A process for operating a mass transfer column

Abstract

The invention relates to a process for operating a mass transfer column comprising internals and at least one liquid distributor (1) for distributing a multi-phase liquid, wherein the liquid distributor (1) comprises a trough (9) for collecting the multi-phase liquid to be distributed onto internals in the mass transfer column, the trough (9) having a bottom (19) and side walls (7), wherein openings (17) for distributing the multi-phase liquid are formed in the trough (9) and / or in drip tubes (15) extending through the bottom (19) into the trough (9), wherein the openings (17) are arranged in at least three different heights. In the process, different phases of the multi-phase liquid separate into different layers in the trough, and the phases flow through openings at different heights, respectively.

Description

[0001] A process for operating a mass transfer column

[0002] Description

[0003] The invention relates to a process for operating a mass transfer column with a liquid distributor comprising a bottom and side walls forming a trough for collecting a liquid to be distributed onto internals in the mass transfer column.

[0004] Mass transfer columns usually are multi-stage separators, in which components are separated by intensive contact between a liquid phase and a gas phase. Processes using such columns for example are distillation, rectification, absorption and gas scrubbing. The liquid phase usually flows from top to bottom of the column and the gas phase in counter-current to the liquid phase from bottom to top of the column. By appropriate internals, both phases are brought into contact for mass transfer between the liquid phase and the gas phase. The low boiling components collect at the top of the column and the high boiling components at the bottom.

[0005] Internals used in the column for example are trays, structured packings or random packings like packed beds, wherein also mixed forms are also known in which different types of internals are present in the same column. Trays which may be used in mass transfer columns for example are tunnel trays, bubble trays, dual-flow trays, sieve trays or valve trays. Packings that can be used in packed beds are, for example, Raschig rings, Pall rings or saddle rings. Structured packings may for example have a cross channel geometry.

[0006] Particularly in columns with structured packings or random packings, it is necessary to provide an essentially uniform distribution of the liquid phase onto the packing to achieve a high separation efficiency. Besides in mass transfer columns, also in fixed bed reactors, a liquid phase needs to be distributed uniformly across the reactor cross section, to avoid hot spots. The gas phase usually is distributed uniformly due to the pressure loss in the packing. The liquid leaving the packing generally is collected in collectors and transported to distributors, by which the liquid is uniformly distributed onto a packing located below the distributor. Thereby it is possible to use separate collectors and distributors or combined collector-distributor-units.

[0007] Common liquid distributors for example are edge deflectors or wall wipers that divert liquid from the wall and release it again at some distance from the column wall. However, this does not result in a uniform density of the liquid spreading over the packing.

[0008] It is further known to use nozzles for distributing the liquid over the cross section of the column. However, the distribution quality is restricted and, thus, nozzles generally are used in simple applications like absorptions or gas scrubbing. Further, liquid distributors are known which have troughs being open on the top and which have branched channels extending across the cross section of the column. The liquid phase runs off via overflow devices, which, for example, consist of serrated weirs, and which have to be aligned exactly horizontally to ensure a uniform liquid distribution. As an alternative, it is also known to use branched pipes or channels as a distributor having openings on the bottom through which the liquid is distributed over the packing. The liquid phase in this distributors is driven by gravity. Such a liquid distributor with branched channels having openings in the bottom is described for example in WO-A 2014 / 204552.

[0009] In several separation applications, the liquid may separate in at least two liquid phases. Such a liquid separation into at least two phases often occurs if the liquid contains water. It is, however, a disadvantage of all known liquid distributors to distribute the liquid phases uniformly on the packing. This non-uniform distribution results in a reduced separation performance of the internals in the column. This reduced separation performance must be compensated by additional height of the internals or increased energy consumption.

[0010] It was, therefore, an object of the present invention to provide a process for operating a mass transfer column with a liquid distributor which does not have the disadvantages of the known separators in applications in which the liquid separates in at least two liquid phases.

[0011] This object is achieved by a process for operating a mass transfer column with a liquid distributor for distributing a multi-phase liquid in a mass transfer column, wherein the liquid distributor comprises a trough for collecting the multiphase liquid to be distributed onto internals in the mass transfer column, the trough having a bottom and side walls, wherein openings for distributing the multi-phase liquid are formed in the trough and / or in drip tubes extending through the bottom into the trough, wherein the openings are arranged in at least three different heights, the process comprising:

[0012] (a) feeding a multi-phase liquid or liquids which form different phases onto the liquid distributor according to the invention, wherein the multi-phase liquid separates into liquid phases which each have a different density in the trough of the liquid distributor,

[0013] (b) distributing the liquid comprising the at least two liquid phases onto the internals in the mass transfer column, wherein the liquid having the highest density flows through the openings arranged at the first height and liquid phases with lower density flow through openings arranged above the openings arranged at the first height, wherein each liquid phase flows through openings at one height, wherein the liquid comprises two liquid phases and the first liquid phase flows through the openings which are arranged at the first height, the first liquid phase or the second liquid phase flows through the openings which are arranged at the second height, depending on the load distribution, and the second liquid phase flows through the openings which are arranged at the third height, if the openings are arranged in three different heights.

[0014] Here, "trough” is used for devices of any shape in which a liquid can be collected and which have a bottom and side walls. The trough may have the shape of a channel or a pan or may be a deck of any shape with side walls. If the trough is a deck with side walls, the side walls may be formed by the inner wall of the mass transfer column.

[0015] Multi-phase liquids usually comprise liquid phases having different densities. The liquid phases separate in the trough of the liquid distributor in such a way that the liquid phase with the highest density forms a first layer directly on the bottom of the trough and the liquid phases with lower density form liquid layers with decreasing density on the first layer. To achieve a uniform distribution of each liquid phase on the internals of the mass transfer column, it is preferred, that openings are arranged in the trough such that each liquid phase flows through openings being arranged in one height.

[0016] The openings in the trough, through which the liquid phase with the highest density flows may be arranged in the bottom of the trough and / or at a first height above the bottom in the side walls and / or in drip tubes. If the openings are arranged in the side walls of the trough or in drip tubes, the height of the openings is such that the phase boundary between the first liquid phase and the liquid phase above the first liquid phase is above the openings during operation, so that only liquid of the first liquid phase flows through these openings. For specifying the flow path it is possible to arrange guide plates on the outer surface of the side walls such that a closed channel is formed. The liquid passing the openings flows into the closed channel, and downwards on the outer surface of the side wall in the closed channel. At the end of the closed channel the liquid phase drips onto the internal in the mass transfer column. To avoid liquid flowing around the side wall to the underside of the bottom of the channel and drip at any position onto the internal of the mass transfer column, it may further be preferred that the side walls extend downwards beyond the underside of the bottom of the channel. In this case it is ensured that the liquid drips onto the internal at the position of the closed channel and a defined distribution of the liquid phases on the internal of the mass transfer column is achieved.

[0017] By the openings which are arranged in at least three different heights, particularly in three different heights, after separation into liquid phases with different densities, each liquid phase flows through openings arranged in one height. As each separate liquid phase flows through openings in one height, in difference to the distributors as known in the art, all liquid phases are distributed uniformly onto the internals.

[0018] While a load change behaves linearly with regard to a change in volume, the height of the liquid in the liquid distributor shows a quadratic behavior. This means, for example, that if the load is doubled, the head in the liquid distributor quadruples. If there are only two rows of holes, in unfavorable cases, the phase boundary layer may shift upwards and reach the second row of holes, which may lead to larger proportions of the first liquid phase in the second liquid phase. By using a liquid distributor having openings in three different heights, generally the openings at the lowest height are used for the first liquid phase and the openings in the second and third height are used for the second liquid phase. The openings arranged at the second height preferably are dimensioned for a small quantity. If there is a change in load, the phase boundary layer may rise to the openings at the second height. In this case the first liquid phase additionally flows through the openings at the second height, but second liquid phase still flows through the openings at the third height. Thus, the proportion of first liquid phase that is distributed onto the internals in the mass transfer column is lower than in a liquid distributor with openings in only two different heights. Therefore, using a liquid distributor with openings in at least three different heights, particularly in three different heights, is advantageous in terms of separation performance of the internals below the liquid distributor.

[0019] If liquids which form different phases are fed onto the liquid distributor, it is possible to feed at least two different liquids which do not mix and, thus, form different phases or to feed at least one one-phase liquid mixture and at least one further liquid and liquid mixture and the formation of the different phases results from mixing the liquids, for example because by mixing the liquids the resulting mixture falls into a miscibility gap and for this reason, the liquid separates into different phases. In the following description, the term "multi-phase liquid” is used for each form of liquid fed onto the distributor, i.e. for multi-phase liquids being fed or for multi-phase liquids which result from feeding at least two liquids which from different phases.

[0020] To ensure that the amount of each liquid phase distributed onto the internals of the mass transfer column corresponds to the amount of the respective liquid phase in the multi-phase liquid it may be necessary to adapt the total cross sectional area of all openings through which one phase flows to the amount of the respective liquid phase in the multi-phase liquid. For this purpose, it is possible, for example, to adapt the number of openings or the cross sectional area of the openings through which one liquid phase flows to the amount of the respective liquid phase. If in a two-phase flow for example the first liquid phase with the higher density has a lower amount than the second liquid phase having the lower density, it is for example possible to design the openings through which the second liquid phase flows with a larger diameter than the openings, through which the first liquid phase flows. Further, it is also possible to provide a larger number of openings through which the second liquid phase flows than openings through which the first liquid phase flows. The larger number may be achieved for example by a smaller distance between two openings in that height through which the liquid phase flows which has the larger amount, by providing a larger number of drip tubes having openings in the height through which that liquid phase flows which has the larger amount or by providing openings in at least two different heights, wherein each of the two different heights is such that the liquid phase which has the larger amount flows through the openings which are arranged in the at least two different heights. It is preferred to arrange the openings in three different heights. In this case, the openings may be arranged in such a way that the first liquid phase flows through the openings which are arranged at the first height, the first liquid phase or the second liquid phase flows through the openings which are arranged at the second height, and the second liquid phase flows through the openings which are arranged at the third height. Thus, the first liquid phase may flow through the openings which are arranged at the first height and at the second height and the second liquid phase flows through the openings which are arranged at the third height, or the first liquid phase flows through the openings which are arranged at the first height and the second liquid phase flows through the openings which are arranged at the second height and at the third height.

[0021] An alternative that a mixture of the first and the second liquid phase flows through the openings which are arranged at the second height may be possible, if the volumetric amount of the second liquid phase does not deviate more than 50 % from the volumetric amount of the first liquid phase, preferably does not deviate more than 20 % from the volumetric amount of the first liquid phase. The volumetric amount of the second liquid phase in this case may be higher or lower than the volumetric amount of the first liquid phase, or the volumetric amounts of the first liquid phase and the second liquid phase may also be the same.

