EP0490117A1 - Method for cleaning a pipe - Google Patents

Abstract

In order to clean a pipe (101) by means of a cleaning fluid, a fluid/gas two-phase stream flows through said pipe. For this purpose, an annular flow is preferably produced in which case the fluid is fed in at at least one point on the circumference of a pipe section (201). The gas and fluid preferably have the same direction of flow. <IMAGE>

Description

The invention relates to a method for cleaning a pipeline according to the preamble of claim 1.

If goods of various types are conveyed through pipelines, it is necessary to clean the pipelines, be it when the goods to be conveyed change or after a certain period of time. It will be necessary to remove residues or sieve particles adhering to the inside of the pipe.

In the case of long pipelines or those which are intended for the transport of toxic substances, the dismantling of the pipeline and the subsequent cleaning of the pipe parts is quite time-consuming, or can only be carried out under carefully observed safety regulations. As an alternative to this, pipe systems of this type have hitherto been completely filled with cleaning liquid, this liquid being pressed through the pipes or also sucked up. It is obvious that large amounts of cleaning fluid are required for this method, which is questionable both from the point of view of environmental compatibility and from the point of view of economy.

In contrast, the object of the invention is to carry out the cleaning of pipelines with the aid of cleaning fluids without the pipelines having to be dismantled, the throughput of cleaning fluid being reduced by a few orders of magnitude compared to the conventional method.

This is achieved by realizing the characterizing features of claim 1.

Advantageous further developments are described in the characterizing features of the dependent claims.

If the two phases liquid and gas flow through a pipeline, extremely different flow patterns are possible, which depend in particular on the proportion of gas throughput, but also on whether horizontal, vertical or inclined pipes are flowed through. In general, gas and liquid flow in the same direction. A countercurrent between gas and liquid is also possible in vertical or strongly inclined pipes. The transitions between the individual areas of existence of the flow forms can be fluid; depending on the phase pair there are also significant shifts for the limit of the flow forms.

In the context of the invention, the cleaning process by means of plug or foam flow is also conceivable. However, it is preferred to use a gas-liquid two-phase flow which flows through the pipeline system in the form of an annular flow. An annular flow is understood to be a flow in which the liquid forms a mostly thin film along the pipe wall and the gas flows in the pipe center. The two phases are separated from each other by a more or less well-defined boundary layer, which corresponds approximately to the inner wall of the pipeline. Both vertical and opposite flow directions for the gas and liquid phases are possible for vertical and in certain cases also for inclined pipes. A comprehensive description of the two-phase ring flow phenomena is given in Hewitt, Hall Taylor: "Annular Two-Phase Flow" (Pergamon Press, 1970), the content of which is hereby disclosed.

Contrary to various literature references, the form in which the liquid is fed into the pipeline is not particularly important for the formation of the ring flow itself. So the liquid could go through one or more central Nozzles are fed into the gas stream, or also in a ring via a porous tube part or a ring line. If the liquid is fed in essentially centrally, a disperse ring flow will generally arise, in which finely divided liquid droplets are entrained in the gas flow.

However, the pressure loss is reduced by a tangential and / or inclined flow direction of the liquid against the pipe axis, since the gas flow has to apply less energy to accelerate the liquid ring, and less liquid will be entrained by the gas in the pipe center.

For more gentle cleaning processes of vertical or less inclined pipes, in which the liquid runs down in the form of a thin film along the inner wall of the pipe and the gas can flow both in the direction of the liquid flow or in the opposite direction, an annular feed must be provided on the pipe circumference.

Baker's diagram, which is known from the literature and has been developed empirically, shows - but only for horizontal pipes - the areas of existence of the various flow types for two-phase flows.

According to the invention, a very specific operating range - regardless of horizontal or vertical pipe routing - proves to be particularly advantageous for the formation of an annular flow with a high cleaning effect and minimal liquid consumption. The values given refer to a liquid-gas two-phase flow with a ratio of 1 m³: 3000 to 7500 m³ or 1 kg: 2.0 to 6.0 kg. For a cleaning time of approx. 10 minutes for a pipe system with a pipe diameter of 65 mm, regardless of its length, this results in a consumption of approx. 30 l of liquid, whereas approx. 80 when the pipe is completely filled with cleaning liquid '000 l of liquid would be necessary.

