5 J OURNAL OF FOREST PRODUCTS & INDUSTRIES, 2012, 1(2), 5-9
Heat Value of Four Hardwood Species from Sudan Tarig O. Khider*1 and Osman T. Elsaki2 1
University of Bahri-College of Applied and industrial sciences, Khartoum Sudan E-mail: tarigosmankhider@gmail.com 2
Institute of Technological Research, NCR, Khartoum, Sudan E-mail: osmantaha2007@yahoo.com (Received October 15, 2012; Accepted October 31, 2012)
Abstract— Four hard woods species namely Acacia mellifera, Acacia senegal, Eucalyptus tereticornis and Moringa oleifera were studied for their suitability for production of fuel wood and charcoal, their heat value were obtained range between 1738619309 KJKg-1 with basic density of 226.3-728 Kg m-3, a regression model for calculation of heat values from chemical components of wood was established and compared with measured heat values. Holocellulose was positively and significantly correlated with heat value while ash was negatively correlated.
Index Terms— Acacia mellifera, Acacia senegal, Eucalyptus tereticornis, Moringa oleifera, Heat value, Basic density, Chemical components
I. INTRODUCTION
S
udan has diverse climate conditions and different tree species with multi-uses. Acacia mellifera (Kitir) is indigenous hardwood species, wide-spread in Africa occurring in Egypt, Sudan, Somalia, Ethiopia, Angola, Kenya, Uganda and Tanzania, Sahel East of Niger River to Southern Arabian Peninsula, Eastern and Southern Africa. It is a resprouting multi-stemmed shrub with an average height of 75 cm [1 and 2]. Acacia senegal is distributed in all countries of Central Africa, extends to Oman, Pakistan and India. Sudan has two main areas of distribution, on stabilized sand with rain fall 280-450 mm and on the dark cracking clays [3 and 4]. Moringa oleifera originated from Arabia and India [5], distributed natively to sub-Himalayan tracts of India, Pakistan, Bangladesh and Afghanistan [3]. Eucalyptus tereticornis originated from eastern side of Australia and New Guinea with rain fall 510-1520mm [3]. The most important sources of fuel, which are the necessities for human kind, are fuel wood (charcoal and firewood), petroleum and peat. Of these, wood makes an outstanding fuel as it is 99% flammable if completely dry. It is the cheapest, the most suitable and accessible energy source in many rural areas [6 and 7]. Woody biomass is a widely-used and favorable material for energy production due to its carbon neutral
* corresponding author
status. Energy is generally derived either through direct combustion or gasification [8]. Wood charcoal is a porous carbon material, with a heterogeneous surface and a disorganized pore structure susceptible of change by adequate thermal treatments to be used as adsorbent [9]. The renewed interest in wood fuel is being driven largely by economic and environmental concerns – wood fuel is increasingly price competitive with fossil fuel alternatives and the environmental benefits of wood fuel are now being recognized and valued. The production and use of wood fuel provides social benefits too, including the creation of additional employment, especially in rural areas [10]. The higher heating value of wood was correlated with lignin and extractive contents. There was a highly significant linear correlation between the higher heating value of the extractive-free wood and lignin content [11] Analysis and modeling of combustion in stoves, furnaces, boilers and industrial processes requires adequate knowledge of wood properties. Detailed computer modeling of combustion processes requires accurate property values, and these properties are not generally available in one reference source [12]. The objectives of the present work are: to indicate the suitability of wood of studied species for production of fuel wood and charcoal and to predict the heat value with a regression model derived from chemical components of the wood. II. MATERIALS AND METHODS The Raw material used on the present study was wood from four species, two indigenous species ( Acacia mellifera and Acacia senegal) and two exotic species ( Moringa oleifera and Eucalyptus tereticornis) were grown in Blue Nile state south east Sudan, all with the same age nine years old, four trees of each species were randomly selected according to TAPPI standards [13 and 14] further felled, delimbed and crossed cut into log of 100 cm length, the logs were sawn into discs of about 2.5 cm thickness for chemical analysis and heat value determination. The average height and diameter were shown in table 1.
6 J OURNAL OF FOREST PRODUCTS & INDUSTRIES, 2012, 1(2), 5-9
Table 1 Heights and diameters of Acacia mellifera, Acacia Senegal, Eucalyptus tereticornis and Moringa oleifera.
