JPH0751201B2 - Evaporative solution evaporation method - 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 evaporating a foamable solution which suppresses foaming and evaporates the solvent particularly in operations involving boiling such as evaporative concentration of a highly foamable solution, solvent recovery and distillation.

[0002]

2. Description of the Related Art In the process of concentrating a foaming solution, an evaporative concentration operation is often performed. When the evaporate becomes a product, the method of suppressing foaming can be applied by using an antifoaming agent, but when the concentrate becomes a product, the antifoaming agent cannot be used in many cases. If it is an important factor, the inclusion of antifoaming agents is not allowed. Examples include saccharides, surfactants, and evaporative concentration operations of aqueous paste solutions.
As a method of suppressing foaming without mixing an antifoaming agent or the like, there is a method of avoiding boiling in a liquid and only surface evaporation. In this case, the thin film evaporation method or the like is adopted because the evaporation surface area is insufficient in a normal evaporation can. However, this thin film evaporation method does not result in complete surface evaporation unless it is in a high vacuum state, and it is difficult to apply it to suppress foaming of a highly foamable solution.
Therefore, conventionally, as exemplified in Japanese Utility Model Laid-Open No. 58-58116, by rotating the evaporation surface like a centrifugal thin film evaporator, a shearing force is applied between the liquid surface and the evaporated vapor to suppress foaming. is doing. In addition, as illustrated in Japanese Utility Model Laid-Open No. 2-40403, a pressure injection nozzle such as a spray nozzle is provided in the upper portion of the evaporation can, and the liquid to be degassed is sprayed through the nozzle to form droplets. There is also known a method of increasing the evaporation surface area and applying a shearing force between the droplet surface and vapor depending on the jetting speed of the droplet to suppress foaming.

[0003]

However, the former method is not economical when a high vacuum state must be obtained, the apparatus is expensive, and the processing capacity is small and the processing amount is large. In the latter method, most of the pressure loss in the pipe from the heater to the pressure injection nozzle is the injection pressure of the pressure injection nozzle, so the pressure at the pressure injection nozzle inlet is the vaporizer pressure, that is, the evaporation pressure. Since the temperature is considerably higher than the above, the ratio of evaporation of the heating liquid in the pipeline up to the pressure injection nozzle is small, or no vapor phase is generated. For this reason,
Most of the evaporation will be performed by flash evaporation from the same nozzle and evaporation from the surface of the droplet after it exits the nozzle. However, in the case of the pressure injection nozzle, since the amount of superheat in the state of droplets is large and the flight speed of the droplets is high, the droplets ejected from the pressure injection nozzle reach the liquid surface of the evaporator. It takes a short time to reach the liquid surface in a state of superheated liquid without sufficient evaporation to lose the amount of heat of superheat. Therefore, the liquid in the evaporator becomes superheated liquid, causing boiling evaporation near the liquid surface and foaming. Although it is conceivable to make the droplet diameter smaller in order to complete the evaporation before the droplets reach the liquid surface, in addition to flash evaporation from the pressure injection nozzle, mist is further increased and operation is Cause trouble. The method of increasing the distance between the liquid surface and the nozzle not only increases the height of the evaporator, but also increases the diameter of the evaporator to prevent droplets from colliding with the side wall surface of the evaporator and boiling or foaming. Also has to be large, which creates problems from economics. Also, by reducing the degree of superheat of the liquid in the heater, if it is attempted to complete the evaporation by the time the droplets ejected from the pressure injection nozzle reach the droplets of the evaporator, In order to evaporate, the amount of circulating liquid must be increased from several times to several tens of times, and in this case, the apparatus becomes large, which is not economical. There is also a method of mechanically striking the bubbles on the liquid surface with a paddle or the like, or spraying droplets having a boiling point or less to give a strong shearing force to the bubbles to destroy the bubbles (Actual No. 52-51331). However, there are drawbacks such as lack of certainty, complicated apparatus, and poor thermal efficiency. There is also a method in which inert gas or steam is sprayed on the foam to dry and break the foam surface (JP-A-59-59).
No. 111914, Japanese Utility Model Laid-Open No. 62-199103 and the like. However, there are drawbacks such as a large condenser for evaporated vapor and poor thermal efficiency.

The present invention solves the above problems,
It is an object of the present invention to provide a method for evaporating a foaming solution that can suppress foaming efficiently and economically without adding a chemical substance such as an antifoaming agent.

