Steam turbines Electric motors How can we rev

Steam turbines & Electric motors “How can we rev you up? ” A Group F’s Production http: //www. revak. com/powergenpics. htm 1

Presentation Outline 1. 2. 3. 4. 5. 6. 7. We’re going to make Typical Applications Motors and Turbines jump through hoops for Types of Drives you! Physical Principles Troubleshooting Safety Operability Capital & Operating Costs 2

So where do drives live in Chemical Engineering Land? They live next to… – – – Pumps Compressors Fans Conveyor belts Crushers Mills And many more places… 3

Types of Drives Electric Motor Steam Turbine & Many More!!! Source: http: //fsvpix. homestead. com/FSVtodaypix. html 4

Drives sub-types Electric Motors • Constant Speed: – A/C Squirrel-Cage Induction, Synchronous A/C, etc. • Variable Speed – Two-Winding, Single. Winding Consequent-Pole, etc. Steam Turbines – Condensing, Noncondensing, Automatic Extraction turbine, etc. Source: http: //www. gi 4 xsf. freeserve. co. uk/imgen. htm A Squirrel Cage Induction Motor. Squirrels not included. No, it doesn't run on squirrels either. 5

Physical Principles Electrical Motors 6

Physical Principles: Electric Motors: • The rotor is wound with wire • Current flows through the wire to create an electromagnet • Motor rotation is achieved through magnetic forces. Source: http: //www. howstuffworks. com/motor 3. htm 7

Ways the Speed of Electric Motors are Varied • Wound-Rotor Induction Motor – Efficiency is sacrificed for controllability • Gearbox control – Gear shift to change rotation speed. – Discrete Operating Curve (Step-curves). – Cheaper Source: http: //www. anaconsystems. com/text/pr 11402 eagle. html Source: http: //www. bostongear. com/ 8

How the Wound-Rotor Induction Motor Works • Rotor is an electromagnetic (wound with wires) • Windings are connected to a slip ring which is connected to brushes • Brushes are connected to a resistance which may be varied – Reduces current through the rotor – Reduces magnetic strength of the rotor – Reduces the speed of the rotor 9

How Gearboxes Vary the Speed of Rotating Equipment • The shaft coupling connects to the gear box • The gear box varies the speed of rotation with gears of varying diameters • Smaller gears = larger rotation speed • Larger gears = smaller rotation speed 10

Physical Principles Steam Turbines 11

Physical Principles: Steam Turbines: • High Pressure Steam expands through a governor valve and a nozzle. • Experiences an increase in velocity and momentum • Pushes the impeller to drive the turbine. http: //home. pacifier. com/~rboggs/HP. GIF 12

Methods Varying of Steam Turbine Speed • Throttling valve • Multi-valve machines – Basic – With overload – With stage valve Salisbury, K. J. , Steam Turbines and Their Cycles. Krieger Pub. Co. , c 1950. 13

How Throttling Machines Work • Flow controlled by varying valve position • Increased steam flow rate results in greater impeller speed • Efficiency greatly reduced at low steam rate Display 14

How Multivalves Machines Work • Flow split into smaller diameter pipes and controlled by on/off valves • Valves operated in sequence by a camshaft • When one valve closes flow is reduced – Resistance across each valve remains constant • Total pressure drop from feed steam into the turbine remains constant • More efficient at low flow rates than throttling Display 15

Physical Principles Connecting the drives 16

Coupling – From Useless Spinning to Useful Shaft Work Many coupling types – Focus on Grid Couplings: • Horizontal Split Cover – Small Footprint – Easily Installed • Vertical Split Cover Source: http: //www. lovejoy-inc. com/catalog/gd. pdf – Ideal for High Speeds • Full Spacer Design – Extremely useful for pump applications. 17

Coupling Selection Procedure: Step 1: Determine: • • • Mover type(Motor/Turbine Type). Duty requirements. Equipment Characteristics (Shaft sizes) Misalignment – Possible? Likelihood of excessive vibrations. Ambient conditions 18

Coupling Selection Procedure: Step 2: Determine Coupling Material Types: 1. Metallic – – – Stiff rotation – Light inertial loads Non-tolerant to misalignment. High Temperature Applications. 2. Elastromeric – – – Soft rotation – High inertial loads Allows for misalignment Low Temperature Applications. 19

Packing– Preventing fluid leakage • Packing = Sealant on shaft bases to prevent leakage of process fluid and reduce misalignment, example: O-ring • Sealant material: – Must be relatively inert to reaction with environment and process fluid. – Low temperature applications: polymeric, rubbery material 20

Troubleshooting 21

Troubleshooting Workshop The efficiency of a turbine in the boiler house has decreased, and Dave has observed vibrations. He shuts down the unit for maintenance and observes water pooled in the bottom of the turbine. What may have happened? How can the problem be prevented? 22

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Common Problems with Steam Turbines • • Vibration Cycling of the governor Sticky valves Temperature bow Erosion Excessive rotation speed Electrostatic discharge Steam condensation 24

