JP2899590B1 - Drift detection method of pressure gauge incorporated in piping system - Google Patents

Abstract

Abstract: [PROBLEMS] Even if the operation of a plant is continued,
It is possible to detect the occurrence of a drift phenomenon in a pressure gauge at an early stage, and to grasp the drift amount. SOLUTION: The pressure in a piping system in which a plurality of automatic control valve units each including a pressure control valve, a pressure gauge, and a controller for controlling a valve opening degree of the pressure control valve based on an indication value of the pressure gauge is incorporated. It is a drift detection method of the meter.
The Cv value is obtained from the valve opening degree of the pressure control valve using the relationship between the valve opening degree and the Cv value inherent to the pressure control valve, which is obtained in advance, the pressure is calculated from the Cv value, and the pressure calculation is performed. The presence / absence of drift of the pressure gauge is detected from the coincidence / mismatch between the pressure value and the pressure measured value by the pressure gauge. The drift amount is estimated from the difference between the pressure instruction value and the calculated pressure value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of detecting a drift phenomenon of a pressure gauge in a piping system incorporating a plurality of pressure control valve units. More specifically, the present invention relates to a method of detecting a valve opening degree and Cv specific to a pressure control valve. The present invention relates to a method of calculating pressure using a value relationship, and detecting the presence / absence of drift of the pressure gauge based on coincidence / mismatch with a value measured by a pressure gauge. This technique is useful for early detection of a drift phenomenon of a pressure gauge while operating a plant that handles fluid gas.

[0002]

2. Description of the Related Art In various plants handling fluid gas, an automatic control valve unit comprising a pressure control valve, a pressure gauge, and a controller for controlling a valve opening of the pressure control valve based on a value indicated by the pressure gauge. Are controlled by controlling the flow rate of a fluid gas flowing through a piping system.

For example, as shown in FIG. 1, a pressure control valve 12 is incorporated in a pipe 10 and an upstream pressure gauge 14 and a flow meter 16 and, if necessary, a downstream pressure gauge 18 are connected.
Here, the pressure gauge 14 pressure instruction value P ₁ of the upstream side to the target pressure, the controller 20 by comparing the pressure readings P ₁ and the target pressure, deviations of the valve opening control instruction pressure regulating valve 12 is output. The pressure control valve 12 receives the instruction and automatically changes the valve opening. Rather than pressure gauge 14 pressure instruction value P ₁ of the upstream side, the downstream pressure gauge 18
Sometimes controlled by the pressure instruction value P _2. Pressure control valve 1
The pressure gauge 2, the pressure gauge (here, the pressure gauge 14 on the upstream side), and the controller 20 constitute an automatic control valve unit.

As a pressure gauge, a seal diaphragm type structure as shown in FIG. 2 is generally used. The internal space of the housing 30 is partitioned by a seal diaphragm 32, one of which is provided with a pressure introducing portion 34, and the other is filled with a sealed liquid 36. A semiconductor pressure sensor 40 is provided between the reference pressure chamber 38 facing the filling liquid 36 and the signal line 42 is drawn out. The absolute pressure introduced from the process is applied to the seal diaphragm 32 and transmitted to the semiconductor pressure sensor 40 via the filling liquid 36. As a result, the resistance value of the semiconductor diffusion gauge changes due to the piezoresistance effect. This is taken out by a bridge circuit and amplified to obtain a pressure signal.

[0005] Pressure indication value by pressure gauge (Pa, Pa ')
Is normal, a pressure value equivalent to the actual pressure (Pb, Pb ') is shown (Pa = P) as shown in FIG.
b, Pa '= Pb'), and the deviation of the pressure change is adjusted to the target pressure by adjusting the valve opening of the pressure control valve (L → L ').

However, a phenomenon in which the indicated value of the pressure gauge suddenly deviates from the actual value during use for a long period of time (this phenomenon is referred to as "drift phenomenon") may occur. It is considered that this is mainly due to plastic deformation of the seal diaphragm. In an automatic control valve unit that controls the valve opening of a pressure control valve with a controller based on the indicated value of a pressure gauge, the pressure control valve is controlled by an indicated value that deviates from an actual value. I can't get it.

