JPH0549801A - Method for evaporating foaming solution - Google Patents

Abstract

PURPOSE:To provide a method for evaporating forming solution by which foaming is effectively and economically eliminated without using chemical substances, such as an antifoaming agent. CONSTITUTION:A heater 3 where foaming solution is superheated to the prescribed temp. by the prescribed amount and an evaporator 1 where a vapor takeoff connection 1a and a pipe end 5 arranged toward the liquid phase part of the bottom part of the evaporator are provided in the vapor phase part of the upper part of the evaporator and, simultaneously, the superheated foaming solution is fed to the pipe end 5 through piping 4 and jetted to the liquid phase part from the pipe end 5 are provided. The flow rate of the foaming solution in the heater 3 and the superheated temp. at the outlet of the heater are controlled so that the foaming solution superheated by the heater 3 may be evaporated in piping leading to the pipe end 5 to form gas-liquid two-phase and the flow configuration of the gas-liquid two-phase may become intermittent or annular flow near the pipe end 5.

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 foaming solution which suppresses foaming and evaporates a solvent, particularly in operations involving boiling such as evaporative concentration of a highly foaming 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, a method of suppressing foaming can be applied by using an antifoaming agent, but when the concentrate becomes a product, it is often impossible to use an antifoaming agent. 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 is difficult to apply to suppress foaming of a highly foamable solution.
Therefore, conventionally, as illustrated 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 part of the evaporator, and the degassed liquid 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 the vapor by 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, the processing capacity is small, and the processing amount is large. In the latter method, most of the pressure loss of the pipe from the heater to the pressure injection nozzle is the injection pressure of the pressure injection nozzle, so the pressure at the inlet of the pressure injection nozzle is the pressure of the evaporator, that is, the evaporation pressure. Since it is considerably higher than the above, the rate 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 are reflected on 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 the operation is reduced. 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 in order to prevent the possibility of droplets 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 before the liquid droplets ejected from the pressure injection nozzle reach the liquid droplets of the evaporator, a predetermined amount of liquid will be discharged. 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, complexity of the device, 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 and Japanese Utility Model Laid-Open No. 62-199103. 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 highly efficiently and economically without adding a chemical substance such as an antifoaming agent.

[0005]

In order to achieve the above object, the evaporation method of the present invention comprises a heater for heating a predetermined amount of a foaming solution supplied through a pump to a predetermined temperature, and an upper part of a can. The vapor phase portion has a vapor outlet and a pipe end arranged toward the liquid phase portion of the bottom of the can, and the superheated foaming solution is supplied to the pipe end through a pipe, and from the pipe end. An evaporating can sprayed toward the liquid phase portion, evaporating the foaming solution heated by the heater in a pipe leading to the pipe end to form a gas-liquid mixed phase, and the pipe To control the flow rate of the foaming solution in the heater and the superheat temperature at the outlet of the heater so that the flow form of the gas-liquid mixed phase near the end is an intermittent flow or an annular flow I am trying. 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.

