GB2303859A - Tyre pyrolysis method and apparatus - Google Patents

Abstract

Tyres are pyrolized by moving them through a furnace (3) having a heating portion and a cooling portion. The tyres are supported on open trays (2). An inert atmosphere is maintained in the furnace. Heat output from the cooling portion is fed back to the heating portion. Some of the products of the pyrolysis are used as fuel to heat the heating portion.

Description

Specification Tyre Pyrolysis Method and Apparatus The present invention relates to apparatus and methods for the pyrolysis of tyres.

In the following, references to tyres shall mean tyres or other items comprising rubber or other carbon based materials, in small, or substantial proportions.

Waste tyres represent a major environmental problem and a potentially important secondary source of valuable materials. Pyrolysis of tyres by heating in the absence of air to cause thermal break-down is well known.

The long chain molecules in the rubber are broken down, and the resulting mixture of short-chain hydrocarbon molecules is made volatile. Carbon and steel are left and can be recovered and separated magnetically. Much of the sulphur present in the rubber is left in the solid phase, rather than in volatile phases. Cooling the volatiles gives an oil and combustible gas fraction. Part of the latter can be used to fire the pyrolysis furnace, and the remainder can be used to generate electricity to run the process.

Various methods of tyre pyrolysis plant have been tried. EP-A-0 049 054 describes a semi-continuous batch process in which shredded tyres are transported in and out of an oven in a covered bin. The bin has an inclined top leading towards an opening at one end which enables the gases created within the bin to flow towards the gas collection zone provided in the top of the oven, which is also sloped upwards towards an opening.

Following heating, in an inert atmosphere in the oven, the bin is removed from the oven along rails, and immediately immersed in water to cool the carbon residue, which would otherwise start to burn on exposure to air.

It is known from US-A-5 095 040 to use a continuous process in which crumbed tyres are fed into a tube furnace, and moved along by an auger screw. Carbon is discharged at a lower end of the tube without quenching, since it is at a sufficiently cool temperature.

Crumbing the tyres before the pyrolysis reduces the problem of heat transfer to the centre of a large mass of rubber, since rubber is a poor conductor of heat. However, crumbing the tyres takes a huge amount of energy, and therefore makes the process uneconomic.

Attempts have also been made to use batch furnace designs. However, such designs are inefficient owing to temperature cycling of the furnace.

Furthermore, they have been unable to guarantee a dry friable residue for further treatment, owing to the problem of heat transfer to the centre of a large mass of rubber.

A continuous pyrolysis process using microwave heating and a conveyor belt is known from WA 89/04355.

All of those known methods suffer either from their inability to heat large masses of rubber efficiently or thoroughly, or from the problem of clouds of carbon dust being emitted and causing external pollution problems,4 or fouling the internal surfaces of the furnace, or contaminating oil condensed out of the combustion products.

Accordingly, there is a need for a pyrolysis method which gives rapid and efficient heating, without causing fouling and pollution emission problems.

The present invention aims to provide an improved method and apparatus.

According to one aspect of the invention, there is provided a method of pyrolizing tyres comprising the step of moving discrete containers retaining the tyres from a heating to a cooling portion of a furnace.

According to another aspect of the invention, there is provided apparatus as set out in claim 11.

The invention retains the thermal efficiency advantage of a continuous process, while enabling smooth handling of the dusty residue with minimum disturbance. The disadvantages of tumbling the powder inherent in prior continuous systems using auger screws or conveyor belts can be avoided.

The advantages of prior batch systems are retained through the use of discrete containers.

Advantageously, the features of Claim 2 facilitate thorough and rapid heat transfers with good efficiency.

In a preferred embodiment using the features of Claim 3, thermal efficiency can be improved as well as minimising pollutants which would be emitted if oxygen is allowed into the furnace.

If the features of Claim 4 are used, thermal efficiency can be improved, and the possibility of carbon dust escaping can be reduced.

Advantageously, the features of Claim 5 can be used to maintain good thermal efficiency.

The features of Claim 6 can likewise maintain good thermal efficiency. The feature of Claim 7 can improve the heat transmission.

