MXPA97010264A - Procedure for the production of sodium bicarbonate, sodium carbonate and ammonium sulfate from so sulfate - Google Patents

Abstract

The present invention relates to: Process for the production of sodium bicarbonate, sodium carbonate and ammonium sulfate from sodium sulfate. The invention provides various processes for generating compounds of sodium carbonate, and ammonium sulfate, in which the compounds are in substantially commercially viable form. In one embodiment, the process involves precipitating sodium compounds by addition of salt, to arrive at a high ty ammonium sulfate fertilizer. Various methods are described, including reduction of sodium ion by ion exchange, cooling, displacement of ammonia and evaporation. The adaptation of the processes to the desulfurization of combustion gases and the production of gypsum is also described. The processes described herein result in the production of ammonium sulfate in a ty that could not be previously obtained by the methods of the prior art.

Description

PROCEDURE FOR THE PRODUCTION OF BICARBONATE OF SODIUM, SODIUM CARBONATE AND AMMONIUM SULFATE FROM SODIUM SULFATE DESCRIPTION OF THE INVENTION TECHNICAL FIELD This invention relates to a process for the production of sodium bicarbonate, sodium carbonate and ammonium sulfate from sodium sulfate, in order to generate compounds of sodium carbonate, and ammonium sulfate, in a commercially available form. viable and substantially pure.

BACKGROUND OF THE INVENTION Various procedures have been developed to make alkaloid carbonate and various sulfate components. These methods have difficulty producing components that are in the pure state, or almost pure, for commercial use. Stiers, in U.S. Patent No. 3,493,329, issued February 3, 1970, teaches a method for making sodium carbonate. The Stiers method is a simultaneous precipitation method and can not provide for the selective precipitation of desired products, since the salts are reciprocal salts and form a double salt. In the Stiers method, the desire is to extract the sulfate anion to be used for the transport of sodium cations from sodium chloride to the bicarbonation process as sodium sulfate. In addition to the above, the Stiers process involves the continuous recycling of the mother liquor, which requires that the ammonium sulfate in the liquor be continuously extracted or reduced from the process stream. If the ammonium sulfate reaches a saturation point in the bicarbonation stage, REF: 24799 Ammonium sulfate will precipitate together with sodium sulfate in the form of a double salt compound or two inseparable salts. Stiers demonstrates a process for generating two salts and double salts instead of a single pure salt, the latter being much more convenient from a commercial point of view. The present invention is aimed at avoiding the previously encountered difficulties of pairs of reciprocal salts. More recent attempts have been made to develop methods for producing sodium bicarbonate and ammonium sulfate from sodium sulfate in substantially pure quality, such that these products can be used as commercial grade soda bicarbonate, and fertilizer. Canadian Patent Application Serial No. 2,032,627 offers an innovative technique for producing suitable pure products. This method employs various evaporation and cooling techniques to alter the solubility of sodium sulfate and ammonium sulfate in solution and selectively precipitate the desired pure components. The laboratory bench scale test of this method showed effective results, however the continuous pilot scale test clearly identified undesirable limitations to the procedure as specified. More specifically, the process is difficult to operate in a consistent and continuous manner and as such is highly susceptible to contamination of ammonium sulfate with sodium sulfate, resulting in a commercially undesirable double salt product. In more detail of the teachings of the Canadian application, it is taught that the brine that remains after separating the sodium sulfate has a temperature of 95 ° C and is saturated with sodium sulfate and ammonium, and that by cooling the mixture of both brines in a crystallizer from 95 ° C to 60 ° C, the solubility of ammonium sulfate decreases while the solubility of sodium sulfate increases. The result is that more ammonium sulfate precipitates, while sodium sulfate remains in solution. Following the teachings, the mixed solution is supersaturated with sodium sulphate due to the evaporations at 95 ° C, and results specifically in the production of double salt when the crystallization step is carried out.

Ammonium sulfate 60 ° C is tried as a continuous process.

INDUSTRIAL APPLICABILITY The methods of the present invention can be applied in the fertilizer, refinery, environment and chemical engineering industries.

EXPOSITION OF THE INVENTION An object of the present invention is to provide an improved process for the recovery of substantially pure sodium bicarbonate and ammonium sulfate, for commercial purposes. Another object of the present invention is to provide a method for being used on a continuous commercial scale, which overcomes the difficulties inherent in the contamination of the product. A further object of an embodiment of the present invention is to provide a process for producing sodium bicarbonate and sodium carbonate, said method comprising: reacting, within a reactor, sodium sulfate in aqueous solution with ammonia and carbon dioxide to precipitate sodium bicarbonate and form a first mother liquor; Separate the sodium bicarbonate and dry it to produce a product of baking soda or calcining it to convert it to sodium carbonate; submit the first mother liquor, from the precipitation of the sodium bicarbonate, to evaporation to precipitate the unreacted sodium sulfate, forming a second mother liquor; cooling the second mother liquor, coming from the precipitation of unreacted sodium sulfate, to precipitate a double salt of sodium sulfate / ammonium sulfate and water, forming a third mother liquor; subjecting the third mother liquor, coming from the precipitation of the double salt, to evaporation to precipitate a substantial pure ammonium sulfate in a purity of more than about 73% by weight, forming a fourth mother liquor; add double salt to the first mother liquor from the precipitation of sodium bicarbonate before evaporation; and adding the fourth mother liquor to the second mother liquor from the evaporation, to precipitate the unreacted sodium sulfate. A process for selectively precipitating sodium bicarbonate and ammonium sulfate from a sodium-containing sulfur compound, characterized in that the process comprises the steps of: (a) providing a source of a sulfur compound containing sodium; (b) contacting the compound with gaseous carbon dioxide and ammonia or ammonium ions to generate a solution; (c) maintaining the solution at a temperature sufficient to form a single precipitate of sodium bicarbonate, to reduce the amount of aqueous sodium ions without precipitation of competitive sodium precipitates; (d) removing the precipitate of sodium bicarbonate from the solution; (e) removing the sodium sulfate; and (f) precipitate ammonium sulfate. By controlling the temperatures and pressures, once a precipitate of bicarbonate is formed, the filtrate can be subjected to a purification step in which the remaining sodium ions are substantially eliminated or made to remain in solution before precipitation of ammonium sulfate. This results in a cleaner precipitate of ammonium sulfate and therefore results in a commercially more convenient product, said product exceeding purity measures not previously found with prior art processes. In a purification possibility, the filtrate can be supersaturated with ammonia in a conditioning reactor operating at substantially cooler temperature, for example 7 ° C. This is an example of an appropriate temperature, an adequate range being between approximately 20 ° C and approximately -40 ° C. This process results in the formation of a mixed salt of ammonium sulfate and sodium sulfate, both being insoluble at this temperature and this excess ammonia. Once precipitated, the filtrate, which therefore has a lower concentration of sodium cations, inherently leads to a less contaminated precipitated ammonium sulfate.

