JPH08117552A - Mixing treatment of collected ash and waste drain water of heavy oil fuel-burning boiler - Google Patents

Abstract

PURPOSE: To recover valuables such as vanadium, ammonia or the like from collected ash and waste drain water to regenerate the same in high purity while reducing the vol. of formed sludge to enable stable operation. CONSTITUTION: After collected ash (b) is mixed with waste drain water (a) to be slurried and reduced in vol., a reducing agent C such as a ferrous salt reducing pentavalent vanadium to tetravalent vanadium in order to recover vanadium of the formed slurry is added to the slurry and an alkali agent such as magnesium hydroxide and/or aq. ammaonia are further added to adjust the pH of the slurry to 3-9 to precipitate tetravalent vanadium as tetravalent vanadium hydroxide. The precipitate (c) containing precipitated vanadium hydroxide in high concn. is separated and calcium hydroxide is further added to the separated soln. containing no vanadium hydroxide to adjust the pH of the separated soln. to 9-12 to form magnesium hydroxide and moisture is evaporated by distillation to concentrate the separated soln. When calcium hydroxide is added, the ammonium ion in the soln. is recovered as aq. ammonia.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating dust collecting ash and drainage and drainage of a boiler using heavy oil as a fuel, and particularly to a dust collecting ash discharged from a thermal power plant using these fuels. The present invention relates to a treatment method advantageously applied to treatment of wastewater.

[0002]

2. Description of the Related Art In the process of treating combustion exhaust gas discharged from a boiler facility that burns fossil fuels such as coal and heavy oil, such as a conventional thermal power plant, a dust collector installed in an exhaust gas flue from the boiler is used. Ash discharged (dust collecting ash)
The wastewater from the wet flue gas desulfurization equipment (wastewater removal wastewater) is treated separately, and the collected ash is humidified, and the wastewater discharged wastewater is treated up to a water quality that meets environmental regulation values. It was discharged from the place to the outside of the system. On the other hand, in recent years, at thermal power plants, etc., we are actively working on diversification of fuels, adding water to heavy oil with high sulfur content, natural orinocotar, or natural orinocotar, mixing and emulsifying, and handling at room temperature. Emulsion fuels that have made it possible (for example, 70% by weight of natural orinocotar and 30% by weight of fresh water and a trace amount of a surfactant mixed to form an emulsion) are attracting attention as new fuels (hereinafter, these fuels are collectively referred to as "fuels"). And called heavy oil). However,
There is little accumulated technology established as a method of treating dust ash emitted from combustion exhaust gas of these heavy oils.

[0003]

Since the heavy oil has a high content of ash, nitrogen, sulfur and heavy metals as compared with the conventional heavy oil, the collected ash from the heavy oil-fired power plant In addition, the properties of waste water and drainage are significantly different from the properties of dust ash and waste water discharged from conventional heavy oil-fired power plants, and new measures are needed. In particular, the dust collection ash has hygroscopicity and jetting properties, which makes it difficult to handle, and the amount of dust collection ash is large compared to the conventional heavy oil-fired boiler, and the volume density of dust collection ash is small, so the volume of dust collection ash is small. However, there is a problem that the capacity of the storage facility becomes large. In addition, since a large amount of ammonium (NH ₄ ⁺ ) is contained in the collected ash and the discharged and discharged water, it is necessary to remove the ammonium content from the environmental measures of the discharged and discharged and collected ash treatment.

In view of the above-mentioned state of the art, the present invention mixes dust collecting ash generated from a dust collecting device provided in an exhaust gas flue of a boiler using the heavy oil as fuel with waste water generated from a flue gas desulfurization device. An object of the present invention is to provide a method capable of reducing the volume, recovering valuable substances with high purity, and reducing the volume of sludge produced, thereby enabling stable operation.

[0005]

Means for Solving the Problems The present invention is (1) generated from a dust ash collected by a dust collector provided in an exhaust gas flue of a boiler using heavy oil as a fuel and a wet flue gas desulfurizer. Mixing waste water to add a reducing agent for reducing pentavalent vanadium to tetravalent vanadium, and adding magnesium hydroxide and / or ammonia water to the mixed solution obtained in the mixing step to adjust pH. 3 to 9 and the solid-liquid separation step of separating the produced high-concentration vanadium-containing precipitate, and calcium hydroxide or calcium oxide is further added to the separated liquid from the solid-liquid separation step to adjust the pH to 9-12. PH
A heavy product characterized by comprising an adjusting step, a distilling step of distilling and concentrating the liquid after the pH adjustment, and a condensing step of condensing vapor generated in the distilling step to recover ammonia water. A mixed treatment method of dust ash of an oil-fuel-fired boiler and drainage / drainage; (2) a magnesium hydroxide separation step of separating calcium sulfate and magnesium hydroxide in the distillation residual liquid concentrated in the distillation step, The heavy oil fuel burning according to the above (1), characterized in that the magnesium hydroxide obtained in the magnesium hydroxide separation step is used as a part or all of the magnesium hydroxide added to the mixed solution in the solid-liquid separation step. Method for mixing treatment of dust ash and discharge / drainage of boiler, and (3) A part of ammonia water for adding ammonia water recovered in the condensation step to the mixed solution in the solid-liquid separation step Is a mixing treatment method of the waste removal and drainage heavy oil fuel boiler fly ash according to the above (1), characterized by using as a whole.