The features of Claim 8 enable a simple construction with fewer moving parts in the furnace, without undue disturbance to the residues.

The features of Claim 9 also enable simple straightforward construction with a reduced number of moving parts to ensure reliable operation, while enabling reduced disturbance to the residues in the trays.

For a better understanding of the invention, and to show how the same may be put into effect, reference will now be made by way of example to the following drawings, in which: Figure 1 shows a plan view of one embodiment of apparatus for carrying out a method in accordance with the invention; Figure 2 shows a transverse section of the apparatus of Figure 1; Figure 3 shows a longitudinal section of the apparatus of Figure 1; Figure 4 shows a schematic drawing of the operation of the invention; Figure 5 shows another schematic drawing of the invention; and Figure 6 shows another schematic drawing of the invention.

Figure 1 shows one example of how to put the invention into effect. It shows a plan view of a furnace in the form of an externally heated muffle kiln which is illustrated as if the top of the kiln were transparent, so that containers and a support track inside the kiln are visible.

An entry gas lock 1 is provided to allow entry of containers in the form of open trays carrying tyres into the kiln 3. The trays pass through a heating zone, followed by a cooling zone, before being taken out of the kiln through an exit gas lock 4. The trays are supported on a track 5 in the kiln.

Burners are provided in the heating zone to heat a muffle of the kiln externally. Exhaust gases from the burners are fed via a flue gas cleaning system 6 to chimney 7.

An exit manifold 8 is provided for the gases produced from the tyres. This feeds a condenser 9, which is connected to a gas cleaning system 10 and a booster pump 11. A return path 12 is provided to enable some of the cleaned gas to be fed back to the burners.

The heating zone and the cooling zone of the kiln are separated by a partition 13 to maintain the temperature differential between the two zones.

As can be seen from the transverse section shown in Figure 2, the roof of the muffle slopes upwards towards a central outlet for the gases produced from the tyres. The trays 2 are relatively flat to allow good heat flow to the tyres, for efficient pyrolysis.

The support tracks 5 are provided at either side of the trays. Support lugs 14 at either side of the tray rest on the support tracks 5. The weight of the trays with the tyres is taken by these support lugs, which slide along the support tracks to enable movement through the kiln with a minimum of moving parts. The support tracks also act as guides to keep the trays in line.

The operation of this embodiment will now be described. The method involves 4 basic steps as follows: a) heating whole or chopped tyres (but preferably not shredded tyres as shredding takes too much energy) in a sealed container to a temperature between 200 and 1000"C (475 to 1275K), preferably between 300 and 800"C ( 575 to 1075K) for a period between 15 and 60 minutes, b) taking the volatile gases produced by the tyres out of the container and condensing oil or oil fractio+n from the gases, c) de-sulphurising uncondensed volatile products and using part of the gas to fire the process, while the remainder of the gas can be sold off or used to generate electricity to power parts of the processor, and d) cooling the solid residue left in the container under an inert atmosphere, and separating the carbon and steel, e.g. by magnetic means.

A commercially viable way of carrying out the steps has not been devised previously, largely because of the practical problems associated with the behaviour of rubber when it is heated.

In the continuous system of the invention, tyres are introduced into the kiln which is held at the operating temperature, and filled with an inert atmosphere. The tyres are subsequently cooled in another stage of the same kiln, without leaving the protective atmosphere. Since only the tyres are cycled from room temperature to pyrolysis temperature and back, only a small amount of heat need to be used to maintain the body of the furnace at the required temperature. Carrying out the process in a sealed container has the advantage of minimising the possibility of carbon dust escaping and causing pollution. The problem of introducing the tyres into the furnace and removing the cooled solid residue, without destroying the inert atmosphere can be solved by using an air-lock system at both ends of the kiln.

A pusher device can be fitted at the entry lock, and/or a puller device at the exit lock, to move the trays along the support track. If the trays are pushed, then no coupling is needed between the trays. A coupling would be needed if the trays are to be pulled through. Motion can be continuous or in steps.

