulation means,
• FIGS. 5a and 5b are two simplified cross-sectional views of this furnace, the sections are made along the plane whose trace AA is marked in FIG. 4a, FIG. 5a also represents the furnace in the same position as on FIG. FIG. 4a and in parallel with FIG. 5b may be associated with FIG. 4b,
• FIG. 7 is a general block diagram of a processing unit according to another embodiment of the invention.
• Figure 8 is a diagram showing the same unit and to highlight its operation in the startup phase
• Figures 9a and 9b are two views in simplified cross sections of another embodiment of the oven.
• Figure 1 shows a unit 1 of heat treatment of wood.
• the wood 2 is disposed on carriages 3 which are housed in heat treatment furnaces 4.
• a single furnace 4 is shown, but the unit could be sized to include several furnaces.
• Furnaces 4 are large units that can handle wooden elements up to 6 m long (logs or sawn timber).
• the wood to be treated at high temperature will have been previously dried in a drying oven 12 (in which the temperature is of the order of 100 0 C). In order to be processed the wood will preferably have a moisture content of less than 12%.
• Each oven 4 thus has the overall shape of a rectangular parallelepiped 10 meters long, 3 meters wide and 5 meters high.
• the oven 4 is heated from the combustion gases from a burner 5 associated with a combustion chamber 6. This mode of heating by the combustion gases makes it possible to control the reduced oxygen content which is required.
• the gases are recovered at the outlet of the hearth ⁇ by a manifold 7 and they are directed to the furnace 4 by conduits: 8al, 8a2, 8b, 8c, 8d, 8e, 8f.
• G gases circulate in the furnace (whose internal structure will be detailed later). They are then discharged at the outlet of the furnace 4 by a pipe 9.
• the burner 5 uses a fuel source 10 which may be gas or fuel oil or preferably residues and scrap wood that can be collected on installation. Therefore, a polyfuel burner 5 will preferably be used.
• the unit comprises at least a first condenser 11 which is arranged so as to cool the combustion gases at their outlet from the hearth 6.
• the condenser 11 causes a sudden cooling of the gases at their outlet from the hearth 6. This cooling causes a condensation of the water contained in the gases, the water flows along the pipe 8a2 and it carries with it the largest part of the dust contained in the combustion gases.
• the water flows along the pipe 8a2 and it accumulates with the dust in a settling means 13.
• the decanting means will be constituted by a tank in which the combustion gases circulate.
• the pipes 8al and 8a2 both open into the tank at its upper wall.
• the dust-laden water accumulates in the tank 13 and is withdrawn periodically by means of a valve V, for reprocessing and removal of residues.
• the condenser 11 is connected to a refrigerating means 14 by TIl pipes which conduct a heat transfer fluid.
• the temperature of the combustion gases is of the order of 210 ° C at the outlet of the hearth 6.
• the condenser 11 is dimensioned to bring the temperature to about 8O 0 C.
• a refrigerating means conveying a fluid circulating at a temperature of the order of 5 0 C and dimensioning the exchange surfaces of the condenser and the cooling means 14 to allow the desired temperature drop.
• a three-way valve 15 is disposed at the outlet of the condenser 11. This valve makes it possible to direct the combustion gases towards the branch 8c which leads to a superheater 16 or to the branch 8b which makes it possible to direct the gases towards an exhaust stack 17.
• the superheater 16 is essential to reduce the combustion gases to the temperature that is necessary to ensure the heat treatment of wood (temperature between 180 ° C and 230 0 C). The calories provided by the superheater 16 also come from the fireplace 6, but through a separate heating means.
• the heating means comprises a hot gas generator 17 which is itself heated by the burner 5.
• the gas generator 17 is disposed in the hearth 6 and comprises tubing which encloses the gas to be heated (for example air). These pipes physically isolate the gas to be heated from the combustion gases, but they are however made of a good heat conducting material (for example metal).
• the number of tubings is chosen to be sufficient for the heat exchange surface to be large and several sets of tubings will also be provided so as to maintain the gas inside the fireplace 6 long enough for its temperature to reach a high level. (of the order of 600 0 C).
