

                                  MEMORANDUM

Tetra Tech, Inc.
10306 Eaton Place, Suite 340
Fairfax, VA 22030
phone	703-385-6000
fax	703-385-6007

DATE: 		November 1, 2011

TO:			Paul Shriner and Lisa Biddle, USEPA
	
FROM:		John Sunda and Kelly Meadows, Tetra Tech

SUBJECT: 	Analysis of Intake Through-screen Velocity at Existing Closed Cycle Cooling System Intakes
As a companion to other analyses on intake velocity, Tetra Tech was tasked with analyzing the intake velocities at facilities utilizing closed-cycle cooling systems.

Table 1 provides a summary of the distribution of the through-screen velocity data reported in the detailed questionnaire (DQ) for power generation facility intakes that were included in the cost analysis and were classified as closed-cycle systems with cooling towers.  Table 2 provides similar data for all intakes reported in both the DQ and short technical questionnaire (STQ) but is limited only to facilities where the entire plant was classified as recirculating (i.e., does not include facilities classified as combination, other, etc.).  Both data sets result in similar screen velocity distributions.
                                    Table 1
           Distribution of Through-screen Velocity for Closed Cycle
                   Power Generation Intakes Used in Costing
                         Through-screen Velocity (fps)
                               Number of Intakes
                               Percent of Total
                                    <=0.5
                                      25
                                      42%
                               >0.5 - <=1.0
                                      11
                                      18%
                               >1.0 - <=1.5
                                       9
                                      15%
                               >1.5 - <=2.0
                                       3
                                      5%
                                    >2.0
                                      12
                                      20%
                                     Total
                                      60
                                     100%
Includes both retrofits and original CCRS

                                    Table 2
           Distribution of Through-screen Velocity for Closed Cycle
             Power Generation Intakes for Both STQ and DQ Intakes
                         Through-screen Velocity (fps)
                               Number of Intakes
                               Percent of Total
                                    <=0.5
                                      47
                                      45%
                                 >0.5 - 1.0
                                      23
                                      22%
                                 >1.0 - 1.5
                                       8
                                      8%
                                 >1.5 - 2.0
                                       7
                                      7%
                                    >2.0
                                      20
                                      19%
                                     Total
                                      105
                                     100%
Includes both retrofits and original CCRS

For comparison, Table 3 shows the distribution for all power generation intakes as reported in the TDD.
                                    Table 3
               Distribution of Design Through-Screen Velocities 
                      For All Power Generation Facilities
                         Through-screen Velocity (fps)
                         Estimated Number of CWISs[1]
                               Percent of Total
                                    <=0.5
                                      148
                                      17%
                                >0.5  -  1.0
                                      200
                                      22%
                                 >1.0 - 2.0
                                      316
                                      35%
                                    >2.0
                                      162
                                      26%
                                     Total
                                      893
                                     100%
            [1] Weighted estimates
            Source: Exhibit 4-17 of TDD

A comparison of Tables 1 and 2 to Table 3 indicates that a much larger portion of the subset of closed-cycle intakes would be able to meet a 0.5 fps velocity standard.  The reduced intake flow volume of a closed-cycle system is likely to be a contributing factor to this trend.

The intakes in Tables 1, 2, and 3 include both cooling water systems originally built as closed cycle plus those that have been converted from once-through to closed-cycle cooling (i.e., retrofits).  To determine if there is any difference in the intake velocity distribution between those two groups, a review of readily available information of facilities with retrofits was performed.  Currently, EPA has identified 10 facilities where closed-cycle retrofits have occurred.  Post retrofit intake through-screen velocity data was available from the technical surveys for those retrofits that occurred prior to the year 2000 and from site visit data for several of the more recent retrofits.  Table 4 identifies the retrofit plants, retrofit dates, and availability of screen velocity data.  The Jeffries plant reported data for two intakes.


                                    Table 4
                      Summary of Known Plants that have 
                       Performed a Closed Cycle Retrofit
Plant
                                     State
                                 Retrofit Year
                    Post Retrofit  Velocity Data Available
Wateree
                                      SC
                                     2006
                                      No
Nearman Creek
                                      KS
                                     2006
                                      No
Brayton Point
                                      MA
                                    Ongoing
                                      No
Linden
                                      NJ
                                   2002-2005
                                     NA[1]
Yates
                                      GA
                                     2004
                                    Yes[2]
McDonough
                                      GA
                                     2008
                                    Yes[2]
Canadys
                                      SC
                                 1972&1975
                                      Yes
Jefferies
                                      SC
                                     1985
                                      Yes
Jefferies
                                      SC
                                     1985
                                      Yes
Pittsburg Unit 7
                                      CA
                                     1976
                                      Yes
Palisades
                                      MI
                                     1974
                                      Yes
			1 Uses gray water as makeup source and no longer has an intake
			[2] Installed 0.5 fps wedgewire screens.

Table 5 summarizes the distribution of the through-screen velocities for the seven intakes at facilities where closed-cycle retrofits have occurred.  A comparison of the distributions in Table 5 to Tables 1 and 2 shows a similar proportion of intakes with through-screen velocities <=0.5.  The most noticeable difference is that no intakes in the known retrofit sample had through-screen velocities >1.0 fps compared to 40% and 33% in the larger samples in Tables 1 and 2 that include both retrofits and original CCRS systems.  

                                    Table 5
           Distribution of Through-screen Velocity at Intakes Where 
               Closed Cycle Retrofits are Known to Have Occurred
                            Through-screen Velocity
                               Number of Intakes
                               Percent of Total
                                    <=0.5
                                       3
                                      43%
                               >0.5 - <=1.0
                                       4
                                      57%
                               >1.0 - <=1.5
                                       0
                                      0%
                                    >1.5
                                       0
                                      0%
                                     Total
                                       7
                                     100%

                                       
                                       


Possible Followup Analysis

As seen in Table 5, two of the retrofit intakes were installed fairly recently and it's possible the design requirements imposed may have been influenced by recent 316(b) regulatory developments.  To help confirm these differences, it would be useful to attempt to identify additional intakes associated with closed-cycle retrofits.  The DQ survey includes questions regarding cooling towers that ask for the "Calendar Year Cooling Tower(s) Installed" on a per Cooling Water System (CWS) basis.  It should be possible to identify other "pre-year 2000" closed-cycle retrofits where through-screen velocity data is available by combining this "year installed" data with EIA data regarding the year(s) generating units came online for those plants with closed cycle systems.  While there may be some difficulty identifying which towers (or CWSs) are associated with each generating unit, for those where the generating units clearly pre-date the cooling towers, the likelihood that a retrofit occurred will be high.


