FR2566099A1 - Furnace for incinerating household and industrial waste - Google Patents

Abstract

Furnace for incinerating household and industrial waste, comprising: a primary combustion chamber 1, a waste feed hopper 2 emerging in this primary chamber 1, a secondary post-combustion chamber 5 communicating with the primary chamber 1 and extended by a chimney 9 for evacuating the smoke, burners 11, 12 mounted in the combustion chambers 1, 5 and means for blowing air into the said chambers, characterised in that it comprises in combination: - a pusher 21 for ashes arranged below the hopper 2 and capable of pushing the waste from one end to the other of the primary chamber 1, this pusher being equipped with a poker tube 22 mounted so as to slide axially projecting externally from the pusher and pierced with holes for the passage of air for drying and combustion of the ashes; - and two Archimedes' screws 23 for supplying the primary chamber 1 placed at the base of the hopper 2. This furnace may have a great capacity whilst remaining reasonably cost-effective, the continuous feed by the screws 23 making it possible to meter, at any moment, the quantity of waste to be burnt, which may be regulated as a function of the temperature of the gases in the chimney 9.

Description

 The present invention relates to an incineration oven for household and industrial waste.

 We know, in particular from French patent 1 093 712. a household waste incineration furnace provided with movable grates which constantly return the waste, in order to obtain rapid combustion, and in which the fumes are partially recycled.

 This type of oven can have a large capacity but the movable grates are expensive and fragile. These grids also have the drawback that they raise dust when they are stirred. Combustible organic dust burns slowly. but not the mineral dust which must therefore be filtered in the exhaust fumes in order to meet the anti-pollution standards for gaseous discharges. which therefore requires equipping the furnace with filtration means. Furthermore. mineral dust will clog the boiler possibly associated with the oven.

 So-called static ovens are also known, in which the grids are fixed, such as that described in French patent 71 13 375 (2 089 718). The feeding of these ovens is intermittent, not mechanized. while their capacity is low and they have to be stopped and cooled to allow slag removal.

More generally, known ovens have many disadvantages
- significant consumption of fuel when the oven is lit and for the incineration of low calorific waste;
- continuous service impossible because the extraction of slag requires cooling the oven. then the opening of a large section door. then mechanical scraping in order to extract the slag;
- inability to increase the size of the ovens due to poor combustion of the core of a large mass in ignition:
- difficulty in obtaining smoke of suitable quality when loading the oven. due to the large instantaneous thermal load created at this time;
- practical impossibility of regulating combustion since there is no means of action other than air control to establish a followed course.

 The invention aims to remedy these drawbacks by providing an oven of medium capacity. relatively inexpensive, - can be automated, ie does not need to be stopped to be able to extract the slag. and able to easily withstand instant thermal overload.

 The furnace targeted by the invention comprises a primary combustion chamber, a hopper for feeding waste leading to this primary chamber which is delimited laterally by grids fixed inclined on a horizontal floor for supporting the waste. a secondary post-combustion chamber communicating with the primary chamber and extended by a smoke evacuation chimney, burners mounted in the combustion chambers and air blowing means in said chambers.

According to the invention the oven is characterized in that it comprises in combination
- a slag pusher disposed below the feed hopper, capable of pushing the waste and slag substantially from one end to the other of the primary combustion chamber, this pusher being equipped with a mounted fire hose axially sliding projecting outside the pusher and pierced with holes for the passage of air for drying and combustion of slag, means being provided for periodically operating the pusher and its fire hose in the primary chamber;
- And mechanical means for continuous supply of the primary combustion chamber, in particular at least two Archiimedes screws placed at the base of the hopper and which can be rotatably adjustable by a motor.

 The pusher. periodically driven on horizontal translation by appropriate means.

allows to slowly stir the mass of litter in ignition, thus avoiding the unburnt in its heart eS by the same to achieve an oven of large size and capacity. In addition, thanks to the slowness of its movements. the pusher does not cause dust to rise. so that the mineral dust is not entrained in the exhaust fumes and it is therefore not necessary to equip the oven with expensive filtration devices to meet anti-pollution standards.

 On the other hand, continuous mechanical feeding, for example by Archimedes screws, advantageously makes it possible to dose at any time the quantity of waste to be burned, therefore the instantaneous thermal load of the furnace by appropriately adjusting the speed of rotation. screws.

