(646d) The Effects of Desublimating CO2 Particles On Turbine Materials

Sub-cryogenic CO2 capture uses some unconventional technology that involves cooling the flue gas stream and separating the SOx and other contaminates by freezing and liquefying them out. CO2 desublimation and separation takes place in a turbine expansion chamber and is the focus of this presentation. Sub-cryogenic CO2 capture requires massive depressurization through an expansion chamber fit with a turbine. This results in very high velocity solid CO2 particle impingement on the turbine blades. Resistance to erosion and abrasion is critical when considering the choice of material for the turbine. Creep, which usually is a critical issue, is negligent because of the low operating temperatures. On the other hand, a new problem caused by ductile brittle transitions becomes a concern in the design process. A combination of hardness and a resistance to stress will create the ideal candidate for turbine material. The performance of different materials that undergo high velocity impingement by solid CO2 particles will be topic discussed. After contacting several companies that liquefy the various components of air, stainless steel was found to be a good candidate. We chose S.S. 304 after reviewing all of the information available from N R Baddoo's paper1 . We reasoned that with the wealth of information already available for S.S 304, it would serve as a basis of comparison for any other materials. We hypothesize that there will be no erosion or material loss from these tests. Our setup is the same as outlined in ASTM standard G 76 ? 072 with slight variations do to the temperature differences. We mounted the sample piece and blasted it with depressurized liquid CO2 that at 280 psi, cools adiabatically as it expands and forms solid particulates. The S.S. samples are subjected to four tests in an attempt to determine whether there will be a detrimental effect caused by the solid CO2 stream. The four tests are 1) a laser reflection test, 2) scanning electron microscope (SEM) analysis, 3) mass analysis, and 4) laser topography measurement. The image reflected from an abraded area was compared with that from a non-abraded area. Later, the addition of a beam expander allowed analysis of the entire sample at one time. Results are not conclusive but will be shown in presentation The SEM has shown the most significant results. The before and after images show that changes are occurring on the surface of the sample. Debris has been cleaned out of microscopic crevices, but has the metal itself been abraded or simply polished? The mass analysis has potential of becoming the most conclusive test, as a significant decrease in mass would be conclusive evidence of erosion. To this point a significant change in mass has not been observed but new tests are being devised to increase the ability of measuring changes in mass. Topographical implications from experimentation will be discussed and extrapolated to show the viability of Stainless Steel 304. The combined results from the test give strong evidence that erosion has occurred. New tests are being run on additional metal candidates and these exciting results will be revealed during the presentation. In addition, there will be discussion on how the exposure time to the impingement stream changes the rates of abrasion. SOURCES 1. A COMPARISON OF STRUCTURAL STAINLESS STEEL DESIGN STANDARDS N. R. Baddoo The Steel Construction Institute Copyright © 2003 The Steel Construction Institute 2. Standard Test Method for Conducting Erosion Tests by Solid Particle Impingement Using Gas Jets: G76-07 © ASTM international

-3-2010-->