Topic 2 - PRIME MOVERS -New Update

TOPIC 2

2.1 PUMPS 2.2 STEAM TURBINES/ENGINE 2.3 GAS TURBINE

CHE 324 PROCESS PLANT OPERATIONS & MAINTENANCE

PUMP APPLICATIONS

Used to move / transfer liquids

Used in a variety of applications & process (e.g: refrigeration, automobiles, home heating systems, water well)

used in refineries/chemical plants to move liquid (similar to conveyor belt used in factories to move solid product)

No pump needed – using gravity flow to transfer liquids

CLASSIFICATION

Classified as dynamic & positive displacement

Both are designed to transfer liquid but the way the transfer is accomplished is different

Dynamic Pumps – accelerate liquids axially or centrifugally

Positive Displacement Pump – transfer liquid using a rotary or reciprocating motion


DYNAMIC

accelerate liquids axially (straight line) or centrifugally (circles)

Operates at high speed to generate large flow rates at low discharge pressure

Transfer of fluid affected by discharge pressure

Centrifugal – Spinning impeller inside a shell casing propel or push liquid outward to the discharge port

Axial – Similar spinning motion to propel liquid, but the liquid moves in a straight line

POSITIVE DISPLACEMENT

Transfer specific amount of liquid by using a rotary or reciprocating motion that displaces liquid on each rotation or stroke

Transfer specific amount of fluid no matter what the discharge pressure is

For rotary – deliver specific amount with each rotation of screw, gears, vanes or similar element

For reciprocating – move fluid by drawing them into a chamber on the intake stroke & pushing them out of the chamber with piston, diaphragm & plunger on the discharge stroke



DYNAMIC

CENTRIFUGAL

VERTICAL

HORIZONTAL

SINGLE STAGE

MULTISTAGE

AXIAL

(1) DYNAMIC PUMPS



ROTARY

SCREW EXTERNAL

GEAR

INTERNAL GEAR

SLIDING VANE

FLEXIBLE VANE

LOBE

RECIPROCATING

PISTON

PLUNGER

DIAPHRAGM

(2) POSITIVE DISPLACEMENT PUMPS


As liquid enters the suction eye, it encounters the spinning impeller and get propelled or pushed in a circular rotation that force it to exit from volute (discharge chute)

Centrifugal force and volute design convert velocity energy to pressure

As the liquid leaves the volute, it slows down, building pressure

Diffuser plates can be added to the impeller and volute area to slow it down

CENTRIFUGAL PUMP

Suction

eye

volute


Not self-priming

Respond poorly to viscous materials or variations in suction pressures

Cheaper & require less maintenance

Operate with a constant head pressure over wide capacity range

Easy to change the element (impeller vs piston) compare to others

Easy to change the driver

The adaptability of the selected driver – variable horsepower & fixed or variable speed

DISADVANTAGES ADVANTAGES

CENTRIFUGAL PUMP


IMPELLER DESIGN

Semi Open Impeller Vane horizontally attached to a plate for structural support

Open impeller Vane are connected only to the shaft Self cleaning but does not have structural support & less efficient at producing pressure

Closed Impeller Vane are sandwiched bet. 2 plates Strongest & most efficient design Use with clear liquid only Most common type in industry

Mixed Flow

Axial Flow


CENTRIFUGAL PUMP DESIGN Vertical or horizontal : refers to shaft (motor) position.

single stage or multiple stage : refers to the number of impellers.

single or multiple suction inlets : refers to number of inlets.

volute or diffuser

axial flow, radial flow or mixed flow

open, semi-open, or closed impeller design

Horizontal

Vertical

INTERNAL SLIP

DYNAMIC

Centrifugal can have 100% slip if the discharge valve is closed

Fluid move from suction inlet into the impeller, flow accelerate into a volute (widen within the pump)

When discharge valve closed & flow stop but circulation continues within the pump & sustained in the volute & discharge pipe up to the discharge valve

Fluid friction heat up the liq. & vaporized, it will expands & hot

Create tremendous pressure that will damage the pump


PD – designed to have minimal slip because displace exact fluid volumes with solid object (e.g. pistons & gears)

Condition when discharge valve is closed on a PD pump:

Very little slip occur within the pump body

Fluid pressure increase with every stroke

Fluid press is transferred equally to all isolated parts

Pump/discharge pipe can be damage if relief valve is not provided


Slip =% of fluid that leak / slips past the internal clearances of a pump over a given time /

difference bet. how much liq. a pump can move & how much it actually does move


HEAD (PRESSURE)

Suction head = pressure required to force/push liquid into a pump which must be sufficient to run the pump without cavitations (formation of gas pockets around the impellers)

