CN1132782C

CN1132782C - Method for producing low salt low potassium heavy mass sodium carbonate by one step process

Info

Publication number: CN1132782C
Application number: CN 00103279
Authority: CN
Inventors: 喻中甫; 喻思皓
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-03-22
Filing date: 2000-03-22
Publication date: 2003-12-31
Anticipated expiration: 2020-03-22
Also published as: CN1314310A

Abstract

The present invention belongs to the field of the preparation of inorganic salt, which particularly relates to a method for producing low salt and low potassium heavy mass sodium carbonate by a one-step method. Sodium bicarbonate is put into a decomposition reacting furnace, superheated steam or saturated steam is directly used as temperature and pressure increasing media, the reaction temperature is from 120 DEG C to 180 DEG C, the reaction pressure is from 0.1MPa to 0.6MPa, the reaction time is from 6 hours to 16 hours, and a decomposition reaction is further carried out to produce low salt and low potassium heavy mass sodium carbonate. Carbon dioxide exhausted by the decomposition is directly conveyed to a multiphase reacting tower through the self pressure to prepare sodium bicarbonate. The method has the characteristics of short technological process, low energy consumption, low cost, high product quality, less investment, etc.

Description

Method for producing low-salt low-potassium heavy soda ash by one-step method

The invention relates to a method for producing low-salt low-potassium heavy soda ash by a one-step method.

The low-salt low-potassium heavy soda ash has the advantages that: the glass has the advantages of high density, large particles, good wear resistance, difficult agglomeration, capability of saving a large amount of packaging cost and transportation cost, and is most suitable for producing high-grade glass such as float glass and the like and water glass. Practice proves that the method is particularly suitable for refining vanadium pentoxide and can greatly improve the product quality.

At present, the method for industrially producing the heavy soda at home and abroad is carried out step by step, firstly, sodium bicarbonate produced by an ammonia-soda process and a combined soda process is added into a rotary furnace, water vapor with the pressure of 2.2-3.2 MPa is used as a heating medium, the sodium bicarbonate is calcined by the rotary furnace at the temperature of 220-235 ℃ to prepare the light soda ash, then the light soda ash is sent into a water mixer, a certain amount of water is added at the temperature of 90-100 ℃ to prepare sodium carbonate monohydrate, and finally the sodium carbonate is sent into the rotary calciner, and the heavy soda is calcined and dried at the temperature of 140-180 ℃ to prepare the heavy soda. As the method necessarily generates an intermediate compound, namely sodium carbonate hydrate, the high-quality and uniform solid dense soda ash is difficult to prepare.

The method for producing heavy soda ash by directly using sodium bicarbonate as a raw material is disclosed in the U.S. patent 3451767, namely, the method for producing heavy soda ash by one-step wet method. The method comprises the steps of adding sodium bicarbonate or a compound containing sodium bicarbonate into a reactor containing sodium bicarbonate slurry, circulating heat to flow through a heat exchanger, maintaining the decomposition temperature at 135-200 ℃, discharging generated sodium carbonate in a suspended state, and finally separating the generated sodium carbonate from mother liquor. The method adopts solid-liquid mixed state reaction, so the operation is more complicated, and the wall of the heat exchanger is easy to agglomerate. Furthermore, the anhydrous sodium carbonate is separated from the mother liquor and then subjected to filtration, washing, drying and other steps. European patent 138076 discloses that 4-5 reactors are used to prepare anhydrous sodium carbonate through multi-step decomposition, and requires a large amount of equipment and a complicated process. The water content of the sodium carbonate prepared in the embodiment of the method is 23-25.34%, the content of the sodium carbonate in the concentrated slurry is only 68-71.24%, and the decomposition rate of the sodium bicarbonate is 94.6-96.1%. The catalytic one-step method disclosed in chinese patent 94111741.3 is used to produce soda ash, and the technology of low-salt low-potassium soda ash is not described, and superheated steam is not used as the drying medium of soda ash.

