(143q) Development of a New Dry Flue Gas Desulphurization Process Utilizing Calcium Silicate Hydrate in Waste Concrete

Flue gas desulphurization (FGD) has been developed to reduce the sulphur dioxide (SO₂) emission associated with coal or oil combustion since early 1970s. Various types of the flue gas desulphurization (FGD) processes have been developed, including wet, semi-dry, and dry FGD processes. Wet FGD process has been widely used for large-scale SO₂ emission sources because of its high SO₂ recovery efficiency. However, a large amount of water is necessary to operate the wet FGD processes, and therefore, it may not be appropriate to apply them to emission sources located where water supply is insufficient and costly, e.g. inland China. Dry FGD processes would be more suitable for such a location, and development of low-cost FGD processes with high SO₂ recovery efficiencies should be necessary to meet the sharp increase of the demand on the FGD processes. Recently, a new type dry FGD process by utilizing calcium silicate hydrate gel (C-S-H gel) as a desulfurization agent has been developed. The C-S-H gel is generated from silica and calcium hydroxide (Ca(OH)₂) by the reaction at the surface of fly-ash particles Sufficiently high SO₂ recovery efficiencies could be realized by the process under the temperature at 57-400 ^oC, which is far below the normal operation temperature of 900 ^oC for the processes using conventional agents such as Ca(OH)₂, or CaCO₃. In this paper, we proposed a new dry desulphurization process by utilizing waste cement particles. Since hydrated cement is composed of alkali calcium compounds such as Ca(OH)₂, C-S-H gel, it is expected that waste cement particles have a high reactivity with SO₂. The reaction kinetics of SO₂ removal was studied by laboratory-scale experiments to examine the potential desulphurization efficiency by the waste cement particles. Desulfurization experiments for Ca(OH)₂ and calcium carbonate (CaCO₃) were also conducted under the same conditions for comparison.

Laboratory experimental studies showed that the waste cement particles have a sufficiently high reaction rate with gaseous SO₂, under the temperature conditions of 100 ~ 400 ^oC. The waste cement would be applicable for the desulphurization process, especially under the lower temperature conditions such as 100 ^oC, under which the desulphurization rate is comparable with that of calcium hydroxide, which has been commonly used as a desulphurization agent but much more expensive than the waste cement. The use of waste cement would be a promising option for a dry desulfurization process.