Subtopic: Concentration and drying of liquid foods – evaporators, tray, drum and spray dryers
Question Statement:
A single-effect evaporator concentrates $5000\text{ kg/h}$ of fruit juice from $10\%$ to $40\%$ total solids. The steam consumed by the evaporator is $4200\text{ kg/h}$. The steam economy of the evaporator is ________ (round off to 2 decimal places).
Answer Key:
0.89
Step-by-Step Solution & Explanation
1. Solid mass balance:
$F \times x_F = P \times x_P$
$5000 \times 0.10 = P \times 0.40 \implies P = \frac{500}{0.40} = 1250\text{ kg/h}$
2. Vapor evaporated $V$:
$V = F - P = 5000 - 1250 = 3750\text{ kg/h}$
3. Steam economy:
$\text{Steam Economy} = \frac{\text{Vapor evaporated}}{\text{Steam consumed}} = \frac{3750\text{ kg/h}}{4200\text{ kg/h}} \approx 0.8928 \approx 0.89$