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Title: Crystal growth and agglomeration of calcium sulfite hemihydrate crystals

Abstract

Flue gas desulfurization (FGD) processes are most commonly utilized to remove sulfur dioxide from stack gases of coal- or oil-fired plants. In the simple slurry technology, SO{sub 2} is absorbed by a slurry of lime/limestone to form calcium sulfite crystals of acicular habit and its strong agglomeration, requiring large clarifiers and filters to dewater the sludge to make an acceptable landfill. Crystal growth and agglomeration of calcium sulfite hemihydrate crystals from solution were studied by reacting Ca(OH){sub 2} with NaHSO{sub 3} in a pH-stat semibatch crystallizer. Single platelet crystals and agglomerates of platelet crystals were produced in the pH range from 5.80 to 6.80. The crystallization mechanism changed from primary nucleation to crystal growth in the progressive precipitation. Using the titration curves, the growth rate was calculated from the titration rate at the final stage of operation. The crystal growth rates of calcium sulfate hemihydrate crystals were found to obey the parabolic rate law in the low supersaturation range. Another point to be noted is that the precipitates of calcium sulfite hemihydrate in agitated suspensions have a tendency to form agglomerates. It was found that the degree of agglomeration is a weak function of relative supersaturation and magma density, whilemore » the pH value is a key factor that affects the degree of agglomeration. Addition of EDTA also has an effect on the agglomeration of calcium sulfite hemihydrates.« less

Authors:
 [1];  [2]
  1. National Taiwan Univ., Taipei (Taiwan, Province of China). Dept. of Chemical Engineering
  2. Long-Hau Junior College, Tao-Yuan (Taiwan, Province of China). Dept. of Chemical Engineering
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
63159
Resource Type:
Journal Article
Resource Relation:
Journal Name: Industrial and Engineering Chemistry Research; Journal Volume: 34; Journal Issue: 4; Other Information: PBD: Apr 1995
Country of Publication:
United States
Language:
English
Subject:
20 FOSSIL-FUELED POWER PLANTS; 01 COAL, LIGNITE, AND PEAT; 02 PETROLEUM; CALCIUM COMPOUNDS; CRYSTAL GROWTH; AGGLOMERATION; SULFITES; LIMESTONE; SULFIDATION; CALCIUM OXIDES; HYDRATES; FOSSIL-FUEL POWER PLANTS; WASTE MANAGEMENT; SULFUR DIOXIDE; AIR POLLUTION CONTROL; RESIDUES; WATER REMOVAL

