CN111747438A - pH regulation and control multistep stabilization modification method for dry/semi-dry desulfurized fly ash - Google Patents
pH regulation and control multistep stabilization modification method for dry/semi-dry desulfurized fly ash Download PDFInfo
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- 238000011105 stabilization Methods 0.000 title claims abstract description 26
- 230000029219 regulation of pH Effects 0.000 title claims abstract description 18
- 238000002715 modification method Methods 0.000 title claims abstract description 14
- 238000000034 method Methods 0.000 claims abstract description 60
- 239000002956 ash Substances 0.000 claims abstract description 49
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims abstract description 48
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 45
- 230000003647 oxidation Effects 0.000 claims abstract description 44
- 239000002699 waste material Substances 0.000 claims abstract description 42
- 239000007788 liquid Substances 0.000 claims abstract description 35
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- 230000004048 modification Effects 0.000 claims abstract description 22
- 238000012986 modification Methods 0.000 claims abstract description 22
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- 239000011259 mixed solution Substances 0.000 claims description 16
- 238000005273 aeration Methods 0.000 claims description 15
- 238000001035 drying Methods 0.000 claims description 15
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- 229910052602 gypsum Inorganic materials 0.000 claims description 9
- 239000007787 solid Substances 0.000 claims description 9
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 8
- 230000001186 cumulative effect Effects 0.000 claims description 8
- 239000010440 gypsum Substances 0.000 claims description 8
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- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 12
- 229910052925 anhydrite Inorganic materials 0.000 description 11
- 229910000019 calcium carbonate Inorganic materials 0.000 description 7
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Chemical compound [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 description 7
- 239000000126 substance Substances 0.000 description 7
- 239000000920 calcium hydroxide Substances 0.000 description 5
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- ZLNQQNXFFQJAID-UHFFFAOYSA-L magnesium carbonate Chemical compound [Mg+2].[O-]C([O-])=O ZLNQQNXFFQJAID-UHFFFAOYSA-L 0.000 description 2
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- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 239000002250 absorbent Substances 0.000 description 1
- 230000002745 absorbent Effects 0.000 description 1
- 239000004480 active ingredient Substances 0.000 description 1
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- 239000003153 chemical reaction reagent Substances 0.000 description 1
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- XLYOFNOQVPJJNP-ZSJDYOACSA-N heavy water Substances [2H]O[2H] XLYOFNOQVPJJNP-ZSJDYOACSA-N 0.000 description 1
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- 229910052717 sulfur Inorganic materials 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F11/00—Compounds of calcium, strontium, or barium
- C01F11/46—Sulfates
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
- B01F25/00—Flow mixers; Mixers for falling materials, e.g. solid particles
- B01F25/20—Jet mixers, i.e. mixers using high-speed fluid streams
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
- B01F35/00—Accessories for mixers; Auxiliary operations or auxiliary devices; Parts or details of general application
- B01F35/20—Measuring; Control or regulation
- B01F35/21—Measuring
- B01F35/2132—Concentration, pH, pOH, p(ION) or oxygen-demand
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
- B01J19/0006—Controlling or regulating processes
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F5/00—Compounds of magnesium
- C01F5/14—Magnesium hydroxide
- C01F5/22—Magnesium hydroxide from magnesium compounds with alkali hydroxides or alkaline- earth oxides or hydroxides
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Inorganic Chemistry (AREA)
- Treating Waste Gases (AREA)
- Processing Of Solid Wastes (AREA)
Abstract
The invention relates to a pH regulation and control multistep stabilization modification method of dry/semi-dry desulfurized fly ash, which comprises the following steps: (1) analyzing and testing raw materials (2) preparing acid liquor; (3) acidifying the raw materials; (4) forced oxidation; (5) regulating and controlling the pH value; (6) multi-step circulation; (7) recovering the product; (8) recycling waste liquid and recovering Mg; (9) finishing the modification; the conventional one-step oxidation process is decomposed into multiple steps, and the solid-liquid ratio and the slurry pH of each step are accurately controlled to avoid SO2While releasing, the reaction rate of the forced oxidation process is obviously improved, and finally the dry method/semi-dry method is overcomeSO caused by instability and high alkalinity of process desulfurization ash2The problems of secondary pollution and slow oxidation rate are solved, and clean and efficient modification is creatively realized; meanwhile, the resource utilization of the dry/semi-dry desulfurized fly ash and the waste sulfuric acid is realized, so that the aims of treating waste by waste and realizing synergistic circulation are fulfilled, and better economic and environmental benefits are obtained.
