|
|
| Line 3: |
Line 3: |
| | | | |
| | The reduction of material density is the reason for undertaking briquetting as it determines both the savings in transport and handling costs and any improvement in combustion over the original material: the art of briquetting. '''This art essentially involves two parts: the compaction under pressure of loose material to reduce its volume and to agglomerate the material so that the product remains in the compressed state.''' Later effect, the cohesion of the particles, is based on three main mechanisms<ref name="kaltschmitt 2009"> The original German version: Kaltschmitt, M.; Hartmann, H. und Hofbauer, H. (2009): Energie aus Biomasse. Grundlagen, Techniken und Verfahren; Springer-Verlag Berlin Heidelberg 2001, 2009, korrigierter Nachdruck 2009</ref>:<br/> | | The reduction of material density is the reason for undertaking briquetting as it determines both the savings in transport and handling costs and any improvement in combustion over the original material: the art of briquetting. '''This art essentially involves two parts: the compaction under pressure of loose material to reduce its volume and to agglomerate the material so that the product remains in the compressed state.''' Later effect, the cohesion of the particles, is based on three main mechanisms<ref name="kaltschmitt 2009"> The original German version: Kaltschmitt, M.; Hartmann, H. und Hofbauer, H. (2009): Energie aus Biomasse. Grundlagen, Techniken und Verfahren; Springer-Verlag Berlin Heidelberg 2001, 2009, korrigierter Nachdruck 2009</ref>:<br/> |
| − |
| |
| | | | |
| | *Generating a positive coupling of particles by fibre connections<br/> | | *Generating a positive coupling of particles by fibre connections<br/> |
| Line 12: |
Line 11: |
| | [[File:Figure 4 Binding mechanisme.jpg|center|400px|alt=Figure 4 Binding mechanisme.jpg]] | | [[File:Figure 4 Binding mechanisme.jpg|center|400px|alt=Figure 4 Binding mechanisme.jpg]] |
| | | | |
| − | <p style="text-align: center"><sub><span style="color: rgb(0, 0, 255)">Figure 4: Binding mechanisms<ref name="Grover 1996"> Picture : Grover, S.D. and Mishra S.K. (1996): Biomass Briquetting: Technology and Practices; FAO Regional Wood Energy Development Programme in Asia, Bangkok, Thailand (1996)</ref></span></sub><br/></p><br/>A '''binding agent''' is necessary to prevent the compressed material from springing back and eventually returning to its original form. This agent can either be added to the process or, when compressing ligneous material, be part of the material itself in form of lignin. Ligning is a constituent in most agricultural residues. It can be defined as the thermo plastic polymer, which begins to soften at temperatures above 100°C and is flowing at higher temperatures. The softening of lignin and its subsequent cooling while the material is still under pressure is the key factor in high pressure briquetting. It is a physic-chemical process related largely to the temperature reached in the briquetting process and the amount of lignin in the original material. The temperature in many machines is closely related to the pressure though in some, external heat is applied.<br/> | + | <p style="text-align: center"><sub><span style="color: rgb(0, 0, 255)">Figure 4: Binding mechanisms<ref name="Grover 1996"> Picture : Grover, S.D. and Mishra S.K. (1996): Biomass Briquetting: Technology and Practices; FAO Regional Wood Energy Development Programme in Asia, Bangkok, Thailand (1996)</ref></span></sub><br/></p><br/>A '''binding agent''' is necessary to prevent the compressed material from springing back and eventually returning to its original form. This agent can either be added to the process or, when compressing ligneous material, be part of the material itself in form of lignin. Ligning is a constituent in most agricultural residues. It can be defined as the thermo plastic polymer, which begins to soften at temperatures above 100°C and is flowing at higher temperatures. The softening of lignin and its subsequent cooling while the material is still under pressure is the key factor in high pressure briquetting. It is a physic-chemical process related largely to the temperature reached in the briquetting process and the amount of lignin in the original material. The temperature in many machines is closely related to the pressure though in some, external heat is applied.<br/>[[File:Figure 5 arrangement of cellulose.jpg|center|400px|alt=Figure 5 arrangement of cellulose.jpg]] |
| − | | + | |
| − | [[File:Figure 5 arrangement of cellulose.jpg|center|400px|alt=Figure 5 arrangement of cellulose.jpg]] | + | |
| | | | |
| | <p style="text-align: center"><span style="color: rgb(0, 0, 255)"><sub>Figure 5: arrangement of cellulose, hemicellulose and ligning in biomass matrix<ref name="Jaya 2010"> Picture : Jaya Shankar Tumuluru et al. (2010): A Review on Biomass Densification Technologies for Energy Application; Idaho national laboratory; 2010</ref></sub></span><br/></p><br/>In general there are '''two immediate ways of classifying briquetting processes.''' One distinction is '''whether or not an external binding agent '''must be added to agglomerate the compressed material. The second way of classifying follows '''the pressure applied''' while briquetting: high, medium or low pressure. For a rough distinction the following numbers might be adopted:<br/> | | <p style="text-align: center"><span style="color: rgb(0, 0, 255)"><sub>Figure 5: arrangement of cellulose, hemicellulose and ligning in biomass matrix<ref name="Jaya 2010"> Picture : Jaya Shankar Tumuluru et al. (2010): A Review on Biomass Densification Technologies for Energy Application; Idaho national laboratory; 2010</ref></sub></span><br/></p><br/>In general there are '''two immediate ways of classifying briquetting processes.''' One distinction is '''whether or not an external binding agent '''must be added to agglomerate the compressed material. The second way of classifying follows '''the pressure applied''' while briquetting: high, medium or low pressure. For a rough distinction the following numbers might be adopted:<br/> |
| Line 30: |
Line 27: |
| | [[File:Figure 6 Reference missing.jpg|center|450px|alt=Figure 6 Reference missing.jpg]] | | [[File:Figure 6 Reference missing.jpg|center|450px|alt=Figure 6 Reference missing.jpg]] |
| | | | |
