A process flow diagram follows:

The seven subsystems include:

1. Wet/Dry Product Silos
2. Mixer
3. Drum
4. Furnace
5. Cyclone Separator
6. Scrubber/Condenser
7. Heat Exchanger

Sub-System 1:  Wet/Dry Product Silos
As shown in the process flow diagram below, two silos are used to store wet and dry sludge.  The wet sludge is typically dewatered by a belt press or centrifuge and is delivered to the silo at approximately 20% solids by weight.  The dry sludge silo stores a portion of the 95% dry pellets produced by the dryer.  Each silo is equipped with a live bottom variable speed screw used to feed a paddle mixer at a predetermined dosage.

Sub-System 2:  Mixer
The paddle mixer combines specific amounts of the wet and dry material from the product silos to produce a 70% solids material. When the two materials are combined in the mixer, the wet material coats the dry pellets over several rotations and forms up to a 5mm sphere.  The coated pellet is then fed to the drum dryer.

Sub-system 3:  Drying Drum
The heart of the system is a rotating drum that evaporates moisture from the sludge through contact with a heated surface.  The drum consists of an internal jacketed cylinder surrounded by an external cylinder that forms an integrated rotating drum.  The jacketed cylinder is heated by hot air formed by the combustion of natural gas (or methane gas) in the furnace.  The pellets are mechanically conveyed through the center of the jacketed cylinder while maintaining constant contact with the hot surface.  An opening at the end of the jacketed cylinder allows the pellets to fall to the annular space between the outside cylinder and the jacketed cylinder.  The pellets are then conveyed in the opposite direction back along the drum where it is finally discharged.

Sub-System 4:  Furnace
The furnace produces the hot air used to heat the jacketed cylinder inside the rotating drum.  The heat is generated through combustion of either natural or methane gas with a modulating type burner.  The burner features a gas feeding mechanism that uses an electric gas ignition, and is equipped with a continuously adjusted servomotor that is used for air and fuel regulation.  A blower forces a steam of air through the furnace, and into the jacketed cylinder located within the rotating drum.  The furnace is lined with ceramic material to provide insulation against the high temperatures and minimize energy loss.

Sub-System 5:  Cyclone Separator
Negative pressure is provided by a centrifugal fan to constantly remove dust and water vapor produced by the drying process.  A cyclone separator, located between the fan and the drum, uses centrifugal force to separate the dust particles from the air stream.  The dust particles are removed from a container at the base of the cyclone separator on a regular basis while the water vapor is conveyed on to the Air Scrubber/Condenser.

Sub-System 6:  Scrubber/Condenser
After particulate removal by the cyclone separator, the air stream is conveyed to an air scrubber/condenser for further removal of small particulate as well as for cooling and condensing of the water vapor.  The air scrubber/condenser consists of a closed tank with a cool water spray.  The air stream enters near the base of the tank and is subjected to continuous contact with cool water.  This spray not only cools and condenses the steam, but also removes fine particles remaining in the air stream.  The condensed water vapor and solids mixture are collected from the bottom of the tank and treated in the wastewater treatment plant.  The relatively dry air stream is conveyed to a heat exchanger before being routed back to the furnace for thermal oxidation.

Sub-System 7:  Heat Exchanger
The dry process air is routed to an air-to-air tube style heat exchanger prior to the furnace.  In this process, energy is recovered from the exhaust stream by preheating the recycled air from the scrubber prior to entering the furnace.  Hot air from a cogeneration facility, or other heat source, can also be used to preheat process air prior to the furnace, further reducing fuel costs.  After being heated, the air is sent directly to the furnace where it is thermally oxidized to remove all traces of Volatile Organic Compounds (VOC’s).