Description
Technical Field
The invention relates to stabilization modification and resource utilization of dry/semi-dry desulfurized fly ash, in particular to a pH regulation multistep stabilization modification method of dry/semi-dry desulfurized fly ash, belonging to the technical field of resources and environment.
Background
In recent years, due to the high importance of our country on the ecological environment protection, and the high importance of our country on SO2The emission requirements are becoming more and more strict, and the flue gas desulfurization process is widely popularized and applied in the industries of coal-fired power plants, steel sintering, industrial boilers, petrochemical industry and the like, wherein the dry/semi-dry desulfurization process represented by CFB, LIFAC, NID, SDA and CDSI has the advantages of small occupied area, low investment, low operating cost, low energy consumption, no sewage and waste acid emission and the like, and becomes the trend of the future development of the flue gas desulfurization technology.
The dry/semi-dry desulfurizing process features that powdered or granular calcium-base absorbent is used to eliminate SO from fume2The desulfurization product is dry powder and mainly comprises CaSO3·1/2H2O、CaCO3、CaSO4·2H2O and a small amount of unreacted Ca (OH)2And the like. Compared with wet desulphurization process, the desulphurization ash produced by dry/semi-dry desulphurization process has much more complex components, and has the characteristics of high sulfur, high calcium and high alkalinity, especially CaSO3The proportion of (A) is high, and the component with poor chemical stability causes the dry/semi-dry desulfurized fly ash to show unusual physicochemical properties. Because the research on the properties, the reaction characteristics and the action mechanism of the solid wastes is not systematic and deep, at present, people have more careful attitude on the comprehensive utilization of the solid wastes, and an effective utilization way is not formed yet, so that the dry-process/semi-dry-process desulfurized ash is accumulated in a large quantity or is simply buried, and a large amount of valuable soil is occupiedLand resources and enterprise burden are increased, and further popularization and application of the dry/semi-dry desulfurization process are restricted. Furthermore, since CaSO3Is unstable and is easy to cause SO after long-term stacking2Release of (a) and pose a potential threat to the environment; meanwhile, the dry method/semi-dry method desulfurized ash has small particle size and light weight, and can fly everywhere to pollute air once blown by wind.
For the comprehensive utilization of the dry method/semi-dry method desulfurized fly ash, the related work at home and abroad does not form a complete system at present, the obtained achievements belong to the research property, any technology for large-scale industrial application is not formed, and the following four aspects are mainly considered:
(1) the chemical composition of the desulphurisation ash is quite complex. The phase compositions of the general dry/semi-dry desulfurized fly ash comprise CaSO4、CaSO3、CaCO3、Ca(OH)2、CaO、MgCO3And the components are complex and diversified in chemical property, so that the comprehensive utilization is more limited and more difficult.
(2) The fluctuation of the content of each component of the desulfurized fly ash is large. Due to the differences of the operation, operation and management levels of different enterprises, the differences of different raw material types and proportioning schemes, the differences of desulfurization efficiencies of different desulfurization processes and the differences of components of different batches of coal, the content of each component of desulfurization ash generated by different desulfurization equipment and different periods of time of the same equipment can fluctuate greatly. Such fluctuations bring about frequent changes in the overall chemistry, which makes its comprehensive utilization difficult.
(3) The chemical nature of the various components in the desulfurized fly ash is unstable. CaSO in desulfurized fly ash3、Ca(OH)2And CaO is chemically unstable and changes with environmental and time changes. CaSO3Easily decomposed in acid environment or under high temperature condition of neutral or reducing atmosphere to make SO2Is released again to cause secondary pollution of the environment, and simultaneously CaSO3Will be oxidized into CaSO in the air4Resulting in the long-term use of the properties of the desulfurized fly ash materialInstability in the process. CaO readily absorbs water to form Ca (OH)2Causing a volume-inhomogeneous expansion, Ca (OH)2Reabsorbing CO from air2To produce CaCO3. These instabilities pose a major obstacle to the comprehensive utilization of the desulfurized fly ash.
