JP3034974B2 - Droplet diameter control method for pressurized two-fluid nozzle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a droplet diameter of a pressurized two-fluid nozzle incorporated in a spray dryer or the like.

[0002]

2. Description of the Related Art Conventionally, a spray drier uses a rotating disk (rotating disk), a two-fluid fine particle jet nozzle, and a pressurizing swirl nozzle. The rotating disk is easy to change the particle size, switch between spraying water and stock solution, and change the throughput, but requires a high-speed rotating machine and is not easy to maintain. The two-fluid fine spray nozzle is of a so-called atomizing type, which atomizes a stock solution by a high-speed air flow, but requires a large amount of high-pressure air, and has a drawback that the operating cost is increased. Therefore, it is common to use a pressurizing swirl nozzle as much as possible.

A pressurizing swirl nozzle imparts swirl to a pressurized liquid, and conveys the liquid from an orifice into a thin film of a conical ring (H).
The liquid film is ejected in the form of an "low cone", and at the leading edge of the conical ring, the liquid film is disturbed by the interaction with air, splits, and forms fine particles. With a pressurized swirl nozzle,
The droplet diameter of the spray is adjusted according to the magnitude of the pressure applied to the liquid.However, when the pressure is changed, the liquid flow rate changes.Therefore, by adjusting the spray pressure and the combination of the nozzle parts, the liquid flow rate is kept constant. It keeps and controls the droplet diameter.

[0004]

However, this adjustment method requires a large number of nozzle parts, it is impossible to continuously produce parts, and requires skill and know-how in selecting nozzle parts. And Also, the viscosity of the liquid,
Concentration, surface tension, and the like may change during operation, and the operation must be stopped once for replacement of nozzle parts. The present invention has been made in view of such a conventional problem, and does not require replacement of nozzle parts, and continuously adjusts and controls the droplet diameter while maintaining a constant liquid flow rate and liquid pressure. It is an object of the present invention to provide a control method capable of performing the control.

[0005]

In order to achieve the above object, the present invention provides a pressure swirling nozzle for pressurizing a liquid and a high-speed gas blowing cylinder provided around the pressure swirling nozzle. A pressurized two-fluid nozzle having a tapered tip, wherein the diameter of the spray droplets formed is controlled by adjusting the flow rate of the high-speed blown gas. The present invention provides a method for controlling a droplet diameter in the above.

[0006]

The pressurized two-fluid nozzle of the present invention is an improvement of the pressurized swirl nozzle, and therefore basically has the performance of the pressurized swirl nozzle. The empirical formulas (expressions 1 and 2) relating to the spray characteristics applied to the pressurizing swirl nozzle are as follows.

[0007]

(Equation 1)

(Equation 2)

As is clear from equations (1) and (2), if the spray pressure P is determined, the droplet diameter _DD and the liquid flow rate W are uniquely determined, but if the liquid pressure P decreases, the liquid flow rate W is proportional to this. And the droplet diameter D _D increases in inverse proportion. The large droplet diameter is further atomized by the high-speed gas flow.

That is, the pressurized two-fluid nozzle has two atomization stages. First, the primary atomization is performed by the pressure of the liquid itself of the pressure swirl nozzle for setting the initial conditions. At this time, the above equations 1 and 2 are applied. The state of the primary atomization in which the liquid is ejected in a conical annular shape from the orifice of the pressurized two-fluid nozzle is as shown in FIG.

Next, in the present invention, the high-speed gas blown from the tip of the blow-off tubular body is intensively collided with the primary atomized liquid droplets to make them secondary fine. Thus, the liquid pressure P is lowered, even those that droplet diameter D _D becomes large, it is possible to atomization by the action.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the illustrated embodiments, but the present invention is not limited to these embodiments. FIG. 1 is a sectional explanatory view showing an example of the pressurized two-fluid nozzle of the present invention, and FIG.

In the pressurized two-fluid nozzle shown in FIGS. 1 and 2, a jacket pipe 3 is provided around a liquid pipe 5 having a pressurizing swirl nozzle 6 at the tip, and the tip of the jacket pipe 3 is squeezed. It has a tapered structure. In the figures, 1 is a liquid pump, 2 is a roots blower, 4
Indicates an air nozzle.

