steam traps manual

8/6/2019 Steam Traps Manual

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STEAM AND STEAM TRAPS

PURGADORES DE CONDENSADO, S.L.


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PURGADORES DE CONDENSADO, S.L. STEAM & STEAM TRAPS

INDEX

1. STEAM: BASIC CONCEPTS Page

1.1 Definitions 1

1.2 Flash steam 3

1.3 Differences between live steam and flash steam 6

1.4 Back pressure problems 7

2. INTELLIGENT STEAM TRAPS AND VALVES

2.1 The steam traps mission 11

2.2 The ideal steam trap 12

2.3 Intelligent steam traps: BiTherm SmartWatch 122.4 Intelligent valves: SmartWatch 16

3. MECHANICAL STEAM TRAPS

3.1 Introduction 19

3.2 Classification of steam traps 19

3.3 Cyclic and continuous trap systems 20

3.4 Orifice plate steam trap 21

3.5 Float steam trap 22

3.6 Inverted bucket steam trap 24

3.7 Thermodynamic disc steam trap 25

3.8 Impulse steam trap 27

3.9 Thermostatic steam trap 28


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CHAPTER 1

STEAM: BASIC CONCEPTS

1.1. DEFINITIONS

Water steam is a thermal fluid widely used in industry due to two main characteristics:

- High energetic content- Easy to transport

The union of this two properties provides with a very simple method for the supply of greatamounts of energy to points located very far from the installation, taking advantage of the steamsown internal pressure to pump the fluid.

The water can be in three phases: solid, liquid and gas or steam. The transition from one state to

the other is known as change of stateand implies an energetic interchange in the shape of heat.When the transition is from solid to steam the process uses energy and when the transition is inthe other way the process gives energy. The process schema is in Fig. 1.1.

Fig. 1.2 represents the process of water evaporation. In the graphic, three zones are clearlydifferentiated:

- Zone 1: Water in liquid phase- Zone 2: Coexistence of water and steam- Zone 3: Superheated steam

Figure 1.1

water + Sensible heat = Boiling water

Boiling water + Latent heat = Saturatred Steam

Evaporation

100 Kca/Kg

640 Kca/Kg

PHASE CHANGES IN WATER

The supplied energy in zone 1 is accumulated in the water in liquid phase, increasing itstemperature till reaching the evaporation point. The amount of heat needed to elevate itstemperature from 0C until boiling point is called sensible heat.

Once reached the boiling point, the evaporati


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on begins, zone 2, which continues until the total evaporation of the water. During this process, thetemperature remains constant while there is water and vapour in coexistence. The producedenergy is used for the vapours formation. The amount of heat needed to evaporate totally theliquid water at the boiling temperature or saturation temperaturereceives the name of latent heat.The generated steam in this process is called saturated steam.

Once the evaporation process is over we entry in zone 3, where any energy contribution producesa new increase in the steams temperature, thus obtaining reheated or superheated steam.

The energetic content of steam is:

Total Heat = Sensible Heat + Latent Heat + Overheating

The graphic in Fig. 1.2 is different for each vapour pressure or operation pressure; representingthis graphic for different pressure values in a tridimensional coordinate system, we would obtain a

surface that would relate the three magnitudes. Thus, the sensible heat, the latent heat and thesaturation temperature depend on the vapours pressure.

Fig. 1.2

VARIATION OF TEMPERATURE AND ENERGY IN THE WATERS EVAPORATION

Fig. 1.3 shows the variation of the vapour saturation temperature with the pressure. This variationcan be also consulted in the table of vapour saturation at the end of this chapter.

During the condensation, evaporation inverted process, the water vapour passes to liquid state,condensate, giving its latent heat, energy which is used in heat exchange processes. In certain

applications even part of the condensate sensible heat is used, the condensate reaches a certainsubcoolingaccording the saturation temperature.


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The heat unit is the calorie (Cal), it is the heat amount that should be supplied to a gram of water toelevate its temperature from 14.5C to 15.5C. The kilocalorie(Kcal) equals to 1000 Cal.

The specific heatof a body is the quantity of heat needed to elevate the temperature of one massunit of the body one degree Celsius. It is expressed in Kcal/KgC. For water the specific heat is 1Kcal/KgC.

The specific volumeof a body is the volume occupied by a mass unit of the body. It is expressed inm3/Kg. The specific volume of steam is very big compared to the one of the water, for this reason ahuge cloud of flash steamis observed in the steam trap discharge, even in correct functioning. Thisphysical process of revaporationof the condensate is produced always as a consequence of theexpansion or decrease of the condensate pressure (see 1.2) and should be differentiated from livesteam or steam generated by heat supply.

