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[[Category:Technologies & Solutions]] | [[Category:Technologies & Solutions]] | ||
[[Pyrolysis]] is the thermal | [[Pyrolysis]] is the [[treatment|thermal treatment]] of a material in the absence of oxygen to produce gas ([[Syngas|syngas]]), liquid and solid char fractions. | ||
==Overview== | |||
[[File:The Biomass Pyrolysis-Cycle.png|600px| | [[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. | ||
[[File:The Biomass Pyrolysis-Cycle.png|600px|center|The Biomass Pyrolysis Cycle. All rights reserved.]] | |||
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Typically, lower temperatures of between 300C to 850C are used during Pyrolysis of materials such as [[MSW]]. Pyrolysis processes tend to prefer consistent feedstocks and there is a limited track record of commercial scale Pyrolysis plant accepting [[MSW]] but a better track record of, for example, Pyrolysis of [[Biomass|biomass]] <ref> Defra, 2013. [https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/221035/pb13888-thermal-treatment-waste.pdf Advanced Thermal Treatment of Municipal Solid Waste.] London. </ref>. | |||
==Context and Definition== | |||
In legal terms, a '''‘waste incineration plant’''' means any stationary or mobile technical unit and equipment dedicated to the thermal treatment of 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/jrc/en/news/new-eu-environmental-standards-waste-incineration 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]]''', | |||
* the nature of the waste (e.g. Hazardous Waste Incinerators), '''and in WikiWaste includes [[Hazardous Waste Incineration]] and [[Clinical Waste Incineration]]''' | |||
* the method/type of incineration (e.g. High Temperature Incinerators). | |||
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: | |||
{|class="wikitable" | |||
!colspan=2|Definitions in Legislation!!rowspan=7 style="padding: 50px"| !!Types!!Temp. Range °C!!Category!!rowspan=7 style="padding: 50px"| !!Kiln/Furnace/Reactor | |||
|- | |||
|rowspan=6|[[Incineration]]||rowspan=3|[[Incineration with Energy Recovery|With Energy Recovery]]||rowspan=2|[[Combustion]]|| rowspan=2|800 - 1450||rowspan=2|[[Treatment|Thermal Treatment]]|| [[Grate]] | |||
|- | |||
|[[Fluidised Bed]] | |||
|- | |||
|rowspan=2|[[Gasification]]||rowspan=2|500 - 1600||rowspan=2| [[Advanced Thermal Treatment]] ([[ATT]] and [[ACT]])||[[Rotary]] | |||
|- | |||
|rowspan=3|[[Incineration without Energy Recovery|Without Energy Recovery]]||[[Plasma]] | |||
|- | |||
|rowspan=2|[[Pyrolysis]]||rowspan=2|250 - 700||rowspan=2|[[Advanced Thermal Treatment]] ([[ATT]] and [[ACT]]) ||[[Heated Tube]] | |||
|- | |||
|[[Surface contact]] | |||
|} | |||
Typically, lower temperatures of between 300C to 850C are used during [[Pyrolysis]] of materials such as [[MSW]]. Pyrolysis processes tend to prefer consistent feedstocks and there is a limited track record of commercial scale Pyrolysis plant accepting [[MSW]] but a better track record of, for example, Pyrolysis of [[Biomass|biomass]] <ref> Defra, 2013. [https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/221035/pb13888-thermal-treatment-waste.pdf Advanced Thermal Treatment of Municipal Solid Waste.] London. </ref>. | |||
==Types of Pyrolysis == | ==Types of Pyrolysis == | ||
The | The [[Pyrolysis]] process can be divided into three subcategories depending on the operating conditions: temperature, heating rate, particle size and solid residence time. The different types of pyrolysis are slow/conventional, fast, and flash: | ||
=== Slow/Conventional === | ===Slow/Conventional=== | ||
Slow/conventional pyrolysis is a process where the heating rate is kept slow (around 0.1-1°C/s) which results in higher char yield than the liquid and gaseous products. This type of pyrolysis has been used for thousands of years for the production of charcoal. [[Biomass]] is heated to around 500°C in slow [[Wood|wood]] pyrolysis and the long vapour residence time in the reactor means the gas-phase products have ample opportunities to react with other products to form char<ref name="ref1">[http://www.eagri.org/eagri50/AENG352/lec10.pdf Principles of Pyrolysis]</ref>. | Slow/conventional pyrolysis is a process where the heating rate is kept slow (around 0.1-1°C/s) which results in higher char yield than the liquid and gaseous products. This type of pyrolysis has been used for thousands of years for the production of charcoal. [[Biomass]] is heated to around 500°C in slow [[Wood|wood]] pyrolysis and the long vapour residence time in the reactor means the gas-phase products have ample opportunities to react with other products to form char<ref name="ref1">[http://www.eagri.org/eagri50/AENG352/lec10.pdf Principles of Pyrolysis]</ref>. | ||
