Micro Hydropower Plant - Coursework Example

MICRO HYDROPOWER PLANT of Affiliation] Table of Contents List of tables 3 Introduction 4 Site Configuration 5 Design Parameters and Considerations 5 Flow duration curve 5 Flow rate measurement 5 Intake location 6 Trash rack design 6 Gates and valves 7 The forebay 7 Penstock design 7 Saddles 8 Tailrace 8 Turbine power 8 Turbine speed 9 Selection of turbines 9 For Francis turbine 10 For Kaplan turbine 10 For cross flow turbine 10 Pelton turbine 10 Cavitation phenomenon 18 Powerhouse 19 Speed increasers 19 Runway and rotational speed 19 Speed governor 20 Proposed Design 20 Water Sources 21 Plant Efficiency 21 Turbines and Compressors 22 The Cost Analysis 22 Environment Effects, Critical Analysis and Discussion 23 Conclusion and Recommendation 24 References 27 List of tables Figure 1: Variation of power to bucket to water jet 11 Figure 2: Parts of a Pelton turbine 12 Figure 3: Six sphere turbine 13 Figure 4: Arrangement of buckets in a pelton turbine 13 Figure 5: Efficiency curve of Pelton turbines 14 Figure 6: Arrangement of buckets in a Pelton turbine 14 Figure 7: Action of water jets on the bucket 15 Figure 8: Water flowing through a bucket in a pelton b) inlet velocity triangle c) outlet velocity triangle 16 Figure 9: Provided dimensions 16 Figure 10: Position of the Pelton turbine 18 Introduction It is appropriate to look into the design parameters of a power plant and the flow processes that take place within the plant. This section focuses on the fundamental principles of steam that play an important role in the operation of the power plants. Some of the fundamentals that have been looked into are the water paths, the gas steam, the processes of combustion, heat exchange parameters and the fuel preparation processes. Now physical aspects are also considered which includes economic power production aspects of the design and the environmental aspects. Better power plants whether small or medium should have certain characteristics some of which include, higher efficiencies, greater operating performance and better maintainability. Similar considerations have been put in place for medium power plants as well. They use the combined cycles for higher efficiencies. The efficiencies of power plants are affected by higher temperatures and increase in water temperatures. Any system disturbance may cause the operation of any power plant to slow down. The sub systems are monitored to ensure that there is smooth operation, which results into a larger output of power. This reduces the environmental pollution as well. A coordinated system of control is put in place in order to facilitate all these principles. The system is to coordinate the operation of the sub systems of the power plant in order to obtain the optimal required output. Production of electricity from hydropower remains the first renewable source that is used to generate electricity. Most of the hydro plants have relatively small storage capabilities. The power is only produced by the turbine when there is flow of water and the generation ceases when the flow falls below some recommended value. Site Configuration The hydropower scheme is used to convert the potential to electrical energy of a mass of water that flows in a stream. The power produced in directly proportional to the head and the water flow rate. The schemes are classified as high head having over 100m, medium head ranging from 30-100m, and low head ranging from 2-30 m. The schemes can be classified as, run-of-river, those having powerhouse located at the base, and the ones integrated on the canal (Fox, McDonald and Pritchard 2004). Design Parameters and Considerations The project is to design a steam power plant that has a power output of 3kW and with higher efficiency in the operation. The design is based on the use of water falling from a stream. Flow duration curve The choice of the type of turbine, size of the turbine, and speed of the turbine is considered based on the maximum flow rate of water and the net head determined by where the turbine is installed. The maximum flow rate capacity of the turbine is determined with the help of flow duration curve. Mean annual flow provides a clue of the stream’s power potential. Flow rate measurement Several methods are used to measure the discharge. For example, velocity area method for large to medium rivers and used to obtain the mean velocity and cross sectional areas. It is used to determine the stream flow with less effort (Massey 2012). To calculate the cross sectional area of the river, it is divided into trapezoidal and calculated as below; A= [a+b]/2 *[h1+h2+h3+......hk]/k Where a and b are widths of top and bottom river in meters [h1+h2+h3+...hk]/k is the average height of the water in meters. It is necessary to measure the velocity of water at different sections since it is not constant. The surface speed is calculated as; V=L/t (m/s)...................................................eqn 1 Determine the average flow rate by multiplying equation 1 by correction factor [0.6-0.85], the accepted average value being 0.75. Vav=0.75V (m/s)...........................eqn 2 Calculate flow rate as below; Q=AVav (m3/s)..........................eqn 3 Intake location Intake is located at the end of the water channel