Zero-emission treatment method for electrolytic aluminum flue gas and application of zero-emission treatment method

Abstract

The invention relates to the technical field of energy conservation and environmental protection, in particular to an electrolytic aluminum flue gas zero-emission treatment method and application. The method comprises the following steps: treating electrolytic aluminum flue gas through an electrolytic aluminum flue gas purification device and a desulfurization device in sequence to obtain electrolytic aluminum desulfurization wastewater; the method comprises the following steps: pretreating electrolytic aluminum desulfurization wastewater to obtain an upper clear liquid and a bottom precipitate; treating the upper clear liquid through a clear water tank, and concentrating the upper clear liquid in a reverse osmosis device to obtain clear water and concentrated wastewater; the clear water is returned to a desulfurization system to be recycled; the concentrated wastewater enters an evaporative crystallization device to be treated, and water and solid crystal salt are obtained. According to the electrolytic aluminum desulfurization wastewater flue gas evaporation process, high-temperature flue gas (90-110 DEG C) obtained after an electrolytic aluminum flue gas purification device is utilized, heat is recycled, and energy consumption is reduced. The electrolytic aluminum desulfurization wastewater flue gas evaporation process is few in newly added equipment, low in power and low in total power consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of energy conservation and environmental protection, and in particular to a zero-emission treatment method for electrolytic aluminum fume and its application. Background Art

[0002] The sulfur dioxide in the flue gas of electrolytic aluminum mainly comes from the pre-baked anode, the raw material of its production. Under the high temperature environment in the cell, the sulfur in the anode carbon block is oxidized to form SO2 which enters the flue gas. At present, the concentration of SO2 in the electrolytic flue gas is mostly 200-400 mg / m 3 It is impossible to meet the emission limit requirements of the "Aluminum Industry Pollutant Emission Standard" (GB 25465) and its amendment. The electrolytic aluminum limestone-gypsum wet desulfurization process will produce desulfurization wastewater. The current treatment technologies mainly include the three-unit process or the wastewater integration process. The above two technical routes can only treat heavy metals in the wastewater, but cannot effectively remove anions such as chloride ions and fluoride ions. At the same time, the sewage treatment plant in the aluminum plant area does not have the ability to treat desulfurization wastewater. If the wastewater is discharged into the sewage treatment plant in the plant area, it will seriously affect the operation of the equipment in the sewage treatment plant. The existing process method uses electric heating to generate steam and then evaporate the wastewater, which has high power consumption and high operating costs. Summary of the invention

[0003] In order to solve the above problems, the present invention provides a zero-emission treatment method and application of electrolytic aluminum fume, and the present invention provides the following technical solutions:

[0004] The present invention provides a zero-emission treatment method for aluminum electrolysis fume, the method comprising:

[0005] The aluminum electrolysis flue gas is sequentially processed through an aluminum electrolysis flue gas purification device and a desulfurization device to obtain aluminum electrolysis desulfurization wastewater;

[0006] Pre-treating the aluminum electrolytic desulfurization wastewater to obtain the upper clear liquid and the bottom sediment;

[0007] After the upper clear liquid is treated in the clean water tank, it enters the reverse osmosis device for concentration to obtain clean water and concentrated wastewater;

[0008] The clean water is returned to the desulfurization system for recycling;

[0009] The concentrated wastewater enters an evaporation crystallization device for treatment to obtain water and solid crystal salt.

[0010] Specifically, the electrolytic aluminum desulfurization wastewater is pretreated to obtain the upper clear liquid and the bottom sediment, including:

[0011] First, the electrolytic aluminum desulfurization wastewater is precipitated to obtain a first clear liquid and a first precipitate;

[0012] After sequentially performing precipitation to remove magnesium and precipitation to remove calcium on the first clear liquid, a second clear liquid, a magnesium hydroxide precipitate and a calcium hydroxide precipitate are obtained;

[0013] After adjusting the pH value of the second clear liquid to 6-9, a flocculant is added to perform flocculation precipitation to obtain an upper clear liquid and a bottom precipitate.

[0014] Specifically, the bottom precipitate is discharged together with the magnesium hydroxide precipitate and the calcium hydroxide precipitate.

[0015] Specifically, the ratio of clean water to concentrated wastewater is (3-5):1.

