RU2803996C1 - Method for automatically controlling gas drying process at complex gas treatment plants in the far north of the russian federation - Google Patents

Abstract

FIELD: natural gas industry.

SUBSTANCE: natural gas treatment for long-distance transport and can be used for automatic control of the gas drying process at complex gas treatment installations - CGTIs in the Far North of the Russian Federation. The automated process control system (APCS) measures the actual specific entrainment U_act of diethylene glycol (DEG) by dried gas at the outlet of the multifunctional absorber (MFA) and compares it to the specific entrainment setpoint U_set. The APCS monitors compliance with the condition of U_act≤U_set and, in case of its violation, the APCS system immediately generates a message to the CGTI operator and switches the MFA control mode to step down the flowrate of the dried gas in it using a PID controller that controls the control valve (CV) installed at the MFA outlet. When the APCS detects that the condition U_act≤U_set is met, it takes the last recorded value of the drying gas flow Q as the value of the new setpoint for the drying gas flowrate Q_set in the MFA and then controls the operation of the MFA in the main mode, taking into account the new setpoint.

EFFECT: automatic maintenance of the gas treatment mode for long-distance transport and the quality of the dried gas sent to the consumer.

2 cl, 2 dwg

Description

The invention relates to the field of preparing natural gas for long-distance transport, in particular, to the automatic control of the gas drying process at integrated gas treatment plants (CGTUs) in the Far North of the Russian Federation.

There is a known method for automatically controlling the process of absorption gas drying, which ensures automatic maintenance of the specified parameters of technological processes at the gas treatment plant [see, pp. 413-416, Isakovich R.Ya., Loginov V.I., Popadko V.E. Automation of production processes in the oil and gas industry. Textbook for universities. M., "Nedra", 1983, 424 p.].

The disadvantage of this method is that it supplies the desiccant - absorbent (in the Far North, diethylene glycol - DEG is used as an absorbent) into the absorber only taking into account the flow rate and moisture content of the dried gas. In this case, in real mode the concentration of the saturated absorbent removed from the absorber and its entrainment with the gas being dried are not controlled.

All these factors together lead to suboptimal consumption of the absorbent supplied to the absorber and to the irretrievable loss of this valuable product. As a result, unnecessary losses of the absorbent occur, energy costs for absorbent regeneration increase, and the quality of gas preparation for long-distance transport decreases, i.e. in general, the efficiency of the gas drying process at the gas treatment plant decreases.

There is a known method for automating an absorption unit, which ensures automatic maintenance of the specified parameters of the gas drying process at a gas treatment plant [see, pp. 352-354, Andreev E.B. and others. Automation of technological processes of oil and gas production and preparation. - M., "Nedra-Business Center", 2008. - 399 p.]

The disadvantages of this method are that the supply of absorbent to the absorber is carried out only taking into account the flow rate and moisture content of the dried gas. At the same time, the concentration of the saturated absorbent removed from the absorber and its entrainment with the gas being dried are not monitored in real time.

There is a known method for determining the specific entrainment of an absorbent during drying of natural or associated gas and a device for its automatic implementation [see RF patent No. 2274483].

The disadvantages of this method and device are that it only works locally. The method makes it possible to identify the specific entrainment of the absorbent with the gas being dried at the gas treatment plant. Further, taking into account the readings of this device for the specific entrainment of the absorbent, the decision to control the gas drying process at the gas treatment facility is made by the installation operator. This reduces the speed of response to dynamically changing values of technological parameters at the gas treatment plant and increases the likelihood of operational personnel taking erroneous actions (the presence of the human factor), which can lead to emergency situations. As a result of excessive loss of absorbent, energy costs for absorbent regeneration increase, the quality of the gas prepared for long-distance transport decreases, and the need for increased purchases of absorbent increases, i.e. in general, the efficiency of the gas drying process at the gas treatment plant decreases

The closest, in technical essence, to the claimed invention is a method for automatically controlling the gas drying process at a gas treatment facility in Northern conditions [see. RF Patent No. 2712665]. The method involves monitoring and managing the main parameters of the technological process using an automated process control system (APCS).

A significant disadvantage of this method is that the automated process control system transfers the control mode of the installation to the operator if the behavior dynamics of the actual consumption of the regenerated absorbent G _{f becomes different and exceeds the permissible threshold.} and the consumption of regenerated absorbent G _pac calculated using the technological process model. In addition, the automated process control system does not take into account the entrainment of the absorbent by the dried gas during control of the technological process in the absorber.

