EP2674228A1 - Method for removing deposits and/or biofilms in a pipe by means of modulating pressure impulses - Google Patents

Abstract

The method involves pressurizing gas or gas mixture in a line with a high pressure by modulating pressure impulses such that mini water blocks are formed in the line. The blocks are driven with a high speed through the line. A pressurized gas supply is directly readjusted with the same or high pressure after temporary lowering of the pressure built by the impulses in the partially emptied line such that other water blocks are formed. The former blocks are impacted by the latter blocks with high speed such that the former blocks obtain supplementary propulsion.

Description

The present invention relates to a method for removing deposits and / or biofilms in a pipeline by modulating pressure pulses.

Methods and apparatus for flushing and cleaning of pipelines, especially drinking water pipes by pressurizing the pipeline with pressure pulses or mixtures of water and gas bubbles have long been known. Already the German PS 67368 describes a method for removing solid sludge deposits from pipelines by introducing a stream of non-condensing gases. In the process, an accelerated cleaning of piping is achieved by pressurized, non-condensing gases such as air, carbon dioxide, or the like. driving through the pipe. In this case, a strong turbulence of the mixture of water and gas bubbles is desired in order to achieve a strong rubbing effect.

In the DE 10 204 737 A1 For example, there is described a method and apparatus for cleaning a pipeline in which nitrogen gas is introduced into the pipeline at intervals by dividing the stream of water in the direction of flow by nitrogen gas bubbles. This produces progressive water and nitrogen bubbles in the pipeline which, due to highly similar flow velocities, lead to severe vortex formation, which results in separation of deposits in the pipeline. In the process, the nitrogen bubbles build up after the opening of the interval valve in about 2 to 5 seconds, so that the interval valve can be closed again after this opening time. In this case, a blocking time is necessary so that the pressure required for the admission of the line of 4 to 8 bar can continue to build. Only after expiration of this blocking period, a new nitrogen blanket in the line are applied.

In the DE 372 25 49 A1 the cleaning takes place via a pulsating compressed air supply into the rinsing liquid, wherein the pressure surges of the rinsing liquid take place either simultaneously or alternately with the pressure surges of the compressed air.

In the DE 350 29 69 A1 describes a process for cleaning pipelines by means of simultaneously introduced pulses of a liquid and a gas, which pulses mix into total pulses, which intermittently enforce the pipeline. In the method, the pulse of the liquid or the pulse of the gas is decomposed into a plurality of individual pulses, whereby the effect of the cleaning is to be increased. For loosening, loosening and flushing of stuck in the pipeline solids occurs the introduction of water and air in the form of rectangular, successive pulses, with the water and the air mix together and prevail as a total pulses the pipe to its open end , The impulses of the air consist of several individual impulses of the same distances, the same amplitude and the same length.

In the DE 44 389 39 C2 a method for the purification of drinking water pipes and for flushing of drinking water networks is proposed, in which the cleaning effect of the flushing process is accomplished by a bubble in an air bubble is applied to the pipeline, which tends at their edges to mix with the rinse water. The mixing takes place under turbulent conditions and under formation of vortices, which are caused by cavitation phenomena, which leads to a detachment of loose deposits in the pipeline. The line is subjected to air bubbles at several intervals. The effect of the rinsing process is mainly based on the introduction of larger compressed air bubbles into running water as well as on cavitation. In some related processes, for the internal cleaning of pipes, an abrasive agent is additionally used in which it is passed through a pipe to be cleaned with at least one liquid and one gaseous fluid (cf. EP 06 34 229 A1 ). A similar procedure is also in the US 2005/0137104 A1 described.

In the EP 10 271 75 B1 For example, there is described a method for removing biofilms in pipelines using a combination of a pressurized gas and a suitable aqueous cleaning solution to create a turbulent environment on or in a tube with a biofilm or debris on the inner or outer surfaces which completely removes biofilm and debris. Also, the method described therein is similar to those already mentioned above, since also here to increase the scouring effect, the pressurized air is pulsed.

Procedures in which a line is acted upon by alternating sequences of gas and water blocks are also part of the DE 10 2010 013167 A1 . DE 10 2008 056523 A1 . DE 10 2008 056522 A1 and DE 10 2008 048710 A1 , In these methods, gas and water blocks are alternately generated, which successively migrate through the line and dissolve via turbulences on the inner surface of the line, the deposits or biofilms.

