Flue gas desulfurization process

• US 4,687,649 A
• Filed: 01/16/1984
• Issued: 08/18/1987
• Est. Priority Date: 09/09/1983
• Status: Expired due to Term

• Current Assignee: Babcock-Hitachi Kabushiki Kaisha (Hitachi, Ltd.)
• Original Assignee: Babcock-Hitachi Kabushiki Kaisha (Hitachi, Ltd.)
• Inventors: Shibata, Kenji, Kanda, Osamu, Hashimoto, Taiki, Nishimura, Tsukasa, Nozawa, Shigeru, Kuroda, Hiroshi, Nishimura, Masakatsu
• Primary Examiner(s): Heller, Gregory A.
• Application Number:
  US06/571,065
• Time in Patent Office: 1,310 Days
• Field of Search: 423/242 A, 423/244 A, 423/242 R, 423/240 R, 423/244 R, 423/555
• US Class Current: 423/243.03
• CPC Class Codes: B01D 53/501 by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound
• CPC Class Codes: B01D 53/508 by treating the gases with solids
• CPC Class Codes: B01D 53/68 Halogens or halogen compounds
• CPC Class Codes: B01D 61/44 Ion-selective electrodialysis
• CPC Class Codes: C01F 11/464 Sulfates of Ca from gases containing sulfur oxides
• CPC Class Codes: C02F 2103/18 from the purification of gaseous effluents
• CPC Class Codes: C02F 2201/46115 Electrolytic cell with membranes or diaphragms
• CPC Class Codes: F28D 15/0266 with separate evaporating and condensing chambers connected by at least one conduit; Loop-type heat pipes; with multiple or common evaporating or condensing chambers F28D15/043 takes precedence

Abstract

A flue gas desulfurization process by which gypsum can be recovered; the amount of water used therein is small, the effluent is treated in a closed system, the equipment used is minimized, and no scaling occurs; and an apparatus therefor are provided, the process including the following first process and second process: the first process comprising a cooling step of cooling and dedusting a SO₂ -containing flue gas and removing acidic gases, an absorption step of contacting the cooled gas with a slurry containing limestone and lime to absorb and remove SO_x and form CaSO₃, a pH-adjusting step of adding H₂ SO₄ to the resulting slurry, an oxidation step of blowing an oxygen-containing gas in the pH-adjusted slurry to form gypsum, a step of concentrating the resulting gypsum slurry, a step of adjusting the concentration of the resulting slurry, a step of centrifugally separating gypsum, and a step of treating the effluent discharged from the cooling step, and the second process comprising, in the first process, further feeding the slurry of the absorption step to the cooling step where unreacted limestone is reacted with SO₂ to form CaSO₃ .

Claims

1. A limestone-gypsum flue gas desulfurization process which comprises:

a cooling step of cooling and dedusting a dust HCl and sulfur oxides (SO_x)-containing flue gas and producing an effluent containing chlorine;

an absorption step of contacting the flue gas cooled in the cooling step with a limestone slurry to absorb and remove SO_x contained in the gas thereby forming CaSO₃ and Ca(HSO₃)₂ and producing cleaned gas;

a pH-adjusting step of adjusting the pH of the resulting slurry containing calcium sulfite CaSO₃ and calcium hydrogen sulfite Ca(HSO₃)₂ formed in the absorption step;

an oxidation step of oxidizing the resulting slurry obtained in the pH-adjusting step, by contacting it with an oxygen-containing gas to form a gypsum-containing slurry;

a liquid-separation concentration step of concentrating the resulting gypsum-containing slurry obtained in the oxidation step to produce clarified water and a concentrated gypsum slurry; and

a step of centrifugally separating gypsum from the concentrated gypsum slurry to produce separated gypsum and a filtrate; and

a step of removing heavy metals, removing COD (chemical oxygen demand) components, and electrodialytically concentrating and eliminating chlorine in the effluent discharged from said cooling step.

2. A flue gas desulfurization process of claim 1, wherein the last mentioned step removes suspended solids.

3. A flue gas desulfurization process of claim 1, including vaporizing the resulting concentrated effluent leaving said electrodialytically concentrating step using a boiler flue gas as heat source therefor to obtain a solid chloride.

4. A flue gas desulfurization process of claim 1, including the step of using, desalted water in said process, obtained in said step of electrodialytically concentrating.

5. A flue gas desulfurization process of claim 3 including the step of conducting the flue gas after evaporation from said step of vaporizing to an electrostatic precipitator attached to the boiler.

6. A flue gas desulfurization process of claim 3, wherein said vaporizing includes spraying the chlorine concentrated effluent into the exit duct of an electrostatic precipitator attached to the boiler to subject it to vaporization to dryness.

7. A flue gas desulfurization process of claim 1 wherein said cooling step and said absorption step are carried out in a single tower.

8. A flue gas desulfurization process of claim 1 wherein said effluent-treating step further includes a step of absorbing dithionic acid in the effluent onto a weakly basic ion exchange resion, followed by desorbing the acid from the resin in advance of said pH-adjusting step.

9. A limestone-gypsump flue gas desulfurization process which comprises:

a cooling step of cooling and dedusting a sulfur oxides (SO_x)-containing flue gas and producing an effluent;

an absorption step of contacting the flue gas cooled in the cooling step with a limestone (lime) slurry to absorb and remove SO_x contained in the gas thereby forming CaSO₃ and Ca(HSO₃)_x and producing cleaned gas;

a pH-adjusting step of adjusting the pH of the resulting slurry containing calcium sulfite CaSO₃ and calcium hydrogen sulfite Ca(HSO₃)₂ formed in the absorption step to be in the range of 4 to 5;

an oxidation step of oxidizing the resulting slurry obtained in the pH-adjusting step, by contacting it with 1.5 to 3 times the theoretical amount of an oxygen-containing gas to form a gypsum-containing slurry;

a liquid-separation concentration step of concentrating the resulting gypsum-containing slurry obtained in the oxidation step to produce clarified water and a concentrated gypsum slurry; and

a step of centrifugally separating gypsum from the concentrated gypsum slurry to produce separated gypsum and a filtrate;

adding the separated gypsum from said step of centrifugally separating to the limestone slurry in said absorption step in an amount of at least 5% by weight of the slurry;

a step of treating the effluent discharged from said cooling, including at least one step of the steps of removing floating solids (FS), removing fluorine (F), removing heavy metals, removing (chemical oxygen demand) components and concentrating chlorine (C), in the effluent wherein said effluent-treating step includes a step of adjusting the pH of the effluent to 1.5 or less for decomposing dithionic acid in the effluent, and a step of heating the effluent of a pH of 1.5 or less to 60 C. or higher; and

said effluent-treating step further including a step of absorbing dithionic acid in the effluent onto a weakly basic ion exchange resin, followed by desorbing the acid from the resin in advance of said pH-adjusting step.