SEDICON SLUICERS AS EFFECTIVE MEHOD OF SEDIMENT REMOVAL FROM DESILTING TANKS AND CHAMBERS

Transcription

1 SEDICON SLUICERS AS EFFECTIVE MEHOD OF SEDIMENT REMOVAL FROM DESILTING TANKS AND CHAMBERS Dr. Tom Jacobsen Technical Director SediCon AS, Norway Mr. P.K. Sood Founding Director & Head of Operations INTRODUCTION Efficient and reliable removal of sand and silt from desilting basins has always been one of the main challenges during development of run-of-river hydropower on sediment carrying rivers. The Norwegian company SediCon AS has developed a new and patented method, the SediCon Sluicer, which overcomes problems such as interrupted power production, high water consumption, risk of mechanical breakdown, risk of mal-operation and the need for constant attention from operators. The sediment Sluicer has absolutely no movable parts except the outlet valve, and uses gravity only the driving force Recently, the technology have been introduced to India. Through a cooperation with HDM Management Limited, SediCon has proposed the SediCon Sluicers for the 6 MW Baner Sangam project located in Kangra District of Himachal Pradesh. The SediCon Sluicers will require a water consumption which is only fraction of what was the original alternative, and will provide extremely reliable sediment removal without any movable parts. We believe this project will be an excellent reference for the many existing and upcoming hydropower projects in India with need for efficient sediment removal. Not least important is the possibility to equip pressurized tunnel desilting basins with SediCon Sluicers. In India, with a tradition for large tunnel desanders, there should be large opportunities for this technology. The SediCon Sluicers extreme reliability is proven in tunnel sand traps such as 60 MW Khimti tunnel in Nepal, which has 15 years of only successful operation and only one inspection. (2008) At the 7 MW Cuyamel in Honduras, the SediCon Sluicers has removed sediments from the 40 meter long tunnel desilting basin since One may think that this technology is only for small and medium sized power plants. This is certainly not so! Late 2013 the SediCon Sluicers were chosen for the 1500 MW Coca Codo Sinclair project in Ecuador. When commissioned in 2016, this power plant will rank as the world s largest high head run of river power plant together with Nathpa Jhakri. The 40 SediCon Sluicer units are designed to remove 6 million ton sand per year - however even this is far from the upper limit. Several upcoming projects verify that international consultants have adopted the technology. Lahmeyer has chosen it for underground desilting basins at Keyal Khwar in Pakistan, Mott McDonald for tunnel sand-traps at Shuakhevi, ELC Electro consult for Deralok in Iraqi Kurdistan and Norconsult for Alto Maipo in Chile. 105

2 ICHPSD DESCRIPTION OF THE SEDICON SLUICER A SediCon Sluicer consists of two permanently fixed pipes with slots underneath. The two slotted pipes are coupled a coupling unit black box that balances flow and concentration and leads the sediment and water to the outlet pipe. The system works by gravity only and has no movable parts, except the outlet gates. The may be more than one SediCon Sluicers in each basin- and each of the SediCon Sluicers will work completely independent of the others The SediCon Sluicers are operated in two phases: 1. Sediment is allowed to deposit on top of the slotted pipe until the thickness of the sediment deposit is sufficient for flushing. Because the slots are on the bottom side sediment will not accumulate inside the pipe. Water can thus flow freely through the slotted pipe and out of the outlet pipe. 2. The valve on the outlet pipe is opened, and flushing of sediment starts. Water is drawn through the slots and picks up sediment close to where the slotted pipe emerges from the sediment deposits (the suction point ). As the sediment is sluiced the suction point moves downstream until all sediment that cover the slotted pipe has been removed. Due its special design the SediCon Sluicers ensures that an absolute minimum of water is used for transport of sediment. The design also ensures that no pumps are required, and that a very low water consumption is required. Abrasion is challenge, therefore SediCon will select pipe material and pipe wall fitted for each of the units. SediCon optimises the SediCon Sluicers carefully taking into account that most sediment and coarsest sediment will deposit close to the intake whereas less and finer sediments will deposit further downstream. Fig. 1: Longitudinal section of desilting basin with two SediCon Sluicers 106

