JPH0122013B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wet flue gas desulfurization method that produces gypsum as a by-product.

As a result of technological development over the past 10 years, wet flue gas desulfurization equipment has been widely used as a device with excellent desulfurization performance and capable of meeting Japan's strict air pollution control regulations.

Furthermore, its economic efficiency has improved significantly compared to its initial stage, and it is now being evaluated as having maintained a reasonable balance between environmental conservation and economic efficiency.

However, although SO ₂ , which is a source of pollution in flue gas, is completely controlled in various wet flue gas desulfurization processes, it is difficult to treat SO2, which is a source of pollution in flue gas. , especially chlorine (including its compounds), fluorine (including its compounds),
Almost no countermeasures have been taken for ammonia (including its compounds), and since these trace components are water-soluble, the trace components captured are discarded as wastewater from flue gas desulfurization equipment. It had been thrown out of the system.

This wastewater has generally been discharged outside the system after undergoing simple post-treatments such as neutralization, air oxidation, and precipitation separation.

The composition of the treated wastewater, other than water, is mainly alkali and alkaline earth metal sulfates, chlorides,
The substance was ammonia salt, etc., and did not have any particular negative impact on the environment, so it was allowed to be discharged into public rivers.

However, this wastewater increases the water consumption of the wet flue gas desulfurization equipment by the amount of post-treatment, placing an extra burden on the installer who thinks that even the evaporated water in the flue gas can be managed. As a reaction to this, the dry method was reconsidered.

Additionally, due to this drainage, location was sometimes restricted, especially in narrow areas.

In particular, sodium salts and calcium chloride, which are water-soluble even after treatment, and sulfates, which remain at equilibrium solubility even after precipitation, are difficult to remove from water, and especially large amounts of Cl ^- Attempts have been made to separate them by electrolysis, but the problem is that they are technically and economically expensive and cannot be carried out industrially. .

The present invention has been made in view of the current situation, and its purpose is to treat wastewater from wet flue gas desulfurization equipment to substantially eliminate the amount of wastewater disposed of outside the system, and to treat wastewater from wet flue gas desulfurization equipment. The aim is to reduce water consumption.

Another purpose is to convert impurities in flue gas into solid matter that is easy to handle, and to discharge it out of the system.

That is, the wet flue gas desulfurization method for producing gypsum as a by-product of the present invention is characterized by comprising the following steps A to C.

B. In a wet flue gas desulfurization method that produces gypsum as a by-product,
After the sulfur oxides in the flue gas have been separated as gypsum, a small amount of the waste water is brought into direct contact with the flue gas at a temperature of 130 to 190°C to evaporate the waste water, and a mixed gas consisting of the steam of the waste water and the flue gas is produced. (b) A step of separating dissolved substances in the waste water formed by evaporation of the waste water from the mixed gas together with the solids in the flue gas and discharging the mixture to the outside of the system; (c) In the mixed gas. A step of desulfurizing the sulfur oxides by a wet flue gas desulfurization method to form gypsum, and supplying a small amount of wastewater after separating the gypsum to the step A.

Thus, water in the wastewater is transferred to the flue gas and
The temperature of the flue gas decreases, the amount of water to be replenished in the subsequent wet flue gas desulfurization equipment decreases, and the amount of water used is reduced.

In other words, the net amount of water used can be suppressed to an amount equivalent to adiabatic cooling of flue gas, regardless of whether or not there is drainage.

Here, a small amount of wastewater in the present invention refers to filtered water after separating sulfur oxides in flue gas as gypsum, which is recycled to the wet flue gas desulfurization equipment, and a portion of the circulating water used to remove impurities in the circulating water. This refers to the liquid that is extracted from the system according to the accumulated amount.

Next, Embodiment 1 of a treatment device for realizing the wastewater treatment method of the present invention shown in FIG. 1 will be explained. G is introduced by a fan 1 through a flue 2 into a direct contactor 4 which is approximately cylindrical and hollow.

