JP3497459B2 - Desulfurization wastewater treatment method and apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a desulfurization wastewater treatment method and apparatus, and more particularly to wastewater of a wet flue gas desulfurization facility in a thermal power plant that burns petroleum-based fuels such as heavy oil (hereinafter simply referred to as "desulfurization wastewater"). (Referred to as) processing method and apparatus.

[0002]

2. Description of the Related Art Wastewater discharged from a wet flue gas desulfurization equipment installed in a heavy oil fired power plant or the like is ammonium sulfate,
Since it contains a large amount of soluble salts such as magnesium sulfate, it is discharged to the adjacent water area after a certain treatment. However, in view of the influence on the surrounding environment, it is naturally required to reduce the amount of soluble salts to the minimum possible. Many of the salts themselves contained in the wastewater are useful, and if they can be efficiently recovered and reused, it will be effective from the viewpoint of the usefulness of resources.

Conventionally, as a method for treating desulfurization wastewater, for example, Japanese Patent Laid-Open No. 10-174946 discloses a dust collector installed in an exhaust gas flue of a boiler that uses heavy oil such as heavy oil or orinocotar. The collected ash and the desulfurization effluent generated from the wet flue gas desulfurization device are mixed, a reducing agent for reducing pentavalent vanadium to tetravalent vanadium is added, and a mixed liquid obtained in the mixing step is added. A solid-liquid separation step of separating the formed high-concentration vanadium-containing precipitate by adding magnesium hydroxide and / or aqueous ammonia to a pH of 3 to 9, and further adding calcium hydroxide or A pH adjusting step of adjusting the pH to 9 to 12 by adding calcium oxide, a distillation step of distilling and concentrating the liquid after the pH adjustment, and calcium sulfate and hydroxy acid in the distillation residual liquid concentrated in the distillation step. A magnesium hydroxide separation process that separates magnesium, a process that supplies the slurry containing calcium sulfate that is separated in the magnesium hydroxide separation process to a wet flue gas desulfurization device, and a vapor generated in the distillation process is condensed A method for mixing and processing dust ash of a heavy fuel oil-fired boiler and wastewater discharge and drainage is described, which comprises a condensing step of recovering ammonia water.

[0004]

The method described in this publication is intended to treat dust ash and desulfurization effluent discharged from combustion gas of heavy oil such as high sulfur-containing heavy oil or orinocotar. Since this heavy oil has a high content of ash, nitrogen, sulfur and heavy metals such as vanadium as compared with the normal heavy oil used in the present invention, the properties of dust ash and desulfurization effluent from a heavy oil fired power plant are high. Is significantly different from the properties of dust ash and desulfurization effluent from ordinary heavy oil-fired power plants, and new measures are needed. The invention described in the above publication is made in view of this point.

Further, in the method described in this publication, a part of the magnesium hydroxide slurry is returned to the upstream solid-liquid separation step, but in this case, the purpose is to utilize this slurry as a reducing agent. (It can be seen from using ammonia water instead of magnesium hydroxide slurry), while supplying gypsum slurry to the deamination process and returning the concentrated filtrate of magnesium hydroxide rich slurry to the evaporation process, This is different from the present invention aiming at stable operation of the apparatus by reducing the change in solid content concentration. Further, there is no description of the technical idea of controlling the solid content concentration of the liquid supplied to the classification step to 5 to 25 wt%. Further, there is no description of a technical idea of suppressing the scaling of gypsum by keeping the solid content concentration in the deaeration step at 3 to 20 wt%. Further, there is no description of the technical idea of increasing the particle size of gypsum and improving the classification performance of gypsum and magnesium hydroxide by using gypsum in gypsum slurry as seed crystals.

The present invention has been made in view of the above points, and an object of the present invention is to remove desulfurization wastewater from a wet flue gas desulfurization facility such as a petroleum (heavy oil) thermal power plant in a deaeration step, an evaporation step and a classification step. , The concentration process, and the gypsum drying process in addition to these (drainage-free process or device) to treat the wastewater efficiently and desulfurization wastewater. It is to provide a desulfurization wastewater treatment method and apparatus that contributes to the preservation of the surrounding environment by eliminating zero, that is, without drainage.