[0005]

In order to achieve the above object, the present invention has a steam outlet in the upper part of the inside of a can and
The effervescent solution has a liquid outlet on the bottom,
After being supplied to the heater through the pump and overheated to the specified temperature
Then, through the pipe, the liquid phase part from the top of the evaporation can to the bottom of the can
Is jetted toward the liquid droplets and reaches the liquid phase portion at the bottom of the can.
At the same time, the solvent is evaporated and removed from the vapor outlet.
In the method of evaporating a foamable solution,
Part is located toward the liquid phase part at the bottom of the can
In the heater, which has a substantially cylindrical tube end connected
Flow rate of foaming solution and superheat temperature at the outlet of the heater
By controlling the above, the foaming solution overheated by the heater is vaporized in the pipe leading to the pipe end to form the gas-liquid mixed phase, and the gas-liquid mixed phase near the pipe end. The flow form of is an intermittent flow or an annular flow ,
Most of the amount of residual heat of superheat in the droplets ejected from the pipe end can
As the latent heat of vaporization in the gas phase part up to the liquid phase part of the inner bottom
The gist is to release it to complete boiling . Further, as a more specific evaporation method of the present invention, it is preferable that the straight pipe portion reaching the pipe end is a twisted pipe. In addition,
The "intermittent flow or annular flow" referred to in the present invention means wine wine.
N. et al. (Int. J. Multiphase Fl
ow Vol. 11, No. 6, 1985)
It is the content.

[0006]

When the highly foamable liquid is boiled below the liquid surface, it is always foamed and bubbles are accumulated in the vapor phase portion of the evaporator, which makes the evaporation operation difficult. Therefore, the method to be adopted when the defoaming agent cannot be used is either surface evaporation, breaking the foam by applying shearing force to the foam on the surface, or drying the foam to break the foam. It is. In the present invention, the superheated liquid is vaporized in the pipe to apply a shearing force to the surface of the gas-liquid mixed phase flow and the surface of the non-liquid by a velocity difference between the gas and the liquid to suppress foaming in the pipe. More specifically, most of the evaporation is carried out in the pipe, but a pipe end is provided at the vapor phase part of the evaporator so that the remaining evaporation is easily performed, and droplets are generated by the jetting force of the evaporated vapor. The surface area is increased and the evaporation is completed by the time the droplet reaches the liquid surface under the evaporator. As described above, in order to cause most of the evaporation in the pipe and generate droplets by jetting from the pipe end, a pressure jet nozzle such as a spray nozzle is not used as in the past, and a circular pipe or twisted pipe is used. One or more pipe ends obtained by cutting a straight pipe are provided in the vapor phase part of the evaporator, and the flow mode of the gas-liquid mixed phase flow near this pipe end is an intermittent flow or an annular flow. It has been found that this can be easily achieved by controlling the operation. The present invention has been achieved based on the above test results. In chemical engineering, the flow pattern of the gas-liquid mixed phase flow in the downward flow is generally classified as shown in FIG. The figure (a) shows falling film flow, the figure (b) shows bubble flow, the figure (c) shows plug flow, the figure (d) shows chain flow, the figure (e) shows semi-plug flow, the figure (f). ) Is an annular flow, (g) is a mound flow, and the flow forms from (c) to (e) are collectively called an intermittent flow.

