Oxyfiring up

The international energy community is watching with great interest as the world’s first oxyfiring coal station powers up in Central Queensland.

It’s no secret that coal-fired power generation contributes significantly to Australia’s greenhouse gas emissions – a whopping two thirds of it, in fact. Around the world, coal-fired power stations produce 11.4 billion tonnes of CO2 every single year – by far the largest single contributor to the over-heating of our atmosphere.

And despite billions of dollars being poured into renewable energy generation, there is also significant R&D going into creating ‘clean’ coal power through carbon capture and storage (CCS).

The Australian Government has committed more than $400 million dollars to accelerate the development and commercial deployment of technologies that reduce emissions from coal-powered electricity generation, while at the same time securing the contribution that coal makes to Australia’s energy security and economic wellbeing.

One of the major projects that has received some $50 million under this scheme is the Callide Oxyfuel Power Station at Biloela in Central Queensland. This world-leading development has just started commissioning and aims to demonstrate how CCS technology can be applied to an existing coal-fired power station to produce electricity with significantly lower emissions.

Project director Dr Chris Spero has been spearheading the project since its inception in 2003 and is clearly excited about the project’s potential impact around the globe.

“This makes real the prospect of having a longer-term coal-fired power generation industry,” Dr Spero told Energy Source & Distribution. “The US and China account for about 51.7 per cent of global emissions. Imagine if we could export what we’re developing at Callide to these two countries alone.

“It’s really a major enabling step that gives us some options before climate change and the greenhouse effect become really chronic issues,” he said.

How it works

Callide is the first power station in the world to be retrofitted with oxyfiring technology, so it’s not surprising that the technology itself is not widely understood.

Essentially, however, it involves firing a conventional coal-fired boiler with oxygen and recycled exhaust gases to produce a concentrated stream of liquid CO2 that is then ‘captured’ and safely stored underground.

The process itself is simply a culmination of existing isolated technologies – separating oxygen from nitrogen, combusting with oxygen and recirculating flue (waste) gases – that for the first time have been brought together to develop a clean coal technology option.

The first stage of the Callide project involved retrofitting the technology to the 30MW Callide A Power Station. The design and development for this works began after funding was secured in 2008, with the first stages of commissioning beginning in March this year.
“The idea of oxyfiring is to modify or enhance the way we burn coal in a normal combustion process,” Dr Spero, a mechanical and chemical engineer by trade, said.

Essentially the difference is that in a normal boiler, coal is being combusted with air, but in oxyfiring the oxygen is separated from the nitrogen before it is injected into the boiler.

From there the flue gas is injected with oxygen, which has the effect of increasing the concentration of CO2 in the flue gas stream.

“In a normal coal-fired power station the carbon dioxide in the flue gas would be about 15 per cent, but in our process it’s about 60 per cent, so in terms of the capture cost, it’s a lot cheaper,” Dr Spero said.

This CO2-rich flue gas is then cleaned through a scrubber to take out some of the other pollutants like sulphur oxides (SOX) and nitrogen oxides (NOX), before being compressed in a conventional gas compressor.

From there, the CO2 is then liquefied from the compressed gas through a cryogenic process, before being safely transported some 300km away from Callide to the Denison Trough where it is injected underground and stored approximately one kilometre below the earth’s surface.

This process of storage is known as geosequestration, which is the same process nature has used since the beginning of time to store vast amounts of naturally formed gases like CO2 in geological formations.

Why Callide?

The Callide Power Station was chosen as the test site for oxyfiring technology for a number of reasons.

First and foremost was the plant’s size.

“At Callide A there are four units and each are a 30MW capacity which we thought was big enough to go beyond the pilot-scale work that had been done around the place, but not too big to be too much of a financial and technical risk,” Dr Spero said.

Having the additional three units on site was also attractive as it meant that there was a lot of spare parts on hand for the retrofitting process.

“The third reason was that the plant was actually available – it had been mothballed and CS Energy was weighing up what they were going to do with the plant and so this initiative came along and was a very good fit,” Dr Spero said.

