Plate-and-frame filter press (washing type): What is the typical ratio of washing rate to the final filtrate rate when arranged for efficient cake washing?

Introduction / Context:
In washing-type plate and frame presses, once the cake reaches the terminal thickness, wash liquid is passed to displace mother liquor. The relative rates of wash and final filtrate influence washing efficiency and cycle time.

Given Data / Assumptions:

• Washing is performed at similar pressure drop and flow paths as the final filtration step.
• Final filtrate rate refers to the terminal (end) filtration rate just before switching to wash.
• Hydraulics of channels, cloth, and cake do not change abruptly at switchover.

Concept / Approach:

Because the driving conditions and resistances are comparable at switchover, the practical design target is to maintain a wash rate close to the final filtrate rate. Matching rates avoids channeling and ensures efficient displacement of mother liquor without over-pressuring or under-washing the cake.

Step-by-Step Solution:

Verification / Alternative check:

Operational guidelines for washing plate-and-frame presses recommend keeping wash flow near the terminal filtrate flow to maintain uniform displacement front and washing efficiency.

Why Other Options Are Wrong:

1/2 or 1/4: Too low and prone to channeling/inefficient displacement. 4: Unrealistically high relative to the same resistance and pressure limits; risks cloth damage and bypassing.

Common Pitfalls:

Confusing average filtrate rate over the cycle with the terminal rate; neglecting cake compressibility effects which may require modest adjustments, not orders of magnitude changes.

Final Answer:

1