Page 340 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Best Practice 5 .15
Steam Turbine Best Practices Best Practice 5 .16

Best Practice 5.15Practice 5.15
Best

Single valve steam turbines in all services should have systems. They resulted in reduced main oil pump reduced
dedicated tachometers to monitor governor linkage turbine speed, which required the oil system motor driven
system condition. auxiliary oil pump to start. In these cases, the auxiliary
Single stage steam turbines have governor mechanical linkages pump did not start in time, causing a unit trip and revenue
and packing that can create friction loads which exceed governor losses that approached and in some instances exceeded
actuator forces. This can render the governor system unable to ac- $1m USD.
commodate steam system condition changes.
Dedicated tachometers allow operators to quickly detect reduced Benchmarks
speeds, and request maintenance activity to free up friction bound
This best practice has been recommended since the 1990s. Clients
bushings and packing before the reduced turbine speed can affect
have reported that past unit trips have been eliminated when ta-
plant operation.
chometers are installed and operators are instructed regarding the
Note that mechanical/hydraulic governors can be easily modified to
monitoring of these systems.
include local tachometers at a minimum cost.
Lessons Learned
Frequent, critical (un-spared), compressor train trips
have resulted from undetected friction-bound governor

B.P. 5.15. Supporting Material
Please refer to material in B.P. 5.14.

Best Practice 5.16Practice 5.16
Best
Always keep single valve turbine hand valves open and do in process unit ESDs costing the plant millions of USD in
not throttle them. lost revenue.
There is a misconception that closing certain hand valves on single Hand valves are too often observed to be closed on main lube oil
valve turbines will save steam and increase efficiency. pump steam turbines. This exposes the turbine to slow down on steam
While it is true that steam consumption can be reduced by closing header interruptions, which will require the auxiliary motor driven pump
hand valves, the efficiency of single stage turbinesdoes not exceed 35%. to immediately start without a drop in oil pressure to the trip level. Many
Single stage turbines are generally used to protect the plant against process unit shutdowns have occurred due to this scenario.
electrical power outages that would shut down critical pump or fan
services. Benchmarks
Closed hand valves expose the steam turbines to reduced speed This best practice has been used for all field auxiliary system audits
during steam header upsets and should always be fully open. since 1990, and has resulted in compressor train reliabilities exceeding
Finally, hand valves are designed to be only fully open or closed and 99.7% in critical compressor trains.
should never be throttled.

Lessons Learned
Keeping hand valves closed in critical services (oil system
main pump drivers, BFW, FD fan drivers, etc.) has resulted

B.P. 5.16. Supporting Material

Please refer to material in B.P. 5.14.

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