Method for improving salt quality in multi-effect salt production

Abstract

The invention provides a method for improving salt quality in multi-effect salt manufacturing, and belongs to the technical field of salt manufacturing, the method comprises the steps that a separation device is arranged on a last-effect evaporation tank of a multi-effect evaporation device, and the last-effect evaporation tank comprises an evaporation chamber, a first circulating pipe, a second circulating pipe, a circulating pump and a heating chamber; one end of the separation device is connected with the evaporation chamber through a first circulating pipe, mother liquor enters the separation device from the evaporation chamber, the other end of the separation device is connected with the circulating pump through a second circulating pipe, and the mother liquor enters the heating chamber through the circulating pump; the separation device comprises a separator and a mother liquor discharging pipe, the mother liquor enters the separator from the evaporation chamber through a first circulating pipe, one end of the mother liquor discharging pipe is arranged on the upper portion of the separator, the other end of the mother liquor discharging pipe is arranged on the evaporation tank of the last effect, and the mother liquor in the separator enters the evaporation tank of the last effect through the mother liquor discharging pipe. According to the method, the content of SO4 < 2-> impurities in the salt product can be reduced, and common salt and high-quality salt products can be produced at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of salt production, and in particular to a method for improving salt quality in multi-effect salt production. Background Art

[0002] The majority of domestic well salt brine is Glauber's salt brine, and many manufacturers use brine purification and non-brine purification. As we all know, brine purification can achieve sufficient brine preheating, greatly improve the thermal utilization rate, and produce high-quality products, but brine purification requires large investment and high operating costs. In the face of the reality of high quality but low price, many salt companies use non-brine purification methods.

[0003] For non-purified mirabilite-type brine, there are mainly several multi-effect vacuum salt production methods: the first is to ensure the salt quality by discharging a large amount of mother liquor to make the Na2SO4 in the evaporation tank unsaturated. Since the solubility of Na2SO4 in saturated NaCl solution is not high, it is necessary to discharge a large amount of mother liquor (especially for medium and high nitrate brine), thereby bringing out a large amount of heat and causing energy waste. Therefore, the consumption is very high, and the salt quality may not be guaranteed in actual production; the second is to ensure the salt quality by discharging old brine after washing the salt. Since there is no need to control the precipitation of mirabilite in the tank, the mother liquor discharge is small, so the heat The utilization rate is much higher than the first method. Since no brine purification is required, the investment is small and the cost is low, but the brine consumption is high and the nitrate resource is seriously wasted. What is more disadvantageous is that the long-term circulation injection of salt-containing nitrate wastewater can cause the Na2SO4 content in the brine to increase, thereby affecting the salt quality and consumption; the third method is to use the reverse dissolution characteristics of Na2SO4 above 17.9℃ to heat the high-nitrate old brine discharged from salt production to about 100℃, add salt mud to the preheated brine or enter the nitrate evaporation tank for evaporation and concentration (so it is also called salting out method), so that the old brine that is unsaturated with NaCl after heating becomes a saturated solution or a nearly saturated solution. + Due to the common ion effect, Na2SO4 is precipitated and saltpeter is separated. The mother liquor after saltpeter extraction (also called refined brine) is sent back to the salt making system to produce salt. For non-purified brine, salt mud, which was a waste in the past, is used as the raw material for salting out, which not only precipitates saltpeter, but also increases the NaCl content of refined brine. At the same time, it also makes it possible to preheat the high-temperature brine that could not be used in the past (brine preheating can greatly improve the thermal utilization rate, but the original brine is easy to scale at high temperature and cannot be used, while the old brine is not easy to scale). Moreover, since there is no need to discharge the mother liquor from the salt system, the heat loss is small, so the consumption is much lower than that of traditional multi-effect evaporation.

[0004] The main impurities of mirabilite-type brine are Na2SO4, CaSO4, and MgSO4. During the production process, MgSO4 has a large solubility and generally will not precipitate out at saturation, while CaSO4 has a small solubility and has reverse dissolution characteristics, and is very easy to precipitate out at supersaturation. When solid mirabilite precipitates in the solution, the two will combine to form calcium mirabilite (CaSO4•Na2SO4) complex salt. Solid calcium sulfate, calcium mirabilite, mirabilite, and soluble Na2SO4, MgSO4, etc. are the main impurities that affect the quality of salt. Since the brine is not purified in the above three methods, the salt product contains SO4 2- The removal of impurities remains a problem.

