Adding generating facilities to non-powered dams in Romania can help maximize the country’s renewable energy potential. This article presents a case study of development of one such facility, 2.663-MW Zavoiul Orbului.
By Valentin Ispir, Radu Sarghiuta, Daniel Gaftoi and Catalin Popescu
The majority of the dams in the world do not have a hydropower component, and the addition of hydropower capabilities at non-powered dams can offer a way to create new energy resources with minimal environmental impact.
This article discusses the 2.663-MW small hydropower project added to the Zavoiul Orbului Dam on the Dambovita River in Romania. The plant consists of two banks of six Archimedes screw turbines. The project is adjacent to the dam spillway and the water intake is cut into the embankment dam body.
Important topics discussed include why Archimedes screw technology was chosen for this site, how the turbines were incorporated into the existing site configuration and how the facility will be operated and controlled.
Adding small hydro
To help overcome a serious challenge in the European Union – climate change due to CO2 emissions – a series of proposed directions were made, including increasing energy production from renewable sources. Directive 2009/28/EC unifies provisions for the electric energy, thermal energy and transport energy produced from renewable sources. The main objectives are to increase the share of renewable energy in final energy consumption to 20% and to increase the share of renewable energy sources in the fuel used by the transport sector by 10%, both by 2020. According to the first annex of the directive, Romania’s target by 2020 is 24%.
For southeast European countries, including Romania, hydropower is the most important source for renewable electricity generation. However, the potential for hydropower sector development in the future is hampered due to difficult approval of new projects and allocation of leases and permissions.
Three viable alternatives are to upgrade the capacity of existing turbines, add new turbines at existing facilities or add hydropower generation to non-powered dams.
|This conceptual image is a downstream view of Zavoiul Orbului Dam and existing spillway that will receive turbines.|
Hydropower in Romania
Romania has 380 operating hydropower plants with a total installed capacity of 6,453 MW. About 46% are small plants (installed capacity of less than 1 MW), 25% are medium-sized (1 MW to 10 MW), and 29% are considered large plants (more than 10 MW). Of these, 90% of the capacity is from large hydropower (6,058 MW) and only 10% (395 MW) is from small or medium facilities.
Romanian strategy regarding the energy sector for 2011 to 2035 stipulates that hydropower potential represents a sustainable alternative for development, considering the limited raw materials available in the country for electricity production and the need to obtain cheap energy that does not produce greenhouse gases. 1
This strategy should also have a negligible affect on the posibility of increasing Romania’s carbon footprint over the long-term energy production process.
Case study: Developing Zavoiul Orbului
Zavoiul Orbului is an earthfill dam on the Arges River, completed in 1988 to supply water for the city of Bucharest and agriculture.
The dam consists of two side dams and a central movable weir that acts as a spillway. It impounds a reservoir with a total volume of 12 million m3, including 1.9 million m3 of flood control volume. The weir has five spillways spans, equipped with five gates and 10 bottom-outlets equipped with tainter gates.
The side dams have a maximum height of 7.8 m and total length of about 7,400 m. The dam has an upstream concrete flat slab, 39.5 m long and 2.75 m thick. In front of the slab, a 5-m-deep cutoff wall was implemented for seepage control and sliding stability in case of high water. The weir continues with a stilling basin that has baffle piers, an uneven concrete slab dissipater and an anti-scour funnel to join the natural riverbed.
The dam is at stage I. In stage II, which has not been completed, flap gates will be installed on the existing structure to raise the reservoir level. Due to actual hydro-development status and river basin operation, stage II of the dam project will not be implemented in the forseable future. On the right side of the dam, on a platform, a hydropower plant was supposed to be implemented during stage II. The hydropower plant is the reason why the dissipater appears to be atypical towards the right bank, as it was supposed also to draw off the water from the plant’s stilling basin.
The irrigation intake is located in the left bank abutment and is made up of four windows 2.5 m by 2.5 m, equipped with sluice gates. The maximum capacity of the intake is 19.66 m3/s. The water from the intake is sent through two concrete rectangular galleries to a distribution basin where it is diverted by siphoning and galleries in two gravitational channels, one on the right and one on the left bank.
An easement intake (for minimum environmental flow) is located on the left bank, consisting of two 2 m by 2.5 m intake portals, equipped with sluice gates that open up into the plunge pool. The intake capacity is up to 44 m3/s. The choice of Archimedes screw turbine was made on the assumption that they do not need major intervention on the existing structures, furthermore making the best use of them. This intervention on the dam body consists in implementing a new intake in the right abutment of the dam. As environment bonus this type of turbine is fish friendly. The project consists of two banks of Archimedes screw turbines, inline and the first bank outlet serving as headrace for the second.
