The part you least expected
It commands …
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Got to expand
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("Expand," by The Damage Manual, 2000)

 

OF COURSE STEAM IS "THE WORKING FLUID" FOR STEAM TURBINES

The most brilliant PTOA Readers and Students ...

those who are reading the PTOA Segments in the intended sequential order ...

learned in  PTOA Segment #191 that The Working Fluid of a Steam Turbine is steam.

Like … Duh!

The steam is not internally generated within the Steam Turbine but rather produced in either a Package Boiler  ...

like the one in the nearby photo which was featured in PTOA Segment #24 ...

or perhaps generated in a Waste Heat Boiler as discussed in PTOA Segment #43.

In either case the steam is delivered by pipe header to the Steam Turbine.

The high pressure steam that is delivered to the Steam Turbine contains a significant amount of thermal energy … aka heat energy.

The nerdy way to say it is that the steam contains The Latent Heat of Vaporization … which is ...

that non-detectable thermal energy absorbed by the molecules of Boiler Feed Water (BFW) which causes the molecules to get so excited that they bump into each other and expand to the point that the water changes state into steam ...

all the while the thermometer just hangs and indicates 100 °C or 212 °F.

The long horizontal red line on the nearby graph indicates The Latent Heat of Vaporization. The internal thermal/heat energy of the steam-water mixture increases as shown on the X axis while the detected temperature of the water-steam mixture remains at 100 °C.

Note that the graph indicates that the sensed temperature on a thermometer will start to increase after all of the water in the steam-water mixture has changed phase into steam. The temperature of steam flowing into a Steam Turbine could be 200 °C to 400 °C.

Wow! That's A LOT of thermal energy!

If any of the above sounds fuzzy just go back and review PTOA Segment #25.

Because understanding exactly how boiling water turns into steam while absorbing the The Latent Heat of Vaporization ...

and how that same steam loses that heat energy as The Latent Heat of  Condensation when it condenses back into water ...

is crucially fundamental to understanding how both Boilers and Steam Turbines work!

 

Righteeo!

That  non-detectable thermal energy called the Latent Heat of Vaporization ...

which is part of the internal energy that the steam contains whilst being delivered from some type of Boiler to the Steam Turbine ...

will be extracted in a Condensing Steam Turbine.

PTOA Readers and Students will learn in the next PTOA Segment that not all Steam Turbines are Condensing Steam Turbines.

However, every Steam Turbine is designed to extract the thermal energy from steam by allowing the volume of the steam to rapidly expand and use the process of expansion to  generate rotational motive power.

Otherwise stated:

All Steam Turbines convert thermal energy into rotational motive power.

 

THE WORKING FLUIDS OF ENGINES AND STEAM TURBINES BOTH EXPAND

Is there an echo in here?

Did the PTOA not just feature a Prime Mover/Driver called an Engine that converted the expansion of a working fluid into rotational power?

In the recent PTOA Segment #192, PTOA Readers and Students learned that The Power Stroke of an Engine begins by igniting a hydrocarbon fuel which  thence causes the immediate expansion of evolving combustion products.

Via mechanical linkage, the Crankshaft converted the movement of the expansion into mechanical/motive power.

Ditto for the Steam Turbine!

The expansion of The Working Fluid steam that flows through a Steam Turbine is also converted into rotational power via a rotating Shaft that is coupled to the Shaft of a Load!

 

The expansion of The Working Fluid steam as it flows through the Steam Turbine creates the rotational power that spins a Load.

 

THE ISA SYMBOL FOR A STEAM TURBINE

The ISA symbol for a Steam Turbine is easy to decode once PTOA Readers and Students understand that the expansion of The Working Fluid steam is precisely what creates the mechanical/motive power.

The magnitude of the vertical ends of the ISA Symbol for a Steam Turbine  visually represent the volume of the steam.

The nearby ISA graphic shows an Air Compressor on the left. The air compressor is "the Load" which is coupled to the conical-shaped Steam Turbine Driver on the right.

The high PV Pressure Working Fluid steam delivered to the Steam Turbine enters the  ISA Steam Turbine Symbol on the short vertical end.

The lower-pressure steam that exits the Steam Turbine ISA symbol has much greater volume after being expanded. Ergo, the Steam Turbine ISA Symbol graphically represents the expanded steam volume with a much taller vertical line.

The slanted top and bottom sides of the symbol represent the expansion of the steam as it flows through one or more stages … aka Rotating Blades …  of the Steam Turbine.

Which brilliant PTOA Readers and Students noticed the ISA Symbol for the (Centrifugal) air compressor is  exactly opposite the Steam Turbine ISA Symbol?

The air that flows out of the air compressor has a much smaller volume that the air that entered the compressor … hence the air has been compressed!

