United States Patent (19) | 1 || 3,975,503 Hauschild et al. |45| Aug. 17, 1976

(54) METHOD FOR PRODUCING ALKAL 3.25.49.46 6/1966 Hass et al...... 423f42 3644()89 2/ 1972 Minz et al...... 423f4 CARBONATE 3,751.56() 8/1973 Neumann...... 42318.9 (75) Inventors: Ulrich Hauschild; Reimar Musall, 3,7739()2 11/1973 Neumann...... 42.3/421 both of Hannovcr; Hans-Jirgen 387 (),784 3/1975 Sueman...... 4231431 Schröder, Pattensen, Hannover, all of Germany FOREIGN PATENTS OR APPLICATIONS 73,794 4/1968 Belgium...... 423/42

Assignee: Kali-Chemie Aktiengesellschaft, 229 3/1971 Japan...... 423f421 Hannover, Germany 2) 43 6/197l Japan...... 4231421 89569() 5/1962 United Kingdom...... 423/42 Filcd: Dec. 13, 1974 Appl. No.: 532,365 Primary Examiner-Oscar R. Vertiz Assistant Examiner-Gary P. Straub Related U.S. Application Data Attorney, Agent, or Firn-Spencer & Kaye 63 Continuation of Ser. No. 436,719, Jan. 25, 1974, abandoned, which is a continuation of Ser. No. 204,058, Dec. 2, 1971, abandoned. 57) ABSTRACT A method for producing alkali carbonate crystals, in 3() Foreign Application Priority Data cluding adding to an alkali carbonate and alkali hy Dec. 8, 97 () Germany...... 206()287 droxide solution stream a 10 to 75 weight-% alkali hy Aug. 27, 197 Germany...... 243 ()()8 droxide solution, charging the resulting mixture into a CO-containing gas whose temperature is from 150 to 52) U.S. Cl...... 423/421; 423/189 700°C, collecting mixture remaining as liquid from the 51 int. Cl...... C01D 7/07 gas at the end of a residence time of mixture in gas of 58 Field of Search...... 423/89, 421 0.1 to 10 seconds, separating alkali carbonate crystals from the collected mixture, and feeding the collected 56) References Cited mixture, following the separating, back in the alkali UNITED STATES PATENTS carbonate and alkali hydroxide solution stream for an 3, ()343 9/1963 Blumenthai...... 423.1421 other adding of alkali hydroxide solution. 3.2()2,477 8, 1965 Leffler, Jr. et al...... 423142 3.22.848 ()/ 1965 Tasiaux...... 423.1421 14 Claims, 1 Drawing Figure C02 NOH CONTAINING GAS SOLUTION

20

REACTION CHAMBER

EXHAUST H20

CRYSTAL POOR STREAM

COLLECTING CONTAINER

SOLUTION OF NO2C03 -- No OH

Na2CO3.H20, WET

FLTRATE 2 DRYER COMBINING WESSEL Na2CO3 U.S. Patent Aug. 17, 1976 3,975,503

5 C02 NOOH CONTAINING GAS SOLUTION

-b 3 4. 45 H20 2 3 REACTION CHAMBER 7 EXHAUST -- H20 4. CRYSTAL POOR STREAM

COLLECTING CONTAINER .