The flow mode of the gas-liquid multiphase flow in the pipe depends on the inner diameter of the pipe D [m] and the physical properties of the liquid to be evaporated next: vapor density ρ _G [kg / m ³ ] liquid density ρ _L [kg / m ³ ] Liquid viscosity μ _L [kgm / m · se
c] If the surface tension σ _L [kg / m] is determined, it is determined by the operating condition, that is, the vapor empty space velocity U _G [m / sec], and the liquid empty space velocity U _L [m / sec]. The formulas for the boundaries of bubbly flow, intermittent flow, annular flow and mound flow are D, ρ _G , ρ _L , μ _L ,
shown as a function of σ _L , U _G , U _L (Two-phase Flow Patterns
and Void Fractions in Down
ward Flow; Int. J. Multiphas
e Flow V ol. 11, No. 6, 1985). In the case of vertical downflow, it is given by the following equations (1) to (7). Boundary equation of mound flow with intermittent flow and annular flow ΔP _L = 2.89 [(ρ _L −ρ _G ) gσ _L ] ^0.5
(1) Boundary equation of annular flow and intermittent flow and falling film flow 1.9 (U _G / U _L ) ^0.125 = K _uG ^0.2 F _rG
^0.36 (2) Boundary equation of falling film flow with intermittent flow and bubbly flow F _rG = 0.43426 (U _G / U _L ) ^1.1
(3) Boundary equation between bubbly flow and intermittent flow F _rG = 0.117 (U _G + U _L ) ^1.6 (gD)
^-0.8 (4) _{where, K uG = U G ρ G} 0.5 [(ρ L -ρ G) gσ L]
^-0.25 (5) _FrG = U _G (gD) ^-0.5
(6) ΔP _L = 2fρ _L U _L ² / D
(7) f is a pipe friction coefficient. g is the gravitational acceleration. In the evaporation method of the present invention, if the type and concentration of the effervescent liquid and the number of pipe ends N [-] pipe end inner diameter D [m] operating pressure P [Torr] are determined, the physical properties of the vaporized liquid Molecular weight M [−] Latent heat of vaporization H [kcal / kg] Boiling point temperature T [° K] Specific heat of liquid C _PL [kcal / kg ·
deg] is determined, the tube is determined only by the flow rate of the foaming solution at the heater inlet, the temperature difference between the liquid temperature at the heater outlet and the boiling point of the liquid at the operating pressure of the evaporator, that is, the superheat temperature ΔT [° C]. The liquid flow rate and vapor flow rate per end are determined.
Therefore, U _G and U _L can be decided and the flow state can be specified. Here, the flow rate of the foaming solution at the inlet of the heater is divided by the number of pipe ends and the flow passage cross-sectional area of the pipe end to obtain the virtual empty liquid flow velocity U _LO of the foaming solution at the pipe end. [M / sec], the liquid temperature at the heater outlet and the operating pressure P of the evaporator
If the temperature difference from the boiling temperature of the liquid at [Torr] is taken as the superheating temperature ΔT [° C], the flow mode of the gas-liquid multiphase flow can be obtained regardless of the number N of end pipes by modifying the above equation of the flow mode boundary line. The distribution can be derived as a function of ΔT and U _LO . That is, the ratio V _f of the generated steam flow rate to the liquid flow rate per tube end is V _f = C _PL ΔT / H, assuming that the entire superheat flow rate at the superheat temperature ΔT is consumed as evaporation latent heat.
Since it is given by (8), the boundary equation (1) between the mound flow and the intermittent flow and the annular flow is F _d = 1.7 [(ρ _L −ρ _G ) gσ _L ] ^0.25
(9) U _LO = F _d / [(2f) ^0.5 (1-V _f )]
(10) The boundary equation (2) of the annular flow with the intermittent flow and the falling film flow is F _a = 169.84 (ρ _G / ρ _L ) ^3.48 (gD)
^{_{1.44 X [(ρ L -ρ G}} ) gρ L / ρ G 2] 0.4 (1
1) U _LO = [F _a V _f / (1-V _f )] ^{1 / 4.48} / V
_f (12) The boundary equation (3) between falling film flow and intermittent flow and bubbly flow is F _f = 0.4343 (gD) ^0.5 (ρ _L / p _G )
^0.1 (13) U _LO = F _f V _f ^0.1 (1-V _f ) ^-1.1
(14) The boundary expression (4) between the bubbly flow and the intermittent flow is F _b = [(ρ _L /0.117ρ _G )] ^5/3 (gD)
^{_{0.5 (15) U LO = F}} b V f -1 [(ρ L -ρ G) / ρ G + 1 / V
_f ] ^−8/3 (16).

FIG. 4 shows that the saponin 2.5% aqueous solution is completely heated in a vertical tube having an inner diameter of 25 mm at an operating pressure of 50 Torr by using the equations (8) to (16) as the boundary of the flow pattern. It shows the distribution of the flow morphology of the vertical downward flow when it is evaporated. However, in actual operation,
Due to the pressure loss in the pipe, the amount of superheat corresponding to ΔT cannot be completely evaporated before reaching the pipe end.
Therefore, in FIG. 4, the superheat temperature Δt is considered to be the temperature difference between the liquid temperature at the superheater outlet and the liquid temperature at the pipe end, and the operating pressure P is considered to be the vapor pressure relative to the liquid temperature at the pipe end. Corresponds to the case. Let the operating pressure be the operating pressure P of the evaporator, and use the temperature difference ΔT between the liquid temperature at the outlet of the superheater and the boiling point of the liquid at the operating pressure of the evaporator as the superheat temperature to determine the actual flow pattern distribution. When obtained based on the test results, FIG. 4 is modified as shown in FIG.

