EA040135B1 - METHODS FOR PRODUCING POTASSIUM SULPHATE AND SODIUM CHLORIDE FROM WASTEWATER - Google Patents

Description

Technical field

The present invention relates to systems and methods for the production of potassium sulfate.

State of the art

One of the difficulties in the production of potassium sulfate is its implementation in a cost-effective and efficient manner. In this sense, the challenge is often how to cost-effectively process the residual solution(s) (such as the mother liquor formed in the glaserite crystallizer) obtained during the production of potassium sulfate in order to achieve an acceptably high yield. The use of refrigeration crystallization or evaporative crystallization, sometimes used in the production of potassium sulfate, requires a large amount of energy, which makes the production of potassium sulfate more expensive.

There is a need for a method for the production of potassium sulfate, enabling cost-effective treatment of residual solutions formed during the production of potassium sulfate.

The essence of the invention

The present invention relates to a process for the production of potassium sulfate and sodium chloride from sources containing sodium sulfate and potassium chloride. During the production of potassium sulfate, a residual solution is formed, such as the mother liquor of the glaserite crystallizer. An anion isolation module is used to extract sulfate from the residual solution. The residual solution is sent to the anion isolation module and a retarded stream or retentate and a filtered stream or permeate are obtained. The retarded stream, or retentate, is rich in sulfate. The filtered stream, or permeate (depleted in sulfate), from the anion isolation module is sent to a sodium chloride crystallizer where sodium chloride crystals are obtained. In one embodiment of the invention, the anion isolation module is a nanofiltration membrane.

In one embodiment of the invention, a source of sulfate, such as sodium sulfate, is mixed with a solution containing potassium. The mixture is subjected to a glaserite crystallization process to obtain glaserite crystals. The glaserite crystals are sent to a potassium sulfate reactor where the glaserite crystals are mixed with a potassium source such as potassium chloride. This leads to precipitation and the formation of potassium sulfate crystals, which are separated from the solution. The mother liquor formed in the glaserite crystallizer is sent to an anion isolation module, such as a nanofiltration membrane module. In the anion isolation module, a retarded stream, or sulfate-rich retentate, is obtained. The filtered stream or permeate formed in the anion isolation module contains sodium and chloride. It is sent to a sodium chloride crystallizer where sodium chloride crystals are formed.

Another embodiment of the invention relates to a process for the production of potassium sulfate from a waste stream. The waste stream is concentrated and a brine is obtained which contains sodium, chloride and sulfate. The method then includes crystallizing mirabilite from brine in a mirabilite crystallizer to obtain mirabilite crystals and a mirabilite crystallizer solution. The mirabilite crystals are separated from the mirabilite crystallizer solution. The method then includes mixing mirabilite crystals with a solution containing potassium in a glaserite reactor to obtain glaserite crystals. Glaserite crystals are separated from the solution. Then the glaserite crystals are sent to the potassium sulfate production reactor. A source of potassium, such as potassium chloride, is mixed with glaserite crystals in a potassium sulfate reactor to form potassium sulfate crystals and a solution containing potassium. Potassium sulfate crystals are separated from the solution.

The process for the production of potassium sulfate just described also includes filtering the mirabilite crystallizer solution to obtain a filtered stream, or permeate, and a retained stream, or retentate. The retentate, or sulphate-rich retarded stream, is recycled to the mirabilite crystallizer. The filtered stream, or sulfate-depleted permeate, is sent to a sodium chloride crystallizer to obtain sodium chloride crystals.

Other objects and advantages of the present invention will become apparent and apparent from a consideration of the following description and the accompanying drawings, which merely illustrate the invention.

Brief description of the drawings

In FIG. 1 is a diagram of a process for the production of potassium sulfate.

In FIG. 2 is a diagram illustrating a similar process for the production of potassium sulfate, which, however, also includes a solar evaporation process to crystallize sodium chloride.

In FIG. 3 is a diagram showing a process for the production of potassium sulphate integrated into a mining potash production process.

In FIG. 4 is a diagram of another embodiment of integrating a potassium sulfate production process into a potash production process.

In FIG. 5 is a diagram of another alternative embodiment of a process for the production of potassium sulfate and sodium chloride crystals.

In FIG. 6 is a diagram of a process for the production of potassium sulfate and sodium chloride crystals using a mirabilite crystallizer downstream of a glaserite reactor.

In FIG. 7 is a diagram of a process for the production of potassium sulfate and sodium chloride, which is

- 1 040135 alternative to the method shown in FIG. 6.

In FIG. 8 is a schematic diagram of a process for producing chemicals or liquid fuels from coal, including processing a wastewater stream from a process for producing chemicals or liquid fuels from coal and producing potassium sulfate and sodium chloride crystals.

In FIG. 9 is another diagram of a process for producing chemicals or liquid fuels from coal, including processing a wastewater stream from a process for producing chemicals or liquid fuels from coal and producing potassium sulfate and sodium chloride crystals.

Fig. 10 is a phase diagram of various salts that can be recovered using the described method.

