PGU_TrbneAeratingRunnerTech.pdf

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Turbine Aerating Runner

Technology


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Educational ObjectivesOn completion of this course, students will:

IntroductionIn recent years, environmental and water quality issues

have become signicant considerations in the operation and

upgrade of many hydropower stations and river systems.

The aeration of water passing through a hydraulic turbine

is rapidly becoming accepted as one eective method of

enhancing dissolved oxygen (DO) levels downstream of

hydropower projects. When coordinated with turbine

refurbishment or re-powering projects, the modications

required to enable aeration of the turbine discharge may be

accomplished in a cost eective manner.

As part of the ongoing hydro modern ization pro-

gram for their Catawba-Wateree Project, Duke Power

elected to upgrade hydraulic turbines at several of their

hydropower stations with various turbine aeration op-

tions. This course will consider the upgrade of Unit 3 at

Duke Power’s Wateree Hydro Station to include turbine

aeration capability as an example of the Turbine Aerating

Runner Technology.

There are a number of dierent options for introducing

air into the turbine discharge. The options are basically dis-

tinguished by the level of DO increase that may be expected,

the exibility of this aeration, the cost for implementation,

and the eect on hydraulic turbine performance. Dissolved

oxygen enhancement at the Wateree Project was accom-

plished by utilizing a new Francis type runner designed to

allow the natural aspiration of atmospheric air from the

trailing edge of the runner vanes.

This proprietary concept was rst proven through ex-

perimentation with a replacement Francis runner, manufac-

tured by Voith Hydro, which was installed by the Tennessee

Valley Authority (TVA) at Norris Dam.1, 2 The runner

installed by Duke Power at the Wateree Hydro Station wasdesigned and manufactured by Voith Hydro after mutual

evaluation of the project goals, the status of the technol-

ogy and the available options. This runner represents the

second generation of this technology and is the rst com-mercial application of the “aerating runner” design. Initial

testing of the Wateree 3 runner has shown excellent perfor-

mance, exibility, and strong DO enhancement capabilities

throughout the entire operating range.

Takingadvantageofopportunities

Typically, the upgrade of a turbine unit includes the

replacement of the existing turbine runner with a

new runner of an improved hydraulic design as well as

refurbishment and design improvement of the other

existing main turbine and/or generator components.

This provides a perfect opportunity to implement the

modifications required for adding turbine aeration ca-

pability on selected generating units in a cost-effective

manner. Duke Power has already implemented turbine

modifications which added “hub venting” capability at

several other hydropower stations (Reference 3). The

hub venting concept was chosen where the maximum de-

sired increase in DO was in the 2 to 3 mg/ l range and the

modifications could be implemented at a relatively smal l

incremental cost. Also, because the in itial focus was on

improving tailrace DO levels during low flow periods,

this fit the capabilities of hub venting well. Hub vent-

ing is most effective during operation of the hydraulic

turbine operating at partial load.

From results of the ongoing Duke Power DO testing

program, the aeration needs were determined to be dif-

ferent at Wateree. Based on historical data, a maximum

DO increase in excess of 3 mg/l would be desirable during

certain low DO periods. The peaking power demand for

Wateree also required the exibility to operate across as

much of the power range as possible. This presented moresignicant economic and technical challenges at Wateree

than for the projects where hub venting was selected and

implemented.

Turbine Aerating Runner Technology

1. Be provided an overview of one method

being used for the enhancement of dissolved

oxygen levels in reservoir water releases.

2. Learn about a variety of designs for aeration.

3. Learn a number of dierent options for

introducing air into the turbine discharge.

4. Understand the benets of the runner discharge

methodology and the aeration methodology.


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SelectingandevaluatingtheoptionsDO enhancement by any method cannot be without cost,

but the costs of some DO enhancement alternatives can ex-

tend far beyond the initial investment. The selection of any

DO enhancement system must consider not only upfront

capital costs, but also associated operation and maintenance

costs, performance degradation impacts on revenue, system

eectiveness for multiple units, site specic DO uptakedesired, and site specic hydrology, among others.

In recent years Voith’s joint R&D eorts with their part-

ners have successfully developed a variety of designs for aera-

tion, including hub aeration, distributed aeration (through

the runner) and peripheral or discharge ring aeration.

There are at least four (4) options to consider to achieve

DO enhancement, as follows:

• Vacuum Breaker Aeration

• Hub Venting DO Enhancement Design (Central Aeration)

• Aerating Runner Design (Distributed System)

• Forebay Oxygen Injection System

Vacuum breaker aeration

Most of the hydropower stations on the Catawba-Wateree

have turbines with settings from 7 feet to as much as 15 feet

above tailwater. Manually operated valves exist to break the

draft tube vacuum, which allows the water to be cleared

from around the turbine runner. This permits the units to

be operated as synchronous condensers with very little pow-

er consumption. These valves also can be opened while the

turbines are generating, and air is admitted to the turbine

discharge thereby boosting its DO level. Modications can

be made to increase the air capacity through these valves.