 

STEAM TURBINE HARDWARE DEFINED

The fundamental hardware of a Steam Turbine includes the following:

The high pressure steam flows into an internal cavity of the Steam Turbine known as the Steam Chest.

In the nearby photo, an arrow within the bottom right quadrant of the picture points to the Steam Chest.

 

 

The Nozzle is a nozzle-shaped device that directs the flow of steam from the Steam Chest onto the first Rotating Blade.

Unfortunately none of the nearby graphics clearly label the Nozzle.

 

 

The Rotor  includes the rotating Shaft and all the Rotating Blades.

Each Rotating Blade is an expansion stage that draws more and more thermal energy out of the steam while the steam is expanded.

 

 

 

Stationary Blades DO NOT ROTATE and are crucially positioned IN BETWEEN the Rotating Blades so that they can target the flow of steam onto the sandwiched Rotating Blades.

The nearby graphic shows the Rotor of a Steam Turbine being carefully lowered into the lower half of the Stationary Blades during assembly.

Some graphics … like the one below .. will label Stationary Blades as "Fixed Blades."

Both terms mean "not-moving."

 

THE FUNCTION OF STEAM TURBINE HARDWARE

Time to learn how the Steam Turbine hardware described above converts the thermal energy of steam into rotational motive power!

Function of The Nozzle

To recap ...

The high pressure steam generated in a Package Boiler or Waste Heat Boiler is delivered via a steam header and flows into the Steam Chest of the Steam Turbine and thence to the Nozzle.

 

 

The  Nozzle increases the velocity of the steam and is precisely positioned to make the flow of steam impact and turn the first Rotating  Blade.

The Nozzle in a Steam Turbine is a severe restriction to flow and thus causes the PV Pressure of the steam to swap into increased steam velocity.

Brilliant PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order could have predicted that the velocity of the steam would increase when the steam flow encountered the small-diameter Nozzle because they learned about the PV Pressure ↔Fluid Velocity Swap back in PTOA  Segment #159.

The second job of the Nozzle is to direct the flow of the high-velocity steam onto a specific location on the first Rotating Blade … which causes the blade to rotate.

A great example that illustrates the function of the Steam Turbine Nozzle would be the puckering up of a child's lips to purposely direct a stream of expelled air to spin the blades of a pinwheel.

Both the pinwheel toy and the Steam Turbine are classified as Impulse Turbines.

The descriptor just means that the impact of The Working Fluid …

 

the expelled air from the child's lungs or the high velocity steam that flows from the Steam Turbine Nozzle …

strikes the Rotating Blade of the pinwheel or Steam Turbine, hence causing the blade to turn.

Any Steam Turbine PTOA Readers and Students operate in a processing plant will be an Impulse Turbine design.

The definition and clarification of a  Reaction Turbine will be covered in a future PTOA Segment.

 

 

 

Function of the Rotor and Rotating Blades

Recall that the Rotor of a Steam Turbine includes the rotating Shaft and one or more Rotating  Blades that rotate with the Shaft.

In PTOA Segment #175, PTOA Readers and Students learned that a Single Stage Centrifugal Pump has one Impeller ...

and a Multistage Centrifugal Pump has more than one Impeller as shown in the below graphic.

 

Likewise …

A small Steam Turbine will have a single Rotating Blade and a large Multistage Steam Turbine will have multiple Rotating Blades.

The more Rotating Blades, the more thermal energy can be extracted from the steam …hence the more rotational power can be produced!

That's right!

Each additional Rotating Blade (aka "Stage") in a Steam Turbine will extract and convert incrementally more of the steam's thermal energy into incrementally more rotational power.

A quick glance at the above Steam Turbine photo reveals that each successive Rotating Blade of a Multi-Stage Steam Turbine will have a greater diameter. This design more efficiently converts the thermal energy of steam into rotational power.

Incidentally, the gradual increase in blade diameter  helps explain the shape of the ISA Steam Turbine Symbol.

To recap ...

The number of Rotating Blades (aka Stages)  enclosed within the Steam Turbine determines the rotational speed and horsepower output of the Steam Turbine.

For comparison …

A small Single Stage Steam Turbine like the one in the nearby graphic will have a rotational speed of 1000 rpm and produce a horsepower of 0.7 hp to 250 hp.

 

 

A large Multi-Stage Steam Turbine  could achieve a rotational speed in the range of 30,000 rpm and produce a horsepower of 500-10,000 hp.

What happens to the PV Pressure of the steam as it flows through the  Steam Turbine?

PTOA Readers and Students learned in PTOA Segment #175 that the PV Pressure increases when a liquid flows through the successive stages of a Centrifugal Pump.

