DD209268A1 - ENVIRONMENTAL DEVICE FOR VOLUME AND FLOW MEASUREMENT FOR GASES, REFLECTING THE REALGAS BEHAVIOR - Google Patents

Abstract

The invention relates to a Umwerteinrichtung for volume and Durchfluffmessung for gases on standard conditions, especially in the large gas measurement under Berichtigsicht.der thermodynamic conditions of temperature and pressure and the Realgasverhaltens. The aim of the invention is to achieve a substantially higher accuracy compared to known measuring devices in the volume conversion of gases, taking into account the current compressibility K. The object, which is achieved according to the invention, is to propose a conversion device in which in addition to the actual volume conversion in each calculation cycle in dependence on pressure and temperature, in particular the compressibility K is calculated separately and taken into account in the conversion. According to the invention, the proposed conversion device, which is preferably designed for a plurality of measuring sections and consists of a programmed digital computer on a microprocessor basis, records the volume and the flow rate, the temperature and the pressure continuously, processes it digitally according to a computer program, monitors the sense of the measured values and in particular in each calculation cycle the compressibility K is calculated as a function of pressure and temperature from the real gas factors according to the method Redlich-Kwong and taken into account in the revaluation. The summation of the converted quantity takes place on non-volatile memory while the instantaneous flow and each measured value can be selected digitally on an operating and display unit.

Description

Umwerteinrichtung for volume and flow measurement for gases taking into account the RealgasVerhaltens

Field of application of the invention

The invention relates to the device-technical device for volume conversion of gases and gas mixtures to standard conditions, especially in the measurement of large amounts of gas, taking into account the thermodynamic state conditions temperature and pressure and the Realgasverhaltens.

Characteristic of the known technical solutions

Ss are volume converters in the volume and flow measurement: of gases known, the mechanical, electrical or electronic way, a re-evaluation of the amount of gas in the operating condition to Uormbedingungen after the Be- .Ziehungen:

as density conversion or

P-

η ^v

as state conversion.

nn.

The transducers for flow measurement work according to the equation

, ρ · HL

ν = ν J ¹

η T · K ·

and especially for differential pressure measurements

V _n = c · f (4)

The compressibility number K characterizes the real behavior of a gas. "Real gases do not exactly follow the gas equation for ideal gases, but differ in different ways. This deviation is denoted by the compressibility number E and determined from the real gas factors Z '' -. ,

The K numbers depend on the gas composition, the pressure and the temperature

 In the formulas mean:

V - volume under operating conditions

V - volume under standard conditions

V - volume flow

V - volume flow under hormone conditions

<ξ - density.

O _n - Density under normal conditions

ρ - pressure (absolute), ρ = p .. * atmospheric pressure Pj-- - overpressure in MPa - differential pressure

T - temperature

K - compressibility number

Z - Real gas factor

Z - Real gas factor under Iform conditions

24 2 3 5 0 5

c - Aperture constant o <- flow rate

E - expansion number

d - aperture diameter standard conditions: p _n = 101325 Pa

T _n = 273,15 K

In density conversion devices made exclusively as electromechanical or electronic devices, the operating density f must be determined continuously while the normal density P _n is generally fixedly input. In particular, the exact determination of the operating density is considerable in practice technical effort and difficulties associated.

Although in the case of the condition correctors according to the relationships (2), (3) and (4) robust and accurate encoders and converters are available for measuring the operating temperature T and the operating pressure p., On the other hand, there is no measuring instrument with which the compressibility number In practice, an average compressibility number K, which is determined by the laboratory, is calculated externally according to certain methods or taken from extensive tables, as a constant together with the values for. the agreed, standard conditions entered into the corrector. As a result, the deviations of the K-numbers in temperature and pressure fluctuations are not detected, so that it can lead to significant errors.

In DE-OS 290 1030 a device arrangement for state quantity conversion is given with simultaneous calculation for the US in the USA supercompatibility factor. The method is based on the calculation equations of the PAR Reserch project ΈΣ 19 of the AGA (American Gas Association). However, the method used is only applicable to high calorific natural gases with a maximum of 15% each nitrogen and carbon dioxide and in a certain density range. Pur other gases, eg. As city and generator gas, as well as for inert natural gases, the method is not suitable.

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Object of the invention

The aim of the invention is to provide a device device for volume conversion of gases and gas mixtures, in particular taking into account the Realgasverhaltens (compressibility K), which is applicable to all gases and does not have the disadvantages mentioned.

