SPECIAL-TASK PIPE FITTINGS PART 2: STEAM TRAPS

You can go your own wayGo your own way

("Go Your Own Way," by Lindsay Buckingham of Fleetwood Mac 2.0, 1976)

Steam Traps are Really Special-Task Valves

Another important Special-Task Pipe Fitting is the Steam Trap. The job of the Steam Trap is to separate the liquid form of steam from the vapor form of steam.

Your Mentor thinks Steam Traps have a confusing name.

Steam Traps should be called "Condensate Traps" because their job is to remove the liquid condensate that condenses from steam that has been used for heat transfer.

Secondly, the crucial hardware component within the Steam Trap is a discharge hole that is called an "orifice." The size of this orifice determines how much steam can be serviced by the trap.

Turn your attention to the nearby spectacular TLV gif that demonstrates how steam, (steam) condensate, and air flow through an Inverted Bucket Steam Trap.

Note that the repeated and intermittent stop-and-go flow of condensate exiting the Steam Trap is controlled by the motion of a flapper-like Valve.

"On-Off flow through an orifice" is a phrase more commonly associated with a Special-Task Valve rather than a Special Task Pipe Fitting.

Ok! Done with ranting! Back to the focused subject matter.

The Condensate Return Line in this graphic collects Condensate from two Drip Traps, Process #1 Steam Trap, and Process #2 Steam Trap. The Condensate collected from these four sources flows into a Vented Receiver and then flows to the suction of a Condensate Return Pump, thence to a Boiler Feed drum.

Steam Traps are a crucially important component of the facility's Condensate Utility.

The Condensate Utility of a Processing Plant/Facility collects condensate (aka "condensed steam") and returns it to the Package Boiler.

The job of a Steam Trap is to control the removal of Condensate (aka "condensed Steam") from the Steam that continues to flow through the Steam Header. Removing the Condensate maintains the internal energy of the flowing Steam.

The effluent stream from a Steam Trap contains Condensate and air. The air is vented, and the condensate is returned to the Boiler where it can be changed back into Steam.

The Function of a Steam Trap
(Greatly Clarified by TLV's Steam-Jacketed Vessel Gif)

Steam Tracing keeps the fluid flowing through this flanged connector hot.

Brilliant PTOA Readers and Students have already learned how steam is generated in Package Boilers (PTOA Segments #23 through #26) and Waste Heat Boilers (PTOA Segments #42 and #43).

Brilliant PTOA Readers and Students have also already learned that steam is intentionally generated in a processing facility specifically for the purpose of transferring its internal energy into a process stream that needs to have its PV Temperature increased.

The Kettle-Type Reboiler works similarly to a Steam-Jacketed Vessel.

Some examples of using steam for heat transfer include wrapping steam tracing around pipes for the purpose of keeping the pipe's contents at a desired flowing PV Temperature(PTOA Segment #29).

The Kettle Type Reboilers featured in PTOA Segment #35 are also an example of using steam for heat transfer. The TLV Steam-Jacketed Vessel Gif spotlighted below operates similarly to a Kettle Type Reboiler.

The conundrum is that the action of transferring heat will purposefully remove latent heat from the steam. When the steam is close to its saturation temperature, steam will condense into "condensate."

"(Steam) Condensate" is hot water with boiler feed chemicals in it.

Condensate does not have sufficient internal energy to perform the work of heat transfer ... like, Duh! ...because it has already lost that internal energy by transferring its heat into another media.

The nearby animated graphic by TLV clearly illustrates:

How heat transferred within a Steam-Jacketed Vessel creates condensate and
Why this condensate must be immediately removed by a Steam Trap.

The pink Steam flows into a Steam-Jacket that surrounds a Vessel containing cool, green liquid.

As heat is transferred from the pink steam into the green liquid, the green liquid turns hot orange.

Simultaneously, some of the steam loses sufficient internal energy and condenses into droplets of blue condensate.

The blue condensate collects in the bottom of the jacket, displacing pink steam. Even though the blue condensate is a hot liquid, it no longer contains sufficient latent heat that is needed to keep the liquid inside the Vessel hot.