(4) CaSO in desulfurized fly ash3Has a high content of and CaSO3The action effect and mechanism of the drug are not clear. CaSO in dry/semi-dry desulfurized fly ash3The content of (A) can be up to more than 50%, and CaSO3The influence on the overall mechanical properties and stability of the material is yet to be further researched and confirmed. For example, when desulfurized fly ash is used as a cement retarder, CaSO3The retarding effect and the influence on the mechanical property of the cement are still greatly controversial.
In conclusion, under the new background that China vigorously advances the construction of 'waste-free cities' and 'waste-free society', the dry-process/semi-dry-process desulfurized fly ash is scientifically treated and finely utilized to realize harmlessness and deep recycling of the desulfurized fly ash, so that the method not only solves the technical problems to be solved urgently in the industries such as coal-fired power plants, steel sintering, industrial boilers, petrifaction and the like in China, but also promotes ecological civilization construction in China, promotes high-quality development, and realizes the inevitable requirements of comprehensive conservation and cyclic utilization of resources.
Based on the basic chemical principles of acid-base neutralization and oxidation-reduction, the dry/semi-dry desulfurization ash is subjected to forced oxidation modification in a sulfuric acid environment, so that the problems in the four aspects of limiting the large-scale comprehensive utilization of the solid waste can be solved at one stroke: CaCO in desulfurized ash under the action of acid-base neutralization reaction3、Ca(OH)2And the basic components such as CaO and the like are all rapidly converted into CaSO4(ii) a And CaSO with poor stability under the action of oxidation reaction3Will also be converted into CaSO4. Thus, the original dry/semi-dry desulfurized fly ash with complex and various components and unstable content and chemical properties of various components is converted into stable CaSO4Is a solid waste with chemical properties similar to those of wet-process desulfurization gypsum as a main component. Because the technical problems of each link in the comprehensive utilization of the wet desulphurization gypsum are basically solved, the modified dry/semi-dry desulphurization ashCan be comprehensively utilized on a large scale according to various technical routes of the wet desulphurization gypsum, thereby thoroughly solving the increasingly urgent treatment problem of the large solid wastes. Meanwhile, the resource utilization of the waste sulfuric acid is realized.
However, due to SO3 2-Will react with excessive H+Combine to form pollutant SO2Therefore, the pH of the reaction solution cannot be too low; meanwhile, the pH value of the solution is rapidly increased in the dissolving process due to strong alkalinity of the desulfurized fly ash, and CaSO3The solubility of (a) is very low and further decreases with the increase of the pH value, so that the oxidation rate is greatly reduced, and therefore, the solid-to-liquid ratio in the dissolving process, namely the pH value of the solution, cannot be too high. In conclusion, the high-efficiency oxidation of the dry/semi-dry desulfurized ash is realized in a one-step method and a conventional slurry manner, and the SO-free desulfurization is realized2Release is very difficult and innovative stabilization modification methods to tailor the characteristics of the desulfurized fly ash need to be developed.
Disclosure of Invention
In order to make up for the defects of the prior art, the invention aims to provide a pH regulation and multi-step stabilization modification method of the desulfurization ash of the dry/semi-dry method, which decomposes the conventional one-step oxidation process into multiple steps, overcomes the problem of slow oxidation rate caused by high alkalinity of the desulfurization ash of the dry/semi-dry method, and avoids the problem of low oxidation rate caused by high alkalinity of the desulfurization ash of the dry/semi-dry method2And releasing, and finally realizing the resource utilization of the dry/semi-dry desulfurized fly ash and the waste sulfuric acid, thereby achieving the purposes of treating waste by waste and realizing synergistic circulation and obtaining better economic and environmental benefits.
