While the increase in carbon dioxide (CO2) in the atmosphere from burning fossil fuel is contributing to climate change, CO2 makes up only a very small proportion of the atmosphere (0.038 per cent).
Trees can easily extract CO2 from the atmosphere, but there is no technology that can effectively do this. What we can use technology for is to stop the CO2 getting into the atmosphere in the first place. The most practical way do this is to capture it at large, stationary sources, such as power stations or industrial plants.
Carbon capture and geological storage (CCS) has been under way for more than a decade as part of petroleum operations, yet many people are only just becoming aware of it and the opportunity it offers to substantially reduce greenhouse gas emissions from major stationary sources of CO2, such as power stations.
CCS involves separating CO2 from other gases, compressing it until it becomes a fluid, transporting it to a suitable site and injecting it into suitable deep geological formation for long-term storage.
This is being done at various places around the world, but we are not doing it at anywhere near the scale that is required to make the necessary deep cuts in emissions. This is partly because of the cost of capturing the CO2. A great deal of research is under way to quickly develop cheaper and more efficient ways to capture the CO2.
At the moment CO2 is captured commercially using liquid solvents. The CO2 is absorbed in the liquid and then removed in concentrated form by changing the temperature or pressure of the liquid. This technique is used in Australia and around the world to provide industry with CO2 for use in dry cleaning or the manufacture of carbonated drinks.
The search is now on for new solvents, as well as adapting other current technologies that can be applied to separating CO2 from flue gases, such as using membranes, which act as nano-sized sieves, or minerals that attract CO2 (like washing powder attracts dirt), or by freezing the CO2. In addition to the separation material, there is a need to develop more energy-efficient methods for the whole process, in order to maximise energy use.
One process being further developed is the gasification of coal, which has the dual benefit of being energy efficient and enabling easier capture of CO2. It also provides a pathway for the production of hydrogen for use as a clean fuel.
Once we have the separated CO2, it is compressed into a fairly dense liquid form and then transported to a storage site by pipeline. Millions of tonnes of CO2 are already transported by pipeline every year in the US and the technology is well known. What is missing in Australia and most other countries is the pipeline infrastructure to transport the CO2.
At the storage site the liquid CO2 is injected into the ground at a depth of about a kilometre or more. Vast amounts of CO2 are trapped naturally in the ground through normal geological processes for millions of years. This CO2 is used in the food industry in various industrial processes and in enhanced oil recovery.
Over the past 30 years, several hundred million tonnes of CO2 have been injected underground as a means of extracting more oil. Also, about 20 million tonnes of CO2 have been geologically stored as part of natural gas and petroleum production in Norway, Canada and Algeria since 1996.
In Australia we recently started the first CO2 storage project – the CO2CRC Otway Project – in western Victoria and have already injected 15,000 tonnes of CO2 into very porous and permeable rocks two kilometres deep. We are confident that the CO2 will stay safely in the ground because the geology of the site is well known and has the right rocks to trap the CO2. In addition, while we do not expect there will be any CO2 leakage, to make doubly sure the site is carefully monitored 24 hours a day using a wide range of sophisticated instruments that directly and indirectly measure CO2 underground, in the soil and in the air.
Do we have enough storage sites for the CO2 in Australia?
There has been a considerable amount of work already done in Australia to find suitable basins to store CO2, such as the Otway Basin, where oil or gas has been produced and where therefore it would be reasonable to expect that CO2 could also be safely trapped in depleted oil and gas fields. Deep underground saline formations provide one of the most important opportunities for geological storage, not only in Australia, but also in many other parts of the world.
The Otway Project will inject into such a saline formation in the next phase of the project. The proposal for the Gorgon LNG Project involves geological storage of approximately three million tonnes a year (tpa) of CO2 in a saline aquifer under Barrow Island, Western Australia. The proposed Monash coal-to-liquids project includes the suggestion of geological storage of 10 million tpa of CO2.
Obviously storage of such quantities of CO2 requires the reservoir rocks to be both porous and permeable to enable the super-critical CO2 to be held within the pore space and in the pore fluids. In addition, a good seal (a very impermeable rock) is necessary to hold in the CO2. Rocks of this type are found in many parts of Australia, although not always near to the major sources of CO2. Some of the best areas are likely to be offshore, which is why the Federal Government’s recent legislation to allow offshore storage of CO2 could be very important to the uptake of this technology.
CCS is certainly not the total answer to greenhouse concerns, but it is an essential part of the answer, along with energy efficiency, greater use of renewable energy and lower carbon fuels.
CCS is also of global significance. For example, each year China puts in more new coal-fired power stations than we have in the whole of Australia now – and those power stations will be emitting CO2 for the next 40 or 50 years. This means that not only do we need to start deploying CCS in new-build power stations, but we also need to be able to retrofit CCS to many of the existing power stations.
There are obviously some challenges ahead in deploying CCS at a large scale. Costs need to come down, but the chemical engineers are on a well-trodden path that will enable them to bring down the cost of capture and improve efficiency. The geologists have a wealth of knowledge of subsurface processes although, surprisingly, our knowledge of the deep rocks of Australia is quite sparse in many areas.
These are not insurmountable barriers – just as well, because all the projections of the International Energy Agency indicate that we will be using more, not less, fossil fuels for power generation in the future.
It is therefore vital that we start to deploy CCS as soon as is technologically and economically feasible as part of our mitigation portfolio. So we just have to get cleaner and smarter in using fossil fuels – which is where CCS comes in. We must ensure that CCS does work or we are in deep trouble.
The Government has committed $100 million to the establishment and operation of a Global Institute, which it has offered to host in Australia, to work cooperatively with other countries to accelerate CCS technology. |
