CN1403373A

CN1403373A - Sulfate radical-eliminating process for underground bittern

Info

Publication number: CN1403373A
Application number: CN 02138308
Authority: CN
Inventors: 张国兴; 赵根庆; 汪春茂; 邢亚琴; 王炳辉
Original assignee: DESIGN INST OF NANJING CHEMICAL GROUP Co
Current assignee: Lianyungang Alkali Plant Of Sinopec Nanjing Chemical Industry Co ltd; NANHUA GROUP DESIGN INST
Priority date: 2002-09-20
Filing date: 2002-09-20
Publication date: 2003-03-19
Anticipated expiration: 2022-09-20
Also published as: CN1193934C

Abstract

The present invention is the sulfate radical eliminating process for underground bittern. Calcium chloride contained in the distilled waste liquid from ammonia alkali process to produce sodium carbonate is made to react with sulfate radical in bittern with the molar ratio between Ca ion and sulfate radical ion being 1.5-1.7. Special multiple-checker square tank reactor is adopted to prolong the effective chemical reaction time for full reaction; the solid material is made to float to avoid deposit; and the suspended material is separated via membrane filtering process. The separated brine product has sulfate radical content less 2 g/L and solid content less than 1 mg/L and may be used as material for ammonia alkali process to produce sodium carbonate.

Description

Method for removing sulfate radical from underground brine

The invention relates to a method for removing sulfate radical from underground brine used as a raw material for preparing soda ash by an ammonia-soda process, belonging to the field of soda ash industry.

[ II]background of the invention

The ammonia-soda process for producing soda ash is characterized by that the saturated salt water, lime and NH are mixed₃、CO₂Sodium carbonate product is generated by reaction and CaCl is discharged₂OfThe distillation waste liquid requires that the sulfate ion in the raw material brine is controlled within 2.0 g/l. At present, most of domestic soda ash enterprises adopt solid sea salt as a raw material, and the sulfate radical content generally can meet the production requirement, so that the removal of sulfate radicals is not needed, but the production cost is higher. The cheap underground brine is adopted to replace sea salt as the raw material of the soda ash, so that the production cost of the soda ash can be reduced, and the problem of supply and demand contradiction caused by the influence of seasons on the yield of the sea salt can be solved. Because underground brine extracted by water solution in China contains 5-60 g/l of sodium sulfate, if the underground brine is directly used for soda production, the evaporation and absorption process can be seriously scaled, so that the production cannot be normally carried out, the underground brine needs to be removed before entering a soda production device, and the key of removing sulfate radicals by an economical and reliable method is related to whether the underground brine can become a soda production raw material.

Method for removing SO from brine by chemical method₄ ^2-Generally, there are two methods, chemical calcium method and chemical barium method, and the chemical reaction formula is as follows: a) chemical calcium method: b) chemical barium method:

BaSO produced by the latter barium method₄The reaction process is complete for insoluble matters, and equimolar Ba is adopted²⁺The reaction can achieve the purpose of removing SO₄ ^2-And (4) requiring. CaSO generated by the calcium method of the former₄·2H₂O is slightly soluble, equimolar Ca²⁺Only SO in brine can be ensured₄ ^2-Except that the amount of SO is 3.5-4.0 g/l₄ ^2-The Ca content in the reaction solution must be maintained below 2g/l required by soda production²⁺In excess. Theoretically, Ca²⁺With SO₄ ^2-When the molar ratio (hypercalcemia ratio for short) of (1.4), SO of the brine after reaction can be ensured₄ ^2-The calcium content is reduced to below 2g/l, and the calcium content ratio is generally required to be controlled to be above 1.7-2.0 in the conventional reaction and sedimentation separation process of industrial production.