• the hot gases generated by the generator 17 come out of the latter through the tube 18. After use, the gases return to the generator 17 through the tube 19. The hot gases are used at the plant for example to supply the furnace (s) drying 12.
• the temperature of the hot gases which is necessary for drying in the oven 12 is regulated by means of a valve 68 which makes it possible to mix with the hot gases generated by the generator 17 a part of the cooled gases which is taken on the tube of return 19 via a tube 69.
• the opening of the valve 68 will be adjusted by electronic control means (not shown) associated with a furnace inlet gas temperature sensor 12 (not shown). Temperature 600 ° C Gas can thus easily reduce the output of the generator 17 to about 100 0 C at the inlet of furnace 12.
• Hot gases at high temperature (600 0 C) are also used at the superheater 16.
• a bypass 20 of the tube 18 makes it possible to drive a portion of the hot gases to the superheater 16.
• the hot gases emerge from the superheater 16 by the tube 21 which leads them to the generator 17.
• a temperature control means is interposed between the gas generator 17 and the superheater 16.
• This means comprises a valve 22 which is controlled by an electronic means 23 for controlling the temperature.
• the means 23 is also connected to a sensor 24 measuring the temperature of the combustion gases flowing in the outlet pipe 8d of the superheater 16.
• the electronic means 23 can be produced in the form of a programmable microcomputer. It will then be possible to control the opening of the valve 22 as a function of the temperature setpoints desired for the gases intended for the oven 4.
• valve 22 causes an increase in the flow rate of the hot gas from the generator 17 and flowing in the superheater 16 thus also an increase in the temperature of the combustion gases G which are sent to the furnace 4 by the pipe 8f.
• the valve 25 makes it possible to direct the combustion gases coming from the condenser 11, not towards the chimney 17, but towards the furnace 4. It is thus possible to isolate completely the superheater 16 and to send to the furnace only the combustion gases coming from condenser 11. It can also be done at the valve
• valve 15 will be positioned in a position supplying the two branches 8b and 8c.
• the electronic means 23 will then regulate the openings and closures of the valves 15, 25, 26 and 22 as a function of the desired temperature for the cooling stages ( or heating) oven.
• Figure 3 shows in more detail the structure of a superheater 16.
• This element comprises a cylindrical chamber 27 inside which the combustion gases G circulate.
• the cylindrical chamber 27 is delimited by an inner wall of an annular pipe 28 which is connected to the hot gas generator 17 via a valve 22a.
• This annular pipe 28 constitutes a first hot gas circulation circuit arranged in the chamber 27.
• the chamber 27 also contains three other hot gas circulation circuits (29, 30 and 31) which are all connected to the hot gas generator 17 by a valve (respectively 22b, 22c and 22d).
• These other three circuits are made in the form of spirally wound tubes so as to increase the heat exchange surface between the hot gas circulation circuits and the combustion gases themselves.
• An outer wall 32 surrounds the superheater 16. It includes thermal insulating materials and avoids heat loss.
• All the circulation circuits 28, 29, 30 and 31 are connected downstream by a manifold 33 which is connected to the tube 21 which carries the gases back to the generator 17.
• An accelerator 34 will regulate the flow of hot gas through the various circuits.
• valves 22a, 22b, 22c and 22d are all controlled by the electronic means 23 which is also connected to a temperature sensor 24 measuring the temperature of the combustion gases at the outlet of the superheater 16.
• FIG. 3 also shows that the different circulation circuits 28, 29, 30, 31 are arranged in such a way that the combustion gases G circulate in a direction which is the reverse of that of the circulation of the hot gases supplied by the generator. Such an arrangement makes it possible to increase the efficiency of the heat transfer. The combustion gases therefore meet the circulation circuits in the vicinity of their outlet of the superheater 16
• the division of the superheater 16 into several circulation circuits also makes it possible to regulate more precisely the amount of heat which is transferred to the combustion gases G. It is thus possible to easily adjust the various temperature levels required.
