FIELD OF THE INVENTION

[0001] The present invention relates to the production of soda ash (sodium carbonate) lye and & utilization of this sodium carbonate or soda ash lye with sodium sulphite for the treatment of brine in chlor-alkali industry.

BACKGROUND OF THE INVENTION

[0002] Chloralkali industry produces caustic soda, chlorine, Hydrogen through membrane electrolysis process. The chloralkali process is an industrial process for the electrolysis of sodium chloride solution (brine). The concentration of caustic soda lye or sodium hydroxide will be in the range of 31-33%.

[0003] For producing caustic soda by membrane electrolysis the major raw material required are power and industrial grade salt.

[0004] Industrial grade salt is dissolved in water and treated for the removal of impurities such as calcium and magnesium. Soda ash or sodium carbonate and caustic soda or sodium hydroxide is used for the removal of calcium and magnesium impurities in the brine respectively. The brine is further treated through ion-exchange resin columns to get ultrapure brine consisting of 290 - 305 gpl of sodium chloride.

The purified brine is fed to the electrolysers for the production of caustic soda, chlorine, and hydrogen.

[0005] After the electrolysis process, depleted brine is produced containing low sodium chloride i.e, 190 - 220 gpl along with free and combined chlorine.

[0006] The free chlorine from the depleted brine is neutralized with sodium sulphite and recycled through the saturator, where raw salt is added to build the concentration of sodium chloride to 290 - 305 gpl of sodium chloride.

[0007] The 31 - 33 % caustic soda lye produced from the electrolyser is concentrated in a concentration plant to 47 - 49 %. Concentration of caustic soda lye takes place in evaporators heated by thermic fluid heater/boiler burning hydrogen + furnace oil as fuel.

[0008] The flue gas coming out of the TFH/boiler consists of carbondioxide to the tune 0 - 12 % & sulphur dioxide to the tune of 2000 - 4000 ppm.

[0009] The proposed method aids in the production of soda ash lye from waste gases/flue gases emanating from hydrogen or dual (hydrogen, F.oil or LSHS) fired source in the chloro alkali process which would eliminate the need to purchase soda ash by the chloro alkali industry. Soda ash manufactured by the conventional process contains traces of ammonia in the product. If this soda ash is used there is a chance of ammonia entering the electrolyser and can lead to the formation of nitrogen trichloride which is an explosive mixture.

[00010] PRIOR ART

[00011] a) EP1866460B1 : The invention relates to an integrated process for jointly Obtaining a chlorine derivative and sodium carbonate crystals. It relates more particularly to an integrated process for jointly obtaining a chlorine derivative and sodium carbonate crystals that is designed to reduce the emissions of carbon dioxide into the environment.

[00012] b) US20090260993A1 : Method for producing sodium carbonate, according to which an aqueous sodium chloride solution is electrolyzed in a membrane-type cell from which an aqueous sodium hydroxide solution is collected, and carbonated by direct contact with carbon dioxide to form a slurry of crystals of anhydrous sodium carbonate .

[00013] c) WO2006094982A1 : Method for producing sodium carbonate, according to which an aqueous sodium chloride solution (5) is electrolyzed in a membrane-type cell (1) from which an aqueous sodium hydroxide solution (9) is collected, and carbonated by direct contact with carbon dioxide (15) to form a slurry of crystals of a sodium carbonate (16), and the slurry or its mother liquor is evaporated (3) to collect sodium carbonate (18).

[00014] d) CN201807288U : Boiler flue gas desulfurization treatment device.

[00015] e) US5759345 : To recover the sodium-sulphur compounds following sodium- based pulp processing, e.g. the ASAM process or basic or acidic sodium sulphite processes, the waste liquor is burnt in a lye burning vat (1) with liquid slag extraction and the exhaust gases are subjected to multi-stage purification with dry fly-ash recovery and the gaseous sulphur compounds are also separated in a multi-stage washing process. The water-soluble components of the fly-ash are taken to the waste liquor to be burnt and thus the sulphur to be recovered in the slag is increased. The slag is dissolved in water and the dissolved sodium compounds are converted by multi-stage carbonisation with a part of the purified flue gas into sodium bicarbonate and H2 S. The hfe S is burnt and finally converted into sodium sulphite so that the desired lye for pulping cellulose can be made up from sodium sulphite and carbonate.

