Technical Overview
The Ardau™ system is an entirely new way of generating heat and power, though there is no new technology involved in the process. It uses tried and tested technologies in a new configuration.
An Ardau installation comprises an Ardau pressure vessel and a turbo-expander generator set together with feed mechanisms to supply the fuel and air to the pressure vessel, and systems to handle the output from the turbo-expander. There is no boiler.
An Ardau pressure vessel is an enclosed system. A mixture of organic matter and (dirty) water is the fuel it uses. A self-sustaining, exothermic chemical reaction inside the pressure vessel creates a special fluid (called “Supercritical Fluid”) at an exceptionally high temperature and pressure. This fluid is then fed into the turbo-expander generator set which uses the heat and power in the fluid to generate electricity. Once the heat has been used the output water and gases can all be captured and stored, reused or sold.
Ardau System Schematic
Turbo Expander
Turbo-expanders are well known devices. The properties of supercritical fluids have been known since 1822 and both are already used extensively in power generation. It is the Ardau pressure vessel that is the technological breakthrough.
From the turbo-expander generator set come electricity, pure water and a mixture of gases which are piped to a storage container. If required these gases can be separated and sold.
Because almost all the heat is used to generate power Ardau systems are much more efficient than traditional boiler systems where much of the heat together with greenhouse gases, particulates and other pollutants go up the chimney.
Ardau installations are scalable
The smallest system will produce around 5MW of electricity. The largest Ardau systems can go up to 50MW. Where greater output is required multiple systems can be installed in parallel.
How does it do it?
The Ardau pressure vessel operates in conditions known as Ultra-Supercritical (USC) at a temperature of around 700º C and a pressure around 300 bar. In these circumstances, water becomes the ‘Supercritical Fluid‘ mentioned earlier. The properties of such fluids are well established. Electricity is generated at over 80% efficiency.
Because of the extreme pressures and temperatures, special alloys are required for the fabrication of the Ardau pressure vessel and turbo-expander. Such alloys have only become available in the last five years, which explains why no USC pressure vessel has yet been built.
A non-supercritical prototype was built then tested and certified by SGS “the world’s leading inspection, verification, testing and certification company” (www.sgs.com). It proved that controlling combustion in an enclosed pressure vessel is achievable. A copy of the certificate is available on request.
Ardau systems can be run continuously for extended periods. Regular maintenance is limited to 20 minutes per annum and 24 hours once every five years.
Supercritical Fluid
Technical details
The Ardau Pressure Vessel
The pressure vessel is the unique part of the Ardau system. It generates heat through an exothermic chemical reaction between its fuel, water and air. That fuel can be any material that contains at least 5% carbon. The fuel is mixed with water to form a slurry which is then fed into the pressure vessel. There it is heated to 170C before it is introduced to the main pressure vessel chamber.
The temperature of the Supercritical Fluid (SCF) ensures that any inorganic material that enters the pressure vessel with the carbon fuel is rendered sterile and inert. It drops to the bottom of the pressure vessel and can be removed without interrupting operations. All toxic compounds are broken down to their constituent elements. Metals are reduced to their elemental form and can be recovered and sold. The residue can be sold as hard core.
SCF at the required pressure then leaves the pressure vessel through a valve and short duct and passes to a turbo-expander.
The turbo-expander generator set
A turbo-expander, also referred to as an expansion turbine, is a centrifugal or axial-flow turbine, in which the SCF expands producing the power. As the gas flows from the high-pressure stream into the turbo-expander it spins the turbine which is coupled to a generator that produces electricity.
In some installations, some of the SCF is taken off before the turbo-expander for other uses such as hydrogen generation.
Turbo-expanders are tried and tested technology and have been in use since the 1930s. They generate electricity at much higher levels of efficiency (around 90%) than the steam turbines used in conventional power stations. They are also smaller, lighter and less expensive to purchase and install.
The outputs from the turbo-expander are electricity, pure water and output gases. There is still considerable heat which is fed back in to the Ardau pressure vessel to heat the fuel slurry to the 170C that is needed before it enters the main pressure vessel chamber.
The water can be tapped off in situations where clean water is otherwise in short supply. Water not removed is reused as a component of the fuel slurry.
The output gases can be stored or separated and sold. A second turbo-expander can be attached to the gas output pipe from the main turbo-expander in order to separate the output gases (hydrogen, nitrogen, carbon dioxide etc) for sale as an additional revenue stream.