Julius Nyerere Hydropower Plant is being Connected to the Tanzanian National Grid

• 95% Overall Construction Progress
• Water Impounding for Dam Reservoir Completed
• Completion of 1.45 Million m3 RCC in the Main Dam Structure
• 158,000 Sqm Kilometers Total Reservoir
• 120 Million Manhours
• 12,500 Manpower at Peak

The?First Turbine?is Scheduled?for the Wet Test on?February 24

In 2018, Tanzania Electric Supply Company Limited (TANESCO) and the Joint Venture of the Arab Contractors and ELSEWEDY ELECTRIC entered into an Engineering, Procurement, and Construction contract for the execution of Julius Nyerere Hydropower Project.

The dam, that is the Fourth largest in Africa, and Ninth largest in the world, is located across the Rufiji River, at Stiegler’s Gorge, in the Selous Game Reserve, Morogoro Region, southwest of Dar Es Salaam, the commercial capital and the largest city of Tanzania.

The project is built to generate power, control floods, and provide environmental and ecological water supply. The total installed capacity of the power station is 2115MW, and the annual power generation capacity is 6307GWh. The normal storage level of the reservoir is 184.00m.

When fully developed, it will be the largest power station in Tanzania, with a reservoir capacity of 34 billion m3. The power generated will be evacuated via a 400kV high voltage power line to a substation where the power is to be integrated into the national electricity grid, providing reliable and affordable electricity to approximately 60 Million Tanzanians, serving the ongoing economic and industrial development, as well as encompass the expected future demand.

In 2023 we were able to successfully complete the RCC of the main dam structure, the reservoir impounding, the installation of the world’s largest main inlet valve (400 ton) 3x sets out of x9, the installation of the power generator’s main components, and the construction of the first turbine generator unit.

As we advance with the works of Julius Nyerere Hydropower project, we are now reaching a crucial milestone of the back energization, and the initiation of the wet testing for the first turbine is scheduled beginning of 2024, that marking a significant step toward delivering on the project's commitment to providing power to the people of Tanzania.

Case Study 1

Saddle Dams

The Problem

Saddle Dams are a crucial element of JNHPP, located approximately 10.0km south of the Main Dam, in areas where the land is lower than the reservoir's water levels. The primary role of the Saddle Dams is to contain reservoir water and manage its level when PMF (Probable Maximum Flood) occurs through an emergency spillway at Saddle Dam 1.

While Saddle Dam 1 is constructed as an RCC (Roller Compacted Concrete) gravity dam, Saddle Dams 2 to 4 are earth-fill embankment dams, spanning a total of 16.0km. Considering the vast amount of materials required for their construction, nearly 5.0 million cubic meters, the design concept should incorporate the characteristics of natural material available at the nearest source to the dam site.

During the final design's Geotechnical Investigation (GI), dispersive soils were identified at the nominated borrow area (i.e., the sources of natural materials) for the construction of Saddle Dams 2 to 4. Due to subsoil chemistry, dispersive soils are known for their susceptibility to erosion when exposed to water saturation.

Challenge

The presence of dispersive soil at the nominated borrow areas poses a significant risk to the proposed Saddle Dams 2 to 4 type at this stage (i.e. Homogenous Earth-Fill Embankment Dam), due to the high erosion potential of embankment material by piping and/or internal erosion when exposed to reservoir water.

Approach

Unfortunately, the chemical behavior of dispersive soil cannot be modeled numerically using the latest engineering software.? Hence, a very detailed lab testing program is carried out on the available material at the nominated borrow areas, to:

• Gain a thorough understanding of the subsoil chemistry;
• Evaluate and categorize the soil’s dispersivity levels as low, intermediate, or high;
• Determine the range of dispersive soil present within the borrow areas.

Action

After acquiring an understanding of various aspects of the issue, the proposed solutions are as outlined below:

a)????? Implement additional design measures to the initially proposed dam type for Saddle Dams 2 to 4, to account the soil dispersity. These design measures could be summarized as follows:

• Introducing a well-designed chimney filter and drainage blanket, which will eliminate the immigration of soil particles with seepage water.
• Chemically treating the soil dispersivity using Lime.

b)????? Implement alternative dam type for Saddle Dams 2 to 4 (ex. Rock-Fill Dam with Asphaltic Concrete Core), which will be constructed by crushed rock instead of dispersive soil.

