CN110186522B - Moisture over-read compensation and flow measurement method combined with vortex street amplitude characteristics - Google Patents

Abstract

The invention relates to a moisture over-reading compensation and flow measurement method combined with vortex street amplitude characteristics. The steps are as follows: collecting pressure p, temperature T and vortex street time series signal s(t) output by a piezoelectric sensor; calculating gas density ρ _g and liquid density ρ _p ; extract the frequency f _VS and amplitude A _VS of the vortex street signal; calculate the apparent gas volume flow rate Q _{g without reading correction, apparent} as the initial iterative value of the gas volume flow rate Q _g ; iteratively calculate until Convergence: Calculate the apparent gas phase velocity U _sg corresponding to the gas volume flow rate Q _g , calculate the signal amplitude when calculating the single-phase gas, calculate the droplet loading φ _p , calculate the over-read factor OR, and calculate the wet gas phase after over-read compensation. volume flow. The final wet gas phase volume flow Q _g and droplet loading φ _p are obtained.

Description

Moisture over-read compensation and flow measurement method combined with vortex street amplitude characteristics

technical field

The invention belongs to the field of gas-liquid two-phase flow measurement, and relates to a wet gas over-read compensation and flow measurement method combined with vortex street amplitude characteristics.

Background technique

Wet gas flow widely exists in the natural gas industry, and its accurate measurement has an important impact on pipeline transportation and trade settlement, and is directly related to environmental protection, energy management and its full utilization [1]. When the gas velocity is high, the annular mist flow is the main wet gas flow pattern, in which the liquid phase exists in the form of entrained droplets and wall liquid film [2]. Vortex flowmeters are widely used in online measurement of wet gas because of their robustness, economy, high turndown ratio and small pressure loss. However, when the traditional single-phase vortex flowmeter is applied to wet gas measurement, a small amount of liquid phase in the wet gas will affect the vortex meter coefficient, making the measured gas phase flow rate on the high side (overreading, overreading, OR), the maximum Can cause 20% measurement error [3]. In order to improve the measurement accuracy of the vortex flowmeter in wet gas, it is necessary to accurately model and reasonably correct the over-reading phenomenon.

Reference [4] pointed out that the droplet mass loading in the liquid phase is the main factor affecting the vortex street overreading through theoretical calculation, aiming at the problem of non-uniform overreading correlations under different pressures and medium working conditions. However, correction of over-reading requires known droplet mass flow or droplet mass fraction in moisture, which is generally measured by microwave method, ray method and isokinetic sampling method [5]. These methods are complicated to operate, costly and difficult to achieve continuous accurate measurements. At present, it is still difficult to achieve accurate measurement of wet gas flow only through a vortex flowmeter.

Patent 201810644726.7 designs a multi-parameter adjustable mist flow experimental system, patent 201810226454.9 provides an annular flow liquid film collection and metering device, patent 201810232606.6 provides an annular flow liquid film separation and mass measurement method .

references

[1] Mehdizadeh P, Marrelli J, Ting V C, "Wet gas metering: trends in applications and technical developments," in Proc.SPE Annu.Tech.Conf, SanAntordo, TX, USA, 2002, pp.1–14.

[2] T.Oshinowo and M.E.Charles, "Vertical two-phase flow part I.Flowpattern correlations," Can.J.Chem.Eng.,vol.52,no.1,pp.25–35,1974.

[3] R.Steven, "Wet gas metering," Ph.D.dissertation, Dept.Mech.Eng.Univ.Strathclyde, Scotland U.K., 2001.

[4] J.X.Li, C.Wang, H.B.Ding, Z.X, Zhang and H.J.Sun, “EMD and spectrum-centrobaric-correction-based analysis of vortex street characteristics inannular mist flow of wet gas”, IEEE Trans.Instrum.Meas. , vol.37, no.5, pp.1150–1160, May 2018.

[5] ASME, ASME MFC-19G-2008, Wet gas flowmetering guideline. American Society of Mechanical Engineers, USA, 2008.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a wet gas flow measurement method that can eliminate the measurement over-reading problem caused by the liquid phase by using only one vortex flowmeter based on the frequency and amplitude characteristics of the vortex piezoelectric sensor in wet gas . The technical scheme of the present invention is as follows:

A moisture over-read compensation and flow measurement method combined with vortex street amplitude characteristics, the method utilizes the frequency and amplitude characteristics of a vortex street piezoelectric sensor in wet gas to perform moisture over-read compensation and flow measurement, and the method is as follows:

1) Collect pressure p, temperature T and the vortex street time series signal s(t) output by the piezoelectric sensor.

2) Calculate the gas density ρ _g and the liquid density ρ _p through p and T respectively; extract the frequency f _VS and amplitude A _VS of the vortex signal.

3) Calculate the apparent gas volume flow rate Q _{g without reading correction according to formula (1), and apparent} as the initial value of the gas phase volume flow Q _g iteration

Q _g,apparent =3600f _VS /K _v (1)

Among them, K _v is the meter coefficient (m ^-3 ) of the vortex flowmeter in single-phase gas.

