CN111362292A - Continuous production system and method for producing low-water-content calcium sulfate from waste sulfuric acid - Google Patents
Continuous production system and method for producing low-water-content calcium sulfate from waste sulfuric acid Download PDFInfo
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- CN111362292A CN111362292A CN202010186899.6A CN202010186899A CN111362292A CN 111362292 A CN111362292 A CN 111362292A CN 202010186899 A CN202010186899 A CN 202010186899A CN 111362292 A CN111362292 A CN 111362292A
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Abstract
The invention provides a continuous production system and a method for producing low-water-content calcium sulfate from waste sulfuric acid, wherein the continuous production system for producing the low-water-content calcium sulfate from the waste sulfuric acid comprises a limestone slurry supply unit, a waste sulfuric acid supply unit, a quicklime slurry supply unit, a four-stage continuous reactor, a solid-liquid separation unit and a tail gas absorption unit; the method accurately controls the reaction process of the waste sulfuric acid, the limestone and the lime, adds the crystal transformation agent and the calcium sulfate crystal seed to regulate and control the particle size of the calcium sulfate particles to obtain large-particle calcium sulfate crystals, so that the free water content of the gypsum product is lower than 10 percent, and the reaction process utilizes the instrument control means such as an electromagnetic flowmeter, a pH on-line instrument and the like to ensure the continuous reaction. The invention has no waste residue and waste liquid, the waste gas reaches the standard and is discharged, the process is clean and environment-friendly, and a new way is provided for the resource utilization of the waste sulfuric acid.
Description
Technical Field
The invention belongs to the technical field of resource utilization of industrial hazardous waste, relates to a system and a method for producing calcium sulfate from waste sulfuric acid, and particularly relates to a continuous production system and a continuous production method for producing low-water-content calcium sulfate from waste sulfuric acid.
Background
A large amount of sulfuric acid is used in the industries of chemical industry, fuel, petroleum, medicine and the like, the utilization rate of the sulfuric acid is low, the large amount of sulfuric acid is discharged along with acid-containing wastewater, and the waste acid is discharged into the environment without being treated, so that not only can water or soil be acidified, but also the ecological environment is harmed, and a large amount of resources are wasted.
The treatment method of the waste sulfuric acid comprises an evaporation concentration method, an incineration method, a neutralization method, an extraction method, an ion exchange resin method, a production transfer method and the like, and the optimal treatment method of the waste sulfuric acid is resource utilization in view of the great hazard of the waste sulfuric acid.
Waste acid with the mass fraction of 20 percent in the titanium dioxide industry can be subjected to evaporation concentration to obtain waste water with the mass fraction of 60-70 percent, the obtained waste acid can be directly recycled, but the requirement on equipment for evaporation concentration of waste sulfuric acid is high, and the problems of large total equipment investment and high operation cost are inevitable.
After harmful substances in the waste acid are removed by extraction, ion exchange or adsorption and other methods, low-concentration sulfuric acid can be used for preparing available resources such as ammonium sulfate, magnesium sulfate or calcium sulfate, but the ammonium sulfate and the magnesium sulfate are mainly used as fertilizers, and if impurities cannot be completely removed in a pretreatment process, the problem of secondary pollution exists.
Calcium sulfate is a building material with a long application history, and is listed as three main supporting column materials in inorganic gel materials together with lime and cement. The calcium sulfate has the advantages of light weight, good fire resistance, small heat and sound transmission, high construction efficiency, harmlessness to human bodies and the like, and is an energy-saving green material which is worried and developed internationally. In the traditional technology, waste sulfuric acid, limestone and quicklime are usually mixed and react through long-time heap leaching, although calcium sulfate dihydrate can be obtained, continuous production cannot be realized through the heap leaching reaction, and the free water content in the obtained calcium sulfate dihydrate product is usually 35-50%, and smooth feeding at a feed inlet of a cement mill in a cement plant cannot be realized, so that gypsum formed after the waste sulfuric acid and the lime or the calcium carbonate are neutralized cannot be used as a corrosion inhibitor of the cement.
In addition, too fine gypsum particles or too high a free water content also makes it impossible to calcine the gypsum produced by the simple neutralization process into building gypsum powders with acceptable chemical properties.
CN 105858705A discloses a method for preparing dihydrate gypsum with low free water content by using waste sulfuric acid solution, which obtains dihydrate gypsum with regular shape and free water content of 13-20% by controlling the process conditions of concentration of crystal transformation agent, granularity of calcium carbonate, concentration of waste sulfuric acid and the like. However, the method only adjusts the process parameters on the basis of the existing neutralization reaction, and a large amount of waste liquid is still generated in the solid-liquid separation process.
CN 103966670A discloses a waste sulfuric acid treatment project and gypsum whisker production integrated method, in the method, a crystal transformation agent is added into filtered waste sulfuric acid, and then the waste sulfuric acid added with the crystal transformation agent is mixed with calcium carbonate slurry, so as to obtain calcium sulfate dihydrate; and adding a stabilizer into the obtained calcium sulfate dihydrate, and then carrying out multi-stage drying treatment to finally obtain the anhydrous gypsum whisker. Although the anhydrous gypsum whisker containing no water can be obtained by the method, additional drying treatment is required, and the energy consumption is high.
Aiming at the defects of the prior art, the system and the method can continuously produce the dihydrate gypsum with the free water content of 5-10%, reduce the generation amount of waste residues and waste liquid and enable tail gas to reach the standard and be discharged are provided, and the system and the method have important significance for reducing the discharge amount of waste sulfuric acid and reducing the negative influence of the waste sulfuric acid on the environment.
Disclosure of Invention
The invention aims to provide a continuous production system and a method for producing low-water-content calcium sulfate from waste sulfuric acid, wherein the continuous production system for producing the low-water-content calcium sulfate from the waste sulfuric acid is used for preparing a calcium sulfate product with the free water content of 5-10%, and waste water generated in the system can be reasonably utilized so as to achieve the effect of reducing the discharge of the waste water and the waste gas. The continuous production system for producing the low-water-content calcium sulfate from the waste sulfuric acid realizes low-cost treatment of the waste sulfuric acid and can continuously run.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a continuous production system for producing low-water content calcium sulfate from waste sulfuric acid, which comprises a limestone slurry supply unit, a waste sulfuric acid supply unit, a quicklime slurry supply unit, a four-stage continuous reactor, a crystal transformation agent supply unit, a solid-liquid separation unit and a tail gas absorption unit.
The four-stage continuous reactor comprises a first-stage reaction chamber, a second-stage reaction chamber, a third-stage reaction chamber and a fourth-stage reaction chamber which are arranged in sequence; the reaction material in the first-stage reaction chamber flows to the second-stage reaction chamber, the reaction material in the second-stage reaction chamber flows to the third-stage reaction chamber, the reaction material in the third-stage reaction chamber overflows to the fourth-stage reaction chamber, and the liquid in the fourth-stage reaction chamber flows back to the first-stage reaction chamber; the first-stage reaction chamber is also provided with a crystal transfer agent inlet, and the crystal transfer agent inlet is connected with a crystal transfer agent outlet of the crystal transfer agent supply unit.
