FR2593091A1 - Method for treating organic waste with heat degradation of foul- smelling impurities and installation for the implementation of this method - Google Patents

Abstract

Method for treating organic waste with heat degradation of foul- smelling impurities; and installation which comprises an enclosure containing the mass of organic waste, a heat-degradation and heating apparatus and ducts connecting these apparatuses. A ventilation apparatus 21 sucks the gases and vapours to be found in the upper part of the enclosure 1 and a duct 36 directly connects the degradation and/or heating apparatus 23 to the means 16 for injecting a gas current into the mass of waste 8 inside the enclosure 1. Application to the drying and baking of organic waste capable of emitting unpleasant odours.

Description

 The present invention applies to a process for treating organic waste comprising a drying phase, using a flow of heat transfer gas in which the heat transfer gas is divided into two streams, the first ensuring the indirect heating of the mass of the waste then being discharged into the atmosphere, if necessary after heat exchange with a stream of fresh air, while the second stream, during the drying phase, is injected into said mass which it passes through in a movement ascending, causing impurities containing malodorous components and the water vapor produced during said drying phase. It also relates to the drying and / or cooking installation for the implementation of this process.

 The treatment of organic waste of animal origin is currently carried out by drying and cooking, causing sterilization and dehydration of this waste which allows its conservation for a relatively long period before further treatment or use in the form of dry food flours for food. animal.

 One of the most serious drawbacks of this treatment resides in the emission by this waste, during the drying phase and especially after cooking, of vapors charged with foul smells as a result of the emission by this waste of smelly gases and solid particles entrained by these vapors.

 It has already been proposed for the elimination of these smelly odors and in order to obtain a better heat transmission between the waste and the heat transfer heat gases, to carry out a heat transmission by convection in a tank inside the waste, in directly conducting a high temperature heat transfer fluid into the mass of the product by means of diffusion nozzles immersed in the latter. As heat transfer fluid, it has been proposed to use the combustion gases of a fireplace heated with gas or any other fuel. The cooled gases and the exhaust gases are sucked into the top of the tank through a cyclone and directed towards the hearth where their smelly components are advantageously destroyed.

 Fresh heated air is simultaneously introduced into the hearth to maintain combustion and the entire gas stream thus regenerated and heated is directed to the tank for a new cycle. The excess flow is directed to a heat exchanger where it gives up its available calories to the fresh air for regeneration and is then "swept through a chimney with the water vapor it contains rid of all its smelly components by following its reheating at high temperature in the hearth.

 Such a drying process has made it possible to carry out the drying of the waste by eliminating odors and other smelly components discharged into the environment, but has proved incapable of exploiting with optimum efficiency, the capacity for transmission of heat by direct convection between waste and heat transfer gases and to carry out a waste cooking phase, the decompression of which takes place without the emission of smelly vapors.

 One of the aims of the present invention is precisely to remedy most of the aforementioned drawbacks while retaining the qualities of exchange and heat balance and the ease of implementation of the process and of the installation for carrying out the process. .

 To this end, the second stream charged with impurities and water vapor and the possible stream of fresh air are introduced into a zone of thermal degradation of the impurities and heating at the outlet from which it (s) form (s). the aforementioned flow of heat transfer gas, the part constituting the second stream is injected directly into the mass of waste without first participating in the indirect heating of this mass. In this thermal degradation zone, the aforementioned second current deodorizes. The second stream is formed from most of the heat transfer gas and is introduced into the thermal degradation zone against a current of a third stream which is constituted by the possible stream of fresh air and / or a recirculation stream of the first current and is heated by a heat source such as a burner.

