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We have undertaken for clients a number of control
system design and performance studies requiring the dynamic simulation of
compressors and compression plant, such as for LNG plant, gas pipeline
booster stations and large air-consuming plant.
Project working arrangements have included both
studies carried out entirely at our premises, and studies carried out
entirely at client's premises - with the dynamic simulation studies
and the results an integral part of the ongoing process and control-system
design and development.
The modelling, simulation
engineering and control-system performance studies were undertaken
ourselves, sometimes with help from our associates to combine the
necessary modelling and engineering skills according to scope.
Simulation engineering was carried out in Simulink®.
Documented test-case results and completed simulations with KHACE
Embedded Technology technology were delivered to the client under
license for archive, for reference and for continued use and development
by the client. Extracts from typical models and plots appear alongside.
LNG Process
In this project the client was a major engineering
contractor undertaking a design study for a proposed new large LNG plant.
We worked with the client on-site to form and train a small
multi-disciplinary team of Control Engineers and Chemical Engineers to
model and engineer a dynamic simulation in Simulink®
with KHACE
Embedded Technology for both the propane and mixed-refrigerant
compression circuits. Compressor models included multi-stage centrifugal
and axial types with inlet-guide-vane adjustment.
We continued to work with the client throughout the
duration of the study phase - helping to perform test-case studies and
developing the models and simulation to meet evolving study requirements.
Test-case studies were typical for the application,
including: trip-studies for sizing of anti-surge and hot bypass valves,
blowdown and start-up sequences - to confirm starter and helper-motor
characteristics for augmenting gas-turbine capability, various
fault-condition test-case scenarios.
In the four-stage propane compressor, particular attention was paid to
examining the interaction between the individual stage recycle-loops
during a trip. It is easy in a multistage compressor for gas recycled from
the high-pressure stage to back-pressure the earlier stages and push them
into surge. To ensure that all stages stay out of surge, the recycle
valves and pipe-work must be designed for dynamic compatibility.
Gas-Reinjection
In this project the client was a major engineering
contractor undertaking a design study for a middle-east oil-field gas-reinjection
plant. We worked with the client on-site to carrry out the modelling and
simulation studies.
Air Compressors
In this project the client was a major
petrochemicals company replacing a number of existing individual air
compressors feeding oxidation reactors with a pair of large-capacity
compressors working into a single bifurcated header feeding all reactors
in parallel.
In this application the dynamic performance of the
compressors and air-headers was of paramount importance. Good regulation
of header pressure at the reactors was essential, not just to ensure
adequate responsiveness to the supply demands of the reactors; but also to
ensure that changes in operation on reactor did not upset parallel
reactors. A fast response by the compressors to major load disturbances,
such as a reactor shut-down, was essential to prevent cascade shutdown of
the whole plant.
We worked with the client through two major stages of the project:
- Feasibility study and selection of compressor vendor.
- Development of the header characteristics and control-system
design.
Feasibility study and selection of compressor vendor.
Feasibility of a common air supply was confirmed by
dynamic simulation using established KHACE compressor and pipe work models
with nominal compressor characteristics. The reaction process was modelled
rigorously, using models supplied by the client, and the downstream gas
processing plant was modelled with sufficient accuracy to provide
realistic simulation of dynamic load responses on the air supply.
The original simulation was then modified to
incorporate rigorous models based on the different specifications of the
competing compressor vendors - to determine which machines would deliver
adequate and best dynamic performance. A key performance measure at this
stage was the dynamic response of the machines to a sudden change
(increase/decrease) in load demand. Different hold-ups in
inter-stage condensers and the number of inter-stage inlet guide-vanes
were found to have a significant influence on overall suction-to-discharge
dynamic performance. Dynamic simulation results were incorporated with
other engineering information to support vendor selection.
Development of the header characteristics and control-system design
Using rigorous models of compressors from the chosen
vendor, dynamic simulation was used to determine the relationship between
header dynamic response, dynamic decoupling between air consumers and
total header capacity and the way it is distributed around the site (close
to compressors, close to consumers). Various header-pressure and flow
control-system options were investigated and overall performance
predictions confirmed for final machine configurations and header layout.
Gas Pipeline Automatic Booster Compression Station
 In
this project the client was a major engineering
contractor designing an un-manned automatic compression booster station to
extract and meter gas from a national pipeline network and supply to a
distant power station.
The compression station comprised parallel
compressors with air-cooling of recycle and gas-fired heaters for
counteracting Joule-Thompson cooling in the control valves.
At periods of high supply pressure, pre-heated
gas could be let down through control valves and no compression was
required. At times of low-pressure supply, compressors would start
automatically to boost the line pressure. Compressors could also be
brought into service for packing the line downstream to take advantage of
periods of low-cost gas supply. The gas supplier placed dynamic
restrictions on the extraction of gas - such as restrictions on the
allowable rate of change of gas flow being extracted.
The compressor station was modelled from
manufacturers equipment data and dynamic simulation was used to test and
verify the sequences for compressor start-up and shutdown, and switching
between the various operational modes. Sequences went through several
cycles of re-design and test using the simulation before final design.
Simulation of Compressor Controls
In this application the client
was delivering a training simulator to an offshore-oil operating company
and required a rigorous model of the Compressor Controls Corporation (CCC)
Series-3 compressor controls that had selected for the plant.
Using original CCC technical documents and with the
assistance of CCC to resolve some ambiguities in teh documentation, we
were able to program a rigorous emulation in FORTRAN of the functionality
of the CCC Series-3 anti-surge and performance controllers.
The emulation of the controls was engineered to use
configuration data in the same format as the native Series-3 configuration
data, so that changes to the controller configuration parameters and
constants could be implemented in the training simulator without the need
to modify the model source code.
Training courses covering the modelling basis, use and extension of the
simulation models for end-users were also supplied on request.
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