Wednesday, 22 February 2012

Energy recovery project in numbers.

We collect wort from our mash tun and heat it in the copper to boiling point, and beyond. The amount of energy (E) required to raise the temperature from T1 to T2 is given by:

E (kJ) = Cp x
Mwort x (T2-T1)

where Cp is the specific heat capacity of the wort (each material/liquid/gas requires different amounts of heat to raise its temperature and this difference is recognised in this constant).

and
Mwort is the mass of the wort in kg.

Assuming a specific gravity of 1.045, and a wort specific heat capacity of 4.0 kJ/kg/K the energy required to raise the temperature to near boiling, say 96
ºC, with a brew length of 2600 litres is therefore 2600 x 1.045 x 4 x (96-60) = 391,248 kJ.

When we boil, a lot of steam is driven up the flue and this contains a lot of potential energy, given by:

E (kJ) =
hfg x Mwater

where
hfg is the latent heat of evaporation, that is, the amount of energy per kg of steam released when a vapour condenses to a liquid. This constant is 2260 kJ/kg for water.

and
Mwater is the mass of steam condensed - which is the amount of water evaporated from the wort.

We boil off 7.5% of the wort volume, ie 195 kg. The energy we can recover by condensing this steam is 195 x 2260 = 440,700 kJ

So our project is aimed at recovering the energy from the steam, as close to all that 440,700 kJ of it, and using it to pre-heat the wort, that 391,248 kJ we're currently paying for. That actually represents over 35% of our brewhouse energy costs.

The trick is to design and build a system that can do this whilst not being prohibitively costly. I believe it can be done and I hope to show you how over the next 6 months. Then you too can look forward to night shifts.




3 comments:

Ed said...

Interesting stuff. Have a delta on me for the next installment: Δ

oracle ebs said...

Love the idea of this Eddie. It may be a mission to set up but I'm sure if you can get it working it will save on running costs.

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