Cape Town May 2014 - Engerati · Cape Town May 2014 Presented by: ... AMEI for the detailed design...

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DESIGN CONSIDERATIONS FOR THE 40 MW KASHIMBILA HYDROPOWER STATION 2014-05-14 Cape Town May 2014 Presented by: Henry-John Wright

Transcript of Cape Town May 2014 - Engerati · Cape Town May 2014 Presented by: ... AMEI for the detailed design...

Page 1: Cape Town May 2014 - Engerati · Cape Town May 2014 Presented by: ... AMEI for the detailed design of the dam, ... steps and drainage gallery.

DESIGN

CONSIDERATIONS

FOR THE 40 MW

KASHIMBILA

HYDROPOWER

STATION

2014-05-14

Cape Town May 2014

Presented by: Henry-John Wright

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Project Location

Kashimbila Multipurpose Dam

Geographic Location of Kashimbila Dam on the

Katsina-Ala River 0060 52’ 15” N 0090 45’ 43” E Lake Nyos, Cameroon

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• In 2008 the Federal Ministry of Water Resources of the Federal Republic of Nigeria appointed S.C.C. (Nigeria) Limited, a Civil Contractor established in Nigeria for over 30 years, to design and construct the multipurpose dam.

• The principal purpose of the dam was to act as a safety buffer dam and protect Nigeria from the possible failure of Lake Nyos, Cameroon.

• The dam was also to be of MULTIPURPOSE use, thus would also be providing: – Domestic water;

– Irrigation water; and

– Electricity generation through hydropower.

• Reservoir capacity was therefore increased from the initial 200 million m3 (required for the flood absorption) to 500 million m3 to provide the multipurpose (sustainable) solution.

Project History

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• In 2009, the Federal Ministry of Water Resources approved Aurecon AMEI for the detailed design of the dam, outlet works and hydropower station.

• Mean Annual Runoff: 13 190 million m3.

• Katsina-Ala River has significant seasonal flow variation: – Minimum mean flow of ~ 60 m3/s in February;

– Maximum mean flow of ~ 1 200 m3/s in September.

Project History (Cont.)

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• The common rock units exposed at the dam site and its designed flood area are defined as the Basement Complex, which is basically derived from granite rock (biotite gneiss granite), but consists of other compositions of igneous or metamorphic rocks.

• The rock outcropped on the banks and in the river bed.

• Sound geology in basin.

• Granite was jointed, thus requiring curtain grouting.

• Consolidation grouting done in cut off trench rock contact and under concrete structures (spillway, tongue walls, power station).

Geology

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Geology (Cont.)

Power Station pit Eastern Excavation Face

(Upstream)

Power Station pit Southern Excavation Face

(LHS)

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• Catchment located mainly in Cameroon and extends to approximately 180 km from the border into Cameroon.

• Overall, the catchment is an area of high relief and is largely natural with elevation starting at 1300 and ending at 170 masl.

• Water use in the catchment was considered as negligible.

• The vegetation type: – Deciduous woodland in

upper catchment; and

– Forest near dam site.

• Catchment Area: 8 467 km2.

• Mean Annual Precipitation (MAP)

was determined to be 2 547 mm.

Hydrology – Stream flow

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Hydrology - Streamflow (Cont.)

Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Flow (million m3) 314 196 138 140 250 567 1091 1847 2581 2399 1347 600

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Hydrology - Streamflow (Cont.)

Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Minimum 39 27 19 18 26 45 63 127 364 274 197 78

Average 131 89 57 63 113 280 520 823 1129 993 586 250

Maximum 193 116 70 375 612 991 1464 1916 2364 1663 1076 416

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Percentage exceeded (%)

% Exceeded 0 20 80 100

200

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50%, 220 m3/s

70%, 100 m3/s

80%, 70 m3/s

20%, 800 m3/s

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• Single site PFA was also carried out using the following: – LPIII;

– GEVmm; and

– GEVpwm.

• Level Pool Reservoir Routing was also carried out.

Hydrology - Floods

RI

(years)

Inflow peak

(m3/s)

Outflow peak

(m3/s)

2 2 675 1750 5 3 110 2020

10 3 375 2190 20 3 610 2340

100 4 106 N/P 200 4 307 N/P

PMF 9 400 7 700

Note: N/P means routing calculation was Not Performed.

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w (

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Outflow Inflow

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Hydrology – Hydropower

• Initial capacity determined in preliminary design phase was 6 MW, and was later increased to 18 MW by the Client demand. Reservoir storage capacity was subsequently increased from 200 mil. m3 to 500 mil. m3. This required the dam height to increase by approx. 10m.

• The Client further requested that a review be carried out to determine the maximum generation potential of the dam.

• Monthly flow rate during an “average hydrological” year varies from 57 m3/s in March to 1 129 m3/s in September.

• Flow variance and the small ‘active’ storage capacity rendered the determination of the flow rate for hydropower generation relatively difficult and considered somewhat of an “extended run-of-river” .

