DEVELOPMENT OF SUCTION SCOOPS FOR MIDAMERICAN ENERGY COMPANY S GEORGE NEAL NORTH CIRCULATING WATER PUMP INTAKE STRUCTURES

Transcription

1 DEVELOPMENT OF SUCTION SCOOPS FOR MIDAMERICAN ENERGY COMPANY S GEORGE NEAL NORTH CIRCULATING WATER PUMP INTAKE STRUCTURES by Tatsuaki Nakato Sponsored by Burns & McDonnell 9400 Ward Parkway Kansas City, Missouri IIHR Technical Report No. 429 IIHR Hydroscience & Engineering College of Engineering The University of Iowa Iowa City, Iowa July 2003

2 ABSTRACT Pump suction scoops were developed and model tested using 1:12 scale models for MidAmerican Energy Company's George Neal North Station to improve circulatingwater pump performance at extremely low river stages. The suction scoops developed were found to reduce head losses at the pump suction bells because they accelerated the pump-approach flows gradually and distributed them uniformly around the pump-suction bells. Furthermore, there were no common free-surface vortex problems surrounding the pump columns because the scoop ceilings prevented any free-surface vortices from forming. ACKNOWLEDGMENTS The model investigation reported herein was conducted for and sponsored by Burns & McDonnell in Kansas City. The project owner was MidAmerican Energy Company. The author thanks Mr. Terry Larson, Burns & McDonnell and Mr. Leon Gertsch of MidAmerican Energy Company s George Neal North Station for their unfailing cooperation throughout the course of this study. The author is also indebted to a variety of IIHR personnel. The IIHR Hydroscience & Engineering shop crew, led by Mr. Darian DeJong, built and modified the model numerous times and demonstrated their skilled craftsmanship. Mr. Michael Kundert also contributed to this project with his skilled draftsmanship with shop drawings. ii

3 TABLE OF CONTENTS Page I. INTRODUCTION 1 II. SIMILARITY LAWS 4 III. SUCTION SCOOP DESIGNED FOR EXISTING UNIT-1 INTAKE 6 IV. SUCTION SCOOP DESIGNED AND TESTED FOR EXISTING UNIT-3 INTAKE 11 V. SUCTION SCOOP DESIGNED AND TESTED FOR EXISTING UNIT-2 INTAKE 29 VI. RECOMMENDATIONS 47 REFERENCES 50 LIST OF TABLES Page Table 3.1 Test result for free-surface vortex formation for Unit-1 intake with suction scoop (note that no surface beam was in place) 10 Table 4.1 A summary of test conditions under as-built conditions and with suction scoop conducted for existing Unit-3 intake 18 Table 4.2 A summary of test results for Cases 1 and 5 for the Unit-3 intake 24 Table 5.1 A summary of test conditions for the as-built conditions and with suction scoop conducted for existing Unit-2 intake 35 Table 5.2 A summary of test results for Cases 1 and 5 for the Unit-2 intake with a vacuum lift wall opening of 3 ft 37 Table 5.3 A summary of test conditions for the as-built conditions and with suction scoop conducted for existing Unit-2 intake with a vacuum lift wall opening of 2 ft 40 Table 5.4 A summary of test results for Cases 1A, 2A, 5A, and 6A 43 Table 5.5 Free-surface vortex types observed in the as-built Unit-2 intake (Case 1A) 46 LIST OF FIGURES Page Figure 1.1 Principal components of suction scoop 3 Figure 3.1 Plan and elevation of existing Unit-1 intake bay 7 Figure 3.2 Pump suction-bell profile of existing Unit-1 intake pump 8 Figure 3.3 Suction scoop layout designed for existing Unit-1 intake 9 iii

4 Figure 3.4 Classification of free-surface and sub-surface pump-intake vortices 10 Figure 4.1 Plan and elevation of existing Unit-3 intake bay 12 Figure 4.2 Pump suction-bell profile of existing Unit-3 intake pump 13 Figure 4.3 Model of existing Unit-3 intake (viewed from upstream) 13 Figure 4.4 Model of existing Unit-3 intake (frontal view) 14 Figure 4.5 Model of existing Unit-3 intake (viewed through backwall) 14 Figure 4.6 Model of existing Unit-3 intake showing model vacuum system 15 Figure 4.7 Model of existing Unit-3 intake with trashracks and traveling screen installed 16 Figure 4.8 Existing Unit-3 intake traveling screen layout 16 Figure 4.9 Suction scoop layout designed for existing Unit-3 intake 19 Figure 4.10 Discharge-river stage relationships obtained in Cases 1 and 5 25 Figure 4.11 Swirl-river stage relationships obtained in Cases 1 and 5 25 Figure 4.12 head losses measured in Cases 1 and 5 26 Figure 4.13 Warm-water supply lines through vacuum lift wall 27 Figure 4.14 Diffusers in vacuum chamber seen through backwall windows 27 Figure 4.15 Relationships between velocity head and total head obtained in Cases 1 and 5 28 Figure 5.1 Plan and elevation of existing Unit-2 intake bay 30 Figure 5.2 Pump suction-bell profile of existing Unit-2 intake pump 31 Figure 5.3 Frontal view of existing Unit 2 intake model 31 Figure 5.4 Rear view of existing Unit-2 intake model 32 Figure 5.5 Side view of existing Unit-2 intake model 32 Figure 5.6 Rear view of model suction scoop for Unit-2 intake 33 Figure 5.7 Suction scoop layout designed for existing Unit-2 intake with 3-ft wall opening 34 Figure 5.8 Discharge-river stage relationships obtained in Cases 1 and 5 38 Figure 5.9 head losses measured in Cases 1 and 5 39 Figure 5.10 Suction scoop layout designed for existing Unit-2 intake with 2-ft wall opening 42 Figure 5.11 Discharge-river stage relationships obtained in Cases 1A and 5A 44 Figure 5.12 head losses measured in Cases 1A and 5A 45 iv

5 DEVELOPMENT OF SUCTION SCOOPS FOR MIDAMERICAN ENERGY COMPANY S EXISTING GEORGE NEAL NORTH CIRCULATING WATER PUMP INTAKE STRUCTURES I. INTRODUCTION The existing fossil-fuel power plant circulating-water pump intake for George Neal North station, owned by MidAmerican Energy Company (MAEC), is located on the left bank of the Missouri River near Sioux City, Iowa. This intake structure for three electric power-generating units consists of six pump-intake bays with two pump bays for each unit. Unit 1 pumps are rated at 37,500 gpm (84 cfs) each, Unit 2 pump are rated at 65,000 gpm (145 cfs) each, and Unit 3 pump are rated at 145,000 gpm (323 cfs) each. The total combined circulating-water cooling capacity is 495,000 gpm (1,102 cfs). To cope with decreased plant availability due to potential circulating-water system failure during low river levels, MAEC was considering construction of a new circulatingwater pump intake. IIHR Hydroscience & Engineering (IIHR) conducted a physical model study of the new water intake (Nakato, et al. 2002). In the meantime, MAEC also considered improving reliabilities of the existing pumps under extremely low river water levels, especially during the wintertime when the release of water from Gavins Point Dam in South Dakota upstream from the power plant is reduced. Subsequently, IIHR was contracted to develop suction scoops for the existing circulating-water pumps at each unit. There is a very unique feature in Units 2 and 3 pump bays in which each pump bay is completely sealed and vacuum is applied therein to raise the water-surface elevation within the pump bay for gaining the net positive suction head. When Gavins Point Dam was constructed in late 1950, along the Missouri River in South Dakota, severe river-bed degradation occurred downstream from the dam. This lowering of the river bed had caused problems with the existing intakes, which necessitated application of vacuum within these pump bays to maintain minimum submergence depths and to satisfy Net Positive Suction Head (NPSH) requirements. 1

