GB2588414A

GB2588414A - Processing of polymeric waste

Info

Publication number: GB2588414A
Application number: GB1915286.7A
Authority: GB
Inventors: Roger Stamp Clive
Original assignee: Rockfuel Innovations Ltd
Current assignee: Rockfuel Innovations Ltd
Priority date: 2019-10-22
Filing date: 2019-10-22
Publication date: 2021-04-28
Anticipated expiration: 2039-10-22
Also published as: GB2588414B; WO2021079105A1; GB201915286D0; EP4048454A1

Abstract

A system for the processing of polymeric waste, the system comprising a combustor arranged to burn polymeric waste and a processing plant operatively connected to the combustor to receive heat energy therefrom. The processing plant is arranged thereby to heat additional polymeric waste, without combustion, to produce a synthesis gas, or synthetic fuel, or fuel oil. The system optionally further comprises a boiler. having an inlet for the introduction of water and an outlet for the release of steam, the boiler being operatively connected to the combustor to receive heat energy therefrom and to heat the water to produce steam and being operatively connected to the processing plant to transfer steam thereto.

Description

PROCESSING OF POLYMERIC WASTE

This invention relates to a system and method for the processing of polymeric waste. Furthermore, the invention relates to the carbon neutral and efficient processing of such waste. The invention may be utilised in the formation of carbon neutral fuels for transport, domestic and commercial use, and the formation of useful carbon neutral or greenhouse neutral gases. In addition, the invention may be utilised in the production of carbon neutral products.

The term "system" is used herein to mean an arrangement of apparatus and, while some of the component parts of the apparatus are conventional and/or known per se, the particular assemblage is novel and wholly inventive. Further, the phrase "carbon neutral" is used herein to mean that the amount of carbon dioxide produced during the process is balanced or offset by the subsequent absorption or capture of an equivalent or even greater quantity of carbon dioxide by calcium oxide produced by the process or by a subsidiary plant incorporated in the apparatus of the process.

The term polymeric should be interpreted as "synthetic" polymer-based material. The invention is concerned primarily with plastic polymeric waste, and therefore a particular emphasis is placed on the processing of waste plastics and the invention is discussed in this context. It is of course feasible that the system and method as described herein could be applicable to the carbon neutral processing of other types of polymeric waste and the scope of the present invention is intended to cover such instances.

Not all plastic can be recycled. There are basically two types of plastic: carbon chain and heterochain; heterochain plastic cannot easily be recycled, if at all. Even where possible, plastic products can only be recycled a few times (sometimes only two or three times) before they lose their original properties and become non-recyclable. The problem is exacerbated by the fact that often recyclable and non-recyclable plastics are not segregated at all. The cost and effort required to sort and segregate recyclable from non-recyclable plastic is high, typically resulting in recyclable plastic being transferred to landfill.

Waste plastic is extremely harmful to marine life. According to the documentary series "The Blue Planet", evidence has been found, even in the remote waters of Antarctica, of plastic killing and harming seabirds. With increasing concerns as to the devastating and potentially catastrophic effect of waste plastic in the environment, there is a need to find solutions to eradicate or significantly reduce the harmful effects of waste plastic.

To address the problem, incineration of waste plastic has been considered. Plastic is formed from natural materials, including natural gas and crude oil and the burning thereof inevitably produces a vast amount of heat energy, which could be utilised. Plastic contains the same amount of energy per pound as premium fuel. A significant drawback with such combustion however is the creation of harmful dioxins, as well as carbon dioxide. Efficient incinerators can largely address the issue by preventing the exposure of dioxins. This does not however address the inevitable production of carbon dioxide. The environmental impact of carbon dioxide has been a growing concern and the need to reduce such emissions increasingly prevalent. Scientists devoting their lives to, and specialising in, climate science warn us that climate change is the largest of all threats that could bring about the extinction of humankind. Of all living scientists, most now agree that climate change is one of the very largest risks to our continued existence as a species. It is incumbent upon all, including innovators and all those involved in the protection of new ideas to try to do all that we can to encourage solutions that will help in the fight against climate change for the sake of all humanity.

The obvious solution to the plastic waste problem is to reduce the amount of plastic produced which contributes to unrecyclable waste. However, the benefits of plastics for packaging, including cost and hygiene, mean such attempts are unlikely to be sufficient. Overall, the consensus has generally been that it is environmentally better to bury plastic than to burn it. This however is a fallacy; there is now known to be significant leakage of methane, a dangerous greenhouse gas, from plastics in landfills. This is caused by the plastic being broken down by bacteria over many years. Investigations have shown that a vast amount of recyclable plastic is not prewashed and dried before being transferred to landfill, thereby increasing prevalence of bacteria.

Plastic breaks down into tiny particles and over long periods of time these particles leak, thereby contaminating soil and water. These particles get into the water table and eventually out into lakes, rivers and seas. Moreover, chemicals added to plastic are also absorbed by humans and animals. Some of these compounds have been found to alter hormones or have other potentially harmful health effects. One example is chlorinated plastic, which releases chemicals that are dangerous to animals and humans.

The great concern among environmental scientists is that landfills are a relatively uncontrolled environment, leaking this largely unmeasured and dangerous pollution from plastic waste, which is a time-bomb for future 25 generations. There has been more plastic waste produced in the 19 years of this century than all of the last century put together, and we cannot keep putting plastic waste into landfill. A solution needs to be found without delay; and that solution needs to be non-toxic and carbon neutral.

To address the foreseeable problems associated with global warming, the process of carbon sequestering is used to capture and supposedly store atmospheric carbon dioxide. Again, this process avoids dealing properly with the issue. Carbon dioxide has been found to leak from sequestration sites. As more carbon dioxide is sequestered, there will be more leakage affecting future generations, which defeats the object of trying to make things better for future generations.