The advantages of this design are that the modications

can usually be implemented without disassembly of the

turbine and at the lowest relative capital cost of the options

considered. The disadvantages are that the eectiveness

varies from station to station and that generally only modest

increases in DO can be realized. Testing results by Duke

Power have shown that at some locations this method can

approach the eectiveness of the hub venting design, but it

cannot achieve higher levels of DO uptake.

Hub venting DO enhancement design

For this design, modications to the turbine are imple-

mented which may allow large quantities of air to be drawn

through passageways in the turbine head cover and directed

to the runner nose cone. Air then travels to the turbine dis-

charge where turbulence in the runner vortex is relied upon

to distribute the air.

The advantages of this option are that larger quantities

of air are added to the turbine discharge than with the simi-

lar vacuum breaker aeration scheme, and the incrementaladditional cost of the modication is still relatively low. The

required turbine modications are not especially complex

and have been successfully completed on various projects by

most of the major turbine vendors. These DO enhancement

systems can be turned on or o as desired and do not have

a signicant eect on performance when not admitting air.

Testing of the units at other Duke Power hydropower sta-

tions has demonstrated that this option is most eective at

increasing DO levels during part load turbine operation and

has lesser enhancement capability as power increases. For

Wateree, it was not expected that the desired levels of DOcould be achieved with this option.

Aerating runner design

This design is similar to the hub-venting concept by using

modications to the turbine that are implemented to allow

large quantities of air to be drawn through passageways in the

turbine head cover. Instead of being directed to the runner

nose cone the air is distributed to the turbine runner, where

it exits from each the trailing edge of each vane. This is de-

signed to provide smaller air bubbles (i.e., higher surface area

for oxygen transfer) and to provide more thorough mixing atall operation levels. Therefore, higher levels of DO uptake are

achieved with less air being admitted than with the hub vent-

ing concept. This lower concentration of air in the draft tube

translates to higher hydraulic performance. Based on model

and prototype testing performed jointly by TVA and Voith

with the Norris turbines, there was reasonable assurance for

Wateree that higher levels of DO uptake could be achieved

with this technology without an unacceptable sacrice in

turbine performance throughout the operating range.

Forebay oxygen injection system

The design of this system uses submerged oxygen dispersion

manifolds in the hydropower station forebays, which are fed

from liquid oxygen storage tanks. This option was employed

at Buzzard Roost Hydro Station due to the diculty in draft-

ing air into the Kaplan turbine design. The advantage of this

system is that it provides an alternative when vacuum breaker

aeration is not sucient and turbine aeration is not viable.

There are however several clear disadvantages to this

option. The initial capital cost of installing this system at

Wateree could exceed the incremental capital cost of an

aerating runner due to the required embedment of the dis-

charge piping. There would also be ongoing annual O&M

cost for purchasing the liquid oxygen. Additional mainte-

nance of the forebay hoses and injection equipment must be

factored into the O&M cost as well.

Evaluation conclusion

From the evaluation performed for Wateree, it was readily

apparent that forebay oxygen injection would be too costly

to be competitive at this site and vacuum breaker venting

would not likely meet the targeted DO uptake. In the nalanalysis, although the aerating runner at Wateree requires

an initial ly greater capital investment than hub venting, the

long term benets for both DO uptake and exibility of op-


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Figure 1 – Aerating Runner Distributor Section

Figure 2 – Aerating Runner

as Viewed from Below

Figure 3 – Relative Efciency and % Airow vs. Power

100%

85%

80%

R

e l a t i v e E f c i e n c y

A i r F l o w

a s a % o

f F l o w ( W a t e r )

75%

0

MW

Index Test Results from Wateree Aeration Testing

1 2 3 4

90%

95%

20%

10%

5%

0%

15%

3 Pipes

2 Pipes

1 Pipe

No Air

4 www.powergenu.com

eration provide sucient cumulative benets to make the

aerating runner the clear economic choice. Of particular

importance is the increased generation capability during

critical periods of the year, when ambient DO may be low

and peaking energy values may be high.

The aerating runner solution

At the time of the Wateree Project, the aerating runnerdesign was very new to the hydropower industry, with only

the second generation going to Wateree. Tests of the rst

generation distributed aeration system employed at Norris

Dam have shown that the runner discharge methodology

is more benecial than the aeration methodology for the

following reasons:

• Provides air over a range of turbine dis-

charges with lower impact to performance

than all other methods evaluated;

• Provides air in small bubbles which are distributed

over a wide area of draft tube inow;• Provides air in a manner which leads to

a high absorption eciency; and

• Requires smaller amounts of air and therefore preserves

more of the operating characteristic of the turbine.

To obtain the airow required to achieve a 3mg/l uptake

in DO, the Wateree blades were fabricated with hollow sec-

tions serving as the distribution path for air.

A cross section of the aerating runner for Wateree is

shown in Figure 1 above. The air enters the turbine through

pipes installed in the existing turbine guide bearing hous-

ing, where valves are located to control the air ow into the

cavity between the head cover and the rotating runner. A

third seal has been added to the head cover and runner to

isolate the air from thrust relief. Holes in the runner crown

allow the air to travel to the specially designed hollow runner buckets. The cavity within the bucket leads to the

discharge edge of the bucket, where specially designed air

distribution nozzles are used to distribute the air into the

water as a desired cloud of ne bubbles. The technology

embodied in the aerating turbine components is protected

by U.S. Patents 4789051 and 5823740 and is also the subject

of several patents pending.

Figure 2 shows the aerating run-

ner as viewed from below. Easily

visible are the nozzles that distrib-

ute the air to the water. Achieving the required air ow to meet the

greater than 3 mg/ l DO uptake

meant the losses for air ow had to

be minimized in all areas of the dis-

tribution system. This was an area

where the Norris Dam solutions fell below expectations;

therefore, this received very high attention in the second

generation design. The results obtained during testing at

Wateree conrmed the design goal was met; air ow was

in fact controlled by the external valves, rather than the

runner passageways choking o the ow and thus limiting the ultimate DO uptake potential. In summary, the primary

design enhancements incorporated at Wateree were air ow

distribution and reductions in air ow losses.

MakingthegradeatWateree–eldtestresultsThe aerating runner at Wateree was tested in two phases.

During the rst phase of testing, conducted in January 1999,

the machine was index tested with no air admission to estab-

lish a baseline for the unit performance and output charac-

teristics. Following the baseline test, the unit performance

characteristics were measured for several dierent air ow

rates. The results of this testing are shown in Figure 3. Several

observations can be made from Figure 3. For example, when

operating with up to 3 air valves open the turbine eciency

dropped no more than 5% from the baseline at BOP, and the

maximum power output dropped less than 3%. It was deter-

mined later in the testing that 3 open valves actually allowed

more air to be admitted than was needed to meet a 3 mg/l

uptake. The measured airow for the various valve congu-

rations is included on Figure 3. For the aerating runner, the

amount of airow at various turbine load settings from 50%

to 100% was largest at the lower water ow rates, dropping

slightly as the wicket gate setting was increased, when calcu-


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Figure 4 – DO Uptake vs. Power

5.00

2.00

1.00

D O U p t a k e m g / l

0.00

9.00

Output MW

DO Uptake At Different Air Flows As A % Of Available Opening For Air Flow

11.00 13.00 15.00 17.00 19.00

3.00

4.00

50% Opening

100% Opening for Air Flow

33% Opening

16% Opening

66% Opening

www.powergenu.com 5

lated as a percentage of ow in SCFM. It should be noted that

the actual air volume under the runner depends on the local

pressures and will dier from site to site.

Phase 2 testing measured DO uptake in the tailrace down-

stream of the plant for various air admission settings. This test

was conducted in July 1999. The DO tests were run over sev-

eral days for several air ow conditions. The airow, turbine

relative ow, and generator output power were correlated withthe data from the Phase 1 testing. Baseline DO measurements

were recorded at the beginning and end of testing each day.

The baseline readings were taken after at least 30 minutes of

operating the Unit 3 turbine near best eciency with no air

admission. No other units were operating during the initial

Unit 3 DO tests (some multi-unit mixing tests are described

later). The results of the DO test are shown in Figure 4.

Figure 4 shows that with two air valves open (i.e., 33%

of the available opening), the DO uptake measured in the

tailrace was observed to reach a maximum of 3.5 mg/l when

the turbine is operating at part load. This characteristic is

also similar for hub aerating runners and is based on the

increased turbulence and vortex below the runner providing

enhanced mixing of the admitted air into the water ow.

When the turbine was brought up to best eciency, the DO

uptake dropped to 2.5 mg/l. This DO uptake then remained

constant up to full load. As further shown in Figure 4 the

desired 3 mg/l DO uptake was exceeded at all operating

conditions with just 3 of the available 6 supply pipes open.

