AU743972B2

AU743972B2 - Pyrolytic oven with dust extraction of the gas stream output resulting from pyrolysis

Info

Publication number: AU743972B2
Application number: AU40461/99A
Authority: AU
Inventors: Rene Willemin
Original assignee: THIDE ENVIRONNEMENT
Current assignee: THIDE ENVIRONNEMENT
Priority date: 1998-06-08
Filing date: 1999-06-07
Publication date: 2002-02-14
Anticipated expiration: 2019-06-07
Also published as: ES2196807T3; FR2779441B1; EP1093506B1; EP1093506A1; DE69906529T2; JP4327358B2; BR9910988A; CZ302188B6; KR100628290B1; KR20010071432A; WO1999064539A1; NZ508718A; PT1093506E; FR2779441A1; CZ20004571A3; ATE236233T1; CA2334638A1; CA2334638C; PL198508B1; DE69906529D1

Abstract

The invention concerns a pyrolytic oven comprising an airtight cavity (50), including an inlet interface for inserting waste in said cavity (50) and an outlet (54) for the gas stream resulting from pyrolysis. A combustion chamber (60) encloses the cavity (50), and a burner (80) has an inlet (84) connected to the cavity outlet (24) and an outlet (86) delivering a fuel gas into the combustion chamber (60). The cavity gas stream outlet (54) comprises at least a discharge duct (GA) comprising one first end connected to the cavity and a second end connected to the burner (80), the duct (GA) being capable of housing a coreless screw (117) for capturing at least part of the solid carbon-containing particles present in the gas stream resulting from pyrolysis and for rotating, under control, so as to send back into the oven cavity the captured particles.

Description

Pyrolytic oven with dust extraction of the gas stream output resulting from pyrolysis The present invention relates to pyrolysis, in particular of urban and/or industrial waste.

It can be applied generally to processing of waste, and more particularly of household waste. It can also be applied to processing of tyres, sewage plant sludge, plastics, paper trade waste, plastics, car-crushing waste, solid industrial waste, biomass, polluted earth, etc.

A plurality of waste pyrolysis installations is already known.

For example, in FR-A-2 654 112, FR-A-2 679 009 and FR- A-2 678 850, a waste pyrolytic oven comprises a substantially cylindrical airtight cavity, which rotates around its longitudinal axis, and comprises an input interface for introduction of the waste into the cavity, and a gas stream output. An envelope encloses the cavity. A burner has an input which is connected to the output of the cavity, and an output which supplies a combustion gas to the envelope.

In practice, the increase in the temperature of the cavity, which is obtained from the combustion stream which circulates in the envelope which encloses the cavity, makes it possible to break down the waste contained in the cavity into solid carbon-containing substances.

Implementation of neutralisation of the pollutants in pyrolysis is relatively easy, even when the original content of the waste varies considerably in terms of pollutants, since the pollutants are processed before use (usually combustion) of the solid carbon-containing substances obtained from the pyrolysis.

Consequently, pyrolysis is better suited to heterogeneous waste than incineration, where the pollutants are processed after combustion of the waste has taken place.

The pyrolysis reaction is produced in an oven sealed against air, at a temperature of between 450 0 C and 600 0

C.

Selection of this temperature is dependent on the nature of the waste processed. The reaction to these temperatures (cracking) produces gas and carbon-containing solids. This reaction is carried out without pressure, in order to avoid subjecting the seals of the rotary oven to stress.

This lack of pressure gives rise to low speeds of output of the composite gas produced by the reaction.

Despite this, and owing to their small particle size and low density, particles of carbon-containing solids are entrained by the gases.

At the output of the oven, the gas which is obtained from the pyrolysis is channelled into piping, and is guided towards the burner, which will assure that combustion of the gas takes place. Gradually, the particles of carboncontaining solids are deposited on the periphery of the discharge duct, until, firstly, the free cross-section of this duct is progressively reduced, and finally it is blocked completely, thus giving rise to stoppages of the supply of fuel to the burner.

The present invention provides a solution to this problem.

The invention relates to a pyrolytic oven, in particular for urban and/or industrial waste, of the type comprising: an airtight cavity, including an intake interface for insertion of the waste into the said cavity, and an outlet for the gas stream obtained from the pyrolysis; a combustion chamber which encloses the cavity; and a least one burner which has an input connected to the gas stream output of the cavity, and an output which can supply a combustion gas to the combustion chamber.

