QUALITY MONITORING & CONTROL
Kilgore Centrifugal Compressor Program
for Windows
The Centrifugal Compressor Simulation programs provide for calculation
of centrifugal compressor performance over a wide range of operations, including, but not
limited to, start-up, normal operation at steady and varying load conditions, normal
shutdown, emergency shutdown, and safety valve relieving conditions. A single compressor
train with one or two services with a maximum of six stages (compressor sections) total
can be simulated.
Input from compressor manufacturer's performance curves and data provides the basis for the generation of a mathematical model of each compressor stage (section). This model develops adiabatic head versus actual volumetric inlet flow which is the basis for calculating performance over a wide range of conditions.
In the graphic display of operating maps below notice that the surge line, anti-surge control line, operating point (and trace), and choke line are shown as well as much pertinent data.
SYSTEM FEATURES (optional) that can be simulated:
Inlet Header
Operating flow range or pressure range
Pressure controller with control valve
to vent excess
Outlet Header
Operating flow range or pressure range
Pressure controller with control valve
to vent excess.
Compressor Suction
(each stage)
Inlet pressure controller and valve
(1st stage only)
Inlet excess pressure regulator valve
Cooler (air or water cooled)
Compressor Discharge
(each stage)
Pressure Safety Valve/s (PSV)
Silencer for Safety Valve/s
Emergency Vent Valve (blowdown)
Cooler (air or water cooled)
Anti-Surge Valve (may connect to suction same
or any previous stage - a cooler may be installed
either upstream or downstream of anti-surge valve
but not both locations)
Interstage Options
Check valve installed
Check valve installed with anti-surge overlap
Check valve not installed
Check valve installed with bypass flow element
External balance gas flow connections
SYSTEM CONTROLLERS
Main Unit Controller
Control mode
No control
Discharge Pressure control
Inlet Header Pressure control
Discharge + Inlet Header Pressure control
Output from any above configuration to:
RPM
Anti-surge valve
1st Stage inlet valve
External discharge to suction by-pass valve
Set point on Discharge Flow Controller
Anti-Surge Controllers
Auxiliary Controllers
Inlet Header Pressure Controller
Outlet Header Pressure Controller
Gas Outlet Temperature Controller for any gas cooler, air or water
cooled
Control Parameters
(standard PID adjustable)
Gain (Proportional)
Reset (Integral)
Derivative
Induction Motor Driver
Use motor manufacturer torque/RPM curve or
program
default curve for acceleration during start.
Typical example - Three Stage Compressor System:
Example Compressor System Description
This system is typical for compressing gas field production for delivery to a pipeline. In this example a three stage gas turbine driven centrifugal compressor is compressing 72.3 MMSCFD (2934 lbs/min) of 22.188 mol wt gas from 30 psig (44.7 psia) inlet header pressure to 1800 psig (1814.7 psia) pipeline pressure. The fuel gas for the gas turbine at 7.0 lbs/1000 bhp is withdrawn from the suction of the third stage. There is a blow-down (vent) orifice and valve at the discharge of each stage. Anti-surge control is provided for each stage. Unit control is via pressure control on the inlet header pressure controlling RPM.
Performance
Summary at Reference Conditions:
(Any number of Reference Conditions may be stipulated for each Compressor
System)
Abbreviations in Performance Summary:
| F #/M | Flow in lbs/minute |
| SucAQ | Flow in actual cubic ft/min at suction conditions |
| Hadbt | Adiabatic Head FtLbs/lb |
| Efncy | Adiabatic efficiency |
| HP | Bhp |
| SrgFc | Flow as fraction of surge flow |
| ChkFc | Flow as fraction of choke flow |
| *SfSuc | Side flow lbs/min +/- at suction of stage |
| *SfDch | Side flow lbs/min +/- at discharge of stage |
| *BgfS | Net external balance gas flow at suction |
| *BgfD | Net external balance gas flow at discharge |
| *If applicable | |
Operating Map at Reference Conditions:
Notes:
The vertical scale is adiabatic head in Ft/FtLb. The horizontal scale is actual cubic ft/min (acfm).
| PS | Pressure suction psia |
| PD | Pressure discharge psia |
| TS | Temperature suction DegF |
| TD | Temperature discharge DegF |
| FQ | Compressor flow lb/min |
| AQ | Compressor acfm |
| FA | Anti-surge valve flow lb/min |
| FV | Safety valve (PSV) flow lb/min |
| N | RPM |
Performance Map for Normal Start Simulation:
'Cross-plots' are at one minute intervals.
Notes:
| PE | Pressure at exchanger (aftercooler) outlet |
| FG | Fuel gas flow lb/min |
| PGM | Program mode |
| NOS | Normal operation simulation |
| +0.0000 | Change in RPM in one calculation iteration |
| ET | Elapsed
Time in seconds (1200 seconds = 20 minutes) |
| FQ | Compressor flow lb/min |
| AQ | Compressor acfm |
| FA | Anti-surge valve flow lb/min |
| FV | Safety valve (PSV) flow lb/min |
| PNH | Pressure inlet header psia |
| PDH | Pressure discharge (outlet) header psia |
| FNH | Flow inlet header lb/min (N/S not stipulated) |
| FDH | Flow discharge header lb/min |
| XNH | Flow excess pressure control inlet header lb/min |
| XDH | Flow excess pressure control discharge header lb/min |
The compressor is accelerated at 467 RPM/Min to the design speed of 4545 RPM. The inlet header pressure is stipulated as constant at 44.7 psia and the pipeline (outlet) header at 1814.7 psia. The anti-surge control valves are maintained open to 3528 RPM when the anti-surge control is activated. This starts closing all anti-surge valves resulting in moving the compressor operating point in each stage toward the surge line. As the operation in each stage crossed the surge control line, the anti-surge controller begins opening the anti-surge valve to maintain operation at or near the surge control line. When the discharge pressure equals the outlet header, compressor flow increases as the anti-surge controllers close the anti-surge valves.
Performance Map During Reduction in Inlet Flow:
'Cross-plots' are at one minute intervals.
Notes:
The inlet supply rate is reduced from 2934 lbs/min (72.3 MMSCFD) to 2000 lbs/min (49.3 MMSCFD) at 250 lbs/min/min (MMSCFD/min). The inlet pressure control senses the resulting reduction in inlet pressure and reduces RPM. Compressor operation approaches the surge-control line in approximately two minutes. The interplay between in the inlet pressure control and the anti-surge controllers stabilizes the compressor operation at stable RPM and anti-surge flow.
Performance Map for Emergency Shutdown:
'Cross-points' at 0.5 second intervals.
Notes:
FB Blowdown (vent) flow lbs/min. This is in lieu of FV Safety Valve flow.
In this simulation the power is stopped instantly. The blowdown valves and anti-surge valves start opening at their respective stroke rates. The work of compression opposes the inertia of the rotating assembly to cause a rapid deceleration in RPM. In the above example the system decayed from 20923 bhp at 4545 RPM to 635 bhp at 2129 RPM in 7 seconds without compressor operation violating the surge line.
Future Program Features:
Option for standard or metric units
Thermodynamic mass balance calculations