Flue gas desulfurization process
First Claim
1. A limestone-gypsum flue gas desulfurization process which comprises:
- a cooling step of cooling and dedusting a dust HCl and sulfur oxides (SOx)-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 SOx 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.
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Accused Products
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 SOx 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 .
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Citations
9 Claims
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1. A limestone-gypsum flue gas desulfurization process which comprises:
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a cooling step of cooling and dedusting a dust HCl and sulfur oxides (SOx)-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 SOx 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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A limestone-gypsump flue gas desulfurization process which comprises:
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a cooling step of cooling and dedusting a sulfur oxides (SOx)-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 SOx 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.
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Specification