Soda ash treatment system

Abstract

The present application relates to the field of alkali ash treatment, and discloses a device comprising a stirring tank, a crystallization tank, a centrifuge and an evaporator connected in sequence, wherein the crystallization tank is provided with a recirculation unit, the recirculation unit comprises a circulation pipeline, a steam pipeline and a heat exchanger, the circulation pipeline passes through the heat exchanger, the steam pipeline is connected to the top of the crystallization tank and the heat exchanger, and the steam pipeline and the circulation pipeline are communicated in the heat exchanger.

Description

Technical Field

[0001] The present invention relates to the field of alkali ash treatment, in particular to an alkali ash treatment system. Background Art

[0002] In order to save costs and protect the environment, pulp mills usually recycle the alkali produced during the pulping process. The black liquor becomes white liquor after passing through the evaporation workshop, alkali furnace combustion and alkali treatment workshop, and is reused in the cooking process.

[0003] Among them, alkali ash is one of the combustion products of black liquor in the alkali furnace. Alkali ash is rich in recyclable potassium chloride and thenardite. The existing technology does not extract and recycle potassium chloride and thenardite in alkali ash, resulting in a large amount of resource waste. Summary of the Invention

[0004] The present invention aims to provide an alkali ash treatment system for respectively recovering potassium chloride and sodium sulfate from the alkali ash.

[0005] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: an alkali ash treatment system includes a stirring tank, a crystallization tank, a centrifuge and an evaporator connected in sequence, a recycling unit is provided on the crystallization tank, the recycling unit includes a circulation pipe, a steam pipe and a heat exchanger, the circulation pipe passes through the heat exchanger, the steam pipe connects the top of the crystallization tank and the heat exchanger, and the steam pipe and the circulation pipe are connected in the heat exchanger.

[0006] The beneficial effects of this program are:

[0007] 1. Stir the alkali ash and water in a mixing tank to form a slurry, which is then passed into a crystallizer. The slurry then flows through a circulation pipe into a heat exchanger for heat exchange and cooling. Since thenite is easily crystallized at high temperatures, while potassium chloride is more easily crystallized at low temperatures, the crystals precipitated in the crystallizer are mainly potassium chloride. The remaining slurry after passing through the centrifuge contains a large amount of thenite. The remaining slurry after passing through the centrifuge may also contain potassium chloride and needs to be recrystallized. The solution containing a large amount of thenite enters the evaporator for evaporation and crystallization, thereby achieving the purpose of separately recovering potassium chloride and thenite from the alkali ash.

[0008] 2. The higher temperature steam rises to the top of the crystallizer, then merges with the slurry in the steam pipe and the circulation pipe, and then cools down through the heat exchanger and returns to the crystallizer, thereby improving the efficiency of cooling the slurry, thereby accelerating the crystallization speed and improving the recovery efficiency.

[0009] Preferably, as an improvement, the crystallizer comprises, from top to bottom, an upper cone, a cylinder, a lower cone, and a salt leg. A demister is provided in the upper cone, and a flushing pipe is provided horizontally at the upper end of the cylinder. One end of the flushing pipe is connected to the outside of the cylinder, and the other end of the flushing pipe is located directly below the demister. A vertically upward nozzle is provided at the other end of the flushing pipe, and the spraying range of the nozzle covers the demister. Such an arrangement has the following effects:

[0010] 1. If particles such as mist entrained by steam enter the steam pipes and heat exchangers, it is easy to cause blockage, scaling or corrosion of equipment. Therefore, a demister is set in this solution. When the steam passes through the demister, due to the inertial impact of the steam, the mist collides with the corrugated plate and the collected droplets are large enough that the gravity generated by the mist exceeds the combined force of the gas's upward force and the liquid's surface tension. The droplets are then separated from the surface of the corrugated plate, thereby avoiding blockage, scaling or corrosion of equipment.