Fig. 1

Strömungsformen von Zweiphasenströmungen in horizontalem Rohr;

Fig. 2

Strömungsformen von Zweiphasenstromen in vertikalem Rohr, wobei

Fig. 2a

gleichgereichtete Zweiphasenströmungen und

Fig. 2b

eine ungleichgerichtete Zweiphasenströmung zeigt;

Fig. 3 a bis d

Varianten für die Einströmgeometrie der Flüssigkeit;

Fig. 4

das Diagramm für die Existenzbereiche der verschiedenen Strömungsformen nach Baker, ergänzt von Scott;

Fig. 5

ein Diagramm zur Berechnung des Druckverlustes bei einer Zweiphasenströmung im horizontalen Rohr;

Fig. 6

die Abhängigkeit des Flüssigkeitsmassenstroms vom Rohrdurchmesser für einen ausgewählten Betriebsbereich; und

Fig. 7

eine Ausführung einer erfindungsgemässen Anlage.

The invention is explained in more detail by way of example with reference to the following drawings. Show it.

Fig. 1

Flow forms of two-phase flows in a horizontal tube;

Fig. 2

Flow forms of two-phase currents in a vertical tube, where

Fig. 2a

rectified two-phase flows and

Fig. 2b

shows an unidirectional two-phase flow;

3 a to d

Variants for the inflow geometry of the liquid;

Fig. 4

the diagram for the areas of existence of the various types of flow according to Baker, supplemented by Scott;

Fig. 5

a diagram for calculating the pressure loss in a two-phase flow in the horizontal tube;

Fig. 6

the dependence of the liquid mass flow on the pipe diameter for a selected operating range; and

Fig. 7

an embodiment of a system according to the invention.

• die Blasenströmung 2, mit Gasblasen im oberen Rohrteil; Gas und Flüssigkeit haben in etwa die gleiche Geschwindigkeit;
• Die Pfropfenströmung 3; geschossförmige Pfropfen bewegen sich im oberen Rohrteil;
• die Schichtströmung 4, bei der die beiden Phasen durch eine glatte Grenzfläche getrennt sind, im Gegensatz zur
• Wellenströmung 5, bei der die Phasengrenze wellig ausgebildet ist;
• bei steigender Gasgeschwindigkeit werden die Wellen der Wellenströmung 5 schwallartig aufgeworfen, es kommt zu Benetzung der gesamten Rohrinnenfläche, wobei ein dünner Film den Zwischenraum zwischen den einzelnen schwallförmigen Wellen an der Rohroherseite ausfüllt; diese Strömungsform wird als Schwallströmung 6 bezeichnet;
• bei weiterer Erhöhung der Gasgeschwindigkeit werden die schwallförmige Wellen von Gas durchdrungen, und es bildet sich eine Ringströmung 7, wobei unter dem Einfluss der Schwerkraft die Filmdicke an der Oberseite des Rohres 1 geringer ist als an der Unterseite.

1 shows various flow forms of a two-phase flow in a horizontal tube 1. The direction of flow is the same for both the liquid and the gas and is indicated by an arrow with the index L for the liquid and an index G for the gas. From top to bottom are shown in Fig. 1:

• the bubble flow 2, with gas bubbles in the upper tube part; Gas and liquid have roughly the same speed;
• The plug flow 3; bullet-shaped plugs move in the upper tube part;
• the layer flow 4, in which the two phases are separated by a smooth interface, in contrast to
• Wave flow 5 in which the phase boundary is wavy;
• with increasing gas velocity, the waves of the wave flow 5 are thrown up like gushes, the entire inner surface of the tube is wetted, a thin film filling the space between the individual gushing waves on the tube side; this type of flow is referred to as surge flow 6;
• as the gas velocity increases further, the gushing waves of gas are penetrated, and an annular flow 7 is formed, the film thickness on the top of the tube 1 being less than on the bottom under the influence of gravity.

Corresponding flow forms arise in vertical pipes; 2a (from left to right) the bubble flow 2, the plug flow 3, the foam flow 8 corresponding to the slug flow 6 in the horizontal tube and the ring flow 7 can be seen. The term semi-ring flow is also used for the foam flow 8, which - like the surge flow 6 in the horizontal tube - represents the transition form between the plug flow 3 and the ring flow 7. The directions of flow of gas and liquid are the same in all these cases.

