US20060133941A1

US20060133941A1 - Pressure regulated method for preventing cavitations in a technical system

Info

Publication number: US20060133941A1
Application number: US10/536,452
Authority: US
Inventors: Hartmut Breithaupt
Original assignee: Endress and Hauser SE and Co KG
Current assignee: Endress and Hauser SE and Co KG
Priority date: 2002-11-27
Filing date: 2003-11-25
Publication date: 2006-06-22
Also published as: WO2004049086A1; AU2003292104A1; DE10255514A1

Abstract

A pressure regulated method for a technical system that serves to prevent cavitations in a liquid medium, which is conveyed inside a conduit section consisting of a pump, a pressure sensor, a flowmeter and of a first valve. The pump pressure of the pump is regulated by the pressure sensor and the flowmeter in such a manner that the liquid pressure does not fall below the vapor pressure of the medium.

Description

So-called buffer tanks, or pressure equalizing containers, are often used in technical systems to aid in the transfer of liquid products between individual system components. The liquid products can be foodstuffs, creams, oils, etc. Especially in the area of foodstuffs, gases are frequently dissolved in the products (champagne, beer, etc.). This dissolved gas can lead to foaming. In the case of beer, the foaming is desired at the bar; however, in the brewery, foaming is disruptive to the bottling process.
Closely associated with foaming is cavitation. “Cavitation”, as used herein, refers to a phenomenon in which gas bubbles are produced in a liquid, and implode under pressure. In such case, pressure spikes arise, which can lead to severe material damage of the system components. This can bring an entire bottling plant to a halt, and incur substantial costs. The availability of the plant is thereby significantly compromised.
Cavitation is also disruptive in the case of sensitive products.
Cavitation appears mainly in cases of large pressure differences in pipelines, when the static pressure of the liquid falls below the vapor pressure. These sudden pressure increases or decreases can occur especially in the opening and closing of valves.
In order to effect cavitation-free transfer of liquid products in the case of a technical system, such as a processing plant, buffer tanks are provided. These buffer tanks are charged with the pressure of air or some other gas in their headspace. Large pressure differences between system components are thereby canceled, and the formation of gas bubbles in the liquid products can be prevented.
The pressure control of the air or other gas in the buffer tank is accomplished using a pressure sensor and a proportional valve. Such buffer tanks are also used in bottling plants. Buffer tanks are generally complex and expensive. They require a significant amount of space, which is not always adequately available. Furthermore, the pressure control for the buffer tank is complex.
In addition, the use of air or some other gas for pressurizing the headspace is not always desired in the case of certain products.
An object of the invention is to provide a pressure control method for preventing cavitation in a technical system, which method does not have the above-listed disadvantages, and which is simple as well as cost-efficient.
This object is achieved through the features given in claim 1.
Advantageous further developments of the invention are given in the dependent claims.
An essential idea of the invention is, with the help of a pressure sensor and a flow rate meter in a section of piping of a technical system, to control the pump pressure of the supply pump such that cavitation is prevented.
The invention will now be described in greater detail on the basis of several examples of embodiments illustrated in the drawings, the figures of which show as follows:
FIG. 1 schematic illustration of a technical system;
FIG. 2 schematic illustration of a section of piping of a technical system, according to a first variant of the invention;
FIG. 3 a section of piping of a technical system, according to a second variant of the invention;
FIG. 4 a section of piping of a technical system with a buffer container, according to a third variant of the invention;
FIG. 5 a section of piping of a technical system according to a fourth variant of the invention; and
FIG. 6 plots of pressure and associated flow rate, both as a function of time t.
FIG. 1 shows a technical system for transferring liquid media (e.g. beer, champagne, creams, oils, etc.) from a tank B1 into a containment B2, which, in turn, can be a tank, or also a bottle, or the like. The medium is transported in a pipeline 10. Arranged in the pipeline 10 are, in addition to a supply pump 1 and a valve 4, various measuring devices, e.g. a pressure sensor 2, and a flow rate meter 3.
FIG. 2 shows a section of the pipeline 10 in greater detail. This section has a pump 1, a pressure sensor 2, and a flow rate meter 3, as well as a valve 4, which are arranged in series. The quantity of medium flowing through the pipeline 10 toward the valve 4 is controlled with the help of the flow rate meter 3 and the valve 4. In the case of bottling plants, the valve 4 opens and closes such that the desired fill quantity of medium M is available on the downstream side of the valve 4. Pressure sensor 2 and flow rate meter 3 are so-called intelligent field devices, with appropriate microprocessors.
A control line L1 leads from the flow rate meter 3 to the valve 4. Furthermore, a control line L3 leads from the flow rate meter 3 to the pressure sensor 2. From the pressure sensor 2, a control line L2 leads to the pump 1.
The control lines L1, L2, L3 transfer digital signals (e.g. 8-bit signals). It is important that the signal transfer occur relatively quickly (<10 msec) in order to enable a meaningful control. With limitations, this is also possible using the 4-20 mA signals generally known in the field of automation technology.
