Investigating calorific values and emissions of loose biomass feedstock in South Africa
- Authors: Shuma, Mikateko R.
- Date: 2018
- Subjects: Biomass chemicals - South Africa , Biomass energy - South Africa
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/285952 , uj:30933
- Description: M.Phil. (Mechanical Engineering) , Abstract: Biomass is a renewable energy source that contributes approximately 12% towards world primary energy needs. However, available natural by-products from agricultural and forestry activities mostly end up in landfills. This could be harnessed for sustainable energy supply with minimal impact on global warming and climate change. Reliance on fossil fuels as a source of energy has negatively impacted the ozone layer leading to increased global warming and climate change. The high level of agricultural and forestry activities in South Africa affords an opportunity to develop a biomass based energy stream. In South Africa, rural communities which live off the electricity grid depend mainly on round wood and animal waste for heating and cooking. To reduce demand on round wood, other sources of biomass that are available from agriculture and forestry activities can be harnessed. These agricultural and forestry wastes include elephant grass, Mopani leaves, saw dust, peanut stalks and shells, maize stalks and leaves and coffee husks. The challenge in using these loose biomass sources is their low energy and physical density. This is usually overcome by using densification technologies. The main aim of this work was to investigate the potential to harness renewable energy from loose biomass residues for a specific village (Maphophe) in the Limpopo Province of South Africa. The loose biomass waste available at this location was identified, samples were collected and characterised in terms of density, moisture content, energy content, compatibility, combustion behaviour and emissions. Based on these parameters, a selection metric was developed to select the best candidates for biomass briquetting. The selected candidate materials were then used to produce briquettes. Optimum pressure and binders for the production of the briquettes was determined. The produced briquettes were also characterised for energy content, combustion behaviour and emissions. The results of this investigation showed that it is possible for off grid communities to harness energy for domestic use from the agricultural and forestry residues that are produced perennially in the localities...
- Full Text:
- Authors: Shuma, Mikateko R.
- Date: 2018
- Subjects: Biomass chemicals - South Africa , Biomass energy - South Africa
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/285952 , uj:30933
- Description: M.Phil. (Mechanical Engineering) , Abstract: Biomass is a renewable energy source that contributes approximately 12% towards world primary energy needs. However, available natural by-products from agricultural and forestry activities mostly end up in landfills. This could be harnessed for sustainable energy supply with minimal impact on global warming and climate change. Reliance on fossil fuels as a source of energy has negatively impacted the ozone layer leading to increased global warming and climate change. The high level of agricultural and forestry activities in South Africa affords an opportunity to develop a biomass based energy stream. In South Africa, rural communities which live off the electricity grid depend mainly on round wood and animal waste for heating and cooking. To reduce demand on round wood, other sources of biomass that are available from agriculture and forestry activities can be harnessed. These agricultural and forestry wastes include elephant grass, Mopani leaves, saw dust, peanut stalks and shells, maize stalks and leaves and coffee husks. The challenge in using these loose biomass sources is their low energy and physical density. This is usually overcome by using densification technologies. The main aim of this work was to investigate the potential to harness renewable energy from loose biomass residues for a specific village (Maphophe) in the Limpopo Province of South Africa. The loose biomass waste available at this location was identified, samples were collected and characterised in terms of density, moisture content, energy content, compatibility, combustion behaviour and emissions. Based on these parameters, a selection metric was developed to select the best candidates for biomass briquetting. The selected candidate materials were then used to produce briquettes. Optimum pressure and binders for the production of the briquettes was determined. The produced briquettes were also characterised for energy content, combustion behaviour and emissions. The results of this investigation showed that it is possible for off grid communities to harness energy for domestic use from the agricultural and forestry residues that are produced perennially in the localities...
