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Fundamental Study of two Selected Tropical Biomasses for Energy: coconut and cashew nut shells
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

 Cashew nut and coconut shells are two potential renewable and environmentally friendly energy sources that are commonly found as agro-industrial wastes in tropical countries. Despite this fact, they are not yet widely studied as such. Given this lack of specific technical and reliable data, technologies for their conversion into energy cannot be designed with confidence as it happens with other commonly studied biomass feedstock. Thus, the need to generate these data guided this research in order to provide technical information for the designing of appropriate thermochemical conversion technologies for energy generation, particularly, in remote areas, where electricity grid is neither a feasible nor an affordable solution.Among thermochemical processes, pyrolysis plays a key role as it is found in both combustion and gasification at their earlier stages. In both technologies, pyrolysis products are generated and later submitted to further transformations according to the process in use.Hence, pyrolysis was selected for thermal characterisation of cashew nut and coconut shells. The main characteristics envisaged are i) pyrolysis profiles; ii) global, semi-global and individual kinetics; iii) pyrolysis global and individual yields; iv) modelled pyrolysis yields at high heating rates; and, v)char combustion kinetics and reactivity. The main technique used for experimental data generation is thermogravimetry and FTIR spectroscopy. Data experimentally generated from TG and TG-FTIR experiments were processed through different methods and codes, such as the Coats and Redfern model-fitting method, the modelfree methods of Ozawa-Flynn-Wall, Friedman and ASTM E698, for semi-global and global kinetics; DAEM and FG-Biomass were used for pyrolysis individual kinetics and yields determination. Proximate and ultimate analyses were performed as well.The study revealed peculiar characteristics compared to the commonly known lignocellulosic biomass. The volatiles content was above 66%w/w; hemicelluloses DTG peak did not overlap with the cellulose peak; the global pyrolysis activation energies were around 200 and 120 kJ/mol for coconut and cashew nut shells, respectively. Hemicelluloses and cellulose showed varying activation energies as 130-216 and 155-208 kJ/mol, respectively. Char combustion showed two steps with activation energies of 135 and 121 kJ/mol (cashew nut shells); 105 and 190kJ/mol (coconut shells). Individual yields and kinetics were determined for 17 compounds, including tars. These data are of key importance for modelling and the consequent data generation for the designing of appropriate thermochemical energy for these biomasses.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , xi, 71 p.
Keyword [en]
Cashew nut shells, coconut shells, biomass, thermogravimetry, pyrolysis, kinetics, combustion
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-9138ISBN: 978-91-7415-079-7 (print)OAI: oai:DiVA.org:kth-9138DiVA: diva2:25243
Public defence
2008-09-30, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100914Available from: 2008-09-24 Created: 2008-09-24 Last updated: 2010-09-14Bibliographically approved
List of papers
1. Cashew Nut Shells Pyrolysis: Individual Gas Evolution Rates and Yields
Open this publication in new window or tab >>Cashew Nut Shells Pyrolysis: Individual Gas Evolution Rates and Yields
2007 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 21, no 4, 2357-2362 p.Article in journal (Refereed) Published
Abstract [en]

Cashew nut shells are one type of the most abundant biomass tropical wastes, which can be used for energy generation. However, there is lack of data for the thermal conversion process of cashew nut shells such as pyrolysis individual gas products, yields, and reaction kinetics. In this research work, the pyrolysis processes of cashew nut shells at low heating rates (10, 30, and 100 K/min) were studied. Thermogravimetric analyzer coupled with a Fourier transform infrared spectrometer (TG-FTIR) was used. The pyrolysis product yields obtained were compared with the available data in the literature for wood and Miscanthus Giganteus. It was found that cashew nut shells have tars and volatiles at levels equivalent to those of wood pellets, both above the tar and volatile content of M. Giganteus. Further, kinetic parameters were obtained from the TG-FTIR results using an approach based on parallel independent first-order reactions with a Gaussian distribution of activation energies and following the Tmax method. The data obtained through this approach included the identification, kinetics, and yield of each gas product precursor. These results are then used as input files for a distributed activation energy model (DAEM) for biomass pyrolysis, based on a functional group analysis, which still does not include the devolatilization, cross-linking competitive reactions. The predicted evaluation data from this model were found to generally agree with that from TG-FTIR analysis. However, the model still demands improvement to accommodate secondary and cross-linking competitive reactions.