According to a general definition of the invention, the gas stream output of the cavity comprises at least one discharge duct, comprising a first end which is connected to the cavity, and a second end which is connected to the burner, the duct being able to accommodate a coreless screw, which can recover at least part of the solid carboncontaining particles which are present in the gas stream obtained from the pyrolysis, and can be rotated under control, in order to return to the oven cavity the particles thus recovered.

The coreless screw firstly gives rise to recovering of the particles of carbon-containing solids, and then assures cleaning of the discharge duct, by returning the particles thus recovered to the oven cavity, for example at programmed intervals.

Preferably, the coreless screw comprises helical threads, the width and pitch of which are selected according to an average speed of discharge of the gas stream obtained from the pyrolysis, such as to trap at least some of the particles which are present in the said gas stream.

According to a preferred embodiment of the invention, the gas stream output from the cavity comprises first and second discharge ducts, each comprising a first and a second end, each first end being connected to the cavity, and each second end being connected to a common node, the output of which is connected to the burner, each discharge duct comprising a shutter and a coreless screw, which, under control, can extract the dust from the associated duct, the shutter of the duct from which the dust is to be extracted being closed, whereas the shutter of the other duct is open for discharge of the pyrolysis gases.

In practice, the shutters are closed alternately.

Thus, when one of the discharge ducts is in service, the other is shut, in order to permit the sweeping sequence which is essential for cleaning of this duct.

The object of the present invention is also an oven, into the cavity of which there is improved introduction of waste.

According to a further characteristic of the oven in which the means for introduction of waste can receive, compact and charge the waste to be processed into the input interface of the cavity, whilst preventing any air from entering the cavity, the input interface of the cavity comprises at least a first and a second input, and the means for introduction of waste comprise a first and a second introduction channel, which are connected respectively to the first and second inputs of the cavity, means which form a press in order to compact the waste and thrust it into the first and second introduction channels, and control means, which can control in a staggered manner the compacting and charging of the waste into the first and second inputs of the cavity, whilst maintaining the impermeability of the cavity.

I

Advantageously, the staggered control of the compacting and charging of the waste in the two inputs of the cavity reduces the effect of dead time of returns of the means for introduction, which permits virtually continuous introduction of the waste into the cavity, and consequently an increase 'in the throughput of the waste processed.

A device of this type also has the advantage that it increases the throughput of the waste processed, without increasing the diameter of the introduction channel, and thus without creating any intakes of air into the cavity.

The virtually continuous introduction of the waste also makes it possible to supply the burner with a constant throughput of gas, which prevents sequential degassing of the waste.

Highly advantageously, the two introduction channels are connected to one another by an air-venting channel, in order to improve further still the impermeability of the introduction of the waste into the cavity.

According to another characteristic of the invention, each introduction channel comprises a first and a second end, the first end being connected to the input which is associated with the cavity, and comprising a drop shutter which closes under control the said input of the cavity, and the second end accommodating a thrust mechanism which can be displaced under control in two directions in the introduction channel, in order to thrust the waste towards the associated drop shutter, and the means for control can control synchronously the displacement of the thrust mechanism and opening/closure of the drop shutter.

Advantageously, the upper part of each introduction channel comprises a trap door to receive the waste.

In practice, each introduction channel is substantially parallelepiped, and substantially parallel to the longitudinal axis of the cavity.

The present invention also relates to a pyrolytic oven which additionally comprises a unit for recovery of the solid carbon-containing substances which are obtained from the pyrolysis cavity, the said recovery unit comprising a discharge channel which forms a syphon/seal, the said discharge channel comprising a container which is connected to the cavity, at the base of which the solid carboncontaining substances accumulate in the form of a stopper which is impermeable to air, and a recovery mechanism which can conduct the solid carbon-containing substances thus accumulated towards a unit for separation and washing.

Advantageously, the unit for separation and washing which is associated with the recovery unit comprises a perforated drum, which can rotate in a decantation and washing container, in particular in order to supply a mixture of water and solid carbon-containing substances, the value of which can be enhanced.