Different different procedures are possible, including reduction of sodium ion by ion exchange, refrigeration and evaporation among others. These will be discussed later. The described procedures also refer to the adaptation of the processes to the desulfurization of the combustion gases and the production of gypsum. The processes described in 4a present result in the production of ammonium sulfate in a purity that could not be previously obtained by the methods of the prior art. Convenient results have been obtained when the conditioning step increases the ammonium concentration from about 10% to about 50%. The precipitate of mixed salt, double salt or pure sodium sulfate can be recycled back to the original feed stream with the sodium sulfate source. It has been found that, using the basic bicarbonate recovery process, the process can be increased to additional utility fields, for example tail gas desulfurization. This was indicated above broadly with respect to the desulfurization of the acid gas stream. The desulfurization of combustion gases, hereinafter FGD (for its acronym in English), of which an example employs a dry absorbent, is generally known in the art. This uses the use of sodium bicarbonate typically for a reduction of the sulfur component from 10% to 90%. The bicarbonate is initially calcined by the heat of the combustion gas, which is typically in the range of 350 ° F to 750 ° F, to sodium carbonate. This then reacts to form sodium sulfate. Because the absorbent is a dry and finely ground powder, there is no negligible cooling effect with the combustion gas and, thus, the stack temperature can be maintained for the dispersion of emissions. Also, sodium sulfate can be recovered in a bag collector or an electrostatic precipitator with or without very fine ash. The absorbent must be processed to a fine particle size, typically 15 μm and then stored under dry conditions to prevent retention and improve the handling capacity of the dry absorbent in silos and other equipment.

A further embodiment of the present invention is directed to a process that can utilize a wet scrubbing system and eliminate corrosion problems, landfill problems and other handling difficulties associated with lime. The method can use bicarbonate or carbonate or a mixture of these. As a further advantage, the process according to the present invention eliminates the drying and sizing step previously found in the methods of the prior art. Additionally, utility has been found in the application of the general procedure in the manufacture of gypsum, for example, of a commercial grade or landfill. By adding lime to the saturated solution of ammonium sulfate, the gypsum can be removed as a precipitate. By practicing the above method, it has been found that a selective precipitation of the single salts at a high level of commercial purity can be achieved on a continuous basis. The procedure is further improved by providing a chemical scheme for the recovery of ammonia and carbon dioxide to minimize the consumption of chemicals to improve commercial viability. It has further been found that, using the basic bicarbonate recovery process, the process can be used for additional utility fields, for example tail gas desulfurization, flue gas desulfurization by wet absorbent injection techniques or dry and additional application to make commercial grade gypsum or land fill and fully recover ammonia chemical.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graphical representation of the solubility of sodium bicarbonate, ammonium sulfate and sodium sulfate expressed as pure components in solution at various temperatures; Figure 2 is a flow chart illustrating the preparation of saturated sodium sulfate brine from the source of natural sodium sulfate known as Glaubers salt and from a source of sodium byproduct sulfate; Figure 3 is a flow chart illustrating the unit of production of sodium bicarbonate and the gas recovery scheme; Figure 4 is a flow chart illustrating the separation scheme for production of ammonium sulfate fertilizer in liquid form and solid crystal; Figure 5 is an alternate embodiment illustrating how the process can be adapted to a tail gas desulfurization scheme; Figure 6 is an alternative alternate embodiment of the method indicated in Figure 5; Figure 7 is a flow chart illustrating how the process can be adapted to regenerate sodium bicarbonate from sodium sulfate captured in a FGD scheme using a Dry Absorbent Injection (DSl) technique; Figure 8 is an alternate embodiment illustrating how the method can be adapted to be used in a scheme of Desulfurization of Combustion Gases by Wet Scrubbing to regenerate the sodium bicarbonate from the captured sodium sulfate solution; Figure 9 is a further embodiment whereby the process can be adapted to produce gypsum and fully recover ammonia; Figure 10 is a flow chart illustrating a possible method route for carrying out the method according to the present invention; Figure 11 is an alternate embodiment of the Figure 2; Figure 12 is an alternate embodiment of the Figure 2; Figure 13 is an alternative alternate embodiment of the method as indicated in Figure 2; Figure 14 is a further alternate embodiment of the process of Figure 2 illustrating a tail gas treatment; Figure 15 is an alternative alternate embodiment of the process as indicated in Figure 6 illustrating an acid gas treatment; Figure 16 is an alternative alternate embodiment of the process in which plaster is produced; Figure 17 is still another embodiment of the process according to the present invention, illustrating a purification process; Figure 18 is a schematic illustration of the general procedure using an operation- with ion exchange unit; Figure 19 is a schematic illustration of the general procedure using an operation with ion exchange unit and a power conditioning operation; Figure 20 is an alternative of the schematic illustration shown in Figure 19; and Figure 21 is a schematic illustration of the general procedure in which an operation with cooling unit is provided.

