KASRAVAND’s technology of dryers’ production allows proposing, for each type of product to be treated, the most suitable thermal dryer, such as:
- Direct Rotary Dryers which can use as heating media:
flue gases, for sand, clay, mineral products treatment; hot air which, produced by heat exchangers, for the drying of plastic material and heat sensible products and which cannot come in direct contact with flue gases.
- Indirect Rotary Dryers which are internally contained to a refractory furnace which is crossed by flue gases, for carbon black drying.
- Steam Tube Rotary Dryers for melamine and soya bean.
- Flue Gas Tube Rotary Dryers for drying of dusty materials with initial low moisture, such as talcum and carbon.
For heating material up to high temperatures, also more than 1000 °C, rotary calciners/ Dryers are used. They are classified as:
- DIRECT DRYERs
Where the material in direct contact with combustion gases, normally in counter-current way is brought up to 1200 ~ 1300 °C
The calciner consists in a revolving cylinder made with carbon steel plates internally refractory lined. At the feed end the cylinder is enclosed in a refractory lined head provided with flanged connection for gas exit and feed chute. At discharge end the cylinder is enclosed in a refractory lined breeching with a central opening for the burner installation. Both feed and discharge ends foresee seals to reduce air infiltrations.
- INDIRECT DRYERs
Where the material is heated up to 1100 °C by combustion gases which cross a furnace. Indirect calciners are used when the product cannot come in direct contact with combustion gases and when it is requested to operate in a controlled atmosphere. The indirect calciner consists principally in a revolving cylinder, made of special alloys, housed, along its active length, in a refractory lined steel furnace. The interior of the cylinder is fitted with spiral flights at the feed end to quickly move the fed material into the active section where agitating flights gently handle the material. The cylinder of the calciner is indirectly heated by means of a series of tangentially-fired burners. At the feed end, the cylinder is provided with an inlet head equipped with feed chute and a flange for exhaust gases outlet.
At the discharge end, the cylinder is enclosed by a breeching equipped with a bottom hopper and a flange for purge air inlet. Both feed and discharge ends foresee seals to reduce air infiltrations. Heating can also be operated electrically, using a furnace provided with series of electric resistors.
STEAM TUBE ROTARY DRYERS
The steam tube rotary dryer consists principally of a revolving cylinder, slightly inclined to the horizontal, supported in two riding rings resting on two trunnion rolls each.
The cylinder is rotated by means of a girt gear meshing with a spur pinion mounted on the slow speed shaft of a speed reducer. In order to avoid clogging and /or sticking of material against the internal wall of the cylinder, outside of cylinder at feed end, clamping bands with a series of hammers are provided.
Internally, the cylinder is provided with rows of steam tubes located in concentric circle and extending the full length of the cylinder. At discharge end, each tube is turned into a header. Each tube has a concentric steam distribution pipe. Flight bars are welded to the cylinder adjacent to each tube to insure intimate contact of material with the heat transfer surface. Steam is introduced to the tubes through a steam header by means of a rotary joint, located at the discharge end of the cylinder, which provides also to evacuate condensate. At discharge end some openings in the cylinder allow the discharge of the product into a discharge breeching. The breeching face encircling the cylinder has two special seal with Teflon friction rings. The top of the breeching has a flanged opening for purge air inlet. Purge air is blown through an air heater into the discharge breeching. The purge air and the feed material pass continuously in opposite direction that is countercurrent flow.
At the feed end the cylinder is provided with an inlet head equipped with screw conveyor feeder and flanged opening for air and vapor removal. A special seal with Teflon friction rings is provided between rotating and static parts. The mixture of air and vapor are exhausted from the dryer to treatment.
In the flue gas tube rotary dryer, flue gas at the generator outlet enters a series of tubes located into the rotating cylinder in concentric circle. The material to be dried passes countercurrent to the gases and externally to the tubes.
At the cylinder outlet, gases pass through a furnace, external to the cylinder, with the purpose to recover a portion of the heat still available and to improve the thermal efficiency of the system.
At the furnace outlet a portion of the gases is recycled to the generator and the balance is discharged through the stack.
The vapor is separately extracted from the internal of the cylinder with purge air and then de-dusted before the discharge to atmosphere.