The invention aims to overcome the defects in the prior art, simplify the process flow and equipment, reduce energy consumption and provide a very economic one-step method for producing low-salt low-potassium heavy soda ash by directly preparing the low-salt low-potassium heavy soda ash by sodium bicarbonate in one step.

The method comprises the steps of adding a raw material sodium bicarbonate into a decomposition reaction furnace 2 (shown in figure 1), directly using superheated steam or saturated steam as a medium for heating, boosting and drying reaction, and sending the mixture into the decomposition reaction furnace 2, wherein the reaction temperature is 120-180 ℃, the reaction temperature is preferably 140-180 ℃, the reaction pressure is 0.1-0.6 MPa,the reaction pressure is preferably 0.2-0.4 MPa, the reaction time is 6-16 hours, a decomposition liquid containing impurities and a mixed gas generated by the reaction are discharged from the bottom of the decomposition reaction furnace 2, namely, the mixed gas generated after the reaction is discharged from an exhaust valve 4, enters a recoverer 20 through a heat exchange evaporator 14, a gas-water separator 15, a carbon dioxide cooler 16 and a gas-water separator 17, and then the carbon dioxide is sent into a multiphase reaction tower 23 by utilizing the self pressure to prepare the sodium bicarbonate; the decomposition liquid containing impurities generated by the reaction is discharged through a valve 5; and when the reaction is carried out for 8-16 hours and the volume ratio of the water vapor to the carbon dioxide in the discharged mixed gas is 60-80: 1-2, introducing superheated water vapor, continuously carrying out reaction drying for 6-12 hours, and when the volume ratio of the water vapor to the carbon dioxide in the mixed gas is about 0, stopping introducing the gas, cooling, and discharging to obtain the low-salt low-potassium heavy soda ash product.

The main reaction equation of the invention is the decomposition reaction equation of the sodium bicarbonate.

The industrial production process of the invention is as follows:

the decomposition reaction furnace 2 (see Chinese patent 9411174.3) adopted by the method is provided with a temperature measuring point and a pressure gauge respectively at the upper part, the middle part and the lower part. The sodium bicarbonate solid is charged into the decomposition reactor 2 at a filling height of about 90% of the effective height of the decomposition reactor. And after the filling is finished, sealing the material filling cover of the reaction furnace and each sealing cover and closing each valve switch. Opening a valve 9 for saturated steam to make superheated steam or saturated steam (see figure, saturated steam is changed into superheated steam through a heat exchanger 10) pass through a gas-water separator 11, then entering the decomposition reaction furnace 2 from the upper part and the lower part of the reaction furnace (from the upper part of the reaction furnace 2 at the beginning) through an opened valve 7, uniformly distributing the superheated steam or the saturated steam through a gas distributor 3, and simultaneously enabling the furnace to be uniformly distributedThe internal pressure is increased to 0.1-0.6 MPa (gauge pressure), so that sodium bicarbonate in the furnace is subjected to decomposition reaction, the generated carbon dioxide enters one or more heat exchange evaporators 14 along with water vapor through an exhaust valve 4, brine or decomposition liquid (discharged liquid of a decomposition reaction furnace) is filled in the heat exchange evaporators 14, and the brine or the decomposition liquid is evaporated and crystallized, so that industrial salt (NaCl) or solid wet sodium carbonate is prepared, the energy loss is greatly reduced, and the cost is reduced. The water vapor in the mixed gas is condensed into liquid water, and the liquid water is carried into the gas-water separator 15 by the mixed gas for separation. The mixed gas separated from the gas-water separator 15 enters a carbon dioxide gas cooler 16, the residual water vapor in the mixed gas is cooled into liquid water, the residual gas is carbon dioxide gas with high purity and the volume percentage concentration of the carbon dioxide gas is 90-100%, the carbon dioxide and the liquid water formed by cooling enter a gas-water separator 17 for separation, the condensate is sent into a recoverer 20 through a liquid discharge valve 19, the carbon dioxide gas enters the bottom of the recoverer 20 through an exhaust valve 18 and is dispersed through a liquid layer (the liquid isthe condensate cooled by the carbon dioxide gas cooler, and the main component of the condensate is the condensate which is dispersed through the liquid layer in a bubbling modeWater and ammonium bicarbonate and carbon dioxide dissolved in water) and takes out the ammonia and the carbon dioxide in the liquid to play a role in recovering the ammonia and the carbon dioxide. The temperature of the recoverer 20 is controlled to be 40-80 ℃ so as to facilitate NH₃And CO₂The temperature of the recoverer 20 is completed by the heater 21, and the discharged carbon dioxide gas has a pressure of 0.1-0.3 MPa, and can be directly sent into the multiphase reaction tower 23 (see Chinese patent 97107482.8) without a carbon dioxide gas compressor to prepare sodium bicarbonate.