Citation Formats

Tai, C.Y., and Chen, P.C.. Crystal growth and agglomeration of calcium sulfite hemihydrate crystals. United States: N. p., 1995. Web. doi:10.1021/ie00043a040.
Tai, C.Y., & Chen, P.C.. Crystal growth and agglomeration of calcium sulfite hemihydrate crystals. United States. doi:10.1021/ie00043a040.
Tai, C.Y., and Chen, P.C.. 1995. "Crystal growth and agglomeration of calcium sulfite hemihydrate crystals". United States. doi:10.1021/ie00043a040.
@article{osti_63159,
title = {Crystal growth and agglomeration of calcium sulfite hemihydrate crystals},
author = {Tai, C.Y. and Chen, P.C.},
abstractNote = {Flue gas desulfurization (FGD) processes are most commonly utilized to remove sulfur dioxide from stack gases of coal- or oil-fired plants. In the simple slurry technology, SO{sub 2} is absorbed by a slurry of lime/limestone to form calcium sulfite crystals of acicular habit and its strong agglomeration, requiring large clarifiers and filters to dewater the sludge to make an acceptable landfill. Crystal growth and agglomeration of calcium sulfite hemihydrate crystals from solution were studied by reacting Ca(OH){sub 2} with NaHSO{sub 3} in a pH-stat semibatch crystallizer. Single platelet crystals and agglomerates of platelet crystals were produced in the pH range from 5.80 to 6.80. The crystallization mechanism changed from primary nucleation to crystal growth in the progressive precipitation. Using the titration curves, the growth rate was calculated from the titration rate at the final stage of operation. The crystal growth rates of calcium sulfate hemihydrate crystals were found to obey the parabolic rate law in the low supersaturation range. Another point to be noted is that the precipitates of calcium sulfite hemihydrate in agitated suspensions have a tendency to form agglomerates. It was found that the degree of agglomeration is a weak function of relative supersaturation and magma density, while the pH value is a key factor that affects the degree of agglomeration. Addition of EDTA also has an effect on the agglomeration of calcium sulfite hemihydrates.},
doi = {10.1021/ie00043a040},
journal = {Industrial and Engineering Chemistry Research},
number = 4,
volume = 34,
place = {United States},
year = 1995,
month = 4
}
  • In slurry scrubbing processes for flue gas desulfurization the precipitation rate of calcium sulfite affects scrubber solution composition, SO{sub 2} absorption, sulfite oxidation, and limestone utilization. Sludge quality and disposal costs are also a function of precipitation kinetics. The nucleation and crystal growth rates of calcium sulfate hemihydrate were measured in a continuous flow crystallizer at conditions that produced agglomerate crystals, At 28 and 55C, the nucleation rate varied from 0.25 to 23 {times} 10{sup 8} {number sign}/m{sup 3}-sec. The suspension density, was varied from 7 to 90 kg/m{sup 3}. The linear growth rate, varied from 0.5 to 9 {times}more » 10{sup {minus}9} m/s as residence time was varied from 42 to 360 minutes. The nucleation rate constant had a maximum near pH 5.5 and was about 50% lower at pH 4.2 and pH 6.5. Gypsum saturation in solution caused both the nucleation and growth rates to decrease.« less
  • The rate of calcium sulfite dissolution in slurry scrubbers and hold tanks for flue gas desulfurization affects SO/sub 2/ absorption, limestone utilization and sulfite oxidation. The dissolution rates of calcium sulfite were measured by the pH-state method. A mass transfer model was developed assuming that calcium sulfite particles behave as spheres in an infinite stagnant solution. The model combined with the Bechtel-modified Radian solution equilibrium program successfully predicts calcium sulfite dissolution rates at pH 3.5 - 5.5, 23 and 55 /sup 0/C, 0.001 - 0.3 M Ca/sup + +/ and 2 - 25 mM dissolved sulfite. The effects of sulfatemore » content in solids and liquids and particle size/shape were also studied. At conditions typical of flue gas desulfurization processes calcium sulfite dissolution was controlled by mass transfer, not surface reaction kinetics. Dissolution was fast at low pH and slowed near the equilibrium pH determined by dissolved Ca/sup + +/ and SO/sub 3/ concentrations in the aqueous solutions, K/sub SP/ of the CaSO/sub 3/ . 1/2H/sub 2/O solids, and temperature. The presence of dissolved Mg/sup + +/ increased the equilibrium pH and enhanced the disolution rate. The presence of dissolved sulfate reduced the dissolution rate and the equilibrium pH. The effect of sulfate was not adequately described by the mass transfer model.« less
  • We conducted greenhouse tests to evaluate the effects of FGD-CaSO{sub 3} applied at rates of 0, 2.2, 4.4, and 8.8 Mg ha(-1) on wheat growth, soil enzyme activities, and the chemical properties of two soils with differing pH (4.0 vs. 6.2). A gypsum treatment applied at the rate of 2.2 Mg ha{sup -1} was used as a positive control. Exchangeable Ca{sup 2+} and water-extractable Ca{sup 2+} and SO{sub 4}{sup 2-} increased significantly with increasing FGD-CaSO{sub 3} application. SO{sub 4}{sup 2-} increased in both soils, indicating rapid oxidation of SO{sub 3}{sup 2-} to SO{sub 4}{sup 2-} when neither water nor oxygenmore » was limiting. No changes in soil pH were measured. Applications of 2.2, 4.4, or 8.8 Mg CaSO{sub 3} ha{sup -1} to the pH 6.2 soil produced no effect on wheat growth or the uptake of N, P, Ca{sup 2+}, and Mg{sup 2+}. The uptake of SO{sub 4}{sup 2-} -S increased, whereas K uptake decreased. No significant differences in the activities of urease, {beta}-glucosidase, alkaline phosphatase, or arylsulfatase were observed relative to a control. In the acid soil, an application of 2.2 Mg ha{sup -1} FGD-CaSO{sub 3} increased wheat root growth and dry matter yield compared with an untreated control. The uptake of N, P, Ca{sup 2+}, and K{sup +} also increased presumably because of enhanced root development resulting from decreases in exchangeable Al{sup 3+} and increases in soluble Ca{sup 2+}. Wheat growth and alkaline phosphatase and arylsulfatase activities were significantly inhibited by addition of 8.8 Mg ha{sup -1} of FGD-CaSO{sub 3} compared with the untreated control or the same soil receiving 2.2 Mg ha{sup -1} gypsum. We conclude that surface applications of FGD-CaSO{sub 3} may be as effective as gypsum for inhibiting soil crusting, improving water infiltration, and promoting the movement of Ca{sup 2+} into acid subsoils. Moreover, application rates of equal to or less than 4.4 Mg ha-1 should have no negative impact on soil microbial activities or plant growth.« less
  • The precipitation of calcium sulfate dihydrate (CaSO/sub 4/.2H/sub 2/O) and calcium sulfite hemihydrate (CaSO/sub 3/.1/2H/sub 2/O) from high, up to 240,000 mg/L, total dissolved solids (TDS) solutions was studied at 50/sup 0/C. The solutions were selected to cover a range of solution compositions of magnesium, calcium, sodium, chloride, and sulfate. Precipitation rates along with crystal habit and size changes were measured to determine the effects of these dissolved species as compared to dilute solution conditions. Calcium sulfate dihydrate (gypsum) precipitation rate was accelerated in the high TDS solutions, especially those containing chloride ion. Alternatively, calcium sulfite hemihydrate precipitation rate wasmore » found to be faster in high sulfate ion containing solutions. Sodium ion appears to produce gypsum crystals more columnar in habit while solutions containing high amounts of calcium produced very lamellar gypsum crystals. Solutions containing magnesium produced acicular gypsum crystals. Calcium sulfite hemihydrate solids precipitated from solutions containing high sulfate concentrations were rod shaped and globular as compared to the lamellar calcium sulfite hemihydrate crystals precipitated from high chloride and dilute solution liquors. Calcium sulfate-calcium sulfite solid solutions were characterized using infrared spectroscopy. Ion scavenging of Na, Mg, and Cl by gypsum and calcium sulfite solids precipitated from these high TDS solutions was also investigated. 10 refs., 21 figs., 13 tabs.« less