3 1.1 Advantages The advantages of SediCon Sluicer can be listed as follows: Continuous power production: It is not required to dewater the desilting basin or tunnel to remove the sediments, sediment removal does not interfere with production. All sediments are removed: The SediCon Sluicer can remove everything from mm stones to cohesive silt and clay. Water saved: A minimum amount of water is used to remove the sediments, as discharged sediment concentration is very high. Any capacity can be obtained: There are no upper limit with respect to the size and sediment removal capacity of each system Reduced construction costs, as outlet tunnel(s) can be made shorter or omitted altogether. Reduced turbine wear: Sediment removal can be performed whenever required and does not have to be scheduled to periods with no production. Easy operation: SPSS has no movable parts except valves, and low maintenance cost and operation does require special skills. Long life: SediCon Sluicers can be designed for 50 years life or more. Installation in all sediment retaining structures: Desilting basins, forebays, pressurized desilting chambers and tunnel sand traps. Environment Friendly: SPSS allows sediment removal at chosen time and concentration, so the ecological impact is small. Low water consumption and efficient sediment removal means more green power. 1.2 The Baner Sangam project General description The Baner Sangam run-of-river H. E. Project is under construction. The project is located in Kanagra District of Himachal Pradesh and will utilise the available discharges of Baner Khad & Manuni Khad, which are tributaries of River Beas in District Kangra of Himachal Pradesh. The scheme envisages diversion of Baner Khad inflows by constructing a raised crested diversion weir where the Khad bed is at EL ± 563 m where ample space is available on the left bank of Baner Khad for accommodating the intake, the conveyance channel as well as the Desilting basin. Baner Sangam has been taken-up for development on Build, Own, Operate and Transfer (BOOT) basis by M/s Yogindera Powers Limited. The diverted inflows will be carried through conveyance channel constructed of RCC box section to a surface Dufour type Desilting basin, which will be designed to exclude all silt particles down to 0.25 mm size. The silt-free water will be carried through a water conductor comprising of a head race tunnel and power channel constructed of RCC box section emptying into a surface forebay. The diverted water shall be led to the surface powerhouse through high pressure surface steel penstock to feed two numbers of Francis turbines of 2.5 MW capacity each. 107

4 ICHPSD Sediment issues at Baner Sangam Baner Khad drains the central part of the Kangra valley and rises as a small snow fed channel on the Southern slopes of the Dhauladhar range near Palampur. The general direction of flow is towards South-West. On its course, many small Khads meet Baner Khad. Major Khads which merge in Baner Khad are Ikku, Maujhi and Manuni Khads. Manuni Khad rises from the Southern slopes of the Dhauladhar range and joins the Baner Khad near Jalari village. Steep slopes form the upper catchment and there is a sharp fall in its gradient. Huge river terraces on the both sides of the river is used for cultivation extensively. Baner Sangam is located just downstream of confluence point of 4 streams namely Baner, Manuni, Iku & Maujhi. All the 4 streams carry a lot of silt and suspended load during the monsoon season hence the water in the Baner Stream (Khad) carries lot of silt during the monsoon months and becomes very muddy. For most part of the year, silt content in Baner Khad water is nil. In flood season, it carries boulders, small stones / pebbles and suspended silt particles. Pebbles and debris shall either roll over the weir crest or shall be flushed out from the undersluice bay and hence not enter the intake. Only the silt particles suspended in water shall enter the intake. 2 THE INITIAL PROPOSAL FOR SEDIMENT REMOVAL: DUFOUR Proposed Desilting basin & Silt Flushing Arrangement - A Dufour type desilting chamber of 22 m width, 50 m length with 19.3 m long upstream transition and 4 m long downstream the transition, is proposed immediately downstream of the conveyance channel to exclude all particles down to 0.25 mm size. The silt flushing arrangement comprises of Four (4) Numbers Silt Trapping Galleries placed below the four (4) chambers of the Desilting basin followed by Four (4) numbers Silt Flushing Pipes which are all connected to One (1) Number, 0.7 m diameter Silt Flushing Pipe with a Silt Flushing Valve arranged inside a Vertical circular shaft to flush out the trapped silt downstream of the diversion weir of Baner Khad. 108

5 Fig. 2: Plan of 22 x 50 m Proposed Dufour Type Desilting basin Fig. 3: Cross Section of Proposed Dufour Type Desilting basin Fig. 4: Photo of Similar Dufour Type Desilting basin constructed 109

6 ICHPSD New proposal, Desilting tank with SediCon Sluicers The SediCon Sluicers shall utilize less water for silt flushing as compared to Dufour type Desilting tank which utilizes 20% of the design discharge for silt flushing. This 20% saving in flushing discharge would be beneficial during lean season when the discharge in Baner Khad is less than the design discharge and it would consequently increase the power production. The reduced discharge for flushing does not only save water. It will also increase trap efficiency, or alternatively allow a smaller Desilting tank with the same trap efficiency. The proposed desilting tank which dimensions (W x L) = 15 x 70 will therefore have a trap efficiency of 98,5%, which is same as for the Dufour system, and the smallest removable particle size would be 0.25 mm in both cases. Fig. 5: Longitudinal section of desilting tank with SediCon Sluicers Fig. 6: Cross section of desilting tank with SediCon Sluicers 110

