JPH05123532A - Treatment of waste water from exhaust gas desulfurizer - Google Patents

Abstract

PURPOSE:To enable automatic operation in reduced maintenance frequency by a reduced number of machineries and simple operation by concentrating waste water after the removal of gypsum in an exhaust desulfurizing method to form cement or a mixture of cement and coal ash, and making the formed matter harmless to discard the same. CONSTITUTION:In a wet exhaust gas desulfurizing method, a solution after the removal of gypsum is filtered by a precoat filter 2. The obtained filtrate is supplied to an electrodyality tank 3 wherein cation exchange membranes and anion exchange membranes are alternately arranged to dyalize and concentrate the chlorine ion in the filtrate. Further, the filtrate is evaporated and conc. in an evaporation boiler 4 and the obtained concentrate is kneaded with cement or a mixture of cement with coal ash in a solidifying device 6 to be solidified and discarded in a harmless state. As a result, automatic operation in reduced maintenance frequency can be performed by a reduced number of machineries and simple operation. Further, the accumulation of the chlorine ion in waste water from which gypsum is removed can be reduced and the corrosion of the apparatus can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a flue gas desulfurization method in which sulfurous acid gas in exhaust gas is fixed and separated as gypsum, and the waste water after gypsum removal is concentrated by an electrodialysis method and an evaporator, which is then cement or cement and coal ash. The present invention relates to a method of kneading, solidifying, and detoxifying the mixture, and disposing of it.

[0002]

2. Description of the Related Art As a method for removing sulfurous acid gas in exhaust gas, a method in which limestone or slaked lime slurry is fixed and separated as gypsum is generally adopted, but a large amount of waste liquid remains after the gypsum is separated. , It is used in circulation to reduce the cost of wastewater treatment for the reasons described below, but chlorine ions are accumulated in the waste liquid. On the other hand, considering the materials used in the flue gas desulfurization equipment, the chlorine ion concentration in the normal waste liquid is 1
It is necessary to make it less than 10,000 ppm, and the waste liquid is extracted with this value as the limit.

However, in addition to calcium chloride, this waste liquid contains substances such as magnesium chloride, iron chloride, fluorine, and chemical oxygen-requiring substances (hereinafter referred to as COD substances) that are symmetrical to pollution control. In order to avoid the next pollution, the following measures for wastewater treatment are conventionally required, which requires a large amount of cost.

A conventional waste water treatment facility is composed of many devices such as an acid decomposition tank for treating COD substances, a solid content separation tank for solid content separation, and a hydrogen ion concentration adjustment tank for adjusting hydrogen ion concentration. Therefore, there are problems that the equipment cost is high, the equipment area is large, and the operation control method is complicated.

[0005]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above-mentioned drawbacks of the prior art.

[0006]

According to the present invention, gypsum is removed in a flue gas desulfurization method in which exhaust gas containing sulfurous acid gas is brought into contact with a slurry of limestone or slaked lime to absorb and remove sulfurous acid gas, and fixed and separated as gypsum. The latter liquid is filtered with a filter, and the filtrate is sent to an electrodialysis tank in which cation exchange membranes and monovalent anion exchange membranes are alternately installed, and the chlorine ions in the liquid are dialysis-concentrated, and then in an evaporator. A method for treating wastewater from a flue gas desulfurization apparatus, which comprises evaporating and concentrating, and then subjecting the concentrated liquid to kneading, solidification, detoxification, and disposal with cement or a mixture of cement and coal ash before disposal.

More specifically, the present invention will be described in more detail. Exhaust gas containing sulfurous acid gas is brought into contact with a slurry of limestone or slaked lime to absorb and remove sulfurous acid gas, and waste water generated in a flue gas desulfurization method in which gypsum is fixed and separated is filtered. After removing the solid concentration of fine gypsum etc. to about 0.2 mg / l by filtration with a machine, dilute sulfuric acid solution is used as an anode in an electrodialysis tank equipped with alternating cation exchange membrane and monovalent anion exchange membrane. Solution, dilute hydrochloric acid solution is used as catholyte, and electrodialysis is performed to remove sulfate ions (chemical formula SO ₄ ²⁻ , the same applies below) while concentrating chlorine ion concentration to, for example, about 10%, and further attaching scale by an evaporator. The amount of liquid is reduced by concentrating the chlorine ion concentration to, for example, about 25% while preventing the above, and this liquid is finally kneaded and solidified with cement or a mixture of cement and coal ash for disposal. To.