Several methods have been proposed to deal with atmospheric carbon dioxide, as an alternative to sequestration. One of those proposals is the conversion of carbon dioxide into carbon and oxygen. The process of splitting carbon dioxide is achievable but requires large amounts of energy. Under the principles of thermodynamics, if that energy is supplied by hydrocarbon fuels the net result will be more carbon dioxide than from the outset.

Catalysts effectively to convert carbon dioxide into carbon monoxide and oxygen or hydrogen have been identified. Such catalysts have been shown to provide highly effective results, but the process requires large amounts of energy, making such conversion inefficient in practice.

There is an urgent need for us all to take action for the sake of the future of humanity. The general consensus of scientific opinion is that we are in a race against time; the clock is ticking. Innovators and all those involved in the protection of new ideas, to reverse the potentially cataclysmic impact of humankind in this area, have a particularly important part to play in encouraging the development of processes that will make a difference at this critical time. It is a principal aim of the present invention to provide a system and method for processing polymeric waste, and which addresses at least some of 5 the environmental problems created by conventional waste processing methods discussed above.

According to a first aspect of a first embodiment of this invention, there is provided a system for the processing of polymeric waste, the system comprising: -a combustor arranged to burn polymeric waste; and - a processing plant operatively connected to the combustor to receive heat energy therefrom, the processing plant being arranged thereby to heat additional polymeric waste to produce a synthesis gas, without combustion; wherein the system optionally further comprises: - a boiler, having an inlet for the introduction of water and an outlet for the release of steam, the boiler being operatively connected to the combustor to receive heat energy therefrom and to heat the water to produce steam and being operatively connected to the processing plant to transfer steam thereto.

According to a second but closely related aspect of this first embodiment, there is provided a method of processing polymeric waste, the method comprising: - burning polymeric waste in a combustor; - transferring heat energy produced by the combustor to a processing plant; and - utilising the heat energy in the processing plant to heat additional polymeric waste to produce a syngas, without combustion; wherein the method optionally comprises: - transferring heat energy produced by the combustor to a boiler; - heating water in the boiler to produce steam; and - transferring the stream produced by the boiler to the processing plant.

According to a first aspect of a second embodiment of this invention, there is provided a system for the processing of polymeric waste, the system corn prising: - a combustor arranged to burn polymeric waste; - a boiler, having an inlet for the introduction of water and an outlet for the release of steam, the boiler being operatively connected to the combustor to receive heat energy therefrom and to heat the water to produce steam; and - a processing plant operatively connected to the boiler to receive steam therefrom, the processing plant being arranged thereby to heat additional polymeric waste to produce a synthesis gas, without combustion; and wherein optionally, the processing plant is also operatively connected to the combustor to receive heat energy directly therefrom.

According to a second but closely related aspect of this second embodiment, there is provided a method of processing polymeric waste, the method comprising: - burning polymeric waste in a combustor; - transferring heat energy produced by the combustor to a boiler; - heating water in the boiler to produce steam; - transferring steam produced by the boiler to a processing plant; and -utilising the steam in the processing plant to heat additional polymeric waste to produce a syngas; wherein the method optionally comprises: - transferring heat energy produced by the combustor to the processing plant further to heat the additional polymeric waste to produce a syngas, without combustion.

According to a first aspect of a third embodiment of this invention, there is provided a system for the processing of polymeric waste, the system comprising: - a combustor arranged to burn polymeric waste; -a boiler, having an inlet for the introduction of water and an outlet for the release of steam, the boiler being operatively connected to the combustor to receive heat energy therefrom and to heat the water to produce steam; and - a processing plant operatively connected to the combustor to receive heat energy therefrom and operatively connected to the boiler to receive steam therefrom, the processing plant being arranged thereby to heat additional polymeric waste to produce a synthesis gas, without combustion.

According to a second but closely related aspect of this third embodiment, there is provided a method of processing polymeric waste, the method corn prising: - burning polymeric waste in a combustor; -transferring heat energy produced by the combustor to a processing plant and to a boiler; - heating water in the boiler to produce steam; - transferring steam produced by the boiler to the processing plant; and - utilising the heat energy in the processing plant to heat additional polymeric waste to produce a syngas, without combustion.

The processing of polymeric waste in two different ways is important. Heating of plastic to produce synthesis gas (syngas) using known methods, such as pyrolysis, is conventionally unsustainable since it is a carbon polluting energy consuming process and more energy may need to be put in to treat the waste than can actually be recovered. However, in the present invention, the burning of polymeric waste produces large amounts of heat energy which can be utilised in the processing plant to heat additional polymeric waste in order to produce carbon neutral or greenhouse neutral syngas. Synthetic fuel (synfuel) may be obtained from the resultant syngas using common methods, as will be appreciated by those skilled in the art.

Various apparatus and methods may be utilised in the processing plant to process the polymeric waste. Such apparatus may include a pyrolysis plant, and/or a gasification plant. Additionally, the processing plant may further comprise a Fischer Tropsch plant to convert synthesis gas into a synthesis fuel. Pyrolysis of polymeric waste in the processing plant may directly produce diesel or fuel oil.