The invention aims to realize the purpose through the following technical scheme, and discloses a pH regulation and control multistep stabilization modification method of dry/semi-dry desulfurized fly ash, which has the technical key points that: the method comprises the following steps:
(1) analysis of raw materials test
Analyzing and testing the components of the original dry/semi-dry desulfurized fly ash to determine CaSO in the desulfurized fly ash3And the contents of various strongly basic compounds;
(2) preparation of acid liquor
Preparing the waste sulfuric acid stock solution with the mass fraction of 2-98% into H with the pH value of 2.2-4.02SO4A solution, placed in an oxidation reactor;
(3) acidification of the feedstock
Gradually moving to H in the step (2)2SO4Adding the dry-process/semi-dry-process desulfurized fly ash obtained in the step (1) into the solution, continuously stirring to obtain a mixed solution, simultaneously monitoring the change of the pH value of the mixed solution in real time, and stopping adding the desulfurized fly ash when the pH value of the mixed solution rises to a certain value within the range of 3.3-5.6 and is kept stable;
(4) forced oxidation
Using air as an oxidant, adopting a jet aerator to carry out jet aeration on the mixed liquid obtained in the step (3), wherein the jet aerator comprises 1-16 aeration heads, the working air pressure is less than or equal to 10m of water column, the working water pressure is less than or equal to 30m of water column, and the working air volume and the water volume of each aeration head are respectively 20-80 Nm3H and 8-18 m3The oxygen transfer efficiency is 9-18 g O2/Nm3·m；
(5) Control of pH
After forced oxidation, when the pH value of the mixed solution is kept stable, the waste sulfuric acid stock solution in the step (2) is gradually added into the solution, so that the pH value of the solution is reduced to a certain value within the range of 2.2-4.0 again and is kept stable;
(6) multiple step cycle
Continuously repeating the steps (3) to (5), wherein solid-phase CaSO gradually exists in the mixed solution in the step (5)4Separating out to obtain slurry with solid content of 5-25%;
(7) recycled product
Discharging the slurry part obtained in the step (6), and performing solid-liquid separation and dehydration treatment to obtain a stabilized modified gypsum product and residual waste liquid;
(8) waste liquor circulation and Mg recovery
Returning the residual waste liquid in the step (7) to the oxidation reactor in the step (2) for recycling, or adding Ca (OH) with purity of more than 90 percent2To prepare Mg (OH)2The product is used for recycling Mg element in the desulfurized ash of the dry method/semi-dry method in the first step;
the Ca (OH)2Amount of additionCalculating according to the Mg content of the original desulfurized fly ash in the step (1) and the cumulative adding amount of the desulfurized fly ash in the step (3);
the calculation method comprises the following steps: ca (OH)2Adding amount which is the cumulative adding amount × (100 percent to the water content of the original desulfurized ash)/24 × 74/(100 percent to Ca (OH) of the original desulfurized ash with the Mg content of × desulfurized ash2Water content of)/Ca (OH)2The purity of (2);
and (9): completion of modification
And (5) repeating the steps (3) to (8), and finally completing the multi-step stabilization modification of the whole dry/semi-dry desulfurization ash.
Further, the oxidation reactor is provided with an exhaust port, a liquid level, a temperature, a pH value and SO2Provided is an online monitoring device.
Further, in the step (3), feeding the desulfurized ash through a metering screw feeder; the agitation is achieved by a mechanical stirrer or a jet aerator.
Further, in the step (5), the waste sulfuric acid is fed by a metering acid liquid pump.
Further, in the step (7), the solid-liquid separation is realized by a hydrocyclone; the dewatering is achieved by a vacuum belt dewaterer or a belt filter press.
Further, in the step (8), the Ca (OH)2And adding the mixture by a metering screw feeder.
Compared with the prior art, the invention has the following beneficial effects:
(1) the pH value of the acidified slurry in the whole stabilizing and modifying process is controlled to be between 2.2 and 5.6 all the time based on the optimal solid-liquid ratio, so that CaSO in the desulfurized fly ash can be avoided3Decompose to release SO2And can ensure enough CaSO3Is in a liquid phase reaction system, thereby obviously improving the reaction rate of the whole modification process.
(2) The conventional one-step oxidation process is decomposed into multiple steps, and the problem of slow oxidation rate caused by high alkalinity of the desulfurization ash by the dry method/semi-dry method is solved by accurately controlling the solid-liquid ratio and the pH value of the slurry in each step of oxidation process, so that the high-efficiency oxidation of the high-alkalinity desulfurization ash is creatively realized.