6 Conventional vertical pumps employ pump bells to withdraw water radially and accelerate flow toward pump impellers. If a pump is installed at the center of a sufficiently large water body, the present technology may function appropriately. However, the space available for the real pump-intake structure is very limited. The normal pump-sump layout is rectangular, and the pump is installed near the backwall. Therefore, the pump-approach flow generally cannot be distributed uniformly around the pump bell because flow in the pump sump approaches the bell from one direction. The suction scoop under development is intended to accelerate the pump-approach flow gradually toward the pump bell and to distribute it evenly around the bell. A basic layout of the suction scoop is shown in figure 1.1 which consists of floor and backwall splitters to suppress formation of boundary-attached subsurface vortices, floor corner fillets, a sloping scoop ceiling to accelerate pump-approach flow, and a horizontal scoop ceiling to prevent any vertical flow components from approaching toward the pump-suction bell. Often flow-straightening vanes are added to the scoop at the scoop entrance to remove lateral velocity components. The suction scoop reduces head losses at the pump suction bell because it accelerates the pump-approach flow gradually and distributes it uniformly around the pump-suction bell. Furthermore, there will be no common free-surface vortex problems because the scoop ceiling prevents any free-surface vortices from developing adjacent to the pump. The first IIHR-designed suction scoop was implemented in the four pump intake bays at the MAEC s Council Bluffs Unit-3 intake during the period between December 1989 and January Since then, the pumps have been operating superbly without any problems. IIHR constructed two existing pump intake models for Units 2 and 3 at an undistorted geometrical scale of 1:12 within the new intake model basin that was utilized to test the new pump intakes (Nakato, et al. 2002). Suction scoops for Units 2 and 3 were then designed based on IIHR s previous experience in suction scoop designs (Nakato, et al. 1996; Nakato and Goss 1998), and they were model tested for their performance. Two identical suction scoops for Unit-1 pumps were designed, but not model tested. During the suction-scoop development strong emphases were given to determining the lowest river water level under which pumps could be operated satisfactorily. 2

7 Backwall Fillet Floor Corner Fillet 45 Deg. Slope Flow Turning Vanes FLOW Pump Bell Backwall Splitter Floor Splitter Line of Sloping Scoop Ceiling Upstream Edge of Suction Scoop C L PLAN VIEW Structural Beams Vertical Baffle Wall Curtain Wall to Prevent Free-Surface Vortex Formation Horiz. Ceiling Sloping Ceiling Vane FLOW Floor Splitter SECTION VIEW Figure 1.1 Principal components of suction scoop 3

8 II. SIMILARILTY LAWS All the existing intake models were built at an undistorted geometric scale of 1:12, which means that the ratio of all the lengths in every model to their corresponding lengths in the prototype was equal: L r =L m /Lp = 1/12 (3-1) where L r : Length ratio L m : Model length L p : Corresponding prototype length Due to the free-surface flow in the models, it was necessary to include the gravitational influence into the calculations of the model discharges, velocities, and times. Therefore, the Froude number similarity between model and prototype discharges was used. The Froude number ratio, F r, must be unity: Fm F r = = 1 (3.2) F p F r : Froude number ratio F m : Froude number of the model F p : Froude number in the prototype where V F = (3.3) 1 ( gl) 2 V: Characteristic flow velocity g: Gravitational constant L: Characteristic length With equations (3-2) and (3-3) the velocity and the time ratios are given by V = L = (3.4) m V r = V p 1 2 r 4

9 T r T 1 = m = L 2 r = (3.5) Tp The discharge ratio follows from (3-4) as Q Q = = V A = L L = L = (3.6) 1 5 m r r r r r r Qp 5

10 III. SUCTION SCOOP DESIGNED FOR EXISTING UNIT-1 INTAKE The existing Unit-1 intake bays are 47 ft 6 in. long and 9 ft 8 in. wide, as shown in figure 3.1. Note that there is no vacuum chamber provided for the Unit-1 intake bays. The pump-suction bell shown in figure 3.2 is 58-1/2 in. in diameter and the floor clearance of the suction bell is 18-3/8 in. The distance from the backwall to the center of the pump column is 5 ft 7 in. On the basis of previous IIHR experience in designing suction scoops for vertical pumps (Nakato 1992; Nakato, et al. 1996; Nakato and Goss 1998), a suction scoop for the Unit-1 intake was designed. The designed suction scoop shown in figure 3.3 includes the following components: 1. The existing backwall is too far from the edge of the pump bell. Therefore, it should be moved upstream by 1ft 6 in. There is no need to build a new backwall over the entire intake depth. Either a step, 1 ft 6 in. deep, 1 ft 6-3/8 in. high, and 9 ft 8 in. wide, or a 1 ft 6-3/8 in. high vertical backwall as a part of the suction scoop, should be fabricated. 2. Install a triangular-shaped floor splitter, 9 ft 6 in. long, 2 ft wide, and 1 ft tall in the center of the pump bay to suppress floor-attached subsurface vortices. 3. Install a triangular-shaped backwall splitter, 2 ft wide, 1 ft deep, and 1 ft 6-3/8 in. tall, on the backwall to suppress flow circulations around the pump-suction bell. 4. Install two triangular-shaped sidewall floor-corner fillets, 9 ft 6 in. long, 1 ft wide, and 1 ft tall, along two sidewalls of the pump bay to suppress sidewall-attached subsurface vortices. 5. Install a triangular-shaped, backwall floor corner fillet, 9 ft 8 in. long, 1 ft wide, and 1 ft tall, along the backwall floor corner to suppress backwall-attached subsurface vortices. 6. Install two vertical triangular-shaped backwall corner fillets, 2 ft wide, 2 ft deep, and 1 ft 6-3/8 in. tall, in two corners of the backwall to eliminate dead areas. 7. Install a suction-scoop ceiling (a 9 ft 6 in. long horizontal ceiling connected to a 5 ft 7 in. long sloping ceiling). A hole, slightly larger than the bell diameter, say, 0.5 in., should be bored in the horizontal ceiling and its gap should be sealed by a circular rubber gasket that is anchored to the bell mouth. 8. Install five, 2 ft long, flow-turning vanes at 1 ft 8 in. intervals underneath the sloping portion of the suction-scoop ceiling in order to straighten angular pumpapproach flows. 6