Keyword
Activation energy, Crosslinking, Fourier transform infrared spectroscopy, Gaussian distribution, Hardwoods, Hulls (seed coverings), Mathematical models, Thermogravimetric analysis
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-9119 (URN)10.1021/ef0604792 (DOI)000248085100068 ()
Note
QC 20100902Available from: 2008-09-23 Created: 2008-09-20 Last updated: 2017-12-13Bibliographically approved
2. Pyrolysis characteristics and global kinetics of coconut and cashew nut shells
Open this publication in new window or tab >>Pyrolysis characteristics and global kinetics of coconut and cashew nut shells
2006 (English)In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 87, no 6, 523-530 p.Article in journal (Refereed) Published
Abstract [en]

Coconut and cashew nut shells are two typical biomass wastes abundant in most of the tropical countries. However, despite their enormous potential as energy sources, they are hardly studied and their thermal characteristics are still not well known. In this study, both biomasses are thermally degraded through thermogravimetry and their characteristics such as devolatilisation profiles and kinetics are analyzed, from 250 to 900 °C, in an inert atmosphere, at two different heating rates, and compared with wood pellets. The results show that their pyrolysis profiles are different from that of the commonly studied woody biomass. In fact, they present two different peaks instead of the one overlapping peak, for hemicellulose and cellulose. In addition, they present activation energies ranging from that are slightly above the commonly known maximum for biomass. At 10 and 20 °C/min the activation energy varied from about 130 to 174 and 180 to 216 kJ/mol, for cashew and coconut shells, respectively.

Keyword
Coconut shells; Cashew nut shells; Pyrolysis; Kinetics
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-9120 (URN)10.1016/j.fuproc.2005.12.002 (DOI)000236432200006 ()2-s2.0-33644890190 (Scopus ID)
Note
QC 20100914Available from: 2008-09-23 Created: 2008-09-20 Last updated: 2017-12-13Bibliographically approved
3. Combining model-free and model-fitting methods for the determination of the global kinetics of cashew nut and coconut shells pyrolysis
Open this publication in new window or tab >>Combining model-free and model-fitting methods for the determination of the global kinetics of cashew nut and coconut shells pyrolysis
2008 (English)In: 27th Annual International Conference on Thermal Treatment Technologies 2008, 2008, 688-708 p.Conference paper, Published paper (Other academic)
Abstract [en]

Thermal characterisation of unique tropical biomass, as coconut (CcNS) and cashew nut shells (CNS) has been the main focus of a research being conducted by the authors of this study. In this work, the objective was assess avoid the influence of the compensation factor in the kinetics results obtained from model fitting approach. This was done by combining model-free methods and model fitting procedures for the determination of pyrolysis global kinetic parameters of these two tropical biomasses. Thus, thermogravimetric analysis was performed at 10, 30 and 100 K/min in an inert atmosphere. Data analysis was primarily performed using model-free methods. Then, results from these analyses were used as reference for the determination of the reaction order. The results were then compared with those obtained previously through Coats-Redfern method. A good agreement between all the results was achieved and the experimental data were predicted with high precision. The average frequency factor and activation energy for CcNS pyrolysis were 3.16E14 1/s and 195.73±8.29 kJ/mol, respectively. For CNS, they were 1.66E08 1/s and 122.34±18.48 kJ/mol, respectively.\br| The averaged deviation was 12.39 1/s for A and 15.233kJ/mol for Eact, in CNS pyrolysis, while for CcNS was 9.33 1/s for A and 12.661kJ/mol for Eact. It had been proved that model-free methods are reliable auxiliar tools for the determination of apparent kinetics especially, as input data in modelling techniques as well as for generating primary data for model-fitting techniques.