(3) The jet aeration technology has the advantages of strong mixing and stirring effects, high oxygenation capacity, high oxygen utilization rate, high oxygen power transfer efficiency, simple structure, no moving parts, reliable work, flexible operation, convenient adjustment, difficult blockage, easy maintenance and management, low operating cost and the like, and can obviously improve the reaction rate of the forced oxidation process.
(4) The method can simultaneously realize the resource utilization of the dry method/semi-dry method desulfurized fly ash and the waste sulfuric acid, thereby achieving the purposes of treating waste by waste and realizing synergistic circulation and obtaining better economic and environmental benefits.
(5) The high-value utilization of the Mg element in the dry/semi-dry desulfurized fly ash can be realized, and the economic and environmental benefits are further improved.
Description of the drawings:
FIG. 1 is a logic flow chart of the pH regulation multistep stabilization modification method of dry/semi-dry desulfurization ash.
In fig. 1, 1 is step (1), 2 is step (2), 3 is step (3), 4 is step (4), 5 is step (5), 6 is step (6), 7 is step (7), 8 is step (8), and 9 is step (9).
FIG. 2 shows the desulfurized ash and 80% concentrated H from a semi-dry process in a steel plant2SO4The reagent is used as a raw material, acidification and forced oxidation laboratory tests are carried out according to the pH regulation and control multistep stabilization modification method, and finally when the solid content of the slurry reaches 10%, the slurry comes from CaSO3S balance of (1).
Detailed Description
The invention is further described with reference to the following figures and specific examples.
Example 1
A pH regulation and control multistep stabilization modification method for desulfurization ash by a dry method/semi-dry method comprises the following steps:
(1) analysis of raw materials test
Analyzing and testing the components of the original dry/semi-dry desulfurized fly ash to determine CaSO in the desulfurized fly ash3And the contents of various strongly basic compounds; using this as an estimateThe solid-liquid ratio between the desulfurized fly ash and the waste sulfuric acid in the oxidation process is based; to clarify CaSO therein3And the content of various strong alkaline compounds, which is used for estimating the solid-liquid ratio between the desulfurized fly ash and the waste sulfuric acid in the oxidation process and providing reference for the subsequent pH regulation process;
(2) preparation of acid liquor
Preparing the waste sulfuric acid stock solution with the mass fraction of 2-98% into H with the pH value of 2.2-4.02SO4A solution, placed in an oxidation reactor;
2% -98% is the concentration of the original waste sulfuric acid in the step, the acidity is very large, the pH value is far lower than 2.2, the step is to dilute the original waste sulfuric acid by adding water, the pH value is stabilized at a certain value between 2.2-4.0, and the step is placed in an oxidation reactor.
(3) Acidification of the feedstock
Gradually moving to H in the step (2)2SO4Adding the dry-process/semi-dry-process desulfurized fly ash obtained in the step (1) into the solution, continuously stirring to obtain a mixed solution, simultaneously monitoring the change of the pH value of the mixed solution in real time, and stopping adding the desulfurized fly ash when the pH value of the mixed solution rises to a certain value within the range of 3.3-5.6 and is kept stable;
(4) forced oxidation
Using air as an oxidant, adopting a jet aerator to carry out jet aeration on the mixed liquid obtained in the step (3), wherein the jet aerator comprises 1-16 aeration heads, the working air pressure is less than or equal to 10m of water column, the working water pressure is less than or equal to 30m of water column, and the working air volume and the water volume of each aeration head are respectively 20-80 Nm3H and 8-18 m3The oxygen transfer efficiency is 9-18 g O2/Nm3M; HSO in solution at this time3 -Will be oxidized to SO4 2-To release H+The pH value of the mixed solution is reduced by 0.4-1.3 through jet aeration;
(5) control of pH
After forced oxidation, when the pH value of the mixed solution is kept stable, the waste sulfuric acid stock solution in the step (2) is gradually added into the solution, so that the pH value of the solution is reduced to a certain value within the range of 2.2-4.0 again and is kept stable; the term "stable" refers to that the pH value is finally maintained at any value point of 3.3-5.6 or 2.2-4.0 after rising or falling and does not change any more, and then the corresponding treatment step can be carried out;
(6) multiple step cycle
Continuously repeating the steps (3) to (5), wherein solid-phase CaSO gradually exists in the mixed solution in the step (5)4Separating out to obtain slurry with solid content of 5-25%;
(7) recycled product
Discharging the slurry part obtained in the step (6), and performing solid-liquid separation and dehydration treatment to obtain a stabilized modified gypsum product and residual waste liquid;
(8) waste liquor circulation and Mg recovery
Returning the residual waste liquid in the step (7) to the oxidation reactor in the step (2) for recycling, or adding Ca (OH) with purity of more than 90 percent2To prepare Mg (OH)2The product is used for recycling Mg element in the desulfurized ash of the dry method/semi-dry method in the first step,
the Ca (OH)2The adding amount is calculated according to the Mg content of the original desulfurized fly ash in the step (1) and the cumulative adding amount of the desulfurized fly ash in the step (3);
the calculation method comprises the following steps: ca (OH)2Adding amount which is the cumulative adding amount × (100 percent to the water content of the original desulfurized ash)/24 × 74/(100 percent to Ca (OH) of the original desulfurized ash with the Mg content of × desulfurized ash2Water content of)/Ca (OH)2The purity of (2);
and (9): completion of modification
And (5) repeating the steps (3) to (8), and finally completing the multi-step stabilization modification of the whole dry/semi-dry desulfurization ash.