In a preferred arrangement, the combustor preferably further comprises a carbon dioxide regeneration arrangement configured to remove and re-introduce carbon dioxide back into the combustor. This serves to produce a limited or controlled oxygen environment and thus can facilitate a "slow burn" which will result in the production of more char. The heat in the combustor and the regeneration arrangement may thereby serve to facilitate the conversion of carbon dioxide (a greenhouse gas) into carbon monoxide (a greenhouse to neutral gas). Carbon monoxide is not considered a greenhouse gas because it does not absorb enough terrestrial thermal infra-red energy to fall within the definition. However, it has been suggested that carbon monoxide is an indirect greenhouse gas because it can indirectly increase the global warming potential of greenhouse gasses. The specific reactions incurred in the process are well known to those in the art. The carbon monoxide produced could either be sold as a valuable calorific gas or utilised in further reactions (such as a water gas shift reaction) for the production of fuels for vehicles. Alternatively, if a strictly carbon neutral system is required then there is the option, in the system herein described, not to produce carbon monoxide from the combustor and any balance of carbon dioxide produced by the combustor may be directed elsewhere for further processing as discussed in more detail later.

In the preferred embodiment the system includes a boiler for converting water to steam, the boiler having an inlet for the introduction of water and an outlet for steam.

Preferably, the system further comprises a limekiln having an inlet for the introduction of limestone, a heater for heating limestone contained therein and an outlet for the release of calcium oxide and carbon dioxide, wherein the heater of the limekiln is in communication with the boiler outlet and is heated thereby. Calcination of limestone by heating releases carbon dioxide and produces calcium oxide (referred to hereinafter as quicklime). Quicklime produced by the heating of limestone may be collected from the limekiln and used to absorb carbon dioxide from the atmosphere. Such quicklime could be used in vehicle exhaust filters or along motorways or other areas of high carbon to dioxide pollution in order to absorb the carbon dioxide. Additionally, or alternatively, the quicklime could be made into mortar-like slabs which could be utilised in sea defences, new quays and the like. Quicklime is particularly good at absorbing carbon dioxide when placed in water and this could be especially beneficial in coastal projects. In fact, quicklime is able to absorb up to twice the carbon dioxide produced in its formation when it is placed in water; thus, quicklime could be used in the sea and coastal works or sewage schemes, to counter any excess carbon dioxide resulting from the system. Where the processing plant comprises a pyrolysis plant arranged to produce diesel or fuel oil, such resultant products can be considered carbon neutral because the carbon dioxide produced in the later combustion of these fuels, for example in an internal combustion engine of a vehicle, will be countered by the quicklime produced by the kiln.

In one arrangement the heater of the limekiln may be in communication with the boiler outlet so that steam from the boiler is supplied directly to the heater to facilitate the heating of limestone within the limekiln.

In another arrangement the heater of the limekiln may be in communication with the boiler outlet indirectly by way of other apparatus so that energy from the steam is supplied to the heater to facilitate the heating of limestone within the limekiln. In this way a portion of the steam output from the boiler may be used to generate electricity. The heater of the limekiln may be an electrical resistance heating element powered by electricity. The system may comprise a turbine-driven generator set connected to the boiler and means to direct steam from the boiler to the turbine of the generator set for the production of electricity for supply to the heater of the limekiln (where an electrical resistance heating element is provided) or elsewhere within the system. If the steam produced by the boiler is less than 900°C, this arrangement is particularly advantageous as it allows the limekiln to be supplied with sufficient heat for the calcination of limestone.

Both of the above discussed arrangements may be used together such that the heater of the limekiln is capable of receiving steam directly from the boiler and also comprises an electrical heating element to provide additional heat within the limekiln. In such an arrangement if the steam produced by the boiler is less than 900°C, a portion of the steam produced by the boiler may be supplied directly to the heater to facilitate the heating of limestone within the limekiln with the remainder of the steam being directed to the turbine for the production of electricity to power the electrical heating element further to heat the limestone within the limekiln and to power the limekiln.

The burning of polymeric waste and the processing of limestone in a limekiln can together produce a marginal excess of carbon dioxide unless the calcium oxide is channeled to marine environments. Otherwise this excess of carbon dioxide could be converted to low carbon fuels and low carbon greenhouse neutral gasses. Preferably, it would be advantageous if that carbon dioxide could be processed further to ensure that that the system is carbon neutral, and this is possible within the system described hereinafter.

Such marginal excess carbon dioxide from the process will be pure and measuring and collecting this from the limekiln and/or the combustor should be relatively straightforward. This excess can be sequestrated or used in making fuels or other processes on the basis that a proportional amount of calcium oxide produced by the process can be used in marine projects where twice the amount of carbon dioxide can be absorbed than the carbon dioxide produced by the systems of the present invention. Alternatively, or additionally, this excess carbon dioxide can be processed in the plant described herein to make the whole process carbon neutral if that is what is required.

To achieve further processing of the carbon dioxide, the system of the present invention may further comprise an electrolysis plant arranged to receive excess carbon dioxide produced by the system and to convert the carbon dioxide into carbon and oxygen by electrolysis. The splitting of carbon dioxide into carbon and oxygen is energy intensive, but by utilising energy derived from elsewhere in the system, the process may become viable.

The system may additionally or alternatively further comprise a chemical processing unit arranged to receive excess carbon dioxide produced by the system and to convert the carbon dioxide to carbon monoxide and oxygen or carbon monoxide and hydrogen. This may require the use of a catalyst. Under normal circumstances, the high energy requirements for converting carbon dioxide into carbon monoxide and oxygen or hydrogen makes the process generally unfeasible, but this may be addressed by exploiting energy which has been produced by the combustion of polymeric waste.

The electrolysis plant and/or the chemical processing unit may be powered by electricity produced by the system The electrolysis plant and/or chemical processing unit may be operatively connected to the combustor to receive excess carbon dioxide produced by the burning of polymeric waste. Alternatively, or additionally, the electrolysis plant and/or chemical processing unit may be operatively connected to the limekiln to receive excess carbon dioxide and/or heat produced by the calcination of limestone.

The electrolysis plant and or chemical processing unit may be operatively connected to the turbine and/or the boiler to receive electricity or steam produced thereby to facilitate the conversion process. The electrolysis plant and/or chemical processing unit may also be operatively connected to the processing plant to receive excess heat therefrom. Heat reclamation from the limekiln and the processing plant can therefore be used to assist the conversion process in the electrolysis plant and/or the chemical processing unit.

In an alternative arrangement or in addition to some or all of the methods hereinbefore described in relation to the processing of excess carbon dioxide, the system of the present invention may include means for the processing of excess carbon dioxide into useful carbon dioxide-based products. Electricity, excess heat and/or excess steam produced by the plant can be utilised for this purpose. There are known processes for the processing of carbon dioxide into carbon neutral products. A selection of those are summarized, as follows: * Researchers at George Washington University have developed a process for the production of carbon wool which can be utilised in the same way as conventional carbon fibers; the process involves the use of sunlight to power apparatus which uses molten electrolysis to produce a carbon nanotube material that can be developed into carbon fibers. Instead of sunlight power, electricity from the plant can be used for this purpose.

* Other processes include the combining of carbon dioxide with waste products to form nanoparticles which are subsequently used as additives in the formation of other materials, such as concrete, and material coatings.

* Additional processes being established include methods for combining carbon dioxide with a microorganism which extracts the carbon therefrom. The carbon can then be processed with hydrogen and oxygen to produce a synthetic PHA-based biopolymer material which is formed into capsules and can subsequently be melted and formed into desired shapes.

* Further processes now exist for this purpose and these do not need to be listed here. It is not controversial to believe that there will be new processes discovered in the future to achieve this desired effect.

It may be possible that a small amount of methane is produced by the system. This could be added to the synfuel "carbon neutral product" as the calcium oxide produced by the plant will absorb the carbon dioxide produced when the fuel is combusted. Alternatively, the high temperatures generated by the system and method may be utilised in a "steam reformation" manner to react the methane into hydrogen and carbon monoxide. Thus, the system and method of the present invention may be used to produce a fully carbon neutral and/or greenhouse neutral fuel in conjunction with the rest of the process.

The systems and methods of the present invention preferably serve to produce fuels, elements and compounds which are carbon neutral. However, in some instances, there may be a demand for cost effective low carbon fuels and low carbon greenhouse neutral gasses. In such instances, the system and process of the present invention may be utilised to supply this demand, in addition to the production of carbon neutral products. For example, excess carbon dioxide remaining following the production of carbon neutral fuel, by the system of the present invention may undergo co-electrolysis with other elements or compounds, such as water or glycerol. Although such processes may not form carbon neutral fuels they can still be a low carbon option.

Essentially, the system and methods of the present invention provide a choice. If complete carbon neutrality is desired this can be achieved. If the desired result is carbon neutral fuels and gasses with less of a concern being placed on the processing of greenhouse neutral gas formed as a minority by-product, then this can also be achieved; this is preferable to drilling and mining for fossil fuels which are neither greenhouse gas neutral nor carbon neutral.

The primary function of the system and process of the present invention is to facilitate the processing of waste plastic in a carbon neutral manner. As discussed above, the process may also be applicable to the low carbon processing of waste plastic rather than total neutrality. It is also feasible that additional waste products can benefit from processing by the system of the present invention. One possible example of this is the waste residue which results from oil refining, namely petroleum coke (petcoke). Petcoke is an extremely damaging carbon polluting fuel which, at present, is exported from around the world to countries such as India and China, where it is burned for fuel. This combustion is one of the worst carbon polluters in the world. The system of the present invention could additionally be utilised to transform petcoke into carbon monoxide which is a valuable calorific greenhouse neutral gas.

So that the invention may be better understood, an embodiment will now be described in detail, but by way of example only, with reference to the following drawings in which: Figure 1 is a simplified diagram of the system for processing polymeric waste, which operates in accordance with the method of this invention; Figure 2 is a diagrammatic axial section through one embodiment of rotary kiln for the production of carbon dioxide from limestone; Figure 3 is a diagrammatic axial section through an alternative embodiment of rotary kiln for the production of carbon dioxide from limestone; Figure 4 is a diagrammatic axial section through yet another embodiment of kiln for the production of carbon dioxide from limestone; and Figure 5 is a diagrammatic axial view through the combustor and boiler of the system of Figure 1.

Referring initially to Figure 1, there is shown a system 10 for the processing of waste plastic. The system 10 includes a combustor 11 which comprises burners 12 for burning waste plastic. The combustor 11 includes an inlet 13 for the introduction of the plastic therein and a plurality of outlets. One outlet 14 is provided to direct noxious particulates and other non-desired gases to a scrubber 14. Another outlet 16 allows carbon monoxide 63 to be emitted and collected; carbon monoxide produced by the process can be sold as a valuable calorific gas or utilised in further reactions (such as a water gas shift reaction) for the production of fuels for vehicles. The combustor 11 also includes a carbon dioxide regeneration arrangement 17 configured to reintroduce carbon dioxide back into the combustor 11. This serves to produce a limited or controlled oxygen environment. The burning of polymeric waste in the combustor 11 produces carbon dioxide and the combustor 11 includes an outlet 18 to direct the carbon dioxide 50 away for further processing. Separation means (not shown) are provided to isolate the various gases following combustion and to direct these to the correct outlet. Such means are known in the art and are not discussed further here.

