JPS59111914A - Defoaming method - Google Patents

Abstract

PURPOSE:When sodium carbonate is recovered by evaporating the extract of sodium carbonate from the sludge obtained on desulfurization and dephosphorization of molten iron, a low-temperature gas is blown into the evaporation column to effect defoaming at the liquid surface, thus increase the recovery efficiency of sodium carbonate. CONSTITUTION:Unreacted sodium carbonate is extracted from the sludge resulting from desulfurization and dephosphorization of molten iron with sodium carbonate and the extract 1 is fed into the evaporation column 2 and evaporated with heat under circulation through the path 5 equipped with pump 3 and heat exchanger 4. As evaporation proceeds, the concentration of sodium carbonate becomes higher to form foams on the surface and hinder the evaporation. Thus, a gas such as air at a temperature about 10 deg.C lower than the solution 1 is blown from the nozzle 8 to effect defoaming and increase the evaporation efficiency, thus increase the recovery efficiency of sodium carbonate crystals.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for eliminating foam, particularly in an evaporation tower during crystallization in a saturated solution of sodium carbonate.

The difficulty in putting into practical use the desulfurization and dephosphorization treatment of hot metal using +3 um, that is, the so-called soda ash process, lies in how efficiently the sodium carbonate from the ash can be recovered and reused. Therefore, many proposals have already been made regarding the recovery of sodium carbonate.

One basic method of recovering sodium carbonate is a method in which a saturated solution of sodium carbonate is evaporated and crystallized in an evaporation tower. However, according to the experience of the present inventors, when a viscous liquid such as a sodium carbonate-containing solution is heated and stirred in an evaporation tower, many bubbles are generated on the liquid surface, which reduces the evaporation capacity of the entire evaporation tower. cause carbonation)
The recovery efficiency of IJum is significantly reduced. therefore,
In conventional methods, the foam generated is eliminated by opening the evaporation tower to the atmosphere, stirring slowly, or using an interfacial antifoaming agent.

The present invention has been developed for the purpose of making the above-mentioned foam extinguishment process even simpler and easier, and its gist is to desulfurize hot metal using sodium carbonate,
In the evaporation tower that evaporates and crystallizes the IJium-containing solution, the solution is blown toward the liquid surface of the solution. This is a method of blowing gas at a temperature lower than that of the solution to eliminate foaming when the solution evaporates.

Thus, according to the present invention, there is no decrease in evaporation capacity due to foaming, and the evaporation f? rk can actually be increased, making efficient operation possible. In addition, the phenomenon of boiling over the contents of the evaporation tower (a phenomenon in which the volume of the contents expands several times due to foaming and overflows) is no longer observed, making operation safer and controlling the liquid level of the evaporation tower at a constant level. becomes possible. Another advantage is that by blowing low-temperature air, crystals grow on the liquid surface and coarse crystals with good separability can be obtained. Because it is a low quality thing,
The crystal growth described above is of particular interest.

The invention will now be further described in connection with the accompanying drawings.

The attached drawing is an explanatory diagram schematically showing an evaporation column 2 that evaporates into a solution 1' containing IJium carbonate, and the solution 1 is circulated through a circulation path 5 provided with a pump 3 and 4 heat exchangers. It's heated. At this time, bubbles 6 are generated on the liquid surface. According to the present invention, a gas, generally air, at a temperature slightly lower than the liquid temperature is blown onto the liquid surface to extinguish the foaming. In the illustrated example, the gas is blown from above the liquid surface like a shower stream from the nozzle port 8 provided at an appropriate position of the distributor 7, but in a modified example, the gas may be supplied along the circumferential direction of the evaporation tower. The gas may be blown onto this liquid surface as a swirling flow in a horizontal plane or as a downward swirling flow. In short, as long as the gist of the present invention is followed, it is possible to blow gas toward the generated bubbles.
-n, its specific form is not particularly limited. Is code 9 a crystal recovery device? show. The collected crystals are then dehydrated and dried in a centrifuge (not shown), and the Na
z Recover as COs crystals.

In a preferred embodiment of the present invention, the gas flow rate supplied to the evaporation tower is 10 to 50 m'/- per unit cross-sectional area (ce) of the evaporation tower.
= (flow rate 0.2 to 1 tn/5ec), pressure 20
01+l+1lH20 or more. A difference of 10° C. between the gas temperature and the solution temperature is generally sufficient. That is, according to the present invention, as already mentioned, in order to eliminate foaming on the surface of a saturated solution of sodium carbonate, when scum, generally air, is blown, the surface of the foam is rapidly cooled, and the surface of the foam is rapidly cooled. The tension, that is, the liquid viscosity weakens, the bubbles burst, and the air pressure causes the bubbles to fly away, constantly producing a new liquid surface and ensuring the necessary evaporation TV. For this purpose, a gas with a pressure and flow rate above a certain limit is required, which is preferably 10 d/m/rr?
Above, 200 amHs 0 or more is required. In addition, the gas flow rate is 50 nl/m/rr? If it exceeds , the liquid level will become too cool, the solution will become supersaturated near the liquid level, and there will be a noticeable tendency for fine crystals to precipitate and adhere to walls, etc.

Next, the present invention will be further explained with reference to all embodiments, but the following embodiments are illustrative of the first half of the present invention, and the present invention is not limited thereby.

EXAMPLE Carbonate solution in soda ash method A carbonate-containing solution having the following composition obtained during the IJum recovery operation was subjected to evaporation and crystallization using an evaporation tower as shown in the attached drawing. However, in this example, the air was supplied not as a shower flow but as a swirling flow within the same plane along the circumferential direction of the evaporation tower, and was blown in the direction toward the evaporated liquid surface.

Table Composition of NazCO3-containing solution (heavy f#ch) The evaporation conditions at this time are summarized as follows.

Air blowing: Industrial compressed air flow rate: 20 tt? /m/ze (Flow rate: 0.3 m/sec) Pressure crab 200'wn⇠O Evaporation tower °: Dimensions: t, zm (diameter) x 24 m (height) Evaporation amount: 500 Kf/hour (Steam: 600 Kg /116) Liquid t: 3- Liquid @: 110°C The obtained sodium carbonate crystals have a size of 100 to 200
It was a rough version of something like μ (diameter).

According to the conventional method, the crystal size is 50 to 100 microns, so it can be seen that the crystal size was grown by the gas blowing according to the present invention.

In addition, in this example, when the air blowing was stopped,
Bubbles were immediately observed, and the amount of evaporation was 200 to 300 Kp/
It declined until the time. The bubbles disappeared by completely restarting air blowing.

[Brief explanation of the drawing]

The accompanying drawing is a schematic representation of an evaporation column for carrying out the method according to the invention. 1: Saturated solution 2: Evaporation column 5: Circulation path 6: Bubbles 7: Distributor 9: Crystal recovery device applicant representative Patent attorney Akira Hirose -75

Claims (1)

[Claims] Desulfurization and dephosphorization of hot metal using IJum, a solution containing sodium carbonate obtained when the sodium carbonate is recovered by treatment with a high slag, and the liquid of the solution is completely evaporated and crystallized in an evaporation tower. A method of blowing gas at a temperature lower than the solution temperature toward a surface to eliminate foaming when the solution evaporates.