A crystallization and salt separation process of sodium sulfate and ammonium sulfate

Abstract

A sodium sulfate and ammonium sulfate crystallization and salt separation process, (1) using an unsaturated solution containing sodium sulfate and ammonium sulfate as a raw material, preheating and entering a concentrating evaporator for evaporation and concentration; (2) the concentrated liquid discharged from the concentrating evaporator enters a sodium sulfate evaporation crystallization tank, evaporates and crystallizes, and obtains sodium sulfate solid and a crystallization mother liquor; (3) the sodium sulfate solid crystallized from the sodium sulfate evaporation crystallization tank is discharged to a centrifuge to remove the mother liquor, and obtains a sodium sulfate product and a first mother liquor; (4) the crystallization mother liquor is heat-exchanged with the circulating mother liquor discharged from the ammonium sulfate cooling crystallization tank, and then enters an ammonium sulfate cooling crystallization tank for cooling and crystallization, and obtains ammonium sulfate solid and a circulating mother liquor; (5) the ammonium sulfate solid crystallized in the ammonium sulfate cooling crystallization tank is discharged to a centrifuge to remove the mother liquor, and obtains an ammonium sulfate product and a second mother liquor; (6) the circulating mother liquor discharged from the ammonium sulfate cooling crystallization tank is preheated and enters the sodium sulfate evaporation crystallization tank in step (2).

Description

Technical Field

[0001] The invention belongs to the technical field of crystallization separation, in particular to a crystallization salt separation process of sodium sulfate and ammonium sulfate. Background Art

[0002] Within the evaporation system temperature range (50-110°C), the solubility of ammonium sulfate increases slightly with increasing temperature, while the opposite is true for Na2SO4, whose solubility decreases with increasing temperature. The (NH4)2SO4-Na2SO4-H2O phase diagram at different temperatures indicates that it is difficult to separate the two salts using conventional evaporation or cooling methods. Therefore, many current methods rely solely on evaporation and crystallization of mixed salts, or on crystallization of one salt and recrystallization of the mother liquor to produce the mixed salts. Both methods only yield or recover a portion of the salt resource, resulting in significant resource waste and adverse environmental impacts. Summary of the Invention

[0003] The invention aims to provide a crystallization and salt separation process for sodium sulfate and ammonium sulfate, which has a short process flow, requires less equipment, saves investment and is easy to operate.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A crystallization and salt separation process of sodium sulfate and ammonium sulfate comprises the following steps:

[0006] (1) Using an unsaturated solution containing sodium sulfate and ammonium sulfate as a raw material, the content of each component in the raw material is: sodium sulfate 0-33.6%, ammonium sulfate 0-50.5%; the raw material is first preheated and enters a concentration evaporator for evaporation and concentration until it is close to saturation, and the evaporation and concentration temperature is 50-105°C;

[0007] (2) The concentrated liquid discharged from the concentration evaporator enters the sodium sulfate evaporation crystallization tank and continues to evaporate and crystallize at a temperature of 80-110°C to obtain sodium sulfate solid and crystallization mother liquor;

[0008] (3) The sodium sulfate solid crystallized from the sodium sulfate evaporation crystallization tank is discharged to a centrifuge to remove the mother liquor to obtain a sodium sulfate product and a first mother liquor;

[0009] (4) The crystallization mother liquor discharged from the sodium sulfate evaporation crystallization tank is heat exchanged with the circulating mother liquor discharged from the ammonium sulfate cooling crystallization tank, and then enters the ammonium sulfate cooling crystallization tank for cooling and crystallization at a temperature of 10-70°C to obtain ammonium sulfate solid and circulating mother liquor;

[0010] (5) the ammonium sulfate solid crystallized in the ammonium sulfate cooling crystallization tank is discharged to a centrifuge to remove the mother liquor to obtain an ammonium sulfate product and a second mother liquor;

[0011] (6) The circulating mother liquor discharged from the ammonium sulfate cooling crystallization tank enters the sodium sulfate evaporation crystallization tank in step (2) after preheating.

[0012] Furthermore, in step (1), a solid containing sodium sulfate and ammonium sulfate is dissolved in water to form the unsaturated solution, which is directly fed into the sodium sulfate evaporation crystallization tank.

[0013] Furthermore, the concentrating evaporator in step (1) is a mechanical vapor recompression falling film evaporator, a forced circulation evaporator, or a multiple-effect evaporation system using steam as a heat source.

[0014] Furthermore, the sodium sulfate evaporation crystallization in step (2) adopts mechanical steam recompression.

[0015] Furthermore, the first mother liquor in step (3) is discharged into a mother liquor temporary storage tank and then fed into the ammonium sulfate cooling crystallization tank in step (4).

[0016] Furthermore, the second mother liquor in step (5) is fed into the sodium sulfate evaporation crystallization tank in step (2).