Although the methods described above, which describe a combination of a water and gas supply either as a mixture or as impulses, have a comparison with a conventional water flushing increased cleaning success, it is especially for stubborn deposits, such as biofilms, still required that the flushing over treated for a long time or several times. The flow rates achieved with these methods are insufficient to clean the line with little impulse. However, an admission of the line with very high pressures or a large number of pulses claimed on the one hand the line, on the other hand requires a much higher energy consumption and additional effort in the implementation. In particular, in the removal of biofilms is therefore dependent on the additional administration of chemical cleaning agents, which is unsatisfactory.

The pulsed impingement of a line with individual pressure pulses either leads to a mixing with the water in the line or to a series of water blocks and gas blocks, which intermittently enforce the line. The height of the pressure to be applied is limited to the respective nominal diameter and length of the flushing path in the line. Especially with very stubborn deposits, these methods do not lead to a satisfactory cleaning result.

Against this background, it is an object of the present invention to provide a comparison with the prior art improved, based on gas supply method for the removal of deposits and / or biofilms in a pipeline, in which an increased cleaning effect at the same time manageable energy and time are accomplished can.

This object is achieved by a method having the features of claim 1. Preferred embodiments can be found in the subclaims again.

The inventive method consists of a preparation phase and a subsequent cleaning phase and is based essentially on the fact that the line to be cleaned with a substantially dominant, line-filling gas volume at low liquid volume is treated under high modulated pressure and repetitive pressure pulses. The flow velocities of the water blocks generated by pressure pulses are so high that wall shear stresses of more than 7000 N / m ² can be achieved. This removes even stubborn deposits, such as biofilms, while at the same time gently treating the pipe. Also, long flushing distances of several hundred meters to kilometers and / or lines with a larger nominal size are possible to clean. This cleaning effect exceeds the effect of known methods in the above-mentioned rinsing.

The method according to the invention can be divided into several phases:

In a first preparatory phase, which also marks the first process step, the line is first partially emptied over a large amount of gas (usually air) with reduced liquid flow to a residual amount of liquid, without generating significant pressure fluctuations. Usually, the liquid is water. Due to the large, line-filling gas component introduced under pressure, a gas bubble is created in the line along the flushing section, which largely displaces the water flowing in the line. Preferably, more than 67%, more preferably more than 75%, more preferably more than 90% of the line is filled with gas. Only at the bottom of the line collects in this first phase, partly due to the backflow of liquid in the sole region, which has been displaced by the pressure bubble, a smaller amount of liquid. However, most of the liquid in the line is displaced by the line-filling pressure bubble. The supply of a large amount of gas creates a very low pressure expansion space, which is required for the pressure gas modulation in the subsequent second cleaning phase and provides the desired high flow rates of the water blocks generated in this phase.

In a subsequent cleaning phase, a modulating compressed gas supply takes place, which, in addition to the first method step just described for creating an expansion space, represents another new feature essential to the invention. In the modulating compressed gas supply, the line is acted upon by a pressure pulse, whereby in the line from the liquid residue small "mini water blocks" are formed, which are driven at high speed through the line. In 10 seconds, for example, a distance of 200 meters can be covered. The pressurizing pressure counteracts the very low pressure of the expansion space created in the preparation phase. Immediately after charging the line with gas and the associated acceleration of the generated "mini water blocks" in the line, the pressure is readjusted taking into account the pipe parameters by the line is subjected to at least the same, preferably a higher pressure. This readjustment generates a further acceleration effect on the mini water blocks in the interior of the pipe, which consist of packages consisting of two or more mini water blocks and gas blocks enclosed between them. In the course of the cleaning section, the flow rate of the miniblocks decreases. By readjusting the pressurized gas supply, subsequent mini water blocks collide at high speed with the enclosed gas blocks and finally with the expanded gas volume in the line. The enclosed gas blocks relax and thereby accelerate the leading mini water blocks again to high speeds. The modulating compressed gas supply can generate additional water blocks, which follow the previously generated miniblocks at high speed and provide further propulsion. The expansion space generated by the gas filling of the line in the first method step, in which the liquid is displaced in the line, thus creates the condition for the subsequent high water movement in the line during the cleaning phase.