The circulation of the heat-transfer gas flow is ensured by the suction produced by ventilation means located upstream of the degradation and heating zone towards which the ventilation means discharge the heat-transfer gas flow loaded with impurities and fat vapor. entrained water
According to another embodiment of the method according to the invention, the stream of fresh air, after heating by heat exchange with the first stream of heat transfer gas constitutes, at least in part, the oxidant of the degradation and heating zone. Despite the aforementioned heat exchange, the mass of gas which constitutes the stream of fresh air is then extracted from the relatively heated installation and the operator has every interest in improving the thermal balance by reducing the flow of fresh air to the minimum value compatible with the maintenance of heating combustion in said degradation zone.

 During a cooking phase of the mass of waste following or preceding the drying phase described above, the degradation and heating zone operates only in the heating zone, and the second stream of the heat transfer stream is directly sucked in by the ventilation means. which it maintains operating conditions and this current does not pass through said mass of organic waste.

 After the completion of a cooking phase at an overpressure of the mass of waste, the overpressure of steam prevailing in said mass of waste is expanded at a flow control by bringing said mass into relation with the zone of thermal degradation and heating.

 The installation for implementing the method consisting of an enclosure intended to contain the mass of organic waste to be treated, in an apparatus for thermal degradation and heating, in means of indirect heating of the enclosure, in means of injection of a gas stream at the bottom of the enclosure, by means of agitation of the mass of waste, in a heat exchanger between the stream of fresh air possibly injected and the gas stream ensuring the heating of the enclosure, in a ventilation device for the suction of gases located in the upper part of the enclosure, and to ensure the circulation of the flow of heat-transfer gas, is characterized in that it comprises a pipe which directly connects the degradation and / or heating device for injecting the gas stream into the enclosure and which is capable of supplying the injection means with most of the flow of heat-transfer gas without this part participating in the heating indirect of the mass of waste. This pipe may include bypass means for interrupting the introduction of the gas stream into said enclosure and connecting said pipe to the ventilation device with reduced flow during a cooking phase in the enclosure.

 To ensure correct operation during the cooking phases, the installation according to the invention comprises control means for reducing the flow rate of the ventilation device during a cooking phase and a circuit for bypassing the heat transfer gases in short circuit of the means for injecting the gas stream as well as means for shutting off the circuit for injecting the gas stream at the bottom of the enclosure with respect to the second stream of heat transfer gas and an expansion circuit with controlled flow of the vapor pressure prevailing in the enclosure.

 As a variant, in order to provide for operation in pure electric heating, the installation comprises, to ensure the heating of the enclosure during a cooking phase, a circuit for bypassing the first gaseous current having ensured the heating of the enclosure towards the zone of thermal degradation and heating as well as switching means making it possible to direct the first gas stream either to the heat exchanger, or directly to the thermal degradation zone, in particular when the latter comprises electrical heating means.

 Other objects, advantages and characteristics of the installation will appear on reading the description of an embodiment of the invention, given without limitation and with reference to the appended drawing where the single figure represents, schematically, a complete installation for implementing the method according to the invention.

 The drying and cooking installation shown in the figure consists of a treatment tank 1 provided with various equipment which will be explained in more detail. The tank 1 has, at its lower part, a double jacket 2 allowing its heating by conduction using a gas circuit 3 3 indirect heating constituting a first heating current. The tank 1 which can be pressurized (normally up to 3 bar to reach temperatures of around 1300C), is closed by a dome 4 crossed by a shaft 5 for rotational drive via a gearmotor 6, a rotary harrow 7 constituting a means of agitation of the mass of waste 8 contained inside the tank. The dome 4 is connected to a pipe 9 for supplying heat transfer gas constituting the second stream and forms with an annular tubular plate 4a a annular chamber 15 for distributing the heat transfer gas using a plurality of injectors 16 leaving the plate 4a to plunge into and to the bottom of the mass of waste 8. A pipe 10 for discharging the heat transfer gas and of the clearance which it entails consisting of smelly components and of water vapor by an annular collecting chimney lb surrounding the shaft 5 inside the ring of the distribution chamber 15, this chimney lb being closed a the upper part of the steam chamber the left free inside the tank 1 above the mass of waste 8. A loading door is provided on the dome 4 in correspondence with a chute 12 for supplying waste and with a loading passage arranged at through the chamber 15. The bottom of the tank 1 and the double jacket 2 are crossed by an unloading door 13 placed in correspondence with a chute 14 for discharging the treated waste. Inside the tank 1, the pipe 9 for supplying heat transfer gas is thus connected, via the annular chamber 15, to the inside of the tank 1 by the plurality of fixed injectors 16 plunging into the bottom of the mass. of waste 8 which is rotated by the harrow 7 and continuously brought back from the surface to the bottom by a spiral or a propeller Sa shows around the shaft 5.

