Premium platform for SolarGas

Engineers and scientists around the world are looking for ways to harness the sun’s thermal energy to replace the diminishing global supplies of fossil fuel with a ‘clean’, carbon-neutral energy source. Australia is particularly well placed to do this, since it has the highest average amount of solar radiation per square metre per year on Earth.

One of the most promising new technologies being trialled at the National Solar Energy Centre in Newcastle (NSEC) is SolarGas, a solar thermally enhanced syngas produced from natural gas and water, in a unique hybrid fossil/solar reaction. The product, sometimes nicknamed ‘bottled sunlight’ could, eventually, be used for all types of electricity generation and for producing hydrogen for use in fuel cells, and was originally developed at the CSIRO Division of Energy Technology’s facility at Lucas Heights in New South Wales.

The process has two major components: the collection and concentration of sunlight onto a reactor, and a chemical reforming process between the fossil fuel and water to produce syngas and hydrogen.

Sunlight is collected by a modular solar array of 200 heliostats, purpose designed and built by Solar Heat and Power. These are mirrors that independently track the sun and reflect its energy onto a reactor mounted on a specially designed tower rising 20 metres above the ground.

The unique feature of this solar array, according to project manager Glenn Hart, is that each mirror tracks the sun independently in relation to the sun and the tower in such a way that, regardless of meteorological conditions, maximises solar exposure.

The heliostats are concave, each with its own focal length, with two actuators driving each, such that it can move in any direction: up, down, around, east, west, north and south. Mr Hart says the process gives the natural gas a higher calorific value by about 24%. “So you now have sunlight in a combustible form,” he said.

The current array has 165 mirrors, with plans for a total of 200, which would generate temperatures up to 1200°C and 500 kW of power, enough to supply 100 homes.

At the moment, the temperature of the reactor driving the reforming process is about 850°C, with plans to reduce it to 600°C, when a larger, more efficient reactor is put into operation in 2008, Mr Hart said.

The reactor consists of concentric tubes with water entering the inner tube and the gas flowing in the outer one. The accumulated solar thermal energy vapourises the water and the resulting steam exchanges heat with the natural gas in the outer tube. Catalysts in the outer tube mediate the chemical reaction. Mr Hart says the new reactor will have 10 times the capacity of the present one.

That puts pressure on the process control of the whole system, but Principal Research Scientist, Dr Regano Benito is confident that the new, flexible control architecture based on Schneider Electric’s Modicon Premium platform and Unity Pro, installed at the NSEC facility last year, will be up to the task.

Dr Benito recalls how he and his team started their research using a computer-based data acquisition and control system. When this proved unwieldy, and in order to improve reliability, they switched to the Modicon Quantum automation platform and Concept PLC with Citect as the SCADA software.

Over the years, the CSIRO team developed a close relationship with Schneider Electric, and was keen to try their new Premium PLC platform with Unity Pro software when they upgraded the system at the NSEC.

“What excites me about this system is that it’s much cheaper and we could implement many things that we could not implement before,” he said and explained that, even with prices generally coming down, the savings with this system were about 50% over the Quantum.

For the future expansion of the project, the advantage of the new process platform, which monitors some 180 thermocouples measuring temperature profiles in the tower alone, is the fact that Unity Pro is compatible with many older platforms.

For Dr Benito, however, perhaps the best feature is that he can remotely access the system in Newcastle and run it from his offices in Lucas Heights.

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