In the further course, the piping empties at the discharge point, the pressure can dissipate in the line (expansion phase) and the line is filled again with liquid.

This cycle consisting of the cleaning phase and the relaxation phase repeats itself several times until the line is free of deposits. Depending on the pipe parameters, 5 to 7 cycles are often sufficient.

The modulating supply of compressed gas preferably takes place via a quickly opening and closing regulating valve, for example from a pressure vessel (for example with a pressure of 10-20 bar). The pressure setting takes into account the pipe parameters. The pressure for the first pressure pulse is in the usual nominal widths and cleaning distances preferably 3 bar to 7 bar. The readjustment is carried out at least with the same pressure, but is preferably higher than the first pressure pulse to counteract the expanding gas volume in the line and thus the back pressure.

It is essential that the pressure generated by the first pressure pulse not be allowed to completely dissipate, i. the second pressure pulse is preferably carried out immediately after the first pressure pulse, preferably after the pressure has fallen, preferably between 10 and 20%, but not more than 50%, with respect to the first pressure peak.

In the subsequent expansion phase, the pressure in the pipe section is reduced by gas and liquid emerge at the exit point. The pipe section contains only a small amount of water at the end of the cleaning phase. As a result of the relaxation of the line, the propulsion of the mini water blocks produced by the modulating compressed gas supply is reduced.

In the known method, the compressed air pulse must displace a large block of water already in the pipeline. In the method according to the invention, however, water blocks only form when the first burst of compressed air passes over the water surface of the partially filled pipeline; the compressed air pulls out and pushes out the water from the partially filled line in a wave. The compressed gas modulation thus creates a dynamic series of air and water blocks within the cleaning phase. In this case, a dynamic is generated, which is due to the fact that move through the second (or further) pressure surge within the cleaning phase, the blocks of water at varying speeds through the pipe. As a result of the modulation, the second or each further pressure surge accelerates the first pre-migratory smaller miniwater block within the forming series of water and gas blocks. This mini water block encounters the following air block, which after compression and decompression then passes on the impulse to the next block of water. The readjustment is therefore like an afterburner understand that provides for additional and required for the cleaning success propulsion of the water blocks.

Preferably, in the modulating compressed gas supply in the partially filled pipe section depending on the pipe diameter and length, a pressure pulse of preferably 3 to 7 bar given. After a brief drop in pressure is readjusted to at least the same pressure, preferably a higher pressure. This lowering and readjustment in the context of modulating compressed gas supply can be carried out several times in varying intensity according to the local conditions and is responsible for the high flow velocities generated. The modulating pressure gas supply and the creation of the expansion space in the preparation phase allows flow rates in the line of more than 15 m / sec. The amplitude and the length of the two pressure pulses in the cleaning phase are preferably selected so that the flow rate of the generated water blocks in the line at least 15m / sec, preferably at least 20 m / sec. is.

Due to the pressure gas modulation, it is possible at the beginning of the cleaning to remove low-adhesion deposits and then to mobilize and deposit more firmly adhering deposits.

The duration of the pressure pulse is dependent on the length of the flushing path, but it gives an indication of the flow rate of the liquid, which can be achieved with the method according to the invention. Based on the maximum flow rate as well as the required minimum flow rate and time to change the drag voltage (Tau) can be calculated. The towing tension is a quantity determined in experimental investigations, which indicates the force of the water per unit area of the investigated line section in order to mobilize sediments, to bring them forward and to discharge them from the pipeline. As explained in the following experiment, a drag voltage Tau is based on a pipeline with DN80 at a flow rate of> 10 m / sec. and at least 200 N / m ² .

In the subsequent relaxation phase, the pipe section is again partially filled with fresh water via the feed point until another Compressed air pulse follows and initiates a new cycle. The inventive method thus combines an increased cleaning performance with reduced water consumption while reducing rinse water accumulation. If necessary, an additional injection with a solid component, preferably a salt or dry ice, can take place in the line, which leads to an increased abrasion of the deposits.

It is thus essential in the method according to the invention that the pressure bladder predominantly fills the line in the preparation phase and partially empties the flushing section except for a residual quantity of liquid, in order to create the expansion space for the subsequently produced water blocks. Thus, the gas volume significantly outweighs the amount of liquid in the line; the method works with a small volume of liquid.

