### RE: High Desert PSD

Boyer, Jon

to:

Anita Lee

04/22/2008 04:34 PM

Cc:
"Balcazar, Ali"

Show Details

Anita,

Please read below for my responses to your question s. My comments are in blue. I’ll work on getting some of the specific temperature information you asked for and forward them to you.

If you have any further questions or clarification requests on this, please forward them to me.

Jon Boyer

Senior Environmental Scientist High Desert Power Project (760) 530-2303 (office) (760) 912-3007 (cell)

From: Lee.Anita@epamail.epa.gov [mailto:Lee.Anita@epamai l.epa.gov]

Sent: Tuesday, April 22, 2008 9:36 AM

To: Boyer, Jon Subject: High Desert PSD

Hi Jon,

Thanks for sending over the information and for our discussion today. As you suggested, I'm including my specific

questions in an email, so here they are:

1. Regarding Table 1 in the letter, I'm wondering i f you have some STG temperature information availab le - rather

than the more labor intensive time series of STG te mperature, would it be easier to pick out times and just note 

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...what the STG temperature was?

Specifically, it would be useful to know the STG te mperature for 10/25/07 for 10:14, 13:44, 14:00, 14: 06, 15:52,

and 23:43.

I’ll send you this information in a separate excel file.

And what is the temperature when startup is conside red complete? When steam is introduced into the STG (265-
300 degF), or when the SCR is at 464 deg F?

The temperature of the SCR is independent of the pr ocess that warms the steam turbine generator. Onc e the SCR reaches a stable 464 deg F, then we can begin t o add ammonia to the SCR. Lower than that temperat ure, ammonia flow will not decrease NOx emissions. The combustion turbines at these lower loads emits a hi gher NOx rate on a ppm basis due to incomplete combustio n in the engine. With SCR treatment during the st artup,

we lower the NOx emissions in the stack in this tim e period of higher emissions from the combustion tu rbine.

Once inner metal temperatures of the steam turbine reach the 265-300 degree range, we can start bringi ng the Steam Turbine Generator up to load, using one of th e combustion turbines to increase the rpms, slowly raising the rpms of each. This is not a fast process and c an take up to 3 to 4 hours until we reach a level w here we do not have to have any combustion turbine operating i n a startup mode. See Table 4.5 on page 17 for a s ummary of example startup recommendations for Hot, Warm, a nd Cold startups.

2. My understanding is that after Turbine 2 tripped , upon restart of Turbine 2, if it had a Cold Start duration limit,

Turbine 3 would not have had to be shutdown and res tarted. Would this be true if Turbine 2 had a warm start duration limit (2.6 hours) instead of a cold start limit (4.5 hrs) upon restart after trip? (If we def ine cold/warm/hot starts by STG temperature, depending on the tempera ture of the STG at 14:06 (when Unit 2 was restarted ), it
may be classified a "warm" start, if so, is that su fficient to avoid having to shutdown Unit 3?)

Our situation would not have been different if the restart of Unit 2 was characterized as a warm start . Keep in

mind that steam turbine drives the duration of a co ld startup, and its profile would remain cold until it is brought to

load. Had Unit 2 been a cold unit on the second fir e, we would have had until 18:36 to bring the unit into compliance. From that table, we would not have had to shutdown and restart Unit 3 in that instance. H owever, even with a cold characterization, if we were unabl e to start the Unit 2 for any reason, Unit 3 would have had to be shutdown at that point. We may not know we have a problem until we attempt to start the unit.

This is part of the reason High Desert Power Projec t has asked to remove the duration limits.

3. Temperatures on page 25 of Toshiba manual (#6) - is it appropriate for conditions at HDPP to use th ose 3 STG temperature ranges to define cold/warm/hot start (r ather than using a time since last firing of CTGs)? Or are the
various temperatures presented in the letter (265/3 00 deg F, 170/235 deg F) more appropriate for HDPP?

The table on page 25 indicates the rate of acceptab le temperature change for the steam turbine inner m etal temperature during pre-warming during a start, even a cold start. If the inner metal temperature is u nder 160F at the start of prewarming, then the guidelines recomm end that we only increase the inner metal temperatu re by 90 deg F/hr. Between 160 deg F and 210 deg F, the temp erature rising rate can be 135 deg F/hr. Above an initial temperature of 210 F, the inner metal temperature c an rise by 215 F/hr. Once the inner metal temperat ure reaches an acceptable range as described in the let ter, we can start the steam turbine and slowly brin g it up to speed. Table 4.5 shows the acceleration rate and a nticipated start times for a Hot, Warm, and Cold St eam Turbine Generator. The total recommended start tim e is approximately 258 minutes. Please take note t hat several factors described in the procedure text can extend or shorten the startup time.

Thanks Jon. Please let me know if any of these ques tions are not clear - it's a little challenging to describe! 

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...Anita

........................... US Environmental Protection Agency Region 9, Air Permits Office 75 Hawthorne Street (AIR-3) San Francisco, CA 94105

ph: (415) 972-3958 fax: (415) 947-3579

........................... 

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