MODES FOR CARRYING OUT THE INVENTION The chemistry involved in accordance with the present invention can be solved in the following equations: CO2 + H2O H + + HCO3- NH3 + H2O * + NH / + OH 'Na2SO4 + 2NH3 + 2H2O + 2CO2 ** 2NaHCO3 + (NH4) 3SO4 Referring now to Figure 1, a graphical representation of the solubility curves for pure components, including sodium bicarbonate, ammonium sulfate and sodium sulfate is shown. The data is expressed as a function of the temperature of the solution. As is evident from the drawing, the solubility of bicarbonate and sodium sulfate have an area of overlap in which there will be a precipitation of these two components. As previously indicated herein, areas where the solubility values are in conflict and the interaction effects of the solubilities of the mixed solution have posed significant difficulties in the prior art, when attempting to obtain a substantially pure precipitate. of sodium bicarbonate and ammonium sulfate without the formation of a precipitate of sodium sulfate, double salts, hydrated salts or any mixed combination.

It has been found that, if the solubility data are simply obeyed, the sodium bicarbonate and the ammonium sulfate can be precipitated from a solution containing the molecular species indicated above without contamination of one precipitate with the other and additionally without the Simultaneous precipitation of sodium sulfate and double salts as a contaminant. If the sodium bicarbonate solution is maintained at a temperature sufficient to prevent the precipitation of sodium sulfate, in view of the data in Figure 1, the sodium bicarbonate may be precipitated while the unreacted sodium sulfate remains in solution . If the temperature falls before the precipitation of the sodium bicarbonate, a solvate or sodium sulphate decahydrate will precipitate out of the solution causing enormous operational difficulties. In a chemical system as discussed with respect to the above equations, the system is generally a complex quaternary system, which has a ratio of reciprocal salt pairs as follows: 2 (NH4) HC03 + Na2SO4 < * 2NaHCO3 + (NH4) 2SO4 In aqueous solutions at more than about 30 ° C the ammonium bicarbonate is unstable and dissociates in solution as ions.

This reduces the system to a complex tertiary system with complications related to the formation of hydrates and double salts. The first step in the procedure is to complete the reaction to boost the equilibrium in the final equation so that the substantially pure sodium bicarbonate crystals are formed. As is known in the art, numerous possible methods can be put into practice to bring the ammonia and carbon dioxide into contact with the sodium sulfate solution. As an example, ammonia can be introduced into a solution of sodium sulfate and carbon dioxide dispersed through the solution, or carbon dioxide dispersed through the saturated solution of sodium sulfate and subsequently added ammonia, or both components can be dispersed through the solution simultaneously. Another possible alternative includes the use of ammonium carbonate or ammonium carbonate compound. Referring now to Figure 2, a route is shown of possible procedure according to the present invention. A natural source of sodium sulfate can be found in vast reserves of Glaubers salt (sodium sulfate decahydrate). Figure 2 schematically illustrates a mechanism for concentrating and conditioning the sodium sulfate feed brine from the Glaubers salt feed stock. Reference is made overall to the procedure with the number 120. In more detail, Figure 2 shows the basic scheme by which a byproduct of sodium sulfate can be introduced into the process. As an example, very fine ash, coming from commercial steam boilers, containing several levels of sodium sulfate, can be collected from hot combustion gas streams and transferred to a collection silo 10. From silo 10, the very fine ash can be separated by commercially known dry or wet methods, indicated globally by 12, whereby the material can be transferred to an atmospheric mixing vessel 14, which is maintained at a temperature between about 32 ° C and 42 ° C. The thick insolubles, for example rocks, sand clay fines, are separated into 16 and 17. The finer material is flocculated and separated from the sodium sulfate solution once it passes through a clarifier 18. The final brine or filtrate, represented by the number 40, is then further clarified and further filtered by filters 19, if necessary, to leave the solution free of ultrafine insolubles and potential heavy metals. The insolubles are extracted and disposed of by suitable means. Heat energy is typically applied. to the melting tank 22. Evaporation may also be required in tank 22 to achieve a sodium sulfate concentration at the desired maximum solution solubility. A circulation pump 24 is required to prevent scale formation in the sulphate brine preparation unit, reducing the temperature increase of the circulating flux solution. One of the main difficulties previously encountered in the prior art was that the temperature of the sodium bicarbonate formation reaction was not maintained within the aforementioned parameters. The result of this is the formation of a solvate or hydrate commonly mentioned as Glaubers salt (Na2SO4 • 10H2O) and the formation of ammonium bicarbonate. By maintaining the temperature within the range stated above, these compounds are not formed and therefore do not affect the process of formation of sodium bicarbonate. Further, at this temperature, a maximum amount of salt can be put into solution, which reduces the required feed flow rate of brine 40. With reference to Figure 3, once the insolubles have been separated by the clarifier and filters, and the brine 40 is concentrated to its highest salt saturation level, the solution or brine 40 is presaturated in tank 42 with ammonia and carbon dioxide and then passed, for example pumped by a pump 41, to at least a first main reactor 44 or multiple reactors where the formation of sodium bicarbonate takes place. The temperature inside the reactor 44 can vary depending on the configuration of the reactor. The final temperature of the solution can be progressively reduced to approximately 21 ° C, the brine feed temperature to reactor 44 being maintained at more than 32 ° C. The final temperature of the solution maximizes the bicarbonate yield and prevents contamination with Na2SO4. The pressure in reactor 44 will preferably be maintained at about 350 kPa (g) to about 1750 kPa (g). Although not essential, this ensures that the ammonia remains dissolved in solution. A crystallizer 46 can be included downstream to effect the crystallization of the sodium bicarbonate. Once the crystals have been formed, they can be separated from the reactor 44 and / or crystallizer 46 through a filter means 46 which can comprise a pressure or non-pressure type filter. Once the crystals are separated, they can be passed to an additional filtration medium (not shown), of which an example can be a filter screen or a rotary centrifuge device (not shown), and at that point the crystals formed they can be washed with brine of saturated sodium bicarbonate or methanol as indicated in 50 and dried with dryer 54 or calcined to form sodium carbonate. A high performance can be achieved. The washing can then be returned by line 52 to the mixing vessel 14. The bicarbonate crystals form two, denoted by 56, can then be separated from the system for later uses. The filtrate or brine 58 from the first reactor 44 is reheated to about 80 ° C to 95 ° C in a gas recovery boiler 60, where reactivated carbon dioxide and ammonia gases are evolved from the brine. The gases are routed to a gas recovery contactor 62 where they are subjected to the raw sodium sulfate feed brine and absorbed in solution to presaturate the feed 41 to the bicarbonate reactor 44. This procedure reduces the product consumption requirements. chemical The filtered solution, denoted by the number 64, in Figure 4 is subjected to a first evaporation step at a temperature of, for example, more than 59 ° C in the evaporator 66 to condition the brine by reducing the level of sodium ion without react and residual in the solution.

