Hydraulic Design of Small Hydro Plants

Version 2 STANDARDS/MANUALS/ GUIDELINES FOR SMALL HYDRO DEVELOPMENT Civil Works – Hydraulic Design Of Small Hydro Plants Lead Organization: Sponsor: Alternate Hydro Energy Center Indian Institute of Technology Roorkee Ministry of New and Renewable Energy Govt. of India May 2011 AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  1 1. GUIDELINES FOR HYDRAULIC DESIGN OF SMALL HYDRO PLANTS This section provides standards and guidelines on the design of the water conductor system.This system includes; head works and intake, feeder canal, desilter (if required), power canal or alternative conveyance structures (culverts, pipelines, tunnels, etc), forebay tank, penstock and surge tank (if required) up to the entry of the turbine, tailrace canal below the turbine and related ancillary works. 1. 1 HYDRAULIC DESIGN OF HEAD WORKS In general head works are composed of three structural components, diversion dam, intake and b ed load sluice. The functions of the head works are: Diversion of the required project flow from the river into the water conductor system.Control of sediment. Flood handling. Typically a head pond reservoir is formed upstream of the head works. This reservoir may be used to provide daily pondage in support of peaking operation or to provide the control volume necessary for turbine operation in the water level control mode. This latter case would apply where the penstock draws its water directly from the head pond. Sufficient volume must be provided to support these functions. There are three types of head works that are widely used on mini and small hydro projects, as below: Lateral intake head works Trench intake head worksReservoir / canal intakes Each type will be discussed in turn. 1. 1. 1 Head Works with Lateral Intakes (Small Hydro) Head works with lateral intakes are typically applied on rivers transporting significant amounts of sediment as bed load and in suspension. The f unctional objectives are: To divert bed-load away from the intake and flush downstream of the dam (the bed load flushing system should be operable in both continuous and intermittent modes). To decant relatively clean surface water into the intake. To arrest floating debris at intake trashracks for removal by manual raking.To safely discharge the design flood without causing unacceptable upstream flooding. AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  2 The following site features promote favourable hydraulic conditions and should be considered during site selection: The intake should be located on the outside of a river bend (towards the end of the bend) to benefit from the spiral current in the river that moves clean surface water towards the intake and bed load away from the intake towards the centre of the river.The intake should be located at the head of a steeper section of the river. This will promote remo val of material flushed through the dam which may otherwise accumulate downstream of the flushing channel and impair its function. Satisfactory foundation conditions. Ideal site conditions are rare, thus design will require compromises between hydraulic requirements and constraints of site geology, accessibility etc. The following guidelines assume head works are located on a straight reach of a river. For important projects or unusual sites hydraulic model studies are recommended.A step by step design approach is recommended and design parameters are suggested for guidance in design and layout studies. Typical layouts are shown in Figures 2. 2. 1 to 2. 2. 3. 1. 1. 2 Data Required for design. The following data are required for design: Site hydrology report as stipulated in Section 1. 3 of this Standard giving: – Qp (plant flow) – Q100 (design flood flow, small hydro) – Q10 (design flood flow, mini hydro) (data on suspended sediment loads) – Cw – H -Q Curves (W. L. rating curves at diversion dam) Topographic mapping of the site including river bathymetry covering all head works structure sites.Site geology report. 1. 1. 3 Site Selection: Selection of the head works site is a practical decision which involves weighing of several factors including hydraulic desiderata (Section 2. 2. 1/1. 0), head optimization, foundation conditions, accessibility and constructability factors. Given the importance of intake design to the overall performance of the plant it is recommended that an experienced hydraulic engineer be consulted during studies on head works layout. 1. 1. 4 Determination of Key Elevations: AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  3For the illustrative example: Qp = 10. 0 m3/s Determine V0 = 0. 5 Q0. 2 (= 0. 792, say 0. 80 m/s) (= 12. 5 m2) A0 = Q ? V0 A0 H= (= 1. 77 m, say 1. 80 m) 4 Assume L = 4H (= 7. 08 m, say 7. 0 m) ye = greater of 0. 5 yo o r 1. 5 m (= 1. 80m) yd = L. S (= 0. 28 m) NOL = Z0 + ye + yd + H NOL = 97. 5 + 1. 80 + 0. 28 + 1. 80 (=101. 38m, say 101. 50 m) Sill = NOL – H (= 99. 7m) Crest of weir or head pond NOL = 101. 5 m Height of weir = 4. 0 m These initial key elevations are preliminary and may have to be adjusted later as the design evolves. 1. 1. 5 Head Works LayoutThe entry to the intake should be aligned with the river bank to provide smooth approach conditions and minimize the occurrence of undesirable swirl. A guide wall acting as a transition between the river bank and the structure will usually be required. Intake hydraulics are enhanced if the intake face is slightly tilted into the flow. The orientation of the intake face depends on river bank topography, for straight river reaches the recommended values for tilt vary from 10o to 30o depending on the author. When this angle becomes too large the intake will attract excessive amounts of sediment and floating debris.It is recommended that t he sill level of the intake is kept sufficiently higher than the sill level of the under sluice. The under sluice should be located adjacent to the intake structure. AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  4 For development of the head work plan, it is recommended that the following parameters be used for layout: Axis of intake should between 100 ° to 105 ° to axis of diversion structure The actual inclination may be finalized on the basis of model studies. Divide wall, if provided, should cover 80% to 100% of the intake.Assume flushing flow equal to twice project flow then estimate the width and height of the flushing gate from orifice formula,: Example should be in appendix. Qf = 0. 6 ? 0. 5W2 Where: Qf = flushing flow W = gate width H = gate height (= 0. 5W) Yo = normal flow depth as shown in 2. 2. 1. 1/2. 0 Sill should be straight and perpendicular to the flow direction. In the sample design (Fig. 2 . 2. 1. 1) the axis of the intake = 105 ° & Qf = 2. 0? 10. 0 = 20m3/s ? 20. 0 = 0. 6 ? 0. 5 W2 ? W = 2. 8 m (say 3. 0m) and H = 1. 5 m. 1. 1. 6 Flood Handling, MFL and Number of Gates.For small hydro a simple overflow diversion weir would be the preferred option if flood surcharge would not cause unacceptable upstream flooding. For purpose of illustration, the following design data are assumed (see Figure 2. 2. 2): Design flood, Q100 = 175 m3/s A review of reservoir topography indicated that over bank flooding would occur if the flood water level exceeded 103. 0 m. Select this water level as the MFL. This provides a flood surcharge (S) of 1. 20 m. Assume weir coefficients as below: Gate, Cw = 1. 70 – – – sill on slab at river bottom. Weir, Cw = 1. 0 – – – – – – -ogee profile. Assume gate W/H ratio = 1:2 H = 4. 0 m ? W = 4. 8 (say 5. 0 m) MFL. = NOL + 1. 50 (= 103. 0m) Qgate = Cw. W. (MFL – ZS)1.. 5 Qweir = Cw. L w. S1. 5 Capacity check for MFL = 103. 0 m No. of Length of Overflow QG Gates Section (m) (m3/s) 0 35. 0 0. 0 1 29. 0 109. 6 QW (m3/s) 82. 8 68. 6 QT (m3/s) 82. 8 178. 2 >175 AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  5 Therefore one gate is sufficient. Where: MFL = Maximum flood level (m) NOL = Normal operating level (m) S = flood surcharge above NOL (m)W = width of gate (m) H = height of gate (m) ZS = elevation of gate sill (m) = weir coefficient (m0. 5s-1) Cw QG, QW, QT = gate, weir and total flows The flow capacity of the sediment flushing gate may also be included in calculating flood handling capacity. 1. 1. 7 Diversion structure and Spillway Plains Rivers: Stability of structures founded on alluvial foundations typical of plains rivers, is governed by the magnitude of the exit gradient. The critical gradient is approximately 1. 0 and shall be reduced by the following safety factors: Types of foundationS hingles / cobbles Coarse sand Fine sand Safety factor 5 6 7 Allowable Exit Gradient 0. 20 0. 167 0. 143 Also diversion structures on plains rivers will normally require stilling basins to dissipate the energy from the fall across the diversion structure before the water can be returned safely to the river. Design of diversion weirs and barrages on permeable foundation should follow IS 6966 (Part 1). Sample calculations in Chapter 12 of â€Å"Fundamentals of Irrigation Engineering† (Bharat Singh, 1983) explain determination of uplift pressure distributions and exit gradients.Further details on structural aspects of design are given in Section 2. 3. 3 of this Standard. Mountain Rivers: Bedrock is usually found at relatively shallow depths in mountain rivers permitting head works structures to be founded on rock. Also the beds of mountain rivers are often boulder paved and are much more resistant to erosion than plains rivers. Therefore there may be no need for a stilling basin. The engineer may consider impact blocks on the downstream apron or simply provide an angled lip at the downstream end of the apron to â€Å"flip† the flow away from the downstream end of the apron.A cut-off wall to bed rock of suitable depth should AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  6 also be provided for added protection against undermining by scour. The head works structures would be designed as gravity structures with enough mass to resist flotation. For low structures height less than 2. 