Corresponding author’s email address: jibolarufai@gmail.com 813 ARID ZONE JOURNAL OF ENGINEERING, TECHNOLOGY & ENVIRONMENT ORIGINAL RESEARCH ARTICLE EFFECTS OF TORREFACTION PARAMETERS ON THE PROPERTIES OF BRIMSTONE (Morinda lucida) WOOD A. R. Nasirudeen1*, F. A. Ola3, O. O. Oniya 3, A. J. Adesope1, D. Lasisi 1, L. A. Balogun1, W. A. Adesope2, I. A. Abdulsalam3 and A. O. Oladiji2 1*Department of Agricultural and Bio-Environmental Engineering, Oyo State College of Agriculture and Technology, Igboora, Nigeria 2Department of Mechanical Engineering, Oyo State College of Agriculture and Technology, Igboora, Nigeria 3Department of Agricultural Engineering, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria *Corresponding author’s email address: jibolarufai@gmail.com ARTICLE INFORMATION ABSTRACT Biomass energy is a possible replacement for the conventional energy due to its environmental effects. However, raw biomass has poor combustible properties which can be enhanced by torrefaction. This research studied the torrefaction properties of brimstone wood as potential energy source. Existing torrefaction device was modified by incorporating a thermocouple and temperature regulator and rectangular reactor was used for the torrefaction of brimstone wood. Harvested samples of the materials were manually processed into smaller pieces and sun dried. The sun-dried samples were crushed and sieved into 8, 10 and 12 mm particle sizes. The sieved samples were subjected to ultimate (Carbon (C), Oxygen (O), Hydrogen (H), Nitrogen (N), Sulphur (S) and energy contents) compositions analysed using standard methods. A 3 by 3 Box- Behnken experimental design in the Design Expert 12.0.2 software was used to design the experiment. The influence of heating temperature (220, 260 and 300 0C), heating time (30, 60 and 90 min) and particle size (8, 10 and 12 mm) on the weight of biochar products were studied. Model equations were developed and used to evaluate Biochar Mass Yield (BMY), Energy Yield (BEY) and Energy density (BED) and evaluated based on the heating temperature, heating time and particle size ranges. The data obtained from the experimental design were analysed statistically with Analysis of Variance (ANOVA) at 95 % confidence level. The carbon, oxygen, hydrogen, nitrogen, sulphur and energy contents for brimstone wood were 52.20, 36.88, 2.40, 0.54, 0.89% and 245.89 kcal/100g. R2 values of BMY, BEY and BED were 0.9499, 0.9348 and 0.9990 at P≤0.05 for brimstone wood. Torrefied brimstone wood has been identified as potential sources of energy, with heating temperature and heating time as critical parameters that affect properties of torrefied materials. Submitted 24 March, 2024 Revised: 12 June, 2024 Accepted: 18 June, 2024 Keywords: Torrefaction Brimstone wood Biochar Heating time Heating temperature Sample size Yield Ultimate compositions © 2024 Faculty of Engineering, University of Maiduguri, Nigeria. All rights reserved. 1.0 Introduction The World’s energy demand is increasing geometrically as evidenced in the increasing demand for fuels for transportation, industry as well as domestic activities (Melgar et al., 2009). The growth and economic development of the world depends on its energy and other factors such as population growth, infrastructural and technological development and this is putting pressure on conventional energy resources. These factors lead to increase in energy demand despite the environmental pollution and global warming effects resulting from the use of petroleum-based fuels (Adeleye et al., 2018). In the last 39 years, about 75% of human made CO2 emissions were from the consumption of fossil fuel resources (Ferro et al., 2004). There is increasing emphasis on renewable energies following the global demand for clean energies which are sustainable. One of the renewable energy sources is biomass which is an alternative source of energy derived from biological materials (plant and animals). Existing technologies to convert biomass to energy include thermochemical and biochemical processes. The thermochemical conversion technique which involves combustion, pyrolysis, AZOJETE December 2024. Vol.20(4):813-827 Published by the Faculty of Engineering, University of Maiduguri, Maiduguri, Nigeria. Print ISSN: 1596-2490, Electronic ISSN: 