JPS5814369B2 - Waste liquid treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating waste liquids, particularly waste liquids such as pulp waste liquids that are incinerated to produce incineration ash containing sodium carbonate and sodium chloride. The purpose is to separate efficiently and advantageously.

Conventional pulp waste liquids include pulp bleaching waste liquid, waste liquid from the chlorinated lignin extraction method, and waste liquid generated during the production of unbleached pulp by pulping wood soaked in seawater using caustic soda, etc. Na2CO3 and NaCυ are generated by incineration. There is a waste liquid that produces incineration ash containing .

For example, alkali-containing wastewater containing organic chlorine compounds also produces similar ash content when incinerated.

Furthermore, the Na2CO3 purged from the alkaline circulating fluid used for bauxite digestion also contains NaCl in addition to organic matter.
It may contain etc.

When these waste liquids are incinerated in a recovery boiler such as a Kraft recovery boiler, the presence of NaCt tends to cause a steam explosion in the dissolution tank, and Na2C03 and NaCl have a small difference in solubility and may form a eutectic, so separation is difficult. Have difficulty.

The present invention deals with N, which is difficult to separate, generated by the above-mentioned incineration.
Treating waste liquid containing a2CO3 and NaCt to produce Na2CD
3 and NaCl are separated, and NaO with low NaCt content is separated.
H aqueous solution or its precursor Na2Fe204
This provides a method for obtaining

As one method for separating Na2C03 and NaCt, pulp waste liquid containing chlorine-based substances is heated in a combustion furnace at a combustion temperature of 1.
The temperature is maintained at 33o'k or above and incinerated, and the smelt containing mainly Na2CO3 is extracted from the lower part of the combustion furnace, and NaCt
It has been proposed to roughly separate Na2C03-NaCt based chemicals in the combustion furnace by collecting dust containing living organisms from the flue at the latter stage of the combustion furnace (Japanese Patent Publication No. 52-49428/This method is Na2COs and Na
Ct is separated by using the difference in vapor pressure at high temperatures, but at combustion temperatures of 850°C or higher, for example, these substances melt and form a uniform liquid, so even though the vapor pressure is high, It is extremely difficult to completely separate NaCt from the liquid phase in a short period of time.

Na2CO3 begins to dissociate at high temperatures of 800°C or higher, and Na20 easily sublimates and disappears in the presence of water vapor, and like NaOH, it has a significant vapor pressure at 800°C or higher, so NaCl in the gas phase has a significant vapor pressure. is contaminated, and therefore the condensate contains NaC which has reacted with CO2 in addition to NaC.
2C03 will be mixed in.

Of course, under incineration conditions the partial pressure of CO2 is quite high, e(1
) reaction is suppressed, but not completely.

Therefore, both the Na2COB king fraction and the NaCL main fraction separated by this method contain other components to some extent.

Therefore, NaOH obtained by causticizing a smelt mainly composed of Na2CO3 contains a considerable amount of NaCt, making it impossible to achieve the intended purpose.

Further, this method is complicated in that it requires a lucifer for producing CaO for causticization.

In desperation, the inventor of the present invention conducted intensive research on an effective treatment method for waste liquid that produces a mixture of Na2CO3 and NaCt, which is considered difficult to separate using normal methods as described above. When iron oxide (Fe20s' powder is added to the concentrated product and mixed well and then dried and roasted, the sodium content corresponding to the amount of Na2C03 produced reacts with Fe203 to form sodium ferrate (Fe20s').
It has been found that NaCt becomes easy to phase separate.

Moreover, this phase-separated NaCl exhibits almost the same vapor pressure as when NaCl exists alone because Na2Fe204 remains in a solid phase up to about 1300°C, and it easily vaporizes and migrates into the combustion gas, almost completely disappearing. It was also found that it can be separated from solid phase Na2Fe2o4.

