MXPA99008895A - Structured packing for mass transfer and/or heat exchange between a liquid and a gas - Google Patents

Abstract

The invention relates to a structured packing (1) for mass transfer or heat exchange between a liquid and a gas. The structured packing comprises a multiplicity of sheets (2, 3) with corrugations (G) parallel to one another. Adjoining sheets are arranged crosswise with respect to the direction of their channels. The corrugations of each sheet have a corrugation height (H) and a corrugation width (B). The ratio of the corrugation height (H) to corrugation width (B) satisfies the equation H/B=0.75, preferably satisfies the equation H/B=1 and even more preferentially satisfies the equation H/B=2. The sheets with corrugations can have a triangular or sine-wave-shaped corrugation profile. The direction of the channels in the sheets can be arranged at an angle of approximately 45°to 70°with respect to the vertical.

Description

STRUCTURED PACKAGING FOR. TRANSFER OF MASS AND / OR EXCHANGE OF HEAT BETWEEN A LIQUID AND A GAS TECHNICAL FIELD The present invention relates to a structured packing for mass transfer and / or heat exchange between a liquid and a gas, wherein the structured packing comprises a multiplicity of sheets with parallel grooves to each other / the grooves in the sheets they delimit channels, and wherein groove bonding sheets are arranged with their transverse channel directions, and wherein the grooves of each sheet have a groove height H and a width B of groove. Structured packings of this type are generally known per se. In the case of sheets having grooves in the shape of a sine wave, in general a value of about the number p is taken for the groove width, while a figure about a value of 1 is taken for the height of the groove . In this context, the unit of rt and the value of 1 is generally in cm. With a structured packing of this type, ribbed connecting sheets (also called grooved sheets) are always arranged transversely one with respect to another, in such a way that the flow channels delimited by the grooved sheets cross one another, the so-called Boundary surfaces are formed at the site where the open sides of two crossing channels cross each other. The gas streams flowing in different directions through channels that cross each other are brought into contact with one another at the boundary surfaces. The pressure drop on a structured packing as a consequence of the flow resistances to which the gas streams flowing through it are held is largely dependent on, on the one hand, the resistance to the flow to which it is subjected. they hold the gas streams on the contact surface with the grooved sheets and, on the other hand, the resistance co or a consequence of flow effects produced at the boundary surfaces, which are also called boundary surface effects, such like the turbulence. The perspective maintained in this context is that the gas phase does not mix well, or mixes less well if the H / N ratio is too large. For this reason, a ratio of groove height to groove width that is less than 0.3 to 0.5, ie, H / B < 0.3 - 0.5, is used in practice. In order to maintain the pressure drop on such relatively small structured packing, the grooved sheets, which in practice are arranged vertically, are arranged with the direction of their channels usually at an angle of approximately 30 ° with respect to the vertical, the angle, however, will not exceed 45 ° in practice. The reason for this is that the resistance to flow over the packing becomes too great when the angle of the direction of the channel with respect to the vertical is (relatively) large. The object of the present invention is to provide an improved structured packing of the type indicated in the preamble. The object is achieved according to the invention in that the ratio of the groove height H to the groove width B satisfies the equation H / B = 0.75. When the H / B ratio increases, the influence of the effects that give rise to resistance to flow in the so-called limit surfaces decreases, because the average distance of the gas from the boundary surface increases in these sites with a relation Larger H / B However, this reduction in flow resistance as a consequence of the so-called limit surface effects is displaced by an increase in the flow resistance experienced at the contact surface between the fluted sheets and the gas streams, since the contact surface per channel between the sheet and the gas stream becomes larger when the H / B ratio increases. Surprisingly, however, it has been found that the increase in flow resistance at the contact surfaces is outweighed by the advantages that are achieved as a result of the reduction in the size of the boundary surfaces (which, incidentally, is also accompanied by a reduction in the total number of limit surfaces in a packaging) and that other expected disadvantages do not arise, or arise only, and are overcome by the advantages achieved. It is found that the surprising and advantageous effect is already apparent in H / B ratios of = 0.75, begins to manifest clearly in H / B = 1 ratios, and is particularly apparent in a H / B = 2 relation. It will be clear that , depending on the type of groove profile, in practice an upper limit will also be imposed on the H / B ratio, since if the H / B values are too large, the flow surface will assume a groove-like shape in a high grade, with the associated disadvantages of turbulence effects and / or effects of resistance to flow. Additionally, in particular in the case of non-rectangular containers, for example cylindrical, there will be a minimum number of sheets necessary to achieve an adequate degree of filling of the container. Especially in the case of metal sheets with grooves, it will be advantageous according to the invention, on the basis of cost, if the sheets have a triangular, trapezoidal or rectangular shaped groove profile. This is because profiles of this type, in particular triangular groove profiles, can be produced relatively easily from rolled metal or suitable plastic sheets by folding. However, on the basis of the flow technology, in practice, preference will often be given according to the invention to a sheet with grooves having a groove profile with approximately sinusoidal waveform, preferably a sinusoidal waveform. pure An important parameter when designing the structured packings of the type mentioned in the preamble, and also in the case of structured packings according to the invention, is the so-called specific surface area, which has m2 / m3 as its unit. The specific surface area is in fact the contact surface of the sheets per cubic meter of packaging. The values widely used in practice for this so-called specific surface area are: approximately 125 irf1, approximately 200 m_1, approximately 250 m "1, and approximately 500 irf 1. Assuming that a specific surface area is required, desired or prescribed, B and H, according to the invention, will advantageously form a solution to the equation: which can be solved numerically. It follows from this equation that, for a certain specific surface area, there is a relationship between B and H that can be represented as a curve in a two-dimensional graph. In order to achieve an optimum flow of liquid over the structured packing it is advantageous according to the invention if the grooved sheets are arranged essentially vertically. According to an advantageous embodiment of the invention, one or more of the grooved sheets are arranged with their channel direction at an angle of at least about 45 ° with respect to the vertical.