A limestone slurry outlet of the limestone slurry supply unit is respectively and independently connected with limestone slurry inlets of the first-stage reaction chamber and the second-stage reaction chamber; the waste sulfuric acid outlet of the waste sulfuric acid supply unit is respectively and independently connected with the waste sulfuric acid inlets of the first-stage reaction chamber and the second-stage reaction chamber; and a quicklime slurry outlet of the quicklime slurry supply unit is connected with a quicklime slurry inlet of the third-stage reaction chamber.
And a slurry outlet of the fourth-stage reaction chamber is connected with a feed inlet of the solid-liquid separation unit, and a liquid outlet of the solid-liquid separation unit is respectively and independently connected with the limestone slurry supply unit, the quicklime slurry supply unit and the tail gas absorption unit.
The gas outlet of the four-stage continuous reactor is connected with a tail gas absorption unit; the slurry outlet of the quicklime slurry supply unit is also connected with the tail gas absorption unit, and the tail gas absorption unit carries out tail gas absorption by using the liquid of the solid-liquid separation unit and the quicklime slurry of the quicklime slurry supply unit.
The continuous production system for producing the low-water content calcium sulfate from the waste sulfuric acid also comprises a conveying device which is indispensable for conveying materials, including but not limited to a pump, and can be reasonably set by a person skilled in the art according to the process requirements.
The low-water-content calcium sulfate is calcium sulfate with the water content of 5-10%. The invention enables limestone and waste sulfuric acid to be fully reacted by arranging the four-stage continuous reactor, and the growth rates of different crystal faces of gypsum crystals are adjusted by adding the crystal transformation agent, so that the crystal morphology of gypsum can be changed. Because the interface energy of each crystal face of the dihydrate gypsum is the same, and the crystal transformation agent selectively adsorbs on different crystal faces, the growth rate of each crystal face is changed, so that the appearance of the dihydrate gypsum is changed, calcium sulfate crystals with larger particles are obtained, the obtained calcium sulfate can be crystallized into calcium sulfate with the free water content as low as 5-10%, no extra drying treatment is needed, and the obtained low-water-content calcium sulfate can be used as a cement slow release agent or a raw material of building gypsum powder. Therefore, the continuous production system for producing the low-water content calcium sulfate by using the waste sulfuric acid can not only treat the waste sulfuric acid at low cost, but also prepare the low-water content calcium sulfate required by the composite industry, improve the utilization efficiency of the waste sulfuric acid and improve the economic benefit of enterprises.
Preferably, the first-stage reaction chamber, the second-stage reaction chamber, the third-stage reaction chamber and the fourth-stage reaction chamber of the four-stage continuous reactor are respectively and independently provided with a stirring paddle. The stirring paddles are arranged to make the feed liquid in each reaction chamber uniform in component.
Further preferably, the first stage reaction chamber, the second stage reaction chamber, the third stage reaction chamber and the fourth stage reaction chamber are respectively and independently provided with a pH meter.
Preferably, flow meters are respectively and independently arranged on connecting pipelines of the limestone slurry outlet of the limestone slurry supply unit and the limestone slurry inlet of the first-stage reaction chamber and the second-stage reaction chamber; flow meters are respectively and independently arranged on connecting pipelines of a waste sulfuric acid outlet of the waste sulfuric acid supply unit and limestone slurry inlets of the first-stage reaction chamber and the second-stage reaction chamber; and a flow meter is arranged on a connecting pipeline between a quicklime slurry outlet of the quicklime slurry supply unit and a quicklime slurry inlet of the third-stage reaction chamber.
Preferably, the limestone slurry supply unit comprises a limestone silo, a limestone rotor scale, a limestone conveyor and a limestone slurry tank which are connected in sequence; the liquid outlet of the solid-liquid separation unit is connected with the liquid inlet of the limestone-petrochemical slurry tank, and the limestone slurry outlet of the limestone-petrochemical slurry tank is respectively and independently connected with the limestone slurry inlets of the first-stage reaction chamber and the second-stage reaction chamber.
Preferably, the quicklime slurry supply unit comprises a quicklime bin, a quicklime rotor scale, a quicklime conveyor and a quicklime slurrying tank which are connected in sequence. The liquid outlet of the solid-liquid separation unit is connected with the liquid inlet of the quick lime slurrying tank, and the quick lime slurry outlet of the quick lime slurrying tank is respectively and independently connected with the quick lime slurry inlets of the first-stage reaction chamber and the second-stage reaction chamber.
The present invention is not particularly limited to the crystal modifier supply unit, as long as the crystal modifier with a concentration meeting the requirement can be continuously supplied. Illustratively, the crystal transfer agent supply unit comprises a crystal transfer agent storage tank and a crystal transfer agent delivery pump, and the crystal transfer agent in the crystal transfer agent storage tank flows into the first-stage reaction chamber under the delivery of the crystal transfer agent delivery pump.
Preferably, the spent sulfuric acid supply unit comprises a spent sulfuric acid metering tank.
And a waste sulfuric acid outlet of the waste sulfuric acid metering tank is respectively and independently connected with waste sulfuric acid inlets of the first-stage reaction chamber and the second-stage reaction chamber.
Preferably, the solid-liquid separation unit comprises a gypsum filter and a solution buffer tank which are connected in sequence.
And a slurry outlet of the fourth-stage reaction chamber is connected with a feed inlet of the gypsum filter.
The liquid outlets of the solution buffer tank are respectively and independently connected with the limestone slurry supply unit, the quicklime slurry supply unit and the tail gas absorption unit.
Preferably, the gypsum filter is a plate and frame filter press.
In a second aspect, the present invention provides a continuous production method for producing low-water content calcium sulfate from waste sulfuric acid, wherein the continuous production method is performed in the continuous production system of the first aspect, and comprises the following steps:
(1) limestone slurry and waste sulfuric acid are respectively and independently mixed in a first-stage reaction chamber and a second-stage reaction chamber, and a crystal transformation agent is also added in the first-stage reaction chamber; the reacted feed liquid flows into the third-stage reaction chamber to perform neutralization reaction with the quicklime slurry, and the reacted feed liquid flows into the fourth-stage reaction chamber;
(2) and filtering the slurry in the fourth-stage reaction chamber to obtain a solid low-water-content calcium sulfate product, wherein the obtained filtrate is independently used for limestone size mixing and quicklime size mixing respectively.
Preferably, the continuous production method further comprises a tail gas absorption step of: and (3) preparing circulating slurry by using the raw lime slurry and the filtrate obtained in the step (2), and absorbing the tail gas of the four-stage continuous reactor by using the circulating slurry.
Preferably, the mass fraction of the recycled slurry is between 0.1 and 0.6 wt%, and may be, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, or 0.6 wt%, but is not limited to the recited values, and other unrecited values within the range of values are equally applicable, preferably between 0.3 and 0.4 wt%.
According to the invention, tail gas such as acid mist and the like generated in the reaction process can be absorbed by the circulating slurry through tail gas absorption, and the continuous production system can stably operate while the tail gas is ensured to be discharged up to the standard.
Preferably, when the limestone slurry in the step (1) is prepared, the particle size of the limestone used is 150-250 meshes, preferably 180-200 meshes.
The particle size of the limestone is 150-250 meshes, which means that the limestone can pass through a 150-mesh screen but cannot pass through a 250-mesh screen. When limestone slurry is prepared by the present invention, the particle size of limestone used is preferably 180 mesh screen, but not 200 mesh screen.
Limestone with too large particle size can cause the limestone and sulfuric acid to be incapable of completely reacting within a specified time, the same quality of sulfuric acid is treated, the consumption of limestone with too large particles is higher, and the obtained calcium sulfate product contains calcium carbonate and has poor gypsum quality; on the other hand, if the particle size of limestone is too small, the cost for limestone treatment increases, and the limestone slurry is likely to be bonded during limestone-petrochemical processing, which is also disadvantageous for the reaction between limestone and sulfuric acid. Therefore, the particle size of the limestone is 150-250 meshes, and the limestone can fully react with the sulfuric acid within the particle size range, so that the gypsum obtained by the reaction has excellent quality.
Preferably, the limestone slurry of step (1) has a mass fraction of 10 to 20 wt%, for example 10 wt%, 12 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt% or 20 wt%, but not limited to the recited values, and other values not recited within the range of values are equally applicable, preferably 15 to 16 wt%.
If the concentration of the limestone slurry is too high, calcium sulfate generated by neutralization reaction can wrap unreacted limestone, so that the limestone cannot fully react with sulfuric acid, and the prepared gypsum contains certain calcium carbonate, so that the quality of the gypsum is reduced. If the limestone slurry concentration is too low, a higher limestone flow rate is required, and the throughput of the reactor is reduced by increasing the circulation volume of the reaction feed liquid without changing the size of the reactor. Therefore, the invention considers the treatment cost and the quality of the calcium sulfate product comprehensively, and sets the mass fraction of the limestone slurry to be 10-20 wt%.
Preferably, the limestone slurry flows into the first stage reaction chamber and the second stage reaction chamber in the step (1) at a mass flow ratio of (55-70): 30-45, such as 55:45, 60:40, 64:36, 65:35 or 70:30, but not limited to the enumerated values, and other unrecited values within the numerical range are equally applicable, preferably (60-65): 35-40.
The particle size of the quicklime is 150-250 meshes, namely the quicklime can pass through a 150-mesh screen but cannot pass through a 250-mesh screen. When the raw lime slurry is prepared by the present invention, the particle size of the quicklime used is preferably 180 mesh screen, but not 200 mesh screen.
Preferably, the raw lime slurry of step (1) has a mass fraction of 10 to 20 wt%, for example 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt% or 20 wt%, but not limited to the recited values, and ranges of values other than those recited apply equally, preferably 15 to 16 wt%.
Preferably, the raw lime slurry in step (1) is added in an amount to make the pH in the third stage reaction chamber 6 to 7, for example, 6, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9 or 7, preferably 6.5 to 7.
Preferably, the mass fraction of the waste sulfuric acid in step (1) is 5 to 20 wt%, for example, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 12 wt%, 15 wt%, 16 wt%, 18 wt% or 20 wt%, but not limited to the recited values, and other values not recited in the range of values are also applicable.
Preferably, the mass flow ratio of the waste sulfuric acid flowing into the first stage reaction chamber and the second stage reaction chamber in the step (1) is (0.8-1.2): (0.8-1.2), and may be, for example, 0.8:0.9, 0.8:1, 0.8:1.1, 0.8:1.2 or 1.2:0.8, but is not limited to the enumerated values, and other unrecited values within the numerical range are equally applicable, preferably 1: 1.
Preferably, the ratio of the total mass flow rate of limestone slurry to the total mass flow rate of sulfuric acid in step (1) is (0.2-1.2):1, and may be, for example, 0.2:1, 0.4:1, 0.5:1, 0.6:1, 0.8:1, 1:1 or 1.2:1, but is not limited to the recited values, and other values not recited in the numerical range are equally applicable.
Preferably, the residence time of the reaction mass in the first stage reaction chamber is between 80 and 150min, for example 80min, 90min, 100min, 110min, 120min, 130min, 140min or 150min, but is not limited to the values listed, and other values not listed in the range of values are equally applicable, preferably 110-.
The residence time of the reaction materials in the first-stage reaction chamber is as follows: the residence time of the limestone slurry and the waste sulfuric acid flowing into the first-stage reaction chamber in the first-stage reaction chamber is as follows:
the effective volume of the first stage reaction chamber divided by the total flow of limestone slurry and spent sulfuric acid into the first stage reaction chamber.
Preferably, the residence time of the reaction mass in the second stage reaction chamber is 70 to 100min, for example 70min, 75min, 80min, 85min, 90min, 95min or 100min, but not limited to the values listed, other values not listed in the range of values being equally applicable, preferably 80 to 90 min;
the residence time of the reaction materials in the second-stage reaction chamber is as follows: the residence time of the limestone slurry and the waste sulfuric acid flowing into the second-stage reaction chamber in the second-stage reaction chamber is as follows:
the effective volume of the second stage reaction chamber divided by the total flow of limestone slurry and spent sulfuric acid into the second stage reaction chamber.
Preferably, the residence time of the reaction mass in the third stage reaction chamber is 70 to 100min, for example 70min, 75min, 80min, 85min, 90min, 95min or 100min, but not limited to the values listed, other values not listed in the range of values being equally applicable, preferably 80 to 90 min;
the residence time of the reaction materials in the third-stage reaction chamber is as follows: the retention time of the feed liquid overflowing to the third-stage reaction chamber and the quicklime slurry in the third-stage reaction chamber is as follows:
the effective volume of the third stage reaction chamber is divided by the effective volume of the third stage reaction chamber, and the effective volume is divided by the effective volume of the third stage reaction chamber.
Preferably, the crystal transforming agent in step (1) comprises any one or a combination of at least two of citric acid, citrate or aluminium sulphate salts, typical but non-limiting combinations include a combination of citric acid and citrate, a combination of citrate and aluminium sulphate salt, a combination of citric acid and aluminium sulphate salt or a combination of citric acid, citrate and aluminium sulphate salt.
Preferably, the citrate salt comprises potassium citrate and/or sodium citrate.
Preferably, the aluminium sulphate salt comprises any one of or a combination of at least two of aluminium sulphate, potassium aluminium sulphate or sodium aluminium sulphate, typical but non-limiting combinations including a combination of aluminium sulphate and potassium aluminium sulphate, a combination of potassium aluminium sulphate and sodium aluminium sulphate, a combination of aluminium sulphate and sodium aluminium sulphate or a combination of aluminium sulphate, potassium aluminium sulphate and sodium aluminium sulphate.
Preferably, the mass fraction of the agent for the crystallization in step (1) is 15 to 25 wt%, for example 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt% or 25 wt%, but not limited to the recited values, and other values not recited in the range of values are equally applicable, preferably 20 wt%.
