Compressor trips

For the standby pump start test, which is an important test to ensure the pumps transfer without large pressure swings, a check should be made to see if the relief valves lift or the pressure falls to a pressure one half the difference between the standby pump start pressure and the compressor trip pressure. The transient pressure is best measured with a multipen chart recorder. The chart speed must be high enough to fully display the pressure variation. While not as good as the chart recorder, a simple shop-made test setup can be substituted. A spare switch is temporarily connected to the same location as the other switches. This switch is calibrated to close at the threshold acceptance pressure. The contacts are wired to a test light through a seal relay. The purpose of the relay is to maintain the cir-... 

The nitrogen backup system was not reconnected. Later, when the instrument air compressor tripped, the auxiliary pneumatic power (nitrogen) was unavailable. Without the... 

Massive canyovo of liquid from the rdlux drum destroyed internals of the overhead compressor and damaged its turbine driver. The incident followed a fire at the product pump, whidi made it and its spare inopmhle. The accumulator level rose past the compressor trip level, but the trip failed to activate. 

Actual Event Train 5 MR Compressor trip on 12 April 2011 -approximately 101 MMSCF flar. ... 

Actual Event Train 4 C3 Compressor trip on 10 January 2013 -approximately 43 MMSCF flared. 

When a compressor is reported to be speed-limited, one should take a tachometer and compare the actual speed of the machine against the nameplate speed. The machinist who set the overspeed trip may have set it too low. The operators are careful not to let the compressor trip off. They avoid this by running at speeds 100 rpm to 200 rpm below the set trip speed. 

Frequently, a major unit shuts down when a compressor trips off. The cause may be low lube- or seal-oil pressure. The pumps providing the lube- and seal-oil pressure are typically spared (backed up). A steam turbine-driven pump is normally backed up by a motor-driven spare. The motor-driven pump should come on when the lube-oil pressure drops below a preset point. 

Operating procedures for the start-up of the process gas compression (PGC) system did not specifically instruct operators to re-verify the position of pneumatically assisted check valves before restarting the compressor following unexpected automatic compressor trips consequently, operators did not re-verify the position of the valve that failed. Re-verification might have enabled operators to observe possible indications of the fifth stage suction check valve s Imminent failure on June 22, 1997. 

The machine control system was set in accordance with the parameters determined during simulation prior to delivery to the site. Following re-routing and hook-up of the piping, the compressors were run to a maximum flow at 2.71 bar (absolute) and 480°C. The generator was disconnected from the grid and the expander tripped accordingly. 

The vibration characteristics, determined by use of the instrumentation, will serve as the basis for acceptance or rejection of the machine. API standards generally require that the equipment be operated at speed increments of approximately 10% from zero to the maximum continuous speed and run at the maximum continuous speed until bearings, lube-oil temperatures, and shaft vibrations have stabilized. Next, the speed should be increased to trip speed and the equipment run for a minimum of 15 minutes. Finally, the speed should be reduced to the maximum continuous speed and the equipment should be run for four hours. API does not require that the four hours be uninterrupted however, it is generally interpreted that way. The interpretation is one of the many test criteria to be discussed. It would seem that a break in the test at the midpoint is not the same as having it cut short five minutes from the end because the vendor s boiler took an upset that was not related to the compressor test. The ibration during the shop test is normally specified as the API limit of 1.0 mils peak to peak, or the value from Equation 10.1, unfiltcred. whichever is lower. 

The operational test of the lube system is, as the name implies, a functional test to check as many of the features as practical under running conditions. The first and last step is a demonstration of the cleanliness of the system. This is followed by a running test of a four-hour duration. The test should simulate the field operation with the compressor in every way practical. All equipment to be furnished with the lube system should be used in the test, including the standby pump start and trip switches. All other instruments should be used to demonstrate their operation. Prior to starting the four-hour run, the system should be thoroughly inspected for leaks and the leaks corrected. If no steam is available for a steam turbine (if one is used), the four-hour run can be made on the electric pump. However, every effort should be made to use an alternate source of energy such as compressed air, to operate the steam turbine. 

