Home > SNGII Sequence of operation

SNGII Sequence of operation

1328 Azalea Garden Rd.
Norfolk VA. 23502
757-855-6006
Fax: 757-855-3761

Date: November 2003

Contact: Product Support ( )

Contents

Scope
Sequence Of Operation
Interface Screens
Main Screen
System Values
System inputs
System Outputs
Output Test
Edit Setpoints
Shutdown/Restart Pressure
Set Oxygen Limits
ACD settings
Overrun and Membrane inlet tempurature Fault
Set System Clock
Maintenance Screen
Last five system Faults
 Stack Lights
Message Center
Fault Codes

Scope

This bulletin describes the general sequence of operation and user interface for the model SNGII Stationary Nitrogen Generators incorporating the BK15.3 high pressure booster with variable inlet pressure. Utilizing a variable inlet pressure booster, the SNGII minimizes generator warm up times by initiating product production under low capacity conditions. This means that product will flow within minutes from the system within the user adjustable purity limits. As the membrane bundle in the center of the system continues to warm, allowing reduced Oxygen content, the SNGII control system automatically ramps up the inlet pressure to the high pressure booster to provide the maximum system capacity at the preset purity setpoints.

Sequence of operation

Upon pressing the start button, SNGII control system will measure the current system outlet pressure. If the outlet pressure is below the preset restart pressure, the low pressure compressor contactor will be energized and the low pressure screw compressor will then begin to rotate and pressurize the membrane bundle. Prior to passing through the membrane bundle, the air will pass through the screw compressor aftercooler and a filter bank, then back through a shell and tube heater exchanger flooded with the hot oil from the low pressure compressor. This will assure a particulate free gas below dew point to the membrane bundle for maximum efficiency.
While the gas is passing through the membrane bundle, the Oxygen in the air stream passes through the membrane fibers allowing for a nitrogen enriched gas stream to be passed on to the high pressure booster system. The control system will monitor the inlet pressure to the booster and upon reaching a pressure greater than 75 psig, the booster motor contactor will be energized and the booster will rotate. The booster inlet pressure will then be ramped up to 99 psig and the automatic condensate drain and high pressure vent valve will be opened in order to purge the booster system. During this time, the onboard Oxygen monitor will measure the oxygen content of the gas being supplied to the high pressure system. Once the Oxygen content drops below the preset upper Oxygen limit, the high pressure vent valve will be closed and the system will begin to pump product down stream.
As the membrane bundle begins to warm up, its ability to separate out the Oxygen in the gas stream improves and the Oxygen content in the gas being supplied to the booster begins to decrease further. Once the purity drops below the lower preset Oxygen limit, the control system will slowly increase the booster inlet pressure. This increase in inlet pressure will provide for an increase in booster capacity, and with the increase in gas flow from the membrane bundle, the separation efficiency will decrease, increasing the Oxygen content of the product flow until in is once again between the upper and lower preset Oxygen limits. This process will repeat itself until the system is supplying the maximum capacity for the O2 limits entered. If the preset O2 limits are such that the booster inlet is increased to its maximum, any further increase in membrane temperature will have the effect of supplying a higher quality gas than required.
While the system continues to pump, the control system will periodically drain any accumulated liquids in the high pressure booster using the Automatic Condensate Drain (ACD) and will monitor the systems fault inputs. It should be noted that during an ACD event, the surge in gas through the booster may cause the gas purity to briefly exceed the preset limits. At this time the control system will automatically purge the booster block by opening the high pressure vent valve and decreasing the booster inlet pressure. This will quickly pull the purity back within limits at which point the pumping of product will continue.
Once the outlet system has been pressurized to the preset system shutdown pressure, the SNGII will shut down the booster and the low pressure system until the outlet pressure falls below the preset restart pressure setpoint.

User Interface Screens

Main Screen:

When power is applied to the SNGII unit, and the E-Stop switch pulled out, the on board touch screen display will illuminate and display the Main screen. The main screen will display the current outlet pressure, the current system time, and the current system status, in addition to the main start and stop push buttons for the unit. When power is cycled to the unit, its default status will be "System Off".
In addition to the Start and Stop buttons, the "Edit Setpoints" and "System Values" buttons will be available. Below the Edit Setpoints and System Values buttons, is a message display area in which the control system will indicate the current system status.
The main screen will also allow access to the system clock via the Set Clock button.

