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Steam turbines & Electric motors

“How can we rev you up?”

http://www.revak.com/powergenpics.htm

A Group F’s Production

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Presentation Outline

1. Typical Applications2. Types of Drives3. Physical Principles4. Troubleshooting5. Safety6. Operability7. Capital & Operating

Costs

We’re going to make Motors and Turbines jump through hoops for you!

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So where do drives live in Chemical

Engineering Land?They live next to…

– Pumps– Compressors– Fans– Conveyor belts– Crushers– Mills

And many more places…

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Types of Drives

Electric Motor Steam Turbine& Many More!!!

Source: http://fsvpix.homestead.com/FSVtodaypix.html

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Drives sub-typesElectric Motors• Constant Speed:

– A/C Squirrel-Cage Induction, Synchronous A/C, etc.

• Variable Speed– Two-Winding, Single-

Winding Consequent-Pole, etc.

Steam Turbines– Condensing, Non-

condensing, Automatic Extraction turbine, etc.

A Squirrel Cage Induction Motor. Squirrels not

included. No, it doesn't run on squirrels either.

Source: http://www.gi4xsf.freeserve.co.uk/imgen/imgen.htm

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Physical Principles

Electrical Motors

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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/motor3.htm

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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/pr11402eagle.html

Source: http://www.bostongear.com/

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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

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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

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Physical Principles

Steam Turbines

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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

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Methods Varying of Steam Turbine Speed

• Throttling valve• Multi-valve

machines– Basic– With overload– With stage

valveSalisbury, K.J., Steam Turbines and Their Cycles.

Krieger Pub. Co., c 1950.

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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

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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

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Physical Principles

Connecting the drives

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Coupling – From Useless Spinning to Useful Shaft

WorkMany coupling types – Focus on Grid Couplings:

• Horizontal Split Cover– Small Footprint– Easily Installed

• Vertical Split Cover– Ideal for High Speeds

• Full Spacer Design– Extremely useful for

pump applications.

Source: http://www.lovejoy-inc.com/catalog/gd.pdf

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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

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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.

Coupling Selection Procedure:

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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

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Troubleshooting

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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?

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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

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Common Problems with Electric Motors

• Vibrations• Mechanical & Electrical Overload• Short-circuits• Excessive rotation speed• Locked Rotor• Under-Voltage• Sparking

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Trouble-shooting Causes:

VibrationsPossible Causes:• Turbine misalignment• Unbalanced turbine• Rubbing parts• Lubrication problems• Steam condensation• Settling of the foundation• Cracked or worn parts

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Troubleshooting: Causes of

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

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Troubleshooting: Causes of Equipment

Overload• Electrical

– Current surge– Short circuit– Rotor sticking– Etc.

• Mechanical– Excessive steam flow– Pressure increase in the steam– Etc.

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Troubleshooting: Sparking

• Charge accumulation• Poor contacting between the stator

and the rotor• Short circuit• Etc.

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Safety

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Safety: Electric Motors

Different area classifications require different motor enclosures– Open, drip-proof– Weather-protected, types I and II– Totally enclosed motorPacking & casing around the coupling

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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

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Cost and Operating Range

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Operability - Steam Turbines

• Operating Window– Typically

Operate below 538ºC (1000 ºF)

– Keep above dew point of process fluid.

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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 Torque*RPM

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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?”

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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

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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.

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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

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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

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References• Perry, H. Perry’s Chemical’s Handbook, 7th Edition, McGraw-Hill, New York,

NY. c1984. • Salisbury, K. J., Steam turbines and their cycles, Krieger Pub. Co.,

1974, c1950.• http://www.lovejoy-inc.com/catalog/m.pdf• http://www.vem-uk.com/1024/frameload.htm?frame2=/1024/

products.html• http://www.bostongear.com/•  Microchip WebSite, http://www.microchip.com/1010/index.htm• http://www.microchip.com/1010/suppdoc/design/mtrcntrl/menufaq/

mtrtypes/• Premium-Efficiency Motors Initiative website, • http://www.cee1.org/ind/motrs/motrs-main.php3• Energy Advisor website,

http://www.ladwp.com/energyadvisor/PA_35fig.html•  Drive system Inc.website, http://www.drivesys.com/asdis.html

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Multivalve Machine

P1

P2F1

F1/3

F1/3

F1/3

F1=F11+F12+F13

F1=v1(Pv2(Pv3(P

From Boiler

Multivalve Machines

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Throttling Machine

From Boiler

P1 F1

P2

F1=v(P/)1/2

Throttling Machine

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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.

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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