Abstract
High temperature CO2 and SO2 sequential capture in a bubbling fluidised bed was investigated using a natural limestone and synthetic composite pellets. Calcination was conducted under oxy-combustion conditions, while carbonation and sulphation occurred in an air-combustion atmosphere. The goal of sequential capture of CO2/SO2 is to desulphurise the flue gas first, followed by cyclic carbonation and calcination. Here, fresh sorbent is first used in the cyclic calcination/carbonation process and then the spent sorbent is sent for sulphation.The pellet carrying capacity is 0.29 g CO2/g sorbents for the first cycle, while that of natural limestone is about 0.45 g CO2/g sorbents. The carrying capacity first fell and then finally plateaued around 0.10 and 0.12 g CO2/g sorbents for limestone and pellets respectively. The SO2 carrying capacity for limestone and pellets after 20 cycles of CO2 capture was 0.17 and 0.22 g SO2/g sorbents respectively. This indicates that the sorbent spent in CO2 capture can be effectively reused for SO2 removal. Abrasion was observed to be the main mode of attrition, but some agglomeration was also found with increasing number of cycles and this may be a concern in the use of Ca-based sorbent for CO2 or SO2 fluidised bed capture.
Highlights
The increased consumption of fossil fuels in power plants and in cinerators has increased emission of air pollutants, including SO2, which can cause acid rain, human respiratory irritation and diseases, and serves as a precursor of extremely fine particulate matter [1]
Manovic et al used a Ca looping system with conditions suitable for both sulphation and carbonation [13]. Their results showed that sulphation and carbonation are competitive reactions when Cabased sorbents are used for cleaning flue gas; and after a few cycles, the CO2 capture capacity of the sorbent becomes negligible
The increase in the activity of a Ca-based sorbent for CO2 capture typically leads to an increase in its activity toward SO2. This means that any effort made for increasing sorbent performance for CO2 capture is less effective if SO2 is present [9,10]. These results suggest that ideally SO2 must be avoided if the objective is CO2 capture from flue gas, especially when more
Summary
The increased consumption of fossil fuels in power plants and in cinerators has increased emission of air pollutants, including SO2, which can cause acid rain, human respiratory irritation and diseases, and serves as a precursor of extremely fine particulate matter [1]. A suitable Ca-based sorbent was developed to maintain an acceptable level of activity over a relatively high cycle number [here selected for a molar ratio of C/S in coal, which has 70 wt% C and 2 wt% S, resulting in a molar C/S ratio of 90]. Using this approach, a Ca-based sorbent employed to capture CO2 can be applied in a real power plant without producing any extra waste product [4,15]
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