Pyrrhotite deposition through thermal projection to simulate iron sulphide slagging in oxyfuel combustion

Abstract

a b s t r a c tOxyfuel combustion is envisaged as one of the main options for near future CO 2 reduction in conventional power production. There are many aspects of oxy-combustion still at the research stage. One of those is the issue of boiler materials resistance to corrosion due to solid deposits formed as a consequence of slagging in CO 2 rich flue gases. The novel approach to the issue is the simulation of realistic slagging by pyrite (FeS 2 ) projection through an oxyacetylene spray gun, flying along a controlled flame and impacting onto metallic surfaces of selected composition for fireside waterwall construction (F22, P91, 409, 347, 304H, and 800HT). Metallic surface temperatures were kept at 400, 500, 600 or 700°C, and after deposition, metallic coupons were aged for long periods (150 and 1500 h) at the selected conditions (O 2 /N 2 , CO 2 /N 2 ). The characterisation of deposits was performed with XRD, SEM-EDX and carburisation tests.The first finding is that the oxidation progression is different when partially transformed pyrite covers metallic surfaces. In that case, no iron oxide (Fe 2 O 3 ) scale is generated, only the chromium oxide (Cr 3 O 4 ) grows between the steel and the deposit as a response to oxidation. There is a clear presence of chromium sulphides in competition with the chromium oxide. On the other hand, comparison of scales in CO 2 vs. air indicates the same chemical composition but different morphology; in air combustion, corrosion layers are thicker and cracked. These results can improve the prediction of operational problems in coal oxy-fuel combustion.

Innovative Methodology for Sulfur Release from Copper Tailings by the Oxidation Roasting Process

“…Moreover, pyrrhotite was formed by desulfurization during the thermal decomposition of pyrite. In an aerobic or carbon dioxide atmosphere, pyrrhotite could be oxidized to form iron oxides and gaseous SO x [16,17]. When the concentration of SO 2 in gaseous SO x reached or exceeded 3%, SO 2 could be collected together to produce sulfuric acid [18], and iron oxides could be recovered in subsequent processing.…”

New approach to materials behaviour studies in high-speed flue gas from oxy-steam combustion

“…A Metco 5P-II Combustion Powder Spray Gun was used to produce high temperature and high speed combustion flames. This lightweight handheld spray gun was originally intended for occasional thermal spray needs but, for this research, it was adapted to produce high speed H 2 O-rich flames from H 2 /O 2 mixtures [44]. A Witt MM-Flex gas mixer, equipped with a proportional mixing valve with a control knob and % scale and variable flow settings, was installed in the H 2 stream to add CO 2 to the system.…”

Study on high‐temperature corrosion in a 600 MW opposed firing boiler

“…The pyrite (FeS 2 ) in coal decomposes to sulfur when the temperature is above 350 C, causing corrosion that has been encountered in boilers. 9,10 The corrosive gas (H 2 S) generated from the sulfur transformation in coal in the course of oxygen-deficient combustion could penetrate the Fe 2 O 3 protective layer to further react with the ferrous oxide and ferrous, leading to the high-temperature corrosion of the water-cooled wall. 6,11,12 The thinning and bursting of the water-cooled wall are easily caused by the high-temperature corrosion, leading to the loss of electricity accounted for 16.35% of the total electricity production.…”

“…The presence of CO takes the responsibility for the high‐temperature corrosion by reacting with the dense protective layer of Fe 2 O 3 and turning it to FeO. The pyrite (FeS 2 ) in coal decomposes to sulfur when the temperature is above 350°C, causing corrosion that has been encountered in boilers 9,10 . The corrosive gas (H 2 S) generated from the sulfur transformation in coal in the course of oxygen‐deficient combustion could penetrate the Fe 2 O 3 protective layer to further react with the ferrous oxide and ferrous, leading to the high‐temperature corrosion of the water‐cooled wall 6,11,12 …”