Development and Performance Evaluation of a Low-Cost Batch Torrefaction Reactor

Background and Objective: An attractive and less expensive process for biomass pretreatment is torrefaction. However, the high cost of torrefaction reactors, difficulties in providing a passive environment, cost of production and design complexities discouraged its utilization as a viable thermochemical alternative to other types of pretreatments. This study presents the development of a cheap and simple design small-scale batch reactor suitable for laboratory torrefaction experiments. Materials and Methods: The concept of co-firing in pulverized coal-fired stoves was utilized in the design reactor, comprising two chambers (the heating chamber and the torrefaction chamber (30 L)) for heating and torrefaction, respectively. Design considerations were such that reactor performance was optimal. Torrefaction temperature was between 250-300̊C with limited air supply at three residence times of 30, 45 and 60 min. Samples of Gmelina arborea sawdust produced from a CD4 band saw machine from a local sawmill were used in experimentation. The results were evaluated by comparing them with international market product standards. Results: The reactor percentage energy yield increased with torrefaction time, (36.33, 58.10 and 69.80%), respectively and torrefaction degree varied from 10.61±0.2, 34.29±0.2 and 71.18±0.2% for 30, 45 and 60 min, respectively and increased with increase in torrefaction time. The percentage weight loss decreased with increase in torrefaction time. The product characteristics are comparable with those of expensive and complex reactors. The product sample characteristics obtained with the developed reactor are comparable with products from expensive and complex reactors in terms of elemental composition, heating value and energy yields. Conclusion: The performance characteristics of the batch reactor and the products obtained were compared satisfactorily with standard reactors and products in literature; hence, a useful tool for producing desired torrefied biomass.