[Stoves] Emissions from Residential Wood Combustion: Effect ofMoisture on Emissions

[Crispin Pemberton-Pigott]

Dear Frank

You guessed quite rightly.

>Is a 'dry basis' 100 grams of dry wood + 20 mls water
>reported as 20% moisture on a dry basis?

Unfortunately the EPA and Canadian tests (Canmet) apparently use dry basis 
(still waiting for confirmation) and we have always talked about wet basis 
because it is directly assessible from a small sample.

WWB v.s. DWB

Example: For wet weight basis 1000 gm wood sample, dried gives 876 gm means 
87.6% wood content, therefore what is left is water = 12.4% moisture WWB.

For dry weight basis 876 gm means ((1000-876)/876) * 100 = 14.15% moisture 
DWB, and the wood content is still 87.6%.

For labs testing things, DWB is no problem, but for a business mixing things 
like the clay project, it is a BIG problem.  The moisture of the ingredients 
has to be assessed each time a clay mix in prepared and WWB is the only 
thing that will do.

Suppose you want to add 15.8 kg of charcoal to a mix.  You weigh 1000 gm, 
dry it, and divide the 15.8 by the result of the second weighing:

Initial mass 1000 (1 Kg)
Final mass 891 mg (0.891 kg)
15.8 / 0.891 = the amount of damp charcoal you should add to the mix.

If I give that calculation to just about anyone, they get it right.  Asking 
them the same question in reverse, "How much moisture was in that piece of 
wood?"  I will get a WWB answer no matter what I write down.

Regards
Crispin