Torrefaction of oil palm wastes

doi:10.1016/j.fuel.2011.03.021

Fuel

Volume 90, Issue 8, August 2011, Pages 2585-2591

https://doi.org/10.1016/j.fuel.2011.03.021 Get rights and content

Abstract

This paper describes the effect of torrefaction on the basic characteristics of agricultural biomass wastes in Malaysia, such as empty fruit bunches (EFB), mesocarp fiber and kernel shell as a potential source of solid fuel. Mesocarp fiber and kernel shell exhibited excellent energy yield values higher than 95%. EFB, on the other hand, exhibited a rather poor yield of 56%.

Highlights

► Torrefaction for converting oil palm wastes into solid fuel. ► Empty fruit bunches, mesocarp fiber and kernel shell were used as feedstock. ► Torrefied mesocarp fiber and kernel shell showed energy yields higher than 95%.

Introduction

Biomass is one of the promising renewable energy sources, and is utilized as solid, liquid and gas fuels. Especially, lignocellulosic biomass wastes are attracting interest worldwide, because of its non edible characteristic. In Malaysia, availability of oil palm wastes is the best among biomass wastes [1].

In order to utilize biomass wastes efficiently, the following drawbacks about biomass compared to fossil fuels must be solved properly:

(1)
Higher energy consumption for collection.
(2)
Heterogeneous and uneven composition.
(3)
Lower calorific value.
(4)
Difficult to transport.

Since it is very difficult to solve all the problems at the same time, we focus on the fourth problem in this paper. There are a few options to solve this; the major ones are pelletization, liquefaction and gasification. Though pelletization is the least expensive option, there are some problems associated with it; lower heat value and quality deterioration by moisture (pellet disintegration, moss growth and bioorganic decomposition). Recently, a low temperature treatment at 200–300 °C under an inert atmosphere has been found to be effective for improving the energy density and the shelf life of biomass. The treatment is called ‘torrefaction,’ and has been reported for wood and grass biomass rather recently. Arias et al. torrefied woody biomass (eucalyptus) at 240–280 °C, and found that the grindability of the biomass is improved [2]. Prins et al. proposed a kinetic model of torrefaction [3], and reported the details of torrefaction mass balance [4]. Some papers focused on the fuel quality [5] and the gasification feedstock quality [6], [7] of the torrefied lignocellulosic biomss. Uslu et al. focused on comparison of torrefaction, fast pyrolysis and pelletization from the viewpoint of the international bioenergy logistics [8]. Currently, experimental torrefaction studies are mostly on woody and grass biomass; wood dusts [8], beech [3], [4], [6], eucalyptus [2], willow [3], [4], [5], [7], larch [3], [4], and canary grass [5]. Few academic papers have been found for torrefaction of agricultural lignocellulosic wastes, such as wheat straw [3], [4], [5], which are one of the promising renewable resources, especially in Southern Asia [1].

In 2008, Malaysia was the second largest producer of palm oil with 17.7 million tonnes, or 41% of the total world supply, while Indonesia was the world’s largest producer of palm oil with 19.3 million tonnes of oil, or 45% of the total world supply. In 2008, productive oil palm plantations in Malaysia covered 4.5 million hectares, a 4.3% increase from the figures in 2007, which stood at 4.3 million hectares. The types of biomass residue generated by the oil palm industry include fronds, trunks, empty fruit bunches (EFB), mesocarp fiber and kernel shell. Fronds and trunks are generated at plantations. EFB, mesocarp fiber and kernel shell are generated at palm oil mills. Fig. 1 shows a process flow diagram of a palm oil mill [9]. EFB is the residue generated at the thresher, where fruits are removed from fresh fruit bunches. Mesocarp fiber is generated at the nut/fiber separator. Kernel shell is from the shell/kernel separator. The annual amount of lignocellulosic residues generated by the oil palm industry is 140 million t, which corresponds to 17 Mtoe (million tons of oil equivalent). Since the current primary energy supply in Malaysia is about 70 Mtoe, the total oil palm biomass energy potential of 17 Mtoe may be able to contribute considerably to the decrease in consumption of fossil fuels (natural gas, coal and oil). Although torrefaction seems to be one of the key technologies to utilize these biomass residues efficiently in Malaysia, the problem is that no papers have been found for torrefaction of oil palm residues.

In this study, we focus on torrefaction of empty fruit bunches (EFB), mesocarp fiber and kernel shell of oil palm, which are typical agricultural wastes in Malaysia as shown in Fig. 1. The effect of torrefaction temperature on the mass and energy yields were investigated for those three types of biomass waste.

From this study, basic data for torrefaction of oil palm wastes were obtained. Another important finding is that the energy yield of mesocarp fiber and kernel shell showed 93% to 100%, whereas that of EFB showed rather lower values of 56% to 83%. From this finding, mesocarp fiber or kernel shell is preferable as a feedstock for torrefaction.

Section snippets

Biomass samples

Three types of biomass waste utilized in this study, empty fruit bunches (EFB), mesocarp fibers and kernel shell, were collected at an oil palm plantation in Kelantan, Malaysia in September 2009. They have been kept in a refrigerator maintained at below 5 °C, and used in this experimental work without any pretreatment.

Torrefaction experiments

Torrefaction of the biomass wastes was carried out using a horizontal tubular type reactor of 100 mm internal diameter, which is shown in Fig. 2. A prescribed amount of waste

Appearance of torrefied samples

In this study, three types of oil palm waste were torrefied. In Fig. 3, photos of all the samples including raw materials and torrefied samples are exhibited. The color of EFB and mesocarp fiber becomes darker as the torrefaction temperature increases. Particularly, EFB torrefied at 300 °C exhibits almost black color. A similar tendency was observed for a woody biomass in a previous paper [6].

Calorific and CHNS analysis

The results of mass measurement, calorimetry, elementary and ash analyses for the dried and torrefied

Conclusions

In this study, torrefaction of empty fruit bunches (EFB), mesocarp fiber and kernel shell of oil palm, which are typical agricultural wastes in Malaysia, was experimentally conducted. The effect of torrefaction temperature on the mass and energy yields was investigated for those three types of biomass waste. Mesocarp fiber and kernel shell showed excellent energy yield values of 96% and 100%, respectively. EFB, on the other hand, exhibited a rather poor yield of 56%.

The biomass samples used in

Acknowledgment

The authors acknowledge that this work was supported financially by the Mitsubishi Foundation.

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Torrefaction of oil palm wastes

Abstract

Highlights

Introduction

Section snippets

Biomass samples

Torrefaction experiments

Appearance of torrefied samples

Calorific and CHNS analysis

Conclusions

Acknowledgment

Fuel Process Technol

J Anal Appl Pyrolysis

Fuel

Fuel

Energy

Energy

Energy Convers Manage

Thermochemica Acta