The raw material adopted by the invention can be sodium bicarbonate containing a trace amount of catalyst produced by the catalytic method of the inventor (see Chinese patent 97107482.8), and can also be sodium bicarbonate produced by an ammonia-soda method or a combined-soda method. However, sodium bicarbonate containing a small amount of catalyst is most effective.

The superheated steam and the saturated steam can be fed into the decomposition reaction furnace 2 separately or alternatively as heating and pressure increasing and decomposition reaction media. After superheated steam and saturated steam enter the decomposition reaction furnace 2, the steam contacts with sodium bicarbonate to transfer most of heat to the sodium bicarbonate to form water, and the temperature of the sodium bicarbonate is raised to 120-180 ℃.

The cooling water formed after the heat transfer of the water vapor and the water generated after the chemical reaction flow downwards along the sodium bicarbonate material layer from top to bottom in the decomposition reaction furnace 2, and in the flowing process, the impurity chlorides (such as NaCl) and sylvite in the sodium bicarbonate material have far higher solubility than sodium carbonate and sodium bicarbonate, so that the impurities chlorides and sylvite are firstly dissolved and taken away by water, and the formed decomposition liquid flows into the furnace bottom. In the initial stage of the reaction, the content of sodium chloride in the decomposition liquid is far larger than that of sodium carbonate and sodium bicarbonate. Along with the continuous progress of the reaction, the condensed water of the water vapor and the water generated by the reaction continuously form a decomposition liquid, the decomposition liquid continuously flows from top to bottom, and the sodium chloride and the potassium salt in the generated heavy sodium carbonate are continuously dissolved and automatically purified, so that the aim of automatically purifying the sodium chloride and the potassium salt in the product in the process of preparing the heavy sodium carbonate is fulfilled.

The decomposition liquid flows into the bottom of the decomposition reaction furnace 2 through the material layer, when the reaction is carried out for 1-2 hours, after a certain amount of decomposition liquid is arranged at the bottom of the reaction furnace 2, the valve 5 is opened, the decomposition liquid and a small amount of mixed gas are discharged into the gas-water separator 12, a certain amount of water is added through the water adding valve after the valve 5 according to requirements, so that pipe blockage caused by condensation and crystallization due to overhigh concentration of the decomposition liquid is prevented, and the mixed gas is discharged into a mixed gas main pipe through the valve 13 at the upper part of the gas-water separator 12. The decomposition liquid is discharged from the lower part of the gas-water separator 12 into a decomposition liquid storage tank 25 through a liquid discharge valve 24, and the decomposition liquid is pumped into a vacuum evaporator 27 through a pump 26, and the heating of the vacuum evaporator is completed by a heater 28. Here, a small amount of NaHCO is present in the decomposition liquid₃Decomposing under vacuum to generate sodium carbonate and CO₂And water, and a small amount of ammonia is evaporated and discharged with carbon dioxide to prepare sodium bicarbonate. The evaporated decomposition liquid is sent to a caustic soda workshop to prepare caustic soda or directly evaporated into wet solid sodium carbonate, and then sent back to the decomposition reaction furnace to prepare heavy soda ash.

