JPS60222135A - Treatment of drainage - Google Patents

Abstract

PURPOSE:To prevent the corrosion of flue material and the accumulation of dust in the flue and to eliminate the adverse effect for low temp. EP due to the firmly stuck dust by spraying the waste liquid of a wet type stack gas desulfurization equipment so that the retention time of droplets in the flue to a dry type dust collecting equipment is reached to the value more than the specified value. CONSTITUTION:The wast gas 2 of a coal combustion boiler 1 is discharged as purified gas 7 via a dry type dust collecting apparatus 3, a cooling tower 8 and a absorption tower 10. One part of the circulating liquid of the cooling tower and one part of the filtrate 25 wherein gypsum has been separated from the limestone slurry fed from the absorption tower are introduced into a neutralizing tank 28 and sprayed into an upstream side duct of the dust collecting equipment 3 as droplets from two fluid nozzle 31 via a line 30. The droplets are mixed with the waste gas in a flue duct or an evaporation-drying equipment 17 to evaporate and dry them and the formed solid content is collected together with the dust and soot contained in the waste gas with the following dust collecting equipment 3. In this case, the droplets are sprayed from the nozzle 31 so that the retention time of the droplets in the flue becomes >=2sec.

Description

[Detailed Description of the Invention] (Field of Application of the Invention) The present invention relates to a method for completely eliminating wastewater and sludge from a wet flue gas desulfurization equipment containing harmful components such as sulfur oxides, nitrogen gas, and soot and dust. It is.

(Prior art) From the perspective of preventing air pollution, the wet limestone-gypsum method has been widely put into practical use as a sulfur oxide removal device, and is widely used for exhaust gas treatment from heavy oil-fired boilers, coal-fired boilers, metal smelting plants, etc. ing. Furthermore, in most cases, a dry type dust collector is employed as the device for removing dust from the exhaust gas.

Coal-fired boiler exhaust gas is one of the most difficult exhaust gases to treat, as it contains sulfur oxides, soot, nitrogen oxides, nitrogen gas, etc. among various exhaust gases, and depending on the treatment technology for coal-fired boiler exhaust gas, It is believed that other exhaust gas treatments can be accomplished relatively easily. The present invention will be specifically described below when applied to the treatment of coal-fired boiler exhaust gas.

A method for treating wastewater in which wastewater and sludge from a wet flue gas desulfurization system containing harmful components is injected from upstream of a dry dust collection system and collected by the dry solids dry dust collection system is disclosed in Japanese Patent Laid-Open Publication No. No. 56-155617.

(Problems with the Prior Art) As a result of conducting various experiments using the method described above, the present inventors found that it is possible to not only inject wastewater and sludge into the flue, but also to evaporate the wastewater in the flue gas. It has been found that if there is no residence time beyond a certain level, the following problems will occur.

fl+ Drainage water adheres to the inside of the flue, which tends to corrode the flue material.

(2) Droplets in the flue fix dust in the exhaust gas,
Develops dust deposits within the flue.

(3) The dust fixed by the droplets sticks to the dust collection electrode and discharge electrode of the low-temperature EP, affecting the charging state of the low-temperature EP and the exit dust, making stable operation of the dust multiplier difficult.

(4) The fixed dust is collected at low temperature Ep and is further fixed in the ash processing equipment that collects the dust, making it impossible for the ash processing equipment to operate smoothly (Objective of the invention) Problems as mentioned above In order to solve this problem, depending on the spray nozzle used and the flue spray amount/gas amount ratio,
It was found that the droplet residence time in the flue is necessary. Specifically, the residence time must be 2 seconds or more.

(Summary of the Invention) That is, the present invention introduces flue gas to a dry type dust collector, removes soot and dust contained in the flue gas, and guides it to a wet type flue gas desulfurization device to purify the flue gas. In a method for treating a waste liquid, in which the waste liquid from a desulfurization device is injected from upstream of the dry dust collector, and the dry solids thereof are collected by the dry dust collector, droplets are collected from upstream of the dust collector. The present invention provides a wastewater treatment method characterized in that the residence time in the flue up to the main body of the dust collector is 2 seconds or more.

An embodiment of the present invention will be described below with reference to FIG.

(Structure of the Invention) Exhaust gas 2 is guided from a coal-fired boiler 1 to a dry dust collector 3, and soot and dust contained in the exhaust gas is discharged as solid content 4 to the outside of the system. Next, the flue gas 5 from which most of the soot and dust has been removed is led to a gas heater 6 for heat exchange with the purified flue gas 7 from the absorption tower, and then led to a cooling tower 8 to remove most of the soot and norogen compounds. Then, it is led to an absorption tower 10 through a line 9 to remove sulfur dioxide (hereinafter referred to as SO□). The purified gas 7 from the absorption tower 10 is heated again by the gas heater 6, and then passes through a line 11 and is discharged into the atmosphere from a chimney 12. In the cooling tower 8, the pump 13 circulates and sprays the cleaning liquid through the circulation line 14' (il-) to clean the exhaust gas, collect dust and rogen compounds, and humidify and cool the exhaust gas. Makeup water 15 is supplied to the cooling tower 8 in order to compensate for the , through line 16 to neutralization tank 28.

In the absorption tower 10, SO2 contained in the exhaust gas passes through the circulation line 18 and is absorbed in contact with a slurry liquid containing limestone that is circulated and sprayed in the absorption tower 10, and becomes calcium sulfite. is circulated by a pump 19, and a part of it is sent to an oxidation tower 21 via a line 20, where it is turned into gypsum slurry by air oxidation. The gypsum slurry liquid from the oxidation tower 21 passes through a line 22 and is sent to a gypsum separator 23 where it is separated into a by-product gypsum 24 and a furnace liquid 25. Most of the furnace liquid 25 is mixed with limestone or slaked lime 26. and returns to the absorption tower 10.

On the other hand, a part of the furnace liquid 25 is supplied to the neutralization tank 28 through a line 27. The liquid supplied to the neutralization tank 28 is an alkali 29 (calcium hydroxide or hydroxide).
It is neutralized by IJum) and the entire amount is supplied to the upstream duct of the dry dust collector 3 via the line 30. The liquid supplied into the duct is sprayed by the two-fluid nozzle 31,
It becomes a droplet.

The droplets and exhaust gas 2 are transferred to a flue duct or evaporative dryer 17
The droplets are evaporated and dried, and the generated solids are collected and discharged as solids 4 together with the soot and dust in the exhaust gas by a downstream dry dust collector 3. FIG. 2 shows an example of the influence diagram of the relationship between the gas temperature drop from the spray nozzle and the distance from the spray nozzle. The droplets sprayed from the nozzle mix with the exhaust gas and evaporate. During this process, the temperature of the exhaust gas decreases, and at around 30 m (residence time of about 2 seconds), the temperature becomes constant and evaporation is complete. The comparative example in FIG. 2 is a case without spraying. Operating conditions of the two-fluid nozzle used in the basic tests that formed the basis of the present invention (
Various tests were conducted by changing the spray flow rate and spray zone, but all required a residence time of about 2 seconds or more.

[Example 1] Flue spray drying was carried out using the plant shown in FIG. 1 which processes 200.000 m''N/hr of coal-fired exhaust gas. The properties of the exhaust gas 2 are shown in Table 1.

Table 1 Exhaust gas properties 600 t1 continuously from the extraction line 16 of the cooling tower 8
It was supplied to the neutralization tank 28 at 1 h. The composition of the cooling tower effluent is shown in Table 2.

Table 2 Composition of liquid drawn from the cooling tower Part of the gypsum separation furnace liquid 25 is continuously supplied from the line 27 to 2
00 t/h was supplied to the neutralization tank 28. The composition of the gypsum separation P solution is shown in Table 3.