| − | <p style="text-align: center"><span style="color: rgb(0, 0, 255)"><sub>Figure 6: from biomass to charcoal [own illustration]</sub></span><br/></p><br/>But, during the carbonization process, the biomass is losing its lignin content and thereby an important binder for briquetting. Charcoal is a material totally lacking plasticity and hence needs addition of a sticking or agglomerating material to enable a briquette to be formed. The binder should preferably be combustible, though a non-combustible binder effective at low concentrations can be suitable.<br/> | + | <p style="text-align: center"><span style="color: rgb(0, 0, 255)"><sub>Figure 6: from biomass to charcoal [own illustration]</sub></span><br/></p><br/>But, during the carbonization process, the biomass is losing its lignin content and thereby an important binder for briquetting. Charcoal is a material totally lacking plasticity and hence needs addition of a sticking or agglomerating material to enable a briquette to be formed. The binder should preferably be combustible, though a non-combustible binder effective at low concentrations can be suitable.<br/><br/><u>Further information:</u><br/> |
| | + | |
| | | | |
| − | <br/><u>Further information:</u><br/>
| |
| | *“Charcoal Production from Alternative Feedstocks” by NL Agency (2013) provides a good overview on charcoal production technologies, on carbonization of biomass and suitable binders including the description of three supply chains presented as case studies. [http://english.rvo.nl/sites/default/files/2013/11/Charcoal production from alternative feedstocks - June 2013.pdf http://english.rvo.nl/sites/default/files/2013/11/Charcoal production from alternative feedstocks - June 2013.pdf]<br/> | | *“Charcoal Production from Alternative Feedstocks” by NL Agency (2013) provides a good overview on charcoal production technologies, on carbonization of biomass and suitable binders including the description of three supply chains presented as case studies. [http://english.rvo.nl/sites/default/files/2013/11/Charcoal production from alternative feedstocks - June 2013.pdf http://english.rvo.nl/sites/default/files/2013/11/Charcoal production from alternative feedstocks - June 2013.pdf]<br/> |
| − | | + | = Briquetting technologies = |
| − | == Briquetting technologies<br/> ==
| + | |
| − | <br/>
| + | |
| − | | + | |
| | Industrial methods of briquetting date back to the second part the the 19th century. Since then there has been widespread use of briquettes made from brown coal, peat and coal fines. The briquetting of organic materials requires higher pressure as additional force is needed to overcome the natural springiness of these materials. Essentially, this involves the '''destruction of the cell walls through some combination of pressure and heat.''' The following overview presents the most common machines used for briquetting biomass.<br/> | | Industrial methods of briquetting date back to the second part the the 19th century. Since then there has been widespread use of briquettes made from brown coal, peat and coal fines. The briquetting of organic materials requires higher pressure as additional force is needed to overcome the natural springiness of these materials. Essentially, this involves the '''destruction of the cell walls through some combination of pressure and heat.''' The following overview presents the most common machines used for briquetting biomass.<br/> |
| | | | |
| − | <br/>'''Piston presses:'''<br/>
| |
| | | | |
| | + | == Piston presses == |
| | In piston presses, pressure is applied discontinuously by the action of a piston on material packed into a cylinder. They may have a mechanical coupling and fly wheel or utilize hydraulic action on the piston. The incoming raw material is pressed against the compacted material inside the pressing tube and leaves the die in the rhythm of the piston action. Through pressure and friction forces inside the pressing tube, the material is strongly heated and cooling mechanisms might be considered. To produce briquettes with high density (up to 1.25 g/m3) the raw material eventually needs to be milled (less than 10 mm) and dried (<15% of water content) before briquetting. The capacity of piston presses depends both on the diameter of the die and the pretreatment of the raw material.<br/> | | In piston presses, pressure is applied discontinuously by the action of a piston on material packed into a cylinder. They may have a mechanical coupling and fly wheel or utilize hydraulic action on the piston. The incoming raw material is pressed against the compacted material inside the pressing tube and leaves the die in the rhythm of the piston action. Through pressure and friction forces inside the pressing tube, the material is strongly heated and cooling mechanisms might be considered. To produce briquettes with high density (up to 1.25 g/m3) the raw material eventually needs to be milled (less than 10 mm) and dried (<15% of water content) before briquetting. The capacity of piston presses depends both on the diameter of the die and the pretreatment of the raw material.<br/> |
| − |
| |
| − | <br/>
| |
| | | | |
| | The capacity spectrum of piston presses range from only 25 up to 1800 kg/hr. Their typical specific energy use requires between 50 and 70 kWh/t.<ref>Kaltschmitt, M.; Hartmann, H. und Hofbauer, H. (2009): Energie aus Biomasse. Grundlagen, Techniken und Verfahren; Springer-Verlag Berlin Heidelberg 2001, 2009, korrigierter Nachdruck 2009</ref><br/> | | The capacity spectrum of piston presses range from only 25 up to 1800 kg/hr. Their typical specific energy use requires between 50 and 70 kWh/t.<ref>Kaltschmitt, M.; Hartmann, H. und Hofbauer, H. (2009): Energie aus Biomasse. Grundlagen, Techniken und Verfahren; Springer-Verlag Berlin Heidelberg 2001, 2009, korrigierter Nachdruck 2009</ref><br/> |
| − |
| |
| | | | |
| | {| border="0" align="center" cellspacing="0" cellpadding="0" style="height: 2px" | | {| border="0" align="center" cellspacing="0" cellpadding="0" style="height: 2px" |
| Line 54: |
Line 45: |
| | | style="text-align: center" | [[File:Figure 6b piston presses.jpg|thumb|right|300px|alt=Figure 6b piston presses.jpg]] | | | style="text-align: center" | [[File:Figure 6b piston presses.jpg|thumb|right|300px|alt=Figure 6b piston presses.jpg]] |
| | |} | | |} |
| − | <p style="text-align: center"><sub><span style="color: rgb(0, 0, 255)">Figure 7: piston presses<ref name="Kaltschmitt 2009">Picture: The original German version: Kaltschmitt, M.; Hartmann, H. and Hofbauer, H. (2009): Energie aus Biomasse. Grundlagen, Techniken und Verfahren; Springer-Verlag Berlin Heidelberg 2001, 2009, korrigierter Nachdruck 2009</ref></span></sub><br/></p><br/>'''Screw compaction or Extrusion'''<br/> | + | <p style="text-align: center"><sub><span style="color: rgb(0, 0, 255)">Figure 7: piston presses<ref name="Kaltschmitt 2009">Picture: The original German version: Kaltschmitt, M.; Hartmann, H. and Hofbauer, H. (2009): Energie aus Biomasse. Grundlagen, Techniken und Verfahren; Springer-Verlag Berlin Heidelberg 2001, 2009, korrigierter Nachdruck 2009</ref></span></sub></p> |