Preferably, the amount of the crystal transformation agent added in step (1) is 0.3-1% of the amount of the waste sulfuric acid, for example, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, but not limited to the recited values, and other values not recited in the numerical range are also applicable.
Preferably, 2-7 wt% of the slurry obtained in the fourth stage reaction chamber of the step (1) is refluxed to the first stage reaction chamber; preferably, 4-5 wt% of the slurry obtained in the fourth stage reaction chamber of step (1) is refluxed to the first stage reaction chamber.
According to the invention, partial slurry in the fourth-stage reaction chamber is refluxed, and the partial slurry is used as calcium sulfate crystal seeds to regulate the particle size of crystal particles.
Preferably, the filtration in step (2) is filter pressing.
Preferably, the free water content of the low-water calcium sulphate product obtained in step (2) is between 5 and 10%, for example 5%, 6%, 7%, 8%, 9% or 10%, but not limited to the values listed, and other values not listed within the range of values are equally applicable, preferably between 7 and 8%.
As a preferable technical solution of the continuous production method according to the second aspect of the present invention, the continuous production method includes the steps of:
(1) limestone slurry and waste sulfuric acid are respectively and independently mixed in a first-stage reaction chamber and a second-stage reaction chamber, and a crystal transformation agent is also added in the first-stage reaction chamber; the reacted feed liquid flows into the third-stage reaction chamber to perform neutralization reaction with the quicklime slurry, and the reacted feed liquid flows into the fourth-stage reaction chamber; 2-7 wt% of the slurry obtained in the fourth stage reaction chamber flows back to the first stage reaction chamber;
the particle size of limestone used when preparing limestone slurry is 150-250 meshes, the mass fraction of the limestone slurry is 10-20 wt%, and the mass flow ratio of the limestone slurry flowing into the first-stage reaction chamber and the second-stage reaction chamber is (55-70): 30-45;
the mass fraction of the waste sulfuric acid is 5-20 wt%, and the mass flow ratio of the waste sulfuric acid flowing into the first-stage reaction chamber and the second-stage reaction chamber is (0.8-1.2) to (0.8-1.2);
preferably, the ratio of the total mass flow of the limestone slurry to the total mass flow of the sulfuric acid in the step (1) is (0.2-1.2): 1;
the particle size of the quicklime used in the preparation of the raw lime slurry is 150-250 meshes, the mass fraction of the raw lime slurry is 10-20 wt%, and the addition amount of the raw lime slurry is such that the pH value in the third-stage reaction chamber is 6-7;
the residence time of the reaction materials in the first-stage reaction chamber is 80-150min, the residence time in the second-stage reaction chamber is 70-100min, and the residence time in the third-stage reaction chamber is 70-100 min;
the crystal transformation agent comprises any one or the combination of at least two of citric acid, citrate or aluminum sulfate salt, the mass fraction of the crystal transformation agent is 15-25 wt%, and the mass flow of the crystal transformation agent is 0.3-1% of the total mass flow of the waste sulfuric acid;
(2) filter-pressing the slurry in the fourth-stage reaction chamber, wherein the obtained solid is a low-water-content calcium sulfate product with the free water content of 5-10%, and the obtained filtrate is respectively and independently used for limestone size mixing and quicklime size mixing;
and (3) preparing the raw lime slurry obtained in the step (1) and the filtrate obtained in the step (2) into circulating slurry with the mass fraction of 0.1-0.6 wt%, and absorbing the tail gas of the four-stage continuous reactor by using the circulating slurry.
The filtrate obtained by pressure filtration in the step (2) of the continuous production method is used for limestone size mixing, quicklime size mixing and tail gas absorption of the four-stage continuous reactor, and the redundant filtrate is discharged to the outside of the system for water treatment.
Compared with the prior art, the invention has the following beneficial effects:
(1) the method accurately controls the reaction process of the waste sulfuric acid, the limestone and the lime, adds the crystal transformation agent and the calcium sulfate crystal seed to regulate and control the particle size of the calcium sulfate particles to obtain large-particle calcium sulfate crystals, so that the free water content of the gypsum product is lower than 10 percent, and the reaction process utilizes the instrument control means such as an electromagnetic flowmeter, a pH on-line instrument and the like to ensure the continuous reaction.
(2) The invention has no waste residue and waste liquid, the waste gas reaches the standard and is discharged, the process is clean and environment-friendly, and a new way is provided for the resource utilization of the waste sulfuric acid.
Drawings
FIG. 1 is a schematic structural diagram of a continuous production system for producing low-water content calcium sulfate from waste sulfuric acid provided by the invention.
Wherein: 1, a limestone silo; 2, limestone rotor scale; 3, a limestone conveyor; 4, a limestone slurry tank; 5, a four-stage continuous reactor; 6, a waste sulfuric acid metering tank; 7, a quicklime bin; 8, a quicklime rotor scale; 9, a quicklime conveyor; 10, a quicklime slurrying tank; 11, a plate-and-frame filter press; 12, a solution buffer tank; and 13, a tail gas absorption tower.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The embodiment provides a continuous production system for producing low-water content calcium sulfate from waste sulfuric acid, and the structural schematic diagram of the continuous production system for producing low-water content calcium sulfate from waste sulfuric acid is shown in fig. 1, and the continuous production system comprises a limestone slurry supply unit, a waste sulfuric acid supply unit, a quicklime slurry supply unit, a four-stage continuous reactor, a crystal modifier supply unit, a solid-liquid separation unit and a tail gas absorption tower 13.
The four-stage continuous reactor comprises a first-stage reaction chamber, a second-stage reaction chamber, a third-stage reaction chamber and a fourth-stage reaction chamber which are arranged in sequence; the reaction material in the first-stage reaction chamber flows to the second-stage reaction chamber, the reaction material in the second-stage reaction chamber flows to the third-stage reaction chamber, the reaction material in the third-stage reaction chamber overflows to the fourth-stage reaction chamber, and the liquid in the fourth-stage reaction chamber flows back to the first-stage reaction chamber; the first-stage reaction chamber is also provided with a crystal transfer agent inlet, and the crystal transfer agent inlet is connected with a crystal transfer agent outlet of the crystal transfer agent supply unit.
The first-stage reaction chamber, the second-stage reaction chamber, the third-stage reaction chamber and the fourth-stage reaction chamber of the four-stage continuous reactor are respectively and independently provided with stirring paddles, and the first-stage reaction chamber, the second-stage reaction chamber, the third-stage reaction chamber and the fourth-stage reaction chamber are respectively and independently provided with a pH meter.
Flow meters are respectively and independently arranged on connecting pipelines of a limestone slurry outlet of the limestone slurry supply unit and limestone slurry inlets of the first-stage reaction chamber and the second-stage reaction chamber; flow meters are respectively and independently arranged on connecting pipelines of a waste sulfuric acid outlet of the waste sulfuric acid supply unit and limestone slurry inlets of the first-stage reaction chamber and the second-stage reaction chamber; and a flow meter is arranged on a connecting pipeline between a quicklime slurry outlet of the quicklime slurry supply unit and a quicklime slurry inlet of the third-stage reaction chamber.