- Full Text:
Optimization of branched piece reinforcements for large diameter dam pipes in South Africa
- Authors: Naicker, Ashley
- Date: 2018
- Subjects: Pipe joints , Strains and stresses , Water-supply engineering , Dams - Design and construction
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/284200 , uj:30689
- Description: M.Tech. (Mechanical Engineering) , Abstract: This dissertation reports on the development of unreinforced and reinforced (with 3 wye branch piece reinforcements) T-section experimental prototypes that were used to validate numerical models (using 2D & 3D Finite Element Method (FEM)). The design of 3 wye branch piece reinforcements according to the American Water Works Association (AWWA) M11 method is accomplished by interpolating the reinforcement profiles from graphs. The methodology used to generate these graphs are not communicated. Rather, more emphasis is placed on the design of the reinforcement rather than showing the optimized performance of the pipe due to the reinforcement. Upon introducing a hole in the barrel pipe for insertion of the branch pipe, there are changes in local geometrical parameters and hence operational conditions are significant to the structural and mechanical performance of the T-section pipe. Pipe profiling severely compromises the localized performance of the T-section pipe especially at the junction points. The main objective was to develop optimized branched piece reinforcement profiles that are less conservative when compared to the AWWA technique without compromising on the performance of the T-section pipe. FEM analysis executed for both the reinforced and unreinforced T-section pipes provided a cost effective tool in identifying and suppressing all prevalent detrimental factors when generating the most optimal profile. Experimental tests on one-to-one scale specimens were carried out by mounting strain gauges on the reinforced and unreinforced T-section pipes which captured induced strains as the pressure was gradually increased to the point of bursting. Data was recorded accordingly. The pipe burst at the radial junction and area of incidents were consistent with the FEM model predictions, that is, the zone requiring reinforcing. The data from the experimental prototypes and numerical models correlated with a great degree of accuracy. Viable solutions to branched piece reinforcements were generated based on validated numerical models. Optimized branched piece reinforcements developed from numerical models are safe for use in pipeline infrastructure.
- Full Text:
- Authors: Naicker, Ashley
- Date: 2018
- Subjects: Pipe joints , Strains and stresses , Water-supply engineering , Dams - Design and construction
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/284200 , uj:30689
- Description: M.Tech. (Mechanical Engineering) , Abstract: This dissertation reports on the development of unreinforced and reinforced (with 3 wye branch piece reinforcements) T-section experimental prototypes that were used to validate numerical models (using 2D & 3D Finite Element Method (FEM)). The design of 3 wye branch piece reinforcements according to the American Water Works Association (AWWA) M11 method is accomplished by interpolating the reinforcement profiles from graphs. The methodology used to generate these graphs are not communicated. Rather, more emphasis is placed on the design of the reinforcement rather than showing the optimized performance of the pipe due to the reinforcement. Upon introducing a hole in the barrel pipe for insertion of the branch pipe, there are changes in local geometrical parameters and hence operational conditions are significant to the structural and mechanical performance of the T-section pipe. Pipe profiling severely compromises the localized performance of the T-section pipe especially at the junction points. The main objective was to develop optimized branched piece reinforcement profiles that are less conservative when compared to the AWWA technique without compromising on the performance of the T-section pipe. FEM analysis executed for both the reinforced and unreinforced T-section pipes provided a cost effective tool in identifying and suppressing all prevalent detrimental factors when generating the most optimal profile. Experimental tests on one-to-one scale specimens were carried out by mounting strain gauges on the reinforced and unreinforced T-section pipes which captured induced strains as the pressure was gradually increased to the point of bursting. Data was recorded accordingly. The pipe burst at the radial junction and area of incidents were consistent with the FEM model predictions, that is, the zone requiring reinforcing. The data from the experimental prototypes and numerical models correlated with a great degree of accuracy. Viable solutions to branched piece reinforcements were generated based on validated numerical models. Optimized branched piece reinforcements developed from numerical models are safe for use in pipeline infrastructure.