SUMMARY OF THE INVENTION

[00016] Accordingly, it is an object of the present invention to provide a method for the production of sodium carbonate lye with sodium sulphite from flue gas coming out from a boiler of thermic fluid heater burning hydrogen and furnace oil/LSHS as the fuel and utilization of this sodium carbonate lye with sodium sulphite for the treatment of brine in a chloralkali industry.

[00017] It is another object of the present invention to provide a method for the production of sodium carbonate lye which would eliminate the need to purchase soda ash by the chloralkali industry.

[00018] It is yet another object of the present invention to provide a method for the production of sodium carbonate lye free of ammonia.

[00019] It is another object of the present invention to provide a method for the production of sodium carbonate lye having the composition of 50-380 gpl of sodium carbonate, 15-40 gpl of sodium hydroxide and 2000-7000 ppm of sodium sulphite.

[00020] It is another object of the present invention to provide a method for the production of sodium carbonate lye for the treatment of calcium impurities in brine in the chloroalkali industry by precipitating it as calcium carbonate.

[00021] It is another object of the present invention to provide a method for the production of sodium carbonate lye with sodium sulphite for neutralization of pH and chlorine present in brine in chloralkali industry.

[00022] It is another object of the present invention to provide a method for the production of sodium carbonate lye by utilizing the waste gases emanating from hydrogen or dual (hydrogen, F.oil or LSHS fired source from the caustic concentration plant in chloralkali industry.

[00023] It is another object of the present invention to provide a method for the absorption of carbon dioxide and oxides of sulphur from a flue gas produced by burning both hydrogen and furnace oil/LSHS as a fuel.

[00024] It is another object of the present invention to provide a method for the production of sodium carbonate lye and using the same for removal of calcium impurities in brine which would not introduce any ammonia as would otherwise come from the use of commercially available sodium carbonate or soda ash. Ammonia in brine after the electrolysis process would lead to the formation of nitrogen trichloride which is an explosive mixture formed in the chlorine stream in a chloralkali industry.

[00025] It is yet another object of the present invention to reduce the emission of carbon dioxide into the atmosphere which will contribute to the reduction of carbon footprint in a energy and water intensive chloralkali industry.

[00026] It is another object of the present invention to provide a method for the production of sodium carbonate or soda ash for captive consumption in a chloralkali industry.

[00027] It is another object of the present invention to provide a method for the production of sodium sulphite and use of the same for captive consumption in a chloralkali industry.

[00028] It is another object of the present invention to provide a method which would totally or reduce the formation of nitrogen trichloride in the chlorine stream making the chloralkali process more safer.

[00029] It is another object of the present invention to provide a method for the production of a stable sodium carbonate lye with excess alkali and reduction of the formation of sodium bicarbonate by maintaining the hydroxide content.

[00030] It is another object of the present invention to provide a method which produces sodium carbonate lye with sodium sulphite which would ensure that the ion exchange resins in the brine treatment section are not attacked with chlorine and the life of the ion-exchange resins are increased substantially.

[00031] It is another object of the present invention to provide a method which would reduce or eliminate the need to purchase brine treatment chemicals such as soda ash and sodium sulphite in a chloralkali industry.