Advantageously, the unit for separation and washing is additionally connected to means for processing of the waters, comprising a plurality of- decantation and washing containers which are connected to one another, and each of which contains a washing solution with a selected concentration, which is different and decreases from one container to the next, as well as pumps and solenoid valves which are controlled by contamination meters and level contactors, in order to drain the washing solution from a container which has a concentration higher than a predetermined threshold, into the previous container, whereas the level of the washing solution of the said container is kept constant by supplying it with the less concentrated washing solution of the following container.

The object of the present invention also consists of use in a glass-making oven of the solid carbon-containing substances thus obtained, by means of the oven of the above-described type.

Other characteristics and advantages of the installation will become apparent from the following detailed description, and the drawings, in which: figure 1 is an overall view of a pyrolysis installation according to the invention; figures 2A to 2D represent schematically the dualinput unit according to the invention, for introduction of waste; figure 3 is a view from beneath of the two channels according to the invention, for introduction of waste; figure 4 is a perspective view of the dual output according to the invention, for the pyrolysis gases; figure 5 is a view in cross-section of the dual gas output described with reference to figure 4; figure 6 is a view of a coreless screw accommodated in a discharge duct according to the invention, for the gas stream obtained from the pyrolysis; figure 7 is a curve which illustrates the efficiency of the dust extractor according to the invention; and figure 8 is a view in cross-section of the unit for recovery and separation of the solid carbon-containing substances obtained from the pyrolytic oven according to the invention.

The drawings contain elements of a certain nature which can assist in understanding the description of the invention, and, where applicable, defining the latter.

With reference to figure 1, a waste pyrolysis installation comprises in general a unit REC for reception and crushing of waste, a drying unit SEC, a pyrolysis unit THE, and a unit for recovery REP and washing LAV of the solid carbon-containing substances obtained from the pyrolysis unit.

The reception unit REC comprises a pit 2 into which there is tipped the waste to be processed, which is for example transported by trucks 4. Advantageously, the waste is crushed in order to reduce the volume to be processed to a more homogeneous size. For example, an overhead crane 6 collects the waste contained in the pit 2, in order to take it to a crusher 8. The mesh size of the crusher 8 is for example 100 to 150 mm, in order to assist transport and exchange of heat in the pyrolysis method which will be described in greater detail hereinafter.

Advantageously, bulky waste (metal bars, pipes) are removed 10. The crushed waste obtained from the crusher 8 is tipped into a pit 12. A conveyor belt 14 conveys the crushed products 12 towards the drying unit SEC.

The pit 12 acts as a buffer between the crusher 8 and the conveyor belt 14, which assures a constant supply to a rotary dryer 20, the purpose of which is to eliminate a substantial part of the water vapour contained in the products to be processed, in order to increase their NCV (net calorific value). In practice, before it enters the dryer, the waste can be sorted magnetically in order to eliminate the ferrous metals 16. This magnetic sorting can be envisaged after the pyrolysis.

It should be noted that in the case of processing of a dry industrial product, this drying step can be eliminated, and the waste then enters directly the hopper of the pyrolytic oven, which will be described hereinafter.

The waste is dried in a rotary enclosure 22, by being put into contact with a stream of hot air 24 obtained from the reception unit REC. This hot air 24 is heated by being passed through a heat exchanger 30 of the gas/gas type, the heating stream 32 of which is obtained from the pyrolysis unit THE.

The reception pit 2 is put partially under vacuum, which prevents any propagation of dust and unpleasant odours when the doors are opened, whilst the trucks 4 are being unloaded.

A shredder (not shown) for plastic bags can advantageously be provided in front of the dryer input The dry products and the water vapour charged with gas obtained from the drying are then separated by means of a separator (cyclonic enclosure) 40, which can separate the solid products from the gaseous products.

The separator unit 40 comprises an input 42, which receives the waste obtained from the drying unit SEC, a first output 44 which supplies the solid waste, and a second output 46 which supplies the gaseous waste.

The pyrolysis unit THE comprises a pyrolytic oven, containing an airtight cavity 50, which is cylindrical, and preferably rotates around its longitudinal axis. The pyrolytic oven additionally comprises an envelope 60, which surrounds the said cavity Means 70 for introduction of waste receive the waste to be processed, obtained from the output 44 of the separator unit 40. The waste thus received is then compacted, and charged thus compacted into the cavity, whilst any air is prevented from entering the cavity.