SOLUTION OF Na2CO3

Nabh CENTRFUGE 3 ity CRYSTAL-RICH STREAM Na2CO3.H20, WET FILTRATE S. DRYER 2 COMBINING G WESSEL Na2C03 3,975,503 1. 2 tion in Winnacker-Kiichler, CHEMISCHE TECH METHOD FOR PRODUCING ALKAL NOLOGIE, 3rd Edition (1970), Volume 1, page 222.) CARBONATE that the produced highly soluble potassium carbonate has been formed first dissolved in solution. The solu CROSS REFERENCE TO RELATED APPLICATION tion has had to be concentrated by evaporation. During This application is a continuation of copending appli cooling of the concentrated solution, hydrated potash cation Ser. No. 436,719, filed Jan. 25, 1974, which of formula KCO. 1% HO crystallizes. This is filtered itself is a continuation of application Ser. No. 204,058, and dried at 120°C to a commercial product containing filed Dec. 2, 1971, both now abandoned. 84 weight-% K2CO3. A product substantially free of 10 water of hydration and free of absorbed water is only BACKGROUND OF THE INVENTION obtained by drying at 250° to 350°C. The filtrate, con The present invention relates to a method for pro taining about 50 weight-% KCOa, is mixed with fresh ducing alkali carbonate from alkali hydroxide and car potassium lye and returned to the carbonating stage. bon dioxide. The previous practice for potassium carbonate pro The production of alkali carbonate from lye by reac 15 duction has not been satisfactory because, above all, tion with carbon dioxide or, more generally, carbon the solution concentrating and crystallizing of carbon dioxide-containing gases has won much interest in the ate require considerable expense for equipment. Be last two years. Due to the increasing need for chlorine cause of the strong temperature dependence of the in industry, increasing quantities of lye are becoming KCO-solubility, there have been difficulties for con available through the electrolysis of alkali choride solu 20 tinuous operation. Crystal precipitation often has led to tions. At least for a portion of this lye, there is no imme the plugging-up of pipe lines, valves, and other equip diate demand. met, The known methods for carbonating lyes have seri ous drawbacks. SUMMARY OF THE INVENTION A direct carbonating of the usual 50 weight-% so 25 An object of the invention, therefore, is to provide a dium hydroxide lye leads, for example, to encrustations method for the carbonating of both sodium and potas and crystal deposits at undesired spots in the apparatus sium lyes which, as compared with the methods previ during the conversion using carbon dioxide, and espe ously contemplated, is technically simple and which cially during the needed concentrating of the resulting operates economically. soda solution, by evaporation, after removal of the 30 This as well as other objects which will become ap precipitate. Moreover, the crystals of alkali carbonate parent in the discussion that follows are achieved, ac often trap within themselves impurities in the form of cording to the present invention, by a method for pro sodium hydroxide or the small metal particles which ducing alkali carbonate crystals, including adding to an are the result of wear. Even the process disclosed in alkali carbonate and alkali hydroxide solution stream a German Published Application (Auslegeschrift) No. 35 10 to 75 weight-% alkali hydroxide solution, charging 1,138,748, which operates in two stages, cannot elimi the resulting mixture into a CO2-containing gas whose nate these disadvantages. temperature is from 150 to 700°C, collecting mixture Evaporation of the excess water entering a process remaining as liquid from the gas at the end of a resi via the sodium lye may be carried out right in the car dence time of mixture in gas of 0.1 to 10 seconds, bonating stage, so that a special evaporating for con 40 separating alkali carbonate crystals from the collected centrating of the above-mentioned soda solution can be mixture, and feeding the collected mixture, following eliminated. Since the released heat of neutralization is the separating, back in the alkali carbonate and alkali not large enough to supply the heat needed to evapo hydroxide solution stream for another adding of alkali rate the requisite amount of water, the necessary en hydroxide solution. ergy must be supplied either before the reaction, for 45 example by strong heating of the high-percentage so BRIEF DESCRIPTION OF THE DRAWING dium lye according to German Laid-Open Application The sole FIGURE is a preferred flow diagram of the (Offenlegungsschrift) No. 1,567,921, or within the method according to the present invention. reactor such as in German Laid-Open Application (Of fenlegungsschrift). No. 1,811, 168 using steam coils. 