System Values:

Pressing the System Values button on the main screen will display the current system values screen. This screen will display the system status (from main screen) at the top and then list the current system values being read by the PLC as follows.
Current Purity: The Oxygen content from the onboard O2 meter. While the unit is running, this will be the purity of the gas leaving the membrane bundle and being supplied to the booster.
Membrane Temp: The inlet temperature of the membrane is monitored as a system fault.
Outlet Pressure: The current outlet pressure is measured and used to start and stop the generator system.
Booster Inlet: When the system is started, the booster inlet pressure is set to its minimum (99 psig) in order to optimize the time taken to generate the required nitrogen purity. As the membrane bundle warms and the oxygen content drops within the required range, the controller will ramp up the booster inlet pressure to provide maximum system capacity while maintaining the required purity.
Next ACD In: During operation, the high pressure booster automatic condensate drain will purge the condensate from the interstage and final separators. This value indicates when the next drain event will occur
Current Runtime: When the unit is not running, this value will indicate the length of time the unit operated. When in operation, this value will indicate haw long the unit has run. This value is used to trip the Overrun system fault.
Hourmeters: The low pressure feed air and high pressure booster hour meters are displayed for maintenance purposes
Maintenance Due: This message is displayed when the 100 hr maintenance timer expires. The Maintenance button should be pressed to access the maintenance requirements. Note: When this message is visible, the system status display will also flash the message "Maintenance is Due" in addition to the current system status.
Buttons
Back: returns to the Main screen
Faults: Displays the last five system faults screen
Maintenance: Displays the Maintenance Screen
Inputs : Displays the current system inputs screen

System Inputs:

The inputs screen displays the current status of the system switches as follows:
Booster Oil Pressure switch:A normally open pressure switch mounted on the back of the booster block, this switch is closed by the increasing oil pressure of the booster when it is started. If the booster oil pressure drops to 25 psig during operation, this switch will open and initiate a low booster oil pressure fault.
Booster high temperature switch: Since the booster has two final stage heads, the block has two normally closed final stage temperature switches wired in series to the second PLC input. If either of these switches opens during operation, the system will fault on High booster temperature.
Feed air temperature switch: A normally open temperature switch/gauge is mounted on the low pressure cabinet and measures the temperature of the air leaving the screw compressor sump. If this temperature reaches the switch setpoint the switch will close and initiate a high temperature fault on the low pressure system
Feed air/ Booster motor interlock: The motor contactors that supply power to the two drive motors contain switches that inform the control system of there status. If the control system has energized the contactors however the contactor has not closed due to over current or have been manually disengaged, the system will fault out using these inputs.

System Outputs:

The system outputs screen displays the status of the individual system loads:
During operation, this screen will indicate which system loads the PLC believes are energized and which are not. If an output is shown as On or "Energized" however the device physically appears to be de-energized, the system should be stopped and the device tested.
If the system is placed in the Off mode, then the "Test" button will become active to allow the output loads to be individually tested using the System Output Test screen.

System Output Test:

The system outputs screen displays the status of the individual system loads and provides test buttons next to each load indicator. Pressing the test button next to the load will energize the output on the PLC to which the load is attached. The load is energized for the period the button is depressed and automatically de-energizes when the button is release. Note: this page only available when the system is placed in the Off Mode (stop button on main screen pressed). If the load does not function when the respective test button is depressed, but the indicator light illuminates indicating that the PLC thinks the load is powered, then the problem at hand would be a physical wiring or defective load issue. If the indicator light does not illuminate when the test button is depressed, then the PLC operation has been halted or a PLC error has occurred.

System Setpoints

The system setpoints screen gives the operator access to the main system parameters. The adjustable system parameters are:
Outlet Pressure: Sets the system pressures at which the generator will start and stop automatically.
Oxygen Limits: During operation, the system will adjust the flow rate through the booster to maintain an product Oxygen content within these limits.
ACD Timers: Sets the interval between and duration of the automatic condensate drain system for the high pressure booster
Overrun, Mem Temp: Part of the system safety functions, the Overrun timer sets the duration in hours that the unit will be allowed to operate without reaching final system pressure. The Membrane temperature value sets the maximum temperature the inlet of the Membrane bundle can operate before tripping a system fault.

Shutdown /Restart Pressure

Touching the values in the shutdown and startup boxes will open a keypad to allow these values to be changed. One should note that the following rules apply:
The shutdown pressure setpoint cannot exceed 5000 psig.
The restart pressure value cannot exceed the shutdown value.
Unless a large volume is connected to the system outlet, the restart pressure should not be set within 500 psig of the shutdown pressure as short cycle operation will occur.

Oxygen Limits

The Oxygen limits setpoints are responsible for the way the control system adjusts the inlet pressure to the booster. After the unit has started, the membrane pressurized and the booster started at a minimum inlet pressure (99 psig), the control system will not close the high pressure vent valve and produce product until the O2 content has dropped below the upper limit.
After the unit is pumping product, the system will not increase the booster inlet pressure, providing maximum system capacity until the oxygen content drops below the lower limit.
Example: If the required nitrogen purity was 99%, the upper O2 limit should be set to 1.00% and in order to maximize capacity, the low limit should be set to 0.90%.

ACD Timers

During operation, the booster block compresses and cools the gas product. It will be possible during this process that liquid water and oil will be condensed into liquid form which must be removed. The booster block uses interstage and outlet separators to collect these liquids and an automatic condensate drain device to purge them from the system. The default value for the interval between drain events is its maximum of 50 minutes. This value can be reduced for testing purposes however surges in gas flow during drain events may cause purity spikes resulting in additional block purging. The drain period sets the time the automatic condensate drain is open during each drain event and should be set between 4 to 6 seconds.

