Measuring and Managing Moisture

by | Nov 6, 2023 | Getting deeper | 0 comments

Managing moisture is crucial to ensure efficient, consistent, and high-quality woodgas production. Moisture in fuel is a central challenge in pyrolysis for making woodgas.

Problems stemming from excess moisture are the following:

  1. Energy Consumption: Moisture requires energy to evaporate, diverting heat that could otherwise be used for pyrolysis, making the process less efficient.
  2. Gas Quality: Excess moisture can dilute the produced gas and lead to the formation of unwanted compounds, reducing the quality and energy content of the woodgas.
  3. Process Stability: High moisture can lead to inconsistent temperatures and conditions, making the pyrolysis process unstable and less predictable.

But how can one measure the moisture level of woodchips?

The oven-drying method is often considered the best and most accurate method to measure the moisture content of woodchips, although it is more time-consuming than using a moisture meter – that does not work very well with material like woodchips.

Here’s a step-by-step guide on how to do it:

  1. Weigh a Sample: Take a representative sample of the woodchips and weigh it. This is the “wet” or “green” weight. Make sure to note this weight down.
  2. Dry the Sample: Place the sample in an oven set at around 103°C (217°F) and let it dry for about 24 hours. This temperature is high enough to evaporate the moisture but not high enough to burn the wood.
  3. Weigh the Dried Sample: After 24 hours, take the sample out of the oven and weigh it again. This is the “oven-dry” weight.
  4. Calculate the Moisture Content: Subtract the oven-dry weight from the green weight to find the weight of the water that was in the sample. Then, divide this by the oven-dry weight and multiply by 100 to get the moisture content as a percentage. The formula looks like this: Moisture Content (%) = ((Green Weight – Oven-dry Weight) / Oven-dry Weight) * 100

For woodchips meant for use as fuel in a biomass system, a moisture content below 30% is generally ideal, though the specific ideal can depend on the specific system. Remember that accuracy in these measurements is key for optimal operation of your wood gasifier or other systems using woodchips as a fuel source.

This method, while more time-consuming than others, is highly accurate and is considered the standard for measuring moisture content in woodchips and similar materials.


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