The burning of plastic in the combustor 11 produces vast amounts of heat which can be utilised further to process more waste plastic. To facilitate this, and referring to Figure 1, in addition to the combustor 11, the system 10 also includes a processing plant 21. The processing plant 21 is in close proximity with and is connected to the combustor 11 by an insulated pipe 22 to allow heat energy generated by the burning of plastic from within the combustor 11 to pass to the processing plant 21. The processing plant 21 includes an inlet 23 for the introduction of additional plastic waste and, in the particular embodiment shown, comprises a pyrolysis plant. The processing plant 21 may alternatively comprise a gasification plant or other apparatus designed to heat material to facilitate decomposition, without combustion.

The processing plant 21 has an outlet 24 for synthetic gas (syngas) produced by the heating of waste plastics therein. Carbon dioxide produced by the combustor 11 may be transported by an insulated pipe (not shown) to the processing plant 21 and used to purge oxygen in the plant 21 in order further to facilitate to production of syngas. Synthetic fuel (synfuel) may be obtained from the resultant syngas using common methods, as will be appreciated by those skilled in the art. This synthetic fuel can be used to replace fossil fuels. The processing plant 21 also includes an outlet 25 for waste and gasses which are passed to an additional scrubber 15 and an additional outlet 26 for excess heat to be expelled from the plant 21 and utilised elsewhere, as described in more detail below.

The system 10 includes a boiler 29 having a water inlet 30 and two steam outlets 31, 32. The boiler 29 receives heat from the combustor 11 to convert water into steam. A turbine-driven generator set 33 is arranged to receive a portion of the steam from one of the boiler outlets 32 and is configured to generate electricity 34 for supply elsewhere in the system 10.

A limekiln 37 is provided for the production of carbon dioxide from limestone. Calcination of limestone by heating releases carbon dioxide and produces calcium oxide (referred to hereinafter as quicklime). The limekiln 37 is in communication with the boiler steam outlet 32 to provide heat to the inner chamber 38 of the limekiln 37 for the heating of the limestone and is also connected to the turbine generator set 33 to receive power therefrom, as discussed in more detail below. The limekiln 37 is provided with an inlet 39 for the introduction of limestone, a heater 40 for heating the limestone, an outlet 41 for the release of carbon dioxide and an outlet 42 for the release of quicklime.

Quicklime produced by the heating of limestone may be collected from the limekiln 37 and used to absorb carbon dioxide from the atmosphere. The calcining of limestone produces carbon dioxide. Along with the combustor 11, the limekiln outlet 41 is configured to direct the carbon dioxide 50 away for further processing.

Excess carbon dioxide 50 produced by the system 10 can be processed in various ways. As shown in Figure 1, the system 10 includes an electrolysis plant 45 arranged to receive excess carbon dioxide produced by the combustor 11 and by the limekiln 37 and to convert the carbon dioxide 50 into carbon and oxygen by electrolysis.

The system 10 also includes a chemical processing unit 46 arranged to receive excess carbon dioxide 50 produced by the combustor 11 and the limekiln 37 and to convert the carbon dioxide 50 to carbon monoxide and oxygen or carbon monoxide and hydrogen. Such processes are known by those skilled in the art and are thus not discussed in detail herein.

The electrolysis plant 45 and the chemical processing unit 46 are powered by electricity 34 produced by the turbine-driven generator set 33. Either or both of these processes can be utilised to process excess carbon dioxide 50.

The system 10 also includes a plastic product processing plant 47.

Additionally, or alternatively, excess carbon dioxide 50 can be processed in the plastic processing plant 47 to produce carbon-based products, using known methods.

Residual heat 48 which has been drawn from the limekiln 37 and from the processing plant 21 and any excess steam 49 produced by the boiler 29 may also be transferred to one or more of the electrolysis plant 45, the chemical processing plant 46 or the plastic product processing plant 47 to provide additional heat and/or steam for the further processing of carbon dioxide 50 produced by the combustor 11 and by operation of the limekiln 37.

An example of a possible configuration for the combustor 11 is shown in Figure 5, though it will be appreciated that the combustor 11 may be differently configured from this example. In the arrangement of Figure 5, the combustor 11 has a base 52 on which is rotatably mounted a platform 53. A motor 54 is provided within the base 52 drivingly connected to the platform 53 to cause the intermittent rotation thereof, one third of a revolution at a time, to allow the performance of a batch process.

The platform 53 supports a partition wall 55 which divides the inner space above the platform 53 into three compartments 56 bound by the outer peripheral wall of the combustor 11. The partition wall 55 is of a suitable reinforced material capable of withstanding the high temperatures likely to be encountered during operation of the apparatus. The compartments 56 are configured to rotate sequentially into three distinct sections, an introduction section 57, a combustion section 58 and a gas processing section 59.

The boiler 29 is located in the apparatus above the partition wall 55 and includes the water inlet 30. The volume within the apparatus and above the boiler is divided by a further partition wall 64 such that steam generated by the boiler 29 leaves the apparatus through the two steam outlets 31, 32, having the functionality described hereinafter.

The introduction section 57 contains the inlet 13 for the introduction of waste plastic to the compartment 56 for the time being aligned with that inlet 13, and the outlet 14 to facilitate the removal of ash. The burners 12 are located at the upper end of the combustion section 58 and are arranged to burn content in the compartment 56 for the time being therebelow, or primarily therebelow, in the course of rotation of the platform 53. The boiler 29 being above the burners 12 facilitates the transfer of heat from the combustion to the boiler 29, thereby to heat water in the boiler 29. The burning of the plastic produces energy, in the form of heat, and carbon dioxide rich gasses. The compartments 56 rotate from the plastic introduction section 57 to the combustion section 58.