[0007]

In order to achieve the above-mentioned object, the desulfurization wastewater treatment method of the present invention comprises a deassertion step of adding lime to the desulfurization wastewater from a wet flue gas desulfurization unit to strip ammonia. , Evaporation process that heats and concentrates the wastewater (deamination slurry) from the deaeration process, and classification that introduces the effluent (concentrated slurry) from the evaporation process into magnesium hydroxide rich slurry and gypsum rich slurry Process, a concentration process for concentrating the magnesium hydroxide rich slurry from the classification process, a gypsum slurry introduction process for introducing the gypsum slurry in the deamination process, and a concentration filter for introducing the filtrate from the concentration process into the evaporation process. And a liquid returning step (see FIGS. 1 and 2).

In the desulfurization wastewater treatment method of the present invention, the desulfurization step of adding lime to the desulfurization wastewater from the wet flue gas desulfurization apparatus to strip ammonia, and the wastewater from the deaeration step are heated and concentrated. Evaporation step, classification step of introducing waste liquid from the evaporation step to classify into magnesium hydroxide rich slurry and gypsum rich slurry, gypsum drying step of drying gypsum rich slurry from the classification step, and from the classification step Consists of a concentrating step for concentrating the magnesium hydroxide rich slurry, a gypsum slurry introducing step for introducing the gypsum slurry in the deaminating step, and a concentrated filtrate returning step for introducing the filtrate from the concentrating step into the evaporating step. (See FIG. 3).

In these methods, ammonia is recovered and reused from the deamination process, water is recovered and reused from the evaporation process, and the gypsum-rich slurry obtained in the classification process is effectively used in the concentration process. By effectively utilizing the obtained magnesium hydroxide-rich slurry, it is possible to achieve no drainage and prevent industrial waste from being produced.

Further, in these methods, the solid content concentration in the waste water in the deaeration step is kept in the range of 3 to 20 wt%, preferably 7 to 10 wt%, the gypsum scaling is suppressed and the slurry is kept in the slurry. The gypsum is used as a seed crystal to increase the gypsum particle size and improve the classification performance in the classification step. If the solid concentration is less than the above lower limit, gypsum scaling is generated in the deamination process, which hinders stable operation. On the other hand, when the amount exceeds the above upper limit, the degree of concentration in the evaporation step becomes large, and stable treatment becomes difficult due to clogging of the device. Moreover, when a hydrocyclone is used for the classifier, the cyclone causes troubles such as blockage.

In these methods, the step of introducing gypsum slurry is configured to introduce the gypsum slurry from the wet flue gas desulfurization apparatus and / or the step of introducing gypsum rich slurry from the classification step.

The solid content concentration of the effluent supplied to the classification step is kept in the range of 5 to 25 wt%, preferably 10 to 15 wt%. When the solid content concentration is less than the above lower limit, the processing amount becomes large and the apparatus becomes large. on the other hand,
If the above upper limit is exceeded, problems such as blockage may occur in a classifier such as a cyclone.

The desulfurization effluent treatment apparatus of the present invention comprises a deaeration tower for adding lime to the desulfurization effluent from a wet flue gas desulfurization apparatus to strip ammonia, and heating and concentrating the effluent from the deaeration tower. And a classifier for introducing waste liquid from the evaporator to classify the magnesium hydroxide-rich slurry and the gypsum-rich slurry into a magnesium hydroxide-rich slurry from the classifier. For concentration, a gypsum slurry introduction system for introducing gypsum slurry into the deaeration tower, and a concentrated filtrate return system for introducing the filtrate from the concentrator into the evaporator (Fig. 1, see FIG. 2).