of water. In the small hydro power plants, the intakes are horizontal followed by vertical or inclined penstock. Location of the intake may depend on a number of factors such as, submergence, environmental considerations, geotechnical conditions and ice formations. The following considerations are taken into account; rectangular to circular cross-section transition to the penstock to meet the entrance, approach walls to minimize the head losses and the flow separation, and piers meant to support the mechanical equipment (Douglas, Gasiorek, Swaffield and Jack 2005). Trash rack design Trash rack design is used to prevent entry of the trash into entrance flume. Trash racks are fixed at slanting positions between the angles 60- 80 degrees to the horizontal. The spacings are 20-30 cm for the pelton turbine, 80-100 cm for Kaplan turbine, and 40-50 cm for the Francis turbine. Gates and valves Sector gates are used to increase the head in the low head schemes that have powerhouse and integral intake. An electric motor or a hydraulic system opens the gate for water to pass underneath. The gate is used to prevent the runways during the maintenance on the shut down turbines. The recommended materials for the gate in micro-hydro systems are steel, timber, cast iron and the plastics. The forebay Forebay helps to distribute the water to various penstocks that lead to the turbine. Water is stored temporarily when the load is rejected by the turbine and withdrawn from it when the load is increased. The forebay also acts as a regulating reservoir. Penstock design Penstock helps to convey water to the powerhouse from the intake. Installations can be done over or under the ground depending on factors like penstock materials, environmental requirements, nature of the ground, and ambient temperature. Penstock diameter is calculated as below; Dp=2.69[np2Q2Lp/Hg] Where np=mannings coefficient Q=water flow rate Lp=penstock length Hg=gross head. The penstock wall thickness depends on the material of the pipe used, the pipe diameter, tensile strength and the operating pressure. The recommended wall thickness is calculated as below; Tp= [Dp+508]/ [400] +1.2mm Where Dp=penstock diameter tp=minimum thickness of the penstock. Saddles Saddles are used to support penstock’s weight full of water. The weight of the vertical component to be supported is calculated as; F= [Wp+Ww] Lmscos Q Where Wp=penstock’s weight Ww=weight of the water Lms=length of the penstock Q=angle between the pipe and the horizontal. Maximum length Lmms=182.61[[Dp+0.0147]4-Dp4]]1/3/pw Tailrace Tailrace is a channel through which water returns to the river after passing via the turbine. It is designed to ensure that the powerhouse is not undermined and protected by the riprap and concretes between the stream and the powerhouse. The design should ensure that the water does not rise higher that tempers with turbine runner especially during high flows. Turbine power Hydroelectric power plants depend on the falling water and streams act as the source of fuel. The power generated by the turbine is given by; Pt= pg*Hn Qnt (watts) Where p=water density Pt=power in watts Q=water flow rate g=gravity acceleration nt=turbine efficiency. Efficiency of the turbine is the ratio of the turbine power to the power absorbed (mechanical power by shaft of turbine to hydraulic power). For the impulse turbine, the head is taken from the point of impact located above downstream water level resulting into reduction of water head. In the estimation of overall plant efficiency, efficiency of the turbine is multiplied by the efficiency of the alternator and speed increaser. Turbine speed Rotating components are requires to ensure the turbine speed is controlled to regulate the water flow rate. The inertia is provided by the flywheel linked to the generator shaft or turbine. Excess power accelerates the flywheel when there is disconnection of the load. Upon reconnection of the load, inertia deceleration supplies power, which minimizes speed variations. dw/dt=1/Jw [pt-pl-Bw2] Where pt=turbine speed pl=load power B=friction torque coefficient of generator and turbine J=moment of inertia. Selection of turbines Once specific speed, turbine type, turbine power, the net head, height above the tailrace are known then installation can be carried out. In case of Francis and Kaplan turbines, the head loss, turbine power and the net head must be recalculated. Pelton turbines are used for high-pressure domains while the francis turbines cover the largest head ranges that overlap to 10m head. The lowest head of domain less than 10m is catered for by Kaplan turbine that has movable blades or fixed blades. For Francis turbine Francis turbine covers wide ranges in speed from 350 m to 50 m that corresponds to low heads and high heads respectively. Dimensions are calculated as below; D3=84.5[0.31+2.49Ns/995][Hn]1/2/N for exit diameter D1=[0.4+94.5/Ns] D3 for inlet runner diameter D2=D3/[0.96+3.810-4Ns for inlet diameter If Ns is less than 163 then D1=D2 For Kaplan turbine De=84.5[0.79+1.610-3Ns]Hn1/2/N for runner exit diameter Di=[0.25+94.5/Ns]De inlet diameter for the runner hub For cross flow turbine Dr=[40Hn1/2]/N for runner diameter Lr=[0.81Q]/[DrHn1/2] runner length Tj=[0.233Q]/[LrHn1/2] nozzle width or jet thickness Pelton