Question

In a continuous scouring operation, a desized fabric (with 40% wet expression) is dipped into a saturator (alkali bath). After saturation the wet expression becomes 100%. The required alkali concentration (w/v) of liquor present in the fabric exiting the saturator is 6%. Considering no liquor interchange in the saturator, the alkali concentration (w/v) in the saturator (in integer) is \underline{\hspace{2cm}.}

Hint:

With no liquor interchange, use a mass balance on the liquor {inside the fabric}: final concentration \(=\) (alkali from new pickup)/(final liquor). Account for any initial moisture as dilution.

Answer 1

Correct Answer: 10

Let dry fabric weight \(=1\) unit.
Initial moisture \(=40%\Rightarrow 0.4\) units of (alkali-free) water.
After saturation, total liquor in fabric \(=100%\Rightarrow 1.0\) unit at \(6%\) alkali.
Amount of liquor taken from bath \(\Rightarrow 1.0-0.4=0.6\) units at bath concentration \(C\) (fraction).
Since the final mix in fabric is \(6%\):
\[ 0.6\,C = 0.06\times 1.0 \Rightarrow C = \frac{0.06}{0.6} = 0.10 = 10%. \] \[ \boxed{\text{Saturator concentration} = 10%} \]