• a circulation circuit 28 having a tubular shape makes it possible to improve the thermal efficiency of the superheater.
• the combustion gases G circulate in fact in a chamber 27 defined by a superheated pipe 28 and they pass through other pipes (those circuits 29,30,31) which are also superheated.
• the quantity of calories transferred to the combustion gases G will be greater or smaller.
• This series connection is a variant of the invention which makes it possible to make the best use of the calories supplied by the gas generator 17.
• the gas coming from the generator 17 and which are cooled through the superheater 16 remains however at a temperature largely sufficient to supply one or more drying ovens 12.
• the gases can however be lowered in temperature before introduction into the drying oven 12. This lowering will be controlled as previously described by a mixture of hot gases with a portion of the cooled gases taken from the return tube 19.
• FIG. 2 shows a more precise way the structure of the combustion gas generator of the heat treatment unit 1 and in particular the structure of the refrigerating means 14 and its various circuits.
• an absorption refrigerating means 14 will be implemented. These means are well known to those skilled in the art.
• a circulation circuit Ca of a fluid to absorb calories from a hot source at a boiler most often the fluid is an ammonia solution.
• This fluid circuit is coupled to an evaporator which causes the change of state of the fluid and thus the production of cold.
• the furnace 6 will be used as a hot source.
• a boiler 35 will be disposed around the collector 7 of the combustion gases.
• the boiler 35 will thus be constituted by pipes surrounding the collector 7.
• the heat transfer circuit Ca (shown in dotted lines) is the fluid circuit for extracting the calories (for example an ammonia solution).
• This circuit Ca is connected to one or more heat exchangers 36 which ensure the vaporization of the ammonia.
• the fluid providing the vaporization is air that will be introduced into the cooling means 14 by means of a fan 37.
• the air leaving the refrigeration means 14 has been heated by the coolant circuit fluid Ca, this heated air is recovered by a tube 38 and directed towards the burner 5 and / or the furnace 6. This heated air makes it possible to improve the burner combustion efficiency 5.
• the coolant vaporizes at a temperature of about 5 0 C (for ammonia).
• One or more refrigerant circuits are coupled to the coolant circuit Ca at the exchanger or exchangers. These circuits are for example water circuits.
• the chilled water is driven by a circuit TlI to the first condenser 11 and allows (as specified previously) to ensure the elimination of water and dust contained in the flue gases.
• the required flow of chilled water is provided by an accelerator 39. It is also possible to provide another accelerator 40 at the circuit Ca to increase the efficiency of the heat exchange.
• the refrigerated water circuit may include other branches that will be described later.
• the unit 1 comprises a second condenser 41 which is disposed at the outlet of the oven 4.
• the combustion gases Gs coming out of the furnace 4 are loaded with both moisture and volatile organic compounds that are extracted from the wood during the heat treatment.
• These volatile compounds essentially comprise condensable hydrocarbons, especially methane and acetone.
• the condenser 41 makes it possible to eliminate the water which is incorporated in the gases leaving the oven as well as the dust or other solid residues.
• a settling means 42 separates the solid and / or liquid fraction and the combustion gases themselves.
• the residues are recovered in a tank 44 for treatment and subsequent removal (with residues extracted at the medium 13).
• a fan 43 makes it possible to regulate the speed of the gases in the furnace 4.
• the duct 45 thus conveys only a combustion gas cooled and charged with volatile organic compounds which are combustible.
• This gas is mixed with air at a mixing stage comprising a three-way valve 46, then directed towards the burner 5 (or to the hearth 6).
• the opening of the valve 46 is controlled by a regulating means 47 which controls the degree of opening of the valve 46 as a function of the measurement of the level of at least one combustible compound included in the combustion gases. This measurement is performed using a sensor 48.
• the methane level will preferably be measured since it is the most reactive gas.
• the air used is preferably that which has been preheated at the level of the refrigerating means 14.