[0017] Furthermore, in the step (5), the ammonium sulfate cooling crystallization tank is provided with an external cooling heat exchanger and a forced circulation pump, and the ammonium sulfate cooling crystallization tank adopts an OSLO type crystallization tank.

[0018] Furthermore, the sodium sulfate product in step (3) and the ammonium sulfate product in step (5) are both dried.

[0019] The beneficial effects of the present invention are:

[0020] (1) The process flow of the present invention is extremely simple, and the main equipment only has an evaporation concentrator, a sodium sulfate evaporation crystallization tank and an ammonium sulfate cooling crystallization tank, so the investment is small;

[0021] (2) The present invention adopts mechanical vapor recompression (MVR) evaporation, which has lower energy consumption than traditional steam evaporators;

[0022] (3) The sodium sulfate and ammonium sulfate products produced by the present invention are of high quality, can achieve efficient recycling of resources, and are environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention is a schematic flow diagram of the crystallization and salt separation process of sodium sulfate and ammonium sulfate. DETAILED DESCRIPTION

[0024] The structure of the present invention and the technical effects to be achieved will be described below with reference to specific embodiments and accompanying drawings. However, the selected embodiments are only for illustration and explanation and are not intended to limit the scope of the present invention.

[0025] like Figure 1 As shown, the present invention provides a crystallization salt separation process of sodium sulfate and ammonium sulfate, comprising the following steps:

[0026] (1) Using an unsaturated solution containing sodium sulfate and ammonium sulfate as raw material, first preheating it and then entering a concentration evaporator for evaporation and concentration until it is close to saturation;

[0027] (2) The concentrated liquid discharged from the concentration evaporator enters the sodium sulfate evaporation crystallization tank, and continues to evaporate and crystallize to obtain sodium sulfate solid and crystallization mother liquor;

[0028] (3) The sodium sulfate solid crystallized from the sodium sulfate evaporation crystallization tank is discharged to a centrifuge to remove the mother liquor to obtain a sodium sulfate product and a first mother liquor;

[0029] (4) the crystallization mother liquor discharged from the sodium sulfate evaporation crystallization tank is heat exchanged with the circulating mother liquor discharged from the ammonium sulfate cooling crystallization tank, and then enters the ammonium sulfate cooling crystallization tank for cooling and crystallization to obtain ammonium sulfate solid and circulating mother liquor;

[0030] (5) the ammonium sulfate solid crystallized in the ammonium sulfate cooling crystallization tank is discharged to a centrifuge to remove the mother liquor to obtain an ammonium sulfate product and a second mother liquor;

[0031] (6) The circulating mother liquor discharged from the ammonium sulfate cooling crystallization tank enters the sodium sulfate evaporation crystallization tank in step (2) after preheating.

[0032] Several specific production examples are listed below to further illustrate the present invention.

[0033] 1. Example 1:

[0034] Wastewater from a certain enterprise contains 9.5% ammonium sulfate and 4.2% sodium sulfate, with a treatment capacity of 65m 3 / hour, and after entering the MVR falling film evaporation and concentration, the solution composition is 37.2% ammonium sulfate, 16.5% sodium sulfate, and the evaporated water volume is 52.5 tons / hour; the falling film concentrate enters the MVR sodium sulfate evaporation crystallization tank, the evaporation temperature is 105℃, and 2700kg / hour of sodium sulfate is produced. The concentration of the discharged crystallization mother liquor is: 40.1% ammonium sulfate, 15.8% sodium sulfate; the crystallization mother liquor discharged from the sodium sulfate evaporation crystallization tank enters the ammonium sulfate cooling crystallization tank, the crystallization temperature is 50℃, and 6150kg / hour of ammonium sulfate is produced. The concentration of the discharged circulating mother liquor is: 37.1% ammonium sulfate, 15.2% sodium sulfate.

[0035] 2. Example 2:

[0036] Wastewater from a certain enterprise contains 9.5% ammonium sulfate and 4.2% sodium sulfate, with a treatment capacity of 65m 3 / hour, and after entering the MVR falling film evaporation concentration, the solution composition is 32.3% ammonium sulfate, 14.3% sodium sulfate, and the evaporated water volume is 49.7 tons / hour; the falling film concentrate enters the MVR sodium sulfate evaporation crystallization tank, the evaporation temperature is 105℃, and the sodium sulfate production is 2700kg / hour. The concentration of the discharged crystallization mother liquor is: 40.1% ammonium sulfate, 15.8% sodium sulfate; the crystallization mother liquor discharged from the sodium sulfate evaporation crystallization tank enters the ammonium sulfate cooling crystallization tank, the crystallization temperature is 50℃, and the ammonium sulfate production is 6150kg / h. The concentration of the discharged circulating mother liquor is: 37.1% ammonium sulfate, 15.2% sodium sulfate.

