JPH06125705A - Spray dryer housed with fluidized bed and method for operating the same - Google Patents

Abstract

PURPOSE:To provide a spray dryer so designed that an exhaust duct arranged in series at the bottom of a pressure spray dryer is connected to cyclones and a fine powder returning line from the cyclones is connected to an in-house type fluidized bed to quickly stabilize the fluidized bed in its startup. CONSTITUTION:An exhaust duct 4 at a pressure spray drying column 1 equipped with an in-house type fluidized bed 3 at the bottom is connected to cyclones 5, 5a, 5b, 5c. Fine powder recovered by the cyclones is brought, through a fine powder returning line via a changeover valve, to the top of the column 1 and the inlet and then outlet 25 of an outer fluidized bed 33. Pipes 31, 32 are connected to the fine powder returning line to blow returned powder into the fluidized bed 3, thus securing the height of the fluidized bed at its initial level in its startup.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is a multi-stage method in which milk is concentrated, the concentrated milk is pulverized by a conventional method, hot-air is used for primary drying, and the fluidized bed is used for secondary drying. The present invention relates to a spray dryer and its operating method.

[0002]

2. Description of the Related Art The types of spray dryers for producing milk powder are roughly classified into three types, namely, a parallel flow type, a counter flow type, and a mixed flow type, depending on the hot air inflow method. Of these, a multi-stage drying technique in which a fluidized bed of a co-current type spray dryer is combined and drying is performed in the fluidized bed in the reduced rate drying period has been put into practical use. The fluidized bed installed inside the spray dryer is called a built-in fluidized bed, and the fluidized bed installed once outside the spray dryer is called an external fluidized bed. Generally, the built-in fluidized bed is highly efficient because it can transfer to fluidized drying with higher water content. When a built-in fluidized bed is used, separation from exhaust air is performed in the lower part of the spray dryer, and fine powder with a relatively small particle size is accompanied by exhaust air and separated by a cyclone. This is conveyed by air with a high pressure blower,
It is a normal operation method to return to the inlet of the external fluidized bed in the normal case, or to return to the upper part of the spray mechanism in the case of producing the granulated powder, and fix the operation to either of them.

[0003]

The biggest problem in operating a built-in fluidized bed is instability at the start of operation. That is, since the particles accumulated in the built-in fluidized bed at the start of operation rely only on the classification effect of being divided into the exhaust duct in the spray drying tower and the built-in fluidized bed, it takes a very long time (1) to obtain a stable fluidized bed. Need more than time). In other words, since the amount of powder in the fluidized bed is small at the start of operation, the hot air for powder flow blows non-uniformly through the fluidized bed. A certain layer height is required to eliminate this blow through. Moreover, since the fluidization is not stable, it is affected by the static pressure fluctuation inside the spray-drying tower, and a blow-through phenomenon occurs due to the insufficient height of the bed, and the fluidization is apt to fall into failure. Once poor fluidization occurs, a flow path for air is created in the powder layer, so that it does not return to a fluidized state unless mechanical agitation is applied to the entire layer.
During that time, only part of the fluidized portion is continuously heated, and although it is overwhelmed as a whole, it causes thermal transformation due to partial overheating, resulting in deterioration of segmentation. The present invention has been made in view of the above points, and an object of the present invention is to provide a spray dryer capable of quickly stabilizing a fluidized bed at the start of operation and a method of operating the spray dryer.