11 PLAN VIEW OF ONE BAY OF UNIT 1 9'-8" CL DISCHARGE PIPE SECTION B-B 47'-6" 29'-1" 12'-10" 5'-7" EL ' 12'-11" 9'-2 1/8" EL ' 4'-10" 4'-10" 1'-3" B 3" 5'-2" FLOW CL A STOP A LOG 9'-8" B CL TRASHRACK 1'-3" 47'-6" 18'-5" CL FINE SCREEN GUIDE 12'-10" 5'-7" 1'-0" 29'-1" 12'-11" 9'-2 1/8" 5'-2" 4'-1/8" 3'-8 7/8" EL ' 1'-0" CL DISCHARGE PIPE MEAN HIGH WATER EL ' EL '-0" 10'-9" 2'-0" 2'-0" CONSTANT WATER LEVEL EL ' 7'-9" EL ' EL ' 1'-0" 6'-3" 9'-3" 4'-9" 2'-9" MEAN LOW WATER EL ' MIN. LOW WATER EL ' EXTREME LOW WATER EL ' 3'-3" 12'-9" 2'-0" 13'-3" 3'-3" 1'-11 5/16" '-1 7/16" 11'-7 9/16" 32'-9" 8" 10'-3" 1'-6 3/8" 10" EL EL RIVER BED EL ' " 4'-10 1/2" 3'-1 3/4" SECTION A-A Figure 3.1 Plan and elevation of existing Unit-1 intake bay 7

12 4'-9" 6 1/4" 4'-10 1/2" 58.5" DIAMETER SUCTION BELL FOR EXISTING UNIT 1 (PROTOTYPE DIMENSIONS) Figure 3.2 Pump suction-bell profile of existing Unit-1 intake pump In order to obtain the lowest river stage under which the existing Unit-1 pumps with suction scoops can still run without air entrainment, the Unit-3 intake model with a suction scoop in place was utilized. The Unit-3 intake has two pump-approach-flow bays that become a single bay. One of the bays was used to simulate the Unit-1 intake. The Unit-3 discharge (145,000 gpm) was scaled down to match the Unit-1 discharge (37,500 gpm) for each of the two bays. The river stage was first set at EL ft above Mean Sea Level (MSL) and incrementally reduced until detrimental air ingestion occurred. The test result indicated that a free-surface vortex harmful for satisfactory pump operations forms just upstream from the suction-scoop inlet at a river stage as high as EL ft, as shown in table 3.1. At a river stage of EL ft, significant air was found to burst into the pump. The formation of a free-surface vortex just upstream from the Unit-1 suction scoop was completely suppressed by means of a surface beam, as shown in figure 3.3 (see figure 3.4 for vortex classification). Once this surface beam was installed, the river stage was able to be lowered down to EL ft without any air entrainment to the pump. The pump-sump elevation just upstream from the surface beam under this river stage was 8

13 EL ft. Therefore, it is recommended that the surface beam shown in figure 3.3 be included as part of the suction-scoop design for the Unit-1 pump intake. SUCTION SCOOP DESIGNED FOR EXISTING GEORGE NEAL NORTH UNIT-1 INTAKE 5'-6" 9'-6" 1'-6" 1'-0" 7'-6" 1'-0" FLOW A 1'-8" 1'-8" 1'-8" 1'-8" 1'-6" 1'-6" 1'-0" 2'-0" 1'-0" Five 2' Long Vanes Backwall Floor Corner Fillet Floor Splitter 58.5" Dia D B B C C Sidewall Floor Corner Fillet Pump Bell 7 3/4" Backwall Splitter 2'-0" 1'-0" PLAN VIEW OF MODIFIED EXISTING UNIT-1 INTAKE D 2'-0" 2'-0" 2'-0" New Backwall Vertical Backwall Corner Fillet 1'-0" 3'-10" 3'-10" 1'-0" 9'-8" A Minimum river water level to avoid air entrainment EL EL Minimum sump water level to avoid air entrainment 1'-0" SURFACE BEAM: needed to suppress free-surface vortex formation 3'-0" 4'-0" 2'-6" 2'-0" 3'-6" 8'-6" 1'-0" 1'-6" Horizontal Ceiling Vanes 2'-1 3/4" 5'-7" 1'-0" 15'-0" 5'-7" Sloping Ceiling (angle: 10 ) 5'-6" 9'-6" 1'-6" 1'-6 3/8" EL ' SECTION A-A 1' 1' 2' 1' 1' SECTION B-B SECTION C-C SECTION D-D Figure 3.3 Suction scoop layout designed for existing Unit-1 intake 9

14 SURFACE SWIRL TYPE 1 VORTEX PULLING DEBRIS BUT NOT AIR TYPE 4 SURFACE DIMPLE TYPE 2 VORTEX PULLING AIR BUBBLES TO INTAKE TYPE 5 ORGANIZED CORE AS OBSERVED BY DYE TRACE TYPE 3 VORTEX PULLING AIR CONTINUOUSLY TO INTAKE TYPE 6 TYPE 1 TYPE 2 TYPE 3 WEAK SWIRL (NOT COHERENT CORE) (a) Classification of free-surface vortices ORGANIZED DYE CORE (COHERENT DYE CORE) ORGANIZED AIR CORE (AIR COMING OUT OF SOLUTION) d:\tn\fcad\surface-subsurface_version3.f cw (6"-9") (b) Classification of boundary-attached subsurface vortices Figure 3.4 Classification of free-surface and sub-surface pump-intake vortices River Stage Comments Vortex Classification above MSL (ft) Surface dimple for a short period Type Very small air bubbles withdrawn into the pump Type Very small air bubbles withdrawn into the pump Type 3 & Type Air bubble ingestion twice in 10 sec Type 3 & Type Air bubble ingestion twice in 10 sec Type Air bubble ingestion more frequently Type Air bubble ingestion almost continuously Type 5 Table 3.1 Test result for free-surface vortex formation for Unit-1 intake with suction scoop (note that no surface beam was in place) 10