These factors together lead to a deterioration in the quality of control of the gas drying process at the gas treatment plant, reduce the efficiency of response to dynamically changing values of process parameters and increase the likelihood of operating personnel taking erroneous actions (the presence of the human factor), which can lead to emergency situations. As a result, excessive losses of the absorbent occur, energy costs for absorbent regeneration increase, and the quality of the gas prepared for long-distance transport decreases, i.e. in general, the efficiency of the gas drying process at the gas treatment plant decreases.

The purpose of the invention is to improve the quality of control of the technological process of gas drying at a gas treatment facility operating in the North of the Russian Federation, within the framework of the norms and restrictions provided for by its technological regulations, and to reduce the role of the human factor in managing the technological process of preparing gas for long-distance transport, while ensuring the specified quality its preparation with the minimum necessary consumption of absorbent and energy consumption for its regeneration.

The technical result achieved from the implementation of the invention is the automatic maintenance of the gas preparation mode for long-distance transport at a gas treatment plant operating in the Far North of the Russian Federation in compliance with technological standards and restrictions provided for by its technological regulations, in various modes of its operation with achieving the minimum required absorbent consumption and energy expenditure for its regeneration.

The specified problem is solved, and the technical result is achieved due to the fact that the method of automatically controlling the gas drying process at a gas treatment facility in the Far North of the Russian Federation includes monitoring and managing the main parameters of the technological process of glycol drying of produced gas using automated process control systems, which monitors the dynamics of the behavior of the actual flow of regenerated gas. absorbent G _f and the consumption of regenerated absorbent G _pac calculated using the technological process model. At the same time, the automated process control system monitors the implementation of the planned target for the volume of supply of dried gas Q to the MGP, ensuring that Q corresponds to the set point for the flow of dry gas Q _set. .

At the same time, the automated process control system in real time with a given discreteness measures the actual specific entrainment U _fact of DEG by the dried gas at the outlet of the multifunctional absorber (MFA) and compares it with the specific entrainment setting U set _. . Value U _ass. entered into the database (DB) of the automated process control system before putting the installation into operation. After the installation is put into operation, the process control system monitors compliance with the condition U _actual ≤U _target. . And if this condition is violated, then the automated process control system immediately generates a message about this to the CGTU operator and switches the MFA control mode to a step-by-step reduction in the flow rate of the dried gas in it with a given discrete time and quantization level using a PID controller that controls the control valve - KR, installed at the MFA output. After each step of covering this CD, the automated process control system waits for a given time interval τ, the duration of which is determined by the end time of the transient processes in the MFA, and only after that it checks whether the condition U _fact ≤U _{set is met.} . And if the process control system detects that the condition U _fact ≤ U _ass. is executed again, then it takes the last recorded value of the flow of drying gas Q passing into the MFA as the value of the new setting of the drying gas flow U _set. . After this, the automated process control system controls the operation of the MFA in the main mode, taking into account the new setting.

Before putting the gas treatment plant into operation, maintenance personnel enter into the APCS DB the value of the lower limit to which the APCS can lower the dry gas flow set point Q _yst. in MFA, and the value of the step for reducing this setting. And if the productivity of the MFA during operation drops to the minimum permissible value of gas flow, which is determined by the passport characteristics of the MFA, below which it is necessary to stop the operation of the MFA, the automated process control system generates a message to the operator about the need to change the operating mode of the installation.

A schematic flow diagram of the main apparatus of the gas drying technology at the gas treatment plant - MFA is presented in Fig. 1, and the block diagram of automatic control of the MFA is shown in Fig. 2.

In fig. 1 the following notations are used:

1 - raw gas input line;

2 - raw gas temperature sensor;

3 - raw gas pressure sensor;

4 - MFA;

5 - MFA filter section;

6 - mass transfer section MFA;

7 - MFA separation section;

8 - dry gas temperature sensor;

9 - dry gas pressure sensor;

10 - dry gas flow sensor;

11 - dew point temperature sensor of dried gas;

12 - sensor for monitoring the mass flow of regenerated DEG (RDEG);

13 - multi-parameter sensor for measuring the concentration and flow of saturated DEG (NDEG);

14 - sensor of specific loss of DEG;

15 - RDEG flow rate control; 16-ASU TP UKPG;

17 - KR flow rate of dried gas;

18 - dry gas output line

19 - RDEG supply line;

20 - NDEG withdrawal line for regeneration;

21 - outlet line for an aqueous inhibitor solution (IRI).