Example 2 Multi-step stabilization modification of semi-dry desulfurized fly ash of certain iron and steel works by pH control
The pH regulation and control multi-step stabilization modification method of the dry/semi-dry desulfurized fly ash comprises the following 9 steps:
step (1): and (4) analyzing and testing raw materials. Analyzing and testing the components of the dry/semi-dry desulfurized fly ash to determine CaSO in the desulfurized fly ash3And the contents of various strongly basic compounds, the results are shown in Table 1;
TABLE 1 original composition of semidry desulfurized fly ash (dry basis)
| Cl- | SO3 | CaCO3 | Dihydrate CaSO4 | CaSO4 | MgCO3 | CaSO3 | Ca(OH)2 | Other impurities |
| 1.02％ | 1.57％ | 32.77％ | 0.36％ | 3.32％ | 8.86％ | 39.65％ | 6.60％ | 5.85％ |
Step (2): and (4) preparing acid liquor.Preparing the waste sulfuric acid with the mass fraction of 80 percent into H with a certain volume and the pH value of 2.72SO4A solution, placed in an oxidation reactor;
and (3): and (4) acidifying the raw material. Gradually moving to step (2) H2SO4Adding the dry method/semi-dry method desulfurized fly ash obtained in the step (1) into the solution, continuously stirring, simultaneously monitoring the change of the pH value of the solution in real time, and stopping adding the desulfurized fly ash when the pH value is raised to 5.5 and kept stable;
and (4): and (4) forced oxidation. Carrying out jet aeration on the solution obtained in the step (3) by taking air as an oxidant, wherein the jet aerator adopts 4 aeration heads, the working air pressure is 5m of water column, the working water pressure is 12m of water column, and the working air volume and the water volume of each aeration head are respectively 30Nm3H and 10m3H, oxygen transfer efficiency of 11g O2/Nm3M, HSO in solution at this time3 -Is oxidized into SO4 2-To release H+So as to reduce the pH value of the solution by 1.3;
and (5): the pH is regulated. When the pH value of the solution obtained in the step (5) is kept stable at 4.2, the waste sulfuric acid obtained in the step (2) is gradually added into the solution, so that the pH value of the solution is reduced to 2.7 again and is kept stable, and the ratio of the added amount of the waste sulfuric acid to the added amount of the desulfurized fly ash obtained in the step (3) is 0.4m3Waste sulfuric acid: 1 ton of desulfurized fly ash;
and (6): and (4) carrying out multi-step circulation. Continuously repeating the steps (3) to (5) to ensure that solid CaSO gradually exists in the solution in the step (5)4Precipitating and finally forming slurry with the solid content of 10%;
and (7): and (5) recovering the product. When the solid content of the slurry in the step (6) reaches 10%, discharging a part of the slurry, and carrying out solid-liquid separation, dehydration and other treatments to obtain a stabilized and modified gypsum product;
and (8): and recycling waste liquid and recovering Mg. For the discharged slurry in the step (7), the residual waste liquid after recovering the gypsum product can be returned to the oxidation reactor in the step (2) for recycling, and Ca (OH) with the purity of more than 90 percent can be added2To prepare Mg (OH)2A product, namely Mg element, specifically Ca in the dry/semi-dry desulfurized ash obtained in the step (1) is recycled(OH)2The adding amount is calculated according to the Mg content of the original desulfurized fly ash in the step (1) and the cumulative adding amount of the desulfurized fly ash in the step (3), and the calculating method comprises the following steps: ca (OH)2Adding amount which is the cumulative adding amount × (100 percent to the water content of the original desulfurized ash)/24 × 74/(100 percent to Ca (OH) of the original desulfurized ash with the Mg content of × desulfurized ash2Water content of)/Ca (OH)2The purity of (2);
step (9); and finishing the modification. And (5) continuously repeating the steps (3) to (8) for the residual slurry in the oxidation reactor, and finally completing the multi-step stabilization modification of the whole dry/semi-dry desulfurization ash.
