How many tons of material required to produce one ton of wood pellet? This figure is named as conversion factor.
Conversion factor depends on: (i) the moisture content of input material and output product, (ii) fuel consumption for dryer, and (iii) dust collection during production.
This post will describe how to calculate conversion factor for wood pellet.
i. Moisture content
The material in each area is different in moisture content. In tropical countries in South East Asia, such as Vietnam, the moisture content can be up to 52%. The output wood pellet moisture content should be less that 10%.
Consider the case producing 100 tons of wood pellet with moisture content 8%. Here, 92 tons are dry weight and 8 tons are water in the content of wood pellet.
The water is evaporated during wood pellet production process, while dry weight is kept the same. This mean 92 tons of dry weight is counted 48% (100% less moisture content 52%) in the wood chip weight.
The wood chip weight (moisture 52%) to produce 100 ton of wood pellet (moisture 8%) is 92/48% = 192 ton.
Wood chip | Wood pellet | |
Material | 192 | 100 |
Moisture | 52% | 8% |
Dry weight | 92 | 92 |
Water weight | 100 | 8 |
ii. Fuel consumption
Fuel consumption rate is the amount of wood fuel used to dry one ton of input material. This rate depends on the input moisture content and dryer technology. There is not such an accurate formula for this rate. This figure is consulted from the dryer supplier. The range for fuel consumption rate is usually around 12% to 20%.
For example, the rate is 15%. This mean the required amount for fuel is 192 x 15% = 29 tons.
iii. Dust loss
Material is loss during production due to dust collection. There is a small percent of material loss, such as 1%-2% if the dust collection system is good enough. This number could be as high as 8%-10% for low tech system.
The total material and fuel without dust loss is 192 + 29 = 221 tons.
Iif the amount of material loss due to dust is 2% of finished product, the dust loss is 2% x 221 = 4 tons.
Therefore, total amount material and fuel required are 221 + 4 = 225 tons.
The conversion factor is 2.25 as it required 225 tons of material to produce 100 tons of wood pellet, given moisture content, fuel consumption and dust loss figure is assumed as above.
The formula for the conversion factor as below:
conversion factor = (1-wood pellet moisture)/(1-input moisture) x (1+ fuel consumption rate) x (1+ dust loss rate)
The excel file to calculate conversion factor as the attached file below: