JPS6013964B2 - Recovery of boron compounds in flue gas desulfurization - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the recovery of boron compounds in the effluent of the overflow flue gas desulfurization method, and more specifically, the present invention relates to the recovery of boron compounds contained in the flue gas of glass factories, etc., by the overflow lime plaster method flue gas desulfurization method. This invention relates to a method of recovering liquid from wastewater and its reloading.

Boron compounds may be dispersed into the exhaust gas from glass factories by gaseous or solid machines.

When such exhaust gas is subjected to wet flue gas desulfurization treatment, the boron compounds removed in the absorption tower are dissolved in the absorption liquid, contained in the waste liquid, and discharged outside the system. Boron is a necessary element for crops, but wastewater containing large amounts of boron compounds is harmful to crops, and it is necessary to remove boron from such boron-containing simulated solutions. However, there is currently no practical method for removing boron from wastewater, and the only known laboratory method is to separate it as a precipitate using the barium borotartrate method. In addition, since boron compounds are in short supply as a resource, it is desirable to recover them. It is difficult to separate boron from wastewater, and we have considered making the system wastewater-free in the wet exhaust gas treatment system mentioned above and using the heat of the ocean to dry the wastewater and recover the boron compounds, but... , HB02. It has become clear that boron compounds such as BQ are extremely volatile in gases containing water vapor, and even when wastewater is dried, the boron compounds sublimed and cannot be recovered as solids.

However, by adding crab substances to the wastewater, the sublimation of the boron compounds during the light mist drying is suppressed, and when the particle size is large, saddle drying occurs, making it easier to collect with a cyclone, etc.
Moreover, it was discovered that the recovered material could be reused as a raw material for glass production.

The object of the present invention is to recover boron contained in flue gas from a glass factory or the like from a wet lime-gypsum process flue gas desulfurization effluent. Another object of the present invention is to recover boron in flue gas in a form that can be reused as a raw material for glass production, and a further object of the present invention is to make a wet lime gypsum flue gas desulfurization device liquid-free. The method of the present invention is a method in which slaked lime or quicklime is added to the liquid discharged from the system during wet flue gas desulfurization, and this is fog-dried using the high-temperature flue gas to be desulfurized as a heat source to recover boron compounds as solids. It is possible to liquefy the liquid discharged from the flue gas desulfurization system into bran scales.

The apparatus of the present invention is a green lime gypsum method flue gas desulfurization apparatus equipped with a liquid passing adjustment device, and a flue gas mist cooling device that enables spray drying of the adjusted liquid. The present invention will be explained below with reference to FIG.

The exhaust gas 1 to be treated is cooled and greened by a spray dryer 2. The spray dryer 2 is supplied with the adjusted scale liquid, which will be described later, and the exhaust gas serves as a heat source for drying the waste liquid, which is flooded and cooled by the scale liquid, and the waste liquid is dried and solidified. After passing through the cyclone 3, the exhaust gas is sprayed with water in the flue to further green and cool, enters the absorption tower 4, comes into contact with the circulating absorption liquid, and becomes S0x,
Dust and boron compounds are removed from the absorption liquid, which is then discharged as clean gas through the demister 5. The SOx absorbed in the absorption liquid reacts with slaked lime and calcium carbonate in the liquid to become calcium sulfite or gypsum, and the absorbed boron compound becomes hydroborate. A part of the absorption tower circulating liquid is extracted by liquid level control and sent to the oxidizer 6. Therefore, sulfuric acid is added to treat unreacted calcium, and the calcium sulfite contained therein is oxidized in the air and converted into gypsum. The slurry extracted from the oxidizer 6 passes through a storage tank 7 and is separated into gypsum 9 and oak liquor in a separator 8. Since the boron compound is water-soluble, it moves to the monkey fluid side, and the passed fluid is temporarily stored in the adjustment tank 10'. During storage, slaked lime or quicklime is added to the bran to make it alkaline. The adjusted hazel liquor is atomized into a spray dryer 2 as a slurry. The sprayed slurry is evaporated to dryness in the spray dryer 2 by the head heat of the high-temperature exhaust gas as described above, and is recovered from the bottom of the spray dryer or the cyclone 3 as a solid containing boron compounds. The canopy lime or quicklime added to the adjustment tank 101 is sufficient as long as the slurry after adjustment produces a slurry with a particle size that can be sprayed in a spray dryer, and it was possible to operate satisfactorily with a particle size of 200 mesh or less. The amount added was sufficient to make the pH of the slurry after adjustment 7.5 or more, and the appropriate amount was about 0.5 to 1 mol per 1 mol of the boron compound. Slurry prepared by adding slaked lime or quicklime suppresses the sublimation of boron compounds during mist drying in a spray dryer, and the undissolved particles of slaked lime act as cores to form a dried product with a large particle size, increasing the yield of the spray dryer. raise. In the above process, if the oak liquor in the separator 8 is dried without adding slaked lime, the boron compound sublimes during drying and enters the absorption tower again, where it is captured by the absorption liquid.