Species Acacia mellifera Acacia senegal Moringa oleifera Eucalyptus tereticornis
Local name
Height range
Kitter Hashab Elrawag Ban
7-7.7 7.5-9 6-7.5 8-10
The average basic density of four studied species was determined as oven-dry mass/ green volume obtained according to B.S.373 [15]. Ten specimens were soaked in water until saturation; the green volume was determined by displacement of water in a graduated constant mass at 105 0C. The average basic density was calculated according to the following equation Basic density, Kgm-3 = Oven-dry mass/ green (soaked) volume Bark to wood ratio by volume was determined by measuring the girth of four discs for each species with and without bark and was calculated as Bark-to-wood-ratio by volume= 1- b2/ a2 Where a = the average girth of the discs including bark B= the average girth of the discs without bark The bark –to- wood ratio by mass was measured on oven dry basis with and without bark The heat value of wood was determined with a Krocher oxygen bomb calorimeter, samples of known moisture content were molded into a pellet with fuse wire inside, weighed and burnt in the calorimeter. The temperature was recorded at 15 sec. intervals until it stabilized, then at one –minute intervals until five minutes after maximum temperature was reached. Each experiment was carried out three times. The heat transferred to the calorimeter was calculated as follows Q= (Mw+ mw+ q)t, cal Where: Mw=mass of water in calorimeter, g mw =mass of water in bomb, g q= mass equivalent of calorimeter, g t= true temperature rise, corrected for heat loss obtained from the group of temperature rise, The heat generated was calculated as Q= MfH+ Mf. hf+ 40Mf, cal Where: Mf= mass of wood, g mf= mass of fuse wire burnt, g H= higher calorific value of the wood,cal/g hf= heat of fusion of fuse wire, cal/g
The higher heat value of the wood, H, was calculated by equating the heat transferred with the heat generated and then transferred into KJ Kg-1 the SI units (cal g-1 = 4.1868 KJ Kg-1)
Average height (meters) 7.3 8.3 6.8 9
Diameter range 7.5- 8 7.5-8.7 16-18 11-14
Average diameter (Centimeters) 7.7 7.8 17 12.5
The chemical composition of four studied species was determined according to TAPPI standard Test methods (T 204-cm-97 for solvents extractives, T207-cm99 for water solubility, T211-om- 93 for ash, T212-om-98 for 1% NaOH extractives, T222-om-02 for lignin and T223-cm-01 for Pentosans).while Kurchner –Hoffer cellulose was measured according to [16]. Meal was prepared using star mill with standard sieve according to TAPPI standard (T11- wd-79). III. RESULTS AND DISCUSSION The average values for basic density of Acacia senegal, Acacia mellifera and Eucalyptus tereticornis were 728, 703 and 673 kgm-3 respectively (Table 2) classify them as high – density woods according to Bin (1970) classification [17], while Moringa oleifera could be classified as low density wood (226K gm-3) as a result of fast growth and presence of a large amount of parenchyma cells. The usual density range for commercial pulp wood is 350-650Kg m-3 [18]. The average bark – to wood ratios by mass (Table 2) for Moringa oleifera and Acacia senegal were moderately high (19 and 16.2% respectively), but for Acacia mellifera and Eucalyptus tereticornis (13.1 and 10.8% respectively) were in the normal range. The average bark-to- wood ratios by volume for A. senegal, A. mellifera and Moringa oleifera were moderately high for commercial woods (20.1, 16.2 and 15.9% respectively) and in the normal range for Eucalyptus tereticornis (11.9) The average gross heat of combustion (Calorific value) for each of species studied and measured with oxygen bomb was given in Table (3). It was to be found in the normal range for tropical hardwoods for Acacia mellifera, Acacia senegal and Eucalyptus tereticornis while for Moringa oleifera it was lower with its lower density. Acacia senegal and Acacia mellifera heat values were more or less similar which was supported further by their chemical composition (Table 4). The heat value for Eucalyptus tereticornis was lower compared to Acacias. These differences might be due to the higher lignin content of both Acacia senegal and Acacia mellifera, while for Moringa oleifera it might be attributed to the high ash content and low density of the wood.
