HOWDEN PROCESS COMPRESSORS Old Govan Road, Renfrew, PA4 8XJ Tel: Fax:

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1 Client: ABB Engineering Services Project Title: Diageo Distilling Ltd. Equipment: Fuel Gas Compressor HPC Contract Reference: SCW9856 Document Title: Control Philosophy Revision Description Prepared by Approved by A First Issue BML 14/01/09 WJC 16/01/09 B Client Comments BML 16/04/09 UST 17/04/09 C As Built WJM 18/06/09 UST 18/06/09-1 -

2 Table of Contents 1. INTRODUCTION REFERENCED DOCUMENTATION OPERATIONAL PRE-REQUISITES MANUAL CHECKS AUTOMATIC START-UP ACTIONS STARTING THE PRIMARY SEPARATOR OIL HEATER CONTROL MODE PRE-START SEQUENCE INITIATING A PRE-START STARTING THE COMPRESSOR START-UP SEQUENCE RUNNING MODE MACHINE MONITORING STANDBY OIL PUMP LUBE OIL TEMPERATURE CONTROL OIL/GAS DIFFERENTIAL PRESSURE CONTROL DISCHARGE PRESSURE CONTROL STOPPING MODE TRIP SHUTDOWN LOGIC EMERGENCY SHUTDOWN LOGIC CONTROL SYSTEM CONTROL SYSTEM HARDWARE CONTROL SYSTEM SOFTWARE HMI COLOUR SCHEMES HMI SCREENS

3 1. Introduction This document details the control philosophy for the Howden fuel gas compressor package being supplied to ABB Engineering Services for the Diageo Port Dundas Distillery in Glasgow. This compressor package consists of a screw compressor, associated lube oil system, main drive motor and a Unit Control Panel. Under normal operating conditions, the compressor will be configured to operate to maintain a set point discharge pressure Referenced Documentation Electrical Block Schematics: SCW9856/EL001 Sheets 1 to 4. Sequence Logic Diagram: SCW9856/EL002 Sheets 1 to 3. P & I Diagrams: SCW9856/02/001 Sheets 1 & 2. Cause & Effect Matrix: SCW9856/EL055 Sheet 1-3 -

4 2. Operational Pre-requisites Various manual operations and checks need to be carried out by the plant operator as part of the pre-start conditions for the compressor package Manual Checks The following checks and operations should be performed:- Ensure compressor auxiliary motors, main motor and oil heaters associated Motor Control Centre (MCC) starters are energised and auto control selected. Ensure that all local stop and emergency stop pushbuttons are reset. Ensure that instrument air supplies are available. Ensure that all manual valves are in the correct position. Ensure cooling water is available. Check the oil level in the Primary Separator and top up if required 3. Automatic Start-up Actions When the UCP, located in the Boiler House, is powered up and all safety signals are healthy, then the compressor control system will automatically perform certain actions. These are detailed below:- Open the unloading valve, XV Inhibit the slide valve load solenoids XY-9012 & XY-9008 and energise the unload solenoids, XY-9011 & XY Inhibit the suction pressure alarm, PAL Bypass the hard-wired oil/gas differential pressure trip, PDALL It should be noted that the associated alarm for this trip will also be inhibited, PDAL Lock the recycle bypass valve, PCV-9000 in the fully open position. Open the compressor s drain valve, XV Close the compressor s manifold isolation valve, XV Close the lube oil re-circulating valve, XV Lock the oil/gas differential pressure control valve, PDCV-9014, at the 50% position. Lock the lube oil temperature control valve, TCV-9006 in the fully open position