2545-5818 www.azojete.com.ng mailto:jibolarufai@gmail.com mailto:jibolarufai@gmail.com http://www.azojete.com.ng/ Arid Zone Journal of Engineering, Technology and Environment, December 2024; Vol.20(4)813-827. ISSN 1596-2490; e-ISSN2545-5818; www.azojete.com.ng Corresponding author’s email address: jibolarufai@gmail.com 814 gasification and liquefaction processes is more familiar. The thermochemical process of torrefaction which is used for the treatment of biomass at low heating temperatures ranging from 200 to 300 °C under an inert atmosphere is known to be effective for improving the energy density and shelf life of biomass materials (Ferro et al., 2004). It has been widely applied to wood and grass biomass over the past 30 years to maximize the solid yield of biomass materials, thus producing large fraction of biochar ranging from 70 to 85% of the input raw material for use in energy, metallurgical fuel, chemical and fertilization applications. Brimstone tree (Morinda lucida) also known as Oruwo in Yoruba language is one of the 80 species in the genus morinda of the pyroidea family and it is a tropical rainforest tree. The wood is yellow hence the name brimstone tree. Morinda lucida is a medium sized tree at maturity up to 18 - 25 years evergreen shrub with bole and branches often crooked or gnarled; bark smooth scaly, grey to brown, stipules ovate or triangular, 1-7 mm long, falling early. Although the plant is very bitter, yet the whole plants; leaves, stem, bark and roots are known to have medicinal properties. The stem has high energy content to be used in production of charcoal for the local gunpowder. These entirely play important role in satisfying human needs for energy and life processes (Adeleye et al., 2018). 2. Materials and Methods 2.1 Materials and Equipment The materials and the equipment used in this study are stated in the following sections: 2.1.1 Materials needed for the Experiment The materials used for the experiment in the course of this study is Brimstone wood 2.1.2 Equipment and Tools used for the Experiment The following equipment were used for the experiment in the course of this study: Electrically heated torrefaction reactor, Laboratory oven drier, electronic weighing scale, Hammer mill, Sieve saker, Bulb calorimeter, Stopwatch, Desiccator, Moisture can, Polythene, Bowl, Sample container, Knife, Cutlass, Thermocouple. 2.2 Methods 2.2.1 Collection and preparation of Brimstone (Morinda lucida) Wood Brimstone (Morinda lucida) wood was collected from brimstone tree from a private farm in Iseyin, Iseyin Local Government Area, Oyo State, Nigeria. The leafy parts of the harvested matured wood were cut away from the woody parts. The fresh wood was cut into small sizes manually using a cutlass and then sun dried for some days to reduce the moisture content of the wood to safe storage level of about 12% moisture content wet basis for further studies. The sun-dried samples were crushed into smaller sizes using hammer mill and sieves into different particle sizes using a set of sieves and the sieve shaker. From the sieving operations, three particle sizes; 12 mm which were particles that passed through sieve size 12 mm and retained on 10 mm sieve, 10 mm which were particles that passed through 10mm and retained on 8mm sieve and also 8 mm particles that passed through sieve size 8 mm and retained on 6 mm sieve were collected separately for the experiments. The particles sizes are shown in plate 1 (a-d). 2.2.2 Determination of the Ultimate Composition of the Solid Biochar Product Samples of the solid biochar products obtained after torrefaction process were characterized using the methods and procedures of the ASTM D3173-86 standard (2007). The ultimate composition of the biochar determined includes nitrogen content, carbon content, hydrogen content, oxygen content and sulfur contents. The higher and lower heating values of the biochar were also determined (Jaya, 2016). http://www.azojete.com.ng/ mailto:jibolarufai@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December 2024; Vol.20(4)813-827. ISSN 1596-2490; e-ISSN2545-5818; www.azojete.com.ng Corresponding author’s email address: jibolarufai@gmail.com 815 (a) (b) (c) (d) Plate 1: Brimstone wood; (a) Raw wood, (b) 12 mm wood particle size, (c) 10 mm wood particle size, (d) 8 mm wood particle size 2.2.3 Determination of Calorific Value The calorific value of the samples was determined using bomb calorimeter in accordance with ASTM D5865 (2010) standard method. The high and low calorific values which were determined by using the dulong formula as given by Equations 1 and 2 HCV = 4.18 ∗ (78 ∗ 𝐶 + 241.3 ∗ 𝐻∗𝑂 8 + 22.1 * S (1) LCV = 4.18 ∗ (94.19 ∗ 𝐶 − 0.550 − 52.14 ∗ 𝐻) (2) where: HCV = Higher calorific value, kcal/100g, LCV = Lower calorific value, kcal/100g, C = Percentage of carbon content, (%), H = Percentage of hydrogen content, (%) and O = Percentage of oxygen content, (%). 