The pyrolytic oven is heated by at least one burner which has a first input 82, which receives the gaseous waste 85 obtained from the output 46 of the separator 40, a second input 84, which receives the gas stream obtained from the output 54 of the cavity 50, and an output 86, which supplies a combustion gas stream to the envelope which surrounds the cavity 50. This gas stream is said to be a combustion gas stream, in that it is designed to bring to a selected temperature the waste introduced into the said cavity 50, in order to carry out the pyrolysis of the said waste.

The gas streams obtained from the drying 85 and the pyrolysis 54 are advantageously used as burner fuels which makes it possible to obtain functioning which is substantially autothermal.

The installation is completed by a heat exchanger of the gas/gas type, which, in the secondary unit, has a heated stream which goes from the second output 46 of the separator unit 40, to the first input 82 of the burner, and in the primary unit, has a heating stream which is obtained from the output 66 of the double envelope 60 of the pyrolytic oven THE.

The combustion chamber which contains the burner 80 is advantageously provided with refractory substance. The burner 80 is, for example, of the low NO, type, and can assure a temperature of 1500 0 C at the flame, and 1000 to 1100 0 C at the output 86.

It should be noted that the installation according to the invention eliminates all pollution caused by dioxins, NO,, and aromatic compounds.

Owing to its composition, the gaseous mixture obtained from the pyrolysis 54, which is kept at a temperature higher than 300 0 C (in order to prevent condensation of the hydrocarbons), can be burnt in the burner 80 without prior treatment, provided that it does not contain any pollutant agent.

In practice, only mercury which is vaporised during the drying requires a recovery system. For example, with reference to figure 1, a recovery system 550 is installed before discharge 560 towards the exterior takes place. This system 550 consists for example of activated carbon equipment, to which the mercury particles become attached.

The applicant aims to improve further still the installation described with reference to figure 1, in particular concerning introduction of the waste into the cavity, in order to improve the throughput of the waste processed.

With reference to figures 2A to 2D and 3 according to the invention, the cavity 50 comprises first and second inputs 51 and 53 for waste.

The means 70 for introduction of waste comprise introduction channels 72 and 74, which are connected respectively to the inputs 51 and 53 of the cavity.

The channel 72 has ends 71 and 75, whereas the channel 74 has ends 73 and 77. The end 71 is connected to the input 51 of the cavity. The end 73 is connected to the input 53.

A drop shutter 76 which is accommodated in the channel 72 shuts under control the input 51 of the cavity. A drop shutter 78 which is accommodated in the channel 74 shuts under control the input 53 of the cavity. Each channel accommodates a thrust mechanism 79, 81 (for example of the piston or jack type), which can be displaced under control in two directions in the associated channel, in order to thrust the waste towards the drop shutter which shuts the associated input of the cavity.

Means for control (not shown) can control the displacement of the thrust mechanism and opening/closure of the drop shutter of each introduction channel, in order to permit introduction of compacted, impermeable small bales in a staggered manner into the cavity.

In practice, the upper part of each introduction channel comprises a trap door 85, 87, which is disposed opposite the hopper 83 for reception of the waste.

In addition, each introduction channel comprises a jack 89, 91 which is perpendicular to the jacks 79 and 81, in order to assist compacting of the waste into the form of impermeable small bales.

In practice, each introduction channel is substantially parallelepiped and substantially parallel to the longitudinal axis of the cavity.

The path of the waste to be processed in the reception hopper 83 comprises for example a first, one-way conveyor 95, which tips the waste onto a second, two-way conveyor 97, which is arranged such as to tip the waste into the respective trap doors 85, 87 of the introduction channels.

Advantageously, the two introduction channels are connected to one another by a channel 88, which can vent air, in order to improve further still the impermeability of introduction of the waste into the cavity.

With reference to figure 3, the piston 81 is in the front position, whereas the piston 79 is in the rear position. The waste 96 is untreated (not compacted) when the piston is in the rear position, whereas it is compacted when the piston is in the front position.

The applicant also set itself the problem of eliminating the accumulation of fine particles in the discharge duct for the gases which are obtained from the pyrolysis.

With reference to figures 4 to 6, a dust extractor device is designed to be accommodated in the discharge duct(s) for the gas stream obtained from the pyrolysis.

