ESET 223 Lecture 2 Impulse Turbines and Reaction Turbine.pdf

ESET-223 Power Engg. & HVAC School of Engineering Technology & Applied Science (SETAS) Lecture 2 Steam Turbines Centennial College - SDRE: ESET 223 1 Steam Turbine • Steam turbine is part of a Thermal power plant. http://www.youtube.com/watch?v=xokHLFE96h8 • steam turbines convert the heat ene...

ESET-223 Power Engg. & HVAC School of Engineering Technology & Applied Science (SETAS) Lecture 2 Steam Turbines Centennial College - SDRE: ESET 223 1 Steam Turbine • Steam turbine is part of a Thermal power plant. http://www.youtube.com/watch?v=xokHLFE96h8 • steam turbines convert the heat energy in steam to kinetic energy in order to perform work. • The heat energy and steam velocity determine the amount of work performed. • Three types of steam turbines commonly used Impulse Reaction Impulse-Reaction Special-purpose steam turbines are designed for specific plant requirements. Centennial College - SDRE: ESET 223 2 Impulse Steam Turbines Impulse turbines change the direction of flow of a high velocity fluid or gas jet. The resulting impulse spins the turbine and leaves the fluid flow with diminished kinetic energy. 3 Centennial College - SDRE: ESET 223 WORKING PRINCIPLE OF IMPULSE STEAM TURBINE In Impulse Steam Turbine, there are some fixed nozzles and moving blades are present on a disc mounted on a shaft. Moving blades are in symmetrical order. The steam enters the turbine casing with some pressure. After that, it passes through one or more number of fixed nozzles into the turbine. The relative velocity of steam at the outlet of the moving blades is same as the inlet to the blades. During expansion, steam's pressure falls. Due to high-pressure drop in the nozzles, the velocity of steam increases. This high-velocity jet of steam flows through fixed nozzles, and it strikes the blade with constant pressure. In an impulse turbine, steam produces only impulsive force to the blades. Now blades are starting to move in the same direction of the steam flow. Due to change in momentum, turbine's shaft is starting to rotate. Centennial College - SDRE: ESET 223 4 Impulse Steam Turbines • Most steam turbines are designed to have a steam velocity that is twice as great as the blade velocity. • Steam velocity increases as steam passes through nozzles in the impulse steam turbine. Centennial College - SDRE: ESET 223 5 Construction of Impulse Steam Turbines • Steam turbines may contain many sets of wheels that can be divided into stages. • A nozzle or nozzles located before each stage cause the steam to expand and increase in velocity. • With the increase in velocity, there is a corresponding decrease in pressure. • The steam velocity returns to Its initial value after passing through the blades before the next stage. • A set of fixed blades is used to reverse the flow of steam between each pair of revolving blades. Centennial College - SDRE: ESET 223 6 Operation (1) of Impulse Steam Turbines • Impulse steam turbines use steam velocity as a force acting in a forward direction on a blade or bucket mounted on a wheel. Consider Fig: 6-3 • To produce the force, steam is routed through a firststage nozzle (1) and gains velocity before striking the rotating blades (2) on the first-stage wheel. • This causes the shaft to rotate. Then steam is passed through stator blade (3) which changes the direction of steam. • Steam is then routed through fixed blades(3), which redirect the flow of steam to the blades (4) on the same wheel of the first stage. • The steam then enters the second-stage nozzle (5), gaining velocity before striking the blades (6) of the secondstage wheel. • Steam exits through the exhaust opening. 7 Centennial College - SDRE: ESET 223 Operation (2) of Impulse Steam Turbines • Steam enters the first-stage nozzle (1) and drops slightly in pressure as it passes through, but the steam velocity increases. • The steam strikes the revolving blades (2) imparting energy to the blades but losing velocity in the process. • There is no pressure drop going through the revolving blades. The steam then enters the fixed blades (3) and changes direction without losing pressure or velocity. • Once again, the steam strikes a second set of revolving blades (4), with the corresponding drop in velocity but not in pressure. This is velocity compounding. 