turbine Pelton turbines are suitable for extraction of power when there is low flow rate of water and the energy of the water is at higher heads. Pelton turbine has a simple working mechanism. When the wheels of the pelton bucket are subjected to high-speed jets of water, it induces impulsive forces that makes the turbine to rotate and the shaft rotates running the generator producing electricity. The turbine converts the kinetic energy of the water to the rotational energy. Depending on the demand of the amount of power required that fluctuates from time to time, the governing mechanism is used that controls the spearhead position. When there is increase in power demand, the spear head moves out increasing the rate of water flow and when the demand decreases, the spear head is moved in at the inlet point. Therefore, controlling the water flow rate meets the amount of power needed when pelton turbine is used. In designing the pelton turbines, a consideration is given to the number of buckets located at the discs. There is loss of water jets when the number of buckets is inadequate and may result into drop in the efficiency of the turbine. The bucket therefore becomes the most vital component of the pelton turbine. They are casted as a unit piece of solid so that fatigue failures are minimized. Jets of water are split into components using a splitter and the shape of the bucket makes water jets to turn at an angle of 180 degrees producing impulsive forces on the bucket, which are shown using Newton’s law of motion. Holes are made at the bottom of the buckets to ensure that water jets are not interfered with by incoming new buckets. Inlet pressure, atmospheric pressure and the exit pressure of the water are equal since the jets are open to the atmosphere. The kinetic energy is therefore the maximum energy that can be absorbed by the bucket. The pelton turbines therefore gain the mechanical energy as kinetic energy of the jet changes thus, pelton turbines are impulsive machines. The higher the jet velocity, the higher the impulsive force and the turbine are most suitable when water is at high altitudes. This type of turbine is aimed at producing maximum power or to maximize efficiency from water jets. Figure 1: Variation of power to bucket to water jet Figure 2: Parts of a Pelton turbine Figure 3: Six sphere turbine Figure 4: Arrangement of buckets in a pelton turbine Figure 5: Efficiency curve of Pelton turbines Figure 6: Arrangement of buckets in a Pelton turbine Figure 7: Action of water jets on the bucket Calculations The deflection of water jets is recommended at 180 degrees. In practice, this is not possible and it is limited at 165 degrees. This is to ensure water leaving the bucket does not hit the backside of the adjacent bucket. Absolute velocity at which water strikes the bucket V1 V1=Cv [2Gh] 1/2 Where Cv is the coefficient of velocity U =the velocity of the bucket U and V1 are collinear since V1 is tangential Vr1 = Relative velocity Vr1= V1-U Therefore, Vw1=V1=Vr1+U Figure 8: Water flowing through a bucket in a pelton b) inlet velocity triangle c) outlet velocity triangle Figure 9: Provided dimensions Area= ½width height A=1/22.70.3 A=0.405 m2 However, the flow rate of water equals the area of the plan Therefore, Q=A m3/s =0.405m3/s The maximum power Pmax=pressure flow rate Pmax= pressure Q But pressure= mgh Therefore Pmax=mgh Q Figure 10: Position of the Pelton turbine Cavitation phenomenon Vapour pockets are formed when pressure hydrodynamic in the flow liquid reduces to value below the liquid vapour pressure. This results into small bubbles that are moved from the low-pressure section and collapses in higher-pressure regions. The formation of bubbles and final collapse is termed as cavitation. When the vapour bubbles and the solid boundary are in contact during collapse, then the forces that are exerted by the fluid generate high localized pressures causing pitting on the solid surface, a phenomenon that is accompanied by vibration and noise. Powerhouse The powerhouse must be completely secured and installed on a stable ground. The excavation eliminates the weathered layer when it is founded on a rock. When it is to be located near riverbanks that have no firm foundation, then it is recommended to recondition the ground. The powerhouse has the following equipment, electrical generators, the turbine, and the drive systems. Speed increasers Turbines and generators operating at same velocity are connected with their shafts in line and have direct coupling as the remedy. Maintenance is minimized in such a system and power losses are equally minimized. The couplings can be either fixed or flexible. Flexible coupling is recommended as it allows for misalignments. Any turbine that operates at speeds lower than 1500 rpm requires speed increaser to meet standard alternator. This method is economical as compared to custom alternator. Runway and rotational speed Turbines rotational speed is a function of the turbines net head and its power. In the selection of the turbine, it must be considered that the turbine is coupled either directly or through a gearbox in order to achieve the synchronous speed. Each runner is characterized by runway maximum speed. The cost of the gearbox and the generator is increased when the