Other features and advantages of the invention will become apparent during the following description of an embodiment of the oven according to the invention with reference to the accompanying drawings:
- Figure 1 is an axial mid-section view in elevation of an embodiment of the oven according to the invention;
- Figure 2 is a top plan view, on an enlarged scale, of the Archimedes feed screws placed at the base of the hopper and visible in Figure 1;
- Figure 3 is a partial top plan view of the oven of Figure 1;
- Figure 4 is a cross-sectional view along IV-IV of Figure 1.

 The oven illustrated in FIGS. 1 to 4 is intended for the incineration of household and industrial waste and comprises: a primary combustion chamber t, a hopper 2 for supplying waste opening at its base into the primary chamber 1, which is delimited laterally by fixed grids 3a, 3b inclined on a horizontal sole 4 for supporting the waste coming from the hopper 2. The grids form two lateral rows 3a, 3b supported on the sole 4 and inclined, of approximately 45 in the example described .

 The primary chamber 1 opens into a secondary post-combustion chamber 5 through an opening 6 made between the hearth 4 and a vertical partition 7 secured to the ceiling or sky 8 of the chamber 1. the secondary chamber 5 being extended upwards by a chimney 9 for discharging fumes and gases into the atmosphere.

 Burners are mounted in the combustion chambers 1, 5, namely a first burner 11 in the primary chamber 1, and a second burner 12 in the secondary chamber 5. The axis of the burner 11 is preferably inclined by 45 towards an opening 13 feed communicating with the base of the hopper 2. and 15 down. while aue the axis of the burner 12 is inclined 45 upward. The oven is Dar elsewhere equipped with movens of air blowing in the chambers 1. 5. constituted Dar of the pipes 14. 15 opening through the olafond 8 Dour blow high-pressure air from top to bottom towards the floor 4 and the waste (not shown) to be burned. and Dar tubing 16 fixed in the secondary chamber 5 to the partition 7 Dour blow laterally in this chamber of high pressure air. The orifice air is blown into the pipes 14. 15 by a fan 17 mounted above the chamber 1. a second fan 17b supplying secondary air to the pipes 16 Dar a piping 13 (Figure 3).

A conduit 19 connected to the chimney 9 and leading to a mixing chamber with fresh air 19b.

itself connected to the input of the fans 17a and 17b. Allows partial recovery of the fumes in the primary chamber 1 and in the combustion chamber 5.

 The oven includes other nart a slag container 21 disposed below the hopper 2. capable of horizontally pushing the waste (not shown) transformed into slag. substantially from one end to the other of the primary combustion chamber 1 thanks to a drive device which will be described below The segment 21 is axially traversed by a fire tube 22 which can slide horizontally projecting externally to pusher 21.

this fire-retardant tube 22 being chapped by a multitude of small holes nourishing the air with drying air and combustion of the waste. In combination with this device, we have 21 t of picnic 22. The invention provides mechanical movens for continuous supply of the primary chamber 1 constituted in the example represented by two Archimedes screws 23 (Figures 1 and 2) placed at the base of the hopper 2, parallel to one another so as to push the waste into the chamber 1 when it is rotated. by a motor 24. in a manner known per se, and adjustable.

 According to a feature of the invention, a burner 25 is formed in the hearth 4 between the primary chamber 1 and the secondary chamber 5 to receive the slag at the end of combustion, this burner 25 being delimited on the side of the primary chamber 1 by a fixed inclined grid 26. Under the bale 25 is disposed a hatch (not shown) for extracting and evacuating slag, produced in a manner known per se.

 The primary air blowing circuit comprises, in addition to the aforementioned pipes 14, 15, pipes 27 which open on each side of the floor 4, transversely to the grids 3a, 3b through which low pressure primary air can thus be breath. This air then passes through a longitudinal channel 28, 29 delimited on each side by the rows of grids 3a, 3b, and by the walls 40 of the chamber 1, and divided into at least three longitudinal sections by at least three transverse partitions 31 retractable by means not shown. The channels 28, 29 open into an inclined conduit 30 separated from the burner 25 by the grid 26.

 The grids 3a, 3b are placed in the immediate vicinity, or tangential to the trajectory that the pusher 21 can follow in the chamber 1, so that the latter can expel, when necessary at least in part, the dust accumulated on the grids 3a, 3b.

