CN114408949A - Process and device for producing low-salt or ultra-low-salt sodium carbonate - Google Patents
Process and device for producing low-salt or ultra-low-salt sodium carbonate Download PDFInfo
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- CN114408949A CN114408949A CN202210096662.8A CN202210096662A CN114408949A CN 114408949 A CN114408949 A CN 114408949A CN 202210096662 A CN202210096662 A CN 202210096662A CN 114408949 A CN114408949 A CN 114408949A
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- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D7/00—Carbonates of sodium, potassium or alkali metals in general
- C01D7/18—Preparation by the ammonia-soda process
Abstract
The invention provides a process and a device for producing low-salt or ultra-low-salt sodium carbonate, which are used for secondarily absorbing ammonia, secondarily adding salt and secondarily carbonizing primary mother liquor discharged from an alkali filter on the basis of the existing sodium carbonate production process, thereby solving the problems of penetration loss and dissolution loss caused by solid-liquid separation of semi-finished heavy alkali and control of product salt in the sodium carbonate production process, reducing the equivalent weight of the mother liquor in the ammonia circulation process of sodium carbonate production, improving the utilization rate of raw salt, reducing material consumption and energy consumption, and simultaneously solving the influence of temperature change on the sodium carbonate production. The method for producing the low-salt or ultra-low-salt soda ash product improves the quality of the soda ash product, reduces material consumption and energy consumption in the production process, reduces the discharge amount of waste liquid, improves the concentration of waste liquid calcium chloride, and reduces the production cost of waste liquid recovered calcium chloride.
Description
Technical Field
The invention relates to a production process and a device for producing low-salt or ultra-low-salt soda ash products by controlling the quality index sodium chloride content of the soda ash products without increasing material consumption and energy consumption.
Background
GB210.1-2004 requires that the sodium chloride content (referred to as salt content) of the superior product of soda II class is less than 0.7%, the requirement of customers on the salt content index of soda products in the production process of actual soda enterprises is controlled to be about 0.4%, part of high-end customers require low-salt soda products with the salt content of less than 0.2% or ultra-low-salt soda products with the salt content of less than 0.1% in soda, the control of the salt content of soda generally uses washing water without salt in the production process to wash semi-finished heavy soda, the salt content of the soda products is controlled by controlling the washing water content, the washing water after washing the salt content enters a mother liquor system, on one hand, partial product dissolution loss is caused, on the other hand, salt consumption and steam consumption are increased, and the equivalent of waste liquid is increased. Due to the change of four seasons, the cooling of the carbonization process is difficult due to high temperature of circulating water in summer, the product has poor crystallization quality, low carbonization conversion rate, large equivalent of mother liquor, low utilization rate of raw salt and larger loss of the produced low-salt product. The invention relates to a low-salt or ultra-low-salt soda production process, which has no loss in the product salt content control process, is not influenced by the four-season environmental temperature in the production process, can stably produce low-salt or ultra-low-salt soda products, improves the added value of the soda products, improves the product competitiveness of enterprises, meets the quality requirement of high-end customers on the low-salt or ultra-low-salt soda products, reduces the discharge amount of waste liquid and waste residue, reduces the material consumption and energy consumption, reduces the carbon emission, and has better economic benefit and social benefit.
The application of low-salt or ultra-low-salt soda ash products in the glass industry can improve the quality of glass products, produce high-grade glass products, improve the added value of the glass products and prolong the service life of a glass kiln. The production of the soda by the existing synthesis method mainly comprises an ammonia-soda process and a combined-soda process, the ammonia-soda process has great influence on the yield, material consumption and energy consumption when producing low-salt or ultra-low-salt soda products, the production cost is greatly increased, and the waste liquid treatment capacity is increased; the combined soda process can not produce low-salt products and ultra-low-salt products due to the balanced requirement of the mother liquor, solves the problems of low-salt or ultra-low-salt soda production, and simultaneously solves the influence of the change of the environmental temperature on the soda production.
In the existing soda production process, low-nitrate sodium chloride-containing underground salt mine is mined or brine is prepared by using sodium chloride raw salt with the sodium chloride content of more than 95 percent to obtain nearly saturated crude brine with the concentration of more than 105 titer (5.25mol/L), the crude brine is refined by a lime soda process to remove a small amount of calcium and magnesium ions in the crude brine to obtain refined brine, the refined brine absorbs ammonia recovered from mother liquor, and the molar concentration ratio of the ammonia to the sodium chloride is 1.13-1.19Sending ammonia salt water and ammonia salt water to a carbonization process, using a normal carbonization tower as a group of four to six carbonization towers, using one carbonization tower as a cleaning tower, adding ammonia salt water and cleaning gas (containing about 40% of CO) into the carbonization cleaning tower2) Cleaning alkali scars formed in the alkali making period of the carbonization tower, simultaneously pre-carbonizing ammonia salt water to obtain neutralized water, taking the rest carbonization towers as alkali making towers, rotating the cleaning towers every 18-24 hours, sending the neutralized water from the cleaning towers to the alkali making tower, introducing middle section gas (containing about 40 percent of carbon dioxide) into the middle lower part of the alkali making tower, and introducing lower section gas (containing more than 80 percent of CO) into the lower part of the alkali making tower2) Obtaining alkali liquor containing sodium bicarbonate crystals, sending the alkali liquor to a filtering process, carrying out solid-liquid separation by an alkali filter to obtain heavy alkali mainly containing sodium bicarbonate, wherein the heavy alkali contains less than 20% of water, washing the heavy alkali with water without salt to obtain the heavy alkali with the sodium chloride content of less than 0.35%, and sending the heavy alkali to a calcining process to calcine to obtain a light soda product and obtain a CO-containing soda product2The concentration of the furnace gas is more than 80%, and the furnace gas is washed, cooled and compressed to obtain CO2The lower section gas with the concentration of 80 percent is sent to the carbonization procedure for producing soda, and part of light soda ash products are further processed to obtain heavy soda ash products. The mother liquor from the alkali filter is sent to a distillation and absorption process, most of free ammonia and carbon dioxide are evaporated in a preheating section of a distillation tower, the obtained preheating mother liquor which mainly contains ammonium chloride and sodium chloride which does not participate in the alkali making reaction at about 90 ℃ is obtained, lime milk (containing 155-170 titer of calcium hydroxide) is added into the preheating mother liquor, most of ammonia in the preheating mother liquor is evaporated by steam after the ammonium chloride reacts with the lime milk, the obtained ammonia gas is cooled and then absorbed by refined brine, the obtained ammonia brine is sent to a carbonization process for alkali making, and meanwhile, the waste liquor containing about 10 percent of calcium chloride is obtained and used for calcium chloride production or environmental protection treatment. Sieving purchased limestone (calcium carbonate content is more than 90%), obtaining qualified raw material with granularity of 50-120mm and coke (25-50mm), sending the qualified raw material and the coke into a lime kiln according to a certain proportion, introducing air into the bottom of the lime kiln, calcining the limestone by heat generated by burning the coke in the lime kiln to obtain calcium oxide of quicklime and CO2About 40 percent of kiln gas, adding water into quicklime to digest the quicklime into lime milk with the calcium hydroxide concentration of 155-170 titer, sending the lime milk to a distillation process to recover ammonia, dedusting the generated kiln gas,Cooling and compressing to obtain CO2The middle section gas and the cleaning gas which are 40 percent are respectively sent to the carbonization working procedure for alkali preparation.