A limestone slurry outlet of the limestone slurry supply unit is respectively and independently connected with limestone slurry inlets of the first-stage reaction chamber and the second-stage reaction chamber; the waste sulfuric acid outlet of the waste sulfuric acid supply unit is respectively and independently connected with the waste sulfuric acid inlets of the first-stage reaction chamber and the second-stage reaction chamber; and a quicklime slurry outlet of the quicklime slurry supply unit is connected with a quicklime slurry inlet of the third-stage reaction chamber.
The solid-liquid separation unit comprises a plate-and-frame filter press 11 and a solution buffer tank 12 which are connected in sequence, the slurry outlet of the fourth-stage reaction chamber is connected with the feed inlet of the gypsum filter, and the liquid outlet of the solution buffer tank 12 is respectively and independently connected with a limestone slurry supply unit, a quicklime slurry supply unit and a tail gas absorption tower 13.
The gas outlet of the four-stage continuous reactor is connected with a tail gas absorption tower 13; the slurry outlet of the quicklime slurry supply unit is also connected with the tail gas absorption tower 13, and the tail gas absorption tower 13 absorbs tail gas by using the liquid of the solid-liquid separation unit and the quicklime slurry of the quicklime slurry supply unit.
The limestone slurry supply unit comprises a limestone storage bin 1, a limestone rotor scale 2, a limestone conveyor 3 and a limestone slurry tank 4 which are connected in sequence; the liquid outlet of the solid-liquid separation unit is connected with the liquid inlet of the limestone-petrochemical slurry tank 4, and the limestone slurry outlet of the limestone-petrochemical slurry tank 4 is respectively and independently connected with the limestone slurry inlets of the first-stage reaction chamber and the second-stage reaction chamber.
The quicklime slurry supply unit comprises a quicklime bin 7, a quicklime rotor scale 8, a quicklime conveyor 9 and a quicklime slurrying tank 10 which are connected in sequence. The liquid outlet of the solid-liquid separation unit is connected with the liquid inlet of the quick lime slurrying tank 10, and the quick lime slurry outlet of the quick lime slurrying tank 10 is respectively and independently connected with the quick lime slurry inlets of the first-stage reaction chamber and the second-stage reaction chamber.
The waste sulfuric acid supply unit includes a waste sulfuric acid metering tank 6. And a waste sulfuric acid outlet of the waste sulfuric acid metering tank 6 is respectively and independently connected with waste sulfuric acid inlets of the first-stage reaction chamber and the second-stage reaction chamber.
When the continuous production system for producing low-water content calcium sulfate from waste sulfuric acid provided by the embodiment is used for treating waste sulfuric acid, a limestone slurry is prepared by using the limestone slurry supply unit, and a raw lime slurry is prepared by using the quicklime slurry supply unit.
Respectively and independently introducing limestone slurry into a first-stage reaction chamber and a second-stage reaction chamber; respectively and independently introducing waste sulfuric acid into a first-stage reaction chamber and a second-stage reaction chamber; a crystal transfer agent is also introduced into the first-stage reaction chamber; and introducing the quicklime slurry into a third-stage reaction chamber.
The feed liquid in the third-stage reaction chamber overflows to the fourth-stage reaction chamber, one part of slurry in the fourth-stage reaction chamber reflows to the first-stage reaction chamber to be used as seed crystals for neutralization reaction, and the other part of slurry is discharged to the plate-and-frame filter press 11 to be subjected to filter pressing treatment. The solid obtained by filter pressing is a calcium sulfate product with 5-10% of free water content, and the obtained solution flows back to the lime-petrochemical slurry tank 4 and the quick lime-slurrying tank 10. Meanwhile, the obtained solution is mixed with the quicklime slurry flowing out of the quicklime slurrying tank 10 to prepare circulating slurry for tail gas absorption, so that the tail gas of the four-stage continuous reactor is absorbed.
Application example 1
The application example provides a method for continuous production by using the continuous production system for producing low-water-content calcium sulfate from waste sulfuric acid, which is provided in the embodiment 1, and the method for continuous production comprises the following steps:
(1) limestone slurry and waste sulfuric acid are respectively and independently mixed in a first-stage reaction chamber and a second-stage reaction chamber, and a crystal transformation agent is also added in the first-stage reaction chamber; the reacted feed liquid flows into the third-stage reaction chamber to perform neutralization reaction with the quicklime slurry, and the reacted feed liquid flows into the fourth-stage reaction chamber; 4 wt% of the slurry obtained in the fourth stage reaction chamber is refluxed to the first stage reaction chamber;
the particle size of limestone used for preparing limestone slurry is 150-250 meshes, the mass fraction of the limestone slurry is 16 wt%, and the mass flow ratio of the limestone slurry flowing into the first-stage reaction chamber and the second-stage reaction chamber is 60: 40;
the mass fraction of the waste sulfuric acid is 5 wt%, and the mass flow ratio of the waste sulfuric acid flowing into the first-stage reaction chamber and the second-stage reaction chamber is 1: 1;
preferably, the ratio of the total mass flow of the limestone slurry to the total mass flow of the sulfuric acid in the step (1) is 0.2: 1;
the particle size of quicklime used in the preparation of the raw lime slurry is 150-250 meshes, the mass fraction of the quicklime slurry is 16 wt%, and the addition amount of the raw lime slurry is such that the pH value in the third-stage reaction chamber is 7;
the residence time of the reaction materials in the first-stage reaction chamber is 120min, the residence time in the second-stage reaction chamber is 90min, and the residence time in the third-stage reaction chamber is 90 min;
the mass fraction of the crystal transformation agent is 20 wt% of citric acid, and the mass flow of the crystal transformation agent is 0.5% of the total mass flow of the waste sulfuric acid;
(2) filter-pressing the slurry in the fourth-stage reaction chamber, wherein the obtained solid is a low-moisture calcium sulfate product with free water content of 7%, and the obtained filtrate is respectively and independently used for limestone size mixing and quicklime size mixing;
and (3) preparing the raw lime slurry obtained in the step (1) and the filtrate obtained in the step (2) into circulating slurry with the mass fraction of 0.4 wt%, and absorbing the tail gas of the four-stage continuous reactor 5 by using the circulating slurry.