8 Centennial College - SDRE: ESET 223 Operation (3) of Impulse Steam Turbines • The velocity drops to the initial value. To increase the velocity, the steam is passed through the secondstage nozzle (5). • The velocity-pressure relationship is then repeated as the steam passes through the second-stage revolving blades (6). • The pressure diagram shows a pressure drop through the first- and second-stage nozzles before exhausting after the second stage. • The diameter of the wheels increases in size from the first stage to subsequent stages to allow for the drop in pressure and increase in volume. 9 Centennial College - SDRE: ESET 223 Parts of Impulse Steam Turbine • Impulse Steam Turbine Parts. Impulse steam turbine parts are the same regardless of the number of stages in the steam turbine. • Parts found on impulse steam turbines include: 1. shaft, 2. nozzles, 3. throttle valve 4. Steam seals 5. Labyrinth packing seals 6. governor, 7. shaft glands, 8. rotor, 9. bearings, 10. bearing lubrication accessories. Centennial College - SDRE: ESET 223 10 The Parts of Impulse Steam Turbines (1) • Shaft (1) supports mounted wheels with blades attached on the outer edges. • Nozzles (2) are fitted before each pressure stage with stationary diaphragms (3) • Stationary diaphragms (3) separate the wheels. The stationary diaphragms seal each stage against steam leakage. • At the points where the stationary diaphragms join the rotating shaft, a steam seal ( 4) must be fitted to prevent the higher pressure of one stage from leaking through to the next stage. • Labyrinth packing seals (5) are commonly used to seal stages. Centennial College - SDRE: ESET 223 11 The Parts of Impulse Steam Turbines (2) • Large impulse steam turbines are equipped with hydraulic governors (6) that maintain a constant speed. • A low-oil pressure cut-off and an overspeed trip are also installed on large steam turbines. • Shaft glands (7) The turbine gland sealing system prevents the escape of steam from the turbine shaft and casing penetrations and the glands of main steam stop and control valves. This system also prevents air leakage into the low pressure turbine glands. • Turbine Wheels/Rotor (8) Source: pumpsandsystems 12 Centennial College - SDRE: ESET 223 The Parts of Impulse Steam Turbines (3) • Bearings (9) are used to maintain the rotating rotor in a fixed position within the casing. • The two types of bearings used are the • radial (main) or Journal bearings/sleeve bearings • thrust bearings. • Journal or Radial bearings/sleeve bearings maintain the vertical position of the rotor. • Thrust bearings maintain the horizontal position of the rotor. • If radial or thrust bearings exceed the specified tolerance, contact between the rotor and casing will occur. • Contact between the rotor and casing results in overheating, distortion, and subsequent damage. Source: pumpsandsystems Centennial College - SDRE: ESET 223 13 Shaft Seal and Packing Of Impulse Steam Turbines 14 Centennial College - SDRE: ESET 223 Reaction Steam Turbines Reaction turbines develop torque by reacting to the gas or fluid's pressure or mass. The pressure of the gas or fluid changes as it passes through the turbine rotor blades 15 Centennial College - SDRE: ESET 223 Operation of Reaction Steam Turbines • Reaction steam turbines function similarly to a lawn sprinkler in which water pressure is converted to kinetic energy. • Water under pressure is introduced at the center of the sprinkler. From the center, the water branches to the arms and leaves the openings in the arms. • As the water leaves, the arms move backward in reaction to the forward force of the water. • Newton's law states that for every action there is an equal and opposite reaction. • Reaction steam turbines operate on this principle for part of their action. Centennial College - SDRE: ESET 223 16 Reaction Steam Turbines Instead of nozzles, a reaction steam turbine uses fixed blades for its first stage. 17 Centennial College - SDRE: ESET 223 Reaction Steam Turbines Videos: https://www.youtube.com/watch?v=1bl1Q3V_79I https://www.youtube.com/watch?v=fERdl_6cu28 https://commons.wikimedia.org/wiki/File:Turbines_impulse_v_reaction.png Centennial College - SDRE: ESET 223 18 Reaction Steam Turbines • Fixed blades are designed so each blade pair acts as a nozzols. • Steam expands between each blade pair. The expanding steam gains velocity in the same manner as the impulse nozzle. • This steam, with its high velocity, enters the blades of the moving element, imparting a direct impulse to it in the same manner as the impulse steam turbine. • Steam is then directed into the nozzle-shaped blade passages instead of being exhausted through the remainder of the blade passage without further expansion as in the impulse steam turbine. 