Steam discharged to a sewer is very inefficient and wasteful! The energy used to convert the water into steam is wasted when steam escapes to a sewer and totally condenses at atmospheric pressure.

The hand valve at the bottom of the vessel can be opened occasionally, releasing the blue condensate to the sewer, but this action creates another problem:

Note that the pink steam is also released to the sewer! Releasing steam to sewer is a waste of the energy that was used to generate steam in a Package Boiler.

How about replacing the hand valve with an automated, intermittent open/close valve (like the automated Blow Down Valve featured in PTOA Segment #257.

That remedy will only be partially successful because fluctuations in the Vessel load and variations in the steam header dynamics would still result in too much steam flow to the sewer utility system.

Furthermore, Fred ...

and this is an important point ...

Remember what happens after a plumber has shut off the water to repair a kitchen or bathroom sink?

Water Hammer is not only loud but also very harmful to pipes.

Remember the sputtering noise and violent pulsations that occur as pockets of air are flushed out of the pipes by the restored flow of water?

Steam, air and condensate each have substantially different reactions to changes in line pressure. These different relationships become obvious to the ears of anyone in the vicinty of the sewer into which the combined stream of air, condensate, and steam are discharged.

The resulting Water Hammer that is caused by releasing steam, condensate and non-compressible gases to sewer is not only ear-splitting but will eventually damage piping.

The Steam Trap installation results in a controlled removal of blue condensate and (yellow) air from the flow of pink steam.

Installing a Steam Trap improves the energy efficiency of the Condensate Utility as well as mitigates hardware damage due to Water Hammer.

To recap, the benefits of installing a Steam Trap are:

The internal heat energy of the of the steam that continues to flow through the steam distribution network is maintained because the much lower heat transfer properties of condensate are continuously removed. Voila! The Condensate Collection Utility makes both the steam generation and steam distribution systems more efficient.
The occurrence of Water Hammer is mitigated. The operational safety and sustained integrity regarding the discharge of condensate, steam, and air from the steam utility system are greatly improved.

MECHANICAL STEAM TRAPS

Specific Gravity is the Density of a substance divided by the Density of Water.

Mechanical Steam Traps take advantage of buoyancy principles and the difference in specific gravity between the different phases of water to efficiently and safely discharge condensate from a steam utility.

Buoyancy was featured in PTOA Segment #147. The importance of understanding the concept of Specific Gravity was featured in PTOA Segment #162.

The Inverted Bucket Steam Trap and the Ball Float (Steam) Trap are both Mechanical Steam Traps.

The flow of condensate effluent from either type of Mechanical Steam Trap depends upon the movement of a plug ... or float ... that rises or falls with the flow of condensate into the Steam Trap.

The Form of an Inverted Bucket Steam Trap
(Greatly Clarified by a TLV GIF of an Inverted-Bucket Trap)

"Inverted" means "upside-down."

The nearby TLV GIF demonstrates the operating mechanics and the components of an Inverted Bucket Steam Trap. The bucket in the Inverted Bucket Steam Trap does, indeed, appear to be upside down with a steam Vent Hole in its bottom ... and since the bucket is inverted ... the bucket's Vent Hole looks like it is at the top!

Note the Valve that is sometimes indicated open and sometimes indicated closed. The movement of the Inverted Bucket determines the status of the Valve.

To begin the cycle, note that the pink steam has been entrained with the flow of the blue condensate that enters the Inverted Bucket.

The vapor characteristics of the pink steam that gathers within the Inverted Bucket makes the bucket buoyant which causes it to rise upward.

The upward action of the Inverted Bucket eventually closes the Valve (note the red Closed Valve label), thus preventing any blue condensate effluent from leaving the trap.

Note the (yellow) Air that fills the space of the vacated effluent piping.

More concisely stated:

The Valve is closed when there is an insufficient amount of condensate contained within the Inverted Bucket.

The steam contained within the Inverted Bucket escapes through the Vent Hole in the bucket and eventually condenses.

When sufficient steam has condensed, the Inverted Bucket loses its buoyancy and floats downward.