As shown in FIG. 5, when the superheat temperature and the virtual empty liquid velocity are relatively small, a falling film flow occurs. When the virtual empty liquid velocity is high and the superheating temperature is high, a spray flow results. When the superheat temperature is relatively low in the range where the virtual blanket liquid flow velocity is faster than the falling film flow, it becomes a bubble flow.However, as the virtual empty liquid flow velocity becomes faster, the pressure loss in the pipe increases, so the superheat temperature is increased. Even if it is increased, the steam ratio in the pipe does not increase, and the range of bubbly flow is widened. As the superheat temperature is made higher than that of the bubbly flow, the state becomes an intermittent flow through a transition state. If the amount of superheat is further increased compared to the falling film flow or the intermittent flow, an annular flow is formed. In the case of intermittent flow or annular flow, most of the evaporation is done in the pipe and is discharged from the pipe end with an appropriate spread of the injection angle with an appropriate injection force, resulting in droplets of appropriate size with less mist and lower part of the evaporator. It was confirmed that the amount of heat of superheat was lost by the time the liquid level reached to the end and boiling evaporation was completed, and neither boiling nor bubbling occurred on the liquid level of the evaporator. The intermittent flow is further classified into plug flow, yarn flow and semi-plug flow. In the case of the semi-plug flow, it has been found that even if the flow form changes depending on the change of operating conditions, it is in the range of chain flow, plug flow (slug flow) or annular flow, and stable operation can be performed without foaming. However, in the case of the plug flow (slug flow) and the chain flow, in which the heating amount is smaller than that of the semi-plug flow, good operation is possible as in the semi-plug flow if the flow form is stable, but slight fluctuations in operating conditions At the transitional area with the bubbly flow, the jet angle of the liquid droplet becomes narrow and approaches the liquid column jet. Therefore, this liquid column collides with the liquid surface of the evaporator and foaming occurs due to the inclusion of bubbles.

As an actual operating condition, even if some foaming occurs, it is possible to operate unless the bubble layer speed due to the collision of the droplets and the foaming rate are balanced so that the bubble layer has a certain height or more. Therefore, it is possible to operate in the range of plug flow (slag flow) and yarn flow. The bubbly flow occurs when the amount of superheat is smaller than that in the intermittent flow, or when the virtual empty liquid velocity is high and the pipe resistance is large, so that sufficient evaporation is not performed. In the case of this bubbly flow, the gas-liquid mixed phase flow discharged from the pipe end becomes a liquid column containing bubbles or droplet ejection with almost no spread angle, and the evaporation surface area is small and the liquid surface from the pipe end to the liquid surface below the evaporator can It cannot release the amount of heat of superheat in the process. When the amount of superheat is reduced, the liquid that comes out of the pipe end does not have the amount of superheat, and the liquid does not evaporate after returning to the liquid surface at the bottom of the evaporator. Since it becomes a liquid column and reaches the liquid surface under the evaporation can, it entrains vapor at the liquid surface and foams. If sufficient evaporation is not performed due to the large piping resistance, the liquid that comes out of the pipe end has a superheat amount of heat and becomes a liquid droplet jet from the pipe end that does not have a liquid column or a spread angle, There are both a phenomenon in which vapor is entrained on the liquid surface to reach the liquid surface in the lower portion of the evaporator and foaming occurs, and a phenomenon in which the liquid evaporates by boiling after returning to the liquid surface in the lower portion of the evaporator can. When the flow velocity of the virtual hollow liquid is slow and the amount of heat of superheat is smaller than that of the annular flow, the falling film flow occurs. In this case, since the amount of the liquid is small, the liquid flows in a thin film on the pipe wall in a state close to the natural flow, and the steam flows in the central portion of the pipe. Therefore, even when the steam flow passage cross-sectional area is relatively large and the amount of superheat is large, the flow velocity of the steam is relatively slow and the jetting force at the pipe end is small, resulting in relatively large liquid droplets in a state close to free fall. It falls on the lower liquid surface. In this case, boiling loss is completed in the pipe because the pressure loss in the pipe is small. However, since the shearing force at the gas-liquid interface is small, it may foam when boiling and evaporating in the pipe and discharge bubbles from the pipe end. In addition, since the droplet diameter is relatively large, foaming due to the entrainment of steam is observed when the droplet drops onto the liquid surface below the evaporator. When the virtual empty cylinder liquid flow velocity becomes faster, it becomes a spray flow.
In actual operation, when the evaporation pressure is lower than atmospheric pressure and the amount of superheat is small, when the liquid flow rate is high, the amount of vapor generated in the pipe is small due to the pressure loss in the pipe, and the state of the spray flow is unstable and It may be in a fluidized form and foam at this time.
When the vapor pressure is higher than atmospheric pressure, the amount of superheat is considerably large, and a stable atomization flow state is observed only when the flow rate of the supply liquid is large. In this case, evaporation occurs in the pipe, but since the pipe resistance is large, a superheat amount remains at the pipe end.
However, since the droplet diameter of the jet is small, the amount of superheat is lost and the boiling evaporation is completed by the time it reaches the liquid surface in the lower portion of the evaporator. The disadvantages in this case are that the device becomes a pressure vessel due to pressure evaporation, the amount of mist increases, and the bubbles generated on the liquid surface under the evaporation can due to fluctuations in evaporation pressure due to fine droplets. The point is that there is no action of breaking bubbles due to the collision of the ejected droplets.