The dust extractor device consists of a coreless screw 117 which is inserted in the discharge duct GA for the gas stream. The outer diameter of the screw is substantially equivalent to the inner diameter of the duct, leaving slight play of a few millimetres. For example, play of 4 mm added to the total is perfectly suitable within the context of a duct which is 20 cm in diameter. The coreless screw 117 consists originally of a flat bar with a rectangular cross-section, which has been provided with a helical shape with a certain pitch. The largest dimension of the crosssection of the flat bar forms an angle of 900 relative to the internal generatrix of the discharge duct.

The coreless screw 117 occupies an annular space. It leaves free the central area of the duct GA. The width of the threads and the pitch of the screw are calculated according to the dust to be recovered and the qualitative analysis of the configuration of flow of the gas.

Advantageously, the coreless screw is reinforced longitudinally, in particular in the vicinity of the drive motor MO, in order to prevent the screw from being twisted as it rotates.

The helical geometry of the screw induces a current which is tangential in rotation around the axis of the discharge duct. In the free central area, the geometry of the dust extractor does not force the gas to acquire a tangential flow. This flow configuration is stable, and constitutes an established flow configuration. The shearing stresses (friction between peripheral layers) depend on the volume mass of the fluid and the kinematic viscosity of the fluid itself. The helical flow established gives rise to release of the dust, under the effect of centrifugal force.

These particles are trapped by the screw 117, which forms a dust extractor. The efficiency of the dust extractor depends on the class of particles, according to the curve described with reference to figure 7.

The advantage of the dust extractor device according to the invention consists in its efficiency in trapping dust with a particle size greater than 2 p. The stream of dust smaller than 2A is very slight, and does not have any effect on the functioning of the installation downstream from the screw, in the direction of propagation of the gas stream F1 obtained from the pyrolysis.

In order to avoid detracting from the functioning of the installation, the dust extractor equipment is doubled.

A first discharge duct is fitted to the rear box 49 of the oven, in order to assure the flow of the gas. When the trapping has reached its reference value, an automatic or manual control rotates the helical screw which occupies the interior of the discharge duct, by means of an entrainment mechanism MO, in order to return the trapped dust to the oven in the direction F2, opposite the direction of propagation of the gases Fl. This operation is preceded by shutting the piping by means of a motorised shutter.

Control of these two operations can be automated, by making them dependent on a differential pressure switch, which measures the variation of the loss of load after dust extraction.

In order to avoid disrupting the functioning of the installation, initiation of the sweeping operation in the first discharge duct is preceded by putting the second discharge duct into service in parallel with the first, by commanding opening of the motorised shutter with which this second duct is provided. The sequence of trapping the dust can then be established in the second duct, until the reference value is reached, which will trigger a new sweeping sequence identical to the previous one.

By this means, and by means of alternating transition from one discharge duct to the other, continuous functioning is obtained, without significant modification of the gas stream obtained from the pyrolysis.

This highly efficient device for extraction of dust from gases with a low flow speed, makes it possible to retain between 98% and 99% of the dust. Only aerosols with a size of less than 2/ can escape recovery (figure 7) With reference to figures 4 and 5, according to the invention, modifications are made to thegas output 54 of the cavity 50 which is connected to the input 84 of the burner 80. According to the invention, this output 54 comprises at least two discharge ducts 102 and 104.

The discharge duct 102 has ends 103 and 105, whereas the discharge duct 104 has ends 107 and 109. The ends 103 and 107 are connected to the fixed part (on the front surface) of the rear box 49 of the oven 50 which contains the solid carbon-containing substances MSC obtained from the pyrolysis. The ends 105 and 109 are connected to a common node 110, the output 112 of which is connected to the input 84 of the burner With reference to figure 6, the ends 103 and 107 of the ducts GA are connected to the upper part (at the top) of the rear box 49 of the oven.

Each discharge duct comprises a shutter 114 and an individual duct dust extractor mechanism 116. The shutter 114 of the dust extractor duct is put into a closed position, whereas the shutter of the other duct is put into an open position for discharge of the pyrolysis gases during dust extraction for the duct from which dust is to be extracted.

With reference to figure 5, the dust extractor mechanism 116 comprises a coreless screw 117, which is accommodated inside the duct.