Disclosure of Invention
The invention carries out secondary ammonia absorption, salt addition, secondary carbonization on primary mother liquor from an alkali filter, alkali liquor obtained by secondary carbonization is thickened to obtain clear liquor as secondary mother liquor, the secondary mother liquor with stable ammonium chloride concentration is sent to an original evaporation process to replace the primary mother liquor to recover ammonia to prepare ammonia brine, the thickened alkali liquor and the primary alkali liquor are subjected to solid-liquid separation together, a filter cake with salt content controlled by washing water is obtained and sent to a calcining furnace for calcination, the salt content of the obtained soda ash product can be stably controlled to be 0.1% or below 0.2%, the product quality requirement of a client is met, the utilization rate of the primary salt is improved, the problem of filtration loss in the soda industry is solved, and the problems of dissolving loss of semi-finished heavy soda, expansion of the mother liquor and the like caused by adding excessive washing water to control the product salt content are solved, thereby completing the invention.
The production process of the low-salt or ultra-low-salt sodium carbonate comprises the following steps:
(1) refined brine (NaCl content greater than 304g/l and calcium and magnesium content less than 15mg/l) absorbs ammonia gas to form ammonia brine (ammonia salt molar concentration ratio of 1.13-1.19: 1, preferably 1.14-1.18:1), which is mixed with CO2The mixture enters a primary carbonization tower to react to generate primary alkali liquor, and preferably CO is controlled2The volume flow of the gas and the volume flow of the ammonia brine are controlled to control the pressure in the carbonization tower to 290-330KPa, preferably 300-325KPa, and the middle reaction temperature to be 55-75 ℃, preferably 60-70 ℃;
(2) the primary alkali liquor discharged from the primary carbonization tower enters an alkali filter for solid-liquid separation to obtain a semi-finished product heavy alkali and primary mother liquor;
(3) sending a primary mother liquor (generally containing 65-72 ℃ of ammonium chloride) from an alkali filter to a carbonization tail gas ammonia-purifying tower to wash ammonia in carbonization tail gas (from one or more of a primary carbonization alkali-making tower, a primary carbonization cleaning tower, a secondary carbonization alkali-making tower and a secondary carbonization cleaning tower), sending the ammonia to a high-vacuum absorption tower (with the vacuum degree of-30 to-60 KPa, preferably-40 kPa to-50 kPa) to absorb ammonia (ammonia is preferably ammonia-containing condensate obtained after cooling an ammonia gas distilled from a distillation tower by a ammonia gas cooler and ammonia-containing condensate obtained by cooling a calcining furnace, sending the ammonia-containing condensate to a weak liquor distillation tower to recover ammonia, supplementing part of the ammonia by ammonia distilled from the secondary mother liquor to obtain an ammonia mother liquor (the free ammonia is an ammonia mother liquor with the titer of 40-55), and the temperature is 40-55 ℃), sending the ammonia mother liquor to a salt melting barrel (salt adding barrel), adding refined crude salt sodium chloride, and obtaining a mixture of free ammonia and sodium chloride with the molar ratio of 1.03-1.1: 1, further sending the ammonia salt mother liquor of 1.05-1.09 to a secondary carbonization tower to react with carbon dioxide to obtain secondary alkali liquor, wherein the temperature of the middle part of an alkali preparation tower of the secondary carbonization tower is, for example, 40-60 ℃, preferably 42-58 ℃, preferably 45-55 ℃, preferably 48-52 ℃ and the temperature of the alkali liquor is, for example, 33-45 ℃, preferably 34-43 ℃, preferably 35-40 ℃, preferably 36-39 ℃;
(4) and (3) conveying the secondary alkali liquor to a thickener for thickening, returning the thickened alkali liquor (containing 30-50% of sodium bicarbonate crystals) discharged from the bottom of the thickener to the alkali filter in the step (2), performing solid-liquid separation together with the primary alkali liquor to obtain a heavy alkali filter cake with reduced salt content by washing water, calcining the heavy alkali filter cake to obtain a low-salt or ultra-low-salt soda ash product, and discharging secondary mother liquor from the upper part of the thickener.
In the present application:
titer: the titer is equal to the molar concentration of a certain solute in the solution multiplied by the valence multiplied by 20.
Low-salt soda ash: soda ash product with sodium chloride content lower than 0.2 wt%.
Ultra-low salt soda ash: soda ash product with sodium chloride content lower than 0.1 wt%.
Further, in the step (4), the heavy alkali is washed by washing water (such as salt-free washing water) on an alkali filter to remove most of sodium chloride, the content of the sodium chloride in the heavy alkali is controlled to be lower than 0.1% or 0.05% by controlling the washing water content, so that the content of the sodium chloride in the final soda product is lower than 0.2% or 0.1%, and the quality requirement of the low-salt or ultra-low-salt soda product is met.
Further, the secondary mother liquor obtained in the step (4) is sent to a distillation process for distillation treatment, and the secondary mother liquor is heated to 88-92 ℃ in a preheating section of a distillation tower to remove the most of the mother liquorPart of CO2Adding lime milk, adding ammonia gas distilled by steam in a distillation tower, sending the ammonia gas into a cooler for cooling, sending the cooled ammonia gas (55-65 ℃) into a low vacuum absorption tower (with the vacuum degree of-10 to-20 kPa), and absorbing with refined brine to generate ammonia brine (entering a primary carbonization cleaning tower and a primary carbonization alkali-making tower); the condensate of the cooler and the furnace gas condensate are sent into a weak liquor distillation tower (with the vacuum degree of-40 to-60 kpa) for distillation, and the ammonia gas distilled out from the weak liquor distillation tower is sent into a high vacuum absorption tower. The distillation waste liquid of the distillation tower is subjected to flash (vacuum degree is between 10 and 20kPa), flash steam of the flash is returned to the distillation tower, the distillation waste liquid of the flash is sent to flash (vacuum degree is between 40 and 60kPa), flash steam of the flash is sent to a weak liquid distillation tower, and the waste liquid of the flash is sent to environment-friendly treatment. The above steps can be performed as in the prior art methods.
Further, the primary carbonization tower comprises a primary carbonization cleaning tower and a primary carbonization alkali making tower, and the secondary carbonization tower comprises a secondary carbonization tower and a secondary carbonization alkali making tower. In the primary carbonization tower, the ammoniacal brine firstly enters a primary carbonization cleaning tower and contains CO2Cleaning the gas, feeding the obtained neutralized ammonia salt water into a primary carbonization alkali-making tower, and reacting the neutralized ammonia salt water with CO2Reacting the gas to obtain primary alkali liquor. In the secondary carbonization tower, the ammonia salt mother liquor firstly enters a secondary carbonization cleaning tower and contains CO2Cleaning gas, feeding the obtained neutralized ammonia salt mother liquor into a secondary carbonization alkali-making tower and adding CO2And (5) reacting the gas to obtain secondary alkali liquor. And in the primary carbonization cleaning tower, the primary carbonization alkali-making tower and the secondary carbonization tower, the generated carbonization tail gas is discharged from the top of the carbonization tower.
