Biomass and Bioenergy 22 (2002) 505–509
Briquetting of palm bre and shell from the processing of palm nuts to palm oil Z. Husain , Z. Zainac, Z. Abdullah ∗
School of Mechanical Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Pulau Pinang, Malaysia Received 6 August 2001; received in revised form 10 January 2002; accepted 10 January 2002
Abstract
Malaysia is the major producer of palm oil in the world. It produces 8.5 million tonnes per year (8 :5 × 106 t y 1 ) of palm oil from 38:6 × 106 t y 1 of fresh fruit bunches. Palm oil production production generates large amounts of process residues such as bre 6 1 6 1 (5:4 × 10 t y ), shell (2:3 × 10 t y ), and empty fruit bunches (8:8 × 106 t y 1 ). A large fraction of the bre and much of the shell are used as fuel to generate process steam and electricity in the palm processing mill itself. However, much is wasted by pile burning in the open air with attendant air pollution, dumped in areas adjacent to the mill, or utilized as manure in the palm oil plantation. In this paper, an attempt has been made to convert these residues into solid fuel. The palm shell and bre is densied into briquettes of diameter 40, 50 and 60 mm under moderate pressure of 5–13:5 MPa in a hydraulic press. Experiments are carried out to determine density, durability, impact and compressive strength of the briquettes. The heating value, burning characteristics, ash and moisture content are other objects of the study. A relationship between press pressure and the briquette density has been established. The produced briquettes have densities between 1100 and 1200 kg m 3 . The briquettes properties are quite good with good resistance to mechanical disintegration, and will withstand wetting. The gross caloric value is about 16:4 MJ kg 1 (maf), and the ash content is about 6% and the equilibrium moisture content is about 12%. Further work is required to acquire complete understanding of the densication process before good quality and durable briquettes could be made free from cracks. ? 2002 Elsevier Science Ltd. All rights reserved. −
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Keywords: Briquettes; Keywords: Briquettes; Palm oil residues; Palm shell; Palm bre; Densication; Mechanical properties
1. Introduction Introduction
Malaysia grows signicant quantities of rice, sugar cane, cane, palm, palm, coconu coconutt and rubbe rubber. r. Palm Palm oil mills mills produ produce ce crude palm oil and palm kernels as their main products. It also produces signicant quantities of residues such as bre (from the masocap), shell (from around the kernel kernel)) and empty empty fruit fruit bunch bunches es (EFB). (EFB). Fibre Fibre
Corresponding author. Tel.: +60-04-593-7788; fax: +60-04594-1025. ∗
and shell are the main thermal energy sources from the palm oil mills. In 1992 bre and shell generated about 650 GW h to meet the electrical energy demand of 265 palm oil mills through combined heat and power production. This amounted to 2–3% of the electrical production of the country. The biowaste readily available from the palm oil industry is renewable energy resource resource.. In general, general, the fresh fruit bunch contains (by weight) about 21% palm oil, 6–7% palm kernel, 14–15 4–15% bre bre,, 6–7% 6–7% shel shelll and and 23% 23% FFB FFB. One One metho method d of upgra upgradin ding g loose loose residu residuee materi material al to improv improvee their their handli handling ng and or combus combustio tion n prope properti rties es is by
0961-9534/02/$0961-9534/02/$- see front matter matter ? 2002 Elsevier Science Ltd. All rights reserved. PII: S0961-9534(02)00022-3
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506
densication into pellets or briquettes of higher density than original bulk density of the material. It has been noted that, there is marked improvement in com bustion characteristics of densied biomass residue (DBR) compared to loose biowaste. DBR’s have been reported to have superior and comparable combustion characteristics to wood-based fuels [1,2]. The properties of importance for any biofuels are its physical and chemical properties which include density, moisture content, heating value, ash content, etc. Also important are its mechanical properties such as impact, com pressive strength, as well as handling and storage [3].