The Inverted Bucket is attached to the Valve via a linkage arm. Hence, as the Inverted Bucket loses buoyancy, the Valve is pulled into the Open Valve position.

Once again, condensate flows out of the Inverted Bucket Steam Trap, displacing the air that has filled the effluent line.

As more entrained steam enters with the condensate, the cycle repeats.

Ball Float (Steam) Traps

TLV's great gif of a Ball Float Steam Trap.

The Ball Float (Steam) Trap is a different structure of a Mechanical Steam Trap which also works because of buoyancy and differences in specific gravity.

Note that the Inverted Bucket Trap discharges condensate intermittently.

The Ball Float (Steam) Trap shown in another nearby TLV Gif is designed to allow a continuous flow of condensate effluent.

OTHER TYPES OF STEAM TRAPS

Thermostatic Steam Traps rely on temperature changes to operate.

Thermodynamic Steam Traps use kinetic energy as an operating principle. These traps rely on changes in fluid velocity and phase changes between the steam and condensate.

SELECTION CRITERIA FOR STEAM TRAPS

As clunky and low-tech as they appear, Mechanical Steam Traps have a significant advantage over the Thermostatic and Thermodynamic designs.

Thermostatic and Thermodynamic Steam Traps only work in processes that are enclosed within structures, thus making it possible to manage the ambient environment and eliminate external factors like rain and wind.

Mechanical Steam Traps are not impacted by the weather and most process units in a big processing facility cannot be enclosed. For this reason, Mechanical Steam Traps are the most popular Steam Trap technology used in process industries.

Inverted Bucket Steam Traps just need to have sufficient condensate production to operate successfully. Without sufficient condensate production, the buoyancy of the entrained steam would keep the Valve more closed than open.

Ball Float Steam Traps are the best trap choice when the processing facility is not enclosed and Superheated Steam is used to transfer internal energy into a different process stream. Superheated Steam does not generate much condensate.

Superheated steam does not generate much condensate even after transferring internal energy to another process stream. For this reason, Inverted Bucket Steam Traps are not a good choice in superheated steam systems.

For superheated steam systems, the Ball Float Steam Trap is a better choice.

TAKE HOME MESSAGES: Many processing facilities use steam to transfer heat into process streams so that the PV Temperature of the process streams can be increased. Once the internal energy of the steam has been transferred and the steam has lost sufficient energy to condense, the condensate of steam will form. This condensate must be removed to allow the remaining steam to efficiently transfer heat.

The condensate of steam is composed of Boiler Feed Water and the chemicals that are added to BFW.

Stream Traps are THE crucial component of the Condensate Collection Utility found in every processing facility that uses steam for heat transfer.

Steam Traps remove the condensate that has been formed during the process of heat transfer. Removal of condensate helps maintain the internal energy of the steam that has yet to be used for heat transfer.

Steam Traps also mitigate Water Hammer, a phenomenon that occurs when a combined stream of air (a gas), condensate (a liquid), and steam (a vapor) are suddenly depressurized within a piping system. Water Hammer is both ear splitting and wearing on piping components.

Mechanical Steam Traps work because of the buoyancy and specific gravity differences between steam and condensate. The Inverted Bucket Steam Trap and the Ball Float (Steam) Trap are Mechanical Steam Traps.

The Inverted Bucket Steam Trap intermittently releases condensate (and air) to the sewer. The Inverted Bucket Steam Trap is closed when insufficient condensate is present in the trap. Since superheated steam does not generate much condensate, Inverted Bucket Steam Traps should not be used in Superheated Steam Utility Systems.

The Ball Float (Steam) Trap continuously releases condensate to sewer. Ball Float (Steam) Traps are a better trap to use in Superheated Steam Utility Systems.

Fancier technologies of Steam Traps only work well in controlled environments, aka enclosed buildings. Most processing facilities are not enclosed, but rather exposed to the weather. For this reason, PTOA Operators and Students do not need to know how they work in detail.

PTOA PV FLOWRATE FOCUS STUDY AREA
PIPING NETWORK HARDWARE

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