As the saturation level of the brine is obtained, sodium sulfate crystallizes from the solution before reaching the saturation level of ammonium sulfate or double salt. The sodium sulfate crystals are filtered in the filter 68 of the first evaporation brine and washed and dried as a high purity sodium sulfate product or recycled as indicated in 70 as feedstock. The filtrate 70 from the first evaporation for conditioning of the brine is then cooled to approximately 20 ° C, where crystallization of sodium sulfate and ammonium sulfate takes place in the form of a double hydrated salt (Na 2 SO 4 • (NH 4) 2 SO 4 • 4H2O; or double salt / pure salt mixture in the crystalliser 72. The double salt crystals are filtered by the filter 74 from the cooled brine and dissolved again in the feed brine 64 to the first evaporator by the line 76. At this point the brine 77 obtained after the double salt is filtered, contains significantly reduced levels of sodium to effect the concentration and / or crystallization of substantially pure ammonium sulfate as a solid or liquid form. This product can then be separated from the system by line 88 as a liquid and stored in the container 90 or transferred to a fertilizer evaporator 78 or crystallizer 80 to be transferred to the solid crystal shape. If a solid crystal form is desired, then the brine of the nearly saturated ammonium sulfate is exposed to a final evaporation step in the crystallizer 80 to precipitate the ammonium sulfate in a substantial crystal size and a purity of more than 73% by weight, allowing it to be used-immediately as agricultural fertilizer. The crystals are filtered with the filter 82. The saturated filtering solution from the second evaporation step is recycled by the line 84 to mix with the feed brine 77 towards the double salt cooler / crystallizer to further improve the process of concentration. The filtered crystals can then be dried with the dryer 86. Advantageously, a liquid fertilizer stored in the container 90, which can be heated, offers the user the opportunity to combine the liquid product with other components of the fertilizer and additionally allows the crystallization of the product. as a convenient mixed form. The liquid in the container 90 may optionally be subjected to evaporation and subsequent concentration to create a supersaturated fertilizer solution. Although it has been indicated that the process as set forth herein is mainly conducted in water, it will be understood by those skilled in the art that any suitable solvent can be used provided that the selection of solvent does not vary the solubility ratio necessary for perform the procedure. As alternatives, glycol or glycol / water mixtures may be used as the solvent. Referring additionally to Figures 3 and 4, the general process may include an additional washing step to wash the precipitates of sodium bicarbonate and ammonium sulfate separately. In a possible configuration, the sodium bicarbonate formed in the reactor can be passed into contact with a washing material, of which an example can be a methanol source. The resulting filtrate can then be returned to a separation vessel. Similarly, crystals of ammonium sulfate can be passed through a second independent source of methanol, the filtrate being returned to a separation vessel. The crystals of ammonium sulfate and bicarbonate may have additional uses. Figure 5 shows a variation of the process in which the bicarbonate recovery systems as set forth herein can be combined to be useful in a sulfur recovery plant. In general, the area designated by the number 100 in Figure 5 illustrates a conventional apparatus used for the recovery of sulfur from an acid gas stream using the modified Claus procedure, which consists of a single or multiple variation of thermal steps and catalytic recovery. Generally, the Claus process includes an acid gas feed, denoted globally by the number 102, which is passed to a vessel 104, for the separation of acid or sulphurous water. The current is then passed to a reaction furnace and residual heat exchanger, denoted by the number 106, where the thermal conversion occurs. The current is then passed to a first catalytic stage conversion system, number 108, and subsequently to an additional conversion, denoted by the number 110 which may comprise "n" stages. The liquid sulfur is separated from the stages at 112. The stream is reheated and passed to a mixing unit 114 and then further to a collection device 116, which may comprise an electrostatic precipitator or bag collector. The solids from the collection device 116 are passed to a silo 118 and subsequently to a feed preparation thereon specifically indicated in Figure 2 as tank 16. From the feed preparation tank 16, the feed is processed in accordance with the bicarbonate recovery system, denoted globally by the number 122 and specifically indicated in the description for Figure 3. The product can then be transferred to a fertilizer recovery unit 124, the details of which were indicated in the description for Figure 4 The resulting product is a commercial grade fertilizer. As an option, the sodium bicarbonate feed from bicarbonate recovery unit 122 can be passed to a dry absorbent injection unit 126 and the bicarbonate then introduced back into the system via line 128.

