pdf lab.manual.sept2014.flowratio

Process Dynamics & Control Lab Experiment 4 Flow Ratio Plant Control

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EXPERIMENT NO. 4 Flow Ratio Plant Control (WF922)

OBJECTIVES

1. To identify the major components of the flow ratio process control system. 2. To perform start-up procedures systematically. 3. To study single loop flow control using PID controller. 4. To study flow ratio control using linear PID controller.

KEYWORDS Liquid flow, PID Controller, Ratio Controller 1.0 INTRODUCTION This model (WF922) uses water to simulate a liquid phase flow process. Three different flow-measuring principles are commonly used in industries. They are (i) differential pressure measurement across by an orifice, (ii) measurement by variable area flow meter, and (iii) measurement by von Karman vortex shedding principles. Flow measurements by all these principles are employed in this model. The flow is controlled by single loop PID controller at different set points. A ratio flow control is also carried out where a wild stream flow rate is measured and the other stream is controlled so as to maintain a constant ratio of their flow rates. 2.0 EXPERIMENTAL EQUIPMENT 2.1 PROCESS PLANT (WF922) The process plant consists of a stainless steel tank (T21), four centrifugal pumps, (P20, P21, P22A/P22B) and the associated pipings, valves and fittings. Water is recirculated by pumps P21 and P22A/B around tank T21. Pump P20 uses the same pipeline as P21. This process plant uses three flow meters. They are a vortex flow meter (FT22), rotameter (FI22), and an orifice plate (FE21). Two pressure gauges are installed at the inlet and outlet of the flow control valve FCV21 to measure pressure drop, which is related to the flow rate. This process plant can be used to study flow PID control as well as flow ratio control. It is possible to select FT21 and its pipeline to be either the controlled flow (CF) or the wild flow (WF). Hence, it is then possible to study any effect of different flow meters on the PID tuning of a flow loop.

a) That ratio control requires that the control valve be installed on the CF line. b) The range of the Ratio value, which can be set, is limited by the available

process flow rate, range ability of the flow meter and the control valve. c) The process plant can be operated either by DCS or by the SCADA system.

2.2 CONTROL SYSTEM AND INSTRUMENTATIONS

The followings are brief descriptions of the control system and major instrumentations.

a) Flow control system: Single feedback PID or Ratio control Measurement: i. FT22, vortex flow meter. ii. FE21, Orifice flow element with FT21, a differential flow transmitter

with square extractor. Control type: i. Single feedback PID flow control: FIC21, panel mount PID controller ii. Ratio control: FIC21 with remote set point from the Wild Flow (WF)

multiplied by the instrument ratio factor, R. Final control element: i. FCV21, control valve complete with Positioner (PP) and Current-to-

Air (I/P) converter, FCY21. b) Other Measurements: FI22: variable area flow meter (Rotameter); PG21, PG22:

Pressure gauges; TG21: Temperature gauge.

c) Recorder: FR21 for FT21 and FT22 (2 Pens).

d) Others: PRV21, PRV22A, PRV22B: Pressure relief valves; IAS: Instrument air supply to the FCY21 and PP Selector switch whereby either FT21 or FT22 can be selected to be either the Controlled Flow (CF) or Wild Flow (WF).

e) Annunciators: FAH: High flow limit alarm for the Controlled Flow (CF) stream; FAL: Low flow limit alarm for the Controlled Flow (CF) stream.


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3.0 EXPERIMENTAL PROCEDURES 3.1 IDENTIFICATION OF MAJOR COMPONENTS Walk around the plant and identify the components given below and mark them in the P&I diagram provided at the end of the lab manual. T21 Stainless steel tank P20, P21, P22A/P22B Centrifugal pumps FT22 Vortex flow meter F122 Variable area flow meter, Rotameter FE21 Orifice plate FT21 Flow transmitter FIC21 Panel mount PID controller FCV21 Flow control valve PG21, PG22 Pressure gauges TG21 Temperature gauge FR21 Recorder Also identify the two pipelines, one is used as the Controlled Flow (CF) pipeline and another is used as the Wild Flow (WF) pipeline: Controlled Flow pipeline, CF: P21-FE21/FT21-CF1-FCV21-T21, Wild Flow Pipeline, WF: P22A/B-FI22-FT22-WF1-T21.

3.2 START-UP PROCEDURES

The following steps constitute the start-up procedures. Go through them before starting any

experiment.

1. Tank T21 should be filled with water up to almost the level of its lower overflow pipe.

2. To operate the plant independently, shut the manual valves at the interconnecting

pipelines from the other plants, WLF922 and WT922.

3. Check and do as follows:

a) All suction, discharge and by-pass valves (B20, B21, B22A & B22B) around pumps (P20, P21, P22A & P22B) are fully open. The pumps’ by-pass valves can be shut after checking that there is water flow in the pipeline when the respective pump is started. b) Shut the manual by-pass valve around the control valve FCV21 and open the two adjacent manual valves around FCV21.

c) Shut the manual drain valve at the bottom of the tank T21. d) Shut the interconnecting manual valve MVX.