Explanation of the essence of the invention

The invention has for its object to provide a device device for Mengenumwertung of gases in the volume measurement by counter and in the flow measurement by the Wirkdruck- or vortex frequency method (Karmansche - vortex street), in addition to the revaluation as a function of pressure and temperature in particular the compressibility K calculated separately and taken into account in the revaluation and at the same time several transmitters for quantity, pressure and temperature

can be connected «..-

According to the invention, the object is achieved, that in addition to the detection of the volume or the flow through known devices such as flow meters, throttle or vortex frequency devices simultaneously the temperature and. the pressure is measured by means of a transmitter and all the signals of a microprocessor-based programmable digital corrector are applied to the time-cyclic calculation. One or preferably several measuring sections consisting of 3 input channels for the signals volume or flow, pressure and temperature can be connected to the conversion device. The signals are interrogated time-cyclically, converted into digital values and further processed. Depending on the connected quantity measuring device, the determination of the volume according to equation (2) or of the flow according to equations (3) or (4) takes place in each calculation cycle. By an intermediate calculation step, in each calculation cycle for the respective calculation channel (measurement)

2423

stretch) the compressibility K as a function of pressure and temperature from the real gas factors Z according to the following Soave-Redlich-Kwong method valid for all gases and gas gasses calculated from:

Z ³ - Z ² - Z (B ² + B - ^A ) - AB = 0 (6)

with A = R ₁ · -§-ς (7)

P and B μ R ₂ ♦ ^ - (8)

The factors R 1 and R 2 preferably become external according to the gas composition, according to the relationships

^x ± ' ^T Xi ^{) 2} ' ⁵ (9)

R ₁ = 0.42747 -

^x ± *

Ττ ~) (10)

{. Xj * J-TT.I

and R ₀ = 0.08664 = -

  temperature of the single component

Pressure of the individual component - percentage molar fraction of the individual component

determined, as a constant entered into the Uinwerteeinrichtung and stored · In a variant of ümwerteeinrichtung the calculation of the factors R ^ and R ₂ after entering the mole percent x ^, the critical temperature Trr and the critical pressure p _{Ei of} the individual components by this _; be carried out by yourself

2423

The solution of equation (6) is carried out in the conversion device iteratively by the Hewton's method up to a predetermined accuracy barrier. In the next calculation step, the compressibility factor from the real gas factors is calculated in the corrector according to equation (5):

The determined compressibility number K is stored in the main memory (read-write memory) and used in each calculation cycle to determine the volume according to (2) or the flow rate according to (3) or (4). The quantities converted to standard conditions are temporarily stored in the main memory and are output to non-volatile, preferably electromechanical, counters by means of an electrical pulse output after each computing cycle of the respective computing channel (measuring path) with a specific input value. "

In the volume measurement according to (2), the instantaneous flow becomes differentiated

y-Iene)

η dt

determined and can be displayed on digital selection on a display device and removed at a separate output as an analog signal.

In the case of the correction device for correcting the flow, after the correction calculation, according to equations (3) and (4), the value of which is likewise selected digitally or, as an analog signal, can be taken from an output, a continuous integration takes place

T _n - / _n V ... dt (12)

24 2 3

in memory. After each arithmetic cycle of the respective computing channel (measuring path), a pulse output via electronic output elements for controlling non-volatile preferably electromechanical counters with enterable significance of the pulses. The integrated amount in the main memory is paid back by the given impulses *

In all input channels for each calculation channel (measuring section) are devices for digital filtering of measured values with settable time constant, the naturalness test, entering the Meßbereichsnormierungswerte for encoder adjustment and dimensionally accurate display and processing and for limit monitoring at specifiable maximum and minimum barriers.

All connected measured values can open. Selection with display of the measuring channel, the dimension and the unit of measurement are displayed digitally. If there is a limit value, sense or due date violation, the disturbed channel is indicated by the flashing light of a light indicator and the present fault, and at the same time is output via a potential-free contact as a collective fault message. The light indicator changes to steady light after acknowledgment, which disappears only after the fault has been rectified. When the naturalness test of an input channel responds, the last calculated instantaneous value remains digital and analog. At the same time, the following functions are triggered in the conversion facility:

- Potential-free contact for external processing

- Display of the faulty channel as well as the function "Meaningfulness test" on an operating and display unit

- Blocking of the pulse output for counter control

- Start of the internal time counting as well as the uncorrected quantity for the time of the failure in the main memory

 After the error has been corrected, the downtime and the uncorrected amount can be queried and deleted from the main memory.

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Vf * ^ p ν

Execution; abeispie.l

The invention will be explained in more detail below on an exemplary embodiment of a conversion device for flow correction calculation according to the differential pressure method according to equation (4), in particular in the case of large gas measurement.

