Elsevier

Energy for Sustainable Development

Volume 23, December 2014, Pages 188-193
Energy for Sustainable Development

Thermal characterization and pyrolysis kinetics of tropical biomass feedstocks for energy recovery

https://doi.org/10.1016/j.esd.2014.09.009Get rights and content

Highlights

  • Characterization and thermal degradation behaviour of Cameroonian biomasses are investigated.

  • Pyrolysis behaviour of Palm Kernel Shells, Mesocarp Fibre, Coffee Husk, Corn Cob and Peanut Shell is assessed.

  • Palm Mesocarp Fibre is the most interesting feedstock with the highest heating value and reactivity.

  • Diffusion and order reaction models are the suitable decomposition mechanisms.

  • Pyrolysis kinetic parameters of the different biomass species are obtained.

Abstract

This paper aims to analyse energy related properties, thermal degradation behaviour and devolatilization kinetics of five Cameroonian biomasses namely, Palm Kernel Shells (PKS), Mesocarp Fibres (PMF), Coffee Husk (CH), Corn Cob (CC) and Peanut Shell (PNS). The thermal degradation was performed using thermogravimetric analysis (TG). Different behaviours related to the presence of chemical constituents such as cellulose, hemicellulose and lignin were obtained. Comparison of the thermal characterization shows that PMF is the most interesting feedstock with the highest heating values and reactivity due to higher volatile content. Decomposition of TG data was analysed by applying diffusion and chemical reaction kinetic models. Obtained results show that biomass pyrolysis is represented by two successive steps. The devolatilization stage characterized by high weight loss rate is well described by diffusion reaction models. In contrast, the char formation stage characterized by low weight loss rate is well described by third order chemical reaction models.

Introduction

The utilization of renewable energy sources is currently crucial to reach the changes required to reduce the increasing global warming impacts. Biomass represents a promising renewable energy with a large potential to substitute fossil fuels (McKendry, 2002a).

Biomass energy is widely used in the third world principally in rural regions where it is frequently the main energy source for cooking. Although the agricultural waste potential in many of these regions, few attentions are given to them.

Cameroon is a country in Middle Africa with about 20.03 million people (2011 census) and 50% of its population are below the national poverty line. Cameroon has the third major biomass potential in sub-Saharan Africa, with amount estimated at 6.3 billion tons (Ackom et al., 2013). Forest resources cover about 28 million ha and represent the three-quarters of the country's territory (Maesano et al., 2013). Wood fuel is the main energy source for cooking in both rural and urban Cameroonian areas. However, the unsustainable use of this resource (e.g. wood extraction-commercial, charcoal production and fuel wood) has led to important deforestation throughout the country (Mbatu, 2010).

This deforestation has encouraged research to identify and to use other biomass resources as a viable substitute of fuel wood. Since Cameroonian agriculture contributes to a great degree to the country's GDP, these generated residues may represent a promising alternative fuel (Ackom et al., 2013).

Soils and climate on the country's coast promote farming of oil palms, bananas and cocoa. The South Cameroon Plateau interior encourages cultivation of cash crops such as coffee, tobacco and sugar. Major agricultural produce in northern country includes cotton, corn, peanuts and rice.

These crops' cultivation as well as their transformation through agro-industrial processes generate in Cameroon a significant amount of residues. Hence, the palm oil extraction in the traditional mills mainly generates Palm Kernel Shells (PKS) and Mesocarp Fibres (PMF). Additionally, the coffee industry induces important amounts of Coffee Husk (CH) before the roasting coffee process. Furthermore, the maize and groundnut productions left certain amounts of Corn Cobs (CC) and Peanut shells (PNS). These valuable residues are usually cheap, widespread, and continuously produced. All these renewable energy resources have the potential to be widely used as source of energy both by the local populations (e.g., cooking and heating) and for industrial energy consumption.

In order to efficiently use them for energy production, various thermochemical conversion processes such as carbonization, combustion, gasification and liquefaction have been developed (McKendry, 2002b). However, these procedures involve pyrolysis because it is the primarily stage of biomass transformation (Yaman, 2004).

Kinetic studies of pyrolysis are usually conducted using a thermogravimetric analyser (Chouchene et al., 2012, Dorge et al., 2011, El may et al., 2012, Jeguirim et al., 2010, Jeong et al., 2014, Masnadi et al., 2014). The kinetic parameters include the activation energy, the frequency factor and the kinetic rate constant K. These parameters are required for the reactor designing since it is necessary to achieve an optimal conversion. Their usefulness with respect to modelling their respective thermochemical conversion processes is acknowledged. In fact, the data obtained from the thermal analysis are provided to kinetic models which use rate laws that follow the fundamental Arrhenius rate expression.

The main purpose of this investigation is to study the thermal characterization and the devolatilization kinetics of five Cameroonian biomass feedstocks: Palm Kernel Shells (PKS), Palm Mesocarp Fibres (PMF), Coffee Husk (CH), Corn Cobs (CC) and Peanut Shells (PNS) using thermogravimetric analysis data and the Coats and Redfern method. Comparison of thermal characteristics of the different biomasses is performed to assess the eventual utilization of the different biomasses for energy recovery.

Section snippets

Raw materials

Five types of Cameroonian biomass were studied: Palm Kernel Shells (PKS), Mesocarp Fibres (PMF), Coffee Husk (CH), Corn Cobs (CC) and Peanut Shells (PNS). PKS and PMF were obtained from the SOCAPALM palm oil mill in Douala. CC samples were provided by MAISCAM agro-industrial company in Ngaoundéré. PNS were provided from a farmer cooperative from the region of Garoua. CH samples were supplied by a farmer cooperative in Nkongsamba. All of these samples were dried naturally to reduce their

Raw material characterization

Elemental compositions as well as the “H/C” and “O/C” ratios of the different Cameroonian biomass species are listed in Table 2.

The analysis shows that elemental compositions of the different samples are in the range of typical composition values of biomass reported in literature (Cocozza et al., 2011, Wilson et al., 2011). Comparison of the different samples shows that CCs have the lowest carbon content, the highest oxygen content and therefore the highest O/C ratio. This characteristic was

Conclusion

Thermochemical conversion of five types of Cameroonian biomass, Palm Kernel Shells (PKS), Palm Mesocarp Fibre (PMF), Coffee Husk (CH), Corn Cob (CC) and Peanut Shell (PNS), was examined using thermogravimetric analysis under nitrogen atmosphere. Decomposition TG and DTG data were used to determine devolatilization kinetic parameters by applying diffusional and chemical reaction kinetic models.

Results show that the thermal degradation of Cameroonian biomass under nitrogen atmosphere could be

References (42)

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