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Pyrolysis: Difference between revisions
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==Overview== | ==Overview== | ||
[[Pyrolysis]] is the [[treatment|thermal treatment]] of a material in the absence of oxygen to produce gas ([[Syngas|syngas]]), liquid and solid char fractions. | [[Pyrolysis]] is the [[treatment|thermal treatment]] of a material in the absence of oxygen to produce gas ([[Syngas|syngas]]), liquid and solid char fractions. Pyrolysis generally requires an external heat source to maintain the temperature required and to avoid the introduction of air. There are a range of different types of kiln/reactor used, often aligned to the waste being processed, and include fixed bed reactors, batch or semi-batch reactors, rotary kilns, fluidized bed reactors, microwave assisted reactors and some innovative solutions like plasma or solar reactors <ref> Czajczyńska et al, 2017. Potential of pyrolysis processes in the waste management sector. Thermal Science and Engineering Progress, [online] 3, pp.171-197. </ref>. The [[Syngas|syngas]] produced in the process can be burnt to raise steam and create electricity, but most plants are exploring the option of cleaning the [[Syngas|syngas]] for use in a gas engine or separating the gas into usable fractions such as hydrogen for use, as an example, as liquid fuels. The solid residue (sometimes described as a char) is a combination of non-combustible materials and carbon. Hydrous pyrolysis/[[Hydrothermal Liquefaction|hydrothermal liquefaction]] is a from of pyrolysis that converts wet biomass into biocrude oil and chemicals. | ||
[[File:The Biomass Pyrolysis-Cycle.png|600px|center|The Biomass Pyrolysis Cycle. All rights reserved.]] | [[File:The Biomass Pyrolysis-Cycle.png|600px|center|The Biomass Pyrolysis Cycle. All rights reserved.]] | ||
<br clear=all /> | <br clear=all /> | ||
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In legal terms, a '''‘waste incineration plant’''' means any stationary or mobile technical unit and equipment dedicated to the [[Treatment|thermal treatment]] of [[Waste|waste]], with or without recovery of any energy generated, or whether the gases resulting from the thermal [[treatment]] are subsequently incinerated <ref>As an example, a [[Pyrolysis]] facility that burnt the produced [[Syngas]] to generate electricity would be Incineration, whereas a [[Pyrolysis]] facility that processed [[Syngas]] for vehicle fuel would not be classed as an incinerator</ref><ref name='ref01'>European Commission, 2010 Industrial Emissions Directive 2010/75/EU of the European Parliament and of the Council of 24 November 2010 on industrial emissions (integrated pollution prevention and control). Official Journal of the European Union.</ref>. If the Incinerator can be shown to meet the energy efficiency measurement of [[R1]] it can be classified as a [[recovery]] facility, if it cannot it is classified as a [[disposal]] facility<ref>https://data.gov.uk/dataset/8287c81b-2288-4f14-9068-52bfda396402/r1-status-of-incinerators-in-england</ref>. This means that an incinerator that generates power, and is a net exporter of power, can be described as an '''[[Energy from Waste]]''' ([[EfW]]) facility. An incinerator that is an [[EfW]] facility that meets the [[R1]] criteria is the only type of incinerator under the legislation that can legitimately describe itself as an '''[[Energy Recovery Facility]]''' ([[ERF]]). | In legal terms, a '''‘waste incineration plant’''' means any stationary or mobile technical unit and equipment dedicated to the [[Treatment|thermal treatment]] of [[Waste|waste]], with or without recovery of any energy generated, or whether the gases resulting from the thermal [[treatment]] are subsequently incinerated <ref>As an example, a [[Pyrolysis]] facility that burnt the produced [[Syngas]] to generate electricity would be Incineration, whereas a [[Pyrolysis]] facility that processed [[Syngas]] for vehicle fuel would not be classed as an incinerator</ref><ref name='ref01'>European Commission, 2010 Industrial Emissions Directive 2010/75/EU of the European Parliament and of the Council of 24 November 2010 on industrial emissions (integrated pollution prevention and control). Official Journal of the European Union.