After the sodium bicarbonate material reacts for 6-16 hours in the decomposition reaction furnace 2 under the pressure of 0.2-0.5 MPa (gauge pressure) and the temperature of 140-180 ℃, when the volume ratio of water vapor to carbon dioxide in the discharged mixed gas is 60-80: 1-2, superheated water vapor with the temperature of 160-360 ℃ is introduced to continue to react and dry for 8-12 hours. When the volume ratio of the water vapor to the carbon dioxide in the mixed gas is about 0, closing the steam valve 7, opening the exhaust valve 4 and the emptying valve 29, reducing the pressure in the decomposition reaction furnace to zero, determining to adopt hot air drying or cold air cooling according to a sampling test result, reducing the temperature by adopting the cold air when the mass percentage concentration of the sodium bicarbonate in the product is more than 98.0%, starting the air blower 30, enabling the air to enter the decomposition reaction furnace through the heater 31 (without heating) and the air inlet valve 32 to reduce the temperature of the material, and taking out the low-salt low-potassium heavy soda ash in the furnace when the temperature of the material in the furnace is reduced to 40-50 ℃. If the content of sodium carbonate is lower than 98.0%, the blown air is heated to 160-360 ℃, materials in the decomposition reaction furnace are dried until the product is qualified, and then cold air is used for cooling.

The medium adopted in the method for decomposing the sodium bicarbonate by raising the temperature and increasing the pressure can be superheated steam or saturated steam, the medium for drying the low-salt low-potassium heavy soda ash is the superheated steam, and the temperature of the superheated steam is 160-360 ℃. The optimal temperature in the decomposition reaction furnace is 140-180 ℃, the reaction pressure is 0.1-0.6 MPa, and the optimal reaction pressure is 0.2-0.4 MPa. The raw material can adopt sodium bicarbonate with sodium chloride impurity content less than 20% (weight percentage concentration).

The low-salt low-potassium heavy soda ash produced by the invention has the weight percentage concentration of 98.4-99.8% of sodium carbonate, 0.02-0.3% of sodium chloride, 0.002-0.01% of potassium chloride and 0.95-1.16 kg/m of apparent density³。

The method for preparing the heavy soda ash can reduce the weight percentage concentration of sodium chloride impurities in the product heavy soda ash to be less than 0.3 percent even if the content of the sodium chloride impurities in the material sodium bicarbonate is about 20 percent. The existing method for producing the heavy soda ash requires that the sodium chloride impurity weight percentage concentration of the raw material sodium bicarbonate is below 0.5 percent. Therefore, the method of the invention has no special requirement on the content of impurities in the process of producing sodium bicarbonate, can omit the process of washing sodium bicarbonate with water, and is beneficial to the water balance in the process of producing sodium carbonate (the water balance is to keep a certain volume of the circulating mother liquor, the volume increase can increase the consumption of raw materials, and the volume decrease can lead the circulation amount of the mother liquor to be insufficient).

The weight percentage concentration of sodium chloride of the heavy soda ash produced by the method is 0.02-0.3%, and the weight percentage concentration of potassium chloride is 0.002-0.008%, while the weight percentage concentration of sodium chloride of the heavy soda ash produced by the existing method is 0.5-1.0%, and the weight percentage concentration of potassium chloride is 0.02-0.05%. Therefore, the heavy soda ash produced by the method belongs to high-quality low-salt low-potassium heavy soda ash.