A small amount of waste water W discharged from the wet flue gas desulfurization device 9, that is, a small amount of waste water W after desulfurization products such as gypsum have been separated, passes through the conduit 3 and is directly sprayed from the top of the decorator 4 by the spray means 22. Then, it comes into contact with the high-temperature flue gas G, evaporates, and discharges from the conduit 7 a gas g consisting of the steam of the waste water W and the flue gas G after contacting with the waste water W, while leaving dissolved impurities as solids.

The gas g from the conduit 7 is further cooled by water l, which is regulated and sent from the conduit 8 as necessary, to a temperature of 40° C., which is suitable for the wet flue gas desulfurization device 9.
It is heated to 80° C. and introduced into the wet flue gas desulfurization device 9 through the conduit 13.

In the wet flue gas desulfurization equipment 9, a neutralizing agent such as coal or limestone, or (and) an oxidizing agent such as oxygen, air, or hypochlorous acid is added and treated.
The gas g' from which SO ₂ has been removed passes through the conduit 11 and is discharged from the chimney 12 into the atmosphere.

The impurities in the waste water W solidified in the direct contactor 4 fall to the lower part thereof and are discharged from the system through the rotary valve 5, which is a solid rotary discharge means.

The solidified impurity 6 is conveyed to an appropriate place,
Or it is transported by truck.

The advantage of the present invention is that the flue gas G, which is relatively high in temperature (130 to 190°C), comes into contact with a relatively small amount of waste water W, so dust and fly ash in the flue gas G are also removed from the waste water W.
It is much easier to handle because it is discharged together with the impurities 6 in a dry state, rather than the wet state obtained in a general wet flue gas desulfurization device.

Furthermore, even if a small amount of fly ash, dust, etc. flows out from the conduit 7 together with solidified impurities 6, they will eventually be captured by the wet flue gas desulfurization device 9, so the solid/gas separation performance of the direct contactor 4 is improved in the present invention. It is another advantage of the present invention that is not critical.

It goes without saying that for greater safety, a normal electrostatic precipitator may be used after the direct contactor 4.

At this time, the solid/gas separation performance of the direct contactor 4 hardly needs to be a problem.

Next, some embodiments of the present invention will be described. The wet flue gas desulfurization equipment 9 to which the treatment method of the present invention can be applied is a coal or limestone washing method (in series or parallel) where the neutralized product is (including the Chiyoda Thoroughbred 121 method), water washing method (including the Chiyoda Thoroughbred 101 method, in which the generated sulfurous acid is oxidized to sulfuric acid, and then the limestone is neutralized afterwards); This includes the double alkali method, which involves cleaning with a clear absorbing liquid and later treating it with lime or limestone.

Here, the waste water from the wet flue gas desulfurization equipment using the limestone cleaning method invented by Japanese Patent Publication No. 55-37295 to treat asphalt combustion gas of 3020 Nm ³ /H is separated from Cl ^- caused by salt in the asphalt. 52/H was required to protect the equipment material SUS316L, but previously this was treated along with other wastewater, but other equipment had stopped operating for rationalization, so this flue gas They were forced to use only desulfurization equipment for treatment.

Therefore, a direct contactor 4 with an outer diameter of 1,080 mm and a total height of 2,800 mm was installed as shown in Figure 1, and as a result of feeding the entire amount of the above-mentioned wastewater into it, even after 12 days of operation, the wet flue gas desulfurization equipment 9 There were no problems with the treatment of wastewater W.

The solid material discharged at this time was black in color, but it was solid and dry enough to be easily handled with a scoop or the like.

Therefore, by applying the treatment method of the present invention, the color tone of the plaster from the flue gas desulfurization equipment was improved and became slightly grayer than black-gray, but the dust in the flue gas was captured by the equipment of the present treatment method. It became clear that this was due to a significant reduction in the dust load on the flue gas desulfurization equipment.

In addition, it was confirmed that due to the application of this treatment method, the amount of cooling water to the flue gas desulfurization equipment decreased from the conventional 188/H to 131/H.

