EP0746401A1

EP0746401A1 - Device for separating droplets of liquid from a stream of gas

Info

Publication number: EP0746401A1
Application number: EP95906311A
Authority: EP
Inventors: Max Zimmermann
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-02-26
Filing date: 1995-01-06
Publication date: 1996-12-11
Also published as: CZ231696A3; DE4406308C1; KR970701090A; WO1995023017A1; PL316021A1

Abstract

In prior art devices of this kind, the droplets are separated by virtue of their inertia on the walls of the ducts to form a film of liquid which, in vertical-flow separators, runs downwards and then drips off. If the flow rate is too high, these drips can be entrained in the gas flow again. The invention proposes that the cross-section of the ducts is larger in the zone where the gas flow changes direction than before or after this zone, the cross-section before the direction-change zone being greater than after this zone and the radius of curvature of the direction-change zone along the internal flow path being in accordance with the condition (A). The invention is suitable for use in industrial droplet separators.

Description

Device for separating liquid drops from a gaseous flow

The invention relates to a device for separating drops of liquid from a gaseous flow, consisting of flow channels running parallel to one another, which have at least one main deflection which has an effect on separation and a further deflection connected downstream thereof.

Devices of this type are known (DE 37 02 830 CI). In these types of construction, at least two deflections which have an effect on separation have been provided and the effective channel cross section between adjacent profiles has been continuously tapered over these two deflections to accelerate gas and liquid drops together. At the same time, the deflections have been dimensioned in such a way that flow detachments in the accelerated flow are avoided. This allows pressure losses to be kept low. The deflections serve to use the centrifugal force as a separating force, by means of which the drops are driven to the outer wall of the deflection. These droplets, centrifuged according to the principle of inertia separation, form a liquid film on the channel wall, which, in the case of horizontally flowing separators, is directed into calm zones, for example catch pockets, where it is more or less perpendicular to the flow under the influence of gravity. Direction of flow of the gas phase flows into a collecting pan attached below the profiles. In the case of vertically flowed droplet separators, the wall film for dewatering the profiles generally runs counter to the "flow direction of the gas phase, again gravity gearbox", to the inlet edge of the separator lamellae and drips back from there into the flow field in the form of large droplets. The latter type of separation therefore presupposes that the inflow is selected from the outset in such a way that the drops intended for dripping are not carried back into the flow. It is also a prerequisite that the forces exerted by the flow on the returning film on the walls are smaller than the forces exerted by gravity on the liquid.

In the case of types of droplet separators according to the aforementioned state of the art, especially when the deflections are too sharp, not only can there be signs of separation, but also the steady acceleration of the flow means that the limit value at which the gas flow is reached too quickly is reached prevents the liquid film from flowing off, in particular on the inner path of the deflection.

In contrast, the invention is based on the object of designing a device of the type mentioned at the outset in such a way that the backflow of the liquid film on the inner path of the main deflection is ensured without the other conditions of the separation process and the flow guidance being adversely affected.

To achieve this object, the invention provides that the cross section of the flow channels in the deflection area is larger than before and after this deflection area, that the cross section before the deflection is larger than after the deflection, and that the Radius of curvature of the deflection on the inner track the dimensioning regulation

Fulfills.

In this formula, V A. _max represents the maximum permissible ^J e

Flow velocity at the flow inlet, T the division of the separation profiles at the inlet, S the mean channel width of the deflection and V the gas velocity at which the liquid film builds up on the vertical wall. This configuration counteracts the occurrence of the excess gas gas phase velocities on the inner web, which are detrimental to dewatering, by the initial widening of the cross-section of the deflection and the delays caused thereby. The subsequent sharp narrowing of the cross-section compensates for the flow delay occurring on the inner path when the channel exits the deflection, while the channel width is essentially constant, and prevents the flow separation usually associated therewith. The flow thus "healthy" enters the outlet section, which is a prerequisite for the goal of a low pressure loss of the separating device.

The dimensioning of the radius of curvature according to the invention avoids film build-up at the point critical for the film flow for inflow velocities less than V A. max.

It is therefore also advantageous that deflection angles can be realized, which to a certain extent can also be greater than 90 °. The effectiveness of the deposition can thus be increased.

Advantageous developments of the main idea of the invention are characterized in the subclaims. So has become the

REPLACEMENT TT (RULE 26) Achieving the flow deceleration in the deflection area has proven to be particularly advantageous if the ratio of the channel width - with a rectangular cross section of the flow channels - is 0.8 to 0.95 after the deflection and before the deflection. The radius of curvature "" of the inner wall is expediently designed to be constant over the entire deflection angle *

In a further development of the invention, the inlet and outlet planes before and after the deflection, which lie on radii of curvature and are perpendicular to the wall, are each connected to channel sections which lie at a point at the inlet and outlet of the device to lead. The length of the duct section lying in front of the main deflection can be dimensioned such that the lateral offset between the part of the inner radius of curvature and the leading edge assigned to the outer duct wall lies within certain limits. The length of the channel section behind the main deflection, which leads to the outlet end, can be dimensioned according to claim 6 together with the respective deflection angles at the inlet and outlet in such a way that the inlet edges and outlet edges of the separating device are essentially flush with one another.

In a further development of the invention, the radius of curvature of the inner path of the deflection at the entrance can be chosen to be one to 1.5 times as large as the radius of curvature of the main deflection. The length of the section between the deflection at the inlet and the main deflection can likewise lie within certain limits predetermined by the division. Finally, the radius of curvature on the inner path of the outlet can also satisfy a dimensioning rule similar to that provided for the main deflection. Finally, a diffuser can also be arranged at the outlet, the central axis of which is inclined to the direction of flow.

The invention is shown in the drawing using two exemplary embodiments and is explained below. Show it: Fig. 1 shows a first embodiment of an arrangement and

Formation of flow channels according to the invention and

2 shows a further embodiment of a droplet separator according to the invention.

1 shows three flow channels of a droplet separator designed according to the invention, which can of course also consist of several such flow channels. The flow channels (1, 2 and 3) are identical to one another. They are formed by the juxtaposition of four identical and parallel wall profiles. The front and rear end of the flow channels form end walls, not shown. The cross section of the flow channels (1, 2 and 3) is rectangular. The flow cross-section is therefore determined by the width of the flow channel, i.e. from the respective distance between the profiles (4, 5, 6 and 7) forming the flow channels (1, 2 and 3).

Each of the profiles (4 to 7) - and thus of course also each of the flow channels (1 to 3) - in the exemplary embodiment shown, in which the inflow of the two-phase mixture from which the liquid is to be removed is in the sense of the arrows (0) takes place from an entry section with the length (e), from a first curvature (9) with the radius (R _iE ) as a substantially straight section with the length (1 ..) and from which it follows Subsequent deflection about 10 ° following deflection (10), which at the same time forms the deflection effective main separation. As can easily be seen, the inside (10a) represents the wall of the flow channel lying on the outside of the deflected flow, while the opposite wall side (10b) represents the inside wall of the flow channel (3) or (1 and 2) . This redirection (10), which is effective in separating, is then followed by a straight section with the length d ₂ ), after which a third redirection

REPLACEMENT BLADE (RULE 26) steering (11) to the upper outlet. In the exemplary embodiment, this deflection (11) is carried out so far that the central axis of the outlet part exceeds the direction of flow by the angle ((). As a result, the angle of incidence of secondary drops on the outer path of this outlet deflection increases. Since the flow on the inner path behind the deflection of the outlet section according to FIG. 1 detaches, the gas largely freed from the liquid nevertheless leaves the flow channels of the droplet separator essentially parallel to the flow direction.

In the exemplary embodiment, all curvatures in the region of the deflections (19 and 11) are designed as parts of circular paths. The first deflection (9) has the radius (Rl. "£ ι), which extends over an angle (<5 _F ). The deflection (10) which acts as a main separator has on the inner wall (10b) a radius (R- _M ) which extends over an angle (<X = ß + /), where (ß) represents the angle, which the radius travels up to a central plane (13) which is horizontal and perpendicular to the flow (8) within the deflection (10) which is effective in the main separation and (] /) is the angle which this radius is from the plane ( 13) from to the section with length d ₂ ). The planes defined by the angles (β and y) are defined as the entry cross section with the width (s ..) of the deflection (10) which is effective for the main separation or with the exit cross section with the width (s ~) of the deflection which is effective for the main separation ( 10).

Finally, the last deflection (11) has on its inner wall (11a) the radius (R- _A ) which extends over an angle (c /,). In the following, explanations will be given about the design of these angles and the radii.

From Fig. 1 it can finally be seen that the apex of the inner wall (10b) has a lateral offset (d) relative to the leading edge of the profile (7). The entry The width of the individual flow channels (1, 2 and 3) in the area of the inflow (8) corresponds to the division (T). The

Length (1 ..) should be measured so that the lateral

Offset (d) lies within the limits T_ ≤ d -≤ »_3 T.

2 2

FIG. 1 also shows that in the deflection effective for main separation, the width (s.,) Is greater than the width (s ₂ ), but that these two widths (s ₁ and s ₂ ) are again smaller than the width (s, - .. _^ ) of the flow channels in the area of the plane (13). This configuration causes a flow delay in the area of the deflection which is effective for separation. A cross-sectional widening takes place over the angular range (β) and a cross-sectional narrowing only over the angular range (). This configuration means that the liquid film formed by the thrown off liquid drops in the area of the inner web (10b) can flow downwards towards the leading edge without interference. This leading edge can, as indicated by dashed lines, be extended downwards so that the leading region is longer than e. At the same time, however, this flow deceleration with the subsequent acceleration also avoids the undesired detachment phenomenon in the region of the inner wall (10b). The cross-sectional widening that takes place via the angle (β) therefore counteracts the occurrence of the excess velocities on the inner track that are detrimental to the drainage. The subsequent sharp narrowing of the cross-section compensates for the flow delay on the inner track which occurs at the essentially constant channel width when exiting the deflection, which takes place over the angular range (ι>) and prevents the flow separation normally associated therewith. The flow thus enters the exit part with the width in a healthy manner (s ₂ ). The section after the main separating deflection (10) is another critical point. There the channel width (s_) takes the smallest value because of the strong deflection (ß + f), where () is larger than (ß). The mean gas speed, however, and thus the interfacial shear stress

SPARE BLADE (RULE 26) the flow takes on the greatest value here. At the same time, the to the wall of the channels forming liquid-keitsfilm driving gravity component parallel to the direction Fließ¬ smallest here because the tendency of the separator wall opposite to the to ^a -nströmrichtung is strongest.

Before going into the dimensioning of these zones, some basics of film flow in the Gegenstron should be given first. The determining factor for the film flow is the interfacial shear stress (£ ^* ".,) Which is exerted by the gas flow on the liquid film. The counterflow required for reliable dewatering of the profiles is only guaranteed if the downward gravity outweighs the shear stress effect of the gas phase. If these forces are the same, however, then the liquid film builds up. This situation should be avoided in the droplet separator. Under normal conditions the congestion limit occurs on the vertical wall for the air / water system under conditions near the droplet separator at a gas velocity of 12 to 15 meters per second averaged over the flow cross-section. Usable results in the dimensioning of the separator according to the invention are achieved if, for this mixture, the value 13 meters per second is used as the average speed at which the accumulation limit sets in.

The opposite flow direction of film and gas in the channel section after the main separating deflection (10) is thus only guaranteed if the following applies to the channel speed:

Vk, ≤ Vgas st.au 1 V / cos ϊy

The factor ^" Vcoεi / takes into account the inclination of the separator wall. Converted to the maximum permissible inflow speed in the direction of the arrows (8), which cannot be of any size if the entrainment of the droplets formed on the lower edges of the profiles (5 to 7) is to be avoided, the above provision gives one first dimer. ^c : ^-! regulation for the values / or S _? namely:

Equation la.

Taking into account the profile thickness (b), the second dimensioning results from the equation:

^S 2 ^{= T cos} / ^"b 2 equation Ib.

where b_ is the wall thickness of the profile in the plane after the main deflection (10).

An essential characteristic of the separator according to the invention is the narrower channel width (s ₂ ) behind the deflection (10) compared to the width (s ..) in front of this deflection, which is effective for main separation. It applies

s ₂ / s »= 0.8-0.95 preferably 0.85-0.9 Equation 2.