The actuating means of the pusher 21 and the fire-stop tube 22 are constituted in the example shown, in the following manner: the pusher 21 is fixed to the front end of a horizontal box 32 whose end opposite to the pusher 21 is integral with a part 33 which meshes with an endless chain 34 mounted on two opposite pinions 35, which can be rotated by means known per se and not shown. Under these conditions, the rotation of the pinions 35 causes a horizontal longitudinal displacement of the box 32 and of the pusher 21, the latter sliding in the chamber 1 between two lateral guide rails 36 fixed to the walls of the chamber 1 immediately above the grids 3a. , 3b
The fire-stop tube 22 passing through the pusher 21 can be actuated for example by a jack 37 whose rod 38 is fixed to the tube 22. The oven is further provided, according to a feature of the invention, with a circuit regulating the feed rate of the primary chamber 1 in waste, as a function of the temperature of the gases and the fumes in the chimney 9.

This circuit includes a thermocouple 39 for detecting the temperature of the fumes in the chimney 9, connected to the control members of the mechanical supply means, that is to say in the example described in the motor 24 for driving the screws. Archimedes 23 by an appropriate connection 41. Inspection hatches such as the hatch 42 formed at the base of the secondary chamber 5 allow intervention inside the chambers 1 and 5 when the oven is stopped.

The operation of the oven which has just been described is as follows
The waste being introduced into the upper part of the hopper 2 as indicated by the arrow in Figure 1, the continuous supply of the combustion chamber 1 is carried out by the two slightly conical Archimedes 23 screws, whose axes are in the same horizontal plane and which rotate in the same direction. The waste spreads on the floor 4 between the grids 3a, 3b, small strokes of the pusher 21 being simultaneously given to spread the waste over almost the entire surface of the floor 4. The ignition of the waste is ensured by putting in on the burner 11 in the primary chamber 1. At the same time, the burner 12 in the post-combustion chamber 5 makes it possible to raise the temperature of the chamber 5 and the chimney 9 around OD'C, in so that the gases emitted are perfectly burned and do not create odors. The heating-up period of the furnace varies with the humidity of the waste to be burned and with the calorific value of the dry matter, this heating-up period generally being of the order of half an hour to one hour.

 The burner 11 is generally stopped first, as soon as the waste self-combustion temperature is reached. Primary air is blown through the pipes 14, 15 and the pipes 27 after the ignition of the burner 11, as is secondary air at high pressure through the pipes 16 in the chamber 5.

 As soon as the burner 11 stops when the self-combustion temperature is reached, the speed of introduction of the waste to be burned into the oven is controlled by the temperature in the primary combustion chamber 1, this speed increasing at the same time as the temperature up to a high temperature level of around 900 ° C. This temperature constitutes a maximum which it is not desirable to exceed for reasons of resistance of the metal parts of the furnace and of melting of the slag. When this temperature level is reached, the blowing of primary air into the lateral pipes 27 under the mass of waste through the grids 3a, 3b is reduced, then stopped. Significant amounts of lean gas continue to distill and help reduce the temperature. This gas is burned in the post-combustion chamber 5, supplied with secondary air through the pipes 16.

The frequency of slag extraction is naturally dependent on the mineral content of the treated waste. In general, it is once an hour for household waste and once every four hours for industrial and commercial waste containing mainly paper. cartons and plastics. The slag extraction is done in the following way
- First, the hatch (not shown) for extracting the slag that has completed combustion in the burner 25 is opened slowly, and the slag falls into the handling system outside the furnace (not shown);
- The pusher 21 is then operated with a stroke sufficient to fill the burner 25, this stroke being for example of the order of 1 m.

 The pusher 21 is normally in its position illustrated in Figure 1, that is to say adjacent to the transverse wall of the primary chamber 1, below the inlet opening 13. It is not pushed inside of the primary chamber 1 only at regular intervals (for example once an hour), by turning the endless chain 34 in the appropriate direction.

This introduction of the pusher 21 into the chamber 1 makes it possible to stir the mass of household or industrial refuse in ignition, therefore to avoid unburnt at its heart and, by the same token, to increase the size of the oven. The pusher 21 pushes the waste step by step along the primary chamber 1, then into the burner 25 from which they are extracted without there being any need to slow down or cool the oven.

 The tubular firebreak 22, consisting of a refractory steel tube pierces many small diameter holes, is supplied with air for drying and combustion of the waste when it is advanced in the mass of garbage being dried. by actuation of its control cylinder 37.

