RU2049063C1 - Process for treating concentrated sulfite-sulfate solution into gypsum - Google Patents

Abstract

FIELD: treatment processes. SUBSTANCE: the process comprises mixing a concentrated sulfide-sulfate solution with hydrochloric acid containing wash water resulting from prewashing the flue gases of electric power stations operating on coal. The sulfur dioxide that evolved is directed to the stage of absorption of limestone or lime with a suspension to obtain gypsum, and the solution containing sodium sulfate and a residual amount of hydrochloric acid is treated with calcium hydroxide and the resulting suspension is directed to the furnace of an electric power station. EFFECT: more efficient treatment process. 2 cl, 1 dwg

Description

 The invention relates to a method for processing concentrated solutions of sulfite and sodium sulfate formed during the desulfurization of flue gases.

Based on the requirements in the Federal Republic of Germany regarding flue gases leaving the firing devices of power plants, flue gases must be desulfurized. For this purpose, up to 87% apply the lime washing method and up to 13% other methods. These particular methods include, in particular, the Wellmann-Lord method, according to which flue gases are washed with a solution of sodium sulfite. The alkali that forms is heated, SO ₂ is removed and sodium sulfite is oxidized in a side reaction. The processing of alkali containing, during the desulfurization of flue gases by the Wellmann-Lord method, as well as by other washing methods based on sodium salt, large amounts of sodium sulfite and sodium sulfate, created significant problems, since their removal and storage were not allowed. In addition, from the point of view of economic aspects, there were no foreseeable prospects for processing such a product alkali.

 The objective of the invention is the creation of a technically feasible method of processing alkali, which is also beneficial from an economic point of view.

To solve this problem, it was proposed to mix alkali with HCl-containing cooling water of the preliminary flushing device of the flue gas desulfurization unit (FGD) of coal-fired power plants, to convert the released SO ₂ fraction by interaction with limestone (CaCO ₃ ) or with lime (CaО) into gypsum (CaSO ₄ ˙2H ₂ O), and convert the fractions of HCl and Na ₂ SO _{4 of} cooling water by interaction with hydrated lime (Ca (OH) ₂ ) into NaCl and gypsum.

 In this case, it is preferable to mix the product alkali with the HCl-containing cooling water in a preliminary washing device in a certain amount agreed with it.

In another embodiment of the method, sodium sulfate, HCl, and cooler water containing a fraction of Na ₂ SO _{4 are} sent to the treatment plant, adding enough slaked lime to completely turn into NaCl and gypsum.

 In a preferred embodiment of the method, the gypsum-containing clarification sludge from the sewage treatment plant is burned in the furnace of the power plant, and the sulfur fraction of the burned clarification sludge is also processed into gypsum in a series-connected flue gas desulfurization unit.

 The proposed method provides the ability to enter the resulting alkali into an existing system and process it, thereby eliminating the need for its processing in special plants and devices. In addition, there is no need for special additives, which makes this method extremely profitable. Another advantage of the proposed method is that there is a decrease in the amount of slaked lime necessary to neutralize hydrochloric acid in the clarifier. The water discharged from the UODG contains significantly less sulfate, because the sulfate additionally contained in the waste water fell out in the form of gypsum. Also, the value of CSB, due to organic substances in the water, is very small, within quite acceptable limits. As for sulfite and thiosulfate, they were not found in waste water.

 The product alkali introduced into the cooling device increases the concentration of sulfate and sodium, however, no effect on the absorber was noted. On the contrary, sodium salts have a positive effect on the contaminants of the droplet separator in the cooler by increasing the solubility of gypsum due to sodium chloride.

 The drawing shows in schematic form the material flow inside the UODG, in which the conversion of product alkali occurs.

PRI me R. 1 m ³ / h of product alkali, consisting of an aqueous solution of sodium sulfate (Na ₂ SO ₄ ), sodium sulfite (Na ₂ SO ₃ ), sodium thiosulfate (Na ₂ S ₂ O ₃ ), and complex-bound EDTA, sent from 160 kg / h of HCl from the flue gas of the power plant and 36 t / h of water to the preliminary flushing device (cooler) of the flue gas desulfurization unit (FGD). As a result of the addition of product alkali to the acidic water of the cooler (pH value less than 1), the following reactions occur with sodium sulfite and sodium sulfate:
2HCl + Na ₂ SO ₃ _ → 2NaCl + H ₂ O + SO ₂
2HCl + Na ₂ S ₂ O ₃ _ → 2NaCl + S + H ₂ O + SO ₂
The hydrochloric acid present in the cooler is partially neutralized by sulfite and thiosulfate and freed up as an equivalent of acid in the form of SO ₂ . Product alkali should be added in such an amount that an excess of acid remains. Thus, the quantitative conversion of both sulfite and thiosulfate in the cooler is ensured. The resulting SO ₂ in an amount of 60 kg / h is washed in a series-connected absorber and processed with 29 t / h of water and 100 kg / h of lime (CaCO ₃ ) into gypsum.

 The heavy metals present in the product alkali are contained only in an insignificant concentration, so that the balance of heavy metals remains practically unchanged.

 Sodium sulfate, introduced with the product alkali into the system, leaves it unchanged and is sent together with waste water to the clarification device.

CaSO₄·2H₂O+2NaCl
Реакция происходит полностью, если избыток хлорида натрия поддерживается в количестве 200 кг/ч при количестве сульфата натрия 90 кг/ч.By neutralizing slaked lime (Ca (OH) ₂ ) from excess hydrochloric acid according to the reaction
Ca (OH) ₂ + HCl _ → CaCl ₂ + 2H ₂ O calcium chloride is formed. On double conversion, gypsum falls out of calcium chloride with sodium sulfate
CaCl ₂ + Na ₂ SO

CaSO ₄ · 2H ₂ O + 2NaCl
The reaction occurs completely if the excess sodium chloride is maintained at 200 kg / h and the amount of sodium sulfate is 90 kg / h.

 Instead of diverted calcium chloride, an equivalent amount of sodium chloride is fed into the water inlet.

 The amount of wastewater from the flue gas desulfurization plant does not change, because part of the need for additional cooler water is covered by productive alkali. As mentioned above, lime is stored in the clarifier.

Claims (2)

 1. METHOD OF PROCESSING FOR GYPSUM OF A CONCENTRATED SULPHITE-SULPHATE SOLUTION, formed during the purification of gases from sulfur dioxide by absorption by sodium sulfite, characterized in that the initial solution is mixed with hydrochloric acid-containing wash water from the preliminary washing stage of the blown gases of power plants and using coal-fired power plants while sulfur dioxide is sent to the stage of absorption by a suspension of limestone or lime to produce gypsum, and a solution containing sodium sulfate and a residual amount of hydrochloric acid, about It is worked up with calcium hydroxide and the resulting suspension is sent to the combustion device of the power plant.  2. The method according to p. 1, characterized in that the wash water for mixing with the initial solution is supplied in an amount providing a residual content of hydrochloric acid in the reaction solution.

Images