</ref>. If the Incinerator can be shown to meet the energy efficiency measurement of [[R1]] it can be classified as a [[recovery]] facility, if it cannot it is classified as a [[disposal]] facility<ref>https://data.gov.uk/dataset/8287c81b-2288-4f14-9068-52bfda396402/r1-status-of-incinerators-in-england</ref>. This means that an incinerator that generates power, and is a net exporter of power, can be described as an '''[[Energy from Waste]]''' ([[EfW]]) facility. An incinerator that is an [[EfW]] facility that meets the [[R1]] criteria is the only type of incinerator under the legislation that can legitimately describe itself as an '''[[Energy Recovery Facility]]''' ([[ERF]]). | ||
The most recent recent [[BAT|BREF]] guidance<ref name="Inc">[https://ec.europa.eu/ | The most recent recent [[BAT|BREF]] guidance<ref name="Inc">[https://eippcb.jrc.ec.europa.eu/sites/default/files/2020-01/JRC118637_WI_Bref_2019_published_0.pdf BAT and BREF for Waste incineration]</ref> also sets out how incinerators can be described by: | ||
* waste origin (e.g. Municipal Incinerators), '''and in WikiWaste includes [[Residual Waste EFW]] and [[Biomass Waste EFW]]''', | * waste origin (e.g. Municipal Incinerators), '''and in WikiWaste includes [[Residual Waste EFW]] and [[Biomass Waste EFW]]''', | ||
* the nature of the waste (e.g. Hazardous Waste Incinerators), | * the nature of the waste (e.g. Hazardous Waste Incinerators), | ||
* the method/type of incineration (e.g. High Temperature Incinerators). | * the method/type of incineration (e.g. High Temperature Incinerators) | ||
In WikiWaste these last two bullet points are covered in '''[[High Temperature and Clinical Waste Incineration]]'''. | |||
However, there are a range of other terms used in the sector to describe different types of incineration, the kiln/furnace used, and the [[subsidy]] that may apply to them, and these are captured in the table below: | However, there are a range of other terms used in the sector to describe different types of incineration, the kiln/furnace used, and the [[subsidy]] that may apply to them, and these are captured in the table below: | ||
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|[[Fluidised Bed]] | |[[Fluidised Bed]] | ||
|- | |- | ||
|rowspan=2|[[Gasification]]||rowspan=2|500 - 1600||rowspan=2| [[Advanced Thermal Treatment]] ([[ATT]] and [[ACT]])||[[Rotary]] | |rowspan=2|[[Gasification]]||rowspan=2|500 - 1600||rowspan=2| [[Advanced Thermal Treatment]] ([[ATT]] and [[ACT]])||[[Rotary Kiln]] | ||
|- | |- | ||
|rowspan=3|[[Incineration without Energy Recovery|Without Energy Recovery]]||[[Plasma]] | |rowspan=3|[[Incineration without Energy Recovery|Without Energy Recovery]]||[[Plasma]] | ||
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==Kiln/Reactor Types in Pyrolysis== | ==Kiln/Reactor Types in Pyrolysis== | ||
=== Fixed Bed Reactor === | === Fixed Bed Reactor === | ||
{| | |||
Fixed bed reactors were traditionally used to produce charcoal due to slow and poor heat transfer resulting in very low liquid charcoal yields. The technology is simple and reliable and utilises relatively uniform particle size. This type of kiln/furnace is divided into downdraft and updraft. | |- | ||