7 J OURNAL OF FOREST PRODUCTS & INDUSTRIES, 2012, 1(2), 5-9 The effect of the chemical composition of wood on its heat value was studied by means of regression analysis on the base of the data for species studied and a number of other Sudanese hardwoods under the same conditions. A regression model was obtained and correlations between heat value and chemical composition were established HV= 18803-515 Ash- 120H.H2O + 155AB + 70 Lig- 0.5 Hol
Where HV= Heat value of wood, kJ kg-1 Ash= Ash content, % H. H2O= Hot water solubles AB= Alcohol- benzene extractives Lig= Lignin content free of ash, % Hol= Holocellulose, %
Table 2 Physical properties of Acacia mellifera, Acacia Senegal, Eucalyptus tereticornis and Moringa oleifera Species Properties
Acacia mellifera Acacia senegal Eucalyptus tereticornis Moringa oleifera X ±SD X ± SD X ±SD X ±SD
Basic density*, Kgm-3 703 25.8 Bark-to-wood ratio by mass,% 13.1 2.6 Bark –to-wood ratio by volume, % 16.2 0.9 *at 12% moisture content X- Average value ± SD – Standard deviation
728 27.8 16.2 0.9 20.1 2.4
673 10.8 11.9
28.4 1.8 3.0
226.3 11.4 19 1.6 15.9 1.6
Table 3 Measured and calculated gross heat values for Acacia mellifera, Acacia senegal, Eucalyptus tereticornis and Moringa oleifera
Wood species Acacia mellifera Acacia senegal Eucalyptus tereticornis Moringa oleifera
Gross Heat value, KJKg-1 Measured Calculated 19188 19117 19309 19097 18773 19485 17386 17515
Table 4 Chemical component of Acacia mellifera, Acacia Senegal, Eucalyptus tereticornis and Moringa oleifera from Sudan Chemical component Acacia mellifera Ash 1.9 Total silica 0.1 Solubility in: Hot water 5.7 Alcohol 4.1 Alcohol-benzene (1:2) 3.0 1% NaOH 14.5 Kurschner-Hoffer Cellulose 51.5 Holocellulose 74.8 Alfa-cellulose 50.8 Pentosans 14.8 Lignin 23.3 Total extractives 7.0 Cellulose/ lignin ratio 2.2 The regression coefficients for predicting variables as well as the t-ratio, standard deviations and probabilities obtained were given in Table 5. The correlation matrix was given in table 6 showed the relationship between the chemical components of
Acacia senegal 1.9 0.1 5.9 3.3 2.9 16.4 47.8 67.7 45.7 19.6 22.2 8.1 2.2
Eucalyptus tereticornis Moringa oleifera 1.3 4.6 0.1 0.4 4.0 4.1 2.2 18.8 45.1 70.9 40.0 22.5 21.8 6.4 2.1
9.3 3.6 3.0 18.6 50.9 68.5 42.6 14.4 24.9 9.2 2.1
hardwood studied and their heat values. The Ash content is highly and negatively correlated with Holocellulose and heat value having a correlation coefficients of -0.676 and -0.756 respectively, and lower negative correlation (-0.112) with
8 J OURNAL OF FOREST PRODUCTS & INDUSTRIES, 2012, 1(2), 5-9 alcohol benzene solubles content, it was positively correlated
with the hot water soluble (0.365).
Table 5 Regression analysis of the data from heat value and chemical composition of wood. Predictor Regression coefficient Ash,% -514.7 Hot water solubles, % -119.58 Alcohol-benzene solubles, % 154.7 Lignin, % 69.9 Hollocellulose, % -0.47 The hot water solubles content was negatively correlated with heat value. Holocellulose and lignin contents (-0.514, -0.228 and -0.189, respectively) but it was positively correlated (0.326) with alcohol-benzene solubles content. Alcoholbenzene solubles content has low positive correlation with heat value and Holocellulose (0.228 and 0.163, respectively). On
Standard deviation 219.2 79.83 85.1 68.8 36.27
t-ratio -2.35 -1.5 1.82 1.02 -0.01
Probability 0.043 0.168 0.102 0.336 0.990
the other hand it was negatively correlated with lignin content with correlation coefficient -0.478. The lignin content has negative correlation with heat value and Holocellulose with correlation of -0.243and -0.246, respectively. Holocellulose has a positive correlation with heat value with a correlation coefficient of 0.564.
Table 6 Correlation matrix for the chemical components and heat value of wood Ash Ash 1 H.H20 0.365 AB -0.112 Lig 0.524 Hol -0.676 HV -0.756 Ash= ash, % H.H20= hot water solubles, % AB= alcohol- benzene solubles, % Lig= Lignin free of ash, % Hol= Holocellulose, % HV= heat value, KJ Kg-1
H.H20 1 0.326 -0.189 -0.228 -0.514
AB
Lig
1 -0.478 0.163 0.228
1 -0.246 -0.243
IV. CONCLUSIONS The heat value of the four species studied, Acacia mellifera, Acacia senegal, Eucalyptus tereticornis and Moringa oleifera is positively and significantly affected by their basic densities and can be predicted directly from their chemical composition using the model obtained while the ash, Holocellulose and lignin contents affect the heat value most significantly, the heat values obtained of Acacia mellifera, Acacia senegal and Eucalyptus tereticornis indicted that wood of these species could successfully utilized as fuel wood or charcoal , while Moringa oleifera does not seem economically suitable for fuel wood and charcoal making. This is important for rational and complete utilization of the logging residues. Finally wood fuels are still the principal energy source for a large proportion of Sudan’s population especially in rural areas. Effective management of the forests in these areas will enhance biodiversity and increase the quantity of managed woodland which supports jobs in the forestry industry. Using firewood can radically diminish our
Hol
HV
1 0.564
1
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