Just so that everyone is aware, the units at Station 4 can be operated at levels above their rated horsepower of 4,000 during periods of lower ambient temperatures.  Clark ambient rating increase from 100% torque at 100degF to 108% torque at 40degF.  I realize that this rating is weather dependent, but the horsepower is available if weather temperatures permit.
	To obtain ambient rating as ambient temperatures permit, three unit modifications would have to be implemented; these might be handled by unit control programming only.  Clark allows ambient rating when jacket water and lube oil temperatures can be driven down proportionally to 135 and 125 degF respectively.  Jacket water and lube oil control valves may be needed to reduce jacket water and lube oil temperature as ambient temperature permits, and unit control programs would require modification to accommodate ambient ratings.  
	There may be environmental emission issues such as permitting the site for the higher horsepower.  Also, previous checks with Legal indicated these units could operate in the ambient rated zone if the units were purchased with this capability; ambient rating capability was part of the original purchase and stated as such in the unit purchase orders.
	Again, I am just making sure everyone is aware of the unit capability at Station 4.
Ken N Young



From:	Eric Faucheaux/ENRON@enronXgate on 10/24/2001 02:11 PM
To:	Darrell Schoolcraft/ENRON@enronXgate, Rich Jolly/ET&S/Enron@ENRON, Arnold L Eisenstein/ENRON@enronXgate, Dan Pribble/ENRON@enronXgate, Gary Maestas/Enron@EnronXgate
cc:	Morgan Gottsponer/ENRON@enronXgate, Steven January/ENRON@enronXgate, John R Keller/ENRON@enronXgate, Ronald Matthews/ENRON@enronXgate, Dennis Alters/ENRON@enronXgate, David Roensch/ET&S/Enron@ENRON, Kenneth Young/ET&S/Enron@ENRON 

Subject:	FW: TW Sta. 4 capacity in 3 unit scenario 

Viewing Tip: maximize window and increase zoom to 150% to get better view of figures below (View, Zoom..., select percent number and type 150)

Based on recent capacity concerns or inquiries by E&C, Gas Control and Operations regarding Compressor Station 4 capacity in a 3 unit Red Rock Project, Planning and Optimization have re-evaluated models to put these concerns to rest.  Figures 1 and 2 below detail steady state results from modeling that Planning used for determining the respective capacities, as have been provided in the past.  

Figure 1 shows the pipeline simulation maximizing horsepower at CS 1, 2 & 3 to pull discharge pressure off of CS 4, thus allowing CS 4 to operate within its Rated HP (11800 BHP).  Note: CS 1, 2, & 3 in the first diagram Figure 1 are modeled conservatively using 83% efficiency; however, Gary Choquette represents that having evaluated the horsepower curves made available by the vendor, there is still much horsepower available for compression at CS 1, 2 & 3.  The compression efficiencies at the stations may be achieved as high as 87%, thus providing more capacity to pull gas from CS4.  It is customary Planning practices to error on the conservative side until facilities are installed.  Once installed and the true performance can be realized then the opportunity shall exist for further optimization.

Based upon the pipeline model with CS1, 2, & 3 at 83% efficiency, the range of conditions that may be expected at CS4 are suction pressures between 769 - 776 psig with discharge pressure at about 923 psig.  The HTSCompress model for CS4 has been modified to closely match field performance testing.  These results shown in Figure 2 also represent that the 1230 MMcfd capacity will be more than achievable even at the lesser operating conditions shown.

However, if any capacity shortfalls might be experienced, several measures can be implemented to improve conditions (some of which are currently planned).
1.	Operate San Juan Junction pressures at or above 960 psig (currently achievable, measure would provide higher suction pressure to CS4) 
2.	Perform engine and compressor overhauls at CS4(work is slated for March-April 2002 timeframe)
3.	Install/modify scrubbers and inlet piping at CS4 to reduce inlet piping losses (work is slated for post Red Rock, scrubbers from CS 1, 2, & 3 will be relocated to CS4)
4.	Relocate evaporative cooling skirts from CS 1 or 2 after Red Rock unit installation to CS 4 to prevent horsepower derating due to high ambient temperatures.
5.	Modify programming at CS4 to optimize speed control maximizing available HP (this done at existing CS 1 & 2 have realized 1% throughput improvements).  Also modifying unloading sequence could be considered.
6.	Pig/clean main and loop lines from CS 5 to CS 4 (pipeline efficiency in this segment is lower compared to segments due west, cleaning would increase suction pressures at CS4 or allow lower junction pressures.)
7.	Maximize available HP at CS1, 2, & 3 (all horsepower at 86% efficiency as shown in second diagram Figure 1)

Should further discussion be required, do not hesitate to give us a call.  A conference call can be scheduled if needed; otherwise, save this information for August 2002.  EF

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