0 m anchors into sound bedrock may be used as the prime stabilization element in dam design. Stability and stress design shall be in accordance with requirements of Section 2. 3. 3 of this Standard. 1. 1. 8 Sediment Flushing Channel To be reviewedThe following approach is recommended for design of the flushing channel: Select flushing channel flow capacity (Qf) = 2? Qp Estimate maximum size of sediment ente ring the pocket from site data or from transport capacity of approaching flow and velocity. In case of diversion weir without gates assume sediment accumulation to be level with the weir crest. (Assume continuous flushing with 3? Qp entering the pocket, for this calculation). Establish entrance sill elevation and channel slope assuming an intermittent flushing mode (intake closed) with Qs = 2Qp, critical flow at the sill, supercritical flow downstream (FN ? 1. 0) and a reservoir operating level 0. 5m below NOL. Determine slope of channel to provide the required scouring velocity, using the following formula which incorporates a safety factor of 1. 5: i = 1. 50 io d 9/7 i0 = 0. 44 6 / 7 q Where: io = critical scouring velocity d = sediment size q = flow per unit width (m3/s per m) Verify that flow through pocket in continuous flushing mode (Qs = 3Qs) will be sub critical, if not lower entrance sill elevation further. Determine height of gate and gate opening based on depth of flow at gate location and corresponding gate width. Increase the above theoretical gate height by 0. 5 m to ensure unrestricted open channel flow through the gate for intermittent flushing mode and a flushing flow of 2 Qp. For initial design a width to height ratio of 2:1 for the flushing gate is suggested. 1. 1. 9 Intake/Head Regulator: In intake provides a transition between the river and the feeder canal. The main design objectives are to exclude bed-load and floating debris and to minimize head losses. The following parameters are recommended: Approach velocity at intake entrance (on gross area) 0. 20 Ve = 0. 5 Q p m / s For trashracks that are manually cleaned, V should not exceed 1. 0 m/s.AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  7 Convergence of side walls 2. 5:1 with rate of increase in velocity not exceeding 0. 5 m/s per linear m. †¢ Height of sill above floor of flushing channel (ye) = greater of 1. 5 m or 50% flow depth. †¢ The floor of the transition should be sloped down as required to join the invert of the feeder canal. Check that the flow velocity in the transition is adequate to prevent deposition in the transition area. If sediment loads are very high consider installing a vortex silt ejector at the downstream end of the transition. Provide coarse trashracks to guard entry to the head gate. The trashrack would be designed to step floating debris such as trees, branches, wood on other floating objects. A clear spacing of 150 mm between bars is recommended. Trashrack detailed design should be in accordance with IS 11388. †¢ The invert of the feeder canal shall be determined taking into consideration head losses through the trashrack and form losses through the structure. Friction losses can be omitted as they are negligible: V2 Calculate form losses as: H L = 0. 3 2 2g Where: V2 = velocity at downstream end of contraction.Calculate trashrack losses as: 4/3 V2 ?t? H L = K f ? ? . Sin? . 2g ?b? Where: Kf = head loss factor (= 2. 42 assuming rectangular bars) T = thickness of bars (mm) B = clear bar spacing (mm) ? = angle of inclination to horizontal (degrees) V = approach velocity (m/s) 1. 1. 10 References on Lateral Intakes and Diversion Weirs. IS Standards Cited: IS 6966 (Part 1) IS 11388 USBR (1987) Singh, Bharat Nigam, P. S. Hydraulic Design of Barrages and Weirs – Guidelines Recommendations for Design of Trashracks for Intakes Design of Small Dams Fundamentals of Irrigation Engineering Nem Chand & Bros. Roorkee (1983) Handbook of Hydroelectric Engineering (Second edition) †¦.. pages 357 to 365 Nem Chand & Bros. – Roorkee (1985) 1. 1. 11 Other References: Bucher and Krumdieck Guidelines for the Design of Intake Structures for Small Hydro Schemes; Hydro ’88/3rd International Conference on Small Hydro, Cancun – Mexico. Bouvard, M. Mobile Barrages and Intakes on Sediment Transporting AHEC/MNRE/SHP Standards/ C ivil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  8 Razvan, E. 1. 2. Rivers; IAHR Monograph, A. A. Balkema – Rotterdam (1992) River Intakes and Diversion DamsElsevier, Amsterdam (1988) SEMI PERMANENT HEADWORKS (MINI HYDRO) For mini hydro projects the need to minimize capital cost of the head works is of prime importance. This issue poses the greatest challenge where the head works have to be constructed on alluvial foundations. This challenge is addressed by adoption of less rigorous standards and the application of simplified designs adapted to the skills available in remote areas. A typical layout is shown in Figure 2. 2. 3. 1. 2. 1 Design Parameters Hydraulic design should be based on the following design criteria: Plant flow Qp) = QT + QD Where: QT = total turbine flow (m3/s) QD = desilter flushing flow (= 0. 20 QT) m3/s QFC = feeder canal flow (= 1. 20 QT) m3/s QF = gravel flushing flow (= 2. 0 QP) Spillway design flow (SDF) = Q10 Where: Q10 = flood peak flow with ten year return period. 1. 2. 2 Layout ? To be reviewed Intake approach velocity = 1. 0 m/s Regulator gate W/H = 2 Flushing channel depth (HD) = 2H + W/3 Flushing channel minimum width = 1. 0 m Assumed flushing gate W/H = 2, determine H from orifice equation, as below: Q f = 0. 53? 2 H 2 . 2 gY1 Y1 = HD for design condition Where: W width of gate (m) H = height of gate (m) Yi = upstream depth (m) = depth of flushing channel (m) HD Select the next largest manufactures standard gate size above the calculated dimensions. 1. 2. 3 Weir AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  9 Determine weir height to suit intake gate and flushing gate dimensions, as shown in Figure 2. 2. 3. For weirs founded on permeable foundations the necessary structure length to control failure by piping should be determined in accordance with Section 2. 2. 1/4. 1 of this Standard.A stepped arrangement is recommended for the downstream face of the weir to dissipate hydraulic energy. The height of the steps should not exceed 0. 5 m and the rise over run ratio should not less than 1/3, the stability of the weir cross-section design should be checked for flotation, over turning and sliding in accordance with Section 2. 3. 1. 1. 3 TRENCH INTAKES Trench intakes are intake structures located in the river bed that draw off flow through racks into a trench which conveys the flow into the project water conductor system. A characteristic of trench intakes is that they have minimum impact on river levels.Trench intakes are applied in situations where traditional headwork designs would be excessively expensive or result in objectionable rises in river levels. There are two quite different applications: on wide rivers and on mountainous streams, but the basic equations are the same for both types. The trench intake should be located in the main river channel and be of sufficient width to collect the design project flow including all flushing flows. If the length of the trench is less than the width of the river, cut off walls will be required into each bank to prevent the river from bypassing the structure.Trench weirs function best on weirs with slopes greater than 4%-5%, for flatter slopes diversion weirs should be considered. The spacing between racks is selected to prevent entry of bed load into the trench. The following terms are sometimes used in referring to trench intake designs. Trench weir, when the trench is installed in a raised embankment. †¢ Tyrolean or Caucasian intakes, when referring to trench intakes on †¢ mountainous streams. Features: AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  10 1. 3. 2 Design ParametersThe following design parameters are suggested for the dimensioning of trench weirs. †¢ Design Flows: The following design flows are recommended: Bedload flushing flo w (from collector box) = 0. 2 QT †¢ Desilter flushing flow = 0. 2 QT †¢ Turbine flow = 1. 0 QT †¢ Total design flow †¢ = 1. 4 QT Dimensional Layout AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  11 The following factors should be considered in determining the principal dimensions: length, breadth and depth of a trench weir: Minimum width (B)= 1. 25 m (to facilitate manual cleaning) Length should be compatible with river cross section. It is †¢ recommended that the trench be located across main river channel. Maximum width (B) ? 2. 50m. Trashrack bars longer than about 2. 50 m †¢ may require support as slenderness ratios become excessive. Invert of collector box should be kept a high as possible. †¢ †¢ Racks †¢ †¢ †¢ †¢ The clear spacing between bars should be selected to prevent entry of bed-load particles that are too large to be conveniently handled by the flushing system. Generally designs are based on excluding particles greater than medium gravel size from (2 cm to 4 cm).A clear opening of 3. 0 cm is recommended for design. A slope across the rack should be provided to avoid accumulation of bed load on the racks. Slopes normally used vary from 0 ° to 20 °. Rectangular bars are recommended. Bar structural dimension shall be designed in accordance with Section 2. 2. 1/5. 0 of this Standard. An appropriate contraction coefficient should be selected as explained in the following sub-section. Assume 30% blockage. Spacing between racks is designed to prevent the entry of bedload but must also be strong enough to support superimposed loads from bedload accumulation, men and equipment.This issue is discussed further in Subsection 2. 2. 3 / 2. 0. 1. 3. 