A duct 66 passes through the boiler 29 and communicates with the combustion section 58, to transfer to the space above the boiler but separated from the steam, the combustion gasses to remove any noxious particulates and other non-desired gases. Those leave the apparatus and pass to the scrubber 14. Following purging the remaining gasses from the scrubber (primarily to carbon dioxide 50) are passed through an inlet 60 into the gas processing section 59 and also the combustion section 58 of the combustor 11. An outlet 16 for carbon monoxide is provided through the apparatus wall in the gas processing section 59. The transfer of combustion gasses through the scrubber and back into the combustion section 58 enables carbon dioxide to be recirculated and thus facilitates a controlled slow burn of plastic waste. The burning of plastics in an oxygen controlled environment produces a carbon dioxide and carbon monoxide mix The production of further carbon monoxide from this mix in this third gas processing section 59 is facilitated by the burnt plastic residue that will exist in this section 59. Separation means (not shown) are provided to isolate the various gases following combustion and to direct these to the correct outlet. Such means are known in the art and are not discussed further here. The carbon monoxide 63 leaves the apparatus through outlet 16 and the carbon dioxide 50 passes out of outlet 18 for further processing.

Carbon monoxide 63 produced by the process can be sold as a valuable calorific gas or utilised in further reactions (such as a water gas shift reaction) for the production of fuels for vehicles. The burning of plastics does not generally produce a large quantity of char but the regeneration of carbon dioxide 50 into the gas processing section 59 serves to produce a limited or controlled oxygen environment which will result in the production of more carbon monoxide 63 as carbon dioxide mixes with the burnt plastic residue in that environment in section 59 as above. Excess carbon dioxide can however be processed further as explained hereinbefore.

Furthermore, at the gas processing section 59 an additional process may be included to increase the amount of char and carbonate material in order to form greater quantities of carbon monoxide and less carbon dioxide Such a process may involve the introduction of petcoke 51 to the gas processing section 59. In this additional process, the mix of carbon dioxide 50 and carbon monoxide 63 from the combustion section 58 will pass over the char and petcoke mix to form more carbon monoxide.

Alternatively or additionally the apparatus may be configured to enable residue and char from the processing plant 21 to be introduced into the gas processing section 59. Such apparatus may be arranged to deposit the material into the top of the gas processing section 59 by a sealed hopper (not shown) contemporaneously with the injection of the combustion gases therein. The hopper may be purged of oxygen before the material is deposited.

In an alternative arrangement, as illustrated in Figures 1 and 5, the carbon dioxide 50 and carbon monoxide 63 gasses may be directed from the 25 scrubber 14 through an insulted pipe to an independent chamber 62 which also communicates with the processing plant 21 and is configured to receive the residue and char remaining after the processing (for example, pyrolysis) in the plant 21 is complete. This will result in more carbon monoxide 63 being produced. Petcoke 51 could also be added to this independent chamber 62 to 5 result in the production of even more carbon monoxide 63. These processes utilise the material remaining in the processing plant 21 and this ensure that this material is not wasted. Any residuary carbon dioxide and carbon monoxide gas mix may then return to the gas processing section 59 of the combustor 11 or be independently processed to separate any carbon dioxide 50 from the to heavy carbon monoxide biased mix.

Referring now to Figures 2 and 3, the limekiln 37 comprises a generally cylindrical vessel 67 having an inner chamber 38 mounted coaxially therein. The vessel 67 is supported on three pairs of horizontally-spaced rollers 68 with the vessel axis inclined at a small angle to the horizontal. At least one roller 68 of each pair includes a motor (not shown) to effect rotation of the vessel 67.

The inlet 39 for the introduction of limestone is provided at the raised end of the limekiln 37, that inlet 39 being provided with a gate valve 69. A stationary inlet duct 70 also provided with a gate valve 71 is arranged so that on rotation of the vessel 67, the inlet 39 will come into register with the duct 70 when the inlet 39 is uppermost. When in register and both gate valves 69, 71 are opened, limestone may pass from the duct 70 to the inlet 39 and so into the vessel 67. The outlet pipe 41 is provided at the raised end of the kiln 37 for carbon dioxide generated within the vessel 67. A gas-type rotary joint (not shown) is arranged between the vessel 67 and the pipe 41 and a valve (also not shown) is disposed within the pipe 41 to control the release of carbon dioxide.

The inner chamber 38 of the limekiln 37 is formed from stainless steel reinforced as necessary to withstand the tumbling of the limestone within the vessel 67.

In the embodiment shown in Figure 2, the heater 40 is a resistive heating element disposed within the chamber 38 and electricity supply cables are connected to that element and are provided with electrical, thermal and mechanical insulation to allow the supply of electricity 34 to the element through an external control unit (not shown). In turn, the turbine and generator set 33 is arranged to receive steam from the boiler outlet 32 and is connected to the control unit so that the heater 40 may be powered from the set to raise the temperature within the limekiln sufficiently to cause calcination of the limestone. In the embodiment of Figure 3, there is no turbine and generator set as steam from the outlet of the boiler 32 is passed directly to the inner chamber 38 to provide heat to the limekiln 37. This arrangement is preferred where the steam from the boiler 29 is of sufficient temperature most efficiently to heat limestone within the limekiln 37. Ideally, this arrangement is used where the temperature of the steam is in the region of 900°C to 1000°C. If the steam is lower than 900°C, the arrangement of Figure 2 may be utilised so as to generate the temperatures necessary for calcination of limestone within the limekiln 37.

In both embodiments, an automatically-operating one-way gate at the steam entrance of the rotary kiln (not shown) serves to prevent steam exiting the limekiln 37 through the inlet 39, in the event of a blowback.

An alternative form of kiln 43 is shown in Figure 4. This kiln comprises a generally cylindrical stationary casing 77 having a furnace 78 housed therein.