50 DESCRIPTION OF THE PREFERRED The solids are continuously removed from the hot sus EMBODIMENTS pension, while the filtrate, which mainly contains soda, The present inventors have discovered a method for is fed back to the reactor. The carbon dioxide or car producing sodium carbonate, preferably in its monohy bon dioxide-containing gas is bubbled from below drate form, by reacting sodium lye with carbon dioxide through the reactor, which may for example be a car 55 or, more generally, carbon-dioxide-containing gases. bonating tower or container equipped with a stirring This method substantially avoids the difficulties of the device. previously contemplated methods as above-described. The above-described processes have the disadvan The method of the invention is characterized by the tages that they work with a relatively large liquid vol feeding of a 10 to 75 weight-% (i.e. grams NaOH per ume and require a not insignificant expense for electri 60 100 grams solution) aqueous sodium hydroxide solu cal energy. Additionally, should there be a failure tion to a continuously circulated aqueous solution of somewhere in the system to cause the liquid to become sodium carbonate and sodium hydroxide, by the charg still, then a critical situation immediately develops be ing of the resulting mixture into hot (150 to 700°C) cause crystals begin to settle in the carbonating con CO2, or CO-containing gas, as finely divided droplets tainer, pipe lines, pumps, etc., to cause a difficultly 65 of the resulting mixture, by collecting that portion of removable plugging-up of the system. the resulting mixture still remaining as liquid from the In the case of producing potassium carbonate, the gas after a residence time of the resulting mixture in the practice has been such (See, for example, the descrip gas of 0.1 to 10 seconds, by separating the formed, 3,975,503 3 4 easily filterable carbonate crystals from the collected burning processes, there is an excess of CO2 available, mixture, and by returning the collected mixture as the so that theoretically the entire NaOH charged to the continuously circulating aqueous solution of sodium reaction chamber could be transformed into sodium carbonate and sodium hydroxide. carbonate. According to the present invention, it is not According to a preferred embodiment of the method necessary and even not desired that the entire sodium of the invention, the collected liquid-phase mixture is lye charged to the reaction chamber be carbonated; the split into two streams and the formed crystals of sodium portion of the charged lye that is carbonated should be carbonate are removed by filtration from only one of equal to that combined with the sodium carbonate and the streams with the filtrate and the other stream then sodium hydroxide solution in the step of adding. There being joined and fed back as the circulating aqueous 10 arises an equilibrium between the degree of carbon solution of sodium carbonate and sodium hydroxide, to ation in the sodium carbonate and sodium hydroxide the point where the sodium hydroxide is added. solution circuit and the CO2 content of the gas in the In contrast to the known processes working in aque reaction chamber, provided that the other parameters ous medium, gas is not introduced in the present inven such as temperature, gas and liquid quantities per unit tion into liquid and distributed there. Rather, the oppo 15 time, etc., are kept constant. If the CO, content of the site is done in that a liquid, the resulting mixture, is gas changes, then the composition of the circuit solu sprayed into a gas. The hot gas is substantially instanta tion is automatically changed. That is, with increasing neously cooled to a temperature between 80 and CO, content, the equilibrium quantity of carbonate in 120°C, while a portion of the water of the warm (be the circuit solution increases, and vice versa. On the tween 75 and 115°C) mixture is transformed to gas in 20 other hand, the degree of carbonation can be held at a the exhaust from the reaction chamber. definite value, if, for different CO contents, for exam The adding of the sodium hydroxide solution, whose ple the residence time of the liquid in the gas or the size NaOH concentration is preferably between 45 and 55 of the liquid droplets is changed correspondingly. weight-%, is controlled in such a manner that the extra From the above considerations, it is evident that the water which it adds to the circuit is immediately evapo 25 method of the present invention is easily adaptable and rated during the charging into the reaction chamber, can rapidly be adjusted to changing conditions. Thus, due to the heat contained in the hot gas and due also to for example, the method of the present invention is the heat of neutralization, so that the amount of the suitable for operation under pressures deviating posi alkali carbonate and alkali hydroxide solution eventu tively or negatively from atmospheric pressure. In such ally circulated back to the step of adding remains con 30 operation, it must be considered that the absorption of stant. Playing a role here are the temperature of the CO, does not momentarily come to an end. Rate of gas, the concentration of CO, in the gas, and the quan absorption depends on a number of factors. The lower tity of the gas, for the higher each of these is, the stron the partial pressure of the CO2, i.e. the lower CO, con ger the evaporation of water. Also the residence times centration, the slower is the carbonating reaction. In of the charged mixture in the gas and of the gas in the 35 creasing temperature likewise slows down the carbon reaction chamber and the degree with which the mix ating. The more sodium lye per unit volume to come in ture is divided in the gas have an effect; with smaller contact with the gas and the higher the NaOH concen droplets and increasing residence times, there is a bet tration, the faster and the greater is the CO2 absorption. ter utilization of the available heat, and the carbonating While pure CO, especially at higher pressure, reacts of the sodium lye improves. 