The present invention relates to a pyrolyser for pyrolysing materials or objects, for example lithium ion batteries, which undergo an exotherm during the pyrolysis process.

Pyrolysers are used in industry to heat materials such as scrap material so as to remove components such as lacquer or paint coatings by vaporization or burning.

However, problems arise when the scrap material undergoes an exotherm when heated as this raises the temperature inside the pyrolyser to high temperatures which may be undesirable. This makes it necessary to find a way of limiting the heat produced by the material while it undergoes pyrolysis.

When lithium-ion batteries are pyrolysed they produce an exotherm once each battery reaches a temperature of about 4300C. The exotherm then raises the temperature of each battery and so raises the temperature of the pyrolyser chamber. The extent of this temperature rise is dependent upon the loading of the batteries and the volume of the chamber. For example, if 500 batteries are processed in a pyrolyser with about 5m3 volume the exotherm can raise the temperature in the pyrolyser chamber to 850°C. This temperature increase can imperil the structural integrity of the pyrolyser chamber.

One way of avoiding the problems caused by this exotherm is by limiting the number of batteries pyrolysed in a given volume. However, the heating and cooling time for a pyrolyser is considerable. This causes the entire cycle from loading to unloading of the pyrolyser to last a long time, typically at least one day. This means that the throughput of the process is very low if it relies on treating a limited batch size once each day. It is therefore important to increase the throughput of the pyrolyser. Pyrolysers which operate continuously are known but are extremely expensive.

Similar problems arise in the treatment of mixed organic and inorganic wastes such as the waste produced when de-inking paper. When a waste material comprising organic and inorganic material is heated, heat is evolved as the organic material combusts. It may be necessary to control the temperature of the reaction in order to control any reactions of the inorganic material. For example, when waste material from de-inking paper is heated the calcium carbonate from the paper will decompose if the temperature of the pyrolyser rises significantly above 8000C.

The production of multilayer circuit boards involves firing ceramic powders combined with organic binders in the presence of metals. The organic binders are removed in the firing process but this must be achieved without oxidising the metal. This is achieved by controlling the temperature and gaseous atmosphere of the firing process, for example in a pyrolyser.

The problem is therefore to increase the amount of material that can be pyrolysed in a batch pyrolyser of a given volume without the temperature of the pyrolyser becoming too great during the pyrolysis .

Accordingly, the present invention provides a pyrolyser comprising a pyrolyser chamber and two or more drawers wherein each drawer comprises sealing means such that the pyrolyser chamber is sealed when each drawer is either fully open or fully shut. In a preferred embodiment the pyrolyser comprises two, three, four, five, six, seven or eight drawers, preferably at least four or five drawers.

The sealing means is any means that enables the drawer to seal when fully open or fully shut. Typically the sealing means is in the form of a thermally stable material on the sealing face of the drawer which forms a gas tight seal with the wall of the pyrolyser. The sealing means may be, for example, a thermally resistant gasket.

In use, the pyrolyser drawers are loaded, when open, with material to be pyrolysed. Typically, one drawer is then closed though this is not essential. Thus, the first drawer to be closed may be heated from cold in the pyrolyser or the first drawer may be closed once the pyrolyser has been turned on and/or reached a desired temperature. The pyrolyser is then turned on and heated to the desired temperature and the drawers are closed sequentially. The desired operational temperature of the pyrolyser depends on the material to be pyrolysed but is typically from 200 to 8000C, more preferably from 400 to 65O0C and most preferably about 5500C.

The time between closing one drawer and closing the next drawer is chosen so as to keep the temperature inside the pyrolyser chamber under control. The timing can be chosen so that an exotherm is occurring for the material in one drawer of the pyrolyser as the next drawer is closed. In this way the excess heat from the exotherm is used at the moment when extra heat is required to bring the cooler material from the newly closed drawer up to temperature for pyrolysis. Alternatively, each drawer may be closed after the exotherm has occurred for the previous drawer. Any material may be pyrolysed. However, the pyrolyser is particularly suitable for pyrolysing materials which cause an exotherm when pyrolysed. In particular the pyrolyser is suitable for processing lithium-ion batteries . The pyrolyser is also suitable for processing other materials where the reaction needs to be controlled.

