DE202008006925U1 - Steam moisture measurement system for wet steam flows - Google Patents

Abstract

Steam moisture measurement system for wet steam flows in a steam line (1), comprising an isokinetic extraction device (2) and a device for producing a heat balance (9), wherein
- the isokinetic removal device (2) has a discharge pipe (11) for the steam in the direction of the steam flow direction and that two openings (12a, 12b) arranged perpendicular to the steam flow direction for the steam flow in the steam line (1) and the extraction steam flow in the extraction pipe (11) are provided and connected to one another via a differential pressure sensor (13) with pressure lines (14) for the differential pressure determination of vapor stream and removal steam stream,
- An expansion element (4) is provided and the differential pressure is designed to compensate balancing and that
- The device for establishing a heat balance (9) has a sampling line (3) and two subsequently arranged power adjustable heating coil (5, 6) and temperature and pressure measuring points (A, B, C, D), wherein the measuring point (A) in the Sampling line (3) in front of the expansion element (4) for the pressure p _A , the measuring point (B) between the expansion element (4) and the first ...

Description

The The invention relates to an arrangement for the continuous measurement of Steam damp of wet steam streams.

The Determination of vapor moisture is in the supply and discharge of machinery, such as As steam turbines, of interest. The humidity of the steam is relevant for plant and process control systems.

Steam humidity measurement systems are in different versions in the prior art known.

For Laboratory applications are optical and extinctive measuring systems for Steam moisture determination used. These are however for Applications in practice, for example, in steam lines after Turbines, not suitable. These solutions enable a vapor moisture determination only up to about 3% and are considered operational measuring points not usable.

Furthermore, measuring systems are known which are based on the cooling of the measuring steam flow and determination of the amount of condensate, as in EP 890 833 A2 disclosed, based.

Another way to determine the quality of steam is, for example, in the US 4,679,947 A In addition to the temperature, the vapor density is determined by means of vibrating tubes.

In EP 1 017 997 B1 is determined by admixing a reference steam and subsequent Enthalpiebestimmung the mixed steam, the steam quality.

From the US 4,932,788 A a generic measuring system is known, which consists of a sampling device, two heating registers and measuring points for pressure and temperature and a steam quantity measurement.

adversely in this device is that the removal of the steam is not isokinetic. This has the consequence that the branched vapor stream may be subject to unrecognized state changes. In order to can not be determined by the subsequent measuring points data the conclusions about the steam humidity before the Allow removal without even the steam mass flow too determine.

at the same time are the heat losses of the system unknown and for the required extraction steam quantity measurement are not suitable measuring arrangements available.

Messanordnungen similar kind are also from the US 4,932,788 A , of the US 5,327,772 A and the US 4,295,368 A known.

all known solutions adheres to the disadvantage that higher Damp dampenings from 3 to 15% not reliable, continuous and without determining the extraction steam quantity.

Of the The invention is therefore based on the object to form a measuring arrangement, which allows an isokinetic steam extraction and thus the Extraction steam flow identical parameters with the main steam flow having.

The Measuring system should not require determination of the withdrawal steam quantity. Steam humidities of up to 15% should be continuously measurable. The Measuring system should be suitable for use as an operating measuring point suitable.

The Object is achieved by a steam moisture measurement system solved for wet steam flows in a steam line, which is an isokinetic removal device and a device for generating a heat balance, wherein the isokinetic Extraction device a sampling pipe for the steam in the direction the vapor flow direction and in each case has an opening perpendicular to the steam flow direction in the steam line and an opening perpendicular to the flow in the sampling tube are arranged. A differential pressure sensor is each by a Pressure line with the openings for differential pressure determination connected by steam flow and extraction steam flow. This differential pressure sensor regulates the organ of expansion with the aim that no difference between the static pressure of the steam flow in the steam line and the static pressure of the withdrawal steam flow is given. This regulation leads to an isokinetic vapor extraction. This will be achieved that the speed in the sampling device equal to the Speed in the steam line is. This ensures that that the vapor flow in the sampling tube in its parameters with the Steam flow in the steam line is identical.

The apparatus for producing a heat balance has a removal line, an expansion element and two subsequently arranged power-controllable heating registers and temperature and pressure measuring points (A, C, D). At measuring point A, which is arranged in the extraction line before the expansion element, pressure p _{A is} determined. At measuring point C, which is arranged after the first heating coil and before the second heating coil, the temperature T _{C is} determined. Measuring point D is located after the second heating register. Here, temperature T _D and pressure p _{D are} measured.

Temperature- and pressure measuring points A, C, D are by means of data transmission lines connected to a control / evaluation unit.

