Dryer Technology
Veolia Separations owns and operates Thermal Dryers used to remove additional water and organic constituents from centrifuge or filter press cake to maximize the volume reduction of hazardous/listed waste streams. The addition of a thermal dryer to a sludge separation/solids recovery process can often result in an overall waste volume reduction of 90 - 98%.
The Dryers are continuous feed units with an enclosed chamber constructed of carbon steel. Each dryer has a large heat transfer surface area designed for use with steam (115psig and 350oF). The process vessel operates at atmospheric pressure in the range of 250 to 350 degrees F. The entire dryer is provided with insulation for heat conservation and operator protection.
A separate carbon steel vapor dome is mounted above the actual drying vessel. The high vaulted vapor space of this dome drastically reduces the velocity of the vapor to allow entrained particulate (solids) to settle out of the vapor stream and back onto the drying bed. The dome is heat traced to minimize condensation of the water and organic vapors and re-wetting of the dried solids.
Energy to effect evaporation of the water and volatilization of the organics (e.g., benzene, etc.) contained in the solids is provided by either plant steam or a mobile boiler. Vapors generated in the Paddle Dryer are extracted through the vapor dome and recovered in the Vapor Recovery Unit (VRU).
The most commonly used VRU is a one-pass, direct contact water scrubber system. The scrubber discharge is typically directed to the plant’s wastewater treatment plant. The alternate VRU is a two-stage system consisting of a direct contact scrubber/condenser followed by an indirect contact shell and tube condenser. Federal and/or local air emission regulations will likely require the addition of activated carbon adsorption to polish the non-condensable vapors. Carbon treatment beds and equipment will also incur additional costs.
