CN101347707A - Flue gas desulfurization technique using dual alkali method with white slime as recycling agent - Google Patents

Abstract

The invention discloses a double alkali flue gas desulfurization technology adopting white slime for regeneration; calcined soda and caustic soda or spent caustic and other alkali liquors are taken as absorbing agent and white slime is taken as regenerant for flue gas desulfurization, absorption liquid is sent into an absorber by a pump and is subject to contact reaction with the flue gas after dust removal and after defogging the desulfurated flue gas is discharged to a chimney; after reaction, the absorption liquid flows into a regeneration pool and reacts with added white slime slurry for regeneration, the regenerated absorption liquid is precipitated, and then supernatant fluid is sent to the absorber for recycling. The desulfurization efficiency of the invention can reach over 90%; by adopting white slime as regenerant, the technology of the invention not only can reduce running cost, but also can embody the development modes of using waste to treat waste, energy conservation and emission reduction, thus having significant environmental, economic and social benefits.

Description

A kind of double alkali method flue gas desulfurization technology of white slime as recycling

Technical field

The present invention relates to the air pollution control technique field, specifically relate in a kind of gas cleaning with alkali lye such as soda ash, caustic soda or salkali waste as absorbent, white clay slurries double alkali method flue gas desulfurization technology as regenerative agent.

Background technology

Flue gas desulfurization (FGD) is the desulfur technology of in the world unique large-scale commercial applicationsization.The FGD technology is so long as utilize absorbent or adsorbent is removed SO in the flue gas ₂, and make it be converted into the compound of comparatively stable sulphur.The FGD technology is of a great variety, but real industrialized have only tens kinds.Dry and wet state in sweetening process can be divided into desulfur technology wet method, dry method and half-dried (half is wet) method to the FGD technology by absorbent and desulfurization product.Wherein the wet process of FGD technology accounts for about 85% of whole industrialization desulfurizer, and wet type limestone/lime method accounts for the nearly 80% of wet method, occupies an leading position in existing flue gas desulfurization technique.

Wet type limestone/lime method flue gas desulfurization technique is to utilize lime stone with low cost or lime as the SO in the absorbent absorption flue gas ₂, generate calcium sulfite hemihydrate or gypsum.This technology is once in that the seventies is big because of its investment, operating cost is high and problems such as burn into fouling, obstruction have influenced its application in thermal power plant.Through practice and improvement for many years, the service behaviour and the reliability of limestone/lime method greatly improve, and investment significantly reduces with operating cost.Two alkaline process grow up for the shortcoming that overcomes easy fouling of limestone/lime method and obstruction just.Two alkaline process absorb SO with the alkaline clear liquid of solubility as absorbent earlier ₂, and then regenerate with milk of lime or lime absorption liquid.The obvious advantage of two alkaline process is, owing to adopt liquid phase to absorb in the king-tower, regenerate in the regenerated reactor of absorbent outside tower, thereby there are not fouling and slurry blockage problem in the tower, and can use efficiently plate column or packed tower to replace present widely used spray column slurry method, reduce the size and the operation liquid-gas ratio on absorption tower, reduce cost.In addition, two alkaline process can obtain higher desulfurization degree, can reach more than 90%, and range of application is wider.

Soda ash is widely used in industries such as metallurgy, chemical industry, building materials, papermaking, medicine, food as important basic chemical industry raw material.In recent years, China's soda ash production development is rapid, and yearly productive capacity is more than 8,000,000 tons, and wherein ammonia-soda process soda ash production capacity is about 4,500,000 tons.In the ammonia-soda process alkali producing process, produce a large amount of waste liquids in ammonia distillation process, the alkaline residue that waste liquid produces after press filtration is commonly called as white clay.Pulping and paper-making factory also can produce a large amount of causticization white claies in alkali recovery process.Owing to can't be dealt carefully with, white clay can only be stacked naturally, and perhaps directly row is extra large.The long-term white clay of stacking has taken a large amount of land resource, and its surperficial weathering produces dust pollution; White clay row Hai Ze causes the marine ecology balance destroyed, harm aquaculture, and might jeopardize the navigation channel after the deposition.Therefore relevant enterprises such as soda ash, papermaking are being perplexed in the pollution problem of white clay always.

