Technical field

The present invention relates to a device for excluding and preventing oxygen or any gas mixture containing oxygen gas, such as air, from flowing into the interior of the reactor in a pyrolysis reactor which is designed for continuous operation. The reactor incorporates means for removing gas released during the pyrolysis process and means for removing residual products such as oil residue products and slag.

Background

Gas generators for segregating combustible material are well known as a phenomenon, not least in the form used previously and they are still used in certain plants for the production of town gas, for example. The basic concept itself is the same, namely anaerobic segregation at increased temperature, and the handling of released gas and residual products. However, the situation is that as far has been determined from exhaustive investigations, no one has so far succeeded in producing a pyrolysis reactor which actually operates continuously. For the unfortunate case that air or free oxygen unintentionally comes into contact with a material undergoing pyrolysis, this unavoidably results in an explosive fire. Basic school physics teaches that three conditions need to be met for combustion, or in common parlance fire, take place: firstly access to a combustible material, secondly the temperature at which the combustible material burns is reached, and thirdly there is access to free oxygen in the required quantity. What, then, is done in a pyrolysis reactor or gas generator? The answer is that conditions must be created for an anaerobic process, more precisely a process in which all the conditions for combustion exist, except for access to free oxygen. Because no one has succeeded in producing a gas generator for continuous pyrolysis of combustible material, designs that have worked so far are characterised in that they must be operated in batches, i.e. a pyrolysis reactor is loaded with a set of pyrolysable material which is then heated under oxygen-free conditions at the same time that the gas released during the process is handled. During the pyrolysis process the pyrolysis reactor is hermetically fully sealed to avoid explosive processes. Prolonged cooling is thereafter required to bring down the temperature in the gas generator to such a level that the residues remaining after pyrolysis do not spontaneously ignite when free oxygen penetrates as the pyrolysis reactor is being opened. This is not, nor has it ever been, a particularly good process, not least because it involves extensive handling relating to loading, heating and cooling. Nor is it all that energy effective.

The invention in brief

It is therefore a principal objective of this invention to indicate a device with which it is ensured that free or bound oxygen does not penetrate the pyrolysis reactor via the devices required for the continuous operation of the reactor, firstly for removing gas released by the process, secondly for removing released slag and residual material products and condensation and thirdly discharged oil residue products.

The objective is achieved with the device according to the invention which, for gas, slag, residual products, condensation and oil residue products has at least one scrubber connected to the reactor or a liquid lock which, for the gas fraction, is connected before at least one gas evacuation pump, which is in turn arranged to maintain a gas pressure in the pyrolysis reactor, which corresponds to an atmospheric pressure surrounding the pyrolysis reactor. Because gas and other discharged fractions are evacuated through a liquid, e.g. water, and because the pressure of the gas is greater than or essentially equal to the surrounding atmospheric pressure, all the conditions for allowing free or bound oxygen to flow into the back of the pyrolysis chamber are eliminated.

In a further developed embodiment of the invention the respective liquid locks have a tap for draining gas condensate produced at a certain level above the bottom of the respective liquid locks.

This prevents the liquid lock from being filled to its width and as a result no longer operates in the intended manner. According to another further developed embodiment of the invention, all the other products released in connection with the anaerobic segregation during the pyrolysis process each have their own separation unit. The separation unit for slag incorporates an intermediate store and oxygen gas and air tight liquid lock arranged after it, which intermediate store is fed by means of a screw conveyor in a duct from the associated outlet chute on the pyrolysis reactor, the intermediate store being intended to be drained intermittently, according to its degree of filling, by means of a screw conveyor arranged essentially horizontally at the bottom of the intermediate store, from the bottom of which liquid lock a screw conveyor, immersed in the liquid at its one end, passes in turn for discharging all the slag out into the surrounding area. No air or other oxygen compound is, in this arrangement, given the opportunity to penetrate the pyrolysis chamber from the back and there cause a fire, in this case probably accompanied by an explosion.

According to yet another further developed embodiment of the invention the separation unit which is designed for oil condensate and other residual products, has a discharge chute which is arranged at the lowest end of the pyrolysis reactor, where an essentially horizontal screw conveyor is located for conveying a mixture of these products to an intermediate store at the bottom of which there is a further essentially horizontal screw conveyor for intermittent conveying of the mixture to a oxygen gas and air tight liquid lock with a closable valve for discharging the products to the surrounding area. Because the quantity of oil condensate and other residual products is small, no continuous operation of this evacuation system is required, but because it still has to be handled this special handling device is developed so that even in this case it is ensured that neither air nor another oxygen gas compound is able to penetrate the pyrolysis reactor during pyrolysis.