[0022] If the first liquid phase flows through the openings which are arranged in the second height, it is preferred that the volume flow of the first liquid phase is more than 30 % larger than the volume flow of the second liquid phase and particularly, the volume flow of the first liquid phase is 30 % to 150 % larger than the volume flow of the second liquid phase. On the other hand, if the second liquid phase flows through the openings which are arranged at the second height, it is preferred that the volume flow of the second liquid phase is more than 30 % larger than the volume flow of the first liquid phase and particularly that the volume flow of the second liquid phase is 30 % to 750 % larger than the volume flow of the first liquid phase.

[0023] If the multi-phase liquid is a two phase liquid and drip tubes are used for distributing the liquid onto the internal, it is preferred that the drip tubes comprise a first group of drip tubes in which the openings are arranged in a first height above the bottom and a second group of drip tubes in which the openings are arranged in a second height above the bottom, wherein the first height is smaller than the second height. By using drip tubes in two groups, the first liquid phase flows through the drip tubes of the first group and the second liquid phase flows through the drip tubes of the second group. As only the liquid of one group flows through one drip tube, it is ensured that each liquid phase flows onto the internal below the liquid distributor. To ensure a uniform distribution of the liquid phases on the internal, the drip tubes of the first group and the drip tubes of the second group are distributed uniformly in the trough of the liquid distributor.

[0024] For arranging the openings in three different heights, it is possible either to provide the drip tubes of the first group with openings in an additional height or to provide the drip tubes of the second group with openings in an additional height. If the drip tubes of the first group comprise openings in two different heights, all openings in the drip tubes of the first group preferably are arranged such that only the first liquid phase flows through the openings. However, it is also possible to arrange the openings in such a way that the first liquid phase flows through the openings in the first height and a mixture of the first and second liquid phases flows through the openings arranged in a height above the openings which are arranged in the first height.

[0025] If, on the other hand, the drip tubes of the second group comprise openings in two different heights, the openings preferably are arranged such that only the second liquid phase flows through the openings or that a mixture of the first and second liquid phase flows through the openings arranged in the second height and the second liquid phase flows through the openings which are arranged in the third height above the openings which are arranged in the second height. Preferably, the drip tubes of the second group additionally comprise the openings in a third height, wherein the second height is smaller than the third height.

[0026] To increase the area on the internal onto which the multi-phase liquid is distributed, it is preferred that each drip tube comprises an extension at an end outside the trough and the extension preferably ends in drip multipliers. The drip multiplier may have any shape as known by the skilled person. Generally, the liquid phase which flows through the openings of drip tube runs downwards on the inner wall of the drip tube. For obtaining more than one drop, the drip multiplier usually comprises at least two extensions along which the liquid phase flows and at the end of each extension drops are formed which drip onto the internal. The extensions may have any suitable shape, for example, the extensions may be triangular with a tip from which the drops fall onto the internal, rectangular with an edge parallel to the top surface of the internal, and drips forming on the edge and falling onto the internal. Further, the drip multipliers may have a semi-circular or a semi-oval shape or any other shape on which drops are formed which then fall onto the internal.

[0027] Usually in a mass transfer process, components are separated by an intense contact between a liquid phase and a gas phase. The liquid phase and the gas phase may flow in co-current or in counter-current through the mass transfer column, preferably, the liquid phase and the gas phase flow in counter-current, the liquid phase from the top to the bottom of the mass transfer column and the gas phase from the bottom to the top of the mass transfer column.

[0028] To allow the gas phase flowing through the liquid distributor, it is necessary to provide flow paths for the gas phase in the liquid distributor. For this purpose, it is for example possible that the liquid distributor comprises at least one chimney extending through the bottom of the trough. The at least one chimney particularly is provided, if the trough extends over the whole cross sectional area of the column. During operation of the mass transfer column, the gas phase flows through the at least one chimney and can pass the liquid distributor in this way.

[0029] For a uniform distribution of the liquid phase onto the internal, the drip tubes are arranged around the at least one chimney. If more than one chimney is provided and the chimneys have a lengthy shape, the drip tubes preferably are arranged in spaces between at least two chimneys. A lengthy shape means for example a rectangular or oval shape of the chimneys. In an embodiment, the chimneys having a lengthy shape extend from edge to edge of the liquid distributor and if in this case more than one chimney is provided, the chimneys preferably are arranged in parallel. If, however, chimneys are used which extend from edge to edge, it is particularly preferred to divide the respective chimney to allow a liquid exchange on the whole distributor.

[0030] Besides a construction with a trough with chimneys, through which the gas phase flows, the liquid distributor may be designed such that the trough comprises a central channel with channels extending from the central channel and the openings are formed in the walls of the channels and / or at least one drip tube is arranged in each channel. Alternatively, the trough of the liquid distributor may be a central channel with drip tubes or openings in the side wall with guiding plates forming a closed channel, wherein the central channel is placed above distributor channels, wherein the drip tubes in the central channel or the closed channels are arranged such that liquid from the central channel flows through the drip tubes or the closed channels into the distributor channels and all drip tubes or closed channels through which liquid flows into the same distributor channel have openings in the same height. Alternatively, is also possible to arrange openings in the central channel in different heights above each distributor channel so that all liquid phases flow into the respective distributor channel. In this case, also each distributor channel comprises openings in different heights for distributing all liquid phases onto the internals. However, particularly preferably, the distributor channels extend from the central channel.

[0031] If the liquid distributor comprises a central channel and distributor channels arranged below the central channel, it is possible to arrange the distributor channels with a space between two distributor channels and to arrange the drip tubes in the central channel in such a way that the liquid phases flow alternating into the distributor channels. If the multi-phase liquid is a two-phase liquid, it is preferred that the second liquid phase flows into the distributor channels next to the distributor channels into which the first liquid phase flows and that the first liquid phase flows into the distributor channels next to the distributor channels into which the second liquid phase flows. However, besides distributor channels for each liquid phase having a space in between, it is also possible to provide distributor channels which have a dividing wall, dividing the distributor channel into segments, wherein one liquid phase flows into each segment and from the segments onto the internal in the mass transfer column. The dividing wall, for example, may be corrugated or zigzag, however, a straight profile is preferred.

[0032] If the liquid distributor comprises a central channel with channels extending from the central channel, it is preferred that in each channel at least one drip tube of the first group and at least one drip tube of the second group are arranged. By this arrangement, a uniform distribution of each liquid phase onto the internal is achieved.

[0033] The number of drip tubes in each channel generally depends on the drip point density (number of drip points per m2). The minimum drip point density depends on the kind of internal below the liquid distributor. Further, the diameter of the openings and the number of openings depend on the amount of each liquid phase in the multi-phase liquid. On the other hand, if the number of drip tubes exceeds the minimum drop point density, it is also possible to choose the number of drip tubes such that it depends on the amount of each liquid phase in the multi-phase flow. However, preferably, the number of drip tubes only depends on the drip point density and the number and / or diameter of the openings in each drip tube depends on the amount of each liquid phase. If the volumetric amount of each liquid phase in the multi-phase liquid does not deviate more than 50 %, preferably not more than 20 % from the volumetric amount of each other liquid phase, it is preferred that the number of drip tubes of each group in each channel is the same. On the other hand, if the deviation of the at least one liquid phase in the multi-phase liquid deviates more than 50 % from the other liquid phases, it is preferred to provide a larger number of openings or bigger openings through which the excess liquid phase flows, or to provide a larger number of openings or openings with a larger diameter in the drip tubes through which the excess liquid phase flows. Preferably, the ratio of the number of drip tubes with openings in one height to the number of drip tubes with openings in different heights or the ratio of the number of openings in one height to the number of openings in the other heights or the ratio of the cross sectional area of the openings in one height to the cross sectional area of the other openings corresponds to the ratio of the amount of the liquid phase which flows through the openings of the drip tubes in this height to the amount of the other liquid phases. By this relationship of drip tubes, number of openings or cross sectional area of openings to the amount of the respective liquid phase flowing through these drip tube or openings, it is ensured that the ratio of the liquid phases which is distributed onto the internal below the liquid distributor corresponds to the ratio of the amount of the liquid phases in the multi-phase liquid.

[0034] The liquid distributor may be used in any mass transfer column, in which a liquid phase is distributed onto internals in the mass transfer column. The process carried out in the mass transfer column may be for example a distillation, a rectification, an absorption or gas scrubbing. Thus, the mass transfer column may be for example a distillation column, a rectification column, an absorption column or a column for gas scrubbing. Depending on the process carried out in the mass transfer column, the mass transfer column may contain one or more internals. Internals which may be used in the mass transfer column, for example, are trays, structured packings or unstructured packings. However, liquid distributors usually are used for distributing a liquid onto structured packings or random packings.

[0035] If the mass transfer column contains more than one internal, particularly more than one structured packing or more than one random packing or at least one structured packing and at least one random packing, it is preferred to provide a liquid distributor above each internal, i.e. above each packing. The multi-phase liquid may be fed into the trough of the liquid distributor through a feeding line. Alternatively, it is also possible, that at least one liquid phase is fed separately into the trough of the liquid distributor. For feeding the liquid into the trough of the liquid distributor any known tube or pipe may be used which passes the wall of the mass transfer column and ends in the trough. If the liquid distributor is located between two internals, at least a part of the multi-phase liquid collected in the trough before being distributed through the openings is flown through the internal above the liquid distributor and may drip from the bottom of the internal into the trough of the liquid distributor. However, preferably, the liquid from the internal above the liquid distributor is collected in a liquid collector, optionally mixed and then fed into the liquid distributor. Further additional liquid may be fed into the trough through a tube or pipe passing the wall of the mass transfer column and ending in the trough of the liquid distributor.

[0036] In the mass transfer column, components are separated by intense contact between a liquid phase and a gas phase. During contact between the liquid phase and the gas phase at least one component from the gas phase is transferred into the liquid phase or at least one component from the liquid phase is transferred into the gas phase. In the mass transfer column, the liquid phase and the gas phase may flow in co-current or in counter-current. However, preferably, the liquid phase and the gas phase flow in counter-current, the liquid phase from the top to the bottom of the mass transfer column and the gas phase from the bottom to the top of the mass transfer column. To allow the gas phase pass the liquid distributors, suitable paths must be provided through which the gas phase can flow. If the trough of the liquid distributor comprises a central channel and channels extending from the central channel or the trough is a central channel which is placed above distributor channels, the gas phase can pass the liquid distributor through the spaces between the channels or the distributor channels. Additionally or alternatively, the liquid distributor may comprise chimneys, through which the gas phase can pass the liquid distributor. Particularly for designs of the trough without channels, for example if the trough has the shape of a tray extending over most of the cross-section of the mass transfer column, preferably over more than 80 % of the cross-section of the mass transfer column, more preferably over more than 90 % of the cross-section of the mass transfer and particularly over the whole crosssection of the mass transfer column. For letting the gas pass the liquid distributor, only one chimney may be provided or more than one chimney. The number of chimneys thereby depends on the amount of the gas stream and the total cross sectional area of all chimneys. The smaller the cross-sectional area of each chimney and the larger the amount of the gas phase is, the more chimneys are needed. The number and the shape of the chimneys can be determined by any known mathematical simulation method, for example by using finite element or finite volume methods.

[0037] Examples of the invention are shown in the figures and explained in more detail in the description below.

[0038] In the figures:

[0039] Figure 1 shows a liquid distributor with a central channel and channels extending from the central channel;

[0040] Figure 2 shows a liquid distributor with a central channel and distributor channels below the central channel;

[0041] Figures 3a to 3c show sections of a channel of the liquid distributor of figure 1 with drip tubes in different embodiments;

[0042] Figures 4a and 4b show sections of a channel of the distributor of figure 1 with openings in the side walls in different embodiments; Figure 5 shows a liquid distributor with drip tubes and channels;

[0043] Figures 6a and 6b show liquid distributors with a trough with bottom and side walls with drip tubes in different embodiments; and

[0044] Figure 7 shows drip tubes with drip multipliers.

[0045] Figure 1 shows a liquid distributor with a central channel and channels extending from the central channel.

[0046] For distributing liquid onto internals of a mass transfer column, a liquid distributor 1 with a central channel 3 and channels 5 extending from the central channel 3 may be used. The central channel 3 and the channels 5 have a bottom, which is not shown in figure 1 and side walls 7 connected to the bottom and thereby form a trough 9.

[0047] The liquid to be distributed is fed into the central channel 3 by a suitable feed line, which may end at any position in the central channel 3 or which ends above the central channel 3. From the central channel 3 the liquid flows into the channels 5 and then is distributed onto the internals of a mass transfer column through openings in the channels. The openings may be arranged in the bottom of the liquid distributor 1, in the side walls 7 and / or in drip tubes which are arranged in the channels 5.

[0048] A liquid distributor 1 with a central channel 3 which is arranged above distributor channels 11 is shown in figure 2.

[0049] For distributing the liquid onto an internal of a mass transfer column, the liquid is fed into the central channel, which may be carried out as described above for the liquid distributor 1 shown in figure 1 . In difference of the liquid distributor 1 of figure 1, in the liquid distributor 1 of figure 2, the liquid flows through openings in the central channel 3, for example in the bottom of the central channel, in walls of the central channel 3 or by using drip tubes with openings, into the distributor channels below the central channel. If the openings are arranged in the wall of the central channel 3 it is further preferred to use guiding plates to ensure that all liquid passing the openings flows into the distributor channels 11 below the central channel 3. From the drip tubes the liquid flows onto the internals of the mass transfer column. For this purpose openings may be arranged in the bottom of the distributor channels, in side walls 13 of the distributor channels 11 and / or in drip tubes in the distributor channels 11 .

[0050] Figures 3a to 3c show different embodiments of drip tubes in channels which extend from the central channel of the liquid distributor shown in figure 1.

[0051] If a multi-phase liquid is to be distributed onto the internal of a mass transfer column, it is necessary that all phases of the multi-phase liquid are distributed onto the internals. For this purpose, drip tubes 15 are used, which have openings 17 in different heights. The embodiments shown here are suitable for multi-phase liquids which separate in two different phases. The drip tubes 15 for distributing the liquid onto the internals of the mass transfer column extend through the bottom 19 of the channels 5, wherein drip tubes 15.1 of a first group and drip tubes 15.2 of a second group are arranged in the channels 5. The drip tubes 15.1 of the first group comprise openings17 in a first height and the drip tubes 15.2 of the second group comprise openings 17 in a second height and a third height.

[0052] During operation of the mass transfer column, the liquid in the channels separates into two phases, a first phase having a higher density, which forms a lower layer and a second phase with a lower density forms an upper layer above the first layer. The liquid of the first layer flows through the openings 17 of the drip tubes 15.1 of the first group and the liquid of the second layer flows though the openings 15 of the drip tubes 15.2 of the second group. As each liquid phase flows though one group of drip tubes 15.1, 15.2, it is ensured that each liquid phase is distributed onto the internal of the mass transfer column.

[0053] In all embodiments of the figures 1 to 3, the number of drip tubes 15.1 of the first group and the number of drip tubes 15.2 of the second group preferably is the same and are arranged alternating in the channels 5.

[0054] The embodiment of figure 3a may be used particularly if the volumetric amount of the first liquid phase and the second liquid phase does not differ more than 50 % from each other, preferably not more than 20 % from each other to ensure that the amount of each phase being distributed onto the internals of the mass transfer column corresponds to the amount of the respective phases in the multi-phase liquid.

[0055] If the multi-phase liquid comprises more than two phases, further groups of drip tubes 15 are arranged in the channels, so that for each liquid phase one group of drip tubes 15 is comprised.

[0056] If the volumetric amount of the first and second liquid phase of the multi-phase liquid does not differ more than 50 %, preferably not more than 20 %, the openings 17 in the drip tubes 15.2 of the second group at the lower height preferably are arranged at a height which corresponds to the height of the phase boundary between the first liquid phase and the second liquid phase, so that at normal operation conditions both phases flow through the openings 17 at the lower height of the drip tubes 15.2 of the second group. If the phase boundary falls below the openings 17 at the lower height in the drip tubes 15.2 of the second group, the second liquid phase having the lower density (the upper phase) flows through these openings17. Accordingly, if the phase boundary rises above the openings 17 at the lower height in the drip tubes 15.2 of the second group, the first liquid phase having the higher density (the lower phase) flows through these openings. By this arrangement, it is ensured that variations in the amount of the first and second liquid phases are levelled.

[0057] The openings 17 in the drip tubes 15.2 of the second group being arranged above the openings at the lower height are in such a height, that during normal operation always the second liquid phase having the lower density flows through these openings 17. Figure 3b shows a channel 5 with drip tubes 15 in a second embodiment. In contrast to the embodiment shown in figure 3a, each drip tube 15 comprises an overflow slot 21.

[0058] The overflow slots 21 ensure that liquid can flow out of the channels 5 if too much liquid is fed into the channels. By the overflow slots 21 , the liquid leaves the channels 5 through the drip tubes 15 and, thus, in a defined way before liquid flows over the side walls 7 of the channels 5. The overflow slots 21 may have any suitable cross sectional area, for example a triangular shape, a square or rectangular shape, a semi-circular shape or a parabolic shape.

[0059] To ensure that each liquid phase is distributed onto the internal in such an amount that it corresponds to the amount of the respective liquid phase in the multi-phase liquid, it is necessary, that the ratio of the number of openings in the drip tubes 15 of one group to the number of openings in the drip tubes 15 of all other groups corresponds to the amount of the liquid phase which flows through the openings in the drip tubes 15 of the respective group to the amount of all other liquid phases.

[0060] If the amount of the second phase of a two-phase liquid is larger than the amount of the first phase, it is necessary that the number openings in the drip tubes 15.2 of the second group is larger than the number of openings in the drip tubes 15.1 of the first group. This is shown as an example in figure 3c. Here the drip tubes 15.2 of the second group each comprise openings 15 in three different heights. The openings may be arranged such that the openings 17 at the lowest height have the same function as described above for the embodiment of figure 3b.

[0061] On the other hand, all openings in the drip tubes 15.2 of the second group may be arranged at heights at which only the second liquid phase flows through the respective openings. This may be applied for the embodiments shown in figures 3b and 3c, respectively.

[0062] If the amount of the first liquid phase is larger than the amount of the second liquid phase, the number of openings in the drip tubes 15.1 of the first group is larger than the number of openings in the drip tubes 15.2 of the second group.

[0063] Independently of the number of openings in each drip tube 15.1 of the first group and in each drip tube 15.2 of the second group, it is preferred that the drip tubes 15 extend through the bottom 15 of the channel 5 and a part of the drip tube protrudes downwards from the bottom 19 of the channel. By this, it is avoided that liquid flows from the inner wall of the drip tube to the underside of the bottom 9 of the channel 5, which would result in a more uneven distribution of the liquid phases onto the internal.

[0064] Additionally or as an alternative, the openings 17 for distributing the liquid phases onto the internals in the mass transfer column may be arranged in the side walls of the channels 5 as shown for example in figures 4a and 4b. In the embodiment shown in figure 4a, the openings 17 are arranged in three different heights, comparable to the arrangement of the openings 17 in the drip tubes 15 as shown in figures 3a and 3b. Also in this case, the first liquid phase having the higher density and forming the lower layer flows through the openings 17 arranged in the lowest height and the second liquid phase having the lower density flows through the openings arranged in the height with the largest distance to the bottom 19 of the channel 5. The openings 17 in the second height between the openings through which the first liquid phase flows and the openings through which the second liquid phase flows during normal operation are arranged in a height which corresponds to the height of the liquid boundary between the first and second liquid phases at optimum process conditions.

[0065] During normal operation, the liquid phases flow through the openings, run along the channel walls 7 outside the channel 5 and drip from the channel wall onto the internal of the mass transfer column.

[0066] To avoid liquid flowing in any direction on the outer surface of the channel walls but straight downwards to achieve a defined position at which the liquid drips onto the internal of the mass transfer column, it is possible to provide guiding plates 23 at the positions where the openings in the side walls 7 are arranged. The guiding plates 23 are fixed to the outer surface of the side walls 7, thereby forming a closed channel 24. This is shown as an example in figure 4b. To avoid liquid flowing from the closed channels 24 onto the underside of the bottom 19 and then drip at any position from the underside of the bottom onto the internal, it may further be preferred that the side walls 7 extends downwards beyond the underside of the bottom 9. Particularly in combination with the guiding plates 23 forming the closed channels 24 the liquid drips at defined positions onto the internal in the mass transfer column, namely at the positions of the closed channels 24.

[0067] To further avoid an uncontrolled overflow of the liquid over the side walls 7 of the channel 5, if the amount of liquid in the channel 5 exceeds the maximum fill level which is defined by the height of the side walls 7, it is preferred to provide overflow slots 21 . By providing the overflow slots, particularly in combination with the guiding plates 23 forming the closed channels 24, the liquid flows through the overflow slots 21 into the closed channels 24 and, thus, is distributed onto the internal at defined positions. By the overflow slots 21 it is avoided that the liquid level in the channel 5 reaches the upper edge of the side walls 7 and overflows the side walls 7 at undefined positions.

[0068] Besides the arrangement of the openings 17 as shown here, any other arrangement is possible, depending on the composition of the multi-phase liquid. The openings may be arranged for example in heights as shown for drip tubes 15 in figures 3a to 3c. However, any other arrangement also may be possible, for example openings 17 in at least two different heights for the first liquid phase with higher density or openings in additional heights for additional liquid phases. If a liquid distributor 1 with a central channel 3 and distributor channels 11 arranged below the central channel 3 as shown in figure 2 is used, the central channel 3 corresponds to the trough 9 with the drip tubes 15 and / or with the openings 17 in the side walls 9.

