Field of the Invention

The invention relates to apparatus, systems and processes for recovering energy from waste materials, primarily using pyrolysis (advanced thermal treatment).

Background to the Invention

There have been many early attempts to develop, build and operate large-scale waste to electrical energy systems with pyrolysis as the main process step rather than gasification or biomass systems. However, such systems have, so far, not met the expectations of the parties. There is a desire for non-combustion of sustainable non-fossil fuel plants in the UK and worldwide. In particular, there is a desire for small local systems using the local waste to generate heat or electrical energy. The power grid is set up to take power into the system due to the recent success of wind power and solar cells. This is being managed and will facilitate communities being provided with electricity generated locally. It would be advantageous for this to be achieved using locally produced waste. This would be particularly desirable for islands or remote locations, allowing those communities to generate their energy, waste heat, and if required desalinated water for drinking.

The inventors have developed a system for recovering energy from waste, using pyrolysis. The energy can be provided in electrical form or combustible fluids such as organic materials, coal, gas or oils. Although renewable organics are preferential in certain countries; fossil fuels can also be utilised or a mixture of both.

Summary of the Invention

The invention provides a system for the recovery of energy from waste. The invention further comprises a method for recovering energy from waste. It also provides a feedstock for use in that method and a method for producing the feedstock.

A detailed description of the invention follows, by way of example, only. It refers to the figures in which:

Figure 1 shows a pyrolyser that may be used in the invention, comprising an oxidiser. Figure 2 shows a multi tube pyrolyser that may be used in the invention.

Figure 3 shows a flow diagram including the various aspects of the system of the invention.

Detailed description of the Invention

The invention provides a method for recovering energy from waste material, the method comprising:

providing a first, typically clean, feedstock; and

pyrolysing the feedstock to produce pyrolysis gas and char.

The heat generated can be used to create steam and hence power via turbine and generators. The combustible gas produced which may be used in a gas engine or turbine to generate power.

The invention further provides an apparatus or system for carrying out the method. It comprises at least one pyrolyser. Typically, the apparatus or system comprises a pyrolysis means and an oxidation or combustion means. The pyrolysis means generally comprises at least one pyrolyser. The combustion or oxidising means generally also comprises at least one pyrolyser, but that pyrolyser is provided with an oxidiser.

Pyrolysis, as known in the art, is the thermochemical decomposition of organic material in the absence of oxygen. It results in the production of char and pyrolysis gas. In the method of the invention, pyrolysis is carried out on a clean feedstock, typically that is a feedstock that is substantially free of fossil fuel, for example it comprises less than 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1 %, 0.5%, 0.1 % fossil fuel. It may also be substantially free of bio- waste, for example it comprises less than 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1 %, 0.5%, 0.1 % bio-waste. Typically, the feedstock is prepared to meet the requirements of government or other funding initiatives that provide a revenue for the use of clean waste to energy systems (such as carbon credits or the ROC system in the UK).

The pyrolysers used in the invention maybe any appropriate pyrolysers. Suitable pyrolysers are described in PCT/GB2015/051939 or EP1465965 at least. The pyrolysers may be single tube or multi tube.

The method may also comprise the steps of providing a second feedstock, typically comprising waste that is not classified as clean. It may further comprise the step of oxidising the second feedstock, optionally following pyrolysis. When the method comprises this step, the heat generated by the oxidising of the second feedstock may be used for the pyrolysis of the clean waste. Accordingly, the method may include the step of using the heat generated by oxidising of second feedstock to pyrolyse the clean waste.

To allow oxidising of non-clean waste, the system or apparatus comprising a combustion or oxidation means, typically at least one of the pyrolysers provided with an oxidiser. Accordingly, the system generally comprises at least two pyrolysers, one of which is provided with an oxidiser. The system may comprise a plurality of pyrolysers, some with oxidisers, some without. For example, the system may comprise at least one, two, three, four, five, six or more pyrolysers without oxidisers. The system may also comprise at least one, two, three or more pyrolysers with oxidisers. In one embodiment, the system comprises six pyrolysers without oxidisers and three pyrolysers with oxidisers. Typically the pyrolysers without oxidisers are multi tube pyrolysers. The system may allow the oxidisers to be switched on or off, allowing all the pyrolysers to run without oxidation, if needed.