The secondary carbonization tower is similar to the original carbonization tower process, namely the primary carbonization tower process, and each group of carbonization towers comprises 4-6 carbonization towers, one of which is a cleaning tower, the other towers are alkali-making towers, and the ammonia salt mother liquor (200-3H) firstly sending the mixture into a secondary carbonization cleaning tower, and introducing 2000-5000m3H of CO2Purge gas (e.g., containing 40% + -10%, preferably about 40% CO)2Cleaning gas), cleaning the alkali scar formed in the alkali making period of the secondary carbonization tower, simultaneously pre-carbonizing the ammonia salt mother liquor for 18-24 hours, cleaning the alkali scar formed in the alkali making period of the carbonization tower, and changing the alkali making tower after the production capacity of the carbonization tower is recovered to obtain the productThe ammonia salt mother liquor after cleaning is called as neutralized ammonia salt mother liquor, carbon dioxide is controlled to be 35-50 titer, the neutralized ammonia salt mother liquor is sent to secondary carbonization alkali-making towers, the flow rate of the ammonia salt mother liquor and the flow rate of the alkali liquor discharged from each secondary carbonization tower are controlled to be 50-140m3H, introducing CO into the lower part of the secondary carbonization tower2(e.g., containing 80. + -.10%, further about 80% CO)2) Lower section gas (same source as the primary carbonization tower) 1500-3000m3The lower and middle portions of the carbonizer are fed with carbon dioxide (e.g., containing 40% + -10%, preferably about 40% CO)2) The middle section gas (same as the primary carbonization tower in source) 2000-6000m3And h, obtaining secondary alkali liquor containing 10-20% of sodium bicarbonate crystals at the temperature of 35-40 ℃, sending the secondary alkali liquor to a thickener, sending 30-50% of the sodium bicarbonate crystals from the bottom of the thickener, further sending the thick alkali liquor of 35-45% to an alkali filter, carrying out solid-liquid separation together with the primary alkali liquor, washing a filter cake to obtain a semi-finished product heavy alkali with qualified sodium chloride content, further processing the semi-finished product heavy alkali into a low-salt or ultra-low-salt light pure alkali product, using a clear liquid overflowing from the upper part of the thickener as secondary mother liquor, and sending the secondary mother liquor to a distillation process to recover ammonia, wherein the ammonium chloride content of the secondary mother liquor reaches about 86 titer.
The secondary mother liquor ammonium chloride is sent to a distillation process, the existing production process can be adopted in the distillation process, the concentration of the ammonium chloride in the mother liquor can be changed due to the fact that salt of a product is controlled to be added into washing water in the primary mother liquor, the concentration of the ammonium chloride in the secondary mother liquor can be stabilized to be about 86 titer, the volume ratio of the secondary mother liquor to the lime milk is controlled to be 1.8-1.95 according to the concentration of calcium hydroxide in the lime milk, the amount of the lime milk only needs to be finely adjusted according to the concentration change of the calcium hydroxide in the lime process, and the content index of the calcium hydroxide in the waste liquor of a distillation tower is kept stable.
The refined brine can be obtained by the following steps: mining from low-nitrate sodium chloride underground salt mine and/or preparing brine by using sodium chloride raw salt with the sodium chloride content of more than 95 percent to obtain nearly saturated crude brine, wherein the concentration is more than 105 titer (5.25mol/L), refining by a lime soda ash method (adding proper amount of pure alkali liquor and lime milk according to the calcium and magnesium content in the brine, and performing sedimentation treatment), and removing calcium and magnesium ions in the crude brine to obtain refined brine (the calcium and magnesium content is less than 15mg/L, and the NaCl content is more than 304 g/L).
Further, the refined brine absorbs ammonia gas recovered from mother liquor distillation, and the molar concentration ratio of ammonia to sodium chloride is 1.13-1.19: 1, sending the ammonia salt water to a carbonization procedure carbonization tower to obtain alkali liquor containing sodium bicarbonate.
Normal carbonizer a group of four to six carbonizers, one of which is used as a cleaning tower, and ammonia brine and cleaning gas (containing about 40% of CO) are added into the carbonizer cleaning tower2) Cleaning alkali scars formed in the alkali making period of the carbonization tower, simultaneously pre-carbonizing ammoniacal brine to obtain neutralized water, taking the rest carbonization towers as alkali making towers, rotating the cleaning towers every 18-24 hours, sending the neutralized water from the cleaning towers to the alkali making tower, and introducing middle section gas (containing about 40 percent of CO) into the middle lower part of the alkali making tower2) And the lower part is introduced with lower gas (containing about 80 percent of CO)2) So as to obtain the primary alkali liquor containing sodium bicarbonate crystals.
The primary alkali liquor from the primary carbonization tower and the thick alkali liquor from the secondary carbonization tower enter an alkali filter together for solid-liquid separation to obtain heavy alkali mainly containing sodium bicarbonate, the heavy alkali contains less than 20% of water, the heavy alkali is washed by water without salt, the content of sodium chloride is lower than 0.1% or 0.05% by controlling the washing water amount, the heavy alkali is sent to a calcination process to be calcined to obtain a light soda product, and CO is also obtained2The concentration of the furnace gas is more than 80%, and the furnace gas is washed, cooled and compressed to obtain CO2The lower section gas with the concentration of about 80 percent is sent to the carbonization procedure for producing soda, and part of light soda ash products are further processed to obtain heavy soda ash products.
In order to improve the crystallization quality of the primary carbonization tower, preferably, the temperature of the alkali liquor discharged from the primary carbonization tower is increased to 35-40 ℃ from the existing index of 27-32 ℃, the utilization rate of the original salt is improved through secondary carbonization, the carbonization conversion rate is not required to be pursued any more for the primary carbonization, so that the crystallization quality of the alkali liquor discharged from the carbonization tower is improved, the phenomenon that the crystallization in the alkali liquor is fine due to the over-quick cooling of the carbonization tower is prevented, the salt content is convenient to control, the moisture content of heavy alkali is reduced, and the steam consumption of the calcination furnace for heavy alkali calcination is reduced.