• In yield analysis, the domestic supply was given priority 1 (100% assurance) whilst the irrigation and hydropower were given priority 2 and 3 (80% assurance).

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Hydrology – Hydropower (cont.)

• Based on first run, maximum installed capacity to keep above the 80% reliability was 75 MW.

• An exercise was carried out for 22, 36, 40 and 75 MW, taking into consideration the economical aspects and the load factor of the various installed capacities. The optimal was found to be at 40 MW without further increasing the height of the dam.

Month Flow rate

(m3/s)

Assurance of Supply

(%)

Maximum Generation

Capacity (MW)*

Monthly Load Factor

Dec - Jan 210 86.5 ~ 81.1 36 0.52 ~ 0.49 Feb to May 60 98.6 ~ 85.1 10 0.14

Jun 100 81.1 17 0.23 Jul - Aug 210 81.1 ~ 95.9 36 0.50

Sep - Nov 440 98.6 ~ 94.6 75 0.98 Theoretical Annual Generation (assuming no downtime) 240 GWh Theoretical Annual Load Factor (assuming no downtime) 0.68

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Spillway

• Conventional mass gravity, uncontrolled ogee crest with downstream steps and drainage gallery.

• Freeboard calculated as per SANCOLD Guideline combinations and was sized for PMF conditions.

• Designed for PMF: 7 700 m3/s with the potential sub-atmospheric pressures on the spillway crest for Ht/Hd ratio = 1.33 (USBR, 1987).

• Apron is 800 mm thick concrete anchored and keyed into spillway wall.

• Tailwater curve was generated by using water surface profile calculations based on the momentum equation which was calibrated to yield flow versus water depth data over a 10 km stretch downstream of the embankment center line that corresponded to the daily average flow values and depths recorded at the dam site.

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Spillway – Hydraulic Model

Flow directing structure added to improve flow conditions

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Outlet Works

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Hydropower Station

Taking into considerations the flow variations, the following combinations were evaluated for the 40 MW installation:

• 2 x 20 MW;

• 2 x 15 MW + 2 x 5 MW; and

• 4 x 10 MW.

Discussion:

• 2 x 20 MW: Not sufficient redundancy; equipment too heavy to be transported in bulk, site assembly;

• 2 x 15 MW + 2 x 5 MW: Loss of energy production during maintenance; complex civil works; two sets of spare parts; and

• 4 x 10 MW: Simplest civil construction; most optimal for operational requirement; spare parts similar for all 4 units.

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Hydropower Station (Cont.)

Turbine type considered (water to wire):

• Vertical conventional Kaplan; and

• Vertical “Saxo” / Tubular arrangement.

Selected Parameters:

• Max Headnet: 20.5 m.

• Rated Headnet: 17.8 m.

• Qrated: 65 m3/s.

• Turbine guaranteed best efficiency point: 93.8%.

Estimated annual energy production:

• 210 GWh/annum (revised after determining downtime)

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Hydropower Station (Cont.)

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Hydropower Station (Cont.)

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Hydropower Station (Cont.)

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Mechanical Works and Hydr0-

mechanical Equipment

Equipment includes:

• Overhead crane (50 ton);

• Portal cranes (3 ton);

• Fine trash rack (15 degrees to vertical);

• Trash cleaning machine;

• Upstream maintenance gate (2 No., balanced conditions);

• Emergency gate (4 No., wheeled gates, close under own weight); and

• Downstream maintenance gate (8 No., balanced conditions).

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Mechanical Works and Hydr0-

mechanical Equipment (Cont.)

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Project Photographs

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Project Photographs

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Project Photographs

Page 26: Cape Town May 2014 - Engerati · Cape Town May 2014 Presented by: ... AMEI for the detailed design of the dam, ... steps and drainage gallery.

Project Photographs

Page 27: Cape Town May 2014 - Engerati · Cape Town May 2014 Presented by: ... AMEI for the detailed design of the dam, ... steps and drainage gallery.

Project Photographs

Page 28: Cape Town May 2014 - Engerati · Cape Town May 2014 Presented by: ... AMEI for the detailed design of the dam, ... steps and drainage gallery.

Project Photographs

Page 29: Cape Town May 2014 - Engerati · Cape Town May 2014 Presented by: ... AMEI for the detailed design of the dam, ... steps and drainage gallery.

Project Photographs

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Concluding Remarks

The works are in a well advanced stage of construction and are being professionally carried out by S.C.C. (Nigeria) Limited with due diligence and excellent workmanship.

This multipurpose project combines the various disciplines of engineering resulting in a sustainable solution to the eastern region of the Federal Republic of Nigeria.

It is an excellent example of a multipurpose project providing:

• Safety (or protection) against flooding should Lake Nyos fail as well as future flood control of the Katsina-Ala River.

• Potable water which contributes to the improvement of public health in the surrounding communities.

• Water for irrigation and thus enhances food security in the area; and

• The generation of electricity to the Federal grid.