[0004]

The present invention provides the following spray dryer and its operating method in order to achieve the above objects. That is, an exhaust duct connected to the bottom of a pressure spray drying tower with a fluidized bed built in at the bottom is connected to a cyclone, and the cyclone and the drying tower top, an external fluidized bed inlet, and an external fluidized bed outlet are switched valves. In what is connected by a fine powder return line through, is a spray dryer that connects the fine powder return line to a built-in fluidized bed,
In such a dryer, the fluidized bed installed at the bottom of the pressure spray drying tower is formed in a double cylinder shape, and a pipe for returning fines is attached in the tangential direction thereof, and further at the bottom of the pressure spray drying tower. The exhaust air separated from the built-in fluidized bed is guided to a cyclone through an exhaust air duct, and the fine powder contained in the exhausted air is collected, and the top of the pressure spray drying tower through a switching valve, the external fluidized bed inlet, the external type A method for operating a spray dryer in which a fine powder returning line from the fluidized bed outlet is returned toward the fluidized bed to concentrate the fine powder in the built-in type fluidized bed to stabilize the entire drying system. At the start of operation, fine powder is returned to the built-in fluidized bed only after the built-in fluidized bed stabilizes, and then fine powder return is switched to the top of the pressure spray drying tower or the inlet of the external fluidized bed to perform steady operation spray drying. It is a method of operation.

[0005]

[Operation] The exhaust air separated from the fluidized bed built in the bottom of the pressure spray drying tower is introduced into a cyclone through an exhaust duct, and the fine powder contained in the exhaust air is collected and dried at the top of the drying tower and outside the fluidized bed. The fine powder is guided from the fine powder return line leading to the inlet and the outlet of the external fluidized bed toward the built-in fluidized bed.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments will be described below with reference to the drawings.
Reference numeral 1 is a drying tower of a pressure spray dryer, which has a spray nozzle 2 at the top, and concentrated milk is sprayed into the drying tower together with the primary hot air for drying. A fluidized bed 3 having a double cylindrical shape is provided at the bottom of the drying tower 1 and has a structure described later. An exhaust duct 4 communicating with the built-in fluidized bed is connected to the cyclones 5, 5a, 5b, 5c, and the exhaust air is exhausted from the exhaust blower 6 to the pipe 7
And it is connected to the exhaust duct 4 through a cyclone.
The fine powders collected by the cyclones 5, 5a5b, 5c are blowers 8, 9 through the pipes 10, 11 and the switching valve 12,
The fine powder is sent from the switching valves 12 and 13 to the top of the drying tower through the pipe 14 by being guided to 13. In addition, the switching valves 12, 13 to the pipes 15, 54
Through the outlet 25 of the external fluidized bed 33 through the pipe 1
From the midpoints of 5 and 45, it is guided to the inlet of the external fluidized bed 33 through the pipes 24 and 18 through the switching valves 16 and 17. The built-in fluidized bed 3 has a blower 19 to a heater 2
Hot air for fluidizing the powder is sent through the pipe 21 through 0.
The built-in fluidized bed 3 has a double cylindrical shape as shown in FIGS. 2 and 3, and the inner cylinder 35 is connected to the exhaust duct 4.
Hot air from the blower 19 is guided into the outer cylinder 36 via the punching metal 39. The powder collected in the built-in fluidized bed 3 overflows from the weir 34, flows into the outer fluidized bed 33 from the outer fluidized bed inlet pipe 40, and cool air is blown from the blowers 55 and 56 through the coolers 22 and 23 to the pipe 44. , 45 cools the external fluidized bed 33, so that the powder is cooled.

The weir 34 moves back and forth by the rod of the cylinder 43. The cylinder 43 is attached to the external fluidized bed inlet pipe 40, and the size of the weir 34 is such that the overflow is left above the slit 41 of the drying tower 1 to close the slit. Therefore, during operation, the weir 34 closes the slit and only overflows are poured into the external fluidized bed 33. When the operation is stopped, the weir 34 is opened by the cylinder 43 so that the entire powder is poured into the external fluidized bed 33. Next, warm air is blown from the blower 27 shown in FIG.
The hot air is blown into the drying tower 1 from the powder adhesion preventing nozzle provided in the middle part of the blower. The blowing direction is the same as the swirling direction of the powder.