• the hot gas generator 17 is supplied with gas by a fan 51 which is coupled to the closed circuit 18-19 by a valve 52. It is thus possible to add gas (generally air ) to the circuit to compensate for losses and maintain the volume of gas necessary for good heat transfers.
• gas generally air
• a third condenser 53 is interposed between the fan 51 and the gas circuit. This condenser makes it possible to dry the external air used, which avoids the production of water vapor in the circuit.
• a fourth condenser 54 finally makes it possible to eliminate from the hot gas circuit 19 the water extracted from the wood at the level of the drying oven 12.
• the third and fourth condensers are both connected to the refrigeration means 14 by chilled water circuits T53 and T54.
• FIGS. 4 to 6 show the structure of the heat treatment furnace used by the unit according to the invention
• the oven 4 is constituted in the form of a parallelepiped block which has two side walls 55a and 55b disposed facing one another and an upper wall 56.
• the oven 4 also comprises two doors 67e and 67s , sealed and thermally insulated, allowing the passage of the trolleys 3 loaded with wood.
• These walls are made of sheet metal and in the form of hollow boxes each defining a volume in which the combustion gases can circulate.
• the upper box 56 carries the pipe 8f which feeds the combustion gases (Ge) and the pipe 9 which discharges the gases (Gs) after their circulation in the furnace 4.
• These Gs gases are (as mentioned above) charged with volatile organic compounds.
• lateral caissons 55a and 55a have been made on the internal walls.
• the gases are introduced into the oven 4 at a lateral box (55a or 55b) and are discharged from the oven through the other side box.
• the upper box is also divided by partitions in two half-boxes.
• the upper box 56 is divided into four compartments 57a, 57b, 58a and 58b by two partitions 59 and 60 which extend along diagonals.
• a first compartment 57a is connected to the pipe 8f of arrival of the combustion gases Ge.
• a second compartment 57b is connected to the flue gas discharge pipe 9 Gs.
• the other two compartments 58a and 58b are each connected to one of the side walls / caissons 55a or 55b.
• compartment 58a is connected to the lateral caisson 55a and that the compartment 58b is connected to the lateral caisson 55b (see also FIGS. 5a and 5b).
• each partition 59 and 60 is interrupted at a middle portion which is occupied by a median pivoting flap 61.
• This flap is controlled by a motor 62 and it can be positioned optionally in the extension of one or the other of the partitions 59 or 60. It is thus possible to share with the flap 61 the upper box 56 in two half-boxes and two different ways.
• FIG. 6a shows the upper box 56 in a position in which the middle flap 61 is in the extension of the partition 59. In this position:
• a first half-box comprises the two compartments 57a and 58a -> a second half-box comprises the two compartments 57b and 58b.
• the gases introduced into the furnace via the pipe 8f are directed towards the lateral caisson 55a and are discharged by the lateral caisson 55b after passing through the furnace 4.
• the movement of the gases in the furnace 4 is that shown in FIG. 5a, from left to right.
• FIG. 6b shows the upper casing 56 in a position in which the median flap 61 is in the extension of the partition 60. In this position:
• a first half-box comprises the two compartments 57a and 58b
• a second half-box comprises the two compartments 57b and 58a.
• the gases introduced into the furnace via the pipe 8f are directed towards the lateral box 55b and are discharged by the lateral box 55a, after passing through the furnace 4.
• the movement of the gases in the furnace is that represented in FIG. Figure 5b, from right to left.
• the pivoting flap 61 thus makes it possible to direct the combustion gases to the choice towards one or other of the side walls / caissons 55a or 55b. It is indeed interesting during the heat treatment of the wood to vary the direction of the transverse flow of the combustion gases through the furnace. Indeed, the wood treatment is homogenized. Cycles may be programmed in which the gaseous flow will be directed on either side of the wood load. Regardless of the transverse direction of the gas flow inside the oven, it is useful to introduce the gas in the lower part of the oven and recover them in the upper part. This ensures that volatile organic compounds are more safely removed. To obtain such a result the perforations 65 are distributed over the entire height of each side wall 55a, 55b.
• Each wall is also provided with a panel 66 which slides vertically on rails 63 by means of a motor 64.