Description of exemplary embodiments of the invention

The present invention relates to a process for the production of potassium sulfate. Before describing specific embodiments of this method, it would be useful to give a brief overview of the process for the production of potassium sulfate, which is the subject of this document. Provide a source of sodium sulfate. The source of sodium sulfate is sent to the glaserite crystallizer. Downstream of the glaserite crystallizer are a potassium sulfate production reactor. The potassium-enriched solution is sent from the potassium sulfate production reactor to the glaserite crystallizer, where the potassium-enriched solution is mixed with a source of sodium sulfate. In the glaserite crystallizer, glaserite crystallizes and glaserite crystals and mother liquor are formed. Glaserite crystals are separated from the mother liquor and sent to a downstream potassium sulfate reactor. The source of potassium chloride is sent to the potassium sulfate production reactor and mixed with glaserite crystals. As a result, crystals of potassium sulfate precipitate in the potassium sulfate production reactor. The potassium sulfate crystals are separated from the solution in the potassium sulfate reactor.

In addition, the mother liquor from the glaserite crystallizer is sent to an anion isolation module such as a nanofiltration module. The anion isolation module produces a sulphate-rich lag stream and a sulphate-depleted permeate stream. The sulphate-rich retained stream is recycled to the glaserite crystallizer and mixed with the sodium sulphate source and the potassium-rich solution from the potassium sulphate reactor. Sodium chloride crystals are obtained from a sulfate-depleted permeate stream.

With regard to FIG. 1 and the method for producing potassium sulfate presented therein, the source of sodium sulfate is sent to the glaserite mold 110. The source of sodium sulfate may be different. In one example, the sodium sulfate source may be simply sodium sulfate crystals or sodium sulfate crystals from an upstream process. In another example, the sodium sulfate source is raw or molten Glauber's salt. In some cases, the source of sodium sulfate may be naturally occurring Glauber's salts, formed as a result of natural evaporation and/or cooling in salt lakes. As shown in FIG. 1, the source of sodium sulfate can also be a brine or suspension of sodium sulfate.

A solution (sometimes referred to as a potassium sulfate solution) enriched in potassium is sent from the downstream potassium sulfate production reactor 114 via line 116 to the glaserite crystallizer 110. In the crystallizer 110 glaserite solution of potassium sulfate is mixed with a source of sodium sulfate. If desired, steam may be used to evaporate the glaserite crystallizer 110. Typically, in one of the examples of the method, the crystallizer operates at a temperature of approximately 40-45°C. As a result, glaserite crystals, mother liquor and (potentially) condensate are formed. By any of a number of known methods for separating solid and liquid phases, the glaserite crystals formed in the glaserite crystallizer 110 are separated from the mother liquor. The separated crystals are sent via line 112 to a reactor 114 for producing potassium sulfate.

The potassium source is sent via line 118 to the potassium sulfate reactor 114 where the potassium source is mixed with glaserite crystals. In general, the purity of the potassium chloride source can be as commercially available, ranging from flotation purity to high purity potassium chloride, or even brines with significant impurities such as sodium chloride, calcium or magnesium compounds, or other compounds that can be recycled. from existing processes or be waste streams or wash streams. As shown in FIG. 1, the potassium source may be a brine or potassium chloride slurry. Potassium chloride brine can be prepared using pure water or condensate to dilute potassium chloride. Alternatively, the dilute solution can be obtained as a mixture of pure water and any mother liquor circulating in the system. In the latter case, the mixture of pure water and mother liquor can be treated to remove hardness salts (calcium and magnesium) in the form of hydroxides, carbonates or sulfates using a common softening agent such as lime, soda ash or caustic soda.

In any case, in the method shown in FIG. 1, a source of potassium is sent via line 118 to a potassium sulfate reactor 114 and mixed with glaserite crystals therein. As a result, potassium sulfate precipitates out of solution, forming potassium sulfate crystals. Potassium sulfate crystals are separated

- 2 040135 from the solution, obtaining, as shown in FIG. 1, potassium sulfate (K2SO ₄ ). It can be seen that when a source of sodium sulfate is introduced into the glaserite crystallizer 110, it may be desirable to limit the sodium concentration in the potassium sulfate reactor by maintaining the sodium concentration below its solubility limit. Of course, this facilitates the precipitation of potassium sulfate from solution in the reactor 114 for producing potassium sulfate. It can also be seen that the potassium source may be partly directed to the glaserite reactor when necessary to control or start the process.

The mother liquor obtained in the glaserite crystallizer 110 is sent via line 120 to the anion isolation module. The function of the anion isolation module is to retain sulfate and at the same time produce a filtrate or permeate that is depleted in sulfate and in this particular case can be used to produce sodium chloride crystals. For this purpose, various anion isolation devices can be used. In the examples given in this document, the nanofiltration module 122 is used. The mother liquor from the glaserite crystallizer 110 is sent via line 120 to the nanofiltration module 122, where a delayed flow and a permeate flow are formed. The delayed stream is rich in sulfate. It is recycled via line 124 to the glaserite crystallizer 110 where it can advantageously be used to produce glaserite crystals. Stream 126 permeate, as noted above, depleted in sulfate. In the nanofiltration module 122, sodium and chloride ions pass through the membranes and eventually enter the sodium chloride crystallizer 128. The permeate is sent via line 126 to a sodium chloride crystallizer 128 fed or driven by steam, where sodium chloride crystals are formed and separated from the mother liquor formed in the sodium chloride crystallizer 128. The sodium chloride crystallizer 128 is steam or MVR (Mechanical Vapor Recompression) driven and in one example operates at a temperature of approximately 60-80°C. The mother liquor formed in the crystallizer 128 is sent via line 130 to the glaserite crystallizer 110 for further processing.

In FIG. 2 shows another method for producing potassium sulfate from sources of sodium sulfate and potassium chloride. In the case of the embodiment of the invention shown in FIG. 2 compared to the method shown in FIG. 1, the sodium chloride crystallizer 128 is changed to a pond, pool, or solar evaporator. This method uses a cheap solar evaporation process to produce sodium chloride crystals. Depending on the geographic location, a pond or pool used for solar evaporation can experience large seasonal temperature fluctuations. During the transition from summer to winter, it may be necessary to change the brine to avoid the deposition of sodium chloride contaminated by additional crystallization of other salts, especially at low temperatures.

In the case of the method shown in FIG. 2, the permeate or filtrate from the anion isolation module is sent via line 126 to the solar evaporation pond or pond. As described with respect to the method shown in FIG. 1, the permeate is depleted in sulfate, but in this case contains sodium ions and chloride ions. During solar evaporation in a pond or pool, the concentration of permeate or leachate increases, causing the sodium chloride to precipitate and crystallize. The sodium chloride crystals are separated from the permeate or filtrate by any of a number of known methods for separating solid and liquid phases. The concentrated permeate, or filtrate, is sent back through line 140 to the glaserite crystallizer 110. Otherwise, the method shown in FIG. 2 is similar to the method shown in FIG. 1.

In some cases, related or other processes that provide potassium can be integrated with the potassium sulfate production process, and the secondary energy obtained or released in one of the processes can be used in another process in order to reduce energy costs. Examples of integrated processes are shown in FIG. 3 and 4. Both processes shown in FIG. 3 and 4 are based on the combination of the potassium sulfate production process and the potash production process.

As shown in FIG. 3, a process for the production of potassium sulfate, similar to that shown in FIG. 1 is integrated with the potash production process, which uses brine obtained from mining. As shown in FIG. 3, the brine is sent to a multi-effect evaporator (MEE) 150. In the multi-stage evaporator 150, the concentration of the brine increases, and during the evaporation process, crystallization occurs and separation of sodium chloride from the brine. The sodium chloride crystals are removed from the concentrated brine until the concentration of sodium and potassium approaches the saturation point.

The concentrated brine is then sent to a solid-liquid separator 152 located downstream of the MEE 150. In the solid-liquid separator 152, calcium sulfate seeds are separated, in this case by settling.

A precisely defined amount of dilution water is added to the concentrated brine; the concentrated brine, together with the dilution water, is cooled in a multi-stage evaporative crystallizer, designated in the figures as multi-stage KCl 154 evaporative crystallizer. High quality and low quality potassium chloride is formed in the various stages of the multi-stage KCl 154 evaporative crystallizer. The residual cold brine formed in the KCl 154 multi-stage evaporative crystallizer is recycled to the MEE 150. The cold brine is recycled until, due to the accumulation of impurities in it, it is necessary to remove part of the cold brine for additional processing or for proper disposal. manner.

The low grade potassium chloride crystals formed in the last stage of the KCl 154 multi-stage evaporative crystallizer are used as the potassium source in the potassium sulfate production process. Note that the potassium chloride crystals from the multi-stage evaporative KCl 154 crystallizer are sent via line 156 to the unit indicated in FIG. 3 brine or suspension of KCl. Thus, the potassium chloride crystals produced in the KCl 154 multi-stage evaporative crystallizer in some cases constitute all or substantially all of the potassium source required for the production of potassium sulfate. In other cases, the potassium chloride crystals produced in the KCl 154 multi-stage evaporative crystallizer may simply supplement the potassium source supplied to the potassium sulfate production process from outside.

In addition, in the process shown in FIG. 3, thermal integration is applied. The waste stream from the MEE 150 at a temperature of approximately 70°C can be used to drive the crystallizer 128 sodium chloride. In addition, this waste stream can be used in a two (or more) stage configuration to drive the glaserite mold 110 as well, or at least as a supplement to the steam supplied to the glaserite mold from outside. Note the one shown in Fig. 3 line Recovered steam from the sodium chloride crystallizer 128 to the glaserite crystallizer 110.

The method shown in FIG. 4 is also an integrated process including the production of potassium sulfate and potash. This process is similar in many respects to the process shown in FIG. 3. However, there are a number of differences. First, the sodium chloride crystallizer 128 of FIG. 3 is excluded. Second, the permeate or filtrate from the anion isolation module or nanofiltration module 122 is sent via line 200 to the MEE 150. As described above, the MEE 150 provides an increase in the concentration of the brine obtained from mining, and in this case, the production of sodium chloride crystals, which separate. Third, the waste stream from the MEE 150 is sent via line 202 to the glaserite crystallizer 110 for actuation. In some cases, the secondary energy coming from the MEE 150 may be sufficient to carry out the process of glaserite crystallization. In other cases, the glaserite mold 110 may require an external steam supply, in which case the waste stream from the MEE 150 simply supplements this energy supply and reduces energy costs. Finally, the cold brine (or any intermediate brine formed in the flash crystallizer) from the multi-stage KCl flash crystallizer 154 is not only recycled to the MEE 150, but a portion of it is also sent via line 204 to the glaserite crystallizer 110.

In FIG. 5 shows another alternative for the production of potassium sulfate as well as sodium chloride from a wastewater stream containing sodium and sulfate. Depending on the composition of the wastewater stream, it may be advantageous (and optimal) to use a membrane separation module, such as a nanofiltration (NF) membrane 13, upstream of the upconcentration process. If such a nanofiltration membrane is used, it may be necessary to use a mirabilite crystallizer, as described below for other processes. In particular, as shown in FIG. 5, the wastewater stream is directed to the membrane separation module. In the embodiment of the invention shown in FIG. 5, a nanofiltration membrane is applied. The nanofilter membrane allows for delayed flow and permeate flow. The delayed flow is fed to the concentration increase module, where the concentration of the brine is increased. This results in a first brine stream, or slurry, which is sent to a downstream glaserite reactor or glaserite crystallizer. The potash solution from one of the subsequent stages is mixed with the first brine stream, or slurry, in the glaserite reactor to form glaserite crystals. Where a glaserite crystallizer is used, the potash solution and the first brine stream or slurry are mixed in the glaserite crystallizer or at a point upstream of the glaserite crystallizer. The glaserite crystals are separated from the potash solution and sent to a downstream potassium sulfate reactor. A source of potassium is fed into the potassium sulfate production reactor and mixed with glaserite crystals to form potassium sulfate crystals. Various sources of potassium can be used, however, in the embodiment of the method shown in FIG. 5, the source of potassium is KCl. The resulting crystals of potassium sulfate are separated from the potassium solution. To provide a source of potassium in the glaserite reactor or glaserite crystallizer, the glaserite reactor or glaserite crystallizer is fed a potassium solution from the potassium sulfate reactor, which forms the source of potassium used in the process.

When in the embodiment of the method shown in FIG. 5, the glaserite production reactor is used, the potassium solution from the glaserite production reactor is sent to the sodium chloride crystallizer, in which sodium chloride crystals are obtained. A sodium chloride depleted mother liquor is formed in the sodium chloride crystallizer and this mother liquor is recycled to the glaserite reactor. When a glaserite crystallizer is used in the processes described herein, it is advantageous to place an anion isolation module between the glaserite crystallizer and the sodium chloride crystallizer. One example of an anion isolation module, as already mentioned above, is a nanofiltration module. In any case, when in the embodiment of the invention shown in FIG. 5, a glaserite crystallizer is used, a potassium solution or a concentrate formed in the glaserite crystallizer is sent to a nanofiltration membrane module operatively connected between the glaserite crystallizer and the sodium chloride crystallizer. In the nanofiltration module or the anion isolation module, a retarded stream, or sulfate-rich retentate, is formed, which is recycled to the glaserite reactor. In the nanofiltration or anion isolation module, a filtered stream, or permeate, usually depleted in sulfate, is produced, which is sent to a sodium chloride crystallizer where sodium chloride crystals are obtained.

The permeate stream formed on the nanofilter membrane 13 is also treated to increase the concentration. In FIG. 5 this is shown as an increase in brine concentration. This produces a second stream of brine. In one embodiment of the invention, the second brine stream is sent to a sodium chloride crystallizer where sodium chloride crystals are obtained, which are separated. As one option, the mother liquor formed in the glaserite reactor can be sent to the same sodium chloride crystallizer. Typically, the solution fed from the glaserite reactor to the sodium chloride crystallizer is relatively enriched in sodium chloride, and the solution returned from the sodium chloride crystallizer to the glaserite reactor is typically depleted in sodium chloride.

In FIG. 6 shows another process for treating a wastewater stream containing sodium and sulfate, which produces potassium sulfate and sodium chloride. Waste water is sent to a concentrator (such as an evaporator) 30. In concentrator 30, waste water is concentrated to a brine containing sodium, chloride, sulfate, and various minor components, and a condensate is obtained. The condensate can be drained. The brine is sent to the cooling crystallizer 32 mirabilite. In it, the brine is cooled and mirabilite crystals (Na ₂ SO ₄ -10H ₂ O) and mirabilite mother liquor, partially depleted in sulfate and partially enriched in chloride, are obtained.

The mirabilite crystals are separated from the mirabilite mother liquor and sent to the reactor 38 for producing glaserite. In it, mirabilite crystals are mixed with a source of potassium. Mirabilite crystals react with potassium to form glaserite crystals (K ₃ Na(SO ₄ ) ₂ ). Potassium mixed with mirabilite crystals can come from various sources. The potassium-rich solution is present in the downstream reactor, which in this case is the potassium sulfate production reactor 40. The potassium-enriched solution from the potassium sulfate reactor 40 is recycled to the glaserite reactor 38 and mixed with mirabilite crystals to form glaserite crystals and a solution corresponding, for example, to point (G) in the phase diagram shown in FIG. 9.

Glaserite crystals are separated from the mother liquor of the glaserite production reactor and sent to the potassium sulfate production reactor 40. A source of potassium, such as potassium chloride (KCl), is added to the potassium sulfate reactor 40 and reacted with glaserite crystals to form potassium sulfate (K ₂ SO ₄ ) and a potassium-rich solution, which is sent from the potassium sulfate reactor 40 to the reactor 38 obtaining glaserite. In one embodiment, the potassium chloride added to the potassium sulfate reactor 40 is in the form of a slurry or slurry. In one exemplary method, the sodium and sulfate introduced into the glaserite composition is kept in solution by limiting the sodium concentration to below the saturation concentration of the glaserite, as shown as point (P) in the phase diagram shown in FIG. 9.

Due in part to the recirculation of the potassium-enriched solution from the potassium sulfate reactor 40 to the glaserite reactor 38, the solution in the glaserite reactor 38 can be enriched in sodium ions and chloride ions. To reduce the concentration of sodium and chloride in the solution of the reactor for obtaining glaserite, the solution from the reactor 38 for obtaining glaserite is sent to the evaporative crystallizer 36 of sodium chloride. In it, the solution coming from the reactor 38 for producing glaserite is heated and sodium chloride crystals are obtained. During the crystallization of sodium chloride, a condensate and a mother liquor are formed. The mother liquor obtained in the sodium chloride crystallizer 36 is depleted in sodium and chloride. The sodium chloride crystals are separated from the solution formed in the sodium chloride crystallizer 36 and the solution is recycled from the sodium chloride crystallizer to the glaserite reactor 38 .

Meanwhile, the solution from the mirabilite crystallizer 32 is processed in an anion isolation module or a filtration module. In one embodiment of the invention, the filtration module is a nanofiltration module 34 . Filtration of the solution from the mirabilite crystallizer results in a permeate stream and a lag stream in the filtration module. Typically, sulfate is retained in the nanofiltration module 34 while sodium and chloride ions pass through the nanofiltration module. In the method shown in FIG. 6, the retained stream is recycled to the mirabilite crystallizer 32 and the permeate stream from the filtration module is sent to the sodium chloride crystallizer 36. In a significant number of applications, the mirabilite crystallizer mother liquor contains

- 5 040135 sulfate, sodium, chloride and even other impurities. The function of the anion isolation module or the nanofiltration module 34 is to effectively separate sulfate from sodium, chloride and other impurities so that sulfate can be efficiently used to produce potassium sulfate. Thus, the retarded stream, or retentate, of an anion isolation module is typically rich in sulfate and recycled and used to produce potassium sulfate. The anion isolation module or nanofiltration module 34 preferably allows sodium and chloride to pass into the permeate stream, which is sent to the sodium chloride crystallizer 36 .

In some embodiments, the mirabilite crystallizer and/or the sodium chloride crystallizer and/or the permeate stream may be diverted with additional wash streams directed to the final drainless (waste) crystallizer. Thus, these streams can be processed for disposal.

In the above description of the embodiment of the invention shown in FIG. 6, the use of a glaserite reactor is considered. In the embodiments of the invention shown in FIGS. 6, 7 and 8, as seen in the drawings, instead of a glaserite reactor, a glaserite crystallizer can be used to produce glaserite crystals. When a glaserite crystallizer is used, in many cases it is preferable to provide an anion isolation module, such as a nanofiltration module, between the glaserite crystallizer and the sodium chloride crystallizer. So, when using the nanofiltration module, the potassium solution or the mother liquor obtained in the glaserite crystallizer is sent to the nanofiltration module. The nanofiltration module produces a lag stream that is recycled to the glaserite crystallizer and a permeate stream that is sent to the sodium chloride crystallizer where sodium chloride crystals form. Significantly, the delayed stream recycled to the glaserite crystallizer is rich in sulfate, while the permeate stream sent to the sodium chloride crystallizer is generally depleted in sulfate.

In FIG. 7 shows an alternative method similar in many respects to the method shown in FIG. 6. There are cases in which it is useful and advantageous to have two separate evaporative sodium chloride crystallizers. This is the case in the embodiment of the invention shown in FIG. 7. This method includes two crystallizers 36 and 42 of sodium chloride. Depending on the composition of the wastewater or brine being treated, in particular if attention is paid to the ratio of Cl7SO ₄ ² ' and other dissolved impurities and the purity of potassium sulfate, it may be preferable to use two sodium chloride crystallizers 36 and 42, as shown in FIG. 7. In some embodiments, the use of a nanofiltration module between the glaserite reactor 38 and the sodium chloride crystallizer 42 may be considered to increase the Cl7SO ₄ ² ' ratio in the sodium chloride crystallizer inlet stream to increase its efficiency, similar to the method illustrated in FIG. 1. This also applies between module 38 and 36 in FIG. 6.

The exemplary methods shown in FIG. 1-7 can be integrated into wastewater treatment methods generated by various processes. One of the types of wastewater that can be treated using the methods shown in FIG. 1-7 are wastewater from processes for the production of chemical products or liquid fuels from coal. An example of this type of processing is shown in FIG. 8.

Let us turn to Fig. 8 and 9. Processes for producing chemicals or liquid fuels from coal produce useful products such as fuels and plastics. Typically, in the process 12 for producing chemical products or liquid fuels from coal, the coal is gasified to form synthesis gas. In one example, gasification occurs when pulverized coal and hydrogen gas, as well as recycled coal-derived liquids, are mixed with a catalyst to form a raw gas. This can be done under high pressure conditions. The raw gas can then be processed into artificial gasoline, diesel fuel or other hydrocarbon products. In one gas processing method, raw gas is brought into contact with water to cool the gas. Cooling makes it possible to obtain a product containing gas and liquid phases. Oil can be separated from the liquid phase, resulting in coal gasification wastewater. The wastewater can then be supercritically treated, brought into contact with oxidizing agents such as organics and ammonium nitrogen, to produce syngas. After gasification, the resulting products can be subjected to further processing, for example, in accordance with some methods of indirect coal processing. After gasification, the synthesis gas is used in the Fischer-Tropsch synthesis, obtaining useful products, as well as steam and tail gas, which can be used to generate electricity. During the production of chemicals or liquid fuels from coal, effluents are generated at various points in the process that contain alkali metals (usually sodium), sulfate and chloride. During the gasification stage, waste water is generated by using water to remove slag and fly ash from the gasifier, to clean the synthesis gas from solid particles and chlorides, and to treat the condensate formed when the synthesis gas is cooled. Typically, these wastewaters contain chloride, ammonia, cyanides and fly ash. sewage

- 6 040135 water is also formed during the Fischer-Tropsch synthesis. They usually contain oxidized hydrocarbons and toxic metals. Other Fischer-Tropsch synthesis processes may produce wastewater containing organic compounds, cyanides, ammonia, and phenolic contaminants. While examples are given here of processing coal to produce chemicals or liquid fuels, those skilled in the art will appreciate that the described methods can be used to treat wastewater from any process for producing chemicals or liquid fuels from coal, or any wastewater, waste brine, or process brines from other processes, especially sulfate-enriched brines sent to effluents in the salt industry.

With regard to the embodiment of the invention shown in FIG. 8, wastewater from the conversion of coal to produce chemicals or fuels is, in some embodiments, sent to a pre-treatment process or process 18. Pre-treatment 18 removes various contaminants, which may use one or several traditional pretreatment methods. For example, pre-treatment may include pH adjustment, membrane filtration (eg, reverse osmosis membrane filtration), ion exchange, chemical treatment such as softening and/or chemical precipitation, or a combination thereof. Those skilled in the art will appreciate that in some embodiments no pretreatment is used, and in those embodiments where pretreatment is used, the type of pretreatment may vary depending on the contaminants present in the water.

After pre-treatment, the wastewater is sent to a concentrator 22. Concentrator 22 removes water and potentially some impurities that can be further processed or removed. Meanwhile, the concentration of the remaining impurities increases. Although various types of concentrators can be used, in some embodiments of the invention, the concentrator 22 is an evaporator, the product of which is water with a high concentration of impurities. In other embodiments of the invention, the concentrator 22 may be a reverse osmosis module, through which a permeate and a delayed stream containing water with an increased concentration of impurities are obtained. In some embodiments of the invention using reverse osmosis modules, the permeate can be recycled to the process of obtaining chemical products or fuels from coal.

A typical composition of wastewater at the outlet of the concentrator 22 may include, among others, sodium (Na ⁺ ): 0.1-10%, more often 5-10%;

sulfate (SO ₄ ² '): 0.1-10%, more often 7-10%;

chloride (Cl ^- ): 0.1-6%, more often 3-6%;

other components such as silicon oxide, organic compounds, potassium, nitrate, ammonia 1-2%.

In some embodiments of the invention, concentrated wastewater from the concentrator 22 is sent to the process 26 for the removal of organic compounds. Various methods can be used to remove organic compounds, such as filtration, adsorption, chemical treatment, biological treatment. In one of the embodiments of the invention, the process 26 removal of organic compounds includes the treatment of concentrated wastewater with activated carbon. Those skilled in the art will appreciate that the removal of organic compounds is optional and its use depends on what impurities are present in the wastewater.