2.2.4 Torrefaction Process Torrefaction of the sample materials were carried out using the modified torrefaction device separately. The prepared samples were processed according to the experimental design layout suggested by the Design Expert software. Equal sample weight of 30 g was used for the two samples in all the experiments. For each experimental run, the desired 30g of the sample was first loaded into the reactor box and then covered up with the lid plate. The heating element connected to electrical source is then switched on and allowed to heat up the heating chamber to the desired preset heating temperature which is read on the temperature monitor. When the preset heating temperature is reached, the loaded reactor is quickly introduced into the heating chamber and allowed to remain in the heating chamber to be heated up to the desired heating temperature for the desired heating time or retention time monitored using a stopwatch. At the end of the retention time, the heating element is switched off and the heated reactor withdrawn from the heating chamber and placed in the desiccator to cool down in the absence of air. After proper cooling, the difference in weight of sample http://www.azojete.com.ng/ mailto:jibolarufai@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December 2024; Vol.20(4)813-827. ISSN 1596-2490; e-ISSN2545-5818; www.azojete.com.ng Corresponding author’s email address: jibolarufai@gmail.com 816 before and after heat treatment is taken as the weight of biochar material remaining and collected from inside the heating reactor. The collected biochar product obtained is weighed, packed, labeled and characterized for the proximate and ultimate compositions. The experimental procedure was repeated for other runs and sample materials. The data collected from the measurement of the weight of the torrrefied solid biochar product was used to evaluate biochar mass yield, energy yield and energy density using Equations 3, 4 and 5, respectively (Bergman et al, 2005). Biochar Mass Yield (BMY): 𝐵𝑀𝑌 = 𝑀𝑝 𝑀𝑟 × 100 (3) Biochar Energy Yield (BEY): 𝐵𝐸𝑌 = 𝐵𝑀𝑌 × 𝐻𝐻𝑉𝑝 𝐻𝐻𝑉𝑟 ∗ 100% (4) Biochar Energy Density (BED): 𝐵𝐸𝐷 = 𝐵𝐸𝑌 𝐵𝑀𝑌 (5) where: BMY= Biochar Mass Yield, %, BEY = Biochar Energy Yield, %, BED = Biochar Energy Density, MP= Mass of torrefied product, (g), Mr= Mass of raw biomass, (g), HHVr = High Heating Value of raw biomass, (MJ/kg), HHVp= High Heating Value of torrefied product (MJ/kg). 2.2.5 Experimental Design and Statistical Analysis The influence of the experimental conditions of heating temperature from 220 to 300 OC (220, 260 and 300 OC) at 40 OC interval and heating time from 30 to 90 min (30, 60 and 90 min) at 30 min intervals and sample sizes from 8 to 12 mm (8, 10 and 12 mm) at 2 mm intervals for both brimstone wood and ackee fruit pod on the solid biochar product yields and on the properties of the solid biochar products were studied. The experimental range and levels of the process variable codes are presented in Table 1. The data obtained were analysed using 3 factors; heating temperature, heating time and sample size at 3 levels of variation each using 3-factor, 3-level Box-Behnken experimental design of 17 runs at significant level of p ≤ 0.05 of the Design Expert 12.0. The experiments were carried out according to the design matrix proposed by the software as presented in Table 2. Table 1: Experimental Range and Levels of Process Variable Codes Parameter Unit -1 0 1 Heating temperature (OC) 220 260 300 Heating time (min) 30 60 90 Sample size (mm) 8 10 12 http://www.azojete.com.ng/ mailto:jibolarufai@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December 2024; Vol.20(4)813-827. ISSN 