[0007]

When such a drift phenomenon occurs, in the pressure control valve unit, the valve opening of the pressure control valve is automatically adjusted in a direction to cancel the change in the indicated value of the pressure gauge, and the apparent value is apparent. Since the above pressure value is maintained,
It is extremely difficult to detect drift phenomena by monitoring normal gauge readings. Therefore, in the related art, unless the operation of the plant is stopped, the pressure gauge is exhausted, and the zero point is not confirmed, the presence or absence of the drift cannot be detected and the drift amount cannot be confirmed.

That is, as shown in FIG. 3B, when a drift of ΔP occurs in the indicated pressure value, the deviation of the indicated pressure value by ΔP is adjusted by adjusting the valve opening of the pressure regulating valve (L → L ′). )
Is adjusted to reach the target pressure. However, although the actual pressure should be Pa = Pb, Pa = Pb
The value is shifted by ΔP from the indicated pressure value, such as −ΔP = Pb ′. And in such an abnormal state,
If the abnormality cannot be found, the fluid gas flows through the piping system, and if the performance of the product varies or is severe, a product with the desired performance cannot be manufactured. However, it is difficult to identify where the cause is.

[0009] Even if the abnormality of the pressure indication value can be estimated, the drift phenomenon cannot be specified unless calibration of each pressure gauge is performed while the supply of the fluid gas is temporarily stopped.

It is an object of the present invention to provide a method capable of early detecting the occurrence of a drift phenomenon in a pressure gauge even when the operation of a plant is continued. Another object of the present invention is to provide a method capable of grasping a drift amount when a drift phenomenon occurs in a pressure gauge.

[0011]

According to the present invention, there is provided an automatic control valve unit comprising a pressure control valve, a pressure gauge, and a controller for controlling a valve opening of the pressure control valve based on a value indicated by the pressure gauge. This is a method for detecting drift of a pressure gauge in a piping system incorporating a large number of the components. In the present invention, the Cv value is obtained from the valve opening degree of the pressure control valve by using the relationship between the valve opening degree and the Cv value inherent to the pressure control valve, which is obtained in advance.
The pressure is calculated from the v value, and the presence / absence of the drift of the pressure gauge is detected from the coincidence / mismatch between the calculated pressure value and the pressure measurement value obtained by the pressure gauge.

More specifically, in a piping system incorporating a large number of automatic control valve units, for example, a pressure gauge is calculated for the pressure gauge of the most downstream automatic control valve unit by using an actually measured flow rate value at the outlet of the piping system. The difference between the pressure measurement value and the pressure measurement value is determined, and then the pressure gauge of the automatic control valve unit on the upstream side also determines the match / mismatch between the calculated pressure value and the measured pressure value. It is determined that drift has occurred in the pressure gauge of the automatic control valve unit on the most upstream side of the unit. Alternatively, the Cv value is obtained from the valve opening degree of the pressure control valve using the relationship between the valve opening degree and the Cv value inherent to the pressure control valve, which is obtained in advance.
Calculates the pressure from the value, finds the match / mismatch between the calculated value and the value measured by the pressure gauge, and anomalies from the correlation of the difference between the pressure calculated value for many automatic control valve units and the pressure measured value by the pressure gauge. An automatic control valve unit indicating

According to the present invention, an automatic control valve unit having a drift caused by the above method is detected, and a difference between a calculated pressure value and a measured pressure value in the automatic control valve unit is corrected by adding the measured pressure value to the measured pressure value. However, the operation of the plant can be continued as it is by controlling the automatic control valve unit based on the correction value.

[0014]

FIG. 4 shows an example of a pressure regulating valve.
A valve body 56 is attached to the lower end of a valve rod 54 that is slidably held in the axial direction with respect to a valve box 52 by a bearing 50 so that the valve body 56 can be freely moved toward and away from a valve seat 58. A coil spring 60 is mounted on the valve rod 54, and a resilient force is constantly applied in the valve closing direction. The proximal end of the valve stem 54 reaches the air chamber 62, and the proximal end of the valve stem 54 is fixed to a diaphragm 64 that partitions the air chamber 62 in an airtight manner. Pressurized air is supplied to one region in the air chamber 62 via an electropneumatic positioner 66, and the displacement of the valve rod 54 can be controlled by an external electric signal. Further, the displacement of the valve stem 54, in other words, the valve opening, can be determined as an electrical signal and / or as a mechanical pointer displacement.
Even during the service period, it can be detected directly from outside at any time. The present invention utilizes the fact that the valve opening can always be detected from the outside.