Preferably, one or more of the grooved sheets are arranged with their channel direction at an angle of about 55 ° to 65 ° with respect to the vertical, such as at an angle of about 60 ° with respect to the vertical. Such angles for the direction of the channel are currently not feasible with structured packings consisting of grooved sheets according to the prior art, since the flow resistance of the packaging then assumes a too high value. However, with relatively larger H / B ratios according to the invention, surprisingly it was found that it is possible to make a larger angle of the channel direction with respect to the vertical, still up to about 70 °. The advantage of a larger angle of the direction of the channel with respect to the vertical is that a better mass transfer is achieved between the gas flowing upwards via the structured packing and the liquid flowing down on the structured packing by this means. It should be noted that, compared to the prior art, according to the invention highly advantageous effects are also achieved with channel directions of less than 45 ° with respect to the vertical, such as in 10-45 ° with respect to the vertical . With such smaller angles, the pressure drop on the packing according to the invention is lower than in the case with conventional packing. To restrict the resistance to gas flow in the edge regions joining the wall or the wall section in the transition from one channel to another channel when the structured packing is arranged in a container in such a way that the fluted sheets delimit channels that they extend between opposite walls or wall sections thereof, especially when the channels are at relatively large angles with respect to the vertical, it is advantageous according to the invention if the grooved sheets are provided with holes at the ends of the channel that join the wall sections. Such holes make it easier for the flowing gas to pass from a channel running in one direction to a channel running in another transverse direction. Especially for containers having a relatively large cross-sectional area, or a relatively large diameter in the case of cylindrical containers, such an edge region will preferably extend up to 10-20 cm from the wall, depending on the so-called specific surface area. In this context it is understood that relatively large cylindrical containers are containers having a diameter of 1 m or more. In the case of relatively small containers, in particular, such edge region will extend over a distance of about 10% to 20% of the width / depth of the container, and in the case of a cylindrical container over a distance of about 10% to 20% of the diameter of the container. According to an advantageous embodiment, the holes will have a diameter of at least 2 mm to / preferably, at most 20 mm, or a flow area equivalent thereto in the case of non-circular orifices. The invention will now be explained in more detail with reference to the drawings. In the drawings: Figure 1 shows, schematically, a triangular groove profile, in which a few parameters thereof have been indicated in more detail; Figure 2 shows a perspective and schematic view of part of a structured packing according to the invention, composed of four layers; Figure 3 shows a schematic view, partly in cross section, of a container according to the invention; Figure 4 schematically shows a groove with a groove profile in the form of a sinusoidal wave; Figure 5 shows a graph of an H / B ratio for a groove profile in the form of a sine wave; and Figure 6 shows a highly schematic representation of a test assembly. Figure 1 shows, schematically, a triangular groove profile having a groove height H and a groove width B. It will be clear that the groove height H and the groove width B are assignable in an identical manner to the grooves of the groove profile in the form of a sinusoidal wave shown in Figure 4. Figure 2 shows, by way of example, in the form highly schematic, a structured packing according to the invention consisting of, by way of example, four layers of sheets with - grooves (also called grooved sheets), each having a triangular groove profile. With reference to the sheet 2 with grooves, it will be clear that each grooved sheet 2 delimits a multiplicity of channels extending transversely to the direction of the groove G.

