Investigating and modeling the pyrolysis kinetic of leaves and stems of pistachio trees for biofuel production

ماشین های کشاورزی

Article 14, Volume 6, Issue 2 - Serial Number 12, 2016, Pages 429-439   

Document Type: Research Article

DOI: 10.22067/jam.v6i2.34266

Authors

M. Ostad Hoseini¹; A. Ghazanfari Moghaddam^{* 1}; H. Hashmipour-Rafsanjani²; A. Ataei²

¹Department of Agricultural Machineris, Shahid Bahonar University of Kerman, Kerman, Iran

²Department of Chemical Engineering, Shahid Bahonar University of Kerman, Kerman, Iran

Abstract

Introduction
The lignocelluloses materials have high potential for producing various types of biofuels. These materials include various parts of plants, especially leaves and stems that are left without a specific usage after annual pruning. These residues can be used through slow or fast pyrolysis process for production of liquid and gaseous biofuels. The slow pyrolysis is taking place at temperatures below 500°C while fast pyrolysis process takes place at a temperature above 700°C. Various studies on production of biofuels from plant residues have shown that the temperature, heating rate and the resident time of pyrolysis process are the main factors that affect the final product quality. At present time, in Iran, there are more than 360 thousands hectares of pistachio growing fields which annually produce over 215 thousands metric tons residues which are mainly leaves and stems. The main objective of this study was to measure the heating properties of the powders prepared from the leaves and the stem of pistachio trees. These properties include higher heating value (HHV), lower heating value (LHV) and thermal gravimetric analysis (TGA) of the powders. Then the powders were separately pyrolysed and the kinetic of the pyrolysis process for producing charcoal from them was investigated.
Materials and Methods
In this research, leaves and stems of pistachio trees were initially analyzed to determine their chemical constituents including moisture content, volatile compounds, carbon (C), hydrogen (H), nitrogen (N), sulfur (S) and oxygen (O) content. Using these constituents the height heating value and low heating value for the leaves and the stems were determined. The thermal gravimetric analysis (TGA) of the powders was made to select a proper heating temperature for pyrolysis of the powders. In each experiment about 10 g of powder powders were pyrolyzed to produce char. Based on TGA results, the pyrolysis experiments were performed at 350, 400, 450 and 500°C with 30 minutes residence time. The instantaneous amount (in decimal) of the produced gas (M) and char (Ms) as a function of time (t) was modeled using the following equations:


For each experiment B is a constant value and is represented by:

Where Ea is the activation energy, R is universal gas constant, T is the temperature of the experiment and A is the pre-exponential constant. By having M or Ms at different times (t), the parameters of A, B and Ea were estimated using the curve fitting tool box of the MATLAB® software.
Results and Discussion
The results of chemical analysis indicated that the leaves powders contained 1.5% N, 42.1% C, 5.5% H, 0.4% S and 48.3% O while the stem samples contained 0.5% N, 46.5% C, 6.1% H, 0.2% S and 44.6% O. Higher amount of carbon and hydrogen in the stem leaves indicates that the stem should have higher energy content. In fact, the calculated high and low heating values for leaves were 17.23 and 16.03 MJ.kg-1, and for the stems were 18.91 and 17.59 MJ.kg-1, respectively which comply with the predicted results from chemical analysis of the powders. The TGA test results indicated that the initial weight loss took place up to 270°C for the stems powder and up to 220°C for leaves powders. This weight loss was due to loss of moisture and volatile compounds. The actual degradation temperature for the stem powders ranged from 300 to 500°C while for the leaves was from 350 to 600°C. The results of pyrolysis experiments indicated that the pyrolysis of stems took place faster than leaves. The pyrolysis time was 10 to 15 min for leaves and 5 to 10 min for stems. The resulting char for pyrolysis of stem was 30% and for stems were 40% of the original materials. The kinetic of pyrolysis was modeled using one-step global model for production of char and gas. The experimental data were fitted to the used model with high degrees of accuracy (R2>0.99). The model parameters, namely activation energy and frequency factors were 10.70 kJ.mol-1, and 0.047 s-1 for stems and 21.72 kJ.mol-1 and 0.312 s-1, respectively.
Conclusions
In general, both HHV and LHV of the stems were higher than those of leaves due to higher carbon content of the stems. The TG curves indicated the pyrolysis time of stems was shorter than that of leaves. The leaves yielded 40% char while the stem yielded 30%.

Keywords

Leaves; Pyrolysis; Pistachio stems; kinetics

References

safflower seed press cake. Bioresource Technology 128: 593-597.

2. Ioannidou, O., and A. Zabaniatou. 2007. Agricultural residues as precursors for activated carbon production – A review. Renewable and Sustainable Energy Reviews 11: 1966-2005.

3. Iranian Pistachio Society. 2012. Internal Newsletter, No 76.

4. Jayas, D. S., S. Cenkowski, S. Pabisand, and W. E. Muir. 1991. Review of thin layerdrying and wetting equations. Dryiung Technology 9: 551-588.

5. Pattiya, D., and S. Suttibak. 2012. Production of bio-oil via fast pyrolysis of agricultural residues from cassava plantations in a fluidised-bed reactor with a hot vapour filtration unit. Journal of Analytical and Applied Pyrolysis 95: 227-235.

6. Phichai, K., P. Pragrobpondee, T. Kumpart, and S. Hirunpraditkoon. 2013. Predicting heating values of lignocellulosics from biomass characteristics. International Journal of Chemical, Nuclear, Metallurgical and Materials Engineering 7 (7): 214-217.

7. Putun, A. E., N. Ozbay, E. P. Onal, and E. Putun. 2005. Fixed bed pyrolysis of cotton staik for liquid and solid products. Fuel Processing Technology 86: 1207-1219.

8. Seo, D. K., S. S. Park, J. Hwang, and T. Yu. 2010. Study of the pyrolysis of biomass using thermo-gravimetric analysis (TGA) andconcentration measurements of the evolved species. Journal of Analytical and Applied Pyrolysis 89: 66-73.

9. Tehranizadeh, M., A. Ghazanfari-moghaddam, and H. Hashemipour-Rafsanjani. 2012. Pyrolysis of date palm trunks to produce active carbon, Journal of Agricultural Engineering Research 13 (3): 77-88.

10. Wampler, T. P. 2006. Applied Pyrolysis Handbook. 2nd ed. CRC Press, Boca Rotan, Florida.

11. Xiu, Sh., Zh. Li, B. Li, W. Yi, and X. Bai. 2005. Devolatilization characteristics of biomass at flash heating rate. Fuel 85: 664-670.

12. Yu, F., R. Ruan, and P. Steele. 2008. Consencutive reaction model for the pyrolysis of corn cob. Food and Process Engineering of ASABE 51 (3): 1023-1028.

13. Yuen, R. K. K., G. H. Yeoh, G. D. V. Davis, and E. Leonardi. 2007. Modeling of pyrolysis of wet wood-I. Three-dimensional formulation and analysis. International Journal of Heat and Mass Transfer 50: 4371-4386.