Energy exploitation of acid gas with high H_2S content by means of a chemical looping combustion system

摘要

In gas and petroleum industry, the waste gas stream from the sweetening process of a sour natural gas stream is commonly referred as acid gas. Chemical Looping Combustion (CLC) technology has the potential to exploit the combustible fraction of acid gas, H_2S, to produce energy obtaining a flue gas highly concentrated on CO_2 and SO_2, which can be cost-effectively separated for subsequent applications, such as sulfuric acid production. At the same time, a concentrated CO_2 stream ready for storage is obtained. The resistance of oxygen carriers to sulfur becomes crucial when an acid gas is subjected to a CLC process since the H_2S content can be very high. In this work, a total of 41 h of continuous operation with acid gas and H_2S concentrations up to 20 vol.% has been carried out in a 500 Wth CLC unit with two oxygen carriers based on Cu (Cu14γAl) and Fe (Fe20γAl). The formation of copper sulfides and the SO_2 emissions in the air reactor made the Cu14γAl material not adequate for the process. In contrast, excellent results were obtained during acid gas combustion with the Fe20γAl oxygen carrier. H_2S was fully burnt to SO_2 in the fuel reactor at all operating conditions, SO_2 was never detected in the gas outlet stream of the air reactor, and iron sulfides were never formed even at H_2S concentrations as high as 20 vol.%. Furthermore, it was found that a H_2S content of 20 vol.% in the acid gas was high enough to turn the CLC process into an auto-thermal process. Based on these results, it can be concluded that the Fe-based materials prepared by impregnation are very adequate to exploit the energy potential of acid gas mixtures with CO_2 capture.