According to the present invention, in the above-mentioned spray dryer, the return powder is sent from the switching valves 29 and 30 through the pipes 31 and 32 into the built-in fluidized bed 3. As shown in FIG. 3, the pipes 31 and 32 are connected to the pipes 37 and 38 to return tangentially and downward to the outer cylinder 36 of the built-in type fluidized bed so that the powder is blown into the built-in type fluidized bed 3. There is.

The concentrated milk sprayed on the drying tower 1 (water content 5
0-60%) is dehydrated and dried instantaneously from the primary hot air (water content 5
~ 7%), part of which falls directly into the built-in fluidized bed 3, and part of which is accompanied by exhaust air from the exhaust duct 4 to the cyclone 5, 5
a, 5b, 5c. The fine powder discharged along with the exhaust air is separated into the exhaust air and the fine powder by the cyclones 5, 5a, 5b and 5c, and the fine powder is carried by the high pressure blowers 8 and 9 in the pipes 10 and 11 by air flow. This transfer line is called a fine powder return line, and the switching valves 12, 13 and 29, 3
When 0, the operation method of returning the whole amount to the built-in type fluidized bed 3 is adopted. After confirming that powder has accumulated in the built-in fluidized bed 3 after a certain period of time and has reached a good flow state, that is, the weir 3
After confirming that the powder overflowed from No. 4 and flowed into the outflow fluidized bed 33, normal powder (average particle size 50 to 80
In the case of (um), switching valves 29 and 30 are switched, and valve 1
6 and 17 are switched to change from pipes 15 and 54 to pipe 18,
The fine powder is returned to the inlet of the external fluidized bed via 24. In this way, the fine powder return line is switched to start steady operation. In the case of semi-granulated powder (average particle diameter 90 to 160 um), the fine powder return line is fixed to the built-in fluidized bed without switching and steady operation is performed. That is, the switching valves 12, 13, 29, 30
Then, the fine powder is returned to the built-in fluidized bed 3, and the fine powder overflowing from the weir 34 is cooled by the external fluidized bed 33 through the pipe 40 and discharged. At this time, the grain size can be adjusted by changing the height of the weir 34. Instant milk powder (granulated powder average diameter 16
In the case of 0 to 260 μm), the granulation is performed by returning to the spraying zone of the atomizing nozzle (desk atomizer). That is, the fine powder is returned from the switching valves 12 and 13 through the pipe 14 to the nozzle 2 at the top of the drying tower.

At the end of the operation, the fine powder return line is switched to the outlet side of the external fluidized bed after spraying the concentrated milk by any operation method, and then the weir 34 is opened in the order of the internal fluidized bed and the external fluidized bed to discharge the powder. That is, the switching valves 12, 1
3, 29, 30 and 16, 17 by switching the pipe 15,
The powder is discharged from 45 to the outlet 25 of the stationary fluidized bed. In this case, the powder of the built-in type fluidized bed 3 is made to flow through the weir 34 so that the powder flows into the external type fluidized bed 33. At this time, the discharge speed is temporarily increased, which may overload the shifter, the transport system, and the like after the external fluidized bed. At this time, as a refuge, the fine powder return line can be switched to a built-in fluidized bed to reduce the load. This can also be applied when an abnormality occurs in the shifter, the transfer system, etc. after the external fluidized bed during normal operation. That is, this is performed by switching the switching valves 12, 13, 29, 30 and opening the pipes 31, 32. As a result, the exhaust duct 4 moves to the cyclone 5, 5
This is done by constructing a circulation circuit that goes from the fine powder returning lines 10 and 11 via a5b and 5c to the exhaust duct again through the pipes 31 and 32.

