1. TURBOEXPANDER OPERATING AND SHUTDOWN PROCEDURES
The following section provides basic startup, shutdown, and defrost procedures. See the CryoMachinery Commissioning Procedure for detailed installation, protection, and commissioning instructions. Refer to the plant P&ID for project-specific valve and equipment numbers.
2. TURBOEXPANDER STARTUP
It is assumed in the start-up procedure that the turboexpander and accessory system are completely isolated. Apply as appropriate.
NOTE
Warm gas and cold gas start-ups should be handled with different degrees of caution. There is considerably more energy available during warm gas startup. Throttling gas flow to the turboexpander may be required to prevent overspeed of the unit.
| 1 | Establish seal gas to the unit and verify all permissives. |
| 2 | Establish lube oil supply to the turboexpander and verify permissives. |
| 3 | Ensure that the recycle valve is fully open. |
| 4 | Adjust expander nozzles. Warm Gas Start-Up Set nozzles to fully closed. Cold Gas Start-Up Set nozzles to normal position. |
| 5 | Open the expander manual discharge block valve (if present). |
| 6 | Open the expander manual inlet block valve (if present). |
| 7 | Open the expander inlet slam valve. Throttle as necessary to maintain desired speed.
NOTE Avoid “No Run Zones.” When expander inlet valve is fully open, adjust expander nozzles to design setting. If high speed prohibits the opening of the nozzles, wait for the process to cool. As the process cools, the speed will drop for a given nozzle position. As the speed drops the nozzles can be opened farther. Continue to open until the design setpoint is reached. For nozzles with automatic control (if applicable), set the nozzle control in automatic. NOTE See the plant operating procedures for information on how to maintain acceptable plant cooldown rates. CAUTION Within acceptable cooldown rates, bring the machine speeds close to their design speeds quickly to avoid over-thrusting the rotors. |
| 8 | If this is an initial startup, make an hourly check of all system indicators. Note all changes in operation such as oil temperature, noise, vibration, and frost spots. |
3. SHUTDOWN
The following procedure addresses controlled and uncontrolled shutdowns.
| 1 | For a controlled shutdown, press the plant control system turboexpander stop button. |
| 2 | Lower the system pressure. Close the nozzles and then close the inlet slam valve. |
| 3 | (Controlled or Uncontrolled Shutdowns) Once the expander inlet slam valve has been tripped, verify that the turboexpander has stopped spinning.
NOTE Speed verification may not be possible if the plant trip involves a loss of power. When this is the case, physically inspect the inlet slam valve to make sure that the valve has closed. |
| 4 | When possible, maintain seal gas and oil. |
| 5 | If the turboexpander is going to be down for an extended period of time or if seal gas and oil are not maintained, block in the expander by closing the inlet and discharge manual block valves (if present) and open the defrost vent. |
| 6 | If the machine cools excessively as indicated by excess frost build-up on the plug-in cartridge, defrost the unit. |
| 7 | Always determine the cause of an uncontrolled shutdown and correct it before restarting the turboexpander. |
4. DEFROST
The following procedure addresses defrost of the expander. Defrost is needed to remove moisture from the expander and thaw the expander bearing if it is cold soaked. See Site Work Instructions Manual (SWIM) for a detailed defrost procedure.
| 1 | Seal gas and lube oil must be established prior to defrost.
CAUTION Ensure that the seal gas header pressure is adequate during expander defrost. If the defrost flow drops the seal gas header pressure too low, it is possible to trip the oil pump and not have lubrication to the bearings. |
| 2 | If manual expander inlet and discharge valves are present, close them. |
| 3 | Open the defrost outlet valve. |
| 4 | Open the defrost inlet valve. |
| 5 | Defrost until the expander bearing is warmer than 15°C (60°F) and acceptable process dewpoints are reached. |
| 6 | When defrost is complete, close the defrost outlet valve. |
| 7 | Close the defrost inlet valve. |
5. ALARM AND SHUTDOWN SETTINGS
Alarms and shutdowns are listed in the CryoMachinery Instrument Summary, located in the Product Definition Specification. In addition to avoiding overspeed, “No Run Zones” should be avoided. These No Run Zones are specific to each wheel design.
CAUTION
At certain speeds the impeller could be excited at one of its natural frequencies, causing fatigue failure of the impeller. A No Run Zone alarm alerts the operator if the compander speed remains in this range for a prolonged period of time. If this occurs, the operator should move the compander out of this speed range. When the compander speed enters this range, the alarm is disabled for three minutes to give the operator time to get through the No Run Zone without getting an alarm. Please see the Instrument Summary in the Product Definition document for any applicable No Run Zones.
Any applicable “no run zones”, as well as the No Run Zone Logic, are listed in the CryoMachinery Product Definition Instrument Summary.