 The discharge line 10 is connected via an isolation valve 17, a measurement venturi 18, a filter 19 or a cyclone (only the version with a filter has been shown, these two devices having the function of stopping particles larger solids) and a shut-off valve 20 has a fan 21 aspirating into the tank 1 and discharging towards the inlet 22 of a thermal degradation and heating apparatus 23.

In order to establish a pressure relief circuit for the tank 1, a bypass line 24 of smaller cross section and itself provided with an expansion and cut-off valve 25 is connected upstream of the isolation valve 17 on the discharge pipe 10 and connected to the inlet of the venturi 18. The valve 25 is thus capable of regulating and regulatingly relaxing a substantially constant vapor flow rate on the venturi 18. The fan 21 (preferably produced under in the form of a centrifugal fan with a single rotor) must, in addition to its function of propulsion of the flow of heat-carrying gas, ensure the propulsion of the water vapor released by the waste and overcome the pressure drops of the second stream through the mass of waste. The variable power that this fan must provide is obtained either by continuous adjustment of the speed of rotation, or by the use of a two-speed electric drive motor.

 The degradation and heating apparatus 23 is made up, inside a casing 26, of an inlet circuit 27 where the gases charged with impurities and brought to the inlet 22, flow against the current d an outlet circuit 28 traversed by hot gases directed towards an outlet smoke box 29 in which an auxiliary heat exchanger 30 can be arranged.

 The gases loaded with impurities are brought into a reflux hearth 31 where they mix with hot gases from a burner 32 operating, for example, with gas in order to obtain an easier adjustment. The hot gases can also come from the licking of an electric resistance bank 33 operating in isolation or in coupling with the burner 32. The hot gases coming from the mixture in the reflux hearth 31, are introduced into the outlet circuit, for example at a temperature of 900 ° C., where they heat the incoming gases charged with impurities against the current, up to a temperature of 8500 ° C. so as to produce a cracking of the smelly gases and a decomposition of the particles which leave only combustible gases which can burn in the presence of fresh air brought in excess around the burner 32 by a pipe 34 for injecting fresh air.

 -At its exit from the smoke box 29, the mixture of burnt gases and recycled gases stripped of their smelly constituents is at a temperature of around 4500C and is brought by a supply pipe 35 to the tank 1 where it separates into two streams. The pipe 35 is connected directly by a pipe 36 via an isolation valve 37, to the pipe 9 for supplying heat transfer gas and via the chamber 15 to the injectors 16 immersed in the mass of waste 8. The pipe 36 is connected at upstream of the valve 37 by a pipe 38 of smaller section provided with an adjustment and / or cut-off valve 39, downstream of the filter or of the cyclone 19 so as to allow gas circulation to be maintained through the fan 21 during the cooking phases when the valves 17 and 37 are closed.

 The gas circuit 3 of the double jacket 2 which is stitched on the pipe 35 and takes at most a quarter of the flow supplied by this pipe, is connected by a pipe 39 provided with an adjustment and / or shutter valve 40 to a heat exchanger bundle 41 housed in a box 42 where it is in a heat exchange situation with fresh air drawn in. The output 43 of the beam 41 is connected to the atmosphere or to the discharge and the temperature of the discharged gases is controlled by a probe 44 which can be coupled to the control circuits of the installation. The fresh air is discharged into the box 42 by a fan 45 provided with adjustment means 46 at the suction. The temperature and pressure characteristics of the aspirated air are measured by the probes 47 coupled like the adjustment means 46 to the adjustment circuits.