As a result, according to the present invention, the following effects can be achieved.

a In the present invention, a small amount of waste water after sulfur oxides in flue gas are separated as gypsum is brought into direct contact with flue gas at a temperature of 130 to 190°C.

Since such waste water has been separated from the gypsum, its amount is small compared to the salt-containing solution formed by reaction with sulfur oxides in the wet flue gas desulfurization process.

The waste water after separating the gypsum only contains water-soluble sodium salts, calcium salts, etc., such as sodium chloride and calcium chloride, and the amount is small, so it comes into contact with high-temperature flue gas, evaporates, and becomes useless. It can be drained.

Furthermore, since the amount of solids precipitated is small, there is an advantage that clogging of the direct contactor 4 can be avoided and stable operation can be achieved.

b As mentioned above, since a small amount of wastewater after separating sulfur oxides as gypsum comes into contact with high-temperature flue gas, the temperature of the flue gas does not decrease much, and as a result, dissolved substances in the wastewater are reduced by evaporation of the wastewater. is obtained in dry form.

Therefore, since the melt discharged from the direct contactor 4 is dry, it is easy to handle and transport, and can be transported by conveyor, truck, etc.

c. Fly ash, dust, etc. in the flue gas are separated at the same time when a waste water solution is precipitated due to contact between the flue gas and a small amount of waste water.

Therefore, the purity of the gypsum obtained in step C of the present invention is increased, and its utility value can be increased.

d) Since a small amount of waste water after separating the gypsum is evaporated, the direct contactor 4 can be downsized.

e Sulfur oxides in flue gas are separated as gypsum, and the waste water is brought into direct contact with high-temperature flue gas, so the amount of waste water discharged outside the system can be reduced to zero, and the process for waste water treatment is completely unnecessary. Become.

Therefore, the amount of water used in the wet flue gas desulfurization process can be significantly reduced.

f Even if part of the fly ash, dust, etc. in the flue gas is not captured due to direct contact with the waste water, it can be captured in the subsequent wet flue gas desulfurization process.

Therefore, the solid-gas separation function of the direct contactor 4 has the advantage of not being critical in the present invention.

The present invention is extremely advantageous in that it not only satisfies the energy saving that is currently required, but also allows the method to be realized with a relatively simple device. This treatment method, which can be extracted in dry form, is a solution to the shortcomings of wet flue gas desulfurization, and not only prevents pollution, but also reduces water and heat consumption, resulting in quality and resource savings. Also, its utility value is extremely large in terms of energy saving.

Furthermore, the processing method and processing apparatus of the present invention include:
It is mainly suitable for treatment from flue gas desulfurization equipment, but even if it is applied to similar wastewater, especially wastewater from denitrification equipment that uses NH ₃ , most wastewater emissions are avoided and NH ₃ to remove solids containing
Moreover, it is easily known by those skilled in the art that it can also be used as a fertilizer.

[Brief explanation of drawings]

FIG. 1 is a schematic process diagram showing an embodiment of the present invention. 2... flue, 3... conduit, 4... direct contactor,
5... Rotary valve, 6... Impurity, 9...
Wet flue gas desulfurization equipment.

Claims (1)

[Scope of Claims] 1. A wet flue gas desulfurization method for producing gypsum as a by-product, characterized by comprising the following steps (a) to (c). B. In a wet flue gas desulfurization method that produces gypsum as a by-product,
After the sulfur oxides in the flue gas have been separated as gypsum, a small amount of the waste water is brought into direct contact with the flue gas at a temperature of 130 to 190°C to evaporate the waste water, producing a mixed gas consisting of the steam of the waste water and the flue gas. (b) a step of separating dissolved substances in the waste water formed by evaporation of the waste water from the mixed gas together with solids in the flue gas and discharging the mixed gas to the outside of the system; A step of desulfurizing the sulfur oxides therein by a wet flue gas desulfurization method to form gypsum, and supplying a small amount of wastewater after separating the gypsum to the step A.