The power consumption of the heating registers (P _H1 , and P _H2 ) is recorded by measuring devices, thus enabling complete heat balancing.

The Concept of the invention is that a removal device is formed, which is the static pressure in the steam line and in the withdrawal line and the difference by an expansion organ matches to zero. This realizes that the vapor velocities in the extraction line and in the steam line identical in the sense are formed by isokinetic.

A heat balance is created via the measuring system. The heat balance results on the one hand by the heat output (P _H1 and P _H2 ) supplied by means of the heating coils and on the other hand by the heat losses (P _V1 and P _V2 ). These amounts of heat as well as pressure and temperature can be determined with the measuring system and, due to the evaluation algorithm, ultimately enable the determination of the vapor moisture in the area of the sampling device. With the determined pressures before the expansion device and after the second heating coil and the temperatures after the first and the second heating coil data are determined, which allow to eliminate the amount of steam from the equation of function. This can be dispensed with the complex, error-prone and costly steam quantity measurement.

The Isokinetic vapor extraction is required to preserve the unadulterated To be able to remove reference steam flow.

at If the removal speed is too high, more steam will be extracted as the actual Absaugquerschnitt with the existing flow rate corresponds, if the removal speed is too low fewer.

Of the Adjustment takes place via the measurement of the static pressure in the main and in the withdrawal flow. By matching the static differential pressure to zero equals the speeds to the same value. This is the isokinetic vapor extraction guaranteed.

Thus, six measured values (temperatures T _C and T _D , pressures p _A and p _D , heating powers of the heating registers P _H1 and P _H2 ) and two loss characteristics to be determined in advance or by heat flow sensors (power losses P _V1 and P _V2 ) necessary.

From the measured values for the pressure after the second heating element p _D and the temperatures after the two heating elements T _C and T _D , the enthalpy of the sample vapor is determined via the equations of the water vapor plate. A suitable water vapor panel is z. In Wagner, W .; Kruse, A .: State variables of water and water vapor, Springer Verlag 1998, ISBN 3-540-64339-7 contain.

The coefficients n _i ⁰ and n _i from the water vapor table are rounded to four decimal places. For a sufficient accuracy is achieved. This eliminates a series of coefficients, so that ultimately 8 coefficients remain for n _i ⁰ and 15 for n _i .

Consequently Both vapor enthalpies are known at measuring points C and D. The enthalpy calculation in point B is carried out by means of a balance over both heating registers. For this purpose, in addition to the two enthalpies the Heating power needed by the two meters be determined for electrical power consumption.

About that In addition, the heat losses in these balancing groups must be known.

The enthalpy at point A of the vapor to be measured corresponds to that at point B because of the adiabatic throttling, h _A = h _B.

The pressure (p _A ) at the measuring point A can thus be used to determine the vapor humidity via the water vapor panel.

With The measuring system according to the invention are steam dampers Up to approx. 15% reliably determinable after a short settling time. A complex determination of the mass flow is not required. The robust removal device allows use as an operating measuring point for almost all requirements. at the same time the measuring system is thus for process control systems suitable. Through the self-regulating isokinetic extraction supplies the measuring system according to the invention reliable Results.

advantageous Embodiments of the vapor moisture measurement system result from the dependent claims.

A advantageous embodiment of the invention is given by the fact that to create the heat balance, the measuring system as a calorimeter is executed. This is a compact design of the measuring system possible.

According to one embodiment of the invention, the invention is designed as a throttle overheating calorimeter. As a result, the functional elements of the measuring device in a unit with low Space requirement can be realized. At the same time the measurement errors are minimized with this embodiment of the invention.

one According to a further advantageous embodiment, the power loss of the calorimeter by heat flow sensors continuously recorded or the power loss in advance on a measuring stand depending various parameters, in particular the temperature, determined and stored as a characteristic or map in the control unit.

In order to a complete heat balance can be created. Thus, the measuring device delivers especially in unsteady Reliable operations after a short settling time Results.

To a further advantageous embodiment of the invention is the first heating registers by measuring the temperature after the expansion element, such as B. a throttle, and comparison with the superheat temperature switched by the control unit. This is also for Wet steam, a moisture determination possible.

With a development of the invention, the second heater is so switched that kept a preset temperature constant becomes. This predefinable temperature is in the range of overheated Steam above the temperature after the first heating coil and can be set on the control and evaluation unit. Thereby it is possible to change the steam humidity even when changing to determine the steam mass flow and to minimize the measurement errors.

