Compressor Anti-Surge Control

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ANTI-SURGE CONTROL AND SURGE PROTECTION

1 General

This specification defines the technical requirements for Anti-surge Control and Surge Protection for LP/HP MR(K-91420/30), Propane(K-91140) and End Flash(K-91450) compressors for the MLNG TIGA project.

As indicated on the PEFS, dedicated anti-surge control and safeguarding systems shall be provided by Compressor Controls Corporation (CCC), Series 4. These systems shall be provided as complete packages including engineering, hardware, and software supply, configuration wiring, testing, installation and commissioning.

1.1 Abbreviations

ASC Anti Surge ControlCCC Compressor Controls CorporationDCS Distributed Control System.EDRS Equipment Data Requisition SheetEMC Electromagnetic CompatibilityENMC Electrical Network Monitoring and ControlEPCC Engineering Procurement Construction and CommissioningFAR Field Auxiliary RoomGT Gas TurbineIPS Instrumented Protective SystemsMCR Main Control Room.MCRB Main Control Room BasementMDF Main Distribution Frame (Field Cable Marshalling Cabinets)MR Mixed RefrigerantMTBF Mean Time Between FailurePCS Process Control SystemPCSI Process Control System IntegratorRDAS Rotating equipment Data Acquisition SystemSD Surge DetectionUPS Uninterruptable Power SupplyVSDS Variable Speed Drive

2 FUNCTIONAL REQUIREMENTS

2.1 General Control Objectives

Vendor's control system shall meet the following control objectives:

(a) Provide control of the overall compressor system to maximize efficiency whilst accurately meeting process control objective requirements, as specified in the process control descriptions.

(b) Protect each stage of the compressor from surge-induced compressor damage and process upsets with minimum recycle. Minimize process upsets resulting from recycle control.

(c) Minimize adverse interactions between the above control functions.

(d) Provide uninterrupted control in the event of hardware failures.

Berry’s Commissioning Handbook


(e) Provide integration with the Distributed Control System (DCS) and with the Rotating equipment Data Acquisition System. (RDAS)

Anti-surge Controllers shall calculate compressor operating point deviations in a manner that is invariable to change in inlet conditions, such as pressure, temperature, gas composition, compressor polytropic efficiency, rotational speed and inlet guide vanes position for the axial compressor.

The preferred method of meeting this requirement is to compute the distance between the operating point and incipient surge limit using an equation based on the specific compressor curves, for ratio of polytropic head to suction volumetric flow. The algorithms used shall be based upon either Shell Report MF 85-0260, the compressor vendor's requirements or the system vendor's proven technology.

Each anti-surge control module will manipulate a recycle valve to maintain an adequate, but not excessive, margin of safety between its compressor stages operating point and surge limit, as described below.

Anti-surge control modules shall provide optional limiting control of both discharge and suction pressure, consistent with the primary goal of preventing surge.

The anti-surge control module shall have three protection shields against surge.

(f) The first shield shall be a control module that opens the recycle valve in case the operating point crosses the configured control line. The control line shall have a margin to surge that is dependent on the speed at which the operating point is moving towards surge.

(g) The second protection line shall be located between the surge limit line and the surge control line. When the operating point of the compressor crosses this line, the anti-surge control module shall increase its output with an increment in order to avoid surge in the compressor. The size of this increment shall be dependent on the speed at which the operating point is moving towards surge. The increment addition to the output of the anti-surge control module will decay at a configurable rate.

(h) The third protection line shall be located to the left of the surge limit line. When the operating point of the compressor crosses to the left of this line, the control module will assume surge in the compressor and increase the initial margins of the first two shields with some pre-determined, configurable level. In addition, the anti-surge control module shall include the capability of detecting actual surge by measuring and recognizing a pre-defined surge signature. When a pre-defined number of surges are detected the compressor shall be tripped via the IPS.

The anti-surge control module shall be capable of recognizing transmitter failures. In case such an error is detected, the anti-surge control module will switch to a more conservative control algorithm and alarm this to the operator. The anti-surge control module shall be able to differentiate between a flow transmitter failure and a actual surge incident, taking appropriate action based on the findings.