[00032] In accordance with one aspect, the present invention, which achieves the objectives, relates to a method for the production of sodium carbonate lye along with sodium sulphite as a by-product in chloro-alkali industry comprising cooling the emitted flue gas comprising carbondioxide, sulphur dioxide and water vapour in a heat exchanger preferably SS316 cooler wherein said water vapour in the flue gas condenses upon cooling;

passing said flue gas through a plurality of fiber reinforced plastic (FRP) towers; providing a plurality of circulation tanks; providing a means for transferring solution from one circulation tank to the other; providing a means for distributing the solution from each circulation tank to its fiber reinforced plastic (FRP) tower; circulating water in at least one fiber reinforced plastic (FRP) tower for absorption of oxides of sulphur and suspended particulates and formation of acidic solution with sodium sulphite which can be utilized for dechlorination of brine or for neutralization of streams in chloralkali industry; circulating sodium hydroxide solution in at least one FRP tower for absorption of carbon dioxide and formation of sodium carbonate; circulating caustic sodium hydroxide solution comprising a mixture of sodium hydroxide and sodium carbonate in at least one fiber reinforced plastic (FRP) tower for absorption of carbon dioxide and oxides of sulphur wherein oxides of sulphur gets absorbed to form sodium sulphite and sodium hydroxide solution gets converted to sodium carbonate lye.

[00033] In accordance with one aspect, the present invention, which achieves the objectives, relates to a A method for the production of sodium carbonate lye along with sodium sulphite as a by-product in chloro-alkali industry comprising cooling the emitted flue gas comprising carbondioxide, sulphur dioxide and water vapour in a heat exchanger preferably SS316 cooler wherein said water vapour in the flue gas
condenses upon cooling and removed; passing the cooled flue gas through a first fiber reinforced plastic (FRP) tower; providing a first circulation tank for circulation of water in said first fiber reinforced plastic (FRP) tower; circulating water from said first circulation tank in said first fiber reinforced plastic (FRP) tower provided with packings for absorption of oxides of sulphur and suspended particulates and formation of acidic solution with sodium sulphite which can be utilized for dechlorination of brine or for neutralization of streams in chloralkali industry; passing said flue gas after absorption of oxides of sulphur and suspended particulates to a second fiber reinforced plastic (FRP) tower; providing a second circulation tank for circulation in said second fiber reinforced plastic (FRP) tower; circulating sodium hydroxide solution from said second circulation tank to said second FRP tower with packings for absorption of carbon dioxide and formation of sodium carbonate; passing the flue gas comprising traces of carbon dioxide from said second FRP tower to a third FRP tower; providing a third circulation tank for circulation in third fiber reinforced plastic (FRP) tower; circulating a dilute sodium hydroxide solution from said third circulation tank to said third FRP tower for further absorption of carbon dioxide and formation of sodium carbonate lye; transferring said caustic sodium hydroxide solution comprising a mixture of sodium hydroxide and sodium carbonate from the third circulation tank to the second circulation tank after completion of each batch in second circulation tank wherein the mixture of sodium hydroxide and sodium
carbonate in said second FRP tower further absorbs carbon dioxide in second tower; whereby sodium sulphite acidic solution produced from said first FRP tower is utilized for neutralization of chlorine and ph of brine; whereby soda ash lye with sodium sulphite produced is utilized for treatment of brine for removal of calcium impurities and neutralization of chlorine.

BRIEF DESCRIPTION OF THE DRAWINGS

[00034] Figure 1 shows a schematic diagram of a system, in accordance with an exemplary embodiment of the present invention;

REFERENCE NUMERALS IN DRAWINGS

DETAILED DESCRIPTION OF THE INVENTION :

[00035] In the caustic concentration plant, the 31 - 33 % caustic soda or sodium hydroxide lye is heated by thermic fluid heater using hydrogen + furnace oil/LSHS as fuel.

[00036] Fig:1 schematically shows an installation for implementation of the first embodiment of the method according to the invention.

[00037] The flue gas coming out of the heater (1) has carbondioxide, sulphur dioxide and water vapour. The concentration of the gases in the flue gas will be as follows :

a) Carbondioxide : 0 -12 %
b) Sulphur dioxide: 2000 - 4000 ppm

[00038] The flue gas (1) from the TFH/Boiler will be at a temperature of 250 285 deg C. The flue gas is cooled in a SS 316 cooler (5), by cooling water.