A further embodiment made possible by the determination of Temperature directly on the surface of the heater the monitoring of the surface temperature. The determined temperatures are evaluated in the controller and turn off the heater when too high a temperature, eg. B. as a result too low steam mass flow, occurs at the heating registers. With the temperature determination can stationary states at the heating registers by the corresponding control of the heating power will be realized. At the same time allows the monitoring the temperatures the detection of stationary conditions at the heating registers. When the measured temperatures are almost unchanged are secured, that the whole of the heating elements is absorbed electrical power is transmitted to the steam. Consequently is an accurate heat balance possible.

faulty Measured values can be unsteady by appropriate determination States are recognized as such. This is a monitoring of Measuring system and an evaluation of the measurement results possible.

In a further advantageous embodiment of the invention is the Removal device realized as a zero pressure probe. This component is a robust, mature, marketable and cost-effective component.

Further Details, features and advantages of the invention will become apparent the following description of exemplary embodiments with reference to the accompanying drawings. Show it:

1 : Schematic representation of the measuring system (R & I scheme),

2 : Detail withdrawal line with heating registers,

3 : Zero pressure probe and

4 : Representation of state changes in the hs diagram.

The measuring system for the continuous determination of the vapor humidity of wet steam flows is realized as follows:
In 1 is a schematic diagram of the measuring system as pipe and instrumentation scheme (R & I scheme) shown.

In the steam line 1 in which the steam to be determined flows in the direction indicated by arrows, projects a removal device 2 into it. The sampling tube 11 the removal device 2 is open against the direction of the flowing steam. It gets out of the steam line 1 led out. To the static pressure difference in the steam line 1 and in the sampling device 2 to determine are at the sampling device 2 openings 12a . 12b perpendicular to the flow direction in the steam line 1 and the sampling tube 11 arranged. These openings 12a . 12b are through pressure lines 14 with a differential pressure sensor 13 connected. By the arrangement of the opening 12a becomes the static pressure in the steam line 1 and through the opening 12b the static pressure in the sampling tube 11 detected.

The differential pressure sensor 13 gives a signal directly or via the control and evaluation unit 8th to that to the sampling tube 11 subsequent pressure-controllable expansion element 4 , here's a throttle 4 , The pressure control represents the pressure loss of the throttle 4 so that the static pressures in the steam line 1 and the sampling tube 11 are the same size. So are the flow velocities in the sampling device 2 and in the steam line 1 identical. In this way, the isokinetic extraction of steam is realized, thus ensuring that the parameters of the steam flow in the extraction pipe 11 and in the steam line 1 identical are.

The described removal device 2 with the openings 12a . 12b for detecting the static pressure is also called zero pressure probe 2 known. At the measuring point A, the pressure p _{A is} determined and by data lines 7 to the control and evaluation unit 8th transfer. For control purposes, the temperature can also be determined here.

In the pressure-adjustable throttle 4 Adiabatic relaxation occurs at about atmospheric pressure, as in 4 shown as section AB. Should the steam flow in the steam line 1 Have negative pressure, is then relaxed to be determined, underlying pressure. Pressure fluctuations play no role in the vapor moisture measurement system according to the invention as long as the isokinetic removal is ensured.

After the throttle 4 closes the sampling line 3 at. Immediately after the steam from the throttle 4 the temperature can be determined by a thermocouple and the pressure at the measuring point B for control purposes. Thereafter, the steam flows through the first heater 5 that by a heating control 15 is controllable. Here isobaric heating of the steam, so that it is the first heating coil 5 As superheated steam in the area of the measuring point C leaves. If there is already superheated steam at measuring point B, there is no heating by the first heating coil 5 required. After exiting the first heating coil 5 At the measuring point C, the temperature T _C and, if necessary, for control purposes, the pressure is determined.

After the measuring point C, the steam flows through the second heating register 6 , Here heat is supplied isobar, so that the steam is further overheated. Target of the heating control 15 is to further increase the exit temperature of the steam to a predetermined value. After the exit of the steam from the second heating register 6 At the measuring point D, in turn, the temperature T _D and the pressure p _D are detected and by means of data lines 7 to the control and evaluation unit 8th transfer. Both heating registers 5 . 6 are through the heating control 15 adjustable in power so that the heat output can be infinitely controlled in comparison to measured temperatures and setpoint specifications, thus ensuring that the actual values come as close as possible to the setpoints. After the measuring point D, the steam is blown off into the atmosphere or returned at a suitable point in the steam cycle.