15 IV. SUCTION SCOOP DESIGNED AND TESTED FOR EXISTING UNIT-3 INTAKE The existing Unit-3 intake bays are 56 ft long with two 11 ft-2 in. channels feeding each pump bay, as shown in figure 4.1. The pump-suction bell shown in 4.2 is 108 in. in diameter and the floor clearance of the suction bell is 2 ft 3 in. The distance from the backwall to the center of the pump column is 6 ft 9 in. Similarly to the Unit-1 suction scoop, IIHR designed a suction scoop for the Unit 3 intake. As mentioned previously, the Unit-3 intake chamber is vacuum controlled to gain the net positive suction head; thereby the pump-sump water surface is raised approximately 6 ft which equates to EL 1056 ft when the low water elevation of EL 1050 ft occurs. The existing Unit-3 intake model was built at an undistorted geometrical scale of 1:12 within the new intake model basin, as shown in figures 4.3 through 4.6. As can be seen in figure 4.6, the model pump-bay vacuum system was installed and vacuum was applied by means of a shop vacuum. Model trashracks and traveling screens were also included in the model in order to accurately predict head losses through them (see figure 4.7). In order to maintain the head-loss coefficient equal both in model and prototype, Papworth's empirical relationship (Papworth 1972) was utilized. The fine screens were modeled for the normal flow condition (145,000 gpm) with the lowest river water level of EL 1050 ft. The prototype wire-cloth dimensions of the screens are such that the opening is 3/8 in., the wire diameter is 1/8 in., and the percent open area is 56.24%. A modified Reynolds number defined by Papworth is given by R e* = Vb ν( 1 s) (4.1) where V = mean approach screen velocity; b = wire diameter; ν = kinematic viscosity of water; and s = solidity parameter = 1 - (screen percent open area) = = in this case. This modified Reynolds number is given by Papworth in terms of K(1-s) 2 /s, where K = head-loss coefficient. The wire cloth designed for this study (Mesh 2 square- 11

16 mesh wire cloth with a wire diameter of in.) produces a K value of 1.31 that is very close to 1.25 in the prototype. The model trashracks (3/8-in. thick, and 3-in. deep bars on 3-in. centers in full size) were also included in the model design (see figure 4.7). 16'-10 1/16" 16'-0" 5'-3" 5'-3" 9'-6 3/8" 6'-6" 3'-3/8" PLAN VIEW 6'-6" 3'-3/8" ELEVATION END VIEW DETAIL OF EXISTING FILLET (Need two of - one opposite hand) (Make both removable) 24'-10" 11'-2" 2'-6" 11'-2" EL ' EL ' 4'-3" EL ' 5'-11" EL ' 5'-11" 3'-3/8" 30.0 EL ' 3'-0" 6'-6" EL ' 5'-3" 7'-2" 7'-2" 5'-3" SECTION B-B 42'-6" 14'-7" 18'-3 3/4" 9'-7 1/4" 10'-4 3/8" 2'-0" 2'-0" 6'-8 3/4" 2'-0" OPNG 76.5 EL '-11" 8'-9" 6'-9" SECTION A-A FLOW 9'-6 3/8" 4'-3" 13'-0" A 5'-3" 7'-2" 7'-2" 5'-3" 6'-6" 9'-6 3/8" 13'-6" CL VACUUM LIFT WALLS 1'-0" 1'-0" 1'-0" 2'-0" CONSTANT WATER LEVEL EL ' 4'-3" 2'-0" BULLNOSE 2'-0" 2'-0" 13'-6" MEAN HIGH WATER EL ' 19'-3" 3'-3" 10'-3" 2'-3" EXTREME EL ' R1'-0" 1'-3" 11'-2" 11'-2" 1'-3" 2'-0" R1'-3" 2'-6" 3'-3/8" 29'-9" 3'-0" 32'-9" 40'-0" 16'-0" 32'-4 3/4" 1'-0" 6" B MEAN LOW WATER EL ' VACUUM LIFT WALL MIN. LOW WATER EL ' 3" 3" 18.2 A UNIT 3 CL TRAVELLING SCREEN GUIDES CL TRASH RACK GUIDES B PLAN VIEW 56'-0" VACUUM LIFT WALL CL DISCHARGE PIPE 8" 10" 8'-3" 2'-0" 9'-3" 80 2'-6" 2'-6" 7'-6" 2'-1" 2'6" 13'-6" 6'-9" 6'-9" 6'-9 7/16" 5'-8 7/16" 13'-6" CL STOP LOG AND FINE SCREEN GUIDES 10'-0" RIVER BED: EL ' SEE DETAIL SAME PAGE SECTION C-C 8'-3 1/4" C C 5" 4'-0" 24'-10" Figure 4.1 Plan and elevation of existing Unit-3 intake bay 12

17 67.00" 56.40" 52.25" R20.620" 98.00" " 108" DIAMETER SUCTION BELL FOR EXISTING UNIT 3 (PROTOTYPE DIMENSIONS) Figure 4.2 Pump suction-bell profile of existing Unit-3 intake pump Figure 4.3 Model of existing Unit-3 intake (viewed from upstream) 13

18 Figure 4.4 Model of existing Unit-3 intake (frontal view) Figure 4.5 Model of existing Unit-3 intake (viewed through backwall) 14

19 Figure 4.6 Model of existing Unit-3 intake showing model vacuum system 15

20 Figure 4.7 Model of existing Unit-3 intake with trashracks and traveling screens installed A 11'-2" 7" 10'-0" 7" 4'-0" 3" 3'-6" 3" 3" 10'-0" FLOW VERTICAL MEMBERS 6"X3"X25'4.5" (NEED 4 PER SCREEN) CROSS BRACES 3"X3" TYPICAL (12 PLACES/FRAME) 3" 25'-4 1/2" 10'-0" SCREEN MESH ON UPSTREAM AND DOWNSTREAM FACES OF FRAME 3" 3" UPSTREAM FACE OF REVOLVING SCREEN FRAME DOWNSTREAM FACE OF REVOLVING SCREEN FRAME 5'-4 1/2" SCREEN BOOT A DOWNSTREAM FACE OF REVOLVING SCREENS NEED TWO OF 3" EL ' CL HEADSHAFT R2'-2" 1 1/2" 1'-4 1/2" 3 1/2" 11" SECTION A-A R5 1/4" 5 11/16" Figure 4.8 Existing Unit-3 intake traveling screen layout 16

21 At the beginning of modeling efforts, multiple tasks listed in table 4.1, including both existing conditions and proposed suction-scoop modifications were specified by MAEC. The suction scoop designed for the Unit-3 intake is shown in figure 4.9, including the following components: 1. Install a triangular-shaped floor splitter, 15 ft long, 3 ft wide, and 1 ft 6 in. tall in the center of the pump bay to suppress floor-attached subsurface vortices. 2. Install a triangular-shaped backwall splitter, 3 ft wide, 1 ft 6 in. deep, and 2 ft 3 in. tall, on the backwall to suppress flow circulations around the pump-suction bell. 3. Install two triangular-shaped sidewall floor-corner fillets, 14 ft 1-9/16 in. long, 1 ft 6 in. wide, and 1 ft 6 in. tall, along two converging sidewalls of the pump bay to suppress sidewall-attached subsurface vortices. 4. Install a triangular-shaped, backwall floor corner fillet, 14 ft 4 in. long, 1 ft 6 in. wide, and 1 ft 6 in. tall, along the backwall floor corner to suppress backwallattached subsurface vortices. 5. Install two vertical triangular-shaped backwall corner fillets, 3 ft 1-7/8 in. by 3 ft 1-7/8 in. by 5 ft 1-3/8 in., and 2 ft 3 in. tall, in two corners of the backwall to eliminate stagnant flow areas. 6. Install a suction-scoop ceiling (a 15 ft 6 in. long horizontal ceiling connected to a 5 ft 11/16 in. long sloping ceiling). A hole, slightly larger than the bell diameter, say, 0.5 in., should be bored in the horizontal ceiling and its gap should be sealed by a circular rubber gasket that is anchored to the bell mouth. 7. Install six vanes, as specified in figure 4.9, underneath the sloping portion of the suction-scoop ceiling in order to straighten angular pump-approach flows. The distance between the first and the last vanes from the sidewalls should be 1 ft 9 in. It should be noted that throughout the model tests, the mean river flow velocity was maintained at 3 ft/s in full scale. As the river stage was decreased or increased, the model river discharge was altered accordingly. It should also be noted that no detailed classification of free-surface vortices was made with the Unit-3 intake model because it was not originally included in the scope of work. As the study progressed to investigate the Unit-1 and Unit-2 intakes, IIHR was asked by MAEC to document the vortex types for some test cases. 17