19 Centennial College - SDRE: ESET 223 Pressure and Velocity of steam in Reaction Steam Turbines • The steam expands in the nozzle-shaped passages and gains additional velocity. • When leaving the steam turbine blades at a high velocity, a backward kick, or reaction, is applied to the blades. This is where the term reaction steam turbine comes. 20 Centennial College - SDRE: ESET 223 Operation (1) of Reaction Steam Turbines • The steam at its initial pressure enters the fixed blades (1) and increases in velocity while losing pressure. • The steam strikes the revolving blades (2), giving up energy and losing velocity. • As the steam leaves, it gives a reactive force to the revolving blades, and a loss of pressure occurs. • The second stage begins as the steam enters the next row of fixed blades (3). • Again. velocity increases and some pressure is lost in the fixed blades. Centennial College - SDRE: ESET 223 21 Operation (2) of Reaction Steam Turbines • Then velocity and pressure decrease through the revolving blades (4). • Because of the difference in pressure between the entrance and exit sides of both fixed and revolving blades, the reaction steam turbine is a full-admission steam turbine. • Admission of steam takes place completely around the wheel. (In impulse steam turbines, only certain nozzles are opened to produce the flow required.) 22 Centennial College - SDRE: ESET 223 Physical Characteristics of Reaction Steam Turbines Because certain characteristics of reaction steam turbine operation differ from impulse steam turbine operation, physical characteristics of the reaction steam turbine differ from the impulse steam turbine. The following are physical characteristics of reaction steam turbines: 1. Close mechanical clearance between tips of fixed blades and shaft; close mechanical clearance between moving blades and casing. 2. Relatively large number of elements permitting small pressure drop per row of blades. 3. Moving blades mounted on drums. 4. Full admission of steam all around the blades. 5. Large axial thrust. resulting from difference in pressure between stages, must be balanced by (a) balancing pistons of various sizes; (b) dummy piston, which is a single balance piston; and (c) double flow of steam. Centennial College - SDRE: ESET 223 23 The Parts of Reaction Steam Turbines Reaction steam turbines commonly include the following parts: • fixed blades, • moving blades. • throttle and governor system, • shaft glands, • radial and thrust bearings, • lubrication accessories, • labyrinth packing seals, and • Sealing strips. Fixed blades are fastened to the housing and act as nozzles when steam enters. 24 Centennial College - SDRE: ESET 223 Parts of Reaction Steam Turbines • Moving blades mounted on drums form the rotor. • Steam releases energy to the blading as it passes through. • The throttle and governor system functions the same as in an impulse steam turbine. • • • • Shaft glands radial and thrust bearings lubrication accessories labyrinth packing seals are used for the same purposes in reaction steam turbines as in impulse steam turbines. 25 Centennial College - SDRE: ESET 223 Sealing Strips of Reaction Steam Turbines • Sealing strips are located in the casing to reduce leakage between stages and warn of excessive radial tolerance. • If the radial tolerance is exceeded, clearance between the sealing strips and rotor blades is eliminated. • Rubbing of the rotor blades on the sealing strips results in a squealing noise. This alerts the operator to a problem before significant damage occurs. 26 Centennial College - SDRE: ESET 223 Pressure Drops across the Blades • The impulse steam turbine wheel revolves in chambers with equal pressure on each side. • There is no axial thrust resulting from unbalanced pressures if the shaft is approximately the same diameter at the highpressure and the exhaust ends. • Axial thrust is an important consideration in reaction steam turbines. • First, there is a cumulative pressure resulting from the drop in pressure across each row of blades. 