E.g. = during operation, centrifugal pump will artificially create low pressure area in suction eye & can cause liquid to boil & cavitations if suction pressure not carefully controlled

Net positive suction head (NPSH) : the head (pressure) in feet (ft.) of liquid necessary to push the required amount of liquid into the impeller of a dynamic pump without causing cavitations. The same principle applied to discharge head

If the tank is closed, the vapor pressure of the liquid must be taken into consideration

Net Positive Suction Head made available the suction system for the pump is named as available NPSHa & calculated with the Energy Equation. When the pump lifts a fluid from an open tank at one level to an other, the energy or head at the surface of the tank is the same as the energy or head before the pump impeller

The NPSHr - Net Suction Head as required by the pump in order to prevent cavitation for safe & reliable operation of the pump & determined experimentally by the pump manufacturer & a part of the documentation of the pump

The available NPSHa of the system should always exceeded the required NPSHr of the pump to avoid vaporization and cavitation of the impellers eye

The available NPSHa should be higher than the required NPSHr to avoid that head loss in the suction pipe & in the pump casing, local velocity accelerations & pressure decreases, start boiling the fluid on the impeller surface CHE 324 PROCESS PLANT OPERATIONS & MAINTENANCE

NPSHa & NPSHr


Factor that affect

suction head pressure

Restriction in the suction

line

Viscosity

Temperature

Level of liquid in

the suction head

Flow rate through the line

HEAD (PRESSURE)


HEAD (PRESSURE)

Solutions to

insufficient NPSH

Smaller horsepower

Lower speed

Lower NPSH requirements

Larger diameter

suction line

Greater feed tank level /

pressure

Cooler feed


• Transfer fluid by pushing it axially/in a straight line (e.g. boat motor)

• Motor turns a set of blades, forcing water to accelerate along a straight line

• Normally located in an elbow on a piping run (vertically / horizontally) – drive shaft extends via the elbow &

into the process flow

– Propeller located end of the drive shaft & sized to fit the inside dia. of pipe

– Balding is engineered to pull fluid axially down the shaft

• Application : - in pipeline service & as primary transfer device on loop reactor

AXIAL PUMP


Specially designed to utilize the venturi effect

Screen (PVC) connect to PVC water pipe (allowed to extend a few ft above ground level)

Pressure in the water pocket causes the water level to pass via the screen & up the pipe

Water level will stop before reaching the top of the pipe & jet pump will lifting the water out of the pipe

Application : - used to lift water from well over 200 ft deep

JET PUMP


During operation, water is forced back down the void between the center drop pipe and outer casing

As water is pumped back into the well casing, the check valve close and pushed the water to flow through the small opening on the jet (venturi effect) along the suction line of the pump

As the pressure increases in the casing, velocity increases across the jet

A low-pressure zone is established inside the drop pipe as water quickly flows up toward the pump.

A back-pressure regulator holds pressure inside the pump until it reaches operating conditions.

When pressures reach operating conditions, water flows is divided as some water circulates down the casing and the excess flows to a storage tank

JET PUMP OPERATION


• Displace liquid with rotary-motion (gears, screws, vanes or lobes)

• The drive shaft turns the rotary elements inside a leaktight chamber that has a defined inlet and outlet

• Require close running clearances between the rotating elements & chamber wall

• most widely used in industry specifically to move the more viscous type of fluids: heavy hydrocarbons, syrup, paint and slurries

• has very little internal slip (can damage the pump if the discharge pump is blocked during operation)

Rotary Pump

POSITIVE DISPLACEMENT PUMPS

• Consist only 1 moving part (rotor)

• When the self-priming rotor turns (inside an elastomer-lined stator), cavities/voids are formed between the rotor & stator

• Voids progress axially from the suction casing to the discharge outlet

• The voids/cavities will fill with fluid during operation

• Advantages: high suction, extremely low shear, & smooth pulsation-free operations

• Used for heavy / viscous fluid service

Single-screw rotary pumps (progressive cavity pump)

SCREW PUMP

Elastomer-lined stator

Suction

casing

screw

Discharge outlet


SCREW PUMP

• Has 2 rotor (power rotor & idler rotor)

• Set of external timing gears and bearing (allow the rotor/screw to turn in unison without making contact with each other)

• Screw do not touch so pump can run empty without damaging the system

• Operation :

– As fluid enter the pump it is divided into 2 equal streams & directed to the 2 end of shaft

– Pumping action of the screw moves 2 stream in a straight line between the close space rotor until they combine at the discharge port

– The rotating rotor are balanced because the 2 streams have equal & simultaneous flow paths

• Advantages : high flow rate & pump any fluid regardless of abrasiveness, lubricity, or viscosity