In contrast, FIG. 2b shows a liquid running down inside a vertical tube 1, which, in order to obtain a closed liquid film layer, should be fed in a ring shape on the tube diameter. The gas can also flow in the opposite direction, i.e. upwards, as long as the speed of the gas does not become too high, so that no waves detach the laminar flow behavior of the liquid film. Such a trickle film 9 is of course also a form of ring currents, but here the mutual influence of gas and liquid phases is comparatively small.

For economical and yet effective pipe cleaning - when comparing the different flow types - the ring flow is certainly preferable, the special case of trickling film is only conceivable for vertical or slightly inclined pipes and gentle cleaning processes. However, grafting 3 or gushing 6 or foam flows 8 could also be used for pipe cleaning with more economical cleaning fluid consumption.

Below, an example is used to compare the consumption values for cleaning by means of a ring flow with those for a pipe filled with liquid.

In Fig. 3 different possibilities are shown how the liquid can be fed into a tube 1. In the cases shown in FIGS. 3a and 3b, the formation of an annular flow is favored. If, according to FIG. 3b, the liquid is introduced via an annular inlet, which is designed here as a porous wall 10, then ring flows flowing in the same direction as well as flowing in the same direction can occur. Feeding the liquid according to FIG. 3a, however, in which the liquid is fed into the tube 1 under pressure via an inlet nozzle 11, is particularly favorable. Since the nozzle 11 is inclined against the pipe axis 12 at an angle α (preferably 45 °) and / or opens tangentially into the pipe circumference, less is required Apply energy through the gas to produce the ring flow; the pressure loss along the pipeline is lower.

In the case of the inlet nozzles 11a and 11b shown in FIGS. 3c and 3d, which essentially feed the liquid into the center of the tube, an annular flow occurs — with a corresponding gas velocity. However, in these cases the "core" gas will generally carry entrained liquid in dispersed form.

4 shows the diagram of Baker, from which a very narrow range can be considered preferred according to the invention, and according to which the areas of existence of the individual flow forms in horizontal tubes can be roughly estimated. The diagram, which is obtained purely empirically, can be used for liquid-gas phases that are comparable to the air-water pair. But even in the latter case, significant deviations from this diagram are observed. The areas of the individual flow forms are identified in FIG. 1 by the reference numerals corresponding to FIGS. 1 and 2.

auf der Abszisse ist gegen den Ausdruck G_G/λ_B aufgetragen, wobei λ eine Dichte- und ψ ein Zähigkeits-Oberflächenspannungsparameter ist. G_L und G_G sind die Massenströme für Flüssigkeit bzw. Gas in lb/h·ft² und λ_B und ψ_B sind durch

definiert. ρ sind die Dichtewerte, σ die Oberflächenspannung, und µ die Viskosität der Flüssigkeit. Die Indizes A und W bezeichnen die Werte für Luft bzw. Wasser; L und G, wie bereits oben angegeben, diejenigen für Flüssigkeit bzw. Gas.The expression ${\text{G}}_{\text{L}}{\text{· Λ}}_{\text{B}}{\text{· Ψ}}_{\text{B}}{\text{/G}}_{\text{G}}$

on the abscissa is plotted against the expression G _G / λ _B , where λ is a density and ψ a toughness surface tension parameter. G _L and G _G are the mass flows for liquid or gas in lb / h · ft² and λ _B and ψ _B are through

Are defined. ρ are the density values, σ the surface tension, and µ the viscosity of the liquid. The indices A and W denote the values for air and water, respectively; L and G, as already stated above, those for liquid and gas.

In the case of a ring-shaped two-phase flow through vertical pipes, the influence of gravity is not the same as with horizontal ones Currents noticeable, namely that the ring thicknesses on the pipe top or bottom can vary by more than an order of magnitude. The vertical ring flow is essentially stable, while the horizontal ring flow is fundamentally unstable. It is therefore important to find an operating area that guarantees an annular flow with the least possible liquid water flow for both horizontal and vertical pipes - i.e. for a complex piping system in which bends also occur. In area 13, for which the value to be observed for the expression of the abscissa is between 0.1 and 0.4 and that of the ordinate between 2 · 10⁴ and 10⁵ in the Baker diagram, satisfactory results are obtained, both for the liquid / gas phases with one in the above specified order of magnitude, whereby in extreme cases these limits can also be exceeded or fallen short of, namely by at least 10%, possibly even by 20%.