Further, the desulfurization wastewater treatment apparatus of the present invention heats the wastewater from the deaeration tower for adding lime to the desulfurization wastewater from the wet flue gas desulfurization equipment to strip ammonia. And a classifier for introducing waste liquid from the evaporator to classify it into magnesium hydroxide-rich slurry and gypsum-rich slurry, and dry the gypsum-rich slurry from this classifier For drying, a concentrating device for concentrating the magnesium hydroxide rich slurry from the classifier, a gypsum slurry introduction system for introducing the gypsum slurry into the deamination tower, and an evaporator for the filtrate from the concentrating device. It is characterized in that it comprises a concentrated filtrate returning system introduced in (3) (see FIG. 3).

In these devices, the gypsum slurry introduction system is a gypsum slurry introduction pipe from the wet flue gas desulfurization device and / or
Alternatively, it is configured to be a gypsum rich slurry introduction pipe from a classifier. Further, it is preferable to provide a reaction tank for introducing the desulfurization wastewater, gypsum slurry and lime to carry out a stirring reaction between the wet flue gas desulfurization apparatus and the deaeration tower. A hydrocyclone, thickener or the like is used as the classifying device, and a filter press, a drum filter, a vacuum filter, a belt filter or the like is used as the concentrating device.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments, and can be appropriately modified and implemented. 1 is a process explanatory view of a desulfurization wastewater treatment method according to a first embodiment of the present invention, and FIG. 2 is a systematic schematic configuration diagram showing an example of an apparatus for carrying out the desulfurization wastewater treatment method shown in FIG. In FIG. 1, combustion exhaust gas from a heavy oil-fired power plant is introduced into a wet flue gas desulfurization device 10 of a limestone / gypsum system or the like and desulfurized. The method in the present embodiment includes a deaeration step 12 of adding lime such as slaked lime and quick lime, for example, slaked lime to the desulfurization wastewater from the wet flue gas desulfurization apparatus 10 and heating the wastewater from the deaeration step 12. An evaporating step 14 for evaporating and concentrating, and a classifying step 16 for introducing the waste liquid from the evaporating step 14 and classifying into a magnesium hydroxide rich slurry and a gypsum rich slurry,
A concentration step 18 for concentrating the magnesium hydroxide-rich slurry from the classification step 16, a gypsum slurry introduction step for introducing the gypsum slurry into the deamination step 12, and a filtrate from the concentration step 18 are introduced for the evaporation step 14. Concentrated filtrate return step.

In the deaeration step 12, stripping with air is performed. In addition, steam stripping, vacuum (reduced pressure) stripping, etc. may be used alone or in combination. Since the magnesium hydroxide-rich slurry classified in the classification step 16 contains gypsum,
This magnesium hydroxide rich slurry is concentrated in the concentration step 18, and the filtrate is returned to the evaporation step 14.

Ammonia separated in the deaeration step 12 is
Recovered as gaseous ammonia or ammonia water,
It is supplied to the electric dust collector or the flue upstream of it and is reused for neutralizing exhaust gas. The water vapor evaporated in the evaporation step 14 is condensed by a condenser or the like and recovered as water, and the recovered water is reused in the wet flue gas desulfurization device. The magnesium hydroxide rich slurry from the concentration step 18 is sold as a magnesium hydroxide raw material to a refiner, or is re-used as a raw material or an auxiliary raw material in a lime-gypsum method flue gas desulfurization apparatus using magnesium hydroxide as a raw material or an auxiliary raw material. Used.

Next, an example of the desulfurization wastewater treatment device will be described with reference to FIG. Desulfurization wastewater and gypsum slurry from the wet flue gas desulfurization device 10 are supplied to a reaction tank 19 together with lime, for example, slaked lime, and after stirring and reacting, they are supplied to a deaeration tower 20 by a supply pump 21. Blower 2 in this relief tower 20
At step 2, air is supplied and bubbling is carried out in the drainage, and / or the upper part thereof is used as a plate column and the plates are brought into contact with each other in a countercurrent to separate and recover the ammonia gas. The recovered ammonia gas is supplied to the flue in front of the electrostatic precipitator and used to neutralize the acidic components in the exhaust gas.