Fig. 1.3

Pressure (bar)

Temperature (C)

2 6 14104 128

50

2018

150

100120

16

170

250

200

0

Water

Saturated steam

WATER STEAM SATURATION CURVE

1.2 FLASH STEAM

The expansion process of the condensate is easily analysed in Fig. 1.4. The graphic shows thetotal energetic content of the flash steam (enthalpy) depending on the steam pressure (the table ofsaturated steam gives the real values in this graphic).

As it is observed, the sensible heat increases when the pressure grows and, on the contrary, thelatent heat decreases when the pressure grows.

Therefore, point 1 represents the energetic content of the saturated steam at the entrance of aheat exchanger. When all the latent heat is transferred we arrive to point 2, where all steam hascondensated; note that during state change (line 1-2) the steams temperature has remainedconstant; this is the theoretical state in which the condensate arrives to the steam trap to be


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eliminated (in practice the condensate is cooled between 10C and 15C before reaching thesteam trap).

Fig. 1.4

ENTHALPY PRESSURE DIAGRAMM OF STEAM

At the exit of the steam trap the pressure decreases suddenly until Pc, line 2-3, remaining thecondensate energetic content. The decrease of pressure from Pv to Pc is known as differentialpressure (Fug. 1.5). However, in point 3, the condensate energetic state is superior than atpressure Pc, point 4. The line 3-4 represents the excess of energy of the discharged condensateby the steam trap, due to the expansion of the condensate. This excess of energy is absorved as

latent heat by the condensate, which suffers a partial revaporation, so that the energeticequilibrium between the steam trap entrance and exit remains.

Summarising, in the condensate discharge some quantity of flash steam necessarily appears,which reestablishes the energetic balance of the fluid before and after the steam trap.

The quantity of flash steam formed per mass unit of evacuated condensate is precisely thequotient between the enthalpy correspondent to line 3-4 and the enthalpy of line 5-4, that is, thequotient between the difference of condensate enthalpies before and after the steam trap (h3-h4)and the latent heat of evaporation at the pressure of the steam traps exit (h5-h4):

Flash steam per mass unit = (h3-h4) / (h5-h4)

LATENT HEAT

SENSIBLE HEAT

STEAM TRAP

PRESSURE

ENTHALPY


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Fig. 1.5

DIFFERENTIAL PRESSURE

For a quick calculation of the flash steam amount per mass unit produced in the expansion of thecondensadte the graphic of Fig. 1.6 can be used in the following way:

Introduce the pressure value of the condensate before the expansion (steam trap operationpressure) in the horizontal axis; from that point draw a vertical line up until it cuts the curve of thecondensate pressure after the expansion (pressure at the steam traps exit); from that point draw ahorizontal line till it cuts the vertical axis, where you can read the percentage in weight of flashsteam produced.

The example of Fig. 1.7 shows the process of flash steam formation.

Special attention should be made to the increase of volume of the revaporated at the exit of thesteam trap, which can induct to error in the diagnostic of its operation.

Note that though the amount of condensate in weight is much bigger than the amount of producedflash steam, when comparing the correspondent volumes is the other way around (276 m3 /h offlash steam compared to 0.840 m3/h of condensate), this is due to the high specific volume of thesteam compared to the one of the condensate.

1.3 DIFFERENCE BETWEEN LIVE STEAM AND FLASH STEAM

There is no difference between live saturated steam and flash steam. The only difference lies onlyin there generation process but once generated both have the same physical and chemicalproperties. This makes the visual detection of live steam leaks in the steam trap discharge moredifficult.

With some experience is possible to differentiate only by view the presence of live steam and flashsteam in the steam trap discharge, but a reliable result can only be obtained with the help ofadequate measuring equipment or leak detectors by ultrasound.

DIFF. PRESS. = P1 P2

STEAM TRAP

BACKPRESSUREOPERATION PRESSURE


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Fig. 1.6

P2=1

bar

1.5bar

2bar

2.5

bar

3bar

3.5

bar

4bar

5bar

6bar

8bar 1

5bar

10

bar

20

bar

30

bar

40b

ar

50

bar

65

bar

1 1.5 2 3 4 5 10 15 20 30 40 60 100

Condensate pressure at saturation temperature P1 (bar)

0

2.5

5

7.5

10

12.5

15

17.5

20

22.5

25

27.5

30

32.5

35

Atmospheric discha rge

Example: Discharging 1 Kg of condensateat saturation temp erature from P1=15 bar

to p2= 5 bar a flowrate of10 % will begenerated (0.1 Kg o f flash steam)

Flashsteam(

%w

eight)

FLASH STEAM

The flash stem goes always with condensate, presenting a more humid aspect than the live steam.Flash steam is lightly opaque and tends to float in the ambient, while saturated live steam iscolourless and comes out with high speed and noise right at the exit of the steam trap. Fig. 1.8 canhelp to recognise the type of discharge in the steam traps.