The mixture of substantially pure Na2Fe204 and excess iron oxide obtained in this way is disclosed in, for example, Japanese Patent Application No. 52-1190.
It was possible to hydrolyze it by the method of No. 15 to obtain a highly concentrated aqueous solution of caustic soda, thus completing the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention will be explained below based on the drawings, which are one embodiment of a waste liquid treatment apparatus used in carrying out the present invention.

An alkali-containing waste liquid 4, such as a pulping waste liquid containing chlorinated substances, is sent to a mixing tank 5, where it is mixed with iron oxide supplied from an iron oxide sludge feed line 6.

Here, iron oxide refers to a precursor of Fe205l and Fe203.

The amount of iron oxide (as Fe203) to be mixed should theoretically be 1 molar equivalent to Na2CO3 to be generated when waste liquid is incinerated, but it is usually 1.1 molar equivalent or more to increase the reaction rate. is used.

A mixed slurry of iron oxide and waste liquid passes through a mixed slurry supply line 7 and is sprayed into the incinerator body 1 from a feed gun 8.

Although the incinerator main body 1 shown in the figure is of a fluidized bed type, a rotary kiln type incinerator may also be suitably used as long as it is of a parallel flow type.

However, a rotary kiln in which solids and gas flow countercurrently cannot be used because volatilized salt accumulates on the supply port side.

In the incinerator main body 1, air heated by waste heat is fed into a wind box 9 from a combustion air supply line 10, passes through a perforated plate 11, and is blown into a fluidized bed 12, where a mixed liquid sprayed from a feed gun 8 is fed. is incinerated, and at the same time as the sodium ferrate production reaction progresses, Nact is vaporized into the combustion gas.

The combustion temperature is 80°C from the viewpoint of sodium ferrate production only.
The temperature may be 0°C or higher, preferably about 900°C, but since the vapor pressure of NaCt is relatively low at 1 to 2n1Hg at this temperature, the temperature should be 1000°C to a melting point of 1345°C at which no jintering occurs, that is, 1000°C to 1300℃
In terms of handling of sodium ferrate, it is preferable to incinerate it, preferably at about 1000 to 1200°C.

NaCt has a vapor pressure of about 10 mmHg at 1000°C, so if the combustion temperature is around this level, normally,
It volatilizes sufficiently into the fuel gas and is discharged.

Of course, if the amount of NaCt precursor in the waste liquid is small, NaCt can be removed even at a low temperature (e.g. around 800°C) required for incineration of organic matter.
It is not impossible to volatilize the Ca content.

Although not shown, when the waste liquid does not self-combust, it is necessary to supplement the combustion with fuel.

If the amount of NaCt in the ash becomes extremely high and the amount of combustion gas for vaporization is insufficient, it is optional to increase the amount of gas appropriately or to reheat the product in two stages.

The residence time during incineration depends on the temperature, but about 15 minutes to 1 hour is sufficient.

Now, after a predetermined average residence time, the reaction product is discharged from the overflow pipe 13, but due to the mixing characteristics of the fluidized bed, the reaction product always contains Na2Fe204 and excess Fe203, as well as some NaCl and unburned matter. is accompanied by

In order to remove this, one method is to use a multi-stage fluidized bed, but if necessary, a header 1 may be installed in the middle of the overflow pipe 13.
4, and by sending heated air from there into the pipe using a nozzle (not shown), it is possible to evaporate the remaining NaCt and burn off the unburned materials while effectively utilizing the heat retained in the overflowing material. .

In some cases, heat may be recovered from the reaction product using cold air.

On the other hand, the combustion exhaust gas containing NaCt vapor is discharged from the duct 16 after removing floating dust by the cyclone 15, and is recovered by exchanging heat with the air sent from the blower 27 by the air preheater 2.

The air preheater 2 can also be a boiler if necessary.

The exhaust gas leaving the fluidized bed is about 100C lower than the bed temperature, but Na
Since the temperature is higher than the melting point of Ct (801C), the flue gas can be cooled by blowing cold air from the cooling air pipe 17 to quickly cool the combustion exhaust gas to a temperature lower than the melting point of NaCt, for example 600-700C, and then recovering the heat. The NaCl inside becomes solid dust, which is discharged and recovered from the dust outlet 18.