Those skilled in the art know that the Claus procedure is useful for desulfurization. In general, the procedure is carried out in two steps, namely: H2S + 3/2 O2 ** H2O + SO2 2 H2S + SO2 «* 2 H2O + 3 / x Sx This generally results in a recovery of approximately elemental sulfur 90% to 96% in a state of liquid sulfur. The remaining sulfur-containing component is recovered in sulfur recovery techniques such as tail gas cleaning units. Using the recovery procedure as previously indicated herein, sodium bicarbonate can be introduced to the oxidized tail gas stream containing residual sulfur compounds, and one result can therefore be the production of ammonium sulfate as described above. indicated in Figure 5. By combining the modified Claus procedure with the procedures indicated herein, the result is a general sulfur separation of the order of at least 95% or greater. Turning now to Figure 6, a variation on the procedure of Figure 5 is shown, but for a lower volume sulfur production plant, which typically has production levels of less than 10 tons per day (MTD for short) in English) where economic constraints prevent the recovery of elemental sulfur as shown in Figure 5. The acid gas stream, as an alternative, can be directly treated with liquid carbonate or sodium bicarbonate solution for desulfurization, and form an alternative sulfur product. In Figures 7 and 8, variations on the general procedure according to the present invention are shown. Referring more specifically to Figure 7, an effective scheme is illustrated by which the recovery process, as indicated herein, can be employed to regenerate the captured dry sodium sulfate from a particulate collection device 150 such as an electrostatic precipitator or sack collector and produce sodium bicarbonate to be injected into the combustion gas stream to reduce mainly the components of sulfur from sulfur sources such as an industrial boiler 180 and released by means of a chimney 152. The practice of injecting a dry chemical into hot combustion gases is commonly referred to as DSl. By adapting the recovery procedure, discussed with respect to Figure 3, to the DSl technique, the general scheme becomes a continuous regenerable process without residual currents or land filling requirements, without appreciable losses, and all by-products are commercially usable immediately. The use of dry sodium bicarbonate as a reactant offers the additional advantages of additional recovery of other undesirable components such as NOx, HCl and SO3 from the combustion gases, and performance improvement of the downstream collection device 150 (i.e. electrostatic precipitator or bag collector). The dry absorbent technique, moreover, will not appreciably affect the temperature of the combustion gases, thereby maintaining or improving the dispersion of effluent emission from the chimney 152. The sodium sulfate compound containing very fine ash it is transferred from the collection device 116 and stored in a silo 118 (Figure 6) and combined in the feed preparation tank 16 of the method denoted by 120 (Figure 6). The feed is processed in the bicarbonate recovery system 122 and the sodium bicarbonate is passed to a dry absorbent injection unit 126 and reintroduced into the system via line 128. The by-product from the bicarbonate recovery unit 122 is transferred to the fertilizer recovery unit 124, and the resulting product is a commercial grade fertilizer. Figure 8 illustrates a scheme by which the process can be modified to produce a pure or mixed bicarbonate or sodium carbonate specific solution that can be adapted for use in a wet scrubber. The combustion gas from the industrial boiler or tail gas unit, denoted overall by the number 180, is passed over an electrostatic precipitator or bag collector 182 or other recovery device to remove the very fine ashes in 184. A Water wash container 186 is 1? provided for circulating wash water in a single-level or multi-level upper section of a wet scrubber 188, and accumulated levels of precipitates and fluids are removed and passed to the lower section of the wet scrubber 188. Separate containers two can also be employed to achieve the desired result. Once the sodium sulfate at the desired concentration level is collected from the bottom of the wet scrubber 188 as a product of the scrubbing process, it is then further transferred to the feed preparation tank 190 for its thickening and clarification to a state saturated to be fed to the reactor 20 (not shown) of the bicarbonate recovery unit, indicated globally as 122 and shown in Figure 3. From the reactor in the bicarbonate recovery unit 122, the sodium bicarbonate is filtered from the solution and washing in open sieve, filter of the type of pressure or combination of these (shown in general in 48 in Figure 3). The bicarbonate precipitate is washed and reduced to less than 10% liquid and then fed as a slurry to a bicarbonate slurry vessel 96 at approximately 700 kPa (g). At this point, the bicarbonate slurry in the container 96 is mixed with clean water supplied to the container 96 from a feed water supply container 98. The feed water is maintained at a temperature of about 48 ° C. The slurry is continuously mixed and its concentration ranges from about 20% by weight to about 40% by weight. The slurry is then transferred to a high pressure solution vessel 200 at a pressure of approximately 1050 kPa (g), where a saturated solution is formed. A saturated bicarbonate solution is created using additional feedwater from the container 98 which is heated to about 176 ° C by an injection water heater 102. The final saturated concentrated solution is then injected into a wet scrubber 188 by means of line 201 for the separation of sulfur dioxide. The temperature, pressure and reagent concentration in the final injection solution can be varied to control the level of separated SO2, the desired pH of the system solutions and the tempera- ture. of the final combustion gas leaving the wet scrubbing process. As a further example, the pressure of the injection system can be reduced to almost the prevailing atmospheric conditions in the wet scrubber 188. The temperature can then be reduced to almost 49 ° C to remove the water heater 102 and the high-pressure reactor-200. This will result in a colder final flue gas temperature resulting from the evaporative cooling effect which may or may not be detrimental to any specific application. It will be appreciated that the wet scrubber 188 may have any form of contacting the reagent solution with the sulfur-containing combustion gas, eg, spray dryers, etc. Additionally, sodium carbonate or other suitable sodium compounds can be used as a replacement or combined in various ratios with sodium bicarbonate to effect or improve the techniques of wet and dry purification, the conversion can be easily achieved by burning the bicarbonate in a dry form or increasing the temperature in a liquid form to alter the bicarbonate to carbonate form. The carbon dioxide used in the process can be recovered in a recovery process as indicated herein. Turning to Figure 9, a further embodiment according to the present invention is shown schematically. In the embodiment shown, a lime mixing vessel 70 is provided to retain lime in any form, for example a slurry or powder form to be introduced to reactor 202 via line 71. Providing this addition to the recovery unit , commercial gypsum or landfill can be produced together with the sodium bicarbonate, as illustrated in the flow chart of Figure 9. As an additional feature, the arrangement shown can include an ammonia recovery unit 204 which will include the usual gas recovery means well known to those skilled in the art. This is useful since ammonia is released after the precipitation of the plaster and therefore can be easily recovered and recycled to the procedure for the production of sodium bicarbonate. As a consequence of the size of the reactor vessel, evaporator and crystallizer, a stratification temperature may exist within the reactors and evaporators as indicated herein or in the crystallization vessels used to improve the growth, stability and performance of -crystals. . In order to avoid the undesirable effects caused by precipitation of hydrates or solvates in large containers, the procedure can be carried out in multiple containers to avoid these difficulties. Referring now to Figure 10, a possible method route according to the present invention is shown. A source of sodium sulfate, such as very fine ash, for example, from commercial steam boilers, which contains several levels of sodium sulfate, can be collected from the hot combustion gas streams and transferred to a silo collection, denoted globally by the number 10 in the drawings. From the silo, the very fine ash can be transferred at a controlled rate to an atmospheric mixing vessel 12, which is maintained at a temperature between about 32 ° C and 42 ° C. The light and heavy insolubles are separated in a slurry form from the mixing vessel 12 in 14. The brine or filtrate is then transferred to a clarifier 16 and further filtered if necessary to release the solution of fine insolubles. The fine insolubles are separated from the clarifier at 18. Once the insolubles have been separated by the clarifier 16, the solution or brine containing a small percentage of ammonia is passed to a first main reactor 20 where the formation of sodium bicarbonate. The final temperature of the solution will be progressively reduced to approximately 21 ° C, the feed temperature of the brine to the reactor being maintained at more than 32 ° C. The pressure in the reactor 20 will preferably be maintained at about 0 kPa to about 1750 kPa to ensure that the ammonia remains in solution to effect the reaction. A crystallizer can be included downstream to effect the crystallization of sodium bicarbonate. Once the crystals have been formed, they can be processed as set forth with respect to Figure 3 by means of the filtering screen 24. The washing can then be returned via line 26 to the mixing vessel 12. The bicarbonate crystals formed can then be separated from the system by line 28 for later use. The filtrate or brine from the first reactor is reheated to about -32 ° C. The solution is maintained at a temperature of at least 32 ° C and then passed to reactor 32. Once in reactor 32, the brine solution is subjected to excess ammonium at a concentration of about 20 weight percent. The pressure in the reactor is carefully controlled by varying the ammonia injection (approximately 450 kPa) thereby controlling the desired concentration of excess ammonium. In reactor 32, injection of the solution with ammonia displaces the equilibrium solubility of the reaction solution, denoted hereinabove, to favor the formation of ammonium sulfate precipitate.