[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, when the defoaming agent cannot be used, the method to be adopted 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 basically evaporated in the pipe to give a shearing force to the surface of the gas-liquid mixed phase flow and the non-liquid surface due to the difference in velocity of the gas and liquid to suppress the foaming in the pipe. More specifically, most of the evaporation is done 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 injection force of the evaporation 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 conventional case, but a circular pipe or a 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 form 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 patterns of the gas-liquid mixed phase flow in the downward flow are generally classified as shown in FIG. The figure (a) is a falling film flow, the figure (b) is a bubble flow, the figure (c) is a plug flow, the figure (d) is a yarn flow, the figure (e) is a 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 mixed phase 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 ] Viscosity of liquid μ _L [kgm / m · sec] Surface tension σ _L [kg / m] Operational conditions, ie, Vapor empty velocity V U _G [m / sec] Liquid empty It is determined by the cylinder velocity _UL [m / sec], and the equations for the boundary line of falling film flow, bubbly flow, intermittent flow, annular flow and mound flow are D, ρ _G , ρ _L , μ _L , σ
_It is shown as a function of _L , U _G , and U _L (Two-phase Flow Patterns and VoidFract
ions in Downward Flow; Int. J. Multiphas
e Flow eVol. 11, No. 6, 1985). In the case of vertical downflow, it is given by the following equations (1) to (7). Mound boundaries expression between fog flow and intermittent flow and annular flow _{△ P L = 2.89 [(ρ} L -ρ G) gσ L] 0.5 (1) boundary equation 1 between the annular flow and intermittent flow and falling film flow. _{9 (U G / U L)} 0.125 = K uG 0.2 F rG 0.36 (2) the boundary equation F _rG the falling film flow and intermittent flow and bubble flow _{= 0.43426 (U G / U L} ) 1.1 (3) the bubble flow and intermittent flow and boundary type _{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) F rG =}} U G (gD) -0.5 (6) △ P L = 2fρ L U L 2 / D (7) f is the pipe friction coefficient. g is the acceleration of gravity. 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, so the flow rate of the foaming solution at the heater inlet and the heater outlet The liquid flow rate and vapor flow rate per tube end are determined only by the temperature difference between the liquid temperature in the tank and the boiling point of the liquid at the operating pressure of the evaporator, that is, only the superheat temperature ΔT [° C].
Therefore, U _G and U _L can be decided and the flow state can be specified. Here, the flow rate of the foamable solution at the inlet of the heater is divided by the number of tube ends and the cross-sectional area of the flow path at the tube ends to obtain a virtual empty liquid flow velocity _UL0 of the foamable solution at the tube end. [M / sec], the liquid temperature at the heater outlet and the operating pressure P [Tor of the evaporator]
r], the temperature difference from the boiling temperature of the liquid
If the above equation of the flow form boundary line is modified as [° C.], the flow form distribution of the gas-liquid multiphase flow is Δ regardless of the number N of end tubes.
It can be derived as a function of T and _UL0 . That is, pipe end 1
The ratio V _f of the generated steam flow rate to the liquid flow rate per line is
Considering that the entire superheat flow rate at the superheat temperature ΔT is consumed as evaporation latent heat, it is given by V _f = C _PL ΔT / H (8), so that the boundary between the mound flow and the intermittent or annular flow is equation (1) is _{F d = 1.7 [(ρ L} -ρ G) gσ L] 0.25 (9) U L0 = F d / [(2f) 0.5 (1-V f)] (10) and the annular flow The boundary equation (2) between the intermittent flow and falling film flow is F _a = 169.84 (ρ _G / ρ _L ) ^3.48 (gD) ^1.44 × [(ρ _L −ρ _G ) gρ _L / ρ _G ² ] ^0.4 ( 11) U _L0 = [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 / ρ _G ) ^0.1 (13) _UL0 = F _f V _f ^0.1 (1-V _f ) ^-1.1 (14) The boundary equation (4) between bubbly flow and intermittent flow is F _b = [(Ρ _L /0.117 ρ _G )] ^5/3 (gD) ^0.5 ( 15) is derived as ^{_{U L0 = 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 pipe having an inner diameter of 25 mm at an operating pressure of 50 Torr by using the equations (8) to (16) as the equations of the flow form boundary line. 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 superheat 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, it becomes an intermittent flow through a transition state. If the amount of heat of superheat is further increased as compared with the falling film flow or the intermittent flow, an annular flow occurs. In the case of intermittent flow or annular flow, most of the evaporation occurs 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 an appropriate size with less mist, and at the bottom of the evaporator. It was confirmed that the amount of heat of superheat was lost by the time the liquid surface reached to the end of boiling evaporation was completed, and neither boiling nor foaming occurred on the liquid surface of the evaporator. The intermittent flow is further classified into plug flow, yarn flow and semi-plug flow. It has been found that in the case of the semi-plug flow, 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 can be performed as with 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 jetting. 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 breaking speed due to the collision of the droplets and the foaming speed are balanced so that the foam 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. In the meantime, it cannot release the amount of superheat. 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 does not occur due to the large piping resistance, the liquid that has flowed out from the pipe end has a superheat amount and becomes a liquid droplet ejection from the pipe end that does not have a liquid column shape or almost a spreading 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 boil-vaporizes after returning to the liquid surface in the lower portion of the evaporator. When the flow velocity of the virtual hollow liquid is slow and the amount of superheat is smaller than that of the annular flow, the falling film flow occurs. In this case, since the amount of 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 if the cross-sectional area of the steam flow path 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 droplets and a vaporizer in a state near free fall. It falls on the lower liquid surface. In this case, since the pressure loss in the pipe is small, the boiling evaporation is completed in the pipe. However, since the shearing force at the gas-liquid interface is small, foaming may occur during boiling and evaporation in the pipe, and bubbles may be discharged 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. As the virtual empty cylinder liquid flow velocity increases, it becomes a spray flow.
In actual operation, when the evaporation pressure is below atmospheric pressure and the amount of superheat is small, when the liquid flow rate becomes faster, less steam is generated in the pipe due to pressure loss in the pipe, and the spray flow state is unstable and It may be in a fluidized form and foam at this time.
When the steam pressure is higher than atmospheric pressure, the amount of heat 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, the amount of superheat remains at the pipe end.
However, since the diameter of the droplets ejected is small, the amount of heat of superheat is lost and the boiling evaporation is completed by the time it reaches the liquid surface in the lower part 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 diameter and number of pipe ends, taking into consideration the thermal stability of the foaming solution, the amount of treatment, changes in physical properties due to concentration, etc. 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 were created. It is preferable to adopt and.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of an evaporation device 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 No. 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. , And 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 portions joined to the pipes 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
In order to avoid changes in flow rate due to fluctuations in pressure loss, etc., to the utmost, a displacement pump is used, and in order to make the supply amount to the heater 3 constant, it can be controlled by the inverter 8 and the flow meter 6. ing. The heater 3 uses steam or the like as a heat medium. The outlet temperature of the heater is detected by a temperature detector so that the outlet temperature of the heater is 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 so that the amount of heat for heating the boiling point liquid becomes constant, and the superheated liquid having a superheating temperature of 15 ° C. is obtained. The superheated liquid leaving the heater 3 is jetted from each pipe end 5 via the pipe 4. The mixture of the sprayed vapor and the droplets is separated at the vapor phase portion in the upper part of the can, the droplets reach the liquid surface, and the vapor containing mist enters the mist separator 11 through the pipe from the vapor outlet 1a. Here, after the mist in the vapor 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 increases 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 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 level 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 by disturbances such as pressure fluctuations that tend to occur at the time of starting the device 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 and ending there. In order to avoid this, the position of the tube end 5 was 600 mm from the liquid surface, and a distance of about 350 mm from the side wall of the can was ensured. 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 liquid 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 pipe end 5 was a semi-plug flow during intermittent flow, and continuous operation was possible in a stable, non-foaming state.

