JPS6082Y2 - crystallizer - Google Patents

Description

[Detailed description of the invention] The present invention relates to an externally cooled crystallizer, which is particularly useful for extracting only dog-shaped crystals that are easy to handle from a stock solution where fine crystals tend to peel and large-shaped crystals are difficult to obtain. This invention relates to an improved crystallizer.

Conventionally, as a cooling crystallization apparatus, there is an apparatus in which a cooling jacket is provided around a crystallization tank, and crystals deposited and deposited on the inner wall of the tank are scraped off by rotating blades for crystallization.

However, in a conventional crystallizer that simply scrapes the raw material, a large amount of fine crystals are produced because the fine crystals tend to form raw skin during scraping and further crystal nuclei are likely to be generated by stirring.

Since these fine crystals are removed with almost no growth, they have the drawback of causing problems when being subjected to filtration and separation and further purification.

The object of the present invention is to provide an improved crystallizer that eliminates the above-mentioned drawbacks.

The present inventor conducted research on separating crystals in an externally cooled crystallizer without containing most of the fine crystals that inevitably form in the tank. When a vortex is created in the center to create an upward flow along the tank wall, the fine crystals ride the upward flow and float to the top, gathering in the central vortex, so when new liquid is supplied here, The fine crystals are melted by the sensible heat, and the liquid with a high degree of supersaturation is drawn into the bottom by the vortex, and precipitation occurs at the bottom where the slurry concentration is high and the crystals are large, further promoting crystal growth. This discovery led to this invention.

As shown in the drawings, the crystallizer of the present invention has a crystallization tank 2 provided with a cooling jacket 1 on the outer periphery, and a blade 3 that scrapes off crystals adhering to the inner wall of the tank 2 and rotates coaxially with the blade 3. A supply pipe 5 is provided with stirring blades 4 that create a downward liquid flow (eddy current) or an upward flow along the tank wall, and is provided with a supply pipe 5 installed above the central part of the tank where the vortex flow is generated. The structure is such that the crystals supplied to the vortex section and precipitated are taken out as a slurry from an extraction pipe 6 at the bottom of the tank.

That is, the crystallization tank 2 is filled with a liquid to be cooled and crystallized, and is cooled from the outer jacket 1 to scrape off the crystals deposited on the tank walls.The blades 3 are rotated to scrape off the crystals adhering to the wall surfaces. While taking the sample, the slurry is made to reach a predetermined concentration at a predetermined temperature.

For this purpose, an amount of raw solution corresponding to the amount of heat removed by the cooling jacket is continuously supplied from the supply pipe 5 to maintain a constant temperature in the crystallization tank, and an amount of slurry corresponding to the amount of supplied liquid is continuously supplied from the supply pipe 5. is continuously taken out from the extraction pipe 6 to keep the liquid level in the tank constant.

When the blades 3 scrape off the crystals deposited on the tank wall in the crystallization tank 2, fine crystals are naturally formed, but the fine crystals are caught in the vortex generated by the stirring blade 4 that rotates coaxially with the blade 3. Once it reaches the bottom of the tank, it floats up on the upward flow generated along the tank wall and is further collected in the vortex section.

A high-temperature stock solution is supplied to this vortex section from the supply pipe 5 installed above, so the fine crystals are dissolved by the sensible heat, and the solution with a high degree of vortex saturation is sent to the bottom of the tank. The slurry concentration is high, and precipitation occurs in large areas of crystals, which further grow, and the precipitated fine crystals float up on the upward flow.

Therefore, the crystals taken out as slurry from the extraction pipe 6 at the bottom of the tank contain almost no fine crystals, and only large crystals can be taken out.

For this purpose, a vortex is generated in the center of the crystallization tank and an upward flow is generated along the tank walls.

The stirring blades used in the present invention are propeller-shaped or paddle-shaped to create a downward liquid flow in the center of the tank, or ribbon-shaped to create an upward flow along the tank wall.

Incidentally, it is preferable that the stirring blade 4 and the scraping blade 3 be attached coaxially to simplify the structure, but it is not necessarily necessary to attach them coaxially.

Further, the rotational speeds of the stirring blade 4 and the scraping blade 3 do not need to be the same even when both are attached coaxially, and the rotational speed is determined depending on the state of crystallization.

Further, the size of the crystallization tank is arbitrary, but it is sufficient that the crystals can stay there for a period of time necessary for crystal growth, and in most cases, a residence time of 3 to 10EI is sufficient.

The slurry concentration in the crystallization tank is preferably 20 to 45% by weight on average, preferably 25 to 4% by weight for ease of handling.

As mentioned above, the present invention remelts the raw fine crystals in the crystallization tank using the sensible heat of the supplied liquid in the same crystallization tank, thereby reducing the number of fine crystals and preventing the growth of crystals at the bottom of the tank. By aiming at this, crystals can be precipitated and separated in a state that contains few fine crystals.

Example A crystallization tank device as shown in the figure is equipped with a scraping blade and a stirring blade that rotates coaxially with the scraping blade and generates a vortex flow inside the crystallization tank with a jacket having a diameter of 600 mm and a height of 50-1 and an internal capacity of about 1401. Petroleum-based naphthalene containing 54% by weight of naphthalene and 4% of impurities was heated at 60°C to 35% by weight using
Crystallization was carried out by supplying the solution at a rate of 9/h.

At this time, the cooling jacket was cooled using 10°C water.
The temperature inside the crystallization tank was adjusted to 27°C.

After retaining the stirring blade for an average of 4 hours while rotating at 20 pm, slurry 35 containing about 2% of crystals was collected from the bottom of the tank.
ko/h was taken out continuously.

The naphthalene crystals thus obtained had an average crystal grain size of 1000 μm calculated from the specific surface area.

[Brief explanation of the drawing]

The drawing is a sectional view of the crystallizer of the present invention. 1... Cooling jacket, 2... Crystallization tank, 3... Bent blade, 4... Stirring blade, 5...
- Supply pipe, 6... Extraction pipe.

Claims (1)

[Scope of utility model registration request] A crystallization tank, a blade installed inside the tank to scrape off crystals attached to the inner wall of the tank, a stirring blade installed inside the tank to generate a downward liquid flow in the center of the tank, and a stirring blade installed inside the tank to generate a downward liquid flow in the center of the tank. A crystallization apparatus including a cooling means provided on the outer periphery and a means for supplying a stock solution containing a fraction to be crystallized to the center of the tank.