Tetra Tech, Inc.

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

DATE: February

6, 2009 TO : Paul Shriner and Jan Matuszko, EPA FROM : John Sunda, SAIC and Kelly Meadows, Tetra Tech SUBJECT: Fine Mesh Screen Use and Feasibility Tetra Tech and SAIC were tasked with summarizing the technical issues regarding cooling water intake screens utilizing fine mesh screens and wedgewire screens) the effect of fine mesh screens on intake velocit y and the size of the intake structure. Fine Mesh Traveling Screens in Facilities with fine mesh traveling There are three primary

sources of information on the use of fine mesh screens at facilities: EPA’s industry questionnaire data Electric Power Research Institute (EPRI) The industry

questionnaire (issued fine mesh screens , but did not request the survey asked respondent s having a mesh size of 5 mm or source to identify

the number of facilities with screens with fine mesh of 2 The survey

data indicate d that, o

1 In this analysis , the term fine mesh less. 

### MEMORANDUM

10306 Eaton Place, Suite 340

February 6, 2009 Paul Shriner and Jan Matuszko, EPA John Sunda, SAIC and Kelly Meadows, Tetra Tech Fine Mesh Screen Use and Feasibility Tetra Tech and SAIC were tasked with summarizing the current use, feasibility technical issues regarding cooling water intake screens utilizing fine mesh (both traveling screens and wedgewire screens)

. 1 Following the results of this research is a discussion of the effect of fine mesh screens on intake velocit y and the size of the intake structure. Fine Mesh Traveling Screens in Use in United States traveling screens primary sources of information on the use of fine mesh screens at EPA’s industry questionnaire data , summary documentation developed by the Electric Power Research Institute (EPRI) , and technology vendors

. industry questionnaire (issued b y EPA in 2000 ) requested information about use of but did not request detailed information about the mesh size s to check a box if they use d fine mesh screens , defined mm or less. As a result, the survey data could not be used as a to identify

the number of facilities with screens with fine mesh of 2 mm or less. that, o f the 227 facilities that completed the detailed
the term fine mesh is defined as screens with an aperture size or slot width of 2.0 mm or feasibility , and (both traveling the results of this research is a discussion of the effect of fine mesh screens on intake velocit y and the size of the intake structure.

primary sources of information on the use of fine mesh screens at

summary documentation developed by the requested information about use of

mesh size

. In stead, defined as the survey

data could not be used as a

mm or less. that completed the detailed aperture size or slot width of 2.0 mm orquestionnaire , 7 faciliti es (3.1 percent) reported using fine mesh screens with a mesh size

of ≤5 mm. In 2007, EPRI published a report on fine mesh utilization ( Fish Protection at Cooling Water Intake Structures: A Technical Reference Manual) , which provide d summary- level information on facilities where fine mesh screens have been installed (or in some cases, only tested) . This report provides a list of facilities that employ fine mesh screens with a mesh size less than 2 mm: Facility name Me sh

size Waterbody type 1 Design intake flow range 1 Fuel type 1 State Barney Davis 0.5 mm Tidal river/ estuary 500 MGD

– 1 BGD Natural gas TX Big Bend 0.5 mm Tidal river/ estuary > 1 BGD Coal FL Prairie Island 0.5 mm Freshwater river 500 MGD

– 1 BGD Nuclear MN Brayton Point 1.0 mm Tidal river/ estuary > 1 BGD Coal MA Brunswick Station 1.0 mm Tidal river/ estuary > 1 BGD Nuclear NC Som erset Station 1.0 mm Great Lake > 500 MGD Coal NY
1 Wa terbody type , design intake flow range, and fuel type identified by EPA. The traveling screen vendor Passavant Geiger identified 3 facilities that employ fine mesh intake facilities : Barney Davis , Big Bend , and Somerset (Anderson 2008). Fine mesh traveling screens are also used at numerous hydroelectric facilities throughout the US , but these facilities are not included in any anal ys es, as the operations of these screens may

be fundamentally

different than for screens at cooling water int akes. International Use of Fine Mesh Traveling Screens Facilities with fine mesh traveling screens A review of sales and installation data from Passavant Geiger indicates that most traveling screens installed in Europe and elsewhere overseas by their firm are fine mesh (Anderson 2008)