Two-screw pump


SCREW PUMP

• Consists power rotor / driver rotor & two idler rotor

• Power screw meshes with idler screws during operation

• The 3 screw is touching each other

• Each screw rotate on a set of heavy bearings

• Operation: – The self-priming screw rotate, creating voids that transfer fluid in a continuous, pulsation-free

flow

Three-screw pump

• Have 2 gears (idler & power) that rotate parallel to each other, allow fluid to be pick up by the gears & transfer out of the pump

• Rotation of driver gear (mounted on top) turns the idler gear (follower gear), trapping fluid & displace it

• Operation : - Once started, air is forced out into the discharged line

and creates a low-level vacuum on the suction line which causes the water to enter the pump

- As the power gear rotates, fluid is swept around the housing and out of the discharge port

- An idler gear turn in opposite direction of power gear

GEAR PUMP Similar to screw pumps in that they can be used in viscous service Can be found in 2 common types: (1) External; (2) Internal

External gear pump

inlet

outlet

Power

gear

Idler

gear


GEAR PUMP

• Have 2 moving part (power gear driving internal idler gear)

• Operation :

- When the power gear rotates, liquid enters the pump via suction line

- Pump is self-priming, the voids between power gear’s teeth and off-center idler gear fill with liquid and separated by crescent-shaped spacer

- Liquid is pressed into spaces above and below the spacer

- As the gears rotate around the circular pump casing, the liquid discharged out of the pump

• Basic components: power gear / rotor, idler gear, idler pin, drive shaft, circular casing, crescent shape spacer, bearings, seals & relief valve

Internal gear pump

inlet

outlet

crescent-

shaped

spacer


• Consist of spring-loaded or non-spring loaded vanes attached to a rotor/impeller that rotates inside an oversized circular casing

• Operation : – As the offset impeller rotates by the inlet

port, liquid is swept into the vane slots

– A small crescent-shaped cavity is formed inside the pumping chamber

– As the liquid nears the discharge port, it is compressed as the clearances narrow & released at the discharge port

• Application : used in hydraulic systems, vacuum systems & low pressure oil systems (liquid that have good lubricating qualities

SLIDING VANE PUMP

inlet

outlet

sliding vane


LOBE PUMP

• Consist of two rotating lobe-shaped screw - mesh during operation

• A set of external timing gears & bearings allows the lobes turn in unison w/o making contact with each other (pump can run empty w/o damage the system)

• Operation : – As lobes turn, voids are created that compress liquids around the outside of

the pumping chamber

– Once fluid enters the pump – it is divided into 2 equal streams

– The lobes moves the liquid in the close space between the casing and the lobes then combine out at the discharge port

• Application : provide high flow rates at low pressure

inlet

outlet

lobes

• Engineered to transfer small volume of liquid at relatively high pressure

• Self-priming and operated at relatively low speed – back-and-forth motion and effects of inertia on internal components

• Deliver consistently high volumetric efficiencies

• Displace liquid using diaphragm, piston or plunger mechanism (pushes the fluid as it moves back & forth inside a cylinder or housing)

RECIPROCATING PUMPS

POSITIVE DISPLACEMENT PUMPS


DIAPHRAGM PUMPS Use flexible sheet to displace fluid

Has eccentric wheel attached to a connecting rod that attach to the center of diaphragm

Pumping chamber below the diaphragm connect to suction & discharge lines.

As the eccentric starts its rotation, the diaphragm connecting rod goes up & down – create a pumping action to displace fluid

The fluid enter through suction valve and leave through discharge valve depending on the pressure in the chamber

diaphragm

Check

valves


PISTON PUMPS Uses a piston – create a back-and-

forth motion to displace fluid

has suction stroke and a discharge stroke (based on piston moving direction)

During suction stroke, low-pressure vacuum develops in the cylinder, causing the discharge valve to close and the suction line to open, filling the cylinder

During the discharge stroke, the suction valve close, & the fluid is forced out the discharge valve

Advantage : pump continue to operate no matter how high the discharge head is

Piston

Inlet line

Outlet line

Check

valves


PLUNGER PUMPS Operate with a back-and-forth motion

and a device called a plunger to displace controlled amounts of liquid

primary difference with piston pumps is in the shape of the piston or plunger element and the way they seal

PISTON - has ring mounted on the piston (moving together) that form a seal

PLUNGER – plunger moves in/out of an O-ring or packing medium to form its stationary seal

Advantage – the pump seals can easily be replaced without major breakdown of the equipment

plunger


TROUBLESHOOTING OF PUMP


TROUBLESHOOTING OF PUMP


TURBINES

Classification : The principle of operation & Type of fluid that turn the turbine