5 3.1. Starting the Primary Separator Oil Heater Assuming that all safety signals are healthy, the primary separator oil heater will be enabled as soon as power is applied to the control panel. The control system (PLC) will switch on/off the oil heater, dependant on the primary separator oil temperature as described below:- The PLC will switch on the oil heater whenever the input from TT-9026 indicates that the temperature has fallen below 30 o C. The PLC will switch off the oil heater, whenever TT-9026 indicates that the temperature has risen above 32 o C. The oil heater has a high temperature protection cut-out device fitted which will be wired in the stop circuit of the heater MCC (TS-9026). In the unlikely event that this device goes into an alarm state, the heater will turn off and be inoperative until the manual reset pushbutton on the heater head is pressed. The PLC will inhibit the heater should a low oil level alarm, LAL-9025, be detected in the primary separator. To rectify this condition, the operator should top up the reservoir with lube oil. In addition, the heater will be switched off when the compressor is running. 4. Control Mode Two modes of control are available for the compressor :- Maintenance Mode The auxiliary motors, heater and valves can be controlled from the panel HMI display or at the compressor skid by utilising local control stations. This mode allows plant personnel to run auxiliary motors, and stroke valves (HMI only) as required during plant maintenance checks. Auto Mode In Auto mode the compressor can be operated from either the control panel HMI or from the HMI located at the Turbine Control Room. Pre-Start and Start/Stop sequences can be initiated from the various HMI screens. Auto or Maintenance control modes are selected via the HMI units, but the PLC defaults into Auto mode on power up of the control panel. NB : a key-lockable selector switch located on the front of the control panel will determine which HMI can be used for operator actions. When Local is selected, the control panel HMI will be active and when Remote is selected, then control will be from the other HMI. Both HMI s will be updated with real-time data from the PLC, independent of local/remote selection

6 5. Pre-Start Sequence The pre-start sequence is initiated from the selected HMI, dependent on the local/remote selector switch. The following pre-requisites have to be completed, prior to initiating a pre-start request: - Select the appropriate duty lube oil pump, via the HMI. Set the lube oil temperature set point, via the HMI. Set the lube oil/gas differential pressure set point, via the HMI. Note that the standby Lube oil pump will be inhibited from starting. At this stage, if the primary separator lube oil temperature, TT-9026 is greater than 10 o C, then a Pre-Start Available message will be displayed on both HMI s Initiating a Pre-Start The following sequence will be executed on initialisation of a pre-start command from the HMI: - The PLC will send a signal to the MCC to start the duty lube oil pump. As soon as the duty lube oil pump starts, the PLC system will release valve PDCV to automatic PID control, to establish oil/gas differential pressure set-point, if the slide valve is not at minimum position (ZT-9010). The oil/gas differential pressure, in conjunction with the unload solenoid valves will force the slide valve to the minimum position, if not already there. Once the slide valve is at the minimum position, the oil re-circulating valve, XV-9022 will be opened automatically by the PLC system. The PLC system will then lock the oil/gas differential pressure control valve, PDCV-9014, at the 50% position. The PLC system will now release valve TCV-9006 to automatic PID control, to maintain the lube oil temperature set point. Lube oil is now being heated and circulated around the oil manifold. Once the primary separator oil temperature, TT-9026 has reached 30 o C, the compressor Ready to Start indication will be displayed on the HMI s. This completes the Pre-Start logic

7 6. Starting the Compressor The Start sequence is initiated from the selected HMI, dependent on the local/remote selector switch. The following pre-requisites have to be completed, prior to initiating a start request: - Set the compressor discharge pressure set point via the HMI Start-Up sequence The following sequence will be executed on initialisation of a Start request: - The compressor drain valve, XV-9007 will be automatically closed by the PLC system. The oil re-circulating valve, XV-9022 will be automatically closed by the PLC system. The PLC system will release valve PDCV-9014 to automatic PID control, to establish oil/gas differential pressure. Once oil/gas differential pressure has been established, the manifold isolation valve, XV- 9004, will be automatically opened by the PLC system after a pre-determined time delay. The hard-wired oil/gas differential pressure trip, PDALL-9013 will be enabled, as well as the associated alarm. The PLC will automatically reset the latched safety relay trips. If all trips are now healthy, the PLC will send a signal to the MCC to start the main motor. (If not, then the PLC system will return to the Ready for Start condition.) It should be noted that once the main drive motor is running the MCC starter panel should set the PLC input main drive motor running. If the PLC system does not receive this signal within a pre-determined time period, then the PLC will abort the start up sequence and return the system to the Ready for Start condition. Once confirmation that the main motor has started is received, the primary separator oil heater will be inhibited by the PLC system. The standby lube oil pump will now become enabled (i.e. if required then it will automatically start). The PLC allows for a pre-determined time delay, to ensure the compressor has reached full speed. At this point, the PLC checks to see if the Load Enable signal is present from the Turbine Control System. (If not, then the compressor will continue to run, but in Recycle mode, i.e. fully unloaded.) After the time delay, the software suction pressure alarm, PAL-9003 is enabled. Unloading Valve, XV-9001 will now automatically be closed by the PLC. The PLC will release the Gas recycle bypass valve, PCV-9000 and the slide valve to automatic control, thus maintaining the compressor discharge pressure set-point. This set-point will be adjustable via the HMI. (Refer to section 7.5) This is the end of the Start-up sequence

