The ArdauTM 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 the patented Ardau carbon reactor and a turbo-expander generator set together with feed mechanisms to supply the fuel and air to the reactor, and systems to handle the output from the turbo-expander. There is no boiler.
An Ardau carbon reactor is an enclosed vessel. A mixture of organic matter and (dirty) water is the fuel it uses. A self-sustaining, exothermic chemical reaction inside the reactor creates ‘supercritical fluid’ at a very high temperature and pressure. This fluid is then fed into the turbo-expander generator set which uses the heat and power in it to generate electricity. Once the heat has been used the output water and gases can all be captured and stored, reused or sold.
Turbo-expanders are well known devices. The properties of supercritical fluids have been known since 1822 and are already used extensively in power generation. It is the Ardau reactor 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 and other pollutants goes up the chimney.
Ardau installations are scalable. The smallest system will produce around 5MWh of electricity. The largest Ardau systems can go up to 50MWh. Where greater output is required multiple systems can be installed in parallel.
How does it do it?
There are two versions available. In ‘Sub-critical mode’ the device will create heat and generate electricity at about 65% efficiency, which is far higher than almost all other fossil fuel based systems. Steam is created at between 200º C and 374º C with pressures between 16 bar and 226 bar. This can be used for general purposes such as drying wood, or to drive a turbo-expander generator set to generate electricity.
A number of prototypes were built. The last of these was tested and certified by SGS “the world’s leading inspection, verification, testing and certification company” (www.sgs.com). A copy of the certificate is available on request.
The Ultra-Supercritical (USC) version operates at 700º C and 300 bar. In these circumstances water becomes a ‘supercritical fluid’. The properties of such fluids are well established. Electricity is generated at over 80% efficiency.
Because of the extreme pressures and temperatures the USC version requires special alloys for the fabrication of the reactor and turbo-generator. Such alloys have only become available in the last two years, which explains why no USC version has yet been built.
Both versions can be run continuously for extended periods. Regular maintenance is limited to 20 minutes per annum and 24 hours once every five years.
The Ardau Carbon Reactor
The reactor is the unique part of the Ardau system. It takes the form of a cylinder and associated controls. The cylinder is approximately 1.8m high and has an internal diameter of between 1m and 1.5m
The reactor 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 reactor. There it is heated to 170C before it is introduced to the main reactor chamber.
When the reactor is started from cold a heating element raises the temperature in the reactor to start the chemical reaction. Once the operating temperature is reached the reaction becomes self-sustaining so the heating element is no longer required. This ‘ramp up’ process takes around 10 minutes
In USC mode the temperature and pressure inside the reactor are sufficiently high to turn the water into a SuperCritical Fluid (SCF). A supercritical fluid is any substance (in our case water) at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist. These special qualities were first identified in 1822 in France, so are well known to physicists.
The temperature of the SCF ensures that any inorganic material that entered the reactor with the carbon fuel is rendered sterile and inert. It drops to the bottom of the reactor and can be removed without interrupting operations. All toxic compounds are broken down to their constituent elements. Metals will be 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 reactor 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 turbo-generator sets used in conventional power stations. They are also smaller, lighter and less expensive to install.
The outputs from the turbo-expander are electricity, potable water and output gases. There is still considerable heat which is fed back in to the reactor to heat the fuel slurry to the 170C that is needed before it enters the main reactor 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.