However, since BaCl₂·2H₂The price of the O raw material is far higher than that of CaCl₂Therefore, the barium process is much more costly than the calcium process, and BaCl₂Is toxic. In contrast, it is not necessary to provide a separate control unitCalcium method for removing SO₄ ^2-Not only the raw material cost is low, but also the usable gypsum byproduct CaSO can be generated₄·2H₂O。

The traditional method for removing sulfate radicals in brine by calcium chloride is to dissolve solid calcium chloride in water, then reactthe solid calcium chloride with brine in a circular tank connected in series, and then separate the solid calcium chloride by settling sand filtration, so as to improve the effects of mixed reaction and solid-liquid separation, a very huge circular tank reactor and a huge clarifying barrel need to be designed to ensure longer reaction time and settling time, but the CaSO₄·2H₂O is in suspension state in the material, the sedimentation is very slow, the separation efficiency is low, even if a huge clarifying barrel is adopted, the solid-liquid separation is still difficult to be complete, the quality of clear liquid is very unstable, and CaSO₄·2H₂O is easy to scale in equipment and pipelines and difficult to clean. Because the reaction and the solid-liquid separation are difficult to be completed, the unreacted SO₄ ^2-And unseparated clean CaSO₄·2H₂O remains in the brine for further subsequent Ca removal²⁺In the treatment, CaSO₄·2H₂O is easily dissolved back to SO₄ ^2-And (4) ions are used for increasing the concentration of sulfate radicals in the brine. To make SO₄ ^2-When the standard is reached, SO must be removed₄ ^2-The calcium ratio is controlled to be higher during the reaction, and the surplus Ca is treated²⁺And the cost is increased due to the consumption of soda ash.

[ III]summary of the invention

The invention aims to provide a novel method for removing sulfate radicals from underground brine, which aims to reduce the calcium passing ratio of chemical reaction, improve the chemical reaction efficiency and the separation effect of suspended materials, realize high removal rate of sulfate radicals and obtain low-price and high-quality production raw materials in the soda industry.

As is known to all, the distillation waste liquid in the ammonia-soda process soda ash production contains a large amount of calcium chloride, and the invention utilizes the supernatant liquid after the ammonia-soda distillation waste liquid is clarified or the waste clear liquid after beach drying (hereinafter referred to as distillation waste liquid) as CaCl required by underground brine for removing sulfate radical₂Of the raw material source of (1), CaCl thereof₂Content (wt.)8 to 20 percent (wt).

The method for removing sulfate radical from underground brine comprises the following steps: a) according to SO in brine₄ ^2-And Ca in the raw distillation waste liquid²⁺Measuring the concentration value, calculating the Ca value²⁺With SO₄ ^2-The weight flow ratio n of the distillation waste liquid to the brine with the molar ratio of 1.5-1.7; b) respectively pumping the distilled waste liquid and the brine into a multi-grid square groove reactor for stirring and mixing, adjusting the flow rate of the distilled waste liquid and the brine to enable the flow rate ratio to meet n, controlling the reaction time of the materials in the groove to be 40-60 minutes, and combining impurity ions in the materials to generate solid suspended matters. In the process, Na in brine₂SO₄With CaCl in the distillation waste liquid₂A chemical reaction takes place, SO₄ ^2-With Ca²⁺Reaction to form CaSO₄·2H₂O solid suspended matter and NaCl as effective component.

c) From the outlet of the multi-grid square tank reactor, the reactor contains CaSO₄·2H₂Pumping the material of the O solid suspended matter into a membrane filter for solid-liquid separation, allowing clear liquid to flow out after permeating membrane pores, collecting saline water without sulfate radical, and allowing the solid-containing material which does not permeate the membrane to remain in the filter and be discharged from the bottom of the filter; the membrane aperture of the membrane filter is 0.5-1.5 microns, and the pressure of the membrane filter during filtration is 0.02-0.3 MPa.

d) Pumping the gypsum salt slurry discharged from the bottom of the filter into a filter press for gypsum drying treatment, wherein the solid phase material is a gypsum product, and the liquid phase containing NaCl is recycled and returned to the reactor for re-separation.