The relationship between the valve opening and the Cv value of each valve is usually measured in advance when the valve is manufactured or when the valve is calibrated. In the present invention, the relationship between the valve opening degree unique to each valve and the Cv value is used. There are several methods for approximating the characteristics of the valve. In any case, the formula for calculating the Cv value is represented by the valve opening L
(%). That is, Cv = f (L). As an approximation method, equal percent characteristics Cv = Cv ₁₀₀ × 50 ^{((L-100) / 100)} Two-stage equal percent characteristics Cv = Cv ₁₀₀ × 3.3323 × 333 ^{((L-100) / 100)}
(0-50%) Cv = Cv ₁₀₀ × 30 ^{((L-100) / 100)} (50-100
%) Linear characteristics Cv = Cv ₁₀₀ × L / 100. Therefore, an approximate expression selected according to the characteristics of the valve incorporated is used. Here, Cv ₁₀₀ is a Cv value when the valve opening is 100%.

As described above, the opening degree of the pressure control valve can be directly detected from the outside as an electric signal and / or as a displacement of a mechanical pointer. Therefore, the Cv value can be calculated from the approximate expression using the detected valve opening L.

[0017] The formula for calculating the Cv value of the pressure control valve, model 1 ... critical ((P ₁ -P ₂₎ In the case of _{≧ P 1/2) Cv =} (Q / 249P 1) (γT) 1/2 ... (1) model 2 ... Nonkurichikaru ((P ₁ -P ₂₎ <in the case of _{P 1/2) Cv = (} Q / 287) (γT / (P 1 2 -P 2 2)) 1/2 ... ( 2) However, P ₁ : upstream pressure of the pressure control valve (kg / cm ² ) P ₂ : downstream pressure of the pressure control valve (kg / cm ² ) Q: volumetric flow rate of the test gas converted to the standard condition (m ³ /
h) at (760 Torr 15.6 ° C.) γ: specific weight ratio of test gas (kg / mol) gas / (kg / mol) air T: absolute temperature (K)

The Cv value obtained from the valve opening degree is calculated based on the Cv value in the above equation.
By substituting the value for each valve characteristic, a relational expression of the flow rate, gas temperature, actual upstream pressure, and downstream pressure at that time depending on the valve opening of the pressure control valve can be obtained, which can be converted into an expression for obtaining the upstream pressure. . In order to calculate the upstream pressure more accurately, the pipe loss value from the upstream pressure gauge to the pressure control valve and the pipe loss value from the pressure control valve to the downstream pressure gauge are calculated or measured and added to the above conversion formula. I do. The drift amount is obtained by comparing the calculated pressure value calculated by the conversion formula with the indicated pressure value of the upstream pressure gauge. The drift amount is: drift amount = pressure indication value−pressure calculation value. If the calculated pressure value matches the indicated pressure value, the drift amount is zero.

If the relationship between the valve opening and the Cv value has not been determined in advance, and the valve is already incorporated in the plant, the actual operation data stored in the past is used to determine the relationship between the two. I just need to derive the relationship. In this case, (a) operation data during a period when there is no drift phenomenon or other abnormality in the pressure gauge (b) operation data during a period when the valve opening of the pressure control valve is used in a wide range (c) operation start (D) Operating data after pressure gauge calibration, etc., using the above formulas (1) and (2),
Calculate the v value. This is performed for each pressure control valve, and a graph of the valve opening and the Cv value is created. An approximation line is drawn on the graph to obtain this approximation formula. The approximation formula obtained here is used as a substitute for the calculation formula based on the characteristics of the valve, and is substituted as the Cv value when calculating the upstream pressure.