• the panel 66 is sized to cover only half of all the perforations 65 carried by a wall.
• control means of the actuators 64 are defined so that, when a panel 66 is in the upper position on one wall, the panel of the other wall is located in the lower position.
• the aim is that the gases are always introduced in the lower position inside the furnace 4 and evacuated in the high position.
• the positioning of the panels must be chosen so as to always ensure a flow of combustion gases passing through the furnace from a lower part of a wall to an upper part of the other wall.
• the structure of the furnace proposed by the invention makes it possible to easily obtain a stream of combustion gases having a transverse orientation directed from one wall of the box to the other wall with the possibility of easily reversing the direction of travel of the gaseous stream to homogenize the treatment.
• the transverse gas stream may also always have an orientation from the bottom to the top of the box even when the flow direction of the current in the furnace is reversed.
• a conventional compression refrigeration unit implementing the electrical energy.
• the absorption means proposed by the invention makes it possible to optimally use the thermal resources of the installation.
• FIG. 7 shows another embodiment of a heat treatment unit 1 according to the invention.
• the hearth 6 is always heated by a burner (not shown) and combustion gases are cooled as they exit the hearth 6 by the first condenser 11.
• the condensation allows removing with water a portion of the dust contained in the combustion gases
• the water is discharged through a pipe 70 to a decanting means 13.
• the water is discharged through a collector 94 to a unit treatment 95.
• the condenser 11 is cooled by an absorption refrigerating means 14 which uses the furnace 6 as the hot source.
• FIG. 7 shows the refrigerant circuit Tn which connects the refrigerating means 14 to the first condenser 11.
• This mode differs from the previous one in that the superheater 16 is constituted by an exchanger disposed in the hearth 6 and heated by the burner itself.
• the combustion gases cooled by the condenser 11 are led by a tube 71 to the superheater 16.
• a valve 72 can isolate this branch of the installation.
• the hot combustion gases are fed to mixers 74 and 75 via a pipe 77 which divides into two branches 77a and 77b.
• bypass 73 which divides into two branches 73a and 73b also conducts a portion of the cold gases leaving the condenser 11 to the two mixers 74 and 75.
• a valve 76 isolates this branch leading the cold gases.
• the processing unit according to this embodiment therefore comprises two separate circuits conducting the combustion gases coming from the condenser 11:
• a cold circuit (73, 73a, 73b) which is shown in phantom in Figure 7.
• a hot circuit (77, 77a, 77b) which is shown in solid lines in Figure 7.
• the means 23 finally provide control of two pumps 78 and 79.
• Each of these pumps is disposed on a separate hot or cold circuit and allows to adjust the flow rate of gas flowing in the circuit.
• the pump 78 is thus disposed on the cold circuit 73 and the pump 79 on the hot circuit (but upstream of the exchanger 16). It is indeed essential that the sum of the flow rates of gas flowing in each of the circuits 73, 77 is equal to the flow rate of gas leaving the condenser 11 so as not to suffocate the combustion. This ensures the draft of the fireplace by maintaining a depression at the fireplace.
• the pump 79 makes it possible to regulate the speed of the gases flowing in the exchanger 16, which makes it possible to ensure the best possible thermal efficiency.
• Flow sensors are arranged on the various circuits (flow sensors on the circuits 73, 77 and on the outlet of the condenser 11). Temperature sensors (not shown) are also provided in the furnaces 4, 12. All these sensors are connected to the regulating means 23 to allow the latter to perform its function.
• the mixers 74, 75 thus make it possible, by dosing the mixture of hot and cold gases, to obtain the desired temperature in each oven 4 or 12.
• This embodiment of the invention makes it possible to obtain an even higher thermal efficiency. Indeed the heat energy supplied by the fireplace 6 is directly used to overheat the combustion gases.
• the mixers 74, 75 make it possible to very finely regulate the temperature of the gases sent to the ovens in a large regulation range (the combustion gas circulates in the cold circuit at a temperature of the order of 80 ° C. whereas the hot gas has a temperature of the order of 500 0 C). ⁇ This flexibility in temperature adjustment
• mixers 74 and 75 leads to a pressure drop in the various circuits of the flue gas.