[0016] Specifically, the concentrated wastewater enters the evaporation crystallization device for treatment, and obtaining water and solid crystal salt includes:

[0017] The concentrated wastewater enters the atomization unit of the evaporation crystallization device for atomization;

[0018] The atomized wastewater enters the evaporation crystallization tower, and is evaporated and crystallized with the flue gas of a predetermined temperature from the electrolytic aluminum flue gas purification device in the evaporation crystallization tower to obtain dry flue gas and solid crystalline salt.

[0019] Specifically, the dry flue gas is pressurized by a fan and then returned to the electrolytic aluminum flue gas purification device.

[0020] Specifically, the solid crystalline salt enters a material box for recovery.

[0021] Specifically, the concentrated wastewater is pumped into an atomizing unit of an evaporation crystallization device for atomization, including:

[0022] Through the dual-fluid spray gun, compressed air and concentrated wastewater are sprayed into the atomization unit at a predetermined pressure for atomization.

[0023] Specifically, the temperature of flue gas evaporation and crystallization in the evaporation and crystallization tower is 90-110°C.

[0024] The invention also provides the application of the above-mentioned zero-emission treatment method for electrolytic aluminum fume in treating electrolytic aluminum fume. The technical effects and advantages of the invention are as follows:

[0025] (1) The concentration of SO2 in the flue gas of electrolytic aluminum is very low, generally between 200 and 400 mg / m 3 The amount of wastewater generated by the desulfurization system is very small, generally less than 1t / h. The heat required to evaporate and crystallize the wastewater is small. The flue gas after electrolytic aluminum purification is used to evaporate the wastewater, thereby achieving zero discharge of desulfurization wastewater. The flue gas evaporation process of electrolytic aluminum desulfurization wastewater uses the high-temperature flue gas (90-110℃) after the electrolytic aluminum flue gas purification device, and the heat is recycled to save energy.

[0026] (2) The flue gas evaporation process for desulfurization wastewater from electrolytic aluminum requires less new equipment, low power and low total electricity consumption.

[0027] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a flow chart of a zero-emission treatment method for electrolytic aluminum fume provided in an embodiment of the present application;

[0029] Figure 2 is a diagram of a preprocessing device provided in an embodiment of the present application;

[0030] Figure 3 is a diagram of a reverse osmosis device provided in an embodiment of the present application;

[0031] Figure 4 This is a diagram of the evaporation crystallization device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] In order to solve the shortcomings of the prior art, the present invention discloses a zero-emission treatment method for electrolytic aluminum fume, such as Figure 1 As shown, the method includes,

[0034] Step 1: The aluminum electrolysis flue gas is sequentially processed through an aluminum electrolysis flue gas purification device and a desulfurization device to obtain aluminum electrolysis desulfurization wastewater;

[0035] Step 2: pre-treating the electrolytic aluminum desulfurization wastewater to obtain the upper clear liquid and the bottom sediment;

[0036] Step 3: The upper clear liquid after sedimentation in the pre-sedimentation tank is treated in the clean water tank and then enters the reverse osmosis device for concentration to obtain clean water and concentrated wastewater; the clean water is returned to the desulfurization system for recycling;

[0037] Step 4: The concentrated wastewater enters an evaporation crystallization device for treatment to obtain water and solid crystalline salt.

[0038] In a specific embodiment of the present invention, Figure 2As shown, the pretreatment device includes a pre-sedimentation tank, a magnesium removal reaction tank, a calcium removal reaction tank, a neutralization tank, a homogenization tank, a flocculation tank, a sedimentation tank, a clean water tank, a pre-sedimentation tank sludge pump, a sedimentation tank sludge pump and a dewatering machine, wherein the pre-sedimentation tank, the magnesium removal reaction tank, the calcium removal reaction tank, the neutralization tank, the homogenization tank, the flocculation tank, the sedimentation tank and the clean water tank are connected in sequence; the bottom of the pre-sedimentation tank is connected to the dewatering machine through the pre-sedimentation tank sludge pump; the bottom of the sedimentation tank is connected to the dewatering machine through the sedimentation tank sludge pump.