The method may also comprise the step of removing the char. The char may be removed using any appropriate means, including, for example, a cyclonic separator. Char and/or ash from the separator may then be removed and collected centrally. The method may also comprise the step of ensuring that the char/ash is inert and, if not, treating it such that it is inert. The system may also comprise at least one, optionally more than one, means for recovering any recoverable product from the char. For example, the product may be recovered by dissolving the char in an acid bath and then boiling off the acid. Alternatively, the char may be used to manufacture products such as building block, paving stones or aggregate as opposed to being sent to land fill sites.

The method may also comprise the step of conditioning the pyrolysis gas. The pyrolysis gas may be delivered to a gas treatment system. The gas treatment system may, for example, combine or reform the gas using typically a steam gas catalytic gas reformer. It may then refrigerate and/or compress the gas. This creates a dense, high calorific value gas or liquid. Undesirable acid components may be removed from the gas using, for example, the solution described in EP1951410. Accordingly, the system may comprise a gas treatment system. It may further comprise a refrigeration system. It may also comprise a compressor. Some or all of the gas may be stored. Stored gas may be used to start the system, if required. Alternatively, to avoid storing excess combustible gas, it may be oxidised in order to generate further steam and heat.

The gas may be used to fuel one or more gas engines. The gas engines may be used to power one or more generators to generate electrical energy. Appropriate gas engines are well known in the art. Accordingly, the method may also include the step of combusting the gas in a gas engine to power a generator to produce electricity. The system of the invention may include one or more gas engines. The gas engine may be connected to the output of the pyrolyser following gas conditioning, or conditioner, by an appropriate conduit. Any waste heat from the system can report to waste heat recovery boilers or heat exchangers and feed a process to generate waste oil capable of driving liquid or dual fuel engine to again drive a generator to produce electrical power.

Alternatively, or additionally, the gas may report to a steam boiler to reduce its temperature. The gas may also be used in an industrial gas turbine or a Rankine cycle.

Where the gas is combusted in an engine, an exhaust will be produced. The exhaust may be delivered to one or more heat exchangers. Heat from the oxidising of the non-clean feedstock may also be delivered to the heat exchangers. Any appropriate heat exchanger may be used, such as a steam recovery boiler. The heat or steam produced may then be used in other steps of the method or parts of the system. For example, it may be used to dry the feedstock before pyrolysis or oxidising or for steam reforming of the gas over a catalytic bed. It may also be used to drive a steam engine, such as an Organic Rankine Cycle engine e.g. Heliex Power and/or the heat engine supplied by Viking. Such engines may be used to generate electrical power. Alternatively, the engines may be used to drive compressors useful for reducing the volume of the pyrolysis vapours.

Low or high grade heat may also be used to drive other systems requiring heat energy if economically viable. An example of this may be to use the heat to drive a system for converting food waste into usable fuel. Food waste, such as potato peelings, may be digested using a crude ethanol system. The waste may be brewed into waste vegetable beer and distilled in a tower to make 70% or above ethanol. The process may be driven by heat generated by the system of the invention. The resultant ethanol may be added to liquid fuels used in or produced by the method of the invention, to increase their energy potential. Dehydrated food waste from process may then be included in the second feedstock. Food waste can also be added into low calorific value refuse derived (RDF) waste material to increase the calorific value.

Alternatively, or in addition, the exhaust may be delivered to one or more Corona plasma plugs in order to dissociate the exhaust gases into solids and OH. The resulting OH may be injected into the gas engine, in effect increasing the calorific value of the engine feedstock. This method uses disassociation of SOx & NOx but has the ability to also disassociate C02.

The used exhaust may then be delivered to an abatement system for the extraction of any acid components and the removal of any solid waste. In particular, undesirable particulates, NOx, SOx may be removed prior to delivery to a stack. This can also be carried out using the solution described in EP1951410. A Continuous Emissions Monitoring System may be provided in the stack to ensure that the final exhaust meets environmental requirements.