In a downdraft fixed bed reactor, the solid material moves slowly down a vertical shaft, with the solid and product gas move downward in a co-current mode which produces a relatively clean gas with low tar and high carbon conversion rate. In an updraft fixed bed reactor, the [[Feedstock|feedstock]] also moves down a vertical shaft but in a counter-current mode. This results in a dirty product gas with high levels of tars which can be alleviated using tar crackers. However, due to the [[Feedstock|feedstock]] not moving during the process, it is difficult to obtain heating of large quantities of [[Feedstock|feedstock]] material on an industrial scale. This could be solved if the reactor used methods that enable better heat transfer such as heat pipes. <ref>[https://www.sciencedirect.com/journal/thermal-science-and-engineering-progress/vol/3/suppl/C Potential of Pyrolysis Processes in the Waste Management Sector]</ref> | | Fixed bed reactors were traditionally used to produce charcoal due to slow and poor heat transfer resulting in very low liquid charcoal yields. The technology is simple and reliable and utilises relatively uniform particle size. This type of kiln/furnace is divided into downdraft and updraft. In a downdraft fixed bed reactor, the solid material moves slowly down a vertical shaft, with the solid and product gas move downward in a co-current mode which produces a relatively clean gas with low tar and high carbon conversion rate. In an updraft fixed bed reactor, the [[Feedstock|feedstock]] also moves down a vertical shaft but in a counter-current mode. This results in a dirty product gas with high levels of tars which can be alleviated using tar crackers. However, due to the [[Feedstock|feedstock]] not moving during the process, it is difficult to obtain heating of large quantities of [[Feedstock|feedstock]] material on an industrial scale. This could be solved if the reactor used methods that enable better heat transfer such as heat pipes. || [[File:Schematic diagram of a fixed bed pyrolysis reactor.png|250px|right|Schematic diagram of a fixed bed pyrolysis reactor. All rights reserved.]]<br clear=all>''Fixed bed reactor''<ref>[https://www.sciencedirect.com/journal/thermal-science-and-engineering-progress/vol/3/suppl/C Potential of Pyrolysis Processes in the Waste Management Sector]</ref> | ||
|} | |||
===Fluidised Bed Reactor=== | ===Fluidised Bed Reactor=== | ||
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==== Bubbling ==== | ==== Bubbling ==== | ||
{| | |||
In bubbling fluidised beds, particles are entered into a bed of hot sand fluidised by a recirculated product gas. The high heat transfer rates from the fluidised sand cause rapid heating of [[Biomass|biomass]] particles and some ablation with the sand particles occurs. This type of reactor is characterised by good temperature control, limited turn down capacity and efficient heat transfer to [[Biomass|biomass]] particles due to high solid density. <ref>[https://www.researchgate.net/publication/318678876_Review_of_Synthetic_Fuels_and_New_Materials_Production_Based_on_Pyrolysis_Technologies Review of Synthetic Fuels and New Materials Production Based on Pyrolysis Technologies]</ref> | |- | ||
| In bubbling fluidised beds, particles are entered into a bed of hot sand fluidised by a recirculated product gas. The high heat transfer rates from the fluidised sand cause rapid heating of [[Biomass|biomass]] particles and some ablation with the sand particles occurs. This type of reactor is characterised by good temperature control, limited turn down capacity and efficient heat transfer to [[Biomass|biomass]] particles due to high solid density. || [[File:Bubbling Fluidised Bed Reactor with an Electrostatic Precipitator.png|250px|right|Bubbling fluidised bed reactor with an electrostatic precipitator. All rights reserved.]]<br clear=all>''Bubbling fluidised bed reactor''<ref>[https://www.researchgate.net/publication/318678876_Review_of_Synthetic_Fuels_and_New_Materials_Production_Based_on_Pyrolysis_Technologies Review of Synthetic Fuels and New Materials Production Based on Pyrolysis Technologies]</ref> | |||
|} | |||
==== Circulating ==== | ==== Circulating ==== | ||
{| | |||
