DE1963474A1 - Process for the simultaneous production of sodium sulfite and sodium carbonate from exhaust gases - Google Patents

Description

KBBlSHA. KA.GAKU KOGYO KABUSHIKI KAISKS., Tokyo, Japan

Process for the simultaneous production of sodium sulfite and sodium carbonate from exhaust gases

The invention relates generally to the production of WatrTui - sulfite and sodium carbonate as well as the use of by-products from industrial waste.

If fuels such as coal or heavy oil are burned in plants such as thermal power stations, the combustion gas obtained contains about Ο, Λ bia 0.2 ^c / a _t sulfur dioxide (SO ₂ ), which is produced by | the combustion of sulfur contained in the fuel is formed, and also about 12 f? Carbon dioxide (COp).

C. '

In particular, the present invention relates to a new process for the continuous and simultaneous production of sodium sulfite (Na ₂ SQj) and sodium carbonate (Na ₂ GO ₅ ) of high purity from such combustion gases. and with low cost for *

The use of sodium hydroxide (j ETaOH) as an alkali connects us to the production of compounds. NaI SQ _2, and Na ₂ CO ^ ₇ is wegjcm its ease of use and its low cost price 'j advantage of this, the sodium hydroxide, in general, a concentration is used .50 fi "3? ÜR the production of one ton

009829/1396

Na ₂ SO, or Na ^ CO, is the amount of water that has to be removed by evaporation or other processes and which is made up of a water component from the 50% sodium hydroxide solution and some neutralization water in the production of Na ₂ SO ^ 777 kg and in the production of Na ₂ e0 "925 kg. For this purpose considerable expenditure of material, energy and labor is required.

The aim of the invention is a process for the continuous *, simultaneous production of Na ₂ SO * and JJa ^ JO ^, in the case of eggs, the above-mentioned water can be removed without the supply of additional thermal energy for evaporation is required. . .

Another object of the invention is a method of the type mentioned in the two Px. "Contacts are produced from waste gases, will they normally vented to the atmosphere."

As a result, waste products can be used and at the same time Time to reduce pollution of the atmosphere.

Another object of the invention is a method of the above mentioned type, which is relatively simple and economical is feasible.

* ι "

Subject of the invention iat; a process for the simultaneous production of sodium sulfite (Na ^ SO,) and sodium carbonate ($ Ι & _ο Φ '> ζ) that is characterized in that qchvjefeläioxid euS an: exhaust gas, which contains sulfur dioxide and carbon dioxide, is combined , a mixture of sodium bisulfite and Natriumuulfit nthält ^ »at a pH We ^ t won 5.0 to 6.5 selectively absorbed and then carbon dioxide by-tO fc» i $ 1S5tiger · 'sodium hydroxide solution and the formation of Hatriumkarbonat absoriieit.

009 8 297139b

In the process according to the invention, the water is made from Process stage of the ΙίΒΐΓϊμιηΚαΓΐοηΒΐβΙίΙϊΓβηηΐΗ ^ from the in the The amount of water contained in sodium hydroxide solution through the aqueous solutions of sodium hydroxide and sodium carbonate in the sulfur dioxide absorption stage transferred, whereby the supply of heat for an evaporator to evaporate water is unnecessary.

The type, principle, details and advantage of the invention are further illustrated below with reference to the drawing and the examples explained. ■

The drawing shows a flow sheet and explains a management Removing _{form a device which is suitable for carrying out the method of the invention j for the continuous and simultaneous production of sodium sulfite and sodium carbonate from waste gases.

According to the drawing; an exhaust gas 1 containing sulfur dioxide and carbon dioxide is placed in a sulfur dioxide absorption column 5 introduced in the following way:

First you bring the gas with water or an absorption liquid by means of a spray 2 in contact to remove dust and adjust the temperature and humidity of the gas. f The gas is then left in a grid arrangement 3 in Countercurrent contact with water or an absorption liquid occur, which is set in flow and sprayed by a pump 4.

When the inlet temperature of the sulfur dioxide absorption column 5 or within the SUt tigungii temper a door kept for adiabatic cooling becomes, the adjustment of the extent of the V / asservcjr- « vaporization possible, and even if aqueous solutions of kaxrium hydroxide, a mixture of sodium hydroxide and sodium carbonate and sodium carbonate as an alkali to compensate for the gebildexe Sodium sulfite is added, there is no disturbance of the water. equilibrium, as the range of variation for the extent

009829/1396

BATH ORIGINAL

the evaporation of water is very large.

