Around the world, the management of organic sludge produced by pulp and paper plants, sewage treatment plants as well as framing, raise important issues: the volume of sludge produced is steadily increasing and conventional treatments for disposal such as landfill and incineration have serious economical and environmental impacts.
Developed by Hydro-Québec, the Plasma-Assisted Sludge Oxidation (PASO), marketed by B & X Industries, is now recognized as an alternative treatment to conventional methods. The PASO is based on a rotary kiln working at abouth 600 - 700° Celsius, slightly below atmospheric pressure and is equipped with an air plasma non-transferred arc torch. The plasma arc supports the oxidation process by creating a catalysis reaction of the organic matter contained in the sludge.
The basic principal behind this technology, of which is in its interest, is to rationalize the use of electricity comsuming less than 125kWh per ton of wet sludge, therefore creating a calorific value of the organic matter contained by using it as a primary source of heat. The sludge containing 20% of organic mass matter actually produces enough oxidized energy to ensure the evaporation of water and heating by-products.
PASO Processing characteristic
The wet oxidation process that is plasma-assisted constitutes a unique heat source in the environmental protection industry seeing as how the other thermal treatment systems use polluting fuel generators and green house gases. The PASO process method is therefore not an incinerator that uses combustion, but rather is characterized by its catalystic oxidation with low air pressure below that of the atmosphere. The gaseous effluents are treated with a cyclonic device and a unique scrubbing design.
The inert residue created through this process can be reused or develop, according to their characteristics. One of the main methods is their use as a raw material in manufacturing cement. The ashes can also be mixed with the soils as a fertilixzer, a purifying agent or as a filler. The PASO process is not affected by the sludge pH, pathogens and solid granulometry. The gases released into the atmosphere can be compared to that of the composting process.
The plasma torch is very effective in terms of energy, with no moving parts and only two accesible parts. The plasma has been used to generate very high temperatures used in well-defined zones. Finally, it requires little external air in a way where the air that does enter the reactor, is available for bio-solid oxidation (~10% excess oxygen).