 The technical effects and advantages of the oven according to the invention are as follows.

 Because of its continuous supply by the Archimedes screws 23, which can moreover be replaced by any other equivalent equivalent means, it is possible to adjust the instantaneous thermal load of the oven by varying the speed of rotation of the screws 23, which can be increased when the volume of waste introduced into the hopper 2 is relatively small, and conversely decreases if this volume is momentarily large. This regulation of the supply is also complementarily ensured by the circuit comprising the thermocouple 39 and the connection 41 with the screw driving motor 24 23, which triggers an increase in the speed of rotation of the latter when the thermocouple 39 detects in the chimney 9 a temperature below a predetermined threshold.

The thermocouple 39 is also connected to the burner 12 of the chimney 9 so as to start the latter as soon as the temperature detected in the chimney 9 is less than 600 or 700-C. In case of
thermal overload, for example by a mass of
rubber pushed into the primary chamber 1, it
forms abundant soot giving rise to black and greasy smoke. The thermocouple 39 then automatically starts the burner 12 which blows air from
oxygen-rich combustion. causing the complete combustion of the soot and the emission into the atmosphere of
clean smoke, possibly with a flame
exit from the chimney 9.

Hot gases recovered by the recycling conduit 19 are introduced into the primary chamber
1, these gases from the mixture of burnt gases (which still contain approximately 10Z of oxygen) and ambient air. These hot gases are used both in the primary chamber 1 and in the burner 25 and in the post-combustion chamber 5. In the primary chamber 1, the hot gases injected through the channels 15 facilitate the drying and pyrolysis of the waste. In the burner 25, these same gases promote the emission of carbon monoxide (following the reaction of the gas carbon dioxide on the red embers on the sole 4} and the emission of a mixture of carbon monoxide and hydrogen (following the reaction of water vapor on the same red embers).

 In the post-combustion chamber 5, the relatively high temperature of the injected gases prevents the distillation gases from cooling and quenching.

 The static grids 3a, 3b inclined on the floor tr and delimiting the lateral channels 28, 29 allow ventilation at the base of the waste, by blowing air at low pressure in the pipes 27 opening into the sections separated by the partitions 31. The numerous holes, for example of 6 mm in diameter, drilled in these grids for the passage of oxidizing gas to the drying, are liable to become blocked or to let the dust pass into the channels 28, 29 of primary air. To avoid this drawback, the pusher 21 passes close enough to the grids 3a, 3b to avoid their blockage and the primary air channels 28, 29 can be swept whenever it is necessary, in principle once a day, by the high-speed air which sends the dust into the bale 25.

 The waste remains, for example, approximately two to three hours on the hearth 4, and at least half an hour in the burner 25, after which their combustion is complete and the resulting slag can be extracted and removed from the oven.

 The arrangement of the pusher 21 provided by the invention has an important advantage linked to the fact that it is advanced only very slowly and periodically, so that its movement does not raise dust and that it is therefore not necessary to provide the furnace with filtration means to meet anti-pollution standards, the mineral dust not being entrained in the chimney 9 by the displacement of the pusher 21. Likewise, the introduction of the firebreak 22 into the mass of waste during combustion also does not raise dust likely to be entrained in the chimney 9. The firebreak 22 allows Ci to ventilate the mass of waste and dry the wettest waste.

 Before their extraction, the waste at the end of combustion is poured onto the burner 25, the volume of which corresponds approximately to one hour of operation of the oven, this burner being supplied with combustion air. Incompletely burnt but in any case very dry parts of the waste to be incinerated, have sufficient time to finish burning in the burner 25, which thus contributes to the possibility of increasing the capacity of this static oven.

 The pusher 21 also has the advantage of allowing the extraction of slag without prior cooling, while such prior cooling is necessary in the previous small static ovens.

 Most of the time the oven will not be operated continuously but semi-continuously, i.e. eight to sixteen hours per day followed by a period of slow combustion and cooling until the next morning. The oven still has a relatively high temperature at this time, of the order of 400, which facilitates its restarting.

 The actual pusher 21 and its box or chassis 32 constitute a massive assembly which therefore does not tend to compress the waste on its path. as tests have shown.

 When it is desired to clean the grids 3a, 3b of the dust which begins to accumulate there and risks gradually closing the holes in the grids, the transverse partitions 31 are retracted so as to completely release the channels 28, 29, and these are swept with a current of air which drives the dust up to the exhaust duct 30 adjacent to the burner 25.

