|The 120 MW Callide A power station, where oxyfuel technology is to be "bolted on" to cut carbon dioxide emissions Source: CS Energy|
In its search for affordable ways to curb its heavy carbon emissions Australia is now at the forefront of investigating several clean coal technologies.
Nicholas Newman, UK
Coal's dominant share cent of Australia's generation mix (around 80 per cent) is poised to halve over the coming decades as more gas and renewable generation come onstream. But how far coal's contribution slips will also hinge on advances in cleaner coal technology, with growing official concern over emissions signalled by a carbon tax due in force next July.
Australia's power sector currently depends heavily on a network of 30 coal fired power plants, most of which date back more than 20 years. Their conventional designs typically allow operational efficiencies of between 33–35 per cent, far below those obtained through supercritical equipment. Only four power plants are currently operating with some form of cleaner coal technology, according to the Australian Parliamentary Library.
Yet cost is crucial in the transition to greener generation. Cheaply mined domestic coal reserves have enabled Australian consumers to enjoy some of the lowest electricity prices in the world. Since 1990 low prices have fuelled a 72 per cent rise in power demand, largely driven by energy-intensive manufacturing such as the production of iron, steel and aluminium from domestically mined bauxite and alumina.
Commercially viable cleaner coal technology would therefore considerably brighten the outlook for Australian companies and consumers. Almost A$1 billion ($1.1 billion) has been allocated for new research and development – about half from the Australian federal government's Low Emissions Technology Demonstration Fund and the rest from state governments, the private sector and countries such as China and Japan. Major technological areas being explored include coal seam gas and methane capture; coal pre-processing and storage, such as demoisturization and pelletization; coal gasification and turbine technology; carbon dioxide (CO2) separation and flue gas cleaning; and CO2 sequestration.
However, this year's federal budget reflected fiscal concerns as well as public scepticism over spending on clean coal research – rather than arguably more promising technologies such as natural gas, solar, wind and tidal power – by cutting investment in carbon capture and storage by A$465 million. Yet research agencies, including the Global Carbon Capture and Storage Institute and the Co-operative Research Centre for Greenhouse Gas Technologies kept their research budgets.
Power plants utilizing clear coal technologies are now being built in the states of Queensland and Victoria. Additional plants have also been proposed in the states of Victoria, New South Wales, Queensland and Western Australia, although these projects must overcome funding, planning issues and public opposition. The federal government plans to introduce national emission standards by the end of 2011 and some form of carbon trading mechanism by 2012, though both proposals are facing delays.
Currently, Australia's cleaner coal technologists are aiming to eventually reduce carbon emissions by 85 per cent from 820 kg to 150 kg per MWh, said David Brockwa, chief of the Energy Technology Division, Commonwealth Scientific and Industrial Research Organization (CSIRO).
Australia's innovators are looking at the three stages of clean coal technology: energy conversion (combustion and gasification); emissions capture; and carbon dioxide sequestration.
Sequestration is among the best developed concepts, but its costs depend heavily on location. While geology is favourable in the states of Queensland and Victoria, it is less promising in New South Wales, which is Australia's most populous state and the location of more than half its coal consumption.
Clean coal technology will need another two decades to become viable in Australia, forecasts Dr Mark Diesendorf at the Institute of Environmental Studies, University of New South Wales. In addition, its implementation is likely to double coal usage costs. The costs and difficulties of introducing the technology also make it more likely to be introduced in purpose-built power plants rather than retrofitted, said Dr Hugh Saddler of Energy Strategies Consultants.
The Callide Oxyfuel Project
The A$206 million Callide Oxyfuel demonstration project in central Queensland aims to prove that oxyfuel technology can be "bolted on" to an existing coal fired power station to produce almost zero-emissions electricity. Project partners include CS Energy, IHI Corporation, J-Power, Mitsui, Schlumberger and Xstrata Coal. Additional funding has come from the Queensland, Australian and Japanese governments.
The 120 MW Callide A power plant is described as the world's largest remote controlled coal fired power station. Its four 30 MW units are designed to generate power at 132 kV. Parsons supplied its turbine, and Mitchell Engineering the boiler, which has a maximum steam temperature of 460 ºC and pressure at 4300 kPa. The plant was commissioned in 1965, refurbished in 1998 and put into 'storage' in 2001 in preparation for its conversion to oxyfuel technology.