 At the outlet of the box 42, the warmed fresh air is discharged through line 34 to the burner 32 to possibly constitute the combustion air of the burner and from there the warmed fresh air is mixed in the reflux hearth 31 with the gas recirculation coolant. The temperature of the heated fresh air is measured by a probe 48 connected to the central monitoring and adjustment circuits and it is noted that a pipe 49 is provided fitted with an adjustment and / or shutter valve 50 and which connects the pipes 39 and 10 (downstream of the isolation valve 17) in short circuit of the heat exchanger bundle 41. An adjustment or shutter valve 51 provided on the pipe 39 downstream of the connection of the pipe 49, makes it possible to impose on the heat transfer gases leaving the double jacket 2, recirculation through the pipe 10 and the fan 21 to the heating appliance 23. A cut-off valve 52 allows, if necessary, to isolate from the pipe 34 the box 42 of the heat exchanger.

 Different temperature and pressure probes are installed on the installation circuits and connected to central adjustment circuits 53. Among these probes, there are the probes 54 of the tank 1, the probe 55 of the discharge pipe 10 at the outlet of the tank, the probe 56 on the pipe 38, the probes 57 on the pipe 58 connecting the fan 21 to the inlet 22 of the degradation and / or heating apparatus 23, as well as the probe 59 on the pipe 35 at the outlet of the smoke box 29. A temperature probe 60 resistant to high temperatures is installed in the return circuit of the heat-carrying gases charged with impurities to the reflux hearth 31, near the inlet of the gases into This hearth. This probe 60 makes it possible to ensure that the gases charged with impurities actually reach a high temperature capable of destroying the malodorous components. In order to ensure that this high temperature, which has been reported to reach 8500C (the gas circuits are made of refractory materials such as stainless steel), is obtained, the probe 60 is coupled in servo via the central circuits. 53 to the burner 32 or to its gas inlet 61 and to the electrical resistance benches 33.

 The operation of the installation for implementing the method will now be explained. At the start of a drying and cooking cycle, after loading the tank 1 with waste 8, the fan 21 is put into operation, the valves 37 and 17 being open and the burner 32 and / or the resistance benches 33 are put in heating. The fan 45 discharges fresh air onto the burner 32 and the reflux hearth 31 and the mixture heated to about 4500C of the fresh air and the recirculating gases forming the gaseous heat flow, is discharged through the pipe 35 into one first indirect reheating current 3 in the jacket 2 and in a second current supplied by line 36, the valve 37 open, the supply line 9, the annular chamber 15, up to the outlet of the injectors 16 at the bottom of the mass of waste 8.

 The second gaseous heat transfer stream, formed by about three quarters of the flow, gives up, during its passage through the mass of waste, part of its heat and becomes charged with water vapor, gas and particles emitted by waste which, in the case of waste of animal origin, emits a particularly unpleasant and nauseating odor. The rotation of the harrow 7 imposes on the mass of waste 8 the maintenance of a minimum porosity limiting the pressure losses of the circuit of the second stream of heat-transfer gas which are overcome mainly by the fact that the fan 21 works in suction and maintains the inside the tank 1 under vacuum under the control of a pressure control, which limits the risk of leakage of bad odors: through the possible gaps in the tank 1 and the circuit.

 The coolant gas cooled after passing through the waste and charged with vapors and bad smells is discharged by the fan 21 and the line 58 in the input circuit 27 of the device 23 where it is heated by the hearth gases against current up to a temperature of the order of 8500C where all the smelly gases are cracked while the particles are carbon with emission of non-smelly combustible gases. The remaining smelly gases are finally burned in the reflux hearth 31 and mixed with the reheated fresh air and any burnt gases from the burner 32.