In fig. 2 the following notations are used:

22 - signal of the actual mass flow rate of the RDEG (arrived from sensor 12 to the input of PID controller 30);

23 - signal of the calculated value G _pac. mass flow rate of the RDEG required for drying the gas (entered at input I ₁ of the correction unit 29 of the mass flow rate of the RDEG from the automated process control system 16);

24 - signal from the dew point temperature sensor 11 of the dried gas (supplied to the PV feedback input of the PID controller 28);

25 - signal for setting the dew point temperature of the dried gas (supplied to the SP input of the PID controller 28 from the automated process control system 16);

26 - dry gas flow signal (arrived from sensor 10 to the PV feedback input of PID controller 31);

27 - signal for the dry gas flow rate setting (enters the SP task input of PID controller 31);

28 - PID controller for maintaining the dew point temperature of the dried gas;

29 - RDEG mass flow correction unit;

30 - PID controller for maintaining the mass flow rate of the RDEG;

31 - PID controller for maintaining the specified flow rate of the gas being dried in MFA 4;

32 - control signal supplied from the CV output of the PID controller 30 to the RDEG flow rate control unit 15;

33 - control signal supplied from the CV output of the PID controller 31 to the KR 17 for the flow of dried gas in the MFA 4.

PID controllers 28, 30 and 31, as well as the RDEG mass flow correction unit 29 are implemented on the basis of the automated process control system of UKPG 16.

A method for automatically controlling the gas drying process at a gas treatment facility in the conditions of the Far North of the Russian Federation is implemented as follows.

Through input line 1, the extracted gas is supplied to separation section 7 of MFA 4, where droplet liquid and mechanical impurities are separated from it. The liquid released from the raw gas - VRI - is collected in the bottom (lower) part of the MFA 4 and is sent through the outlet line 21 either for regeneration or disposal. Gas from separation section 7 MFA 4, through a semi-blind plate, enters its mass transfer section 6. A solution of RDEG with a concentration of 98-99% is supplied towards the gas flow. On the contact plates, bubbling mass exchange occurs between counter flows of the dried gas and RDEG (moisture is removed from the gas due to absorption, and DEG is saturated with moisture). The amount of RDEG with a controlled concentration required for gas drying is determined by the flow rate and moisture content of the gas passing through the installation.

NDEG is collected on a semi-blind plate of mass transfer section 6 MFA 4 and sent for regeneration along the outlet line 20. The dried gas from the mass transfer section 6 enters the filter section 5, which captures the DEG solution carried away with the gas. Dust-like particles of DEG, carried away by the gas, coagulate on the filter cartridges and flow down their outer surface onto a plate, from which the DEG is directed through a remote pipeline (not shown in Fig. 1) to a semi-blind absorber plate and then, along the outlet line 20, is sent for regeneration . The NDEG level on the semi-blind plate acts as a water seal, preventing the passage of gas through the remote pipeline into the filtering part 5 of the MFA 4.

From MFA 4, gas dried to a given dew point temperature is supplied via output line 18 to the dried gas collector of the gas treatment plant. The process of gas drying at the gas treatment facility is implemented by ASU TP 16, keeping the parameters it controls within the specified boundaries provided for by the technological regulations, and supplies the required amount of RDEG to MFA 4, which automatically calculates in real time using the measurement results of devices connected to it.

To determine the amount of RDEG that must be supplied for gas drying in MFA 4, the automated process control system 16 measures the following basic parameters with a given discreteness:

- temperature and pressure of raw gas at the input of MFA 4 (sensors 2 and 3, respectively);

- NDEG concentration (multi-parameter flow sensor 13);

- temperature, pressure, flow rate and dew point temperature of the dried gas (sensors 8, 9, 10 and 11, respectively).

The amount of RDEG required for submission to MFA 4 ACS 16 is determined by the formula [see, page 111, Bekirov T.M., Shatalov A.T. Collection and preparation for transportation of natural gases. - M.: Nedra, 1986. - 261 p.]:

where Gpac _. - calculated mass flow rate of RDEG (kg/hour);

Q is the specified flow rate of dried gas through the MFA 4, thousand m ³ /hour;

ΔW is the specific amount of moisture extracted as a result of gas drying in MFA 4, kg/1000 m ³ ;

W _in , W _out - moisture content of incoming and outgoing dry gas in MFA 4, respectively, kg/1000 m ³ ;

X _RDEG , X _NDEG ^- concentration of RDEG and NDEG, respectively, % wt.

The values of W _in and W _out are determined from the Bukachek formula [see. p. 14, Klyusov, V.A. Technological calculations of absorption gas drying systems. Reference manual. Publisher: Tyumen: TyumenNIIgiprogaz. 140 pages; 2002]:

where p _in , p _out - gas pressure at the inlet and outlet of MFA 4, measured by pressure sensors 3 and 9, respectively;

_Tin , _Tout - gas temperature at the inlet and outlet of MFA 4, measured by temperature sensors 2 and 8, respectively.