In conclusion, the invention adopts a specially designed multi-grid reactor, materials can keep longer effective reaction time in the reactor, and Na in brine is ensured₂SO₄Sufficiently converting the reaction slurry into solid suspended matter by using a membrane filter, and separating solid particles (CaSO) by using the nanofiltration characteristic of the membrane₄·2H₂O and solid suspended matters) are thoroughly separated from the solution, the removal rate of the solid reaches 99.9 percent, the quality of the filtered clear liquid is easy to ensure, and compared with the traditional sedimentation separation method, the occupied area of the filter is very smallThe area is small, the separation efficiency and the separation quality are greatly improved, SO that the SO required by the brine serving as the raw material for producing the calcined soda in the filtered clear brine is achieved₄ ^2-The index of less than or equal to 2g/l and the solid content of less than or equal to 1 mg/l. Therefore, the method can achieve the full reaction and the full separation of solid-liquid materials, thereby the quality of the refined brine is high. In addition, the invention further reduces the cost of removing sulfate radicals from brine by using the waste distillation waste liquid generated in the production of soda ash as the raw material, thereby reducing CaCl in the distillation waste liquid₂The pollution is discharged, the effective component NaCl is generated, and the NaCl in the waste liquid is recycled.

The invention designs a special multi-grid square groove reactor for the chemical reaction, and aims to prolong the effective reaction time of materials in the reactor and facilitate the reaction to CaSO₄·2H₂The generation of O and the scale formation of products in the device are avoided, so that the addition of the distillation waste liquid is effectively controlled, the consumption of soda ash is reduced, and the cost is reduced.

The multi-grid square groove reactor provided by the invention is provided with a material inlet and a material outlet, the groove of the reactor is divided into a plurality of square reaction areas, each grid is internally provided with a stirrer, the partition plates of two adjacent grids in the material flowing direction are provided with material overflow ports, a flow guide hopper with a wide upper part and a narrow lower part is arranged above the overflow ports in the front grid of the partition plate, a flow guide groove extending downwards from the overflow ports is arranged in the rear grid of the partition plate, the flow guide hopper in the front grid and the flow guide groove in the rear grid are respectively arranged on two sides of the same partition plate, and the two flow guide hoppers are communicated with each other at the material overflow ports. In addition, the reaction tank of the invention also comprises the following characteristics:

four corners of each square reaction area are provided with baffles in opposite angle directions, so that dead angles of materials are avoided. The blade surface of the stirrer is an arc transition twisted surface with gradually narrowed width, and the edge of the blade is also in an arc transition curve; the stirrer is fixed through the frame.

In the reactor, the reaction mass passes through the compartments in the tank in a predetermined flow direction until it finally flows out of the reactor. The diversion hopper, the material through hole and the diversion trench are used for feeding materials from the lower part and discharging materials from the upper part of each reaction area, so that the retention time in the material areas is prolonged, and the full reaction is ensured.Because of the special structure of the stirrer blade of the reactor, the stirrer can fully stir materials in the reaction zone, so that the materials can fully react, and simultaneously, the generated crystal can be kept in a suspended state without being crushed, thereby preventing deposition. The baffle plate can prevent dead angles and blind areas, and has the function of changing the flow direction of the materials, so that the materials react more fully. Therefore, the multi-grid square-groove reactor can realize enough material residence time in the reactor under the condition of smaller reaction volume and occupied area, and ensure SO₄ ^2-With Ca²⁺Sufficiently combines and effectively prevents fouling, thereby making the reaction low in Ca²⁺/SO₄ ^2-Implementation of the molar ratio scheme, SO₄ ^2-Can be reduced to 1g/l or even lower, and the residual Ca in the materials after the reaction²⁺The content is reduced to 3.5-4.0 g/l, and the residual Ca is saved²⁺The cost of the process.

(IV) description of the drawings

FIG. 1 is a process flow diagram for the removal of sulfate from an underground brine in accordance with the present invention.

FIG. 2 is a schematicview showing the structure of a multi-cell reactor for sulfate removal reaction according to the present invention, and FIG. 3 is a plan view of FIG. 2. FIG. 4 is a perspective view of one blade of the agitator.