As additional air pipes were opened up to the total of 6, the

DO uptake stabilized as the physics of the oxygen transfer

dynamics became saturated.

Completesystembenets

It is important to not only increase the DO levels in the

tailrace, but to use representative DO measurements in

evaluating tailrace aeration. From the raw data, it was

observed that for diering wicket gate positions that the

diering rotation of the draft tube swirl could tend to aect

the direction of the discharge ow and slightly bias the DOreadings at the three monitoring locations across the tail-

race. Therefore, the readings from all three monitors were

allowed to stabilize for each gate position and the readings

were then averaged to get a representative DO uptake. Fig-

ure 5 (above) tracks the averaged DO uptake at the tailrace

monitoring stations (50 yards from the powerhouse) with

four open air valves (~66% of the available opening). Ad-

ditionally, Figure 5 shows the DO uptake present when the

ow from a second adjacent unit, not having enhancement

capability, is mixed with the aerated output of Unit 3 (two

unit mixing occurs from 3:00 to 4:00 pm on the graph). The

mixed ow shows a greater combined DO than the arithme-tic average of the separate DO readings from the two units.

Thus, incremental air volumes above the volume absorbed in

the aerating unit had a benecial eect on the tailrace DO

when the ow from Unit 3 was mixed with other unit dis-

charges. This ability to improve mixed ows may enable the

station to operate aerated and non-aerated units together and

still provide adequate DO enhancement in the tailrace.

Conclusions

These tests have shown that the aerating runner system at

Wateree can eectively enhance tailrace dissolved oxygen

levels while simultaneously retaining much of the generation

capacity and exibility that is so valuable to the hydropower

owner. Although long-term, water quality improvements

in the Catawba-Wateree basin will require the continued

cooperation of water users and regulators, the new aerating

runner at Wateree hydropower stands ready to do its part.

References:1Hopping, P., March, P., Brice, T., Cybularz, J., Update on Development

of Auto-Venting Turbine Technology,” Proceedings, Waterpower

’97, pp. 2020-2027.

2March, P. A. , Brice, T.A. , Mobley, M.A. , and Cybularz, J.M.,“Turbines for Solving the DO Dilemma,” Hydro Review, March1992.

3Ganey, S. R., Jablonski, T. A. ,and Kirejczyk, J. ,”Using HydroTurbines To Enhance Dissolved Oxygen Levels,” Hydro

Review, August 1999, pp. 10-14.

Acknowledgements:

This course is based on the presentation entitled “Using HydroTurbine Aerating Runner Technology to Enhance DissolvedOxygen Levels” as presented at HydroVision International 2000.The authors for this paper are acknowledged as J. C. Sigmon,Duke Engineering & Services, Inc., G.D. Lewis, Duke Power,G.A. Snyder, Voith Hydro, Inc., and J.R. Beyer, Voith Hydro, Inc.Portions of the original paper have been modied for this course.

Figure 5 – DO Uptake vs. Time5

2

0

D O U p t a k e m g / l

1 1 : 4

5 A M

1 1 : 2

5 A M

1 2 : 0

5 P M

1 2 : 2

5 P M

1 2 : 4

5 P M

1 : 0

5 P M

1 : 2

5 P M

1 : 4

5 P M

2 : 0

5 P M

2 : 2

5 P M

2 : 4

5 P M

3 : 0

5 P M

3 : 2

5 P M

3 : 4

5 P M

4 : 0

5 P M

4 : 2

5 P M

5 : 0

5 P M

5 : 2

5 P M

5 : 4

5 P M

4 : 4

5 P M

Time of Day

1

3

4Avg DO mg/l 50 Yards Downstream


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Questions

OnlineCompletionUse this page to review the questions and choose your answers. Return to www.powergenu.com and sign in. If you have not previously purchased the program

select it from the “Online Courses” listing and complete the online purchase. Once purchased the exam will be added to your User History page where a Take

Exam link will be provided. Click on the “Take Exam” link, complete all the program questions and submit your answers. An immediate grade report will be

provided and upon receiving a passing grade (70%) your “Certicate of Completion” will be provided immediately for viewing and/or printing. Certicates of

Completion can be viewed and/or printed anytime in the future by returning to www.powergenu.com, sign in and return to your User History Page.