The invention further provides a low-salt or ultra-low-salt soda ash production device, which comprises:
a low vacuum absorption tower, a primary carbonization cleaning tower, a primary carbonization alkali-making tower, an alkali filter, a carbonization tail gas ammonia-purifying tower, a high vacuum absorption tower, a salt adding barrel, a secondary carbonization cleaning tower, a secondary carbonization alkali-making tower, a thickener, a distillation tower, a calcining furnace, a cooler and a light liquid distillation tower,
wherein the low vacuum absorption tower is provided with a distillation tower ammonia gas inlet pipe and a refined brine inlet pipe, a discharge port of the low vacuum absorption tower is connected with a feed inlet of the primary carbonization cleaning tower through a middle buffer barrel and a pump, a carbon dioxide inlet pipe is also connected with a feed inlet of the primary carbonization cleaning tower, a liquid outlet of the primary carbonization cleaning tower is connected with a feed inlet of the primary carbonization alkali-making tower through a pump, preferably, the primary carbonization tower (the primary carbonization alkali-making tower and the primary carbonization cleaning tower) is provided with a middle section gas, a lower section gas and a cleaning gas carbon dioxide feed inlet,
a liquid outlet of the primary carbonization alkali-making tower is connected with a feed inlet of an alkali filter through an alkali outlet buffer tank, a solid material outlet of the alkali filter is connected with an inlet of a calcining furnace through a heavy alkali belt, a furnace gas outlet of the calcining furnace is connected with a first cooler, and a gas outlet of the first cooler is connected with gas inlets of the primary carbonization alkali-making tower and a secondary carbonization alkali-making tower through a compressor;
the primary mother liquid outlet of the alkali filter is connected with the liquid feed inlet of the carbonized tail gas ammonia purifying tower through a pipeline, a mother liquid buffer barrel and a pump, the gas feed inlet of the carbonized tail gas ammonia purifying tower is also connected with the tail gas outlets of the primary carbonization tower and the secondary carbonization tower (the secondary carbonization alkali-making tower and the secondary carbonization cleaning tower) through pipelines, the cleaning solution outlet of the carbonized tail gas ammonia purifying tower is connected with the inlet of a high vacuum absorption tower through a pump, the inlet of the high vacuum absorption tower is also connected with an ammonia gas feed pipe from a weak liquor distillation tower and/or an ammonia gas feed pipe of a distillation tower (after the ammonia gas distilled by the distillation tower is cooled by a cooler), the liquid outlet of the high vacuum absorption tower is connected with the inlet of a salt adding barrel through a pump, the outlet of the salt adding barrel is connected with the inlet of the secondary carbonization cleaning tower through an ammonia salt mother liquid buffer barrel and a pump, the cleaning gas feed pipe is also connected with the inlet of the secondary carbonization cleaning tower, the liquid outlet of the secondary carbonization cleaning tower is connected with the inlet of the secondary carbonization alkali-making tower through a pump, the liquid outlet of the secondary carbonization alkali-making tower is connected with the inlet of a thickener, the bottom outlet of the thickener is connected with the inlet of an alkali filter, the upper outlet of the thickener is connected with the feed inlet of a distillation tower through a mother liquor buffer barrel and a pump, a lime milk feed pipe and a steam feed pipe are also connected with the feed inlet of the distillation tower, the gas outlet of the distillation tower is connected with a second cooler, the liquid outlet of the second cooler is connected with the liquid inlet of a thin liquid distillation tower, the thin liquid distillation tower is also provided with a steam inlet, and the gas outlet of the second cooler is connected with the gas inlet of a low vacuum absorption tower.
THE ADVANTAGES OF THE PRESENT INVENTION
1. The salt content of the soda ash product can be stably controlled to be below 0.1 percent or 0.2 percent, the quality requirement of high-end customer products is met, and the added value and the market competitiveness of the soda ash product can be improved.
2. Reduce the equivalent of mother liquor and the equivalent of waste liquid by 1m3More than t alkali, the steam consumption is reduced, the stone consumption, the coke consumption and the ammonia consumption are reduced, the concentration of the clear waste liquid calcium chloride is improved, the production cost of the calcium chloride is reduced, and the environmental protection treatment difficulty of the waste liquid is reduced.
3. The carbonization conversion rate is not required to be excessively pursued, the utilization rate of the raw salt is improved by adopting a secondary carbonization process, the carbonization crystallization quality is improved by controlling the carbonization reaction temperature, the heavy alkali moisture is reduced, and the steam consumption of a calcining furnace is reduced.
4. The production process is not influenced by the change of the environmental temperature, the salt content of the product is controlled according to the requirements of customers, the production is not influenced, and the yield and the consumption of the soda ash are relatively stable all the year round.
5. The carbonized tail gas and the absorbed tail gas are washed by the mother solution and then washed by the refined brine, so that the ammonia purification effect of the carbonized tail gas is improved, and the environmental protection level of enterprises is further improved.
6. The system interface is removed in the old soda plant transformation process, the influence on production is not caused, and partial carbonization towers, tail gas ammonia purification towers, absorption towers, salt dissolving barrels, thickeners and other matching equipment are added according to the production scale, so that the production capacity of the device is improved by more than 20 percent with lower investment, the utilization rate of raw materials is improved, the potential of the whole device is excavated, and the production efficiency of the soda plant is improved.
Drawings
FIG. 1 is a process flow diagram of an embodiment of the present invention involving primary mother liquor ammonia absorption, salt dissolution, carbonization, thickening.
Figure 2 is a flow chart of a complete process of the inventive arrangement.
Detailed Description
The invention is further illustrated by the following examples in connection with the accompanying drawings. In this application,% is typically weight percent unless otherwise specified.
As shown in fig. 1 and 2, the low-salt or ultra-low-salt soda ash production apparatus of the present invention comprises:
the system comprises a low vacuum absorption tower, a primary carbonization cleaning tower, a primary carbonization alkali-making tower, an alkali filter, a carbonization tail gas ammonia-purifying tower, a high vacuum absorption tower, a salt adding barrel, a secondary carbonization cleaning tower, a secondary carbonization alkali-making tower, a thickener, a distillation tower, a calcining furnace, a cooler and a light liquid distillation tower.
The low vacuum absorption tower is provided with a distillation tower ammonia gas feeding pipe and a refined brine feeding pipe, a discharge port of the low vacuum absorption tower is connected with a feeding port of a primary carbonization cleaning tower through a middle buffer barrel and a pump, a carbon dioxide feeding pipe is also connected with a feeding port of the primary carbonization cleaning tower, a liquid outlet of the primary carbonization cleaning tower is connected with a feeding port of a primary carbonization alkali-making tower through a pump, the primary carbonization is provided with a middle section gas, a lower section gas and a cleaning gas carbon dioxide feeding port, a liquid outlet of the primary carbonization alkali-making tower is connected with a feeding port of an alkali filter through an alkali outlet buffer tank, a solid material outlet of the alkali filter is connected with an inlet through a heavy alkali belt, a furnace gas outlet of the calciner is connected with a first cooler, and a gas outlet of the first cooler is connected with a gas inlet of the primary alkali-making tower and a gas inlet of the secondary alkali-making tower through a compressor;
the primary mother liquid outlet of the alkali filter is connected with the liquid feed inlet of the carbonized tail gas ammonia purifying tower through a pipeline, a mother liquid buffer barrel and a pump, the gas feed inlet of the carbonized tail gas ammonia purifying tower is also connected with the tail gas outlets of the primary carbonization tower and the secondary carbonization tower through a pipeline, the washing liquid outlet of the carbonized tail gas ammonia purifying tower is connected with the inlet of a high vacuum absorption tower through a pump, the inlet of the high vacuum absorption tower is also connected with an ammonia gas feed pipe from a light liquid distillation tower and/or an ammonia gas feed pipe of the distillation tower (after the ammonia gas distilled from the distillation tower is cooled by a cooler), the liquid outlet of the high vacuum absorption tower is connected with the inlet of a salt adding barrel through a pump, the outlet of the salt adding barrel is connected with the inlet of a secondary carbonization cleaning tower through an ammonia salt mother liquid buffer barrel and a pump, the washing gas feed pipe is also connected with the inlet of the secondary carbonization cleaning tower, the liquid outlet of the secondary carbonization cleaning tower is connected with the inlet of the secondary carbonization alkali making tower through a pump, the liquid outlet of the secondary carbonization alkali making tower is connected with the inlet of a thickener, the bottom exit linkage alkali filter import of stiff ware, the feed inlet of distillation column is connected through mother liquor buffer bucket, pump to the upper portion export of stiff ware, and distillation column feed inlet is also connected to lime breast inlet pipe and steam feed pipe, and the gas outlet of distillation column connects the second cooler, and the liquid outlet of second cooler connects thin liquid distillation column liquid inlet, and thin liquid distillation column still is equipped with steam inlet, and the gas outlet of second cooler connects the gas inlet of low vacuum absorption tower.