[0069] In this case the drip tubes 15 and / or the openings 17 in the side walls 9 may be arranged such that only one liquid phase flows into one distributor channel 11 . The distributor channels 11 may be designed such that they contain a dividing wall forming two separate sections in each distributor channel 11. In this case, the drip tubes 15 or the openings in the side walls 9 are arranged such that only one liquid phase flows into one segment. By this distribution of the liquid phases into the distributor channels 11 it is ensured that each distributor channel or section of a distributor channel contains only one liquid phase which is distributed from the distributor channel or each section of the distributor channel onto the internals of the mass transfer column. Alternatively, it is also possible to arrange openings in the walls of the central channel 3 or drip tubes 15 in the central channel 3 in such a way that all phases flow in each distributor channel 11 below the central channel 3. In this case, also the distributor channels 11 comprise openings at different heights and / or drip tubes with openings at different heights so that all liquid phases collected in the respective distributor channel 11 flow onto the internal below the liquid distributor 1 .

[0070] As only one liquid phase is contained in each distributor channel 11 or each section of the distributor channel 11 , it is sufficient to provide openings either in one height in the side walls or to use drip tubes with only one hole. However, preferably, the distributor channels or the sections in the distributor channels comprise openings in their bottom through which the liquid phase drips from the distributor channel 11 onto the internal of the mass transfer column.

[0071] Besides liquid distributors 1 having a central channel 3 and channels 5 extending from the central channel 3 or having a central channel 3 and distributor channels 11 as shown in figures 1 and 2, it is also possible to provide a tray as a liquid distributor. Such a liquid distributor 1 is shown as an example in figure 5.

[0072] The liquid distributor 1 shown in figure 5 comprise a bottom 19 which preferably has the same shape as the cross sectional shape of the mass transfer column. The liquid distributor 1 then is mounted as a tray in the mass transfer column, wherein the walls of the mass transfer column simultaneously form the side walls of the liquid distributor 1.

[0073] Such a liquid distributor may be used particularly as a liquid distributor which is arranged between two internals in the mass transfer column. In this case, all liquid leaving an upper internal drips onto the liquid distributor, may be mixed with additional liquid which can be fed onto the liquid distributor through a suitable feed line and then in distributed onto an internal below the liquid distributor.

[0074] For distributing a multi-phase liquid, drip tubes 15 extend through the bottom 19 of the liquid distributor, each drip tube 15 having at least one opening 17. In the embodiment shown in figure 5, the drip tubes 15 are arranged in drip tubes 15.1 of a first group having openings in a first height and in drip tubes 15.2 of a second group having openings 17 in a second height and a third height being above the openings 17 in the first height of the drip tubes 15.1 of the first group.

[0075] Besides the arrangement of openings shown in figure 5, the openings 17 may have any other arrangement, for example any arrangement as described above for drip tubes being arranged in channels 5 of a liquid distributor as shown in figures 3a to 3c.

[0076] The drip tubes may end flush with the underside of the bottom 19 of the liquid distributor or may extend downwards beyond the underside of the bottom 19 as shown in figure 4b. The alternative with the drip tubes 15 extending downwards beyond the underside of the bottom 19 of the liquid distributor 1 being preferred, so that the liquid drips form the drip tubes 15 onto the internal in the mass transfer column at defined positions.

[0077] To allow the gas phase pass the liquid distributor upwards, chimneys 25 are provided. The height of the chimneys is such that no liquid may overflow the chimneys and, thus flow through the chimneys onto the internal below the liquid distributor 1. For this purpose, it is preferred that the height of the chimneys is at least the same as the height of the drip tubes 15 extending above the bottom 19. Particularly if the drip tubes do not comprise overflow slots, it is further preferred if the chimneys 25 are higher than the drip tubes 15.

[0078] Further alternatives for liquid distributors having a bottom 19 and side walls 7, forming a trough 9 are shown in figures 6a and 6b.

[0079] In contrast to the liquid distributors 1 shown in figure 5, the liquid distributors 1 shown in figures 6a and 6b may be mounted in a mass transfer column in such a way that there is a space between the side walls 7 and the inner walls of the mass transfer column. Therefore, it is not necessary to provide chimneys 25 and the liquid distributor may only comprise drip tubes 15 as shown in figure 6a.

[0080] However, depending on the space between the side walls 7 of the liquid distributor 1 and the inner walls of the liquid column and the gas flow rate, it may be preferred to provide additional chimneys 25 through which the gas may flow upwards through the liquid distributor.

[0081] If the liquid distributor 1 is used for distributing a two-phase liquid, the drip tubes 15 preferably are arranged in drip tubes 15.1 of a first group and drip tubes 15.2 of a second group. The openings in the drip tubes may have any suitable arrangement, for example one opening in the drip tubes 15.1 of the first group and two openings 17 in the drip tubes 15.2 of the second group. However, any other arrangement of openings may be suitable, depending on the number of liquid phases in the multi-phase liquid and the amount of each liquid phase in the multi-phase liquid. For this purpose, the openings 17 may be arranged in the drip tubes 15 for example as described above for the drip tubes 15 in the channels 5 of a liquid distributor as shown in figure 1.

[0082] For further spreading the liquid phase onto the internal below the liquid distributor, it may be further preferred to provide each drip tube 15 with a drip multiplier 27. This is exemplary shown in figure 7.