27 Centennial College - SDRE: ESET 223 Pressure (2) of Reaction Steam Turbines • Second, there is also an axial thrust resulting from pressure on the end of each drum when the diameter changes. • The Kingsbury thrust bearing controls axial thrust by using one collar on the shaft, which bears against pivoted shoes. • When the shaft is rotated, the shoes pivot to form a wedge-shaped film of lubricating oil on the bearing surfaces. Centennial College - SDRE: ESET 223 28 Balance Piston or Dummy Piston Of Reaction Steam Turbine • Reaction steam turbines commonly use one balance piston or dummy piston to balance all thrust at full load on the machine. • Any inequalities of thrust at other loads are compensated by the thrust bearing itself. Because the dummy piston is exposed to high pressure, some anti leakage packing must be provided. • Labyrinth packing is placed between the dummy piston and dummy cylinder. • Pressure on each side of every row of blades is different. 29 Centennial College - SDRE: ESET 223 Pressure difference In Reaction Steam Turbine Parts: • The pressure difference is necessary for steam to gain velocity in each row of blades. • This pressure difference can cause steam leakage around the tops of the revolving blades and under the bottoms of the fixed blades. • To minimize steam leakage, clearances should be reduced, and a small steam pressure difference should be present across each row of blades. http://wms26.streamhoster.com/protrainer2003/CC_English%20 Demo/ST_vs1_labeled_r1.wmv 30 Centennial College - SDRE: ESET 223 Rankine cycle analysis https://www.youtube.com/watch?v=H1aKEcM2YOo&t=76s ESET 223, Winter 2022 31 Ideal Rankine Cycle: P-v & T-s ▪ 1-2 or 1 '-2 ': adiabatic reversible expansion through the turbine. The exhaust vapor at 2 or 2' is usually in the twophase region. ▪ 2-3 or 2' -3: constant temperature and, being a two-phase mixture process, constant pressure heat rejection in the condenser. ▪ 3-4: adiabatic reversible compression by the pump of saturated liquid at the condenser pressure, 3, to subcooled liquid at the steam-generator pressure, 4 . ▪ Line 3-4 is vertical on both the P-V and T-S diagrams because the liquid is essentially incompressible and the pump is adiabatic reversible. ESET 223, Winter 2022 32 Ideal Rankine Cycle: P-v & T-s ▪ 4 - 1 or 4 - 1 ': constant-pressure heat addition in the steam generator. Line 4 – B – l – l’ is a constant-pressure line on both diagrams. ▪ The portion 4 - B represents bringing the subcooled liquid, 4, to saturated liquid at B. The section 4-B in the steam generator is called an economizer. ▪ The portion B - 1 represents heating the saturated liquid to saturated vapor at constant pressure and temperature (being a two-phase mixture), and section B-1 in the steam generator is called the boiler or evaporator. ▪ Portion 1 - 1', in the superheat cycle, represents heating the saturated vapor at 1 to 1 '. Section 1-1 ' in the steam generator is called a superheater. ESET 223, Winter 2022 Week# 1&2 - Power Plants33 Ideal Rankine Cycle Processes: 1-2: Expansion through turbine, Isentropic & Adiabatic 2-3: Condensation in condenser, Isothermal & Isobaric 3-4: Compression by pump, Adiabatic 4-1: Heat addition in Boiler, Isobaric ESET 223, Winter 2022 Week# 1&2 - Power Plants34 Efficiency of Turbine: Thermal efficiency is the ratio of the heat energy used in the turbine to the heat energy available in the steam. The enthalpy of steam supplied to the steam turbine minus the enthalpy of exhaust steam indicates how much heat was used in the steam turbine. 35 Centennial College - SDRE: ESET 223 Example: Efficiency of Turbine In a Rankine cycle powerplant a 2500 kW steam turbine operates with a steam pressure of 200 psia at 600 ºF. It exhausts into a condenser (x=0.9) with a vacuum of 28.5“ Hg. Note: All values are obtained from Dry Saturated and Superheated Steam tables. To find the enthalpy of the condensate, the vacuum in inches of Hg should be converted to psia. Hints: 1 inch Mercury = 0.491 psi, 1 cm Mercury = 1.33 kPa Find: 1. Thermal efficiency of the turbine. 2. Power input (in kW) to the boiler considering boiler thermal efficiency of 85%. 3. Power (in kW) wasted in the condenser. 4. Percentage of Power wasted in respect to the input power. 5. Find the value in Dollar of the energy wasted in one day in the condenser considering the price of each kW.Hr is $0.11. 