[0005] Therefore, it is necessary to provide a method for improving salt quality in multi-effect salt production to solve the problems existing in the above-mentioned prior art. Summary of the invention

[0006] In view of this, the present invention provides a method for improving the quality of salt in a multi-effect salt production process, reducing the content of SO4 in the salt product. 2- The impurity content is reduced, and both ordinary salt and high-quality salt products can be produced at the same time.

[0007] To achieve the above object, the present invention provides a method for improving salt quality in multi-effect salt production, comprising the following steps: A separation device is arranged on the circulation pipe of the last-effect evaporation tank of the multiple-effect evaporation device, wherein the last-effect evaporation tank comprises an evaporation chamber, a first circulation pipe, a second circulation pipe, a circulation pump and a heating chamber, one end of the separation device is connected to the evaporation chamber through the first circulation pipe, and the mother liquid enters the separation device from the evaporation chamber, and the other end of the separation device is connected to the circulation pump through the second circulation pipe, and the mother liquid enters the heating chamber through the circulation pump; The separation device comprises a separator and a mother liquid discharge pipe. The mother liquid enters the separator from the evaporation chamber through the first circulation pipe. One end of the mother liquid discharge pipe is arranged on the upper part of the separator, and the other end is arranged on the evaporation tank before the last effect. The mother liquid in the separator enters the evaporation tank before the last effect through the mother liquid discharge pipe.

[0008] Optionally, the feed rate of the last-effect evaporator and the discharge rate of the mother liquid from the mother liquid discharge pipe meet Formula 1: Formula 1 M1×C1-M2×C2=M3×C3 M1 is the feed amount of the last-effect evaporator; M2 is the amount of mother liquor brought out by the last-effect salt discharge; M3 is the amount of mother liquor discharged from the mother liquor discharge pipe; C1 is the concentration of sodium sulfate in the feed of the last-effect evaporator; C2 is the concentration of sodium sulfate in the mother liquor brought out by the last-effect salt discharge; C3 is the concentration of sodium sulfate in the mother liquor discharged from the mother liquor discharge pipe.

[0009] C3≤C t -10g / L, C tIt is the concentration of sodium sulfate when salt and nitrate are saturated at the temperature in the final effect evaporator.

[0010] Optionally, the feeding method of the multiple-effect evaporator is single feeding of the last effect, and the feeding methods of other effects are parallel flow feeding, countercurrent feeding, cross flow feeding or horizontal flow feeding.

[0011] Optionally, the multiple-effect evaporation device is a six-effect evaporation device.

[0012] Optionally, the salt slurry discharged from the last-effect evaporation tank is collected separately, washed, and dehydrated to obtain a high-quality salt product.

[0013] Optionally, the salt washing uses a primary flotation washer or a secondary flotation washer, and the dehydration uses a centrifuge.

[0014] Optionally, the salt slurry discharged from the evaporation tanks other than the last effect of the multiple-effect evaporation device enters a salt collecting box, where it is washed, dehydrated, and dried to produce a common salt product.

[0015] The above technical solution of the present invention includes at least the following beneficial effects: The present invention arranges a separation device on the last-effect evaporation tank, introduces the feed liquid in the last-effect evaporation tank into the separation device, and the first circulation pipe extends into the separator, and a jacket area is formed between the outside of the first circulation pipe and the separator. The jacket area cross-sectional area and the amount of mother liquid discharged are reasonably designed, so that the material in the jacket area has a suitable rising speed. Since the NaCl crystal particles are regular and the particle size is large, the sedimentation speed is fast. When the sedimentation speed is greater than the rising speed, the NaCl crystal particles will flow back to the evaporation tank with the circulation pipe feed liquid. However, calcium sulfate has a slow sedimentation speed due to its small particles and irregular shape. When the sedimentation speed is less than the rising speed, the calcium sulfate particles will be discharged from the mother liquid discharge pipe together with the external mother liquid. Therefore, the salt and solid impurities can be separated by the difference in sedimentation velocity. On the one hand, the mother liquor discharged from the separation device takes out the solid impurities with slow sedimentation velocity and reduces the content of CaSO4 solid in the feed liquid. On the other hand, the mother liquor with high Na2SO4 content is extracted to keep the Na2SO4 concentration in the mother liquor in the last-effect evaporation tank less than the saturation concentration and reduce the content of soluble impurities such as MgSO4 to avoid salt precipitation in the last-effect evaporation tank. Since there is no precipitation of solid thenardite in the last-effect evaporation tank, calcium thenardite complex salt will not be produced. Extracting part of the mother liquor rich in sulfate ions can reduce the content of sulfate ions in the salt product and improve the quality of the salt product.