To implement the device-specific functions, a modular microcomputer structure with the functional units shown in Figure 1 is used. The central unit (a) contains in addition to the microprocessor 7 K-byte program memory and 1 K-byte main memory. It also generates the device-internal bus system (i). The control of the puncturing unit operation and display (c) ^ ird over a simple parallel interface (b) by the central unit (a) made · The acquisition of the input quantities p, T and 4 P via the puncturing units current / voltage converter Cf) and analog / digital - or «digital / analog converter (d) · These puncturing units are multi-channel and ensure the detection of a maximum of 12 input variables in the standard signal ranges 0 ... 20 mA, 4» ·· 20 mA, O ... 5 mA or O ... 10 IT. About electronically controlled holding members Cc) is the time-division multiplexed output of up to 4 analog signals in the range 0 .... 10 T for the Hormdurchfluß Y _n based on lormbedingungen * The output of the detected by the device group disturbances and the control of the counter for the integration of the SOrmdurchflusses is performed by the binary signal output (g).

It represents a simple parallel interface, which, like the functional unit (b), is implemented via a ΡΙΟ-block.

The supply of the puncture units with the required voltages is made via the Stromversorgungsnulul Ch). The control and display unit Cc) enables the acquisition of permanently programmed via an operator keyboard

242350

Data records from the program memory into the main memory, the direct programming as well as the selection and inquiry of the input channels and the disturbance counter. The data display is digital with indication of the channel and parameter. Disturbed channels are indicated by LEDs,

The calculation of the required quantities is carried out in a time-cyclic and program-controlled manner, based on the functional processing structure illustrated in FIG. 2 for each computing channel (measuring section). In the program blocks (1), the input variables pressure, temperature and flow are processed in several individual operations (see FIG. 3) in such a way that they are made available to the computational block (3) in a dimensionally appropriate manner for further processing. The determined status of the signals is forwarded to the error evaluation block (2). In calculation block (3), the calculation of the Uormdurchflusses and the standard volume from the input variables pressure, temperature and flow and taking into account the compressibility K. With undisturbed measured variables takes over the acquisition of the determined Bormvolumens by controlling electromechanical counter (4) · The Formdurchfluß is for registration purposes provided as an analogous quantity of O ♦. * 10 V (5). In block (2), the analysis of the fault messages from the blocks (1) takes place with the aim of influencing the computing processes in block (3). communicated central Störsignalisations- and acknowledgment block (6) »The conversion unit can realize a maximum of 4 of the described calculation channels.

The individual functions of the preparation of the input signals provided in program blocks (1) are as shown in the illustration

- A / D conversion block (1.1)

- Sense test block (1.2) (test for disturbed signal)

- digital filtering (filter 1st order block (1.3) with insertable time constant T ^)

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- dimensional conversion and Horniie block (1.4) to specified basic values MUf, MAJ

- Limit value monitoring to specified block (1.5) limit values OG, UG ·

- Disturbance signal formation in the case of disturbed signals block (1.6) or "when the specified limit values are exceeded or fallen short of

At the end of the arithmetic processes in the blocks (1.1 to 1.4), the input quantities are dimensionally appropriate for further processing in the arithmetic channel according to FIG. Input variables of the calculation channel are the processed process variables pressure, temperature and flow stored in block (3 * 1) as well as additional parameters or constants characterizing the measuring path. On the basis of the disturbances mediated in the input signal processing block 1.2, an analysis of the same occurs in program block 3 »2, $ obei the states

- no mistake

- Input signals pressure or temperature disturbed - Error

- Input signal flow disturbed - Error 2

Depending on this, different calculation processes are carried out * Calculation processes with no error:

- Calculation of the Kourpressibility Number K (3.3)

- Calculation of the standard flow rate V '(3 * 4)

V dt (3.5)

- Counter control with input

Impuisvalence (3.7)

    · ·.

- Analog value output for T (3.6) Calculation processes for error 1:

-Performance of the processes (3.3 to 3.6)

Here, in the program block (3.4), the last valid undisturbed measured value is used for the calculation.

- summation of the integral jV _Q dt to an internal fault counter (3.8)

242350

- Totaling downtime to an internal fault counter (3.9)

Calculation processes at error 2:

- Reduction of the downtime to an inter- (3.9) Number of disturbances

The calculation of the Uormdurchflusses according to equation (4) is carried out using pressure transmitters using the tailored calculation equation

V = ^rVVV * ⁽ Pd ⁺ ° ^{> 1013)} (3-D η ^C 1 · ^C 2 t T

The aperture and conversion constant c. is calculated

and can be entered separately for each calculation channel according to the given conditions of use.