For compressor protection (i.e. to enable the Compressor to be shutdown by the plant IPS after multiple surges or after a suitable delay), the Anti-surge Controller shall incorporate a separate surge detector which provides contact output (minimum 300 msec duration) to the IPS. Surge detection shall be based on a defined algorithm

Provisions must also be made for recording and displaying the maximum observed rate of change for each of those variables as an aid to basing these thresholds on the results of a surge test on the given machine.

Anti-surge Controller shall exchange information with all other Anti-surge Controllers regulating the same compressor in order to implement appropriate feed-forward control responses that minimize loop interactions and maintain the quality of surge protection.

The Anti-surge Controller shall incorporate features that fully open the recycle valve, by IPS, when the compressor is shut down. These states shall be selected on the basis of binary signal inputs and/or the compressor's rotational speed, flow rate and suction pressure.

Provisions for manual control of the recycle valves shall be included.



3 HARDWARE REQUIREMENTS

This section provides the hardware requirements for anti-surge applications which are to be implemented dedicated systems: CCC Series 4. Other anti-surge control and surge protection applications will be implemented in the plant DCS and IPS.

The anti-surge control and safeguarding system shall comprise one redundant anti-surge control module for each compressor stage.

They shall be configured such that failure of either (internal or transmitter input signal) shall automatically transfer both analogue and binary output functions and connections to the healthy unit. This status shall be alarmed and maintained until the failed unit is replaced and the system is manually reset.

Independent and separate Flow, Pressure and Temperature transmitter signals shall be connected to the primary (for control) and secondary (for safeguarding) units.

The hardware / software shall be capable of providing full functionality during various process operating conditions i.e:- start up- steady state

The Anti-surge Controller units shall be arranged in redundant configuration such that failure of a single unit will not cause any upset to compression operation. Deviation calculations between the controllers shall be presented to the DCS / RDAS.

On-line replacement of a failed unit or input transmitter shall be possible without causing any process upset, .

The anti-surge control modules shall be capable of scanning all inputs, executing control algorithms and updating all outputs at least every (vendor to advise) milliseconds.

The control modules shall utilize common hardware to simplify maintenance and reduce spare part requirements.

Control modules shall provide filtered analog input channels for obtaining process data.

Control modules shall accept discrete input signals for triggering startup/shutdown/ purge logic idle 1, idle 2, rated, etc.

Control modules shall provide output circuits which can be assigned for signaling various control module's or process status conditions.

The turbomachinery control system shall be capable of working in a fault tolerant configuration with automatic and bumpless transfer between common control functions.

Control modules shall be capable of transforming their output signal to compensate for non-linear final control element characteristics (i.e., quick-opening or equal-percentage control valves or valve hysteresis).

Control modules shall utilize serial communication for exchanging information with each other and other (higher level) systems.

Data communication links, dual redundant, with the Distributed Control System (DCS) shall be provided.

All non-critical / data exchange communication shall be communicated via dual serial link.



Serial RS232/422/485 links employing Modbus RTU protocol shall be used.

Communication to Rotating equipment Data Acquisition System (RDAS) will be through Ethernet TCP/IP link.

Safety signals (i.e. tripping of a machine) shall be via potentially free contacts for hardwired connections to the shutdown system.

The DCS shall not override anti-surge control and protection systems, however, a hardwired manual loading station (HIC) will be available on DCS for manual opening of the recycle valve.Similar connections from DCS (e.g. inlet guide vane control) shall be hardwired.

Appropriate analogue and binary signals, to/from Gas Turbine Mark V and helper motor switchgear, shall enable an integrated Train start up and operating control and protection system.

The data communication links to DCS and RDAS shall meet the monitoring requirements for the CCC software packages displays on DCS and RDAS as described in Section 4.

Vendor shall provide IBM Compatible PC software providing enhanced display, configuration, testing, and tuning of the compressor control system.

The systems shall include a portable workstation including printer suitable for system configuration and also to enable system operation data to be recorded for subsequent analysis and diagnostic solving purposes. As a minimum duplicate magnetic media copies of workstation operating software shall be included.

Each Anti-surge Controller may include control and protective functions which manipulate the analogue signal output to a recycle valve and also a safeguarding function which will operate a switch to provide an output after a preset number of surge events have occurred.

All field signals to and from the system shall be intrinsically safe. Barriers, if required, shall be active type and located in the MDF. Barriers and MDF will be supplied by others.Controller configuration and tuning parameters shall be stored in non volatile Read Only Memory for long term storage, as well as in RAM for short term storage.