The concentration value of X _NDEG in the process control system 16 comes from the multi-parameter control sensor 13 (mass flow meters from the KROHNE company from the OPTIMASS series or Micro Motion from the Metran company can be used as sensor 13).

The concentration value of X _RDEG in automated process control system 16 comes from the regeneration workshop of the gas treatment plant. Maintaining the DEG concentration value, as well as maintaining its temperature within the specified boundaries provided for by the technological regulations of the gas treatment plant, is ensured by the DEG regeneration workshop.

Automated process control system 16 maintains the set value of the dew point temperature T _t.r.z of the dried gas, using a cascade circuit of PID controllers 28 and 30 with a correction unit 29 for the mass flow rate RDEG, and to maintain the set flow rate of the dried gas in MFA 4, uses PID- regulator 31, control KR 17.

Experience in operating a gas treatment plant shows that the actual dew point temperature of dried gas is always several degrees higher than the theoretical one, i.e. calculated [see, page 111, Bekirov T.M., Shatalov A.T. Collection and preparation for transportation of natural gases. - M.: Nedra, 1986. - 261 p.]. Taking into account the above and the experience of operating the gas fields of Yamburg and Zapolyarny, the proposed technical solution introduces a correction block 29, which allows you to automatically adjust the calculated value G _p of the mass flow rate of the absorbent so as to guarantee the specified value of T _t.r.z. dew point temperature of the dried gas at the absorber outlet.

Solving this problem, the automated process control system 16 monitors in real time the deviation of the actual value of the dew point temperature T _t.r.f. from the value of its setting T _t.r.z. To do this, it supplies the signal 25 of the T _t.r.z. setting to the input of the SP task of the PID controller 28. , the value of which is determined according to OST 51.40-93 and entered into the DB of the automated process control system. At the same time, signal 24 is supplied to the feedback input PV of the same PID controller of the automated process control system 16 - the actual value of the dew point temperature T _g.r.f. , recorded by sensor 11. Comparing these two signals, the PID controller 28 at its output CV continuously generates the current value of the correction Δ, which is necessary to correct the value of the RDEG mass flow rate calculated by formula (1). The signal of this correction is supplied to input I ₂ of the correction unit 29 for the mass flow rate of the RDEG. At the same time, a signal 23 of the mass flow rate of the RDEG, calculated by formula (1), is supplied to input Ii of the correction block 29 of the automated process control system 16.

Having received these two signals, block 29 calculates the mass flow rate of the RDEG, taking into account the correction Δ, using the following expressions:

if T _t . _r . _f. >T _t.r.z. , then G _cor. =G _pac. +Δ,

if T _t.r.f. =T _t.r.z. , then G _cor. =G _dis. ,

if T _t.r.f. <T _t.r.z. , then G _cor. =G _pac. -Δ.

Determined value of G _cor. block 29 supplies the SP task input of the PID controller 30. The feedback input PV of the same PID controller receives a signal 22 of the actual flow rate of the RDEG, controlled by sensor 12. Comparing these two signals, the PID controller 30 generates a control signal 32 at its output CV , which it supplies to KR 15 for RDEG flow. As a result, automatic control of the supply of the required amount of RDEG to MFA 4 is ensured, sufficient to dry the gas to a given dew point temperature.

The automated process control system 16 maintains the specified value of the dry gas flow rate as follows. It supplies the set point signal 27 for the flow rate of the dried gas Q _{set to the input of the SP task of the PID controller 31.} on installation. At the same time, signal 26 is supplied to the feedback input PV of the same PID controller of the automated process control system 16 - the actual value of the flow rate of the drying gas _Qf , measured by flow sensor 10. Comparing these two signals, PID controller 31 generates a control signal 33 at its output CV, which supplies to KR 17, maintaining the specified flow rate of the dried gas in MFA 4.

ACS 16 in real time with a given discreteness measures the actual specific entrainment of DEG by dried gas at the outlet of MFA 4 using sensor 14 and monitors compliance with the condition

by comparing the actual value of the specific loss of DEG U _fact from MFA 4 with its value U _ass. , which in the form of a specific entrainment setting is entered into the database of the automated process control system 16 before the installation is started by maintenance personnel.

If condition (2) is met, the automated process control system, using PID controller 31, maintains the specified value of the dry gas flow rate in MFA 4.

If condition (2) is not met, which means that the quality of the incoming gas from the wells has deteriorated (there has been a release of formation water, the amount of fur impurities coming with the produced gas has increased, etc.), or the condition of the equipment has changed, then the automated process control system 16 immediately generates a notification about this to the CGTU operator and begins to reduce the load on MFA 4 in order to prevent an increase in DEG losses in the system.