The furnace 78 includes a rotatable annular outer vessel 79 formed by coaxial inner and outer cylindrical walls 82, 81. A reaction chamber 82 is defined between the inner cylindrical wall 82 and the outer cylindrical wall 81 and is arranged to receive limestone to be calcined The casing 77 includes an annular gas containment area 83 and insulation 84 is provided between the containment area 83 and the furnace 78.

The casing 77 and outer vessel 79 may be constructed of a conventional refractory material, reinforced as necessary, in a manner well known to those skilled in the art, but further use may be made of the specialist materials, as hereinbefore discussed (or other materials) if particular longevity is required for specific furnaces. The furnace 78 has, at one end (the first end 85), an inlet 86 for the introduction of limestone, that inlet 86 being provided with a mechanical feed system 87, which will be explained in more detail below. The outer vessel 79 of the furnace 78 is horizontally positioned such that the other end of the furnace (the second end 88) is at the same height as the first end 85 and includes a distal protrusion 89 for the introduction of limestone into the reaction chamber 82.

The inner cylindrical wall 80 defines an inner chamber 90. Heating means 91 is disposed within the inner chamber 90. The heating means 91 is an electrical resistance heating element arranged to be supplied with electricity 34 derived from the turbine generator set 33. The heating element 91 extends in an annular or a half annular configuration and is located against the bottom half of the furnace, against the inner cylindrical wall 80. In practice, limestone will gather in the lower half of the outer vessel 79 as it is conveyed along the reaction chamber 82. The heating element 91 extends along the length of the outer vessel 79 in order to maximise heat transfer. In this arrangement, the electrical resistance heating element 91 is electrically powered to raise the temperature within the furnace 11. Electricity supply cables 92 are connected to that element and are provided with electrical, thermal and mechanical insulation to allow the supply of electricity 34 to the element. The element 91 is connected to the turbine generator set 33 to receive power therefrom.

The apparatus includes a curved blade 93 within the reaction chamber 82 arranged to channel limestone introduced into the reaction chamber 82 toward and along the inner cylindrical wall 80. The curved blade 93 is mounted to both the inner and outer cylindrical walls 80, 81. The blade 93 extends the full axial length of the outer vessel 79, including along the distal protrusion 89 thereof and is curved to define a spiral shape along the length of the reaction chamber 82; this arrangement provides a defined path for the limestone. The presence of the blade 93 ensures that limestone is conveyed along the path in measured amounts. The processing of the limestone is thereby carried out in a uniform fashion facilitating full and even processing. The blade 93 is also curved transversely to define a concave surface for the channelling of limestone towards the heating element. The spacing between adjacent turns in the spiral blade 93 is uniform as too is the pitch of the blade.

A plurality of outlets 94, in the form of gas valves, are provided, equidistantly spaced around the outer cylindrical wall 81 of the outer vessel 79, for the release of carbon dioxide. Alternatively or additionally, these could be gas permeable membranes. The gas valves are defined in the outer cylindrical wall 81 of the outer vessel 79 and openings 95 are provided in the insulation 84 to allow carbon dioxide to escape from the reaction chamber 82 to the containment area 83 of the casing 77. A fan 96 is provided adjacent the containment area 83 of the casing 77 to assist the drawing away of carbon dioxide from the vessel 79.

The gas valves are designed to regulate the release of carbon dioxide from the furnace 78 so that it can be conveniently captured whilst maintaining an optimum level of pressure within the reaction chamber 82.

Figure 1 shows a further embodiment which combines the heater arrangements of the embodiments of both Figures 2 and 3. In this way, the heater 40 comprises a resistive heating element connected to an electricity supply cable and additionally steam from the outlet of the boiler 32 is passed directly to the inner chamber 38 to provide heat to the limekiln. Such an arrangement may be used to ensure that sufficient heat may be supplied to the limekiln 37 for the heating of limestone therein and also to power actual operation of the limekiln 37.

At the lower end of the vessel 67, there is provided a door 75 which, when the inlet 39 is in register with the inlet duct 70, comes into register with an outlet duct 76, to enable the removal of quicklime produced by the calcination of limestone within the kiln. Carbon dioxide produced by the combustion of synfuel, formed by the processing plant 21, can be absorbed by quicklime expelled from the limekiln 37. As such, synfuel produced by the processing plant 21 can be considered carbon neutral.

The present invention employs combustion to address the problems associated with polymeric waste but does so in an environmentally and efficient way. The invention makes use of the energy produced during combustion to facilitate processing of excess carbon dioxide, which would otherwise be emitted as a by-product, into useful carbon neutral or greenhouse neutral gases or into carbon neutral products. The system and process of the present invention thus serves to address the problems associated with processing of waste plastics