As a variant, the dust extractor mechanism comprises a mechanism for blowing by means of a neutral gas, or a mechanism which can give rise to vibratory impact on the duct from which dust is to be extracted.

The invention thus uses two gas outputs and two systems for separation of dust, one on each discharge duct.

In practice, when the loss of load caused by the dust deposited increases above a certain limit which is displayed on a control pressure switch (not shown), a motorised shutter 114 is actuated in order to permit discharge on the second duct. This cleaning of the dirty discharge duct can therefore be carried out automatically by rotating the screw 117.

The length of the horizontal pipe is several metres, for example 6, and the length of the coreless screw is several metres, for example 3.

The coreless screw gives rise to a spiral helical flow, and plays a centrifuging role. In addition, the spiral flow created by the screw is maintained for a significant part of the straight section of the pipe which does not contain the screw, and continues to play its centrifuging role, despite the absence of the screw. As a result, the overall efficiency of the dust extractor is hardly affected by extension of the screw. Thus, in the most probable hypothesis, extending the screw along the entire length of the pipe would be useful only for recovering all the particles with a size of between 1.5 and 2.5 A, which represent only 2% of the total mass of incident particles (figure In addition, there is every probability that most of these particles will be recovered by the swirling flow which is maintained along the straight section, downstream from the screw.

The radius of the discharge duct can be equivalent to 0.1 m, and the pitch of the screw can be approximately 0.06 m. As a variant, in the case of a higher throughput of waste, the radius of the discharge duct can be 0.185 m, and the pitch can be 0.12 m.

With reference to figure 8, the pyrolysis installation comprises a unit REP for recovery of the solid carboncontaining substances MSC obtained from the cavity after pyrolysis of the waste has taken place.

According to the invention, the recovery unit REP comprises a discharge channel 200 which forms a syphon/seal, and is connected to the fixed part of the base of the output of the oven 49.

The discharge channel 200 comprises a container 202, which is inclined from the base upwards, and at the base of which the solid carbon-containing substances MSC accumulate in the form of a stopper which is impermeable to air.

A recovery mechanism 204 (for example of the screw type) conducts the solid carbon-containing substances MSC thus accumulated from the base upwards, towards another unit for separation SP and washing, in order to separate the inert substances IN and the mixture of water and solid carbon-containing substances KK.

Advantageously, the discharge channel 200 comprises a perforated drum 206, which can rotate in a decantation container 208, the output 210 of which is connected to the unit for processing of the waters LAV, which will be described in greater detail hereinafter.

This output 210 supplies the mixture of water and solid carbon-containing substances KK, enhancing of the value of which will be described hereinafter.

The fixed part of the base of the output of the oven 49 (figures 4, 5 and 8) comprises for example two valves/drop shutters, which are actuated by a hydraulic, pneumatic or mechanical jack, which assures sealing of the oven at the product output MSC.

With reference once more to figure i, according to the invention, the solid substances MSC which are output from the pyrolysis unit THE are washed and separated in the device REP described with reference to figure 8, into inert substances IN on the one hand, and into a mixture of water and solid carbon-containing substances KK on the other hand. The mixture of water and solid carbon-containing substances KK which is obtained from the output 210 is recovered in a series of containers 300, in order to wash the substances KK and remove from them pollutants which are attached to the carbon particles, in the form of chloride or sulfate.

After being decanted and washed, the fine particles of carbon are collected and conveyed by a wet medium, by means of a peristaltic pump 400 towards a belt-type dryer 402, thus eliminating most of the water contained in the solid carbon-containing substances KK obtained from the pyrolysis.

The drippings 404 from the belt-type dryer 402.are then returned towards the solid carbon-containing washing chain.

The carbon part PC is guided towards a micron dryer 500, which is automatically supplied with the gases 510 obtained from the aforementioned heat exchangers 90 and The solid carbon-containing substances KK are stored 600 and transported 602 to a selected place of use.

The washing waters for the carbon-containing solids are processed for example by mechanical steam compression, which functions as follows.

The waters which are obtained from the primary washing container 302 are guided towards an evaporator 304, when their concentration of dissolved salt reaches a reference value. Their temperature is maintained by the permanent water circuit of the primary container, the latter being heated by the stream of carbon-containing solids KK obtained from the pyrolytic oven.