The dimensioning rule for the first partial angle results from this requirement. ) of the main separating deflection (10):

ß = arccos ((s, + b.) / T)). Equation 3.

where b, in turn, is the wall thickness of the profile in the plane before the deflection (10).

If the flow in the deflection (10) is approximated by the law of the potential vortex and the values of the inflow are incorporated using the continuity equation, the result is

REPLACEMENT TT (RULE 26) following dimensioning rule for the curvature radius R. of the inner track (10b)

V ( ^l Ri.M) '= Va max T r VGas congestion

R. _M .ln (l ₊ S) in equation 4.

With such a dimensioning, the flow of the liquid film is also ensured on the inner track (10b) without, however, the deflection angle in the deflection (10), which is effective in the main separation, having to remain below 90 ° or being limited to this value of 90 °.

As already mentioned before, the section (1.) between the first deflection (9) and the deflection (10) which is effective in the main separation is dimensioned such that there is sufficient lateral displacement of the apex of the inner wall (10b) with respect to the leading edge of the neighboring profile is achieved. This displacement (d), which is said to be in the order of magnitude specified above, prevents relatively large drops from being able to pass the separator without wall contact and gives the division (T) a greater range of variation. The length of section d ₂ ) is selected such that the inlet and outlet edges of the separator, ie, in each case the inlet edge (7a, 6a, 5a, 4a) of each profile, are aligned with the associated outlet edge (7b) (6b, 5b, 4b) , that is, in the exemplary embodiment lie essentially in a vertical plane. The section (e) between the leading edge (7a) and the beginning of the first deflection (9) prevents the liquid from entering the separator channel in the event of an incorrect flow and serves because of the still comparatively low gas velocity and the maximum force of gravity Acceleration of the film on the way to the leading edge. Its length is within the limits (0.3T less than e less than 0.7T, preferably 0.5T.

In order to keep the braking effect of the gas flow on the liquid film along the inner path of the inlet deflection (9) small.

REPLACEMENT BUTT (RULE 26) it is advantageous to select 1 to 1.5 times the radius of curvature ( ^R - _M ) * ^ ^er inner path (10b) of the deflection (10) which is effective for the main separation as the radius of curvature (R. ").

c. FIG. 2 shows a droplet separator in which the individual profiles (4 'to 7 ¹ ) do not have the same wall thickness (b) as in the exemplary embodiment according to FIG. 1. The profiles (4 * to 7 ') are manufactured, for example, as extruded profiles. The wall thickness (b) of these profiles (4 'to 7') is reinforced in the area of the deflection (10) which is effective for separation and in the area of the outlet section.

The outlet section of the droplet separator has the task of aligning the flow parallel to the inflow direction and, if possible, in alignment, apart from applications where an oblique outflow is desired. In the embodiment of Fig. 2, the arrows (12), i.e. offset by the angle (Λ) to a vertical plane. The outlet part accordingly has the task of capturing the primary drops still remaining in the flow, in particular drops and film fragments formed during the drop film interaction, as well as reflected drops, i.e. so-called secondary drops, and also the pressure loss of the gas flow when it emerges from the outlet to keep the separator as small as possible.

It has been shown that it is very advantageous if the dimensioning rule specified for the radius (R- _M ) of the deflection effective for the main separation is also provided for the deflection (11) in the area of the outlet part, so that R- _A over the angle - £ ■ _? ,) must be interpreted accordingly. Depending on the application requirements, it can also be advisable, as shown in FIG. 2, to make the outlet-side end of the lamellae thickened in the form of an impact diffuser or essentially with the same lamella thickness. The version shown has the advantage that the pressure loss of the separator is considerably reduced by a discharge part through which there is no separation. decorates. This is achieved if the exit section is designed according to the following dimensioning guidelines:

In analogy to the design of the redirection (10) which is effective in the main separation, the relationship here also applies to the ratio of the Kenaib before and after the redirection

s ₃ / s ₂ = 0.85-0.95, preferably 0.9, equation 6.