When the exhaust gas temperature is high, the water vapor saturation temperature is low, and the removal of harmful substances such as dust, · is not required; or if contamination by filtering the absorption liquid can be removed, the exhaust gas can directly into the Absorption column 5 are passed, with a large amount of water evaporated from the absorption liquid.

By using the alkaline liquid from sodium carbonate production In the case of sodium sulfite production, this additional possibility for water evaporation is the water the sodium carbonate process to maintain the water weight evaporates. This has no adverse effect on the Quality of the sodium sulphite formed.

It has been found that an aqueous solution mixture can be used as an absorption liquid for the selective absorption of sulfur dioxide from a gas mixture of sulfur dioxide and carbon dioxide. of sodium sulfite and sodium bisulfite with a composition corresponding to a pH value of 5.5 to 6.5 is most suitable. When the pH is higher than 6.5, carbon dioxide is absorbed, thereby lowering the purity of the sodium sulfite and at the same time increasing the amount of absorbent liquid and thereby increasing the cost of the process. On the other hand, when the pH is lower than> 5.5 _; The partial pressure of sulfur dioxide increases due to the sodium bisulphite content, so that the absorption rate decreases. ~

The pH value is kept within the above-indicated expedient range in which it is passed through liquid returned by means of a pump S and by means of a pump 12 and a,. Pump 18 in the carbon dioxide absorption step delivered alkaline liquid or by introducing 50 μl of sodium hydroxide solution

009829 / 139b "~

from a source 9 adjusts.

If the sodium bisulfite in the absorption liquid in one Crystallizer 10 neutralized by a thawing liquid Sodium sulphite is formed, and then anhydrous sodium sulfite precipitates if the temperature is kept above the transition temperature of 53 ° C, v / ground the so formed Separated crystals and removed in a separator 11.

The remaining filtrate is a liquid with a pH value of 11 to 15, which contains 10 to 22 ? /> Sodium sulfite and a small amount of free sodium hydroxide solution. The liquid is first fed to an absorption liquid reservoir 7 by means of pump 12, where it is mixed with the absorption liquid from the Absorptionskolonne5, and a part of erhaItenen _v mixture is zurückge- by pump 8 to the absorption column 5. leads to use it for sulfur dioxide absorption.

A part 6a of the exhaust gas 6, from which sulfur dioxide has been removed, is fed from the flue 6b through a branch line to a carbon dioxide absorption column 13, where carbon dioxide is absorbed by 10 to 20% sodium hydroxide solution and the formation of a nutritive carbonate solution. The concentration of the carbon dioxide absorption liquid is adjusted by regulating the flow rate of the liquid which, next by allowing it to flow through a first crystallizer 15 and a second crystallizer 17, is introduced into the carbon dioxide absorption column 15 will.

The absorption liquid from the carbon dioxide absorption bin 15 first flows into the first crystallizer 15 and a clear alkaline liquid of high concentration is added to this liquid by means of the pump 18 from the second crystallizer 17, whereupon sodium carbonate monohydrate (Na ₂ CO, 'H ₂ O) is obtained. The monohydrate of the first crystallizer 15 flows into the second crystallizer 17, where 9 50 $ ige from the source

0 * 0982971396

Sodium hydroxide is added. If the mixture obtained is kept at a temperature above the transition temperature, it is obtained one anhydrous sodium carbonate. As a result, crystals formed are separated in a separator 19 and removed.

While the amount of water that must be removed per ton of sodium carbonate is 925 kg, the exhaust gas is 6a that goes into the carbon dioxide absorption column 13 occurs, which is why there is no further possibility for water evaporation.

According to the invention, the sodium carbonate solution obtained is!

