Troubleshooting a flat-bed dryer

flatbed-dryer01What is a flat bed dryer?

A dryer is a machine that removes the water from wet grains by forcing heated air through the grain bulk. In a flat bed dryer, the same quantity of grain is kept stationary in a holding bin until drying is completed. A flat bed dryer consists of a drying bin, an air distribution system with a plenum chamber, a fan, and a furnace or burner for heating the drying air.

Some problems in drying operation: causes and remedies

Symptoms Causes Remedies
Grain breakage upon milling
  • Too high drying temperature
  • Immediate milling after drying
  • Adjust drying temperature to below 45oC.
  • Wait 1day before milling.

Loss of germination due to drying

  • Too high drying temperature
  • Adjust drying temperature to below 42oC.

Non-uniformity of final MC (more than 2.5 %)

  • Packed bed due to excessive stepping over 
  • Non-uniform material (mixed wet and dry, clean and dirty grain)
  • Non-uniform grain depth Perforated floor is partially stuck (holes are filled with dust)
  • Avoid stepping on the grain mass (use a woodboard if necessary).
  • Pre-clean the grain to remove gross impurities.
  • Adjust depth at local spot after 2/3 of the drying time is spent.
  • Clean the floor after three batches.


Too much ash in the
plenum (under the bin)

  • Ash precipitation chamber full of ash
  • Exit spout of the furnace too close to the fan inlet
  • Clean ash from the precipitation chamber
  • Move the spout farther from the fan inlet

Smoky combustion

  • Excessive husk feeding rate
  • Lack of secondary air for combustion
  • Wet rice husk
  • Reduce feeding rate.
  • Check the air inlet supply.
  • Use dry rice husk.

Prolonged drying time

  • Not enough airflow
  • Leakage of drying air
  • Very wet intake paddy
  • Close shed, not suited for ventilation
  • Increase engine speed (diesel engine) or change pulley size (electric motor). 
  • Close leak points.
  • Reduce grain layer depth.
  • Clear obstruction around the shed.

Compiled by:

Postharvest Unit, Crop and Environmental Sciences Division
DAPO Box 7777, Metro Manila, Philippines
Tel.: (63-2) 580-5600, Fax: (63-2) 580-5699

With information from:

Center for Agricultural Energy and Machinery, Nong Lam University, NLU
Thu-Duc District, Ho Chi Minh City, Vietnam

For more information:

Visit the Rice Knowledge Bank Web Site (, email; or call +63 2 580 5600

Prepared by M. Gummert with inputs from JF Rickman (2004); updated by M Gummert (2010)