Quench Water

[rob194]

I am working on a project for a wheat cooking process. Currently we use 140 gal of water to fill the kettles and then wheat is added. This mixture is then heated to a temperature of 200 degrees F. After cooking the wheat needs to be quenched to a temperature of 140 degrees F. Currently we add 140 gal of quench water @ 70 degree F city water to achieve this temperature.

The idea is to convert to using chilled water that is at a temperature of 50 degrees F. What kind of calculation can I use to find the expected quench water reduction?

Thanks.

 

[Lalbatros]

Roughly, the final temperature will be given by:

Tf = (w cw Tmix + q1 cq Tmix + q2 cq Tq2)/(w cw + q1 cq Tq1 + q2 cq)

where

w and q indicate wheat and water quantities respectively
and 1 stands for preparation water
and 2 stands for quench water
cw is the wheat specific heat
cq is water specific heat
Tmix is the preparation temperature before quench
Tq2 is the quench water temperature
Tf is the final temperature after quench

This is a simplification from many points of view, but should be enough.
You still have to decide if you want to change the final temperature of not, then you can solve the problem.

 

[Lalbatros]

Please remove Tq1 from the denominator.
Word processing mistake.

 

[rob194]

Ok, but since the amount of wheat is constant for the process, does it matter.

 

[Lalbatros]

rob194,

It is just as important as the equation tells us.
If w<<q1 and w<<q2, then assuming w=0 will only lead to a small error.
Since you did not mention the quantity of wheat, I gave you the general solution (though also approximate). How much kg of water ar using to cook 1 kg of wheat?

 

[rob194]

2.9 kg of water per 1 kg of wheat. The problem that I am having is finding the specific heat of the wheat. I know that the specific heat of the water is much higher than the wheat. Thanks for the help.