In the desulfurization wastewater supplied to the reaction tank 19,
Contains ammonium sulfate and magnesium sulfate,
It reacts with the added slaked lime according to the following formula. MgSO_Four+ Ca (OH)₂+ 2H₂O → CaSO_Four・
2H₂O + Mg (OH) ₂ (NH_Four)₂SO_Four+ Ca (OH)₂→ CaSO_Four・ 2
H₂O + 2NH₃ Instead of stripping with air, steam
Stripping or vacuum (reduced pressure) distillation
There are also cases.

The drainage water from the relief tower 20 is extracted by a pump 24.
It is introduced into the evaporator 26 via the and is heated to evaporate water to be concentrated. As an example of heating method,
A method is employed in which the liquid at the bottom of the can is extracted by a circulation pump 28, a heater 30 is provided in the circulation line, and indirectly heated by steam or the like. The inside or outside of the evaporator 26 may be heated. The water vapor evaporated in the evaporator 26 is cooled and condensed in the condenser 32 and recovered as water, and the recovered water is reused in the flue gas desulfurization device 10.

The concentrated waste liquid from the evaporator 26 is temporarily stored in a concentrated liquid tank 34 via an outlet branch pipe of a circulation pump 28, and then introduced into a classification device, for example, a liquid cyclone 38 by a concentrated liquid pump 36. , Magnesium hydroxide rich slurry and gypsum rich slurry. In this case, the magnesium hydroxide-rich slurry having a small particle size is extracted from the upper part of the cyclone 38, and the gypsum-rich slurry having a large particle size is extracted from the lower part of the cyclone 38. The magnesium hydroxide rich slurry from the liquid cyclone 38 is introduced into a magnesium hydroxide concentrator, for example, a filter press 40, and separated into a magnesium hydroxide slurry having a low gypsum content and a filtrate containing gypsum, and the filtrate is evaporated. It is supplied to the can 26. The magnesium hydroxide slurry containing a small amount of gypsum is once stored in the magnesium hydroxide slurry tank 42, then carried out of the system by the slurry pump 44, and effectively used as a magnesium hydroxide raw material.

The gypsum rich slurry from the liquid cyclone 38 is introduced into the wet flue gas desulfurization apparatus 10 via the gypsum rich slurry pipe 54. In addition, this gypsum rich slurry may be introduced into the reaction tank 19. In this embodiment, the gypsum slurry pipe 52 and the gypsum rich slurry pipe 56 serve as a gypsum slurry introduction system, and the filtrate pipe 58 from the filter press 40 is used.
Is the concentrated filtrate return system.

The solid content concentration in the waste water in the deaeration tower 20 is 3
It is kept at -20 wt%, preferably 7-10 wt%. By doing so, the scaling in the deaeration tower 20 is suppressed, and the gypsum in the added gypsum-containing slurry becomes seed crystals to increase the gypsum particles and improve the classification performance in the subsequent classification step. Let Further, the solid content concentration of the concentrated effluent supplied to the hydrocyclone in the classification step is 5 to 25 wt.
%, Preferably 10 to 15 wt%. By doing so, stable operation of the device can be continued.

As described above, the gypsum-rich slurry classified by the liquid cyclone 38 is returned to the desulfurization device 10, and the magnesium hydroxide contained in the gypsum-rich slurry is
It is used as a desulfurizing agent by the following reaction. _{Mg (OH) 2 + SO 4} 2- → MgSO 4 + 2OH - gypsum filtration apparatus for recovering gypsum produced in the desulfurization apparatus 10 conduct (not shown) in the washing operation, preferentially soluble salts such absorbed by the desulfurizer Then, it is collected by a waste water treatment device (not shown).

In this embodiment, gypsum slurry is supplied in addition to the gypsum filtrate (desulfurization drainage) in the deamination process, and gypsum in the gypsum slurry is used as seed crystals. Thereby, the scaling is suppressed and the gypsum particle size is increased, so that the classification performance in the classification step is improved. It is also possible to use the gypsum rich slurry classified in the classification step as a seed crystal. Furthermore, by continuously supplying the filtrate from the magnesium hydroxide concentration step to the evaporation step, the increase in the slurry concentration in the evaporation step can be reduced, so that stable operation of the evaporator and the classifier can be achieved. Further, by this operation, chlorine contained in the desulfurization wastewater can be more efficiently concentrated, and an increase in chlorine concentration in the desulfurization device can be suppressed.

