JP2010131486A - Method for removing moisture in air - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of removing moisture from wet air for removing moisture in air without using heat energy, recovering the latent heat energy possessed by the moisture in air as latent heat energy and satisfying a demand for increasing a moisture removing speed by the minimized energy from the outside. <P>SOLUTION: By rotating a cylindrical rotary body, on which a flat hydrophilic porous membrane 3 is mounted, by utilizing the flowing force of wet air when moisture is removed from the wet air in a case that the absolute humidity of the wet air is higher than that of the atmosphere, three kinds of mechanisms of pore diffusion, surface diffusion and dissolving diffusion through the membrane are utilized to move the moisture of the wet air into the atmosphere. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a method for removing moisture contained in a gas by using a film. More specifically, the present invention relates to a method of removing moisture from a moist gas (temperature T ₁ ) whose absolute humidity is higher than the absolute humidity of the atmosphere (temperature T ₂ ) using a porous flat membrane.

    In the industry, the drying process is one of the processes that consume energy, and its improvement is constantly being studied as an energy saving measure. In the home, a technique for removing moisture in the gas is used for drying after washing or dehumidification in the room. As a method of removing moisture from the gas, water is removed as liquid water by lowering the temperature of the air using a cooler and setting the temperature below the dew point of the air. It is possible to remove only moisture in the gas by heating again after removal. In the method using this cooler, (a) the latent heat of vaporization of water vapor becomes energy to be added during cooling, and it can be said that the method is inferior in energy efficiency. (B) There is a problem in that it becomes a closed system spatially with the outside, and dehumidifying efficiency decreases if an open part is provided.

    As a method for removing moisture on a laboratory scale, there is a method using a desiccant. It can be used as a method of securing an appropriate humidity using activated carbon, or reducing the humidity in the air to near 0% with a hygroscopic agent (silica gel, calcium chloride, etc.). This method is convenient as a small-scale water removal method in a closed system.

    A method of removing moisture from a moist gas using a polymer film has been proposed (Patent Document 1). The presence of pores in the membrane used in this method cannot be confirmed with an electron microscope, and water molecules move through the membrane by a so-called dissolution / diffusion mechanism. For this reason, the film removal rate of moisture is small, and a large membrane area and pressure difference are required for application on an industrial scale. This method is an open system for all component molecules in the gas, but rather loses the energy of the moist gas out of the system in order to actively move the components in the gas out of the system. Generally, when moisture is removed in an open system, energy flows out of the system at the same time as moisture.

A method has been proposed in which the porous polymer membrane is made of a hydrophilic material, the energy of the wet heat gas is maintained by specifying the pore diffusion and the operating conditions, and only the moisture is taken out of the system (Patent Document 1). ). In this method, assuming that the total amount of flow of wet hot air and dry air is V, the average pore diameter γa of the membrane, the area A of the membrane, and the porosity Pr of the membrane, | ΔP | Must not.
| ΔPl | /d≦3.0×10 ⁻⁵ V / (Pr · ra ² · A) (1)
In this method, it is pointed out that the speed of the amount of the component passing through the membrane as a fluid needs to be equal to or less than a certain ratio of the sum V of wet hot air and dry air. Later, when heat recovery was carried out by this method, it was clarified that the flow rate of dry air must be at least three times the flow rate of wet hot air. Necessary (Patent Document 2). There is a problem that the amount of new energy is comparable to the energy recovered by the method, which is insufficient as an energy recovery technique possessed by wet hot air.

  As a technique for solving the problem of Patent Document 2, an energy-saving dehumidification system has been developed by arranging a structure with more unevenness on the film surface in contact with the dry air side than on the humid hot air side (Patent Document 3). . This technique completes an open system for constituent molecules in the gas and a closed system for microbial particles. This technology does not use (a) the sensible heat energy of wet hot air (such as the velocity as a fluid in the form of temperature or kinetic energy). (B) It is difficult to produce a membrane module because of the complicated structure on the back side of the membrane. Leave the problem of the point.

    In a structure having a heating element inside the room and having a heating element, the absolute humidity increases with time, and water droplets are generated inside the structure due to daily fluctuations in the atmospheric temperature. For this reason, rust is generated inside the structure, or electrical troubles occur due to poor insulation of electrical wiring. For this measure, measures are taken to install a high-temperature heating element, but this leads to a vicious cycle, and measures must be taken to remove moisture from the system. Moisture countermeasures using a method in which the relative humidity is lowered by a heating element is not a fundamental countermeasure. Moisture removal in an almost enclosed space is an important issue for unattended facilities in remote locations.

JP 54-152679 A Japanese Patent Publication No.4-130006 Japanese Patent No.38991808

    The present invention intends to simultaneously solve the following problems that cannot be solved by the prior art. That is, (1) removing moisture in the gas without using thermal energy, (2) collecting latent heat energy of moisture in the gas as sensible heat energy, and (3) gas in space for component molecules in the gas Closed space for fine particles (retroviruses, bacteria, mycoplasma, etc. with a diameter of 0.08μm or more) dispersed inside (4) Minimizing the energy required from outside to increase the water removal rate (5) Provided is a method for removing moisture in the air that satisfies the five requirements of a structure that can be easily produced as a film to be used.

    In order to remove moisture in the gas outside the system without using thermal energy, it is optimal to remove it through a membrane. However, if membrane filtration is used as a mechanism for removing water molecules through the membrane, other component molecules (such as enzymes and nitrogen) in the gas also flow out of the system. Since the outflow of molecules results in a loss of thermal energy of the gas, it is necessary to minimize the contribution to mass transport by the membrane filtration mechanism. For this purpose, there is a limit to increasing the hole diameter. On the other hand, although a dissolution / diffusion mechanism can be expected by reducing the pore size, it is necessary to set a mechanism for increasing the selectivity of permeation of water molecules and increasing the membrane movement speed of water molecules.

    The latent heat energy of water molecules in the gas means the heat of evaporation. That is, when the water molecules in the liquid evaporate and change to gaseous water molecules, the heat of evaporation is obtained to become vapor phase water molecules. Therefore, the enthalpy of the vapor phase water molecule is increased by the amount of heat of vaporization compared to the liquid phase water molecule. This increase is latent heat energy. In order to convert latent heat energy into sensible heat energy, it is necessary to cause a phase change again.

    In order to create an open space for the component molecules in the gas and a closed space for the fine particles dispersed in the gas, the membrane that separates the two spaces must have a special pore structure or move the substance. There is no choice but to give special power to the driving force. As a special pore structure, the pore size distribution is considered to be either very sharp or a multilayer structure film expressed by a layered structure. Here, the multilayer structure film is a film in which a laminated structure of a thin film having a thickness of about 0.2 μm is observed when a longitudinal section of the film is observed with a transmission electron microscope. A film having 20 or more laminated thin films is defined as a multilayer structure film.

    In order to increase the removal rate of water molecules through the membrane, it is clarified that a special structure is required on the back side of the membrane as described in Patent Document 3. In addition to the optimum design of the membrane structure, it is conceivable to adopt means for reducing the moisture content on the back side of the membrane. In the present invention, a means for replacing a complicated film structure is proposed without applying energy from an external system.

The center of the object to which the present invention is applied is a high-humidity high-temperature gas (temperature T ₁ ) that comes out after drying the substance, a gas in a high-temperature and high-humidity space (eg, power supply room, animal house), For example, gas in a space where water vapor is generated. The present invention provides a technique that is used in a form directly connected to a device (such as a blower) for flowing these gases.