[00039] The heat exchanger for cooling the flue gas is a shell and tube type made of SS 316 (5). The exchanger has a surface area sufficient to cool the flue gas from 250 - 285 deg C to 35 - 60 deg C. It is a two pass heat exchanger with a surface area ranging between 10-50 sq.m. The gases are sucked through all the towers by means of a blower of capacity 3000 -4000 cu.m/hr @ 50 -700 mmwc.

[00040] The water vapour in the flue gas will condense upon cooling and are removed from the stream through a seal pot. The cooled gas is then passed through the first FRP tower (16). A temperature indicator (8) is provided for monitoring the temperature of the flue gas .

[00041] The first tower is made of FRP (16) with Derakane 470-300 resins capable of withstanding a temperature upto 120 deg C. Water is circulated in this tower for absorption of oxides of sulphur and suspended particulates. The FRP tower is provided with packings for effective contact of the gas with the liquid to facilitate high efficiency of absorption. The packing is of 2" Intalox Certamic saddles with a packing factor of 40. The height of the FRP tower will be 3 - 6 mts and the packing height will be 2 - 5 mts.

[00042] Water will be circulated from a circulation tank also made of FRP (18). The circulation tank is made of FRP with Derakane resin - 411, which can withstand a temperature upto 100 deg C. Circulation is effected through a poly propylene pump (17). The water enters the tower from top through a distributor and is discharged (14) from the bottom into the circulating tank (18). The discharge pipe is dipped into the water in circulation tank (18) to maintain the vacuum for absorption of the flue gas. A draught gauge (9) is provided at the inlet flue gas line (3) & (46) for monitoring the negative pressure or draught.

[00043] Rotameter of capacity 2-20 cu.m/hr (10), 2.5 - 25 cu.m/hr (23, 34), pressure guage (7,22,33) are provided for monitoring the flow and the pressure of the circulating fluid in all the three towers.

[00044] This is a method in the invention wherein, the first tower (16) absorbs oxides of sulphur and the suspended particulates forming acidic solution with sodium sulphite. The pH will be between 2-6, with a sodium sulphite concentration ranging between 50 - 1000 ppm. After attaining a pH 2 - 3 , the whole of the batch is transferred to a storage tank from where it will be utilized for dechlorination of brine or for the neutralization of streams in the chloralkali process. The temperature of the charge is between 40 - 55 deg C. The operating conditions of the working examples has been described and recorded in the following table-l, where the figures in parenthesis correspond to the reference numerals shown in the drawing.

[00045] TABLE : I
cu.m = cubic meter ppm = Parts per million gpl = grams/litre

[00046] This is a method by which, the solution obtained from the first tower (18) will be used for the neutralization of chlorine in the brine or dechlorination of brine streams in the chloralkali process.

[00047] The flue gas (13) from the first tower (16) after absorption of the oxides of sulphur and other suspended particles is taken to the second tower (27). The second tower is made of FRP with Derakane 411-350 resins capable of withstanding a temperature up to 120 deg C. Dilute caustic soda or sodium hydroxide solution circulated s through a stainless steel pump (25) to the tower for absorption of Carbondioxide for the formation o? sodium carbonate or soda ash. The FRP tower is provided with packings for effective contact of the gas with the liquid to facilitate higher efficiency of absorption. The packing is of 2" plastic pall rings with a packing factor of 26. The height of the FRP tower will be 3 - 6 mts and the packing height will be 2 - 5 mts.

[00048] The whole system operates on a batch mode. The caustic soda solution from the third tower (44) circulation tank (38) is transferred to the circulation Tank (29) after completion of each batch in circulation tank (29). The caustic soda solution from circulation (38) will be a mixture of caustic soda + sodium carbonate as some absorption would have taken place during the process in the third tower (44).

[00049] TABLE : II

[00050] A conductivity meter is provided in stream (20) for monitoring the progress of the reaction. The conductivity of the caustic soda + Soda ash solution would be ranging from 350 - 400 milli mhos at the time of transfer of the solution and will reduce to 120 - 150 milli mhos at the time of completion of the reaction.