Table 3 Composition of Gypsum Separation P Solution Neutralization Tank In the tank 28, 0a(OH)2 powder 29 was added to the neutralization slurry so that 7 to 8 was added. Neutralized slurry in the neutralization tank tank from line 30 at a flow rate of 1 m”
/ hr, and was sprayed into the exhaust gas together with air at 200 m'N/hr from a two-fluid nozzle installed at the center of a circular duct with an inner diameter of 2 m. The temperature of the exhaust gas 2 is 163℃, the moisture content is 8.7 VO1%, it is an unsaturated gas, and the flow rate is 1 m''.
The neutralized slurry sprayed with hydrogen evaporates, and the exhaust gas temperature becomes 147° C. and the water content becomes 92 vol. After guiding this exhaust gas to the dry dust collector 3, it is supplied to the gas gas heater. The cooling tower outlet gas temperature was 49°C, the absorption tower exit gas temperature was 49°C, and the smoke inlet temperature was 97°C.

[Example 2] This practical example is shown in FIG. 3, and is completely the same as Example J except that the cooling tower 1 and oxidation tower 21 are omitted. The exhaust gas properties are as shown in Table 1.

Part of the gypsum separation furnace liquid 25 is continuously transferred from the cell line 27 to 8
Table 4 shows the composition of the gypsum separated P solution supplied to the neutralization tank at 0.007/h.

Table 4: Gypsum Separated Tear Composition In the neutralization tank 25, 29 g of Oa(OH)2 powder was added without stirring and mixing, and the volume of the neutralized slurry was controlled to be 80 g. The exhaust gas temperature, water composition, time to complete evaporation, etc. were the same as in Example 1.

(Effect of the invention) The present invention has the following effects.

+11 Since the droplets sprayed in the flue completely evaporate, corrosion of the flue material is not a particular problem.0 (2) Since the droplets sprayed in the flue completely evaporate, the dust There is no dust accumulation phenomenon in the flue that occurs when the dust is stuck.

(3) There is no change in the charging status of the low-temperature EP or the outlet soot and dust concentration.

(4) There were no substances stuck to the low-temperature EP discharge electrode, dust collection electrode, or ash processing equipment, making it possible to operate the equipment for a long period of time.

[Brief explanation of drawings]

Fig. 1 is a flow note showing one embodiment of the present invention, Fig. 2 is an influence diagram of the gas temperature effect from the spray nozzle section and the distance from the spray nozzle, and Fig. 3 is a flow note showing an embodiment of the present invention. This is an example in which the cooling tower and oxidation tower in FIG. 1 are omitted from the fo-sort showing an embodiment of the invention. Boiler, 2. Flue, 3. Low-temperature electrostatic precipitator, 4.. Solid content discharged from the dust collector, 5.. Exhaust gas from which dust has been removed, 6.. Gas gas heater, 7. Purification from absorption tower. Exhaust gas, 8... Cooling tower, 9 Line from cooling tower to absorption tower, 10... Absorption tower, 1 Line from gas heater to chimney, 12... Chimney, 13... Cooling tower circulation pump, 14... ... Cooling tower circulation line, 15. Make-up water, 16. Line from cooling tower circulation line to wastewater treatment equipment, 17. Flue or drying device, 18. Absorption tower circulation line, 19. Absorption tower Circulation pump, 20... Line from the absorption tower circulation line to the oxidation tower, 21... Oxidation tower, 22... Line from the oxidation tower to the solid-liquid separator, 23.
...Solid-liquid separator, 24...Solid containing gypsum, 25...
Furnace liquid from solid-liquid separator M machine, 26. Limestone, 27. Branch line for P liquid from solid-liquid separator, 28. Neutralization tank, 29. Slaked lime, 30. Smoke from neutralization tank. Line at road 1, 31...Two-fluid nozzle

Claims (1)

[Claims] The flue gas is led to a dry type dust collector, the soot and dust contained in the flue gas is removed, and the flue gas is led to a wet type flue gas desulfurization equipment. In a waste liquid treatment method in which the dry solids are injected from upstream of the device and collected by the dry dust collector, the retention time of the liquid droplets in the flue from upstream of the dust collection device to the main body of the dust collector is A wastewater treatment method characterized in that the treatment time is 2 seconds or more.