Production, cost and properties of charcoal produced after logging and sawing, by the earth pit method from Tectona grandis wood residues

Smallholders who own Tectona grandis plantations receive limited profit from residues. Charcoal production from wood residues allows smallholders to become part of the commercial chain. The purpose of this study was to examine the process of making charcoal from T. grandis wood residues using the earth pit method, as well as the costs and economic potential along with the physical, energy, mechanical, and chemical characteristics of the charcoal produced using this technique. Lumber in green condition (L-G), non-commercial logs in green condition (NL-G), and non-commercial logs in air-dried condition (NL-A) were utilized to produce charcoal. The charcoal recovery yield obtained from NL-A was 24%, with a carbonization time of 4.3 days, while for the NL-G and NL-A conditions, the recovery yield varied from 8 to 14.5%. The investment cost was US$1247 and the production cost was US$0.71/kg. The estimated total annual production is 11470 kg of charcoal, with annual profits of US$4863.3/year. The charcoal presented moisture content between 4.16 and 6.13%; density between 0.27 and 0.47 g/cm³; a calorific value between 31.3 and 32.6 MJ/kg; ash content between 1.5 and 3.3%; volatile content between 9.4 and 18.7%; fixed carbon content between 73.3 and 80.1% and the maximum compressive strength was about 120–132 kg. Statistical differences were found in carbon, fixed carbon content, nitrogen (N) and potassium (K) contents. The charcoal produced from NL-G raw material presents less quality than the charcoal from NL-A and L-G. This is because it presents less proportion of fixed carbon content. Finally, the results indicate the possibilities for smallholders to produce charcoal.