3 Hydraulic Design of Trench Intake The first step in hydraulic design is to decide the width of the trench intake bearing in mind the flow capacity required and the bathymetry of the river bed. The next step in hydraulic design is to determine the minimum trench breadth (B) that will capture the required design flow. The design approach assumes complete capture of river flow, which implies, that river flow is equal to plant flow for the design condition. Hydraulic design is based on the following assumptions: Constant specific energy across racks. †¢ Effective head on screen is equal to base pressure (depth) †¢ Approach velocity is subcritical with a critical section at the entry to the structure as shown in figure 2. 2. 3/1. The set of equations proposed is based on the method given by Lauterjung et al (1989). †¢ First calculate y1: AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  12 2 y 1 = k. H0 3 – – – – – – – – – – – (1) Where: y1 = depth at upstream edge of rack Ho = the energy head of the approach ing flow k = an adjustment factor (m) m) (-) k is a function of inclination of the rack and can be determined from the following table: Values of k as a Function of Rack Slope (? ) Table: 2. 2. 1/1 ? = 0 ° 2 ° 4 ° 6 ° 8 ° 10 ° 12 ° k = 1. 000 0. 980 0. 961 0. 944 0. 927 0. 910 0. 894 ? = 14 ° 16 ° 18 ° 20 ° 22 ° 24 ° 26 ° k = 0. 879 0. 865 0. 851 0. 837 0. 852 0. 812 0. 800 Then calculate the breadth of the collector trench from the following equations (2) to (4) 1. 50 q – – – – – – – – – – – – – – (2) L= E1. E 2 C. cos? 3/2 . 2gy 1 Where: L = sloped length across collector trench (m) E1 = blockage factor E2 = Effective screen area = e/mC = contraction coefficient ? = slope of rack in degrees y1 = flow depth upstream from Equation 1. (m) q = unit flow entering intake (m3/s per m) e = clear distance between bars (cm or m) m = c/c spacing of bars (cm or m) Assu me E1 = 0. 3 (30%) blockage. â€Å"C† can be calculated from the following formula (as reported by Raudkivi) Rectangular bars: ?e? C = 0. 66 ? ? ?m? ?0. 16 ?m? .? ? ?h? 0. 13 Assume h = 0. 5 y1. This formula is valid for 3. 5> – – – – – – – – – – – – – (3) h e >0. 2 and 0. 15< < 0. 30 m m Finally, the required breadth (B) can be determined as below: B = L cos ? – – – – – – – – – – – – -(4) AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  13 1. 3. 4 Hydraulic Design of Collector Trench Normally a sufficient slope on the invert of the trench is provided to ensure efficient flushing of bed-load particles that would otherwise accumulate on the invert of the trench. A suitable scouring slope can be estimated from the following equation: Ss = 0. 66 d 9 / 7 6/7 qo Where: d = sediment size (m) qo = flow per unit width (Q/B) at outlet of trench (m3/s per m) Ss = design slope of trench invert.The minimum depth of the trench at the upstream and is normally between 1. 0m to 1. 5 m, based on water depth plus a freeboard of 0. 3 m. For final design the flow profile should be computed for the design slope and the trench bottom profile confirmed or adjusted, as required. A step-by-step procedure for calculating the flow profile that is applicable to this problem can be found in Example 124, page 342-345 of â€Å"Open-Channel Hydraulics† by Ven. T. Chow (1959). In most cases the profile will be sub critical with control from the downstream (exit) end.A suitable starting point would be to assume critical flow depth at the exit of the trench. 1. 3. 5 Collector Chamber The trench terminates in a collector box. The collection box has two outlets, an intake to the water conductor system and a flushing pipe. The flushing pipe must be design with the capacity to flush the bed-load sediment entering from the trench, while the project flow is withdrawn via the intake. The bottom of the collection box must be designed to provide adequate submergence for the flushing pipe and intake to suppress undesirable vortices.The flushing pipe should be lower than the intake and the flushing pipe sized to handle the discharge of bed load. If the flushing pipe invert is below the outlet of the trench, the Engineer should consider steepening the trench invert. If the trench outlet invert is below the flushing pipe invert, the latter should be lowered to the elevation of the trench outlet or below. The deck of the collector box should be located above the design flood level to provide safe access to operate gates. AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  14 1. 3. Flushing Pipe The flushing pipe should be designed to provide a high enough velocity to en train bed-load captured by the weir. A velocity of at least 3. 0 m/s should be provided. If possible, the outlet end of the pipe should be located a minimum of 1. 0m above the river bed level to provide energy to keep the outlet area free from accumulation of bed load that could block the pipeline. 1. 3. 7 References on Trench weirs CBIP, (2001): Manual on Planning and Design of Small Hydroelectric Scheme Lauterjung et al (1989): Planning of Intake Structures Freidrich Vieweg and Sohn, Braunswchweig – GermanyIAHR (1993): Hydraulic Structures Design Manual: Sedimentation: Exclusion and Removal of Sediment from Diverted Water. By: Arved J. Raudkivi Publisher: Taylor & Francis, New York. Chow (1959): Open- Channel Hydraulics Publisher: McGraw-Hill Book Company, New York. 1. 4 RESERVOIR, CANAL AND PENSTOCK INTAKES The designs of reservoir, canal and penstock intakes are all based on the same principles. However, there are significant variations depending on whether an intake is a t the forebay reservoir of a run-of-river plant or at storage reservoir with large draw down or is for a power tunnel, etc.Examples of a variety of layouts can be fond in IS 9761 Hydropower Intakes – Criteria for Hydraulic Design or Guidelines for Design of Intakes for Hydropower Plants (ASCE, 1995). The features common to all designs are shown in the following sketch: AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  15 The objectives of good design are: To prevent entry of floating debris. †¢ To avoid formation of air entraining vortices. †¢ To minimize hydraulic losses. †¢ 1. 4. 1 Control of floating debrisTo prevent the entry of debris a trashrack is placed at the entry to the intake. For small hydro plants the trashrack overall size is determined based on an approach velocity of 0. 75 m/s to 1. 0m/s to facilitate manual raking. Trashracks may be designed in panels that can be lowered into p lace in grooves provided in the intake walls or permanently attacked to anchors in the intake face. The trashracks should to sloped at 14 ° from the vertical (4V:1H) to facilitate raking. The spacing between bars is determined as a function of the spacing between turbine runner blades.IS 11388 Recommendations for Design of Trashracks for Intakes should be consulted for information about spacing between trashracks bars, structural design and vibration problems. Also, see Section 2. 2. 1/5 of this Standard. 1. 4. 2 Control of Vortices First of all the direction of approach velocity should be axial with respect the intake if at all possible. If flow approaches at a significant angle (greater than 45o) AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  16 from axial these will be significant risk of vortex problems.In such a situation an experienced hydraulic engineer should be consulted and for important projects hydra ulic model studies may be required. For normal approach flow the submergence can be determined from the following formulae: S = 0. 725VD0. 5 S D V = submergence to the roof of the gate section (m) = diameter of penstock and height of gate (m) = velocity at gate for design flow. (m/s) Where: A recent paper by Raghavan and Ramachandran discusses the merits of various formulae for determining submergence (S). 1. 4. 3 Minimization of Head lossesHead losses are minimized by providing a streamlined transition between the entry section and gate section. Minimum losses will be produced when a streamlined bellmouth intake is used. For a bellmouth intake the transition section is formed with quadrants of ellipses as shown in the following sketch. The bellmouth type intake is preferred when ever the additional costs are economically justified. For smaller, mainly mini hydropower stations, simpler designs are often optimal as the cost of construction of curved concrete surfaces may not be offse t by the value of reduction in head losses.Details on the geometry of both types are given †¢ Bellmouth Intake Geometry Geometries for typical run-of-river intakes are shown below: A gate width to height of 0. 785 (D): 1. 00 (H) with H = D is recommended. This permits some reduction in the cost of gates without a significant sacrifice in hydraulic efficiency. There is a second transition between the gate and penstock, rectangular to circular. For a gate having H = D and W= 0. 785D the flow velocity at the gate will be equal to the velocity in the penstock so no further flow acceleration is produced in this section. A length for this transition of 1. x D should be satisfactory. AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  17 The head loss co-efficient for this arrangement in Ki =0. 10 Details for layout of bell mouth transitions connecting to a sloping penstock are given in IS9761. †¢ Simplified layout (Mini-Hydro): For smaller/mini hydro projects intake design can be simplified by forming the transition in plane surfaces as shown below: The head loss for this design (Ki) = 0. 19V2/2g. AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  18 . 4. 4. AIR VENT An air vent should be placed downstream of the head gate to facilitate air exchange between atmosphere and the penstock for the following conditions: †¢ Penstock filling when air will be expelled from the penstock as water enters. †¢ Penstock draining when air will enter the penstock to occupy the space previously filled by water. The air vent (pipe) must have an adequate cross section area to effectively handle these exchanges of air. The following design rules are recommended: Air vent area should the greater of the following values Where: (m3/s) AV = 0. 0 Ap or QT AV = 25. 0 (m2) AV = cross-section area of air vent pipe AP = cross-section area of penst ock (m2) QP = turbine rated flow ( ? QT of more than one turbine on the penstock) The air vent should exhaust to a safe location unoccupied by power company employees on the general public. 