Among other emissions, Carbon dioxide is a headache for many cement producers. Finding the right balance between environmental-responsibility and financial-stability is difficult. For industrial plants shifting towards carbon capture and sequestration (CCS), economic performance suffers due to the high cost of installing and running the necessary equipment. However, a way of offsetting those costs is now in development at Sandia National Laboratories.
A new type of turbine, utilizing supercritical carbon dioxide (S-CO2) instead of traditional steam, is being tested at Sandia. These turbines use the S-CO2 compressed at 73 bar and at 33 °C and run on the Brayton Cycle (where steam turbines utilize the Rankine Cycle). The benefits of this new type of system lie in footprint in the plant along with initial investment. The use of the Brayton Cycle allows for a drastic reduction in turbine size. A 300 MWe S-CO2 turbine has an outside diameter of approximately 1 meter and needs only three stages of turbomachinery. The corresponding steam turbine would require a diameter of five meters with 22-30 stages of turbomachinery. This reduction in size translates to a decrease in the initial investment on the system.
Any plant that could employ this system successfully should see the device pay for itself over a short interval of time. Depending on the turbine size chosen, a plant could remove itself from the grid by generating all its own power needs and perhaps even sell power back to the utility companies. With the ever-changing technology, what was once a headache for the cement industry might turn out to be a godsend for the financial competitiveness.
Information gathered for this article appears in the January 2012 issue of Mechanical Engineering, the official magazine of ASME. The article was entitled, “Mighty Mite” and was authored by Steven Wright.