From the above, specific conditions for designing an evaporator are as follows: operating pressure, pipe end diameter and number of pipe ends in consideration of thermal stability of foaming solution, treatment amount, change in physical properties due to concentration, etc. Was determined and a flow morphology distribution map as shown in Fig. 5 was created from the physical properties of the foaming solution, and the liquid flow rate U _L0 [m / sec] and the superheat temperature ΔT [° C] on the boundary line between the intermittent flow and the annular flow. It is preferable to adopt and.

[0012]

FIG. 1 shows an example of an evaporator used in the evaporation method of the present invention. In addition, although an evaporative concentration example of a saponin 2.5% solution is shown as an example of the effervescent solution in the examples, the present invention is not limited to this example and can be applied to various effervescent solutions. The evaporator shown in FIG. 1 has an evaporator 1 arranged in a substantially vertical state, a heater 3 for heating a saponin solution supplied by a circulation pump 2, and a solution heated by the heater 3 to the evaporator 1. A pipe 4 for guiding, four pipe ends 5 attached to the upper part of the evaporator 1 and connected to the pipe 4, a flow meter 6 for adjusting the flow rate of the solution supplied to the heater 3, and a heater. The temperature detector 7 and the like provided at the outlet of 3 are provided. The evaporator 1 has an inner diameter of 1400 mm and a straight body length of 1500 mm, and has a vapor outlet 1a provided in the vapor phase portion in the upper part of the can and a liquid outlet 1b provided in the bottom of the can. , Has a schematic structure in which each pipe end 5 is arranged toward the liquid phase portion at the bottom of the pipe. Each pipe end 5 has a cylindrical shape with an inner diameter of 25 mm, and although only two pipe ends are shown in the figure, the pipe ends 5 are arranged substantially parallel to each other and are inserted into the can with the upper end portion joined to the pipe 4. There is. A thermometer 10 was installed at the injection port of the tube end 5 so that the temperature TI of the superheated steam injected from the tube end 5 could be measured from outside the can. The solution at the bottom of the can is supplied into the heater 3 by the circulation pump 2 through each pipe. In this case, the circulation pump 2 has a pipe end 5
The capacity type pump is used in order to avoid the flow rate change due to the fluctuation of pressure loss etc. up to the maximum, and it can be controlled by the inverter 8 and the flow meter 6 to keep the supply amount to the heater 3 constant. ing. The heater 3 uses steam or the like as a heat medium, and the outlet temperature of the heater is detected by a temperature detector so that the outlet temperature of the heater becomes constant with respect to the boiling point of the solution, and the temperature controller TIC7 supplies the flow rate of steam. Is controlled by the adjusting valve 9 to heat the boiling point liquid so that the amount of heat for heating is constant, and the superheated liquid has a superheating temperature of 15 ° C. The superheated liquid leaving the heater 3 is jetted from each pipe end 5 via the pipe 4. The sprayed mixture of vapor and droplets is separated in the vapor phase portion above the can, the droplets reach the liquid surface, and vapor containing mist enters the mist separator 11 from the vapor outlet 1a through a pipe. Here, after mist in the steam is separated, it is condensed in the condenser 12 and taken out of the system by the discharge pump 14 via the receiving tank 13. The mist separated by the mist separator 11 becomes a drain and is returned to the evaporator 1 via a pipe. The upper outlet of the condenser 12 is connected to a vacuum pump 15 via a pipe, and the vacuum pump 15 allows the evaporator 1 and the mist separator 1 to be connected.
1, the internal pressure of the condenser 12 and the receiving tank 13 is maintained at a constant vacuum degree of 50 Torr.