Analog output signals from the Controllers to the recycle valves be 4-20 mA DC.

Interconnection of critical safeguarding and control signals between the systems cabinet and other instrumentation systems shall be by hardwiring via the external marshaling racks. (MDF)38/32 ELCO sockets shall be provided in the system cabinets for these interconnections which shall be implemented with systems cables. Refer to DEP 32.37.20.31-Gen. "Systems Cables".

Anti-surge and control system components for each Compressor shall be housed in standard 19” racks. They shall be installed, assembled and completely wired in free standing cabinets.

Redundant power supply units required for the system shall also be located in / on-top-of the cabinet. Duplicate electrical power supplies to the cabinet shall be from duplicate UPS at 240 VAC, 50Hz. Cable entry shall be at the bottom. (Computer floor) All cabinets will be located in environmentally controlled - non hazardous area- Field Auxiliary Rooms. (FAR's)

Refer to T-11.510.124 (S-000-1371-007) "System Cabinets Requirements"



4 MONITORING

Normal plant operations will be controlled from operating consoles in the existing Main Control Room (MCR) via a Distributed Control System (DCS).

The "single window" concept will be applied for operation of the LNG plant. (Single window means that all operator information shall be displayed via the DCS).

During EPCC, the Process Control System Integrator (PCSI) will be appointed. The PCSI will coordinate the development of interfaces between PCS subsystems. During PCS integration testing all subsystems (including marshalling) shall be provided to enable complete functional testing. Integration testing will be performed at a location which will be nominated by the PCSI.

4.1 Compressor monitoring and display software

Vendor shall provide in conjunction with the compressor controls system, compressor/turbine monitoring and display software package (e.g. COMMAND) . This monitoring system shall have a composite main display that includes one compressor map, an overview window, an annuciator window, an operator advisory window, and five trend graphs. The compressor map will instantaneously plot the operating point, surge limit and surge control curves for a single compressor stage. Choke limit and choke control lines, when required, need to be implemented as well. The coordinates for this plot shall be in terms of head vs. flow, the actual coordinates will vary depending on the application. When plotting discharge pressure or compressor ratio against flow, all curves need to be dynamically updated to reflect changing inlet conditions.

The overview window must provide instantaneous digital display of up to fourteen process variables and be capable of presenting all the defined compressor map data. An automatic critical event archiving shall be included. When a critical event, such as an approach to surge, is detected, all variables are recorded before, during, and after the event. Vendor to propose method and durations.

Any configuration shall be in password protection.The overview window shall also be made available in the DCS via the X-Window link and in RDAS.

4.2 Control Module Installation Support Software

The vendor shall provide software modules to help Start-up and maintenance engineers configure, test and tune the compressor control system (e.g. Toolbox).

The software modules shall provide a way to determine and change parameters of the compressor control system as well as upload a control modules entire parameter set, view it on screen, print it out, modify it as needed, and download to the control module. An ability to monitor, record, and play back input signals is essential during the tuning of a control system. The analog inputs of up to 20 control modules need to be recorded simultaneously, this data needs to be displayed in a strip-chart format, X - vs.-time, Y-vs.-time, or X-Y plot format. It shall be possible to print the data in strip-chart format, with or without a table of numeric data.

The displayed information shall also be available in DCS and RDAS.



5 ENGINEERING REQUIREMENTS

The system vendor shall provide the following engineering services in order to define the anti-surge control scheme;

5.1 Control Definition

The system vendor shall develop the optimum control system design which will protect the Compressors) from surge and ensure maximum availability of the compressor train during all operating cases based on purchaser's control objectives.

5.2 Design Review

As a vital part of the Dynamic Simulation and Analysis of the Refrigeration Compression System as specified in the EDRS, the Vendor shall review the piping and line lengths, the locations of vessels, flow elements, check valves and recycle valves for compatibility with optimum surge protection and energy efficiency.

5.3 Design Specifications

Vendor shall recommend / advise specific requirements necessary for field transmitters, flow elements, recycle control valves, valve positioners, and volume boosters needed to ensure compatibility with the surge control system. Engineering data requisition sheets will be prepared for these items based on Vendor recommended requirements.

Typically the System Vendor shall specify these important features for instrumentation on ISA standard specification sheets.