The invention provides a new method for industrially producing low-salt low-potassium heavy soda ash. The invention changes high pressure (22 kg/cm)²～32kg/cm²) The boiler is at low pressure (4-8 kg/cm)²) The boiler changes a rotary calcining furnace into a decomposition reaction furnace, and does not need a complicated alkali return process. Therefore, the required mechanical transmission equipment is less, the maintenance cost is low, the equipment is simple, the manufacturing cost is low, the occupied area is small, and the investment is low. And due toThe production process of the heavy soda ash is changed from the existing hydration multi-step method into the one-step decomposition and drying method, and two working procedures (hydration and drying working procedures) of the common production are saved. Meanwhile, the method can automatically purify impurities in the heavy soda ash in the process of producing the heavy soda ash, and produce high-quality low-salt low-potassium heavy soda ash. Which is not achieved by other domestic and foreign industrial production methods. The carbon dioxide discharged from the decomposition reaction furnace by the method is 1.0-4.0 kg/cm²Pressure, without CO₂The gas compressor can be directly sent to a multiphase reaction tower to prepare sodium bicarbonate. Compared with the modern industrial production technology at home and abroad, the method embodies the first six:

the first method does not use a compressor to convey carbon dioxide gas to produce sodium bicarbonate, so that the equipment investment of all compressors is saved, and the electric energy consumption is reduced;

the first one is 6-10 kg/cm used in the production process²The low-pressure boiler replaces 22-32 kg/cm²The high-pressure boiler of (1);

the first step is that the sodium bicarbonate with the impurity content of sodium chloride less than or equal to 20 percent and other impurities is automatically purified in the reaction process of generating the heavy sodium carbonate, so that the content of the impurity sodium chloride in the heavy sodium carbonate is reduced to 0.02-0.33 percent, and the content of the impurity potassium chloride is reduced to 0.002-0.01 percent;

firstly, adopting a standing fixed decomposition reaction furnace to produce high-quality low-salt low-potassium heavy soda ash in one step;

firstly, drying a product by using superheated steam in the later reaction stage of heavy sodium carbonate generation;

the first method is to carry out industrial production without adopting a water-free washing method for sodium bicarbonate (namely, sodium bicarbonate is not used for washing impurities such as sodium chloride and the like by using water in a centrifugal filtration process).

Compared with the existing production flow of the heavy soda ash, the method has the characteristics of short process flow, simple equipment, low energy consumption, low cost and low investment.

The low-salt low-potassium heavy soda ash produced by the method has special functions. When the method is used for producing the water glass, the light soda ash produced by other manufacturers is used as a raw material to produce the water glass, so that more waste residues and less yield are produced; the water glass produced by using the low-salt low-potassium heavy soda ash produced by the invention as a raw material basically has no waste residue, and the product quality is high (high purity, good stereoscopic impression and high strength). And (3) producing 600-1200 kg of qualified water glass under the same process conditions for each ton of low-salt low-potassium heavy soda ash.

The low-salt low-potassium heavy soda ash produced by the method is more particularly suitable for refining vanadium pentoxide. For example: the vanadium pentoxide is required to be less than 0.5% in foreign countries, the total alkali content for refining the vanadium pentoxide by adopting other domestic sodium carbonates is far greater than the index, and the total alkali content of the vanadium pentoxide produced by adopting the low-salt low-potassium heavy soda ash produced by the method is less than 0.5%. The content of the potassium chloride of the heavy soda produced by other production methods is 0.02-0.05%, while the content of the potassium chloride of the low-salt low-potassium heavy soda produced by the method is 0.002-0.01%, which is 5-10 times lower than that of the potassium chloride of the soda produced by the common method. Therefore, in the process of producing vanadium pentoxide, the low-salt low-potassium heavy soda ash produced by the method has the advantages of easy washing of sodium ions, strong adhesion of potassium ions and difficult washing and removal. Therefore, the low-salt low-potassium heavy soda ash produced by the method has high purity of the refined product, improves the price and simultaneously ensures that the consumption of the soda ash is about 80 percent of the consumption of the common soda ash.

The technical solution of the present invention is further described with reference to the accompanying drawings and examples.

FIG. 1 is a schematic process flow diagram of the present invention.