 The first stream, which provides indirect heating of the tank 1 by the double jacket 2, is discharged through line 39 at a relatively high temperature of the order of 3500C. It then passes into the heat exchange bundle 41 of the box 42, where the distinct stream of fresh combustion air discharged by the fan 45 is heated.

This first current is then discharged into the atmosphere at a more moderate temperature of the order of 2000C and this thermal recovery by the combustion air makes it possible to improve the thermal balance of the installation. As a variant, when the condensed vapors are not aggressive for the environment, it is possible to lower the outlet temperature at 43 of the first current to a value below the dew point under the supervision of the probe 44 and to evacuate at least part of the vapor emitted in the form of condensed water. In all other cases, the mass of gas leaving the bundle 41 consists of that of the air discharged by the fan 45, fuel injected into the burner 32 and cracked vapors and impurities emitted by the mass of waste 8.

 When the waste has dried sufficiently, it is possible to cook it, thereby reducing the amount of heat necessary to bring the waste to cooking temperature. To this end, the valves 37 and 17 are closed and the valve 38a is open to maintain a circulation of gas through the fan 21.

 The tank 1 rises in pressure as a result of heating and the cooking temperature is established throughout the mass of the waste. At the end of cooking, the pressure prevailing in the tank 1 is relieved by the valve 25 and the circuit 24 so that the particularly smelly gases emitted by the waste 8 during cooking are deodorized by heating in the appliance. 23 and that the vapor is then evacuated to the atmosphere. For this, the valve 25 ensures the expansion of a substantially constant vapor flow which can between monitored by the venturi 18 and which corresponds to the degradation capacity of the device 23. When the pressure # in the tank 1 is lowered to the level of atmospheric pressure, it is possible to resume drying to complete it until bringing the water content of the waste to low values between 12 and 81 guaranteeing their long-term conservation. During this last drying phase, the cooling of the heat transfer gas is significantly lower and the power of the burner 32 as well as the flow of fresh air must be reduced accordingly, which is done automatically by the aforementioned control of the burner 32 and / or of the bench 33 of electrical resistances at the "overheating" temperature of the smelly gases detected by the probe 60.

 It will be noted in this subject that the fan 21 is advantageously entralné, as mentioned previously by an electric motor (in particular an asynchronous motor) with two rotational speeds. The slow speed is used for starting the fan and stabilizing the heat transfer circuit after the ignition of the burner 32, as well as during the cooking phase where only the reduced flow rate supplied by the pipe 38 transits, and during the final drying phase. after cooking. The rapid speed of the fan, corresponding to the initial drying of the waste 8 until it is cooked, is thus used for only about half the duration of the treatment process, which. not only reduces the consumption of electric propulsion energy (recovered in the form of heat participating in drying) but above all the wear of the moving parts and the valves of the heat transfer gas circuit.

 The arrangement of the annular coolant gas distribution chamber 15 with its lower tube plate 4a eliminates the risks of accumulation of solid or greasy particles, these particles being preferably retained by a cyclone mounted upstream of the venturi 18 for measurement and adjustment. , the filter 19 no longer playing a security role. The injector tubes 16 retained in a fixed position by the tube plate are distributed and oriented so as to impose on the mass of waste 8, driven in rotation by the harrow 7, an additional stirring which maintains the porosity of this mass to the injected heat transfer gases. The pressure drop of the heat transfer gases at the crossing of the mass of waste being substantially proportional to the height of this mass, the increase in the power of the devices will preferably be carried out by increasing their diameter rather than their height.

 Of course the present invention is not limited to the embodiments described and shown, but it is capable of numerous variants accessible to those skilled in the art without departing from the spirit of the invention.