Application example 2
The application example provides a method for continuous production by using the continuous production system for producing low-water-content calcium sulfate from waste sulfuric acid, which is provided in the embodiment 1, and the method for continuous production comprises the following steps:
(1) limestone slurry and waste sulfuric acid are respectively and independently mixed in a first-stage reaction chamber and a second-stage reaction chamber, and a crystal transformation agent is also added in the first-stage reaction chamber; the reacted feed liquid flows into the third-stage reaction chamber to perform neutralization reaction with the quicklime slurry, and the reacted feed liquid flows into the fourth-stage reaction chamber; 5 wt% of the slurry obtained in the fourth stage reaction chamber flows back to the first stage reaction chamber;
the particle size of limestone used for preparing limestone slurry is 150-250 meshes, the mass fraction of the limestone slurry is 15 wt%, and the mass flow ratio of the limestone slurry flowing into the first-stage reaction chamber and the second-stage reaction chamber is 65: 35;
the mass fraction of the waste sulfuric acid is 10 wt%, and the mass flow ratio of the waste sulfuric acid flowing into the first-stage reaction chamber and the second-stage reaction chamber is 1: 1;
preferably, the ratio of the total mass flow of the limestone slurry to the total mass flow of the sulfuric acid in the step (1) is 0.6: 1;
the particle size of the quicklime used in the preparation of the raw lime slurry is 150-250 meshes, the mass fraction of the raw lime slurry is 15 wt%, and the addition amount of the raw lime slurry is such that the pH value in the third-stage reaction chamber is 6.5;
the residence time of the reaction materials in the first-stage reaction chamber is 110min, the residence time in the second-stage reaction chamber is 80min, and the residence time in the third-stage reaction chamber is 80 min;
the mass fraction of the crystal transformation agent is 15 wt% of sodium citrate, and the mass flow of the crystal transformation agent is 0.7% of the total mass flow of the waste sulfuric acid;
(2) filter-pressing the slurry in the fourth-stage reaction chamber, wherein the obtained solid is a low-moisture calcium sulfate product with free water content of 8 percent, and the obtained filtrate is respectively and independently used for limestone size mixing and quicklime size mixing;
and (3) preparing the raw lime slurry obtained in the step (1) and the filtrate obtained in the step (2) into circulating slurry with the mass fraction of 0.3 wt%, and absorbing the tail gas of the four-stage continuous reactor 5 by using the circulating slurry.
Application example 3
The application example provides a method for continuous production by using the continuous production system for producing low-water-content calcium sulfate from waste sulfuric acid, which is provided in the embodiment 1, and the method for continuous production comprises the following steps:
(1) limestone slurry and waste sulfuric acid are respectively and independently mixed in a first-stage reaction chamber and a second-stage reaction chamber, and a crystal transformation agent is also added in the first-stage reaction chamber; the reacted feed liquid flows into the third-stage reaction chamber to perform neutralization reaction with the quicklime slurry, and the reacted feed liquid flows into the fourth-stage reaction chamber; 3 wt% of the slurry obtained in the fourth stage reaction chamber is refluxed to the first stage reaction chamber;
the particle size of limestone used for preparing limestone slurry is 150-250 meshes, the mass fraction of the limestone slurry is 13 wt%, and the mass flow ratio of the limestone slurry flowing into the first-stage reaction chamber and the second-stage reaction chamber is 55: 45;
the mass fraction of the waste sulfuric acid is 15 wt%, and the mass flow ratio of the waste sulfuric acid flowing into the first-stage reaction chamber and the second-stage reaction chamber is 1: 1;
preferably, the ratio of the total mass flow of the limestone slurry to the total mass flow of the sulfuric acid in the step (1) is 0.6: 1;
the particle size of the quicklime used in the preparation of the raw lime slurry is 150-250 meshes, the mass fraction of the raw lime slurry is 13 wt%, and the addition amount of the raw lime slurry is such that the pH value in the third-stage reaction chamber is 6.7;
the residence time of the reaction materials in the first-stage reaction chamber is 110min, the residence time in the second-stage reaction chamber is 80min, and the residence time in the third-stage reaction chamber is 80 min;
the mass fraction of the crystal transformation agent is 25 wt% of aluminum sulfate, and the mass flow of the crystal transformation agent is 0.6% of the total mass flow of the waste sulfuric acid;
(2) filter-pressing the slurry in the fourth-stage reaction chamber, wherein the obtained solid is a low-moisture calcium sulfate product with free water content of 7.3 percent, and the obtained filtrate is respectively and independently used for limestone size mixing and quicklime size mixing;
and (3) preparing the raw lime slurry obtained in the step (1) and the filtrate obtained in the step (2) into circulating slurry with the mass fraction of 0.2 wt%, and absorbing the tail gas of the four-stage continuous reactor 5 by using the circulating slurry.
Application example 4
The application example provides a method for continuous production by using the continuous production system for producing low-water-content calcium sulfate from waste sulfuric acid, which is provided in the embodiment 1, and the method for continuous production comprises the following steps:
(1) limestone slurry and waste sulfuric acid are respectively and independently mixed in a first-stage reaction chamber and a second-stage reaction chamber, and a crystal transformation agent is also added in the first-stage reaction chamber; the reacted feed liquid flows into the third-stage reaction chamber to perform neutralization reaction with the quicklime slurry, and the reacted feed liquid flows into the fourth-stage reaction chamber; 2 wt% of the slurry obtained in the fourth stage reaction chamber flows back to the first stage reaction chamber;
the particle size of limestone used in the preparation of limestone slurry is 180-mesh and 200-mesh, the mass fraction of the limestone slurry is 10 wt%, and the mass flow ratio of the limestone slurry flowing into the first-stage reaction chamber and the second-stage reaction chamber is 55: 45;
the mass fraction of the waste sulfuric acid is 20 wt%, and the mass flow ratio of the waste sulfuric acid flowing into the first-stage reaction chamber and the second-stage reaction chamber is 0.8: 1.2;
preferably, the ratio of the total mass flow of the limestone slurry to the total mass flow of the sulfuric acid in the step (1) is 1.2: 1;
the particle size of the quicklime used in the preparation of the raw lime slurry is 180-200 meshes, the mass fraction of the raw lime slurry is 10 wt%, and the addition amount of the raw lime slurry is such that the pH value in the third-stage reaction chamber is 6.9;
the residence time of the reaction materials in the first-stage reaction chamber is 80min, the residence time in the second-stage reaction chamber is 70min, and the residence time in the third-stage reaction chamber is 70 min;
the mass fraction of the crystal modifier is 20 wt% of sodium aluminum sulfate, and the mass flow of the crystal modifier is 0.3% of the total mass flow of the waste sulfuric acid;
(2) filter-pressing the slurry in the fourth-stage reaction chamber, wherein the obtained solid is a low-moisture calcium sulfate product with free water content of 7.7 percent, and the obtained filtrate is respectively and independently used for limestone size mixing and quicklime size mixing;
and (3) preparing the raw lime slurry obtained in the step (1) and the filtrate obtained in the step (2) into circulating slurry with the mass fraction of 0.1 wt%, and absorbing the tail gas of the four-stage continuous reactor 5 by using the circulating slurry.