| | + | == <br/>'''Screw Compaction or Extrusion''' == |
| | + | The aim of compaction using an extruder is to bring the smaller particles closer so that the forces acting between them become stronger, providing more strength the densified bulk material. During extrusion, the material moves from the feed port, with the help of a rotating screw, through the barrel and against a die, resulting in significant pressure gradient and friction due to biomass shearing. The combined effects of wall friction at the barrel, internal friction in the material, and high rotational speed of the screw, increase the temperature in the closed system and heat the biomass. This heated biomass is forced through the extrusion die to form the briquettes with the required shape. If the heat generated within the system is not sufficient for the material to reach a pseudo-plastic state for smooth extrusion, external heat might be added. In principle, screw presses reach slightly higher compaction but lower capacity (tons per hour) when compared to piston presses. |
| | | | |
| − | <br/>
| |
| − |
| |
| − | The aim of compaction using an extruder is to bring the smaller particles closer so that the forces acting between them become stronger, providing more strength the densified bulk material. During extrusion, the material moves from the feed port, with the help of a rotating screw, through the barrel and against a die, resulting in significant pressure gradient and friction due to biomass shearing. The combined effects of wall friction at the barrel, internal friction in the material, and high rotational speed of the screw, increase the temperature in the closed system and heat the biomass. This heated biomass is forced through the extrusion die to form the briquettes with the required shape. If the heat generated within the system is not sufficient for the material to reach a pseudo-plastic state for smooth extrusion, external heat might be added. In principle, screw presses reach slightly higher compaction but lower capacity (tons per hour) when compared to piston presses.
| |
| | | | |
| | {| border="0" align="center" cellspacing="0" cellpadding="0" style="width: 10px; height: 10px" | | {| border="0" align="center" cellspacing="0" cellpadding="0" style="width: 10px; height: 10px" |
| Line 65: |
Line 55: |
| | | style="width: 1px" | [[File:Figure 7b screw presses.jpg|thumb|right|300px|alt=Figure 7b screw presses.jpg]] | | | style="width: 1px" | [[File:Figure 7b screw presses.jpg|thumb|right|300px|alt=Figure 7b screw presses.jpg]] |
| | |} | | |} |
| − | <p style="text-align: center"><span style="color: rgb(0, 0, 255)">Figure 8: screw presses [left image<ref> Picture : http://www.soi.wide.ad.jp/class/20070041/slides/03/index_12.html </ref>; right image<ref name="Eriksson 1990"> Picture: Eriksson, S. and Prior, M. (1990): The briquetting of agricultural wastes for fuel, FAO Environment and Energy Paper 11, FAO of the UN, Rome, 1990</ref>]</span><br/><br/></p>'''Pan grinder presses for pelletizing'''<br/><br/> | + | <p style="text-align: center"><span style="color: rgb(0, 0, 255)">Figure 8: screw presses [left image<ref> Picture : http://www.soi.wide.ad.jp/class/20070041/slides/03/index_12.html </ref>; right image<ref name="Eriksson 1990"> Picture: Eriksson, S. and Prior, M. (1990): The briquetting of agricultural wastes for fuel, FAO Environment and Energy Paper 11, FAO of the UN, Rome, 1990</ref>]</span><br/></p> |
| − | | + | == '''Pan Grinder Presses for Pelletizing'''<br/> == |
| | Pellets are the result of a process which is closely related to the briquetting processes described above. The main difference is that the dies have smaller diameters and each machine has a number of dies arranged as holes bored in a thick steel disk or ring. The material is forced into the dies by means of rollers moving over the surface on which the raw material is distributed. The pressure is built up by the compression of this layer of material as the roller moves perpendicular to the centerline of the dies. Thus the main force applied results in shear stresses in the material. The pellets will still be hot when leaving the dies, where they are cut to lengths normally about one or two times the diameter. Successful operation demands that a rather elaborate cooling system is arranged after the densification process.<br/>There are two main types of pellet presses: flat and ring types. The flat die type has a circular perforated disk on which rollers rotate whereas the ring die press features a rotating perforated ring on which rollers press on the inner perimeter. The output of pellet presses range from about 200 kg/hr up to 8 ton/hr. Their specific energy consumption is reported to be around 1,5% of the energy content of the final peletts<ref name="Kaltschmitt 2009"> Kaltschmitt, M.; Hartmann, H. und Hofbauer, H. (2009): Energie aus Biomasse. Grundlagen, Techniken und Verfahren; Springer-Verlag Berlin Heidelberg 2001, 2009, korrigierter Nachdruck 2009</ref>.<br/><br/> | | Pellets are the result of a process which is closely related to the briquetting processes described above. The main difference is that the dies have smaller diameters and each machine has a number of dies arranged as holes bored in a thick steel disk or ring. The material is forced into the dies by means of rollers moving over the surface on which the raw material is distributed. The pressure is built up by the compression of this layer of material as the roller moves perpendicular to the centerline of the dies. Thus the main force applied results in shear stresses in the material. The pellets will still be hot when leaving the dies, where they are cut to lengths normally about one or two times the diameter. Successful operation demands that a rather elaborate cooling system is arranged after the densification process.<br/>There are two main types of pellet presses: flat and ring types. The flat die type has a circular perforated disk on which rollers rotate whereas the ring die press features a rotating perforated ring on which rollers press on the inner perimeter. The output of pellet presses range from about 200 kg/hr up to 8 ton/hr. Their specific energy consumption is reported to be around 1,5% of the energy content of the final peletts<ref name="Kaltschmitt 2009"> Kaltschmitt, M.; Hartmann, H. und Hofbauer, H. (2009): Energie aus Biomasse. Grundlagen, Techniken und Verfahren; Springer-Verlag Berlin Heidelberg 2001, 2009, korrigierter Nachdruck 2009</ref>.<br/><br/> |
