Pyrolysis System

Abstract

A pyrolysis system 10 comprising: an mixer 12 comprising an entry chamber 14, a venturi shaped exit channel 20, and an inlet port 16 through which particulate matter may be introduced into the entry chamber; a steam entry 18 for providing superheated steam coaxially or in parallel with a longitudinal axis L of the venturi shaped exit channel; and a rotary furnace 24 positioned at the venturi shaped exit channel. The rotary furnace may have a greater diameter than the venturi channel. The rotary furnace may comprise an internal baffle, which may be helical. There may be a solid / vapour separator downstream of the rotary furnace. The heating rate at steam entry may exceed 200oC / min. A method of cellulose thermolysis using the apparatus wherein a vapour residence time within the rotary furnace is less than 10s and a solid residence time is greater than 30s.

Description

The present invention relates to a pyrolysis system for performing cellulose thermolysis. The invention further relates to a method for performing cellulose thermolysis. As explained in EP 2483331B (Nova Pangaea), there are environmental problems that arise from the use of fossil fuels, so that use of biomass as a source for fuel and organic chemicals would be advantageous. Woody or lignocellulosic biomass is largely composed of hemicellulose, cellulose and lignin. Cellulose is principally comprised of C6 sugars while hemicellulose comprises both C5 and C6 sugars. Lignin is a complex polymer which gives physical strength to the biomass but which is tightly bound to the other components. Consequently, it is not straightforward to remove the sugars from the remainder of the biomass. EP 2483 331B teaches a method of fractionating lignocellulosic biomass by a sequence of steps. Biomass may be fed into a hemicellulose hydrolysis reactor to hydrolyse hemicellulose, so a liquid component includes the products of hemicellulose hydrolysis for example in water, and so that the remaining solid component includes cellulose and lignin. The remaining solid component is then fed to a cellulose hydrolysis reactor which may apply steam at a temperature of between about 400° and 550°C, so as to hydrolyse cellulose and vaporise the resulting sugars; and then condensing the resulting vapours. The remaining solids may be in the form of a lignin char. GB2592275A discloses a plant for performing cellulose thermolysis comprising a thermolysis reactor which comprises a reactor duct having a longitudinal axis, and an mixer at one end of the reactor duct. The mixer has an entry chamber and a venturishaped exit channel, a nozzle, a sloping deflector plate above the nozzle, and an inlet port through which particulate material may be fed onto the deflector plate and into the entry chamber. The nozzle and the venturi-shaped exit channel are aligned with the longitudinal axis. A superheater provides superheated steam at a temperature above 450°C to flow through the nozzle. In GB2592275A, the reactor duct is configured to ensure that the particles of particulate material reach the end of the reactor duct in less than 1s. It is therefore suitable for comparatively slow pyrolysis processes to produce high proportions of biochar. The present invention seeks to provide a pyrolysis system suitable for fast pyrolysis processes which are not feasible with the arrangement of GB2592275A. According to a first aspect of the invention, there is provided a pyrolysis system comprising: an mixer comprising an entry chamber, a venturi shaped exit channel, and an inlet port through which particulate matter may be introduced into the entry chamber; a steam entry for providing superheated steam coaxially or in parallel with a longitudinal axis of the venturi shaped exit channel; and a rotary furnace positioned at the venturi shaped exit channel. Rotary furnaces have been traditionally used in slow pyrolysis systems due the comparatively slow heating profile of rotary furnaces themselves. However, by using a superheated steam steam entry in an educator, fast heating of the biomass is achieved in the mixer, before being transferred into the rotary furnace. This allows for fast pyrolysis to occur, which products very different yields to slow pyrolysis systems. Optionally, the rotary furnace may have a greater diameter than that of the venturi shaped exit channel. The pressure differential created by the larger dimensioning of the rotary furnace relative to the venturi ensures that the solid matter is correctly entrained into the rotary furnace. Preferably, the rotary furnace may comprise an internal baffle to assist with conveying solid material through the rotary furnace. To ensure that the solid material has sufficient residence time within the rotary furnace, one or more baffles may be provided to impede the throughput of solids therethrough. The internal baffle may be a helical baffle. A helical shape of baffle will encourage travel through the rotary furnace slowly Optionally, the rotary furnace may comprise a heating mantle. It is preferred that indirect heating of the biomass occur within the rotary furnace in order to produce the desired material yields. The pyrolysis system may further comprise a solid / vapour separator downstream of the rotary furnace. The main outputs of the pyrolysis system are solid biomass and gaseous output. As such, is it preferred that a separator is provided to extract the correct product components for onward processing. A heating rate of the pyrolysis system at the steam entry may exceed 200°C / min, and more preferably a heating rate of the pyrolysis system may exceed 1000°C / min. The purpose of the present invention is to achieve fast pyrolysis, not normally achievable with rotary furnaces. The mixer used here allows this to be achieved. Preferably, a vapour residence time within the rotary furnace may be less than 10s. The vapour residence time within the rotary furnace may be less than 1s. Optionally, a solid residence time within the rotary furnace may be greater than 30s. Preferably, the mixer may comprise a sloping deflector plate above the steam entry. It is preferred that incoming biomass be prevented from contacting the superheated steam entry, and a deflector plate can direct biomass into the correct place to achieve his. Optionally, the steam entry may comprise a nozzle. A nozzle may provide more directed steam into the mixer and towards the rotary furnace. According to a second aspect of the invention, there is a method for performing cellulose thermolysis, the method comprising the steps of: a] introducing particulate matter into an entry