The biggest carbon capture plant yet installed at an Australian power station has begun operation at International Power Australia’s Hazelwood plant in the Latrobe Valley.
The AUS$10 million pilot project is designed initially to capture up to 25 tonnes of carbon dioxide (CO2) per day from one of the power station’s generating units. Eventually, the plant has the potential to capture up to 50 tonnes a day.
The Hazelwood project includes an alliance with Process Group Australia and the Co-operative Research Centre for Greenhouse Gas Technologies (CO2CRC) and was awarded a grant in October 2006 under the Australian Federal Government’s UAS$500 million Low Emissions Technology Demonstration Fund (LETDF).
The carbon capture plant was designed and built by Process Group. Funding support for the plant was also provided by CO2CRC in order to facilitate access for further research in carbon capture and storage (CCS).
The carbon capture technology absorbs CO2 from the power station flue gas using a solvent solution. In a novel process, the captured CO2 is then used to reduce the pH of the power station’s ash water before it leaves the site. The CO2 reacts with the ash water to produce an inert and commercially usable product, calcium carbonate.
Later stages of the project have the potential to produce commercial quantities of liquid CO2, which could be stored and used in a range of manufacturing processes.
The carbon capture pilot at Hazelwood will be regularly reviewed and assessed for its potential for larger scale research programmes.
Solvent based carbon capture technology - how it works
A slipstream of flue gas from the power station enters the carbon capture plant where it is first cooled in a direct contact cooler before being ‘scrubbed’ in the absorber with a proprietary water-based solvent, which absorbs the CO2 from the exhaust. As the exhaust rises through the column, the CO2 level is progressively reduced. The ‘waste’ gas leaving the absorber contains oxygen, nitrogen, water vapour and small quantities of CO2 and is vented to atmosphere.
The CO2-rich solvent drains into the sump of the absorber from where it is then pumped via a recovery heat exchanger to the regenerator. This exchanger preheats the solvent prior to entering the regenerator. Further heat for the regeneration of the solvent is provided via a steam-heated reboiler. In order to maximise heat recovery, lean (i.e. low CO2) solvent from the reboiler is cooled by heat exchange with the incoming rich solvent in the recovery heat exchanger. The lean solvent then passes through a final cooler before returning to the absorber.
The recovered CO2 removed from the solvent exits the regenerator via a condenser. This unit is designed to condense as much of the associated water vapour as possible so that the process is ‘water neutral’, i.e. it does not result is any water losses.
Process Group and International Power have developed a novel method whereby the CO2 captured by the plant will be used to treat the power station waste water. This will eliminate the need for expensive water treatment chemicals because the CO2 will neutralize the waste water and form chalk as a harmless by-product.
When CO2 is injected into the effluent, it reacts with the dissolved calcium hydroxide to form calcium carbonate (CaCO3), which precipitates as fine particles. The reaction lowers the effluent pH and has the added advantage of sequestering the injected CO2 in the solid calcium carbonate.
Calcium carbonate is a non-hazardous, stable mineral widely found throughout nature in, for example, natural chalk, limestone and marble deposits, and is essential for the existence of many plants and animals. Industrially, calcium carbonate is widely used as an additive in various cements, paints, plastics, adhesives, ceramic glazes and paper products.
Fig 1: The capture and sequestration process at Hazelwood.
Research and development
The capture plant has been designed to allow future research into other separation technologies to drive down costs of post combustion carbon capture.
At 20,000 tonnes per annum, the carbon capture project at Hazelwood represents a world class demonstration and research facility. With ongoing involvements from both Process Group and the CO2CRC, the plant will be used to test and develop new generation carbon capture solvents, construction materials and optimize the process. A facility of this scale is truly unique in the world today and will allow for significant process development and enhancements, which are critical if CCS is to become part of the solution for global warming.
The future: geo-sequestration
The Hazelwood project focuses on the successful demonstration of carbon capture technology to help assess its potential for future large-scale post-combustion CO2 capture. The project is not performing a geo-sequestration trial.
However, the project’s technology partner, the CO2CRC, is currently performing such a trial of CO2 geo-sequestration in the Otway Basin. This first ever injection and storage of CO2 in deep geological structures in Australia has now been in operation for over 18 months at Nirranda, in Victoria.
The CO2CRC Otway Project is designed to demonstrate the safety and security of the transport, injection and storage of CO2 in the deep subsurface. The project takes naturally occurring CO2 from the Butress reservoir, a previously abandoned well drilled during exploration for natural gas, and reinjects it into a depleted natural gas reservoir.
A second well has been drilled by the CO2CRC as part of the project to allow ‘down hole’ monitoring of the injection process. This monitoring, coupled with surface and ground water monitoring, makes Otway one of the most significant injection sites because of the volume and comprehensive nature of the data that is being collected.
The Process Group also played a key role in this project by assisting in the development of the overall method for the geosequestration. It designed and supplied the gas processing and compression equipment for the project, which exploits a novel technology that prevents the formation of solids and allows the re-injection of CO2 in its supercritical state.
The geosequestration package is designed to process CO2-rich gas from the Buttress wellhead and compress the gas to up to 137 bar before re-injection into the depleted Naylor reservoir, located approximately 2 km away.
The project allows the injection of wet or water-saturated CO2. This is unusual for geo-sequestration because the presence of water would normally cause the formation of hydrates, a water/CO2 solid that in this case would have formed at temperatures as high as 17°C. Process Group developed a process that avoids the formation of such hydrates by using the waste heat of compression to maintain CO2 above its hydration point. It is believed that this may be the first time that the specific technology has been used. Process Group believes this process could reduce the cost of future geosequestration projects where the injection site is close to the carbon capture plant. If the CO2 needs to be transported any reasonable distance, these savings will be offset by the high cost of stainless steel pipelines that would be necessary for wet CO2.
The next five years
With global research into carbon capture and storage ever increasing, it would appear that the next five years is going to prove pivotal if this technology is to offer some hope of reducing greenhouse gas emissions. The need to make dramatic reductions in plant capital and operating costs is upon us.
Currently, there are a number of demonstration projects planned worldwide in the 100,000 tonne to 1,000,000 tonne per annum range, which will be undertaken over the next few years. All of these projects rely on government funding in the absence of a sufficient ‘price’ against the carbon captured and stored to make the projects self funding. In addition, the international legal framework for the development and operation of geological CO2 storage sites remains a further hurdle some of these projects are yet to clear. Further delay may be caused by issues of access to such sites and the absence of the necessary reservoir data.
For further information:
Managing director, Process Group
27 October 2009