The channels 6, which are open on the bottom side, or the channels 7, which are open at the top, thus have a channel direction K that extends transversely to the direction of the groove G. It will be clear that in this example according to Figure 2, the grooved sheets 3 are identical to the grooved sheets 2, except for their orientation. However, as will be clear to an average person skilled in the art, it is by no means necessary, as far as the essence of the invention is concerned, that the sheets with grooves 2 and 3 are identical, except for their orientation. , nor that the sheets with grooves in the layers 2 are identical to each other. As far as the essence of the invention is concerned, it is also not important that G and K are perpendicular to each other. As will also be apparent from Figure 2, where channels 7, open towards the upper part / and channels 6, open towards the lower part, intersect, imaginary boundary surfaces 4 are formed, which delimit the channels at this site. Additionally, it will be apparent that when the gas flows through the channels of adjacent sheets, the effects of the boundary surface will arise at the site of the boundary surfaces, the effects having an adverse influence on the flow resistance of the pack as a whole. Additionally, the gas flowing through the packing will be subjected to additional flow resistance upon contact with the grooved sheets themselves. According to the invention, it has been found that when a value of > 0.75 for the ratio of the groove height H to the groove width B there is an improvement in the flow resistance on the overall packing. Especially with H / B = 1 ratios and larger than this it is so obvious that greater advantages are achieved, the advantages can be increased even more if the H / B ratio is = 2. The modality according to Figure 3 shows a container according to the invention that is provided with a packaging 1 according to the invention. With such a container, liquid is distributed over the packaging via a spray device 10 at the top. The liquid flows down on the surfaces of the grooved sheets in such a way that a film of liquid forms on the surfaces of the sheets. A gas is supplied in the lower part of the packing, the gas flows up through the packing in counter-current to the liquid (film). The transfer between the liquid and the gas can take place during the counter-current flow. It is emphasized that the flow of gas and liquid through the packing may also optionally take place in co-corri or transverse flow. With packings according to the invention, advantages are also obtained with co-current and transverse current flow. With this assembly, the corrugated sheets of the packaging 1 are arranged vertically with a channel direction K at an angle substantially greater than 50 ° with respect to the vertical (however, angles of less than 50 ° are also usable, and offer significant advantages in accordance to the Invention). A lower packing 11 is also arranged below the upper packing 1. In the case of the upper packing 1, the direction of the channel runs at an angle of approximately 60 ° with respect to the vertical. In the case of the lower packing 11, the direction of the channel runs at an angle of approximately 45 ° with respect to the vertical, the angle under certain circumstances can also be smaller than 45 ° with respect to the vertical, such as, for example , 30 °. The so-called "flooding" problems are counteracted by making the angle of the channel direction with respect to the smaller vertical in the lower packing 11. It is understood that flooding in this context means that a droplet is suspended from the bottom of the packing / the droplet is easily dragged by the gas flowing up.This phenomenon of droplets that are suspended is counteracted by placing the channels of the lower section of the packaging at a more inclined angle.It is noted that the location of the channels in the section The lower packing angle at a more inclined angle to counteract the flood can also be employed independently of a relatively larger H / B ratio and also independently of relatively large angles for the direction of the upper packing channel 1, however, if, as is advantageously possible according to the invention, and using relatively large angles for the direction of the channel with respect to the vertical, in particular angles in a range of 50 ° to about 70", the so-called flood problem at the bottom of the packing is then exacerbated.

