Patent Description:
Pyrolysis is a type of thermolysis, and is most commonly applied to organic materials exposed to high temperatures. It also occurs in fires where solid fuels are burning or when vegetation comes into contact with lava in volcanic eruptions. In general, pyrolysis of organic substances produces gas and liquid products and leaves a solid residue richer in carbon content, char. High-density polyethylene HOPE plastic wastes, polypropylene PP, or low-density polyethylene LDPE are pyrolyzed at temperature of less than <NUM> and char, or solid residues, derived therefrom may be used for several purposes, including producing briquettes, it may be used as a fuel for the combustion process, or boiling water, etc..

<CIT> discloses a pyrolysis chamber which is agitated by rotation of at least two helical blades arranged to rotate close to an internal surface of the pyrolysis chamber; the pyrolysis chamber is further agitated by a central auger, wherein the auger is located so that reverse operation of it causes output of char via a char outlet. This document does not describe a solution for removing the char from the pyrolysis system in a secure manner; yet, for doing so, the operator would need to wait for a predetermined period of time, approximately <NUM> hours, to open a chamber where the char may be stored. Otherwise, the char may spontaneously ignite in the presence of high temperature, such as <NUM>-<NUM> after having passed the pyrolysis process, and the oxygen entering said chamber. This time consuming method is not efficient in industrial premises leading due to the need of stopping a plant for waiting to the char to be removed.

<CIT> discloses a method for processing of plastic waste comprising a last step of directing the dust and gases to a gas cooling apparatus comprising at least two synchronized screw conveyors, wherein the gases are cooled and wherein the dust and the condensate are directed to a filter filled with the char; and wherein the mixture of char is fed back to a microwave pyrolysis reactor. This document discloses a screw conveyor for transporting the char horizontally. These kind of systems of the state of the art are not adapted to safely remove the char at the end of the processing of plastic.

<CIT> discloses a process for converting waste materials into a carbon-rich char material and includes the use of a cooling screw conveyor.

The present invention allows to securely remove the char at the end of a method for processing of plastic waste, namely from a pyrolysis process, and also to do it in a reduced period of time compared to the solutions of the state of the art.

The present invention is a process according to claim <NUM>. Dependent claims define particular embodiments of the invention. All the features described in this specification including the claims, description and drawings and/or all the steps of the described method can be combined in any combination, with the exception of combinations of such mutually exclusive features and/or steps.

In the context of the present invention, physically isolated means that the cooling chamber and the char contacting surface are airtight or liquid tight isolated. This means that no cooling fluid or cooling medium or air or liquid in the cooling chamber can get into contact with the char being removed or conveyed.

An advantage of the present invention with regard to the state of the art is that the cooling chamber allows for a heat exchange between a cooling fluid and the char on the char contact surface of the screw conveyor in operation. The cooling fluid may be water at a lower temperature than the pyrolysis temperature, for example lower than <NUM>. Said heat exchange reduces the time needed to wait until the temperature of the char allows opening the system with no risk of spontaneous ignition. This allows to continuously discharge char whilst also cooling to safe temperature in a short time, namely <NUM> hours, therefore removing batch bottlenecks and maximising plant throughput.

Besides, the fact that the cooling chamber and the char contact surface are physically isolated avoids the contact between any cooling fluid, such as water, or liquid nitrogen, or cold air, with the char; this avoids the contamination of the dried char so that it can be recovered in its initial status for any purpose.

Other advantages in line with the mentioned are that the present invention allows to securely remove the char at the end of a method for processing of plastic waste, whilst cooling to a safe temperature of below <NUM>.

In an embodiment the screw conveyor comprises the cooling chamber in an inner cavity.

In an embodiment the screw conveyor unit comprises a screw chamber, the screw chamber comprising the screw conveyor, and the cooling chamber is concentrically arranged with respect to the screw chamber.

Advantageously this embodiment allows a uniform distribution of the cooling fluid along the cooling chamber in such a way that the heat exchange is uniformly performed and thus in an efficient manner.

In an embodiment the screw conveyor and the cooling chamber are arranged such that, in operation, both the char contacting surface and the cooling fluid perform the heat exchange along the complete length of the screw conveyor.

For example, this embodiment may be implemented by a screw conveyor of a certain length and an elongated cooling chamber of the same or larger length, so that the entire char contact surface of the screw conveyor is cooled down and therefor the char deposited on it in operation.

Advantageously this embodiment decreases the heat exchange time between the char and the cooling fluid in operation, compared to the situation where only one part of the char contacting surface performs the heat exchange with the cooling fluid.

In an embodiment the screw conveyor is void and an inner area of the void screw conveyor comprises the cooling chamber.

