Simultaneous Carbonation and Sulfation of CaO in Oxy‐Fuel CFB Combustion

Abstract

For anthracites and petroleum cokes, the typical combustion temperature in a circulating fluidized bed (CFB) is > 900°C. At CO 2 concentrations of 80-85 % (typical of oxy-fuel CFBC conditions), limestone still calcines. When the ash which includes unreacted CaO cools to the calcination temperature, carbonation of fly ash deposited on cool surfaces may occur. At the same time, indirect and direct sulfation of limestone also will occur, possibly leading to more deposition. In this study, CaO was carbonated and sulfated simultaneously in a thermogravimetric analyzer (TGA) under conditions expected in an oxy-fuel CFBC. It was found that temperature, and concentrations of CO 2 , SO 2 , and especially H 2 O are important factors in determining the carbonation/sulfation reactions of CaO.

A Comprehensive Review of Ash Issues in Oxyfuel Combustion of Coal and Biomass: Mineral Matter Transformation, Ash Formation, and Deposition

“…Wang et al investigated simultaneous carbonation and sulfation of CaO under oxyfuel CFBC conditions. 111 The results showed that, when the ash containing CaO cooled calcination temperature, carbonation of fly ash deposited on cool surfaces occurred. Simultaneously, indirect and direct sulfation of limestone would also occur, possibly leading to more deposition.…”

“…This was ascribed to the inhibition of sulfation by the high CO 2 partial pressure and the reduction of alkali metals in the fly ash. Wang et al also found that, under conditions of oxy-FBC, ash carbonation was faster than sulfation . The ashes generated in a 10 kW th fluidized bed unit using a Victorian brown coal in both air and oxyfuel combustion were characterized .…”

“…However, the presence of sulfur oxides in the flue gas can make the processes more complex, because ash sulfation can occur at the same time. Wang et al investigated simultaneous carbonation and sulfation of CaO under oxyfuel CFBC conditions . The results showed that, when the ash containing CaO cooled to the calcination temperature, carbonation of fly ash deposited on cool surfaces occurred.…”

“…Wang et al also found that, under conditions of oxy-FBC, ash carbonation was faster than sulfation. 111 The ashes generated in a 10 kW th fluidized bed unit using a Victorian brown coal in both air and oxyfuel combustion were characterized. 115 The results showed that the particle size distributions of fly and bed ashes from oxyfuel combustion (15%, 21%, and 30% O 2 ) were similar to those from air combustion.…”

Condition Monitoring of Limestone and Soft Sensing Model of SO2 Emissions in a Circulating Fluidized Bed Boiler

“…Calcination is the first step, then followed by sulfation. The calcination reaction is faster than the sulfation reaction; meanwhile, CO 2 that is produced during calcination could form a Stefan flow that can make sulfation start to occur until the end of calcination, in principle. , In addition, both processes require much time and are greatly affected by the combustion process. , As a result, for a large amount of CaCO 3 and CaO particles, calcination and sulfation are not entirely separate processes: they are stored and recycled in the furnace under different conditions like coal particles. Therefore, the developments of soft sensing models for the desulfurization process have important practical significance.…”