1596-2490; e-ISSN2545-5818; www.azojete.com.ng Corresponding author’s email address: jibolarufai@gmail.com 817 Table 2: Experimental Design Layout for the Sample Materials Std Run A (OC) B (Min) C (mm) 1 1 220 30 10 9 2 260 30 8 11 3 260 30 12 12 4 260 90 12 17 5 260 60 10 15 6 260 60 10 7 7 220 60 12 2 8 300 30 10 8 9 300 60 12 13 10 260 60 10 14 11 260 60 10 16 12 260 60 10 5 13 220 60 8 10 14 260 90 8 3 15 220 90 10 6 16 300 60 8 4 17 300 90 10 A: Heating Temp; B: Heating Time; C: Sample Size. 3. Results and Discussion 3.1 Modified Torrefaction Reactor and Torrefied Biomass Materials The torrefaction device system consisting of the heating chamber, reactor, the thermocouple for the regulation of the required heating temperatures and the cooling system used for the experiment. Samples of the torrefied biochar materials subjected to various conditions of heating temperature and heating time and obtained after the torrefaction process are shown in plate 2 for the brimstone wood. The biochars obtained from the sample materials as shown in plate 2 were observed to vary in colours from visual image observation with variation in heating temperature and heating time. It was observed that the higher the heating temperature and heating time the darker the biochar from visual image observation. This indicates that the colour of the torrefied products (biochar) changes with increasing torrefaction conditions. Similar morphological changes in colour of paddy straw from yellowish to brown and then dark with torrefaction duration was reported by Swapnaja et al. (2020). http://www.azojete.com.ng/ mailto:jibolarufai@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December 2024; Vol.20(4)813-827. ISSN 1596-2490; e-ISSN2545-5818; www.azojete.com.ng Corresponding author’s email address: jibolarufai@gmail.com 818 Plate 2: Torrefied brimstone wood Samples Note: Ti,ii,iii = 220, 260, 300 0C; ti, ii, iii = 30, 60, 90 min; Si, ii, iii = 8, 10, 12 mm T = Heating Temperature, 0C; t = Heating time, min; S = Sample Size, mm. 3.2 Effects of Torrefaction Processing Parameters on Biochar Mass Yield, Energy Yield and Energy Density The result of the effects of heating temperature, heating time and sample size on the biochar mass yield, energy yield and energy density of the torrefied samples; brimstone wood are presented in this section. 3.2.1 Effects of processing Parameters on Brimstone Wood Biochar Mass Yield The design matrix and results of the biochar yields and density obtained for brimstone wood are presented in Table 3. The software presented a model and regression analysis to correlate the biochar mass yield with the independent variables of heating temperature, heating time and sample size considered for the study using a first order polynomial equation for the brimstone wood biochar mass yield as presented in Equation 6. 𝐵𝑏𝑚𝑦(%) = +300.84187 − 0.947062 𝐴 − 0.354917 𝐵 − 11.26875 𝐶 − 0.001333 𝐴𝐵 + 0.021875 𝐴𝐶 + 0.036250 𝐵𝐶 + 0.000861 𝐴² + 0.001447 B² + 0.150625 C² (6) T i S i t i T i S i t ii T i S ii t i T i S iii t ii T ii S i t i T ii S ii t i T ii S ii t ii T ii S iii t ii T iii S iii t iii T iii S ii t iii T iii S ii t ii T iii S i t ii T iii S i t i http://www.azojete.com.ng/ mailto:jibolarufai@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December 2024; Vol.20(4)813-827. ISSN 1596-2490; e-ISSN2545-5818; www.azojete.com.ng Corresponding author’s email address: jibolarufai@gmail.com 819 where: Bbmy = Biochar mass yield of brimstone wood, %, A = Heating temperature, 0C, B = Heating time, min, C = Sample size, mm. The ANOVA results and statistical parameters of the analysis which describes the relationship between the independent variables and the dependent variable, biochar mass yield is as presented in Table 4. The probability of the model p-value and F-value of 0.0009 and 14.75 of brimstone wood biochar mass yield, indicates that the model suggested by the software for the material was significant at 95% confidence level. The R2 value evaluated for the biochar yields of brimstone wood is 0.9499 meaning 94.99% of the variability can be accounted for and showing the regression model was satisfactory for the prediction of the biochar mass yield from brimstone wood. The ANOVA results of the model terms presented in Table 4 shows that A, B and