CN110186522A - Reading compensation and flow-measuring method are crossed in conjunction with the moisture of vortex street amplitude characteristic - 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 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 signal; calculate the apparent gas phase volume flow Q _{g without over-reading correction, apparently} as the initial value of the gas phase volume flow Q _g iteration; iterative calculation until Convergence: Calculate the superficial gas velocity U _sg corresponding to the gas phase volume flow rate Q _g , calculate the signal amplitude of single-phase gas, calculate the droplet loading φ _p , calculate the overreading factor OR, and calculate the wet gas phase after overreading compensation volume flow. Get the final gas phase volume flow rate Q _g and droplet loading φ _p in wet gas.

Description

Humidity overreading 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 moisture overreading compensation and flow measurement method combined with vortex street amplitude characteristics.

Background technique

Moisture 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, annular mist flow is the most dominant wet gas flow pattern, in which the liquid phase exists in the form of entrained droplets and liquid film on the wall [2]. Vortex flowmeters are widely used in the on-line measurement of moisture due to 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 flow rate high (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 correct the overreading phenomenon reasonably.

Literature [4] aimed at the problem of inconsistency of the overreading correlation under different pressure and medium conditions, through theoretical calculations, it was pointed out that the droplet mass loading in the liquid phase is the main factor affecting the vortex street overreading. However, the correction of over-reading needs to know the droplet mass flow or droplet mass fraction in the moisture, which is generally measured by microwave method, ray method and isokinetic sampling method [5]. These methods are complex in operation, high in cost and difficult to achieve continuous and accurate measurement. At present, it is difficult to achieve accurate measurement of wet gas flow with only one vortex flowmeter.

Patent 201810644726.7 designed a multi-parameter adjustable mist flow experimental system, patent 201810226454.9 provided an annular flow liquid membrane collection and metering device, and patent 201810232606.6 provided an annular flow liquid membrane 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, San Antordo, 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 annular 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.

Contents of the invention

The purpose of the present invention is to provide a wet gas flow measurement method that can eliminate the measurement overreading 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 . Technical scheme of the present invention is as follows:

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

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

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

3) According to formula (1), calculate the apparent gas phase volume flow rate Q _{g without overreading correction, and apparently} serve as the iterative initial value of gas phase volume flow rate Q _g

Q _g,apparent ＝3600f _VS /K _v (1)

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

4) Calculate the superficial gas phase velocity U _sg corresponding to the gas phase 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 signal in formula (4) and the droplet loading φ _p , calculate the droplet loading φ _p

7) Calculate the overread factor OR according to formula (5)

OR＝1+271.08φ _p ρ _g /ρ _p (5)

8) Calculate the wet gas phase volume flow after overreading compensation according to formula (6)

Q _g ＝ Q _g,apparent /OR (6)

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

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

Description of drawings

Figure 1: Signal Acquisition Flowchart

Figure 2: Schematic diagram of annular mist flow pattern

Figure 3: Relationship between overreading and droplet loading

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

Figure 5: The relationship between dimensionless vortex signal amplitude and droplet loading in wet gas

Figure 6: Iterative Algorithm Flowchart

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

Figure 8: Prediction Error Distribution of Gas Phase Volume Flow in Wet Gas

Detailed ways

The present invention will be further described in conjunction with accompanying drawing and implementation now.

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

The flow chart of signal acquisition is shown in Figure 1: the working condition pressure p, the working condition temperature T and the sequence number s(t) of the vortex street are collected, where s(t) is collected by the piezoelectric sensor: the piezoelectric probe converts the flow signal into It is an 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 20kHz, and the number of sampling points is 131072, and displayed and stored by Labview software, so as to obtain the vortex street timing signal s(t).

The vortex flowmeter is a velocity flowmeter, the fluid volume flow rate can be obtained by measuring the vortex shedding frequency f _VS

Wherein, K _v (=4St ₀ /πD ² d) is the meter factor (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 single-phase gas conditions, which is constant within a certain range of Reynolds number. In this example, St ₀ =0.251, d=4.2mm, D=15mm, K _v =338182.4m ^-3 .

In the flow of wet gas, the existence of a small amount of liquid phase makes the measured gas phase volume flow rate Q _g,apparently higher than the actual gas flow rate Q _g during the process of measuring wet gas with a vortex flowmeter, which is called "overreading" Phenomenon. In order to correct the vortex street overreading, a correction factor OR with a dimension of 1 is introduced, expressed as

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

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

Define the droplet mass loading parameter φ _p

Among them, m _p and m _LF represent the mass flow rate of liquid droplet and liquid film, respectively, and m _l and m _g represent the mass flow rate of liquid phase and gas phase, respectively.

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

Firstly, the over-reading and amplitude characteristics of the vortex sensor in humidity 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 by patents 201810226454.9 and 201810232606.6, the mass loading φ of different liquid phases and the mass under different pressures p are measured Droplet loading φ _p .

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

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

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

Based on the above modeling and calibration results of the 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 overreading 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) Acquisition of pressure p, temperature T and vortex time series signal s(t) output by the piezoelectric sensor.

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

3) According to formula (1), calculate the apparent gas phase volume flow rate Q _{g without overreading correction, and apparently} serve as the iterative initial value of gas phase volume flow rate Q _g

Q _g,apparent ＝3600f _VS /K _v (7)

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

4) Calculate the superficial gas phase velocity U _sg corresponding to the gas phase 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 signal in formula (4) and the droplet loading φ _p , calculate the droplet loading φ _p

7) Calculate the overread factor OR according to formula (5)

OR＝1+271.08φ _p ρ _g /ρ _p (11)

8) Calculate the wet gas phase volume flow after overreading compensation according to formula (6)

Q _g ＝Q _g,apparent /OR (12)

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

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

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

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

Claims (1)

1. a kind of moisture of combination vortex street amplitude characteristic crosses reading compensation and flow-measuring method, this method is existed using vortex street sensor Frequency and amplitude characteristic in moisture carry out moisture and cross reading compensation and flow measurement.Method is as follows:

1) the vortex street clock signal s (t) of pressure p, temperature T and piezoelectric transducer output is acquired；

2) gas density ρ is calculated separately by p and T_gWith fluid density ρ_p；Extract the frequency f of vortex signal_VSWith amplitude A_VS；

3) it is calculated according to formula (1) and did not carried out reading modified apparent gas phase volume flow rate Q_g,apparentAs gas phase volume flow rate Q_g Iterative initial value

Q_g,apparent=3600f_VS/K_v (1)

Wherein, K_vInstrument coefficient (the m for being vortex-shedding meter in single-phase gas^-3)；

4) gas phase volume flow rate Q is calculated according to formula (2)_gCorresponding apparent gas phase velocity U_sg

U_sg=4Q_g/πD² (2)

Wherein, D is pipeline nominal diameter；

5) signal amplitude A when single-phase gas is calculated according to formula (3)₀

6) according to the relationship of vortex signal feature amplitude and drop loading capacity in formula (4), drop loading capacity φ is calculated_p

7) reading factor OR was calculated according to formula (5)

OR=1+271.08 φ_pρ_g/ρ_p (5)

8) it was calculated according to formula (6) and reads compensated moisture gas phase volume flow rate

Q_g=Q_g,apparent/OR (6)

If 9) | Q_g-Q_g,last|≤δ, δ are sufficiently small positive real numbers, then iteration terminates, otherwise, by calculated gaseous phase volume stream Measure Q_gInitial value as next iteration re-executes the calculating of 4~8 steps, until convergence；

10) gas phase volume flow rate Q in final moisture is obtained_gWith drop loading capacity φ_p。