The above-mentioned apparatus will be described in more detail below, including the function and effect in the evaporative concentration process. When the apparatus is activated and becomes stable, the outlet of the heater 3 is in a state of superheated liquid containing almost no steam due to pressure loss of the pipe 4 and the pipe end 5, and the pressure becomes closer to the pipe end 5 as it approaches the pipe end 5. Since it becomes low, evaporation gradually occurs and a gas-liquid two-phase flow occurs. At this time, the flow state in the pipe 4 becomes faster as the vapor ratio increases, and becomes an intermittent flow or an annular flow in the downward vertical pipe that reaches the pipe end 5 from the bubble flow through the transition state. By the time the pipe end 5 is reached, the superheated liquid releases most of the amount of superheat as evaporation latent heat, and the pipe end 5 has a slight degree of superheat.
Then, in the state of the intermittent flow or the annular flow, the superheated liquid jetted at a high speed from the pipe end 5 becomes droplets to increase the surface area thereof and the remaining slight amount of superheat reaches the liquid surface in the evaporator 1 Is discharged as latent heat of vaporization to reach the liquid surface as saturated droplets. Droplets ejected at high speed from the tube end 5 in an intermittent or annular flow state have a small amount of mist and have an appropriate droplet diameter,
Bubbles on the liquid surface generated due to disturbances such as pressure fluctuations that tend to occur at the time of starting the apparatus are defoamed by the impact force due to collision of droplets. In addition to utilizing the defoaming action of the liquid droplets, when the superheated liquid droplets jetted at high speed from the pipe end 5 reach the side wall surface or liquid surface of the evaporator 1 without releasing the amount of superheated heat, Since it evaporates by boiling and foams, in order to avoid this, the position of the tube end 5 was secured to be 600 mm from the liquid surface and a distance of about 350 mm from the side wall of the can. Also, the pipe end 5
The droplet ejection angle was set to about 60 degrees so that all the droplets would reach the liquid surface without hitting the side wall surface of the evaporator 1.

In the steady operation of this embodiment, the virtual empty cylinder liquid flow velocity U _L0 = 1.5 m / sec, the superheat temperature ΔT = 15 ° C., which corresponds to the point a plotted in FIGS. 4 and 5. I did it. The flow pattern at the tube end 5 was a semi-plug flow during intermittent flow, and continuous operation was possible in a stable, non-foaming state.

In the above device, the set value of the superheat temperature ΔT is changed, the number of the pipe ends 5 is changed, the discharge flow rate of the circulation pump 2 is changed by the control of the inverter 8, and the like. An example of changing the injected virtual empty cylinder liquid flow rate U _LO is plotted at points b to j on FIGS. 4 and 5. The superheat temperature Δt in FIG. 4 is the difference between the heater outlet temperature and the pipe end temperature, and the superheat temperature ΔT in FIG. 5 is the difference between the heater outlet temperature and the boiling point temperature at the evaporator operating pressure. It is the difference. For example, in the case of point a, the superheater outlet temperature is 56.
The tube end temperature is 5 ° C., the tube end temperature is 48.9 ° C., the boiling point temperature at 50 Torr is 41.5 ° C., the overheating temperature ΔT is 15 ° C., and the overheating temperature Δt is 7.6 ° C. Therefore, the points with the same reference numerals in FIGS. 4 and 5 indicate test data under the same operating conditions.
Hereinafter, an example in which the virtual empty cylinder liquid flow rate U _LO is changed will be described.