In the case of constant pressure (target pressure) control, the valve opening degree of the pressure control valve and the Cv value have a relationship as shown in FIG. That is, when the pressure gauge is normal, Cv = A × Q / P ₁ where A is a constant, and even if a pressure change occurs, as shown in FIG. 5A, the pressure is constant (P ₁ ). The relationship between the valve opening and the Cv value does not change simply by moving on the line. On the other hand, when a drift of ΔP occurs in the pressure gauge, Cv = A × Q / (P ₁ + ΔP), and the line with a constant pressure is as shown in FIG.
The curve becomes (P ₁ + ΔP), and the initial relationship between the valve opening degree of the pressure control valve and the Cv value is shifted.

From the above, as shown in FIG. 6, in the approximation formula showing the relationship between the valve opening and the Cv value, the Cv value becomes flat (movement indicated by a broken arrow) regardless of the valve opening when a drift occurs. . Such a phenomenon has been confirmed in past data at the time of actual drift phenomenon occurrence. The opposite phenomenon (the movement indicated by the solid arrow in which the Cv value changes with a constant valve opening) is presumed to be due to clogging of a valve or piping. Since Cv = A × Q / P, it becomes P + ΔP when drift occurs and Q−ΔQ when clogging occurs.

Considering the installation location of the pressure gauge and the orifice for measuring the flow rate, etc., in order to calculate the accurate pressure immediately before and immediately after the pressure regulating valve and the upstream pressure, the pipe loss is calculated or actually measured. Correct the value. For example, in the case of a piping system as shown in FIG. And pressure in h ₃ calculates a pressure regulating valve upstream pressure = P ₁ (upstream pressure gauge readings) -P ₃
(Orifice differential pressure gauge readings) · h-pressure calculating the pressure regulating valve of the ₄ downstream pressure = P ₂ (downstream pressure gauge readings) + h ₄
~h ₅ of the pipe pressure loss value

The calculation of the pressure is performed as follows. When the pressure is continuously adjusted by the individual pressure adjusting valves as shown in FIG. 8, the method of calculating each pressure is as follows. P ₁ = A ₁ Q ₁ / Cv ₁ P ₂ = A ₂ Q ₂ / Cv ₂ P ₃ = A ₃ Q ₃ / Cv ₃ where P _{1 to} P ₄ : pressure gauge readings A _{1 to} A ₃ : constant (when the fluid gas temperature constant) Q ₁ ~Q _3: indicated value thus flow meter, if you want to calculate the actual pressure of a pressure gauge, Cv value of the pressure regulating valve downstream of the pressure gauge and It is calculated using the indicated value of the flow meter.

Incidentally, a differential pressure gauge having a structure similar to that of the pressure gauge shown in FIG. 2 is often used as a flow meter. In that case, the drift phenomenon may occur even in the differential pressure gauge, and the measurement value of the flow meter is not always accurate. However, a flow value is required for calculating the pressure as described above. However, in a plant, the flow rate can be accurately measured on the most downstream side (product outlet). Therefore, based on the pressure gauge, based on the pressure gauge on the most downstream side, sequentially calculating the match / mismatch between the calculated pressure value and the measured pressure value of the manometer of the self-adjusting valve unit, a series of the self-regulating valves in which the mismatch occurs It can be determined that drift has occurred in the pressure gauge of the automatic control valve unit on the most upstream side of the unit. In addition, when there are many automatic control valve units, the correlation between the calculated pressure value and the measured pressure value of each automatic control valve unit can be determined without measuring the accurate flow rate at the most downstream side. Even if is used, it is possible to identify the automatic control valve unit showing the abnormality because it exhibits a peculiar behavior.

[0025]

For example, when the fluid gas is UF ₆ , the above equations (1) and (2) are as follows: Model 1 P ₁ = 4.147 × 10 ⁻² × Q × (273.15+
t) ^1/2 / Cv Model 2 P ₁ = 3.6046 × 10 ⁻² × Q × (273.15+
t) becomes a ^1/2 / Cv + P _2. Needless to say, pipe loss values are calculated or measured and added to them as necessary. By comparing the calculated pressure value with the indicated value of the upstream pressure gauge, the presence or absence of the drift and the amount of the drift, if any, are determined.