40 relatively quickly with the charged mixture, operation In place of pure carbon dioxide, gas coming from a with exhaust gas from burning processes brings the burning process, containing about 10 to 20 volume-% difficulty that with a fall in the CO, percentage of the CO, can be used. It depends on the end use of the gas there is a decrease in the NaOH content in the resulting soda as to what extent a cleaning of these charged mixture, so that the conditions for a quantita gases of damaging impurities (dust particles or gases) 45 tive absorption of the CO, become worse in this case. must be carried out. In many cases, a mechanical sepa In spite of this more unfavorable situation in the case rating of dust is already sufficient cleaning. of using exhaust gas as compared with pure CO, there The temperature of the gas can lie within wide limits, are no real difficulties when exhaust gas is used in the principally between 150 and 700°C. Often, gases from method of the present invention. Should the desired burning processes are available at a temperature of 50 degree of CO, utilization not be achieved during a 250 to 600°C and possess more heat than required for residence time of liquid mixture in gas of preferably 0.2 evaporation of the water in the added sodium hydrox to 3 seconds, then, as already stated above, the mixture ide solution. The volume of the sodium carbonate and is charged with a finer spray, or the residence times are sodium hydroxide solution in the circuit can then nev increased. It is possible to feed a portion of the gases ertheless be maintained constant simply by adding 55 exhausted from the reaction chamber back through the some additional water to make up for the extra water reaction chamber, or the liquid in the chamber can be evaporated. conducted by mechanical deflecting devices, in order Under the prevailing operating parameters, i.e. gas to increase the residence times. temperature, ratio of gas to liquid, concentration of the The container material for the present invention is added NaOH solution, the CO, content of the gas, etc., 60 corrosion resistant, for example stainless steel, nickel, there results a definite temperature at any point on the nickel-contaning metal alloys, and nickel-plated metal; path of the circulated liquid. After the collecting of the useful for the liquid conducting and containing vessels, mixture remaining as liquid from the gas, the liquid pipe lines, and framework, is plastics material such as temperature lies between 75° and 115°C, preferably polyethylene, polypropylene, polytetrafluoroethylene, between 80 and 95°C. 65 or plastics-coated steel sheet. For reasons of economics, attention must be paid to Referring now to the sole FIGURE, a preferred em a substantially complete utilization of the CO2. Fre bodiment of the continuously operating method of the quently, especially when using hot exhaust gas from invention will be explained. 3,975,503 S 6 A NaCO3- and NaOH-containing solution circuit is present invention can be applied also for the simple and maintained in continuous pipe line flow by pump 1. At economical production of potassium carbonate. connection 4, an aqueous sodium hydroxide solution, The method of the present invention for the produc as above-described, is added to the sodium carbonate tion of potassium carbonate is preferably characterized and sodium hydroxide solution circuit. Using the pres by the adding of a 10 to 60 weight-% aqueous potas sure created by pump 1, the resulting mixture is sium hydroxide solution to a circulating aqueous solu sprayed by nozzle 2 into reaction chamber 3. Hot gas tion of potassium carbonate and potassium hydroxide, exhausted from a burning process, i.e. CO2-containing by the spraying of the obtained mixture into hot (150 gas, is sucked in through pipe line 5 by the action of th to 700°C) CO-containing gas, by the collecting of sprayed mixture. The mixture and gas come into inti O mixture remaining as liquid from the gas after a resi mate contact and react immediately. In collecting con dence time of 0.1 to 10 seconds, by removing the tainer 6, mixture remaining as liquid is collected from formed crystals from the collected mixture, and by the the gas. The gas, heavily laden with water vapor, is returning of the remaining liquid portion as the circu exhausted through pipe line 7. The exhaust gas may be lating aqueous solution of potassium carbonate and washed with water at connection 14, if desired. In order 15 potassium hydroxide. to prevent a possible encrustation at the level of nozzle The circulating working solution of potassium car 2, water can be sprayed in at connection 13. The car bonate and potassium hydroxide contains, before the bonated and concentrated mixture remaining as liquid adding of the potassium lye, a quantity of potassium in container 6 contains precipitating crystals of Na2CO carbonate and potassium hydroxide such that the total . H2O. These crystals grow rapidly and deposit in the 20 alkali content, expressed as KOH, lies preferably