Throughput & Hopper What sets the vessel size

Polymer Throughput kg/h

Required Residence Time h

Chip Bulk Density kg/m3

PET chip about 850, nylon about 700

Moisture & Air What sets the duty

Incoming Chip Moisture ppm

Target Moisture at the Extruder ppm

PET for fibre normally below 50 ppm

Process Air Dew Point deg C

Drying Temperature deg C

Return Air Temperature deg C

Process Air Ratio m3/kg

Cubic metres of process air per kilogram of throughput

Required Hopper Volume

— m3

To hold the stated residence time at this throughput

Water, Air & Energy

Chip Held in the Hopper: — kg
Water Removed: — kg/h
Absolute Humidity at the Dew Point: — g/m3
Process Air Flow: — m3/h
Process Heater Duty: — kW
Specific Drying Energy: — kWh/kg
Moisture Reduction Factor: — x
Air Mass per Unit Water Removed: — x

The hopper volume is the working volume for chip and takes no account of freeboard, cone geometry or the distribution cone, so a real vessel will be larger. Residence time assumes plug flow; a hopper with poor mass flow will channel and give some of the chip far less than the nominal time while the rest sits, which is a common cause of intermittent IV variation with no process change to point at. Heater duty is sensible heat on the process air only and excludes desiccant regeneration, which on a twin-tower system can be comparable in size, and excludes losses through the vessel wall. Air density is taken at the metering condition rather than at temperature; blowers are normally rated volumetrically at inlet, which is the convention followed here. The moisture figures are mass ppm as determined by Karl Fischer or equivalent, not the volumetric ppm sometimes quoted for gases.

Polymer Drying Hopper Volume, Dew Point & Heater Duty — free, with the formula and a worked example, at Textile School.