• a balancing circuit at each circuit of hot or cold combustion gases.
• This balancing circuit makes it possible to reinject part of the hot or cold gases upstream of the pump of the considered circuit.
• a branch 80,83 which is connected to the circuit 77 by a valve 81 and a three-way valve 82. Part of the hot gases taken upstream of the mixers 74,75 are thus renewed , at the outlet of the valve 82, via the pipe 83 upstream of the pump 79.
• a branch 84,85 which is connected to the circuit 73 by a valve 86 and a tap three 87. A portion of the cold gases taken upstream of the mixers 74,75 are thus returned, at the outlet of the tap 87, through the pipe 85 upstream of the pump 78.
• valves 81, 86 and the valves 82, 87 are controlled by the regulating means 23 as a function of the measurement of the depression at the focal point 6 which is measured by means of a suitable sensor (not shown). It is indeed easier to measure a depression at the focus than to measure the flow rate of the gases generated by the combustion and then treated at the condenser 11. In the operation thus described is the control of the depression over the focus that regulates the rate of combustion, so the flow of gas generated.
• FIG. 7 Two furnaces are shown schematically in FIG. 7: a drying oven 12 and a treatment furnace 4. Each furnace is supplied with combustion gas at a controlled temperature from a separate mixer 74 or 75. Embodiment of the invention the structure of each furnace is simplified.
• FIGS 9a and 9b show an enlarged structure of furnaces 4,12.
• Such an oven has two side walls 55a, 55b facing one another. These walls are made in the form of boxes in which circulate the combustion gases. However here each side wall is divided into two separate half-boxes 55al, 55a2 and 55bl, 55b2.
• a lower box 55al or 55bl is intended to receive the combustion gases that are provided by the mixer 74 or 75.
• An upper box 55a2 or 55b2 collects the gases for their evacuation after their passage in the furnace 4,12.
• a three-way valve 88 or 89 is arranged upstream of the lower caissons 55a1, 55b1.
• Another valve three, lanes 90 or 91 is disposed downstream of the upper boxes 55a2, 55b2.
• FIG. 9a thus shows an oven in which the gases circulate from right to left.
• the three-way valve 88, 89 is controlled to send the combustion gases to the right bottom box 55bl.
• the gases exit from this box through the perforations 65 and they move in the direction represented by the arrows to the upper left box 55a2.
• the valve 90, 91 has been ordered to isolate the right upper box 55b2 and connect the upper left box to the gas evacuation circuit (to the second condenser 41).
• Gray is shown in Figures 9a, 9b the inactive boxes. It is no longer necessary with this embodiment of the invention to provide a sliding shutter to hide the perforations of the walls. The gases naturally follow the path that is accessible to them.
• FIG. 9b shows that, by reversing the directions of the valves 88, 89 and 90, the flow of the gases takes place in a reverse direction: from the lower left box 55al to the upper right box 55b2.
• Such an embodiment of the furnaces is simpler and more robust design than that described above with reference to Figures 4 to 6. It also facilitates the sealing of furnaces and thus limit gas leaks and losses.
• FIG. 7 shows, downstream of the furnaces, the second condensers 41 which make it possible to eliminate the water which is incorporated in the gases leaving the furnaces.
• These condensers 41 are connected to the cooling means 14 by tubings T41.
• the residue-laden water is received in tanks 92, 93. It can be seen in FIG. 7 that (the oven 12 being a drying oven) the gases leaving the oven 12 incorporate only water and that the latter can thus be conducted at the outlet of the tank 92 directly to the collector 94 which conducts the water to a reprocessing station 95.
• the oven 4 is a wood heat treatment furnace, the condensate of the gases leaving the furnace thus contains many volatile organic compounds such as condensable hydrocarbons.
