Compressor Presentation 1
Compressor Presentation 1
Compressor Presentation 1
Types of Compressor
Compressor Control
100 MPa
(14,500 psia)
Discharge Pressure
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10 MPa
(1,450 psia)
Positive Displacement Data from CAGI
Compressors
1 MPa
D
© 2011 Compressor C
(145 psia)
Dynamic Compressors
.1 MPa
(14,5 psia)
1 m3/h 10 m3/h 100 m3/h 1000 m3/h 10,000 m3/h 100,000 m3/h
(0.6 CFM) (6 CFM) (60 CFM) (600 CFM) (6,000 CFM) (60,000 CFM)
Compressor Performance
Rc
Dynamic -
Variable Flow,
Constant
Pressure
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Positive Displacement
- Variable Pressure,
C
Constant
t t Fl
Flow
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Q
Constraint Control - Operating Envelope
Speed
p Limit ((Maximum))
Surge limit ? ?
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Stonewall or
choke limit
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Speed Limit
(Minimum)
Flow
Compressor Control
• Compressors are the control element for the
process, so good control is needed for good
product quality
• Compression
C i consumes h huge amountst off
energy so good control normally translates to
energy and cost saving
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Compression Systems
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Typical Motor Driven
Turbocompressor
Section 1 Section 2
out
PIC UIC Serial UIC
1A 1A network 1B
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Section 1 Section 2
out
Serial
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Control of Primary Process Variable via Performance, and helped by Recycle when required
Cost Points – Tight Antisurge Control
with Minimized Recycle
Section 1 Section 2
out
Serial
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Cost Points
Section 1 Section 2
out
Serial
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Section 1 Section 2
out
Serial
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Examples
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© 2011 Compressor C
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© 2011 Compressor C Controllability Examples
2
Shaft qr
power
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Compressor Flow
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User Flow
Saudi Example
installed and
commissioned the valve
fully closed
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LP: Normal Condition Winter: 1376 BHP, Normal Condition Summer: 1438 BHP.
Assuming recycling is 20% in summer and 30% in winter, then Power Loss in Recycling (using 0.746 factor) = 261.
Considering the following formula: 261 * 365 * 24 * 0.95 * 0.23 / 3.75 = USD 133,218 / Year is the Energy Loss Value.
D
Developing
l i Algorithms
Al i h for
f
Compressor Control - a Urea Plant
Case Study
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Developing Control Solutions?
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Press
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Flow
Press
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Flow
Algorithm Issues
The problem with commonly used (OEM provided)
coordinate systems of the compressor map is that these coordinates are
NOT invariant to suction conditions as shown
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Algorithm Issues
The surge limit thus becomes a surface rather
than a line
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• For control purposes we want the SLL to be presented by a single curve for
a fixed geometry compressor
3
Advanced Control - Developing
Invariant Coordinates
• The following variables are used to design and to characterize compressors
• Through dimensional analysis (or similitude) we can derive two sets of invariant coordinates
or Similitude Ne Ne
α α
J = f1(Q, ω, μ, ρ, a, d, α) jr jr
Re Re
where:
• Hp = Polytropic
P l t i head
h d
© 2011 Compressor C
where:
• J = Power • hr = Reduced head
• Q = Volumetric flow rate • qr = Reduced flow
• ω = Rotational speed • Ne = Equivalent speed
• μ = Viscosity • α = Guide vane angle
• ρ = Density • jr = Reduced power
• a = Local acoustic velocity • Re = Reynolds number
• d = Characteristic length • Rc = Pressure Ratio
• α = Inlet guide vane angle
Algorithm Issues
NOT invariant coordinates Invariant Coordinates
(hr, qr2)
(Hp, Qs)
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© 2011 Compressor C
where:
• Hp = Polytropic head
• Qs = Volumetric suction flow
• hr = Reduced head
• qr2 = Reduced flow squared
Algorithm Issues
NOT invariant coordinates Invariant coordinates
(Rc, Qs) (Rc, qr2)
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© 2011 Compressor C
where:
• Rc = Pressure ratio
• Qs = Volumetric suction flow
• qr2 = Reduced flow squared
PT PT FT
1 2 1
UIC
1
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Uncontrollable Surge - One Antisurge
Controller Monitoring 3rd Section
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Why?
• CCC developed a High Fidelity Dynamic Simulation of
the installation using actual installation data and
Compressor Maker’s Curves
– stage mismatch was found - where the 1st section
could be in surge while the 4th in stonewall
– the valve on its own is not sufficient to prevent surge
during large upsets - using a larger valve did nothing
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Decoupling
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Interaction of Control Loops
Control
Measurement
Recycle Valve
Control
Antisurge
M
Measurement
t
Speed
Process Variable
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SG
Compression
System
ST Driver Compressor
PIC
1
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UIC
2
Q
Integration of Control Loops
SG
ST Driver Compressor
PIC
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Peer-to-Peer
Serial Communication
UIC
2
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Integration/Decoupling of Antisurge
and Capacity Control
We are operating at point A
Large disturbance occurs
The operating point rides the curve
Rc to point B
This time we ‘decouple’ the action
of the performance controller
The antisurge controller tells the
B
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V2
V1
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Suction Process
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Bypass valve
Extraction
Steam Header
V2
V1
SIC XIC FT PsT PdT
1 2 1 1 2
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RSP
FT Suction UIC
Process
2
1
PT
2 PdT
3
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Extraction OUT
Steam Header PIC
1
Serial
network
avoided surge, and kept the compressor train on line. Before the
retrofit, the pneumatic system would definitely trip the machine
in such event, and in the worst case the machine would be
damaged due to surge.
Comment from Chinese Customer After
Retrofit
With CCC TTC system, the direct energy saving was
calculated. It was 6.4 Million RMB (US$790,000) saving
per year at the same number of tons of urea produced
per year before the retrofit. All investment for the retrofit
including cost of equipment, freight cost, customs duty,
taxes, installation etc.,) was recovered less than 10
months.
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© 2011 Compressor C
Unique PC
Dedicated PC
Future Direction
Q&A
Compressor Performance Monitoring