[0039] In step 2, pre-treating the aluminum electrolytic desulfurization wastewater to obtain the upper clear liquid and the bottom sediment comprises the following steps:

[0040] First, the electrolytic aluminum desulfurization wastewater is pre-precipitated in a pre-precipitation tank to obtain a first clear liquid and a first precipitate;

[0041] The first clear liquid enters the magnesium removal reaction tank, and the reagent NaOH is added to generate Mg(OH)2 solid precipitation to remove Mg 2+ The upper clear liquid of the magnesium removal reaction tank enters the calcium removal reaction tank, and the reagent Na2CO3 is added to generate CaCO3 solid precipitation to remove Ca 2+ , obtaining a second clear solution;

[0042] The second clear liquid enters the neutralization tank. Because the reagents NaOH and Na2CO3 are added upstream, the pH value of the wastewater is relatively high. H2SO4 needs to be added to neutralize the pH value and adjust the pH value of the second clear liquid to 6-9; the upper clear liquid of the neutralization tank enters the homogenization tank, and coagulants are added to enlarge the solid particles; the effluent of the homogenization tank enters the flocculation tank, and flocculants are added to enlarge the alum flowers, and slowly stirred at the same time to make the solid particles grow fully; the upper clear liquid of the flocculation tank enters the sedimentation tank, and after free sedimentation, the upper clear liquid enters the clean water tank. The sludge at the bottom of the pre-sedimentation tank is conveyed to the vacuum belt dehydrator by the pre-sedimentation tank sludge pump for dehydration and discharge. The sludge at the bottom of the sedimentation tank and the magnesium hydroxide precipitate and calcium hydroxide precipitate are all conveyed to the vacuum belt dehydrator by the sedimentation tank sludge pump for dehydration and discharge. Most of the suspended matter in the desulfurization wastewater can be removed in this step, and the upper clear liquid after treatment meets the "Water Quality Control Index of Limestone-Gypsum Wet Desulfurization Wastewater in Thermal Power Plants" (DL / T997) standard.

[0043] In a specific embodiment of the present invention, Figure 3 As shown, the reverse osmosis device includes a pipe network reverse osmosis membrane concentration unit, a concentrate pump and a water outlet pump, wherein the first outlet of the network reverse osmosis membrane concentration unit is connected to the atomization unit through the concentrate pump; the second outlet of the network reverse osmosis membrane concentration unit is connected to the desulfurization device through the water outlet pump.

[0044] For step 3: the upper clear liquid after the precipitation in the pre-precipitation tank is treated in a clean water tank and then enters a reverse osmosis device for concentration to obtain clean water and concentrated wastewater, wherein the treated upper clear liquid (wastewater) collected in the clean water tank is pumped into a reverse osmosis system for concentration by a clean water pump, and an ultrafiltration pretreatment device is provided in the reverse osmosis system to remove larger solid particles, and then the wastewater is passed through a pipe network membrane column by a high-pressure pump, and the ratio of clean water and concentrated wastewater produced is (3-5): 1. Preferably, clean water accounts for 70-75%, and concentrated wastewater produced accounts for 25-30%, which greatly reduces the amount of wastewater, and also recycles clean water to the desulfurization system, reducing the water consumption of the desulfurization system.

[0045] In a specific embodiment of the present invention, Figure 4 As shown, the evaporation crystallization device includes an atomization unit, an evaporation crystallization tower, a high-efficiency dust collector and a material trough, wherein the atomization unit, the first inlet of the evaporation crystallization tower, the outlet of the evaporation crystallization tower, the inlet of the high-efficiency dust collector, the first outlet of the high-efficiency dust collector and the material trough are connected in sequence; the second outlet of the electrolytic aluminum fume purification device is connected to the second inlet of the evaporation crystallization tower; the second outlet of the high-efficiency dust collector is connected to the second inlet of the electrolytic aluminum fume purification device through a fan.

[0046] For step 4: the concentrated wastewater enters the evaporation crystallization device for treatment to obtain water and solid crystal salt, including the following steps:

[0047] Step 401: using a dual-fluid spray gun, spraying compressed air and concentrated wastewater into an atomization unit at a predetermined pressure for atomization;

[0048] Step 402: the atomized wastewater enters an evaporation crystallization tower, and is evaporated and crystallized with the flue gas of a predetermined temperature from the electrolytic aluminum flue gas purification device in the evaporation crystallization tower. The evaporation and crystallization temperature of the flue gas in the evaporation crystallization tower is 90-110°C, and dry flue gas and solid crystalline salt are obtained. In this process, the flue gas temperature in the electrolytic aluminum industry is relatively low (90-110°C), and there is no other heat source such as steam, but the discharge of wastewater from wet desulfurization of electrolytic aluminum is small (the discharge of wastewater from each desulfurization device is generally less than 1t / h), and the required heat is correspondingly small. At present, there is no engineering application that uses flue gas evaporation to achieve zero discharge of flue gas wastewater from electrolytic aluminum.