The power plant is designed to burn pulverized coal in a mixture of oxygen and recirculated waste gases in order to create a high concentration of CO2 in the gases departing from the boiler. As combusting coal in pure oxygen would cause the boiler to melt, recycled exhaust gases are injected to keep the boiler temperature at about 500 °C.
Once the CO2 is captured, it will be purified and compressed into a liquid form and kept stable at -30 °C for transportation to an underground storage site for geo-sequestration. Suitable sites include sedimentary basins with permeable rock to absorb the CO2 and a natural upper seal of non-permeable rock. Depleted gas fields could offer great potential as their geological characteristics enabled natural gases to be stored for millions of years. The Callide Oxyfuel project team is assessing potential geo-sequestration sites to the west of Biloela in the Northern Denison Trough and at other locations in southeast Queensland.
The first stage of commissioning was completed in March 2011 and the Callide A power station is scheduled to start generating electricity in oxy-firing mode from August 2011 and to demonstrate CO2 capture by the end of the year. The "firing up" of the power station unit signals the first step in a multifaceted commissioning process that will take place over the coming months, said project director Dr Chris Spero. "Commissioning will ensure the oxyfuel power plant and associated CO2 capture facility is fully operational by the end of the year," he said.
Dual Gas Demo Project in victoria
This new 600 MW project is being proposed by Dual Gas Pty Limited, a subsidiary of HRL Limited, in co-operation with China's power utility Harbin Power. The project's primary purpose is to demonstrate that the technology utilized in the integrated drying gasification combined-cycle (IDGCC) process can be viable on a commercial-scale.
The IDGCC technology process combines the pressurized drying and gasification of brown coal with gas turbine combined-cycle power generation. It is intended to achieve lower CO2 emissions and less water usage than current power generation with Latrobe Valley brown coal.
The demonstration project aims to enable retrofitting of CO2 capture technology when commercially viable, said HRL managing director Gordon Carter. Backing for the project includes A$100 million from the Australian government's Low Emissions Technology Demonstration Fund and A$50 million from the state government of Victoria's Energy Technology Innovation Strategy.
The A$750 million demonstration power station will also use dry cooling equipment, which should cut water required per MWh by 70 per cent from the figure for current brown coal fired power stations in the Latrobe Valley, said the company. Reducing the moisture content of local mined coal is vital as domestically mined Victorian brown coal has a moisture content of some 61.5 per cent.
Arckaringa Coal-to-Liquids and Power Project
This project uses local mined coal to generate power and make fuel including petrol for cars at a plant in northern South Australia. Sponsors behind the venture are China National Offshore Oil Corporation and Altona Resources.
The project can be summarized as a conventional open cut coal mine combined with processing and an oil refinery/petrochemicals plant, where an efficient integrated 560 MW combined-cycle power plant captures and uses waste heat. Prepared coal is processed in a gasifier with oxygen to produce raw syngas and slag/black water by-products. The raw syngas is then cooled and its components separated and cleaned, with the resulting low-pressure steam sent to the combined-cycle power plant. Unwanted gases – mainly CO2 and hydrogen sulphide – are separated from the valuable syngas. Sulphur is extracted from the hydrogen sulphide gas, and can be sold.
The synthesis gas stream of hydrogen and carbon monoxide is then conditioned to meet the feed specification for the Fischer-Tropsch (FT) synthesis unit. Large parts of the gasification and FT processes are exothermic and the project will capture this heat to generate electricity and export it to the national grid using some of the most efficient processes available.
The power generation island features gas turbines powered by syngas and steam turbines capturing the energy from otherwise waste heat, similar to conventional combined-cycle gas turbine technology. The current base case scenario envisages 1140 MW produced from these two processes, of which about half will be consumed on-site leaving around 560 MW available for export to the national grid.
A feasibility study will also consider trade-off analyses for diverting syngas to produce additional electricity when South Australia's electricity demand peaks. These times coincide with the highest electricity prices, although exporting additional power to meet this demand would cut production of liquid fuels.