In this application, send original distillation column with the secondary mother liquor that the stiff ware came out, the transformation process does not influence current device production except ammonia, mother liquor, carbon dioxide gas and former system interface. The dosage of salt washing water is controlled by increasing an alkali filter, the product salt is controlled to produce low-salt or ultra-low-salt soda ash products, the primary mother liquor absorbs ammonia, adds salt and carbonizes for the second time, the alkali outlet temperature of a primary carbonization alkali-making tower is increased to 35-40 ℃, the influence of the primary carbonization environment temperature on the conversion rate of sodium chloride alkali-making and the washing loss of added washing water on semi-finished products are solved, the secondary mother liquor is thickener overflow liquor, the product salt washing water is added to the alkali filter and is controlled not to enter the secondary mother liquor, and the problems of large increase of the product salt washing water quantity, difficulty in waste liquid treatment and the like are solved.
Example 1
The method comprises the steps of mining from low-nitrate sodium chloride-containing underground salt mines to obtain nearly saturated crude brine with the concentration of more than 105 titer (5.25mol/L), refining by a lime soda ash method (adding a proper amount of soda ash and lime milk according to the calcium and magnesium content in the brine, and performing sedimentation treatment), and removing a small amount of calcium and magnesium ions in the crude brine to obtain refined brine (the calcium and magnesium content is lower than 15mg/L, and the NaCl content is higher than 304 g/L).
Absorbing ammonia gas with refined bittern to obtain ammonia salt water (ammonia salt molar concentration ratio 1.13-1.19: 1), introducing into a primary carbonization cleaning tower, and introducing compressed water containing 40% CO2The obtained neutralized ammonia salt water enters into a primary carbonization systemAlkali tower and CO-containing2Gas reaction, introducing into the alkali-making tower by primary carbonization to compress CO2Middle stream gas and CO with concentration of 40%2Generating primary alkali liquor by using lower section gas with the concentration of 80%;
and (3) feeding the primary alkali liquor discharged from the primary carbonization tower into an alkali filter for solid-liquid separation, washing the heavy alkali by using salt-free washing water on the alkali filter to remove most of sodium chloride in a filter cake, controlling the content of the sodium chloride in the heavy alkali to be lower than 0.1%, and enabling the content of the sodium chloride in the final soda product to be lower than 0.1%, so that the quality requirement of the low-salt or ultra-low-salt soda product is met.
The primary mother liquor (containing 65-72 titer of ammonium chloride) from the alkali filter is firstly sent to a tail gas ammonia purifying tower of a carbonization tower to wash ammonia in carbonized tail gas, then sent to a high vacuum absorption tower to absorb ammonia (ammonia in condensate recovered from a weak liquor distillation tower, insufficient ammonia is supplemented by ammonia recovered by secondary mother liquor distillation) to obtain ammonia mother liquor (free ammonia is 40-55 titer of ammonia mother liquor with the temperature of 40-55 ℃), the ammonia mother liquor is sent to a salt dissolving barrel, refined crude salt sodium chloride is added to obtain ammonia salt mother liquor with the molar ratio of the free ammonia to the sodium chloride of 1.03-1.1, the ammonia salt mother liquor is sent to a secondary carbonization cleaning tower, CO is introduced to the secondary carbonization cleaning tower, and the ammonia salt mother liquor is obtained2About 40% of cleaning gas, the resulting mother liquor of neutralized ammonia salt and a mixture containing 40% of CO2Middle stream gas and gas containing 80% CO2The lower section gas reacts to obtain secondary alkali liquor.
The secondary carbonization tower is similar to the original carbonization tower process, i.e. the primary carbonization tower process, each group of carbonization towers has 4 bases, one of the towers is a cleaning tower, the other towers are alkali-making towers, the ammonia salt mother liquor is firstly fed into the secondary carbonization cleaning tower, and about 3500m is introduced into the secondary carbonization cleaning tower3Cleaning the alkali scar formed in the alkali making period of the secondary carbonization tower by using cleaning gas (the source is the same as that of the primary carbonization tower), pre-carbonizing the ammonia salt mother liquor, cleaning for 18-24 hours, recovering the production capacity of the carbonization tower, changing the carbonization tower into the alkali making tower to obtain the cleaned ammonia salt mother liquor, namely, the neutralized ammonia salt mother liquor, controlling the carbon dioxide to be 35-50 titer, sending the neutralized ammonia salt mother liquor to the secondary carbonization alkali making tower, and controlling the flow of the ammonia salt mother liquor and the flow of the alkali liquor discharged from each secondary carbonization tower to be about 100m3H, introducing CO into the lower part of the secondary carbonization tower2About 80% or more of the lower stage gas (same as in the primary carbonizer)Source) about 2000m3H, introducing CO into the middle lower part of the carbonization tower2About 40% of the middle gas (from the same source as the primary carbonizer) is about 3000m3And h, obtaining secondary alkali liquor containing 10-20% of sodium bicarbonate crystals at the temperature of 35-40 ℃, sending the secondary alkali liquor to a thickener, sending the thick alkali liquor containing 30-50% of the sodium bicarbonate crystals from the bottom of the thickener to an alkali filter, carrying out solid-liquid separation with the primary alkali liquor, washing a filter cake to obtain a semi-finished product heavy alkali with qualified sodium chloride content, calcining the heavy alkali to further process the heavy alkali into a low-salt or ultra-low-salt pure alkali product, using clear liquid overflowing from the upper part of the thickener as secondary mother liquor, enabling the ammonium chloride content of the secondary mother liquor to reach about 86 titer, and sending the secondary mother liquor to a distillation process to recover ammonia.