In the present invention, the heavy oil includes heavy oil having a high sulfur content as described above, natural orinocotar, and emulsion fuel obtained by adding water to natural orinocotar and mixing it. The method of the present invention can of course be applied to the treatment of exhaust gas from a boiler that uses other heavy oil as a fuel, such as residual oil from a petroleum refining process.

In the method of the present invention, after collecting dust ash and drainage and drainage are mixed and slurried to reduce the volume and improve operability such as fluidity, the pentavalent valence is used for recovering vanadium in the slurry. A reducing agent that reduces vanadium to tetravalent vanadium is added, and an alkaline agent is further added to adjust the pH to 3 to 9.
Adjustment to deposit tetravalent vanadium as tetravalent vanadium hydroxide. The use of magnesium hydroxide and / or aqueous ammonia as the alkaline agent is one of the features of the present invention. The precipitate containing the precipitated vanadium hydroxide at a high concentration is separated, and calcium hydroxide or calcium oxide is further added to the separation liquid containing no vanadium hydroxide to adjust the pH to 9 to 12, and sulfate ions in the liquid and Calcium sulfate and magnesium hydroxide are formed by reacting with magnesium ions, and then distilled to evaporate water to concentrate. When calcium hydroxide or calcium oxide is added, ammonium ions in the liquid become ammonium hydroxide, which is desorbed from the liquid in the distillation process and once moved to the gas phase, and then condensed water of vapor generated in the distillation process. It re-migrates to and is recovered as ammonia water. The ammonia water recovered here can be used as a part or the whole of the alkaline agent for vanadium precipitation.

The distillation residual liquid may be carried out of the system and treated separately, but it is desirable to provide a magnesium hydroxide separation step after the distillation step to separate and recover calcium sulfate and magnesium hydroxide. When magnesium hydroxide is used as the vanadium-precipitating alkaline agent in the solid-liquid separation step, it is preferable to reuse the magnesium hydroxide separated here as a part or all thereof. The liquid containing no solid content after separating calcium sulfate and magnesium hydroxide is taken out of the system and treated.

[0009]

[Action]

1. The reduction and precipitation of vanadium in the mixing step and the solid-liquid separation step are performed by the following actions. (1) V in the liquid phase of the mixed liquid in which the dust ash and the drainage water are mixed
The (pentavalent) is reduced to V (tetravalent) by Fe (divalent) added as a reducing agent at a pH of 3 or less.
This main reaction occurs in a dissolved state and is represented by the following equation.

[Chemical Formula 1] 1/2 V ₂ O ₇ ^4- (pentavalent) → VO ₂ (tetravalent) (dissolved state) (1) Fe ²⁺ (divalent) → Fe ³⁺ (trivalent) (2) Here Although divalent iron was mentioned as an example of the reducing agent, it is possible to reduce pentavalent vanadium to tetravalent, and other reducing agents can be used without any trouble as long as they do not affect the present treatment method.

(2) Magnesium hydroxide {Mg (OH) ₂ } or aqueous ammonia (NH ₄ OH) as an alkaline agent is added to the mixed solution of the above (1), and the pH is adjusted to 3 to 9 to effect coagulation-precipitation. According to the formula, VO (OH) ₂ (tetravalent)
Will precipitate.

Embedded image VO ₂ (tetravalent) + Mg (OH) ₂ → VO (OH) ₂ ↓ + Mg ²⁺ (3) VO ₂ (tetravalent) + 2NH ₄ OH → VO (OH) ₂ ↓ + 2NH ₄ ⁺ (4)

(3) Since magnesium hydroxide {Mg (OH) ₂ } or aqueous ammonia (NH ₄ OH) is used as the alkaline agent in the above item (2), hydroxide ion (OH ⁻ ) is dissolved. It does not react with the Ca ions and is only used for neutralizing acidic components (H ⁺ etc.). In parallel with this, magnesium ion (Mg ²⁺ ) or ammonium ion (NH ₄ ⁺ ) reacts with sulfate ion (SO ₄ ²⁻ ) and magnesium sulfate (MgSO ₄ ) or ammonium sulfate {(NH ₄ ) ₂ SO ₄ } However, since this substance has high solubility, it is dissolved in the liquid and VO (OH) ₂
After the solid-liquid separation, it remains in the liquid and is supplied to the next pH adjusting step. The reaction here is as follows.