The flow rate of the medium M through the pipeline 10 is registered with the help of flow rate meter 3. The current, measured value of flow rate is forwarded to the pressure sensor 2 via control line L3. Pressure sensor 2 determines the current pressure in the liquid. In pressure sensor 2, the two measured values, pressure and flow rate, are evaluated, and the pump 1 is so controlled via the control line L2, that the fluid pressure does not sink below the vapor pressure of the medium M. Through the pressure sensor 2 and the flow rate meter 3, the danger of cavitation formation is thus accounted for, and prevented, by controlling the pump 1. The resolution of pressure sensor 1 alone is not enough to effectively prevent cavitation formation. For this, a quick controlling of the pump output, especially in the low pressure region, is necessary. This pressure region is reached when the flow rate is relatively low, that is, at the end of the closing process, and at the beginning of opening process, of the valve. Per the invention, this information is supplied by the flow rate meter 3.
Plots of pressure and flow rate versus time in pipeline 10 at the pressure sensor 2 are illustrated in FIG. 6.
On the one hand, the control provides that the pressure increase at the closing of the valve 4 does not become too great. At the same time, as a result of the moderated pressure increase, a shooting of the medium is prevented when the valve is opened.
At the opening of the valve 4, the control provides that the pump output is again quickly increased accordingly, in order to ensure an adequate product supply, and to prevent a pressure drop.
FIG. 3 shows a further example of an embodiment of the invention, with two valves, 6 and 4, being arranged downstream from the flow rate meter 3, which alternately open and close. A control line L4 leads from the flow rate meter 3 to the valve 6. The example of the embodiment in FIG. 2 functions essentially according to the same principle as the example of the embodiment in FIG. 1.
FIG. 4 shows a further example of an embodiment of the invention. In this example, a buffer container 5 is arranged in the pipeline 10 between the pump 1 and flow rate meter 3. In the buffer container 5, a gaseous medium (gas/air) is located above the medium 5. With the help of the pressure sensor 2, the pressure in the buffer container 5 is registered, and controlled via a valve 6 a. A control line L3 leads from the flow rate meter 3 to the pressure sensor 2. From the pressure sensor 2, a control line L2 leads to the pump 1, and a control line L4 to the valve 6. Also here the pressure sensor 2, in connection with the flow rate meter 3, controls the pump pressure of the pump 1. The fill level in the buffer container 5 is basically constant. The flow rate meter 3, together with the pressure sensor 2, recognizes the ideal refill quantity, and, for this reason, controls the pump output of the pump 1. In order to keep the vapor pressure in the buffer container 5 relatively constant, the pressure sensor 2 and the flow rate meter 3 control the valve 6, via the control line L4. On the basis of the control according to the invention, the buffer container 5 can be considerably smaller than conventional buffer containers.
In FIG. 5, a fourth example of an embodiment of the invention is shown in greater detail. In the case of this example of an embodiment, the section of pipeline 10 no longer has a flow rate meter 3, for which reason an additional pressure sensor 7, and a valve 6, are arranged after the valve 4. The pump 1 is controlled via the pressure sensor 2.
The valve 4 controls the coarse flow of the liquid product. The fine discharge is controlled with the valve 6. The pressure sensor 7 supplies the coarse parameters, and the pressure sensor 2 supplies the fine parameters for the control. Also here the pump pressure is adjusted such that no cavitation occurs.
FIG. 6 illustrates the behavior of pressure and flow rate in the pipeline 10, at the opening and closing of the valve 4, as a function of time t. The pressure is determined with the pressure sensor 2, and the flow rate with the flow rate meter 3. For better comprehension, an ideal plot is illustrated in each case.
At point in time t1 the valve 4 begins closing and the flow rate decreases until point in time t2, when the valve 4 is completely closed and no flow rate is available.
At point in time t3 the valve 4 begins opening again and the flow rate increases. At point in time t4, the flow rate reaches its maximum value.
In the accompanying pressure diagram, two curves, K1 and K2, are illustrated, which reflect the uncontrolled and controlled cases, respectively.
In the uncontrolled case (curve K1), when the valve closes, an enormous pressure builds up, which suddenly drops when the valve opens.
In the controlled case (curve K2), the pressure increase at the closing of the valve is considerably smaller, and therefore also the drop at opening of the valve is considerably less.
As seen from the two curves K1 and K2, the control is applied at exactly the point at which, in the uncontrolled case, drastic pressure changes occur.
Naturally, the supply pump 1 can also be replaced with a controllable modulating valve, which controls the drainage e.g. from an elevated container into a section of pipeline. In this case, the modulating valve controls the product quantities and the corresponding pressure in the section of pipeline.

Claims

1-3. (canceled)

4. A pressure control method for a technical system, for preventing cavitation in a liquid medium which is transported in a section of piping, the system comprising a pump, a pressure sensor, a flow rate meter, and a first valve (4), the method comprising the step of:

controlling the pump pressure of the pump with the pressure sensor and the flow rate meter such that the liquid pressure does not sink below the vapor pressure.

5. The pressure control method as claimed in claim 4, wherein: a second valve is arranged parallel to the first valve, said method further comprising the step of:

alternately opening and closing the two valves.

6. The pressure control method as claimed in claim 4, wherein: a buffer container, with the second valve and the pressure sensor, is arranged between pump and flow rate meter, said method further comprising the steps of:

registering the headspace pressure in the buffer container;

controlling the head space pressure with the second valve; and

actuating the second valve by the flow rate meter and the pressure sensor.