Therefore, boron compounds are not discharged out of the system except for those accompanied by the water adhering to the gypsum separated in the separator 8, so the concentration of boron compounds in the absorption liquid gradually increases and the moat liquid is discharged out of the system. It becomes necessary. According to the present invention, the transferred liquid after gypsum separation is circulated to a spray dryer, and the boron compound is recovered by mist drying, the system is rendered scale-free, and the recovered boron compound can be used as a raw material for glass production.

Test Example Sublimation Test of Boron Compounds A sublimation test of boron compounds was conducted using a rhombus tube shown in FIG.

Absorption pin 12 containing water kept at 65℃ at Kaki Onsu 1 1
A dry gas of 80% N2, 10% CO2, and 10% C02 is passed through it at a rate of 3 sops/min to humidify the material to about 20% moisture, and the material is kept warm so that the water does not condense and passed through the annular furnace 13. A boat 14 containing about 2 samples was loaded into the annular furnace 13.
The temperature is maintained at a constant temperature within the range of 0 to 250°C. Annular furnace 1
The gas that has passed through 3 advances to an absorption bottle 15 containing N/1 dish of aOH aqueous solution and absorbs the accompanying boron compound. The amount of boric acid was measured by spectrophotometry using carminic acid as the absorption liquid, and the amount of gas passed was recorded with a gas meter 16.
The results are shown in FIG. 3 for boric acid crystals, dust collected from a glass factory (which is thought to be mostly boric acid based on the analytical values), and a dried product obtained by adding equimolar amounts of slaked lime to boric acid water.

It is clear that both boric acid crystals and glass factory dust exhibit remarkable sublimation in gas containing moisture, and that the sublimation of the slaked lime-added sample is significantly suppressed. Example A boron-containing solution prepared by adding 1 to 2% boric acid to a simulated flue gas desulfurization solution, and a solution obtained by adding 0.7 mole of slaked lime per mole of boron to the boron-containing solution were dried.

A spray dryer with a drying chamber diameter of about 200 m² was used, and the atomizer was rotated at about 800 pm.

As the heat source of the spray dryer, a high-temperature gas of about 80 psi was generated in a hot air generator using A heavy oil as fuel, and the gas was diluted with air to a temperature of 200 to 300°C. The amount of liquid that can be dried is 30 evenings/hour, and gas grass can be dried at about 10 evenings/hour. The dried materials enter the cyclone together with the exhaust gas, where they are collected. In addition to boric acid, the effluent from flue gas desulfurization is thought to contain gypsum, chlorine ions in the industrial water, and magnesium as impurities from lime.
A liquid containing MgS04 and having the following components was used as a simulated liquid.

ratio BQI9.5 (evening/split) Ca20.007 (m.

1 noku) * S-0.02 (mol/so) CIIO○ (mg/so) PH
In the 52 test, the following four points were measured and the material balance of boric acid was calculated.

{1' Amount of boric acid treated with a spray dryer: Calculated from the amount of treated liquid and boric acid concentration in the liquid, '21 Amount of collected boric acid: Calculated from the collected amount of evaporated solids and boric acid concentration in the solid content,
'31 Sublimated boric acid grass: Calculated from exhaust gas amount, gaseous boric acid concentration in exhaust gas (collected with aqueous aOH solution on the N/1 side using an absorption bottle), '4' amount of scattered solid boric acid (not collected by cyclone) The results are shown in Table 1. The results are shown in Table 1.

Table 1 1 Spray drying test of spray dryer Note: Murata collection rate = Sagi side o Murata sublimation rate = 迄・oo Solid boric acid scattering rate Koko X・oo Boric acid construction rate Deca boric acid sublimation rate + solid boric acid Although the total acid scattering rate is not 100% but 8 to 90%, this value is a reasonable value since it is thought that some boric acid adhered to the inner wall of the spray dryer.

From Table 1, when drying fake hair with a spray dryer using a boron-containing waste liquid (as is), the boric acid bridge collection rate is 1%, and most of it sublimates and becomes a gas and scatters, but in the case of slaked lime-added waste liquid, the boric acid collection rate is 1%. reaches 70%, and the boric acid sublimation rate is also high. It is clear that the reduction is suppressed to a low level.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the process of the apparatus of the present invention, FIG. 2 is an explanatory diagram of the boron compound sublimation test apparatus, and FIG. 3 is a graph showing the sublimability of boron compounds. 1... Exhaust gas, 2... Spray dryer, 4... Absorption tower, 6... Oxidizer, 8...
...Separator, 10...Adjustment tank. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. In flue gas desulfurization using the wet lime plaster method, slaked lime or quicklime is added to the liquid discharged from the system, and the boron compound is recovered as a solid by spray drying. 2. The method according to claim 1, wherein the high-temperature exhaust gas to be desulfurized is used as a heat source for spray drying the discharge liquid to which slaked lime or quicklime has been added, and the exhaust gas is humidified and cooled to make the system liquid-free. 3. In a wet lime-gypsum method flue gas desulfurization system that includes a flue gas spray cooling device, an absorption tower, an oxidizer, and a separator, a filtrate adjustment device is installed to adjust the pH by adding slaked lime or quicklime to the waste liquid from the separator, A flue gas desulfurization device that enables the spray cooling device to spray dry the adjusted filtrate and recovers a boron compound to eliminate liquid discharge.