A2 are significant model terms, while it is shown in Equation 6 that AC, BC, A2, B2 and C2 model terms have synergistic effect on biochar yield and A, B, C and AB have antagonistic effect. Table 3: Design Matrix and Results of Brimstone Wood Biochar Mass Yield, Energy Yield and Energy Density Std Run A (OC) B (min) C (mm) Brimstone Wood Mass Yield (%) Energy Yield (%) Energy Density 10 1 260 90 8 38.7 44.07 1.14 14 2 260 60 10 56.1 63.23 1.13 9 3 260 30 8 73.3 76.79 1.05 15 4 260 60 10 54.7 61.86 1.13 17 5 260 60 10 53.9 61.05 1.13 16 6 260 60 10 55 62.09 1.13 13 7 260 60 10 53.6 56.90 1.06 1 8 220 30 10 89.7 93.38 1.04 7 9 220 60 12 82.7 86.63 1.05 6 10 300 60 8 50.7 56.80 1.12 3 11 220 90 10 85.3 91.58 1.07 4 12 300 90 10 39.7 45.77 1.15 12 13 260 90 12 34 38.99 1.15 5 14 220 60 8 86.3 92.65 1.07 11 15 260 30 12 71.7 79.31 1.11 2 16 300 30 10 63.3 70.04 1.11 8 17 300 60 12 40.3 45.72 1.13 A: Heating Temp; B: Heating Time; C: Sample Size http://www.azojete.com.ng/ mailto:jibolarufai@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December 2024; Vol.20(4)813-827. ISSN 1596-2490; e-ISSN2545-5818; www.azojete.com.ng Corresponding author’s email address: jibolarufai@gmail.com 820 Table 4: ANOVA Result of Mass Yield for Brimstone Wood Source Sum of Squares df Mean Square F-value p-value Conclusion Model 4950.78 9 550.09 14.75 0.0009 Significant A 2812.50 1 2812.50 75.40 < 0.0001 Significant B 1257.51 1 1257.51 33.71 0.0007 Significant C 51.51 1 51.51 1.38 0.2784 Not significant AB 92.16 1 92.16 2.47 0.1600 Not significant AC 11.56 1 11.56 0.3099 0.5951 Not significant BC 2.40 1 2.40 0.0644 0.8070 Not significant A² 679.92 1 679.92 18.23 0.0037 Significant B² 19.15 1 19.15 0.5133 0.4969 Not significant C² 23.60 1 23.60 0.6327 0.4525 Not significant Residual 261.11 7 37.30 Lack of Fit 257.22 3 85.74 88.12 0.0004 Significant Pure Error 3.89 4 0.9730 Cor Total 5211.90 16 Statistical Parameters R2 = 0.9499 Adj R2 = 0.8855 Pred R2 = 0.2092 Adeq Precision = 13.3585 The three-dimensional surface graph (3D) and two-dimensional contour (2D) in Figure 1 (a, b and c) showed the effects of heating temperature, heating time and sample size on the biochar mass yield of brimstone wood. The combined effect of heating temperature and heating time on the biochar mass yield of brimstone wood is shown in Figure 3a in three-dimensional surface and contour graphs. Figure 1a shows that biochar mass yield decreased with increase in heating temperature and heating time. The maximum and minimum biochar mass yields were obtained to be 85.3 and 39.7% at 220 0C, 90 mins and 300 0C, 90 mins respectively. Figure 1b for the combined effect of heating temperature and sample size shows that biochar mass yield decreases with an increase in heating temperature. The maximum and minimum biochar mass yields of 82.7 and 40.3% were obtained at 220 0C, 12 mm and 300 0C, 12 mm respectively. While it is shown in Figure 1c for the combined effects of heating time and sample size that increased in heating time results in decreases in biochar mass yield and vice versa. The maximum and minimum biochar mass yields were obtained to be 71.7 and 34.0% at 30 min, 12mm and 90 min, 12 mm, respectively. Similar decreases in biochar mass yield of patula pine wood and wood pellet from 67.75 – 98.46% and 39.2 – 80.3%, respectively at heating temperature range of 200 – 300 OC was reported by Sergio Ramos et al. (2017) and Ozge et al. (2022), respectively. http://www.azojete.com.ng/ mailto:jibolarufai@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December 2024; Vol.20(4)813-827. ISSN 1596-2490; e-ISSN2545-5818; www.azojete.com.ng Corresponding author’s email address: jibolarufai@gmail.com 821 (a) (b) (c) Figure 1: Response surface of biochar mass yield of brimstone wood as influenced by (a) heating temperature and heating time, (b) heating temperature and sample size, (c) heating time and sample size 3.2.2 Effects of Processing Parameters on Brimstone Wood Biochar Energy Yield The design matrix and results of the biochar energy yield obtained for brimstone wood (Bbey) is presented in Table 5. The software presented a model and regression analysis to correlate the biochar energy yield with the independent variables of heating temperature, heating time and sample size considered for the study using polynomial equation for the brimstone wood biochar energy yield as presented in Equation 7. 