be funneling bottom portion of container 6. While a freely tween 45 and 55 weight-%. The KOH content of the flowing crystal-rich stream is continuously withdrawn solution individually amounts to 8 to 20 weight-%, with from the bottom of container 6 through a removal that of KCO lying at from 35 to 52 weight-%. device 8 and into centrifuge 9, a second stream of the By spraying the resulting mixture into the hot gas, the charged mixture remaining as liquid is withdrawn from 25 gas is substantially instantaneously cooled to a temper container 6 through pipe line 10. The second stream is ature from 80 to 125C, while the mixture is warmed a crystal-poor stream having only few, fine, suspended to 75° to 120°C. Due to the heat introduced by the gas crystals. The second stream is fed directly into combin and the released heat of neutralization, a portion of the ing vessel 11, where it is recombined with the filtrate water in the resulting mixture is evaporated. This por from the first, crystal-rich stream. From vessel 11, the 30 tion corresponds exactly to the amount of excess water combined streams are moved through pump 1 in the caused by the adding of the potassium lye and by water sodium carbonate and sodium hydroxide solution cir added for other reasons as above disclosed. Thus, the cuit. The centrifuge-wet sodium carbonate monohy volume of the potassium carbonate and potassium hy drate is fed into dryer 12, heated directly with CO droxide solution circuit remains constant. containing gas. The direct contacting of the wet sodium 35 As in the case of sodium carbonate production ac carbonate monohydrate with CO2-containing gas cording to the invention, pure carbon dioxide gas can causes, in addition to a drying of the crystals, a carbon be used when producing potassium carbonate; it is ating of sodium lye present amongst the carbonate preferred to use the exhaust gas from a burning pro crystals. Drying above 100°C yields a heavy soda prod cess, the exhaust gas containing about 10 to 20 volume Ct. 40 % CO. As compared with known processes, the method of The portion of water evaporated in the reaction the present invention has principally the following ad chamber is higher, the higher the temperature of the vantages: CO-containing gas, the higher the concentration of 1. Preferred utilization of hot exhaust gas from burn CO, in the gas, and the higher the amount of the gas ing processes; 45 supplied. Usually, the hot exhaust gas from a burning 2. Small liquid volume in the working medium; process contains significantly more heat energy than 3. The gas is sucked into the reaction chamber, so needed to evaporate excess water in the charged result that no gas compressor is necessary; ing mixture. Thus, the excess water resulting from the 4. Intensive mixing of liquid and gas - thus short added, diluted potassium hydroxide solution, whose residence times are required; 50 KOH concentration lies preferably between 42 and 54 5. Small and simple equipment; weight-%, cannot cover the water loss caused by the 6. Small electrical energy requirements; heat in the gas. Therefore, ordinarily, water must be fed 7. Good utilization of the heat energy of the CO in at suitable locations in the apparatus. The amount of containing gas; heat transferred and the reaction are influenced as in 8. Great flexibility in the system. 55 the case of sodium by the degree to which the liquid is Depending on the reaction conditions, there arises in divided in the gas and residence times of the liquid in the sodium carbonate and sodium hydroxide solution the gas and of the gas in the reaction chamber, for, with circuit a certain NaCOs and NaOH concentration. smaller droplets and increasing residence times, both Ordinarily, the total alkali content, expressed as NaOH, heat exchange and degree of conversion to carbonate lies between 22 and 27 weight-%, and this is the result 60 are increased. of the combined effect of the NaCO3, at 13 to 18 Following the collecting of the mixture remaining as weight-%, and the NaOH, at 8 to 14 weight-%. The liquid at the end of the chosen residence time of the weight ratio NaOH: NaCO should lie preferably mixture in the gas, the mixture has a temperature deter below 1 : 1 before the adding of the sodium lye. mined by the various process parameters such as the The system potassium lye?potassium carbonate is 65 ratio of gas to liquid, the gas temperature, the concen very different from the system sodium lye/sodium car tration of the potassium lye, and the CO-content of the bonate, because the solubilities and the hydrate steps gas. The higher these parameters lie, the higher is the are quite different. Nevertheless, the method of the temperature of the collected liquid. Generally, the 3,975,503 7 8 collected liquid has a temperature from 75 to 120°C, residence time of the mixture in the gas equal to about predominantly however in the range of 85 to 105°C. 0.5 seconds, the remaining liquid was separated from A determinative factor for the hydrated water con the gas in a collecting container of 280 liters capacity. tent of the potassium carbonate solids obtained accord The gas exhausted from the reaction chamber left with ing to the invention is the composition of the solution in a temperature of 85°C and was passed through a small the potassium carbonate and potassium hydroxide solu water scrubber in pipeline 7. Rapidly growing crystals tion circuit. If the KCO content in the solution is high, of NaCOs. HO settled in the collecting container. At for example 50 weight-%, and thus the KOH content is the foot of the container, the thickened crystal suspen low, then, under the above-given reaction conditionis, sion was continuously withdrawn and fed into a centri the precipitation of KCO . 