Pumps and solenoid valves which are controlled by contamination meters and water contactors are provided in order to drain the washing solution of a container which has a concentration higher than that of the previous container, whereas the level of the washing solution of the said container is kept constant by supplying it with the less concentrated washing solution of the following container.

The water vapour which is present in'-the evaporator 304 is extracted continuously by a compressor 306, and is guided towards a condenser 308. The temperature of the condenser 308 is kept permanently below the dew point of the water vapour at the set pressure of the condenser, by circulation of water from the final rinsing container 305.

The condensates to be recovered are recycled periodically towards the final rinsing container 305, the concentration of which is lower than the previous container.

The salts and/or brines 310 are extracted periodically from the evaporator 304. The extraction is carried out by gravity through a lock chamber, in the case of brine, or by a screw provided in the lock chamber, in the case of crystallised salt.

One of the advantages of the present invention is also that water 320 is not consumed, since, after treatment, the waters generated by the system are recycled, either after the dryer or after condensation by evaporation.

Consequently, since the water used in the method is in excess, decompression is necessary. Since this operation is carried out after the water has been processed, the volumes of water discharged to the network are non-polluting.

The solid carbon-containing substances KK thus processed and dried, which are obtained from the pyrolysis, can become a recoverable fuel, the value of which can be enhanced, with a high calorific power. These solid carboncontaining substances can be stored and transported to a place of use which can be of several types, for example a molten cinder cyclone furnace which makes it possible to vitrify the cinders and trap the heavy metals which are contained in the carbon, or a fluidised bed.

Another use can be envisaged for the present invention. This consists of using the solid carboncontaining substances in a glass-making oven, in which the product is advantageous in two substantial functions, i.e.

heating of the oven, and vitrification of the cinder part, which makes it possible to obtain ceramics.

The quality of the products obtained (gas and solid carbon-containing substances or coke) depends substantially on the selection of the means for control/command, as well as on the location of the latter in the pyrolysis chain.

These means for control/command are the following elements (for the combustion chamber); a sensor for high temperature in the combustion gases (11000C); a pressure sensor in the combustion gas pipe; a transmitter to indicate the pressure of the combustion gases; a sampler for the combustion gases; an oxygen analyser which is connected to the sampler for the combustion gases; a contactor for very low temperature in the combustion gases (for example lower than 8500C), in order to activate a safety sequence corresponding to opening of the external fuel supply to the burner, so as to keep the combustion at a level which is in accordance with the legislation, i.e.

for example 850C; a contactor for very high temperature in the combustion gases (for example higher than 1250 0 which triggers a safety sequence which consists of stopping charging of the waste into the pyrolytic oven. This safety sequence also corresponds to stoppage of the external fuel supply to the burner, and opening of an air pipe to cool the gases; a transmitter to indicate the pressure which acts on the speed regulator of the downstream fan 31, which is disposed at the output of the exchangers 30 and 90; and a regulator for the speed of rotation of the downstream fan 31.

The units for control/command of functioning of the pyrolytic oven are the following elements: a sensor for the temperature of the skin of the rotary cylinder (this temperature may not exceed 700 0 and an alarm for a very high temperature of the skin of the rotary cylinder, which actuates a safety process.

For example, the safety process is characterised by the following steps: stoppage of the supply of waste to the furnace; stoppage of the supply of external fuel to the burner; opening of the by-pass of the air input for cooling the fumes; and stoppage of the unit, if the normal functioning situation is not re-established.

The regulation installation also comprises three sensors for the temperature of the skin of the cylinder, which are placed on the various sections of the cylinder, as well as temperature sensors for the fumes output from the oven, sensors for the temperature of the solid carboncontaining substance at the output of the-oven, and sensors .for the pressure inside the oven.

The pyrolysis makes it possible to dispense with heavy devices for processing of the fumes. It is genuinely advantageous compared with incineration, owing to its simplicity of implementation, and the savings which it makes possible to obtain, compared with other installations with the same power.

The dust extractor system (coreless screw) according to the invention can be applied to any pipe for transporting gases which are charged with solid particles.

The coreless screw is applied mainly in cases in which the speeds of transport are low (lower than 8 and/or the temperatures of the gases are high.

