[Stoves] Calculation help

[ajheggie at gmail.com]

Hi all please find below a post from Frank Shields that didn't propagate 
to the list for some reason. My uneducated way of addressing this would 
be to consider what would the outcome be with a fossil fuel with 
negligible water. So I would calculated on the oven dry mass and then 
subtract the latent heat of the water from the hydrogen in the fuel at 
the temperature it was discarded as vapour. This would give the LHV of 
the oven dry sample. I tend to look on un chemically bound water a bit 
like salts of hydration and would then deduct their latent heat from the 
LHV to give me the actual available heat.

Mind I'm not looking at losses to the 4th decimal place so I think in 
approximations and genrally use a figure of -2.7MJ for water discarded up 
the flue. 

I'm open to argument for a more precise approach.

Also there is a potential ambiguity if we don't specify the basis on which 
our moisture content is calculated, for this purpose I feel it should be 
on the gross wet weight of the sample.

AJH

********************

Dear Stovers,

 

A few questions and checks on some calculations if you don't mind.

 

1)      Should the HHV value be reported as if the biomass is 100 grams of
oven dried material or reported on the dry fraction of a 100 g sample
received? 

2)      Having an analysis: Dry wt.

Percent dry wt.

N = 1.5

C = 42.0

H = 6.2

S = 0.03

Ash = 1.6

Water in receiving sample

Water = 17.6%

 

The HHV = 20.37 based on the dry sample and 16.79 based on the weight of 
an
as-Received sample and the formula I am using.

 

Now questions about determining the LHV:

17.6 g water per 100 grams wet compost or 0.176 g water per gram wet
compost.

It takes 0.0552 kj to take the temperature from 25c to 100c

It takes 0.3964 kj to 100c water to 100c vapor

It takes 0.0907 kj to 100c vapor to 400c vapor

 

Total = 0.5423 kj lost from the water moisture

 

 

Then we have the water produced from the hydrogen in the biomass. 

If we start with 6.2 % hydrogen and find the char has retained 2.2 so 4.0%
hydrogen has converted to water vapor.

That is 0.04 g hydrogen per gram biomass

That is 0.18 g water vapor starting at 450c per gram biomass 

 

Total 0.5901 kj energy lost in the vapor at 450c

 

 

The HHV = 20.37 kj/g on a dry sample

 

The HHV = 16.79 kj/g on the dry fraction of an as-received biomass sample

 

The LLV = 16.79-(0.5423 + 0.5901) =15.66 kj/g as-Received biomass

 

 

Thanks 

 

Frank

 

 

 

 

 

Frank Shields

42 Hangar Way

Watsonville,  CA  95076

(831) 724-5244 tel

(831) 724-3188 fax

frank at bioCharlab.com