[0016] The present invention uses a multiple-effect evaporation device. By arranging a separation device on the last-effect evaporation tank, high-quality salt products can be prepared. At the same time, the remaining evaporation tanks can be produced normally, thereby achieving the effect of preparing high-quality salt and ordinary quality salt products at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1It is a front view of the last-effect evaporation tank and the separation device in Example 1 of the present invention; Figure 2 This is a structural diagram of the separation device and the first circulation pipe in Example 1 of the present invention; Figure 3 is a top view of the separation device in Example 1 of the present invention; Figure 4 The process flow chart of the last-effect evaporation tank and the first-effect evaporation tank before the last effect in Example 1 of the present invention is shown.

[0018] In the figure: 10, last effect evaporation tank; 11, evaporation chamber; 12, first circulation pipe; 13, second circulation pipe; 14, circulation pump; 15, heating chamber; 20, separation device; 21, separator; 22, mother liquor discharge pipe. DETAILED DESCRIPTION

[0019] To make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the following will be combined with the appended drawings of the embodiments of the present invention. Figures 1 to 4 , the technical scheme of the embodiment of the present invention is clearly and completely described. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0020] Example 1 A VI effect evaporation device is adopted, and the feeding method of the VI effect evaporation device is horizontal feeding. The use of steam and condensed water in the VI effect evaporation device is the same as that of the traditional process. The feeding from effect I to effect V is the same as that of the traditional process, and old brine or original brine can be fed. Original brine is fed into the last effect evaporation tank 10, i.e., the VI effect evaporation tank. The original brine enters the VI effect evaporation tank for evaporation after heat exchange with condensed water through a plate heat exchanger. A separation device 20 is arranged on the VI effect circulation pipe. The separation device 20 includes a separator 21 and a mother liquid discharge pipe 22. The VI effect evaporation tank includes an evaporation chamber 11, a first circulation pipe 12, a second circulation pipe 13, a circulation pump 14 and a heating chamber 15. One end of the separator 21 is connected to the evaporation chamber 11 through the first circulation pipe 12. The first circulation pipe extends downward into the separator. The cross-sectional area of ​​the circulation pipe and the cross-sectional area of ​​the separator form an area. The mother liquid enters the separator 21 from the evaporation chamber 11. The other end of the separator 22 is connected to the circulation pump 14 through the second circulation pipe 13. The mother liquid enters the heating chamber 15 through the circulation pump 14. The discharged mother liquid enters the V-effect evaporation tank through the mother liquid discharge pipe 22.

[0021] The liquid inlet of the VI-effect evaporator and the liquid outlet of the extraction pipe satisfy the following formula: M1×C1-M2×C2=M3×C3 M1 is the feed amount of the last-effect evaporator; M2 is the amount of mother liquor brought out by the last-effect salt discharge; M3 is the amount of mother liquor discharged from the mother liquor discharge pipe; C1 is the concentration of sodium sulfate in the feed of the last-effect evaporator; C2 is the concentration of sodium sulfate in the mother liquor brought out by the last-effect salt discharge; C3 is the concentration of sodium sulfate in the mother liquor discharged from the mother liquor discharge pipe.

[0022] C3≤C t -10g / L, C t It is the concentration of sodium sulfate when salt and nitrate are saturated at the temperature in the final effect evaporator.

[0023] In this embodiment, the temperature in the VI evaporator is controlled at 49°C, i.e. t is 68g / L, when M3 is about 35m 3 / h, C3 is about 46g / L, which satisfies the above formula. That is, by controlling the amount of liquid extracted from the separation device and the amount of liquid inlet to the VI-effect evaporator, the concentration of sodium sulfate in the VI-effect evaporator is less than the saturated concentration of sodium sulfate, thereby avoiding the precipitation of nitrate in the VI-effect evaporator and not producing calcium glauberite double salt. In addition, solid impurities such as CaSO4 with slow settling speed and soluble impurities are discharged through the mother liquor discharged from the separation device, thereby improving the quality of the prepared salt product.