Embedded image H ⁺ + OH ⁻ → H ₂ O (5) Mg ²⁺ + SO ₄ ^2- → MgSO ₄ (6) 2NH ₄ ⁺ + SO ₄ ^2- → (NH ₄ ) ₂ SO ₄ (7)

2. Functions in the pH adjusting step, distillation step, condensing step and magnesium hydroxide separating step. Since calcium oxide (CaO) or calcium hydroxide {Ca (OH) ₂ } is used as an alkaline agent in the pH adjusting step, it has the following effects.

(1) Gypsum by adjusting the pH to 9 to 12 by adding calcium oxide (CaO) or calcium hydroxide {Ca (OH) ₂ } to the supernatant of the coagulating sedimentation step in the pH adjusting step (Calcium sulfate) precipitates and the gypsum supersaturation of the liquid decreases. In parallel with this, dissolved magnesium ions (Mg ²⁺ ) are precipitated / precipitated as magnesium hydroxide {Mg (OH) ₂ }. Even when only ammonia water is used as the alkaline agent in the solid-liquid separation step, magnesium hydroxide precipitates because the dust ash contains Mg.

(2) When this liquid is distilled, the ammonia in the supernatant liquid is changed from liquid to gas by the reactions shown in formulas (8) and (9), and when cooled, ammonia gas is produced by the reaction shown in formula (10). The liquid is condensed (ammonia water) and the ammonia water is recovered. Part or all of the recovered ammonia water can be reused as part or all of the alkali agent for vanadium recovery in the solid-liquid separation step.

Embedded image NH ₄ ⁺ + OH ⁻ → NH ₄ OH (liquid) (8) (OH ⁻ is supplied from calcium hydroxide) NH ₄ OH (liquid) → NH ₃ (gas) ↑ + H ₂ O (9) NH ₃ (gas) + H ₂ O → NH ₄ OH (liquid) (10)

(3) In the distillation step, the liquid is concentrated.
Along with this, dissolved gypsum is newly deposited and becomes gypsum scale, which may cause a decrease in heat transfer rate in the distiller. However, as described in the above (1), the solid gypsum deposited in the distiller feed solution is described. Is present, and the gypsum becomes a seed crystal, so no problem occurs due to the gypsum scale.

(4) Gypsum deposited in the pH adjusting step as the residual liquid in the distillation step and gypsum deposited due to the concentration of the liquid in the distillation step and magnesium hydroxide {Mg (OH) ₂ } precipitated in the pH adjusting step. It is included. This residual liquid may be carried out of the system and treated separately, but it is preferable to provide a magnesium hydroxide separation step to separate the precipitated gypsum and magnesium hydroxide from the supernatant liquid and reuse them. The separation step is composed of two steps: a step of separating gypsum and magnesium hydroxide, and a step of separating magnesium hydroxide from the liquid. Both separations are performed by using centrifugal force using a liquid cyclone or a sedimentation centrifuge.
It is separated by adjusting the difference in crystal size and the centrifugal force applied in the separator. In addition, a usual solid-liquid separation method such as weight classification or floating classification can be applied depending on the state of the liquid.

(5) By returning part or all of the separated magnesium hydroxide to the solid-liquid separation step, it can be reused as part or all of the alkaline agent for vanadium recovery.

[0018]

【Example】

(Embodiment 1) One embodiment of the present invention will be described with reference to FIG. In this example, magnesium hydroxide is used as an alkaline agent in the solid-liquid separation step. First, the wastewater effluent a, the dust collecting ash b and the first iron salt c as a reducing agent are mixed in the mixing step 1 to dissolve the dust collecting ash b. 5 to 10% by weight of unburned carbon (C), vanadium (V), magnesium (Mg) and fixed ammonia (NH ₄ ⁺ ) are contained in the collected ash b depending on the operating condition of the boiler, and 2 to 5% by weight, respectively. %, 5-10% by weight and 5-10% by weight
include. The mixing ratio of the collected ash b is 5 to 40% by weight with respect to the discharged and discharged wastewater a, and is preferably 30% by weight or less in order to improve the treatment efficiency in the subsequent steps. Also, ferrous salt c
For example, ferrous chloride or ferrous sulfate can be used. The injection rate of the ferrous salt c may theoretically be an equimolar ratio with respect to the pentavalent vanadium (V) in the mixed solution d. It is preferred to add. The drainage / drainage a is a weakly acidic gypsum saturated liquid, but the pH of the mixed liquid d is 2-3. In this step, pentavalent vanadium (V) is reduced to tetravalent, but the tetravalent vanadium (V) is dissolved because the pH is low.