| | + | |
| | | | |
| | {| border="0" align="center" cellspacing="0" cellpadding="0" style="width: 0px" | | {| border="0" align="center" cellspacing="0" cellpadding="0" style="width: 0px" |
| Line 74: |
Line 65: |
| | | [[File:Figure 8b pan grinders.jpg|thumb|right|300px|alt=Figure 8b pan grinders.jpg]] | | | [[File:Figure 8b pan grinders.jpg|thumb|right|300px|alt=Figure 8b pan grinders.jpg]] |
| | |} | | |} |
| − | <p style="text-align: center"><sub><span style="color: rgb(0, 0, 255)">Figure 9: pan grinders<ref name="Kaltschmitt 2009">Picture: The original German version: Kaltschmitt, M.; Hartmann, H. und Hofbauer, H. (2009): Energie aus Biomasse. Grundlagen, Techniken und Verfahren; Springer-Verlag Berlin Heidelberg 2001, 2009, korrigierter Nachdruck 2009</ref></span></sub><br/></p><br/>'''Manual '''<br/> | + | <p style="text-align: center"><sub><span style="color: rgb(0, 0, 255)">Figure 9: pan grinders<ref name="Kaltschmitt 2009">Picture: The original German version: Kaltschmitt, M.; Hartmann, H. und Hofbauer, H. (2009): Energie aus Biomasse. Grundlagen, Techniken und Verfahren; Springer-Verlag Berlin Heidelberg 2001, 2009, korrigierter Nachdruck 2009</ref></span></sub></p> |
| | + | == <br/>'''Manual''' == |
| | + | For sure the simplest way to produce small briquettes is hand-shaped briquettes: a slurry of biomass in water is left soaking for some days to enhance binding properties. The pulp is either squeezed by hand or pressed into a mould e.g. an ice-cube tray. Rearranged fibres assisted by a binder like paper pulp keep the briquette in shape during drying and use. A part of hand-shaped briquettes there are plenty of small manual briquetting machines which were developed by different producers and scientists all over the world. A very good overview on existing low cost briquetting machines, from perforated bottles to wooden lever presses, can be found in the manual “Micro-gasification: Cooking with gas from biomass” by Christa Roth (2011)<ref>https://energypedia.info/wiki/File:Micro_Gasification_Cooking_with_gas_from_biomass.pdf</ref>.<br/><br/> |
| | | | |
| − | <br/>
| |
| − |
| |
| − | For sure the simplest way to produce small briquettes is hand-shaped briquettes: a slurry of biomass in water is left soaking for some days to enhance binding properties. The pulp is either squeezed by hand or pressed into a mould e.g. an ice-cube tray. Rearranged fibres assisted by a binder like paper pulp keep the briquette in shape during drying and use. A part of hand-shaped briquettes there are plenty of small manual briquetting machines which were developed by different producers and scientists all over the world. A very good overview on existing low cost briquetting machines, from perforated bottles to wooden lever presses, can be found in the manual “Micro-gasification: Cooking with gas from biomass” by Christa Roth (2011)<ref>https://energypedia.info/wiki/File:Micro_Gasification_Cooking_with_gas_from_biomass.pdf</ref>.<br/><br/>
| |
| | | | |
| | {| border="0" align="center" cellspacing="0" cellpadding="0" style="width: 10px; height: 0px" | | {| border="0" align="center" cellspacing="0" cellpadding="0" style="width: 10px; height: 0px" |
| Line 87: |
Line 77: |
| | <p style="text-align: center"><span style="color: rgb(0, 0, 255)"><sub>Figure 10: examples of low cost briquetting machines<ref>Pictures: http://home.fuse.net/engineering/ </ref></sub></span><br/></p><br/>However, it remains unclear, whether any manual densification process can ever be commercially viable even in circumstances where labour is very cheap. Considering their very low throughput, such techniques often require almost as much capital investment as the mechanical processes. The savings achieved are essentially a labour for electricity substitution rather than labour for capital.<br/> | | <p style="text-align: center"><span style="color: rgb(0, 0, 255)"><sub>Figure 10: examples of low cost briquetting machines<ref>Pictures: http://home.fuse.net/engineering/ </ref></sub></span><br/></p><br/>However, it remains unclear, whether any manual densification process can ever be commercially viable even in circumstances where labour is very cheap. Considering their very low throughput, such techniques often require almost as much capital investment as the mechanical processes. The savings achieved are essentially a labour for electricity substitution rather than labour for capital.<br/> |
| | | | |
| − | '''Roller Presses'''<br/> | + | == '''Roller Presses''' == |
| | Densification of biomass using roller presses works on the principle of pressure and agglomeration, where pressure is applied between two counter-rotating rolls. Ground biomass, when forced through the gap between the two rollers, is pressed into a die, or small pockets, forming the densified product. Roller presses are considered the world standard technology to produce ovoid (pillow-shaped) charcoal briquettes from a variety of biomass types. In a roller press, a mixture of charcoal and binder is fed to the tangential pockets of two rollers to produce briquettes. The smooth production of charcoal briquettes using this technology requires high-quality rollers with smooth surfaces on which the briquettes are shaped. The type of roller determines the shape of the briquettes. Currently, roll presses available in developed countries have production capacities of 1 t/hr and more. The 1 tonne/hr capacity press with controlled feeding device costs about $ 320,000. Much cheaper roller-type charcoal briquetting machines can be sourced in India and China: Seboka (2009) indicates that a roller press with a capacity of 1.5 tonne/hr costing $ 19,000 can be found in India<ref>Seboka, Y. (2009): Charcoal Production: Opportunities and Barriers for Improving Efficiency and Sustainability. In: Bio-carbon Opportunities in Eastern & Southern Africa, UNDP, 2009</ref>.