[0011] 2. After long-term use, steam causes slurry or crystallization in the demister, which can easily cause clogging of the demister, thereby reducing the gas-liquid separation effect of the demister. In this solution, the demister is sprayed under the flushing pipe to avoid clogging of the demister.

[0012] Preferably, as an improvement, one end of the circulation pipe is connected to the barrel, and the other end of the circulation pipe is connected to the lower cone. In this arrangement, the slurry in the circulation pipe is cooled by the heat exchanger and then returns to the crystallizer. Since the temperature is lower when it returns to the primary crystallizer, the cooled slurry sinks in the barrel and gradually mixes with the slurry originally in the crystallizer, thereby accelerating the cooling of the slurry in the crystallizer.

[0013] Preferably, as an improvement, the salt leg is provided with a drain port, a discharge port, and three feed ports, namely, an upper feed port, a middle feed port, and a lower feed port. With this arrangement, if only a single feed port is provided, the slurry enters the crystallizer at a relatively high speed, resulting in uneven slurry dispersion and affecting cooling efficiency. In this embodiment, however, the slurry enters the salt leg simultaneously through multiple feed ports, colliding with the sidewalls of the salt leg to form a vortex, which spreads upward, thereby evenly distributing the slurry within the crystallizer.

[0014] Preferably, as an improvement, a transition portion is provided at the lower end of the lower cone, which is inserted into the upper end of the salt leg. The upper feed port is horizontally arranged between the outer wall of the transition portion and the inner wall of the salt leg, and the middle feed port, discharge port, and lower feed port are all located on the axis of the salt leg. This arrangement has the following effects:

[0015] 1. The slurry entering the circulation pipe is continuously cooled, and potassium chloride crystals precipitate and slide down the side wall of the lower cone 213 into the salt leg. However, the side wall of the lower cone 213 is an inclined surface, and some crystals expand at low temperatures and combine with the side wall of the lower cone 213, and do not slide into the salt leg. After a long time, the surface of the side wall of the lower cone 213 will become rough, and more crystals cannot slide into the salt leg, making it difficult to collect the crystals. In this solution, a transition part is provided, and the slurry entering the salt leg from the upper feed port cannot directly enter the lower cone upward. 213, it is impossible to exchange temperature with the slurry in the lower cone 213, so the slurry between the salt leg and the transition part cools down slowly, and the slurry is sprayed horizontally from the upper feed port to impact the outside of the transition part. The transition part is in contact with the slurry in this part, and the temperature is higher than that of the lower cone. Therefore, when the crystal passes through the transition part, the expansion effect is smaller and it is easier to slide into the salt leg; and the lower cone is also connected to the lower end of the circulation pipe. The part connected to the lower end of the circulation pipe has greater fluidity, so there is no need to worry about the problem of the crystal not being easy to slide into the salt leg.

[0016] 2. After the slurry sprayed from the upper feed port collides with the transition part, it flows in the annular space on the outer wall of the transition part, thereby driving the slurry in the salt leg to form a vortex. After the slurry is sprayed downward from the middle feed port and the lower feed port, it rushes upward in the opposite direction and is accelerated into the crystallization tank under the drive of rotation, so that the slurry is more evenly distributed in the crystallization tank.

[0017] Preferably, as an improvement, the middle feed port faces downward and is located just above the discharge port. In this arrangement, the slurry enters from the middle feed port and continuously flushes the discharge port to prevent the discharge port from being blocked.

[0018] Preferably, as an improvement, the drain port is located at the bottom of the salt leg, and the lower feed port is downwardly facing, and the lower feed port is located between the drain port and the discharge port. In this arrangement, the slurry enters from the lower feed port to continuously flush the drain port, preventing the drain port from being blocked, and facilitating the removal of crystals at the bottom of the salt leg.