In the step (2), the oxidation reactor is provided with an exhaust port, a liquid level, a temperature, a pH value and SO2Provided is an online monitoring device.
And (3) feeding the desulfurized ash through a metering screw feeder.
In the step (3), stirring is realized by a mechanical stirrer or a jet aerator.
In the step (5), the waste sulfuric acid is added by a metering acid liquid pump.
In the step (7), the solid-liquid separation is realized by a hydrocyclone.
In the step (7), the dehydration is realized by a vacuum belt dehydrator or a belt filter press.
In step (8), Ca (OH)2And adding the mixture by a metering screw feeder.
Acidizing and forced oxidation tests are carried out according to the pH regulation and control multistep stabilization modification method, and when the solid content of the final slurry reaches 10%, the final slurry comes from CaSO3S-balance of (a) is shown in fig. 2. Table 2 shows the ingredients of the resulting modified product. As can be seen, CaSO is the most main component in the original semi-dry desulfurized fly ash3And CaCO339.65% and 32.77%, respectively, and a certain amount of MgCO3And Ca (OH)2Equal high alkalinity component, CaSO4The content of (A) is very low. By the pH regulation and control multistep stabilization modification method, almost all CaSO in original semi-dry desulfurization ash3、CaCO3And Ca (OH)2Are all converted into dihydrate CaSO4Modified product of dihydrate CaSO4The content of the active ingredients reaches 93.97 percentAnd a good modification effect is obtained.
TABLE 2 ingredients of modified products (dry basis)
| Cl- | SO3 | CaCO3 | Dihydrate CaSO4 | CaSO4 | MgCO3 | CaSO3 | Ca(OH)2 | Other impurities |
| 0.09％ | 0.08％ | 0.00％ | 93.97％ | 0.39％ | 0.00％ | 0.21％ | 0.00％ | 5.26％ |
The embodiments described above are intended to enable those skilled in the art to fully understand and effectively use the invention. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above-mentioned embodiments, and modifications made by those skilled in the art according to the teachings of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.
The principle of the invention is as follows:
(1) and (2) controlling the pH value of the acidified slurry in the whole stabilization modification process to be between 2.2 and 5.6 all the time by taking the optimal solid-liquid ratio as a basis, wherein the optimal solid-liquid ratio is embodied by controlling the pH value of the solution to be within a certain range all the time when each step of oxidation is carried out: firstly, adding desulfurized ash to stabilize the pH value of the solution at a certain value within the range of 3.3-5.6, wherein a solid is added; and adding waste sulfuric acid to stabilize the pH of the solution at a certain value within the range of 2.2-4.0, wherein one waste sulfuric acid is added. The so-called optimal solid-to-liquid ratio is the ratio between these two quantities.
(2) Increase oxidation rate and avoid SO2Releasing
The conventional one-step oxidation process is decomposed into multiple steps, the solid-liquid ratio and the slurry pH value of each step of oxidation process are accurately controlled, and meanwhile, the jet aeration technology adopted has strong mixing and stirring effects and higher oxygenation capacity, oxygen utilization rate and oxygen power transfer efficiency, SO that SO is avoided2And when the high-alkalinity desulfurization ash is released, the high-efficiency oxidation of the high-alkalinity desulfurization ash is creatively realized.