<br/><br/> | | Densification of biomass using roller presses works on the principle of pressure and agglomeration, where pressure is applied between two counter-rotating rolls. Ground biomass, when forced through the gap between the two rollers, is pressed into a die, or small pockets, forming the densified product. Roller presses are considered the world standard technology to produce ovoid (pillow-shaped) charcoal briquettes from a variety of biomass types. In a roller press, a mixture of charcoal and binder is fed to the tangential pockets of two rollers to produce briquettes. The smooth production of charcoal briquettes using this technology requires high-quality rollers with smooth surfaces on which the briquettes are shaped. The type of roller determines the shape of the briquettes. Currently, roll presses available in developed countries have production capacities of 1 t/hr and more. The 1 tonne/hr capacity press with controlled feeding device costs about $ 320,000. Much cheaper roller-type charcoal briquetting machines can be sourced in India and China: Seboka (2009) indicates that a roller press with a capacity of 1.5 tonne/hr costing $ 19,000 can be found in India<ref>Seboka, Y. (2009): Charcoal Production: Opportunities and Barriers for Improving Efficiency and Sustainability. In: Bio-carbon Opportunities in Eastern & Southern Africa, UNDP, 2009</ref>.<br/><br/> |
| | | | |
| | [[File:Figure 10 roller press.jpg|center|300px|alt=Figure 10 roller press.jpg]] | | [[File:Figure 10 roller press.jpg|center|300px|alt=Figure 10 roller press.jpg]] |
| | | | |
| − | <p style="text-align: center"><span style="color: rgb(0, 0, 255)"><sub>Figure 11: roller presses<ref name="Eriksson 1990">Picture: Eriksson, S. and Prior, M. (1990): The briquetting of agricultural wastes for fuel, FAO Environment and Energy Paper 11, FAO of the UN, Rome, 1990</ref></sub></span><br/></p><br/>'''Agglomeration''' | + | <p style="text-align: center"><span style="color: rgb(0, 0, 255)"><sub>Figure 11: roller presses<ref name="Eriksson 1990">Picture: Eriksson, S. and Prior, M. (1990): The briquetting of agricultural wastes for fuel, FAO Environment and Energy Paper 11, FAO of the UN, Rome, 1990</ref></sub></span></p> |
| − | | + | === <br/>'''Agglomeration''' === |
| | <br/>Agglomeration is a method of increasing particle size by gluing powder particles together. Usually the equipment consists of a rotating volume that is filled with balls of varying sizes and fed with powder and often a binder. The rotation of the agglomerator results in centrifugal, gravitational and frictional forces from the smooth rolling balls. These forces, together with inertial forces, press the balls against the powder, helping them to stick together and grow. NL Agency<ref>NL Agency (2013): Charcoal Production from Alternative Feedstocks; final version 2013</ref> reports applied agglomeration technology in small-scale briquetting processes in several developing countries. The charcoal is milled to powder, binders are added, the components are mixed together, and the mix is then agglomerated. Agglomerated charcoal briquettes are produced using a motor-driven agglomerator, the typical nominal capacity of which is 25-50 kg/hour. Agglomerated charcoal briquettes are spherical and typically have diameters between 20-30 mm. The briquettes can be used for household cooking as well as for fuelling industrial furnaces. Agglomerated briquettes are said to be stronger than most other briquette types '''(Reference numbered as "5". It is missing and does not match order).'''<br/><br/> | | <br/>Agglomeration is a method of increasing particle size by gluing powder particles together. Usually the equipment consists of a rotating volume that is filled with balls of varying sizes and fed with powder and often a binder. The rotation of the agglomerator results in centrifugal, gravitational and frictional forces from the smooth rolling balls. These forces, together with inertial forces, press the balls against the powder, helping them to stick together and grow. NL Agency<ref>NL Agency (2013): Charcoal Production from Alternative Feedstocks; final version 2013</ref> reports applied agglomeration technology in small-scale briquetting processes in several developing countries. The charcoal is milled to powder, binders are added, the components are mixed together, and the mix is then agglomerated. Agglomerated charcoal briquettes are produced using a motor-driven agglomerator, the typical nominal capacity of which is 25-50 kg/hour. Agglomerated charcoal briquettes are spherical and typically have diameters between 20-30 mm. The briquettes can be used for household cooking as well as for fuelling industrial furnaces. Agglomerated briquettes are said to be stronger than most other briquette types '''(Reference numbered as "5". It is missing and does not match order).'''<br/><br/> |
| | + | |
| | | | |
| | {| border="0" align="center" cellspacing="0" cellpadding="0" style="width: 10px" | | {| border="0" align="center" cellspacing="0" cellpadding="0" style="width: 10px" |
| Line 108: |
Line 99: |
| | | | |
| | <p style="text-align: center"><span style="color: rgb(0, 0, 255)"><sub>Table 1: Comparision of different densification equipments<ref>Jaya Shankar Tumuluru et al. (2010): A Review on Biomass Densification Technologies for Energy Application; Idaho national laboratory; 2010</ref></sub></span><br/></p><br/>Problems arise often if the die has not been shaped correctly or if the feeding mechanism has not been sized for the material to be used. It is normal for machines made in Europe or North America to be designed to operate on wood wastes. The use of agroresidues normally de-rates the throughput and may require some modification to the feeder. Therefore, when searching for briquetting machines, best is finding machines which are already running with similar raw material and under similar conditions.<br/><br/>'''Further information:''' | | <p style="text-align: center"><span style="color: rgb(0, 0, 255)"><sub>Table 1: Comparision of different densification equipments<ref>Jaya Shankar Tumuluru et al. (2010): A Review on Biomass Densification Technologies for Energy Application; Idaho national laboratory; 2010</ref></sub></span><br/></p><br/>Problems arise often if the die has not been shaped correctly or if the feeding mechanism has not been sized for the material to be used. It is normal for machines made in Europe or North America to be designed to operate on wood wastes. The use of agroresidues normally de-rates the throughput and may require some modification to the feeder. Therefore, when searching for briquetting machines, best is finding machines which are already running with similar raw material and under similar conditions.<br/><br/>'''Further information:''' |
| − |
| |