First, the heater outlet temperature is set to 56.5 ° C., the superheat temperature ΔT = 15 ° C. is kept constant, and the flow rate is increased from point a to U _L0 = 2.8 m / sec to reach point b. .
This point b corresponds to the transition region between the bubbly flow and the intermittent flow, and the jet state from the tube end 5 became an unstable state in which the liquid column jet and the droplet jet are alternately repeated. The bubbles spread over the entire surface of the liquid, but when the droplets were ejected, the droplets collided with the bubbles and were broken by the defoaming action, so that the bubbles were settled in a certain amount. Further, if the flow rate is increased to U _L0 = 3.0 m / sec, the flow reaches the point c and becomes a complete bubbly flow. In this case, the injection state from the pipe end 5 was a liquid column injection, and an increase in accumulation of bubbles was observed due to liquid surface boiling and vapor entrainment. On the contrary, the flow rate is reduced to U _L0 =
When it is set to 0.6 m / sec, the point reaches point f, and enters the transition region between the falling film flow and the intermittent flow. The injection from the tube end 5 was in a state where droplet injection and vapor injection were alternately repeated. In the vapor jetting state, the liquid flowing along the pipe wall of the pipe end 5 dropped from the pipe end 5 into large liquid drops and dropped onto the liquid surface, and the vapor was entrained to generate bubbles. At this point f, when the droplets were ejected, the bubbles were broken by the collision of the droplets, so that operation could be managed. When the flow rate was further reduced to U _L0 = 0.3 m / sec, point g was reached and a falling film flow occurred. The injection from the pipe end 5 was in a vapor injection state, and the liquid flowing along the pipe wall dropped into large liquid droplets from the pipe end 5 onto the liquid surface, entraining the vapor and generating bubbles. Although the generation rate of this bubble is not high, it has no defoaming ability. Therefore, when it is operated for a long time, the bubble gradually accumulates and becomes inoperable. On the other hand, when the temperature at the outlet of the heater was lowered to 46.5 ° C. and was lowered to U _L0 = 0.2 m / sec, the point h was reached and the falling film region was completely reached. Here, the steam jetting force became weak, and bubbles were generated in the pipe, and the aggregate of bubbles was intermittently jetted from the pipe end 5. As in the case of point a, _UL0 = 1.5 m / sec, and when the set value of the heater outlet temperature is lowered to 48.5 ° C, point d is reached. Here, as in the case of point b, the operating state became unstable in the transition region between the bubbly flow and the intermittent flow, but the defoaming action at the time of droplet ejection could somehow continue the operation. In addition, set the heater outlet temperature to 4
When the temperature was lowered to 6.5 ° C., point e was reached, the bubble flow region was completely entered, and a liquid column injection state was reached, and the accumulation of bubbles was observed and operation was not possible. When the outlet temperature of the superheater is set to 76.5 ° C. and U _L0 = 3.0 m / sec, it becomes point i in the annular flow region. Here, as compared with point a, the jetting force of the liquid droplet became stronger and the mist in the evaporated vapor increased, but the operating state was extremely stable, and no bubbles were seen on the liquid surface at the bottom of the can.
Then, among the four tube end attached to the can, comprising the insert the Mekuraban to two and U _L0 = 6.0m / sec and j in terms of spray flow region. The droplet ejection here was unstable and became liquid column ejection or droplet ejection. Even when the droplets were ejected, almost atomized droplets were ejected, or the droplet ejection state was similar to that at the point i of the annular flow, and the ejection force was weak. During injection of the liquid column, the injected liquid reaches the liquid surface of the can at a high speed while leaving a large amount of superheat, and bubble formation due to steam entrainment and boiling below the liquid surface caused a rapid increase in the bubble layer, making operation impossible.

As described above, as an operating condition for suppressing foaming, it is preferable to control so that the flow form of the gas-liquid mixed phase near the pipe end is a semi-plug flow or an annular flow. Even if some foaming occurs, it is possible to operate if the bubble layer due to collision of droplets and the foaming rate are balanced and the foam layer does not exceed a certain height, plug flow (slug flow) It was also confirmed that the system could be operated in the range of the yarn flow.

A wire demister partially immersed in the liquid was placed on the liquid surface below the evaporator for test purposes.
In this case, even if the region of the plug flow (slab flow) in which the generation of droplets is unstable or the distance between the pipe end 5 and the liquid surface below the evaporator or the wall surface of the evaporator is insufficiently short, It was confirmed that the impact on the surface was relieved and stable operation was possible. Further, even if air bubbles accumulate on the wire demister, when the distance between the pipe end 5 and the liquid surface is shortened, the impact force due to the collision of the liquid droplets is large and the defoaming time is strong, so that the time until the bubbles disappear. It turned out that can be shortened. The thickness of the wire demister on the liquid surface may be determined in consideration of the packing density of the wire so that the droplet does not directly contact the liquid surface. It is not necessary to specify the thickness below the liquid surface,
Consideration should be given so that the liquid level does not rise above the surface due to fluctuations in the liquid level. It is preferable to attach a float to the wire demister so as to keep the positional relationship with the liquid surface constant.