𝐵𝑏𝑒𝑦(%) = +540.17519 − 4.05095 𝐴 + 0.88720 𝐵 + 19.73375 𝐶 − 0.004681 𝐴𝐵 − 0.015813 𝐴𝐶 − 0.031667 𝐵𝐶 + 0.007758 𝐴² + 0.001947 B² − 0.747562 C² (7) where: Bbey = Biochar energy yield of brimstone wood,%, A = Heating temperature, 0C, B = Heating time, min, C = Sample size, mm The ANOVA results and statistical parameters of the analysis which describes the relations between the independent variables and the dependent variable, biochar energy yield is as presented in Table 5. The probability of the model p-value and F- value of 0.0022 and 11.15 for brimstone wood biochar energy yield, indicates that the model suggested by the software for the material was significant at 95 % confidence level. The R2 value evaluated for biochar energy yields of brimstone wood is 0.9348 meaning 93.48 % of the variability can be accounted for, showing the regression models was satisfactory for the prediction of biochar energy yield of brimstone wood. The ANOVA results for the model terms presented in Table 5 shows that A, B and A2 are significant model terms. While it is shown in Equation 7 that B, C, A2 and B2 have synergistic effect on biochar energy yield while A, AB, AC, BC and C2 have antagonistic effect. http://www.azojete.com.ng/ mailto:jibolarufai@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December 2024; Vol.20(4)813-827. ISSN 1596-2490; e-ISSN2545-5818; www.azojete.com.ng Corresponding author’s email address: jibolarufai@gmail.com 822 Table 5: ANOVA Result of Energy Yield for Brimstone Wood Source Sum of Squares Df Mean Square F-value p-value Conclusion Model 4778.13 9 530.90 11.15 0.0022 Significant A-HT 2661.22 1 2661.22 55.91 0.0001 Significant B-Ht 1227.85 1 1227.85 25.80 0.0014 Significant C-SS 48.31 1 48.31 1.02 0.3472 Not significant AB 126.23 1 126.23 2.65 0.1475 Not significant AC 6.40 1 6.40 0.1345 0.7247 Not significant BC 14.44 1 14.44 0.3034 0.5989 Not significant A² 648.69 1 648.69 13.63 0.0077 Significant B² 12.93 1 12.93 0.2716 0.6183 Not significant C² 37.65 1 37.65 0.7910 0.4033 Not significant Residual 333.19 7 47.60 Lack of Fit 309.44 3 103.15 17.37 0.0093 Significant Pure Error 23.75 4 5.94 Cor Total 5111.32 16 Statistical Parameters R2 = 0.9348; Adj R2 = 0.8510 Pred R2 = 0.0241; Adeq Precision = 11.5762 The three-dimensional surface graph (3D) and two-dimensional contour (2D) in Figure 2 (a, b and c) shows the effect of heating temperature, heating time and sample size on the biochar energy yield of brimstone wood. The combined effect of heating temperature and heating time on the biochar energy yield on brimstone wood is as shown in Figure 2a in the three-dimensional surface and contour graphs. Figure 2a shows that energy yield increase as the heating temperature and heating time increase. The maximum and minimum biochar energy yields were obtained to be 93.38 and 45.72 % at 220 0C, 30 min and 300 0C, 90 min, respectively. Figure 2b reveals that energy yield decreased with increase in heating temperature only. The maximum and minimum biochar energy yields of 92.65 and 50.7% were obtained at 220 0C, 8 mm and 300 0C, 12 mm, respectively. While Figure 2c shows that increase in heating time gives decrease in biochar energy yield and vice versa. The maximum and minimum biochar mass yields were obtained to be 76.79 and 38.99% at 30 min, 8 mm and 90 min, 12 mm, respectively. Decrease in biochar energy yield of patula pine wood and wood pellet from 78.51 to 99.46% and from 59.9 to 85.4% at heating temperature range of 200 to 300 O C was reported by Sergio Ramos et al. (2017) and Ozge et al. (2022), respectively. http://www.azojete.com.ng/ mailto:jibolarufai@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December 2024; Vol.20(4)813-827. ISSN 1596-2490; e-ISSN2545-5818; www.azojete.com.ng Corresponding author’s email address: jibolarufai@gmail.com 823 (a) (b) (c) Figure 2: Response surface of biochar energy yield of brimstone wood as influenced by (a) heating temperature and heating time (b) heating temperature and sample size (c) heating time and sample size 3.2.3 Effects of Processing Parameters on Brimstone Wood Biochar Energy Density The result of the effects of heating temperature, heating time and sample size on the