1. 4. 5 PENSTOCK FILLING A penstock should be filled slowly to avoid excessive and dangerous â€Å"blowback†. The recommended practice is to control filling rate via the head gate. The AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  19 ead gate should not be opened more than 50 mm until the penstock is completely full. (This is sometime referred to as â€Å"cracking† the gate. ) 1. 4. 6 REFERENCES ON PENSTOCK INTAKES: †¢ 1. 4. 7 Indian Standard Cited. IS 9761: Hydropower Intakes – Criteria for Hydraulic Design OTHER REFERENCES †¢ Guidelines for Design of Intakes for Hydroelectric Plants ASCE, New York (1995) †¢ Validating the Design of an Intake Structure : By Narasimham Raghavan and M. K. Ram achandran, HRW – September 2007. †¢ Layman’s Guidebook European Small Hydro Association Brussels, Belgium (June 1998)Available on the internet. †¢ Vortices at Intakes By J. L. Gordon Water Power & Dam Construction April 1970 1. 5. TRASHRACKS AND SAFETY RACKS 1. 5. 1 Trashracks: Trashracks at penstock intakes for small hydro plants should be sloped at 4 V: 1H to facilitate manual raking and the approach velocity to the trashracks limited to 1. 0 m/s or less. Use of rectangular bars is normal practice for SHP’s. Support beams should be alignment with the flow direction to minimize hydraulic losses. Detailed trashrack design should be done in accordance with IS 11388. 1. 5. 2Safety Racks: Safety racks are required at tunnel and inverted siphon entries to prevent animals or people who may have fallen into the canal from being pulled into these submerged water ways. A clear spacing of 200 mm between bars is recommended. Other aspects of design should be in accordance with IS 11388. 1. 5. 3 References on Trashracks IS11388 – â€Å"Recommendations for Design of Trashracks for Intakes†. ASCE (1995) –â€Å"Guidelines for Design of Intakes for Hydroelectric Plants†. AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  20 DRAWINGS:AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  21 AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  22 2. HYDRAULIC DESIGN OF WATERWAYS The waterways or water conduction system is the system of canals, aqueducts, tunnels, inverted siphons and pipelines connecting the head works with the forebay tank. This Section provides guidelines and norms for the hydraulic design of these structures. 2. 1 2. 1. 1 CANALS Canals for small hydro plants are typically constructed in masonry or reinforced co ncrete.Several typical cross section designs are shown below: AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  23 Lined canals in earth, if required, should be designed in accordance with Indian Standard: IS 10430. A further division of canal types is based on function: – Feeder canal to connect the head regulator (intake) to the desilter – Power canal to connect the desilter to the Forebay tank. 2. 1. 2 Feeder Canals 2. 1. 2. 1 Feeder canal hydraulic design shall be based on the following criteria: = Turbine flow (QT) + Desilter flushing flow (QF).Design flow (Qd) AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  24 2. 1. 2. 2 Scouring velocity: A sufficiently high velocity must be provided to prevent deposition of sediment within the canal. This (scouring) velocity can be determined from the following formulae: d 9/7 S C = 0. 66 6 / 7 n = 0. 015 q 1 1 ? VS = . R 2 / 3 . S C/ 2 n Where: Sc = Scouring slope d = Target sediment size (m) q = Flow per unit width (Q/W) (m/s/m) R = hydraulic radius (m) Vs = scouring velocity (m/s) n = Manning’s roughness coefficient 2. 1. 2. 3 Optimization:The optimum cross section dimensions, slope and velocity should be determined by economic analysis so as to minimize the total life time costs of capital, O&M and head losses (as capitalized value). The economic parameters for this analysis should be chosen in consultation with the appropriate regional, state or central power authorities these parameters include: – Discount rate (i) – Escalation rate(e) – Plant load factor – Service life in years (n) – Annual O+M for canal (% of capital cost) – Value of energy losses (Rs/kWh). Also see Section 1. 7 of this Standard. The selected design would be based on the highest of Vs or Voptimum. . 1. 2. 4 Freeboard: A freeboard allowance above the steady state design water level is required to contain water safely within the canal in event of power outages or floods. A minimum of 0. 5 m is recommended. 2. 1. 3 Power Canals: Power canal design shall be based on the following criteria a) Design flow = total turbine flow (QT) b) Power canal design should be based on optimization of dimensions, slope and velocity, as explained in the previous section. For mini-hydro plants Q < 2. 0 m3/s optimal geometric design dimensions for Type 1 (masonry construction) can be estimated by assuming a longitudinal slope of 0. 04 and a Manning’s n value of 0. 018. Masonry construction would normally be preferred for canals with widths (W) less than 2. 0 m (flow area = AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  25 2. 0 m2). For larger canals with flow areas greater than 2. 0m2, a Type 3, box culvert design would be preferred – based on economic analysis. c) Fr eeboard: A freeboard allowance above the steady state design level is required to contain water safety within the canal in event of power outages. The waterway in most SHP’s terminates in a Forebay tank.This tank is normally equipped with an escape weir to discharge surplus water or an escape weir is provided near to the forebay tank. For mini-hydro plants a minimum freeboard of 0. 50 m is recommended. The adequacy of the above minimum freeboard should be verified for the following conditions: †¢ Maximum flow in the power canal co-incident with sudden outage of the plant. †¢ Design flow plus margins for leakage losses (+0. 02 to +0. 05 QT) and above rated operation (+ 0. 1QT). †¢ Characteristics of head regulator flow control. The freeboard allowance may be reduced to 0. 5 m after taking these factors into consideration. The maximum water level occurring in the forebay tank can be determined from the weir equation governing flow in the escape weir. 2. 1. 4 Reje ction Surge Designs which do not incorporate downstream escape weirs would be subject to the occurrence of a rejection surge in the canal on sudden turbine shutdown, giving above static water levels at the downstream end, reducing to the static level at the upstream (entry) end of the water way. Methods for evaluating water level changes due to a rejection surge are explained in Section 2. 2. 2 / 7. 0 of this Standard. . 2 AQUEDUCTS Aqueducts are typically required where feeder or power canals pass over a gully or side stream valley. If the length of the aqueduct is relatively short the same channel dimensions as for the canal can be retained and there would be no change in hydraulic design. For longer aqueducts design would be based on economic analysis subject to the proviso that flow remains sub critical with NF ? 0. 8 in the flume sections. The following sketch shows the principal dimension of aqueduct entry and exit transitions and flume section. AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design OfSmall Hydro Plants /May 2011  Ã‚  26 The changes in invert elevation across the entry and exit structures can be calculated by Bernouli’s equation as below: †¢ Entry transition – consider cross – section (1) and (2); V2 V2 Z 1 + D + 1 = Z 2 + d + 2 + hL 2g 2g and 2 †¢ b? V ? hL = 0. 10 ? 1 ? ?. 2 ? B ? 2g Z2 can be determined from the above equations, since all geometrical parameters are known. Flume – Sections (2) to (3) The slope of the flume section is determined from Manning’s equation 2 †¢ ? Vn ? ( S ) = ? 2 / 3 ? . A Manning’s n = 0. 018 is suggested for concrete channels. ?R ?Some designers increase this slope by 10% to provide a margin of safety on flow capacity of the flume. Exit transition – consider cross section (3) and (4): V2 V2 Z 3 + d + 3 = Z 4 + D + 4 + hL 2g 2g AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  27 and 2 b? V ? hL = 0. 20 ? 1 ? ?. 3 ? B ? 2g Z4 can be determined from the above equations, since all geometrical parameters are known. The same basic geometry can be adapted for transition between trapezoidal canals sections and rectangular flume section, using mean flow width (B) = A/D. . 3. INVERTED SYPHONS 2. 3. 1 Inverted syphons are used where it is more economical to route the waterway underneath an obstacle. The inverted syphon is made up of the following components: †¢ Entry structure †¢ Syphon barrels †¢ Exit structure †¢ Entry Structure: Hydraulic design of the entry structure is similar to the design of reservoir, canal and penstock intakes. Follow the guidelines given in Section 2. 2. 2/2. of this Standard. †¢ Syphon barrels: The syphon barrel dimensions are normally determined by optimization ? V? ? does not tudies, with the proviso that the Froude Number ? N F = ? gd ? ? ? exceed 0. 8. Invert elevations are determine d by accounting for head losses from entry to exit of the structure using Bernouli’s equation. For reinforced concrete channels a Manning’s â€Å"n† value of 0. 018 is recommended. The head loss coefficients for mitre bends can be determined from USACE HDC 228. 2. AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  28 AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  29 Exit structure: The exit structure is designed as a diverging transition to minimize head losses; the design is similar to the outlet transition from flume to canal as discussed in Subsection 2. 2. 2/2 of this Standard. The following sketches show the layout of a typical inverted siphon. AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  30 2. 3. 2 Reference on Aqueducts and Inverted Syphons â€Å"Hyd raulic Structures† By C. D. Smith University of Saskatchewan Saskatoon (SK) Canada 2. 