1% H2O is favored. In O fuge, where 58.1 kg/hour NaCOa. HO with 8 to 10% contrast, with increasing KOH content, i.e. with sinking free water content was separated. The filtrate and the KCO content, more and more water-free KCO is overflow from the collecting container were combined obtained in solid form. Thus, it is possible by appropri in the combining vessel and then fed again toward the ate measures according to the present invention to point of NaOH addition. The overflow contained only obtain in crystal form either the hydrate potash, K2CO 15 little suspended crystalline material. The water fed into . 1% HO or the water-free KCOa. Preferably, 46 to 52 the system was regulated to maintain the liquid volume weight-% KCOa is used for the hydrated carbonate in the sodium carbonate and sodium hydroxide solution production and 35 to 46 weight-% K2COa for the non circuit constant. The moist crystalline product was hydrated carbonate production. dried in a dryer heated directly with CO2-containing The isolating of the potassium carbonate crystals proceeds preferably by dividing the mixture remaining gases to provide a dewatered heavy soda. as liquid into two streams as above-described for so EXAMPLE II dium carbonate. Only the crystalline slurry depositing at the bottom of the collecting container is subjected to In a process modified from the FIGURE only as indi filtration or centrifuging. The filtrate and the other 25 cated in the following, 405 kg of a warm (96°C) work stream, which contains relatively little, very fine crys ing solution of potassium carbonate and potassium tals, are brought back to form the potassium carbonate hydroxide were moved in circuit by pump 1. The solu and potassium hydroxide solution circuit. tion had a composition of 45.6 weight-% potassium The process for potassium carbonate production is carbonate and 12.2 weight-% potassium hydroxide, likewise very adaptable and can be rapidly adjusted to 30 thus 49.2 weight-% total alkali (expressed as KOH). changing conditions. Here also, pressures above and Through connection 4, 46 weight-% potassium hydrox below atmospheric pressure can be used equally well. ide solution was fed at the rate of 100 kg/hour into the Preferably, the charged mixture and gas are allowed to potassium carbonate and potassium hydroxide solution react with one another for 0.2 to 3 seconds. In the circuit. The resulting mixture reached the reaction exception that this contact time is not sufficient to 35 chamber, was sprayed into the chamber, and acted to obtain the desired utilization of the CO, then the resi suck into intimate contact with itself 150 standard dence times for the liquid in the gas and for the gas in meters/hour hot exhaust gas from a burning process. the reaction chamber are increased or the droplet size The exhaust gas from the burning process had a tem is decreased. For example a portion of the gas ex perature of 480°C and a CO-content of 15 volume-%. hausted from the reaction chamber may be fed back to 40 At the level of the nozzle, 5 liters/hour water was the reaction chamber, or the charged mixture can be sprayed into the reaction chamber. After an average deflected by suitable mechanical devices, before the residence time of about 0.5 seconds in the reaction collecting of the mixture remaining as liquid. chamber, the gas and liquid were separated by entrance The flow diagram for the potassium method is sub into the 280 liter collection container. The gas ex stantially the same as that for sodium - as depicted in 45 hausted from the reaction chamber left with a tempera the FIGURE; the product is either a defined hydrate or ture of 98°C after it was passed through a small water a hydrate-free potassium carbonate. The same advan scrubber in pipeline 7. The formed crystals grew and tages over the prior art are obtained by the potassium settled to the bottom of the collection container. The process that are obtained by the sodium process. crystal slurry was continuously withdrawn from the Further illustrative of the present invention are the 50 lower end of the funnel section of the collection con following examples. tainer and fed to a centrifuge. Per hour, 56.7 kilograms of KCOa product with about 10% free water content EXAMPLE I was produced. The filtrate was combined with the over In the process of the FIGURE, 390 kilograms of a flow from the collection container in the combining warm (80°C) working solution of sodium carbonate 55 vessel and fed then back into the potassium carbonate and sodium hydroxide were moved in circuit by pump and potassium hydroxide solution circuit. Only rela 1. The solution contained 16.6 weight-% sodium car tively little, fine crystals were suspended in the over bonate and 1 1.5 weight-% sodium hydroxide, thus