biochar energy density of the torrefied samples, brimstone wood were presented in this section. The design matrix and results of the biochar energy density obtained for brimstone wood are presented in Table 6. The design matrix and results of the biochar energy density obtained for brimstone wood (Bbed) is presented in Table 6. The software presented a model and regression analysis to correlate the biochar energy yield with the independent variables of heating temperature, heating time and sample size considered for the study using polynomial equation for the brimstone wood biochar energy density as presented in Equations 8. Bbed(%) = −0.244531 + 0.011109 𝐴 − 0.000354 𝐵 − 0.039063 𝐶 + 2.08333E − 06 𝐴𝐵 + 0.000125 𝐴𝐶 + 0.000063 𝐵𝐶– 0.000022 A2 – 2.08333E-06 B2 + 0.000156 C2 (8) where: Bbed = Biochar energy density of brimstone wood, A = Heating temperature, 0C, B = Heating time, min, C = Sample size, mm The ANOVA results and statistical parameters of the analysis which describes the relations between the independent variables and the dependent variable, biochar energy density is as presented in Table 6. The probability of the model P-value and F-value of 0.0001 and 2803.33 of brimstone wood biochar energy density, indicates that the model suggested by the software for the material was significant at 95 % confidence level. The R2 value evaluated for biochar energy density of brimstone wood is 0.9990 meaning 99.90 % of the variability can be accounted for showing the regression model was satisfactory for the prediction of biochar energy density brimstone wood. The ANOVA results for the model terms presented in Table 8 shows that A, B, AB, AC, BC and A2 are significant model terms, while it is shown from Equation 8 that A, AB, AC, BC and C2 have synergistic effect on biochar energy density and B, C, A2 and B2 have antagonistic effect. http://www.azojete.com.ng/ mailto:jibolarufai@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December 2024; Vol.20(4)813-827. ISSN 1596-2490; e-ISSN2545-5818; www.azojete.com.ng Corresponding author’s email address: jibolarufai@gmail.com 824 Table 6: ANOVA Result of Energy Density of Brimstone Wood Source Sum of Squares Df Mean Square F-value p-value Conclusion Model 0.0184 9 0.0020 543.84 < 0.0001 Significant A 0.0105 1 0.0105 2803.33 < 0.0001 Significant B 0.0015 1 0.0015 405.00 < 0.0001 Significant C 2.083E-06 1 2.083E-06 405.00 0.4896 Not significant AB 0.0000 1 0.0000 6.67 0.0493 Significant AC 0.0004 1 0.0004 106.67 0.0001 Significant BC 0.0000 1 0.0000 7.50 0.0409 Significant A2 0.0041 1 0.0041 1083.000 < 0.0001 Significant B2 0.0000 1 0.0000 3.00 0.1438 Not Significant C2 1.250E-06 1 1.250E-06 0.33333 0.5887 Not Significant Residual 0.0000 5 3.750E-06 Lack of Fit 0.0000 2 9.375E-06 Pure Error 0.0000 3 0.0000 Cor Total 0.0184 14 Statistical Parameters R2 = 0.9990 Adj R2= 0.9971 Pred R2= 0.2959 Adeq = Precision 68.384 The three-dimensional surface graph (3D) and two-dimensional contour (2D) in Figures 3 (a, b and c) shows the effect of heating temperature, heating time and sample size on the biochar energy density of brimstone wood. The combined effect of heating temperature and heating time on the biochar energy density on brimstone wood is shown in Figure 3a in form of three-dimensional surface graph. Figure 3a shows that energy density increases as the values of heating temperature and heating time increases. The maximum and minimum biochar energy density was obtained to be 1.15 and 1.04 at 300 0C, 90 mins and 220 0C, 30 mins respectively. Figure 3b shows that the energy density increased with increase in heating temperature and sample size. The maximum and minimum biochar energy density of 1.14 and 1.05 obtained at 300 0C, 12mm and 220 0C, 8mm respectively. Also, Figure 3c shows that increase in heating time gives increase in biochar energy density and vice versa. The maximum and minimum biochar energy density were obtained to be 1.15 and 1.11% at 90 mins, 8 mm and 30 mins, 8 mm respectively. Similar increase in biochar energy density of poplar chip from 0.99 to 1.15 at temperature range of 200 to 300 OC was reported by Xun Luo (2011). (a) (b) http://www.azojete.com.ng/ mailto:jibolarufai@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December 2024; Vol.20(4)813-827. ISSN 