FIG. 9 shows an example of a change in pressure when a drift phenomenon actually occurs. When a drift occurs, the calculated pressure value changes immediately, even though the indicated pressure value is constant, so that an abnormality can be detected early. FIG. 10 shows the transition of the Cv value with respect to the valve opening at that time. Even though the Cv value was constant, a change was observed in which the valve opening increased steadily. From such a phenomenon, it is possible to detect the occurrence and the degree of the drift.

[0027]

According to the present invention, it is possible to detect a drift and grasp the amount of the drift early while the operation of the plant is continued. As a result: By evaluating the drift amount, the pressure gauge can be calibrated without stopping the operation of the plant. 2. Even if a drift phenomenon occurs, the accuracy of the product can be prevented from being impaired by setting the operating conditions in consideration of the drift amount. 3. By performing continuous monitoring, even if the drift phenomenon gradually progresses, the drift phenomenon can be easily found, and furthermore, a prediction can be made in the future based on the chronological tendency of the drift amount, and a prompt response can be made. 4. By applying the method of the present invention, it is also possible to discover abnormalities of the pressure control valve such as clogging. And the like.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an automatic control valve unit incorporated in a piping system.

FIG. 2 is an explanatory diagram showing an example of a pressure gauge.

FIG. 3 is an explanatory diagram showing a relationship between a pressure and a pressure instruction value.

FIG. 4 is an explanatory view showing an example of a pressure control valve.

FIG. 5 is a graph showing a relationship between a valve opening and a Cv value.

FIG. 6 is an explanatory diagram showing a relationship between a valve opening and a Cv value during a drift phenomenon.

FIG. 7 is an explanatory diagram of pipe loss calculation in a pipe system.

FIG. 8 is an explanatory diagram of pressure calculation in a piping system incorporating a number of automatic control valve units.

FIG. 9 is an explanatory diagram of a pressure transition during an actual drift phenomenon.

FIG. 10 is an explanatory diagram of a Cv value transition during a drift phenomenon.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Piping system 12 Pressure control valve 14 Pressure gauge on the upstream side 16 Flow meter 18 Pressure gauge on the downstream side 20 Controller

Claims (4)

(57) [Claims] 1. A piping system in which a plurality of automatic control valve units each including a pressure control valve, a pressure gauge, and a controller for controlling a valve opening of the pressure control valve based on an indication value of the pressure gauge are provided. The Cv value is obtained from the valve opening of the pressure control valve by using the relationship between the valve opening and the Cv value specific to the pressure control valve, which is obtained in advance, and the pressure is calculated from the Cv value. A drift detection method for a pressure gauge incorporated in a piping system, wherein the presence / absence of a drift of the pressure gauge is detected from a match / mismatch between a calculated value and a pressure measurement value obtained by the pressure gauge. 2. A method for determining whether there is a difference between a calculated pressure value and a measured pressure value for a pressure gauge of an automatic control valve unit at the most downstream side by using an actually measured flow rate value at an outlet of a piping system. Also for the pressure gauge of the control valve unit, find the match / mismatch between the calculated pressure value and the measured pressure value.Drift occurs in the pressure gauge of the most upstream automatic control valve unit in the series of automatic control valve units where the mismatch occurs. 2. The method for detecting drift of a pressure gauge incorporated in a piping system according to claim 1, wherein the drift is determined to have occurred. 3. A piping system in which a plurality of automatic control valve units each including a pressure control valve, a pressure gauge, and a controller for controlling a valve opening of the pressure control valve based on an indication value of the pressure gauge are incorporated. A Cv value is obtained from the valve opening degree of the pressure control valve using the relationship between the valve opening degree and the Cv value specific to the pressure control valve, which is obtained in advance, and the pressure is calculated from the Cv value, and the calculation is performed. Calculate the agreement / disagreement between the measured value and the measured value of the pressure gauge, and determine the automatic control valve unit that shows an abnormality from the correlation between the calculated value of many automatic control valve units and the presence or absence of the difference between the pressure measured value by the pressure gauge. A drift detection method for a pressure gauge incorporated in a piping system. 4. A self-regulating valve unit in which a drift has occurred according to any one of claims 1 to 3, and a difference between a calculated pressure value and a measured pressure value in the self-adjusting valve unit is corrected by adding to the measured pressure value. A method for operating the plant, wherein the automatic control valve unit is controlled based on the correction value.