chamber of an mixer via an inlet port; b] providing superheated stem coaxially or in parallel with a longitudinal axis of a venturi shaped exit channel of the mixer; and c] using a rotary furnace, heating an output of the venturi shaped exit channel, wherein a vapour residence time within the rotary furnace is less than 10s and a solid residence time within the rotary furnace is greater than 30s. The present method provides a means of providing fast pyrolysis with a rotary furnace, which cannot otherwise be achieved in the art. The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a diagrammatic representation of one embodiment of a pyrolysis system in accordance with the first aspect of the invention. Referring to Figure 1, there is a shown a pyrolysis system, referenced globally at 10, and which is suitable for treating biomass such as wood chips so as to obtain Cs and Ce sugars by breaking down the hemicellulose and cellulose polymers within the biomass. An mixer 12 is provided which comprises an entry chamber 14 with an inlet port 16, a nozzle 18 for inflow of steam forming a steam entry, and a venturi-shaped exit duct 20 whose diameter narrows down and then broadens out. The nozzle 18 and the exit duct 20 are aligned with a longitudinal axis L of the pyrolysis system 10. A sloping deflector plate 22 is mounted above the open end of the nozzle 18. The venturi-shaped exit duct 20 is coupled to a rotary furnace 24 which comprises a rotating barrel 26 within a heated mantle 28, with rotary seals 30 provided at either end of the rotating barrel 26. The heated mantle 28 provides indirect heating of the biomass. Inside the rotating barrel 26 there is preferably a baffle 32 which assists with transfer of solid material through the rotating barrel 26. A single helical baffle 32 is shown, but paired helices could be provided as an alternative. The rotary furnace 24 is dimensioned to have a length great enough to provide a solid residence time which exceeds that of the vapor residence time. The baffle 32 assists with this process. The rotary furnace 24 ideally has a greater diameter than that of the venturi shaped exit duct 20 of the mixer 12. At an exit 34 of the rotary furnace 24 it is preferred to have a solid / vapour separator 36 which allows for efficient extraction of the solid biomass product, for instance, extracted under gravity, and an output for the gas phase product, which can be extracted through venting. In one possible use scenario, the process uses two different reaction steps that are performed at different temperatures, and may also be carried out at different pressures, but both use water as the reactant. However, prior to performing the reaction steps the biomass may be chopped into small pieces, and may be heated to evaporate vapours for example of naturally-occurring oils such as turpentine or eucalyptus oil if these are present in significant concentration. After performing any such pre-treatment, the biomass is impregnated with a strong acid, for example with dilute sulphuric acid (i.e. about 1 mole / L) typically at a rate of between 1 - 2 wt % of the dry biomass, before being introduced by a screw conveyor into a prereactor in which the biomass is contacted with steam / water at a temperature of between 150° and 180°C and a pressure of between 6 bar and 10 bar, for example at 165C and a pressure of 6.5 bar (gauge); there is little air present This may be a tube reactor along which the biomass travels along with the high-pressure steam / water. Under these reaction conditions the hemicellulose breaks down mainly to form Cs sugars, with also some Ce sugars, and organic acids, depending on the inherent composition of the biomass being processed. At the operating pressure of 6.5 bar, the water at 165°C is liquid as long as the pressure is maintained. As the material leaves the pre-reactor it may be cooled by depressurisation, exploding the biomass. A proportion of the water evaporates, typically about 10%, cooling the remaining biomass to below 100° C. For example, the mixture of biomass and hot water may be released in slugs from the reactor. As mentioned above, it is necessary to remove the liquid phase from the treated biomass before it can be subjected to the second reaction step, both to remove sugars and to remove alkali material and any inorganic acid. Although some of the liquid may be removed by compression, this doesn't enable all the liquid to be expelled. It is therefore preferable to remove the liquid phase by a washing step. The solid material that has been subjected to the hydrolysis step in the reactor is therefore then washed, for example using an aqueous solution, and / or clean water. The washed material is then dried at step to evaporate excess moisture, and may be further comminuted (not shown) to ensure all the particles small enough to heat up quickly. The material is then introduced into a hopper, for instance, with a twin screw outlet, and then into the mixer 12. It may also be feasible that no pre-treatment occurs, and that the material is directly introduced into the pyrolysis system 10. In the mixer 12, the solid material is entrained into a flow of superheated steam at a significantly higher temperature, for example 550°C. The particles of solid material cool the superheated steam while being heated up, and typically reach a final temperature of 370°C to 450°C. The particles are effectively subjected to a temperature in the range for example 370°C to 410°C or 420°C, ideally for at least 30s, whilst the vapours are extracted in less than 1s. Under these reaction conditions the cellulose undergoes thermolysis, mainly producing Ce sugar derivatives which are volatile under these conditions. The rotary furnace 24 thus allows for longer residence time for the solid material, whilst allowing gases to pass quickly through the freeboard region of the rotary furnace 24. It is noted that rotary furnaces 24 at the correct Froude number give better transfer of sugar derivatives from the solid to the gas. It is therefore possible to achieve fast pyrolysis of a biomass material using an educator which entrains the particulate matter in superheated steam, before directing the sample then into a rotary furnace. The necessary heating to produce fast pyrolysis outputs is achieved using the biomass material, enabling the use of rotary furnaces for this processing method. The words ‘comprises / comprising’ and the words ‘having / including’ when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps, or components, but do not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention as defined herein.