Many materials for pyrolysis are heavy. Therefore in a preferred embodiment, the pyrolyser further comprises support means for the drawers when open.

In a preferred embodiment, the pyrolyser drawers are opened and closed by remote operation. For example, a pneumatic ram may be used to close the drawers remotely. This reduces the exposure of personnel to off-gas from the pyrolyser some of which escapes as each drawer is closed. The same mechanism is typically used to open the drawers, owing to their weight. The remote operation of the drawers may be controlled in such a manner, for example by computer software, so as to prevent the time interval between one drawer being closed and the next drawer being closed from being less than a certain number of minutes or hours.

The pyrolyser typically comprises off-gas treatment equipment. Typically this takes the form of an after burner to combust the off-gas followed by a gas scrubber. The off-gas is then typically vented to the atmosphere.

The pyrolyser typically has the advantage that it is easier to treat the off-gas from the pyrolyser compared to a conventional pyrolyser as the off-gas is produced over a longer period for a given amount of material being pyrolysed, and therefore the cleaning/scrubbing equipment for treating the off-gas can be in the form of a smaller unit than otherwise required for a pyrolyser of a given volume.

A specific construction of a pyrolyser embodying the invention will now be described, by way of example only, and with reference to the drawings filed herewith, in which:

Figure 1 is a schematic cross-section of part of a pyrolyser according to the present invention;

Figure 2 is a perspective view of the pyrolyser of Figure 1; and

Figure 3 is a perspective view of the pyrolyser of Figure 1.

Figure 1 shows a section through part of a pyrolyser 10. The pyrolyser 10 comprises a pyrolyser chamber 1 and a drawer 2 which is supported on an internal frame 5 when closed and on an external frame 6 when open. The drawer 2 slides along the internal frame 5 by means of the runner 4 which incorporates castors (not shown) and slides along the external frame 6 by means of another such runner 4. The front of the drawer 2 and the back of the drawer 2 has a sealing face 3 which incorporates a thermal gasket (not shown) which forms a gas tight seal with the front or back face of the front of the pyrolyser chamber 1 respectively when the drawer is fully open or fully shut. The drawer 2 may be opened and shut by means of the handle 9. However, typically the weight of the drawer when loaded is such that additional means such as a pneumatic ram is provided.

Figure 2 shows a perspective view of the pyrolyser 10. The pyrolyser 10 comprises four drawers 2 which are shown in the closed position, pushed fully into the pyrolyser chamber 1. (The drawer handles have been omitted from the drawing for clarity) . The pyrolyser 10 also has an external structure 6 which supports the drawers 2 when they are open. The pyrolyser 10 has an abatement section 7 to treat the off gases.

Figure 3 shows a perspective view of the pyrolyser 10 (the pyrolyser chamber 1 of which is indicated schematically by the dotted line) . One drawer 2 of the pyrolyser is shown in the open position. The drawer 2 rests on the external structure 6 only part of which is shown in the Figure.

Purely as an example, the operation of the pyrolyser 10 of Figure 1 is described below for the pyrolysis of lithium ion batteries.

In operation of the pyrolyser 10 of Figure 1 each drawer 2 is loaded in turn in the open position with lithium ion batteries when the pyrolyser is cold. One drawer 2 is then shut using a pneumatic ram (not shown in the Figures) and the pyrolyser chamber 1 is brought up to temperature. For batteries a typical operational temperature is about 55O0C.

As the pyrolyser chamber 1 reaches about 4300C, the batteries undergo an exotherm for about 15 minutes. This may raise the temperature within the pyrolyser chamber 1 as high as 8000C. As soon as the exotherm has ceased and the pyrolyser chamber 1 returns to the operational temperature of about 5500C, a further drawer 2 is shut using the pneumatic ram.

This process is repeated until all the drawers 2 are shut and the batteries in each drawer 2 have undergone an exotherm. The pyrolyser 10 is then typically run for another hour before being turned off. The pyrolyser chamber 1 is then allowed to cool which may take up to 12 hours depending on the amount of insulation in the walls of the pyrolyser chamber 1. The drawers 2 are then opened one at a time using the pneumatic ram, and unloaded.

As an alternative, each drawer 2 may be shut as the batteries in the previous drawer 2 undergo their exotherm. In this way, the heat produced by the exotherm is used to heat up the cold batteries .