 Throughout the day, a large part of the slag is extracted with, however, a certain accumulation on the downstream part of the furnace. At the end of the working day, the oven is loaded to ensure normal operation for part of the night. However, the temperature in the primary chamber 1 drops regularly. When it reaches 500 ′, the oven is put on standby, the fans 11, 12 are stopped and reduced combustion continues in natural draft, which has the advantage of cooling the supply screws 23. In fact, most of the combustion air then passes through the feed hopper 2.

 The next morning, the entire contents of the oven are emptied by progressive action of the pusher 21.

Numerical example
An oven whose primary chamber 1 has a volume of 25 m3 and whose post-combustion chamber 5 (including the chimney) has a volume of 15 m3 is capable of burning 1.8 tonnes / hour of waste with a lower calorific value is 1700 therms / ton.

It emits about 12 tonnes / hour of smoke at this temperature at a temperature of 850-. which corresponds to an excess of air of 160
The dust content of the fumes emitted is less than 600 mmg / Nm3 reduced to 7% of CO2, which makes any filtration of the fumes unnecessary.

 The invention is not limited to the embodiment described and may include numerous variant embodiments. Thus the pusher 21 can be entrained in its reciprocating movements inside the primary chamber 1 by any suitable device, for example hydraulic means replacing the endless chain 34 and the sprockets 35.

Claims (7)

 1 - Incineration oven for household and industrial waste, comprising: a primary combustion chamber (1), a hopper (2) for supplying waste opening into this primary chamber <i) which is delimited laterally by grids (3a , 3b) fixed inclined on a horizontal floor (4) for supporting the waste, a secondary chamber (5) of post-combustion communicating with the primary chamber (1) and extended by a chimney (9) for evacuating smoke, burners (11, 12) mounted in the combustion chambers (1, 5) and means for blowing air into said chambers, characterized in that it comprises in combination:  - a pusher (21) with slag placed below the feed hopper (2), capable of pushing the waste and slag substantially from one end to the other of the primary combustion chamber i1), this pusher being traversed axially by a fire-stop tube (22) which can slide horizontally projecting externally from the pusher and pierced with holes for the passage of air for drying and combustion of slag, means being provided for periodically operating the pusher (21) and its fire tube (22) in the primary chamber (1) ;;  - And mechanical means for continuous supply of the primary chamber (1> of combustion, in particular at least two Archimedean screws (23) placed at the base of the hopper 12) and which can be rotated in an adjustable manner by a motor (24),  2 - Oven according to claim 1, characterized in that it comprises a burner (25) formed between the primary chamber (1) and the secondary chamber (5) for combustion to receive the slag at the end of combustion, a trap door extraction of the burnt slag being provided below the burner (25).  3 - Oven according to one of claims 1 and 2, characterized in that it comprises a circuit for regulating the feed rate of the primary chamber (1) in waste, depending on the temperature of the gases and fumes in the chimney (9), this circuit comprising a thermocouple (39) for detecting the temperature of the fumes in the chimney (9) connected to control members of the mechanical supply means, in particular to the motor (24) for driving in rotation of Archimedes' screws (23).  4 - Oven according to one of claims 1 to 3, characterized in that it comprises, -on each side of the two rows of side grids (3a, 3b), a longitudinal channel (28, 29) divided into at least three sections by at least three transverse partitions (31), retractable to allow periodic sweeping of these channels by a stream of primary air intended to expel and evacuate towards the burner (25) the dust accumulated under the grids (3a, 3b ), the latter being placed in the immediate vicinity of the trajectory of the pusher (2) so that it can also at least partially expel the dust accumulated on the grids (3a, 3b).  5 - Oven according to one of claims 1 to 3, characterized in that the pusher (21) is actuated either by a hydraulic device, or by an endless chain (34) mounted on pinions (35) and engaged with a part (33) integral with a box (32) fixed to the pusher (21).  6 - Oven according to one of claims 1 to 5, characterized in that its post-combustion chamber 5 is equipped with a burner (12) making it possible to complete the combustion of unburnt products in the event of a temporary thermal overload due to the introduction of a large mass of waste.  7 - Oven according to one of claims 1 to 6, characterized in that the pusher (21) cooperates with rails (36) of lateral guide, fixed to the longitudinal walls (40) of the primary chamber (1).