 

The opposite happens in the Steam Turbine! The PV Pressure of the high pressure steam delivered to the Steam Turbine decreases as it flows through the Steam Turbine.

Some of the pressure is converted into velocity and some is lost because the volume of the steam is increased.

 

The steam exits the Steam Turbine with less PV Pressure, less thermal energy in the form of BTUs, and at a much greater volume (like maybe even 1000 times more volume than it had in the Steam Chest).

 

Hence the thermal energy of the high PV Pressure steam that was delivered to the Steam Turbine has been extracted and converted into rotational motive power in the form of a spinning Rotor that is coupled to shaft of a Load.

 

The Load might be an electricity generator, a pump, or a compressor.

 

The Function of the Stationary Blades

The PTOA Department of Redundancy Department wishes to clarify that the  Stationary Blades of the Steam Turbine are not part of the Rotor and do not spin around and around with the Shaft and the Rotating Blades.

Typically the Stationary Blades are assembled in halves (called "Diaphragms")  that fit into grooves that have been cut into the casing of the Steam Turbine.

Stationary Blade Diaphragms have Nozzles which direct the steam that has been expanded in the prior Rotating Blade onto the next Rotating Blade.

Once again, the nearby photo shows a Rotor with its Rotating Blades being carefully lowered into the bottom half Diaphragm of Stationary Blades.

As shown in the picture, the Rotating Blades of the Rotor are designed to fit snugly in between the Stationary Blades. Who is surprised to learn that extremely precise manufacturing technology is required to build and repair Steam Turbines?

Uh-oh!

Fred is a little confused about how the Rotating and Stationary Blades of a Steam Turbine work together to expand the steam and thus rotate the Rotor that is coupled to and thus spinning a Load.

So that means it is time to ...

You Tube and Chill!

 

 

THANK YOU SULZER TURBO SERVICES FOR THE STEAM TURBINE YOU TUBE 

Thank you to Sulzer Turbo Services for the Sulzer Steam Turbine You Tube which shows via animation how a Steam Turbine works.  PTOA Readers and Students just need to watch the first minute.

The Sulzer Turbo Services Steam Turbine You Tube can be accessed  by clicking HERE  

or directly below.

Note how the feedrate of red steam from a Boiler changes color to yellow as the steam is expanded and thus loses thermal energy while flowing through successive Rotating and Stationary Turbine Blades.

The Steam Turbine featured in the You Tube extracts all of the latent thermal energy from the steam. The steam condenses into a green liquid condensate. 

Condensing and Non-Condensing Steam Turbine designs are featured in the upcoming PTOA Segment #194 so do not stress about that now.

 

 

The PTOA focus on Steam Turbine will continue and feature:

• Why a Steam Turbine would be chosen as a Prime Mover/Driver instead of an Engine or a Motor.
• Common and Unique Steam Turbine hardware.
• Condensing and Non-Condensing Steam Turbine designs.
• Steam Turbine operations.

 

 

TAKE HOME MESSAGES: Steam Turbines are designed to extract thermal energy from high pressure steam by allowing the steam to expand in volume. The expansion of steam greatly increases steam volume while simultaneously decreasing the internal energy of the steam and the pressure of the steam. 

The controlled expansion of the steam (aka extraction of steam thermal energy) is accomplished with a Rotor (aka Rotating Blades and Shaft) and Stationary Blades. Since the Shaft of the Rotor is coupled to the shaft of a Load, the controlled expansion of steam results in dependable rotational power that spins the Load.

An "Impulse Design Steam Turbine" means that a Nozzle is used to increase the velocity of steam fed to the Turbine and thence direct the flow of high velocity steam onto a Rotating Blade which causes the blade to spin.

Steam Turbines and Engines are alike in that they are both Prime Movers/Drivers that expand a Working Fluid to produce rotational power.

Steam Turbine Hardware includes:

• Steam Chest
• Nozzle(s)
• Rotor = Shaft and Rotating Blade(s)
• Stationary aka Fixed Blades, usually grouped into sections called Diaphragms.

 

Each Rotating Blade on a Rotor is a "Stage of Expansion." The more Rotating Blades (aka Stages) the more thermal energy is extracted from the steam, the more the volume of the steam expands, and the more rotating power is generated.

Each successive Rotating Blade of a Multi-Stage Steam Turbine has a slightly greater diameter. The increasing diameter of the Rotating Blades and the increasing volume of the steam are hinted at in the Steam Turbine ISA symbol.

Thank you to Sulzer Steam Turbines for the You Tube that shows how Steam Turbines work.

 

©2018 PTOA Segment 0193

PTOA Process Variable Pressure Focus Study Area
PTOA PV Pressure Rotating Equipment Focus Study
PTOA PV Pressure Prime Mover/Driver of Rotating Equipment Extension Study

 

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