22 Test Case For Unit 3 Intake Vacuum Lift Wall Opening (ft) As-Built or Suction Scoop Winter Discharge Line (Yes/No) Task 1 4 As-Built No Produce relationship between pump discharge and river stage and relationship between pump swirl and river stage 2 4 As-Built No Find critical river stage for safe vacuum chamber operation 3 3 As-Built No Find critical river stage for safe vacuum chamber operation 4 4 As-Built Yes Design and fabricate a winter discharge supply line downstream from the vacuum lift wall to supply a discharge of 15,000 gpm to the vacuum chamber/investigate its effect in raising the critical water depth in front of the vacuum lift gate for safe vacuum chamber operation 5 4 Suction Scoop No Produce relationship between pump discharge and river stage and relationship between pump swirl and river stage 6 4 Suction Scoop No Find critical river stage for safe vacuum chamber operation 7 3 Suction Scoop No Find critical river stage for safe vacuum chamber operation 8 4 New Suction Scoop Extended Upstream from Vacuum Lift Wall * Head Loss Measurements Yes Modify suction-scoop layout so that it extends upstream from the vacuum lift gate/supply a discharge of 15,000 gpm to the vacuum chamber and investigate its effect in raising the critical water depth in front of the vacuum lift gate for safe vacuum chamber operation Design and fabricate model trashracks and traveling screens to simulate head losses within each pump-intake bay *All test cases will be conducted with model trashracks and traveling screens installed. Table 4.1 A summary of test conditions under as-built conditions and with suction scoop conducted for existing Unit-3 intake 18

23 24'-6" 2" 11'-2" 2'-6" 1'-6" 9'-0" 1'-6" 3'-0" 1'-6" 5'-3" 7'-2" 7'-2" 5'-3" CL VACUUM LIFT WALLS SECTION B-B B B EL VACUUM RAISED TO EL.1056' A SECTION A-A FLOW A VACUUM LIFT WALL LOW WATER EL.1050' 1'-6" Backwall Splitter Backwall Floor Corner Fillet 2'-3" 9" Floor Corner Fillet Bell Diam: 9' 9" Floor Splitter 1'-6" Vane C 12'-0" 1'-6" 1'-6" 12'-7 9/16" Floor Corner Fillet 5'-0" 15'-6" Horizontal Ceiling Sloping Ceiling PLAN VIEW Pier Nose C 5'-11/16" 9'-0" 3'-0" 15'-6" 2'-1 1/4" 5'-0" 2'-6" 5'-3" 14'-4" 5'-3" 2'-3" Ø9'-0" 24'-10" 6'-9" 11'-2" 6" 16'-10" 4'-6" 16'-0" 2" PLAN VIEW OF SUCTION SCOOP 24'-10" 9" 1'-6" 2'-3" '-10" 3'-6" 3'-1 7/8" 2'-8" Vane A 3'-6" Vane B 5'-1 3/8" Vane C 3'-4" 2'-6" 2'-6" 2'-6" 3'-0" Vane B Vane A 1'-6" 12'-0" 11'-2" Vane A: 5'- 3 1/4" Long Vane B: 5'-13/16" Long Vane C: 5'-0" Long 4'-0" 5'-8" 5'-8" 3'-1 7/8" 3'-0" 5'-3" 14'-4" 5'-3" Figure 4.9 Suction scoop layout designed for existing Unit-3 intake 19

24 Case 1 and Case 5 To obtain relationships between the pump discharge and the river stage, Case 1 under the as-built condition and Case 5 with the model suction scoop were run with the river stage incrementally varied. In Case 5, the vacuum lift wall opening was maintained at 4 ft. In each case the discharge passing through the withdrawal pipe was measured by means of an orifice meter. The empirical relationships obtained are shown in figure In both Cases 1 and 5, the pump discharge generally decreased as the river stage increased. Although figure 4.10 shows that the discharge was higher in Case 1 than in Case 5, their differences are insignificantly small. For example, a difference of 600 gpm in prototype discharge is merely 0.42% (600 gpm/142,000 gpm), which is within experimental errors. Note that the horizontal axis in figure 4.10 is drawn for a very narrow range of prototype discharge. We were not able to demonstrate in this model that the suction scoop can deliver more flow than the as-built intake layout. It may well be due to the small model scale that was used. However, the pump-column swirl speed with the suction scoop was much smaller than that under as-built conditions, as shown in figure The swirl angle, θ, is defined by θ = tan -1 (V θ /V z ) (4.2) where V θ = 2πrω/60 = tangential velocity at the tip of the vortimeter blade; r = radius of pump column; ω = angular velocity of vortimeter in rpm; and V z = average axial velocity of pump-column flow. The maximum swirl angle in Case 1 was 10.5 which is much higher than the critical swirl angle of 5. On the other hand, the maximum swirl angle in Case 5 was 4.9, as can be seen in table 4.2. The measured head losses through the trashracks and traveling screens are also shown in table 4.2 and plotted in figure At a river stage of EL 1051 ft, the total head loss through the clean trashracks and traveling screens was found to be about 1.0 ft and it generally decreased as the river stage increased, as can be seen in figure