1. Charging hole 2, decomposition reaction furnace 3, gas distributor 4, exhaust valve

5. Sieve plate 6, valve 7, valve 8, boiler

9. Valve 10, heat exchanger 11, gas-water separator 12, gas-water separator

13. Exhaust valve 14, heat exchange evaporator 15, gas-water separator

16. Cooler 17, gas-water separator 18, exhaust valve 19 and drain valve

20. Recoverer 21, heater 22, gas distributor 23, multiphase reaction tower

24. Drain valve 25, storage tank 26, pump 27 and vacuum evaporator

28. Heater 29, emptying valve 30, blower 31 and heater

32. Inlet valve 33, outlet

Example 1

14600 kg of sodium bicarbonate produced by a catalytic method is loaded into a decomposition reaction furnace 2 through a charging opening 1 (the weight percentage concentration of the sodium bicarbonate is 86.8 percent, the sodium chloride is 10.2 percent, and the water content is 3.0 percent), and then the charging opening and all sealing openings are sealed; while closing the corresponding valve. And (3) opening a water vapor valve 7, introducing saturated water vapor into the decomposition reaction furnace 2 through the gas-water separator 11 and the gas distributor 3, increasing the pressure of the reaction furnace to 0.2-0.5 Mpa (gauge pressure), increasing the temperature in the furnace to-0-160 ℃, and carrying out decomposition reaction on the sodium bicarbonate. Then opening the exhaustThe valve 4, the mixed gas (mainly comprising carbon dioxide gas and water vapor) discharged from the decomposition reaction furnace, enters the heat exchange evaporator 14(s), and most of the water vapor in the mixed gas transfers heat to the evaporation medium (brine or decomposition liquid from the decomposition reaction furnace) and then is condensed into liquid water. Then, the mixed gas is separated from the condensed water by a gas-water separator 15, and then enters a carbon dioxide gas cooler 16, the remaining water vapor is condensed into liquid water, the remaining gas is almost all carbon dioxide, the volume percentage concentration of the carbon dioxide is 90-98%, the condensed liquid water and the carbon dioxide enter a gas-liquid separator 17, and the separated condensate (the main components are water and ammonium bicarbonate and carbon dioxide dissolved in water) is sent to a liquid discharge valve 19And (3) the separated carbon dioxide gas enters a recoverer 20 through a valve 18, enters the bottom of the recoverer 20, is dispersed in liquid, carries out ammonia and carbon dioxide in the liquid (the temperature of the recoverer is controlled to be 40-80 ℃ by a heater 21), and the carbon dioxide can be directly sent into a multiphase reaction tower 17 by utilizing the pressure of the carbon dioxide to be absorbed so as to prepare sodium bicarbonate. After the reaction is carried out for 1-2 hours, a certain amount of decomposition liquid is arranged at the bottom of the decomposition reaction furnace, the valve 5 is opened, the decomposition liquid generated by the reaction is discharged into a decomposition liquid storage tank 25 through a valve 24 at the lower part of the gas-water separator 12, and meanwhile, part of mixed gas generated by the reaction is sent into a mixed gas main pipe through a valve 13 at the upper part of the gas-water separator. In the whole reaction process, the pressure in the decomposition reaction furnace is kept at 0.3-0.4 MPa (gaugepressure), the temperature is kept at 140-160 ℃, the reaction is carried out for about 12 hours, and water vapor and CO are treated₂When the volume ratio is 60: 1-2, introducing 160-280 ℃ superheated steam, and continuing to react for about 12 hours until the steam and CO react₂And when the volume ratio is 300: 0.2-300: 1, closing the water vapor, and opening the exhaust valve 4 and the emptying valve 29 to reduce the pressure in the furnace to zero. Opening a cooling system valve 32 of an air blower, starting the air blower, reducing the temperature in the furnace to 40-50 ℃ by using cold air, then opening a discharge hole 33 to take out the low-salt low-potassium heavy soda ash in the furnace (if the weight percentage concentration of sodium carbonate sampled from the furnace is lower than 98%, hot air is blown for drying, the air of the air blower 30 firstly passes through a heater 31 to raise the temperature of the air to 150-160 ℃ and then the materials in the furnace are dried, and the productAnd blowing cold air for cooling after the product is qualified). The decomposition liquid discharged from the decomposition reaction furnace can be sent to a caustic soda plant to prepare caustic soda, and can also be evaporated to prepare solid soda. The total weight of the low-salt low-potassium heavy soda ash removed was 6288 kg. The weight percentage concentration of the sodium carbonate, the weight percentage concentration of the potassium chloride and the weight percentage concentration of the sodium chloride are respectively 99.4%, 0.005%, 0.05% and the apparent density of the product is 1.06 kg/L.