Figure 3 further illustrates what is meant by an edge region joining the wall or the wall section of the container. In this figure the edge region is indicated by R, and the magnitude of R will generally be approximately 10-20 cm for vessels having a diameter of 1 m and more, while for vessels having a smaller diameter the R will be approximately 10% to 20% of the diameter. The ribbed sheets are provided with holes 5 in the so-called edge region, the holes making it easier for the gas to pass from a channel sloped in one direction to a crossing channel, inclined in the other direction, in the edge regions , in order to reduce the flow resistance of the packaging. It will be advantageous to provide the edge regions of the packing with such holes 5 especially when, according to the invention, relatively large angles are used for the direction of the channel with respect to the vertical. The manner in which, starting from a certain surface area Ap, can be determined values for B and H in the case of a grooved sheet having a profile with sinusoidal wave form will be illustrated below with reference to Figures 4 and 5.

A sheet bent in the form of a sine wave can be described as follows in terms of parameters: y = (H / 2) (1-cos a) where a = 2p (X / B), so that X = > (a / 2p) B (1) The length of a small section of the sheet (see Figure 4) can then be described as: ds = dy2 + dx2 (2) Starting from equation (1) dy and dx can now be written as: dy = H / 2sen gives, and dx = (B / 2p) gives (3) Introducing equation 3) into equation (2) gives then; The integral of equation (4) (5) - ? r: »'« * [H? * - * ^ '"* (- then gives the total length of the sheet, which is usable for the determination of the specific surface area Ap according to equation (6) given below: 2s BHz = J "H <" (^) da (6) The relation of equation (6) can now be solved numerically for B as a function of H or vice versa, when a value for Ap is taken. Figure 5 shows the relationship between B and H when Ap is taken as 250 m_1. This curve is indicated by F. The line H = 0.75B has also been drawn in Figure 5. Looking at the intersection of the line with the curve F it can be seen that the intersection is located a little above that point on the curve F which is closest to the origin. In this context it is understood that the origin is the point H = 0 and B = 0. With reference to equation (6) and Figure 5 it can also be pointed out that corresponding curves can be produced for other values of Ap in a simple way about the base of Figure 5, For example, the curve for Ap = 500 irT1 can be obtained by simply dividing all values for B and H in Figure 5 by 2. If Ap is taken as 100 m "1, all values for B and H of Figure 5 should then be multiplied by 2.5.The curves for additional values of Ap can also be determined correspondingly, as will be obvious to a person skilled in the art.A number of experiments were performed using an assembly of test as shown highly schematically in Figure 6, in which experimental packings according to the invention were compared with prior art packings.

EXPERIMENT I In a first experiment six packaging units, numbered 21 and 22, were placed one above the other in a cylindrical container having a diameter of 19.2 cm. In this experiment each packaging unit 21, 22 consists of a number of vertically arranged sheets with grooves parallel to one another. As shown schematically in Figure 6, the grooved sheets 21 and 22 of adjacent packaging units are located perpendicular to each other. In the packaging units the channel direction of each sheet is in all cases at an angle of 45 ° to the vertical. The groove profiles in this experiment are essentially triangular in shape, with a groove height H and a groove width B, as indicated schematically in Figure 1. In other respects, two test assemblies were used. specific structural elements of which are given in the table below: TABLE 1 As can be seen from table 1, the so-called surface area specified by packing was set at Ap = * 250 m "" 1, and assembly I was designed for an H / B ratio of 0.49, and assembly II was designed to an H / B ratio of 1.13, for which the H and B can then therefore be deduced from the graph in Figure 5. Air was fed through both assemblies I and II at the so-called surface velocity Ug of the gas, successively, 1, 2, 3 and 5 m / second. The air was fed from the bottom to the top through the packings arranged in a cylinder, according to Figure 6. In this experiment the pressure drop on the column was then measured by mounting and surface velocity of the gas, in each case. In this context it is understood that the superficial gas velocity ug (in m / sec) is the average flow velocity of the air with respect to the cross-sectional area of the cylinder, the cross-sectional area therefore being 289.53 cm2 here. For this experiment, the air aspirated from the environment was at a temperature of 20 ° C and at an atmospheric pressure. The results of the measurements in this experiment are given in Table II below.