After removal of the organic compounds, the wastewater may be treated according to, for example, the method shown in FIG. 6. Specifically, the wastewater is treated in the brine concentration module 30 to remove water and potentially volatile compounds in the form of condensate and produce a concentrated brine. The concentrated brine from the brine concentration increasing module 30 is sent to the mirabilite crystallization module 32, where it is subjected to cooling crystallization to obtain mirabilite crystals. Then, the mirabilite crystals formed in the mirabilite crystallization module 32 are separated from the mother liquor; raw, molten or dissolved mirabilite crystals are sent to the reactor 38 to obtain glaserite. In the glaserite reactor 38, mirabilite crystals are reacted with a potassium-enriched solution to produce glaserite. Glaserite is separated from the solution and sent to the reactor 40 to obtain potassium sulfate. There it is mixed with potassium chloride. The reaction produces potassium sulfate crystals and a sodium and chloride-enriched wash stream. Potassium sulfate crystals are separated from the sodium and chloride-enriched wash stream. The wash stream is returned to the reactor 38 for producing glaserite. Since sodium and chloride accumulate in the potassium solution in the glaserite reactor, this solution is sent to the sodium chloride crystallizer 36 . Here sodium chloride crystallizes, and the remaining solution, already depleted in sodium and chloride, is recycled to the glaserite reactor. Meanwhile, the wash stream from the mirabilite crystallizer 32 can be filtered in the nanofiltration module 34, while the delayed stream is recycled to the mirabilite crystallizer 32. The permeate from the nanofiltration module 34 is sent to a sodium chloride crystallizer 36 or a separate sodium chloride crystallizer, or partially discarded.

Sometimes the residual wash stream from the chloride crystallizer can be sent to the final crystallizer for further processing and removal of contaminants. This, among other things, can be obtained in demand sulfates and chlorides, which can be put up for sale or used in other processes.

When treating wastewater generated during coal conversion in the exemplary manner shown in FIG. 8, as well as other methods described herein, the amount of contaminants discharged into the environment is significantly reduced. Instead of wasting large quantities of water, the water is treated and disposed of in a safe manner. In addition, the described methods provide useful pure salts from the waste stream, which can be offered for sale or used in other processes. These methods optimize salt recovery and reduce operating costs and waste.

The process for converting coal into chemicals or fuels, shown in FIG. 8 may be modified by including one of the processes shown in FIG. 1-4. For example, in FIG. 9 shows a process for producing chemical products or fuels from coal using the basic method shown in FIG. 1 and described above. Those. waste water generated during the conversion of coal into chemicals or fuels can be concentrated to obtain a brine containing sodium sulfate. This sodium sulfate containing brine may be directed to the glaserite crystallizer 110 shown in FIG. 1-4, and the methods presented in these figures can be applied to the production of potassium sulfate using sources of sodium sulfate and potassium chloride.

Although the present methods and processes have been shown and described in sufficient detail with respect to a few specific exemplary embodiments thereof, those skilled in the art should understand that this description is not intended to limit the methods or processes to these embodiments, as various modifications, omissions or omissions are possible in the described embodiments. additions, essentially not going beyond the novelty and advantages of the described invention.

Example

In this example, a source of sodium sulfate and a source of potassium chloride were used to produce crystals of potassium sulfate and sodium chloride according to, for example, the method shown in FIG. 1.

source of sulfate

Serving Glauber's Salt 2.30 t/h* Na ₂ SO ₄ -10H ₂ O 95, 50 % weight. NaCl 0.14 % weight. _CaSO4 0.03 % weight. MgCl ₂ 0.03 % weight. Moisture 4.30 % weight.

* tons per hour

Source of potassium

Submission KS1 eleven t/h* KS1 95.00 % weight. NaCl 3.70 % weight. MgCl ₂ 0.40 % weight. _CaSO4 0.40 % weight. Insoluble 0.50 % weight.

* tons per hour

The sulfate source can be prepared by melting Glauber's salt (at about 35-55° C.) using a waste stream from a glaserite crystallizer or a sodium chloride crystallizer. Potassium chloride solution can be prepared using pure condensate. Alternatively, a mixture of pure water and mother liquor can be used. In this alternative, impurities can be removed from the mixture by adjusting the pH of the mixture to more than 10 to precipitate hardness salts (calcium and magnesium) in the form of hydroxide, carbonate or sulfate. In this case, a softening agent, such as caustic soda, soda ash or lime, can be added to the mixture in order to remove hardness salts. The molten Glauber's salt is fed into the glaserite crystallizer and mixed with the mother liquor recycled from the nanofiltration module 122, as well as with the potassium solution coming from the downstream potassium sulfate reactor. This usually produces approximately 1.3 t/h of glaserite crystals at 40-45°C. The mother liquor formed in the glaserite reactor typically contains about 33.5% dissolved ionic components, mainly in the form of chlorides (30 g NaCl/100 g H ₂ O and

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11.4 g KCl/100 g H2O). The sulfates in the mother liquor typically range from about 2.4 g/100 g H2O for potassium salts to 6.4 g/100 g H2O for sodium salts.