wobei der Wert für den Druckabfall im Zähler bzw. Nenner dem wert entspricht, der sich einstellen würde, wenn nur Flüssigkeit bzw. nur Gas durch das Rohr strömen würde. An der Ordinate können die Wurzeln aus den Ausdrücken (Δp/Δℓ)_ZP/(Δp/Δℓ) bzw. (Δp/Δℓ)_ZP/(Δp/Δℓ)_G, abgelesen werden. Die Werte für den Nenner sind dabei bekannt, es können demnach die Druckdegradieten für die Gas- bzw. Flüssigkeitsphase der Zweiphasenströmung (Index ZB) bestimmt werden.The correlation of Lockhart and Martinelli shown in FIG. 5 enables the pressure loss for two-phase flows to be calculated, the individual curves being based on the premise that the two phases flow through the pipeline unaffected by one another. Curves 14a-d and 15a-d correspond to liquids or gases with turbulent to laminar flow behavior. The abscissa of the diagram corresponds to the root of the relationship

where the value for the pressure drop in the numerator or denominator corresponds to the value that would occur if only liquid or only gas would flow through the pipe. The roots can be read on the ordinate from the expressions (Δp / Δℓ) _ZP / (Δp / Δℓ) or (Δp / Δℓ) _ZP / (Δp / Δℓ) _G. The values for the denominator are known, so that the pressure degrades for the gas or liquid phase of the two-phase flow (index ZB) can be determined.

The diagram shown in FIG. 6 shows the mass flow G _L calculated for a selected operating point 16 in the Baker diagram (FIG. 4) for water with different pipe diameters.

The horizontal ring flow, which is fundamentally to be regarded as unstable, proves to be substantially more stable if the horizontal pipe is flowed through after a vertical pipe section; longer horizontal pipe sections should therefore be able to flow through according to vertical pipe sections, which should be taken into account when designing a pipe system to be cleaned in the manner according to the invention.

FIG. 7 shows a simplified system for carrying out the method, with a conveying pipeline 101 (which corresponds to the pipe 1 of FIGS. 1 to 3), into which normally conveyed material is fed from a feed container 17 in a known manner in an initial section 201. This initial section 201 is connected to a non-conveying line section 301 with a blower 18 as a compressed gas source (generally compressed air source, unless another gas, such as inert gas, is used for special reasons). The conveyance takes place via a steep section 401 and a pipe diverter 19, which is only schematically indicated, into a separator (cyclone) 20.

If the delivery line 101 is now to be cleaned, the pipe switch 19 is changed over in such a way that the cleaning liquid (water, cleaning or solvent or the like) is fed to a separator 21. Both separators 20, 21 are connected via discharge lines 22 to a gas discharge, not shown, which can optionally be common to both separators 20, 21 and, if necessary, also has a suction fan. In any case, the pressure blower 18, possibly together with such suction blowers, is designed and dimensioned such that the two-phase flow explained above is established.

After switching the diverter 19, a pump 24 connected to a liquid supply 23 is activated, which pumps the cleaning liquid into the pipeline 101 in the manner described above at a point conveniently located in the initial region 201. It can be seen that the connection the pump 24 is provided via a supply line 111 at a point which is after the mouth of the feed elbow 26 emanating from the container 17 (only indicated by dash-dotted lines), but it may be desirable to provide the mouth of the line 111 in front of the elbow 26. It is known in the prior art to have a plurality of stub lines, distributed over the length of the delivery line 101, open into the latter, and it would also be possible to provide a plurality of lines 111 which are fed by the liquid source 23, 24, and which open at various points on line 101. In general, however, this will not be desirable, since on the one hand this leads to a higher outlay, and on the other hand, the amount of liquid contained in the line 101 only increases with the length of the line 101. Such a solution would only be conceivable for very dirty goods in which the cleaning liquid quickly forms a saturated solution which is then not readily suitable for further cleaning work. In the normal case, however, it is preferred if there is only a single line 111 (with a nozzle 11 according to FIGS. 1-3) for the liquid supply.