=== Fast === | ===Fast=== | ||
Fast pyrolysis provides conditions to maximise the production of the liquid fraction of the products that are bio-oils (e.g. pyrolysis oil and biocrude). The primary goal is producing a renewable fuel intermediate in the pathway to finished hydrocarbon fuels from [[Biomass|biomass]] feedstock<ref>[https://www.sciencedirect.com/science/article/pii/B9780128182130000011 Pyrolysis of Biomass for Fuels and Chemicals]</ref>. The typical fast pyrolysis conditions are: moderate pyrolysis treatment temperatures (600-1000°C), rapid heating rates of biomass particles (>100°C/min), combined with short residence times of the biomass particles and pyrolysis vapours (0.5-2s) at high temperatures. Combination of medium pyrolysis temperature with short vapour residence time ensures high yield of good quality pyrolysis liquids while keeping the char and gas yields to a minimum. Due to the low thermal conductivity of [[Biomass|biomass]], small particle sizes are required to achieve the high heating rate needed<ref>[https://www.sciencedirect.com/science/article/pii/B9780081004555000217 Handbook of Biofuels Production]</ref>. Fluidised bed reactors are best suited for this type of pyrolysis due to offering high heating rates, rapid devolatilization and are easy to operate<ref name="ref1" />. | Fast pyrolysis provides conditions to maximise the production of the liquid fraction of the products that are bio-oils (e.g. pyrolysis oil and biocrude). The primary goal is producing a renewable fuel intermediate in the pathway to finished hydrocarbon fuels from [[Biomass|biomass]] feedstock<ref>[https://www.sciencedirect.com/science/article/pii/B9780128182130000011 Pyrolysis of Biomass for Fuels and Chemicals]</ref>. The typical fast pyrolysis conditions are: moderate pyrolysis treatment temperatures (600-1000°C), rapid heating rates of biomass particles (>100°C/min), combined with short residence times of the biomass particles and pyrolysis vapours (0.5-2s) at high temperatures. Combination of medium pyrolysis temperature with short vapour residence time ensures high yield of good quality pyrolysis liquids while keeping the char and gas yields to a minimum. Due to the low thermal conductivity of [[Biomass|biomass]], small particle sizes are required to achieve the high heating rate needed<ref>[https://www.sciencedirect.com/science/article/pii/B9780081004555000217 Handbook of Biofuels Production]</ref>. Fluidised bed reactors are best suited for this type of pyrolysis due to offering high heating rates, rapid devolatilization and are easy to operate<ref name="ref1" />. | ||
=== Flash === | === Flash === | ||
Flash pyrolysis (sometimes referred to as very fast pyrolysis) is characterised by rapid heating rates (>1000°C/s) and high reaction temperatures (900-1300°C), producing high yields of bio-oil with low resulting water content and conversion efficiencies of up to 70%. The residence time is shorter than fast pyrolysis at less than 0.5 seconds. The [[Biomass|biomass]] feedstock must go through vigorous pre-treatment to reduce particle size as much as possible (around 105-250 μm) which is required to achieve such high heating and heat transfer rates<ref>[https://www.sciencedirect.com/science/article/pii/B9780444538789000096 New and Future Developments in Catalysis]</ref>. Entrained flow or fluidised bed reactors are considered the best pyrolyzers for this purpose<ref name="ref1" />. | Flash pyrolysis (sometimes referred to as very fast pyrolysis) is characterised by rapid heating rates (>1000°C/s) and high reaction temperatures (900-1300°C), producing high yields of bio-oil with low resulting water content and conversion efficiencies of up to 70%. The residence time is shorter than fast pyrolysis at less than 0.5 seconds. The [[Biomass|biomass]] feedstock must go through vigorous pre-treatment to reduce particle size as much as possible (around 105-250 μm) which is required to achieve such high heating and heat transfer rates<ref>[https://www.sciencedirect.com/science/article/pii/B9780444538789000096 New and Future Developments in Catalysis]</ref>. Entrained flow or fluidised bed reactors are considered the best pyrolyzers for this purpose<ref name="ref1" />. | ||