By way of example, reference can be made to the following: combustion fume pipes; piping for discharge of air for transport of aggregates; and pipe for transport of small coals.

Use of the dust extractor system can be envisaged either as a replacement, or in addition, upstream from conventional filtering systems (ballistic filters, bag filters, cyclones etc).

The present invention has applications other than pyrolysis of urban/industrial waste, such as processing of biomass, or thermal resorption of polluted earth.

EDITORIAL NOTE NO 40461/99 Claim pages are numbered 1-4.

Claims

2. Oven according to claim i, characterised in that the coreless screw comprises helical threads, the width and pitch of which are selected according to an average speed of discharge of the gas streams obtained from the pyrolysis, such as to trap at least some of the particles which are present in the said gas stream.
3. Oven according to claim 1 or claim 2, characterised in that the gas stream output from the cavity (54) comprises first and second discharge ducts (102, 104), each comprising a first and a second end, each first end being -connected to the cavity, and each second end being connected to a common node (110), the output of which is connected to the burner (80) of the combustion chamber, each discharge duct comprising a shutter (114) and a coreless screw (116), which, under control, can extract the dust from the associated duct, the shutter (114) of the duct from which the dust is to be extracted being closed, whereas the shutter (114) of the other duct is open for discharge of the pyrolysis gases.
4. Oven according to claim 3, characterised in that the shutters (114) are closed alternately. Oven according to any one of the preceding claims, wherein means for introduction of waste can receive, compact and charge the waste to be processed into the input interface of the cavity, whilst preventing any air from entering the cavity, characterised in that the input interface of the cavity (50) comprises at least a first and a second input (51, 53), and the means for introduction of waste comprise a first and a second introduction channel (72, 74), which are connected respectively to the first and second inputs (51, 53) of the cavity, means which form a press (79, 81) in order to compact the waste and thrust it into the first and second introduction channels (72, 74), and control means, which can control in a staggered manner the compacting and charging of the waste into the first and second inputs (51, 53) of the cavity, whilst maintaining the impermeability of the cavity.
6. Oven according to claim 5, characterised in that each introduction channel (72, 74) comprises a first and a second end (11,75, 73,77), the first end (71, 73) being connected to the input (51, 53) which is associated with the cavity, and comprising a drop shutter (76, 78) which closes under control the said input of the cavity, and the second end (75, 77) accommodating a thrust mechanism (79, 81) which can be displaced under control in two directions in the introduction channel, in order to thrust the waste towards the associated drop shutter, and in that the means for control can control the displacement of the thrust mechanism and opening/closure of the drop shutter of each introduction channel.
7. Oven according to claim 5 or claim 6, characterised in that the upper part of each introduction channel comprises a trap door (85, 87) to receive the waste.
8. Oven according to any one of the preceding claims, characterised in that it additionally comprises a unit for recovery of the solid carbon-containing substances (MSC) which are obtained from the pyrolysis cavity, the said recovery unit (REP) comprising a discharge channel (200) which forms a syphon/seal, the said discharge channel (200) comprising a container (202) which is connected to the cavity, at the base of which the solid carbon-containing substances (MSC) accumulate in the formof a stopper which is impermeable to air, and a recovery mechanism (204) which can conduct the solid carbon-containing substances (MSC) towards a unit (206) for separation and washing.
9. Oven according to claim 8, characterised in that the unit for separation and washing which is associated with the recovery unit (REP) comprises a perforated drum (206), which can rotate in a decantation and washing container (208).
10. Oven according to claim 9, characterised in that the perforated drum can supply a mixture of water and solid carbon-containing substances the value of which can be enhanced.
11. Oven according to claim 9, characterised in that the unit for separation and washing (206) is connected to means for processing of the waters (LAV), comprising a plurality of decantation and washing containers (300) which are connected to one another, and each of which contains a washing solution with a selected concentration, which is different and decreases from one container to the next, as well as pumps and solenoid valves which are controlled by contamination meters and level contactors, in order to drain the washing solution from a container which has a concentration higher than a pre-determined threshold, into the previous container, whereas the level of the washing solution of the said container is kept constant by supplying it with the less concentrated washing solution of the following container.
12. Application of the coreless screw as a dust extractor according to any one of claims 1 to 4, for any pipe for transport of gases which are charged with solid particles.