If the gypsum quality in the desulfurization device 10 is acceptable, by eliminating the washing with a gypsum separator (not shown),
A part of the soluble salts can be discharged as a gypsum deposit liquid. In this case, since the chlorine concentration in the system is inevitably low, it is possible to eliminate the evaporation step.

FIG. 3 shows a desulfurization wastewater treatment equipment according to a second embodiment of the present invention. In the present embodiment, the gypsum-rich slurry classified in the classification step is supplied to the dryer 60 and collected as gypsum. In FIG. 3, as an example, a drum-type dryer having a drum heated by steam or the like is shown, but the dryer is not limited to this type, and another type of dryer can be used. Is. Other configurations and operations are similar to those of the first embodiment.

[0029]

Since the present invention is configured as described above, it has the following effects. (1) Contributes to the preservation of the surrounding environment by efficiently removing useful substances in desulfurization effluent from wet flue gas desulfurization equipment, and also contributes to the preservation of the surrounding environment. By returning it to the flue gas desulfurization unit for reuse, it is possible to reduce equipment operating costs. (2) Purity of recovered magnesium hydroxide is 50%
Since it can be maintained above, it can be used as a desulfurizing agent. Moreover, by classifying the recovered gypsum into a level that does not cause a quality problem even if it is mixed with desulfurization gypsum from the wet flue gas desulfurization apparatus, it is possible to realize a system that does not generate industrial waste. (3) Since the filtrate generated when concentrated in the magnesium hydroxide concentration step is supplied to the evaporation step, it is possible to suppress a rapid change in the solid content concentration in the wastewater in the evaporation step. The solid content concentration of the liquid supplied to the classifying device in the classifying step is 5 to 25 wt%, preferably 10 to 15 wt%.
Stable operation of the device becomes possible by controlling to%. (4) Both the gypsum-containing slurry and the desulfurization wastewater are supplied to the deaeration process at a constant ratio, and the solid content concentration in the deaeration process is always 3 ~.
By maintaining the content at 20 wt%, preferably 7 to 10 wt%, scaling can be suppressed and operation and maintenance costs can be reduced. Further, by using gypsum in the slurry as seed crystals, the gypsum particle size can be increased, and the purity of magnesium hydroxide recovered in the classifying / concentrating step and the purity of gypsum recovered in the classifying step can be increased.

[Brief description of drawings]

FIG. 1 is a process explanatory diagram of a desulfurization wastewater treatment method according to a first embodiment of the present invention.

FIG. 2 is a systematic schematic configuration diagram showing an example of an apparatus for carrying out the desulfurization wastewater treatment method shown in FIG.

FIG. 3 is a systematic schematic configuration diagram of a desulfurization wastewater treatment device according to a second embodiment of the present invention.

[Explanation of symbols]

10 Wet Flue Gas Desulfurization Equipment 12 Release process 14 Evaporation process 16 classification process 18 Concentration process 19 Reaction tank 20 relief tower 21 Supply pump 22 Blower 24 Extraction pump 26 evaporation cans 28 Circulation pump 30 heater 32 condenser 34 Concentrated liquid tank 36 Concentrate pump 38 Hydrocyclone (classification device) 40 Filter press (concentrator) 42 Magnesium hydroxide slurry tank 44 slurry pump 52 gypsum slurry tube 54,56 Gypsum rich slurry pipe 58 Filtrate tube 60 dryer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI C02F 9/00 C02F 9/00 504E 1/04 1/04 C 1/20 1/20 B (56) Reference JP-A-9 -271630 (JP, A) JP-A-9-57051 (JP, A) JP-A-57-204220 (JP, A) JP-A-2000-24638 (JP, A) JP-A-51-17180 (JP, A) JP-A-48-196 (JP, A) JP-A-2000-24639 (JP, A) JP-A-57-56084 (JP, A) JP-A-9-75915 (JP, A) JP-A-6-91132 ( JP, A) JP-A-5-317646 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C02F 9/00 C02F 1/04 C02F 1/20 B01D 53/34