8 7. Running Mode Once the compressor is running, the PLC system will continually monitor a number of process values & signals and if required take appropriate corrective action, as detailed in the following sections Machine Monitoring The PLC will monitor the compressor casing vibration (VXE-9035 & VYE-9035) and the main motor bearing temperatures (TE-9033 & TE-9034). The main motor winding temperatures (TE-9030, TE-9031 & TE-9032) will be connected to the client s ESD Panel, with repeat signals being sent to the Howden control panel for display on the HMI s Standby Oil Pump When the Main Drive Running signal is received, after a short time delay the PLC will begin to monitor for a low oil/gas differential pressure, PDAL If this goes into an alarm state, then the PLC will generate a start signal to the MCC for the standby lube oil pump. Once the standby pump is running, it will remain running until the alarm is reset via the HMI. Alternatively, if the PLC loses the duty pump running signal, then the standby pump will be started automatically and become the new duty pump. During compressor running the operator has the option to change the duty selection, which will start the new duty pump and stop the original pump Lube Oil Temperature Control This PID loop, TIC-9006, controls the lube oil temperature in the manifold. The component parts of this loop are detailed below: - Lube Oil Temperature Set Point (Deg C), adjustable via the HMI. TCV-9006 Control Valve (Control Variable). TT-9006 Temperature Transmitter (Process Variable). The control valve is mounted in a bypass piping configuration with regards to the oil cooler. As the oil temperature increases above the set point, the control valve modulates in the closing direction, thus forcing more flow through the cooler, and vice versa if the temperature falls below the set point

9 7.4. Oil/Gas Differential Pressure Control This PID loop, PDIC-9014, controls the oil/gas differential pressure. The component parts of this loop are detailed below: - Oil/Gas Differential Pressure Set Point (Bar), adjustable via the HMI. PDCV-9014 Control Valve (Control Variable). PDT-9014 Differential Pressure Transmitter (Process Variable). The oil/gas differential pressure is controlled via the modulating valve, PDCV This control valve is mounted in a bypass piping configuration with regards to the lube oil circuit. As the differential pressure decreases below the set point, the control valve modulates in the closing direction, thus forcing more flow through the lube oil circuit, and visa versa if the differential pressure increases above the set point. This loop ensures that the compressor s oil injection and lubrication oil flow are of sufficient magnitude. An adequate oil/gas differential pressure is also required when unloading the slide valve Discharge Pressure Control This loop, PIC-9000 controls the compressor s discharge pressure. The component parts of this loop are detailed below: - Discharge Pressure Set Point (Bar). Set via the HMI. PCV-9000 Gas Recycle Control Valve (Control Variable). PT-9029 Discharge Pressure Transmitter (Process Variable). Compressor Slide Valve. There are two control elements within this loop, the gas recycle control valve PCV-9000 and the compressor slide valve, working in conjunction to control the discharge pressure. The slide valve provides coarse control of the discharge pressure and operates with a wider deadband to the set-point (HMI adjustable). The hydraulic slide valve is controlled via load & unload solenoids. The compressor Slide Valve control has a significant dead band, thus allowing fine control to be performed by the Gas Recycle Valve. The Recycle Valve flow is constrained, thus allowing the Slide Valve to compensate for larger shifts in demand. PCV-9000 provides the fine control required to maintain a stable discharge pressure and operates within a tight deadband

10 The PLC will monitor the gas pressure at the compressor skid outlet by utilising pressure transmitter PT The PLC will modulate the Gas Recycle Valve PCV-9000 and the Slide Valve to maintain the discharge pressure set point. The set point can be adjusted on the selected HMI screen. Slide valve Operating Principles:- The slide valve controller compares the input signal from the pressure transmitter with the set point value. The loading and unloading relays are energised depending on the outcome of the comparison. A pressure signal lying below the load proportional band setting results in a continuous load signal being produced. As the pressure signal passes into the load proportional band the load signal begins to pulse off and as the pressure signal continues to rise, the mark space ratio of the load signal reduces linearly until, at the edge of the dead band, the control action is nil. The opposite applies to operation in and above the unload proportional band

