Capture of CO2 from Flue Gas by Fly Ash/Ca(OH)2 Sorbents
Date Issued
2012
Date
2012
Author(s)
Yang, Chih-Hsiang
Abstract
A differential fixed-bed reactor was employed to study the effects of the flue gas components (CO2, O2, NOx, SO2, H2O) on the carbonation reaction of Ca(OH)2 and fly ash/Ca(OH)2 (FA/HL) sorbents under the conditions similar to those in the bag filters of spray-drying flue gas desulfurization system. The FA/HL sorbents prepared by slurrying and drying processes contained foil-like calcium silicate hydrates and had a greater surface area and pore volume than Ca(OH)2.
The carbonation of Ca(OH)2 was enhanced by relative humidity and was not affected by CO2 or O2 concentration when NOx and SO2 were not present. The carbonation of Ca(OH)2 was greatly enhanced with increasing relative humidity when NOx, O2, and CO2 were present simultaneously; in this case, relative humidity had a significant effect, temperature had a negligible effect, CO2 concentration had a negative effect, but NOx concentration had a positive effect. When SO2 was present with CO2, O2, and NOx, the fraction of calcium carbonate decreased, but it increased with decreasing SO2 concentration (<500ppm).
The carbonation of FA/HL(30/70) sorbent was enhanced by relative humidity and was not affected by CO2 or O2 concentration when NOx and SO2 were not present. The carbonation of FA/HL sorbent were enhanced with decreasing relative humidity by the presence of NOx/O2 with CO2; in this case, the effect of relative humidity was less marked, and the effect of CO2 or NOx concentration was negligible. Under the same carbonation conditions, carbonation conversions for FA/HL(30/70) sorbent were much higher than those for Ca(OH)2 when NOx/SO2 were absent in the gas mixture, but were close to those for Ca(OH)2 at high relative humidities when NOx and O2 were also present. When SO2 was also present, the extent of carbonation of FA/HL(30/70) sorbent decreased, but it increased with decreasing SO2 concentration (<1000ppm).
The reactivity of FA/HL sorbent varied with the FA/HL weight ratio. The sorbent with a ratio of 30/70 had the highest 1 h CO2 capture(0.253g of CO2/ g of sorbent at 60oC, 70% RH, and 12.6% CO2), when CO2 alone was present in humid N2. However, Ca(OH)2 had the highest 1 h CO2 capture(0.379g of CO2/ g of sorbent at 60oC, 70% RH, 12.6% CO2, 5% O2, and 600ppm NOx) when NOx and O2 were also present.Under gas the mixture with the typical flue gas composition, Ca(OH)2 had the highest 1 h SO2 capture(0.534 g of SO2/ g of sorbent at 60oC, and 70% RH), and the SO2 capture decreased with increasing FA/HL weight ratio.
Subjects
Calcium Hydroxide
Carbon Dioxide
Fly ash
Flue Gas
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-101-R99524090-1.pdf
Size
23.54 KB
Format
Adobe PDF
Checksum
(MD5):d814da7268230567ec7e9881dbb4ee15