runway speed increases. Speed governor Governor is a group of mechanisms and devices that are used to detect deviations in speed converting the speed into change of position of the servomotor. The commonly used governor is the mechanical governor. A sensor is used in the electric-hydraulic governors to sense the speed of the turbine. In order to regulate the speed of the turbine, rotating components of inertia are needed which are supplied by the flywheel or the generator shaft. Flywheel provides a stabilizing effect on the rotating components while the water column offers destabilizing effects on the rotating components. The starts-up time is calculated as; Tr=Wtr2N2/[91270pt] Where r= is radius of gyration N=turbine speed pt=turbine power. Proposed Design When designing a small hydropower plant that produces power of 3kW, few parameters are needed. The power is generated using the water flow and mechanical energy is converted to electrical energy (Moran & Shapiro 2000).  Water Sources In steam power plants, several feed water lines are employed using several pumps. The pumps are powered by the electric motors. The motors get their power from the turbines located within the plant. There is direct proportionality between the power needed by the electric pumps and the flow rate of the liquid. The efficiency is directly proportional to the rate of flow. Pumps are useful in overcoming the losses due to frictional pressures and the passages of the water flow. Plant Efficiency The plant efficiency of may be experienced as a function of ratios of pressure, the air temperature, elements of the turbine, ambient temperature of air, and cooling requirements of the turbine blade. The efficiency of newer plants is higher as compared to the efficiency of power plants that have been in operation for some time. The power units designed for emergency purposes generate less power and are less efficient in performance. Higher efficiencies are experienced in hydropower plants designed for prime power and stations. The power units for emergency purposes are designed for a given number of hours and are allowed to have higher emission rates as compared to the turbines designed for continuous duties. The total efficiency of a system is experienced with relation to the amount of energy that can be recovered from the exhaust materials. When the HRSG stack temperature is low, and then a greater percentage of the energy is recovered. This results into subsequent higher total system efficiency. HRSG is a function of pressure and the fuel type. As the flow rate increases, pressure also increases. The e efficiency of hydropower plants remains high when it is subjected to part load conditions. Turbines and Compressors The turbine is rotated by the falling water. The shaft rotates converting the mechanical energy into electrical energy. A rotor motion is generated by a starter unit until a required design speed is generated that is enough to maintain the whole unit running. Several modules brought together forms gas generator. These modules include combustor module, turbine module and the compressor module (Dechamps, 1998). The Cost Analysis There must be adequate financial planning for any undertaking. A serious investment is necessary when establishing a new hydropower plant whether small or medium plant. The planning is set rolling before any design principles is laid down. The cost analysis therefore proceeds as design process progresses throughout the whole period (Kaplan 2010). This cost that is used to construct a hydropower plant is called capital cost and it is determined by the expected output of the power plant. Further additional costs are needed to ensure continuous operation of the plant. These operational costs may be regular throughout the life of the plant. The expenses include such costs as salary expenses, the fuel costs and the plant maintenance costs. These operating costs are classified into two categories thus, the initial costs of establishing the plant and the recurring costs (Mujtba, 2012).  Hpa=hpat Qpa Where hpa=price of the fuel T=operating time Qpa=fuel power Environment Effects, Critical Analysis and Discussion When establishing the hydropower plants, it is worth noting to consider the environmental aspects. Environmental issues are categorized into two parts thus, the impacts that are linked to the power conveyance and the effects of the power plants. There are primary and secondary environmental impacts. Smoke from the power plants to the environment is a primary impact while the effects caused by the smoke to the environment is a secondary impact and it is easier to assess the secondary impacts as compared to the primary impacts. A major issue of the environment is the quality of air. This must be looked into details before establishing a power plant. A number of pollution regulations have been put in place to monitor the operations of the power plants. Irrespective of the type of conveyance used, the impacts are all related in one-way or another for example in both the conveyances there is emission of dust particles especially during the construction stages (Mujtba, 2012).  