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Cost-benefit study is conducted to assess each proposal and determine the best course of action.

Result

Finally, Saddle Dams 2 to 4 designs incorporate a well-designed chimney filter with a drainage blanket and a layer of lime-treated soil at both U/S and D/S sides (i.e. Solution “a”) as an effective design measure for soil dispersivity.

The construction of Saddle Dams 2 to 4 utilizing different materials with certain specifications was a challenging job.

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Case Study 2

Turbine Shaft-seal System

The Problem

The turbine shaft seal is a crucial component of a hydro-turbine. Its main function is to ensure a leak-proof connection between the turbine shaft and its head cover. This not only minimizes water leakage but also boosts the turbine's overall efficiency by reducing power loss.

To prolong the seal's lifespan and maintain its sealing effectiveness, a consistent water flow is essential. This flow provides the necessary cooling and lubrication, minimizing wear on the sealing surfaces.

It's imperative that the water supply to the turbine's shaft seal remains steady, clean, and at a constant pressure and flow rate, even during emergency turbine shut-downs or power outages.

Challenge

Two primary challenges were encountered to achieve this milestone;

The initial challenge was the disruption in the water supply to the shaft seal whenever there was a power loss to the pump. Even with the use of two redundant pumps for each turbine to ensure consistent water flow and pressure to the shaft seal, a power outage remained a concern. If one pump failed, the other would activate, but this didn't address the overarching problem of power interruptions.

A proposed solution was to employ a backup DC-motor-driven pump and connect it to the UPS (Uninterruptible Power Supply) batteries. However, this approach came with significant drawbacks: high initial costs, shorter lifespan, low speeds, and increased maintenance expenses. Thus, there was an urge to find alternative solutions.

The second challenge was the vast amount of clean water needed to seal all nine turbines during operation. Each turbine demanded 20 m3/hr., amounting to approximately 4320 m3/day for all turbines combined which would require a huge water treatment plant, and that would significantly increase both initial and ongoing costs.

Approach

Prior mentioned challenges were analyzed and deeply studied by different disciplines of the engineering department to find proper alternatives using different techniques to achieve the required quality, quantity, and continuity of the water supply to the shaft seal without compromising the initial and operation costs.

?Several potential solutions were explored and simulated using the latest software. The supply chain department provided insights into the cost and time implications for each option, while the construction team assessed the feasibility of implementing these solutions. Ultimately, the most effective and efficient solution was chosen and put into action to meet the water supply requirements.

Action

For the first challenge, since continuous water supply to the shaft seal during power cut-off is required, a backup line from the turbine penstock, before the main inlet valve, was tapped. The backup line will utilize the high pressure of water in the penstock besides the continuous availability of water before the main inlet valve. The shaft-sealing water tapped from penstock -upstream MIV- will be supplied to the turbine shaft seal after pressure reduction to match the required pressure for the shaft seal during the period of the turbine shut-off after power loss.

For the second challenge to achieve the required water quality automatic self-cleaning strainers were used to filter the water from the solids and debris, after that a second filtration stage was added using a cyclone separator to reach the required water quality to preserve the seals with minimum initial cost and regular maintenance costs.

Results

The implemented solutions achieved the requirement of the turbine sealing system however they reduced the expected initial cost of other alternatives maintaining the safe and reliable operation of the system.

The backup line from the penstock provided a reliable uninterrupted backup water supply for the pumps in case of a power cut. Also, the solution provides a long lifespan compared to using DC motor-driven pumps. Also, this solution reduces the cost of purchasing these custom-made pumps and the related batteries required to run the pumps during power cuts.

Additionally, the integration of an automatic self-cleaning strainer with a Cyclone separator enabled us to establish a water treatment plant with a capacity of just 15 m3/day, a significant reduction from the previously estimated 4320 m3/day. This not only led to savings in initial costs, space, construction time, and procurement but also reduced operational and maintenance expenses. The power saved from this efficient setup enhanced the project's total net power output.