Trips should normally be designed so that they operate if the power supply is lost. If this will cause a dangerous upset in plant operation, then an alarm should sound when power is lost. Trips should be tested at startup if they have been worked on during a shutdown. Particularly important trips, such as those on furnaces and compressors and high-oxygen concentration trips, should always be tested after a major shutdown. 

Observations should be made that the plant is not being manually coaxed, that it is not humidifying and that the compressors have not tripped but are cycling under part-load conditions. Instruments should be indicating correctly. In cases where it is impractical to fully load the plant, ascertain that an appropriate amount of refrigeration is being employed. This situation is best avoided, as much of the plant is not being demonstrated to full capacity. 

Before the incident, the facility had experienced a power failure that led to the shutdown of an olefins unit. For several hours, a restart had been attempted and the compressor had tripped on high vibration at low speed. This caused the check valve to close, which placed additional stresses on the valve shaft. Failure to execute a smooth planned start-up was a key contributor to the timing of this incident. However, given the design defects inherent in the valve, an ultimate failure was inevitable. 

Permanent gamma ray scanning equipment was installed on each separator along with foam density and level recorders in the process control room. An emergency trip system that automatically shuts a valve in the appropriate separator gas line to isolate the separator from the compressor suction drums when a high foam level occurs was added also. A similar trip system was insulted in the gas feed line from the HP separator to the power station... 

Let s say we have a centrifugal refrigeration compressor, driven by a motor. The motor is tripping off because of high amperage. Should we open or close the suction throttle valve shown in Fig. 22.2 Answer— close it. Of course, both the evaporator vapor outlet temperature and the process fluid outlet temperature will increase. But that is the price we pay for having too small a motor driver on the compressor. Does this mean that when our home air conditioner gets low on freon, our electric bill drops Correct. But the price we pay is a hot home. 

Poor Jane The compressor s motor driver now trips off, on high amps In her efforts to avoid surge, she has run afoul of the real-world fact, that the motor amps required to drive a centrifugal compressor are approximately proportional to the molecular weight of the gas—in apparent contradiction to the Second Law of Thermodynamics. 

A reduction in volumetric efficiency reduces the work required from the driver. For reciprocating compressors, we intentionally reduce the volumetric efficiency, to reduce the load on the driver. Sometimes this is done to save energy sometimes this is done to prevent a motor driver from tripping off on high amps. 

Eventually, the fouling deposits on the rotor will become so thick that they start to break off, especially if you shut the compressor down for a few hours for minor repairs to the lube-oil system. When the compressor is put back on line, bits and pieces of grayish salt break off, and unbalance the rotor. At 8000 rpm, the high-vibration trip cuts off the fuel to the gas turbine, and the machine is taken off line for repair. 

Compressors also have vibration trips. These trips measure the amplitude of the vibrations—which, if they become excessive, will shut off the fuel, steam, or electricity to the compressor s driver. 

Compressors are also served by high-liquid-level trips in their upstream knockout drums. These high-liquid-level trips work in the same way as the low-level boiler trips discussed above, except that the mercuroid switch is activated by a rising, rather than a falling, liquid level so as to protect the compressor from a slug of liquid. 

In addition to following the load, protective overrides prevent the development of excessively low suction pressures (PIC-02), which could result in drawing oil into the compressor and from overloading the drive motor and thereby tripping the circuit breaker (KWIC). In order to prevent reset windup when the controller output is blocked from affecting the SIC set point, external feedback (EFB) is provided for all three controllers. 

Unfortunately the temporary filter was placed between the compressor and a low suction pressure trip. The compressor suction pressure was reduced to a vacuum and air intruded into the system. The air reacted within the system. A decomposition occurred further downstream and a major fire caused many months delay in the startup of this unit. 

Test running of compressors and drivers, making vibration trip, governor, and safety device checks, and any other operating tests and adjustments as required. 

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