2. Methodology
water around 50% of the residue. The samples tested under three dierent conditions at room temperature for 6 hours, dried in oven at 60 C for 6 hours, and at ambient condition under the sun for 8 hours before putting in press. The relative humidity is 85% at room temperature of 32 C. ◦
2.1. Raw material procurement
The bre and shell residues are collected from a nearby palm oil mill in the ratio of 60:40 which is the usual practice in mills to re the boilers fresh, and their—as received state. The proximate analysis of solid oil palm residues are as follows:
Volatile matter (wt%) Fixed carbon (wt%) Ash (wt%)
Fig. 1. Three dierent sizes of the briquettes.
Fibre
Shell
EFB
72.8 18.8 8.4
76.3 20.5 3.2
75.7 17 7.3
The ultimate analysis of solid residues are as follows: Component (wt%)
Fibre
Shell
EFB
Hydrogen Carbon Sulphur Nitrogen Oxygen Ash
6 47.2 0.3 1.4 36.7 8.4
6.3 52.4 0.2 0.6 37.3 3.2
6.3 48.8 0.2 0.7 36.7 2.3
The residues are dried and ground to powder in a milling machine to approximately 60–75 m. The bre and shell as raw materials in powder form are then mixed with water and starch as binders to make briquettes. The mixing is done in a mixer until it reached required condition to make moulds. Starch is 10% of the weight of the residue (bre and shell) and hot
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2.2. Briquetting process
The moulds are made in dierent ratios on weight basis to obtain an optimum mix. Die moulds then sub jected to high pressure in a press. The cylindrical briquettes were made of diameters 40, 50 and 60 mm as shown in Fig. 1. The pressure applied is from 5– 13:5 MPa against a back-up piston. The diameter to length ratio of briquettes was kept constant at 0.75. The optimum die charges were generally proportional to the cross-sectional area and ranged from 113 g for 40 mm die to 380 g for 60 mm.
3. Results and discussion
3.1. Pressure–density relationships
The relationship between pressure and density has been studied by many research workers. Wheeler [4] proposed a relationship between pressure and density for straw in the form of a simple power-law at high densities. Ooi Chin [5] have worked on pellets and found a dierent exponential relationship between die pressure and density of the form D = a‘nP + b;
(1)
Z. Husain et al./ Biomass and Bioenergy 22 (2002) 505 – 509
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14 13 12 ) 11 a P 10 M ( e r u s s e r P
9
40mm mold diameter
8
50mm diameter 60mm diameter
7
Linear (40mm mold diameter)
6
Linear (60mm diameter)
5
Linear (50mm diameter)
4 1100
1120
1140
1160
1180
1200
1220
1240
1260
1280
1300
Density ( kg/m3)
Fig. 2. Pressure versus relaxed density for three dierent sizes of the briquettes.
where a; b are empirical constants which vary for different types of feed stocks viz saw dust, rice, husk, coconut bre, etc. Osobor [6] and Faborode [7] have also proposed relationships between pressure and density. In the present analysis, after the briquette is removed from the die after 1 week drying at room tem perature, the measured length was used to calculate the relaxed density of the briquette. Fig. 2 shows the graph between relax density and die pressure for the three sizes of the mould diameter. There is an exponential increase in pressure with increase in relax density. The relationship is in the form P = aebD ;
(2)
where P is measured in MPa, D is the relax density expressed in kg m 3 and a; b are empirical constants. The value of these constants for densied biomass residue (DBR) are as follows: −
40 mm diameter ;
a = 0 :0389;
b = 0 :0045;
50 mm diameter ;
a = 0 :0871;
b = 0 :0036;
60 mm diameter ;
a = 0 :189;
chines. Wheeler [4] has obtained for barly straw values in the range of 5–25 MJ t 1 . Taha [8] quotes a value of specic energy 7 :2 MJ t 1 for compression of cotton stalks in circular dies. In our study DBR in circular dies gives value of specic energy in the range of 5–10 MJ t 1 depending on biomass residue density. −
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3.3. Heating value of DBR
The heating value of DPR was measured by Bomb Calorimeter. The higher caloric value of DBR obtained by experiment is 16 :38 MJ kg 1 (maf). −
3.4. Compressive strength
The briquettes were subjected to vertical force in a compressive testing machine as shown in Fig. 3. The failure load is read directly on the dial in kilonewtons. The average compressive strength for DPR is 2:56 kN m 2 . −
b = 0 :0033:
The density ratio (relaxed density = initial density) for DBR is 0.65. 3.2. Specic energy
The specic energy required to form briquettes is of critical importance for the design of practical ma-
3.5. Moisture content
The strength and durability of briquette is aected by moisture content, density and humidity. The relaxed density is measured at atmospheric conditions with relative humidity 85% and the moisture content measured as 12.5%.