Claims

CLAIMS1. A system for the processing of polymeric waste, the system comprising: - a combustor arranged to burn polymeric waste; and - a processing plant operatively connected to the combustor to receive heat energy therefrom, the processing plant being arranged thereby to heat additional polymeric waste to produce a synthesis gas without combustion; wherein the system optionally further comprises: - a boiler, having an inlet for the introduction of water and an outlet for the release of steam, the boiler being operatively connected to the combustor to receive heat energy therefrom and to heat the water to produce steam and being operatively connected to the processing plant to transfer steam thereto.
2. A system for the processing of polymeric waste, the system comprising: - a combustor arranged to burn polymeric waste; - a boiler, having an inlet for the introduction of water and an outlet for the release of steam, the boiler being operatively connected to the combustor to receive heat energy therefrom and to heat the water to produce steam; and - a processing plant operatively connected to the boiler to receive steam therefrom, the processing plant being arranged thereby to heat additional polymeric waste to produce a synthesis gas, without combustion; and wherein optionally, the processing plant is also operatively connected to the combustor to receive heat energy directly therefrom.
3. A system for the processing of polymeric waste, the system comprising: -a corn bustor arranged to burn polymeric waste; - a boiler, having an inlet for the introduction of water and an outlet for the release of steam, the boiler being operatively connected to the combustor to receive heat energy therefrom and to heat the water to produce steam; and -a processing plant operatively connected to the combustor to receive heat energy therefrom and operatively connected to the boiler to receive steam therefrom, the processing plant being arranged thereby to heat additional polymeric waste to produce a synthesis gas, without combustion.
4. A system as claimed in claim 2 or claim 3, further comprising a limekiln having an inlet for the introduction of limestone, a heater for heating limestone contained therein and an outlet for the release of carbon dioxide and calcium oxide wherein the heater of the limekiln is in communication with the boiler outlet and is heated directly or indirectly by steam therefrom.
5. A system as claimed in any of the preceding claims, further comprising an electrolysis plant arranged to receive excess carbon dioxide produced by the system and to convert the carbon dioxide into carbon and oxygen by electrolysis.
6. A system as claimed in claim 5, when dependent upon claim 4, wherein the electrolysis plant is operatively connected to the limekiln to receive excess carbon dioxide and/or heat produced by the calcination of limestone.
7. A system as claimed in any of the preceding claims, further comprising a chemical processing unit arranged to receive excess carbon dioxide produced by the system and to convert the carbon dioxide into carbon monoxide and oxygen or carbon monoxide and hydrogen.
8. A system as claimed in claim 7, when dependent upon claim 4, wherein the chemical processing unit is operatively connected to the limekiln to receive excess carbon dioxide and/or heat produced by the calcination of limestone.
9. A system as claimed in claim 5 or claim 6, wherein the electrolysis plant is operatively connected to the combustor to receive excess carbon dioxide produced by the burning of polymeric waste.
10. A system as claimed in any of claims 7 to 9, wherein the chemical processing unit is operatively connected to the combustor to receive excess carbon dioxide produced by the burning of polymeric waste.
11. A system as claimed in any of the preceding claims wherein the processing plant comprises a pyrolysis plant.
12. A system as claimed in any of claims 1 to 10 wherein the processing plant comprises a gasification plant.
13. A system as claimed in any of claims 11 or 12 wherein the processing plant further comprises a Fischer Tropsch plant to convert synthesis gas into a synthesis fuel.
14 A system as claimed in any of the preceding claims, wherein the combustor further comprises a carbon dioxide regeneration arrangement configured to remove and re-introduce carbon dioxide back into the combustor.
15. A method of processing polymeric waste, the method comprising: -burning polymeric waste in a combustor; - transferring heat energy produced by the combustor to a processing plant; and - utilising the heat energy in the processing plant to heat additional polymeric waste to produce a syngas, without combustion; wherein the method optionally comprises: - transferring heat energy produced by the combustor to a boiler; - heating water in the boiler to produce steam; and - transferring the stream produced by the boiler to the processing plant.
16. A method of processing polymeric waste, the method comprising: -burning polymeric waste in a combustor; - transferring heat energy produced by the combustor to a boiler; - heating water in the boiler to produce steam; - transferring steam produced by the boiler to a processing plant; and - utilising the steam in the processing plant to heat additional polymeric waste to produce a syngas; wherein the method optionally comprises: - transferring heat energy produced by the combustor to the processing plant further to heat the additional polymeric waste to produce a syngas, without combustion.
17. A method of processing polymeric waste, the method comprising: - burning polymeric waste in a combustor; - transferring heat energy produced by the combustor to a processing plant and to a boiler; - heating water in the boiler to produce steam; -transferring steam produced by the boiler to the processing plant; and - utilising the heat energy in the processing plant to heat additional polymeric waste to produce a syngas, without combustion.
18. A method as claimed in claim 16 or claim 17, further comprising the step of heating limestone in a limekiln having an inlet for the introduction of to limestone, a heater for heating limestone and an outlet for the release of carbon dioxide yielded by the heated limestone, and wherein steam is passed from the boiler to the heater of the limekiln to heat the limestone within the limekiln.
19. A method as claimed in claim 18, wherein quicklime produced by the calcination of the limestone is collected from the limekiln and is used to absorb 15 carbon dioxide from the atmosphere.
20. A method as claimed in any of claims 15 to 19 wherein excess carbon dioxide produced by a system performing the method is passed to an electrolysis plant and is therein converted to carbon and oxygen by electrolysis and/or is passed to a chemical processing unit and is therein converted to carbon monoxide and oxygen or carbon monoxide and hydrogen.
21. A method as claimed in claim 20, when dependent upon claim 18 or 19, wherein excess carbon dioxide yielded by heated limestone is passed from an outlet of the limekiln to the electrolysis plant and/or to the chemical processing unit.
22 A method as claimed in claim 20 or claim 21, wherein excess carbon dioxide produced by the burning of polymeric waste is passed from an outlet of the combustor to the electrolysis plant and/or chemical processing unit.
23 A method as claimed in any of claims 20 to 22 wherein the electrolysis plant and/or chemical processing unit is supplied with excess heat generated by apparatus operating in a system for performing the method.
24 A method as claimed in claim 23 wherein excess heat generated by the production of syngas in the processing plant is directed to the electrolysis plant and/or to the chemical processing unit.
25. A method as claimed in claim 23 or claim 24, wherein excess heat from a limekiln generated by the calcination of limestone, is directed to the electrolysis plant and/or to the chemical processing unit.
26. A method as claimed in any of claims 20 to 25 wherein the electrolysis plant and/or chemical processing unit is supplied with electricity from the turbine-driven generator set.