4. LOW PRESSURE PIPELINESLow pressure pipelines may be employed as an alternative to pressurized box culverts, aqueducts or inverted syphons. Concrete, plastic and steel pipes are suitable depending on site conditions and economics. Steel pipe is often an attractive alternative in place of concrete aqueducts in the form of pipe bridges, since relatively large diameter pipe possesses significant inherent structural strength. Steel pipe (with stiffening rings, as necessary), concrete and plastic pipe also have significant resistance against external pressure, if buried, and offer alternatives to inverted syphons of reinforced concrete construction.Generally pressurized flow is preferred. The pipe profile should be chosen so that pressure is positive through out. If there is a high point in the line that could trap air on filling an air bleeder valve should be provided. Otherwise, hydraulic desi gn for low pressure pipelines is similar to the requirements for inverted syphons. The choice of type of design; low pressure pipeline land pipeline material), inverted syphon or aqueduct, depends on economic and constructability considerations, in the context of a given SHP. Manning’s â€Å"n† Values for selected Pipe Materials Material Welded Steel Polyethylene (HDPE) Poly Vinyl Chloride (PVC)Asbestos Cement Cast iron Ductile iron Precast concrete pipe Manning’s â€Å"n† 0. 012 0. 009 0. 009 0. 011 0. 014 0. 015 0. 013(2) Note: (1) From Table 5. 4 Layman’s Guide Book – ESHA (2) From Ven T. Chow – Open Channel Hydraulics AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  31 2. 5. TUNNELS 2. 5. 1 Tunnels often provide an appropriate solution for water conveyance in mountainous areas. Tunnels for SHP are generally of two types. †¢ Unlined tunnels †¢ Concrete li ned tunnels On SHP tunnels are usually used as part of the water ways system and not subject to high pressures. . 5. 2 Unlined tunnels: Unlined water tunnels can be used in areas of favourable geology where the following criteria are satisfied: a) Rock mass is adequately water tight. Rock surfaces are sound and not vulnerable to erosion (or erodible zones b) are suitably protected. The static water pressure does not exceed the magnitude of the minor field c) rock stress. Controlled perimeter blasting is recommended in order to minimize over break and produce sound rock surfaces. Additionally, this construction approach tends to produce relatively uniform surfaces and minimizes the hydraulic roughness of the completed tunnel surfaces.Design velocities of 1. 5 to 2. 0 m/s on the mean AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  32 cross section area give optimal cross section design. It is normal practice to provi de a 100mm thick reinforced concrete pavement over leveled and compacted tunnel muck in the invent of the tunnel. IS 4880: Part 3 provides additional guidance on the hydraulic design of tunnels and on the selection of appropriate Manning’s â€Å"n† values. 2. 5. 3 Lined Tunnels Where geological are unfavourable it is often necessary to provide concrete linings for support of rock surfaces.IS4880: Parts 1-7 give comprehensive guidelines on the design of lined tunnels. 2. 5. 4 High Pressure Tunnels Design of high pressure tunnels is not covered in this standard. For high pressure design, if required, the designer should consult an experienced geotechnical engineer or engineering geologist. For the purpose of this standard, high pressure design is defined as tunnels subject to water pressures in excess of 10m relative to the crown of the tunnels. 2. 5. 5 Reference on Tunnels IS Standards: IS 4880 â€Å"Code of Practice for the Design of Tunnels Conveying Water†. Ot her References: Norwegian Hydropower Tunnelling† (Third volume of collected papers) Norwegian Tunneling Society Trondheim, Norway. www. tunnel. no Notably: Development of Unlined Pressure Shafts and Tunnels in Norway, by Einar Broch. 2. 6. CULVERTS AND CROSS-DRAINAGE WORKS Small hydro projects constructed in hilly areas usually include a lengthy power canal routed along a hillside contour. Lateral inflows from streams and gullies intercepted by SHP canals often transport large sediments loads which must be prevented from entering the canal. The first line of defense is the canal upstream ditch which intercepts local lateral runoff.The flow in these chains must be periodically discharged or the drain capacity will be exceeded. Flow from these drains is usually evacuated via culverts passing underneath the canal. These culverts would normally be located where gullies or streams cross the canal alignment. The capacity of canal ditches should be decided taking into consideration t he average distance between culverts. In the rare cases when distance between culverts is excessive, consideration should be given to diverting AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  33 itch flows across the canal in flumes or half round pipes to discharge over the downhill side of the canal at suitable locations. Culverts are usually required where the canal route crosses gullies or streams. Culverts at these points provide for flow separation between lateral inflows and canal inflows and often present the most economical solution for crossing small but steep valley locations. It is recommended that culverts design be based on the following hydrological criteria. †¢ For mini hydro projects, 1 in 10 year flood (Q10) †¢ For small hydro projects, 1 in 25 year flood (Q25)Where it is practical to extract the necessary basin parameters, the procedures given in Section 1. 4 should be applied. Otherwise design flows should be estimated from field measurements of cross section area and longitudinal slope at representative cross section of the gully or side stream. A survivable design approach is further recommended with canal walls strengthened to allow local over topping without damage to the canal integrity when floods exceed the design flood values. Detailed hydraulic design should be based on information from reliable texts or design guidelines – such as: â€Å"Design of Small Bridges and Culverts† Goverdhanlal †¢ †¢ 2. 7 2. 7. 1 â€Å"Engineering and Design – Drainage and Erosion Control†. Engineering Manual EM 1110-3-136 U. S. Army Corps of Engineers (1984) www. usace. army. mil/publications/eng-manuals Manufacturer’s guides, notably: – American Concrete Pipe Association www. concrete-pipe. org – Corrugated Steel Pipe Institute www. cspi. ca Power Canal Surges Power canals that are not provided with escape weirs near their downstream end will be subject to canal surges on rapid load rejections or load additions.The rejection surge will typically cause the downstream water level to rise above static level and may control the design of canal freeboard. For load additions there is a risk that the level will fall to critical at the downstream end and restrict the rate at which load can be taken on by the unit. The following formulae taken from IS 7916: 1992 can be used to estimate the magnitude of canal surges. AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  34 Maximum surge height in a power channel due to load rejection may be calculated from the empirical formulae given below:For abrupt closure hmax = K 2 + 2 Kh For gradual closure within the period required for the first wave to travel twice the length of the channel: K hmax = + V . h / g 2 Where: hmax = maximum surge wave height, K = V2/2g = velocity head, V = mean velocity of flow, and area of cross sec tion h = effective depth = top width †¢ Maximum water level resulting from a rejection surge at the downstream of a canal: Maximum W. L. = Yo + hmax †¢ Minimum water level resulting from by a start up surge at the downstream end of a canal: Minimum W. L. = YS – hmax Where: Yo YS = steady state downstream water level static downstream water level. The maximum water level profile can be approximated by a straight line joining the maximum downstream water level to the reservoir level. 2. 7. 2 Canal Surges on Complex Waterways: For waterway systems comprising several different water conductor types, the above equations are not applicable. In such cases a more detailed type of analysis will be required. The U. S. National Weather Service FLDWAV computer program can be used to solved for the transient flow conditions in such cases (Helwig, 2002). 2. 7. 3 References IS Standards cited:IS 7916: 1992 â€Å"Open Channel – Code of Practiceà ¢â‚¬ . Other References â€Å"Application of FLDWAV(Floodwave) Computer Model to Solve for Power Canal Rejection Wave for Simple and Complex Cases†. P. C. Helwig Canadian Society for Civil Engineering Proceedings, Annual Conference Montreal, Canada (2002). AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  35 3. HYDRAULIC DESIGN OF DESILTERS 3. 1 BACKGROUND Sediment transported in the flow, especially particles of hard materials such as quartz, can be harmful to turbine components.The severity of damage to equipment is a function of several variables, notably: sediment size, sediment hardness, particle shape, sediment concentration and plant head. The control of turbine wear problems due to silt erosion requires a comprehensive design approach in which sediment properties, turbine mechanical and hydraulic design, material selection and features to facilitate equipment maintenance are all considered (Naidu, 200 4). Accordingly the design parameters for desilter design should be made in consultation with the mechanical designers and turbine manufacturer.Where the risk of damage is judged to be high a settling basin (or desilter) should be constructed in the plant waterway to remove particles, greater than a selected target size. 3. 1. 1 Need The first design decision is to determine whether the sediment load in the river of interest is sufficiently high to merit construction of a desilter. There is little guidance available on this topic; however, the following limits are suggested by Naidu (2004): Table 2. 2. 3/1. 0 Concentration Suggested Maximum Allowable Sediment versus Plant Head. Parameter Head Maximum allowable sediment concentrationLow and Medium Head Turbines ? 150 m High Head Turbines > 150 m 200 ppm 150 ppm 3. 1. 