Method for recovering heat in settling and washing process of red mud

Abstract

The invention relates to a method for recovering heat in a red mud settling and washing process, and belongs to the technical field of aluminum oxide production. Heat exchangers are respectively arranged at air drawing cylinders at the tops of a plurality of red mud settling tanks, low-temperature red mud washing water sequentially passes through the heat exchangers according to the sequence from low temperature to high temperature, and the heated red mud washing water enters a hot water tank; the heat exchange device is arranged between the last washing settling tank and the red mud filter pressing process, so that the filtered red mud filtrate exchanges heat with the high-temperature red mud slurry discharged from the last washing settling tank, the heated red mud filtrate enters a hot water tank, and the red mud slurry enters the hot water tank; the red mud filtrate which is mixed and heated in the hot water tank, the red mud washing water which exchanges heat with the heat exchanger at the top of the red mud settling tank, external incoming water and the mixed washing water enter the tail tank of the red mud washing tank for washing the red mud. According to the method, the heat loss is reduced on the premise of meeting the washing efficiency and reducing the hydrolysis loss.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of alumina production, and particularly relates to a method for recovering heat in a red mud settling and washing process. BACKGROUND

[0002] In the red mud settling and washing process of alumina production, the separated red mud needs to be washed multiple times with water, with the purpose of recovering as much alkali and alumina as possible carried by the red mud and reducing the pollution risk of the environment caused by the red mud after being stored.

[0003] In order to improve the washing effect of the red mud and reduce the amount of hydrolysis reaction occurring in the washing process, high-temperature washing water is often used in production, and steam is introduced into the settling tank to maintain the operation of the settling system in a high-temperature operating environment. Although this operation mode can improve the washing efficiency and inhibit the hydrolysis loss from the temperature condition, it causes a large amount of heat loss. A gas extraction cylinder is usually arranged on the top of the red mud settling tank, and the high-temperature red mud slurry in the tank continuously flashes steam through the gas extraction cylinder to be emitted to the atmosphere, which not only causes heat loss, but also loses water. In addition, in the process of red mud pressure filtration, the high-temperature alkali-containing red mud can accelerate the deformation of the filter plate of the red mud filter, shorten the service life, and if not replaced in time, it is easy to cause material spraying accidents under high-pressure operating conditions, causing personal injury to workers, and a large amount of steam is also generated in the filtration process of high-temperature materials, resulting in a poor working environment. SUMMARY

[0004] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present application provides a method for recovering heat in a red mud settling and washing process, which reduces heat loss under the premise of meeting the washing efficiency and reducing hydrolysis loss.

[0005] In order to achieve the above-mentioned purposes, the main technical solutions adopted by the present application include: A method for recovering heat in a red mud settling and washing process, wherein a heat exchanger is arranged at each gas extraction cylinder on the top of a plurality of red mud settling tanks, low-temperature red mud washing water is sequentially heated in each heat exchanger in order from low temperature to high temperature, and the heated red mud washing water enters a hot water tank, the flashed steam from the red mud settling tank is emitted to the atmosphere after passing through a heat exchange device, and a heat exchange device is arranged between the last washing settling tank and the red mud pressure filtration process, so that the filtered red mud filtrate is heat-exchanged with the high-temperature red mud slurry discharged from the last washing settling tank, the heated red mud filtrate enters the hot water tank, and the mixed heated red mud filtrate, the red mud washing water after being heat-exchanged with the heat exchanger on the top of the red mud settling tank, and external water are mixed, and the mixed washing water is used for red mud washing in the last tank of the red mud washing tank.

[0006] Further, the heat exchanger at the gas extraction cylinder on the top of the red mud settling tank is an indirect heat exchanger, the heat exchange surface is provided with fins or protruding steel belts, and the medium flow mode in the indirect heat exchanger is baffle.

[0007] Further, the red mud filtrate includes filtrate obtained after red mud filtration and water recovered from a red mud stockpile.

[0008] Further, a pipe jacket heat exchanger is arranged between the last tank of the red mud washing tank and the red mud filter pressing process, the pipe passage transports red mud slurry, the shell passage transports red mud filtrate, and a thermal insulation layer is arranged on the outer wall of the shell passage of the pipe jacket heat exchanger.

[0009] Further, a plate heat exchanger is arranged between the last tank of the red mud washing tank and the red mud filter pressing process, including a wide channel plate heat exchanger, a spiral plate heat exchanger and a tube shell heat exchanger.

[0010] Further, the water temperature of the mixed red mud filtrate in the hot water tank, the red mud washing water after heat exchange of the red mud settling tank top heat exchanger and external incoming water is 90-95 DEG C.