[0019] Preferably, as an improvement, the crystallizer is provided with a plurality of manholes, sight glasses, liquid level gauges and pressure gauges. In this arrangement, the manholes are provided so that the interior of the crystallizer can be easily accessed for inspection at any time; the sight glasses, liquid level gauges and pressure gauges are provided so that various parameters can be constantly monitored to ensure that the slurry crystallizes under optimal conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram of an embodiment;

[0021] Figure 2 Be the crystallization tank structural figure of embodiment. DETAILED DESCRIPTION

[0022] The following is further described in detail through specific implementation methods:

[0023] The figure marks in the drawings of the specification include: stirring tank 1, crystallization tank 2, upper cone 211, cylinder 212, lower cone 213, transition portion 214, salt leg 215, demister 221, flushing pipe 222, nozzle 223, pressure gauge 231, liquid level gauge 232, sight glass 233, steam outlet 241, population 242, recycling inlet 243, recycling outlet 244, drain port 245, feed pipe 250, upper feed port 251, middle feed port 252, lower feed port 253, discharge pipe 260, discharge port 261, centrifuge 3, evaporator 4, circulation pipe 510, steam pipe 520, heat exchanger 530.

[0024] Example

[0025] The embodiment is basically as follows Figure 1 As shown: the alkali ash treatment system includes a stirring tank 1, a crystallization tank 2, a centrifuge 3 and an evaporator 4 connected in sequence.

[0026] like Figure 2 As shown, the crystallizer 2 includes an upper cone 211, a cylinder 212, a lower cone 213 and a salt leg 215 from top to bottom. A demister 221 is bolted to the upper cone 211. A steam outlet 241 and two pressure gauges 231 are provided on the upper left side of the upper cone 211. An inlet 242 and a pressure gauge 231 are provided on the upper right side of the upper cone 211. The demister 221 is a plate-type demister. A flushing pipe 222 is horizontally welded on the upper end of the cylinder 212. The right end of the flushing pipe 222 is connected to the outside of the cylinder 212. The left end of the flushing pipe 222 is located directly below the demister 221. The left end of the flushing pipe 222 is integrally formed with a vertical An upward nozzle 223 has a spraying range covering the lower surface of the wave plate of the demister 221. A sight glass 233 and two liquid level gauges 232 are provided on the left side of the cylinder 212. A recirculation inlet 243 is provided on the upper right side of the cylinder 212, and an inlet 242 is provided on the lower right side of the cylinder 212. A recirculation outlet 244 is provided on the lower left side of the lower cone 213. A vertically arranged cylindrical transition portion 214 is provided at the lower end of the lower cone 213. The diameter of the transition portion 214 is smaller than the diameter of the cylindrical salt leg 215. The transition portion 214 is inserted from above the salt leg 215, and the upper end of the salt leg 215 is welded to the outer side of the lower cone 213.

[0027] The lower end of the salt leg 215 is provided with a drain port 245, the right side of the salt leg 215 is provided with a discharge pipe 260, the left end of the discharge pipe 260 is a discharge port 261, the discharge port 261 is inclined to the upper left, and the discharge port 261 is connected to the centrifuge 3. Three feed pipes 250 are horizontally provided on the left side of the salt leg 215. The discharge pipe 260 and the three feed pipes 250 are provided with branches for flushing. The angle between the uppermost feed pipe 250 and the side wall of the salt leg 215 is less than 90 degrees. The right end of the material pipe 250 has, from top to bottom, an upper feed port 251, a middle feed port 252 and a lower feed port 253. The upper inlet is located on the side wall of the salt leg 215, horizontally to the right and located between the outer wall of the transition portion 214 and the inner wall of the salt leg 215; the middle feed port 252 and the lower feed port 253 are both facing downward, and the middle feed port 252, the discharge port 261, the lower feed port 253 and the drain port 245 are vertically aligned from top to bottom and are all located on the central axis of the salt leg 215.