The invention is explained in more detail in the following drawings and the investigations and experiments presented here.

To investigate the effectiveness of the method according to the invention and to determine the physical quantities responsible for the cleaning action, a pipeline with a length of 50 m was constructed. In one section artificial deposits were introduced into the pipeline. These are steel particles that are both different geometric shapes and different sizes, such as steel gravel. To simulate the adhesion serve different strengths magnets that are located outside the tubes. The steel particles adhere to the area of the pipe section where the magnets are located. Steel gravel creates structures reminiscent of lichens on the inner wall of the pipeline. The adhesive force can thus be determined exactly on the basis of the known magnets. In a further experiment tubes with "real" deposits were used for the feasibility of the method according to the invention.

To determine the pressure curve, pressure sensors were installed at intervals of 5 m each on the 50 m long pipeline. With the pressure sensors used, measurements could be carried out in 0.1 second intervals and the pressure course during cleaning could be monitored. A flow meter in front of a backflow preventer ensures that the water requirement can be measured and the time course can be determined. The flow measurement can also be registered in 0.1 second intervals.

In Fig. 1 the pressure curve during the cleaning phase at the first pressure sensor (01) is shown directly at the feed point and at the last sensor (11) immediately before the Ausspeisungspunkt. The pressure curve during the preparation phase is not shown; During this phase, the pipeline was partially learned and filled with a large volume of gas to create an expansion area. In the Fig. 1 You can see seven cycles with pressure pulses, which walk through the line in series. The duration of one cycle is 15.4 seconds in this example. This is also the frequency at which the cycles follow each other. Each pressure pulse can in turn be divided into three phase sections I to III via the pressure curve measured at the pressure sensors.

In the first phase section I, which corresponds to the cleaning phase, the line which has been partially emptied in the preparation phase is subjected to a pressure pulse at high pressure upstream of the feed point. This leads to the formation of mini water blocks, which are driven through the line at a high flow rate without exceeding the static pressure of the pipeline. Immediately after acting on the pressure pulse, the compressed gas supply is readjusted with the same or higher pressure. The last mini water block compresses the bubble to the leading mini water block and gives further propulsion. Depending on the setting, other new mini water blocks can form, which compress the air to the leading mini water block at high speed and then accelerate it. As a result, cleaning distances of several hundred meters are readily possible. If necessary, several pressure pulses are applied to the line during the cleaning phase. After the line has been relieved, water flows in via the feed point and the cycle begins again.

At the end of the cleaning phase, liquid underdeveloped under reduced pressure, which fills the pipe section to about one third of its volume, preferably leaving more than 67%, more preferably more than 75%, more preferably more than 90% of the pipe filled with air , Because of the partial filling of the pipe there is virtually no pressure in the pipe section until the next compressed air pulse.

The correlation of the pressure profile at the first pressure sensor with the profile of the volume flow at the flow meter proves that no water can flow into the pipe section in the first phase section I (cf. Fig. 3 ). In the course of the second phase section II, the pressure in the pipe section decreases and fresh water begins to flow. In the third phase III of the fixed volume flow of the inflowing water is reached. It forms a very low pressure by filling the pipe volume.

The pressure course during the relaxation phase, i. the second and third phase sections II-III, is almost the same for all pressure sensors. This is significantly different in the first phase I section. Here, the pressure peak of the maximum pressure at the last sensor is offset in time with the first sensor. In the pilot plant, the distance from the first to the last sensor is 50 m. The duration of the pulses corresponds to the time difference of the maximum pressure between the last and the first sensor. The distance of the sensors divided by the transit time gives the speed of the pulse and thus information about the flow velocity. The flow rate of the pulses is an important parameter for evaluating the efficiency of cleaning pipelines. By this parameter and especially by the change of the flow velocity with the time the drag voltage Tau is calculated.

Normally, the flow rate of the incoming water when cleaning existing pipe section is not measurable. However, pressure sensors at the feed point and at the exit point allow measurement based on the pressure history.
This can be transferred to real pipelines or sections in pipe networks. Thus, with a known length of the pipe section via a pressure measurement, the flow velocity and finally the drag voltage can be determined.