[00051] The mixture of caustic soda solution and sodium carbonate in the circulation tank (29) will further absorb the carbondioxide in the second tower and attain a concentration of 50 - 380 gpl with an excess sodium hydroxide of 15 - 40 gpl. The temperature of the mixture is maintained between 40 - 60 deg C. During the process of absorption of carbondioxide, oxides of sulphur also get absorbed in the caustic forming sodium sulphite. The operating conditions of the working examples has been described and recorded in the following table-ll, where the figures in parenthesis correspond to the reference numerals shown in the drawing.

[00052] From the average results the mass balance of the second tower or the product is as follows:

a) Soda ash or sodium carbonate 5750 X 337 gpl = 1932 kgs
b) Sodium hydroxide or caustic soda 5750 X 28 gpl = 161 kgs
c) Sodium sulphite 5750 X 5.4 gpl = 31 kgs
d) Water 5750 X 1.2948 - 2124 = 5321 kgs

[00053] In a preferred embodiment of this method of invention wherein the caustic soda solution is converted to soda ash lye with 250 - 380 gpl of sodium carbonate and 15 - 40 gpl of sodium hydroxide and 2000 - 7000 pprn of sodium sulphite. This mixture has all the suitable elements for the removal of impurities in brine in a chloralkali industry.

[00054] In another embodiment of the invention, the soda ash lye from circulation tank (29) comprising of above mentioned components in [0013] will be used for the treatment of brine with respect to calcium impurities. Traces of chlorine if present in the brine will be neutralized by the sodium sulphite present in this mixture. By this method the excess sodium sulphite is maintained in the brine stream which would increase the life of the ion-exchange resin downstream.

[00055] This method according to the invention will be producing soda ash lye (29) by which would eliminate the purchase of soda ash by the chloralkali industry. Soda ash manufactured by the conventional process contains traces of ammonia in the product. If this soda ash is used there is a chance of ammonia entering the electrolyser and can lead to the formation of nitrogen trichloride which is an explosive mixture.

[00056] The stream (28) from the second tower (27) with traces of carbondioxide is put into the third tower (44) where the fresh charge of caustic soda solution is taken in circulation tank (38) after completion of each batch. Water free from hardness is added to the circulation tank (38)
for dilution. The construction of the third tower is same as second tower.

The caustic soda concentration in the circulation tank(38) will be 150 - 400 gpl @ temperature of 40 - 56 deg C. The caustic soda solution is circulated through the tower by means of a stainless steel pump (36)
through a circulation tank (38). The carbondioxide in the flue gas (31) will be completely stripped off in this tower before the flue gas (31) goes into the suction of the centrifugal blower. The charge in the circulation tank (38) will be transferred to the circulation tank (29) after transferring the product from the circulation tank (29). The product is transferred to the process (39) through a SS 316 pump (42). The operating conditions of the working examples has been described and recorded in the following table-
Ill, where the figures in parenthesis correspond to the reference numerals shown in the drawing.

[00057] TABLE: III


[00058] The carbondioxide and the oxides of sulphur get absorbed in the three towers. The flue gas that exit the third tower has traces of carbondioxide , water vapour and other components of atmospheric air
before being finally discharged through the stack through the centrifugal blower (48), (50).

[00059] The suction pressure or draught is maintained in the tower by adjusting the frequency of the blower motors. The negative pressure or draught is maintained between 50 - 650 mmwc.

[00060] The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included in so far as they come within the scope of the invention as claimed or the equivalents thereof.
Other modifications will be apparent to those skilled in the art and, therefore, the invention is defined in the claims.