[0028] like Figure 1 Shown, crystallizer 2 is provided with recirculation unit, recirculation unit comprises circulation line 510, steam pipe 520 and heat exchanger 530, circulation line 510 one end is connected with recirculation inlet 243, circulation line 510 the other end is connected with recirculation outlet 244, circulation line 510 passes through heat exchanger 530, steam pipe 520 communicates steam outlet 241 and heat exchanger 530, steam pipe 520 and circulation line 510 are communicated in heat exchanger 530, and the solution separated by centrifuge 3 is communicated with circulation line 510.The quantity of crystallizer 2 can be adjusted according to actual demand, and multiple crystallization is carried out by series connection multiple crystallizers 2, and the amount of potassium chloride crystallization can be improved.

[0029] The specific implementation steps are as follows:

[0030] 1. Alkali ash and water are stirred in agitator tank 1 to form a slurry. The slurry is then passed into crystallizer tank 2. The slurry then flows through circulation pipe 510 and continuously enters heat exchanger 530 for heat exchange and cooling. The crystals precipitated in crystallizer 2 are primarily potassium chloride. The remaining slurry passes through centrifuge 3, leaving a large amount of sodium sulfate. The remaining slurry, which may also contain potassium chloride, returns to crystallizer 2 through circulation pipe 510 for recrystallization. The solution containing a large amount of sodium sulfate enters evaporator 4 for evaporation and crystallization, thereby recovering the potassium chloride and sodium sulfate from the alkali ash.

[0031] 2. The higher temperature steam rises to the top of the crystallizer 2, then passes through the steam pipe 520 and merges with the slurry in the circulation pipe 510, and then passes through the heat exchanger 530 to cool down and return to the crystallizer 2, thereby improving the efficiency of cooling the slurry, thereby accelerating the crystallization speed and improving the recovery efficiency.

[0032] The above is only an embodiment of the present invention, and the common knowledge such as the specific technical solutions and / or characteristics in the solution are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the description can be used to interpret the content of the claims.

Claims

1. Alkali ash treatment system, characterized by: The invention comprises a stirring tank, a crystallizing tank, a centrifuge and an evaporator connected in sequence. The crystallizing tank is provided with a recycling unit, which comprises a circulation pipe, a steam pipe and a heat exchanger. The circulation pipe passes through the heat exchanger, and the steam pipe connects the top of the crystallizing tank and the heat exchanger. The steam pipe and the circulation pipe are connected in the heat exchanger. The crystallization tank consists of an upper cone, a cylinder, a lower cone and a salt leg from top to bottom. A demister is provided in the upper cone. A flushing pipe is provided horizontally at the upper end of the cylinder. One end of the flushing pipe is connected to the outside of the cylinder. The other end of the flushing pipe is located directly below the demister. A vertical upward nozzle is provided at the other end of the flushing pipe. The spraying range of the nozzle covers the demister. There are three horizontal feed pipes on the left side of the salt leg. The discharge pipe and the three feed pipes are all equipped with branch pipes for flushing. The angle between the top feed pipe and the side wall of the salt leg is less than 90 degrees. The right ends of the three feed pipes are: upper feed port, middle feed port and lower feed port from top to bottom; the middle feed port and the lower feed port are all facing downwards; A transition portion is provided at the lower end of the lower cone, which is inserted into the upper end of the salt leg. The upper feed port is horizontally arranged between the outer wall of the transition portion and the inner wall of the salt leg. A drain port is provided on the salt leg, which is located at the bottom of the salt leg. The lower feed port is located between the drain port and the discharge port.

2. The alkali ash treatment system according to claim 1, characterized in that: One end of the circulation pipe is connected to the cylinder, and the other end of the circulation pipe is connected to the lower cone.

3. The alkali ash treatment system according to claim 1, characterized in that: The middle feed port, discharge port and lower feed port are all located on the axis of the salt leg.

4. The alkali ash treatment system according to claim 3, characterized in that: The middle feed port is located just above the discharge port.

5. The alkali ash treatment system according to claim 1, characterized in that: The crystallization tank is equipped with several manholes, sight glasses, liquid level gauges and pressure gauges.

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