25 Case 2 and Case 3 To obtain critical river stages for two different vacuum lift wall openings at which the intake vacuum system fails, Cases 2 and 3 were conducted under the as-built conditions. The river stage was gradually reduced from EL 1051 ft at an interval of 0.1 ft. With a 4-ft vacuum lift wall opening, small air bubbles started entering the vacuum chamber at a river stage of EL ft, and the vacuum system completely failed when the river stage was set at EL ft. When the vacuum lift gate was lowered by 1 ft (3 ft opening), this critical river stage value was found to be at EL ft. The critical river stage was reduced by only 0.3 ft by lowering the gate by 1 ft. It should be pointed out that because the mean velocity ratio by lowering the gate by 1 ft from a 4-ft opening to a 3-ft opening becomes 4/3, the head loss through the vacuum lift gate would become (4/3) 2 = 1.78 times larger when the gate is lowered. Case 4 and Case 8 Case 4 involved design and fabrication of a warm winter-discharge supply line downstream from the vacuum lift wall to feed a prototype discharge of 15,000 gpm to the vacuum chamber in an attempt to raise the critical sump water level in front of the vacuum lift wall. In the model, two 3-in. diameter warm-water supply lines were brought in just upstream from the vacuum lift walls, as shown in figure Each supply line was then connected to a 2-in. diameter and 10-in. long tee diffuser which was attached to the downstream face of the vacuum lift wall, as shown in figure On either side of the tee, a 2-1/2 in. long and 5/16-in. wide rectangular diffuser slot was provided. Each diffuser slot was located such that the discharge jet impinges downward against the vacuum lift wall at 45 to minimize flow disturbances. Because the higher water level within the vacuum chamber is maintained by vacuum, there is little differential head produced across the vacuum lift gate. Therefore, there should not be any flow moving upstream underneath the vacuum lift wall even if we supply warm water to the vacuum 21

26 chamber. Furthermore, surface flow disturbances produced by winter-water discharge had negative impacts on the critical low river stage under which the pumps operate satisfactorily. Unstable water-surface elevations within the vacuum chamber prohibited us from collecting any experimental data. Case 8 was tested for two discharges, 7,500 gpm and 15,000 gpm each. However, the surface disturbance produced by the warm discharge was found to cause airentrainment problems in which air was eventually withdrawn by the pump. Although the plant vacuum system may be able to lift the water level higher than 6 ft, it is still a major task to discharge warm water without creating surface disturbance within the vacuum chamber. We were unable to complete Case 8 due to this air-entrainment problem. Case 6 and Case 7 Tests similar to Cases 2 and 3 were conducted with the suction scoop in Cases 6 and 7. The test results were very similar to those obtained in Cases 2 and 3. The critical river stage when the vacuum lift gate opening was 4 ft was found to be EL ft, and that when the gate was lowered by 1 ft was EL ft. Head Loss Prediction Using the experimental data obtained in Case 1 and Case 5, head-loss coefficients through trashracks and traveling screens were obtained for these two cases. The head loss coefficient, λ, is defined by the following relationship: 2 V H = λ 2g (4.3) 22

27 where H is the head loss, and V 2 /2g is the velocity head based on the mean velocity (pump discharge divided by the pump-bay width and the water depth based on the river stage). Relationships between H and V 2 /2g for Case 1 and Case 5 are shown in figure Because the model scale is 1:12, extremely small head losses at higher river stages (for velocity heads lower than 0.03, approximately) were not able to be measured accurately. As can be seen in figure 4.15, the data are seen to scatter at lower head losses. Regression analyses produced λ = for the as-built condition (Case 1) and λ = for the suction-scoop case (Case 5) although the correlation coefficient in Case 5 was lower than that in Case 1. Note that these values are for clean trashracks and traveling screens. Summary The most convincing aspect of using the suction scoop developed for the Unit-3 intake is the fact that the suction scoop stabilizes the water surface elevation within the vacuum chamber. Under the as-built conditions, strong unsteady surging actions were found to occur within the vacuum chamber. It was estimated that the amplitude of this water surface surging was on the order of more than a foot in prototype dimensions. This type of unsteady surging is not good for pumps. Furthermore, the suction scoop reduced the swirl angle within the critical value of 5 and improved the pump-approach-flow distributions significantly as compared with the as-built pump-bay layout. Therefore, it is recommended that the suction scoop whose layout is shown in figure 4.9 be installed. 23

28 River Stage above MSL River Bed EL above MSL As-Built Condition - Unit-3 Intake (Case 1) Head Loss Through Clean Trash Racks (ft) Head Loss Through Clean Traveling Screens (ft) Total Head Loss Discharge Swirl Speed in CCW Direction Swirl Angle in CCW Direction (ft) (ft) (ft) (gpm) (rpm) (degree) , , , , , , , , River Stage above MSL River Bed EL above MSL Suction Scoop - Unit-3 Intake (Case 5) Head Loss Through Clean Trash Racks (ft) Head Loss Through Clean Traveling Screens (ft) Total Head Loss Discharge Swirl Speed in CCW Direction Swirl Angle in CCW Direction (ft) (ft) (ft) (gpm) (rpm) , , , , , , , , (degree) Table 4.2 A summary of test results for Cases 1 and 5 for the Unit-3 intake 24

29 Unit-3 Intake d:\gnn1\test results\q-h_ab1.spw (9-4-01) Q-H Relationship - As Built (Case 1) (Vacuum Liftwall Opening = 4 ft) Regression Curve Q-H Relationship with Suction Scoop (Case 5) (Vacuum Liftwall Opening = 4 ft) Regression Curve - Suction Scoop River Stage above MSL, H (ft) Discharge, Q (gpm) Figure 4.10 Discharge-river stage relationships obtained in Cases 1 and Unit-3 Intake d:\gnn1\test results\swirl.spw ( ) River Stage above MSL, H (ft) Case 1 - As Built Regression Curve for Case 1 Case 5 - Suction Scoop Regression Curve for Case Swirl, Ù (rpm) - Counterclockwise Figure 4.11 Swirl-river stage relationships obtained in Cases 1 and 5 25

30 1065 Unit-3 Intake (As-Built) d:\gnn1\test results\htr_ab.spw ( ) River Stage above MSL, H (ft) Through Trashracks Through Traveling Screens Total Loss Regression Curve for Total Loss Head Losses (ft) 1065 Unit-3 Intake (Suction Scoop) River Stage above MSL, H (ft) Through Trashracks Through Traveling Screens Total Loss Regression Curve for Total Loss Head Losses (ft) Figure 4.12 head losses measured in Cases 1 and 5 26

31 Figure 4.13 Warm-water supply lines through vacuum lift wall Figure 4.14 Diffusers in vacuum chamber seen through backwall window 27

32 1.2 Head Loss Through Trashracks & Traveling Screens Unit-3 Intake: Vacuum Lift Wall Opening = 4 ft Total Head Loss, H (ft) Measured Regression Line AS-BUILT (Case 1) H = 12.29(V 2 /2g) (r 2 = 0.95) Velocity Head, V 2 /2g (ft) 1.2 Total Head Loss, H (ft) Measured Regression Line SUCTION SCOOP (Case 5) H = 10.99(V 2 /2g) (r 2 = 0.79) Velocity Head, V 2 /2g (ft) Figure 4.15 Relationships between velocity head and total head obtained in Cases 1 and 5 28