7 2.2 Results from 1:10 model tests A small model test was performed in the premises of the Norwegian university of Science and technology in January A 10 meter long section of the prototype Desilting tank was represented in a scale 1:10 model. All geometrical measurements were to scale however the sand used has the same diameter as is expected for the Desilting tank. (In other words, a much coarser sand, d50 = 1,7 mm was actually represented in the model) Fig. 7: Calculated of particle size distributions (PSD s) or discharged and passing sediment; based on assumed incoming PSD Model (One unit) Scale Prototype (one unit) Particle size 0,17 N/A* 0,17 Length 1, Width 0,6 10 6,0 Depth 0,5 10 5,0 Measured water consumption (m3/s)** 0, * 0,407 Measured Sediment concentration (by volume) 8,4 % N/A 12,9 % Calculated sediment removal rate (t/hour) 0,56 874* 489 *) These values do not follow Froude s model laws. The reason is that the sediments cannot be scaled geometrically. We have decided to use same sediments in model as in prototype. Froude s law would predict flow is scaled 10 2,5 _= 316, whereas the too coarse sediments give higher ration for water flow and not least sediment transport. 111

8 ICHPSD Comparison between Dufour and SediCon Sluicer Dufour SediCon Sluicer Basin size (area) Water consumption 0,025 m3/s * Trap efficiency 98 % 98,5 % Sediment removal capacity 940 ton/hour *) Theoretical water consumption =176,114 m3 + 50% averaged over a period of 4 months 3 EXPERIENCE FROM OTHER PROJECTS 3.1 Cuyamel, Honduras Cuyamel HPP in Honduras is a 7.0 MW run-of-river plant with a gross head of 133 m and a 40 meter long underground desilting chamber as its only sediment handling facility. The desilting chamber is equipped with two SediCon Sluicers with capacity of approximately 1000 ton sediments per hour each. As a result of using SediCon Sluicers the discharge tunnel through which SPSS has outlet could be moved upstream closer to the dam and made considerably shorter. The SediCon Sluicers have been working as predicted since 2007, removing all sediments in the desilting basin once operators activate the outlet valves. Fig. 8: Cuyamel underground desilting chamber 3.2 Khimti tunnel sand trap and desilting basin SediCon also four SediCon Sluicer units at Khimti in Nepal in During SAT, operators measured a capacity of 4000 ton sediments per hour for all units combined. At the same power plant, two smaller SediCon Sluicers has removed sediments from the pressurized tunnel sand trap since The sand trap have only been inspected once (in 2008) when everything was found to be perfectly ok MW Coca Codo Sinclair in Ecuador Late 2013, the Chinese contractor Sinohydro awarded SediCon AS of Norway the contract for sediment removal system for 1500 MW Coca Codo Sinclair hydropower project in Ecuador. The 40 SediCon Sluicers shall be able to remove 6 million ton sediments annually by using 112

9 gravity as the only driving force. The instantaneous capacity will be ton sediment per hour if all SediCon Sluicers are operated simultaneously. One of the reasons for selecting SediCon Sluicers for Coca Cod Sinclair is that the outlet can be at a higher level than the bottom of the desilting basin. During floods, the available head at Coca Codo Sinclair is 8 meter, whereas the desilting basins are 15 meter deep. Within this year, the complete system shall be installed and ready for use when the power plant is commissioned first half of Fig. 9 Intake complex, May 2014.River is flowing from right to left, intake and desanders are on the far side of the river. Fig. 10: Schematic of desilting basin with SediCon Sluicers discharging through outlet pipes in the gallery and into the bypass channel CONCLUSIONS The SediCon Sluicer has a range of advantages over other systems, and is therefore recommended for Baner Sangam. The SediCon Sluicer is suitable for all sizes of desilting facilities, both open desilting basins as well as large underground desilting chambers. Experience from the past 15 years has led consultants to choose the SediCon Sluicers for new projects, foremost is the 1500 MW coca Codo Sinclair to be commissioned With introduction to India, we believe Baner Sangam Hydropower project will get the best possible solution for its sediment removal needs. SediCon is confident that the project will serve as a reference for future projects in India, and point forward to installation of SediCon Sluicers in larger desilting basins and underground desilting chambers. 113