[0011] The beneficial effects of the present application are: (1) In the present application, the red mud washing water with different water quality and temperature is used to absorb heat in the red mud settling and washing process, the heat exchange equipment can be selected according to the quality of heat source and the configuration of the plant, and high heat exchange efficiency can be achieved to maximize heat recovery.

[0012] (2) In the present application, the red mud washing water is used to absorb the flash steam of the settling tank in series from low temperature to high temperature by indirect heat exchange, which simplifies the process, and the heat exchanger type and flow channel are specially designed to improve the heat exchange efficiency.

[0013] (3) In the present application, the red mud filtrate is used to recover the heat carried by the red mud slurry, which realizes heat recovery, delays the deformation of the filter plate of the red mud filter, reduces the probability of material spraying accidents caused by filter plate deformation, reduces the steam of the red mud filter pressing plant and improves the working environment of workers. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The present application is a red mud settling and washing process heat recovery flow diagram. In the figure: 1 - separation settling tank, 2 - first tank of washing settling tank, 3 - last tank of washing settling tank, 4 - hot water tank, 5 - air cylinder I, 6 - air cylinder II, 7 - air cylinder III, 8 - heat exchanger I, 9 - heat exchanger II, 10 - heat exchanger III, 11 - heat exchanger IV. DETAILED DESCRIPTION

[0015] In order to better explain the present application, the following will be described in detail by specific embodiments in combination with the drawings.

[0016] As Figure 1As shown, the present application provides a method for heat recovery of red mud settling and washing process, heat exchangers are arranged at the top of the gas extraction cylinder of each red mud settling tank, specifically, the red mud settling tank includes a separation settling tank 1, a first washing settling tank 2, a plurality of washing settling tanks, and a last washing settling tank 3, the top of the separation settling tank 1 is provided with a gas extraction cylinder III 7, the gas extraction cylinder III 7 is provided with a heat exchanger III 10, the top of the first washing settling tank 2 is provided with a gas extraction cylinder II 6, the gas extraction cylinder II 6 is provided with a heat exchanger II 9, the top of each washing settling tank is provided with a gas extraction cylinder, and the top of the last washing settling tank 3 is provided with a gas extraction cylinder I 5, the gas extraction cylinder I 5 is provided with a heat exchanger I 8. The low-temperature red mud washing water is sequentially heated by each heat exchanger in the order of low temperature to high temperature, and then enters the hot water tank 4, and the steam flashed from the red mud settling tank is discharged to the atmosphere after being passed through the heat exchange device. Specifically, the low-temperature red mud washing water first exchanges heat with the flash steam of the last washing settling tank 3 through the heat exchanger I 8, then sequentially flows through each washing settling tank in the reverse direction to exchange heat with the heat exchanger, and finally exchanges heat with the heat exchanger III 10 at the top of the separation settling tank 1 and then enters the hot water tank 4. The low-temperature red mud washing water sequentially exchanges heat with each heat exchanger in the order of low temperature to high temperature, and finally enters the hot water tank 4 after being heated. Specifically, the heat exchanger at the top of the gas extraction cylinder of the red mud settling tank is an indirect heat exchanger, the heat exchange surface is provided with fins or protruding steel belts, and the medium flow mode in the indirect heat exchanger is baffle.

[0017] A heat exchange device, specifically a heat exchanger IV 11, is arranged between the last washing settling tank 3 and the red mud filter pressing process, so that the filtered red mud filtrate exchanges heat with the high-temperature red mud slurry discharged from the last washing settling tank 3, and the heated red mud filtrate enters the hot water tank 4. The hot water tank 4 is filled with the mixed and heated red mud filtrate, the red mud washing water exchanged with the heat exchanger at the top of the red mud settling tank, and external water, and the water temperature in the hot water tank is 90-95℃ after the mixed and heated red mud filtrate, the red mud washing water exchanged with the heat exchanger at the top of the red mud settling tank, and the external water are mixed. The mixed washing water enters the last washing settling tank 3 for red mud washing. Specifically, the red mud filtrate includes the filtrate obtained after the red mud is filtered and the water recovered from the red mud stockyard.

[0018] Specifically, when the distance between the last washing settling tank and the red mud filter pressing process is far, for example, more than 200 meters, a tube-in-tube heat exchanger is arranged between the last washing settling tank 3 and the red mud filter pressing process, the tube side transports the red mud slurry, the shell side transports the red mud filtrate, and a heat preservation layer is arranged on the outer wall of the shell side of the tube-in-tube heat exchanger. When the distance between the last washing settling tank and the red mud filter pressing process is close, for example, within 200 meters, a plate heat exchanger is arranged between the last washing settling tank 3 and the red mud filter pressing process, including a wide channel plate heat exchanger, a spiral plate heat exchanger, and a tube-shell heat exchanger.