The real savings

The hype surround oxyfiring technology comes from its predicted ability to reduce CO2 emissions from traditional coal-fired power stations by more than 90 per cent.

“It is a nero-zero emission technology in terms of all of the emissions. Even though its main purpose is to capture CO2 for greenhouse mitigation, it in fact addresses all of the major pollutants from coal-fired generation,” Dr Spero said.

For economical reasons, the Callide project only captures and treats approximately 20 per cent of the total flue gas released, with the remaining component being released into the atmosphere in the normal way.

Even in this scenario, however, the plant is expected to capture about 75 per cent of the CO2 that’s produced, 98 per cent of the SOX emissions, 95 per cent of the NOX emissions and 99 per cent of the particulate emissions.

Where to now?

Now that the testing of oxyfiring technology has commenced, the project’s two-year ‘demonstration’ phase will begin in June 2012.

“We’ve got two years of operation where we try and run this plant like a normal plant, working connected to the grid, and while we’re doing this normal operation we’ve got a number of experiments or technical studies that we’re doing to test different operating conditions, different combustion conditions, different coals and different coal characteristics to see how all of these different variables affect the performance of the technology,” Dr Spero said.

In fact, of the $160 capital works program for the power plant retrofit, Dr Spero says some $20-$30 million of that was for additional technology to test a broader range of parameters.

This included things such as an intermediate flue gas treatment process within the flue gas recycling group, a water removal system to test drying the gas and the effect of that in combustion, and a direct oxygen inject system.

“We’ve allowed the provision to inject oxygen through what we call oxygen lancers directly into the combustion flame in the boiler and we’re doing this just as a trial to see if that’s potentially a more effective way of doing the oxyfiring,” Dr Spero said.

Measuring success

“Success at Callide will be measured first and foremost in terms of technical viability,” Dr Spero said. “The prime motivation for the technology is to have what is essentially pure CO2 that can be stored underground – that’s the ultimate prize.”

The second barometer of success will be to what extent the technology developed at the Callide Oxyfuel Power Plant can be commercialised, with clear guidelines as to how it can be scaled up to be applied at a large-scale commercial facilities.

“We don’t have a particular ambition to globally commercialise this in Australia, but what we’d really love to see is the technology being take up wherever it can – in Japan, or in Europe, the US, or Australia – and people run with it,” Dr Spero said. “And to that extent we’ve been fairly generous in sharing the knowledge we’ve gained so far.”

In the past 18 months alone, the plant has been visited by more than 200 international visitors keen to learn just how this technology could change the face of coal-fired power stations, particularly in an era where ageing power plants is becoming an increasingly pressing issue.

“At the end of the day, this is really an early action plan that people are excited about because it gives us options for the future,” Dr Spero says.


 

The backers

The Callide Oxyfuel Project is a joint venture between CS Energy, the Australian Coal Association, Xstrata Coal, Schlumberger, and Japanese participants, JPower, Mitsui and IHI Corporation. The project has also received $50 million in financial support from the Federal Government under the Low Emissions Technology Demonstration Fund and $17.5 million from the Japanese Government. The Queensland Government has also contributed to the project financially, while JCOAL has provided technical support.

Learning from Germany

While Callide is the first project of its kind in the world, there is a smaller demonstration facility at the Schwarze Pumpe Power Station in south-eastern Germany that is also testing oxyfiring technology.

“It’s not a complete facility like ours though,” Dr Spero says. “It’s demonstrating using a single burner as opposed to a complete boiler; they basically made a test furnace with a large single burner but they’re also capturing the CO2.”

Developed by a company called Vattenfall, Sweden’s national energy company, the 30MW Schwarze Pumpe facility began commissioning in 2008 as the world’s first ‘carbon-dioxide free’ oxyfuel test facility in pilot scale.

Dr Spero and his team have visited the plant on a number of occasions and regard it as the forerunner of oxyfiring technology. He is quick to defend Callide, however, as being the first complete power station to harness CO2 capturing technology, not to mention it currently being the largest of its scale in the world.