It can be seen from the data of the experimental measurements in Table II that the packing according to the invention (in assembly II) has a pressure drop that is generally about 25% less than the pressure drop in the case of assembly I.

EXPERIMENT II Experiment II was conducted using the same assemblies I and II used for Experiment I. The difference in this case is that in Experiment II a film of water was also introduced to the packings, spraying water on the top of the assembly shown in Figure 6. The amount of water is expressed here in g / sec / m2, ie in kg of water per second distributed over a cross-sectional area of the cylindrical container, which in this case is approximately 289.5 cm2, as indicated above. In Experiment II the surface velocity Ug of the gas at which a pressure drop per meter of packaging of 800 Pa / m is obtained was determined for three quantities of water W by assembly. The results obtained in this experiment are shown in Table III.

It can be seen from Table III that with assembly II, 25% higher gas velocities are permissible before a pressure drop of 800 Pa / m is obtained. This means that with a packing according to the invention, a capacity is feasible. of yield approximately 25% higher for a given pressure drop, which in this example is 800 Pa / m.

Claims (13)

1. CLAIMS 1. Structured packing for the transfer of mass and / or heat exchange between a liquid and a gas, where the structured packing comprises a multiplicity of sheets with grooves parallel to one another, the grooves in the sheets delimit channels, and wherein joint sheets are disposed transversely with respect to their channel direction / and wherein the grooves of each sheet have a groove height H and a groove width B, characterized in that the ratio of the height H from groove to width B of groove satisfies the equation H / B = 0.75.
2. 2. Structured packing according to claim 1, characterized in that the ratio of the groove height H to the groove width B satisfies the equation H / B = 1.
3. 3. Structured packing according to claim 1 or claim 2, characterized in that the ratio of the groove height H to the groove width B satisfies the equation H / B = 2.
4. 4. Structured packing according to one or more of the preceding claims 1-3, characterized in that one or more of the grooved sheets have a triangular groove profile.
5. 5. Structured packing according to one or more of the preceding claims 1-3, characterized in that one or more of the grooved sheets have a groove profile in the form of a sinusoidal wave.
6. 6. Structured packing according to one or more of the preceding claims, wherein the grooved sheets have a groove profile in the form of a sinusoidal wave / characterized in that for a certain specific surface area Ap desired, B and H form a solution of the equation: which can be solved numerically.
7. 7. Structured packing according to one or more of the preceding claims, characterized in that the grooved sheets are arranged essentially vertically.
8. 8. Structured packing according to claim 7, characterized in that one or more of the grooved sheets are arranged with their channel direction at an angle of approximately 45 ° to 70 ° with respect to the vertical,
9. 9. Structured packing according to claim 7 or claim 8, characterized in that one or more of the grooved sheets are arranged with their channel direction at an angle of about 55 ° to 65 ° with respect to the vertical, for example in a angle of approximately 60 ° with respect to the vertical.
10. 10. Container, in particular a container of an exchanger, provided with a structured packing according to one of the preceding claims, wherein the corrugated sheets delimit channels extending between opposite walls or wall sections of the container, characterized in that the sheets with grooves they are provided with holes in the ends of the channel that join the wall sections.
11. 11. Container according to claim 10, characterized in that the holes are made in a region of the end joining the wall or the wall section and extending up to 10-20 cm from the wall.
12. 12. Container according to claim 10 or claim 11, characterized in that the orifices are made in a region of the edge that joins the wall or the wall section and extends over a distance of about 10% to 20% of the diameter of the container,
13. 13. Container according to one or more of claims 10-12, characterized in that the holes have a diameter of at least 2 mm up to, preferably, at most 20 mm, or have a flow surface area equivalent thereto.