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Fig. 3. Briquette failure under compressive force.
Table 1 Burning rate, air–fuel ratio and ash content of DBR and coal
Specimen DPR Coal
Mass (g)
Burning time (min)
Consumption (kg s 1 )
91.7 136
50 109
3:05 × 10 2:08 × 10
−
5
−
5
−
Mass ow rate of air (kg s 1 ) −
3:1 × 10 3:1 × 10
4
−
4
−
Burning rate in (W)
A=F ratio
% ash
500 683
10.2 14.9
5.8 6.8
3.6. Combustion characteristics
3.7. Crack analysis
The combustion process of DBR was studied using a locally made stove. Air for combustion is supplied under pressure from air compressor through three perforated pipes with four holes in each pipe. The DPR briquettes were placed over the hearth of the stove. The arrangement is typical of a coal-red boiler. The mass ow rate of air is calculated as: ma = velocity of air × cross-sectional area of holes × no: of holes. The velocity of air is measured by an anemometer. The ow rate of air is controlled by a valve. With known quantity of DBR and time for complete com bustion of the biomass, its consumption ( m b ) and burning rate are calculated. From the experimental results the burning rate is 500 W, air–fuel ratio is 10.2 and ash content is 5.8% (Table 1).
The crack analysis is made after keeping the briquettes for 4 days at atmosphere conditions. The cracks fall into two categories: surface (S) and deep (D) cracks. The crack length is measured in the axial direction ( x) and the depth of the crack in the radial direction (r ). Table 2 shows the crack analysis for dierent specimen diameters. The crack length in the axial direction increases with diameter of briquettes. The briquettes withstood the impact when allowed to fall freely from a height of 1–2 m. Also the briquettes when immersed in water for a period of 30–360s do not show signs of disintegration which indicate that they do not require shielding from driving rain during transport and storage.
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Table 2 Crack analysis for densied biomass residue (DBR)
d = 40 mm
d = 50 mm
d = 60 mm
Specimen
x (mm)
r (mm)
Category
x (mm)
r (mm)
Category
x (mm)
r (mm)
Category
1
51.2
S
77.7
54.7
4
56.9
5
59.6
S S S S D S D S S
28.6
3
9.8 28.7 6.7 43.2 9.9 27.2 11.2 11.8 9.8
76.9
52.3
D S S S D S D S D S
63.2
2
10.8 22.3 7.1 28.5 6.9 17.2 11.2 39.6 7.2 32.7
13.9 57.6 11.2 34.6 11.4 46.7 11.4 46.7
D S D S S S S S
64.2 65.2 65.5 67
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78.9 80.9 80.9
[5] Ooi CC, Bari S, Siddiqui KM. Densication and properties of briquetted wastes. Renewable Energy 1998;16:1981–4. [6] Osobov VL. Reaction to the pressing of brous plant materials. vestik selskokozaisistrennoi Nauki 1968;13: 115–9. [7] Faborode MO, O’Callagham JR. Theoretical analysis of compression of brous agricultural materials. Journal Agricultural Engineering 1986;35:175–9. [8] Abd Elrahim YM, Huzayin AS, Taha IS. Dimensional analysis and wafering cotton stalks. Transaction of the American Society of Agricultural Engineers 1981;24: 829–32.