. Attachment B contains a list of hundreds of Geiger installations dating back to 1937 ; the me sh size for the majority of these installations is in the 1mm to 3mm range , with some as low as 0.5 mm and v ery few exc eeding 4 mm. Design considerations for European screens The ty pical design for intakes in Europe is slightl y different than for U

. S

. installations , often employing an intermediate set of mechanically raked bar racks with more closel y spaced bars in between the 3

- 4 in ch spaced bars (ty picall y called the trash rack) and the fine mesh screens. The second set of bar racks serves to protect the fine mesh screens and help reduce loading of larger debris on the traveling screens. The intent of this design is to minimize condenser fouling and optimize condenser efficiency and downtime ( i.e., minimizing injury

to fish was not a primary design consideration). Use of a second set of bar racks in addition to new traveling screens would increase traveling screen technologycapital costs b y about 75%, while O&M costs would be much lower than for the

downstream traveling screens as there are fewer moving parts (Anderson 2008). Capital costs could be even significantly lower if the cleaning rake s ys tem can serve mult iple screen channels. Such intermediate bar rack s ys tems could potentially be retrofitted on existing U

. S

. plants , but w ould be dependent on site design ; EPA has not analyzed this technology

for the proposed rule. The installation data does not give through

- screen intake velocities for these screens, which are generall y a center
- flow design

. Some of the design data needed to calculate approach velocities is available , but other information is not provided

. Making so me basic assumptions, 2 estimates for some of the < 2.0 mm installations in the data result in approach velocities of approximately 0.5 to 1.0 fps. A corresponding calculation of through

- screen velocities for conventional traveling screens 3 with approach ve locities of 0.5 to 1.0 fps would be 1.2 to 2.4 fps. Fine Mesh Wedgewire Screens EPRI(2007) provides several examples of facilities that have installed fine mesh wedgewire screens. Facility name Me sh

size Waterbody type 1 Design intake flow range 1 Fuel ty pe 1 State Logan 0.5 mm Tidal river/ estuary < 100 MGD Coal NJ We stchester RESCO 0.5 mm Freshwater river < 100 MGD Solid waste NY Cope 2.0 mm Freshwater river < 100 MGD Coal SC 1 Wa terbody type , design intake flow range, and fuel type identified by EPA. As with fine mesh traveling screens, fine mesh wedgewire screens are in use at a variety of facilities. Attachment D presents a list of w edgewire screen installations p rovided by the Hendrick S creen Company . Unfortunately , s lot width data was not provided for most installations

. In general, Hendrick Screens has installed many 1.75 mm mesh i nstallations in the west ern stat es of Washington, Oregon, and California due to Federal requirements for fisheries protection , with m any of these installations being associated with hydroelectric dams , using either flat panel or T

- screens (I sbill 2008)

. Hendrick Screens was not aware of any specific operational problems at any of their installations

. Other example s provided b y the vendor include a facility with 2 mm slot width on the Lehigh River (Conectiv Power), another with 3 mm on the Chattahoochee River (McDonough Plant cooling tower makeup), and one with 3.175 mm on the Ohio River (Buckeye Water

2 Assumptions include a freeboard of 10 feet, available screen area of 83% of the channel cross

- section, and that the mesh percent open area is 50%. These assumptions are based on best professional judgment for a ty pical screen configuration. 3 In center

- flow screen designs, critical data to calculate intake velocity vary. Here, a comparison to standard traveling screens is provided as a reference point. Typ ically, the through

- screen velocity for a center
- flow screen would be lower, as there is a larger wetted screen surface.District) (Isbill 2008)

. Unlike trave ling screen retrofits, T

- screens can be designed with a

low through

- screen velocity , thus limiting the debris accumulation rate. Itis a general design requirement that T

- screen installations have a maximum through

- screen velocity of 0.5 fps. Mesh Size and Sediment The traveling screen vendor representative for Eimco stated that 0.5 mm fine mesh requires low screen velocities (i.e., approximately 0.5 fps ) and that retrofitting a high velocity traveling screen with 0.5 mm mesh c ould be very difficult on large rivers such as the Mississippi and Missouri Rivers ( Gathright 2008)