2 Removal Size There are also considerable divergences of opinion on the selection of design size for sediment removal. Nozaki (1985) suggests a size range of between 0. 3 mm to 0. 6 mm for plant heads ranging from 100 m to 300 m. Indian practice is to design for a particles size of 0. 20 m regardless of head. Some authors suggest that removal of particles smaller than 0. 20 mm is not practical. The adoption of 0. 20 mm is the design (target) sediment size is recommended for Indian SHP designs.AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  36 3. 1. 3 Types of Desilters There are two basic types of desilters: Continuous flushing type Intermittent flushing type Guidelines for design of both types are given in this section. 3. 2. DESIGN CONSIDERATIONS 3. 2. 1 Data Requirements (Small Hydro Plants) It is recommended that a program of suspended sediment sampling be initiated near the intake site from an early stage during site investigations to ensure that sufficient data is available for design.The sampling program should extend through the entire rainy season and should comprise at least two readings daily. On glacier fed rivers where diurnal flow variations may exist, the schedule of sampling should be adjusted to take this phenomenon into account and the scheduled sampling times be adjusted to coincide with the hour of peak daily flow with another sample taken about twelve hours later. While it is often assumed that sediment load is directly related to flow, this is only true on the average, in a statistical sense.In fact it is quite likely, that the peak sediment event of a year may be associated with a unique upstream event such as a major landslide into the river. Such events often account for a disproportionately large proportion of the annual sediment flow. Therefore, it would also be desirable to design the sediment measurement program to provide more detailed information about such events, basically to increase the sampling frequency to one sample per 1 or 2 hours at these times. A five year long sediment collecting program would be ideal. Less than o ne monsoon season of data is considered unsatisfactory.Some authors suggest that the vertical variation of sediment concentration and variations horizontally across the river be measured. However, on fast flowing rivers inherent turbulence should ensure uniform mixing and sampling at one representative point should be sufficient. The data collected in a sediment sampling program should include: †¢ Mean daily concentration of suspended sediment (average of two readings twelve hours apart) †¢ Water temperature †¢ Flow (from a related flow gauging program) The following additional information can then be derived from collected samples.AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  37 †¢ †¢ †¢ A sediment rating curve (sediment concentration versus flow – where possible) Particle size gradation curve on combined sample Specific gravity of particles. It is also recommended that a pet rographic analysis be carried out to identify the component minerals of the sediment mix. It is likewise recommended that experiments be made on selected ranges of particles sizes to determine settling velocities. A further discussion on the subject of sediment sampling is given in Avery (1989)The characteristics of the sediment on a given river as obtained from a data collection program will assist in selection of appropriate design criteria. 3. 2. 2 Data Requirements (Mini Hydro Plants) On mini hydro projects where resources and time may not be available to undertake a comprehensive sampling program, selection of design parameters will depend to a great extent on engineering judgment, supplemented by observations on site and local information. The following regional formula by Garde and Kothyari (1985) can be used to support engineering decision making. 0. 19 ?P ? 0 Vs = 530. 0 P0. 6. Fe1. . S0. 25 Dd . 10 .? max ? ?P? Where Vs = mean sediment load in (tonnes/km2/year) s = average slope (m/m) Dd = drainage density, as total length of streams divided by catchment area (km/km2) P = mean annual precipitation (cm) Pmax = average precipitation for wettest month (cm) Fe = ground cover factor, as below: 1 Fe = [0. 80 AA + 0. 60 AG + 0. 30 AF + 0. 10 AW ] ? Ai = arable land area AA = grass land area (all in km2) AG AF = forested area AW = waste land area (bare rock) 3. 2. 3 Design Criteria The principle design criteria are: 1. The target size for removal (d): d = 0. 20 mm is recommended 2.Flushing flow: QF = 0. 2 QP is recommended 3. Total (design) flow: QT = QP + QF = 1. 2 QP. Where QP is plant flow capacity in (m3/s). AHEC/MNRE/SHP Standards/ Civil Works – Guidelines For Hydraulic Design Of Small Hydro Plants /May 2011  Ã‚  38 3. 2. 4 Siting The following factors control site selection 1. A site along the water way of appropriate size and relatively level with respect to cross section topography 2. A site high enough above river level to provide adequate head for flushing. For preliminary layout a reference river level corresponding to the mean annual flood and minimum flushing head of 1. 0 m is recommended. In principle a desilting tank can be located anywhere along the water conductor system, upstream of the penstock intake. Sometimes it is convenient to locate the desilting basin at the downstream end of the waterway system where the desilter can also provide the functions of a forebay tank. However, a location as close to the head works is normally preferred, site topography permitting. 3. 3 Hydraulic Design A desilter is made up of the following elements: †¢ Inlet section Settling tank †¢ Outlet section †¢ †¢ Flushing system 3. 3. 1

Bharti Enterprises Essay

Ensuring that the look and feel of the store is as per guidelines/standards Ensuring/ reporting Inventory and Stock availability as per the norms to prevent stock-outs Provide suggestions /feedback to improve store productivity People Development / Team Management: Acting as a mentor and trainer for store staff To ensure daily roistering & briefing to inbound & outbound store staff Customer Experience: Manage staff allocation based on demand at point in time Personally step in to handle demanding customers Provide suggestions for improvements in CE 4. A. On Diversity and Cultural spread in Africa, As Africa consists of 53 countries, to operate successfully it is important to understand the dynamics of each country, including differences in culture, language and especially regulations. Bharti would do well to put in place as few expatriates as possible and have most of its top management from Africa. b. On Infrastructure sharing and cost / capital issues, The biggest driver of network sharing will be the shift in approach of the biggest operators, who had been unwilling to share network to sustain competitive advantage. There is visible network sharing in the markets of Nigeria, Ghana and South Africa, and that this is likely to pick up in other markets. c. On Bharti Airtel’s Minute Factor Model, Network sharing and IT outsourcing would help operators bring down costs. While costs could trend down, however they will be higher than in India because of some of the structural costs caused by power shortage and poor infrastructure. 5. Bharti Airtel has a history of making first moves and emerging as the winner just because of that. This is what built the company’s success in India, where it remains the top MNO and second-largest fixed-line operator. In fact, thanks to the massive market it serves at home, at the time it acquired the Zain portfolio in March 2010 Airtel was reckoned to be the fifth largest mobile operator in the world on a proportional subscriber basis, putting it behind the likes of China Mobile, Vodafone Group, American Movil and Telefonica, but ahead of China Unicom. As has been widely covered for over a year now, Airtel has been looking at Africa as a new growth market. While it has a deal with Vodafone for the Channel Islands, Africa is the only other territory outside the Indian subcontinent (including Bangladesh and Sri Lanka) that the company has entered. The commonalities are compelling: similar markets, needs and infrastructure. The realities on the ground are somewhat more challenging: logistics, legislative compliance and serious local competition being foremost. The logistics of infrastructure in Africa are an equal challenge for all MNOs. That is a given. Where Airtel might have been overly optimistic is in hoping its Africa model would run similarly to its success in India, based on a first-to-market approach and having some leverage to overcome legislative obstacles. Unfortunately, while Airtel has a 30-year history of being first in India (with pushbutton phones, cordless phones and then mobile), they were not first in Africa. There were major EU, Middle East and South African players there ahead of them. In fact, Airtel’s African expansion is largely thanks to its takeover of Kuwait’s Zain mobile operations in 15 countries. This was a beachhead, not a conquest. Zain only held dominant market share in a few countries. Going up against market leaders such as MTN of South Africa, Airtel applied a strategy of extensive cost cutting. This followed on what it achieved in India, cutting a deal with Ericsson for per-minute fees (rather than upfront payment) that enabled very low-cost call rates from the outset. Airtel has an all-Africa, five-year deal in place with Ericsson for network management that offers similar advantages. Elsewhere, Airtel is engaged with Nokia Siemens Networks and Huawei, not keeping all its eggs in one basket, of course. As a Plan B, possibly following on the indecisive outcome of Airtel’s low-cost invasion, the company has previously been negotiating a takeover of or (maybe) a joint venture with MTN itself. How this putative deal is described depends on which company is talking. This has been going on for some four years without a definitive ending. Even if it never happens, it is a signpost of just what Airtel would consider to get its Africa operations truly established.