The secondary mother liquor is sent to a distillation process, the existing production process can be adopted in the distillation process, the concentration of ammonium chloride in the mother liquor can be changed due to the fact that salt of a product is controlled to be added into washing water in the primary mother liquor, the concentration of the ammonium chloride in the secondary mother liquor can be stabilized to be about 86 titer, the volume ratio of the secondary mother liquor to the lime milk is controlled to be 1.8-1.95 according to the concentration of calcium hydroxide in the lime milk, the amount of the lime milk only needs to be finely adjusted according to the concentration change of the calcium hydroxide in the lime process, and the content index of the calcium hydroxide in the waste liquor of a distillation tower is kept stable. The distillation process comprises heating the secondary mother liquor to 88-92 deg.C in the preheating section of the distillation tower to remove most of CO in the mother liquor2Then lime milk is added, ammonia gas recovered by the distillation tower is sent to a cooler for cooling, the cooled ammonia gas is sent to a low vacuum absorption tower (the vacuum degree is between 10 below zero and 20kpa), and refined brine is used for absorption to obtain ammonia brine; the ammonia-containing condensate generated by the cooler and the ammonia-containing condensate generated by cooling the furnace gas are sent into a thin liquid distillation tower (the vacuum degree is between 40 and 60kpa, and the temperature is between 78 and 84 ℃) for distillation, and the ammonia gas evaporated by the thin liquid distillation tower enters a high vacuum absorption tower. The distillation waste liquid of the distillation tower is subjected to flash (vacuum degree is between 10 and 20kpa), flash steam of the flash is returned to the distillation tower, the distillation waste liquid of the flash is sent to flash (vacuum degree is between 40 and 60kpa), flash steam of the flash is sent to a light liquid distillation tower, and the waste liquid of the flash is sent to environment-friendly treatment.
Wherein the heavy alkali is sent to a calcining procedure to be calcined to obtain a light soda ash product and simultaneously obtain a product containing CO2The furnace gas with concentration over 80 percent is washed, cooled and compressedThen the obtained product is sent to the carbonization working procedure for alkali preparation by the lower stage gas with the carbon dioxide concentration of 80 percent.
Sieving purchased limestone (calcium carbonate content is more than 90%), obtaining qualified raw material with granularity of 50-120mm and coke (25-50mm), sending the qualified raw material and the coke into a lime kiln according to a certain proportion, introducing air into the bottom of the lime kiln, calcining the limestone by heat generated by burning the coke in the lime kiln to obtain calcium oxide of quicklime and CO2About 40 percent of kiln gas, adding water into quicklime to digest the lime into lime milk with the titer of 155-170 calcium hydroxide concentration, sending the lime milk to a distillation process to recover ammonia, and dedusting, cooling and compressing the generated kiln gas to obtain the kiln gas containing CO2About 40 percent of the middle section gas and the cleaning gas are sent to a carbonization procedure for alkali preparation.
Example 2
Similar to example 1, except that crude salt brine with sodium chloride content higher than 95% is prepared, nearly saturated crude brine with concentration above 105 titer (5.25mol/L) is obtained, and the nearly saturated crude brine obtained by mining underground salt mine containing low-nitre sodium chloride in example 1 is replaced.
According to the invention, the refined sodium chloride brine absorbs ammonia gas to obtain ammonia brine, and CO is introduced into the ammonia brine2And performing primary carbonization on the gas to obtain primary alkali liquor, performing secondary ammonia absorption, adding refined original salt sodium chloride and performing secondary carbonization on primary mother liquor obtained by solid-liquid separation of the alkali liquor, so that the sodium chloride is converted into sodium bicarbonate and ammonium chloride by the obtained alkali liquor, and the titer of the ammonium chloride in the alkali liquor can be improved to about 86 from 72-75 of the primary alkali liquor. The utilization rate of the raw salt of the ammonia-soda process and the similar soda process is 72-75%, in order to pursue the utilization rate of the raw salt and improve the concentration of ammonium chloride in the alkali liquor, the temperature of the alkali liquor is required to be controlled to pursue the conversion rate of carbonized alkali liquor, the conversion rate of the alkali liquor is not required to be excessively pursued in the primary alkali liquor discharge process, the salt which is not converted can be recycled in the secondary carbonization process, and the influence on the yield, the consumption and the like caused by the higher temperature of cooling water in summer is solved.
The mother liquor entering the distillation system comes from secondary mother liquor overflowing from a secondary carbonized alkali liquor thickener, the secondary mother liquor does not pass through an alkali filter, the problem of filtration loss in the soda industry is solved, and the problems of dissolution loss of semi-finished heavy alkali, mother liquor expansion and the like caused by the fact that excessive washing water is added to control the product salt content are solved.
Alkali liquor obtained after the mother liquor is subjected to secondary ammonia absorption, salt addition and secondary carbonization is thickened through a thickener, the thickened alkali liquor and primary alkali liquor enter an alkali filter together for solid-liquid separation to obtain semi-finished heavy alkali, secondary mother liquor ammonium chloride overflowing from the upper part of the thickener can reach about 86tt and is about 14tt higher than primary mother liquor ammonium chloride obtained by filtering the primary alkali liquor, the equivalent weight of distillation mother liquor is reduced, and the production capacity of the pure alkali in a distillation tower is improved by about 20%.
In order to control the salt content, the traditional alkali making process adds salt-free washing water to semi-finished heavy alkali for washing, the amount of the washing water is adjusted according to the salt content requirement of the product, so that the concentration fluctuation of the ammonium chloride of the mother liquor is caused, and the ratio of the lime milk to the mother liquor is difficult to control when the ammonia is recovered in the distillation process.
The ammonia-soda process primary carbonization process simultaneously needs to pursue carbonization conversion rate and quality of heavy alkali crystals, the low-salt or ultra-low-salt soda production process does not need to excessively pursue carbonization conversion rate and mainly pursue carbonization crystallization quality, the temperature of the alkali liquor discharged from the primary carbonization tower can be controlled to be 35-40 ℃ by controlling the carbonization cooling process, the temperature index of the alkali liquor discharged from the primary carbonization tower is increased by 5-10 ℃ compared with the existing production index, the adverse effect on the carbonization crystallization quality caused by over-emergency cooling is prevented, the operation difficulty of the carbonization process is reduced, the influence on soda production caused by over-high temperature of circulating water produced in summer is solved, and the pressure steam consumption in the calcination process is reduced.
The treatment difficulty of the hot alkali liquor in the production process of the soda is high, the problem of the treatment of the hot alkali liquor can be solved before the hot alkali liquor is mixed with primary mother liquor for ammonia absorption according to production requirements, the alkali liquor can be recycled, and the treatment difficulty and treatment cost of the hot alkali liquor are reduced.
The primary mother liquor is used as a primary washing agent for tail gas in the carbonization and absorption processes, and then refined brine is used for secondary washing to recover brine and ammonia gas carried in the tail gas, the carbonized tail gas is washed by the primary mother liquor, the brine in the carbonized tail gas is recovered, the temperature of the carbonized tail gas is reduced, the ammonia purification effect of the tail gas is improved, the ammonia absorption amount required by the mother liquor is reduced, and meanwhile, the concentration of the refined brine is reduced by reducing water vapor in the carbonized tail gas.
The secondary carbonization tower can be arranged into an independent group according to the primary carbonization tower, each group of four to six carbonization towers comprises one carbonization tower as a secondary cleaning tower and other carbonization towers as secondary alkali making towers, the secondary cleaning tower is cleaned by ammonia salt mother liquor, and 2000-5000m of ammonia salt mother liquor is introduced into the secondary cleaning tower3H containing about 40% CO2The cleaning gas is used for cleaning alkali scars formed in the alkali making period of the secondary carbonization tower, the cleaning time is 18-24 hours, the alkali making tower is changed after the production capacity of the secondary carbonization tower is recovered, the obtained cleaned neutralized ammonia salt mother liquor is sent to the secondary carbonization tower for alkali making, the flow rate of the ammonia salt mother liquor and the flow rate of the alkali liquor are designed according to about twice of the tower for alkali making by primary carbonization, the tower type is the same as that of the primary carbonization tower, and the primary carbonization tower and the secondary carbonization tower can be used in a mutual replacement mode.
