Paper Machine Drying Rate Calculator
Calculate evaporative load and drying rate per unit area (Rw)
Calculation Results
Production Rate (lb/hr):
0
Water Evaporated (lb/hr):
0
Total Drying Surface Area (ft²):
0
Drying Rate (lb water/hr/ft²):
0
Understanding Paper Machine Drying Rates
The drying rate of a paper machine is a critical performance metric used by process engineers to evaluate the efficiency of the dryer section. It measures how much water is removed from the sheet per hour, relative to the available drying surface area. This calculation is essential for benchmarking against industry standards (such as TAPPI norms) and identifying bottlenecks in production.
The Core Calculation Formula
The drying rate (Rw) is typically defined as pounds of water evaporated per hour per square foot of drying area. The process involves three main steps:
- Determine Production Rate: Production (lb/hr) = [Speed (ft/min) × Basis Weight (lb/3000ft²) × Trim (in) × 60 min/hr] / [12 in/ft × 3000 ft²].
- Calculate Water Evaporated: Evaporation (lb/hr) = Production × [(100 – %MoistureOut) / (100 – %MoistureIn) – 1].
- Calculate Surface Area: Total Area (ft²) = π × Diameter (ft) × (Trim Width (in) / 12) × Number of Dryers.
- Calculate Drying Rate: Rw = Evaporation / Total Area.
Example Calculation
Suppose you have a paper machine with the following parameters:
- Speed: 2,000 ft/min
- Basis Weight: 42 lb/3000 ft²
- Trim Width: 200 inches
- Moisture In: 58% | Moisture Out: 6%
- Dryer Section: 40 dryers of 5 ft diameter
First, we find the production at the reel: (2000 * 42 * 200 * 60) / (12 * 3000) = 28,000 lb/hr. Next, we calculate the water evaporated: 28,000 * [(100 – 6) / (100 – 58) – 1] = 34,666 lb/hr. Finally, the drying area: 3.14159 * 5 * (200 / 12) * 40 = 10,472 ft². The resulting drying rate is 3.31 lb/hr/ft².
Why Drying Rate Matters
If your calculated drying rate is lower than the TAPPI average for your specific grade (e.g., Linerboard, Newsprint, or Tissue), it may indicate issues such as:
| Potential Issue | Impact on Drying |
|---|---|
| Poor Condensate Removal | Higher thermal resistance inside the cylinder. |
| Foul or Dirty Surfaces | Reduced heat transfer from steam to the sheet. |
| Inadequate Pocket Ventilation | High humidity in dryer pockets limits mass transfer. |
| Poor Sheet-to-Dryer Contact | Low felt tension reduces conduction efficiency. |