Also provided is a method for producing a clean feedstock suitable for use in the system of the invention. It is advantageous to produce such a feedstock, so that the quantum and quality of the gas produced in the pyrolysers can be controlled. In particular, the feedstock typically has a minimum calorific value of between 15 and 24mJ/kg. The feedstock typically has a moisture content between 4 - 8%. Generally, the feedstock may be in the form of a pellet, puck or continuous log that expands when it enters the pyrolyser. Such pellets and pucks are well known in the art.

The method of producing the feedstock may comprise the step of receiving waste material, typically at a weighbridge. The material may be sampled, to ascertain its makeup. It may then be separated into combustible and non-combustible material and into clean and non- clean waste material. The separation step may comprise removal of inert waste, such as sand or glass, removal of ferrous material using a magnetic conveyor and removal of plastics and other light non-desirable components using an eddy conveyor. The material sampling may utilise a fanning laser with a vibrometer and the use of seismic measurements which produce a detailed 3D density map based on the sounds go around or through the material with a database recognising the velocity changes of the sound signal used to identify materials such as plastic building waste etc.

Once separated, the material may be shredded, and then dried. The material may be dried using heat from the energy recovery method.

The material may then be blended with a binding agent or filler, such as woodchip or sawdust. A heat carrying high density material, such as sand, glass beads or metal may be included with the material. That high density material may be removed following pyrolysis recycled back into the feed, as described in WO2009/138757-A2 (Aston University, UK). The material may then be compressed by pressing through a die.

The waste materials included in the feedstock have different melting and vapour temperatures. By setting the temperature in the pyrolysers appropriately, it is possible to control the output of the pyrolysers. For example, setting the correct temperature can allow coal to be partially pyrolysed, to produce ash or char containing pyrites. The pyrites may be removed from the ash or char and recyclyed. The partially pyrolysed coal and ash may then be used to produce coke for use as a smokeless household fuel or for use in a solid fuel boiler

Figures 1 and 2 below show pyrolysis units for use in the invention. Figure 2 shows a modular pyrolysis multi tube unit for use in pyrolysis of the clean feedstock. As an example, such a unit can treat 10,000 tonnes per annum of treated RDF to produce the pyrolysis gas. Figure 1 shows a multiple tube pyrolyser with a single oxidiser. It can be used for combustion of non-clean feedstock, in order to generate the heat required to feed the pyrolysis units in figure 2 i.e. provide a parasitic heat load. Typically, the unit in figure 2 will require 30% of the heat produced to pyrolyse the feedstock. In an embodiment comprising six pyrolysing units and three combustion units, only two of the combustion units should be needed to run the pyrolysers. The remaining combustion unit may be on standby, or used to generate heat for use in other parts of the system.

As shown in the process diagram in figure 3, in section 1 , waste material is processed into pellets. The material is received, inspected, separated, and dried if necessary. It may be combined with filler or binding agent and/or with heat storing material. It is then pelleted or otherwise compressed, into individual or continuous feedstock pucks.

As shown in figure 3, the waste(s) are transferred to the various pyrolysers as required. The material is pyrolysed and the pyrolysis gas reports to the char removal cyclone/gasifier, depending upon its confirmation. Char and any other solids are removed within the cyclone. Any gas produced is then transferred to a pyrolysis product treatment unit which may contain gas and oil treatment systems. Any gas from the gas conditioning unit may be cooled and compressed, as shown in the gas treatment section of figure 3, and stored as desirable fuel to drive internal combustion engines, or turbines, in order to produced rotational energy as the case may be: for example, electricity generation for power export, displacement of fluids for stored energy systems.

Exhaust from the engines, or turbines, may be passed to one or more systems which incorporate plasma corona plugs, to generate OH following the disassociation of acid components. The exhaust may also be delivered to a heat exchanger, the resulting steam may be used to run one or more turbines. The exhaust may be treated, for example with MonoChem® solution, to remove acidic components and delivered to the discharge stack, or, if the calorific value proves to be beneficial to the pyrolysis process this can then be reincorporated to the feed process, to use the heat energy available.