4. Shut the manual discharge valve at the discharge of pump P20. Check and adjust the

instrument air supply (IAS) to the pressure indicated.

NOTE that at the Recorder FR21:

Red Pen (Channel 1) is recorded controlled flow CF: FT21

Green Pen (Channel 2) is recorded wild flow WF: FT22

3.3 PID SINGLE LOOP FLOW CONTROL (NORMAL OPERATION) SINGLE LOOP: FT21-FIC21-FCY21/PP/FCV21

1. Switch ON the main power supply at the front cubicle. The panel instruments will lit

up. a) Put the "PANEL, SCADA/DDC" selector switch at "PANEL, SCADA" position. b) If there is any ANNUNCIATOR get activated, silence the alarm by pressing

ACKNOWLEDGE button. c) Turn the controller FIC21 to Manual (M) mode by pressing “M” button on the

PID controller panel. Make sure its MV = 106.3% to open the control valve FCV21 fully.

d) Turn the SELECTOR switch to position 1: "FT21 = PV = CF", for NORMAL OPERATION.

e) OPEN fully CFl/WF1. f) SHUT fully CF2/WF2, manual valve MVX, manual discharge valve of pump

P20, MF. g) OPEN manual suction and discharge valves of the pumps: P21, P22A and P22B

with their by-pass valves. h) Switch ON only pump P21, make sure that there is water flow from P21 into

pipelines then shut its manual by-pass valve B21. 2. Start the recorder FR21 by pressing its “RCD” button with the front swing cover

opened. 3. FIC21 is a single loop PID controller configured for Ratio Control using one PID (PID1).

Be familiar with the controller as follows: a) Display FIC21 and change from Auto (A) to Manual (M) mode and vice versa.

Observe the controller when in Auto (A) and Manual (M) mode. b) With the controller FIC21 is in Manual (M) mode at MV = 100%. Set this PID

trial values, (first (I) trial PID values):


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PB1 = 100%, TI1 = 5 sec, TD1 = 0 sec c) Set the SV = 1.8 m3/hr. d) Manually adjust MV so that MV = PV, and then switch the controller to Auto (A)

mode. OBSERVE THE RED PEN (CF) STEADY AT THE SETPOINT TO WITHIN (i.e. ±0.02 m3/hr). WRITE DOWN THE SET POINT (SV) AND PID VALUES (PB, TI, TD) ON THE CHART PAPER. 4. Make sure pump P21 is ON and its by-pass valve B21 is fully shut. 5. FIC21 remais in Auto (A) mode and observe the response. SETPOINT STEP TEST (NORMAL OPERATION)

6. Make sure the Set Point remains SV = 1.8 m3/hr. 7. Step increase the set point to SV = 2.4 m3/Hr. Observe the flow response (Red Pen) till

it is stable. 8. The PID controller is still using the first (I) PID trial values.

PB1 = 100%, TI1 = 5 sec, TD1 = 0 sec 9. Step increase the set point to SV = 2.6 m3/hr, then, observe the flow response (Red Pen)

till it is stable. 10. Repeat Step 9 with the following SV: 2.8 m3/hr, 3.2 m3/hr, 3.8 m3/hr and 4.2 m3/hr.

(While observing the flow response, look also for irregular fluctuation and different flow response/behavior between various SV – setpoint changes and mark them on the chart)

11. With PID controller in Manual (M) mode, set the PID values using second (II) PID trial values:

PB1 = 150%, TI1 = 10 sec, TD1 = 0 sec 12. With PID controller in Auto (A) mode, repeat setpoint step tests above as in Step 9 and

10. IF POOR RESPONSE IS OBSERVED & THIS IS DUE TO POOR CONTROL: HIGHER PB% AND TI% CAN IMPROVE DAMPING BUT THE CONTROL RESPONSE MAY STILL BE UNSATISFACTORY. THE POOR RESPONSE BECOME SLOWER & SLUGGISH AND RESULTS IN POOR SET POINT RECOVERY. NOTE THAT:

- First trial (I) PID values may be ABLE to control LOWER FLOW (flow at SV = 1.8 to 2.4 m3/hr) and for the HIGHER FLOW (at SV = 2.6 to 3.8 m3/hr) the flow response may be TOO OSCILLATORY. To damp out the OSCILLATORY, LARGER PB% & TI have to be used.

- If the poor response (FLUCTUATING ERRATICALLY or not oscillating),

the problem is may be due to the measurement problem such as improper installation/application of flow meter. Conclude that GOOD CONTROL CANNOT BE ACHIEVED.