And (3) respectively washing the carbonized tail gas, increasing the concentration of free ammonia of the secondary mother liquid by about 10tt after washing, absorbing ammonia distilled from a weak liquid distillation tower, increasing the concentration of ammonia of the mother liquid by about 10tt, supplementing insufficient ammonia recovered from the mother liquid distillation tower, and controlling the ammonia absorption index of the secondary mother liquid by using the secondary mother liquid high vacuum absorption tower with the negative pressure higher than the low vacuum absorption tower.
And (3) index control of a secondary carbonization tower: the temperature of the discharged alkali liquor is 35-40 ℃, the temperature of the ammonia salt mother liquor is 40-55 ℃, the reaction temperature of the middle part is 45-60 ℃, and the gas amount of the lower part is 1500-3/h, middle section gas 2000-3/h。
The ammonia-containing condensate from the calcining process and the evaporation and absorption process is distilled in high vacuum, the obtained ammonia gas is absorbed by secondary mother liquor, the insufficient ammonia is supplemented by a mother liquor distillation tower, the total ammonia of the ammonia mother liquor is increased from 95tt to 110-120tt, and the free ammonia is increased from 25-30tt to 40-55 tt.
Adding salt into the ammonia mother liquor in a salt adding barrel to obtain ammonia salt mother liquor, wherein the equivalent of the ammonia salt mother liquor is 5.0-7.0m3The ratio alpha of free ammonia to sodium chloride is controlled to be 1.03-1.1 per ton of alkali, and the total chlorine is controlled to be 110-120tt, so that ammonium chloride crystallization is prevented in the secondary carbonization process.
The process can adopt full salt to prepare alkali, also can adopt partial brine and partial refined salt to prepare alkali, adopts brine and refined salt to prepare alkali, and the secondary addition of refined salt accounts for about 20-40% of the total salt, and the utilization rate of the secondary addition of refined salt reaches more than 90%.
Carbonizing the mother liquid of ammonium salt to obtain secondary alkali liquid, controlling the temperature of the secondary alkali liquid to be 35-40 ℃, and keeping the equivalent of the alkali liquid to be 0.8-2m after the secondary thickening3T alkali, overflow secondary mother liquor equivalent of 4.2-5.0m3T base.
Because the crystallization quality of the heavy alkali is good, the change rate of the solid-liquid separation of the alkali liquor is not excessively pursued, the alkali filter can use a centrifugal machine, the process flow of the solid-liquid separation of the alkali liquor is simplified, equipment such as a vacuum machine, a tail gas filtering ammonia purification tower and the like is not required to be configured, the power consumption of a vacuum machine is reduced, a large amount of vacuum tail gas is not generated any more, the vacuum waste gas discharge required by the solid-liquid separation of the alkali liquor is reduced, the influence of the waste gas discharge on the environment is reduced, the moisture content of the heavy alkali is reduced, and the pressure steam consumption in a calcining furnace is reduced.
While preferred embodiments of the present invention have been described above, it should be understood that the above description is for illustrative purposes only and is not to be construed as limiting the present invention in any way. Many modifications and equivalents may be made thereto without departing from the spirit and scope of the invention, and such modifications and equivalents are intended to be included within the scope of the invention.
Claims (10)
1. A production process of low-salt or ultra-low-salt sodium carbonate comprises the following steps:
(1) refined brine (NaCl content is more than 304g/l, calcium and magnesium content is less than 15mg/l) absorbs ammonia gas to form ammonia brine (ammonia salt molar concentration ratio is 1.13-1.19: 1), and the ammonia brine and CO are mixed2The mixture enters a primary carbonization tower to react to generate primary alkali liquor;
(2) the primary alkali liquor discharged from the primary carbonization tower enters an alkali filter for solid-liquid separation to obtain a semi-finished product heavy alkali and primary mother liquor;
(3) sending a primary mother solution (containing 65-72 titer of ammonium chloride) from an alkali filter to a carbonization tail gas ammonia purification tower to wash ammonia in carbonization tail gas (from one or more of exhaust gas of a primary carbonization alkali-making tower, a primary carbonization cleaning tower, a secondary carbonization alkali-making tower and a secondary carbonization cleaning tower), sending the ammonia to a high vacuum absorption tower (with the vacuum degree of-30 to-60 KPa, preferably-40 kPa to-50 kPa) to absorb ammonia (preferably ammonia is ammonia-containing condensate obtained by cooling an ammonia gas cooler distilled from a distillation tower and ammonia-containing condensate obtained by cooling a calcining furnace, sending the ammonia-containing condensate into a weak liquor distillation tower to recover ammonia gas, supplementing part of the ammonia gas by ammonia distilled from the secondary mother solution to obtain an ammonia mother solution (the free ammonia is 40-55 titer), sending the ammonia mother solution to a salt melting barrel, adding refined sodium chloride, obtaining the free ammonia and sodium chloride with the mol ratio of 1.03-1.1: and (2) sending the ammonia salt mother liquor of the step (1) to a secondary carbonization tower, reacting with carbon dioxide to obtain (4) secondary outlet alkali liquor, sending the secondary outlet alkali liquor to a thickener, returning the thick alkali liquor (containing 30-50% of sodium bicarbonate crystals) from the bottom of the thickener to the alkali filter in the step (2), carrying out solid-liquid separation together with the primary outlet alkali liquor to obtain a heavy alkali filter cake, calcining the heavy alkali filter cake to obtain a low-salt or ultra-low salt soda ash product, and taking clear liquid from the upper part of the thickener as secondary mother liquor.
2. The process according to claim 1, wherein in step (4), the heavy alkali is washed by washing water (preferably salt-free washing water) on an alkali filter, most of sodium chloride in the heavy alkali is removed by controlling the amount of the washing water, the content of the sodium chloride in the heavy alkali is controlled to be lower than 0.1% or 0.05%, and the content of the sodium chloride in the final soda product is controlled to be lower than 0.2% or 0.1%.
3. The process according to claim 1 or 2, wherein the secondary mother liquor obtained in step (4) is sent to a distillation process for distillation treatment, and the secondary mother liquor is heated to 88-92 ℃ in a preheating section of a distillation tower to remove most of CO in the mother liquor2Adding lime milk, steaming out ammonia with steam, cooling the ammonia gas from the distillation tower in a cooler, and absorbing the cooled ammonia gas (55-65 deg.C) in low vacuumAbsorbing ammonia gas with refined brine (preferably refined brine obtained after washing carbonized tail gas ammonia) to generate ammonia brine in a tower (vacuum degree is-10 to-20 kPa); and feeding ammonia-containing condensate generated by the distilled ammonia gas cooler and ammonia-containing condensate generated by condensing the calcining furnace gas into a weak liquor distillation tower for distillation, and feeding ammonia gas evaporated from the weak liquor distillation tower into a high vacuum absorption tower.
4. The process of claim 3 wherein the distillation effluent from the distillation column is flashed, flash vapor from the flash is returned to the distillation column, flash vapor from the flash is sent to the flash, and flash vapor from the flash is sent to the thin liquid distillation column for use as a heat source.
