Patent Application
20210154594
The present invention relates to a liquid distributor for a separation device, such as for a mass transfer column and in particular for a packing column for absorption, stripping, scrubbing or distillation, to a respective column for mass transfer including such a liquid distributor as well as to the use of such a separation device and column.
Mass transfer columns are employed for an intensive gas-liquid or liquid-liquid contact in a wide variety of processes, such as in absorption, stripping, scrubbing, distillation, extraction and the like. Distillation columns, for example, are designed to separate a specific substance from a liquid mixture comprising two or more substances by selective evaporation and condensation. For this purpose, distillation columns comprise a boiler at the bottom and a condenser at the top so that during the operation vapour rises upwardly and liquid descends so as to enable a gas-liquid contact for effecting the mass transfer between both phases. The substance with the higher boiling point will concentrate in the liquid phase, whereas the substance with the lower boiling point will concentrate in the gas phase. In order to achieve an intensive gas-liquid contact, such columns are typically filled with an internal to optimize the gas-liquid mass transfer. Examples of such an internal are trays and packings, for instance random packings and structured packings, such as in particular a packing with cross channel structure. An essential requirement for an optimal mass transfer between both phases is that liquid is uniformly distributed over the cross-section of the tray or packing, respectively. Moreover, it is important in particular for packing columns, i.e. columns including a random or structured packing, that the liquid flows on the surface of the packing as a thin film so as to maximize the contact area and contact time between the liquid phase and the gas phase. For both aforementioned purposes, usually liquid distributors are provided at the top of the packing or each of the packing layers, respectively.
Such liquid distributors are available in several principal construction designs. One of these principal designs is a liquid distributor comprising one or more distributor members, such as for instance in the form of troughs, for collecting liquid therein, wherein each of the troughs includes two or more, usually a plurality, of outlet openings in the trough wall, wherein the outlet openings are located in the trough wall so that they are beneath the liquid level, which is adjusted inside the trough during the operation of the liquid distributor. Thus, during the operation the liquid collected in the trough flows out through the outlet openings in the form of jets. In order to form a thin liquid film, one or more screens in the form of specifically formed guide walls are arranged in front of (or ahead of, respectively) the outlet openings, onto which the liquid jets impinge in a specific impact angle so as to avoid at least substantially the formation of splashes of small liquid drops at the site of impact on the screen. In tendency, the impact angle of the liquid onto the screen should be small in order to avoid such a splashing. The liquid film, which is formed on the screen surface, flows down the screen surface to the lower end of the screen, which forms a drip edge, from which the liquid falls down in the form of liquid drops onto the surface of the packing or packing layer, respectively, which is located closely underneath the drip edge of the screen.
Since these screens are in permanent contact with the liquid during operation, they need to be made of a material with a high chemical resistance and in particular with a high corrosion resistance, if used in a corrosive medium, as well as with a high mechanical stability, such as sufficiently high stiffness. On account of these reasons, such screens are usually made of a metal, such as in particular of titanium, of tantalum or of zirconia. However, due to their high densities and price, screens made of such materials are comparably heavy and expensive. Moreover, the wettability of these materials is not excellent, so it is difficult, if not impossible to form a broad and smooth liquid film on screens made of such materials. The formation of a uniform and thin liquid film is in particular difficult in the case of a low liquid loading in the column of for example less than 5 m3/m2·h. However, the formation of a broad and smooth liquid film would be advantageous, because the better the screen is covered by the liquid the better will be the distribution of the liquid onto the packing arranged below the liquid distributor. Even if it is known that the wettability of such screens may be improved by covering the metal screens with meshes, this leads to an increase of costs, since such meshes are generally, if available at all, very expensive. In addition, screens made of a metal cannot be easily and inexpensively shaped into complex shapes, for example by bending or folding metals or by assembling and joining metallic pieces together. However, complex shapes are necessary in order to optimize the screen construction for an optimized form/geometry and thus to optimize its desired function.
It has been discovered that, in order to address the previously mentioned deficiencies, an improved liquid distributor is needed for a mass transfer column in which the liquid distributor and the screen have an excellent chemical resistance and an improved wettability, and the liquid distributor is lightweight and cost-efficient. It is also desirable that the screen be made of a material which can be easily and inexpensively shaped into a complex shape.