In a further developed embodiment of the invention the discharge point for slag comprises a first screw conveyor which opens out beside a descending pipe dropping down under a liquid surface in a liquid lock in which there is a conveyor screw partially immersed in the liquid for discharging wetted slag product to a tank open to the surrounding area. Because slag, which consists largely of carbon black, constitutes a large fraction of the constituents in which the material introduced into the pyrolysis chamber is segregated during the process, a device that can be operated continuously is required for this fraction. For this purpose the screw which is partially immersed in the liquid, and which is consequently assembled obliquely in relation to the horizontal plane, ensures that, despite the fact that the process is continuous, the slowly rotating screw rotating at a pace of preferably from 40 to 45 rpm never allows a backflow, under the liquid surface, of free or bound oxygen gas.

Brief description of the drawings

The invention will below be described in greater detail in the following on the basis of a preferred exemplary embodiment shown in the attached drawings, in which

Fig 1 shows schematically a cross-section through a pyrolysis reactor from the side thereof,

Fig 2 shows schematically the same reactor as in Fig. 1 from above.

Fig 3 shows in more detail, as a schematic view in the longitudinal direction of the pyrolysis reactor, the device for evacuating slag at the further end of the reactor, and

Fig 4 shows more in detail, as a cross-sectional view, the device for evaluating residual material or liquid fraction drooping down from the belt.

Detailed description

Fig 1 shows schematically a pyrolysis reactor 100 for continuous operation. It should be noted that the entire reactor 100 is suitably arranged at an angle of inclination of approximately 5° to the horizontal plane. At the feed-in end of the reactor there is a feed hopper 1 in which material, e.g. fragmented car tyres, is fed down. At the bottom of the feed hopper 1 there is a feed screw device 3 driven by a motor 2, which device propels the fragmented material at an inclination of 10 and 20°. Around the feed screw there is a preheating jacket 5 for heating the material to a little under 100 ⁰ C, firstly in order to expel any moisture containing bound oxygen from this and secondly to soften the material so that it can be compacted more easily. At the upper end of feed screw device 3 there are nozzles (not shown) for supplying nitrogen gas which, because it is lighter than both air and oxygen gas, will lie over the oxygen gas or air due to the inclination of device 3, so that it will expel any oxygen gas or air present at the feed hopper 1. Besides the above-mentioned nozzles for nitrogen gas, a further feed screw device 6 driven by at least one motor 4, with double screws 7 which are driven in the same direction of rotation, but at a lower speed than feed screw device 3, is connected to the upper end of feed screw device 3. One end 8 of feed screw device 6 is arranged connected so that it is tightly sealed against the surrounding air some distance into a reactor chamber 9, at whose end is arranged a hatch 10 which is manoeuvrable between a closed and an open position. The function of hatch 9, when initiating a continuous pyrolysis process, is to enable an establishment of an initial press mass of process material from which all the oxygen can be expelled so that it can be driven out, in the manner described above, to the feed pocket via feed screw devices 3 and 6 respectively. The feed screw device 6 is followed by the reactor chamber 9, to the bottom of which the press mass falls out onto a slow moving conveyor belt 11. A levelling plough 12 is arranged in the initial section of a belt 11 in order to distribute the press material evenly over the belt. During a continuous process a fragment which is to be pyrolysed remains in chamber 9 for approx. 3 minutes, wherein the chamber in a hot zone 13 keeps an essentially constant temperature of approx. 550 ⁰ C. In roof 14 of hot zone 13 there are heating elements 15, preferably electrically heated elements of the infra-radiation type, which is why, because the heat supplied is of the radiation type, hot zone 13 is demarcated by radiation protection device 16 at the respective ends of hot zone 13. The radiation protection devices are intended primarily to concentrate the heat discharge within the area in hot zone 13 intended for this. After passage through zone 13 there remains a residual fraction of the material intended for pyrolysis which consists mainly of carbon black which, at the end of conveyor belt, falls down to a conveyor screw 18 arranged in an outlet duct 17 for conveying to an oxygen sealed intermediate store (not shown), which is emptied instantaneously if necessary. A certain proportion of the material intended for pyrolysis will unavoidably behave in a manner that is not desirable and will either drop down alongside belt 11 , or will adhere to this and will therefore possibly spontaneously fall off the same at a later stage, whilst the material is located along the underside of the belt. Depending on the position in which this takes place, it either happens that it is handled in the intended manner and drops out as carbon black onto duct 17, or it drops onto the underside of belt 11 in the form of residual material. For this extremely likely eventuality a further conveyor screw 18 is arranged at the bottom of reactor chamber 9, which screw feeds such material and any liquid fraction to an outlet 19 arranged at the feed-in end of reactor chamber 9, from which a feed screw 20 feeds this material to an oxygen- sealed intermediate storage which, like the intermediate storage mentioned above, is instantaneously emptied if required.