This alternative allows reducing the space needed to implement the screw conveyor unit in a pyrolysis system, since the cooling chamber is integrated in the screw conveyor used for transporting the char.

In an embodiment where the screw conveyor unit comprises a screw chamber, the cooling chamber is external and concentric to the screw chamber.

This alternative allows adapting any existing screw unit by simply adding an external and concentric chamber, which may be in cylindrical shape or any other shape, adapted to contain a cooling fluid and adapted to physically isolate the cooling fluid from the char in operation.

The screw conveyor may include cooling fluid tubes inside an auger. The screw conveyor may be present to drive the char forward however cooling fluids can be located inside the auger as well as on the outside jacket.

In an embodiment the screw conveyor unit comprises an inlet for the reception of a cooling fluid.

Advantageously the cooling fluid may be inserted in the cooling chamber via the inlet in such a way that the cooling fluid can be renewed.

In an embodiment the screw conveyor unit comprises an outlet for dropping out a cooling fluid.

Advantageously the cooling fluid may be dropped out from the cooling chamber via the outlet in such a way that the cooling fluid can be renewed.

In an embodiment the screw conveyor unit comprises an inlet for the reception of a cooling fluid and an outlet for dropping out a cooling fluid. The inlet and outlet may be in the form of water tubes inside an auger.

Advantageously the cooling fluid may be flowing continuously or in batches via the inlet and outlet in such a way that a low temperature is maintained. Low temperature means a temperature allowing the heat exchange between the cooling fluid and the char contacting surface to be performed so that the char is cooled down.

In an embodiment the system for treatment of waste plastics further comprises a valve for the delivery of char from a pyrolysis reactor or pyrolysis chamber, or autoclave, to the screw conveyor unit, wherein the valve:.

In an embodiment the valve is made of fire safe material rated to <NUM>. The valve may also be built in materials not building up contaminant of char and metals on sealing face leading to leak path, such as ceramics, and maybe polymer based coatings.

Advantageously such a valve allows minimising leak paths from the pyrolysis reactor, or pyrolysis chamber, or autoclave, towards the screw conveyor unit.

In an embodiment the valve is a triple offset butterfly valve that allows for scraping of sealing face with self-cleaning nature and removal of body away from contaminant flow path.

In an embodiment the valve is a segmented ball valve comprising metal seat that allows gas seal but also cuts contamination build up and does not allow build up due to lack of packing to seal.

Advantageously the heat exchange between the cooling fluid and the char contacting surface of the screw conveyor unit directly allows to perform a heat exchange between the char contacting surface and the char therefore lowering the temperature of the char.

In an embodiment of the method the cooling fluid is provided simultaneously to receiving the char into the screw conveyor unit.

In an embodiment of the method conveying the char by the screw conveyor is simultaneously performed to descending the temperature of the char by heat exchange.

Advantageously this embodiment allows cooling down the char while the cooling fluid is renewed in the screw conveyor unit so that the cooling temperature is maintained constant and the heat from the char coming from a pyrolysis chamber does not heat the cooling fluid; therefore the heat exchange increases in efficiency and the time to cool down the char is reduced significantly.

Waste plastics provided in the pyrolysis reactor are advantageously first melted through a step of melting the waste plastics materials that can take place in an extruder for example.

The step of providing waste plastics into the pyrolysis reactor is performed preferably at a <NUM> temperature of the pyrolysis reactor. This feeding step lasts as long as the pyrolysis reactor is not sufficienltly fed with waste plastics.

The amount of waste plastics fed into the pyrolysis reactor depends on the side of the pyrolysis reactor. For example, a <NUM>-<NUM><NUM> pyrolysis reactor can be fed until approximately <NUM> tonnes in order to provide an efficient conversion of waste plastics to fuel. The amount of waste plastics provided into the pyrolysis reactor per hour may be of <NUM> kgs an hour. It can, in this example, last for about <NUM> to <NUM> hours.

After, the predetermined amount of waste plastics to be fed in the pyrolysis reactor is reached, the step of providing waste plastics into the pyrolysis reactor is stopped. Then, the pyrolysis step of heating, at a first temperature, waste plastics in the pyrolysis reactor to provide pyrolysis gases and char is performed. Preferably, the first temperature is comprised between <NUM> and <NUM>. An agitator agitate the inside of the pyrolysis reactor. Inside of the pyrolysis reactor, during the pyrolysis step, waste plastics are pyrolysed in an oxygen-free atmosphere while being agitated. Agitation is performed by a double helical agitator. The agitation aims at improving the heat transfer inside of the pyrolysis reactor in order to improve the pyrolysis step.