. The Missouri River is known for having high levels of suspended sediment, which can create problems in “blinding ” of the intake screens. Blinding of the screens occurs when the sediment and debris accumulate on the screens at a rapid rate. If increased screen rotation and backwashing is not sufficient to remove the sediment , then the desired cooling pumping rate may not be sustained, which would force the facility to reduce the pumping rate or cease withdrawals, leading to a reduction (or cessation) of power generation

. Ty pically , the problem of screen blinding in rivers with high sediment loading diminishe s as the screen mesh size approaches 1.0 mm and does not present a problem if 2 .0 mm screens are used (Gathright 2008)

. The primary

reason for th e difference in performance of screens with different mesh sizes is due to the ty

pical distribution of sand particle size in the river water. In a study of s and grain size distribution from the Fraser River Port in British Columbia , 90% of the sand particles were < 0.5 mm in size, with the percent content increasing rapidly below 0.5 mm (Sm ith 200 7)

. The particle size distribution graph shows that 0.5 mm was somewhat of an inflection point where grain size content diminished more graduall y as the size increased, approaching 0% at 2 mm. Thus, a screen with a mesh size of 0.5 mm would capture a significant portion of the suspended material , while a screen with a mesh size near 2.0 mm wo uld capture very little of it. Problems with larger , less

- dense debris particles such as leaves will not be affected as much by mesh size, since such debris particles will be captured on the screen regardless of mesh size and , therefore, no changes in operati on would be expected with finer mesh. In summary , EPA recognizes that high sediment waterbodies pose a challenge for fine mesh screens. However, a mesh s ize of 2.0 mm has been shown to be effective in handling the high sediment loads. EPA also acknowledges that facilities located on high sediment rivers face constant challenges related to sediment, as existing intake screens may become clogged or suffer premature failure or condenser tubes may require more frequent cleaning.Effects on Through
- Screen Velocity

When retrofitting from a coarse mesh screen to a fine mesh screen, the open area of the screen is reduced, which leads to an increase in the through

- screen velocity. 4 To avoid increased impingement that would result from an increase in intake velocity, EPA assumed that a facility

would enlarge its existing intake structure to regain the lost open area, thereb y accomplishing the installation of fine mesh while retaining the same through

- screen velocity. As discussed in the TDD, EPA evaluated regulatory alternatives that contain compliance requirements for maximum mesh sizes and/or maximum through

- screen velocities. At an existing facility , replacin g a traveling screen with one that has a different mesh size or a different through

- screen velocity affects the size of the screen surface area necessary for compliance. The screen area available for intake flow is the total area of the wetted surface of the screen material (i.e., effective screen area) and does not include screen framing, screen panel edges, or other structural elements. Replacing a conventional traveling screen with a fine

- mesh traveling screen As discussed above, replacing a coarse mesh screen with a fine mesh screen will reduce the effective screen area and may also increase the through

- screen velocity. Tables 1 and 2 illustrate the magnitude of the change in the required effective screen size associated with different screen technology mesh sizes and through

- screen velocity requirements. To illustrate these effects, EPA anal yz ed two through

- screen velocity scenarios: one where the maximum allowable through

- screen velocity is 2.5 fps (Table 1) and another where the maximum allowable through

- screen velocity is 0.5 fps (Table 2). 5 EPA also anal yz ed three fine mesh slot width scenarios: 2.0 mm, 1.0 mm, and 0.5mm. The tables calculate the “c ompliance s creen area f actor” which represents the increase in effective screen area needed to comply with the applicable mesh size and through

- screen velocity requirements. For example, a compliance screen area factor of 3.0 means that the area of the compliance screens (i.e., the new CWI S) will need to be three times larger, and thus a new intake s ys tem with a similar design would need to be roughly three times the size of the existing one. A factor of 1.0 means the existing intake is already large enough and that screen upgrades would simply involve th e replacement of existing screen units. The existing sy stem design parameters, especiall y the design through