Claims

1. A pyrolysis system comprising:an mixer comprising an entry chamber, a venturi shaped exit channel, and an inlet port through which particulate matter may be introduced into the entry chamber;a nozzle for providing superheated steam coaxially or in parallel with a longitudinal axis of the venturi shaped exit channel; anda rotary furnace positioned at the venturi shaped exit channel.

2. A pyrolysis system as claimed in claim 1, wherein the rotary furnace has a greater diameter than that of the venturi shaped exit channel.

3. A pyrolysis system as claimed in claim 1 or claim 2, wherein the rotary furnace comprises an internal baffle to assist with conveying solid material through the rotary furnace.

4. A pyrolysis system as claimed in claim 3, wherein the internal baffle is a helical baffle.

5. A pyrolysis system as claimed in any one of the preceding claims, wherein the rotary furnace comprising a heating mantle.

6. A pyrolysis system as claimed in any one of the preceding claims, further comprising a solid / vapour separator downstream of the rotary furnace.

7. A pyrolysis system as claimed in any one of the preceding claims, wherein a heating rate at the steam entry exceeds 200°C / min.

8. A pyrolysis system as claimed in claim 7, wherein a heating rate at the steam entry exceeds 1000°C / min.

9. A pyrolysis system as claimed in any one of the preceding claims, wherein a vapour residence time within the rotary furnace is less than 10s.

10. A pyrolysis system as claimed in claim 9, wherein the vapour residence time within the rotary furnace is less than 1s.

11. A pyrolysis system as claimed in any one of the preceding claims, wherein a solid residence time within the rotary furnace is greater than 30s.5 12. A pyrolysis system as claimed in any one of the preceding claims, wherein the mixer comprises a sloping deflector plate above the steam entry.

13. A pyrolysis system as claimed in any one of the preceding claims, wherein the steam entry comprises a nozzle.1014. A method for performing cellulose thermolysis, the method comprising the steps of:a] introducing particulate matter into an entry chamber of an mixer via an inlet port;15 b] providing superheated stem coaxially or in parallel with a longitudinalaxis of a venturi shaped exit channel of the mixer; andc] using a rotary furnace, heating an output of the venturi shaped exit channel, wherein a vapour residence time within the rotary furnace is less than 10s and a solid residence time within the rotary furnace is greater than 30s.

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