The greatest feature of the present invention is that when a moisture is removed from the moist gas having a high absolute humidity (temperature T ₁ ) through the film to the atmosphere located on the opposite side, the film is installed by the flow force of the gas. The point is to rotate the module. FIG. 1 shows a conceptual diagram of the module. By rotating the film, the film (thin layer part where the gas flow is stopped) existing on the film surface is thinned, and the evaporation of water from the surface in contact with the atmosphere side of the film is facilitated. The same effect as increasing the flow velocity of gas and atmosphere when the membrane is stationary is expected. Further, the water that has become liquid in the film by the centrifugal force accompanying the rotation is blown off into the atmosphere by the centrifugal force. By rotating the film in this way, there is no need for a complicated structure on the back surface of the film as in Patent Document 3, and a structure that can be easily produced as a film used in the present technology is sufficient.

The force that rotates the membrane is the force of gas flow (wind power). Wind turbine blades are installed in the gas flow to turn the wind power into rotation. By devising the shape of the blade, the rotation and the flow of gas can be actively brought closer to the film surface. By using this gas flow as wind power, energy (such as rotational force) applied from the outside in order to increase the water removal rate can be minimized.

The second feature of the present invention is that a hydrophilic porous flat membrane is used as the membrane. The term “new aqueous solution” refers to a substance having a solubility parameter hydrogen bond component δ _h of 8 (cal ^1/2 cm ^−3/2 ) or more. For example, cellulose and polyvinyl alcohol. The porosity is a film having a porosity of 30% or more, and the presence of pores of 5 nm or more on both sides of the film can be observed with an electron microscope. A flat membrane is a membrane having a thickness of 10 μm to 1 mm, a membrane plane having a width of 1 cm or more and a length of 1 cm or more.

  The hydrophilic film absorbs moisture in the air and generates heat of adsorption. Adsorption reduces the water concentration in the air and at the same time increases the temperature of the air. That is, adsorption changes latent heat to sensible heat. The moisture adsorption performance is also a result of the affinity between the membrane material and water molecules. Regenerated cellulose is particularly desirable because of its ease of film formation and hydrophilic strength. In the case of cellulose, a differential adsorption heat of about 300 kj per kg of cellulose is generated for a gas having a relative humidity of 60%. The degree of temperature rise due to heat of adsorption is determined by the specific heat relationship between the membrane and air.

    The third feature of the present invention is that three kinds of diffusion mechanisms of pore diffusion, surface diffusion and dissolution diffusion are used as the movement of moisture through the membrane. Here, pore diffusion is the diffusion of molecules in the pores, and the diffusion coefficient is approximately inversely proportional to the 1/2 power of the molecular weight. The pore diffusion is more likely to occur as the pore diameter is around 100 nm and the gas pressure is lower. Surface diffusion means that the adsorption layer of water molecules on the surface of the pore wall in the film forms a two-dimensional liquid surface, which means diffusion on this liquid surface, and is likely to occur in pores having a pore diameter of 5 to 80 nm. Dissolving diffusion means the diffusion of water molecules in the material polymer of the porous membrane and diffusion in the material polymer entity. These diffusions increase the diffusion rate of water molecules in the film. By using the diffusion mechanism, moisture in the gas can be removed without using thermal energy.

    Mass transfer in the membrane based on the diffusion mechanism is as follows: (b) There is no clogging of the pores compared to the filtration mechanism; (b) Large particle removal performance (c) It is necessary to add energy necessary for mass transfer Although there is a feature such as no energy required for water removal (minimum), on the other hand, there is a problem that the mass transfer rate is low. Since the mechanism of moisture movement in the membrane used in the present invention is diffusion, the transmembrane pressure difference (ΔP) is unnecessary in principle. When ΔP increases, mass transfer as a fluid occurs, so that heat energy is lost outside the system, and ΔP has an optimum value.

When the temperature (T ₁ ) of the wet gas is higher than the temperature T ₂ of the atmosphere and the difference between them is ΔT = T ₁ −T ₂ , thermal diffusion occurs through the film. Due to this thermal diffusion, water molecules also move from the high temperature side to the low temperature side. As the moisture moves, other molecules in the gas (such as enzymes and nitrogen) move from the high temperature side to the low temperature side, causing a loss of heat energy of the gas. In order to suppress this flow, it is desirable to keep ΔP negative.

