Selection of Ca/S ratio and bed temperature for Indian lignite based CFBC boiler using simplified sulphur capture model

Abstract

In circulating fluidized bed combustion (CFBC) boilers, the method of feeding of limestone with fuel into the furnace gives high desulphurization efficiency and avoids the usage of pulverization equipment in the plants. Ca/S molar ratio and bed temperature play an important role in the process of sulphur capture. Generally, Ca/S ratio ranges between 2 and 6 and bed temperature is around 800–900 ​°C in the commercial CFBC boilers. Higher value of Ca/S ratio and optimum value of bed temperature provide higher desulphurization efficiency. The present work focuses on providing the stipulated value of Ca/S molar ratio (1–6), bed temperature (800oC–925 ​°C) which are required to achieve 95% sulphur capture efficiency for Indian lignite based CFBC boiler operating with 210MW steam parameters using simplified sulphur capture model. The work also shows the effect of Ca/S molar ratio and bed temperature on the values of sulphur emissions, reaction rate of sulphation, limestone feed rate and boiler efficiency for three lignite samples which are popularly available and used in commercial operations of Indian CFBC boilers.

Keywords

• CFBC
• Boiler
• Ca/S ratio
• Lignite
• Sulphur capture
• Bed temperature