Keyword
pyrolysis, kinetics, isoconversional, model-free, model-fitting methods
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-9139 (URN)2-s2.0-55849136212 (Scopus ID)978-160560379-7 (ISBN)
Conference
27th Annual International Conference on Thermal Treatment Technologies 2008. Montreal, QC. 12 May 2008 - 16 May 2008
Note
QC 20100914. Updated from submitted to published, 20120315Available from: 2008-09-24 Created: 2008-09-24 Last updated: 2012-03-15Bibliographically approved
4. Combustion kinetics and reactivity of char from coconut shells pyrolysis
Open this publication in new window or tab >>Combustion kinetics and reactivity of char from coconut shells pyrolysis
2008 (English)In: 7th International Symposium of High Temperature Air Combustion and Gasification (HTACG 2008), 2008, , 7 p.Conference paper, Published paper (Refereed)
Abstract [en]

Combustion process has been the main thermochemical energy conversion technology known since ages. However, as the research on combustion increases, it becomes undeniable that combustion is a very complex process with a number of different parameters and features that cannot be studied at the same time and therefore, they are still not well known as such. In this study, coconut char, produced through pyrolysis at three different heating rates in a thermogravimetric analyzer, is submitted to a combustion using a binary mixture of O2 and He to study its reactivity and determine the respective combustion kinetics. The reactivity is studied by using the critical temperature approach while kinetic parameters are determined through software that allows the determination of the frequency factor, the activation energy and the reaction mechanism, through both model free and predefined model approaches. The results obtained are compared to the similar data available from the literature for other biomasses. The critical temperature was found to vary from 377 to 388oC. The kinetic triplet was found to be comparable with the same data from other biomasses, presenting values as E1,act=101 to 132 kJ/mol and E2,act=166 to 215 kJ/mol (activation energy); A1=2,57E6 to 2.95E10s-1 and A2=6.8E10 to 2.44E14 s- 1(frequency factor); n1=0.38 to 0.80 and n2=0.95 to 1.55 (reaction order).

Publisher
7 p.
Keyword
char, combusion, reactivity, kinetics
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-9141 (URN)
Note
QC 20100914Available from: 2008-09-24 Created: 2008-09-24 Last updated: 2010-09-14Bibliographically approved
5. Modelling Individual Evolved Gas Yields from Cashew Nut and Coconut Shells Pyrolysis
Open this publication in new window or tab >>Modelling Individual Evolved Gas Yields from Cashew Nut and Coconut Shells Pyrolysis
2007 (English)In: Clean Air, ISSN 1561-4417Article in journal (Other academic) Submitted
Abstract [en]

Coconut and cashew nut shells are some of the biomass wastes typically available in many tropical countries. As renewable resources, they are eligible as important green sources for energy generation. Despite this evident fact, they are not yet commonly studied as such. In fact, while coconut shells are commonly known as activated carbon raw material, cashew nut shells are mostly known as cnsl precursors. Both products are of great importance commercially. In this research study, a non-isothermal pyrolysis of these two biomass wastes is performed using TGFTIR, at moderate heating rates (10, 30 and 100 K/min) with the objective of identifying the evolved gases and determine the respective intrinsic kinetics. This TG-FTIR system continuously monitors i) the time dependent evolution of volatiles, ii) the tars evolution rate, and iii) the weight of char. FT-IR spectra were obtained every 30 seconds and quantification of all volatiles (except tars) was done from quantification routines obtained from calibration runs with pure compounds. The data are used to generate input files that are used in a code based on the distributed activation energy model (DAEM). Using the code and the input files generated, the gas yields were predicted for comparison with the experimental results, at the same conditions. The prediction results showed a good agreement with the experimental data. Thus, the code was extended to very high heating rates (1000 and 10,000 K/s). The results at low heating rates are compared to the literature available data obtained under analogous conditions.

Keyword
biomass wastes, pyrolysis, kinetics, yields
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-9143 (URN)
Note
QS 20120314Available from: 2008-09-24 Created: 2008-09-24 Last updated: 2017-12-13Bibliographically approved

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