The rate at which moisture moves to the atmosphere increases as the film thickness d decreases. If d is too small, the effect of thermal diffusion is increased and a loss of thermal energy of the gas occurs. d is preferably 5 μm or more, but when ΔT (unit ° C.) increases, d needs to be increased. In consideration of the fact that ΔT becomes negative, it is desirable that d (μm unit) satisfies the formula (2) in order to prevent loss of heat energy of the gas.
d ≧ 30 + 5ΔT (2)

    When a multilayer structure film is employed as a film structure used in the present invention, it is possible to create an open space for molecules and a closed space for particles between the gas and the atmosphere. Here, the multilayer structure film is a film that can be confirmed by the presence of stripes having a width of about 0.2 μm along the film plane when the cross section of the film is observed with a transmission electron microscope. A film in which 20 or more streaks are observed is defined as a multilayer structure film. The multilayer structure film has excellent particulate removal performance. Examples of harmful fine particles that may be mixed from the atmosphere include bacteria, viruses, and nanoparticles. Since the diffusion coefficient of these fine particles is much smaller than that of water molecules, the fine particles cannot pass through the membrane by the technique of the present invention. Furthermore, if the average pore diameter of the membrane is 300 nm, it is possible to almost completely prevent fine particles from passing through the membrane.

    By making the average pore diameter of the membrane surface on the side in contact with the gas smaller than the average pore size on the surface in contact with the atmosphere in the multilayer structure film, water molecules can be easily desorbed from the film, and the movement of fine particles from the atmosphere to the moist gas can be achieved. Be blocked. Further, when the flat membrane is folded into a pleated shape and modularized, the area in contact with the moist gas and the atmosphere increases, and the removal rate of water molecules increases. Since the pressure applied to the flat membrane is small, a support for supporting the flat membrane is not always necessary. However, when the regenerated cellulose nonwoven fabric is folded during pleating, the shape can be easily maintained.

    The technology of the present invention enables (1) dehumidification using minimized energy and recycling of dry air, (2) energy recovery using latent heat of evaporation as sensible heat, and (3) reduction in size and weight of the dehumidification process. Achieved, dehumidification systems can be designed for mobile spaces (spaces such as cars, airplanes, trains, etc.), industrial and civilian. (4) Sufficient ventilation is naturally provided for carbon dioxide and oxygen, and since particulates are isolated, they are used as a ventilation method for a bathroom in a hospital or home.

    The cellulose acetate porous membrane obtained by the microphase separation method is saponified with caustic soda to produce a regenerated cellulose flat membrane (3 in FIGS. 1 and 2). This is mounted in a star shape of 6 to 12 corners (8 corners in FIGS. 1 and 2) in the module shown in FIG. When the regenerated cellulose non-woven fabric and the flat membrane are overlapped when the flat membrane is folded into a star shape, the mechanical properties of the membrane are improved. The inner cylindrical portion of the flat membrane folded in a star shape has a hollow rotating body 5, and a plurality of screws 10 that convert wind force into rotational force are provided on the lower side of 5. The rotating body 5 has twelve shallow grooves, and a flat membrane support can be sandwiched in the grooves if necessary. The rotating force is transmitted to the flat film 3 folded in a star shape by a bar 11 which is the center of rotation above and below the rotating body 5 and a bar 12 which is connected to the bar 11 at a right angle. Rotate around 11. The flat membrane is embedded and fixed with a polymer embedding material P.

  The star-shaped flat membrane module in FIG. 1 is surrounded by a nylon net or a metal net 2 to prevent foreign objects from colliding with the outside. The net forms an outer cylinder of a flat membrane module, and the outer cylinder is fixed with a cap 1. The cap of the outer cylinder and the embedded portion of the flat membrane are contacted by bearings 8 and 9, and the outer cylinder cap and the center bar are contacted by the bearing. When the wet high temperature gas from the inlet 7 flows in, the star-shaped folding part of the flat membrane rotates by the inflowing wind force.