• the tank 93 is thus connected to a decanting means 42 (for example of the overflow type) which makes it possible to separate the waters and the oils (or fatty acids) which are recovered in a tank 44 for later reuse ( upgrading in the chemical industry or use as fuel).
• the water from the means 42 is discharged to the collector 94.
• the gaseous fractions of the effluents may be recovered and conducted to the burner as has been described with reference to the previous embodiment.
• the second condensers 41 are connected downstream to a collector 100 for evacuating gases to the atmosphere.
• This collector has a fan 43
• venturis 96 and 97 which ensure a slight depression of furnaces 4, 12.
• the depression is adjusted by means of valves 98 and 99 which are controlled by the control means 23.
• valves 98, 99 thus make it possible to precisely manage the speed of the gases flowing in the furnaces. It is indeed desirable that this speed be as low as possible (a few tens of centimeters per second) so that the heat treatment performed is close to a steaming which avoids the twisting and bursting of organic materials treated (wood).
• valves 98 and 99 may be arranged upstream of the second condensers 41. It will then be possible to associate several furnaces with one and the same condenser 41. Each valve
• this embodiment of the invention is particularly economical and makes it possible to optimally use the heat energy supplied by the furnace, as well as to generate a gas that is poor in oxygen, as well as for the heat and regulate its temperature and circulation in the ovens.
• This embodiment however requires a particular start-up phase which will be described with reference to FIG. 8.
• the absorption refrigerating medium 14 During this start-up phase, it is necessary to start the operation of the absorption refrigerating medium 14. The latter must reach an operating mode ensuring a given temperature at the condenser 11 (between 5 ° C. and 20 ° C.) allowing to ensure the condensation of the impurities contained in the combustion gases.
• the start-up phase will therefore use the thermal energy of the burner to initiate the operation of the refrigerating means. It is in fact the heat exchanger 35 which takes the necessary thermal energy from the cooling medium 14.
• furnaces 4, 12 are completely isolated from the gas circuits.
• valves 72 and 76 are thus closed and the combustion gases do not circulate in the cold circuit 73.
• the mixers 74 and 75 are also in a position ensuring the insulation of the furnaces 4 and 12.
• FIG. 8 shows in solid lines the active gas circuits and in broken lines the inactive gas circuits.
• a nonreturn valve 104 is interposed between the pump 79 and the hot circuit 77 upstream of the superheater 16.
• the superheater circuit 16 does not receive at the start of the flow of combustion gases. In order not to deteriorate during this phase, fresh dehydrated air is circulated in this one. This air is supplied by a ventilation unit 106 through a non-return valve
• the condensed water is discharged to the decanting means 13.
• the check valves 104 and 105 insure the fresh start air and flue gas circuits. It suffices to prohibit the passage of the air supplied by the ventilation unit 106 to the pump 79 (valve 104), and to reverse the return of the combustion gases of the superheater 16 to the fan unit 106 during the permanent operation (valve 105).
• the dehydrated air is then led to the superheater 16 and it goes into the hot circuit 77. It can not go to the ovens (mixers 74,75 closed) and it borrows the circuit
• a condenser 101 is disposed at the circuit 80. This condenser is connected to the absorption refrigeration means 14.
• the heated air from the circuit 80 may possibly be led to the furnace 6 to ensure preheating.
• valves 72 and 76 open gradually while the valve 102 closes gradually and that the pumps 78 and 79 come into operation. route (and fan group 106 stops).
• the different valves and mixers are then controlled so as to balance the flow rates according to the desired temperatures for the furnaces.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Life Sciences & Earth Sciences (AREA)
• Sustainable Development (AREA)
• Drying Of Solid Materials (AREA)
• Incineration Of Waste (AREA)
• Chemical And Physical Treatments For Wood And The Like (AREA)

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• 2006
  • 2006-10-25 FR FR0609357A patent/FR2907884B1/fr not_active Expired - Fee Related
• 2007
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  • 2007-10-22 EP EP07866416A patent/EP2142871A2/fr not_active Withdrawn
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  • 2007-10-22 US US12/311,799 patent/US20100043251A1/en not_active Abandoned
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