6. Find the value in Dollar of the energy wasted in one day in the Chimney considering the price of each kW.Hr is $0.11. Note: Ignore the feedwater pump. 36 Centennial College - SDRE: ESET 223 Electric Efficiency of Turbine System Electric efficiency is the ratio of the electrical energy output to the heat energy input of the turbine system. Electric Efficiency = Electrical Energy Output (kW)/Heat Energy Input(kW) 37 Centennial College - SDRE: ESET 223 Efficiency of Turbine Problems: Problem 1: A 100,000 kW steam turbine operates with a steam pressure of 450 psia at 9000F. The quality of exhaust steam at turbine exit is 90%. It exhausts into a condenser with a vacuum of 23.83" Hg. What is the thermal efficiency of the steam turbine? Problem 2: A gas turbine powerplant is running on natural gas. The power of heat addition by burning fuel is 192 MW. The calorific value of natural gas is 48000 kJ/kg. The gas turbine is producing 64 MW mechanical power available for producing electric power. The plant is producing 57.6 MW of electric power. Calculate the thermal efficiency of the GT plant and electric efficiency. 38 Centennial College - SDRE: ESET 223 Example: In a Rankine cycle powerplant a 2500 kW steam turbine operates with a steam pressure of 200 psia at 600 ºF. It exhausts into a condenser (x=0.9) with a vacuum of 28.5“ Hg. Note: All values are obtained from Dry Saturated and Superheated Steam tables. To find the enthalpy of the condensate, the vacuum in inches of Hg should be converted to psia. Hints: 1 inch Mercury = 0.491 psi, 1 cm Mercury = 1.33 kPa Find: 1. Thermal efficiency of the turbine. 2. Power input (in kW) to the boiler considering boiler thermal efficiency of 85%. 3. Power (in kW) wasted in the condenser. 4. Percentage of Power wasted in respect to the input power. 5. Find the value in Dollar of the energy wasted in one day in the condenser considering the price of each kW.Hr is $0.11. 6. Find the value in Dollar of the energy wasted in one day in the Chimney considering the price of each kW.Hr is $0.11. Note: Ignore the feedwater pump. 1. Thermal efficiency of the turbine ɳt. P1 = 200 psia T1 = 600 ℉ from steam table h1 = 1322.3 btu/lb P2 = -28.5”Hg x 0.491 + 14.7 = 0.7 psia At point 2, from steam table, hv = 1100.4 btu/lb, hL = 58.10 btu/lb h2 = 0.9 x 1100.4 + (1-0.9) x 58.10 = 996.17 btu/lb h3 = hL = 58.10 btu/lb ɳt = (h1-h2)/(h1-h3) =26% 2. Power input (in kW) to the boiler considering boiler thermal efficiency of 85%. Pb-input: Power input of the boiler Pt-output: Power output of turbine Pt-output = 2500 kW ɳb: Boiler thermal efficiency ɳT: Total thermal efficiency of the power plant ɳT = ɳb x ɳt = 85% x 26% = 22.1% Pb = Pt / ɳT = 2500 kW/22.1% = 11312.2 kW 3. Power (in kW) wasted in the condenser Pcond. Pt-input: Power input to the turbine Pt-input = Pt-output / ɳt = 2500/26% = 9615.4 kW Pcond = Pt-input - Pt-output = 9615.4 – 2500 = 7115.4 kW 4. Percentage of Power wasted in respect to the input power: ɳ-waste. Pb-waste: Power waste by the turbine Pb-waste = Pb x (1-85%) = 11312.2 x 15% = 1696.83 kW PT-waste = Pcond + Pb-waste = 7115.4 + 1696.83 = 8812.23 kW ɳ-waste = PT-waste/Pt-input x100%=8812.23/11312.2 x 100%= 77.9% or ɳ-waste = 1 - ɳT = 1- 22.1% = 77.9% 5. $cond = 7115.4 kW x 24 hr x $0.11 = $18784.65 6. $boiler = 1696.83 kW x 24 hr x $0.11 = $4479.63 Problem 1: A 100,000 kW steam turbine operates with a steam pressure of 450 psia at 900 ℉. The quality of exhaust steam at turbine exit is 90%. It exhausts into a condenser with a vacuum of 23.83" Hg. What is the thermal efficiency of the steam turbine? P1 = 450 psia T1 = 900 ℉ from steam table h1 = 1468.6 btu/lb P2 = -23.83 x 0.491 + 14.7 = 3 psia At point 2, from steam table, hv = 1122.2 btu/lb, hL = 109.39 btu/lb h2 = 0.9 x 1122.2 + (1-.09) x 109.39 = 1020.92 btu/lb h3 = hL = 109.39 btu/lb ɳ = (h1-h2)/(h1-h3) =32.94% Problem 2: A gas turbine powerplant is running on natural gas. The power of heat addition by burning fuel is 192 MW. The calorific value of natural gas is 48000 kJ/kg. The gas turbine is producing 64 MW mechanical power available for producing electric power. The plant is producing 57.6 MW of electric power. Calculate the thermal efficiency of the GT plant and electric efficiency. Pf: power of fuel Pf = 192 MW Hg: Heat of gas Hg = 48000 kJ/kg Pt: power output of turbine Pt = 64 MW Pe: electric power output Pe = 57.6 MW ɳ1: thermal efficiency of GT plant ɳ1 = Pt/Pf x 100% = 33.3% ɳ2: electric efficiency ɳ2 = Pe/Pt x 100% = 90%