April 07, 2015
The numbers and the necessity are controversial but societies are steadily moving to control the amount of carbon they emit. Every tool in the box is being tried and tested, from economic disincentives (“carbon tax”) to substitutions to lower carbon emissions (fuel oil to natural gas) or to have zero operational carbon (hydro and other weather-influenced renewables and geothermal).
Another path is to gain the energy from global superabundant coal resources while preventing the carbon dioxide produced from entering the atmosphere where it would impact the climate. This approach requires carbon capture and sequestration—CCS—and its promise is being tested for the first time on an industrial scale at the Boundary Dam coal-fired power station in Saskatchewan, Canada. And nickel-containing materials are used very extensively.
Pulverized lignite coal is burned to produce heat which is used to make steam, with the flue gases flowing to the CCS facility. Firstly, 100% of the sulphur dioxide (SO2) is captured by a dedicated amine chemical absorber column and stripper circuit. The gases then pass to a 52 metre high absorber column with amine chemicals that capture 90% of the carbon dioxide (CO2) after which the treated flue gas leaves the system.
The carbon-rich amine solution goes to a CO2 stripper for separation, condensation and compression. The now lean (low carbon) amine solution is cleaned and recycled back into the absorber column. Both the CO2 and SO2 amine circuits are closed.
This is a simplified description (see chart) of a very complex interplay of chemical reactions, temperatures and demanding material specifications for piping systems, linings, pumps, heat exchangers, compressors and supporting machinery, almost all of which depend on some nickel content for their reliable and long service life.
The objective of the CCS facility is to reduce emissions—the facility avoids the emission of one million tonnes of carbon dioxide every year. The need of the facility is to generate revenue. In addition to the electricity that is sold at market rates and the sales of CO2 for enhanced oil production, the fly ash from combustion has a low but real value as an addition to concrete. And the SO2 is turned into sulphuric acid, an input for many industrial processes.
The CO2 from Boundary Dam has two destinations. The majority is piped to an oil field 65km away where it is injected into the field to increase pressure and thus the amount of recoverable oil. The remainder is injected into a stable saline aquifer 3.4km underground.