ABSTRACT:

Oxyfuel combustion is considered as one of the most promising technologies to facilitate CO2 capture from flue gases. In oxy-fuel combustion, the fuel is burned in a mixture of oxygen and recirculated flue gas. Flue gas recirculation increases the levels of fireside CO2, SO2, Cl and moisture, and thus promotes fouling and corrosion. It has been suggested that oxide scales developing in O2/CO2/H2O atmospheres are not well protective and internal carburization may occur. In this study three boiler tube steels X20CrMoV11-1, UNS S34710 and UNS S31042 were subjected to oxidation/corrosion testing at 600 and 650°C under simulated oxyfuel fired atmospheres (60% CO2-30% H2O-4% O2-Ar) with and without CaCO3-CaSO4 deposit up to 1000 h. With extended exposure time, the oxide scale properties may change to enable metal carburization. The exposure with CaCO3-CaSO4 deposit at 650°C resulted in corrosion of all tested alloys and clear carburization of steels X20CrMoV11-1 and UNS S34710.

INTRODUCTION

The demand for reduced emissions requires the development of efficient combustion technologies suited for carbon capture and storage (CCS) systems. Oxyfuel combustion of fossil fuels is one of the most promising technologies for reducing CO2 emissions and can be built as a retrofit solution for existing boilers. Compared to conventional air-fired combustion, the oxyfuel process will use oxygen or oxygen-enriched air to reduce the nitrogen in the flue gas and to increase the CO2 content for easier capture. Oxyfuel combustion can be expected to differ from combustion in air by e.g. modified distribution of fireside temperatures, much reduced NOx but increased levels of fireside CO2 and H2O with small amounts of O2, Ar, N2 and some impurities like SO2 and Cl. The risk of enrichment of corrosive species in the flue gas environment strongly increases due to recycling of flue gas in oxy-fired combustion compared to air firing.

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