On the other hand, diluted water containing sulfate ions generated by electrodialysis is circulated and used in a desulfurizer. Therefore,
The flue gas desulfurization apparatus using the present invention does not generate secondary waste water.

Various types of filters can be considered as the filter used in the present invention, and it is necessary to remove the solid content up to a concentration of about 0.2 mg / l according to the requirement of the electrodialyzer in the next step. Therefore, a device capable of microfiltration is generally used.

The electrodialysis apparatus used in the present invention comprises a concentrate chamber, a dilute chamber and a cathode plate at both ends of the concentrate chamber and the dilute chamber, which are formed by alternately arranging cation exchange membranes and monovalent anion exchange membranes. The cation exchange membrane selectively permeates cations such as calcium and magnesium, and the monovalent anion exchange membrane selectively permeates monovalent anions such as chlorine. The concentrated liquid contained in and the diluted liquid in which the dissolved salt is diluted are taken out.

FIG. 2 shows a schematic diagram of the structure of the electrodialysis device and the movement of ions. As shown in Fig. 2, calcium ion, magnesium ion, and chlorine ion, which are the main components in the waste water, calcium chloride (CaCl ₂ ) and magnesium chloride (MgCl ₂ ) are electrically driven by the electric field formed between the positive and negative plates. It migrates and during this period is selectively blocked or permeated by the cation and anion exchange membranes, resulting in a concentrated solution or diluted solution, which is taken out from the electrodialysis device. For example, cations such as calcium and magnesium migrate toward the cathode plate, permeate the cation exchange membrane, and enter the concentrate chamber.
Further, it tries to migrate toward the cathode plate, but is blocked by the monovalent anion exchange membrane and remains in the concentrate chamber. On the other hand, chloride ions migrate toward the anode plate, permeate the monovalent anion exchange membrane, enter the concentrate chamber, and try to migrate further toward the anode.
It is blocked by the cation exchange membrane and remains in the concentrate chamber, where it is combined with cations that have migrated from the opposite direction and is carried by the concentrate that is the transfer medium and taken out from the electrodialysis device.

By the way, the reason why the monovalent anion selective membrane is used as the anion exchange membrane is to prevent scaling due to gypsum precipitation in the evaporation step for further concentrating the concentrated waste water from the electrodialysis device. This is because the performance deteriorates, mechanical damage occurs, and the long-term stability of the evaporation process is lost.

Although any evaporator can be used in the present invention, it is preferable to use a vacuum evaporator, a thin film evaporator and the like.

The kneading machine for kneading the concentrate and cement or the cement and coal ash used in the present invention is used for solidifying the fly ash of a conventional municipal waste incinerator such as a screw feeder type or a vibration type. It is possible to use the same device.

An example of the mixing ratio of the concentrate and the cement or the mixture of the cement and the coal ash is shown. When only the cement is used, the concentrate: cement = 2: 1, and when the cement and the coal ash are used, the concentrate. : Cement: Coal ash = 3:
1: 2 is suitable from the viewpoint of operating cost and equipment cost,
This mixing ratio changes depending on the required physical properties such as the priority of operating costs and equipment costs, and the hardness of the kneaded product to be produced. Further, the kneaded product from the kneader is optionally molded, cured (including dried), and then disposed.

[0016]

According to the present invention, the gypsum separation filtrate is separated into a dilute solution having a low chloride ion concentration and a concentrated solution having a high chloride ion concentration and a low sulfate ion concentration, and the former is used as water for preparing a desulfurizing agent slurry. By doing so, it is possible to eliminate the harmful effects of the accumulation of chlorine ions in the desulfurization system, and to prevent the formation of gypsum scale in the evaporator when the liquid discharged to the outside of the system is concentrated in the evaporator. it can.