Claims (10)

(57) [Claims] 1. A deamination step of adding lime to the desulfurization effluent from a wet flue gas desulfurization apparatus to strip ammonia.
An evaporation process that heats and condenses the wastewater from the deaeration process, a classification process that introduces the waste liquid from the evaporation process into a magnesium hydroxide-rich slurry and a gypsum-rich slurry, and magnesium hydroxide from the classification process. It is characterized by comprising a concentration step for concentrating the rich slurry, a gypsum slurry introduction step for introducing the gypsum slurry in the deaeration step, and a concentrated filtrate return step for introducing the filtrate from the concentration step into the evaporation step. Desulfurization wastewater treatment method. 2. A deannealing step of adding lime to the desulfurization effluent from the wet flue gas desulfurization apparatus to strip ammonia.
The evaporation process that heats and condenses the wastewater from the deaeration process, the classification process that introduces the waste liquid from the evaporation process into magnesium hydroxide rich slurry and gypsum rich slurry, and the gypsum rich slurry from the classification process Gypsum drying step to dry the gypsum, a concentration step to concentrate the magnesium hydroxide rich slurry from the classification step, a gypsum slurry introduction step to introduce the gypsum slurry to the deaeration step, and an evaporation step of the filtrate from the concentration step A process for desulfurization wastewater treatment, comprising: 3. Ammonia is recovered and reused from the deamination process, water is recovered and reused from the evaporation process, and the gypsum-rich slurry obtained in the classification process is effectively used and obtained in the concentration process. The desulfurization wastewater treatment method according to claim 1, wherein the magnesium hydroxide rich slurry is effectively used. 4. The solid content concentration in the wastewater in the deaeration process is 3 to.
The desulfurization wastewater treatment method according to claim 1, 2 or 3, which is maintained in a range of 20 wt% to suppress scaling, and to increase the gypsum particle size by using gypsum in the slurry as seed crystals to increase the gypsum particle size. . 5. The desulfurization wastewater treatment according to claim 1, wherein the gypsum slurry introduction step is a step of introducing gypsum slurry from the wet flue gas desulfurization apparatus and / or gypsum rich slurry from the classification step. Method. 6. The desulfurization wastewater treatment method according to claim 1, wherein the solid content concentration of the waste liquid supplied to the classification step is maintained within a range of 5 to 25 wt%. 7. A deamination tower for adding lime to the desulfurization effluent from the wet flue gas desulfurization unit to strip ammonia, and an evaporator for heating and concentrating the effluent from the deaeration tower. A classifier for introducing the effluent from the evaporator to classify it into magnesium hydroxide-rich slurry and gypsum-rich slurry, a concentrator for concentrating the magnesium hydroxide-rich slurry from this classifier, A desulfurization wastewater treatment device comprising: a gypsum slurry introduction system for introducing gypsum slurry into Anto, and a concentrated filtrate return system for introducing the filtrate from the concentrator into an evaporator. 8. A deamination tower for adding lime to the desulfurization effluent from the wet flue gas desulfurization apparatus to strip ammonia, and an evaporator for heating and concentrating the effluent from the deaeration tower. A classifier for introducing the waste liquid from this evaporator to classify it into magnesium hydroxide-rich slurry and gypsum-rich slurry, a dryer for drying the gypsum-rich slurry from this classifier, and a classifier Concentration device for concentrating magnesium hydroxide rich slurry of, a gypsum slurry introduction system for introducing gypsum slurry into the deamination tower, and a concentrated filtrate return system for introducing the filtrate from the concentrator into the evaporator. A desulfurization wastewater treatment device comprising: 9. The desulfurization wastewater treatment device according to claim 7, wherein the gypsum slurry introduction system is a gypsum slurry introduction pipe from a wet flue gas desulfurization device and / or a gypsum rich slurry introduction pipe from a classification device. 10. The desulfurization wastewater treatment equipment according to claim 7, 8 or 9, wherein a reaction tank is provided between the wet flue gas desulfurization equipment and the deaeration tower.