Application example 5
The application example provides a method for continuous production by using the continuous production system for producing low-water-content calcium sulfate from waste sulfuric acid, which is provided in the embodiment 1, and the method for continuous production comprises the following steps:
(1) limestone slurry and waste sulfuric acid are respectively and independently mixed in a first-stage reaction chamber and a second-stage reaction chamber, and a crystal transformation agent is also added in the first-stage reaction chamber; the reacted feed liquid flows into the third-stage reaction chamber to perform neutralization reaction with the quicklime slurry, and the reacted feed liquid flows into the fourth-stage reaction chamber; 7 wt% of the slurry obtained in the fourth stage reaction chamber is refluxed to the first stage reaction chamber;
the particle size of limestone used in the preparation of limestone slurry is 180-mesh and 200-mesh, the mass fraction of the limestone slurry is 20 wt%, and the mass flow ratio of the limestone slurry flowing into the first-stage reaction chamber and the second-stage reaction chamber is 70: 30;
the mass fraction of the waste sulfuric acid is 18 wt%, and the mass flow ratio of the waste sulfuric acid flowing into the first-stage reaction chamber and the second-stage reaction chamber is 1.2: 0.8;
preferably, the ratio of the total mass flow of the limestone slurry to the total mass flow of the sulfuric acid in the step (1) is 1: 1;
the particle size of the quicklime used in the preparation of the raw lime slurry is 180-200 meshes, the mass fraction of the raw lime slurry is 20 wt%, and the addition amount of the raw lime slurry is such that the pH value in the third-stage reaction chamber is 6;
the residence time of the reaction materials in the first-stage reaction chamber is 150min, the residence time in the second-stage reaction chamber is 100min, and the residence time in the third-stage reaction chamber is 100 min;
the mass fraction of the crystal modifier is 20 wt% of potassium citrate, and the mass flow of the crystal modifier is 1% of the total mass flow of the waste sulfuric acid;
(2) filter-pressing the slurry in the fourth-stage reaction chamber, wherein the obtained solid is a low-moisture calcium sulfate product with free water content of 7.5 percent, and the obtained filtrate is respectively and independently used for limestone size mixing and quicklime size mixing;
and (3) preparing the raw lime slurry obtained in the step (1) and the filtrate obtained in the step (2) into circulating slurry with the mass fraction of 0.6 wt%, and absorbing the tail gas of the four-stage continuous reactor 5 by using the circulating slurry.
Application example 6
The application example provides a method for continuous production by using the continuous production system for producing low-moisture calcium sulfate from waste sulfuric acid provided in the application example 1, and the method is the same as the application example 1 except that the mass fraction of limestone slurry is 8 wt%.
Since the concentration of the limestone slurry is excessively low, the amount of the limestone slurry to be used increases, and the treatment efficiency of the four-stage continuous reactor 5 decreases.
Application example 7
The application example provides a method for continuous production by using the continuous production system for producing low-moisture calcium sulfate from waste sulfuric acid provided in the application example 1, and the method is the same as the application example 1 except that the mass fraction of limestone slurry is 22 wt%.
Because the concentration of the limestone slurry is too high, calcium sulfate generated by neutralization reaction wraps unreacted limestone, so that the limestone cannot fully react with sulfuric acid, the prepared calcium sulfate product contains calcium carbonate, the quality of the obtained calcium sulfate product is greatly reduced, the calcium sulfate product contains more than 20% of calcium carbonate, a pump is easily blocked, and the operation is difficult.
In conclusion, the reaction process of the waste sulfuric acid, the limestone and the lime is accurately controlled, the crystal transformation agent and the calcium sulfate crystal seed are added to regulate and control the particle size of calcium sulfate particles, large-particle calcium sulfate crystals are obtained, the free water content of a gypsum product is lower than 10%, and the reaction process utilizes the control means of instruments such as an electromagnetic flowmeter, a pH on-line instrument and the like, so that the continuous reaction is ensured. The invention has no waste residue and waste liquid, the waste gas reaches the standard and is discharged, the process is clean and environment-friendly, and a new way is provided for the resource utilization of the waste sulfuric acid.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.
Claims (10)
1. The continuous production system for producing the low-water-content calcium sulfate from the waste sulfuric acid is characterized by comprising a limestone slurry supply unit, a waste sulfuric acid supply unit, a quick lime slurry supply unit, a four-stage continuous reactor, a crystal modifier supply unit, a solid-liquid separation unit and a tail gas absorption unit;
the four-stage continuous reactor comprises a first-stage reaction chamber, a second-stage reaction chamber, a third-stage reaction chamber and a fourth-stage reaction chamber which are arranged in sequence; the reaction material in the first-stage reaction chamber flows to the second-stage reaction chamber, the reaction material in the second-stage reaction chamber flows to the third-stage reaction chamber, the reaction material in the third-stage reaction chamber overflows to the fourth-stage reaction chamber, and the liquid in the fourth-stage reaction chamber flows back to the first-stage reaction chamber; the first-stage reaction chamber is also provided with a crystal transfer agent inlet which is connected with a crystal transfer agent outlet of the crystal transfer agent supply unit;
a limestone slurry outlet of the limestone slurry supply unit is respectively and independently connected with limestone slurry inlets of the first-stage reaction chamber and the second-stage reaction chamber; the waste sulfuric acid outlet of the waste sulfuric acid supply unit is respectively and independently connected with the waste sulfuric acid inlets of the first-stage reaction chamber and the second-stage reaction chamber; a quicklime slurry outlet of the quicklime slurry supply unit is connected with a quicklime slurry inlet of the third-stage reaction chamber;
a slurry outlet of the fourth-stage reaction chamber is connected with a feed inlet of the solid-liquid separation unit, and a liquid outlet of the solid-liquid separation unit is respectively and independently connected with the limestone slurry supply unit, the quicklime slurry supply unit and the tail gas absorption unit;
the gas outlet of the four-stage continuous reactor is connected with a tail gas absorption unit; the slurry outlet of the quicklime slurry supply unit is also connected with the tail gas absorption unit, and the tail gas absorption unit carries out tail gas absorption by using the liquid of the solid-liquid separation unit and the quicklime slurry of the quicklime slurry supply unit.
2. The continuous production system for producing low-moisture calcium sulfate from waste sulfuric acid according to claim 1, wherein the limestone slurry supply unit comprises a limestone silo, a limestone rotor scale, a limestone conveyor and a limestone slurry tank which are connected in sequence;
the liquid outlet of the solid-liquid separation unit is connected with the liquid inlet of the limestone-petrochemical slurry tank, and the limestone slurry outlet of the limestone-petrochemical slurry tank is respectively and independently connected with the limestone slurry inlets of the first-stage reaction chamber and the second-stage reaction chamber.
3. The continuous production system for producing low-water content calcium sulfate from waste sulfuric acid as claimed in claim 1 or 2, wherein the raw lime slurry supply unit comprises a quick lime bin, a quick lime rotor scale, a quick lime conveyor and a quick lime slurry tank which are connected in sequence;
the liquid outlet of the solid-liquid separation unit is connected with the liquid inlet of the quick lime slurrying tank, and the quick lime slurry outlet of the quick lime slurrying tank is respectively and independently connected with the quick lime slurry inlets of the first-stage reaction chamber and the second-stage reaction chamber.
4. The continuous production system for producing low-water content calcium sulfate from waste sulfuric acid according to any one of claims 1 to 3, wherein the waste sulfuric acid supply unit comprises a waste sulfuric acid metering tank;
and a waste sulfuric acid outlet of the waste sulfuric acid metering tank is respectively and independently connected with waste sulfuric acid inlets of the first-stage reaction chamber and the second-stage reaction chamber.
