Plasma-assisted sludge oxidation (PASO)

Fabgroups Technologies Inc. has a licensing agreement with Hydro Québec to develop, manufacture and market a rotary kiln equipped with an electric plasma torch. Plasma-assisted sludge oxidation (PASOFabgroups Technologies Inc.) is an emerging technology that can be used to process organic sludge from a variety of sources.

This energy-efficient technology, which consumes less than 100 kWh of electricity per wet ton of sludge, (fans not included) offers an excellent alternative to incineration, landfill disposal, or sludge spreading- three methods that can be highly detrimental to the environment. Plants that produce sufficient quantities of sludge will be able to reduce their waste by 95% and generate green energy.

PASO is based on a rotary kiln working at about 600-700 °C slightly below atmospheric pressure, equipped with an air plasma non-transferred arc torch. It is designed to treat sludge after conventional dewatering processes with at least 20% organic content. Plasma generation is a rational application of electricity, because the calorific value of the organic material in the sludge is used as a principal heat source.  Typically, the energy produced by the sludge is 10 times as great as the plasma energy required for catalysis, so the process has significant potential for generating electrical power, steam, or hot water. The process is simple, safe and robust.

Fabgroups - Plasma TorchThe oven consists of a refractory-lined rotary reactor.  The lining acts as heat insulation and adds to the thermal inertial of the process, ensuring the operational stability. Sludge and oxidation air are introduced continuously and concurrently into the furnace, after being preheated by a heat exchanger which transfers heat from the combustion gases to increase the energy efficiency.  Drying and oxidation occur inside the oven in the presence of a plasma generator located in the output end.  Ashes accumulating in the furnace act as a heat exchange medium between newly introduced sludge and the furnace walls.  Surplus ashes are evacuated continuously by an overflow in the exhaust end and are dry, inert, sterile, and odourless.  Flying ash particles which are entrained in the outlet gases are trapped in a cyclonic device that also provides preheating of incoming combustion air.  Ashes remain fluid, granular and friable due to the mechanical rotation of the furnace.  Ash fusion, sintering, or eutectic formation with the furnace refractory is not a problem, because the operating temperatures are relatively low. Ashes typically represent about 5% of the initial sludge volume. There are a number of potential applications for the ash resulting from the process including as a cement aggregate or composting additive. (Ash is generally Class A and dry)

Fabgroups - PASO ovenPost-treatment of gas is accomplished by a system of dust removal, scrubbing, and gas/vapour interaction.  When the gas is finally exhausted to the atmosphere, it contains virtually no particulate, most pollutant gases have been absorbed into water for further treatment, and the remaining flue gas has been cooled to about 50 °C.

The plasma generator works to offset the heat losses and to support the oxidation reaction of the wet sludge.  PASO differs from other applications of plasma to waste destruction.  Plasma has been used to generate very high temperatures for destroying things such as medical wastes and nerve gases.  In PASO, the process uses the high enthalpy of plasma, the fact that plasma consumes no oxygen, and the very high UV content of the arc to heat relatively wet biosolids to the point where they will oxidize. Sludge oxidation takes place very efficiently, since it requires little excess oxygen. (~10% excess oxygen)

This considerably reduces the total volume of combustion gases, the overall carbon dioxide emission and the amount of dust compared with a conventional burner, improving the energetic performance of the process by not diluting the heat in adding supplementary air normally required for oxidizing fossil fuels.  Less than 3% of the needed air flows through the plasma torch plume, the furnace temperature is relatively low, and little excess air is used, so NOx production is kept to the strict minimum.

  • Plasma Oxidation Advantages
  • OHAP - Une technologie verte• Complete stabilisation process destroying all volatile solids and pathogens
    • Large volume and mass reduction lowers truck traffic as compared to other sludge handling alternatives
    • Lowest life cycle cost for most medium and large facilities.
    • Low potential for onsite odours and no offsite odours.
    • Requires small land area and can operate continuously for all weather conditions
    • Lower emissions versus other thermal sludge processes (incineration) and landfilling.
    • Energy Recovery
    • Does not require sludge stabilisation (digestion) prior to processing.
  • Population growth, decreasing landfill space, and concerns over energy have spurred the development of many waste-to-energy technologies. Quite simply, PASO promises to be one of the most environmentally and socially acceptable means of achieving beneficial reuse of sludge.

  • Treatment
  • Ash after treatment

  • After the PASO treatment