Pump 18, crystallizer 10, separator 11, pump 12, absorption liquid storage tank 7 and pump 8 are ^{fed to the sulfur dioxide »1} ;» - sorption column 5, where an additional possibility. j consists of water evaporation; the water evaporation is caused due to the unsaturated moisture state of the exhaust gas 1. When the sodium carbonate is mixed with the sulfur dioxide absorbing liquid, it is converted to sodium sulfite by sulfur dioxide and sodium bisulfite, which causes no trouble. Since in this way the V / ater, so> JCreate in 4 he aqueous sodium hydroxide solution, the j for producing the Natriumculfits and sodium carbonate is used, the 3ation by neutralization \ water formed to evaporate in the exhaust gas, a special heat source for evaporation dispensable} Whereby The system and operation will be considerably simplified and designed more appropriately. ■;

The efficiency; The process is low when using sodium sulfate

and sodium carbonate are produced independently of one another, f and will only be safe if the products are produced together if only sodium sulphite is produced Virdj ' is the rate of water evaporation extraordinary j high, which is why water must be supplied from outside; also -J the carbon dioxide contained in the exhaust gas cannot be used.

009829/1396

On the other hand, if only sodium carbonate is produced, the sulfur dioxide cannot be used, of course must be removed to ensure the purity of the sodium carbonate 1 iron st en; moreover, it becomes impossible to compensate for the amounts of water that are formed during "manufacture".

Therefore give the production of sodium sulfite and of sodium. carbonate an organic entanglement when carried out together. More precisely, because of the sulfur dioxide content of ordinary exhaust gas that is produced during the combustion of fuels, 0.1 to 0.2% and its carbon dioxide content. % of 10 to 20 $ the amount of sodium carbonate that can be made from this gas, always greater than the amount / sodium sulfate. For this reason, part of the exhaust gas has to be diverted through a second line in order to equalize the ratio of the two products. Since water evaporation occurs only in the sulfur dioxide absorption process, the production size is naturally limited by the water balance.

The following examples serve to further explain the ILi discovery.

Example 1. . I.

Exhaust gas was obtained at a temperature of 165 ° C from a plant of a thermal power plant, and 0.15 f> sulfur dioxide, 12 - / = carbon dioxide and 15 contained i> water was at a temperature of 165 ⁰ C and a flow rate of 200 nr (20 ⁰ G, Afv-v.-spherical pressure) per hour in a packed column geleixei ,, ir; which was absorbed by the use of 55 kg of an absorption liquid sulfur dioxide at a pH value of 6.5. All the exhaust gas used had previously been carefully removed from dust and harmful components by spraying and allowing it to escape through a grid-shaped water spray system.

0 0 9829/1396

At an inlet temperature of 00 ° C. and a temperature at the outlet of the sulfur dioxide absorption column 5 of 62 ° C., adiabatic cooling was carried out for a relative humidity of 95%. The rate of water evaporation was 2.73 kg per hour. At that time, the sulfur dioxide absorbing liquid contained 15 % sodium sulfite and 8% sodium bisulfite while not sodium carbonate ^; . was formed. A clear liquid of the following compositions was then added to this liquid from the second crystallizer in sodium carbonate, a process for separating sodium sulfite at a flow rate of 2.47 kg per hour: 41.5 % sodium hydroxide, m.p. 0.38 % sodium carbonate and 58.12 % V / water.

Thereafter, part of the exhaust gas exiting the sulfur dioxide absorption column 5 was discharged into the carbon dioxide absorption column 13 through the secondary pipe to cause absorption of carbon dioxide. The liquid obtained was then passed into the first crystallizer 15 and the above-mentioned clear liquid from the second crystallizer 17 was added to it in order to achieve a separation of 1. 135 kg of sodium carbonate mohohydrate (Na ₂ CO-Z · H ₂ O) , which was fed to the second crystallizer 17 in the form of a 42-6 slurry.

^ 3.8 kg 50 & Lge caustic soda was then added to this slurry added, and the sodium hydroxide concentration of the second Crystallizer 17 was held at 41.5%, leaving crystals formed by anhydrous sodium carbonate. These crystals were separated from the mother liquor in the separator 19, whereupon 1.145 kg of anhydrous sodium carbonate were obtained.