Summary of the invention

The invention provides a kind of double alkali method flue gas desulfurization technology of white slime as recycling, as the desulfurization regeneration agent, reach the purpose of the treatment of wastes with processes of wastes against one another, reduce the white clay disposal of pollutants, also reduced flue gas desulfurization operating cost simultaneously with the discarded object white clay.

A kind of double alkali method flue gas desulfurization technology of white slime as recycling, flue gas after the dedusting and desulfurization absorption liquid haptoreaction, remove sulfur dioxide after, discharge through demist; Absorption liquid after the desulfurization and white clay slurries carry out the regenerative response postprecipitation, and the supernatant of post precipitation is recycling, with flue gas contact desulfuriation.

Described desulfurization absorption liquid is a soda, such as soda ash, caustic soda or contain soda ash and/or the salkali waste of caustic soda etc.; Na ion concentration is 0.05-0.5mol/L in the absorption liquid.

The mass percentage concentration of described white clay slurries is 5～35%, and the calcium carbonate content of looking in the white clay is fixed.

The pH value of described regenerative response is 7-9, can guarantee the calcium carbonate higher utilization rate of when regeneration in the white clay.

Course of reaction of the present invention is (is absorbent with soda ash):

1, start-up course: system the startup stage, soda ash is mixed with certain density absorption liquid, in the absorption tower with flue gas in SO ₂Following reaction takes place:

Na ₂CO ₃+SO ₂→Na ₂SO ₃+CO ₂ (1)

Na ₂SO ₃+SO ₂+H ₂O→2NaHSO ₃ (2)

System mainly based on reaction (1), subsequently based on reaction (2), begins regeneration after the pH value slowly drops to 7 in a period of time after startup.

2, regenerative process: regeneration is undertaken by adding the white clay slurries in the regenerated reactor outside the absorption tower, and the Main Ingredients and Appearance of white clay is CaCO ₃:

3, absorption process: system is after operation a period of time, and the regeneration absorption liquid that enters the absorption tower carries out following reaction:

Na ₂CO ₃+SO ₂→Na ₂SO ₃+CO ₂ (5)

Na ₂SO ₃+SO ₂+H ₂O→2NaHSO ₃ (6)

Owing to have a small amount of sodium ion to discharge desulphurization system, therefore before the regeneration absorption liquid is recycling, can in the regeneration absorption liquid, replenish suitable alkali lye according to actual conditions with desulfurization slag or waste water.

For keeping the stable operation of desulphurization system, need clay wash liquid is carried out preliminary treatment such as grid, sand setting, remove suspension and bulky grain thing, guarantee that the composition and the physicochemical property of white clay meets the desulfurization requirement, the white clay particle passes through 300 orders more than 90%.

In two alkaline process systems, Na ₂SO ₃Be main absorbents, the existence of oxygen can reduce the concentration of sodium sulfite greatly, works as SO ₃ ^2-Be oxidized to SO ₄ ^2-After, the desulfurization performance of absorption liquid descends.The white clay composition is based on calcium carbonate, in addition, white clay also contains the lime (existing with the calcium hydroxide form) of excessive adding in the causticization process, the vulcanized sodium that calcium silicates, residual hydrogen sodium oxide molybdena and have owing to fibrous raw material is different do not wait, aluminium, iron, magnesium compound, dust impurity etc.Compare with lime stone, white clay contains more reducing substances, as Na ₂Therefore S etc. utilize white clay as regenerative agent, and reducing substances wherein can effectively suppress the oxidation of sodium sulfite, thereby guarantee active Na ion concentration in two alkaline process systems.

Compare with the traditional double alkaline process, the present invention has following advantage: the one, with the white clay replacing lime, realized the purpose of the treatment of wastes with processes of wastes against one another; The 2nd, for the discarded object white clay of relevant chemical enterprise searches out a suitable approach that utilizes again, realized the purpose of recycling economy; The 3rd, white clay contains reducing substances, can effectively suppress oxidation, improves the utilization rate of absorbent; The 4th, this method desulfuration efficiency can reach more than 90%, and greatly reduces the operating cost of desulfurization.

Description of drawings

Fig. 1 is the flow chart of technology of the present invention.