[0017]

EXAMPLES In order to verify the effectiveness of the treatment of wastewater according to the present invention, an experiment was conducted with the apparatus having the configuration shown in FIG. Figure 1
In the figure, 1 is a tank that temporarily stores the wastewater from the flue gas desulfurization device (not shown), 2 is a precoat filter that removes suspended matter in the wastewater, 3 is an electrodialysis device that performs primary concentration of the wastewater, and 4 is a primary An evaporator for reconcentrating the concentrated wastewater, a condenser 5 for condensing vapor generated in the evaporator 4, and a solidifier 6 for kneading the wastewater secondarily concentrated in the evaporator 4 with cement or cement and coal ash to solidify Reference numeral 7 denotes a powder supply device that supplies cement to cement the wastewater or cement and coal ash after mixing in a fixed amount to the solidifier 6, and 8 denotes a pump that supplies the wastewater in the tank 1 to the precoat filter 2 in a fixed amount.

In FIG. 1, the salt concentration 2 from the flue gas desulfurization unit
Wastewater of [wt% as chlorine] 500 kg / hour was received in the tank 1 through the line a. Table 1 shows the composition of the main components of the waste water.

[Table 1]

The drainage of the tank 1 is 500k by the pump 8.
g / h supplied to the precoat filter 2. Diatomaceous earth was used as the filter medium of the precoat filter 2, and the turbidity water concentration in the wastewater at the outlet of the precoat filter 2, that is, the line c was 0.2 mg / l. Note that the precoat filter 2 was washed after being operated for a predetermined time because turbid components were accumulated and the filtration resistance increased with time.

The wastewater from the precoat filter 2 is sent to the electrodialysis device 3 and separated into a concentrated liquid having a high salt concentration (hereinafter referred to as a primary concentrated liquid) and a diluting liquid having a low salt concentration, which are lines d and e, respectively. The primary concentrated solution was discharged to the evaporator 4 via the, while the diluted solution was discharged to the outside of the system. Table 2 shows the specifications and operating conditions of the electrodialysis device 3 at this time.

Table 3 shows the salt concentrations in the primary concentrated liquid, the diluting liquid, and the flow rate in this embodiment. The primary concentrated liquid was 10 [wt% as chlorine], and the diluted liquid was 1.13 [. wt% as chlorine] and the flow rate is 48 kg /
The time was 452 kg / hour.

[Table 2]

[Table 3]

The primary concentrated liquid from the electrodialysis device 3 is supplied to the evaporator 4 through the line d, and the salt concentration is 25 [w] in the can.
t% as chlorine] (hereinafter, this concentrated solution is referred to as a secondary concentrated solution). As the evaporator 4, a thin film type evaporator was used in this embodiment, the pressure inside the can was -660 mm (mercury column), and the drainage temperature inside the can was controlled to 85 ° C.

The vapor generated in the evaporator 4 is supplied to the condenser 5 via the line f, and is cooled and condensed by the cooling water supplied from the line g. The cooling water was discharged to the outside of the system through the line h and the condensed water through the line i. The secondary concentrated liquid of 19.2 kg / hour from the evaporator 4 was supplied to the solidifying device 6 via the line j.

The cement and coal ash required for the solidifying device 6 are sent from the line 1 and the line k to the powder supply device 7 in a fixed amount, and the powder supply device 7 is mixed with cement and coal ash. It was supplied to the solidification device 6 through the quantitative line m.
The amounts of cement and coal ash supplied from the lines 1 and k were 6.4 kg / hour and 12.8 kg / hour. In the solidifier 6, the secondary concentrated waste water, cement, and coal ash are kneaded to form a kneaded product. The kneaded product was discharged to the outside of the system through line n.

The cement used in this example was a commercially available ordinary Portland cement, and the coal ash was generated at a domestic coal-fired power plant (using domestic coal) that is currently in operation.