The technological process for removing sulfate radical in the brine is shown in figure 1. Raw brine is sent into a multi-grid square groove reactor 4 from a raw brine storage tank 1 through a raw brine pump 3, distilled waste liquid from the storage tank 2 is sent into the reactor 4 through a raw brine pump 3' to be stirred and mixed with the raw brine, materials after reaction are sent into a membrane filter 6 from an outlet of the reactor 4 through a material pump 5, the materials are filtered and separated through a porous organic membrane in the reactor, solid suspended matters in the materials are blocked outside the membrane, clear liquid is discharged from the top of the filter through membrane holes and flows into a brine storage tank 10, and the clear liquid is sent to a brine refining system of a soda device through a brine pump 11 to be used as a raw material for producing soda. Most of the suspended matters which are not permeated by the filter are settled and discharged from the bottom of the filter, the suspended matters are sent to a salt mud filter press by a pump 8 to remove the brine in the salt mud filter press to obtain a gypsum byproduct, and the brine separated by the filter pressing is returned to the reactor 4 to participate in the re-separation. With the progress of the filtration process, the amount of solids adhering to the surface of the porous membrane increases, and when the separation efficiency decreases to a certain extent, the automatic control system controls the pump 5 to stop the pump, the overflow clear liquid in the filter 6 temporarily stops outputting, and the liquid level automatically drops and flows back to the reactor 4 through the pipem. In the process, the solid on the surface of the membrane falls off due to the recoil action of the saline water and sinks into the bottom of the filter by gravity, so that the membrane surface is cleaned, and the next filtration is started again. The operation of the filter is kept under high flow and low filtration resistance by the circulation.

As can be seen from FIGS. 2 and 3, the square groove 18 of the multi-compartment reactor is divided into a plurality of reaction zones in the form of lattices by partition plates 13, in this example four reaction zones are divided, and the raw material is fed from zone A, passed through B, C, D in sequence, and finally discharged through outlet pipe 16. The division plates between the intervals A, B, B, C, C and D are respectively provided with a flow guide device 21 which comprises a flow guide hopper 21-1 and a flow guide groove 21-2, wherein the flow guide hopper 21-1 and the flow guide groove 21-2 are respectively arranged at the front side and the rear side of the same division plate and are respectively positioned at the upper side and the lower side of an overflow port 22 (see figure 2); fig. 2 shows that the diversion hopper 21-1 is in a hopper shape with a wide top and a narrow bottom, and the diversion trench 21-2 extends downwards from the overflow port 22 and is communicated with the overflow port 22. The flow sequence of the materials in each grid of the reactor can be designed according to the needs, the feeding grid and the discharging grid can be selected at will, only one of the four discharging ports 16 in the figure 2 is actually selected, and the rest of the four discharging ports are closed when not used. Fig. 3 shows that each reaction zone is provided with diagonally oriented baffles 15 at the four corners of the grid, which prevent dead spots of material. The stirrer 20 is fixed by a frame 14 arranged above the reactor, the shape of a stirrer blade 20-1 is shown in figure 4, the blade surface of the stirrer blade is a twisted surface with gradually narrowed width and arc transition, and the edge of the blade is an arc transition curve. The arrows in FIG. 2 indicate the change in the flow of material from reaction zone B to reaction zone C. The material in the B area after the stirring reaction passes through the diversion hopper 21-1 from the upper part and enters the lower part of the C area downwards along the diversion trench 21-2 through the overflow port 22, and then is continuously reacted after additional stirring and then is guided upwards into the next reaction area through the diversion device. Therefore, the materials are in curved three-dimensional tumbling flow in the reactor, so that the effective reaction residence time is prolonged, and the reaction is more complete. The special structure of the stirrer can not only fully mix the materials, but also ensure that coarse crystals of solid products are not damaged and the suspension state of the crystals can be kept, thereby effectively preventing deposition and scaling and creating conditions for the subsequent separation process.

Detailed description of the preferred embodiments

Example 1:

9.36g/l sulfate radical and 290g/l sodium chloride containing underground brine of Huaiyin in China and CaCl are added into a six-grid square tank reactor₂12.5 percent ammonia-soda distillation waste liquid, the reaction temperature is 31 ℃, the adding proportion is that the weight flow ratio n of the distillation waste liquid and the brine is 0.13, after stirring and reacting for 50 minutes, a pump is used for pumping into a polytetrafluoroethylene film filter with the film aperture of 0.8 mu m for filtering, and the filtering pressure is 0.18 Mpa. Using EDTA back titration method to filter the refined brine; determination of SO₄ ^2-Content, turbidity (SS) by FAU turbidimetry, Ca by EDTA titration²⁺；SO₄ ^2-1.64g/l, no SS detected, Ca²⁺It was 3.65 g/l. SO (SO)₄ ²The SS content completely meets the requirement of producing soda by ammonia-soda processAnd (6) obtaining.

