Carbon capture and storage (CCS) systems, which can reduce CO2 emissions into the atmosphere, are about to enter into large-scale industrial use. The following article explains the emerging technology and how Allianz and its clients are involved.
Carbon-based technologies dominate about 75 percent of the world’s power generation, according to most estimates. While renewable and non-carbon-based energy sources are coming on line, this dominance is likely to continue for the foreseeable future. Therefore, an effective carbon dioxide (CO2) emission control strategy should target these power systems. It will consist of cleaner power plants and “smarter” electricity grids and also stop the CO2 created in the process of burning fuels from entering the atmosphere. Recovering CO2 from exhaust gases and limiting CO2 release to the atmosphere is a more or less new aim for power plants and energy generation in general. Up to now, power plants have developed gas treatments to recover hydrogen sulphide, sulphur, nitrous oxide and other compounds considered to be pollutants.
Long considered relatively neutral in its effects, little attention had been paid to CO2 until it entered the public discussion on climate change, as observers point to significant growth in CO2 emissions in recent years. Recent requirements coming from state regulations have now pushed companies to improve the CO2 capture in their exhaust and find ways of storing it. Processes for carbon capture and storage (CCS) were therefore first seriously investigated in the 1990’s but experienced a significant development beginning this century.
Three kinds of capture
In the current state of development, CCS processes can be divided into three main types: post-combustion, precombustion and oxyfuel-combustion. Each of them has different advantages that in turn need to be weighed against their costs and their overall effects on fuel efficiency.
Post-combustion CCS processes, as the name suggests, handle exhaust after the fuel is burned. Here again, there are three major groups (see graphic next page). The first, amine and advanced amine processes, are proven in natural and synthetic gas purification and were developed and specialized to capture CO2. Flue gas is treated with aqueous amine solution, which reacts with CO2 by absorption, and at raised temperatures CO2 is released and solution recovered for re-use or directly by processes consuming CO2 or stored as condensed and liquefied CO2, in deep geological formations, in deep ocean masses, or in the form of mineral carbonates. There are different types of amines that are suitable for CO2 separation under different conditions. Advanced amine processes involve more specialized amines with a better efficiency, a higher tolerance against oxygen and trace contaminants and lower solvent degradation rates. Composition of flue gas could be a challenge. Corrosion is possible and therefore adequate materials are necessary.
This area has a lot of competitors such as all oil & gas manufacturers, Alstom, Dow Chemical, Mitsubishi and Siemens. A new project in Canada could be the largest implemented in the world using amines specifically for sulphides and CO2.
The second group of post-combustion CCS comprises the chilled ammonia processes. These are also well known processes where the flue gas is cooled, absorbed in a rich ammonia-water-based solution and then regenerated to be used or liquefied like the amine processes.
This is a highly efficient solution with low heat of reaction, easy and low temperature regeneration and tolerance to oxygen and contaminations in gas. However, there is a risk of toxic release of ammonia and buyers need to be found for the ammonia sulphate that is a byproduct of the process. Again corrosion is possible and therefore adequate materials are necessary. The main incident up to now is clogging.
Finally, a new kind of post-combustion CCS is the antisublimation process. In this case, flue gas is cooled and conditioned to be dried and then CO2 is frosted and liquefied. No chemicals are involved, but efficiency seems to be low. Up to now, they have not been tested at a pilot plant and are still under investigation at laboratory level.
The pre-combustion processes are based on an integrated gasification combined cycle with steam reformer, partial oxidation and a shift reactor to convert carbon monoxide to CO2. This is followed by the capture of CO2 (as in post-combustion unit) and use of hydrogen and nitrogen in a gas turbine. The process needs oxygen coming from an air separation unit. This is the shortest term for market and the easiest to realize. Up to 90 to 95 percent of the CO2 could be captured.
Oxyfuel-combustion processes were designed based on technologies used for the treatment of ethylene and in boilers in combination with proven technologies given by referenced companies in order to supply a global process management to their clients. It is a combined process for power plants using fuel or coal where the end gas processing unit can catch and release CO2. Using this method, 100 percent of the CO2 could be captured. However, the efficiency of power plants would be lowered to below 70 percent, while costs rise by about 30 percent. Oxygen content needs to be controlled to below 25 percent. Supercritical CO2 is used in some processes to allow pumping of CO2 and requires some special equipment. Material selection is essential and experiments have been done to select them. Cold boxes for the cryogenic recovery of CO2 and condensers require the use of aluminium and dedicated processes of welding. Temperature control is needed to prevent hydrate and dry ice formation.
With benefits come costs
Capturing and compressing CO2 requires a great deal of energy and would increase the fuel needs of a coal-fired plant with CCS by 25 to 40 percent. These and other system costs are estimated to increase the expenses of energy from a new power plant with CCS by 21 to 91 percent. Therefore, cost-effective carbon sequestration schemes could be identified as a key need for dealing with the impact of CO2 on global climate change.
The main challenge of CO2 capture and storage is the high cost of technologies using the current state-of-the-art technologies. Separation and compression of CO2 account for the bulk of these costs, while the costs of transportation and injection are comparatively lower. Another issue could be the energy and CO2 release used to capture CO2 versus the efficiency of the capture process. All of the research and development studies related to CO2 capture and storage are of significant interest for these objectives.
As a result, Allianz works closely with its customers developing such processes. It offers them insurance warranties for running pilot phases and pre-industrial phases as well. This support means understanding the technologies they are developing and what the main technical concerns are in order to create more appropriate insurance solutions based on the exposures they could face.
Allianz Risk Consulting, France