In view of the state of the known technology, one aspect of the present disclosure is to provide a liquid distributor for a separation device, such as for a mass transfer column, in particular for a packing column for absorption, stripping, scrubbing or distillation, in which the liquid distributor comprises at least one distributor member having two or more outlet openings for an outflow of liquid in the form of jets, and at least one screen which is arranged in front of the outlet openings so that liquid jets outflowing through the outlet openings of the distributor member impinge onto the surface of the at least one screen and are deformed thereon to thin flowing liquid films, wherein at least one of the at least one screen is made at least partially of a carbon composite material.
The term “carbon composite material”—as used herein refers to a material made of two or more constituent materials, wherein one of the constituent materials is a matrix of plastic or carbon, respectively, in which the residual constituent material(s) is/are dispersed. Prominent examples thereof are fiber reinforced plastic and fiber reinforced carbon, which comprise fibers, which are embedded in a carbon or plastic matrix, respectively, such as carbon fiber reinforced plastic and carbon fiber reinforced carbon, which comprise carbon fibers, which are embedded in a carbon or plastic matrix, respectively.
The term “screen” as used herein refers to any element that is suitable for performing, for example in a liquid distributor of a mass transfer column, the function of deforming liquid jets impinging onto its surface to thin downwardly flowing liquid films and of distributing the liquid of the liquid films to a mass transfer element, such as a packing, which is located underneath the liquid distributor. Such screens are sometimes referred to in the technical field as skirts, drain elements, meshes or webbing.
The present disclosure is based on the surprising discovery that, by producing the screen of a liquid distributor of a carbon composite material, such as in particular of a carbon fiber reinforced carbon, the wettability of the screen surface is significantly increased. The present inventors believe that this may be due to the chemical nature of the carbon surface in combination with the porosity of the carbon surface of carbon composite materials. This excellent wettability of the screen surface produces the effect that liquid impinging onto the screen surface forms a broad and smooth liquid film on the screen surface, allowing a uniform liquid distribution of the liquid onto the packing arranged in the mass transfer column below the liquid distributor. Moreover, a screen made of such a material has an excellent chemical resistance as well as an excellent mechanical stability, and in particular an excellent corrosion resistance and stiffness. In addition, carbon composite materials have a drastically lower density and are cheaper than metals, such as titanium, tantalum or zirconia, so that the liquid distributor in accordance with the present disclosure is also comparably light and cost-efficient. Another advantage thereof is that it is in comparison to bending or folding metals or assembling and joining metallic pieces together easier and more inexpensively possible to shape a carbon composite material into complex shapes compared to a metal. In turn, complex shapes allow optimization of the screen construction for an optimized form/geometry and thus allow for optimization of the desired function of the screen. As a result of these properties, the liquid distributor in accordance with the present disclosure is perfectly well suited for being used in a mass transfer column and in particular a packing column of the type comprising one or more distributor members including each a plurality of outlet openings and further comprising at least one screen which is arranged in front of the outlet openings.
In an embodiment, the carbon composite material, from which the at least one screen of the liquid distributor is at least partially made, is a fiber reinforced plastic. The term “fiber reinforced plastic” as used herein refers to any composite material in which fibers are embedded in a matrix of plastic, preferably a phenolic resin based plastic.
Particularly good results with respect to the mechanical properties, and notably with respect to the stiffness, are obtained when the carbon composite material is a fiber reinforced carbon. In particular, fiber reinforced carbon shows significantly better results than fiber reinforced plastic with respect to wettability. Therefore, in accordance with an embodiment, the carbon composite material is a fiber reinforced carbon. The term “fiber reinforced carbon” as used herein refers to any composite material in which fibers are embedded in a matrix of carbon or graphite, respectively.
In general, the present disclosure is not limited with regard to the chemical nature of the fiber of the fiber reinforced carbon or fiber reinforced plastic. For example, the fibers are selected from glass fibers, carbon fibers, organic fibers, ceramic fibers, metal-coated fibers, metal fibers or combinations thereof. The fibers may be included in the fiber reinforced carbon or fiber reinforced plastic in the form of a textile, such as a woven fabric, and preferably in the form of a unidirectional fabric made out of several carbon fiber rovings.