The temperature in the reactor is maintained at 32 ° C to keep the free sodium cations soluble and prevent contamination of the ammonium sulfate with undesirable solvates. When desired, the concentration of ammonia can be altered by changing the pressure control. Similar to the description for reactor 20, reactor 32 may include a downstream crystallizer to effect the formation of ammonium sulfate crystals. Once formed, the crystals can be passed over a pressure filter medium 34 and washed with a suitable wash. The ammonium sulfate crystals thus formed can then be separated by line 36 for later use. The wash can be returned to the mixing vessel 12 via line 38 for later uses. The ammonia-containing filtrate, which remains after the precipitation of the ammonium sulfate crystals, can be ignited, compressed and condensed, and collected in a compensation drum 40 as is known in the art. Once collected, the ammonia solution can be used to be injected back into the system. The final recovered solution, which contains soluble levels of ammonia, can be recycled to the mixing vessel 12 to complete the continuous operation. By implementing the above method, you can achieve a purity of ammonium sulfate greater than 50% by weight. Advantageously, the ammonia can be substantially recovered for reuse, which has positive economic advantages for the entire process. Figure 11 shows a further variation on the procedure according to Figure 10. In Figure 11, a brine conditioning step is employed between reactors 20 and 32. The brine conditioning step is effective to purify the feed stream for its introduction to the reactor 32 for the eventual formation of ammonium sulfate by further reducing the concentration of sodium ion from the feed stream entering the reactor 32. Once the sodium bicarbonate reaction is completed, the bicarbonate precipitate is separated as indicated herein with respect to Figure 10 and the brine is transferred to intermediate reactor 42. In reactor 42, the concentration of ammonia is increased to saturate the solution, while the reactor temperature is lowered to approximately 7 °. C. This results in the formation of a precipitate comprising pure sodium sulfate, or a mixed precipitate of sodium sulfate and ammonium sulfate. These precipitates are then filtered by the filter 44 and the crystals are eventually passed back into contact with the mixing vessel 12. The filtrate is fed to the reactor 32 and kept under at least the same pressure conditions as indicated for Figure 10. Once in reactor 32, the filtrate undergoes the reaction as indicated above, and the result is the formation of ammonium sulfate precipitate, however, the precipitate is formed in an environment where the concentration of sodium cation is significantly reduced in view of the intermediate process using intermediate reactor 42. The result of the process is a concentration in solution of ammonium sulfate which will effect a precipitate of a concentration greater than 73% by weight. Referring now to Figure 12, a further alternative arrangement is shown by which the process can be put into practice. In Figure 12, the general procedure may include a separate wash step to wash the bicarbonate precipitates.