In circulating fluidised beds, [[Biomass|biomass]] particles are introduced into a circulating bed of hot sand. The recirculated product gas, sand and [[Biomass|biomass]] move together in the reactor. The high heat transfer rates from the sand ensure rapid heating of the [[Biomass|biomass]] and ablation is more prevalent than bubbling fluidised beds. This reactor is characterised by good temperature control and high heating rates. The residence time for the tar produced is around the same for the vapour and gas and can be separated by cyclone.<ref name="ref2">[https://www.researchgate.net/publication/330335978_Design_of_A_Fluidized_Bed_Reactor_For_Biomass_Pyrolysis Design of A Fluidized Bed Reactor For Biomass Pyrolysis]</ref> | |- | ||
| In circulating fluidised beds, [[Biomass|biomass]] particles are introduced into a circulating bed of hot sand. The recirculated product gas, sand and [[Biomass|biomass]] move together in the reactor. The high heat transfer rates from the sand ensure rapid heating of the [[Biomass|biomass]] and ablation is more prevalent than bubbling fluidised beds. This reactor is characterised by good temperature control and high heating rates. The residence time for the tar produced is around the same for the vapour and gas and can be separated by cyclone. || [[File:Circulating Fluidised Bed Reactor.png|250px|Circulating fluidised bed reactor. All rights reserved.]]<br clear=all>''Circulating fluidised bed reactor''<ref name="ref2">[https://www.researchgate.net/publication/330335978_Design_of_A_Fluidized_Bed_Reactor_For_Biomass_Pyrolysis Design of A Fluidized Bed Reactor For Biomass Pyrolysis]</ref> | |||
|} | |||
=== Vacuum Furnace Reactor === | === Vacuum Furnace Reactor === | ||
{| | |||
For a vacuum furnace reactor, the [[Biomass|biomass]] is thermally decomposed under reduced pressure. This produces vapours which are quickly removed from the vacuum and recovered as bio-oil via condensation. This reactor has the ability to produce larger particles than most fast pyrolysis reactors and there is less tar in the bio-oil product due to lower gas velocities. The typical liquid yields for dry [[Biomass|biomass]] feed produced from vacuum furnace reactors range from 35% to 50%. <ref>[https://www.researchgate.net/publication/333827218_Liquefaction_of_Biomass_and_Upgrading_of_Bio-Oil_A_Review Liquefaction of Biomass and Upgrading of Bio-Oil]</ref> | |- | ||
| For a vacuum furnace reactor, the [[Biomass|biomass]] is thermally decomposed under reduced pressure. This produces vapours which are quickly removed from the vacuum and recovered as bio-oil via condensation. This reactor has the ability to produce larger particles than most fast pyrolysis reactors and there is less tar in the bio-oil product due to lower gas velocities. The typical liquid yields for dry [[Biomass|biomass]] feed produced from vacuum furnace reactors range from 35% to 50%. || [[File:Schematic for a Vacuum Pyrolysis Reactor.png|250px|right|Schematic for a vacuum pyrolysis reactor. All rights reserved.]]<br clear=all>''Vacuum furnace reactor''<ref>[https://www.researchgate.net/publication/333827218_Liquefaction_of_Biomass_and_Upgrading_of_Bio-Oil_A_Review Liquefaction of Biomass and Upgrading of Bio-Oil]</ref> | |||
|} | |||
=== Ablative Reactor === | === Ablative Reactor === | ||
{| | |||
The ablative reactor provides high relative motion between the reactor wall and the particles in the presence of high pressure exerted by the particles of the hot reactor wall. The system is intensive and the process is mechanically driven so the reactor is complex. This type of reactor has advantages over fluidised bed | |- | ||
| The ablative reactor provides high relative motion between the reactor wall and the particles in the presence of high pressure exerted by the particles of the hot reactor wall. The system is intensive and the process is mechanically driven so the reactor is complex. This type of reactor has advantages over fluidised bed: | |||
*No pre-treatment/sorting of the [[Biomass|biomass]] is required because it is in direct contact with the hot surface so is not influenced by particle size | *No pre-treatment/sorting of the [[Biomass|biomass]] is required because it is in direct contact with the hot surface so is not influenced by particle size | ||