In the above apparatus, the set value of the overheat 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 in which the flow velocity U _{L0 of the} virtual cavity liquid injected from is changed is plotted at points b to j on FIGS. 4 and 5. In FIG. 4, the superheat temperature Δt is the difference between the heater outlet temperature and the pipe end temperature, and in FIG. 5, the superheat temperature ΔT is the heater outlet temperature and the boiling point temperature at the evaporator operating pressure. Is the difference. For example, in the case of point a, the superheater outlet temperature is 56.5.
C., the tube end temperature is 48.9.degree. C., the boiling point temperature at 50 Torr is 41.5.degree. C., the superheat temperature .DELTA.T is 15.degree. C., and the superheat temperature .DELTA.t is 7.6.degree. 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 cavity liquid flow velocity U _L0 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 jetting state from the tube end 5 became an unstable state in which the liquid column jetting and the droplet jetting are alternately repeated. The bubbles spread over the entire surface of the liquid, but at the time of jetting the droplets, the droplets collided with the bubbles and were decompressed 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 bubbly flow completely. In this case, the injection state from the tube end 5 was a liquid column injection, and the 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 f is reached, and it 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 repeated alternately. In the vapor injection state, the liquid flowing along the pipe wall of the pipe end 5 became large droplets from the pipe end 5 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 the operation was manageable. 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 became large droplets from the pipe end 5 and dropped to the liquid surface, and the vapor was entrained to generate 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 film fell completely into the falling film region. 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 transitional 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 the liquid column injection state was reached, and the accumulation of bubbles was observed and the operation could not be performed. When the superheater outlet temperature 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 under 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 liquid droplets were ejected, the liquid droplets were almost atomized, or the liquid droplets were in a state similar to the case of the point i in 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 foaming due to steam entrainment and boiling below the liquid surface caused a sudden increase in the bubble layer, making it inoperable.

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 can be operated unless the bubble layer due to collision of droplets and the foaming speed are balanced and the bubble layer is above 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 a test.
In this case, even if the region of the plug flow (slab flow) in which droplet generation is unstable or the distance between the pipe end 5 and the liquid surface under 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 force is strong, so 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. The thickness below the liquid surface does not need to be specified,
Care should be taken so that the liquid level does not rise above the liquid level due to fluctuations. 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 the above 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 became uniform and stable operation was possible. This is because a rotary motion is applied to the gas-liquid multiphase flow, the liquid is pressed against the tube wall by the centrifugal force, and it becomes easy to form a continuous air column along the tube axis, resulting in a semi-plug with an intermittent flow of bubbles. 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 specifically 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 a 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 and developments can be made within the scope of the claims.

[0020]

As described above, in the present invention, the foaming solution is suppressed in advance by controlling the flow form 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 in the past, and there are mechanical moving parts for breaking bubbles, and 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. In addition, since the flow form control is controlled by the superheat temperature-flow rate, the operation is easy, and stable evaporation can be performed by 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 view 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 a 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 evaporation can, 2 circulation pump 3, heater, 4 piping 5, pipe end, 6 flow meter 7, temperature controller, 8 inverter 10 thermometer.

Claims (2)

[Claims] 1. A heater for heating a predetermined amount of a foaming solution supplied through a pump to a predetermined temperature, a vapor outlet in the upper part of the can, and a liquid outlet part in the bottom of the can. And a pipe end disposed therein, the superheated foaming solution is supplied to the pipe end through a pipe, and the evaporator is sprayed from the pipe end toward the liquid phase portion. The effervescent solution superheated in (1) is evaporated in the pipe leading to the pipe end to form a gas-liquid mixed phase, and the flow form of the gas-liquid mixed phase near the pipe end is an intermittent flow or an annular flow. A method for evaporating a foaming solution, wherein the flow rate of the foaming solution in the heater and the superheat temperature at the outlet of the heater are controlled so that 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.