The radius of curvature of the inner track (11a) follows from the dimensioning specification according to equation 4. The opening angle of the exit diff, us _j opς.s following the last deflection, may be the normally usual 7 ° because of its short running length of up to 2T that are required for a non-detachable flow through diffuser and exceed values of up to 15 °, preferably 10 ° to 12 °. The portion of the opening angle lying on the outside of the deflection may be made 2 ° to 3 ° larger than on the inner web which is liable to be detached. It is advisable to choose the deflection angle of the outlet part so large that the central axis of the outlet diffuser (direction 12) exceeds the inflow direction by up to a maximum of 10 °, preferably 3 ° to 8 °. This is the angle (Λ).

Pressure loss coefficients between 1 and 2 of a separator according to the invention designed in this way can be achieved. The higher material requirements due to the thickened trailing edge and the resulting additional costs should e.g. for use in a natural draft cooling tower, the usable pressure difference of which results from the comparatively expensive tower height. Another advantage of a thickened trailing edge is the increased stability, which in turn is useful for the accessibility of the separator packs.

ERSAΓZBLATΓ (RULE 26) For use as a pre-separator, where the cheapest possible version is often required, but also for producing the separator from materials of constant wall thickness, such as sheet metal. Execution of the outlet part with constant wall thickness nrc Fig. I the more appropriate solution. The detachment-related backflow occurring on the inside of the deflection also facilitates the penetration of cleaning fluid into the separator channels on the outflow side, which is advantageous when separating crust-forming liquids. The same dimensioning regulations apply to the alignment of the center axis of the diffuser and the deflection radius of the inner track, of the constant-width section constructed with constant wall thickness. Depending on the application, it is of course also conceivable for the outlet section to be in between the solutions described.

In conclusion, the course of the design of the main separator-effective deflection of the separators according to the invention should be summarized briefly.

The requirement for a certain theoretical limit drop diameter for a certain inflow velocity leads to a first definition of the parameters according to the known Bürckholz formula

o <= + = total angle of the deflection effective for main separation and s = the mean channel width of the deflection effective for main separation (10) with corresponding division (T).

From the desired maximum permissible flow velocity v A ΪUclX, which of course is due to the drainage mechanisms

If limits are set, the channel width (s ₂ ) after the deflection and the partial angle (/) of the deflection (10) follow via equations la and lb. From the requirement s ₂ / s ₁ = 0.7-0.95, preferably 0.85-0.9, the channel width (s ..) results before the main separating deflection and from this, using equation 3, the partial angle ( ß) the main separation effective deflection (10).

REPLACEMENT BLAIT (RULE 26) The still missing radius of curvature (R- _M ) of the inner track (10b) in the deflection which is effective in the main separation is determined iteratively with equation 4. With s = 0.5 ^* (s, + s) the limit droplet diameter can then be checked using the known Bürckholz formula: "> ^{* ■} * - ^* -....> ^■ -.-"" ^•

If the droplet separator according to the invention is to be designed for a roof arrangement at an angle of inclination, it should be considered that the upward flow compared to the horizontal installation position has a different and less effective profile contour (with different channel widths, deflection angles and -radii). In addition, it should be noted that when the lamellae are arranged in a roof-shaped manner, the separated liquid no longer necessarily has to drip off, but now has the possibility of running along the inclined leading edge, e.g. in specially designed quiet areas. The maximum inflow velocity can be increased by such measures. Correspondingly larger values can then be used for v in equations la and 4.

The separator according to the invention is distinguished by a higher tear-through speed than previous types available on the market. It can therefore be designed for a higher flow velocity. In addition to the better overall separation and a cost-saving reduction in cross-section, this results in greater self-cleaning of the separator because the centrifuged drops hit the separator wall at a higher speed. At the same time, a higher inflow speed is generally associated with a greater liquid entry into the separator, as a result of which the film thickness and thus the flow speed of the film on the separator wall increase. Also

REPLACEMENT BUTT (RULE 26) this manifests itself in a stronger self-cleaning of the separator. If the better overall separation due to the higher inflow velocity is dispensed with and the separation of the separator fins is increased, there is still the advantage of the higher liquid entry into the separator.

