Example:
A gas turbine lube oil system requires a flow rate of
15 gpm at 100 psig system pressure. The maximum
operating pressure is 115 psig. When the stand-by
pump accelerates from the idle condition to operating
speed, or in the case of the main oil pump shutdown,
the system pressure must be maintained within 10%
of the system pressure for at least 15 seconds.
Size an accumulator to supply oil in the case of pump
shuts down.
Sizing
The required volume of fluid needed from the
accumulator:
Vx = (15 gpm / 60) x 15 seconds x 231= 866.25 cu.
inches.
Minimum system pressure (within 10% of the system
pressure):
P3 = (100 x 0.90) + 14.7 = 90 + 14.7 = 104.7 psia.
Maximum operating pressure:
P2 = 115 + 14.7 = 129.7 psia.
Polytropic constant for Nitrogen: n = 1.4
Precharge pressure of the accumulator:
P1 = 70 % of P3 = 0.70 x 104.70 = 73.29 psia.
For more information, contact Joe Cheema, Senior Project Engineer,
at Fluid Energy Controls Inc.
E-mail: jc@fecintl.com
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By inserting the above values into the formula (1) the
following accumulator size V1will be obtained:
V1 = 7,878.28 cu. inches, or 34.11 gallon.
If the calculations do not give a standard size, the next
larger standard size should be picked. A larger
accumulator is always safer than a smaller one.
Figure 7. API 614 lube-oil console featuring 80 gallons, 500 psi
accumulator; Console flow rate: 1175 gpm. Industry application: power
generation. |
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