The specific embodiment

As shown in Figure 1, boiler smoke 7 is introduced into deduster 6 by air-introduced machine 3, flue gas is drawn from top after by absorber 1 desulfurization after the dedusting, clean flue gas 4 is through smoke stack emission, absorber 1 can be plate columns such as rotating stream tray scrubber, sieve-plate tower, bubble column and packed tower, venturi, spray column etc., and absorber 1 top has demister 17 and rinse water 8; Adding alkali 16 in pump forebay 13 (can be NaOH, Na ₂CO ₃, spent lye etc.) be mixed with absorption liquid 2, Na ion concentration is 0.05-0.5mol/L in the absorption liquid, is sent into by circulating pump 5 to start desulphurization reaction in the absorber 1; White clay 14 enters lime slaker 9 with fresh water (FW) 15, under the stirring of lime slaker agitator 21, mix, making concentration is the white clay slurries 20 of 0.5-35%, white clay slurries 20 are delivered to regenerated reactor 11 by white clay stock pump 10, absorption liquid 18 mixes under the stirring action of regenerated reactor agitator 19 and reacts completely after the desulfurization that comes with gravity flow at the bottom of tower, and the pH value during the control reaction is 7-9.Absorption liquid behind the regenerative response enters sedimentation basin 12, and after precipitation, clarification, supernatant enters pump forebay 13, replenishes alkali 16 according to sodium ion loss situation in the pump forebay, and absorption liquid 2 is sent back in the absorber 1 by circulating pump.

Calcium sulfite and calcium sulfate precipitation thing in the sedimentation basin are transported in the slag treatment system by slag stock pump or grab bucket, and after filtering, be sent to oxidation pond and be oxidized to calcium sulfate, the preparation gypsum, or directly send landfill outside.Filtrate is still sent absorption liquid circulatory system circulating and recovering back to.Absorption liquid is generally 7-9 by pH control system control pH value in the pump forebay 13.Clay wash concentration maintains 5-35% in the lime slaker 9.

Application examples 1

Certain paper mill, 2 75t/h fluidized-bed combustion boilers adopt the desulfurization of this technology, Na ion concentration 0.5mol/L, regenerated reactor pH value is controlled at 7.5, white clay concentration of slurry 15%, liquid-gas ratio is selected 3L/m for use ³, import sulfur dioxide concentration 2300mg/m ³, the outlet sulfur dioxide concentration is 162mg/m ³, desulfuration efficiency 93%.

Application examples 2

Certain paper mill, 1 130t/h coal-powder boiler boiler adopts the desulfurization of this technology, Na ion concentration 0.3mol/L, regenerated reactor pH value is controlled at 7.0, white clay concentration of slurry 18%, liquid-gas ratio is selected 4L/m for use ³, import sulfur dioxide concentration 1800mg/m ³, the outlet sulfur dioxide concentration is 144mg/m ³, desulfuration efficiency 92%.

Claims (6)

1, a kind of double alkali method flue gas desulfurization technology of white slime as recycling is characterized in that: flue gas after the dedusting and desulfurization absorption liquid haptoreaction, remove sulfur dioxide after, discharge through demist; Absorption liquid after the desulfurization and white clay slurries carry out the regenerative response postprecipitation, and the supernatant of post precipitation is recycling, with flue gas contact desulfuriation.

2, the double alkali method desulfurizing technology of white slime as recycling according to claim 1 is characterized in that: described desulfurization absorption liquid is soda ash solution, soda bath or contains soda ash and/or the spent lye of caustic soda.

3, the double alkali method desulfurizing technology of white slime as recycling according to claim 2 is characterized in that: Na ion concentration is 0.05-0.5mol/L in the described desulfurization absorption liquid.

4, the double alkali method desulfurizing technology of white slime as recycling according to claim 1 is characterized in that: the mass percentage concentration of described white clay slurries is 5～35%.

5, the double alkali method desulfurizing technology of white slime as recycling according to claim 1 is characterized in that: the pH value of described regenerative response is 7-9.

6, the double alkali method desulfurizing technology of white slime as recycling according to claim 1 is characterized in that: the white clay particle in the described white clay slurries passes through 300 orders more than 90%.