[0049] Step 403: The dry flue gas is pressurized by a fan and returned to the electrolytic aluminum flue gas purification device to recover the solid crystals. The dry flue gas after evaporation of the crystallization wastewater contains solid crystalline salt, which is then separated by a high-efficiency dust collector. The clean flue gas is pressurized by a fan and returned to the electrolytic aluminum flue. The separated solid crystalline salt is disposed together with the solid waste of the aluminum plant.

[0050] The present invention also provides an application of the above-mentioned zero-emission treatment method for electrolytic aluminum flue gas in treating electrolytic aluminum flue gas. The traditional thermal power plant desulfurization wastewater zero-emission treatment process adopts flue evaporation technology. The evaporated flue gas is taken from the high-temperature flue gas before the air preheater (about 300-380°C), with high heat, short evaporation time, and large amount of evaporation treatment wastewater. The flue gas temperature in the electrolytic aluminum industry is relatively low (90-110°C), and there is no other heat source such as steam, but the discharge of electrolytic aluminum wet desulfurization wastewater is small (the discharge of wastewater from each desulfurization device is generally less than 1t / h), and the required heat is correspondingly small. At present, there is no engineering application that uses flue gas evaporation to achieve zero discharge of wastewater.

[0051] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A zero-emission treatment method for electrolytic aluminum fume, characterized in that: The method comprises, The aluminum electrolysis flue gas is sequentially processed through an aluminum electrolysis flue gas purification device and a desulfurization device to obtain aluminum electrolysis desulfurization wastewater; Pre-treating the aluminum electrolytic desulfurization wastewater to obtain the upper clear liquid and the bottom sediment; After the upper clear liquid is treated in the clean water tank, it enters the reverse osmosis device for concentration to obtain clean water and concentrated wastewater; The clean water is returned to the desulfurization system for recycling; The concentrated wastewater enters an evaporation crystallization device for treatment to obtain water and solid crystal salt.

2. The zero-emission treatment method for electrolytic aluminum fume according to claim 1 is characterized in that: Pre-treat the electrolytic aluminum desulfurization wastewater to obtain the upper clear liquid and bottom sediment, including: First, the electrolytic aluminum desulfurization wastewater is precipitated to obtain a first clear liquid and a first precipitate; After sequentially performing precipitation to remove magnesium and precipitation to remove calcium on the first clear liquid, a second clear liquid, a magnesium hydroxide precipitate and a calcium hydroxide precipitate are obtained; After adjusting the pH value of the second clear liquid to 6-9, a flocculant is added for flocculation and precipitation to obtain an upper clear liquid and a bottom precipitate.

3. The zero-emission treatment method for electrolytic aluminum fume according to claim 2 is characterized in that: The bottom precipitate is discharged together with the magnesium hydroxide precipitate and the calcium hydroxide precipitate.

4. The zero-emission treatment method for electrolytic aluminum fume according to claim 1 is characterized in that: The ratio of clean water to concentrated wastewater is (3-5):

1.

5. The zero-emission treatment method for electrolytic aluminum fume according to claim 1 is characterized in that: The concentrated wastewater enters the evaporation crystallization device for treatment, and obtaining water and solid crystal salt includes: The concentrated wastewater enters the atomization unit of the evaporation crystallization device for atomization; The atomized wastewater enters the evaporation crystallization tower, and is evaporated and crystallized with the flue gas of a predetermined temperature from the electrolytic aluminum flue gas purification device in the evaporation crystallization tower to obtain dry flue gas and solid crystalline salt.

6. The zero-emission treatment method for electrolytic aluminum fume according to claim 5 is characterized in that: The dry flue gas is pressurized by a fan and then returned to the electrolytic aluminum flue gas purification device.

7. The zero-emission treatment method for electrolytic aluminum fume according to claim 5 is characterized in that: The solid crystalline salt enters the material box for recovery.

8. The zero-emission treatment method for electrolytic aluminum fume according to claim 5 is characterized in that: The concentrated wastewater is pumped into the atomization unit of the evaporation crystallization device for atomization, including: Through the dual-fluid spray gun, compressed air and concentrated wastewater are sprayed into the atomization unit at a predetermined pressure for atomization.

9. The zero-emission treatment method for electrolytic aluminum fume according to claim 5 is characterized in that: The temperature of flue gas evaporation and crystallization in the evaporation and crystallization tower is 90-110℃.

10. Application of the zero-emission treatment method for electrolytic aluminum fume as described in any one of claims 1 to 9 in treating electrolytic aluminum fume.

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