Prevention of Calcium Carbonate Precipitation in Synthetic Formation Waters

A new graduated table inhibitor for bar of Ca carbonate precipitation in man-made formation Waterss Abstraction In this probe, a new repressive chemical composing was developed. The made inhibitor is based on the aqueous solutions of oxiethilidendiphosphone acid, hydrochloric acid, ammonium chloride, polyethylene polyamine-N-methylphosphonic acid and isopropyl intoxicant to forestall the precipitation of Ca carbonate in a long clip operation of the well. The laboratory surveies of new inhibitor showed that the developed inhibitor has a greater suppression efficaciousness and continuance of desorption in comparing with the tried inhibitor SNPH-5312, which is widely used in the Fieldss in Russia to forestall the precipitation of Ca carbonate. The efficiency and corrosion aggressivity of new developed inhibitor were evaluated in three different man-made formation Waterss, which contained assorted ion concentrations and were disposed for precipitation of Ca carbonate. Introduction Huge sums of H2O are injected into the reservoir to keep the reservoir force per unit area at the needed degree, whereby, salt deposition occurs as a consequence of the H2O combination [ 1 ] . As the depletion of the oil field and its transportation to the late phase of development with increasing high H2O cut Wellss, scaling job is aggravated. Besides, there is the demand for backdown residuary oil, necessitating the usage of modern engineerings to better oil recovery, including physical and chemical exposure, which besides stimulates the deposition of salts. The chief grounds of deposition of salts are altering of thermobaric conditions in the procedure of production and the mutual exclusiveness of injected and formation Waterss [ 2 ] . Inorganic salts deposition on the interior surface of oilfield equipment takes topographic point in the procedure of field development of production of moire oil. Salt precipitation occurs in all operation methods of Wellss, but the most negative effects of scaling occur during oil production by electric submergible pumps ( ESPs ) [ 3 ] . Intense deposition of Ca carbonate on impellers ESP is due to the flow temperature addition of produced fluids, which is caused by the heat emanation of runing the submergible motor. Along with salt deposition in Wellss, intense salt precipitation is observed in the wellspring, oil grapevine assemblage, metering devices and installations for the readying of oil and besides in reservoir force per unit area care systems [ 4 ] . The procedure of precipitation of Ca carbonate occurs in three phases. In the first measure, ions of Ca combine with carbonate ions to organize the molecule. Following, molecules combine in microcrystals that serve as crystallisation centres for the reminder of the solution. Crystal aggregates grow and precipitate or attached to the walls of equipment at certain sizes [ 5, 6 ] . Calcium carbonate is found in the signifier of solid white crystals. Factors act uponing the formation of carbonate sedimentations include that formation H2O must be supersaturated with Ca, carbonate or hydrogen carbonate ions [ 7 ] . All control engineering of grading is divided into bar and remotion of scaling. The most effectual method is chemical method of bar by utilizing scale inhibitors. Basic technologies of inhibitor injection are divided as follows: reagent bringing into the wellbore and into the formation. Dose into the well is carried out by agencies of batcher dosing into the ring, into a given point along the capillary and the periodic injection into the ring through collectors. Dose into formation is done through squashing scale inhibitor, injection via injection Wellss ( in force per unit area care system ) , add-on of inhibitor by proppant during fracturing ( ScaleProp ) and injection of the inhibitor with the fracturing fluid during fracturing ( ScaleFrac ) [ 8, 9 ] . The intent of this work is increasing of operational efficiency of bring forthing Wellss by bar of formation of Ca carbonate in the downhole equipment, utilizing the developed inhibiting composing. Methods In the conducted research lab experiments for the readying of chemical solutions was used distilled H2O, in connexion with necessity to extinguish the influence on the belongingss of the composing and the consequences of experiments of ion finding, which were contained in different fresh H2O in assorted concentrations and ratios of their common concentrations. In the readying of look intoing composing harmonizing to the needed volume of the composing and concentrations of constituents, were weighed deliberate sum of H2O and reagents. Medical panpipes and high preciseness research lab balances were used for the exact values aˆâ€ ¹aˆâ€ ¹of the reagents multitudes. Scale inhibitor should be to the full compatible with formation H2O without the precipitation formation while salvaging their belongingss [ 10 ] . For the analysis, man-made solution, the ionic composing of which is near to the composing of formation H2O, is prepared. Inhibitory belongingss mostly depend on the content of Ca in the formation Waterss. Therefore, the compatibility standards can be that if in the readying of the inhibitor solutions in the H2O with a certain content of Ca2+, turbidness is non observed within 24 hours, the inhibitor at a given concentration is considered compatible with the given H2O. The prepared graduated table inhibitor should be more effectual and stable. The effectivity of the inhibitor is evaluated by its consequence on formation H2O or man-made theoretical account of H2O. Using theoretical accounts provides high truth measurings [ 11 ] . Determination of an inhibitor ‘s effectivity is made by appraisal of mass alteration of precipitation, which is formed in mineralized H2O in the presence of inhibitor with regard to H2O with no inhibitor [ 12 ] . Calculation of the protective consequence of an inhibitor is carried out harmonizing to the equation: E % =? 100( 1 ) Where Tocopherol is the scale inhibitor efficiency, m0and m are the multitudes of salt precipitate in the H2O with inhibitor and without inhibitor in gm, severally. The new graduated table inhibitor must hold the low corrosiveness. Corrosiveness of the developed composing is evaluated through the mass decrease of mention samples after their submergence in the inhibitor solution. Corrosion aggressivity of reagents was evaluated by hydrometric method – the weight loss of the samples. The corrosion rate of samples ( denseness of steel samples is 7821 kg.m-3) was calculated from the equation: Voltdegree Celsiuss=( 2 ) Where Vdegree Celsiussis the corrosion rate of the used sample in mm/year, m1and m2are the mass of the metal samples before and after the trial in gm, severally, S is the surface country of samples in m2, t is the trial clip in hr. Scale inhibitors should hold good adsorption-desorption features, heat opposition and minimum toxicity [ 13 ] . Evaluation of surface assimilation and desorption ability of suppressing composing is performed through research lab filtering of suppressing solutions for nucleus samples. Filtration surveies of developed inhibitor on nucleus samples are investigated by utilizing the setup FDES-645 ( Formation Damage Evaluation System ) . Reservoir temperature and force per unit area conditions are applied when utilizing this setup. Result and treatment The consequences of surveies to find the ionic composing of the man-made formation Waterss are shown in table 1. Table 1. Characteristic of man-made formation WaterssParametersMan-made formation H2OFirstSecondThirdpH6.927.347.13Density, kg.m-3101210231018Ion content, mg/lHCO3–206541633122784Carbon monoxide32-108951547312871Chlorine–240508372Calcium2+171942146919836Milligram2+348952874173Sodium+10759741248K+647518692Entire dissolved salts, g/l54.1960.5661.98Type of H2O harmonizing to the Sulin ‘s systemChloride-calciumChloride-calciumChloride-calciumHarmonizing to the categorization Sulin ‘s system, all man-made formation Waterss are a Ca chloride type. Sulin ‘s system is more descriptive of crude oil formation Waterss than are the other systems [ 14 ] . The entire mineralization of Waterss is located in the scope of 54 – 62 g/l. The theoretical accounts of H2O have the big concentration of hydrogen carbonate, carbonate and Ca ions, which are the chief factor of formation of Ca carbonate salt in the H2O because formation H2O must be supersaturated with thes e ions to precipitate this salt [ 15 ] . The developed composing of inhibitor is evaluated by finding the residuary content of scale inhibitors in samples of liquid. The concentration finding of P of inhibitor in the formation H2O is based on the reaction of phosphate ion with molybdate in acerb medium [ 16 ] . The optical density ( optical denseness ) of the obtained solutions is measured by a exposure tintometer at length ?