[0019] Example 1 30℃ of red mud washing water (new water) flows through the washing and settling tank end tank 3 tank top gas cylinder I5 matched heat exchanger I8, after the heat exchanger I8 heat exchange of red mud washing water along the red mud material direction reverse respectively through the washing tank top gas cylinder set heat exchanger, until the washing and settling tank first tank 2 top gas cylinder II6 set heat exchanger II9, the temperature of red mud washing water rises to 35℃, continue to enter the separation and settling tank 1 top gas cylinder III7 matched heat exchanger III10, the temperature of red mud washing water rises to 45℃, the hot water after heat exchange and temperature rising enters the hot water tank 4. 90℃ of washing and settling tank end tank 3 bottom discharge, flows through the tube side of the jacketed heat exchanger IV11 to the red mud filter pressing process, the temperature drops to 80℃, 70℃ of red mud filter pressing filtrate flows through the shell side of the jacketed heat exchanger IV11 returns to the hot water tank, the temperature increases to 78℃, the heat exchange of high temperature red mud slurry and low temperature red mud filtrate is completed in the jacketed heat exchanger IV11, and heat recovery is realized. The shell side of the jacketed heat exchanger is provided with a heat preservation layer, so as to reduce heat loss.

[0020] Example 2 50℃ of red mud washing water (water obtained after sewage treatment) flows through the washing and settling tank end tank 3 tank top gas cylinder I5 matched heat exchanger I8, after the heat exchanger I8 heat exchange of red mud washing water along the red mud material direction reverse respectively through the washing tank top gas cylinder set heat exchanger, until the washing and settling tank first tank 2 top gas cylinder II6 set heat exchanger II9, the temperature of red mud washing water rises to 60℃, continue to enter the separation and settling tank 1 top gas cylinder III7 matched heat exchanger III10, the temperature of red mud washing water rises to 70℃, the hot water after heat exchange and temperature rising enters the hot water tank 4. 85℃ of washing and settling tank end tank 3 bottom discharge flows through the plate heat exchanger IV11 to the red mud filter pressing process, the temperature drops to 75℃, 65℃ of red mud filter pressing filtrate flows through the plate heat exchanger IV11 returns to the hot water tank, the temperature increases to 73℃, the heat exchange of high temperature red mud slurry and low temperature red mud filtrate is completed in the heat exchanger IV11, and heat recovery is realized. The red mud slurry pipe and the red mud filtrate pipe are provided with a heat preservation layer, so as to reduce heat loss.

[0021] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present application, and any modification, replacement, modification and variation of the above embodiments made by those skilled in the art are within the scope of the present application.

Claims

1. A method of heat recovery from a red mud settling wash process characterised by: Heat exchangers are arranged at the gas extraction pipes at the top of the several red mud settling tanks, the low-temperature red mud washing water is sequentially heated in the heat exchangers from low temperature to high temperature, and the heated red mud washing water enters the hot water tank, the steam flashed from the red mud settling tank is dissipated to the atmosphere after passing through the heat exchange device, a heat exchange device is arranged between the last washing settling tank and the red mud filter pressing process, the filtered red mud filtrate is exchanged with the high-temperature red mud slurry discharged from the last washing settling tank, the heated red mud filtrate enters the hot water tank, the heated red mud filtrate, the red mud washing water exchanged with the heat exchanger at the top of the red mud settling tank and the external incoming water are mixed in the hot water tank, and the mixed washing water is used for red mud washing in the last tank of the red mud washing tank.

2. A method of heat recovery from a red mud settling and washing process according to claim 1, characterised in that: The heat exchanger at the gas extraction pipe at the top of the red mud settling tank is an indirect heat exchanger, the heat exchange surface is provided with fins or protruding steel belts, and the medium flow mode in the indirect heat exchanger is baffle.

3. A method of heat recovery from a red mud settling and washing process according to claim 1, characterised in that: The red mud filtrate includes the filtrate obtained after red mud filtration and the water recovered from the red mud storage yard.

4. A method of heat recovery from a red mud settling and washing process according to claim 1, characterised in that: A tube-in-tube heat exchanger is arranged between the last tank of the red mud washing tank and the red mud filter pressing process, the red mud slurry is transported in the tube side, the red mud filtrate is transported in the shell side, and a heat preservation layer is arranged on the outer wall of the shell side of the tube-in-tube heat exchanger.

5. A method of heat recovery from a red mud settling and washing process according to claim 1, characterised in that: A plate heat exchanger is arranged between the last tank of the red mud washing tank and the red mud filter pressing process, including a wide channel plate heat exchanger, a spiral plate heat exchanger and a tube-shell heat exchanger.

6. A method of heat recovery from a red mud settling and washing process according to claim 1, characterised in that: The temperature of the mixed water in the hot water tank is 90-95 DEG C.

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