Drying-Gas Recycle and Purge: Moisture Can Accumulate in a Closed Loop

Define the Material or Thermodynamic Model

ANDRITZ’s dryer description distinguishes internal air recirculation from exhaust and inlet streams. For a steady hypothetical circuit without condensation, the water exported by the purge minus water imported with fresh gas must equal water added by the product.

Review a Hypothetical Comparison

Assign circulating dry air of 100 kg/h, fresh and purge flows of 20 kg/h, fresh W = 0.005 and product water release of 2 kg/h. The external balance gives 20Wpurge − 20(0.005) = 2, so Wpurge = 0.105. Recycling 80 kg/h at 0.105 and adding 20 at 0.005 gives dryer-inlet W = 0.085; the dryer adds 0.020 kg/kg. A 100 kg/h circulation reading alone does not establish the 2 kg/h export.

Keep the Evidence with the Decision

Draw both the whole-circuit and single-dryer boundaries. Record purge and makeup on dry-gas mass bases, then test whether the assigned humidity inventory closes across both.

This is a deliberately simplified closed account, not a recommended recycle fraction. A condenser, leakage, solvent stream or transient water accumulation changes the external balance and must appear explicitly.

What purge and makeup flows prevent an unsupported steady humidity assumption?

This blank worksheet is for your own project. It contains no H M machine trial result.

Customer Questions

Primary References

These references support the technical principles discussed in this guide. The worked examples and review questions are educational.

• ANDRITZ’s dryer description
• Reference from hmpharmamachines.com