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Green machining of titanium based powder compacts
- Authors: Tambani, Mulalo Trace
- Date: 2019
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/399067 , uj:33249
- Description:
Abstract : This project investigated the drilling of Titanium (Ti) and Ti6Al4V powder compacts made using uni‐axial powder compaction. The aim was to determine whether green machining can improve the machinability of Ti‐based alloys. The objective of the study was therefore to understand the interaction between the properties of the compacted powders (green compacts) and the drilling parameters with a view of providing some understanding of the green machinability. Green machining needs powder compacts with sufficient strength to withstand the clamping and machining forces. Two approaches were used to enhance the (green) strength of the powder compacts in this study: changing the binder used during powder compaction and using different pressures (430 and 600 MPa) to compact the powders. An unconventional polymeric binder based on poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA), was investigated as a green strength enhancer. The investigation involved understanding the thermal behavior of the blended polymers using thermogravimetric analysis (TGA) and swelling tests, molecular bonding using Fourier Transform Infrared (FTIR) spectroscopy, and finally, optimizing the quantity of binder by determining the green strength of powder compacts using the Brazilian Disk test. Green compacts for drilling experiments were produced using the optimized polymeric binder. For comparison purposes, compacts made using conventional Acrawax (at 0.7wt. %) as a binder were also produced. The green compacts were characterized for density, using mass and volume, and strength using the Brazilian Disk test. Some of the compacts with polymeric binder were subjected to a curing treatment in order to increase their strength. The compacts were then subjected to drilling experiments. Two types of twist drills, the cheaper uncoated high speed steel (HSS‐Co), which cannot machine wrought Ti‐based components, and the more expensive TiAlN‐coated solid tungsten carbide‐cobalt (WC‐Co), which is the main machining tool for Ti‐based components, were used. The drilling speed and feed rates were varied. Machinability was characterized using the size of breakouts, the iv surface roughness of the drilled holes, and for one set of drilling parameters, and the drilling/cutting force. Analysis of the polymeric binder indicated it possessed the ability to form a network structure of higher strength when cured (heated to an optimized temperature of 200 ⁰C and soaked for an optimized duration of 1 hour). When used as a binder, the polymeric binder considerably increased the green strength of Ti powder compacts compared to when Acrawax C was used. This was attributed to the curing that was observed to have occurred in the polymeric binder. For this reason, its use was extended to the Ti6Al4V powder compacts. The drilling tests showed that all the powder compacts investigated could be clamped and machined, regardless of their green strength and type of tool used. This was an important observation, because using the cheaper HSS‐Co tools has potential to lower the cost for machining Ti‐based alloys. However, except for the observation that Acrawax imparted better machinability than the polymeric binder on Ti compacts did, the results did also indicate that generalizations could not be made regarding the machining responses of the powder compacts because the behaviour was a function of the type of powder, type of binder, and tool used. For example, using Acrawax as a binder for Ti powders, increasing feed rate and cutting speed reduced machinability (increased breakout sizes) for samples machined using HSS‐Co but increasing speed enhanced machinability (decreased breakout sizes) for machining with the carbide twist drills. On the other hand, regardless of the tool used, the breakout size in Ti powder compacts pressed with polymeric binder increased with speed and feed rate. In the case of Ti6Al4V, compacts obtained using the polymeric binder, breakout size increased with increasing cutting speed and reducing feed rate (i.e. a lower feed rate increased the size of the breakout). In the same vein, this research found that green strength was not a good indicator of machinability. For Ti compacts, the machinability of Acrawax and uncured polymeric binder compacts was improved by a higher green strength. However, for the cured polymeric binder, a lower green strength conferred better machinability. For Ti6Al4V powder v compacts, different green strengths gave similar breakout sizes and/or higher green strengths caused larger breakouts. Also, while the cutting force increased with green strength (Acrawax
- Full Text:
- Authors: Tambani, Mulalo Trace
- Date: 2019
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/399067 , uj:33249
- Description:
Abstract : This project investigated the drilling of Titanium (Ti) and Ti6Al4V powder compacts made using uni‐axial powder compaction. The aim was to determine whether green machining can improve the machinability of Ti‐based alloys. The objective of the study was therefore to understand the interaction between the properties of the compacted powders (green compacts) and the drilling parameters with a view of providing some understanding of the green machinability. Green machining needs powder compacts with sufficient strength to withstand the clamping and machining forces. Two approaches were used to enhance the (green) strength of the powder compacts in this study: changing the binder used during powder compaction and using different pressures (430 and 600 MPa) to compact the powders. An unconventional polymeric binder based on poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA), was investigated as a green strength enhancer. The investigation involved understanding the thermal behavior of the blended polymers using thermogravimetric analysis (TGA) and swelling