The control of the compressed air supply influences the pressure curve in the pipeline. The modulating compressed air supply drives several, in quick succession following air / water blocks with flow rates of more than 15 m / sec. during the cleaning phase through the pipe section. This is exemplary in the Fig. 1 shown. Here, a pressure pulse of 3 bar was given in a practically unpressurized, partially filled pipe section in the example shown. After a brief drop in pressure was readjusted to 3 bar. The Running time of the pressure pulse in Fig. 1 lasts 2.9 sec. This results in a flow velocity of 17.2 m / sec. Based on the flow velocity, the drag tension Tau can be calculated. In the conventional water rinse flow rates of about 3.7 m / sec. will be realized. An extrapolation of the flow rate from the curve shows that, for example, at a flow rate of 8 m / sec. a drag voltage of about 200 N / m ^{2 is} achieved (see. Fig. 4 ). The flow rate of the water in the partially filled pipe before the cleaning phase is almost zero. In the method according to the invention, the towing tension exceeds that of a conventional water rinse by more than 10 times (cf. Fig. 4 ).

In the Fig. 4 the drag tension of the water blocks during the cleaning is shown with the method according to the invention in comparison with the drag tension in the water flushing. A factor for the significantly higher towing tension is the acceleration component, where the fluid of 0 m / sec. down to the maximum flow velocity v in m / sec. is accelerated within 0.1 seconds. In the flow rates of> 18 m / sec generated in the process according to the invention. Thus, drag voltages of more than 7000 N / m ^{2 are} possible, which certifies an excellent cleaning performance.

Claims (11)

A method for the removal of deposits and / or biofilms in a pipeline, in which before the scavenging at a feed point to be carried out by means of pressure pulses acting on the at least partially filled with liquid line with a gas or gas mixture, characterized in that in a first preparation phase the line with a line-filling gas or gas mixture is partially emptied to create a liquid expansion chamber to create an expansion space, wherein the pressurized gas bubble in the line almost completely occupies the volume of the flushing in the preparation phase, and in a subsequent second cleaning phase, a modulating compressed gas supply takes place at the gas or gas mixture is acted upon by at least one pressure pulse at high pressure in the line, which form mini water blocks in the line, which are driven at high speed through the line u nd in which the supply of compressed gas after brief drop in the pressure built up by the pressure pulse in the partially empty line is readjusted immediately thereafter with the same or a higher pressure, which can again form blocks of water that bounce at high speed on the voreailenden mini water blocks, which thereby a received additional propulsion. A method according to claim 1, characterized in that the line relaxes in a subsequent phase and the pipe section is filled during this relaxation phase with newly fed liquid via the feed point again. A method according to claim 1 or 2, characterized in that the readjustment is carried out in the modulating pressure gas supply in the cleaning phase with a higher pressure than the pressure of the first pressure pulse. Method according to one of the preceding claims, characterized in that the compressed gas supply and its readjustment in the cleaning phase are selected so that the flow rate of the water blocks generated in the Line at least 15 m / sec, preferably at least 20 m / sec. is. Method according to one of the preceding claims, characterized in that the cleaning path to form the expansion space in the partially empty line before the cleaning phase with more than 67%, more preferably 75%, more preferably 90% is filled with the gas or gas mixture. Method according to one of the preceding claims, characterized in that the loading pressure and its readjustment in the cleaning phase is between 3 and 7 bar. Method according to one of the preceding claims, characterized in that the readjustment of the pressure during the cleaning phase takes place when the pressure of the first pressure pulse has dropped between 10 and 50%, preferably between 10 and 20%. Method according to one of the preceding claims, characterized in that the duration of the pressure pulse in the cleaning phase at a flushing distance of 50 m between 2 and 4 seconds. Method according to one of the preceding claims, characterized in that the drag tension Tau with respect to a pipeline with DN80 at a flow rate of> 10 m / sec. is at least 4000 N / m ² . Method according to one of the preceding claims, characterized in that in addition to the pressurized gas treatment is additionally carried out an injection with a solid component, preferably a salt or dry ice in the line. Method according to one of the preceding claims, characterized in that in addition the flow speed and drag voltage is determined by a synchronous pressure measurement takes place at the feed and Ausspisungsstelle with known length of the cleaning section.

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