Since the combustion exhaust gas after heat recovery still contains fine NacL particles, it is removed by the dust collector 3 and released into the atmosphere from the chimney 19.

The incinerated ash (reaction product) 20 discharged from the fluidized bed can be stored by blocking the outside air, but it is then stored in a ball mill 2.
1, it is wet-pulverized together with water sent from a water supply pipe 22, and then hydrolyzed under pressure at 150 to 200°C in an autoclave 23.

The slurry in which NaOH and Fe203 are suspended is passed through the door filter 24.
The NaOH aqueous solution is stored in a tank 25.

The separated Fe203 cake 26 is reused.

Although the concentration of NaOH is determined by the amount of water used for hydrolysis after wet grinding, it is easy to obtain a concentration of 20 or more by this method.

In some cases, sodium ferrate may be used as it is for other purposes, ie, for absorbing acidic gases or neutralizing acidic liquids, without being hydrolyzed.

The present invention will be specifically explained below with reference to Examples.

Example Organic matter 38.5%, Na9.8%, Ct0.7%, H2
051.0% and a calorific value of 5800 KJ/kg was treated in the manner shown in the figure.

The operating conditions were as follows.

Mixing tank conditions (Fe203F moisture 50 parts/100 parts Fe203) Treatment liquid/Fe203 (dry) = 2.4471.00 weight ratio (Fe203/Na20 = 1.27 mol/mol) Preheated air temperature for fluidized incinerator combustion Average 400℃ Excess air ratio for combustion 50% (including the amount introduced into the overflow pipe) Supply slurry moisture 44-45% Fluidized bed temperature 1000-1050C Output log gas temperature Approximately 950C Recovered soda liquid (alkali content recovery rate 98-99%) Solid minutes
24-25% NaOH in solids 95-97% Na2CO3 3-5% NaCt Trace The present invention mixes iron oxide with waste liquid containing sodium and chlorine below its equivalent amount and incinerates the excess. The sodium content is fixed and recovered as sodium ferrate, and at the same time, the NaCt content is vaporized and separated into the combustion exhaust gas and recovered from the flue in the latter stage, thereby easily separating the alkali content and salt.

Therefore, the ash that should be produced by normal incineration contains Na.
A crystallization separation device for Ct-Na2CO3-based mixtures is not required.

By the method of the present invention, a high concentration of N containing almost no NaCt is obtained.
An aOH aqueous solution is obtained directly from sodium ferrate.

Therefore, it has great advantages such as no need for a causticizing process using Na2CO3.

[Brief explanation of drawings]

The figure is a flow sheet of a waste liquid treatment device showing an example of an embodiment of the present invention. 1... Incinerator, 2... Waste heat recovery device, 3... Dust collector, 4... Waste liquid, 5... Mixing tank, 6... Supply line, 7... Mixed slurry Supply line, 8...
Feed gun, 9... Wind box, 10...
Combustion air supply line, 11... perforated plate, 12... fluidized bed, 13... overflow pipe, 14... header, 15...
...Cyclone, 16...Duct, 17...Cooling air pipe, 18...Dust outlet, 19...Chimney, 20
... Incineration ash, 21 ... Ball mill, 22 ... Water supply pipe, 23 ... Autoclape, 24 ... Furnace filtration machine,
25...tank, 26...Fe203 cake, 27
...Blower.

Claims (1)

[Claims] 1. A method for treating waste liquid that produces ash containing sodium carbonate and sodium chloride by incineration,
A sufficient amount of iron oxide to convert the sodium carbonate in the ash to sodium ferrate is mixed with the waste liquid and then incinerated, and the sodium chloride is volatilized into the combustion gas to produce an incineration residue mainly composed of sodium ferrate. A method for treating waste liquid characterized by obtaining 2 Iron oxide in an amount sufficient to convert sodium carbonate to sodium ferrate is the sodium content of sodium carbonate (Na2
2. The method for treating waste liquid according to claim 1, wherein the amount of Fe203 is 1.1 mol or more relative to 0).