Biomass Dryer System

Flash Dryer ( FD Series)

The Dryer system would a conventional pneumatic flash dryer. The pneumatic or ‘flash’ dryer is used with products that dry rapidly owing to the easy removal of free moisture . The hot gas carries the materials pneumatically and drying would be achieved by intimate mixing of hot gas with the wet material as they travel together in the Dryer columns. Drying takes place in a matter of seconds. 

Product is separated using cyclones, and /or bag filters.

The Dryer would consist of the following sub-systems :

  1. Hot Gas Generator
  2. The hot gas generator consists of a furnace (solid fuel fired ), which generates hot flue gas at 800 - 1000 oC. The temperature of the flue gas is reduced to 400 oC by mixing it with fresh air after it exits the furnace system. The furnace is of refractory construction with one layer of refractory brick, followed by a layer of insulation bricks. The temperature of furnace surface would be restricted to around 100 oC only, by proper insulation.

    The choice of the fuel to be fired would depend on the users requirement and economics of utilization of the fuel.

    The solid fuel furnace would have a horizontal grate for combustion of the fuel fired.

  3. Material( Feed ) Conveyor with Rotary Screen
  4. The material conveyor would transfer the wet biomass from the feed hopper into the dryer system. The material conveyor would be a screw conveyor of sufficient capacity. It shall be located between the hot gas generator system and the dryer system. Rotary Screen will be mounted on the top of the feed conveyor hopper to segregate oversize material & other foreign matter. The rotary screen will be driven by motor.

    The screw conveyor would be driven by a motor through reduction gear. The motor is provided with a variable frequency drive so that the speed of the screw conveyor can be varied and the quantity of material fed into the system is controlled. Thus, if the moisture content of the wet material is much more than 40%, then the material feed may be reduced and thus the moisture content at the exit can be maintained at the desired levels, and vice versa.

  5. Dryer Columns
  6. As mentioned earlier, the Dryer would be of pneumatic type. The Dryer columns would be of fabricated M.S construction. The Dryer system would consist of dryer columns of sufficient length in a single loop. The wet material would be fed into the system just ahead of the dryer.

    Immediately on entering the system, the due to the high temperature gradient available there would be instantaneous drying of surface moisture which would bring down the temperature of the hot gas to 200 - 250 oC. The removal of the remaining moisture would be completed in the dryer columns by direct heat transfer between the material and the hot gas which carries it.

    All parts of the dryer column would be well insulated by mineral / glass wool type insulation for reducing the heat loss and restrict the surface temperatures to 70 oC.

    The entire system would be powered by a centrifugal blower located immediately after the dryer columns. The blower would be belt driven by an electric motor.

  7. Dust Collection System
  8. The dust collection system would consist of high efficiency cyclone for trapping the dry biomass.

    The material collected at the cyclone bottom hopper would be removed by a two no's rotary air lock valve. This would eliminate the dust pollution at the bottom of the cyclone where the dried material would be discharged.

    The each RAV's shall be driven by motors through a speed reducing gear.

  9. Electricals
  10. All electrical motors are controlled from the main panel. The Screw feeder motor speed control shall also be from the panel. The panel would also include temperature indicators of the various drying zones. The electric motors would be provided with Star Delta starters and the remaining smaller motors shall be connected through DOL starters.

  11. Instrumentation
  12. The electrical panel would contain voltmeters and ammeters for the blower motor.

    The Dryer system would be fitted with two thermocouples with the indicator mounted on the electrical panel. These would greatly reduce the risk of fires within the column.

  13. Supports
  14. All supports for the furnace, screw feeder, dryer columns and cyclone separator would be from the ground. The foundation for all supports shall be provided by the client.

    The blowers with their motors would be mounted on their own concrete foundations which shall be provided by the client.

Salient feature of flash dryer

Design & Performance Parameters

Dryer Model FD 750 FD 1500 FD 2500 FD 3500 FD 5000
Dry material output kg/h 550/850 1250/1750 2250/2850 3250-3850 4500/5500
Material to be dried Biomass ( Powder/Fibrous/granular)
Size < 4 mm
Moisture content of material at inlet of the dryer % < 45 %
Moisture content of material at exit of the dryer % < 12 %
Dust content in exhaust gas Mg/mm3 < 150
Blower motor Rating hp 7.5 + 3 15 + 5 25 + 7.5 30 + 10 40 + 15
Screw feeder motor rating hp 2 3 5 5 7.5
Rotary air lock motor rating hp 2 1.0 X 2 = 2 2.0 X 2 = 4 3.0 X 2 = 6 3.0 X 2 = 6
Screen hp 0.5 0.5 1 2 3
Total Connected Load hp 15 25.5 42.5 53 71.5
Actual Power consumption kw 8 14 24 29 38
Fuel For the Furnace Firewood/Briquette with 3500- 4500 kcal/kg calorific value
Fuel consumption at 30 % Initial Moisture Kg/h 60 110 150 220 300
Fuel consumption at 45 % Initial Moisture Kg/h 110 230 350 480 650


Biomass Dryer system

Terminal Points for Dryer

Power - 440 V, 3 ph at Inlet of main control panel & individual motors
Wet Biomass - Inlet to Rotary screen mounted on top of screw conveyor hopper
Dry Biomass - Exit of RAV