The obtained filtrate was passed through the second crystallizer passed into the first crystallizer, and the clear liquid, from the crystallizer, the 15 / S sodium hydroxide and about 10% Containing sodium carbonate, was returned to the absorption column 13, where it served as a carbon dioxide absorbing liquid. The data and results of the procedure are in table I summarized. . '

009829/1396

TABLE E I

■ Absorption
column | üü _{2,. :}
liibsorptions-
'column Exhaust gas inlet temperature (C) 80 61 .Exhaust gas outlet temperature ( ⁰ C) 62 60 Gas flow rate
(mVhour) *) 200 2.27 [- Water evaporation rate
speed (kg / hour) 2.73 I.
i
0 Absorption rate
(kg / hour) 0.81 5 0.477. Absorption { ^c / °) 95 \ 90 Rate of water increase
(kg / hour) 1, 67 1.06 Sodium sulfite or carbonate
Production speed
(kg / hour) 1, 602 1.145; Exhaust branch ratio 100 1.01

*) Volume reduced to 20 ⁰ O / 760 mmHg,

The rate of increase in water within the system was 1.67 + 1.06 = 2.73 kg / hour, and; the water evaporation gas speed in the sulfur dioxide siphon column 2.73 kg / hour. As a result, water formation and -Distance in equilibrium. .

00 98 29/1396

- ίο -

Example 2.

A gas of the same composition as that of the exhaust gas 1 in Example T was passed through a Cöttrell separator and a G-as "filter and then immediately introduced into a sulfur dioxide siphon column without cooling, after which the same treatment as described in Example 1 was carried out was,.. _;

The results of this procedure are summarized in Table II.

• j

009829 / $ 139

TABLE II

• SO ₂ -
Absorption
column
(Na ₂ SO ₅ ) Ou ₂ -
AiDsorption
column
(Wa ₂ CO ₃ ) Exhaust gas inlet temperature ■ ( ⁰ C) 165 61 Exhaust gas outlet temperature ( ⁰ O) 62 ^; 60 Gas flow rate
"(mVhour) *) 200 24.5 Water evaporation rate
speed (kg / hour) 14.53 0 Absorption rate
(kg / hour) 0.815 0.579 Absorption ( '/ ») 95 90
I. Speed of Wassorzunahme
(kg / hour) 1.67 I.
12.86 Sodium sulfite or carbonate
Production speed
(kg / hour) 1.602 13.95 Exhaust branch ratio 100. ' 12.3

*) Volume reduced to 2O ⁰ C / 760 mmHg Γ

. The rate of increase in water within the system was T.67 + 12.86 = 14.55 kg / hour, and the water evaporation in the sulfur dioxide absorption column was 14.53 kg / hour, so that water formation and removal were in equilibrium stood together.

009829/1396

Example 3.

The same gas as described in Example 1 was used, and the water flow rates in Spray 2 and the Grid apparatus 3 of the sulfur dioxide absorption column inlet was set so. that they do not adversely affect Product and equipment exercised whereupon the results summarized in Table III were obtained.

These results showed that the regulation of production speeds of sodium sulfite and sodium carbonate possible is.

009829/1396

T A]) E L L E I'll

SO ₂ -:
Absorption CO ₂ - *
Absorption column column (Na ₂ SO ₃ )
- - ■ "" (Na ₂ CO ₃ ) Exhaust gas inlet temperature ( ^υ Ο) -93 61 Exhaust gas outlet temperature ( ⁰ O) 62 60 Grass flow rate 200 6.47 Water evaporation rate
speed (kg / hour) 4.71 0 Absorption rate '
(kg / hour) ■ 0.815 1.37 Absorption. {f °) 75 90 Rate of water increase
(kg / 3 hours) "1.665 3.045 Sodium sulfite or carbonate
Production speed
(kg / hour) 1.60 ^: 3.30 Exhaust branch ratio 100 • 3.24

*) Volume reduced to 2O ⁰ C / 760 mmHg

009829/1396

Claims (3)

Claims MjVerfahren for the simultaneous production of sodium sulfite (Na ₂ SO *) and sodium carbonate (Na ₂ COj), characterized in that one contains sulfur dioxide from an exhaust gas, the sulfur dioxide uride carbon dioxide with an absorption liquid which contains a mixture of sodium sulfite and sodium bisulfite, at a pH value of 5.0 - 6.5 is selectively absorbed and then carbon dioxide by means of 10 to 15 % sodium hydroxide solution. and the BMung. absorbed by sodium carbonate. 2. The method according to claim 1, characterized in that g e k e η η ζ e i c h η e t that one while avoiding the supply of heat to evaporate "-water" the water contained in aqueous sodium hydroxide solution the sodium carbonate separation process using aqueous solutions of sodium hydroxide and sodium carbonate in the 'sulfur dioxide absorption process convicted. 3. sodium sulfite or. Sodium carbonate produced by the process according to claim T or 2. 0 0 9 8 29/1396