During this pyrolysis stage, all the pyrolysis gases are extracted from the pyrolysis reactor which is left with wet and sticky char. Char is to be evacuated from the pyrolysis reactor through a screw conveyor unit. Char may be paste-like in consistency and thus difficult to be removed through the screw conveyor unit.

The cook-off step helps to reduce the wetness of the char and turn it into a dry powder easier to remove from the pyrolysis reactor. The cook off step is performed once the viscosity of the char has reached a predetermined threshold. The cook-off step can last for about three to four hours. The second temperature is preferably <NUM>% higher than the first temperature. It can be comprised between <NUM> and <NUM>, preferably around <NUM>.

The measure of the viscosity, or dryness, of the char is obtained through measuring the load of the means for agitating the inside of the pyrolysis reactor. A good indicator of the load of the agitator is the current of the agitator. For a <NUM>-3m3 pyrolysis reactor, the normal operation current of the agitator is around <NUM>-<NUM> A and the predetermined threshold is around <NUM>-55A. Once again, it depends on the size of the pyrolysis reactor.

Advantageously, the pyrolysis gases are evacuated to a contactor or a reflux column. The third temperature of the contactor or of the reflux column is measured, preferably at the outlet of the contactor or of the reflux column. When it reaches a predetermined value, the cook-off step is stopped and the char is provided to the screw conveyor unit for its removal from the pyrolysis reactor. A drop of the third temperature of the outlet of the contactor is an indicator that you have driven hydrocarbon liquid off the char because there is no more flowing upwards past the temperature probe.

<FIG> shows an example of a screw conveyor unit (<NUM>) for removing char (<NUM>) from a system for processing plastic waste used in the method according to the invention, the screw conveyor unit (<NUM>) comprising.

The screw conveyor (<NUM>) and the cooling chamber (<NUM>) are arranged such that.

For a heat exchange to be allowed between the cooling fluid (<NUM>) and the char (<NUM>) when the cooling chamber (<NUM>) contains a cooling fluid (<NUM>), materials such as steel are preferably used for the screw conveyor (<NUM>) and/or for the char contacting surface (<NUM>) and/or for the cooling chamber (<NUM>). Steel or mild steel properties are appropriate for high and low temperatures such as temperatures in the range of [from ambient - <NUM>] or [from ambient - <NUM>] or [from ambient -<NUM>] or [<NUM>-<NUM>], where ambient may be <NUM>, or <NUM>, or <NUM>, or <NUM>, or <NUM> or <NUM> or <NUM>. Stainless steel may reach a maximum temperature around <NUM>, and mild steel may reach a maximum temperature around <NUM>.

<FIG> also shows points A, B, C and arrows indicating:.

In <FIG> the cooling fluid may be inserted into a side point of the cooling chamber, for example into point <NUM>. The cooling fluid (<NUM>) may also be extracted from point <NUM>. The cooling fluid (<NUM>) may be continuously inserted and even simultaneously to the load of char into the screw conveyor unit (<NUM>). The feeding speed of the cooling fluid may be regulated to allow an improved heat exchange between the char and the cooling fluid, for example in a configuration of.

it is possible to reduce the temperature of the char from <NUM> to <NUM>° in less than <NUM> hours, whilst continuously discharging at <NUM>/hr.

<FIG> shows an elevated view of a screw conveyor unit (<NUM>) comprising a screw conveyor not represented in the interior of a screw chamber (<NUM>), and a cooling chamber (<NUM>) or cooling jacket concentric and external to the screw chamber (<NUM>).

The screw conveyor unit (<NUM>) of <FIG> may present the following configuration:
Construction materials: mild steel but others and same material than the screw.

The screw conveyor and the cooling chamber being <NUM> meters long, allow conveying char at a rate of <NUM>/hour.

The cooling fluid (<NUM>) is water. Preferably the flowrate of water <NUM> times the char flow. The input of water may be performed via flexible hoses.

This configuration allows cooling down the char from <NUM>-<NUM>'c to below <NUM> in less than <NUM> hours.

In an example, the char is fed into the screw conveyor unit via a valve, this valve being, in an example, a butterfly valve triple offset butterfly valve. This type of valve provides.

In an embodiment, the triple offset butterfly valve is adapted to provide.

The advantages of a segmented ball valve are the same, however, a segmented ball valve comprises a metal seal rather than packing that allow for no contamination and build-up from solids as well as better scraping.

In an example the valve comprises airtight means and/or gas tight means and/or metal tight means for isolating the pyrolysis chamber from the screw conveyor unit.