According to the present invention, the bed height of the built-in fluidized bed can be first secured at the start of the operation by installing the inlet of the fine powder return line in the built-in fluidized bed. , 38 are the outer cylinders 36 as described above.
It flows in tangentially to and has a slight downward angle. This is to reduce the accumulation of powder in the pipes and CI
This is for draining after P. The inflow from the tangential direction gives a rotational force to the entire fluidized bed of powder, which is an air dispersion plate at the bottom of the fluidized bed, that is, an anti-adhesion air blowout installed in the punching metal 39 or the middle portion of the spray dryer main body. The direction of rotation of the nozzle ring 26 is matched.

FIG. 5 shows a case in which the fine powder is returned to the built-in fluidized bed at the start of operation, and then the fine powder return line is switched to the external fluidized bed after the height of the bed is constant and when the fine powder is returned to the external fluidized bed from the beginning. The result of having measured the change with time of the bed height of a mold fluidized bed is shown. From this result, it is apparently effective to return the fine powder to the built-in fluidized bed.
While it was in a stable steady state at 0 minutes, it is hard to say that it is still stable at 60 minutes when returning to the external fluidized bed from the beginning.

[0013]

According to the conventional multi-stage spray dryer, stable operation of the built-in fluidized bed is considered to be quite difficult. However, as in the present invention, the inlet of the fine powder return line is installed in the built-in type fluidized bed, and the fluidized bed is stabilized by first ensuring the bed height of the built-in type fluidized bed at the start of operation, and thereafter the fine powder return line No matter where you switch to, stable operation is possible. In addition, since the built-in fluidized bed can be used as a temporary balance tank, emergency response can be carried out quickly and safely.

[Brief description of drawings]

FIG. 1 is an overall schematic diagram of a multi-stage drying system.

FIG. 2 is a plan view of a built-in fluidized bed.

FIG. 3 is a front view of the above.

FIG. 4 is a sectional view of a weir portion.

FIG. 5 is a diagram showing a change with time of the bed height of the built-in type fluidized bed from the start of spraying.

[Explanation of symbols]

 1 Drying Tower 2 Spray Nozzle 3 Built-in Fluidized Bed 4 Exhaust Duct 5 Cyclone 12 Switching Valve 13 Switching Valve 16 Switching Valve 17 Switching Valve 29 Switching Valve 30 Switching Valve 31 Fine Powder Return Line 32 Fine Powder Return Line

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryoji Machida 1067 Suwa, Takatsu-ku, Kawasaki-shi, Kanagawa No. 401 Snow Brand Company House (72) Inventor Eiichi Kojima 3-12-3, Takuhoku, Kita-ku, Sapporo, Hokkaido (72) Invention Takeyoshi Yoshiyuki Horonobe 155-1 Horonobe-cho, Teshio-gun, Hokkaido

Claims (4)

[Claims] 1. A cyclone is connected to an exhaust air duct connected to the bottom of a pressure spray drying tower having a fluidized bed built in at the bottom, and the cyclone and the top of the drying tower, an external fluidized bed inlet, and an external fluidized bed outlet are provided. A spray dryer in which the fine powder return line is connected to a built-in fluidized bed in which the fine powder return line is connected via a switching valve. 2. The spray dryer according to claim 1, wherein the fluidized bed installed at the bottom of the pressure spray drying tower is formed in a double cylindrical shape, and a fine powder returning pipe is attached in a tangential direction thereof. 3. Exhaust air separated from a fluidized bed built in the bottom of a pressure spray drying tower is introduced into a cyclone through an exhaust duct, and fine powder contained in the exhaust air is collected and pressure is applied through a switching valve. From the fine powder return line leading to the top of the spray drying tower, the inlet of the external fluidized bed, and the outlet of the external fluidized bed, the fine powder is guided toward the fluidized bed and the fine powder is concentrated in the built-in fluidized bed to stabilize the entire drying system. How to operate the spray dryer. 4. The steady operation is carried out by returning fine powder to the built-in fluidized bed only when the operation is started and then switching the fine powder return to the top of the pressure spray drying tower or the inlet of the external fluidized bed after the built-in fluidized bed is stabilized. A method for operating the described spray dryer.