- screen velocity , have a direct effect on the compliance screen area factor. Table 1 shows the increase in screen area required for intakes when the maximum allowable through

- screen velocity is 2.5 fps for two different fine mesh slot sizes (2.0 mm and 0.5 mm) and for two existing

4 Assuming that the intake flow volume remains constant. 5 If, after installing fine mesh screens, the new through

- screen velocity exce eds the given threshold, then the CWIS must be expanded to a point w here the velocity requirement is met. Table 2 shows a scenario where a facility would both install fine mesh screens and be required to meet a 0.5 fps threshold.through

- screen velocities (1.5 fps and 2.5 fps). 6 The anal ys is assumes that the existing

screens are conventional 3/8 i nch (9.5 mm) coarse mesh traveling screens. Table 1. Screen A rea Increase Factors with a Ma ximum Through - Screen Velocity of 2.5 fps Mesh Size (mm) Percent Open Area (%) 1 Ex isting Through
screen Velocity (fps) Replacement

Screen Velocity Increase Factor2 C ompliance

Screen Area Factor3 2.0 50 1.5 1.4 1.0 2.0 50 2.5 1.4 3.4 0.5 33 1.5 2.1 3.1 0.5 33 2.5 2.1 5.2 1 Open area of the selected mesh size. For reference, a 9.5 mm screen (coarse mesh) has an open area of 68%. 2 Change in through
- screen velocity resulting from replacing a coarse mesh screen with a fine me sh screen

. 3 Assumes new larger intake screens have a reduced design through
- screen velocity of 1.0 fps. Larger intake screens (and larger intake) are assumed to be needed if design through
- scree n velocity for replacement screens exceeds 2.5 fps. As can be seen in Table 1, facilities with existing through

- screen velocities close to or below the median value of 1.5 fps would require no increase in screen area for 2mm mesh screens and a size increa se factor of 3.1 for 0.5mm mesh screens . Facilities with existing through

- screen velocities close to the value of 2.5 fps would require screen size increase b y a factor of 3.4 for 2mm mesh screens and an increase in size by a factor of 5.2 for 0.5mm mesh screens . Table 2 shows that the screen area requirements increase considerabl y when the maximum allowable through

- screen velocity is reduced from 2.5 fps to 0.5 fps. Table 2. Screen A rea Increase Factors with a Ma ximum Through - Screen Velocity of 0.5 fps Mesh Size (mm) Percent

Open Area (%) 1 Ex isting Through
screen Velocity (fps) Replacement

Screen Velocity Increase Factor2 Compliance

Screen Area Factor3 2.0 50 1.5 1.4 4.1 2.0 50 2.5 1.4 6.8 0.5 33 1.5 2.1 6.2 0.5 33 2.5 2.1 10.3 1 Open area of the selected mesh size. For reference, a 9.5 mm screen (coarse mesh) has an open area of 68%. 2 Change in through
- screen velocity if replacing existing screens with similar screen design. 3 Assumes all compliance screens have a design through
- screen velocities equal to 0.5 fps. For facilities with existing through

- screen velocities close to or below the median value of 1.5 fps, 2mm mesh screens increase the required screen area 4.1 and 6.2 times the existing intake screen area, respectivel y. For facilities wi th an existing through

- screen

6 The selected velocities represent the median value reported for existing Phase II intakes in the 316(b) industry survey (1.5 fps) and a typical design value for older intakes (2.5 fps). Note that these values are the assumed existing through

- screen intake velocities.velocity of 2.5 fps, 0.5mm mesh screens increase the required screen area were 6.8 and 10.3 times the existing intake screen area, respectively. 7 Implications for facility costs In general, the capital costs for replacement of existing traveling screens with fine mesh traveling screens are about the same as for replacement with coarser mesh screens, but the operations and maintenance (O&M) costs may be about 30% greater (Gathright 2008). This difference is primarily due to en ergy

requirements and equipment wear due to continuous use and increased screen rotation speed. 8 If the analy sis estimated a total screen area required that is greater than what is available at the existing intake (i.e., the compliance screen area factor is greater than 1.0), a new intake with a larger screen area will be needed. EPA assum ed the new larger intake would have a through