Fig. 2 shows pyrolysis reactor 100, viewed from above instead of from its one side, as in Fig. 1. From the left, the motor 2 for the feed screw device 3, followed by the feed hopper 1 , then feed screw device 3 surrounded by preheating jacket 5 are shown. Device 3 connects to feed screw device 6, which is in turn connected to reactor chamber 9 in the vicinity of a hatch 10 at the outlet end of device 6. Connected to the reactor chamber is firstly a gas outlet pipe 21 , via which gas released as a result of the pyrolysis process is handled, secondly the outlet duct 17 for carbon black or the like and thirdly outlet the duct 19 for residual material and liquid fraction according to the above description. The ducts 17 and 19 respectively, and pipe 21 , are provided with an intermediate storage functionality, which requires to be emptied occasionally. This takes place, of course, without giving oxygen or air the opportunity, so to speak, to get in through the back door and disturb the process in the pyrolysis chamber.

Fig. 3 shows in more detail, as a schematic view in the longitudinal direction of pyrolysis reactor 100 the device for evacuating slag at the farther end of the reactor. A drop shaft 23 has its upper opening 22 at the end of conveyor belt 11 and is designed to collect all the material except for a small residual fraction which has passed through the reactor chamber, and consists essentially of carbon black. At the bottom of drop shaft 23 there is a screw conveyor 24 which is designed to feed the material falling down into the shaft on to an intermediate store 25. Since the quantities of material are small, pyrolysis reactor 100 can be operated for a considerable time, in terms of hours, before the intermediate store has been topped up to such an extent that it needs to be emptied. In other words such emptying takes place intermittently after a signal has been received from an overfilling protection device marked at 26, and is carried out as follows. At the bottom of intermediate store 25 there is another screw conveyor denoted by 27, which feeds the content of the intermediate store on to a liquid sluice, preferably a water lock 28 into which the content from the intermediate store drops and sediments at its bottom 29. At the bottom of water lock 28 there is a further, and at this outlet final screw conveyor 30, which is fitted obliquely upwards from its feed end. Because of this oblique device screw conveyor

30 becomes a part of the water lock 28, and will only convey solid material out to a device suitable for the purpose at the other end of conveyor 30 for further handling of the fraction constituting the result of the handling just described.

Finally, Fig 4 shows a cross-sectional view of a device for evacuating residual material falling from the belt and a possible liquid fraction consisting of condensed oils for further handling. Outlet 19, which in connection with this figure is called a fall chute

31 and which to a certain extent is reminiscent of fall shaft 23 at the other end of pyrolysis chamber 100, also incorporates a "pip" 32 from which the oils mentioned drops or runs down into fall chute 31 due to the slight inclination of the pyrolysis chamber towards the end in question, in which chute they are mixed with residual products that have dropped from belt 11 at unintended points, as described above, and are conveyed by means of a screw conveyor 20 away to an intermediate store 33.

Intermediate store 33, which may consist of any liquid tight and sufficiently large tank, is emptied at its bottom by means of a horizontally arranged further screw conveyor 35 to a liquid lock 36. This liquid lock 36 is intended to be emptied intermittently by opening and closing a valve 37 intended for this purpose, from which a pipe feeds the material drained from it to a tank 38 for onwards conveying of the residual material for further use or to a landfill. Pyrolysis reactor 100 arranged for continuous operation slopes downwards towards the feed-in end. Feed hopper 1 is so large that continuous operation can be maintained without any practical problems. Motor 2 is of such a type that its speed can be varied so that effective compression towards double screw 7 can be guaranteed under all conditions, regardless of the type of material fed in. For effective compression, and to ensure that all moisture is expelled from the material intended for pyrolysis, this material should reach a preheating temperature of 120 ⁰ C in front of hatch 10 for hot zone 13 of reactor chamber 9. Hatch 10 is spring loaded to an open position, but is kept closed by a lock (not shown) as long as an oxygen gas detector (not shown), arranged in the conveyor pipe of feed screw device 6, indicates that there is oxygen gas in the compression zone of the pipe or in hot zone 13. This oxygen gas detector also controls, by means of a computer suitable for the purpose and associated software, whether nitrogen gas is to be supplied or not. For example, if a fault occurs in any of the motors 2, 4 of the feed screw devices, all feed-in and heating elements 15 are closed, as is also hatch 10 with positively controlled means (not shown) arranged according to the intended use. Under such conditions it is appropriate to maintain a nitrogen gas atmosphere in the feed screw pipes and reactor chamber 9 until the temperature in it has dropped enough so that there is no longer a fire risk in the material intended for pyrolysis. The temperature in hot zone 13, which is maintained by means of heating elements fitted in its roof, is controlled by thermostats and software in a computer so that it is kept at around 550 ⁰ C +/- 5°, as a result of which as complete a degassing as possible of material supplied and levelled by means of plough 12 as it passes through hot zone 13.

The invention should not be regarded as being limited by this description of a preferred embodiment of the same but should only be regarded as limited by the attached claims.