REPLACEMENT BUTT (RULE 26)

Claims

claims

1. Device for separating drops of liquid from a gaseous * - *** ™ flow, consisting of flow channels' running parallel to one another, which have at least one separating main deflection and a further deflection connected downstream thereof, characterized in that the cross section of the flow channels (1, 2, 3) is larger, at least in the area of the main deflection (10), than before and after this deflection area, that the cross-section (s,) before the deflection (10) is larger than after the deflection (s "), And that the radius of curvature (R .. the deflection on the inner track (10b) the dimensioning rule

V T V

A max. -≤; Gas jam

^R im (ι + s) ^R iM fulfilled, where ^v _sm = _v ⁼ the max. permissible flow velocity at the device's flow inlet,

T = the division of the flow channels at the inlet, s ^" = the mean channel width of the deflection and

V _{r ς} = the average gas velocity at which the liquid film builds up on the vertical wall.

2. Device according to claim 1, characterized in that the cross section of the flow channels is rectangular and the ratio of the channel width (s_) before the deflection and the channel width (s.) After the deflection

j> ₂ = 0.8-0.95.

3. Device according to claim 1 and 2, characterized gekennzeich¬ net that the deflection angle () between the cross section with the greatest width (SJ _TTJ ) of the main _deflection and the cross section with

REPLACEMENT BUTT (RULE 26) the width (S ..) after redirecting the following dimensioning rule is sufficient:

/ = arc cos // V „Gasst, au

VAmax S2

4. Device according to claims 1 to 3, characterized ge indicates that the deflection angle (ß) between the cross section before the deflection with the ^■ width (S ..) and the cross section with the greatest width ( ^s _HWu ) of the following dimensioning ¬ script suffices: ß = arc cos ((S- ^ + b ^ /)

where b. is the wall thickness of the profile in the plane of the deflection (10).

5. Device according to claims 4 and 3, characterized gekenn¬ characterized in that the radius of curvature (R- _M ) of the inner wall over the size of the two angles (ß-f-) is designed to be constant.

6. The device according to claim 5, characterized in that the entry and exit planes before and after the Hauptum¬ deflection (10) lie on the radii of curvature and are therefore perpendicular to the wall (10b), and that these entry and exit planes Connect duct sections (1 or 1 ₂ ) to the deflection, which lead to the further deflection (9) located at the outlet (11) and to an upstream further deflection (9) located at the inlet of the device.

7. Device according to one of claims 1 to 6, characterized in that the length (1.) of the channel section lying in front of the main deflection (10) is dimensioned such that the lateral offset (d) between the apex of the inner curvature zone dius (R- _M ) and the leading edge assigned to the outer duct wall (10b) lies within the limits T / 2 ■ = d - ^ 3/2 T.

ERSAΓZBUTΓ (RULE 26)

8. Device according to one of claims 1 to 7, characterized in that the length ₂ ) of the duct section lying behind the main deflection (10), which leads to the outlet end, and the respective deflection angles at the inlet and outlet are dimensioned such that inlet edges and trailing edges of the separating device are substantially aligned with one another.

9. The device according to claim 6, characterized in that the radius of curvature (R._) of the inner path (10b) of the deflection (9) at the entrance 1 to 1.5 times as large as the radius of curvature (R. _j .) Of the main deflection ( 10) is.

10. The device according to claim 9, characterized in that the length (e) of the section between the deflection (9) at the inlet and the inlet edge (7a) is within the limits 0.3T <e <0.8T.

11. The device according to claim 6 and 8, characterized gekennzeich¬ net that the radius of curvature (R- _Ä ) on the inner path (11a) of the outlet deflection (11) of the dimensioning specification

V. T -≤ V

^{A max} R. _a m (ϊ + s7) ^{gas jam} ^R iA

is sufficient, S _{2 being} the channel width in the channel section extending behind the main deflection (10).

12. The apparatus according to claim 6, characterized in that the deflection (11) is provided at the outlet with the features of claims 1 and 2.

13. The apparatus according to claim 11, characterized in that a diffuser is provided at the outlet, the central axis about the angle is inclined to the flow direction.

REPLACEMENT BUTT (RULE 26)

14. The apparatus according to claim 13, characterized in that the average opening angle (f) of the diffuser is 5 ° to 15 °, preferably 10 ° to 12 °.

REPLACEMENT BUTT (RULE 26)