Overrun and Membrane inlet temperature:

The Overrun timer sets the maximum period the unit will be allowed to operate without reaching the final pressure shutdown setting. This fault is design to prevent the unit from running continuously in the event the downstream piping system develops leaks that are greater that the systems capacity. The default setting is 8 hours and can be set as high as 24 hours.
The membrane over temp sets the maximum allowable membrane inlet temperature. The actual temperature will be controlled by a thermal valve after mounted after the oil to air heat exchanger in the low pressure feed air cabinet. In the event the thermal valve fails and excessive heat is supplied to the inlet air, the high membrane inlet fault will protect the membrane fibers.

Set Clock

The PLC contains a running clock that is used to time stamp system events. Pressing the set clock button on the main screen will open this screen and allow the systems calendar and clock to be edited. The date and time information will be displayed along with the last five system faults in the System faults screen, accessible from the System values screen. The date and time stamp information will also be used to stamp the last five system run times that are accessible through the external BC_LINK interface software.

System Maintenance

Available by pressing the "Maintenance " button on the System Values screen, the maintenance screen will display the amount of time left on the maintenance timer and the maintenance to be performed when the timer expires. (default setpoint of 100 hours). If the timer is allowed to expire, the amber light on the Stacklights will begin to flash and the message center will indicate "Maintenance Due". When the maintenance screen is accessed, the system hourmeters will also be displayed. The maintenance required at the 500 hour, 1000 hour, 2000 hour and 3000 hour intervals will also be available by pressing the respective button on the maintenance screen.

Last Five System Faults

Pressing the "Faults" button on the System Values screen will display the last five system faults and the date and time at which they occurred. Pressing the fault # on the left of each fault code will display the fault message that would have appeared on the screen during the fault trip. While displaying the fault message, the current message center information will be displayed at the top of the page.

Stack lights

The SNGII has a stack light mounted above its control panel. The individual lights in the stack will be illuminated in the following manner:

Unit status Stack light status
Unit not powered
Unit Power, Control PLC Halted		 No Lights On
Unit Powered, Stop switch pressed
System Off		 Green Light on Steady
System On
Running or standby with system Full		 Amber Light On
System On
Maintenance timer expired		 Amber light Flashing
System On, faulted Red light flashing

Message Center

During Operation, the line of text below the "Edit Setpoints" and "System Values" buttons on the Main Screen will display the current system status. While the unit is turned off, the message will simply indicate "SYSTEM OFF" however after the "Start" button has been pressed, the message center will indicate one of the following messages. In the event that the maintenance timer has expired, the standard message will be displayed however the "Maintenance Due: message will be flashed for a period of one second every 3 seconds. It should be noted that the message information will also be displayed on the top of other more commonly used display screens. The messages displayed are as follows:

EventMessage
System Powered/ Stop Button Pressed System: Off
System Powered/ Start Button Pressed
Outlet pressure below setpoint
unit about to start		 Caution: Unit Starting
System Powered/ Start Button Pressed
Feed Air Compressor Running Only		 Pressurizing Membrane
Feed Air Compressor running, Booster inlet pressure > 75 psig
Booster about to start		 Caution: Starting Booster
Booster running, Oxygen Content of product above
Upper limit, High pressure vent valve Open		 Purging Booster
Booster running, Oxygen Content of produce
below upper limit, High pressure vent valve closed		 Pumping Product
System has fully pressurized the outlet system
and has shut down, will restart if outlet pressure falls below restart setpoint		 System Full
System has faulted Faulted:Fault Code

System faults.

During operation, the system monitors the following fault devices. When tripped, they will generate fault codes that will be displayed on the message center and will flash the fault light next to the display screen and the red stack Light a pre-set number of flashes. The flashes will consist of the fault light being turned on for a period of 1 second and then of for a period of one second until the last flash which will only flicker the light and then hold it off for a period of 3 second before re-starting.

Fault Input Code # of Flashes
Booster Low oil Pressure X0 low_oil 2
Booster High tempurature X1 hptemp 3
Booster Low inlet pressure Analog low_inlt 4
Booster High inlet pressure Analog highinlt 4
Feed air High temperature X2 Lp_temp 5
Membrane High inlet tempurature Analog mem_temp 6
Overrun timer trip Runtimer OVERRUN 7
Booster air circuit breaker X4 bstr_cbr 8
Feed air circuit breaker X4 feed_cbr 8

When the system faults, in addition to the fault lights flashing, the interface screen will display a message elaborating the fault at hand and possible actions to prevent reocurrence. After the fault has been reset by pressing the Stop switch on the main screen the last five system faults can be displayed by pressing the "Faults" button on the system values screen. This button will display the Last Five Faults screen from which the operator can redisplay the messages. Click the fault code in the above table to see the message that would be displayed if the fault was redisplayed after the system was restarted. If the system was still faulted, the message center information at the top of the screen would still read "Faulted:faultcode".
** In order to prevent the unit running while an excessive leak has developed in the high pressure piping and distribution system, the control circuit is programmed to fault out if the setpoint pressure has not been reached within a pre-set period. The default setpoint is 8 hours runtime, resetable from the System setpoints screen.