The mother liquor obtained in the glaserite crystallizer is pumped under pressure into the nanofiltration module at a flow rate of approximately 15 to 30 t/h, while the permeate is from 25 to 50%, and the operating pressure is usually from 15 to 40 bar abs. In the same example, about 0.4 to 1 t/h of dilution water is added to the glaserite crystallizer mother liquor to avoid saturation due to the sulfate concentration gradient. In the nanofiltration module, a delayed stream is obtained in which the sulfate concentration is increased to about 3-10 g per 100 g H2O, while the chloride concentration is only slightly affected due to the polarization effect and the Donnan effect in the nanofiltration module. A typical permeate stream produced in a nanofiltration module contains less than 0.5 g accumulated sulfate per 100 g H2O. The permeate stream is sent to the sodium chloride crystallizer at a rate of about 7 t/h. At this stage, the typical ratio of sodium to potassium is from about 2.5 to 2.7 and decreases to about 1.1-1.3 after crystallization of about 0.9 t/h NaCl at a temperature in the sodium chloride crystallizer from 60 to 80° WITH. This range varies depending on the temperature used in the sodium chloride crystallizer. The evaporation rate generally reaches about 2.3-2.6 tons per ton of potassium sulfate produced. The mother liquor produced in the sodium chloride crystallizer and recycled to the glaserite crystallizer typically contains about 35.3% dissolved ionic components, mainly chlorides (approximately 29.2 g NaCl/100 g H2O and approximately 24.8 g KCl/100 g H2O ). The sulfates in the mother liquor formed in the sodium chloride crystallizer are typically 0.8-1 g/100 g H ₂ O for the potassium and sodium salts.

Glaserite crystals in a potassium sulfate reactor operating as a typical example are converted to potassium sulfate at a temperature of 25 to 35°C. The consumption of dilution water can be 3-3.3 t/h, provided that essentially pure crystals of potassium sulfate are obtained. The mother liquor formed in the potassium sulfate reactor is recycled at a rate of about 4-4.4 t/h to the glaserite crystallizer, where evaporation of about 1.5-1.9 t/h per ton of potassium sulfate produced is induced. The mother liquor formed in the potassium sulfate reactor typically contains about 32% dissolved ionic components, mainly in the form of chlorides (9 g NaCl/100 g H ₂ O and 25 g KCl/100 g H ₂ O). Sulfates in the mother liquor formed in the potassium sulfate reactor typically range from 2.4 g/100 g H ₂ O for potassium salts to 0.9 g/100 g H ₂ O for sodium salts.

In this example, it is assumed that the productivity of the process is about 1.25 t/h of potassium sulfate with a degree of purity of about 50-52% in terms of potassium oxide.

The present invention, of course, may be practiced differently than specifically described herein without departing from the essential features of the invention. The present embodiments of the invention are to be considered in all respects as explanatory and not restrictive; all changes consistent with the meaning and range of equivalents of the appended claims are deemed to be incorporated herein.

Claims (8)

CLAIM 1. Method for the production of potassium sulfate from a waste stream, including the stage, which concentrate the waste stream to obtain a brine or slurry; crystallizing mirabilite from brine or suspension in mirabilite crystallizer to obtain mirabilite crystals and mirabilite crystallizer solution; separating the mirabilite crystals from the mirabilite crystallizer solution; mix mirabilite crystals with a potassium solution; glaserite crystals are obtained or formed from mirabilite crystals and a potassium solution in a glaserite production reactor or a glaserite crystallizer; separating glaserite crystals from potassium solution; sending glaserite crystals to a potassium sulfate production reactor; mixing the potassium source with glaserite crystals in a potassium sulfate reactor to form potassium sulfate crystals and a potassium solution; recirculating the potash solution from the potassium sulfate reactor to the glaserite reactor or the glaserite crystallizer; the mirabilite crystallizer solution is filtered and a sulfate-depleted filtrate or permeate and a sulfate-rich retentate or retard stream are obtained; the retentate circulates the retentate, or retarded flow, into the mirabilite crystallizer; sending the filtrate, or permeate stream, to a sodium chloride crystallizer and crystallizing to obtain sodium chloride crystals; and separating the sodium chloride crystals. 2. The method according to claim 1, in which glaserite crystals are obtained in a glaserite production reactor, and - 9 040135 sob includes the direction of the potash solution from the reactor for the production of glaserite to the sodium chloride crystallizer. 3. The method of claim 1, wherein a potassium-containing concentrate is formed in the sodium chloride crystallizer, the method comprising directing at least a portion of the concentrate from the sodium chloride crystallizer to a glaserite reactor and mixing the concentrate with mirabilite crystals. 4. The method of claim 1 wherein the potassium source is potassium chloride and the potassium chloride is introduced into the potassium sulfate reactor in the form of a slurry or brine. 5. The method of claim 1 wherein the mirabilite mold is a cooling mold. 6. The method according to claim 1, wherein the mirabilite crystallizer solution is depleted in sulfate and partially enriched in chloride. 7. The method according to claim 1, in which the recirculation of the potash solution from the potassium sulfate reactor to the glaserite reactor leads to the fact that the potash solution is enriched with sodium and chloride ions, while reducing the concentration of sodium and chloride ions in the potassium solution by directing at least part of the potassium solution into a sodium chloride crystallizer, in which a mother liquor depleted of sodium and chloride ions is formed; and the mother liquor is recycled from the sodium chloride crystallizer to the glaserite production reactor. 8. The method of claim 1, wherein filtering the mirabilite crystallizer solution includes directing the mirabilite crystallizer solution to an anion separation module where a permeate stream and a lag stream are obtained.