However, particularly good results are obtained with regard to the wettability and the mechanical properties when the carbon composite material is a carbon fiber reinforced carbon. Therefore, in an embodiment, the carbon composite material is a carbon fiber reinforced carbon.
In accordance with an embodiment of the present disclosure, the at least one screen of the liquid distributor consists of, i.e., is completely made of, the carbon composite material. The carbon composite material is preferably a carbon fiber reinforced carbon. Thereby, the wettability of the screen surface, as well as the mechanical properties of chemical and corrosion resistance of the screen, are significantly improved.
In an embodiment, if the liquid distributor comprises more than one screen, each screen of the liquid distributor is made at least partially of a carbon composite material. More preferably, each screen of the liquid distributor consists of carbon fiber reinforced carbon.
Any of the at least one screen may be a closed or at least partially porous solid. Any of the at least one screen may also have one or more surface structures, such as channels or the like.
In order to adjust the wettability of the screen surface into a desired range, in an embodiment, the carbon composite material of the at least one screen of the liquid distributor has a porosity of 5 to 30%.
In principle, the liquid distributor in accordance with the present disclosure may have any design, as long as it comprises at least one distributor member having two or more outlet openings for an outflow of liquid in the form of jets, wherein the liquid distributor further comprises at least one screen made of the aforementioned composite material which is arranged in front of the outlet openings so that liquid jets outflowing through the outlet openings of the distributor member impinge onto the surface of the at least one screen and are deformed thereon to thin flowing liquid films. In particular, the liquid distributor in accordance with an embodiment is designed for a packing column, i.e. for a column, which includes one or more packings, such as structured packings or random packings, the at least one distributor member is at least substantially tubular or at least substantially trough-like, and the at least one screen is arranged so that it shields the outlet openings against a gas stream flowing upwardly in the column.
The present disclosure is not limited with regard to the orientation of the outlet openings to the screen, as long as during the operation of the liquid distributor, liquid jets outflowing through the outlet openings of the distributor member impinge onto the surface of the at least one screen and are deformed thereon to thin flowing liquid films. In accordance with an embodiment, the at least one screen is arranged in front of the outlet openings so that in the event of a maximum outflow, the liquid jets outflowing through the outlet openings of the distributor member impinge onto the surface of the at least one screen at angles of less than 60°, preferably of less than 30° and more preferably of less than 10°. The angles are defined as angles between the direction of liquid jet outflowing through the outlet openings and the tangent at the point of the surface of the screen, where the liquid jet impinges. This assures that a uniform thin liquid film is formed on the screen surface without any, or at least essentially without the formation of, splashes of small liquid drops at the site of impact on the screen.
In order to allow the liquid film formed on the screen(s) of the liquid distributor to pass downwards so as to be uniformly distributed over the cross-section of the part underneath the liquid distributor, which will be after its assembly into a packed column a packing, in an embodiment of the present disclosure, the lower end of the screen(s) of the liquid distributor is formed as a drip edge. For this purpose, it is preferred that at least one of the at least one screen and even more preferred that each of the at least one screen has, as seen in the vertical direction as well as in the jet-parallel section, the shape of a sigmoidal curve. Still more preferably, the sigmoidal curve is curved downwardly so that the drip edge is formed at the lowest point of the screen. The lower drip edge may be jagged or may have a waveform so that liquids with strong cohesion forces, like water, can collect at the wave or jagged edge tips of the drip edge and then drip off.
However, it is not necessary that the at least one screen is formed at its lower end as a drip edge. This is because the screens of the present disclosure, because they are made of a carbon composite material, have an excellent wettability. Therefore, jets of liquid impinging thereon spread out and remain in a parabola form so that the liquid flows down the screen surface as a broad film, such that the broad liquid film is uniformly distributed over the cross-section of the tray or packing, respectively, located underneath the liquid distributor. In contrast thereto, jets of liquid impinging on conventional screens made of metal tend to spread out and then recoalesce or rejoin to form a narrow liquid stream.