[0024] The salt slurry discharged from the VI-effect evaporation tank is collected separately, washed with salt in the secondary flotation washer, and then dehydrated in the centrifuge to produce high-quality salt products.

[0025] The salt slurry discharged from the evaporation tanks from effect I to effect V enters the salt collecting box, and is washed with raw brine to help remove some soluble impurities and solid impurities in the salt slurry. It is then dehydrated, dried, measured and packaged to produce ordinary salt products.

[0026] Example 2 A VI-effect evaporation device is used, and the feeding method of the VI-effect evaporation device is horizontal feeding. The use of steam and condensed water in the VI-effect evaporation device is the same as the traditional process. The feeding from effect I to effect V is the same as the traditional process. Old brine can be fed, and original brine can be fed. The last effect evaporation tank 10, that is, the VI-effect evaporation tank, feeds original brine. The original brine enters the VI-effect evaporation tank for evaporation after heat exchange with condensed water through a plate heat exchanger. A separation device 20 is arranged on the VI-effect circulation pipe, and the separation device 20 includes a separator 21 and a mother discharger. Liquid pipe 22, the VI effect evaporator includes an evaporation chamber 11, a first circulation pipe 12, a second circulation pipe 13, a circulation pump 14 and a heating chamber 15. One end of the separator 21 is connected to the evaporation chamber 11 through the first circulation pipe 12, and the mother liquid enters the separator 21 from the evaporation chamber 11. The other end of the separator 22 is connected to the circulation pump 14 through the second circulation pipe 13. The mother liquid enters the heater 15 through the circulation pump 14, and the discharged mother liquid enters the V effect evaporator through the mother liquid discharge pipe 22.

[0027] The liquid inlet of the VI-effect evaporator and the liquid outlet of the extraction pipe satisfy the following formula: M1×C1-M2×C2=M3×C3 M1 is the feed amount of the last-effect evaporator; M2 is the amount of mother liquor brought out by the last-effect salt discharge; M3 is the amount of mother liquor discharged from the mother liquor discharge pipe; C1 is the concentration of sodium sulfate in the feed of the last-effect evaporator; C2 is the concentration of sodium sulfate in the mother liquor brought out by the last-effect salt discharge; C3 is the concentration of sodium sulfate in the mother liquor discharged from the mother liquor discharge pipe.

[0028] C3≤C t -10g / L, C t It is the concentration of sodium sulfate when salt and nitrate are saturated at the temperature in the final effect evaporator.

[0029] In this embodiment, the temperature in the VI evaporator is controlled at 43°C, i.e. t is 72g / L, when M3 is about 32m 3 / h, C3 is about 50g / L, which satisfies the above formula. That is, by controlling the amount of liquid extracted from the separation device and the amount of liquid inlet to the VI-effect evaporator, the concentration of sodium sulfate in the VI-effect evaporator is less than the saturated concentration of sodium sulfate, thereby avoiding the precipitation of nitrate in the VI-effect evaporator and not producing calcium glauberite double salt. In addition, solid impurities such as CaSO4 with slow settling speed and soluble impurities are discharged through the mother liquor discharged from the separation device, thereby improving the quality of the prepared salt product.

[0030] The salt slurry discharged from the VI-effect evaporation tank is collected separately, washed with salt in the secondary flotation washer, and then dehydrated in the centrifuge to produce high-quality salt products.

[0031] The salt slurry discharged from the evaporation tanks from effect I to effect V enters the salt collecting box, and is washed with raw brine to help remove some soluble impurities and solid impurities in the salt slurry. It is then dehydrated, dried, measured and packaged to produce ordinary salt products.

[0032] Example 3 Compared with Example 1, the difference is that a five-effect evaporation device is used, and the separation device is arranged on the V-effect evaporation tank. In this embodiment, the temperature in the V-effect evaporation tank is controlled at 49°C, i.e., C t is 68g / L, when M3 is about 42m 3 / h, C3 is about 46g / L, satisfying the above formula. The rest is consistent with Example 1.