- screen velocity of 1.0 fps when estimating the screen area factor and technology

costs for a new larger intake. 9 The size and cost of this new screen technology

are directl y related to the required screen surface area. 10 Technical feasibility of fine mesh screens and expanded CWISs In an August 2008 presentation to EPA, EPRIstated that field deploy ment of fine mesh traveling screens with favorable screen operating performance (i.e., can properly handle debris loading) i ncluded eight power plant sites in the US (Dixon 2008). 11 These plants represent various waterbody types, flows, fuel typ es, configurations, and locations throughout the country

. The wide variety of operating conditions at facilities with fine mesh traveli ng screens suggests that with proper design and operation, these screens are technically feasible at most facilities. 12

7 Similarly , even if a coarse mesh screen with a 1.5 fps existing through

- screen velocity were subject to a maximum allowable through

- screen velocity requirement of 0.5 fps, there would be a required increase in screen area by a factor of 3.0. 8 EPA notes that its co mp liance cost estimates consider the increased operating energy requirements and equipment replacement costs for fine mesh traveling screens. 9 The design through

- screen velocity of 1.0 fps for new expanded intakes is not a regulatory requirement ; it simpl y reflects a best professional judgment (BPJ) design standard for a new intake structure. In part, EPA assumed that a new facility would be designed using a more conservative through

- screen velocity to avoid operational problems involving debris accumulat ion 10 See Chapter 8 of the TDD, which describes the costing model used for the proposed rule. Module 3 contains the costs for expanding an existing intake structure. 11 The facilities listed were Hanford Generating Project, Barney Davis, Indian Point, Big Bend, Brunswick, Somerset, Dunkirk, and Prairie Island. 12 Further, the technology vendors stated that the distribution of fine mesh traveling screens has been limited due to the fact that few facilities have been required to install fine mesh screens. EPRI also concluded that the potential for future use of fine mesh screens is favorable , as handling procedures and screen designs have continue d to improve (Dixon 2008).However, a s the size requirement of the compliance screens increases (i.e., as the screen

compliance factor increases), the potential fo r problems associated with the availability of space to construct a larger intake also increases. This is especially true for shore

- based intake technologies, since water depth is generally relativel y shallow, thereby requiring any screen expansion to cov er a proportionall y longer length of shoreline. 13 The availability

of additional shore space at many existing intakes may be limited due to existing structures and other considerations. 14 In some cases, the expanded intake structure would be built in front of the existing intake, which may lead to interference with vessel traffic or other uses. In anal yz ing various compliance options involving fine mesh screens, EPA anal yz ed an option where all facilities would install 2.0 mm mesh screens and found that ap proximately

33% of facilities would be forced to expand their intake structure b y more than 5 times its current width. Another option where all facilities would install 0.5 mm mesh screens would have required as many as 68% of facilities to expand their i ntake more than 5 times its current width.

13 New construction would be lateral along the shoreline; costs to deepen the existing intake wells as a way to expand the screen area would be expensive. 14 Examples might include limited ownership of shoreline property or conflicting uses of the shoreline.References

Anderson, Dave. Passavant Geiger. Telephone Contact Record. Contacted by John Sunda , SAI C on October 13, 2008. Smith, David, Thurber Engineering Ltd. Technical Aspects of River Sand. Summary of Dredged Sand Tests

. March 27, 2007. Accessed on November 20, 2008 at website: http://www.fraserportauthority .com/pdf/2.%20Thurber%20Engineering%20Ltd.%20

- %20Technical%20Specifications%20of%20River%20Sand.pdf EPRI

. Fish Protection at Cooling W ater I ntake Structures: A Technical Reference Manual

. Palo Alto, CA: 2007. 1014934. Dixon, Doug. EPRI . Black, Jon. Alden. Fine

- mesh Traveling Screens. Presentation for EPRI

- EPA Meeting. August 26, 2008. Gathright, Trent. Eimco. Telephone Contact Record. Contacted by John Sunda, SAI C on October 14 , 2008. Isbill, Mike. Hendrick Screen Company. Telephone Contact Record. Contacted by John Sunda, SAI C on October 8 , 2008.