Taurus Group 60 - Manual (Page 17)

Turbomachinery Package Specification Taurus 60 Compressor Set and Mechanical Drive
Seal Gas System
The seal gas system consists of a primary and secondary gas face seal to prevent the
escape of process gas for each shaft end. The primary dry seal takes the full pressure
drop. It is used to provide the main sealing function. The secondary or backup seal acts
as an emergency barrier between the process gas and the atmosphere and operates at a
zero pressure differential.
The system can use clean and dry process gas or an independent clean and dry gas
source as seal gas. A customer-furnished separation gas source of air or nitrogen is
required to isolate lube oil from the seal gas. The separation gas must be available at all
times during lube oil pump operation.
Typical seal gas supply flow is 1.34 to 3.35 nm 3 /min
(50 to 125 scfm) at 689 kPag (100 psig) above maximum suction pressure, depending on
the compressor model and suction pressure.
The seal gas flow rates are metered by
maintaining a constant pressure drop across a flow-limiting orifice in each seal gas
supply line to each compressor seal capsule. Differential pressure switches provide low
flow alarm and shutdown functions.
The seal gas supply flow is higher than the primary seal leakage. The majority of the seal
gas flow travels past the compressor shaft labyrinth seals and into the compressor case.
This ensures the dry seal cavity is flushed with clean dry gas and that the dry seal
operates in a clean environment. The seal gas may be supplied from the compressor
discharge, preferably downstream of the gas cooler, provided the process gas is clean
and dry.
The onskid duplex seal gas coalescing filters are designed for typical clean transmission
pipeline conditions. If larger particle or liquid loads are expected, a larger off-skid filtration
system with a high pressure external seal gas supply is recommended. When the seal
gas is supplied from the compressor discharge but the compressor is not operating with a
pressure ratio (start-up, shutdown, or pressurized hold), there is no flow of seal gas
through the filters. During these times, the gas leakage across the dry seals is raw
process gas from the compressor case.
This is normally not a problem on clean transmission pipeline applications; however, it
may be an issue on new pipelines during initial operation, or on pipelines handling wet
and/or dirty gas. Under these conditions, an external high-pressure seal gas supply is
recommended. Leakage past the primary dry seals is measured by monitoring the
pressure drop across an orifice run. High leakage flow alarms and shutdowns are
provided by pressure switches. Primary and secondary seal vent lines must be vented by
the customer to a safe location.
Separation Gas System
A circumferential buffer air or nitrogen circumferential-segmented split-ring type seal
provides a barrier between the compressor bearing lube oil and the dry gas seals. It is
the most outboard component of the complete seal assembly.
Air flows between the seal
rings and the compressor stub shaft. Separation gas flowing past the outboard seal
mixes with lubricating oil and drains to the lube oil reservoir. Air flowing past the inboard
seal is vented through the secondary seal gas/buffer air vent.
The separation gas source may be clean dry shop air, instrument air, or nitrogen. The
system includes a hand valve for maintenance, a coalescing filter, a differential pressure
regulator, and pressure switches and gauges to monitor the separation gas differential
pressure. The system forms a positive separation between the lube oil and the dry seal.
Flame arrestors are supplied for the primary and secondary vents. Leakage seal gas and
separation gas must be piped away by the customer to selected safe areas.
© 2009 Solar Turbines Incorporated. All rights reserved. TPS60CSMD/309
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