=540 nanometer in cells with an absorbing bed thickness of 30 millimeter. The optical denseness should non transcend one. Control sample is taken as a standard solution. Each sample is measured on photoelectrocolorimeter two or three times, the arithmetic obtained values are used for the consequence of measuring. From the obtained informations, a standardization curve is plotted by utilizing on the horizontal axis the concentration of inhibitor in mg/l, and on the perpendicular axis the magnitude of its matching optical denseness. As shown in figure 1, the ensuing values of the optical denseness are cor related with the standardization graph and the concentration of inhibitor is found in the trial solution as a consequence of the experiments. Figure 1. The alteration in optical denseness of the solution, depending on the content of the inhibitor in H2O Evaluation of the effectiveness action of graduated table inhibitors by their ability to forestall the salt precipitation were carried out in the liquid solution of man-made formation Waterss. Trials were performed at a temperature of 25 ?C at the exposure clip of 24 hours. The consequences are presented in table 2. Table 2. Evaluation of the effectivity graduated table inhibitorsScale inhibitor figureChemical composing of graduated table inhibitorScale suppression efficiency ( in 30 mg/l of inhibitor ) , %First H2OSecond H2OThird H2O1Oxiethilidendiphosphone acid 3 % , ammonium chloride 4 % , polyethylene polyamine-N-methylphosphonic acid 4 % , hydrochloric acid 10 % , isopropyl alcohol 2 % , H2O – balance9190922Oxiethilidendiphosphone acid 1 % , ammonium chloride 6 % , polyethylene polyamine-N-methylphosphonic acid 2 % , hydrochloric acid 5 % , isopropyl alcohol 6 % , H2O – balance8987883SNPH-5312, the composite reagent of P878581As shown in table 2, the consequences of the experiment revealed that the developed chemical composings have the necessary protective consequence ( effectivity of more than 85 % ) for Ca carbonate in dosing rate of 30 mg/l. The inhibitor figure 1 gives the higher effectivity for bar of Ca carbonate precipitation in all formation Waterss. The difference be tween the inhibitors figure one and two is the alteration in mass fraction of inhibitor constituents. Inhibitor SNPH-5312 is an industrial inhibitor for bar of Ca carbonate formation, which is used in oil field. This inhibitor is based on the composite reagent of P. Table 2 illustrates that SNPH-5312 can protect Ca carbonate formation up to 87 % . Surveies have been conducted to find the compatibility of scale inhibitors with the formation Waterss. All inhibitors were compatible in three man-made formation Waterss, and the consequences showed all the above chemical composing can be prepared in the formation Waterss. The usage of chemical reagents for forestalling the deposition of salts in the Wellss is associated with the usage of chemically aggressive environments. A scale inhibitor is anticorrosion if there is no opposing on the surface of the sample and corrosion rate does non transcend 0.1 mm /year. The caustic activity of above graduated table inhibitors was carried out by hydrometric method by utilizing metal home bases through soaking for 72 hours at 25 ?C. Table 3. Consequences of probe of the corrosion rate of graduated table inhibitorsScale inhibitorTest continuance, hourFirst H2OSecond H2OThird H2OMass decrease, gCorrosion rate, mm/yearMass decrease, gCorrosion rate, mm/yearMass decrease, gCorrosion rate, mm/year1720.00130.04040.00150.04670.00170.05292720.00170.05290.00190.05910.00200.06223720.00210.06530.00210.06530.00220.0684From the informations in table 3, it can be noted that all the above chemical composings showed an allowable corrosion rate ( less than 0.1 mm/year ) . Therefore, these reagents can be considered as reagents to forestall grading in Wellss. The initial concentrations of the reagents in suppressing composings are different, and so it is possible to compare the kineticss of the comparative concentrations of the solutions. The used nucleus samples had mean porousness of 20 % and permeableness of 70 mendeleviums. Figure 2 shows the consequences of finding of the comparative concentrations of the inhibitor reagents in the composings for the surface assimilation procedure at temperature of 120 ?C and force per unit area of 300 standard pressure. Laboratory surveies showed that the confining surface assimilation is achieved when pumping 14 pore volumes for suppressing composings figure 1 and 2, for complete surface assimilation of SNPH-5312, 15 pore volumes must be pumped. By comparing the comparative concentrations of reagents in figure 2 during surface assimilation, it can be concluded that the surface assimilation is faster when utilizing suppressing composings figure 1 and 2. Harmonizing figure 2, more unvarying surface as similation is observed in the composing figure 1. Figure 2. Concentration alterations of the inhibitor solution in the surface assimilation procedure in the nucleus Once the nucleus left for 24 hours to find the surface assimilation equilibrium, formation H2O is pumped into the nucleus to displace suppressing composing. Consequences of finding of the comparative concentrations of inhibitors are shown during the desorption procedure in figure 3. The optimum and recommended concentration of oxiethilidendiphosphone acid in the composing for field conditions, is 10-15 mg/l, it corresponds to the comparative concentration of 0.0001. Harmonizing to figure 2, utilizing the inhibitor SNPH-5312 can supply the needed remotion of the inhibitor, which is sufficient for effectual protection of precipitation of Ca carbonate, when pumping through the nucleus sample of 27 pore volumes of H2O. Effective protection against formation of Ca carbonate under similar conditions persists in pumping 37 pore volumes of H2O when utilizing the developed suppressing composing figure 1, and 32 pore volumes of H2O by composing figure 2. This demonstrates that the developed co mposing have 1.37 times greater continuance of desorption in comparing with the inhibitor SNPH-5312. ( a ) ( B ) Figure 3. Concentration changing of the inhibitor solution in the desorption procedure on the nucleus, ( a ) from 5 to 20 pore volumes, ( B ) from 20 to 40 Data analysis on remotion of considered repressive composings show that a important part of the free inhibitor ( non-adsorbed ) is passed in pumping the first two volumes of pore infinite. The efficiency of the developed composing is explained by the mechanism of influence on the stone acidic additives belonging to its composing. Decisions Inhibitory chemical composing was developed for the bar of deposition of Ca carbonate with an optimum ratio of constituent oxiethilidendiphosphone acid 3 % , ammonium chloride 4 % , polyethylene polyamine-N-methylphosphonic acid 4 % , hydrochloric acid 10 % , isopropyl alcohol 2 % , H2O – balance. The used graduated table inhibitor was evaluated in footings of influence on corrosion actions and it was in the scope of 0.040-0.053 mm/year when the maximal allowable rate is 0.1 mm/year. The new inhibitor was effectual for scale bar of Ca carbonate up to 92 % . The research lab surveies showed that the developed composings have about 1.37 times longer continuance in comparing with the desorption of the tried inhibitor SNPH-5312, which is widely used in the Fieldss for forestalling formation of Ca carbonate. Mentions [ 1 ] Chunfang Fan, Amy Kan, Ping Zhang, Haiping Lu, Sarah Work, Jie Yu, Mason Tomson. Scale Prediction and Inhibition for Oil and Gas Production at High Temperature/High Pressure. Society of Petroleum Engineers ( SPE ) 2012 ; 17 ( 2 ) : 379-392. Department of the interior: 10.2118/130690-PA [ 2 ] J. Moghadasi, H. Muller-Steinhagen, M. Jamialahmadia, A. Sharif, M. Model Study on the Dynamicss of Oil Field Formation Damage Due to Salt Precipitation from Injection. Journal of Petroleum Science and Engineering 2004 ; 43 ( 3-4 ) : 201–217. Department of the interior: 10.1016/j.petrol.2004.02.014 [ 3 ] Neil Poynton, Alan Miller, Dmitry Konyukhov, Andre Leontieff, Ilgiz Ganiev, Alexander Voloshin. Squashing Scale Inhibitors to Protect Electric Submersible Pumps in Highly Fractured, Calcium Carbonate Scaling Reservoirs. Presented at the SPE Russian Oil and Gas Technical Conference and Exhibition28-30 October 2008 ; Moscow, Russia. ( in Russian ) . Department of the interior: 10.2118/115195-RU [ 4 ] Mackay EJ. Scale Inhibitor Application in Injection Wells to Protect Against Damage to Production Wells: When does it Work. Presented at SPE European Formation Damage Conference 25-27 May 2005 ; Scheveningen, Netherlands. Department of the interior: 10.2118/95022-MS [ 5 ] Mona El-Said, Mahmoud Ramzi, Thanaa Abdel-Moghny. Analysis of oilfield Waterss by ion chromatography to find the composing of scale deposition. Desalination 2009 ; 249 ( 2 ) : 748-756. Department of the interior: 10.1016/j.desal.2008.12.061 [ 6 ] Tomson, N.B. , G. Fu, M.A. Watson, A.T. Kan. Mechanisms of mineral scale suppression. Society of Petroleum Engineers ( SPE ) 2003 ; 18 ( 3 ) : 192-199. Department of the interior: 10.2118/84958-PA [ 7 ] T. Kumar, S. Vishwanatham, S.S. Kundu. A research lab survey on pteroyl-l-glutamic acid as a scale bar inhibitor of Ca carbonate in aqueous solution of man-made produced H2O. Journal of Petroleum Science and Engineering 2010 ; 71 ( 1-2 ) : 1-7.s DOI:10.1016/j.petrol.2009.11.014 [ 8 ] Khormali A, Petrakov D. Scale Inhibition and its Effectss on the Demulsification and Corrosion Inhibition. International Journal of Petroleum and Geoscience Engineering 2014 ; 2 ( 1 ) : 22-33. [ 9 ] Olesya Vladimirovna Levanyuk, Alexander M. Overin, Almaz Sadykov, Sergey Parkhonyuk, Bernhard R. Lungwitz, Philippe Enkababian, Alexander Vladimirovich Klimov, Sergey Legeza. A 3-Year Results of Application a Combined Scale Inhibition and Hydraulic Fracturing Treatments utilizing a Novel Hydraulic Fracturing Fluid, Russia. Presented at the SPE International Conference and Exhibition on Oilfield Scale 30–31 May 2012 ; Aberdeen, UK. Department of the interior: 10.2118/155243-MS [ 10 ] Richard A. Dawe, Yuping Zhang. Dynamicss of Ca carbonate scaling utilizing observations from glass micromodels. Journal of Petroleum Science and Engineering 1997 ; 18 ( 3-4 ) : 179-187. Department of the interior: 10.1016/S0920-4105 ( 97 ) 00017-X [ 11 ] Matty JM, Tomson MB. Effect of multiple precipitation inhibitors on Ca carbonate nucleation. Applied Geochemistry 1988 ; 3 ( 5 ) : 549-556. Department of the interior: 10.1016/0883-2927 ( 88 ) 90026-1 [ 12 ] Drela I, Falewicz P, Kuczkowska S. New rapid trial for rating of scale inhibitors. Water Research 1998 ; 32 ( 10 ) : 3188-3191. DOI:10.1016/S0043-1354 ( 98 ) 00066-9 [ 13 ] Ada Villafafila Garcia, Kaj Thomsen, Erling H. Stenby. Prediction of mineral graduated table formation in geothermic and oilfield operations utilizing the Extended UNIQUAC theoretical account: Part II. Geothermics 2006 ; 35 ( 3 ) : 239-284. Department of the interior: 10.1016/j.geothermics.2006.03.001 [ 14 ] A. G. Ostroff, Comparison of Some Formation Water Classification Systems, AAPG bulletin American Association of Petroleum Geologists, 1967 ; 51 ( 3 ) : 404-416. [ 15 ] Chen T, Neville A, Yuan M. Calcium carbonate graduated table formation—assessing the initial phases of precipitation and deposition. Journal of Petroleum Science and Engineering 2005 ; 46 ( 3 ) : 185-194. Department of the interior: 10.1016/j.petrol.2004.12.004 [ 16 ] MacAdam J, Parsons SA. Calcium carbonate graduated table formation and control. Reviews in Environmental Science and Bio/Technology 2004 ; 3 ( 2 ) : 159-169. DOI:10.1007/s11157-004-3849-1

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