== Pyrolysis | ==Kiln/Reactor Types in Pyrolysis== | ||
=== Fixed Bed Reactor === | === Fixed Bed Reactor === | ||
[[File:Schematic diagram of a fixed bed pyrolysis reactor.png|250px|right|Schematic diagram of a fixed bed pyrolysis reactor. All rights reserved.]] | [[File:Schematic diagram of a fixed bed pyrolysis reactor.png|250px|right|Schematic diagram of a fixed bed pyrolysis reactor. All rights reserved.]] | ||
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 | 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 moves slowly down a vertical shaft | 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> | ||
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===Fluidised Bed Reactor=== | |||
Fluidised bed reactors are typically used for fast pyrolysis and are characterised by a high heating rate and small particle size. This type of reactor can be split into bubbling and circulating fluidised bed: | |||
==== Bubbling ==== | ==== Bubbling ==== | ||
[[File:Bubbling Fluidised Bed Reactor with an Electrostatic Precipitator.png|250px|right|Bubbling fluidised bed reactor with an electrostatic precipitator. All rights reserved.]] | [[File:Bubbling Fluidised Bed Reactor with an Electrostatic Precipitator.png|250px|right|Bubbling fluidised bed reactor with an electrostatic precipitator. All rights reserved.]] | ||
In bubbling fluidised beds, | 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> | ||
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==== Circulating ==== | ==== Circulating ==== | ||
[[File:Circulating Fluidised Bed Reactor.png|250px|right|Circulating fluidised bed reactor. All rights reserved.]] | [[File:Circulating Fluidised Bed Reactor.png|250px|right|Circulating fluidised bed reactor. All rights reserved.]] | ||
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. | 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> | ||
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=== Vacuum Furnace Reactor === | === Vacuum Furnace Reactor === | ||
[[File:Schematic for a Vacuum Pyrolysis Reactor.png|250px|right|Schematic for a vacuum pyrolysis reactor. All rights reserved.]] | [[File:Schematic for a Vacuum Pyrolysis Reactor.png|250px|right|Schematic for a vacuum pyrolysis reactor. All rights reserved.]] | ||
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%. | 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> | ||
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=== Ablative Reactor === | === Ablative Reactor === | ||
[[File:Ablative Pyrolyser.png|250px|right|Ablative pyrolysis reactor. All rights reserved.]] | [[File:Ablative Pyrolyser.png|250px|right|Ablative pyrolysis reactor. All rights reserved.]] | ||
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<ref name="ref2" />: | ||
*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 | ||
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=== Rotating Cone Reactor === | === Rotating Cone Reactor === | ||
[[File:Rotating Cone Pyrolysis Reactor.png|250px|right|Rotating cone pyrolysis reactor. All rights reserved.]] | [[File:Rotating Cone Pyrolysis Reactor.png|250px|right|Rotating cone pyrolysis reactor. All rights reserved.]] | ||
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. | 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" /> | ||
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=== Auger Reactor === | === Auger Reactor === | ||
[[File:Diagram of an auger pyrolysis reactor.png|250px|right|Diagram of an auger pyrolysis reactor. All rights reserved.]] | [[File:Diagram of an auger pyrolysis reactor.png|250px|right|Diagram of an auger pyrolysis reactor. All rights reserved.]] | ||
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<ref name="ref1" /> | ||
<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>: | |||
*Compact size | *Compact size | ||
*No carrier gas required | *No carrier gas required | ||
*Lower operating temperature (400°C) | *Lower operating temperature (400°C) | ||
==References== | ==References== | ||
<references /> | <references /> |