Example 2

Adding 15.36g/l sulfate radical-containing and 285g/l sodium chloride underground Huaian brine into a six-grid square tank reactor, and simultaneously adding CaCl-containing underground brine according to a proportion₂8 percent of ammonia-soda distillation waste liquid, the reaction temperature is 24 ℃, the adding proportion is that the weight flow ratio n of the distillation waste liquid and the brine is 0.23, after stirring and reacting for 45 minutes, a pump is used for pumping into a polytetrafluoroethylene film filter with the film aperture of 0.10 mu m for filtering, and the filtering pressure is 0.15 Mpa. Filtering with a membrane filter, and measuring SO in the filtered refined brine by EDTA back titration₄ ^2-Turbidity (SS) by FAU specific etching and Ca by EDTA titration²⁺As a result of SO₄ ^2-1.52g/l, turbidity 0.16mg/l, Ca²⁺It was 3.84 g/l. SO (SO)₄ ^2-And SS can meet the production requirements of soda ash by an ammonia-soda process.

Claims

1. The method for removing sulfate radical from underground brine is characterized in that distillation waste liquid produced by soda ash by an ammonia-soda process is used as a raw material, and comprises the following steps:

a. according to SO in brine₄ ^2-And Ca in the raw distillation waste liquid²⁺Measuring the concentration value, calculating the Ca value²⁺With SO₄ ^2-The weight flow ratio n ofthe distillation waste liquid to the brine with the molar ratio of 1.5-1.7;

b. respectively pumping the distilled waste liquid and the brine into a multi-grid square groove reactor for stirring and mixing, adjusting the flow rate of the distilled waste liquid and the brine to enable the flow rate ratio to meet n, controlling the reaction time of the materials in the groove to be 40-60 minutes, and enabling impurity ions in the materials to generate solid suspended matters.

c. From the outlet of the multi-grid square tank reactor, the reactor contains CaSO₄·2H₂And pumping the material of the O solid suspended matter into a membrane filter for solid-liquid separation, wherein clear liquid flows out after permeating membrane holes, collecting the saline water without sulfate radicals, and settling the material which does not permeate the membrane at the bottom of the filter for discharge.

d. Pumping the solid suspended matter discharged from the bottom of the membrane filter into a filter press for further filter pressing, recovering the separated NaCl-containing liquid phase to the reactor for re-separation, wherein the fixed material is a gypsum byproduct.

2. The process of removing sulfate from underground brine according to claim 1, wherein the membrane filtration in step c has a pore size of 0.5 to 1.5 μm.

3. A process for the removal of sulfate from underground brine according to claim 1 or 2, wherein the membrane filter in step c has a filtration pressure of 0.02 to 0.3 Mpa.

4. A multi-grid square-tank reactor special for the method of claim 1, which has a material inlet and a material outlet, and is characterized in that the interior of the reactoris divided into a plurality of square-shaped reaction zones by partition plates, each square-shaped reaction zone is provided with a stirrer, the partition plates of two adjacent squares arranged according to the material flow program are provided with material through holes, the front square of each partition plate is provided with a flow guide hopper which is gradually widened upwards from the material through holes, the rear square of each partition plate is provided with flow guide grooves which extend downwards from the material through holes, and the flow guide hopper and the flow guide grooves are respectively arranged on two sides of each partition plate and are communicated with each other at the material through.

5. A multi-cell square tub reactor according to claim 4, wherein each of the four corners of each of the square-shaped reaction zones is provided with a baffle plate in a diagonal direction.

6. A multi-cell square tank reactor as claimed in claim 4 or 5, wherein the agitator has a twisted surface with a narrowing width and an arc transition, and the edge of the blade is curved with an arc transition.