tests, molecular bonding using Fourier Transform Infrared (FTIR) spectroscopy, and finally, optimizing the quantity of binder by determining the green strength of powder compacts using the Brazilian Disk test. Green compacts for drilling experiments were produced using the optimized polymeric binder. For comparison purposes, compacts made using conventional Acrawax (at 0.7wt. %) as a binder were also produced. The green compacts were characterized for density, using mass and volume, and strength using the Brazilian Disk test. Some of the compacts with polymeric binder were subjected to a curing treatment in order to increase their strength. The compacts were then subjected to drilling experiments. Two types of twist drills, the cheaper uncoated high speed steel (HSS‐Co), which cannot machine wrought Ti‐based components, and the more expensive TiAlN‐coated solid tungsten carbide‐cobalt (WC‐Co), which is the main machining tool for Ti‐based components, were used. The drilling speed and feed rates were varied. Machinability was characterized using the size of breakouts, the iv surface roughness of the drilled holes, and for one set of drilling parameters, and the drilling/cutting force. Analysis of the polymeric binder indicated it possessed the ability to form a network structure of higher strength when cured (heated to an optimized temperature of 200 ⁰C and soaked for an optimized duration of 1 hour). When used as a binder, the polymeric binder considerably increased the green strength of Ti powder compacts compared to when Acrawax C was used. This was attributed to the curing that was observed to have occurred in the polymeric binder. For this reason, its use was extended to the Ti6Al4V powder compacts. The drilling tests showed that all the powder compacts investigated could be clamped and machined, regardless of their green strength and type of tool used. This was an important observation, because using the cheaper HSS‐Co tools has potential to lower the cost for machining Ti‐based alloys. However, except for the observation that Acrawax imparted better machinability than the polymeric binder on Ti compacts did, the results did also indicate that generalizations could not be made regarding the machining responses of the powder compacts because the behaviour was a function of the type of powder, type of binder, and tool used. For example, using Acrawax as a binder for Ti powders, increasing feed rate and cutting speed reduced machinability (increased breakout sizes) for samples machined using HSS‐Co but increasing speed enhanced machinability (decreased breakout sizes) for machining with the carbide twist drills. On the other hand, regardless of the tool used, the breakout size in Ti powder compacts pressed with polymeric binder increased with speed and feed rate. In the case of Ti6Al4V, compacts obtained using the polymeric binder, breakout size increased with increasing cutting speed and reducing feed rate (i.e. a lower feed rate increased the size of the breakout). In the same vein, this research found that green strength was not a good indicator of machinability. For Ti compacts, the machinability of Acrawax and uncured polymeric binder compacts was improved by a higher green strength. However, for the cured polymeric binder, a lower green strength conferred better machinability. For Ti6Al4V powder v compacts, different green strengths gave similar breakout sizes and/or higher green strengths caused larger breakouts. Also, while the cutting force increased with green strength (Acrawax
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Determining the optimum welding material of 3CR12 stainless steel
- Molabe, Ramaisele Mapule Constance
- Authors: Molabe, Ramaisele Mapule Constance
- Date: 2018
- Subjects: Stainless steel - Welding
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/280493 , uj:30141
- Description: M.Ing. (Mechanical Engineering) , Abstract: This research study called for investigation on a filler metal, which would yield improved benefits, when welding 3CR12 stainless steel. The compared filler metals included AISI 308L, 309L and 316L. The study was performed by welding 2mm thick 3CR12 test plates – using the TIG welding process by testing of welded material’s behaviour by tensile testing, microstructural analysis, and hardness testing. The experimental set-up and procedure were based on the findings from previous studies and recommendations. Defect-free welds were achieved on all the welded samples. The parent metal showed ferrite and pearlite microstructure; while the Heat Affected Zone (HAZ) contained coarse grains, as compared with Base Material (BM) and the fusion zone, it had more ferrite and less pearlite microstructure. The coarse grains were due to the higher heat input in this region. The fusion zone consisted of austenite, ferrite and martensite laths; this was probably due to the dissimilar weld joints of the austenitic filler metal and the ferritic base metal. The fracture of the tensile specimens was consistently located in the parent-metal zone, suggesting that the strength of the welded joint is greater than that of the parent metal. The ultimate tensile strength of all the samples is above the minimum (450MPa) ultimate tensile strength of the 3CR12. Owing to their fine grains at the weld joint, the welded joints displayed a higher tensile strength than that of the parent metal. The microstructural analysis indicated that the 309L sample has larger grains on the HAZ than on the PM and fusion zone; this implies that the 309L is more susceptible to heat in the HAZ when compared with the 308L and 316L samples. The maximum hardness was found to be in the fusion zone in all the welded samples; as a result of the fine solidification structure. The hardness values for 309L samples are lower than those of 308L and 316L samples. The root of the weld was weaker than the weld cap for all the filler metals tested. Filler metal 308L was found to be the optimum welding material for 3CR12; and it can be recommended for producing welds with high quality and strong integrity.
