[Stoves] Burning wet wood

[Kevin]

Dear Dale

----- Original Message ----- 
From: "Andreatta, Dale A." <dandreatta at sealimited.com>
To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org>
Sent: Wednesday, June 12, 2013 12:39 PM
Subject: [Stoves] Burning wet wood


> Have we ever looked at the question of how to design a stove to burn
> wood that is higher in moisture?  

# You ask the most difficult questions!! :-)

It would seem that this is very
> important practical issue, and that a stove that could burn wet wood
> would be very popular. 

# Yes, indeed!!

 What makes a stove burn wet wood well or poorly?

# The fundamental problem is that of "lack of sufficient energy in the primary combustion zone to gasify the fuel." So-called "Dutch Oven Furnaces" are specifically designed for burning "wet" biomass fuels. What they do is use an insulated gasifying chamber, so that as much as possible of the heat released when primary air is introduced to gasify the fuel, and some of the heat released on secondary air combustion, is reflected back onto the "wet fuel pile" to permit the "Gasification Plus Combustion Reaction" to continue.

> The only time I remember someone saying something about this was
> Crispin, who I believe said recently that preheating the primary air
> makes it possible to burn wetter wood. 

# Preheating of combustion air is certainly practical, and a "step in the right direction", but it is only helpful to a degree, in that the energy that preheated air can bring to the Primary Air Zone is limited.

 This would be easy with a batch
> stove, harder with continuous feed.  

# Certainly, if you had a "good fire going", it would be relatively easy to add some wet wood, without it quenching the fire. However, it would be very difficult to start with a batch of wet wood, and bring it up to "good combustion conditions." I would suggest that the best way to deal with consistently wet wood would be to:
1: Start the fire with a batch of dry wood, to get the system up to temperature
2:  When the stove/furnace is "up to temperature", switch over to "wet wood"
3: Run continuously.

Other than that, I can think of a
> couple things that might help burn wetter wood. 

# There are a number of things that can be done, if it is necessary that one burn wet biomass fuel, most of which complicate the burning operation and lead to a more costly "stove/furnace" system. The simplest solution, if it is practical, is to dry the fuel adequately beforehand, but if this is impractical, then these other techniques can be employed.

Best wishes,

Kevin
> 
> Dale Andreatta 
> 
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