Figs. 5 and 6 give the improvement of grade and total removal
efficiency of fine particles by the WFGD system for both cases
which can be described as without steam addition, steam addition
in the particle growth region. The liquid-to-gas ratio (L/G) was
10 L Nm3 and the amount of steam added was 0.08 kg Nm3.
The temperature of desulfurization liquid is in the range of 15–
20 C. It can be seen from Figs. 5a and 6 that in the case without
steam addition the removal efficiencies are negative. That is, the
number concentration of fine particles enhances during the desulfurization
process. This can be explained from the following two
factors. On the one hand, when CaCO3 is used as the reagent, the
product sulfates and sulfites tend to form fine crystals as a consequence
of their slight solubility in water, and unreacted limestone
particulates can also be present. The fine particles in flue gas are
hence a mixture of sulfates, sulfites, unreacted limestone and
coal-fired fly ash, leading to the increase of fine particle concentration.
On the other hand, the negative efficiencies are mainly due to
the initial particle size and number concentration distribution
characteristics (see Fig. 3). Kim et al. [20] found that the particles
smaller than 0.1 lm tend to collide and adhere into larger particles
by mechanisms of diffusional deposition and Brownian coagulation.
Since the peak of initial particle number concentration is in
the range of 0.04–0.1 lm, some of the particles may coagulate into
larger ones of 0.2–1.0 lm. As the initial particle number concentration
in 0.2–1.0 lm is very low, number concentration increase is
remarkable. However, the conventional scrubber is inefficient in
capture fine particles in 0.2–1.0 lm size range, resulting in the
negative removal efficiencies.
Figs. 5 and 6 give the improvement of grade and total removal
efficiency of fine particles by the WFGD system for both cases
which can be described as without steam addition, steam addition
in the particle growth region. The liquid-to-gas ratio (L/G) was
10 L Nm3 and the amount of steam added was 0.08 kg Nm3.
The temperature of desulfurization liquid is in the range of 15–
20 C. It can be seen from Figs. 5a and 6 that in the case without
steam addition the removal efficiencies are negative. That is, the
number concentration of fine particles enhances during the desulfurization
process. This can be explained from the following two
factors. On the one hand, when CaCO3 is used as the reagent, the
product sulfates and sulfites tend to form fine crystals as a consequence
of their slight solubility in water, and unreacted limestone
particulates can also be present. The fine particles in flue gas are
hence a mixture of sulfates, sulfites, unreacted limestone and
coal-fired fly ash, leading to the increase of fine particle concentration.
On the other hand, the negative efficiencies are mainly due to
the initial particle size and number concentration distribution
characteristics (see Fig. 3). Kim et al. [20] found that the particles
smaller than 0.1 lm tend to collide and adhere into larger particles
by mechanisms of diffusional deposition and Brownian coagulation.
Since the peak of initial particle number concentration is in
the range of 0.04–0.1 lm, some of the particles may coagulate into
larger ones of 0.2–1.0 lm. As the initial particle number concentration
in 0.2–1.0 lm is very low, number concentration increase is
remarkable. However, the conventional scrubber is inefficient in
capture fine particles in 0.2–1.0 lm size range, resulting in the
negative removal efficiencies.
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