Common Problems with Electric Motors • • Vibrations Mechanical & Electrical Overload Short-circuits Excessive rotation speed Locked Rotor Under-Voltage Sparking 25

Trouble-shooting Causes: Vibrations Possible Causes: • Turbine misalignment • Unbalanced turbine • Rubbing parts • Lubrication problems • Steam condensation • Settling of the foundation • Cracked or worn parts 26

Troubleshooting: Causes of Excessive Rotation Speed • • • Mechanical Overload Steam flows which are too high Loose gears or loose bearings Decoupling Aged gears (worn gears) 27

Troubleshooting: Causes of Equipment Overload • Electrical – – Current surge Short circuit Rotor sticking Etc. • Mechanical – Excessive steam flow – Pressure increase in the steam – Etc. 28

Troubleshooting: Sparking • Charge accumulation • Poor contacting between the stator and the rotor • Short circuit • Etc. 29

Safety 30

Safety: Electric Motors Different area classifications require different motor enclosures – Open, drip-proof – Weather-protected, types I and II – Totally enclosed motor Packing & casing around the coupling 31

Safety: Steam Turbines • Slug of water may damage the turbine – Moisture separator prevents water from entering the turbine • Rotor imbalance • Need to prevent high inlet pressure • Temperature bow – Bends the shaft 32

Cost and Operating Range 33

Operability - Steam Turbines • Operating Window – Typically Operate below 538ºC (1000 ºF) – Keep above dew point of process fluid. 34

Operability – Electric Motors • Trade-off between Torque and Speed. – Typical motors have an optimal point of max. power between max torque and speed. Source: http: //www. airmotors. com/template. cfm? page=1 Power a Torque*RPM 35

Capital Cost • Principal Correlating Factor: – Drive Power (bhp). • Auxiliary Factors: – Electrical motors: • Rotation Speed (RPM), • Enclosure Type/Design – Steam Turbines: • Pressure (psig) • Superheat (ºF) “So, how much would the squirrel cage induction motor cost, if we wanted squirrels? ” 36

Operating Cost: Factors Affecting the Operating Cost: • Electric Motors: • • Price of Electricity Age of the Motor (efficiency) Coupling alignment Bearing wear • Steam Turbines: • • Cost of Steam Blade degradation Coupling alignment Bearing wear 37

When to choose what? • Requirement: small torque and low flows. – Electric motors easily fitted into process. • Requirement: large torque and high flows – Steam turbines prove to be more efficient. • Excessive amounts of high pressure steam in process – Steam Turbines to minimize cost. • If sufficient budget and steam – build both and alternate to minimize cost. 38

Considerations in Drive Selection Steam Turbine • Pressure and Temperature of steam available • Desired pressure and temperature exiting the turbine • Steam cost, and turbine efficiency • Flexibility in turbine speed • Level of control required 39

Considerations in Drive Selection Electric Motor • Cost of electricity • Required Power • Efficiency and applications (pump, fan, etc. ) • Time in service • Required flexibility of speed • Variable Speed is 4 times more expensive than single speed (at 3000 hp) • Maintenance 40

References • • • Perry, H. Perry’s Chemical’s Handbook, 7 th Edition, Mc. Graw-Hill, New York, NY. c 1984. Salisbury, K. J. , Steam turbines and their cycles, Krieger Pub. Co. , 1974, c 1950. http: //www. lovejoy-inc. com/catalog/m. pdf http: //www. vem-uk. com/1024/frameload. htm? frame 2=/1024/products. html http: //www. bostongear. com/ Microchip Web. Site, http: //www. microchip. com/1010/index. htm http: //www. microchip. com/1010/suppdoc/design/mtrcntrl/menufaq/mtrtypes/ Premium-Efficiency Motors Initiative website, http: //www. cee 1. org/ind/motrs-main. php 3 Energy Advisor website, http: //www. ladwp. com/energyadvisor/PA_35 fig. html Drive system Inc. website, http: //www. drivesys. com/asdis. html 41

Multivalve Machine F 1/3 From Boiler F 1/3 P 2 P 1 F 1/3 F 1=F 11+F 12+F 13 1/2 1/2 F 1=v 1(DP/r) + v 2(DP/r) + v 3(DP/r) Multivalve Machines 42

Throttling Machine From Boiler P 1 P 2 F 1=v(DP/r) 1/2 Throttling Machine 43

Troubleshooting Explanation • Steam condensing within the turbine. – A temperature drop in the steam • Poor insulation • Reduction in boiler efficiency • Etc. – An excessive pressure drop across the nozzle • A blockage in the nozzle • Decrease in inlet steam pressure • Etc. 44

Troubleshooting Solution • Monitor the steam pressure and temperature from the boiler – Increase boiler load if either is too low • Check and fix the insulation where applicable • Monitor the pressure drop into the turbine – Clean nozzles and other parts if necessary 45