11 8. Stopping Mode Normal Stop of the compressor can be initiated from either a pushbutton on the front of the UCP or via the HMI s. When a normal stop is initiated the following sequence is implemented: - The unload solenoids, XY-9011 & XY-9009 drive the slide valve back to its minimum position, ZT Once the slide valve is at minimum position (or a pre-determined timer has timed out, if minimum position not reached), the PLC system will remove the Run signal to the MCC for the main motor. The software suction pressure alarm, PAL-9003 is inhibited. The compressor unloading valve, XV-9001 is now automatically opened by the PLC system. The PLC system will fully open the gas recycle valve, PCV The hard-wired oil/gas differential pressure trip, PDALL-9013, bypass circuit is enabled and associated alarm inhibited. The PLC system will inhibit the operation of the standby lube oil pump. The lube oil re-circulating valve, XV-9022 is now automatically opened by the PLC system. Once the main motor has fully stopped (time delayed), the oil manifold isolation valve, XV will be automatically closed by the PLC system. The PLC system will lock the oil/gas differential pressure control valve, PDCV-9014, at the 50% position. The compressor drain valve, XV-9007 is now automatically opened by the PLC system, after a pre-determined time delay. The PLC system will re-enable the oil heater circuit. This will then allow the PLC system to maintain the oil temperature as detailed in section 3.1. The oil is now being heated and circulated around the system (duty lube oil pump will still be running) in preparation for a machine restart. After the main drive has been stopped the PLC system will prevent a restart being initiated for a pre-determined time period. After this time has expired the operator is free to restart the compressor. This completes the stop sequence

12 9. Trip Shutdown Logic The machine protection is provided by hard-wired safety relay circuits which monitor the critical process trips. These circuits operate as part of a Safety Instrument System (SIS) and are independent from the PLC control system. The SIS utilises trip amplifiers and safety relays to ensure a safe shutdown of the compressor in a trip condition, regardless of the PLC system operation. UCP hard-wired trips are as follows: High High Discharge Pressure, PAHH-9017 High High Discharge Temperature, TAHH-9019 Low Low Oil/Gas Differential Pressure, PDALL-9013 NB : PLC generated trips will include compressor casing high high vibration and main motor high high bearing temperature. When a trip condition occurs, the relevant safety relay will be latched in the trip state. This relay can be re-energised by pressing the trip reset button on the HMI, after all relevant trips have been returned to the healthy state. NB: - Trip safety relays are also automatically reset during the start sequence prior to starting the main drive motor. Each safety relay has an auxiliary contact interfaced to the PLC system for trip annunciation. When activated by one of the safety trip circuits, the main motor Safety Trip signal to the MCC will become open circuited thus stopping the main motor instantaneously. (The Run signal will also be removed.) In addition to the hard-wired trip action, the PLC system will immediately activate the following sequence of events:- Initiate the compressor stop sequence (as detailed in section 8). The PLC system will trigger the relevant trip message on the HMI s. After the shutdown logic has been initiated, the PLC will prevent a reset of the trip circuit for a pre-determined time period. After this period has elapsed and the associated trip alarms have returned to the healthy state, the operator can then reset the trip circuit by pressing the trip reset button on the HMI. After any faults or trips associated with the shutdown have been fully investigated and rectified, the operator will be free to restart the compressor, as described in section 6. This completes the Shutdown logic