The heating registers 5 . 6 are as electrical heating elements 5 . 6 executed. The electrical power consumption P _{H1 of} the first heating element 5 and the power consumption P _{H2 of} the second heating element 6 each by a corresponding meter 16a . 16b determined and by data transmission lines 7 to the control and evaluation unit 8th forwarded. From the control and evaluation unit 8th in turn, signals go to the heating control 15 the heating elements 5 . 6 , The with the gauges 16a . 16b determined electrical power consumption correspond to the heat supplied to the steam or heat quantity. This power is provided by the control and evaluation unit 8th considered as an input variable for the determination of the vapor humidity.

The most important electrical components include the heating regulations 15 for the electric heating coil 5 . 6 , As the electric heater 5 . 6 Even if they are the largest consumers, they also determine the grid feed-in and voltage distribution. For an advantageous embodiment, the electrical power requirement of 1500 W per heater 5 . 6 (165 V, 50 Hz) has been determined by thermal engineering interpretation. The mains voltage is transformed to 165 V. After secondary protection, two tyristor actuators are used to control the heating coils 5 . 6 connected. The control of the heating power takes place for each heating coil 5 . 6 separately. This has the advantage that the temperatures do not become unnecessarily large after the second overheating. To be achieved is an overheating of 50 K per heater 5 . 6 to keep the error as small as possible.

by virtue of this definition as well as the given process parameters was added the rating of the power of the isolating transformer 230 V / 165 to be used V, 50 Hz calculated with a simultaneity factor of 0.5. In order to Size and weight of the measuring system are comparatively low.

During the measurement, the measured heating power of the two heating registers 5 . 6 with at the control / evaluation unit 8th adjustable upper limits compared and monitored. Each time the upper limit value is reached, a message is displayed and the heating output by the heating control 15 limited.

In 2 is the device for creating a heat balance 9 with the expansion organ 4 out 1 shown in more detail. In the to the expansion organ 4 subsequent sampling line 3 are the heating registers 5 . 6 arranged.

In addition to 1 Here are the temperature sensors 18a to 18f shown. These temperature sensors 18a to 18f are directly on the surface of the heater 5 . 6 arranged. The temperature sensors 18a to 18f are used to control the heating power and to monitor the temperature of the heating coil 5 . 6 , In each case, three temperature sensors are advantageous - one sensor 18a . 18d in the Be rich in steam, a sensor 18b . 18e in the middle area and one temperature sensor each 18c . 18f in the area of the steam outlet from the respective heating register 5 . 6 , By the temperature sensors 18a to 18f can cause overheating of the respective heating coil 5 . 6 determined and by the control unit 8th a reduction of the heating power can be effected. With the monitoring and control of the temperatures, in particular the respective average temperature sensors 18b . 18e on the surface of the heating register 5 . 6 can be achieved that a near-steady state on the heating registers 5 . 6 is adjustable and can be registered at the same time. The stationary state is given when passing through the heating elements 18a to 18f determined temperatures are almost constant. This in turn leads to the conclusion that the whole through the gauges 16a . 16b determined power consumption is transferred to the steam.

Of the stationary state of the vapor moisture measurement system is after reached a settling time of 2 to 3 minutes.

The measuring system is of the throttle 4 until after leaving the second heating register 6 as a throttle and overheating calorimeter 9 executed. That means the entire elements with a thermal insulation 17 are surrounded and that the heat losses of the calorimeter 9 are known. The determination of the heat losses can be done by heat flow sensors 10a . 10b done continuously.

Another possibility is to reduce the heat loss of the calorimeter 9 as a characteristic curve or characteristic field before commissioning of the measuring system and the values in the control and evaluation unit 8th to deposit.

The known heat losses of the calorimeter 9 can be eliminated from the calculation. _2Go is ultimately results in the supplied heat _1zu P and P from the heating registers of the 5 . 6 supplied electrical power P _H1 or P _H2 (by the measuring devices 16 determined) less by the heat flow sensors 10a , respectively. 10b determined heat loss power (P _V1 and P _V2 ). All sensors 18a to 18f , Measuring points A, B, C, D and measuring devices 16a . 16b and the heat flow sensors 10a 10b are through data lines 7 with the control and evaluation unit 8th connected.

In 3 is a sampling device 2 as zero pressure probe 2 shown. The one in the steam line 1 flowing steam enters the extraction tube 11 one. Laterally at the extraction tube 11 arranged grasps the opening 12a the static pressure in the steam line 1 and the opening 12b in the sampling tube 11 , The openings 12a . 12b are through pressure lines 14 with the differential pressure sensor 13 connected.

The 4 shows the hs diagram.

The Enthalpy h is on the y-axis and entropy s on the x-axis applied. The x = 1 line is the saturated steam limit. The others x-lines show the lines of the same vapor humidity.