PID CONTROLLER TUNING (NORMAL OPERATION) The following procedures have to be conducted before running the Flow Ratio Control Experiment. Note that: PID controller FIC21 becomes FLOW RATIO controller by switching to Cascade (C) Mode. THIS MEANS THE SV IS NO LONGER OPERATOR SET, BUT IS REMOTELY CASCADED FROM THE FT22. PROCESS RATIO, PR = CONTROLLED FLOW (FT 21)/WILD FLOW (FT 22). To achieve good ratio control, PR should be equal to instrument ratio, R. 13. With FIC21 in Manual (M) mode and MV =100%, set the first trial (I) PID values.

PB1 = 100%, TI1 = 5 sec, TD1 = 0 sec 14. Make sure FIC21 remains in Manual (M) mode with its MV = 100% for maximum

flow. 15. Check maximum flow rate for CF and WF as follows:

- For CF, start pump P21 and observe flow rate CF until it is stable. Record the maximum value of CF as stated at the recorder FR21 (Red Pen/Channel 1).

- For WF, start both pumps P22A/P22B and observe flow rate WF until it is stable. Record the maximum value of WF as stated at the recorder FR21 (Green Pen/Channel 2).

- Make sure all the by-pass valves (B21, B22A & B22B) are shut to ensure maximum flow in pipelines.

- Note CF and WF value and calculate the process ratio value, PR.

- Switch off all pumps P21, P22A/P22B. 3.4 FLOW RATIO CONTROL, LINEAR PID (NORMAL OPERATION) For this experiment, second (II) PID trial values will be used throughout the experiment.

PB1 = 150%, TI1 = 10 sec, TD1 = 0 sec Four tests will be run to observe the performance of flow ratio control system. Disturbance is applied by switching on and off WF pumps. CF pump is switched on throughout.


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Test 1: Using One WF pump, with instrument ratio, R=1. 1. Start with using one WF pump only. Start pumps P21 (CF pump) and P22A (WF pump).

Shut fully their manual by pass valves (B21, B22A as well as B22B) but open fully their discharge manual valves.

2. Set the R=1 at CGN1 at the “PARAMETER” page on controller panel. 3. Switch the controller FIC21 to Cascade(C) mode so that the controller is functioned as

RATIO CONTROLLER. (How to change Cascade (C) Mode: From Manual (M) mode, press Auto(A ) then press Cascade(C))

4. Observe the recorder FR21 (Red pen/Channel1) and FT22 (Green pen/Channel 2). Wait till the Red (FT21) and Green (FT22) pen are almost steady (i.e. within ±0.02 to ±0.05 m3/hr) or it continues to oscillate even after 3 cycles.

5. Note and calculate the Process Flow Ratio (PR) (computed from the actual process flow rate, then, compare PR to R).

6. Observe also the PV and SV when the flow rate is steady. (Is PV = SV?) Test 2: Using Two WF pumps, with instrument ratio, R = 1. 1. Now disturb WF by switching on its second pump P22B. 2. Observe the recorder FR21 (Red pen/Channel1) and FT22 (Green pen/Channel 2). Wait

till the Red (FT21) and Green (FT22) pen are almost steady (i.e. within ±0.02 to ±0.05 m3/hr) or it continues to oscillate even after 3 cycles.


4. Observe also the PV and SV when the flow rate is steady. (Is PV = SV?) Test 3: Using One WF pump, with instrument ratio, R = 1.8. 1. Now, switch off pump P22B. 2. Set the instrument ratio, R = 1.8 at CGN1 at the “PARAMETER” page. 3. Observe the recorder FR21 (Red pen/Channel1) and FT22 (Green pen/Channel 2). Wait



5. Observe also the PV and SV when the flow rate is steady. (Is PV = SV?)

Test 4: Using Two WF pumps, with instrument ratio, R = 1.8. 1. Now disturb WF by switching on its second pump P22B. 2. Observe the recorder FR21 (Red pen/Channel1) and FT22 (Green pen/Channel 2). Wait



4. Observe also the PV and SV when the flow rate is steady. (Is PV = SV?)

4.0 SHUTDOWN PROCEDURES 1. Stop the recorder chart drive by pressing the 'RCD' button at the front cover of the

recorder. 2. Stop all pumps. 3. Switch the controller FIC21 to Manual (M) mode with its control output MV=0%. 4. Switch OFF the main power supply. 5. SHUT OFF the instrument air supply (IAS) by turning off the respective manual valve.

5.0 RESULTS

The report should contain: a) The P&I diagram (as supplied at the end of the manual) with all major components

marked clearly. b) Dynamic Response curves for single loop with different PID controller values. Include

all the details such as setpoint, PID controller values. c) Flow Ratio Controller response with different test with different ratio. d) Discussion on the response characteristics and performance of ratio controller with

different ratio and different disturbances (please refer notes).

P&I Diagram for WF922 Flow Ratio Plant Control

pdf lab.manual.sept2014.flowratio

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