5. The continuous production system for producing low-content calcium sulfate from waste sulfuric acid as claimed in any one of claims 1 to 4, wherein the solid-liquid separation unit comprises a gypsum filter and a solution buffer tank which are connected in sequence;
the slurry outlet of the fourth-stage reaction chamber is connected with the feed inlet of the gypsum filter;
the liquid outlets of the solution buffer tank are respectively and independently connected with the limestone slurry supply unit, the quicklime slurry supply unit and the tail gas absorption unit.
6. A continuous production method for producing low-water content calcium sulfate from waste sulfuric acid, which is carried out in the continuous production system of any one of claims 1 to 5, and is characterized by comprising the following steps:
(1) limestone slurry and waste sulfuric acid are respectively and independently mixed in a first-stage reaction chamber and a second-stage reaction chamber, and a crystal transformation agent is also added in the first-stage reaction chamber; the reacted feed liquid flows into the third-stage reaction chamber to perform neutralization reaction with the quicklime slurry, and the reacted feed liquid flows into the fourth-stage reaction chamber;
(2) and filtering the slurry in the fourth-stage reaction chamber to obtain a solid low-water-content calcium sulfate product, wherein the obtained filtrate is independently used for limestone size mixing and quicklime size mixing respectively.
7. The continuous production process of claim 6, further comprising a tail gas absorption step: preparing circulating slurry by using the raw lime slurry and the filtrate obtained in the step (2), and absorbing tail gas of the four-stage continuous reactor by using the circulating slurry;
preferably, the mass fraction of the circulating slurry is 0.1 to 0.6 wt%, preferably 0.3 to 0.4 wt%.
8. The continuous production method as claimed in claim 6 or 7, wherein the particle size of the limestone used in the preparation of the limestone slurry in the step (1) is 150-250 mesh, preferably 180-200 mesh;
preferably, the limestone slurry of step (1) has a mass fraction of 10 to 20 wt%, preferably 15 to 16 wt%;
preferably, the mass flow ratio of the limestone slurry flowing into the first-stage reaction chamber and the second-stage reaction chamber in the step (1) is (55-70): (30-45), preferably (60-65): (35-40);
preferably, when the raw lime slurry in the step (1) is prepared, the particle size of the used quicklime is 150-250 meshes, preferably 180-200 meshes;
preferably, the mass fraction of the raw lime slurry in the step (1) is 10-20 wt%, preferably 15-16 wt%;
preferably, the raw lime slurry in the step (1) is added in an amount to ensure that the pH value in the third-stage reaction chamber is 6-7, preferably 6.5-7;
preferably, the mass fraction of the waste sulfuric acid in the step (1) is 5-20 wt%;
preferably, the mass flow ratio of the waste sulfuric acid flowing into the first-stage reaction chamber and the second-stage reaction chamber in the step (1) is (0.8-1.2): (0.8-1.2), preferably 1: 1;
preferably, the ratio of the total mass flow of the limestone slurry to the total mass flow of the sulfuric acid in the step (1) is (0.2-1.2): 1;
preferably, the residence time of the reaction materials in the first-stage reaction chamber is 80-150min, preferably 110-120 min;
preferably, the residence time of the reaction materials in the second-stage reaction chamber is 70-100min, preferably 80-90 min;
preferably, the residence time of the reaction materials in the third-stage reaction chamber is 70-100min, preferably 80-90 min;
preferably, the crystal transforming agent in the step (1) comprises any one or a combination of at least two of citric acid, citrate or aluminum aluminate;
preferably, the mass fraction of the crystal transforming agent in the step (1) is 15-25 wt%, preferably 20 wt%;
preferably, the mass flow of the crystal transformation agent in the step (1) is 0.3-1% of the total mass flow of the waste sulfuric acid.
9. The continuous production process according to any one of claims 6 to 8, wherein 2 to 7 wt% of the slurry obtained in the fourth stage reaction chamber of step (1) is refluxed to the first stage reaction chamber; preferably, 4-5 wt% of the slurry obtained in the fourth stage reaction chamber of step (1) is refluxed to the first stage reaction chamber;
preferably, the filtration in the step (2) is filter pressing;
preferably, the free water content of the low-water calcium sulphate product obtained in step (2) is between 5 and 10%, preferably between 7 and 8%.
10. The continuous production method according to any one of claims 6 to 9, comprising the steps of:
(1) limestone slurry and waste sulfuric acid are respectively and independently mixed in a first-stage reaction chamber and a second-stage reaction chamber, and a crystal transformation agent is also added in the first-stage reaction chamber; the reacted feed liquid flows into the third-stage reaction chamber to perform neutralization reaction with the quicklime slurry, and the reacted feed liquid flows into the fourth-stage reaction chamber; 2-7 wt% of the slurry obtained in the fourth stage reaction chamber flows back to the first stage reaction chamber;
the particle size of limestone used when preparing limestone slurry is 150-250 meshes, the mass fraction of the limestone slurry is 10-20 wt%, and the mass flow ratio of the limestone slurry flowing into the first-stage reaction chamber and the second-stage reaction chamber is (55-70): 30-45;
the mass fraction of the waste sulfuric acid is 5-20 wt%, and the mass flow ratio of the waste sulfuric acid flowing into the first-stage reaction chamber and the second-stage reaction chamber is (0.8-1.2) to (0.8-1.2);
preferably, the ratio of the total mass flow of the limestone slurry to the total mass flow of the sulfuric acid in the step (1) is (0.2-1.2): 1;
the particle size of the quicklime used in the preparation of the raw lime slurry is 150-250 meshes, the mass fraction of the raw lime slurry is 10-20 wt%, and the addition amount of the raw lime slurry is such that the pH value in the third-stage reaction chamber is 6-7;
the residence time of the reaction materials in the first-stage reaction chamber is 80-150min, the residence time in the second-stage reaction chamber is 70-100min, and the residence time in the third-stage reaction chamber is 70-100 min;
the crystal transformation agent comprises any one or the combination of at least two of citric acid, citrate or aluminum sulfate salt, the mass fraction of the crystal transformation agent is 15-25 wt%, and the mass flow of the crystal transformation agent is 0.3-1% of the total mass flow of the waste sulfuric acid;
(2) filter-pressing the slurry in the fourth-stage reaction chamber, wherein the obtained solid is a low-water-content calcium sulfate product with the free water content of 5-10%, and the obtained filtrate is respectively and independently used for limestone size mixing and quicklime size mixing;
and (3) preparing the raw lime slurry obtained in the step (1) and the filtrate obtained in the step (2) into circulating slurry with the mass fraction of 0.1-0.6 wt%, and absorbing the tail gas of the four-stage continuous reactor by using the circulating slurry.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2022104737A1 (en) * | 2020-11-20 | 2022-05-27 | 成都千砺金科技创新有限公司 | Production method for full resource recycling of wastewater from sulfuric-acid-method-based titanium dioxide production |
| CN112408453A (en) * | 2020-12-01 | 2021-02-26 | 任杰 | Process for producing calcium sulfate by using waste sulfuric acid |
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