1. Name two signicant considerations

that have become important in theupgrade of a hydropower plant:

1. environmental issues

2. economic issues

3. time schedule

4. water quality issues

a. 1 & 2

b. 2 & 3

c. 1 & 4

d. 3 & 4

e. All of the Above

2. There are a number of dierent

options for introducing air into

the turbine discharge. The options

are distinguished by two of the

following:

1. the level of DO increase that

may be expected

2. type of method used

for air injection

3. the cost for implementation

4. ease of maintenance for

DO injection system

a. 1 & 3

b. 1 & 4

c. 2 & 4

d. 2 & 3

e. All of the Above

3. Implementing the modications

required for adding turbine

aeration capability on selected gen-

erating units is not cost-eective

to include when replacing an

existing turbine runner.

a. True

b. False

4. The hub venting concept was

chosen where the maximum desired

increase in DO was in the __ to

__ mg/l range and the modica-

tions could be implemented at a

relatively small incremental cost.

a. 1 to 3

b. 2 to 4

c. 2 to 3

d. 1 to 4

5. Hub venting is most eective

during operation of the hydraulic

turbine operating at partial load.

a. True

b. False

6. The selection of any DO enhance-

ment system must consider not only

upfront capital costs, but also:

1. Associated operation

and maintenance costs

2. Performance degradation

impacts on revenue

3. System eectiveness

for multiple units

4. Site specic DO uptake desired

5. Site specic hydrology,

among others.

a. 1 & 2

b. 2 & 5

c. 1 & 4

d. 3 & 4

e. All of the Above

7. In recent years, Voith’s joint R&D

eorts with their partners have

successfully developed a variety of

designs for aeration, including:

a. hub aeration

b. distributed aeration (through

the discharge ring)

c. perpendicula r aeration

d. head cover aeration

8. There are at least four (4) options

to consider to achieve DO enhance-

ment, as follows:

1. Vacuum Breaker Aeration

2. Hub Venting DO Enhancement

Design (Central Aeration)

3. Aerating Runner Design

(Distributed System)

4. Tailrace Oxygen

Injection System

a. True

b. False

9. The advantages of the Vacuum

Breaker Aeration design are that

the modications can usually be

implemented without disassembly

of the turbine and at the lowest

relative capital cost of the options

considered. The disadvantages

are that the eectiveness varies

from station to station and that

generally only modest increases

in DO can be realized.

a. True

b. False


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Questions

OnlineCompletionUse this page to review the questions and choose your answers. Return to www.powergenu.com and sign in. If you have not previously purchased the program

select it from the “Online Courses” listing and complete the online purchase. Once purchased the exam will be added to your User History page where a Take

Exam link will be provided. Click on the “Take Exam” link, complete all the program questions and submit your answers. An immediate grade report will be

provided and upon receiving a passing grade (70%) your “Certicate of Completion” will be provided immediately for viewing and/or printing. Certicates of

Completion can be viewed and/or printed anytime in the future by returning to www.powergenu.com, sign in and return to your User History Page.

10. One advantage of the Hub Venting

DO Enhancement Design is that

smaller quantities of air are added

to the turbine discharge than with

the similar vacuum breaker aeration

scheme, but the incremental

additional cost of the modication

is relatively high. These DO en-

hancement systems can be turned

on or o as desired and do not have

a signicant eect on performance

when not admitting air. This option

is most eective at increasing DO

levels during full load turbine

operation and has lesser enhance-

ment capability at partial loading.

a. True

b. False

11. There are several disadvantages

to the Forebay Oxygen Injection

System:

1. The initial capital cost

of installing this system

2. Ongoing annual O&M cost for

purchasing the liquid oxygen

3. Additional maintenance

of the draft tube hoses

and injection equipment

4. Impact to sh passage

a. 1 & 4

b. 2 & 3

c. 1 & 2

d. 3 & 4

e. All of the Above

12. The runner discharge methodol-

ogy is more benecial than

the aeration methodology

for the following reasons:

a. Provides air over a range of

turbine discharges with lower

impact to performance than

all other methods evaluated

b. Provides air in large bubbles

which are distributed over a

wide area of draft tube inow

c. Provides air in a manner which leads

to a high absorption concentration

d. Requires smaller amounts

of air, but large amounts

of oxygen, and therefore

preserves more of the operating

characteristic of the turbine

13. In the Waterlee, testing determined

that __ open valves actually allowed

more air to be admitted than was

needed to meet a 3 mg/l uptake.

a. 2

b. 3

c. 4

d. 5

14. For the aerating runner, the

amount of airow at various

turbine load settings from 50% to

100% was largest at the ____ ____

water ow rates, dropping slightly

as the wicket gate setting was

____ __ __, when calculated as a

percentage of ow in SCFM.

a. lower/decreased

b. higher/increased

c. lower/increased

d. higher/decreased

15. It is important to not only

increase the DO levels in the

tailrace, but to use representa-

tive DO measurements in

evaluating tailrace aeration.

a. True

b. False

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