flow. Water addition to the system in the pipeline ex about 24 weight-% total alkali (expressed as (NaOH). hausting gas from the collecting container and in the Shortly before this solution was sprayed into the reac 60 spray reactor was able to keep the fluid volume in the tion chamber, it was continuously mixed with 75 solution circuit constant. The warm crystalline material kg/hour 50 weight-% sodium hydroxide solution. By obtained from the centrifuge was immediately fed to a the suction action of the reactor, to which 5 liters per dryer heated directly with CO-containing gas. hour water was additionally fed, the resulting mixture The average residence times in the two examples came into intimate contact with 150 standard (0°C, 1 65 were determined by measuring the quantity of gas atmosphere pressure) cubic meters/hour of hot sucked from 5 and the volume of the reaction chamber, (480°C) exhaust gas from a burning process. The gas considering the temperature relations. The volume contained 14 volume-% CO2. Following an average flow rate for the solution circuit of the 390 kilograms or 3,975,503 10 405 kilograms respectively at the point of connection 4 3. A method as claimed in claim 1, wherein the tem was 2.5 cubic meters per hour. perature of the liquid mixture after collection in step The diameter of the nozzle 2 was 8 mm, the droplet (c) is controlled to be at 75 to 115°C. size distribution was estimated by the usual charts and 4. A method as claimed in claim 3, wherein the tem the calculated flow rate. perature of the liquid mixture after collection in step Heavy soda is a product with a bulk weight of more (c) is controlled to be at 80 to 95°C. than 1.05 tons per cubic meter. 5. A method as claimed in claim 1, wherein the tem It will be understood that the above description of the perature of the gas in the step of charging is in the present invention is susceptible to various modifica range of from 250° to 600°C and wherein the gas tem O perature at the step of collecting is in the range of from tions, changes and adaptations, and the same are in 80 to 120°C. tended to be comprehended within the meaning and 6. A method as claimed in claim 1, wherein the resi range of equivalents of the appended claims. dence time in the step of charging is in the range of We claim: from 0.2 to 3 seconds. 1. A method for producing alkali carbonate crystals, 15 7. A method as claimed in claim 1, wherein the step comprising the steps of: of separating includes the dividing of the collected a. adding to an alkali carbonate and alkali hydroxide mixture into two streams, the removing of alkali car recycle stream that contains at least 8% by weight bonate crystals from only one of the streams, and the of alkali hydroxide, a 10 to 75 weight-% alkali combining of the two streams, following the step of hydroxide solution to form a resulting solution 20 removing, to form the recycle stream. which has an alkali hydroxide content of at least 8. A method as claimed in claim 1, wherein the alkali 8% by weight; carbonate and alkali hydroxide recycle stream contains b. spraying the resulting solution into a CO-contain 13 to 18 weight-% sodium carbonate and 8 to 14 ing gas whose temperature is from 150 to 700°C to weight-% sodium hydroxide. react a portion of the alkali hyroxide in said result 25 9. A method as claimed in claim 1, wherein the alkali ing solution with the CO-containing gas and form carbonate and alkali hydroxide recycle stream contains a liquid mixture containing alkali carbonate 35 to 52 weight-% potassium carbonate and 8 to 20 formed from reaction of alkali hydroxide with the weight-% potassium hydroxide. CO-containing gas, the amount of alkali hydroxide 10. A method as claimed in claim 9, wherein the being reacted to form alkali carbonate being equal 30 alkali carbonate and alkali hydroxide recycle stream to the amount of alkali hydroxide added to the contains 46 to 52 weight-% potassium carbonate for recycle stream during the step of adding; producing KCOa. 1%H0. c. collecting said liquid mixture containing said 11. A method as claimed in claim 9, wherein the formed alkali carbonate from the gas at the end of alkali carbonate and alkali hydroxide recycle stream 35 contains 35 to 46 weight-% potassium carbonate for a residence time of said mixture in said gas of from producing KCOs free of water of hydration. 0.1 to 10 seconds; 12. A method as claimed in claim 1, further compris d, separating alkali carbonate crystals from the col ing drying the alkali carbonate crystals with gas con lected liquid mixture, and; taining CO2. e. recycling the collected liquid mixture, following 40 13. A method as claimed in claim 12, wherein the the step of separating, as the said alkali carbonate alkali is sodium and the step of drying is a step for and alkali hydroxide recycle stream to the step of dewatering the sodium carbonate crystals to heavy adding. soda. 2. A method as claimed in claim 1, wherein the alkali 14. A method as defined in claim 1, wherein the hydroxide solution added to the alkali carbonate and 45 alkali hydroxide solution that is added to the recycle alkali hydroxide recycle stream is a 45 to 55 weight-% stream contains 10 to 60 weight-% alkali hydroxide. solution. k ck k k k

50

55

60

65