By these means, although the tyres are moved through the furnace, they can remain static relative to their tray and therefore there is little tendency for the carbon dust to be shaken into the atmosphere. The trays can be moved smoothly along the support track through the kiln.

Notably the use of relatively flat trays carrying a thin layer of tyres either whole or chopped into large pieces, for example larger than 10 cm by 10 cm, enables the hot gases to flow around the tyres more easily, and therefore carry heat to, and volatile gases away from, the tyres more easily. In the embodiment illustrated in Figure 2, the height of the layer is approximately 20 - 30 cm, or 1/3 of the width of the tray. The rate of heat transfer can be a limiting factor when laboratory scale plants are scaled up to handle tons of tyres. Accordingly, the optimum thickness of the layer of tyres will vary according to how much the tyres are chopped, and the shape and width of the trays. It may be appropriate to use a layer as thick as a single tyre laid on its side.

Figure 4 is a schematic diagram showing an example of the thermal energy flows around the system. In particular, this shows that energy can be fed back to the pyrolysis chamber from the cooling of the solids. A proportion of the energy in the flue gases can be fed back. Also, gases derived from the products of pyrolysis can be fed back to contribute to the heating of the pyrolysis chamber, or to generating electricity for sale.

Figure 5 shows the process in the form of a flow diagram. A tyre cutter 14 and a loader 16 are shown feeding the chamber via the entry air lock. The cooling chamber uses forced air for cooling. To contribute to thermal efficiency, the air warmed by the cooling chamber is fed to the burners heating the pyrolysis chamber.

Figure 6 shows another embodiment using radiant burners 17 inside the kiln.

The entry and exit gas locks 1, 4 are provided with feed pipes 18 to assist in changing the atmosphere from air to the inert gas of the kiln.

The gases given off by the tyres are processed by an optional electrostatic precipitator 19, and a condenser/distillation unit 20. The precipitator 19 could be replaced by a venturi scrubber, or other gas cleaning equipment.

Features from this embodiment, and from that shown in Figure 5 may be added or interchanged with features of the embodiment shown in Figures 1 to3.

The method and apparatus described may be arranged to process approximately 90 tyres per hour, which corresponds to approximately 5000 tons per year. In operation, the cooling of the solid residue should be below a temperature of approximately 240"C, above which, the carbon may ignite on exposure to air. The trays may be designed with a carrying area of 2 2 approximately 1 m2, and the tyres can be cut to pieces between 2.5 cm2 and 10 cm2, to be loaded into the trays as a layer 20 - 30 cm deep.

The apparatus can be supported above ground level to enable gravity feed at the exit of the kiln. The kiln could be tilted to facilitate gravity feed of the trays along the support track. Other variations can be envisaged within the scope of the invention as defined by the claims.

Claims (12)

Claims:

1. A method of pyrolizing tyres comprising the step of moving discrete containers retaining the tyres from a heating to a cooling portion of a furnace.

2. The method of claim 1 wherein the containers comprise open trays, carrying a thin layer of tyres.

3. The method of Claim 1 or 2 wherein the furnace has entry and exit air locks to maintain an inert atmosphere in the furnace.

4. The method of any preceding claim wherein the solid residue from the pyrolysis is cooled in the cooling portion sufficiently to avoid combustion in air, before removal from the furnace.

5. The method of Claim 4 wherein heat output from the cooling portion is used for heating tyres in the heating portion of the furnace.

6. The method of Claim 1 wherein the products of pyrolysis are used to heat the tyres in the heating portion.

7. The method of any preceding claim wherein the tyres are cut before heating.

8. The method of any preceding claim wherein the containers are moved in the furnace by being pushed by a following container, or being pulled by a preceding container.

9. The method of any preceding claim wherein the containers are movable by sliding on runners.

10. A method of pyrolizing tyres substantially as hereinbefore described with reference to the accompanying Figures.

11. Apparatus for carrying out the method of any preceding claim, comprising containers for retaining the tyres, a furnace comprising a heating portion and a cooling portion and means for moving the containers from the heating portion to the cooling portion of the furnace.

12. Apparatus substantially as hereinbefore described with reference to the accompanying Figures.