[0083] In the embodiment of figure 7, the drip tubes 15 are arranged in drip tubes 15.1 of a first group having one openings 17 and drip tubes 15.2 of a second group having two openings 17 being arranged one above the other and the lower one in a greater height from the bottom 19 of the liquid distributor 1 than the openings in the drip tubes 15.1 of the first group. During operation, a two phase liquid separates into a first liquid phase 29 and a second liquid phase 31 , the first liquid phase 29 having a higher density than the second liquid phase 31. The first liquid phase 29 forms a first lower layer on the bottom 19 of the liquid distributor and the second liquid phase 31 forms a second layer above the first liquid phase 29, the liquid phases being separated by a phase boundary 33. The openings 17 in the drip tubes 15.1 of the first group are arranged in a height such that only the first liquid phase 29 flows through the drip tubes 15.1 of the first group. The openings 17 in the drip tubes 15.2 of the second group are arranged such that the openings 17 being arranged at a lower height above the bottom 19 close to the phase boundary 33 between the first liquid phase 29 and the second liquid phase 31 . Depending on the amount of the first phase 29 in the liquid distributor, the phase boundary 33 may be below the lower openings 17 in the drip tubes 15.2 of the second group so that liquid of the second liquid phase flows through these openings or the liquid boundary may rise above the lower openings in the drip tubes 15.2 of the second group so that liquid of the first liquid phase flows through these openings. If the phase boundary is at the same height as the lower openings in the drip tubes 15.2 of the second group, both liquid phases flow through these openings 17.

[0084] For spreading the liquid which flows through the drip tubes 15 onto the internal below the liquid distributor, it is preferred that each drip tube 15 ends in a drip multiplier 27. The drip multipliers for example have extensions 35. The liquid flows on the inner surface of the drip tubes along the extensions 35 and drips from the end of the extension 35 onto the internal below the liquid distributor 1. The extensions 35 may have a rectangular shape as shown here or, alternatively, may have a triangular shape with the tip of the triangle facing the upper surface of the internal, or may have a half-elliptical shape or a semicircular shape. However, besides these shapes any other shape may be possible being such that drips form at the end of the extensions 35 and fall onto the internal in the mass transfer column. To increase the area onto which the liquid of one drip tube 15 drips, the diameter of the drip tubes increases at their lower end and particularly the ends of the extensions 35 facing the internal below the liquid distributor have a larger distance to the central axis of the drip tubes 15 than the wall of the drip tube above the bottom 19 of the liquid distributor.

Claims

Claims1 . A process for operating a mass transfer column comprising internals and at least one liquid distributor (1) for distributing a multi-phase liquid, wherein the liquid distributor (1) comprises a trough(9) for collecting the multiphase liquid to be distributed onto internals in the mass transfer column, the trough (9) having a bottom (19) and side walls (7), wherein openings (17) for distributing the multi-phase liquid are formed in the trough (9) and / or in drip tubes (15) extending through the bottom (19) into the trough (9), wherein the openings (17) are arranged in at least three different heights, the process comprising:(a) feeding a multi-phase liquid or liquids which form different phases onto the liquid distributor (1) according to any of claims 1 to 9, wherein the multi-phase liquid separates into liquid phases which each have a different density in the trough (9) of the liquid distributor (1),(b) distributing the liquid comprising the at least two liquid phases onto the internals in the mass transfer column, wherein the liquid having the highest density flows through the openings (17) arranged at the first height and liquid phases with lower density flow through openings (17) arranged above the openings (17) arranged at the first height, wherein each liquid phase flows through openings (17) at one height, wherein the liquid comprises two liquid phases and the first liquid phase (29) flows through the openings (17) which are arranged at the first height, the first liquid phase or the second liquid phase flows through the openings (17) which are arranged at the second height, depending on the load distribution, and the second liquid phase (31) flows through the openings (17) which are arranged at the third height, if the openings (17) are arranged in three different heights.

2. The process according to claim 1, wherein the drip tubes (15) comprise a first group of drip tubes (15.1) in which the openings (17) are arranged in a first height above the bottom (19) and a second group of drip tubes (15.2) in which the openings (17) are arranged in a second height above the bottom (19), wherein the first height is smaller than the second height.

3. The process according to claim 1 or 2, wherein the drip tubes (15.2) of the second group additionally comprise the openings (17) in the third height, wherein the second height is smaller than the third height.

4. The process according to any of claims 1 to 3, wherein each drip tube (15) comprises an extension at an end outside the trough (9).

5. The process according to claim 4, wherein the extension preferably ends in drip multipliers (27).

6. The process according to any of claims 1 to 5, wherein the liquid distributor (1) comprises at least one chimney (25) extending through the bottom (19) of the trough (9).

7. The process according to claim 6, wherein the drip tubes (15) are arranged in spaces between at least two chimneys (25) or around the at least one chimney (25).

8. The process according to claim 7, wherein the trough (9) comprises a central channel (3) and channels (5) extending from the central channel (3) and the openings (17) are formed in the walls (7) of the channels (5) and / or at least one drip tube (15) is arranged in each channel (5) or wherein the trough (9) of the liquid distributor (1) is a central channel (3) with drip tubes (15) or openings (17) in the side wall with guiding plates (19) forming a closed channel (24), wherein the central channel (3) is placed above distributor channels (11) and the drip tubes (15) in the central channel (3) or the closed channels (24) are arranged such that liquid from the central channel (3) flows through the drip tubes (15) or the closed channels (24) into the distributor channels (11).

9. The process according to claim 8, wherein in each channel (5) at least one drip tube (15.1) of the first group and at least one drip tube (15.2) of the second group are arranged.

10. The process according to any of claims 1 to 9, wherein a gas stream flows in counter current to the liquid phase and through chimneys (25) in the liquid distributor (1).11 . The process according to any of claims 1 to 10, wherein the internals are at least one of trays, structured packings or random packings.

12. The process according to claim 10 or 11, wherein the process is a distillation, a rectification, an absorption or gas.

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