Adding the hydro component
Adding a small hydro facility to the existing dam involved a number of structural changes:
- Cutting a 17 m by 1.55 m window in the cutoff wall for laying out the slab at elevation 170.9 m (founded at elevation 170.6 m);
- Replacing a section of the front right bank dam, 17 m long, with the front intake and headrace channel of the future arrangements; and
- Using 30-m-wide portions of the existing stilling basin, to the right bank, for the headrace channel of the second Archimedes screw bank. This section is set out from the existing stilling basin by a routing concrete wall with double soles, anchored by the stilling basin apron.
Work to replace the 17 m portion of the front right bank earth dam involved laying the intake foundation slab, with 10 m lengths, and the intake block. The foundation slab is a reinforced concrete structure between the left and right bank abutments. The structure has an intermediate elevation foundation slab at elevation 173.20 m, serving as access to the trashracks, followed by the sluice gates headwall, 16 m by 2.55 m in size.
This solution ensures a good connection between the existing dam front and new works designed for the hydropower development. The sensitive areas needed to provide continuity are the gap between the cutoff wall and the small hydropower plant foundation slab, as well as the connection between the piling wall and the revetment of the existing dam.
The water intake is composed of piles embedded in a slab foundation ensemble, thus forming four openings.
The intake is to be equipped with a coarse trashrack (10 cm of rod spacing and 2.8 m by 2 m dimensions). At the top of the racks up to the sluice gates, a slab causeway serves for operating followed by four manually operated sluice gates. The openings are closed off with reinforced concrete headwalls up to elevation 175.75 m. The intake assembly is incorporated into the existing dam by routing it between the two lines (right and left) of synthetic sheet piling. The slab foundation of the intake leans on the earth dam cutoff wall sealing as it raises to the right bank closure dam by about 1.3 m.
The trapezoidal headrace channel is lined with concrete slabs measuring 3.5 m by 3.5 m by 0.2 m. The channel length is 75 m and the width of the base is 14 m.
The hydraulic circuit, after the intake, conducts water toward the first bank of Archimedes screws through the headrace channel. The two sheet metal conduits support the dam crest road. The pipe is laid in the trench created by the piles, much like in the case of the intake. Filling the space between their upper surface and trench sheeting with concrete and compacted earth reinforces the 24 m pipes. The road elevation will thus be equal to the dam crest elevation of 176.75 m.
Six 3.545 m by 2 m gates control flow entering the first six-screw bank. The gates are activated hydraulically and some screws can be stopped when inflows fall below the design flow of 6.45 cm/s per screw unit. Turbine flow using a gabion mat is discharged to the Arges River by a rectangular 14-m-long concrete channel.
Operating the facility
The facility (see Figure 1) is in its design and permitting phase.
|The works at the Zavoiul Orbului project are: 1 Water intake with two trashracks, 2 Manual sluice gates, 3 Steel culvert, 4 Headrace channel for first bank of Archimedes screws, 5 Hydraulically operated sluice gate for first bank, 5A Electrical equipment for first bank, 6 First bank of six Archimedes screws, 7 Dissipater acting as headrace channel for second bank of screws, 8 Reinforced concrete wall for mechanical equipment protection, 8A Reinforced concrete wall, 9 Hydraulically operated sluice gates in front of second bank, 9A Electric equipment for second bank, 10 Second bank of screws, 11 Concrete tailrace, 12 Gabion mat foundation joining to riverbed|
The operating rules of the two plants are subordinated to the operating rules of the existing reservoir and dam. The Archimedes screws will operate in a range of flows between minimum flow and maximum flow recorded in the section (mean multiannual flow 39.2 cm/s and maximum Q1% 1305 cm/s). The plant buildings for each of the banks of Archimedes screws are above ground, set on the screws’ reinforced concrete structure. The light infrastructure for the electrical equipment housing is equipped with a mono-beam cross-role bridge crane that has an electric drive for handling or equipment repair. The control system will ensure the operation of the installations from a dispatch center, which will enable remote command, signaling and automatically switching. Visis Best Proiect SRL, project developer, will manufacture and supply all of the project’s hardware and control systems.
On the basis of the assumption that the hydropower development will be achieved by the same company that actually designs, supplies and manufactures the hardware, the total costs can be assumed as US$2.6 million for the total 2663 kW installed power. With energy generated, yearly between minimum 18.198 MWh/year and maximum 22.227 MWh/year, we can conclude this type of hydro development, by adding turbines to an existing non-powered dam, is cost effective and environmentally friendly.
1Stematiu, D., and I. Iacob, “Aspecte privind hidroenergia ca sursa de energie support a dezvoltarii durabile,” Hidrotehnica, Volume 60, No. 3, 2015, pages 35-42.
Valentin Ispir is general manager of Visis Best Proiect SRL. Radu Sarghiuta, PhD, is a professor, Daniel Gaftoi, PhD, is a teaching assistant and Catalin Popescu, PhD, is a lecturer at the Technical University of Civil Engineering of Bucharest, Romania.