Page 380 - Compression Machinery for Oil and Gas

Drivers Chapter 7 361

Auxiliaries
Sealing steam system—These systems are used with condensing turbines in
order to seal HP, LP packing from atmospheric pressure during start-up and
low load conditions.
Gland leakoff system—These systems are used with all turbines in order to
minimize outward leakage of steam from HP, LP packing to atmosphere and
toward bearing housings. Systems often include a gland condenser and steam
ejector in order. Negative pressure is obtained in packing drains in order to
encourage flow toward gland condenser, as shown in Fig. 7.49 of a typical sys-
tem for a condensing turbine application.
Lubrication system—System supplies lubrication oil, seal oil, control oil,
and/or trip oil to rotating equipment. System typically includes pumps and reg-
ulation system and reservoir.
Trip valve—Mounts ahead of steam chest connection is an integral part of
steam chest. Trip and trip and throttle valves serve to isolate steam from turbine
during a trip condition. T&T valves also serve to throttle steam to turbine for
start-up (Fig. 7.50).
Nonreturn valve—Use with extraction turbines to eliminate reverse flow
from extraction header if internal pressure in casing falls below extraction
pressure.
Surface condenser—Used with condensing turbines. Condenses exhaust
flow as well as leakoff flows from steam turbine.
Venting equipment—Part of surface condenser system. Hogger, first- and
second-stage ejectors used to remove non-condensible’s (air) from exhaust
steam flow during start-up and operation.
Full flow relief valves—Used in exhaust line of back pressure turbines to
protect exhaust casing from overpressure condition.
Rupture disks/atmospheric relief valves—Used with condensing turbines to
protect exhaust case from overpressure condition.
Governor control systems—Range from simple mechanical and hydraulic
speed control applications such as fly-weight governors and Woodward PG
governors, to sophisticated electronic governor systems which can be pro-
grammed to control speed, or a process variable. Since the early 1990s, industry
has trended toward supply of new turbines with electronic speed control as well
as electronic overspeed trip control.

Steam Turbine Maintenance/Reliability
Steam–Steam purity guidelines are followed by customers who are concerned
with the quality of steam used for steam turbines, such as shown in Fig. 7.51.
End-user reliability departments are interested in instrumentation including
radial vibration, phase angle, bearing metal temperatures, bearing oil throw off
temperatures, bearing load cells, oil analysis, rotor thrust position, grounding
brush current, and steam quality. These and many others are key points of