STEAM TURBINE (Impulse movement) – rotor turns in response to the force (velocity) ofa gas

GAS TURBINE Use high pressure gases

HYDRAULIC TURBINE (Reaction movement) – rotor turns in response to the pressure of a liquid

WIND TURBINE (windmills) – use air pressure


STEAM TURBINES CLASSIFICATION

Condensing Turbine Exhaust steam flows to surface condensers and it operates at vacuum pressure

Noncondensing Turbine Exhaust steam is utilized in low-pressure steam applications

Reaction Turbine Steam is discharged from a nozzle mounted on the rotor. Movement is a reactive response to the release of steam from an internal source

Impulse Turbine A steam turbine with a blading design that cause rotation of the blades & shaft when high-velocity steam from external source push on it

Each of these designs can have one or more stages (impeller/turbine blade number)


STEAM TURBINES

Basic principle - convert steam energy (kinetic energy) into mechanical energy

– used to drive rotating equipment Application :- use to drive pumps,

compressors, ocean vessels & electric power generation

Operation:-

As high-pressure steam enter a turbine, it passes a nozzle (restrict the flow to increase steam velocity) and hit the turbine blade - causing it to rotate

Steam passes through alternate sets of fixed and revolving blades, it constantly expands as it moves along

High

pressure

steam

Rotating shaft

TYPE OF STEAM TURBINES

2 types of steam turbines:

a) Impulse –

• Have a blading design that causes rotation of the blade and shaft assembly (rotor) – high velocity steam pushes on the blade.

• External source of steam.

b) Reactive –

• Occurs when steam escapes from a fixed nozzle attached to the rotor and propelling the rotor.

• Internal source of steam.

Both impulse and reactive steam turbines operate under similar principles.

Both impulse and reaction turbines can be either condensing or

noncondensing.

a) Condensing

• Exhaust steam into a heat

exchanger (surface condenser)

that cools and condenses the

steam.

• Condensate is sent to boiler –

converted back to steam.

• The most efficient type –extract

the maximum amount of energy

from the steam.

b) Non condensing (extraction type)

• Multistage turbines.

• Use high pressure steam, and

some portion of the steam are

extracted for other use.

• As the pressure steam passes

over the turbine wheel, the steam

expands.

• This expansion allow the turbine

to divert low pressure steam to

other units.

ASSIGNMENT 2:

Explain function of each basic components of a steam turbine:

a) Rotor

b) Fixed Parts

c) Fixed Blades

d) Casing

e) Steam chest

f) Nozzle

g) Bearings

h) Seals

i) Governing Mechanism

j) Lubrication system


STEAM TURBINES PROBLEMS

Vibration Excessive vibration could indicate failing bearings or internal problems 2 types of vibration – radial vibration & axial movement Radial vibration increases when turbine surges / after a cold start when the machinery passes through critical speed Surging affect axial movement in the rotor Monitoring & troubleshooting vibration problems must consider the axial movement

Hunting Steam turbine designed to be operated at a controlled speed Hunting occur when a turbine’s speed fluctuates while the controller searches for the correct operating speed (operated above / below normal operating set point) Cause by:

Mechanical linkage binding also can cause steam turbine to speed up & slow down Inlet steam pressure problems can also cause a steam turbine to hunt


STEAM TURBINES – STARTING UP PROCEDURE

Visually inspect turbine for damage. Reset overspeed trip. Check lube oil level for turbine governor. Ensure that rotating equipment covers are in place.

Drain condensate from turbine. Slowly back-feed low pressure steam into turbine exhaust.

Check lubrication system’s constant-level oiler. Check cooling system. Check seal system where the shaft enters the casing.

Slowly open the throttle valve & bring the turbine speed up 10% to 20% normal operating speed.

Bring turbine up to operating speed by opening the throttle valve, listening for line-out sound, and checking governor linkage.


GAS TURBINES

Basic principle – use high pressure combustion gases to turn a series of turbine wheel to provide rotational energy to turn an axle or a shaft

Consist of 3 parts: (1) axial compressor; (2) combustion chamber; (3) gas turbine

Application :- drives the electric generators, ships and racing cars, & a primary component of jet aircraft engines


Compression Combustion Gas turbine

Air Exhaust

gas

During operation, a fraction of the power generated by turbine is used to run the compressor

The compressed air mixes with fuel in the combustion chamber and ignited by spark plug

Higher pressure allows the mixture to burn better

The hot combustion gases rush into the gas turbine, causing the turbines wheels to turn

Hot exhaust gases are discharged from the body of the gas turbine

The air compressor and the gas turbine are mounted to the same axle, which is connected to the workload

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Topic 2 - PRIME MOVERS -New Update