Post on 04-Jun-2018
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CONTROL SYSTEMS
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INTRODUCTION
General, pump curve - System curve
Parallel operation
Series operation
Compressor control
Pump control bulletin
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GENERAL DISCUSSION
Are recurring problems a responsibility of maintenance?
Controls/procedures may result in equipment failure
May need coordination with process group
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CURVE SHAPES
120
100
80
60
40
00 20 40 60 80 100 120 140 160
Flow (Percent)
Head
(Percent)
Full EmissionConcentric Bowl & ETADouble Log Spiral
Z Series
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TOTAL SYSTEM HEAD
Capacity, Q
Head, H
System static head
System friction head
System head
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IMPACT OF VALVE THROTTLING
Capacity, Q
Head, H
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OPERATING SYSTEM
Capacity, Q
Head, H
Q2 Q1
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BY-PASS REQUIRED?
Capacity, Q
Head, H
Bypass Flow
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INTERSECTION OF PUMP AND SYSTEMCURVES
Capacity, Q
Head, H
Under-sized pump
Properly sized pump
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IMPACT OF WEAR
Over a period of time, system and pump characteristics getdeteriorated
After 15 years, friction losses in pipe are 60% more important!
To be taken in account in the choice of the pump
Minor loss for pump performances
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MINIMUM FLOW
2 Types of Minimum flow phenomena:
At start-up
During normal operation
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MINIMUM FLOWat start-up
Start-up shock wave
Water Hammering
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MINIMUM FLOWduring operation
Minimum Continuous stable flow
Minimum Continuous thermal flow
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MINIMUM FLOWFlow surging
May happen if a air/gas pocket is located in the downstream line
Can be seen as a simple spring-mass system
Need a excitation to happen
Can be reduced / solved by having a flow control valve close from thepump discharge
Predominent for compressors
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MINIMUM FLOWSurging reduction
Control valve within 3m of discharge
Flexible lines only after control valve
A straight pipe of at least 10 times diameter length on the discharge
Choose correct size of valve
Install low flow by pass
Eliminate air and gasses trapped
Operate at higher flow
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MINIMUM FLOWMinimum flow control
S FS
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MINIMUM FLOWPhenomenon
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MAXIMUM FLOWPhenomenon
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CONTROLLING
120
100
80
60
40
00 20 40 60 80 100 120 140 160
Flow (Percent)
Head
(Perc
ent)
Full EmissionConcentric Bowl & ETADouble Log SpiralZ Series
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PARALLEL OPERATION
Always use discharge check valve.
Need differential to open check valve
Low gravity fluid may vaporize - Pump deadheaded.
Unstable operation results in equipment damage
Always use bypass control valve.
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PARALLEL OPERATION WITH FLOW
CONTROLLED BYPASS ON EACH PUMP
FLOW SENSOR
CONTROLLER
BLOCK
CHECK
BYPASS
CONTROL
VALVE
CONTROLLER
FLOW SENSOR
BLOCK
CHECK
BYPASSCONTROL
VALVE
THROTTLE
CONTROL
VALVE
A
B
STARTUP SEQUENCE
1. SET EACH BYPASS FORMIN. ALLOWABLE FLOW
2. CLOSE PROCESS FLOW
CONTROL VALVE3. START PRE-LUBE PUMPS
IF APPLICABLE4. START A AND STABILIZE
START B AND STABILIZE5. SET DESIRED PROCESS
FLOW RATE
PARALLEL OPERATION
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SERIES OPERATION
Capacity, Q
Head, H
PUMP A OR B
PUMP A AND B
SYSTEM HEAD CURVE
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SERIES OPERATION
Requires extra measure of care (for second unitespecially)
Pre-lube normally advisable on 2nd unit.
Tandem seal & suitable buffer probably required.
Flange rating to be reviewed
Thurst bearing capacity to be increased
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STARTUP SEQUENCE1. SET BYPASS FOR MIN. ALLOWABLE FLOW2. CLOSE PROCESS FLOW CONTROL VALVE3. START PRE-LUBE PUMPS IF APPLICABLE
4. START 1ST UNIT AND STABILIZE5. START 2ND UNIT AND STABILIZE6. SET DESIRED PROCESS FLOW RATE
BYPASS FLOW
CONTROL
SENSOR CHECK
CHECKCONTROLLER
PROCESS FLOW
CONTROL VALVE
SERIES OPERATION - PREFERRED