<FIG> shows an example of a system for treatment of waste plastics in a process according to the invention wherein there are represented:.

<FIG> also represents:
A screw conveyor unit (<NUM>) for removing char (<NUM>) from the system for treatment of waste plastics, the screw conveyor unit (<NUM>) comprising.

In the system of <FIG> the first screw conveyor (<NUM>) of the state of the art may convey the char (<NUM>) at a temperature of <NUM> until the char (<NUM>) is dropped down towards the screw conveyor unit (<NUM>) of the invention. Water (<NUM>) at a temperature of <NUM> may be inserted into the cooling chamber (<NUM>) to heat exchange with the char coming from the first screw conveyor (<NUM>) according to the state of the art and from the second pyrolysis reactor (<NUM>). The result is that the char is cooled down in less time than in the state of the art and the char can be extracted in less time than in the state of the art, therefore avoiding delays in treatment of waste plastics.

In the system of <FIG> the screw conveyor of the state of the art may convey the char (<NUM>) at a temperature of <NUM> until the char (<NUM>) is dropped down towards the screw conveyor unit (<NUM>) of the invention, where water (<NUM>) at a temperature of <NUM> may be inserted to cool down the char coming from the screw conveyor (<NUM>) according to the state of the art and the second pyrolysis reactor (<NUM>).

In the pyrolysis reactors (<NUM>) or pyrolysis chambers or autoclaves the step of drying/lowering viscosity of the char takes place.

Melted waste plastics are provided to the pyrolysis reactor (<NUM>). Pyrolysis at a first temperature happens in the pyrolysis reactors (<NUM>). During pyrolysis, melted plastics are agitated inside of the pyrolysis reactor (<NUM>) through agitating means.

During this step of pyrolysis, both pyrolysis gases and char are produced. Pyrolysis gases are to be sent to a contactor downstream of the pyrolysis reactors (<NUM>) for further cracking of fuel molecules. Char remains on the inner wall of the pyrolysis reactors. It is very important to avoid extraction of char to the contactor. The pollution of end-of-cycle fuel through char particles is to be avoided. Thus, removal of char from the pyrolysis reactors is critical.

However, at the end of the step of heating at the first temperature, char particles accumulate into the pyrolysis reactor and stick to the inner wall of the pyrolysis reactors and are difficult to remove through the screw conveyor unit.

Measurement of the viscosity of the char in the pyrolysis reactor is performed through measurement of the load of agitating means. When the viscosity reaches a predetermined threshold, the pyrolysis step is stopped and the cook-off step begins. The cook-off steps aims at drying the char in order to lower its viscosity and turn it into an easily to be removed char powder.

Claim 1:
A method for processing of plastic waste comprising:
- a step of providing waste plastics into a first pyrolysis reactor said first pyrolysis reactor comprising an agitator configured to agitate said waste plastics therein;
- a pyrolysis step of heating, at a first temperature, waste plastics in the pyrolysis reactor to provide pyrolysis gases and char;
- a step of measuring the dryness of the char in the first pyrolysis reactor by measuring the load of said agitator,
- a completion step of completing the pyrolysis step;
- a cook-off step of heating at a second temperature, the inside of the first pyrolysis reactor when the load of said agitator reaches a predetermined threshold, said second temperature being higher than the first temperature.
and, after completing said cook-off step, - a step of removing char from a system for treatment of waste plastics comprising a screw conveyor unit (<NUM>, <NUM>, <NUM>) for removing char from said system, said screw conveyor unit comprising:
- a screw conveyor (<NUM>,<NUM>,<NUM>), comprising a char contacting surface (<NUM>, <NUM>) and
- a cooling chamber (<NUM>, <NUM>, <NUM>) adapted to contain a cooling fluid (<NUM>),
arranged such that
- the cooling chamber (<NUM>, <NUM>, <NUM>) is physically isolated from the char contacting surface (<NUM>, <NUM>) of the screw conveyor (<NUM>, <NUM>, <NUM>) and
- the screw conveyor (<NUM>, <NUM>, <NUM>) and the cooling chamber (<NUM>, <NUM>, <NUM>) are configured to allow, in operation, a heat exchange between the cooling fluid (<NUM>) and the char (<NUM>) when the cooling chamber (<NUM>, <NUM>, <NUM>) contains a cooling fluid (<NUM>),
said step of removing char comprising:
- providing a cooling fluid to the screw conveyor unit;
- receiving the char into the screw conveyor unit;
- conveying the char by the screw conveyor wherein the char is in contact with a char contacting surface of the screw conveyor;
- lowering the temperature of the char by heat exchange between the cooling fluid and the char contacting surface of the screw conveyor unit.