Monday, May 19, 2014

What happens when wood burns?

1. Evaporation of water
2. The emission of smoke
3. The charcoal phase

Evaporation of water: Up to half the weight of a freshly cut log is water. After proper seasoning the water content is reduced to about 20 percent. As the wood is heated in the firebox, this water boils off, consuming heat energy in the process. The wetter the wood, the more heat energy is consumed.

That is why wet firewood hisses and sizzles and is hard to burn, while properly seasoned wood ignites and burns easily.

Re-fueling with wet or unseasoned wood in a catalytic stove will send moist smoke to the catalytic combustor and cause the combustor to stop working. It will cause the stove to struggle and not operate properly. In addition re-fueling with wet or unseasoned wood and operating the stove with the by-pass closed, can cause damage to the catalytic combustor.

The emission of smoke:
As the wood heats up above the boiling point of water, it starts to smoke. The smoke is visible result of the decomposition of the solid wood as it vaporizes into a cloud of combustible gases and tar droplets.

The smoke will burn if the temperature is high enough and oxygen is present. When the smoke burns, it produces the bright red flames that are characteristic of wood combustion.

If smoke does not burn in the firebox, it will exit the appliance and into the chimney where it will either condense forming creosote deposits or be expelled as air pollution. unburned smoke represents an efficiency loss because it contains a large part of the total energy in the wood.

However, catalytic stoves with the use of a catalytic combustor, burns this smoke before it is expelled as air pollution and burns it as a fuel to produce heat that can be 2-3 times hotter than the firebox temperature. This also gives a higher efficiency out of the stove.

At the same time, the catalytic combustor will burn up to 90% of the creosote contained in the smoke.

The charcoal phase:
As the fire progresses and most of the gases and tars have vaporized out of the wood, charcoal remains. Charcoal is almost 100% carbon and burns with a red glow and very little flame or smoke. Charcoal is a good fuel that burns easily and cleanly when enough oxygen is present.

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