Nato sodium and ammonium sulfate separately. In a possible configuration, the sodium bicarbonate that is formed in the reactor 20 can be passed into contact with a washing material, of which one example can be a source of methanol 50. The resulting filtrate can then be returned to the mixing vessel 12 through line 52. Similarly, ammonium sulfate crystals formed in reactor 42 can be passed through a second independent source of methanol 54, the filtrate being returned to the mixing vessel via line 56. The crystals of ammonium sulfate and bicarbonate can then be used for additional uses. Referring now to Figure 13, a further variation of the schematic procedure shown in Figure 10 is shown. In the procedure shown in Figure 13, the filtrate recovered from the sodium bicarbonate reaction can be converted to a liquid product. substantially pure, for example a fertilizer in the almost saturated state. This facilitates the mixing of the liquid product with other fertilizer components or allows the crystallization of the product in the desired form. The liquid product can be passed from the reactor 20 to the brine conditioning vessel 42, wherein the temperature of the solution is reduced to about 7 ° C as previously indicated herein with respect to Figure 11. In this form of In this embodiment, the concentration of ammonia is increased from about 10% to about 50% or more by weight, to thereby provide a supersaturated solution. The result is the precipitation of contaminated sodium sulfate or mixed salts of sodium sulfate and ammonium. The filtrate in this situation is substantially saturated liquid ammonium sulfate, which can then be passed to a storage unit 60. As a further alternative, a user can simply take the liquid ammonium sulfate or, alternatively, the ammonium sulfate. Can be pumped to an evaporator (crystallizer) conventional 62 to offer the mixing of the liquid with additional fertilizer components, to cause the final product to crystallize. The brine conditioning can be done in a single step or it can be conditioned in multiple steps to achieve increased separation of sodium cations; this inherently leads to an increased purity of the ammonium sulfate fertilizer. The above-mentioned steps may be any combination of known steps (precipitation by addition of salt), i.e., evaporation, addition of excess ammonia, ion exchange, cooling, among other techniques. Typically, the evaporation is carried out at a temperature of more than 59 ° C while other operations of the unit are carried out at a temperature lower than 59 ° C. Figure 14 shows a variation of the process in which the bicarbonate recovery systems can be combined to be useful in a sulfur recovery plant. The area designated by number 70 in Figure 14 illustrates the conventional apparatus used for the recovery of sulfur from an acid gas stream, using the modified Claus procedure, consisting of a single or multiple variation of thermal and recovery steps. catalytic Using the recovery procedure as previously indicated herein, sodium bicarbonate can be introduced into the tail gas stream containing residual sulfur compounds and the result can therefore be the production of sulphate of sodium sulfate. ammonium as indicated in Figure 14. The general modified Claus procedure, denoted by the number 70, can be combined with the general procedure to produce ammonium sulfate, of which the group of steps is generally indicated by the number 115 in the figure . The broad steps as illustrated in the figure are generally steps common to those shown in Figures 10 and 11. Combining the modified Claus procedure with the procedures indicated in this, the result is a sulfur separation of the order of at least 95% or greater. Figure 15 illustrates a further process variation for a sulfur plant producing lower BAT volume. The steps for the procedure are similar to those for Figure 14 and the treatment of the sulfur compound is generally denoted by the sequence of events indicated by the number 115. As an alternative, the acid gas stream may be treated directly with liquid carbonate or sodium bicarbonate solution for desulfurization and form an alternate sulfur product. Turning to Figure 16, a further embodiment is schematically shown. A lime mixing vessel 70 is provided to retain lime in any form, for example a slurry, a powder, etc., to be introduced to reactor 32 by line 72. By providing this addition to the bicarbonate process, gypsum can be produced commercial or landfill together with the sodium bicarbonate, as illustrated in Figure 16. The arrangement shown may include an ammonia recovery unit 74 which will include the usual gas recovery means known to those skilled in the art. This is useful since ammonia is released after the precipitation of the plaster and therefore can be easily recovered. Turning now to Figure 17, an additional variation of the general procedures is shown. In Figure 17, a FGD process that binds a wet scrubbing system for desulfurization uses bicarbonate or sodium carbon as the active reagent. In the illustrated embodiment, a combustion gas from an industrial boiler or tail gas unit, denoted globally by the number 90, is passed over an electrostatic precipitator or bag collector 92 or other recovery device to remove the very fine ash at 93. A water wash vessel 94 is provided to circulate wash water in the upper section of the scrubber, and accumulated levels of precipitates and fluids are removed from the vessel 94 and passed to the lower section of the scrubber. 95. Once the sodium sulfate is collected from the bottom of the scrubber 95 as a product of the scrubbing process, it is then further transferred to a mixing vessel 12 for its thickening and clarification to a saturated state for its feed to the reactor 20. From reactor 20, the sodium bicarbonate is filtered from the solution and washed in open sieve filters, of the pr This type of vacuum, type of vacuum, type of centrifuge or cyclone or any combination of these (shown in general in 97). The bicarbonate-to precipitate is washed and reduced to less than 10% liquid and then fed as a slurry to a bicarbonate slurry vessel 96 at approximately 700 kPa. At this point, the bicarbonate slurry in the container 96 is mixed with clean water supplied to the container 96 from a feed water supply container 98. The feed water is maintained at a temperature of about 48 ° C. The slurry is continuously mixed and its concentration varies between about 20% by weight and about 40% by weight. The slurry is then transferred to a high pressure solution vessel 100, at a pressure of about 1050 kPa, where a saturated solution is formed. A saturated bicarbonate solution is created using additional boiler feed water from the vessel 98, which is heated to about 176 ° C by an injection water heater 102. The final saturated concentrated solution is then injected into a wet scrubber 95 for the separation of sulfur dioxide. The temperature, pressure and reagent concentration in the final injection solution can be varied to control the level of S02 separated and the temperature of the final combustion gas leaving the wet scrubbing process. As an additional example, the temperature and pressure can be reduced to almost the atmospheric conditions that prevail in the scrubber. The temperature can then be reduced to 45 ° C to remove the water heater 102 and the high pressure reactor 100. This will result in a colder final flue gas temperature resulting from the evaporative cooling effect which may or may not be be harmful to any specific application. further, it will be appreciated that the wet scrubber 204 can have any form of contacting the reagent solution with the sulfur-containing combustion gas, eg spray dryers, etc. As an alternative to reducing the sodium ion content, the treatment with excess ammonia can be replaced by an operation in ion exchange unit. In this operation, sodium ions can be replaced with ammonium ions to prevent the formation of undesirable sodium compounds, among others.

As is known in the art, the ion exchange design depends on three broad parameters, namely, the type of resin, the resin capacity and the selectivity. As an option, by using ion exchange in one operation, the resin can be initially charged through the use of a regeneration solution, for example ammonium carbonate with ammonium ions. When a flowing stream of sodium and ammonium sulfate finds the resin, which is loaded with ammonium, there will be a propensity to exchange sodium. This propensity will also advantageously ensure that the fluid always finds a fresh resin charged only with ammonium. The ion exchange scheme can be used at any number of locations in the process as previously indicated herein to enrich the current with ammonia ions in exchange for sodium. An example of the process using an ion exchange scheme for the treatment of the brine from the reactor is shown in Figure 18. The ion exchange scheme preferably uses several columns in different modes of operation, examples of which include exchange , regeneration and reservation. The example shown in Figure 18 employs a reactor unit 220 in the production of the resin regeneration solution using ammonia containing condensed water from the evaporator / crystallizer unit as one of the feed components. The exit liquor from the regeneration of the resin can be recycled in the system. Figures 19 and 20 show additional examples of the location for the ion exchange unit along with optional conditioning steps using the conditioner 42 as previously indicated herein. Those skilled in the art will appreciate that Figures 18 to 20 are only examples of those positions where the ion exchange system 220 could be employed. Figure 21 illustrates a general schematic view of a further option that employs cooling to effect the desirable results according to the present invention. Refrigeration can be used as an additional alternative to the techniques of evaporation, ammonia displacement or ion exchange to reduce the content of sodium ion, to thereby result in a stream having a higher concentration of ammonium sulfate. One possible scheme is to cool the feed stream by cross-switching with a much colder current. As an example, the feed can be cooled within a range of 0 ° C to -40 ° C. A convenient temperature is -11 ° C. Due to the sub-freezing ranges required for cooling, a standard closed-loop cooling system can be used to cool the liquid in exchange with the power supply. Some propane and ammonia refrigerants, glycols and any other acceptable refrigerant that remains functional in the given temperature range can be used in the system. Figure 21 illustrates a possible arrangement in which the operation of the refrigeration unit is denoted in general by the number 222. At cold temperatures, the solubility of the components present in the system is substantially reduced. The salts that can not be kept in solution precipitate. The primary precipitate will be hydrated sodium sulfate and minor amounts of sodium bicarbonate and ammonium. The liquid phase 224, which leaves the refrigeration unit 222, will contain less sodium ions than the liquid phase entering the operation of the refrigeration unit as a result of the precipitation of sodium compounds. Some ammonium sulfate can precipitate if the concentration in the feed solution is high and the temperature is low enough. Although this is the case, proportionally more ammonium compounds remain in the liquid phase than the sodium compounds. The result is a liquid phase that has a much lower sodium ion content to be used for the production of ammonium sulfate. This is a clear advantage incorporating the refrigeration operation 222 based on the phase relationship of the compounds in the system. The precipitated solids can be separated from the liquid phase of the cold stream by means of any suitable solids separation device (not shown). The solids can be recirculated through the system as indicated by number 226. It has been found that the cooling scheme can be further increased by adding excess ammonia in the conditioning step with a concentration range ranging up to 20% in weight and typically 10% by weight, depending on the residual level of sodium desired in the feed brine of the fertilizer evaporator.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects or products to which it refers. Having described the invention as above, property is claimed as contained in the following:

Claims (25)

R E V I N D I C A C I O N S

1. - Process for selectively precipitating sodium bicarbonate and ammonium sulfate from a sodium-containing sulfur compound, characterized in that the process comprises the steps of: (a) providing a source of a sulfur compound containing sodium; (b) contacting said sulfur compound containing sodium with gaseous carbon dioxide and an ammonia-containing compound to generate a solution; (c) maintaining said solution at a temperature sufficient to form a single precipitate of sodium bicarbonate, to reduce the amount of aqueous sodium ions without precipitation of competitive sodium precipitates; (d) removing said precipitate of sodium bicarbonate from the solution; (e) removing the sodium sulfate; and (f) precipitate ammonium sulfate.

2. Method according to claim 1, characterized in that the process is conducted at a temperature below 59 ° C.

3. Method according to claim 1, characterized in that the method additionally includes the step of reducing the concentration of sodium ion before step (e).

4. Method according to claim 3, characterized in that said concentration of sodium ion is reduced using exchange of Ones

5. Method according to claim 1, characterized in that said concentration of sodium ion is reduced using a cooling process.

6. Process according to claim 5, characterized in that said cooling process precipitates at least one of hydrated sodium sulfate, sodium sulfate, ammonium bicarbonate and sodium bicarbonate.

7. Process according to claim 1, characterized because said sodium ion is reduced by using excess ammonia and cooling.

8. Method according to claim 1, characterized in that said concentration of sodium ion is reduced using an ion exchange and cooling combination.

9. Process according to claim 1, characterized in that the sodium concentration is reduced by increasing the weight percentage of ammonia and forming sodium sulfate and a mixed precipitate of sodium sulfate and ammonium sulfate in said solution.

10. Process according to claim 1, further comprising the step of recovering ammonia and carbon dioxide.

11. Process according to claim 1, characterized in that the method further comprises recycling the remaining carbon dioxide and ammonia to the reactor from the precipitation of the sodium bicarbonate before evaporation.

12. Process according to claim 1, characterized in that said carbon dioxide is separated by pH modification.

13. Method according to claim 1, characterized in that said carbon dioxide is separated by heating.

14. Process according to claim 1, characterized in that at least a part of the carbon dioxide and ammonia is fed to the reactor in the liquefied state.

15. Process according to claim 1, characterized in that at least a part of the carbon dioxide and ammonia is fed to the reactor in gaseous form.

16. Process according to claim 1, characterized in that the content of the reactor is maintained at a pH of from about 7 to about 9.

17. Process for producing sodium bicarbonate and sodium carbonate, characterized in that the process comprises steps of: reacting, within a reactor, sodium sulfate in aqueous solution with ammonia and carbon dioxide to precipitate sodium bicarbonate and form a first mother liquor; Separate the baking soda and dry it to produce a Sodium bicarbonate product or calcined to convert it to sodium carbonate; submit to the first mother liquor, from the precipitation of sodium bicarbonate, to evaporation to precipitate unreacted sodium sulfate, forming a second mother liquor; cooling the second mother liquor, coming from the precipitation of unreacted sodium sulfate, to precipitate a double salt of sodium sulfate / ammonium sulfate and water, forming a third mother liquor; subjecting the third mother liquor, coming from the precipitation of the double salt, to evaporation to precipitate a substantial pure ammonium sulfate in a purity of more than about 73% by weight, forming a fourth mother liquor; add double salt to the first mother liquor from the precipitation of sodium bicarbonate before evaporation; and adding the fourth mother liquor to the second mother liquor from the evaporation, to precipitate the unreacted sodium sulfate.

18. Method according to claim 17, characterized in that said process is conducted at a temperature of at least 59 ° C.

19. Process according to claim 17, which additionally includes the step of recovering ammonia and carbon dioxide.

20. Process according to claim 17, characterized in that the method further comprises recycling carbon dioxide and ammonia to the reactor from the mother liquor from the precipitation of the sodium bicarbonate before evaporation.

21. Process according to claim 19, characterized in that said carbon dioxide is separated by modification of pH.

22. Process according to claim 17, characterized in that said carbon dioxide is separated by heating.

23. Process according to claim 17, characterized in that at least a portion of the carbon dioxide and ammonia is fed to the reactor in the liquefied state.

24. Method according to claim 17, characterized in that at least a part of the carbon dioxide and ammonia fed to the reactor are fed in gaseous form.

25. - Process according to claim 17, characterized in that the content of the reactor is maintained at a pH of from about 7 to about 9.