| | *Bhattacharya, S.C.: biomass energy and densification: A Global Review with Emphasis on Developing Countries; Energy Program, Asian Institute of Technology; Thailand gives an overview on different technologies used for briquetting in many countries in Asia, South America and Africa. Link: [http://cenbio.iee.usp.br/download/documentos/apresentacoes/swedendensificationpaperfinal.pdf http://cenbio.iee.usp.br/download/documentos/apresentacoes/swedendensificationpaperfinal.pdf] | | *Bhattacharya, S.C.: biomass energy and densification: A Global Review with Emphasis on Developing Countries; Energy Program, Asian Institute of Technology; Thailand gives an overview on different technologies used for briquetting in many countries in Asia, South America and Africa. Link: [http://cenbio.iee.usp.br/download/documentos/apresentacoes/swedendensificationpaperfinal.pdf http://cenbio.iee.usp.br/download/documentos/apresentacoes/swedendensificationpaperfinal.pdf] |
| | *<br/> | | *<br/> |
| − | *When searching for “briquetting” in the internet a huge number of producers will appear. A list of mainly European briquetting machines sellers can be found under [http://www.tfz.bayern.de/mam/cms08/festbrennstoffe/dateien/pelletier_briketiertechologie.pdf http://www.tfz.bayern.de/mam/cms08/festbrennstoffe/dateien/pelletier_briketiertechologie.pdf].<br/><br/> | + | *When searching for “briquetting” in the internet a huge number of producers will appear. A list of mainly European briquetting machines sellers can be found under [http://www.tfz.bayern.de/mam/cms08/festbrennstoffe/dateien/pelletier_briketiertechologie.pdf http://www.tfz.bayern.de/mam/cms08/festbrennstoffe/dateien/pelletier_briketiertechologie.pdf]. |
| − | == Auxiliary equipment<br/> ==
| + | |
| | + | = Auxiliary Equipment<br/> = |
| | <br/>Only in few cases will the briquetting press be the only equipment needed to set up a briquetting plant. From the starting point, the complexity of briquetting plants increases up to the fully automated woodwaste briquetting plants in which the raw material is fed by a tractor into a hopper from where it is crushed, screened, stored, dryed, stored again, fed into the presses and transported to the product storage in fully automatic process, supervised by a couple of operators. Without going into details, the following text is a brief listing of a few common types of necessary auxiliary equipments and their applications which might have to be considered as also important economical factors:<br/> | | <br/>Only in few cases will the briquetting press be the only equipment needed to set up a briquetting plant. From the starting point, the complexity of briquetting plants increases up to the fully automated woodwaste briquetting plants in which the raw material is fed by a tractor into a hopper from where it is crushed, screened, stored, dryed, stored again, fed into the presses and transported to the product storage in fully automatic process, supervised by a couple of operators. Without going into details, the following text is a brief listing of a few common types of necessary auxiliary equipments and their applications which might have to be considered as also important economical factors:<br/> |
| | + | |
| | | | |
| | *Storage (rainy seasons, both the raw material and the product) | | *Storage (rainy seasons, both the raw material and the product) |
| Line 126: |
Line 118: |
| | [[File:Table 2 charcoal production chain.jpg|center|550px|alt=Table 2 charcoal production chain.jpg]] | | [[File:Table 2 charcoal production chain.jpg|center|550px|alt=Table 2 charcoal production chain.jpg]] |
| | | | |
| − | <p style="text-align: center"><span style="color: rgb(0, 0, 255)"><sub>Table 2: Charcoal production chain of selected feedstocks<ref name="NL 2013">NL Agency (2013): Charcoal Production from Alternative Feedstocks; final version 2013</ref></sub></span><br/></p><br/><br/> | + | <p style="text-align: center"><span style="color: rgb(0, 0, 255)"><sub>Table 2: Charcoal production chain of selected feedstocks<ref name="NL 2013">NL Agency (2013): Charcoal Production from Alternative Feedstocks; final version 2013</ref></sub></span><br/></p><br/><br/><br/> |
| | | | |
| | | | |
| Line 132: |
Line 124: |
| | <br/>The financial costs of briquetting are very dependent upon the nature of the project, in particular upon the raw material used and the plant location. They depend upon a number of operating costs, including labour, maintenance, power, raw material cost and transport etc. as well as of capital cost component. Whether or not briquetting is economic in any given location will depend critically upon how these unit costs relate to the price of the likely substitute fuels.<br/> | | <br/>The financial costs of briquetting are very dependent upon the nature of the project, in particular upon the raw material used and the plant location. They depend upon a number of operating costs, including labour, maintenance, power, raw material cost and transport etc. as well as of capital cost component. Whether or not briquetting is economic in any given location will depend critically upon how these unit costs relate to the price of the likely substitute fuels.<br/> |
| | | | |
| − | '''Capital costs'''<br/>
| |
| | | | |
| − | <br/> | + | == '''Capital costs'''<br/> == |
| | | | |
| | The capital costs of a plant are not always easy to establish on a consistent basis. In different circumstances there may be different conventions about what is included in capital cost: for example, do spare parts count for capital costs or operational cost? Is the plant a stand-alone operation or is it part of an existing agro plant and maybe existing buildings can be used? | | The capital costs of a plant are not always easy to establish on a consistent basis. In different circumstances there may be different conventions about what is included in capital cost: for example, do spare parts count for capital costs or operational cost? Is the plant a stand-alone operation or is it part of an existing agro plant and maybe existing buildings can be used? |
| Line 142: |
Line 133: |
| | <br/>Another important aspect of capital costs are the engineering and design standards of the plant. For example, it is likely that in a plant where little or no use is made of mechanical handling, there will be a need to have spacious buildings to avoid problems of dust and dangerous overcrowding. Briquetting machines which are squeezed into residue-producing plants to utilize existing buildings may naturally have lower capital costs than briquetting plants with firm floors, proper electrical fittings etc. | | <br/>Another important aspect of capital costs are the engineering and design standards of the plant. For example, it is likely that in a plant where little or no use is made of mechanical handling, there will be a need to have spacious buildings to avoid problems of dust and dangerous overcrowding. Briquetting machines which are squeezed into residue-producing plants to utilize existing buildings may naturally have lower capital costs than briquetting plants with firm floors, proper electrical fittings etc. |