Cellulose acetate having an average degree of substitution of 2.45 (average degree of polymerization of 200) was dissolved in acetone at 15 wt%, and methanol, water, calcium chloride, and cyclohexabul were added to this solution to prepare a casting solution. The solution composition was determined with reference to literature values (Kamide, Manabe, Matsui, Sakamoto, Iwata, Kobunshi Shigaku, Vol. 34, p. 205 (1977)). The obtained porous cellulose acetate membrane was changed to regenerated cellulose with 0.1 N caustic soda, and this membrane was dried by a water displacement method using acetone. The characteristics of the regenerated cellulose porous membrane after drying are given below.
Film thickness: 400 μm, average pore diameter: 300 nm, porosity: 83%
Here, the average pore diameter is a value obtained by the filtration rate method.

As shown in FIGS. 1 and 2, the membrane is folded into an octagonal star. The effective membrane area was 0.3 m ² /, the diameter of the wire mesh was 15 cm, the length was 50 cm, and the diameter of the octagonal circumscribed circle was set to 12 cm. The temperature of the atmosphere was 15 ° C., the relative temperature was 65%, the temperature of the moist gas at the inlet of the apparatus was 80 ° C., and the relative humidity was 80% (water vapor pressure 0.38 atm). The moist air was pressurized at 0.4 atm (0.4 atm from atmospheric pressure), and the inside of the apparatus was flowed at 40 l / min. The temperature of the humid air at the outlet was 80 ° C., the relative humidity was 40%, and the humidity was halved. The water removal rate by this apparatus was 2 g / min.

    Used in all industries with a drying process. The energy cost required for drying can be reduced. It could also be used for isolation of infection sources in hospitals, animal experiment facilities, home dryers, and bathrooms.

: Schematic of the dehumidifying part of the present invention : Cross section taken along line AA 'in FIG.

Explanation of symbols

1: Outer cylinder supporting a rotating part such as a mesh frame and a flat membrane folded in a star shape 2: A wire mesh or nylon mesh 3: A flat membrane folded in a star shape 4: A hollow inner cylinder 5: An inner cylinder Grooved groove 6: Pole bearing between the center rod and the outer cylinder cap 7: Moist air inlet / outlet 8: Pole bearing at the contact between the outer cylinder cap and the flat membrane folded in a star shape and the inner cylinder 9: outer cylinder cap 10: blades that rotate by wind force 11: center rod 12: rod-shaped support arranged perpendicular to the center rod P: polymer filler for embedding the flat membrane and the rod-shaped support

Claims (3)

Force of gas flow in removing moisture through the membrane into the atmosphere with lower absolute humidity on the opposite side than the humid gas (temperature T ₁ ) where the absolute humidity is higher than the absolute humidity in the atmosphere (temperature T ₂ ) Rotating a cylindrical rotating body fitted with a hydrophilic porous flat membrane using water, water can be obtained using any or all of the three mechanisms of pore diffusion, surface diffusion and dissolution diffusion through the membrane. A method for removing moisture, which comprises moving the water into the atmosphere. In claim 1, the flat membrane is composed of regenerated cellulose, the pore structure of the membrane is expressed by a multilayer structure membrane, the average pore diameter of the membrane is 300 nm or less and 5 nm or more, and the film thickness d (μm unit) is a temperature difference Δ A moisture removal method selected so as to satisfy the following relationship with T (° C.) (= T ₁ −T ₂ ):
d ≧ 30 + 5ΔT 3. A method for removing moisture according to claim 1, wherein the flat membrane is a pleated module, the average pore size of the membrane surface in contact with the moist gas is smaller than the average pore size of the membrane surface on the side in contact with the atmosphere.