5. The process of any one of claims 1 to 4, wherein the primary carbonation tower comprises a primary carbonation cleaning tower and a primary carbonation soda tower, and the secondary carbonation tower comprises a secondary carbonation cleaning tower and a secondary carbonation soda tower; in the primary carbonization tower, the ammoniacal brine firstly enters a primary carbonization cleaning tower and is introduced with CO2The obtained neutralized ammonia brine enters a primary carbonization alkali-making tower and contains CO2Reacting the gas to obtain primary alkali liquor; in the secondary carbonization tower, the ammonia salt mother liquor firstly enters a secondary carbonization cleaning tower and is introduced with CO2The obtained neutralized ammonia salt mother liquor enters a secondary carbonization alkali making tower and contains CO2Reacting the gas to obtain secondary alkali liquor; and in the primary carbonization cleaning tower, the primary carbonization alkali-making tower and the secondary carbonization tower, the generated carbonization tail gas is discharged from the top of the carbonization tower.
6. The process as claimed in any one of claims 1 to 5, wherein the secondary and primary carbonizers are each provided with 4 to 6 carbonizers, one of which is a cleaning tower and the others are alkali-making towers, and the ammonia mother liquor (200 m and 500 m)3H) firstly sent into a secondary carbonization cleaning tower and introduced into (2000 once more 7000 m)3H) containing CO2The cleaning gas cleans the alkali scar formed during the alkali preparation of the secondary carbonization tower, simultaneously carries out pre-carbonization on the ammonia salt mother liquor (preferably, the cleaning time is 18-24 hours), and the cleaning of the alkali scar is changed after the production capacity of the carbonization tower is recoveredThe obtained ammonia salt mother liquor after cleaning is called as neutralized ammonia salt mother liquor, CO, for the alkali making tower2Controlling the titer at 35-50, and sending the neutralized ammonia salt mother liquor to a secondary carbonization alkali-making tower for treatment (preferably, the flow rate of the ammonia salt mother liquor and the flow rate of the alkali liquor discharged from each secondary carbonization tower are controlled at 50-140m3H, introducing CO into the lower part of the secondary carbonization tower21500 + 3000m lower section gas3H, introducing CO into the middle lower part of the carbonization tower2Middle section gas 2000-6000m3And/h), obtaining secondary alkali liquor containing 10-20% of sodium bicarbonate crystals at the temperature of 35-40 ℃, conveying the secondary alkali liquor to a thickener, conveying the thick alkali liquor containing 30-50% of the sodium bicarbonate crystals from the bottom of the thickener to an alkali filter, carrying out solid-liquid separation with the primary alkali liquor, washing a filter cake to obtain a semi-finished product heavy alkali with qualified sodium chloride content, further processing the semi-finished product heavy alkali into a low-salt or ultra-low-salt light soda ash product, and conveying clear liquid overflowing from the upper part of the thickener to a distillation process to recover ammonia.
7. Process according to any one of claims 1 to 6, characterized in that the refined brine is obtained by: mining from underground salt mine containing low-nitrate sodium chloride or preparing brine by using sodium chloride raw salt with the sodium chloride content of more than 95 percent to obtain nearly saturated crude brine with the concentration of more than 105 titer (5.25mol/L), and refining by a lime soda ash method to remove a small amount of calcium and magnesium ions in the crude brine to obtain refined brine (the content of calcium and magnesium is less than 15 mg/L).
8. The process of claim 7, wherein the refined brine absorbs ammonia gas recovered from distillation of the mother liquor to obtain a molar concentration ratio of ammonia to sodium chloride of 1.13-1.19: 1, sending the ammonia salt water to a primary carbonization tower to obtain primary alkali liquor containing sodium bicarbonate.
9. The process according to any one of claims 1 to 8, wherein the primary carbonizer effluent lye temperature is from 35 to 40 ℃.
10. A low or ultra-low salt soda ash production plant, comprising: a low vacuum absorption tower, a primary carbonization cleaning tower, a primary carbonization alkali-making tower, an alkali filter, a carbonization tail gas ammonia-purifying tower, a high vacuum absorption tower, a salt adding barrel, a secondary carbonization cleaning tower, a secondary carbonization alkali-making tower, a thickener, a distillation tower, a calcining furnace, a cooler and a light liquid distillation tower,
the low vacuum absorption tower is provided with a distillation tower ammonia gas feeding pipe and a refined brine feeding pipe, a discharge port of the low vacuum absorption tower is connected with a feeding port of a primary carbonization cleaning tower through a middle buffer barrel and a pump, a carbon dioxide feeding pipe is also connected with a feeding port of the primary carbonization cleaning tower, a liquid outlet of the primary carbonization cleaning tower is connected with a feeding port of a primary carbonization alkali-making tower through a pump, a liquid outlet of the primary carbonization alkali-making tower is connected with a feeding port of an alkali filter through an alkali outlet buffer tank, a solid material outlet of the alkali filter is connected with an inlet of a calcining furnace through a heavy alkali belt, a furnace gas outlet of the calcining furnace is connected with a first cooler, and a gas outlet of the first cooler is connected with gas inlets of the primary alkali-making tower and a secondary alkali-making tower through a compressor;
the primary mother liquid outlet of the alkali filter is connected with the liquid feed inlet of the carbonized tail gas ammonia purifying tower through a pipeline, a mother liquid buffer barrel and a pump, the gas feed inlet of the carbonized tail gas ammonia purifying tower is also connected with the tail gas outlets of the primary carbonization tower and the secondary carbonization tower through a pipeline, the washing liquid outlet of the carbonized tail gas ammonia purifying tower is connected with the inlet of a high vacuum absorption tower through a pump, the inlet of the high vacuum absorption tower is also connected with an ammonia gas feed pipe from a light liquid distillation tower and/or an ammonia gas feed pipe of the distillation tower (after the ammonia gas distilled from the distillation tower is cooled by a cooler), the liquid outlet of the high vacuum absorption tower is connected with the inlet of a salt adding barrel through a pump, the outlet of the salt adding barrel is connected with the inlet of a secondary carbonization cleaning tower through an ammonia salt mother liquid buffer barrel and a pump, the washing gas feed pipe is also connected with the inlet of the secondary carbonization cleaning tower, the liquid outlet of the secondary carbonization cleaning tower is connected with the inlet of the secondary carbonization alkali making tower through a pump, the liquid outlet of the secondary carbonization alkali making tower is connected with the inlet of a thickener, the bottom outlet of the thickener is connected with the inlet of an alkali filter, the upper outlet of the thickener is connected with the feed inlet of a distillation tower through a mother liquor buffer barrel and a pump, a lime milk feed pipe and a steam feed pipe are also connected with the feed inlet of the distillation tower, the gas outlet of the distillation tower is connected with a second cooler, the liquid outlet of the second cooler is connected with the liquid inlet of a thin liquid distillation tower, the thin liquid distillation tower is also provided with a steam inlet, and the gas outlet of the second cooler is connected with the gas inlet of a low vacuum absorption tower;
preferably, the primary carbonization tower is provided with a middle section gas, a lower section gas and a cleaning gas carbon dioxide feeding hole.
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