*They have good heat transfer with high heating rates and relatively small contact surface because their compact design | *They have good heat transfer with high heating rates and relatively small contact surface because their compact design | ||
*They have high energy and cost efficiency as no heating and cooling of fluidizing gases is required | *They have high energy and cost efficiency as no heating and cooling of fluidizing gases is required | ||
*They allow installation of condensation units with a small volume, requiring less space at lower costs | *They allow installation of condensation units with a small volume, requiring less space at lower costs | ||
<br clear=all /> | || [[File:Ablative Pyrolyser.png|250px|right|Ablative pyrolysis reactor. All rights reserved.]]<br clear=all>''Ablative reactor''<ref name="ref2" /> | ||
|} | |||
=== Rotating Cone Reactor === | === Rotating Cone Reactor === | ||
{| | |||
The rotating cone reactor is a novel type for flash pyrolysis. It is characterised by rapid heating, a short residence time for solids and negligible char formation. [[Biomass]] materials ([[Wood|wood]], rice husks, olive stones) are pulverised and fed into the rotating cone pyrolyzer. There is also a riser for sand recycling and a bubbling char combustor for char burn off in which carrier gas is required. Relatively fine particles are needed to produce good liquid yields of 60% to 70% of dry feed. However, this type of reactor is still at pilot scale as there is no commercial applications as of yet.<ref name="ref2" /> | |- | ||
| The rotating cone reactor is a novel type for flash pyrolysis. It is characterised by rapid heating, a short residence time for solids and negligible char formation. [[Biomass]] materials ([[Wood|wood]], rice husks, olive stones) are pulverised and fed into the rotating cone pyrolyzer. There is also a riser for sand recycling and a bubbling char combustor for char burn off in which carrier gas is required. Relatively fine particles are needed to produce good liquid yields of 60% to 70% of dry feed. However, this type of reactor is still at pilot scale as there is no commercial applications as of yet. || [[File:Rotating Cone Pyrolysis Reactor.png|250px|right|Rotating cone pyrolysis reactor. All rights reserved.]]<br clear=all>''Rotating cone reactor''<ref name="ref2" /> | |||
|} | |||
=== Auger Reactor === | === Auger Reactor === | ||
{| | |||
In an auger reactor, hot sand and [[Biomass|biomass]] particles enter at one end of a screw. The screw mixes these inputs and conveys them along, providing good control of the [[Biomass|biomass]] residence time. The process does not dilute the pyrolysis products with the carrier or fluidising gas, but the sand must be reheated in a separate vessel. Mechanical reliability is a concern and so there is currently no large-scale implementation of this reactor type. Advantages of this reactor | |- | ||
| In an auger reactor, hot sand and [[Biomass|biomass]] particles enter at one end of a screw. The screw mixes these inputs and conveys them along, providing good control of the [[Biomass|biomass]] residence time. The process does not dilute the pyrolysis products with the carrier or fluidising gas, but the sand must be reheated in a separate vessel. Mechanical reliability is a concern and so there is currently no large-scale implementation of this reactor type. Advantages of this reactor: | |||
*Compact size | *Compact size | ||
*No carrier gas required | *No carrier gas required | ||
*Lower operating temperature (400°C) | *Lower operating temperature (400°C) | ||
<ref name="ref1" /> | |||
|| [[File:Diagram of an auger pyrolysis reactor.png|250px|right|Diagram of an auger pyrolysis reactor. All rights reserved.]]<br clear=all>''Auger reactor''<ref>[https://www.researchgate.net/publication/272494234_Effect_of_Temperature_on_Product_Yield_from_the_Pyrolysis_of_Soybean_Cake_in_an_Auger_Reactor Effect of Temperature on Product Yield from the Pyrolysis of Soybean Cake in an Auger Reactor]</ref> | |||
|} | |||
==References== | ==References== | ||
<references /> | <references /> | ||