[0033] Example 4 Compared with Example 2, the difference is that a four-effect evaporation device is used, and the separation device is arranged on the IV-effect evaporation tank. The rest is the same as Example 2.

[0034] The high-quality salts prepared in Examples 1 to 4 were analyzed and the results are shown in Table 1.

[0035] Table 1 Analysis of high quality salt products prepared in Examples 1 to 4

[0036] The common salts prepared in Examples 1 to 4 were analyzed and the results are shown in Table 2.

[0037] Table 2 Analysis of common salt products prepared in Examples 1 to 4

[0038] Combining Table 1 and Table 2, it can be seen that the sulfate ion content in the common salt product obtained by the process provided by the present invention is about 0.3%, and the sulfate ion content in the high-quality salt product is less than 0.15%.

[0039] In the present invention, unless otherwise clearly specified and limited, for example, it can be a fixed connection, a detachable connection, or an integral one; unless otherwise clearly limited, for ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0040] The above are preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for improving salt quality in multi-effect salt production, characterized in that: The following steps are involved: A separation device (20) is arranged on a circulation pipe of a last-effect evaporation tank (10) of a multiple-effect evaporation device, wherein the last-effect evaporation tank (10) comprises an evaporation chamber (11), a first circulation pipe (12), a second circulation pipe (13), a circulation pump (14) and a heating chamber (15); one end of the separation device (20) is connected to the evaporation chamber (11) via the first circulation pipe (12), and mother liquid enters the separation device (20) from the evaporation chamber (11); the other end of the separation device (20) is connected to the circulation pump (14) via the second circulation pipe (13), and mother liquid enters the heating chamber (15) via the circulation pump (14); The separation device (20) comprises a separator (21) and a mother liquid discharge pipe (22); the mother liquid enters the separator (21) from the evaporation chamber (11) through the first circulation pipe (12); one end of the mother liquid discharge pipe (22) is arranged at the upper part of the separator (21), and the other end is arranged at the evaporation tank of the previous effect of the last effect; the mother liquid in the separator (21) enters the evaporation tank of the previous effect of the last effect through the mother liquid discharge pipe (22).

2. The method for improving salt quality in multi-effect salt production according to claim 1, characterized in that: The feed amount of the last-effect evaporator and the amount of the mother liquid discharged from the mother liquid discharge pipe conform to Formula 1: Formula 1 M1×C1-M2×C2=M3×C3 M1 is the feed amount of the last-effect evaporator; M2 is the amount of mother liquor brought out by the last-effect salt discharge; M3 is the amount of mother liquor discharged from the mother liquor discharge pipe; C1 is the concentration of sodium sulfate in the feed of the last-effect evaporator; C2 is the concentration of sodium sulfate in the mother liquor brought out by the last-effect salt discharge; C3 is the concentration of sodium sulfate in the mother liquor discharged from the mother liquor discharge pipe.

3. The method for improving salt quality in multi-effect salt production according to claim 2, characterized in that: C3≤C t -10g / L, C t It is the concentration of sodium sulfate when salt and nitrate are saturated at the temperature in the final effect evaporator.

4. The method for improving salt quality in multi-effect salt production according to claim 1, characterized in that: The feeding method of the multi-effect evaporator is single feeding of the last effect, and the feeding methods of other effects are parallel flow feeding, counter-current feeding, cross-flow feeding or horizontal flow feeding.

5. The method for improving salt quality in multi-effect salt production according to claim 4, characterized in that: The multiple-effect evaporation device is a six-effect evaporation device.

6. The method for improving salt quality in multi-effect salt production according to claim 1, characterized in that: The salt slurry discharged from the last-effect evaporation tank is collected separately, washed, and dehydrated to obtain a high-quality salt product.

7. The method for improving salt quality in multi-effect salt production according to claim 6, characterized in that: The salt washing uses a primary flotation washer or a secondary flotation washer, and the dehydration uses a centrifuge.

8. The method for improving salt quality in multi-effect salt production according to claim 6, characterized in that: The salt slurry discharged from the evaporation tanks other than the last effect of the multi-effect evaporation device enters the salt collecting box, and is washed, dehydrated, and dried to become a common salt product.

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