1596-2490; e-ISSN2545-5818; www.azojete.com.ng Corresponding author’s email address: jibolarufai@gmail.com 825 (c) Figure 3: Response surface of biochar energy density of brimstone wood as influenced by (a) heating temperature and heating time (b) sample size and heating temperature (c) heating time and sample size 3.3 Ultimate Composition of Torrefied Brimstone Wood Solid Products The results obtained for the ultimate analysis of the solid torrefied brimstone wood products are as presented in Table 7. In the Table, the torrefaction holding time for the experiments was 60 min. From Table 7, it can be inferred that the weight percentage of carbon in the torrefied solid products increased from 55.21 - 67.40% for the brimstone wood as the torrefaction temperature is increased from 220 to 300 OC. Similar increase in carbon content of Colombian wood species from 52.73 to 55.01 as torrefaction temperature is increased from 200 to 300 OC have been reported by Margareta et al. (2021). The increase in the carbon content is only an apparent increase due to the decrease in the oxygen content from 43.74 to 38.05% for patula pine at torrefaction temperature range of 200 to 300 OC. These results indicate that the torrefaction process increases the energy density of the products by removing oxygen (Sergio Ramos et al., 2017 and Jinxia Fu et al., 2021). From Table 7, it can be deduced that the nitrogen content increased slightly from 0.57 to 0.83% for the brimstone wood. This result is similar with increase in nitrogen from 0.13 to 0.15% for the patula pine torrefied from 200 to 300 OC reported by Sergio Ramos et al. (2017). The increase in nitrogen is a relative increase due to decrease level of oxygen (Jaya, 2018). While sulfur content did not vary much with an increase from 0.87 to 0.64% and from 1.70 to 1.55% for the brimstone wood at torrefaction temperature between 200 to 300 OC. Similar observations were made by Jaya (2016) that sulfur content decreased from 0.25 to 0.11 % for 160 and 270 OC torrefaction temperature for lodge pine grind. From Table 7, the energy content obtained for the brimstone wood products as presented shows that the energy content increased from 26.20 to 28.55 MJ/Kg for brimstone wood with increased in torrefaction temperature from 220 to 300 OC. Similar increases in energy content were reported for wood waste from 20.18 to 24.00 MJ/kg by Margareta et al. (2021) at torrefied temperature range of 225 to 300 OC. The energy content of the products indicates the ability to do work. The higher the energy contents of a sample the higher the work that will be done (Unroto et al., 2020). Table 7: Ultimate Composition of Raw and Torrefied Brimstone Wood Heating Temperature, 0C Sample Properties Unit Raw 220 260 300 Brimstone Wood Carbon Content % 52.20 55.21 57.96 67.40 Oxygen Content % 36.88 35.55 33.40 29.50 Hydrogen Content % 2.40 2.32 2.21 2.13 Nitrogen Content % 0.54 0.57 0.67 0.83 Sulfur Content % 0.89 0.87 0.71 0.64 Energy Content MJ/kg 24.59 26.20 27.85 28.55 http://www.azojete.com.ng/ mailto:jibolarufai@gmail.com Arid Zone Journal of Engineering, Technology and Environment, December 2024; Vol.20(4)813-827. ISSN 1596-2490; e-ISSN2545-5818; www.azojete.com.ng Corresponding author’s email address: jibolarufai@gmail.com 826 4. Conclusions i. The surface colour of the torrefied products (biochar) changes with increase in torrefaction conditions. Biochar mass yield decreases with increases in torrefaction conditions for the biomass materials. Biochar energy yield increases as the value of torrefaction conditions decreased for the two samples. While Biochar energy density increases as the torrefaction condition increases. Similar results were reported by (Sergio Ramos et al., 2017 who worked on patula pine wood. ii. The values of ultimate ecomposition of carbon, oxygen, hydrogen, nitrogen, sulfur and energy contents of biochar products for the brimstone wood have been obtained. The energy content increased from 26.20 to 28.55 MJ/kg for brimstone wood with increased in torrefaction temperature from 220 to 300 OC. References Adeleye, OO., Ayeni, OJ. and Ajamu, MA. 2018. Traditional and Medicinal uses of Morinda lucida. Journal of Medicinal Plants Studies, 6(2): 249-254. ASTM Standard D3173 2007. 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