Kogan Creek Solar Boost
In southeast Queensland, government-owned CS Energy is busy adding a compact linear fresnel reflector (CLFR) solar thermal system to its existing 750 MW supercritical black coal power station at the Kogan Creek coalfields. The current A$1.2 billion power plant – described as Australia's largest and most energy efficient power station – opened in 2007 and features technology supplied by an international consortium led by Siemens and including Babcock-Hitachi.
|The 750 MW Kogan Creek supercritical coal fired power plant will feature a solar thermal system aimed at cutting coal consumption and therefore carbon emissions Source: Siemens|
Construction of the CLFR 'Solar Boost' solar thermal system began in April with a goal of reducing coal consumption and carbon emissions. The Solar Boost project is currently expected to cost A$104.7 million and represent the largest incorporation of solar technology in the world when completed in 2013. Funding for the project comes from a variety of sources, including A$70 million from CS Energy, A$35.4 million from the Queensland government and A$34 million from the federal government. The scheme involves a CLFR solar thermal system with a 44 MW capacity at peak solar conditions. Its provision of extra steam to the power station turbine will displace coal consumption and reduce emissions by 0.8 per cent, at a cost of A$3000 per tonne of carbon.
The Kogan Creek Solar Boost project will also enhance the conventional feedwater process at Kogan Creek. Steam from the turbine is currently used to preheat water entering the boiler. Solar technology will help preheat the station's feedwater, thereby freeing up more turbine steam for electricity generation.
Kogan Creek Solar Boost is using technology developed by French owned Areva, a solar thermal technology provider that has teamed up with CS Energy to install the solar thermal addition. The technology is already in use at a pilot plant at Liddell power station in New South Wales and at a stand alone 5 MW solar power plant in California, USA. But the Kogan Creek Solar Boost is the first commercial solar project to use this technology in Australia.
Post-combustion capture pilot plant
Tarong Energy together with CSIRO is constructing a A$5 million post-combustion capture (PCC) pilot plant at Tarong power station as part of the Asian Pacific Partnership on Clean Development and Climate (APP) programme, in which China and Australia are leading partners.
The A$5 million Tarong pilot plant began capturing CO2 in November 2010 as Queensland's first coal fired power designed to capture carbon dioxide through PCC technology. In the PCC process flue gas is delivered through a sorbent where 85–95 per cent of the CO2 is captured. The sorbent is then heated to release the CO2, which is compressed and cooled to form a liquid ready for pipeline transport to a sequestration site. The APP programme also includes the establishment of other PCC pilot plants in New South Wales and Victoria, as well as China.
The Tarong pilot plant is designed to capture around 1000 tonnes of CO2 per annum using the liquid absorbent monoethanolamine. The project aims to capture 85 per cent of the CO2 in the incoming flue gas stream and to establish online analysis of gas compositions and offline measurement of liquid sorbent samples. Thermal and electrical energy requirements of the pilot plant will also be analyzed. However, the pilot plant will not immediately decrease emissions from the Tarong power station. Instead, the information that is gathered through research at the site will be used in assessing the technology for commercial-scale applications.
The Wandoan Power Project
A proposed scheme for a site near Wandoan in Queensland's Surat Basin consists of a 400 MW power station using integrated gasification combined-cycle (IGCC) with carbon capture and storage technologies. The Wandoan Power consortium brings together global partners including GE Energy with Stanwell, a leading energy generator in Queensland.
The Wandoan Power project features established IGCC technology along with carbon capture technology that has been functioning for decades around the globe. The CO2 storage strategy covers deep geological storage and enhanced oil recovery opportunities.
The proposed location is within 200 km of promising CO2 sinks, many of which have naturally stored CO2 for thousands of years. These sinks will be assessed as part of the study process. The Wandoan Power project is now in the pre-feasibility stage, having completed project definition and scoping studies. A series of assessment processes are now underway to attract the government and industry funding required for moving to the feasibility study stage.
How close is cleaner coal?
Australia's efforts clearly make the country a world leader in developing cleaner coal. But cleaner coal technology faces a crisis. It now looks destined to miss its target of delivering viable solutions before rival renewable technologies become competitive by the end of the decade.
Both investors and customers are deterred by the cost of cleaner coal technology, and adjusting energy markets to favour such equipment would also be politically unsustainable for most governments. Without dramatic political technological developments, the prospects for clean coal technology over the next decade look far from bright.