For this, the automated process control system 16 with a given time discreteness and the quantization level in magnitude produces a step-by-step covering of the control system 17. For this, the automated process control system 16 successively reduces the value of the signal 27 at the input of the SP task of the PID controller 31, i.e. adjusts the dry gas flow rate setting Q _set. in MFA 4. As a result, there is a step-by-step reduction in gas consumption in MFA 4. After each step of covering the CR 17, the process control system 16 checks compliance with condition (2), waiting for a specified time interval, the duration of which is determined by the end time of transient processes in MFA 4. If the process control system 16 detects that condition (2) is met again, then it records the last value of the task signal 27 supplied to the SP input of the PID controller 31 in its database as the dry gas flow rate setting in the MFA 4 and switches the PID controller 31 to control mode gas drying process in MFA 4 with this new setting. At the same time, the automated process control system 16 generates a message about this to the CGTU operator.

A situation is possible when the automated process control system 16, performing a step-by-step covering of the control valve 17 after condition (2) has been violated, will bring the performance of the MFA 4 to the minimum permissible value of gas flow, which is determined by the passport characteristics of the MFA, below which it is necessary to stop the operation of the MFA, then it immediately generates a message to the maintenance personnel of the gas treatment plant about the need to make a decision to change the operating mode of the installation.

Tuning of PID controllers is carried out according to well-known methods, set out, for example, in the “Encyclopedia of Process Control Systems”, section 5.5, PID controller, resource http://www.bookasutp.ru/Chapter5_5.aspx#HandTuning.

A method for automatically controlling the gas drying process at a gas processing facility in the conditions of the Far North of the Russian Federation has been partially implemented at the Zapolyarnoye oil and gas condensate field at UKPG-1S, UKPG-2S and UKPG-3S by Gazprom Dobycha Yamburg LLC, PJSC Gazprom. The implementation results showed its high efficiency. The claimed invention can be widely used in other existing and newly developed gas condensate fields in the Far North of the Russian Federation.

The use of this method makes it possible to improve the quality of control of the technological process of gas drying at a gas treatment facility operating in the Far North of the Russian Federation, within the framework of the norms and restrictions provided for by its technological regulations, and reduces the role of the human factor in managing the technological process of preparing gas for long-distance transport. Thanks to this, it is possible to maintain the specified quality of the dried gas sent to the consumer in the event of deviations during the technological process at the gas treatment plant and eliminate the human factor when making control decisions.

Claims (2)

1. A method for automatically controlling the gas drying process at complex gas treatment plants - CGTU in the conditions of the Far North of the Russian Federation, including control and management of the main parameters of the technological process of glycol drying of produced gas using an automated process control system - automated process control system, which monitors the dynamics of the behavior of the actual flow rate regenerated absorbent G _f. and the consumption of regenerated absorbent G calculated from the technological process model _. , and also monitors the implementation of the planned target for the volume of supply of dried gas Q into the main gas pipeline, ensuring compliance of Q with the set point for the flow of dried gas Q _set. , characterized in that the automated process control system in real time with a given discreteness measures the actual specific entrainment U _fact of diethylene glycol - DEG by dried gas at the outlet of the multifunctional absorber - MFA and compares it with the specific entrainment setting U _ass. , which is entered into the database - DB of the process control system before putting the installation into operation, after which the process control system monitors compliance with the condition U _fact ≤U _set. , and if this condition is violated, then the automated process control system immediately generates a message about this to the CGTU operator and switches the MFA control mode to a step-by-step reduction in the flow rate of the dried gas in it with a given discrete time and quantization level using a PID controller that controls the control valve - KR , installed at the output of the MFA, and after each step of covering the CR, the process control system checks compliance with the condition U _fact ≤U _set. , after waiting for a given time interval τ, the duration of which is determined by the end time of transient processes in the MFA, and if the process control system detects that the condition U _fact ≤U _set. is executed again, then it takes the last recorded value of the drying gas flow Q as the value of the new drying gas flow setting Q _set. in the MFA and then controls the operation of the MFA in the main mode, taking into account the new setting. 2. The method according to claim 1, characterized in that the maintenance personnel, before putting the gas treatment plant into operation, enters into the DB of the process control system the value of the lower limit to which the process control system can lower the set point for the flow rate of the dried gas Q _set. in the MFA, and the value of the step to reduce this setting, and if the performance of the MFA drops to the minimum permissible value of gas flow, which is determined by the passport characteristics of the MFA, below which it is necessary to stop the operation of the MFA, the automated process control system generates a message to the operator about the need to change the operating mode of the installation.

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