Densification of Sawdust of Tropical Hardwoods and Maize Cobs at Room Temperature Using Low Compacting Pressure Without a Binder

This dissertation reports the findings of densifying maize cobs and sawdust of six selected tropical hardwood timber species at room temperature (25oC) using low compacting pressure (CP) varied from 10 MPa to 50 MPa, without a binder. The maize cobs was crushed using a hammer mill. Particle size 1mm or less of the maize cobs was used for the study. Sawdust of the six timber species were sun dried and graded into particle sizes (P): P ≤ 1 mm, 1 mm < P ≤ 2 mm and 2 mm < P ≤ 3.35 mm. Briquettes were produced using a laboratory hydraulic press and a piston. Physical and mechanical characteristics of briquettes determined were briquettes' stability, relaxed density, compressive strength (CS) in cleft, impact resistance index (IRI) and water resistance (WR) quality. Additionally, some physico-chemical and thermal properties of the biomass materials used for the study were determined. The study revealed that at 5% level of significance the density of timber species used for the study had significant negative correlation with CS in cleft, IRI and WR quality of briquettes produced. Furthermore, species density significantly and positively correlated with relaxed density of briquettes produced. Generally, species, particle size and CP had significant effect on stability in length and diameter, relaxed density, CS in cleft, IRI and WR quality of briquettes produced (p-value < 5%). Linear regression models established between the research factors and dependent variables suggested that species density, particle size and CP were good predictors of stability in length and diameter, relaxed density, CS in cleft, IRI and WR quality of briquettes produced. The multiple correlation coefficient (R) and adjusted R2 for the regression models ranged from 0.74 - 0.93 and 0.54 - 0.87 respectively with p-values less than 5%. The result further indicated that mixing sawdust of C. pentandra with P. africana or T. superba significantly improved upon the CS in cleft, IRI and WR quality of briquettes 6 produced. The mixing ratio of the sawdust also had significant effect on the mechanical and physical properties of the briquettes produced. The study further revealed that briquettes produced from maize cobs at low CP and room temperature had low CS in cleft, IRI and WR quality. However, these properties were significantly improved when maize cobs was combined with sawdust of C. pentandra, T. superba and P. africana. The gross calorific values of the six hardwood timber species were adequate and they ranged from 20.16 to 22.22 MJ/kg. The biomass materials used for the study were also found to be environmentally friendly since they contained low amount of nitrogen, sulphur and ash content. From this study it could be concluded that briquettes with adequate physical and mechanical properties could be produced from sawdust of tropical hardwood species and their mixture at room temperature using low CP. Additionally, briquettes with adequate physical and mechanical characteristics could be produced from maize cobs at room temperature using low CP when maize cobs particles are combined with sawdust of Ceiba pentandra. These findings could enhance the existing technology for densifying sawdust and maize cobs, especially in the rural communities.

Source: KNUST