Claims (11)

 1.- Process for treating a mass of organic waste comprising a drying phase, using a flow of heat transfer gas in which the heat transfer gas is divided into two streams, the first ensuring the indirect heating of the mass waste, then being discharged into the atmosphere, if necessary after heat exchange with a stream of fresh air, while the second stream, during the drying phase, is injected into said mass which it crosses in an upward movement by entraining impurities containing malodorous components and the water vapor produced during said drying phase, characterized in that the second stream charged with impurities and water vapor and the possible stream of fresh air are introduced into a zone of thermal degradation of impurities and of heating at the outlet from which it (s) form (s) the aforementioned heat transfer stream, the part constituting the second stream is injected directly into the mass of waste without participate in the indirect heating of this mass.  2.- Method according to claim 1, characterized in that most of the flow of heat transfer gas forms the second stream.  3.- Method according to claim 1 or 2, characterized in that the second stream is introduced into the thermal degradation zone against the current of a third stream which is constituted by the stream of fresh air and / or a stream recirculation of the first stream and is heated by a heat source, such as a burner.  4.- Method according to any one of claims 1 to 3, characterized in that the circulation of the flow of heat transfer gas is ensured by the suction produced by ventilation means located upstream of the degradation and heating zone.  5.- Method according to any one of claims 1 to 4, characterized in that the fresh air stream after heating by heat exchange with the first stream of heat transfer gas constitutes, at least in part, the oxidizer of the zone degradation and heating.  6.- Method according to one of claims 1 to 5, characterized in that during a cooking phase of the mass of waste, the degradation and heating zone operates only in the heating zone, and in that the second stream heat transfer stream is directly sucked by the ventilation means which it ensures the maintenance of operating conditions without passing through the area containing said mass of organic waste.  7.- Method according to one of claims 1 to 6, characterized in that after the completion of a cooking phase in excess pressure of the mass of waste, the vapor pressure prevailing in said mass of waste is expanded to flow rate controlled by placing said mass in relation with the thermal degradation and heating zone.  8.- Installation for the implementation of the method according to any one of claims 1 to 7, consisting of an enclosure intended to contain the mass of organic waste to be treated, in a thermal degradation and heating apparatus, in means indirect heating of the enclosure, by means of injecting a stream of gas inside the mass of waste, by means of agitation of the mass of aforementioned organic waste, by a heat exchanger between the fresh air possibly injected and the gas stream ensuring the aforementioned indirect heating, in a ventilation device for the suction of the gases located in the upper part of the enclosure and for ensuring the circulation of the flow of heat-carrying gas, characterized in that it comprises a line (36) which directly connects the degradation and / or heating device (23) to the injection means (16) of the gas stream in the enclosure (1) and which is capable of bring to the injection means (16) the most large part of the heat transfer gas flow without this part participating in the indirect heating of the mass of waste (8).  9.- Installation according to claim 8, characterized in that the pipe (36) comprises bypass means (3t, 38, 17) for interrupting the introduction of the gas stream into said enclosure (1) and connecting said pipe ( 36) to the ventilation device (21) with reduced flow during a cooking phase in the enclosure (1).  10.- Installation according to claim 8 or 9, characterized in that it comprises control means capable of reducing the flow rate of the ventilation device (21) during a cooking phase and a bypass circuit (38) heat transfer gases in short circuit of the means for injecting (16) the gas stream as well as means for shutting off (37, 17) the injection circuit (16) of the gas stream at the bottom of the enclosure (1 ) relative to the second stream (3) of heat transfer gas and an expansion circuit (25, 24) with a controlled flow rate of the vapor pressure prevailing in the enclosure (1).  11.- Installation according to one of claims 8 to 10, characterized in that it comprises, to ensure the heating of the enclosure (1) during a cooking phase, a bypass circuit (49) of the first gas stream (3) having provided the heating of the enclosure (1) towards the thermal degradation and heating zone (23) as well as switching means (50, 51, 52) making it possible to direct the first gas stream (3) either to the heat exchanger (41, 42 ',, either directly to the thermal degradation device (23), in particular when this includes electrical heating means (33).