- Full Text:
- Authors: Molabe, Ramaisele Mapule Constance
- Date: 2018
- Subjects: Stainless steel - Welding
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/280493 , uj:30141
- Description: M.Ing. (Mechanical Engineering) , Abstract: This research study called for investigation on a filler metal, which would yield improved benefits, when welding 3CR12 stainless steel. The compared filler metals included AISI 308L, 309L and 316L. The study was performed by welding 2mm thick 3CR12 test plates – using the TIG welding process by testing of welded material’s behaviour by tensile testing, microstructural analysis, and hardness testing. The experimental set-up and procedure were based on the findings from previous studies and recommendations. Defect-free welds were achieved on all the welded samples. The parent metal showed ferrite and pearlite microstructure; while the Heat Affected Zone (HAZ) contained coarse grains, as compared with Base Material (BM) and the fusion zone, it had more ferrite and less pearlite microstructure. The coarse grains were due to the higher heat input in this region. The fusion zone consisted of austenite, ferrite and martensite laths; this was probably due to the dissimilar weld joints of the austenitic filler metal and the ferritic base metal. The fracture of the tensile specimens was consistently located in the parent-metal zone, suggesting that the strength of the welded joint is greater than that of the parent metal. The ultimate tensile strength of all the samples is above the minimum (450MPa) ultimate tensile strength of the 3CR12. Owing to their fine grains at the weld joint, the welded joints displayed a higher tensile strength than that of the parent metal. The microstructural analysis indicated that the 309L sample has larger grains on the HAZ than on the PM and fusion zone; this implies that the 309L is more susceptible to heat in the HAZ when compared with the 308L and 316L samples. The maximum hardness was found to be in the fusion zone in all the welded samples; as a result of the fine solidification structure. The hardness values for 309L samples are lower than those of 308L and 316L samples. The root of the weld was weaker than the weld cap for all the filler metals tested. Filler metal 308L was found to be the optimum welding material for 3CR12; and it can be recommended for producing welds with high quality and strong integrity.