The kneaded product was dried with hot air at 107 ° C. for 60 minutes so that the water content was approximately 30 wt%. As a result of a dissolution test using the method prescribed by the Prime Minister's Office, it was confirmed that the dissolution standard value of the same law was satisfied.

The concentration flow rate in each line of this embodiment described above is summarized in Table 3 above.

In this example, the continuous operation was carried out for 350 hours, and the operation was possible without any trouble in the apparatus, and the effectiveness of the present invention could be demonstrated.

[0029]

INDUSTRIAL APPLICABILITY The present invention is a flue gas desulfurization method in which exhaust gas containing sulfurous acid gas is brought into contact with a slurry of limestone powder or slaked lime to absorb and remove sulfurous acid gas, and fixed and separated as gypsum. There is no adhesion of scale due to the precipitation of gypsum when concentrating, by kneading and solidifying the concentrated liquid with cement or a mixture of cement and coal ash, it has an excellent effect that it is rendered harmless and no drainage, Furthermore, there are advantages that the number of devices is small, the operation is extremely simple, almost automatic operation is possible, and the maintenance frequency is significantly less than that of conventional equipment.

Further, it is possible to reduce the accumulation of chlorine ion concentration in the wastewater from which the gypsum has been removed, and the corrosion of the equipment is prevented.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of the principle of the electrodialysis device used in the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location B01D 61/58 8014-4D C02F 1/04 C 6647-4D 1/44 K 8014-4D 1/469 9/00 Z 6647-4D 11/00 101 Z 7824-4D (72) Inventor Tatsunori Miwada 1 Higashishinmachi, Higashi-ku, Nagoya-shi, Aichi Chubu Electric Power Co., Inc. (72) Inventor Hiroshi Yoshida Nagoya-shi, Aichi Chubu Electric Power Co., Inc. 20-20, Kitakanyama, Otakamachi, Midori-ku (72) Inventor Mamoru Toriyao 1-20, Kitakanyama, Otaka-cho, Midori-ku, Nagoya, Aichi Chubu Electric Power Co., Inc. In-house (72) Hiroyo Tsutsui 2-5-1, Marunouchi, Chiyoda-ku, Tokyo Sanryo Heavy Industries Co., Ltd. (72) Inventor Shinichiro Kotake 2-5-1, Marunouchi, Chiyoda-ku, Tokyo 3 In Hishiju Kogyo Co., Ltd. (72) Inventor Naohiko Ugawa 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries Ltd. Hiroshima Research Institute (72) Inventor Susumu Okino 4-6 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture 22 Mitsubishi Heavy Industries, Ltd. Hiroshima Research Institute (72) Inventor Seki Nakamura 4-6 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture 22-22 Mitsubishi Heavy Industries Ltd. Hiroshima Research Institute (72) Inventor Shiro Fukui 2-chome Kameido, Koto-ku, Tokyo No. 25-14 Asahi Glass Co., Ltd. Chemical Engineering Department (72) Inventor Nori Uemachi and No. 25-14, Kameido, Koto-ku, Tokyo Asahi Glass Co., Ltd. Chemical Engineering Department (72) Inventor Ryosuke Aoki 10 Goi Kaigan, Ichihara, Chiba Prefecture Asahi Glass Co., Ltd. Chiba factory

Claims (1)

[Claims] 1. In a flue gas desulfurization method in which exhaust gas containing sulfurous acid gas is brought into contact with a slurry of limestone or slaked lime to absorb and remove sulfurous acid gas, and fixed and separated as gypsum, the liquid after removal of gypsum is filtered by a filter. After filtration, the filtrate is sent to an electrodialysis tank in which a cation exchange membrane and a monovalent anion exchange membrane are installed alternately, and the chlorine ions in the solution are dialysis-concentrated, and then evaporated and concentrated in an evaporator, and then the concentrated solution. A method for treating wastewater from a flue gas desulfurization device, characterized by kneading, solidifying and detoxifying cement and a mixture of cement and coal ash and detoxifying.