33 V. SUCTION SCOOP DESIGNED AND TESTED FOR EXISTING UNIT-2 INTAKE The existing Unit-2 intake bays are 47 ft 6 in. long and 11 ft 2 in. wide, as shown in figure 5.1. The pump-suction bell shown in figure 5.2 is 80 in. in diameter and the floor clearance of the suction bell is 3 ft. The distance from the backwall to the center of the pump column is 5 ft 7 in. Similarly to the Unit-1 suction scoop, IIHR designed a suction scoop for the Unit 2 intake. As mentioned previously, the Unit-2 intake chamber is vacuum controlled to gain the net positive suction head and the pump-sump water surface is raised to EL 1056 ft which is 6 ft above the low water elevation of EL 1050 ft. The existing Unit-2 model constructed is shown in figures 5.3 through 5.6. As in the Unit-3 intake tests, test cases shown in table 5.1 were specified by MAEC. The suction scoop designed for the Unit-2 intake is shown in figures 5.7 (vacuum lift wall opening of 3 ft), including the following components: 1. Install a triangular-shaped floor splitter, 12 ft 6 in. long, 3 ft 6 in. wide, and 1 ft 9 in. tall in the center of the pump bay to suppress floor-attached subsurface vortices. 2. Install a triangular-shaped backwall splitter, 3 ft 6 in. wide, 1 ft 9 in. deep, and 3 ft tall, on the backwall to suppress flow circulations around the pump-suction bell. 3. Install two triangular-shaped sidewall floor-corner fillets, 12 ft 6 in. long, 1 ft 9 in. wide, and 1 ft 9 in. tall, along two sidewalls of the pump bay to suppress sidewallattached subsurface vortices. 4. Install a triangular-shaped, backwall floor corner fillet, 11 ft 2 in. long, 1 ft 9 in. wide, and 1 ft 9 in. tall, along the backwall floor corner to suppress backwallattached subsurface vortices. 5. Install two vertical triangular-shaped backwall corner fillets, 1 ft 9 in. wide, 1 ft 9 in. deep, and 3 ft tall, in two corners of the backwall to eliminate stagnant flow areas. 6. Install a suction-scoop ceiling (a 12 ft 6 in. long horizontal ceiling connected to a 4 ft 3/4 in. long sloping ceiling). A hole, slightly larger than the bell diameter, say, 0.5 in., should be bored in the horizontal ceiling and its gap should be sealed by a circular rubber gasket that is anchored to the bell mouth. 29

34 7. Install five, 2 ft long, flow-turning vanes at 1 ft 11 in. intervals underneath the sloping portion of the suction-scoop ceiling in order to straighten angular pumpapproach flows. The distance between the first and the last vanes from the sidewalls should be 1 ft 9 in. PLAN VIEW OF ONE BAY OF UNIT 2 47'-6" 18'-5" 11'-2" SECTION B-B EL ' EL ' 1'-3" FLOW 12'-10" 5'-7" CL VACUUM LIFT WALLS 1'-0" 29'-1" 12'-11" 9'-2 1/8" 5'-2" 4'-1/8" 3'-8 7/8" EL ' 1'-0" CL DISCHARGE PIPE VACUUM LIFT WALL (Adjustable) EL '' 47'-6" 29'-1" 12'-10" 5'-7" 12'-11" B 9'-2 1/8" 5'-2" 1'-0" CL A STOP A LOG EL ' 26'-4" C.L. Traveling Screen 3" 5'-7" 5'-7" B CL TRASHRACK 1'-3" 11'-2" 15'-0" 3'-0" C.L. of Traveling Screen MEAN HIGH WATER EL ' EL '-0" 10'-9" 29'-9" 2'-0" 2'-0" CONSTANT WATER LEVEL EL ' 7'-9" 6'-3" 9'-3" 4'-9" 2'-9" MEAN LOW WATER EL ' MIN. LOW WATER EL ' 2'-0" BULLNOSE 3'-0" 3'-3" EXTREME LOW WATER EL ' 12'-9" 2'-0" 1'-11 5/16" 13'-3" 3'-3" 3 2'-0" 32'-9" 12 21'-1 7/16" 11'-7 9/16" 32'-9" 3'-0" 9'-9" 8" 3'-0" 10" 10'-3" 6'-8" 2'-3" EL RIVER BED: EL ' R1'-0" " SECTION A-A Figure 5.1 Plan and elevation of existing Unit-2 intake bay 30

35 66.480" " PIPE O.D " " 4.500" 0.240" 0.240" 9.000" " PIPE I.D " " 9.000" " " " " " " " THROAT R28.200" " " " " " 80" DIAMETER SUCTION BELL FOR EXISTING UNIT 2 (PROTOTYPE DIMENSIONS) Figure 5.2 Pump suction-bell profile of existing Unit-2 intake pump Figure 5.3 Frontal view of the existing Unit 2 intake model 31

36 Figure 5.4 Rear view of existing Unit-2 intake model Figure 5.5 Side view of existing Unit-2 intake model 32

37 Figure 5.6 Rear view of model suction scoop for Unit-2 intake 33

38 SUCTION SCOOP DESIGNED FOR EXISTING GEORGE NEAL NORTH UNIT-2 INTAKE 16'-6" 1'-5" 2'-0" 2'-0" 1'-9" 9'-0" 1'-9" Backwall Floor Corner Fillet FLOW A 1'-9" 1'-11" 1'-11" 1'-11" 1'-11" 1'-9" Floor Splitter Five 2-ft Long Vanes B B C Ø6'-8 1/4" 6" D D A 1'-9" 2'-1" 3'-6" 2'-1" 1'-9" 11'-2" Sidewall Floor Corner Fillet C Backwall Splitter PLAN VIEW OF ONE BAY OF UNIT 2 (Suction scoop ceiling not shown) Vertical Backwall Corner Fillet 12'-4" 17'-11" 5'-7" CL Pump Column 1'-5" Sloping Ceiling (angle: 10 deg.) 4'-3/4" 6'-8 1/4" 12'-6" 6" 1'-3" 3'-0" 3'-8 1/2" 1'-3" 1'-9" 1'-9" 3'-0" 2'-0" 2'-0" 3'-6" 1'-9" 9'-0" 1'-9" SECTION A-A 1'-9" 1'-9" 1'-9" 1'-9" '-9" 1'-9" '-9" ( Dimensions) October 3, 2001 SECTION B-B SECTION C-C SECTION D-D Figure 5.7 Suction scoop layout designed for existing Unit-2 intake with 3-ft wall opening 34