The screen preferably has a largely constant curvature in the region in which the liquid jets impinge onto the surface of the at least one screen, in order to assure that a particular uniform thin liquid film is formed on the screen surface.
Also, in order to assure that a particularly uniform thin liquid film is formed on the screen surface, the at least one screen is preferably arranged in front of the outlet openings so that liquid jets outflowing through the outlet openings of the distributor member impinge onto the surface of the at least one screen essentially tangentially.
The distributor member of the liquid distributor may be made of any material, such as of a metal, such as of titanium, tantalum or zirconia, or of a plastic. However, in view of cost efficiency, of weight reduction, of excellent chemical and corrosion resistance as well as of mechanical stability, in an embodiment, the distributor member of the liquid distributor is also made of a carbon composite material. The carbon composite material is preferably a fiber reinforced carbon and, most preferably, a carbon fiber reinforced carbon.
In another embodiment, a column for mass transfer, in particular for absorption, stripping, scrubbing or distillation, is provided, wherein the column includes at least one packing and at least one liquid distributor as described above.
In such a packing column, the at least one distributor member is preferably tubular or trough-like, and the at least one screen is arranged so that it shields the outlet openings against a gas stream flowing upwardly through the column. The screen is preferably a sigmoidal curved screen, wherein the sigmoidal curve is curved downwardly and the sigmoidal curve preferably has a largely constant curvature in the region in which the liquid jets impinge onto the surface of the at least one screen.
Preferably, the column comprises two or more parallel distributor members with each of the one or more screens comprising drip edges, wherein the distributor members are arranged so that the distributor members subdivide a gas stream flowing upwardly in the column into a plurality of partial streams so that stagnation zones form beneath the distributor members, and wherein the drip edges of the screens are arranged inside the stagnation zones.
In accordance with another embodiment, a screen for a liquid distributor for a separation device, such as for a mass transfer column in particular for a packing column for absorption, stripping, scrubbing or distillation, is provided, wherein the screen is designed such that, when it is installed in a liquid distributor further comprising at least one distributor member having two or more outlet openings for an outflow of liquid in the form of jets, with the screen being arranged in front of the outlet openings, liquid jets outflowing through the outlet openings of the distributor member impinge onto the surface of the screen and are deformed thereon to thin flowing liquid films, wherein the screen is made at least partially of a carbon composite material.
According to an embodiment, the liquid distributor or the above described column may be used for performing a separation process, such as absorption, stripping, scrubbing or distillation.
Due to the excellent corrosion resistance of carbon composite materials, such as fiber reinforced plastic and in particular carbon fiber reinforced carbon, the use in accordance with the present disclosure is particularly suitable for applications in which corrosive components are involved.
Moreover, on account of the excellent wettability of screen surfaces made of carbon composite material, such as fiber reinforced carbon and in particular carbon fiber reinforced carbon, the use in accordance with the present disclosure is particularly suitable for performing a separation process with comparable low liquid loadings, such as for performing a separation process with a liquid irrigation density of less than 20 m3/m2·h, preferably of less than 10 m3/m2·h, more preferably of less than 14 m3/m2·h and most preferably of less than 5 m3/m2·h. The irrigation density is expressed in volumetric flow rate of liquid in relation to the cross-section of the column.
The invention will be explained in more detail hereinafter with reference to the drawings.
The mass transfer column 10 shown in
As shown in
The liquid distributor 18 with the screen 30 shown in
As set out further above, the screen made of a carbon composite material as used in the liquid distributor in accordance with the present disclosure has an excellent wettability effecting that a liquid jet impinging onto the screen surface forms a broad and smooth liquid film on the screen surface. This is shown in
In contrast thereto, jets of liquid impinging on conventional screens made of metal tend to spread out and then recoalesce or rejoin to give a narrow liquid stream. This is schematically shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 17176977.1 | Jun 2017 | EP | regional |
This application is a U.S. National Stage application of International Application No. PCT/EP2018/065456, filed Jun. 12, 2018, which claims priority to European Patent Application No. 17176977.1, filed Jun. 20, 2017, the contents of each of which are hereby incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/065456 | 6/12/2018 | WO | 00 |