Example 2

14400 kg of catalyst-free sodium bicarbonate (produced by the ammonia-soda process, the combined-soda process or other processes) was charged into the decomposition reactor 2 through the charging port 1 (sodium bicarbonate, sodium chloride, water, in concentrations of 85.8%, 10.6%, 3.8% by weight, respectively) and the charging port and all the sealing ports were sealed while the respective valves were closed. In the whole reaction process, the pressure in the decomposition reaction furnace is kept at 0.3-0.4 MPa (gauge pressure), the temperature is kept at 140-160 ℃, the reaction is carried out for about 18-28 hours, and 160-280 ℃ superheated steam is introduced when the volume ratio of the steam to the carbon dioxide is 60: 1-2. And continuing the reaction for about 16-24 hours, turning off the water vapor when the volume ratio of the water vapor to the carbon dioxide is 300: 1-300: 2, opening an exhaust valve 4 and an emptying valve 29 to reduce the pressure in the furnace to zero, opening a valve 32 of a cooling system of the air blower, reducing the temperature in the furnace to 40-50 ℃ by using cold air, and then opening a discharge port 33 to take out the low-salt low-potassium heavy soda ash (if the weight percentage concentration of the sodium carbonate sampled from the furnace is lower than 98%, hot air drying is carried out, the air of the air blower 30 is heated to 150-160 ℃ by a heater 31, then the materials in the furnace are dried, and the cold air is blown to cool after the product is qualified). The decomposition liquid discharged from the decomposition reaction furnace can be sent to a caustic soda plant to prepare caustic soda, and can also be evaporated to prepare solid soda. The total weight of the low-salt low-potassium heavy soda ash taken out is 5500 kg. The weight percentage concentration of the sodium carbonate, the weight percentage concentration of the potassium chloride and the weight percentage concentration of the sodium chloride are respectively 98.2%, 0.004%, 0.1% and 0.96kg/L respectively.

Claims

1. A production method of low-salt low-potassium heavy soda ash is characterized in that raw material sodium bicarbonate is sent into a decomposition reaction furnace, then superheated steam or saturated steam which is used as a medium for raising temperature and boosting pressure is sent into the reaction furnace, decomposition reaction is carried out under the temperature of less than 140 ℃ to 120 ℃ and the pressure of 0.1-0.2Mpa, decomposition liquid generated by the reaction is discharged from a liquid discharge valve (5), and exchanges heat, evaporates and crystallizes with mixed gas discharged by an exhaust valve (4) in a heat exchange evaporator (14) to form solid wet sodium carbonate, the mixed gas after heat exchange enters a gas-water separator (15), a carbon dioxide cooler (16) and a gas-water separator (17) and enters a recoverer (20), then carbon dioxide enters a multiphase reaction tower (23) by utilizing the pressure of the carbon dioxide to prepare sodium bicarbonate, when the volume ratio of the steam to the carbon dioxide in the discharged mixed gas is 60-80: 1-2, and introducing superheated steam of 160-360 ℃, drying until the volume ratio of the steam to the carbon dioxide in the mixed gas is 300: 0.2-1, stopping introducing the gas, cooling, and discharging to obtain the product, namely the heavy soda.

2. The method for producing the low-salt low-potassium dense soda ash as claimed in claim 1, wherein the sodium chloride content in the sodium bicarbonate is 10.2% -10.6%.

3. The method for producing low-salt low-potassium dense soda ash as claimed in claim 1, wherein the content of potassium chloride in the sodium carbonate product is 0.002-0.01%.