13 10. Emergency Shutdown Logic Emergency shutdown can be initiated by various emergency stop pushbuttons, via a ESD signals and also initiated by the PLC watchdog timer relay. The first ESD signal is the panel mounted emergency stop (ES-1) compressor skid mounted emergency stop pushbutton (ES-1, the second is, and the third is the external plant ESD signal. All of these signals are utilised within a hard-wired safety relay circuit and operate independently from the PLC control system. When an ESD is initiated, the main motor Safety Trip signal to the MCC will become open circuited thus stopping the main motor instantaneously. (The Run signal will also be removed.) In addition, the PLC system will immediately activate the following sequence of events:- Stop the lube oil pump(s). Inhibit the lube oil heater. Open the compressor unloading valve, XV Open the recycle bypass valve, PCV Annunciate the shutdown on the HMI s. Turn off all internal PLC signals e.g. Pre-start completed. The operator can reset the emergency stop circuit by pressing the trip reset button on the HMI, assuming that all safety circuits are in a healthy condition. NB: A Safety Shutdown should only be activated in emergency situations and should not be used as the normal method of shutting down the compressor. This completes the Safety Shutdown logic for the compressor

14 11. Control System Control System Hardware The compressor control system takes the form of a Unit Control Panel (UCP), located in the Boiler Room, with a graphical operator interface (HMI) mounted on the front door and a Programmable Logic Controller (PLC) within. A duplicate panel mounted HMI will be supplied and located at the Turbine Control Room. PLC Hardware The PLC control platform is from the Allen Bradley ControlLogix PLC range. There is one CPU rack with local I/O. Refer to the PLC rack configuration in UCP drawing (SCW9856/EL022 Sheets 1 & 2) for PLC module details. HMI Hardware Two separate Panel View 1000 Plus HMI units provide the user operator interface. A Local/Remote key-switch on the front of the UCP allows the operator to lock out one HMI and make the other one available for all operations, subject to the various levels of password access. The HMI has a column of K programmable function key push-buttons on both vertical sides of the main display screen. Below the main display screen there are also two rows of F programmable function key push-buttons (as shown below)

15 System Communication The PLC system utilizes Ethernet for PLC / HMI communications, via an unmanaged Ethernet switch Control System Software PLC Software The following software package has been utilized for PLC system configuration and application logic: - RSLogix5000 Version HMI Software The HMI application database has been developed on RSView Studio Machine Edition Release

16 11.3. HMI Colour Schemes Instrument Loops Analogue Displays All instrument analogues will be displayed on the HMI. Each analogue s display will consist of the actual numeric scaled value (in engineering units) and a display background colour. The analogue display background colour is dependant on the signal status, as detailed below: - Green Steady - Signal healthy, no alarms. Red Steady - Signal in alarm. Red Flashing - Signal in alarm, loop fail. Motor Displays All motors status will be displayed on the HMI. The motor display background colour is dependant on the status of the motor, as detailed below: - Red Steady - Running. Green Steady - Stopped. Red Flashing Motor fail alarm. Valve Displays The status of all valves will be displayed on the HMI. The solenoid valve display background colour is dependant on the status of the valve, as detailed below: - Red Steady - Opened. Red Flashing Alarm condition. Green Steady - Closed. The modulating valve s position is displayed adjacent to the vale symbol (It should be noted that this is an inferred position, based on PLC positional output value)

17 11.4. HMI Screens Process Overview This screen is the default display after the HMI is powered up and it contains all the main process information for the compressor package. All the main gas and lube oil instrumentation is displayed on this screen, as well as motor and valve status indication. There are function keys on the HMI unit located below the screen, which enable navigation to other screens and also Sequence Start and Stop buttons

18 Gas System This screen displays all the process information for the compressor gas system. Function keys navigate the operator to the control screens for the compressor Slide Valve and the Recycle Valve

19 Lube Oil System This screen displays all the process information for the compressor lube oil system. Function keys navigate the operator to the control screens for the manifold oil temperature control valve and the oil/gas differential pressure control valve. The operator can select the duty lube oil pump and initiate a Pre-Start Sequence to prepare the compressor package for operation

20 Condition Monitoring This screen displays all the machine condition monitoring information for the compressor drive train, including main motor winding & bearing temperatures and also the compressor casing acceleration

21 Login Screen This screen provides engineers and operators with a suitable level of access to modify parameters for the PID controllers and the Slide Valve controller

22 PID Control This screen displays all the relevant information for the selected control loop and facilitates PID parameter adjustment. This screen will be utilised for the following control loops :- PIC-9000 TIC-9006 PDIC

23 Slide Valve Control This screen displays all the relevant information for the slide valve controller and facilitates parameter adjustment

24 Main Menu This pop-up menu displays all the screens available to operators and engineers