Gross to Net Calorific Value

[gmannix2011]

Having obtained gross calorific values for a range of materials by testing in a bomb calorimeter, I need to convert these to net calorific values for inputting these into design formulas... Is there any way of converting gross to net?

Any help would be appreciated.

 

[macmet]

Both these sites should help,

http://lmgtfy.com/?q=Gross+to+Net+Calorific+Value

and,

http://en.wikipedia.org/wiki/Heat_of_combustion

 

[21121956]

Hello everybody:

In the thread481-143839 you can find some help. In addition to that, the Handbook of Mechanical Engineering Calculations (

http://www.digitalengineeringlibrary.com),

Section 6, Internal Combustion Engines indicates:

Higher Heating Value = 17680 + (60 * °API).


El que no puede andar, se sienta.

 

[21121956]

Hello everybody:

I really beg your pardon, I forgot to indicate the dimensional units:

Higher Heating Value = 17680 + (60 * °API) [BTU/lb]

El que no puede andar, se sienta.

 

[MortenA]

The difference between gross and net is that gross includes condensing any water developed during the chemical reaction from steam to water. This may or may not be possible in a burner and hence the two values.

So - if you dont have a table you could calculate the amount of water that will be produced from your reaction (burning) and subtract the amount of energy transferred when then water condenses. Or just use the tables.

Best regrads

Morten

 

[gmannix2011]

Thanks guys.

These formulae seem to be more for oil and diesel fuels etc rather that actual materials e.g. carpets, timbers etc?

Any further ideas because I am stumped!

 

[MortenA]

Get a condensing boiler ;-)

My guess would be that there are experimental results out there. You may have to pay for them but i think they will be there!

I'm not much into the experimental stuff - but if you had a bomb calorimeter where all the condensed water was measured then you could use this to back calculate the net calorific value.

Best regrads

Morten

 

[gmannix2011]

Pity I hadn't kept track of the condensed water now! I don't know what I'll do to convert my results now!

Is there any formula whereby I knew the moisture content of the sample that I could backtrack?

 

[MortenA]

The water comes from two sources:

-Hydrogene that combines with oxygene and forms water
-Water in the material that you burn.

Both will contribute to the difference between net and gross - but only the chemically bounded hydrogene will contribute to the overall value (but that besides the point).

I wood and similar i think the hydrogene content compared to carbon is low. But there may be some water. Maybe you could disregard the hydrogene and use a number for the dryness of the wood (as an average). Im running out of good idears here

Best regrads

Morten

 

[dcasto]

the exact method is defined in the standard GPA 2172.