We claim:

1. A method for the production of sodium carbonate lye along with sodium sulphite as a by-product in chloro-alkali industry comprising:

a) cooling the emitted flue gas comprising carbondioxide, sulphur dioxide and water vapour in a heat exchanger preferably SS316 cooler wherein said water vapour in the flue gas condenses upon cooling;

b) passing said flue gas through a plurality of fiber reinforced plastic (FRP) towers;

c) providing a plurality of circulation tanks;

d) providing a means for transferring solution from one circulation tank to the other;

e) providing a means for distributing the solution from each circulation tank to its fiber reinforced plastic (FRP) tower;

f) circulating water in at least one fiber reinforced plastic (FRP) tower for absorption of oxides of sulphur and suspended particulates and formation of acidic solution with sodium sulphite which can be utilized for dechlorination of brine or for neutralization of streams in chloralkali industry;

g) circulating sodium hydroxide solution in at least one FRP tower for absorption of carbon dioxide and formation of sodium carbonate;

h) circulating caustic sodium hydroxide solution comprising a mixture of sodium hydroxide and sodium carbonate obtained in step (g) in at least one fiber reinforced plastic (FRP) tower for absorption of carbon
dioxide and oxides of sulphur wherein oxides of sulphur gets absorbed to form sodium sulphite and sodium hydroxide solution gets converted to sodium carbonate lye.

2. The method of claim 1 further comprising providing a temperature indicator for monitoring the temperature of said flue gas.

3. The method of claim 1 further comprising providing packings in said plurality of fiber reinforced plastic (FRP) towers for effective contact of said flue gas and facilitating high efficiency of absorption.

4. The method of claim 1 further comprising providing a rotameter for monitoring the flow and
pressure of circulating fluid in the plurality of fiber reinforced plastic (FRP) towers.

5. The method of claim 1 further comprising providing a suction pressure or draught between 50-650 mmwc in said plurality of fiber reinforced plastic (FRP) towers.

6. A method for the production of sodium carbonate lye along with sodium sulphite as a by-product in chloro-alkali industry comprising:

a) cooling the emitted flue gas comprising carbondioxide, sulphur dioxide and water vapour in a heat exchanger preferably SS316 cooler wherein said water vapour in the flue gas condenses upon cooling and removed;

b) passing the cooled flue gas through a first fiber reinforced plastic (FRP) tower;

c) providing a first circulation tank for circulation of water in said first fiber reinforced plastic (FRP) tower;

d) circulating water from said first circulation tank in said first fiber reinforced plastic (FRP) tower provided with packings for absorption of oxides of sulphur and suspended particulates and formation of acidic solution with sodium sulphite which can be utilized for dechlorination of brine or for neutralization of streams in chloralkali industry;

e) passing said flue gas after absorption of oxides of sulphur and suspended particulates to a second fiber reinforced plastic (FRP) tower;

f) providing a second circulation tank for circulation in said second fiber reinforced plastic (FRP) tower;

g) circulating sodium hydroxide solution from said second circulation tank to said second FRP tower with packings for absorption of carbon dioxide and formation of sodium carbonate;

h) passing the flue gas comprising traces of carbon dioxide from said second FRP tower to a third FRP tower; i) providing a third circulation tank for circulation in third fiber reinforced plastic (FRP) tower;

j) circulating a dilute sodium hydroxide solution from said third circulation tank to said third FRP tower for further absorption of carbon dioxide and formation of sodium carbonate lye;

k) transferring said caustic sodium hydroxide solution comprising a mixture of sodium hydroxide and sodium carbonate from the third circulation tank to the second circulation tank after completion of each batch in second circulation tank wherein the mixture of sodium hydroxide and sodium carbonate in said second FRP tower further absorbs carbon dioxide in second tower; whereby sodium sulphite acidic solution produced from said first FRP tower is utilized for neutralization of chlorine and ph of brine; whereby soda ash lye with sodium sulphite produced is utilized for treatment of brine for removal of calcium impurities and neutralization of chlorine.

7. The method of claim 6 further comprising providing a temperature indicator for monitoring the temperature of said flue gas.

8. The method of claim 6 further comprising providing a rotameter for monitoring the flow and pressure of circulating fluid in the plurality of fiber reinforced plastic (FRP) towers.

9. The method of claim 6 further comprising providing a suction pressure or draught between 50-650 mmwc in said plurality of fiber reinforced plastic (FRP) towers.