5.4 Electro Magnetic Compatibility

The electrical system shall be engineered in accordance with:- EN50081-2, Generic emission standards,- EN50082-2, Generic immunity standards,- T-11.513.152 (S-000-1380-012) Specification for EMC- Requirements for EPCC.

6 INSPECTION AND TESTING

6.1 SYSTEM 'BURN IN'

During staging the system is to be continuously energized for a period of at least four (4) weeks, 24 hours per day at operating temperature and maximum rated load, to burn-in the system and minimize the possibility of process shutdowns caused by infantile failures.

Load taking devices shall be simulated at the input/output terminals. Vendor is to advise the environmental conditions under which the burn-in takes place. (i.e. ambient temperature and humidity) Vendor is to have available for Purchaser inspection, a listing of components which failed during burn-in period. This list should include the length of tome which the failed component was running prior to it's failure. This would be most conveniently accomplished by maintaining a record of the burn-in running hours with an indication on the record (against time) for any failure of equipment. During system energized time, normal equipment checking and calibration may continue.



6.2 FACTORY ACCEPTANCE TEST

Vendor shall submit the Factory Acceptance Test procedure for purchasers approval prior to the Factory Acceptance Test start.

Testing shall be witnessed by the purchaser and shall consist of a loop-by-loop functional test of each input, logic interlock, serial interface signals output and alarm to prove proper operation. The test shall be performed using simulated inputs. All test equipment, signal generators, meters, test panels (including test lights, switches, adjustable pot, etc.) test cables and any other test devices shall be provided by the Vendor.

Purchaser approved system upset simulation tests shall be conducted by the Vendor in addition to performance testing.

Full functional testing of the serial data link communications with the DCS to prove accurate data transfer and operability, including operating station displays, shall be carried out. This test shall be conducted at the PCSI vendor's staging location.

Vendor shall provide qualified technicians to perform the test and debug the system during the scheduled Factory Acceptance Test.

Vendor shall maintain a test log and shall document all changes made to the hardware and software during the Factory Acceptance Test.

6.3 System Integration Testing

During PCS integration testing all subsystems (including marshaling) shall be provided to enable complete functional testing. Integration testing will be performed at a location which will be nominated by the PCSI.

Vendor shall provide all hardware and software for PCS integration testing to enable functional testing or simulation of operating conditions at full load, or as near as practicable.

Vendor shall agree with the PCSI the required availability of equipment, tools and personnel necessary for integration testing.Prior to the PCS integration testing all Vendors PCS equipment shall be independently and successfully Factory Acceptance Tested as required per vendors / manufacturers agreement with Contractor .

6.4 SITE TESTING AND INSPECTION

6.4.1 System Inspection

This shall be completed on the compressor, the piping, the primary control elements, the check valves and the instrumentation. The primary control elements shall be calibrated and checked for accuracy, repeatability and speed of response. Transmitters and transducer shall be calibrated.

6.4.2 Inspection of the Compressor Control System

The wiring of the controller and the inter-controller wiring (including power, ground, shield, isolation) shall be checked. The controller shall be powered up and their proper installation shall be evaluated. Controller calibration shall be checked along with verification of vendor determined parameters and a test of the required algorithm operation.

6.4.3 Compressor Start-up

Prior to testing and tuning, Vendor's technician or engineer shall monitor the input and output signals of the controllers to check for validity while the compressor are started up and operated.

Vendor shall observe the operation of each compressor for sufficient time to confirm proper functionality of the system.



6.4.4 Surge Testing and Tuning

The Anti-surge Controllers and Performance Controllers shall be tuned by Vendor to establish all control objectives. The Vendor engineer or technician must be experienced and capable of performing surge testing to satisfaction of the Contractor.

7 DOCUMENTATION

The final system engineering manual shall include;

- Technical documentation specific to all hardware/software supplied.- The project specific technical documentation and drawings.- Design review reports and specifications.- Inspection, testing, start-up and tuning reports.- Final systems configuration printouts with magnetic media copies.- Maintenance / Operation manuals.

8 SPARE PARTS

A quotation shall be provided for two years operational spare parts. Refer to DEP 70.10.90.11 - GEN for spare parts requirements.

9 TRAINING

Quotation shall detail the cost, venues, content, dates, etc. of training required for operation and maintenance.


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Compressor Anti-Surge Control