The mixed liquid d obtained in the mixing step 1 is sent to the solid-liquid separation step 2, and magnesium hydroxide {Mg (O
H) ₂ } e is added and mixed. The pH at this time is 3 ~
9, preferably 4-8. In this step, it is preferable to add the polymer coagulant f. As the polymer flocculant, a polymer flocculant used in ordinary wastewater treatment can be used. The precipitate generated by this operation is separated by sedimentation to obtain a precipitate g and a supernatant h. The precipitate g obtained in the solid-liquid separation step 2 contains 8% by weight or more of vanadium (V), and the other components are unburned carbon (C), Fe, Al and the like. This precipitate g can be separately used as a raw material for vanadium recovery. Note that vanadium (V) was added to the supernatant h.
Is hardly contained (total vanadium (V) in the supernatant h is 1 mg / liter or less).

The precipitate g is discharged out of the system, and the supernatant h is sent to the next pH adjusting step 4. In the pH adjusting step 4, the pH is adjusted to 9 by adding calcium hydroxide {Ca (OH) ₂ } n.
After adjusting to ~ 12, send to distillation step 5. The pH of this solution is kept at 9 to 12 for the production of gypsum and magnesium hydroxide and for improving the efficiency of the next operation. In the distillation step 5, besides steam stripping, a normal distillation operation such as vacuum distillation can be applied. By this operation, the ammonia gas k is separated from the liquid, and the ammonia water k ′ is condensed in the condensation step 6.
Will be collected as The recovery rate of ammonia in the distillation step 5 and the condensation step 6 is 95% or more of the amount of fixed ammonia contained in the mixed liquid d. The recovered ammonia water k'can be carried out of the system and used for neutralizing the flue gas. The treatment liquid 1 remaining after the distillation in the distillation step 5 is a slurry of gypsum and magnesium hydroxide precipitated in the pH adjusting step 4, and is carried out of the system and treated separately.

By using magnesium hydroxide as the alkali agent in the solid-liquid separation step 2 as described above, the vanadium (V) content in the precipitate g can be increased to 8% by weight or more. Further, in the pH adjusting step 4, calcium hydroxide {C
Since a (OH) ₂ is used, the degree of supersaturation of gypsum in the pH adjustment step 4 and the distillation step 5 can be reduced, so that the generation of gypsum scale can be suppressed.

(Embodiment 2) A second embodiment of the present invention will be described with reference to FIG. In this example, a magnesium hydroxide separation step is provided in addition to the process of Example 1, and the recovered magnesium hydroxide is reused in the solid-liquid separation step. First, in the same manner as in Example 1, the waste water Drainage a and the dust collecting ash b are treated in each step from the mixing step 1 to the condensation step 6. At that time, the magnesium hydroxide e separated in the magnesium hydroxide separation step 7 described below is used as the magnesium hydroxide {Mg (OH) ₂ } e used in the solid-liquid separation step 2, but the other is the same as in Example 1. .
Next, the distillation residual liquid o in the distillation step 5 is separated into a gypsum slurry p and magnesium hydroxide e in a magnesium hydroxide separation step 7. In the magnesium hydroxide separation step 7, a separation means such as a hydrocyclone or a sedimentation centrifuge can be used. The separated magnesium hydroxide e is the solid-liquid separation step 2 of the previous step.
Will be returned to. The treatment liquid l separated in the magnesium hydroxide separation step 7 is subjected to an appropriate solidification treatment and then discharged out of the system. If the magnesium hydroxide used in the solid-liquid separation step 2 is insufficient with the recovered product only at the beginning of the reaction or during the reaction, the magnesium hydroxide may be appropriately replenished from outside the system.