Further, in the test, the working effect when the twisted pipe 20 shown in FIG. 2 was used for the straight pipe portion reaching the pipe end 5 was examined. The figure (a) is a sectional view of the twisted tube 20, and the figure (b) is an external view of the twisted tube 20. The twisted tube 20 has an outer diameter OD of 21.
mm, inner diameter ID1 is 22 mm, inner diameter ID2 is 23 mm,
The twist pitch P is 25 mm, and the twist groove 21 is provided.
After replacing with the twisted tube 20, when the operating conditions were made to be the same as those of the points a and b, the liquid column injection state seen in the case of the straight tube disappeared, and no bubbles were generated on the liquid surface in the can. It was found that the injection state from the pipe end was uniform and stable operation was possible. This is a semi-plug with intermittent flow of bubbles as a result of the rotary motion being added to the gas-liquid multiphase flow and the centrifugal force pushing the liquid against the pipe wall, creating a continuous air column along the pipe axis. It is speculated that the flow, the chain flow, and the plug flow (slab flow) could be made into an annular flow. Here, the twisted tube 20 is not limited to the concretely exemplified one, and the point is that the pressure loss in the tube is small,
It means a twisted tube shape in which a rotational motion is applied to the fluid and the fluid is pressed against the tube wall by a centrifugal force to obtain a continuous air column along the tube axis. Thus, the method of the present invention is
Various modifications or developments can be made within the scope of the claims.

[0020]

As described above, according to the present invention, the foaming solution is preliminarily controlled by controlling the flow morphology of the gas-liquid mixed phase so that the foaming solution itself does not foam in the evaporator. Yes, there is no need for centrifugal force or high vacuum equipment as before, and mechanical moving parts for breaking bubbles are provided, or operations such as blowing gas or steam that impair the thermal efficiency are performed. Since it is not necessary to do so, the structure of the evaporator can be greatly simplified, and it is excellent in industrialization or mass production. Further, since the flow form control is controlled by the superheat temperature-flow rate, the operation is easy, and stable evaporation can be performed due to the high foaming suppression effect.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of an evaporation device used in an evaporation method of the present invention.

FIG. 2 is a diagram showing an example of a twisted pipe used in a straight pipe portion reaching a pipe end of the evaporation device.

FIG. 3 is a classification diagram showing a flow form of gas-liquid mixed phase flow in engineering.

FIG. 4 is a theoretical distribution diagram of a gas-liquid mixed phase flow in the present embodiment.

FIG. 5 is a flow pattern distribution diagram in which the distribution diagram is modified to an actual operation.

[Explanation of symbols]

 1 evaporator, 2 circulation pump 3, heater, 4 piping 5, pipe end, 6 flow meter 7, temperature controller, 8 inverter 10 thermometer.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C02F 1/06

Claims (2)

[Claims] 1. A can having a steam outlet at the top of the can
The effervescent solution has a liquid outlet on the bottom,
After being supplied to the heater through the pump and overheated to the specified temperature
Then, through the pipe, the liquid phase part from the top of the evaporation can to the bottom of the can
Is jetted toward the liquid droplets and reaches the liquid phase portion at the bottom of the can.
At the same time, the solvent is evaporated and removed from the vapor outlet.
In the method for evaporating a foaming solution, the gas phase part in the upper part of the can is distributed toward the liquid phase part in the bottom part of the can.
Has a substantially cylindrical pipe end that is placed and connected to the pipe.
The flow rate of the foaming solution in the heater and the heater
By controlling the superheat temperature at the outlet, the foaming solution superheated by the heater is evaporated in the pipe leading to the pipe end to form a gas-liquid mixed phase, and near the pipe end. The residual liquid in the droplets jetted from the tube end is adjusted so that the flow form of the gas-liquid mixed phase in the liquid phase becomes an intermittent flow or an annular flow.
Most of the heat is generated in the gas phase until it reaches the liquid phase at the bottom of the can.
A method for vaporizing a foamable solution, characterized in that it is released as latent heat of vaporization in the section to complete boiling . 2. The method for evaporating a foaming solution according to claim 1, wherein the straight pipe portion reaching the pipe end is a twisted pipe.