4) Calculate the apparent gas phase velocity U _sg corresponding to the gas volume flow rate Q _g according to formula (2)

U _sg =4Q _g /πD ² (2)

Among them, D is the nominal diameter of the pipe.

5) Calculate the signal amplitude A ₀ (unit: mV) of single-phase gas according to formula (3)

6) According to the relationship between the characteristic amplitude A _VS of the vortex street signal and the droplet loading amount φ _p in Eq. (4), calculate the droplet loading amount φ _p

7) Calculate the over-read factor OR according to formula (5)

OR=1+271.08φ _p ρ _g /ρ _p (5)

8) Calculate the wet gas gas phase volume flow rate after over-read compensation according to formula (6)

Q _g =Q _g,apparent /OR (6)

9) If |Q _g -Q _g,last |≤δ, and δ is a small enough positive real number, the iteration ends; otherwise, the calculated gas volume flow rate Q _g is used as the initial value of the next iteration to re-execute 4 to 8 step by step until convergence.

10) Obtain the final wet gas phase volume flow Q _g and droplet loading φ _p .

Description of drawings

Figure 1: Signal Acquisition Flowchart

Figure 2: Schematic diagram of annular mist flow pattern

Figure 3: Overread-Droplet Loading Graph

Figure 4: The relationship between the amplitude of the vortex street signal and the apparent gas velocity and gas density in a single phase

Figure 5: Dimensionless Vortex Signal Amplitude-Droplet Loading Relationship Diagram in Wet Gas

Figure 6: Flowchart of iterative algorithm

Figure 7: Comparison of predicted and actual gas phase volume flow rates in wet gas

Figure 8: Distribution of prediction error of gas phase volume flow in wet gas

Detailed ways

The present invention will now be further described with reference to the accompanying drawings and implementation.

This example is the specific implementation of the moisture over-read compensation and flow measurement method combined with the vortex street amplitude characteristic. The wet gas working condition pressure p=270～440kPa, the gas phase volume flow rate Q _g =9～17m ³ /h, the liquid phase mass flow rate m _l =1.7～17kg/h.

The signal acquisition flow chart is shown in Figure 1: the working condition pressure p, the working condition temperature T and the vortex street sequence number s(t) are collected, where s(t) is collected by the piezoelectric sensor: the piezoelectric probe converts the flow signal into For the electrical signal, the original signal is amplified by charge and voltage by the hardware circuit, and after band-pass filtering (f=200 ~ 2500 Hz), the data is collected by the NI-USB acquisition card, the sampling frequency is 20 kHz, and the number of sampling points is 131072, and is displayed and stored by Labview software, so as to obtain the vortex time series signal s(t).

The vortex flowmeter is a kind of velocity flowmeter, which can obtain the fluid volume flow by measuring the vortex shedding frequency f _VS

Wherein, K _v (=4St ₀ /πD ² d) is the meter coefficient (m ^-3 ) of the vortex flowmeter in single-phase gas. D is the nominal diameter of the pipeline, d is the width of the upstream surface of the generating body, and St ₀ is the Strouhal number under the single-phase gas condition, which is a constant within a certain range of Reynolds number. In this example, St ₀ =0.251, d = 4.2 mm, D = 15 mm, K _v =338182.4 m ^-3 .

In the wet gas flow, the existence of a small amount of liquid phase makes the measured gas volume flow Q _g,apparently higher than the actual gas flow Q _g in the process of applying the vortex flowmeter to measure the wet gas, which is called "overreading" Phenomenon. In order to correct the vortex street over-reading, a correction coefficient OR whose dimension is 1 is introduced, which is expressed as

Wherein, St is the Strouhal number of the vortex street in the wet gas, St=f _VS ·d/U _sg , U _sg is the apparent flow velocity of the gas phase, and U _sg =4Q _g /πD ² .

According to the research conclusion of the literature [4], the droplet loading φ _p is the main factor affecting the over-reading OR. The mist flow pattern of the wet gas ring is shown in Figure 2: a part of the liquid phase flows at a low speed on the tube wall in the form of a liquid film, and a part is entrained by the airflow in the form of discrete droplets.

Define the droplet mass loading parameter φ _p

where m _p and m _LF represent the mass flow rates of the droplet and liquid film, respectively, and m _l and m _g represent the mass flow rates of the liquid and gas phases, respectively.

In order to accurately measure the gas-phase flow in a wet-gas two-phase flow, the over-read OR must be accurately modeled and properly corrected. This patent proposes a moisture over-read compensation and flow measurement method combined with the vortex street amplitude characteristic.

Firstly, the over-read and amplitude characteristics of the vortex sensor in moisture are modeled. Using the multi-parameter adjustable mist flow experimental system in patent 201810644726.7, and the annular flow liquid film collection device and mass measurement method provided in patents 201810226454.9 and 201810232606.6, the liquid phase mass loading φ and different pressure p were used to measure the Droplet loading φ _p .