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Potential for producing sustainable energy from bio-waste through thermal decomposition
- Authors: Manala, Cecil Khosi
- Date: 2017
- Subjects: Waste products as fuel , Refuse and refuse disposal , Biomass energy , Decomposition (Chemistry)
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/280125 , uj:30095
- Description: M.Ing. (Mechanical Engineering) , Abstract: Energy in its different forms is an important asset to man‟s day-to-day activities from general house hold applications such as cooking and heating to large scale industrial applications such as power generation. However, the current reliance on fossil fuel based energy has become a central concern with respect to sustainable development. Fossil fuels are associated with greenhouse gas emissions and global warming which have been attributed to the dramatic weather and climate change patterns on the planet today posing significant threat to life e. There is, therefore, a need to find more sustainable sources of energy for the planet. Biomass based energy has been used by humanity as a primary source of energy long before the episode of fossil fuel usage. Harnessing of this form of energy has become of overwhelming interest largely due to global warming. It has also been realized that producing renewable energy locally can offer a viable alternative, and facilitate socio-economic development in communities as evidenced by several sustainable energy production projects around South Africa. Biomass contributes 14% of the World‟s primary energy supply. About 75% of its usage is in developing countries. In this work, the organic fraction of municipal solid waste (OFMSW) was quantified at a landfill site in Johannesburg. This was part of a wider project to produce biogas from municipal waste. The potential of that waste to produce syngas by thermal decompositions needs to be investigated as an alternative to anaerobic bio digestion. Furthermore, a bamboo species known as bambusa lacooa, which is currently being introduced for mine dumps rehabilitation in South Africa, was identified as a potential syngas production feedstock. If bamboo based mine dump rehabilitation succeeds, the economic value of the then widely available bamboo needs to be investigated. Production of syngas by pyrolysis becomes one such economic value chain. The aim of this work was therefore to investigate the optimum production of syngas from OFMSW and bamboo by pyrolysis. Specimens of these materials were prepared for thermal decomposition. Bamboo was categorised into wet and dry bamboo and dried in the sun for a period of 14 days. OFMSW made up of mixed food waste was collected from the waste dump landfill site and dried in the sun for a period of 24 hours. The candidate bio-waste materials were subjected to thermal decomposition in a specially designed pyrolysis reactor. Fumes produced during the thermal decomposition were collected at 100˚C temperature intervals from 0 ˚C to 700 ˚C. Dry bamboo produced the highest yield quality of syngas (24% - 23% quality) between 200 ˚C and 400 ˚C. Wet bamboo produced lower syngas yield quality than dry bamboo. The...
- Full Text:
- Authors: Manala, Cecil Khosi
- Date: 2017
- Subjects: Waste products as fuel , Refuse and refuse disposal , Biomass energy , Decomposition (Chemistry)
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/280125 , uj:30095
- Description: M.Ing. (Mechanical Engineering) , Abstract: Energy in its different forms is an important asset to man‟s day-to-day activities from general house hold applications such as cooking and heating to large scale industrial applications such as power generation. However, the current reliance on fossil fuel based energy has become a central concern with respect to sustainable development. Fossil fuels are associated with greenhouse gas emissions and global warming which have been attributed to the dramatic weather and climate change patterns on the planet today posing significant threat to life e. There is, therefore, a need to find more sustainable sources of energy for the planet. Biomass based energy has been used by humanity as a primary source of energy long before the episode of fossil fuel usage. Harnessing of this form of energy has become of overwhelming interest largely due to global warming. It has also been realized that producing renewable energy locally can offer a viable alternative, and facilitate socio-economic development in communities as evidenced by several sustainable energy production projects around South Africa. Biomass contributes 14% of the World‟s primary energy supply. About 75% of its usage is in developing countries. In this work, the organic fraction of municipal solid waste (OFMSW) was quantified at a landfill site in Johannesburg. This was part of a wider project to produce biogas from municipal waste. The potential of that waste to produce syngas by thermal decompositions needs to be investigated as an alternative to anaerobic bio digestion. Furthermore, a bamboo species known as bambusa lacooa, which is currently being introduced for mine dumps rehabilitation in South Africa, was identified as a potential syngas production feedstock. If bamboo based mine dump rehabilitation succeeds, the economic value of the then widely available bamboo needs to be investigated. Production of syngas by pyrolysis becomes one such economic value chain. The aim of this work was therefore to investigate the optimum production of syngas from OFMSW and bamboo by pyrolysis. Specimens of these materials were prepared for thermal decomposition. Bamboo was categorised into wet and dry bamboo and dried in the sun for a period of 14 days. OFMSW made up of mixed food waste was collected from the waste dump landfill site and dried in the sun for a period of 24 hours. The candidate bio-waste materials were subjected to thermal decomposition in a specially designed pyrolysis reactor. Fumes produced during the thermal decomposition were collected at 100˚C temperature intervals from 0 ˚C to 700 ˚C. Dry bamboo produced the highest yield quality of syngas (24% - 23% quality) between 200 ˚C and 400 ˚C. Wet bamboo produced lower syngas yield quality than dry bamboo. The...
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