39 Test Case For Unit 2 Intake Vacuum Lift Wall Opening Sump Condition: As-Built or Suction Scoop Winter Discharge Line (Yes/No) Task (ft) 1 3 As-Built No Produce (Q-H)/(H-Head Loss) curves 2 3 As-Built No Find critical river stage for safe vacuum chamber operation 3 2 As-Built No Find critical river stage for safe vacuum chamber operation 4 3 As-Built Yes Design and fabricate a winter discharge supply line downstream from the vacuum lift wall to supply a discharge of 15,000 gpm to the vacuum chamber/investigate its effect in raising the critical water depth in front of the vacuum lift gate for safe vacuum chamber operation NOT applicable based on the Unit-3 intake study 5 3 Suction Scoop No Produce (Q-H)/(H-Head Loss) curves 6 3 Suction Scoop No Find critical river stage for safe vacuum chamber operation 7 2 Suction Scoop No Find critical river stage for safe vacuum chamber operation *All test cases were conducted with model trashracks and traveling screens in place. Table 5.1 A summary of test conditions for the as-built conditions and with suction scoop conducted for existing Unit-2 intake Case 1 and Case 5 Table 5.2 shows the principal test results for Case 1 and Case 5 that were operated at different river stages between EL 1051 ft and EL 1058 ft. Under the as-built conditions there was a strong prerotation within the pump column at each river stage (note exclusively counterclockwise). The measured swirl angle varied between 1.3 for a river stage at EL 1058 ft and 5.2 at EL 1056 ft. The critical swirl angle for satisfactory pump operations is 5. When the suction scoop was in place, the swirl angle became very small, as shown in table 5.2. The maximum swirl angle, 2.1, was observed at the lowest river stage of EL 1051 ft. The suction scoop produced very stable vacuum-chamber conditions, as compared to those without the suction scoop in which the water surface elevation fluctuated considerably, approximately 6 in. to 1 ft in prototype dimensions. 35

40 There were no unstable water-surface surges with the suction scoop. The measured discharges and head losses in Cases 1 and 5 are also shown in table 5.2 and are plotted in figure 5.8 and 5.9, respectively. Cases 2 and 6 Cases 2 and 6 indicated that the critical river stage to operate the vacuum system safely without any air entrainment was at EL ft in both cases. Cases 3 and 7 When the vacuum lift wall is lowered to a 2-ft deep opening, the mean pumpapproach flow velocity through a 11 ft 2-in. wide and 2-ft high cross section becomes 6.48 ft/s (145 (cfs)/11.17 (ft)/2 (ft) = 6.48 ft/s) which is excessively high as pumpapproach flow velocity. The mean velocity for a 3-ft opening on the other hand is 4.32 ft/s (145 (cfs)/11.17 (ft)/3 (ft) = 4.32 ft/s). This means that the high velocity head will produce extremely high head losses at the vacuum lift wall when it is lowered to a 2-ft opening. Therefore, tests for Cases 3 and 7 were not conducted. MAEC was interested in lowering the vacuum lift wall to a 2-ft opening to secure safe pump operations under extremely low river stages. Based on their successful pump operations at a lift wall opening of 3 ft, MAEC was interested in lowering the pumping capacity from 65,000 gpm to 45,000 gpm at a lift wall opening of 2 ft, yielding a mean velocity through the opening of 4.49 ft/s which is comparable with that under the existing operation (65,000 gpm at a 3-ft lift wall opening). It should be noted that reduction of pumping capacity during the winter period does not significantly affect the power production because the river water temperature is extremely low during the winter. Therefore, new test cases different from Cases 3 and 7 for a vacuum lift wall opening of 2 ft were added to the study program, as shown in table 5.3. The suction scoop layout in these cases is shown in figure

41 River Stage above MSL EXISTING UNIT-2 INTAKE As-Built Condition - Existing Unit-2 Intake (Case 1) River Bed EL above MSL Head Loss Through Clean Trash Racks (ft) (1) Head Loss Through Clean Traveling Screens (ft) (2) Total Head Loss Discharge Swirl Speed in CW/CCW Direction Swirl Angle in CW/CCW Direction (ft) (ft) (ft) (gpm) (rpm) (degree) (1)+(2) , (CW) 3.2 (CW) , (CW) 3.4 (CW) , (CW) 3.8 (CW) , (CW) 4.6 (CW) , (CW) 4.7 (CW) , (CW) 5.2 (CW) , (CW) 3.7 (CW) , (CW) 1.3 (CW) River Stage above MSL River Bed EL above MSL Suction Scoop - Existing Unit-2 Intake (Case 5) Head Loss Through Clean Trash Racks (ft) (1) Head Loss Through Clean Traveling Screens Total Head Loss Discharge Swirl Speed in CW/CCW Direction Swirl Angle in CW/CCW Direction (ft) (ft) (ft) (ft) (gpm) (rpm) (degree) (2) (1)+(2) , (CW) 2.3 (CW) , (CW) 0.6 (CW) , (CCW) 0.9 (CCW) , (CW) 0.6 (CW) , (CW) 0.2 (CW) , (CCW) 0.3 (CCW) , (CCW) 0.3 (CCW) , (CCW) 2.1 (CCW) Table 5.2 A summary of test results for Cases 1 and 5 for the Unit-2 intake with a vacuum lift wall opening of 3 ft 37

42 Unit-2 Intake Q-H Relationship - As Built (Case 1) (Vacuum Lift Wall Opening = 3 ft) Q-H Relationship - Suction Scoop (Case 5) (Vacuum Lift Wall Opening = 3 ft) 1058 River Stage above MSL, H (ft) Discharge, Q (gpm) Figure 5.8 Discharge-river stage relationships obtained in Cases 1 and 5 38

43 Unit-2 Intake (As-Built) 1065 River Stage above MSL, H (ft) Through Trashracks Through Traveling Screens Total Loss Regression Curve for Total Loss Head Losses (ft) River Stage above MSL, H (ft) Unit-2 Intake (Suction Scoop) Through Trashracks Through Traveling Screens Total Loss Regression Curve for Total Loss Head Losses (ft) Figure 5.9 head losses measured in Cases 1 and 5 39

44 Existing Unit-2 Intake 2-ft Vacuum Lift Wall Opening & Lower Pump Discharge of 45,000 gpm Test Case For Unit-2 Intake Vacuum Lift Wall Opening Sump Condition: As- Built or Suction Scoop Task (ft) 1A 2 As-Built Produce (Q-H)/(H-Head Loss) curves 2A 2 As-Built Find critical river stage for safe vacuum chamber operation 5A 2 Suction Scoop Produce (Q-H)/(H-Head Loss) curves 6A 2 Suction Scoop Find critical river stage for safe vacuum chamber operation *All test cases were conducted with model trashracks and traveling screens in place. Table 5.3 A summary of test conditions for the as-built conditions and with suction scoop conducted for existing Unit-2 intake with a vacuum lift wall opening of 2 ft Cases 1A and 5A Case 1A was conducted for a river stage varying between EL ft and EL 1058 ft. The critical river stage which allows safe pump operation under the as-built condition was found to be EL ft. The test results are shown in table 5.4. The measured swirl angle varied between 3.1 for a river stage at EL 1052 ft and 7.7 at EL 1055 ft. The swirl angle with a river stage at EL ft was 1.5 and that at EL ft was 5.1. The lower swirl angle at EL ft was a result of the vortimeter rotating in both clockwise and counterclockwise directions. At the lowest river stage of EL ft, the prototype water-surface disturbance within the vacuum chamber was observed in the model. It is expected to be about 6 in. to 9 in. near the vacuum lift wall and about 1.5 in. near the backwall. The reason for the higher fluctuation near the lift wall as compared to the backwall is due to upward flows created by reverse flows after high velocity flows impinge the backwall and bounce back from the backwall. It should be pointed out that no surface disturbance was observed with the suction scoop in place. 40