| | | | |
| − | <br/>Apart of these direct production capital costs, in many countries additional costs have to be considered and can range widely from country to country. For example credit costs or custom duties on imported machines.<br/><br/> | + | <br/>Apart of these direct production capital costs, in many countries additional costs have to be considered and can range widely from country to country. For example credit costs or custom duties on imported machines. |
| − | | + | |
| − | '''Operating costs'''
| + | |
| | | | |
| | + | == '''Operating costs''' == |
| | <br/>The first obvious operating cost is the price to be paid for the raw material. This costs are very project and site-specific. The raw material might have a specific price when its use is competing with alternative uses. However, even if the residue is free, it is common for a transport cost to be incurred in bringing the residue to the briquetting plant. In the case of briquetting plants sited at the residue production point this is avoided but for other situations the transport cost may be a significant part of operational costs. These transport costs may be added into general labour costs if fulltime drivers are employed but certainly a more common situation is to hire appropriate transport for a given period of collecting the raw material. | | <br/>The first obvious operating cost is the price to be paid for the raw material. This costs are very project and site-specific. The raw material might have a specific price when its use is competing with alternative uses. However, even if the residue is free, it is common for a transport cost to be incurred in bringing the residue to the briquetting plant. In the case of briquetting plants sited at the residue production point this is avoided but for other situations the transport cost may be a significant part of operational costs. These transport costs may be added into general labour costs if fulltime drivers are employed but certainly a more common situation is to hire appropriate transport for a given period of collecting the raw material. |
| | | | |
| Line 155: |
Line 145: |
| | | | |
| | <br/>Other costs which might have to be considered when operating a briquetting plant are: taxes, insurance, consumables such as lubricating oil, packaging etc. | | <br/>Other costs which might have to be considered when operating a briquetting plant are: taxes, insurance, consumables such as lubricating oil, packaging etc. |
| | + | |
| | | | |
| | {| border="1" align="center" cellspacing="1" cellpadding="5" style="width: 600px" | | {| border="1" align="center" cellspacing="1" cellpadding="5" style="width: 600px" |
| Line 175: |
Line 166: |
| | *The economic viability of briquetting plants depends crucially on whether or not these factory costs are comparable or less than the prices of the main competitive fuel. | | *The economic viability of briquetting plants depends crucially on whether or not these factory costs are comparable or less than the prices of the main competitive fuel. |
| | |} | | |} |
| − |
| |
| | = Further Information = | | = Further Information = |
| | * | | * |
| − |
| |
| | = Reference = | | = Reference = |
| | <references /> | | <references /> |
| | | | |
| | + | [[Category:Charcoal]] |
| | + | [[Category:Biomass]] |
| | + | [[Category:Briquettes]] |
| | + | [[Category:Cooking_Energy_Compendium_(GIZ_HERA)]] |
| | [[Category:Cooking_Energy]] | | [[Category:Cooking_Energy]] |
| − | [[Category:Cooking_Energy_Compendium_(GIZ_HERA)]]
| |
| − | [[Category:Briquettes]]
| |
| − | [[Category:Biomass]]
| |
| − | [[Category:Charcoal]]
| |
The reduction of material density is the reason for undertaking briquetting as it determines both the savings in transport and handling costs and any improvement in combustion over the original material: the art of briquetting. This art essentially involves two parts: the compaction under pressure of loose material to reduce its volume and to agglomerate the material so that the product remains in the compressed state. Later effect, the cohesion of the particles, is based on three main mechanisms[2]:
is necessary to prevent the compressed material from springing back and eventually returning to its original form. This agent can either be added to the process or, when compressing ligneous material, be part of the material itself in form of lignin. Ligning is a constituent in most agricultural residues. It can be defined as the thermo plastic polymer, which begins to soften at temperatures above 100°C and is flowing at higher temperatures. The softening of lignin and its subsequent cooling while the material is still under pressure is the key factor in high pressure briquetting. It is a physic-chemical process related largely to the temperature reached in the briquetting process and the amount of lignin in the original material. The temperature in many machines is closely related to the pressure though in some, external heat is applied.
must be added to agglomerate the compressed material. The second way of classifying follows
while briquetting: high, medium or low pressure. For a rough distinction the following numbers might be adopted:
Usually high pressure processes will release sufficient lignin to agglomerate the briquette. Medium pressure machines may or may not require binders, depending upon the raw material whilst low-pressure machines invariably require binders. Such external binders might be: starch, clay, molasses or wood tar etc.. All briquettes using inherent binders (lignin) or external hydrophilic binders (starch, molasses, gum, clay) are not waterproof and will disintegrate when they come into contact with water or stored under humid conditions.
But, during the carbonization process, the biomass is losing its lignin content and thereby an important binder for briquetting. Charcoal is a material totally lacking plasticity and hence needs addition of a sticking or agglomerating material to enable a briquette to be formed. The binder should preferably be combustible, though a non-combustible binder effective at low concentrations can be suitable.