The Points A, B, C, D correspond to the measuring points. The connection AB shows the adiabatic throttling and BC the isobaric heating first heating register. Here, the x = 1 line (saturated steam line) cut, and thus the steam at C is in the overheated Area. The line CD shows the second isobaric warming in the second heating register.

1

steam line

2

isokinetic Extraction device, zero pressure probe

3

withdrawal line

4

Expansion element, throttle

5

first power adjustable heating element / heating element

6

second power adjustable heating element / heating element

7

Data transmission lines, data lines

8th

Tax- and evaluation unit

9

contraption for creating a heat balance, calorimeter, throttle overheating calorimeter

10a

Heat flow sensors for the first heating coil

10b

Heat flow sensors for the second heating coil

11

sampling tube

12a

opening to the steam line

12b

opening to the sampling tube

13

Differential Pressure Sensor

14

pressure lines

15

Heating control

16a

gauge for electrical power consumption / heat output / heat quantity of the first heating register

16b

gauge for electrical power consumption / heat output / heat quantity of the second heating register

17

thermal insulation

18a to 18f

temperature sensors on the surface of the heater

A

Print- and / or temperature measuring point

B

Print- and / or temperature measuring point

C

Print- and / or temperature measuring point

D

Print- and / or temperature measuring point

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 890833 A2 [0005]
• US 4679947 A [0006]
• - EP 1017997 B1 [0007]
• US 4932788 A [0008, 0011]
• US 5,327,772 A [0011]
• US Pat. No. 4,295,368 A [0011]

Cited non-patent literature

• - Wagner, W .; Kruse, A .: State variables of water and water vapor, Springer Verlag 1998, ISBN 3-540-64339-7 [0025]

Claims (8)

Steam moisture measurement system for wet steam flows in a steam line ( 1 ), comprising an isokinetic removal device ( 2 ) and a device for creating a heat balance ( 9 ), wherein - the isokinetic sampling device ( 2 ) a sampling tube ( 11 ) for the vapor in the direction of the vapor flow direction, and that two openings (perpendicular to the direction of vapor flow) ( 12a . 12b ) for the steam flow in the steam line ( 1 ) and the withdrawal steam flow in the withdrawal tube ( 11 ) and via a differential pressure sensor ( 13 ) with pressure lines ( 14 ) are connected to each other for the determination of the differential pressure of the vapor stream and the extraction steam stream, - wherein an expansion element ( 4 ) is provided and the differential pressure is designed to compensate balancing and that - the device for creating a heat balance ( 9 ) a sampling line ( 3 ) and two subsequently arranged power adjustable heating registers ( 5 . 6 ) and temperature and pressure measuring points (A, B, C, D), wherein the measuring point (A) in the sampling line ( 3 ) in front of the expansion organ ( 4 ) for the pressure p _A , the measuring point (B) between the expansion element ( 4 ) and the first heating register ( 5 ), the measuring point (C) for the temperature T _C between the heating registers ( 5 . 6 ) and the measuring point (D) after the second heating register ( 6 ) For the temperature T _D and pressure P _D are disposed, and that - the temperature and pressure measurement points (A, B, C, D) (by means of data transmission lines 7 ) with a control / evaluation unit ( 8th ) and that - the power consumption of the heating registers ( 5 . 6 ) by measuring devices ( 16a . 16b ) and in the control / evaluation unit ( 8th ) is formed processable. Steam moisture measuring system according to claim 1, characterized in that the device for producing the heat balance ( 9 ) a calorimeter ( 9 ). Steam moisture measuring system according to claim 2, characterized in that the calorimeter ( 9 ) a throttle overheating calorimeter ( 9 ). Steam moisture measuring system according to one of claims 1 to 3, characterized in that heat flow sensors ( 10a . 10b ) are arranged, the heat losses of the device for the preparation of a heat balance ( 9 ) to capture. Steam moisture measuring system according to one of claims 1 to 4, characterized in that the first heating coil ( 5 ) by the control unit ( 8th ) is switchable, if at the temperature measuring point (B) a temperature is registered, which is below the superheat temperature of the steam. Steam moisture measuring system according to one of claims 1 to 5, characterized in that the second heating coil ( 6 ) by the control unit ( 8th ) is formed switchable, as soon as a set temperature determined at the temperature measuring point (D) is reached. Steam moisture measuring system according to one of claims 1 to 6, characterized in that temperature sensors ( 18a to 18f ) directly on the surface of the heating registers ( 5 . 6 ) are arranged. Steam moisture measuring system according to one of claims 1 to 7, characterized in that the isokinetic sampling device ( 2 ) and the static pressure sensing openings ( 12a . 12b ) as zero pressure probe ( 2 ) are executed.