What is Super Critical Water Oxidation?
When water’s temperature and pressure are above 374 °C (700°F) and 221 bar (3,000 psi), respectively, it enters a supercritical condition or ‘fourth phase’, i.e. an additional phase to its more familiar solid, liquid and gaseous phases. Under these conditions the physical properties of water change.
• its density is less than that of the liquid;
• its viscosity is the same as the gas; and
• its diffusivity is mid-way between the liquid and the gas.
Most importantly the solubility of gases and organic compounds are increased to almost 100%, while inorganic compounds become insoluble. When oxygen is added to organic contaminants under these conditions, a very rapid reaction occurs, resulting in the almost complete destruction of the organics.
Unlike incineration, the only gaseous emissions from this process are carbon dioxide (CO2) and nitrogen (N2) at room temperature.
Phosphorous and coagulant can be recovered from the inert residue.
What is AquaCritox®?
The AquaCritox® process is a patented Super Critical Water Oxidation process developed to completely destroy organic material with no harmful emissions to air or water. The process uses the unique properties of supercritical water to completely destroy through oxidation all organic contaminants.
The solids are mineralized within the AquaCritox® process into a clean water , sterile inert inorganic clay, carbon dioxide and nitrogen .
As the oxidation process is exothermic the process generates significant amounts of surplus heat which can be recovered for heat applications or for the generation of electricity.
Super critical water oxidation is able to achieve high destruction rates (99.99 %+) without the requirement for expensive dewatering equipment upstream. Due to the unique properties of super critical water, SCWO achieves greater destruction efficiencies than incineration or wet air oxidation with the advantage in larger plants of excess electricity production above that required to run the process i.e. positive energy balance.
We operate a 250 litre/hr (14,000 pop equivalent) demonstration AquaCritox® plant in Cork Ireland. This plant can be visited by appointment.
AquaCritox® Super Critical Water Oxidation is the most efficient processes for destruction of water treatment solids with energy recovery. Water may exist in three phases: solid, liquid and gas; however at elevated temperatures and pressures above the critical point (374°C and 221bar) water enters another phase known as the super critical phase. Supercritical water is neither a liquid nor a gas, but it has properties between the liquid and gas phase. Density approaches the liquid phase and diffusivity and viscosity approach the gas phase.
At the critical point hydrogen bonds disappear and water becomes similar to a moderately polar solvent. Oxygen and all hydrocarbons become extremely miscible and mixing occurs almost instantaneously. The solubility of inorganic salts drops to parts per million (ppm).
The low viscosity and high diffusivity of organic compounds in super critical water permit a much higher mass-transfer rate. The unique physical properties of supercritical water allow for a very rapid reaction rate and high efficiency destruction (99.99% +).
The AquaCritox ® process will oxidise:
* Organic Carbon to CO2
* Organic Nitrogen to N2 with no NOx formation.
* Organic sulphur to S04 with no SOx formation.
* Soluble metals oxidised to their highest oxidation state
* Inorganic insoluble materials within the sludge are not changed
It is possible to generate small amounts of Nitrous Oxide which is easily removed from the gas stream by a catalytic reduction system.
SLUDGE TREATMENT WITH AQUACRITOX
In the AquaCritox® process the sludge waste stream is pumped from a feed tank, to the system, in excess of 250bar. The feed enters the economiser where it is pre-heated by the reactor effluent to above the supercritical point. The hot feed enters the reactor where the required amount of oxygen is added. Oxidation of the organics commences immediately. The reaction is exothermic and the final temperature is controlled to a maximum of 600 °C. Reaction time is under 60secs. From the reactor the effluent is directed to the economiser, where it heats the incoming stream.
The waste heat from the economiser/reactor set is used to generate steam or hot water and in larger plants for power generation. In this case a heat exchanger effectively takes the place of a boiler in a standard steam loop. The steam generated is then used to drive turbines for power generation. The size and type of turbine will depend on the quantity of waste treated, however in general condensing turbines are used. The condensed steam then returns through the loop to be reheated by the reactor/economiser waste heat.
* Reduces your carbon foot print
* Removes nutrient load from land.
* Allows phosphorous & coagulant recovery.
* Generates renewable electricity.
* No odour
* No hazardous by products or emissions
* 99.9999% conversion of contaminants
o Organic carbon to CO2
o Organic & inorganic nitrogen to N2 (no NOx)
o Organic & inorganic halogens to H-X
o Organic & inorganic sulphur to H2SO4 (no SOx)
* Complete destruction of the organic fraction
* Closed process
* Heavy metals are oxidised to highest oxidation state
* Carbon dioxide is generated in a concentration and purity suitable for re-sale.
* Not weather dependent
* Does not rely on land bank availability
* Eliminates truck movement
* Long term solution – 10-20 years
* No difficulties with permit or licence. (no stack or toxic emissions).
* AquaCritox® is not incineration. Incineration directives do not apply.