It is understandable that it would be conceivable to have the liquid flow in the vertical section of the pipeline 101 also in the opposite direction to the gas flow, in which case the arrangement of the separators would have to be changed accordingly.

In order for the cleaning process described to work properly, it must be ensured that no projections protrude into the interior of the pipe in the flange connections between the individual pipe sections. The flow should be as smooth as possible inside walls. Strong bends and abrupt changes in the pipe diameter should also be avoided. Otherwise there is the possibility - albeit not with the same effectiveness - of having the pipe cleaning process alternate in two directions.

Two examples of the implementation of the method are given below.

Example 1:

Flüssigkeitsverbrauch (Wasser) :

30 l in 10 min. (bei vollgefülltem Rohr wären dazu vergleichsweise ca. 80'000 l nötig)

Pipe length 25m; Air pressure: 1.3 bar (pressure operation)
Pipe diameter 65 mm
Air speed: up to 60 m / sec

Liquid consumption (water):

30 l in 10 min. (comparatively about 80,000 l would be necessary for a full pipe)

Example 2:

Rohrdurchmesser:

80 mm
bei Rohrlängen über 50 m (abhängig auch von der Rohrqualität hinsichtlich der sich ergebenden Verlustreibung, allfällige Dichteverluste, etc.) muss Luft zugesetzt werden, da sonst die Luftdichte zu stark gesunken.

Suction mode

Pipe diameter:

80 mm
with pipe lengths over 50 m (depending on the pipe quality with regard to the resulting loss of friction, possible loss of density, etc.) air must be added, otherwise the air density will drop too much.

Claims (10)

Method for cleaning a pipeline (1), in which cleaning fluid flows through the pipeline (1), characterized in that a two-phase flow - liquid and at the same time gas, preferably air - flows through the pipeline (1). A method according to claim 1, characterized in that the two phases, liquid and gas, flow as an annular flow (7) through the pipeline (1). A method according to claim 1 or 2, characterized in that the liquid is fed in at least one point (10; 11) on the circumference of a section of the pipeline (1), and that the liquid preferably against the axis (12) of the pipeline (1) - preferably inclined at 45 ° and / or fed tangentially with respect to the pipe circumference. Method according to one of the preceding claims, characterized in that gas and liquid flow in the same direction. Method according to one of claims 1 to 3, characterized in that gas and liquid flow in the opposite direction. Method according to one of the preceding claims, characterized in that the value of the expression

${\text{G}}_{\text{L}}{\text{· Λ}}_{\text{B}}{\text{· Ψ}}_{\text{B}}{\text{/G}}_{\text{G}}$

between 0.1 and 0.4, preferably between 0.15 and 0.3, and the value of the expression

${\text{G}}_{\text{G}}{\text{/ λ}}_{\text{B}}$

is between 2 · 10⁴ and 10⁵, preferably between 3 · 10⁴ and 8 · 10⁴, where G _L and G _{G are} respectively the mass flow for liquid and gas in lb / h ft², and the parameters lambda and psi

are defined, where ρ _L and ρ _{G are} the densities of liquid or gas in the given system, sigma the surface tension, _/ µ _{L is} the viscosity of the liquid, and the indices A and W refer to the corresponding values for gas and Draw off liquid at normal pressure. A method according to claim 6, characterized in that - for water - at an inflow speed of 80 m / sec, for example, the water mass flow is given by the following values depending on the diameter of the pipeline: Pipe diameter in m: Liquid mass flow in kg / sec: 0.05 0.03 0.09 0.10 0.11 0.15 0.13 0.20 0.16 0.30 0.20 0.48 Method according to one of the preceding claims, characterized in that the ratio of gas to liquid is in the order of 3000 to 7500 m³: 1 m³ or in the order of 2.0 to 6.0 kg: 1 kg. System for performing the method according to one of claims 1 to 8, with a delivery line (1; 101) and a pressurized gas source (18) which is formed on the delivery line (1; 101) for blowing a delivery gas, characterized in that the delivery line (1; 101) is also connected to at least one liquid source (23, 24) via at least one liquid line (11; 111), and that the pressurized gas source (18) is dimensioned and designed to generate a two-phase flow. System according to claim 9, characterized in that only a single liquid line (111) is provided for the supply of liquid from the liquid source (23, 24), preferably in the region (201) of the delivery line (101) performing the delivery tasks.

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