Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
Author: Subject: Does wood pyrolysis generate heat ??
International Hazard

Posts: 697
Registered: 7-9-2010
Member Is Offline

Mood: Reactive

[*] posted on 7-2-2021 at 03:34
Does wood pyrolysis generate heat ??

I read on wiki that pyrolyzing wood releases energy. I always thought that that process is endothermic (i.e. costs energy) and this is one of the reasons, only dry wood burns well, as only the burning of the pyrolyzed gases release energy, which is partially used by the pyrolyzing of the logs in the wood fire.

If this is true, then burning wood (assumed dry wood and complete combustion of the gases, so no PAH release) is more efficient than I thought ?

[Edited on 2021-2-7 by metalresearcher]
View user's profile View All Posts By User
International Hazard

Posts: 1646
Registered: 24-9-2005
Member Is Offline

Mood: Bored

[*] posted on 7-2-2021 at 10:40

The reason why wet wood burns (and heats) poorly is simple, all that water needs to be boiled away. If every pound of wood need to boil off a pound of water there is less energy left to produce heat.

We're not banging rocks together here. We know how to put a man back together.
View user's profile View All Posts By User
Hazard to Others

Posts: 213
Registered: 26-5-2019
Location: Sweden
Member Is Offline

[*] posted on 14-2-2021 at 09:54

I don't think that part of the wiki article is correct. Doesn't make sense. As a chemical reaction I think it is endothermic. If viewed from a bigger perspective and if the gasses that are evolved are actually burned, then it could be considered exothermic.

Burning wood is always a two step process. First is pyrolysis, where volatiles are being boiled out of the wood and combusted, generating lots of flames. Once pyrolysis is complete, step two starts which is the combustion of rhe charcoal that's left. This step can get much hotter since it's not being cooled down from boiling volatiles.
View user's profile View All Posts By User

Posts: 4
Registered: 11-1-2021
Member Is Offline

[*] posted on 18-2-2021 at 07:23

The pyrolysis process is exothermic. The reaction starts at about 200 degrees C. The heat of reaction is sufficient to increase the temperature to about 350 degrees. The heat of reaction is about 1600 J/gram which is 8-10% of the heat of combustion.

Source: Ullmanns Encyklop├Ądie der technischen Chemie, 4th edition.

If the heat needed to heat up the wood to 200 degrees is included the reaction is probably endothermic.
View user's profile View All Posts By User

  Go To Top