The impacts that are associated with the conveyance and construction are temporary and minor. The ozone may be generated during the operation of power lines, which results into health problems. When carrying out the design analysis, hazard analysis techniques are considered. This is to minimize the occurrence of accidents to human species and other related risks. Hazard analysis involves identifying and understanding the activities that cause the accidents. Accident models can be categorized into three sectors thus, systemic models, epidemiological models and the sequential models. These models have helped to understand the nature of accidents that are most likely to be caused by the power plants. The systemic models consider the accidents from the plants as the emergent phenomena, which are because of the interaction of the plant parts. The interactions may be hard to analyse and understand. The analysis of the type of accident that is likely to be caused by the system parts is analysed using such methods as, failure analysis and the fault tree analysis. The efficiencies of hydropower plants are affected by higher temperatures and increase in water temperatures. Any system disturbance may cause the operation of any power plant. The sub systems are monitored to ensure that there is smooth operation, which results into a larger output of power. This reduces the environmental pollution as well. A coordinated system of control is put in place in order to facilitate all these principles. The system is to coordinate the operation of the sub systems of the power plant in order to obtain the optimal required output. Conclusion and Recommendation Micro-hydro power gradually grows and they are feasible when well established and the main requirements are water sources, generators, turbines, and the proper installation and design. Run-of-water turbine schemes are used to generate electricity with the help of water that is provided by the river. Generation ceases when the water level reduces below some recommended value. High head and medium head plants use weirs in order to divert water and conveyed into turbines through the penstock. The turbine choice depends on pressure head and the rate of water flow. Impulse turbine is driven by water jets and are recommended for low flow rates and high heads. Reaction turbines use both linear momentum and angular momentum of the running water to move the rotor and are meant for both low and medium heads. The micro-hydro plants installations are run-of-river and do not require a dam and installed on the available water flow. Intake structure channels water through the penstock to the turbine before water is released to the down-stream. Considering the climates of warming zones, there is a major loss of efficiency in the design of the current systems. There is also a tremendous increase in the fuel consumption rate. The society needs to invest heavily in the design of power plants to help increase the amount of power generated and to minimize the losses. There are a number of adaptations that must be employed when designing power plants to increase on its efficiency and sustainability. The factors are, improve on the performance level of the cooling system and improve on the coolant discharge plume management. In order to minimize on the environmental effects, one needs to fit to the plant the cooling towers. The additional fitting of such parameters require enough space to enhance the further enhancements. The project should be made such that it is able to adapt to the changes in the environment over time. The report has looked into the details all the factors needed to establish a small power plant of 8.8 MW, the benefits to the society, the environmental impacts to both human beings and other animals in the ecosystem. The report has discussed the cost analysis that is needed to establish a small power plant, the design procedures and the proposed design. The parts of the design network and the operating principles of every part of the design network. It is advisable that people to invest in the establishment of the power plants for sufficient energy supply to the entire population. Energy is such an important parameter in the day-to-day operation of the society. The machines require energy to operate and human beings need energy to carry out their activities. The methods of energy supply to the ecosystem should be those that have less negative effects on the environment and whose cost of production is low. References Balaji, C. 2011. Essentials of thermal system design and optimization. New Delhi, India: Ane Books Pvt. Douglas J.F., Gasiorek, J.M., Swaffield J.F., and Jack L.B. 2005. Fluid Mechanics, Pearson/Prentice Hall. Dechamps, P. J. 1998. "Advanced combined cycle alternatives with the latest gas turbines." Journal of Engineering for Gas Turbines and Power 120(2): 350-357. Kaplan, S. 2010. Power plant characteristics and costs. New York: Nova Science Publishers. Massey, B. 2012 Mechanics of Fluids, 9th edition, Taylor and Francis. Fox, R.W., McDonald A.T. and Pritchard, P.J. 2004. Introduction to fluid mechanics, 6th edition, Wiley. Mujtba, M. S. 2012. Small Hydro Electric Power Plant Schemes: Designing Hydro Electric Power Plant Scheme using Pelton Wheel over low water heads. Saarbrücken: LAP LAMBERT Academic Publishing. Moran, M. J., & Shapiro, H. N. 2000. Fundamentals of engineering thermodynamics. New York, Wiley. Read More