Project Background
In tropical developing countries, small and medium-sized wood processing enterprises commonly face two major challenges: the lack of reliable and affordable conventional energy sources (such as fuel oil or coal for steam boilers) to operate drying kilns, and the difficulty of disposing of large quantities of sawdust, offcuts, and other processing residues. Utilizing these wastes as a heat source for drying offers an effective solution to both issues.
In 2021, the Philippines' Department of Science and Technology - Forest Products Research and Development Institute (DOST-FPRDI) designed, constructed, and tested a prototype air-heated vacuum furnace type dryer powered by a biomass gasification furnace. This unit was specifically intended for drying timber and bamboo to meet quality requirements for both domestic and export markets.
Technical Solution
The core of this solution is to use high-temperature flue gas generated from biomass gasification as the heat source, supplying heat to the drying chamber via a hot-air system, combined with vacuum technology to accelerate the drying process.
Key Technical Specifications:
Drying Capacity: 500 board feet (approx. 1.18 m³)
Heat Source System: A biomass gasification furnace connected to a heat exchanger inside the kiln via an 8-inch diameter x 10-foot long flue pipe
Vacuum System: Double-stage liquid ring vacuum pump with a maximum pumping capacity of 1.5 m³/min and an ultimate vacuum pressure of -750 mmHg
Temperature Control: Operating temperature range of approximately 47-53°C, with a vacuum level of 30-40 kPa
Operating Data
Testing was conducted from March to June 2021. Due to COVID-19 restrictions, the kiln was operated intermittently (maximum 8 hours of operation per day).
Drying Performance:
| Material | Initial MC | Final MC | Drying Time |
|---|---|---|---|
| Yemane (25mm thick) | 106.3% | 10.2% | 168 hours (~7 days) |
| Mahogany (25mm thick) | 57.7% | 9.0% | 88 hours (~3.7 days) |
| Kawayan tinik bamboo | 115% | 9.4% | 73 hours (~3 days) |
Source: DOST-FPRDI 2021 Annual Report
Economic Analysis
Drying Cost (per board foot):
| Material | Cost (PHP/board foot) | Approx. USD/m³ |
|---|---|---|
| Yemane | 29.78 | ~$54/m³ |
| Mahogany | 20.68 | ~$38/m³ |
| Bamboo | 17.21 | ~$31/m³ |
Note: Exchange rate approximated at 1 USD ≈ 55 PHP. Cost is expected to decrease as dryer capacity increases.
Equipment Fabrication Cost:
Total Cost: PHP 572,123.60 (approx. USD 10,400)
Materials: PHP 394,568; Labor: PHP 177,555.60 (approx. 45% of material cost)
Lessons Learned & Replicability
This project validated the feasibility of using biomass gasification technology to supply heat for small-scale timber kilns in developing countries that lack access to steam heat sources. Using processing residues as fuel effectively reduced operating costs, while the introduction of vacuum technology significantly shortened the drying cycle for high-moisture-content timber and improved product quality. The kiln can be operated by a single worker, lowering the labor skill requirement.
This technical model is particularly suitable for small and medium-sized timber processing plants, bamboo processing facilities, and primary processing sites at the forestry level in tropical regions. It offers a sustainable technological pathway for adding value to products by utilizing self-generated waste materials.