Industrial methods of briquetting date back to the second part the the 19th century. Since then there has been widespread use of briquettes made from brown coal, peat and coal fines. The briquetting of organic materials requires higher pressure as additional force is needed to overcome the natural springiness of these materials. Essentially, this involves the destruction of the cell walls through some combination of pressure and heat. The following overview presents the most common machines used for briquetting biomass.
In piston presses, pressure is applied discontinuously by the action of a piston on material packed into a cylinder. They may have a mechanical coupling and fly wheel or utilize hydraulic action on the piston. The incoming raw material is pressed against the compacted material inside the pressing tube and leaves the die in the rhythm of the piston action. Through pressure and friction forces inside the pressing tube, the material is strongly heated and cooling mechanisms might be considered. To produce briquettes with high density (up to 1.25 g/m3) the raw material eventually needs to be milled (less than 10 mm) and dried (<15% of water content) before briquetting. The capacity of piston presses depends both on the diameter of the die and the pretreatment of the raw material.
The capacity spectrum of piston presses range from only 25 up to 1800 kg/hr. Their typical specific energy use requires between 50 and 70 kWh/t.[5]
The aim of compaction using an extruder is to bring the smaller particles closer so that the forces acting between them become stronger, providing more strength the densified bulk material. During extrusion, the material moves from the feed port, with the help of a rotating screw, through the barrel and against a die, resulting in significant pressure gradient and friction due to biomass shearing. The combined effects of wall friction at the barrel, internal friction in the material, and high rotational speed of the screw, increase the temperature in the closed system and heat the biomass. This heated biomass is forced through the extrusion die to form the briquettes with the required shape. If the heat generated within the system is not sufficient for the material to reach a pseudo-plastic state for smooth extrusion, external heat might be added. In principle, screw presses reach slightly higher compaction but lower capacity (tons per hour) when compared to piston presses.
Pellets are the result of a process which is closely related to the briquetting processes described above. The main difference is that the dies have smaller diameters and each machine has a number of dies arranged as holes bored in a thick steel disk or ring. The material is forced into the dies by means of rollers moving over the surface on which the raw material is distributed. The pressure is built up by the compression of this layer of material as the roller moves perpendicular to the centerline of the dies. Thus the main force applied results in shear stresses in the material. The pellets will still be hot when leaving the dies, where they are cut to lengths normally about one or two times the diameter. Successful operation demands that a rather elaborate cooling system is arranged after the densification process.
There are two main types of pellet presses: flat and ring types. The flat die type has a circular perforated disk on which rollers rotate whereas the ring die press features a rotating perforated ring on which rollers press on the inner perimeter. The output of pellet presses range from about 200 kg/hr up to 8 ton/hr. Their specific energy consumption is reported to be around 1,5% of the energy content of the final peletts[6].
For sure the simplest way to produce small briquettes is hand-shaped briquettes: a slurry of biomass in water is left soaking for some days to enhance binding properties. The pulp is either squeezed by hand or pressed into a mould e.g. an ice-cube tray. Rearranged fibres assisted by a binder like paper pulp keep the briquette in shape during drying and use. A part of hand-shaped briquettes there are plenty of small manual briquetting machines which were developed by different producers and scientists all over the world. A very good overview on existing low cost briquetting machines, from perforated bottles to wooden lever presses, can be found in the manual “Micro-gasification: Cooking with gas from biomass” by Christa Roth (2011)[9].
However, it remains unclear, whether any manual densification process can ever be commercially viable even in circumstances where labour is very cheap. Considering their very low throughput, such techniques often require almost as much capital investment as the mechanical processes. The savings achieved are essentially a labour for electricity substitution rather than labour for capital.
Densification of biomass using roller presses works on the principle of pressure and agglomeration, where pressure is applied between two counter-rotating rolls. Ground biomass, when forced through the gap between the two rollers, is pressed into a die, or small pockets, forming the densified product. Roller presses are considered the world standard technology to produce ovoid (pillow-shaped) charcoal briquettes from a variety of biomass types. In a roller press, a mixture of charcoal and binder is fed to the tangential pockets of two rollers to produce briquettes. The smooth production of charcoal briquettes using this technology requires high-quality rollers with smooth surfaces on which the briquettes are shaped. The type of roller determines the shape of the briquettes. Currently, roll presses available in developed countries have production capacities of 1 t/hr and more. The 1 tonne/hr capacity press with controlled feeding device costs about $ 320,000. Much cheaper roller-type charcoal briquetting machines can be sourced in India and China: Seboka (2009) indicates that a roller press with a capacity of 1.5 tonne/hr costing $ 19,000 can be found in India[11].
As seen above, there are different technologies to produce densified biomass briquettes. The following table 1 summarizes their main characteristics. For the right choice of an adapted machine, two main issues should be considered:
Problems arise often if the die has not been shaped correctly or if the feeding mechanism has not been sized for the material to be used. It is normal for machines made in Europe or North America to be designed to operate on wood wastes. The use of agroresidues normally de-rates the throughput and may require some modification to the feeder. Therefore, when searching for briquetting machines, best is finding machines which are already running with similar raw material and under similar conditions.
To demonstrate the necessary steps for charcoal briquetting of different raw materials, NL Agency (2013) created table 2 below. Charcoal dust has the shortest supply chain, only a collection and briquetting step is needed to produce charcoal briquettes. On the contrary, the charcoal production chain based on the growing of dedicated energy crops involves a considerable number of steps. Each step in the supply chain represents efforts, money and possible complications, and this indicator shows that charcoal dust and processing residues have a logistic advantage over other types of feedstocks.
The capital costs of a plant are not always easy to establish on a consistent basis. In different circumstances there may be different conventions about what is included in capital cost: for example, do spare parts count for capital costs or operational cost? Is the plant a stand-alone operation or is it part of an existing agro plant and maybe existing buildings can be used?