Then the calibration of the correlation coefficient in the model correlation is carried out. The change of over-read OR with φ _p is shown in Figure 3, and the over-read correlation can be obtained

Under the single-phase gas condition, the changes of the signal amplitude A ₀ (unit: mV), the apparent gas velocity U _sg and the gas phase density ρ _g are shown in Fig. 4 , there are

The variation of the dimensionless vortex signal amplitude A ^* =A _VS /A ₀ is shown in Fig. 5, there are

Based on the above modeling and calibration results of vortex street frequency and amplitude characteristics in wet gas, the wet gas measurement model can be obtained, which is summarized as follows:

Based on the above modeling and calibration results, the moisture over-read compensation and flow measurement combined with the vortex street amplitude characteristics are carried out, as shown in Figure 6, and the method is as follows:

1) Collect pressure p, temperature T and the vortex street time series signal s(t) output by the piezoelectric sensor.

2) Calculate the gas density ρ _g and the liquid density ρ _p through p and T respectively; extract the frequency f _VS and amplitude A _VS of the vortex signal.

3) Calculate the apparent gas volume flow rate Q _{g without reading correction according to formula (1), and apparent} as the initial value of the gas phase volume flow Q _g iteration

Q _g,apparent =3600f _VS /K _v (7)

Among them, K _v is the meter coefficient (m ^-3 ) of the vortex flowmeter in single-phase gas.

4) Calculate the apparent gas phase velocity U _sg corresponding to the gas volume flow rate Q _g according to formula (2)

U _sg =4Q _g /πD ² (8)

Among them, D is the nominal diameter of the pipe.

5) Calculate the signal amplitude A ₀ (unit: mV) of single-phase gas according to formula (3)

6) According to the relationship between the characteristic amplitude A _VS of the vortex street signal and the droplet loading amount φ _p in Eq. (4), calculate the droplet loading amount φ _p

7) Calculate the over-read factor OR according to formula (5)

OR=1+271.08φ _p ρ _g /ρ _p (11)

8) Calculate the wet gas gas phase volume flow rate after over-read compensation according to formula (6)

Q _g =Q _g,apparent /OR (12)

9) If |Q _g -Q _g,last |≤δ, and δ is a small enough positive real number, the iteration ends; otherwise, the calculated gas volume flow rate Q _g is used as the initial value of the next iteration to re-execute 4 to 8 step by step until convergence.

10) Obtain the final wet gas phase volume flow Q _g and droplet loading φ _p .

In order to verify the above-mentioned moisture over-read compensation and flow measurement method combined with vortex street amplitude characteristics, the comparison between the actual and predicted gas volume flow under different conditions is shown in Figure 7. The error distribution between the predicted value and the actual value is shown in FIG. 8 , where the error PE(%)=(predicted value−true value)/true value×100. In the wet gas measurement, the prediction errors of the gas volume flow rate are all within ±1.5%, and the average absolute error is 0.37%, indicating that the model prediction accuracy is high.

By modeling the frequency characteristics and amplitude characteristics of the vortex flowmeter in wet gas, the invention proposes a wet gas over-read compensation and flow measurement method combined with the vortex street amplitude characteristics. The invention does not need other complicated and expensive liquid phase flow measuring devices and measuring methods, and provides a measuring method that can realize accurate measurement of wet gas flow only through one vortex flowmeter, which is simple, economical and has high prediction accuracy.

Claims (1)

1. A moisture overreading compensation and flow measurement method combining vortex street amplitude characteristics utilizes frequency and amplitude characteristics of a vortex street sensor in moisture to perform moisture overreading compensation and flow measurement, and comprises the following steps:

1) pressure acquisitionpTemperature ofTAnd vortex street time sequence signal output by piezoelectric sensors(t)；

2) By passingpAndTseparately calculating gas density

And density of liquid

(ii) a Extracting frequency of vortex street signalf _VS Sum amplitudeA _VS ；

3) Calculating the apparent gas phase volume flow without reading correction according to the formula (1)Q _g,apparentAnd as the gas phase volume flowQ _g Initial value of iteration of, i.e.Q _g = Q _g,apparent

（1）

Wherein,K _v meter coefficient (m) for vortex shedding flowmeter in single phase gas^-3)；

4) Calculating the gas phase volume flow according to equation (2)Q _g Corresponding superficial gas phase velocityU _sg

（2）

Wherein,Dis the nominal diameter of the pipeline;

5) calculating the signal amplitude of single-phase gas according to the formula (3)A ₀

（3）

6) Calculating the liquid drop loading amount according to the relation between the vortex street signal characteristic amplitude and the liquid drop loading amount in the formula (4)

（4）

7) Calculating the over-reading factor OR according to equation (5)

（5）

8) Calculating the overreading compensated moisture gas phase volume flow according to the formula (6)Q _g

（6）

9) If it is not

If the real number is small enough, the iteration is ended, otherwise, the calculated gas phase volume flow is calculatedQ _g Performing the calculation of the steps 4) -8) again as an initial value of the next iteration until convergence;

the final gas phase volume flow in the wet gas is obtained from the last iteration calculation resultQ _g And droplet loading

。

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