Safety:
Three key ‘ingredients' are necessary for hazardous conditions to be present in any drying system, they are:
- Oxygen - Minimum threshold conditions for Oxygen concentrations for biosolids to ignite have been documented to be as low as 5%.
- Temperature - Minimum threshold temperatures for biosolids to spontaneously ignite have been document to be as low as 115C (239F)
- Fuel (dust)
The key to any successful drying operation is the successful and reliable management of these ingredients under all possible operating conditions such as start-up, shut-down, normal operation, and even upset conditions.
Schwing Bioset's fluid bed dryer operates under inert conditions as the Oxygen concentrations are held to less than 3% (typically <1%) and operates at a temperature of 85C (185F). Any dust that is generated is instantly removed from the fluid bed and captured as it passes through a cyclone.
Automation:
This mode of operation allows for the system to be completely automated and even operate unattended. The dryer is controlled by maintaining a constant energy balance over the dryer by monitoring the gas temperature as it exits the dryer. The first level of control, as the gas temperature increases or decreases, is to vary the speed at which wet cake is pumped into the dryer with the Schwing Bioset piston pump. The second layer of control is to then change the heat input from the indirect heating source. This simplistic method of control requires minimal Operator attention and allows the fluid bed dryer to accommodate fluctuations in the dry solids content of the incoming wet cake.
Reliability:
As there are very few moving parts within the entire system, and the equipment used is of the highest Schwing Bioset quality, equipment availability of over 90% in any given year is possible.
Thermal Efficiency:
Utilizing heat exchange tubes submerged within the fluidized layer, the fluid bed achieves extremely high thermal efficiencies. The self cleansing action of the fluidized bed prevents the heat exchangers from becoming fouled and losing efficiency.
Additional Features:
- Wet cake is fed directly into the fluid bed without the need for pre-conditioning the wet cake or recycling any dried biosolids.
- Low off gas requirements - equal to volume of gas that is entrained in the wet cake.
- Drying, cooling, and dry granulate storage all operate under inert conditions as off gas is used in each process before treatment.
- Final product is virtually dust free
- 90% of dried pellets are 1-4 mm in size. No additional milling, screening, or classifying is necessary.
- Dryer can start-up and shut-down in approximately 30 minutes.
System Supply:
Schwing Bioset is the only manufacturer who can offer the wet cake storage, pumps, dryers and dry granulate storage from a single manufacturer. As the upstream and downstream components are equally important to any successful drying installation, the proper integration of high performance equipment is a must. By selecting a drying system from Schwing Bioset, the Customer is assured all components will be seamlessly integrated.