[0037] 3. Example 3:

[0038] The solid waste of a certain enterprise contains 55% ammonium sulfate and 45% sodium sulfate, with a processing capacity of 5 tons / hour. 7 tons of water are added for dissolution, and the total solution volume is 12 tons / hour. The solution composition is 22.9% ammonium sulfate and 18.7% sodium sulfate. The MVR sodium sulfate evaporation crystallization tank has an evaporation temperature of 105°C, produces 2155kg / hour of sodium sulfate, and the concentration of the discharged crystallization mother liquor is: 40.1% ammonium sulfate and 15.8% sodium sulfate; the crystallization mother liquor discharged from the sodium sulfate evaporation crystallization tank enters the ammonium sulfate cooling crystallization tank, the crystallization temperature is 50°C, and produces 2500kg / hour of ammonium sulfate. The concentration of the discharged circulating mother liquor is: 37.1% ammonium sulfate and 15.2% sodium sulfate.

[0039] The beneficial effects of the present invention are:

[0040] (1) The process flow of the present invention is extremely simple, and the main equipment only has an evaporation concentrator, a sodium sulfate evaporation crystallization tank and an ammonium sulfate cooling crystallization tank, so the investment is small;

[0041] (2) The present invention adopts mechanical vapor recompression (MVR) evaporation, which has lower energy consumption than traditional steam evaporators;

[0042] (3) The sodium sulfate and ammonium sulfate products produced by the present invention are of high quality, can achieve efficient recycling of resources, and are environmentally friendly.

[0043] (4) The present invention does not produce double salts during the production process, and the process route is simpler than the existing technology. In addition, since no double salts are formed, the quality of the obtained product will be higher.

[0044] The present invention is defined by the claims, but those skilled in the art may make various obvious changes or modifications based on the claims, all of which are within the spirit and scope of the present invention.

Claims

1. A crystallization and salt separation process of sodium sulfate and ammonium sulfate, characterized in that: The following steps are involved: (1) An unsaturated solution containing sodium sulfate and ammonium sulfate is used as raw material, wherein the content of each component in the raw material is: sodium sulfate 0-33.6%, ammonium sulfate 0-50.5%; the raw material is first preheated and enters the concentration evaporator for evaporation and concentration until it is close to saturation, and the evaporation and concentration temperature is 50-105°C; (2) The concentrated liquid discharged from the concentration evaporator enters the sodium sulfate evaporation crystallization tank and continues to evaporate and crystallize at a temperature of 80-110°C to obtain sodium sulfate solid and crystallization mother liquor; (3) The sodium sulfate solid crystallized from the sodium sulfate evaporation crystallization tank is discharged to a centrifuge to remove the mother liquor, thereby obtaining the sodium sulfate product and the first mother liquor; (4) The crystallization mother liquor discharged from the sodium sulfate evaporation crystallization tank exchanges heat with the circulating mother liquor discharged from the ammonium sulfate cooling crystallization tank, and then enters the ammonium sulfate cooling crystallization tank for cooling and crystallization at a temperature of 10-70°C to obtain ammonium sulfate solid and circulating mother liquor; (5) The ammonium sulfate solid crystallized in the ammonium sulfate cooling crystallization tank is discharged to a centrifuge to remove the mother liquor to obtain an ammonium sulfate product and a second mother liquor. The ammonium sulfate cooling crystallization tank is equipped with an external cooling heat exchanger and a forced circulation pump. The ammonium sulfate cooling crystallization tank adopts an OSLO type crystallization tank; (6) The circulating mother liquor discharged from the ammonium sulfate cooling crystallization tank is preheated and enters the sodium sulfate evaporation crystallization tank in step (2).

2. The crystallization and salt separation process of sodium sulfate and ammonium sulfate according to claim 1, wherein: In the step (1), a solid containing sodium sulfate and ammonium sulfate is dissolved in water to form the unsaturated solution, which is directly fed into the sodium sulfate evaporation crystallization tank.

3. The crystallization and salt separation process of sodium sulfate and ammonium sulfate according to claim 1, characterized in that: The concentrating evaporator in step (1) is a mechanical vapor recompression falling film evaporator, a forced circulation evaporator, or a multi-effect evaporation system using steam as a heat source.

4. The crystallization and salt separation process of sodium sulfate and ammonium sulfate according to claim 1, characterized in that: The sodium sulfate evaporation crystallization in step (2) adopts mechanical steam recompression.

5. The crystallization and salt separation process of sodium sulfate and ammonium sulfate according to claim 1, characterized in that: The first mother liquor in step (3) is discharged into a mother liquor temporary storage tank and then fed into the ammonium sulfate cooling crystallization tank in step (4).

6. The crystallization and salt separation process of sodium sulfate and ammonium sulfate according to claim 1, characterized in that: The second mother liquor in step (5) is fed into the sodium sulfate evaporation crystallization tank in step (2).

7. The crystallization and salt separation process of sodium sulfate and ammonium sulfate according to claim 1, characterized in that: The sodium sulfate product in step (3) and the ammonium sulfate product in step (5) are both dried.

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