For agreed standard conditions for volume calculation, which deviate from the standard conditions, eg. B, temperature 288,15 K .. the constant c «changes accordingly.

The correction number

o ₂ - ~ (3-3)

or the compressibility K is pressure and temperature dependent and is determined in each computing cycle on the real gas factor Z according to the equations (6) to (10) of Soave-Redlich-Ksvong:

Z ³ - Z ² -ZxC -D = O (3-4)

A = R ₁ . (p _ü + 0.1013) / T ² » ⁵ (3-5)

B = R ₂ . (p _ü + 0.1013) / T (3-6)

C = B ² + 3 - A (3-7)

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The real gas factor Z is calculated iteratively in the device according to Hewton's method as follows:

_{1 + 1} = Z _± - f (Z ₁ ) / f '(Z ₁ ) (3-9)

With

f (Z ₁ ) = Z ₁ ³ - Z ₁ ² - C. Z ₁ - D _{(> 10)}

f'iZj.) = 3 Z ₁ ² - 2 Z ₁ - C (3-11)

Z ₀ = 1 (3-12)

Equation (3-9) determines the real gas factor with an accuracy of less than 0.001, which requires 2 ... 3 iteration steps *

The correction constant c2 results according to equation

= / 1 / K

1 / K = / A _N / A (3-13)

Z is the real gas factor calculated with ρ = ρ and T = S _n and Z is the real gas factor for the current p, T values.

The factors R1 and R2 necessary for calculating the real gas factor can be entered by the puncture unit for operation and display.

Claims (10)

~ ^ Invention claim 1. Umwerteinrichtung of gases to standard conditions in volume and flow measurements, characterized in that measured in addition to the volume or the flow rate, the temperature and the pressure of the flowing gas, converted into electrical signals and these are supplied to the conversion device, in addition to the actual conversion in particular, calculated in a time-cyclical manner in each calculation operation as a function of the input constants for the gas composition of the measured temperature and the pressure, the compressibility factor K according to the method of Soave-Redlich-Kwong according to equations (6) to (10) and taken into account in the revaluation. 2. Revaluation device after. Point f, characterized in that in the volume measurement by counter, the device in addition to the calculation of the compressibility K the punctures ρ · T V "= V 'and η p_. T · K η
realized. 3. Revaluation device after. Item 1, characterized in that in the flow measurement, the device in addition to the calculation of the compressibility K the functions   * '. P. τ v_ = ν ⁿ η - T.. K. p _n and in the special case at Wirkdruc.kmeß ν experience ZUlöb V - "η ~ ° V τ K
with subsequent integration · ^dt realized. - 4. Umwerteinrichtung according Funkt i, characterized in that the device consists of a programmed digital microprocessor-based computer preferably for a plurality of measuring sections. 5. conversion device according to item 1, characterized in that the device consists of the modular functional units central unit, Strora, voltage converter, analog-digital and digital-to-analog conversion with holding elements, binary signal output and a parallel interface for controlling the separate control and display unit. 6. Umwerteinrichtung according to Pitnkt 1, characterized in that each calculation channel functionally from the program blocks lingangssignalverarbeitung, correction calculation, error evaluation, Störsignalisation and. Acknowledgment, analog signal and dimensionally accurate digital output and pulse output for counter control exists. 7. Umwerteinrichtung after Funkt 1 _? characterized in that each input signal processing from the program blocks analog / digital conversion, meaningfulness test, digital filtering with filter time inputable constant, dimensional conversion and formation with insertable pairs of support values, monitoring for lower and upper limit values, Störsignalbildung in Sinnfälligkeits- and / or limit violation exists. 24 2 8. Umwerteinrichtung according to item 1, characterized in that the Störsignalverarbeitung the computing channel in its processing influenced such that in a Sinnfälligkeitsverletzung in the input channel for pressure and / or temperature, the Uormdurchflusses from the last undisturbed measured values takes place as well as the Durchflußintegral and the downtime be summed up in each case a separate fault counter. 9 »Umwerteinrichtung according to item 1, characterized in that the Störsignalverarbeitung affects the computational channel in its processing such that in a SinnfälligkeitsVerletzung in the input channel for differential pressure, the calculation of the Worm- flow and the Durchflußintegrals interrupted and the downtime is summed up in the disturbance counter. 10 · revaluation unit according to item 1, characterized in that the operating and display unit allows the display of parameters, channel, data, dimension and disturbance sovrie via a keyboard selection, display and input. Hferzo_iiL__Se! Fen drawings