[0013] As described above, since the cross-sectional area of the leading end opening of the jacket pipe 3 in the pressurized two-fluid nozzle is small,
The high-speed gas is accelerated and expanded by the air nozzle 4 at the opening. Due to the acceleration and expansion of the gas, the primary atomized liquid of the thin film which is extruded while being swirled in a conical ring from the orifice provided at the center of the tip of the pressure swirl nozzle 6 is further atomized (secondary atomization). Will be done. Here, as described above, there is a correlation between the droplet diameter of the secondary spray and the gas flow velocity.

Hereinafter, specific experimental examples will be described. (Experimental Example 1) The relationship between the gas flow rate and the droplet diameter was experimentally confirmed under the condition that the liquid pressure was constant. In the experiment, an SX nozzle manufactured by Spraying System Co., Ltd. was used as a pressurizing swirl nozzle, room temperature water was used as a liquid, and a normal temperature air was used as a gas. / Cm
^{(2) While} keeping the pressure constant, the flow rate of the blown air was changed by changing the air pressure in the jacket pipe 3, and the air flow rate and the average droplet diameter of the spray were measured. To measure the water droplet diameter,
A particle size distribution analyzer (LDSA-1300A type, manufactured by Tonichi Computer Co., Ltd.) using a laser light scattering method was used. Table 1 shows the conditions used in the experiment.

[0015]

[Table 1] Table 2 shows the measurement results of the air flow velocity and the average droplet diameter of the spray.

[0016]

[Table 2]

As is clear from the above, the tendency that the average water droplet diameter is reduced by increasing the air flow velocity can be read from the above measurement results. Further, although not shown in Table 2, the blown air flow rate was 20 to 200 m / s.
By adjusting the jacket pipe 3
It was confirmed that by adjusting the internal air pressure in the range of 0.05 to 5 kg / cm ² , it was possible to control the water droplet diameter of the spraying, but the present invention is not limited to these. It may be used outside the above numerical range.

(Experimental Example 2) A spray-drying test was performed using a solution in which a natural polysaccharide was dissolved as the solution. Table 3 shows a comparison between the case where the pressurizing swirl nozzle without blown air alone is used and the case where atomization is further performed by the pressurized two-fluid nozzle.

[0019]

[Table 3]

(Experimental Example 3) Using a pressurized two-fluid nozzle having a large capacity nozzle with an orifice diameter of 4.0 mm of a pressure swirl nozzle, a low-pressure stock solution is sprayed to obtain a target small droplet diameter. did it. The air nozzle diameter is 23 mm. Table 4 shows the measurement results at that time.

[0021]

[Table 4]

[0022]

As described above, according to the present invention,
Compared to the conventional method of controlling the diameter of spray droplets by adjusting the liquid pressure inside the pressure swirl nozzle, it does not require many nozzle parts, does not require know-how to select a combination of nozzle parts, and has a temporary Since the droplet diameter can be controlled without the need to stop the operation, a required product particle size can be obtained, and it is possible to cope with various types.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view showing an example of a pressurized two-fluid nozzle of the present invention.

FIG. 2 is a partial cross-sectional explanatory view showing a tip portion of the nozzle device of FIG. 1;

FIG. 3 is an explanatory diagram showing a state of primary atomization in which a liquid is ejected in a conical annular shape from a pressurizing swirl nozzle.

[Explanation of symbols]

 Reference Signs List 1 liquid pump 2 roots blower 3 jacket pipe 4 air nozzle 5 liquid pipe 6 pressure swirl nozzle

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-194901 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B05B 7/10 B01D 1/20

Claims (1)

(57) [Claims] 1. A pressurized two-fluid nozzle comprising a pressure swirl nozzle for liquid pressurized blow-off and a high-speed gas blow-off tubular body provided around the pressure swirl nozzle, the tip of which is tapered. A method for controlling a droplet diameter of a pressurized two-fluid nozzle, wherein a droplet diameter of a formed spray is controlled by adjusting a flow velocity of a blowing high-speed gas.