Claims (6)
1. A pH regulation and control multi-step stabilization modification method of dry method/semi-dry method desulfurized fly ash is characterized in that: the method comprises the following steps:
(1) analysis of raw materials test
Analyzing and testing the components of the original dry/semi-dry desulfurized fly ash to determine CaSO in the desulfurized fly ash3And the contents of various strongly basic compounds;
(2) preparation of acid liquor
Preparing waste sulfuric acid stock solution with the mass fraction of 2% -98% into H with the pH value of 2.2-4.02SO4A solution, placed in an oxidation reactor;
(3) acidification of the feedstock
Gradually moving to H in the step (2)2SO4Adding the dry-process/semi-dry-process desulfurization ash obtained in the step (1) into the solution, continuously stirring to obtain a mixed solution, simultaneously monitoring the pH value change of the mixed solution in real time, and stopping adding the desulfurization ash when the pH value of the mixed solution rises to 3.3-5.6;
(4) forced oxidation
Using air as an oxidant, adopting a jet aerator to carry out jet aeration on the mixed liquid obtained in the step (3), wherein the jet aerator comprises 1-16 aeration heads, the working air pressure is less than or equal to 10m of water column, the working water pressure is less than or equal to 30m of water column, and the working air volume and the water volume of each aeration head are respectively 20-80 Nm3H and 8-18 m3The oxygen transfer efficiency is 9-18 g O2/Nm3·m；
(5) Control of pH
After forced oxidation, gradually adding the waste sulfuric acid stock solution obtained in the step (2) into the solution when the pH value of the mixed solution is kept stable, and reducing the pH value of the solution to 2.2-4.0 again;
(6) multiple step cycle
Continuously repeating the steps (3) to (5), wherein solid-phase CaSO gradually exists in the mixed solution in the step (5)4Separating out to obtain slurry with the solid content of 5-25%;
(7) recycled product
Discharging the slurry part obtained in the step (6), and performing solid-liquid separation and dehydration treatment to obtain a stabilized modified gypsum product and residual waste liquid;
(8) waste liquor circulation and Mg recovery
Returning the residual waste liquid in the step (7) to the oxidation reactor in the step (2) for recycling, or adding Ca (OH) with purity of more than 90 percent2To prepare Mg (OH)2A product for recycling Mg element in the dry/semi-dry desulfurized fly ash of the step (1)，
The Ca (OH)2The adding amount is calculated according to the Mg content of the original desulfurized fly ash in the step (1) and the cumulative adding amount of the desulfurized fly ash in the step (3);
the calculation method comprises the following steps: ca (OH)2Addition = original desulfurized ash Mg content × desulfurized ash cumulative addition × (100% -original desulfurized ash water content)/24 × 74/(100% -Ca (OH)2Water content of)/Ca (OH)2The purity of (2);
and (9): completion of modification
And (5) repeating the steps (3) to (8), and finally completing the multi-step stabilization modification of the whole dry/semi-dry desulfurization ash.
2. The method for multi-step stabilization and modification of desulfurization ash by pH regulation of dry/semi-dry process as claimed in claim 1, which is characterized in that: the oxidation reactor is provided with an exhaust port, a liquid level, a temperature, a pH value and an SO value2Provided is an online monitoring device.
3. The method for multi-step stabilization and modification of desulfurization ash by pH regulation of dry/semi-dry process as claimed in claim 1, which is characterized in that: in the step (3), feeding the desulfurized ash through a metering screw feeder; the agitation is achieved by a mechanical stirrer or a jet aerator.
4. The method for multi-step stabilization and modification of desulfurization ash by pH regulation of dry/semi-dry process as claimed in claim 1, which is characterized in that: in the step (5), the waste sulfuric acid is added through a metering acid liquid pump.
5. The method for multi-step stabilization and modification of desulfurization ash by pH regulation of dry/semi-dry process as claimed in claim 1, which is characterized in that: in the step (7), the solid-liquid separation is realized by a hydrocyclone; the dewatering is achieved by a vacuum belt dewaterer or a belt filter press.
6. The pH-regulated multi-step stabilization of dry/semi-dry desulfurized fly ash according to claim 1The chemical modification method is characterized by comprising the following steps: in the step (8), the Ca (OH)2And adding the mixture by a metering screw feeder.
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