(Embodiment 3) A third embodiment of the present invention will be described with reference to FIG. In this example, in the solid-liquid separation process,
Ammonia water is used as the alkaline agent.
By the same method as in Example 1, drainage and drainage a and dust collecting ash b
Is processed by each step from the mixing step 1 to the condensation step 6. At that time, the alkaline agent used in the solid-liquid separation step 2 is the ammonia water k'recovered in the condensation step 6, but the other conditions are the same as in Example 1. The remaining ammonia water is discharged out of the system. The distillation residual liquid o in the distillation step 5 is separated into gypsum water slurry p and magnesium hydroxide e by magnesium hydroxide separation 7. Magnesium hydroxide is carried out to the outside of the system for reuse or is subjected to an appropriate solidification treatment together with the treatment liquid 1 after separating gypsum and magnesium hydroxide in the magnesium hydroxide separation step 7, and then discharged to the outside of the system. To be done. When the amount of the ammonia water used in the solid-liquid separation step 2 is insufficient with the recovered product only at the initial stage of the reaction or during the reaction, it may be appropriately replenished from outside the system.

[0024]

According to the present invention, the following effects are brought about in addition to the effects peculiar to the above embodiment. (1) In the conventional heavy oil-fired boiler, the dust ash and the waste water discharged and discharged, which have been treated in different places, can be collectively treated, so that the treatment efficiency and the economical efficiency of the apparatus can be significantly improved. (2) Valuable materials such as vanadium (V) and ammonia (NH ₃ ) can be recovered from the dust ash and the wastewater discharged, and the resources can be reused. (3) The content of vanadium (V) in the precipitate obtained in the solid-liquid separation step is such that calcium hydroxide or the like is used as the alkali agent by using magnesium hydroxide or ammonia water that does not generate the precipitate as the alkali agent. When it is used, it is 2 to 3% by weight, but it can be increased to 8% by weight or more. This facilitates the operation of further increasing the purity for use as a valuable resource.

(4) In the distillation step, gypsum is newly deposited from the liquid due to the concentration and becomes gypsum scale on the heat transfer surface, which may reduce the heat transfer rate.
By adding calcium hydroxide or calcium oxide in the H adjustment step, gypsum is precipitated before the distillation step and solid gypsum is left in the liquid to form seed crystals. It is possible to prevent the deposition of gypsum in the above, and to prevent a decrease in thermal efficiency. (5) By adding calcium oxide or calcium hydroxide in the pH adjusting step and returning magnesium hydroxide separated from the distillation residual liquid or ammonia water recovered in the condensation step to the solid-liquid separation step, economical operation can be achieved. In addition, the alkali brought in from outside the system can be integrated into calcium hydroxide, which simplifies the equipment.

[Brief description of drawings]

FIG. 1 is a flow chart showing an embodiment of the present invention.

FIG. 2 is a flowchart showing a second embodiment of the present invention.

FIG. 3 is a flowchart showing a third embodiment of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B09B 3/00 ZAB B09B 3/00 ZAB 304 G (72) Inventor Gouji Oishi Chiyoda-ku Tokyo Marunouchi two Chome 5-1 Sanryo Heavy Industries Co., Ltd. (72) Inventor Susumu Okino 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima-shi Hiroshima Prefecture Kannon Shinmachi 4-6-22 Mitsubishi Heavy Industries Ltd. Hiroshima Research Institute (72) Inventor Satoshi Iba 5-1-6 Komatsu-dori, Hyogo-ku, Hyogo Prefecture

Claims (3)

[Claims] 1. A pentavalent vanadium is obtained by mixing dust ash collected by a dust collector installed in an exhaust gas flue of a boiler using heavy oil as fuel and wastewater generated from a wet flue gas desulfurization device. A reducing agent for reducing tetravalent vanadium to a mixture, and adding magnesium hydroxide and / or aqueous ammonia to the mixed solution obtained in the mixing step to adjust the pH to 3 to 9 to generate the high-concentration vanadium. The solid-liquid separation step of separating the contained precipitate, and the pH obtained by further adding calcium hydroxide or calcium oxide to the separated liquid from the solid-liquid separation step.
PH of 9 to 12, a distillation step of distilling and concentrating the liquid after pH adjustment, and a condensing step of condensing vapor generated in the distillation step to recover ammonia water. A method of mixing and processing dust ash and wastewater discharged and discharged from a heavy oil fuel-fired boiler. 2. A magnesium hydroxide separating step for separating calcium sulfate and magnesium hydroxide in the distillation residual liquid concentrated in the distilling step is provided, and the magnesium hydroxide obtained in the magnesium hydroxide separating step is solidified by the solidification step. The mixed treatment method of the dust ash and the drainage / drainage of a heavy oil fuel-fired boiler according to claim 1, characterized in that it is used as a part or all of magnesium hydroxide added to the mixed solution in the liquid separation step. 3. The heavy oil according to claim 1, wherein the ammonia water recovered in the condensing step is used as a part or all of the ammonia water added to the mixed solution in the solid-liquid separation step. A mixed treatment method of dust ash and drainage and drainage of a fuel-fired boiler.