The ambient temperature and the relative humidity of the air affect very much the aspect of thesteam trap discharge. In cold and humid days the flash steam is much more visible than in hot andshiny days.

Tracing is an outstanding exception in the purge of condensates, because the discharge

temperature oscilates between 80C and 100C. This case will be treated in more detail later dueto its economical importance in the chemical industry.

1.4 BACKPRESURE PROBLEMS

Backpressure is one of the most important problems in the condensate return collectors in all bigsteam installations. This problem is always present in oil refineries and big petrochemicalindustries and is an important source of economical losses because it affects not only theinstallations operation but also its energetic efficiency, maintenance, etc.


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Fig. 1.7

FLASH STEAM IN THE STEAM TRAP DISCHARGE

Its origin is very diverse:

- Live steam leakage through steam traps- Flash steam in steam trap discharge- Inadequate selection of steam traps- Incorrect dimensioning of steam traps

- Incorrect temperature of discharge in steam traps- Steam leakage in steam trap by-pass valves- Inefficient steam trap control- Scarce steam trap maintenance- Incorrect dimensioning of condensate return collectors- Successive amplifications of the installation without modifying collectors

Its effects are very noxious:

- Decrease of the installations thermal efficiency- They contribute to the appearance of waterhammering- Decrease of evacuation capacity of steam traps

- Increase of steam losses in thermodynamic steam traps- Difficulty in recuperating the residual energy of condensates

INLET PRESSURE 10 BAR

STEAM FLOW 1000 KG/H

CONDENSATE FLOW 0.84 M3/H

FLASH STEAM 276 M3/H

ATMOSPH. PRESS.

16% FLASH STEAM

CONDENSATE FLOW 1000 KG/H

STEAM TRAP

HEAT EXCHANGER


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- Increase of the installation maintenance costs

Fig. 1.8

STEAM TRAP DISCHARGE

The solutions are various depending on the origin of the problem. Nevertheless, one of the mostefficient measures that can be adopted to resolve the problem is to control the revaporation in thesteam trap discharge.

Thus, the flash steam produced in the steam trap discharge originates a strong local backpressuredue to its huge specific volume, which affects nearby steam traps and the rest of the installation indifferent ways:

- Generally the evacuation capacity of the seam trap is reduced

- In thermodynamic steam traps the discharges are prolonged and the cycle cadenceincreases, therefore, live steam losses in the steam trap increase.

- The recuperation of the condensate residual energy is more difficult

- The problem expands throughout the installation fast and progressively.

Therefore, the steam trap is a lot of times cause of the problem and the problem itself affects thesteam trap very unfavourably, creating a circle of very difficult exit.

The energy saving techniques used actually and the use of intelligent steam traps (see chapter 2)capable of selfdetecting internal leaks of live steam or any variation of the operation conditions ofthe steam trap, resolve this problem and increases the thermal efficiency of the installation at thesame time.

LOW CAPACITY

SMALL LIVE STEAM LEAKDISCHARGE WITHSTEAM LEAK

NORMAL OPERATIONWITH FLASHING

NORMAL OPERATIONHIGH FLOW

LIVE STEAM LEAK


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Note that the absence of live steam leaks in steam traps doesnt assure in any way the reduction ofbackpressure in big installation, due to that generally it is associated with the presence of highamounts of flash steam in the condensate return collectors.

Remember that to reduce the formation of flash steam it is necessary to decrease line 3-4 in Fig.1.4, which is the same as descending position of point 2. The situation of point 2 depends on theoperation pressure, which cannot be changed easily because its imposed by the process itself, butalso depends on the condensate discharge temperature, which can only be modified when usingthermostatic steam traps with external adjustment of the operation temperature of the steam trap.This function is also monitored in intelligent steam traps.

In summary, the solution to the problem requires various simultaneous actions:

- Elimination of live steam leaks- Efficient control of the formation of flash steam- Review of the steam trap design- Review of the dimensioning of condensate return collectors


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TABLE OF SATURATED STEAM


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CHAPTER 2

INTELLIGENT STEAM TRAPS AND VALVES

2.1 THE STEAM TRAPS MISSION

In all steam installation four functionally different parts can be considered (Fig. 2.1):

- Steam generation unit (boiler)- Steam distribution lines- Process equipment (steam consumers)- Condensate return collectors

There are two differentiated zones in the installation:

- Steam zone, of high energetic level

- Condensate zone, of low energetic level

The steam traps mission is to establish a physical barrier of separation between both zones,avoiding the pass of energy from the high level zone to the low energetic level zone. Therefore, it isevident that the steam traps function is essential to reach a high efficiency in the installation.

Fig. 2.1

Boiler

Heat Exchang er

Steam traps

Condensate return collector

Steam net distribution

FeedTank

Pump

SIMPLIFIED SCHEME OF AN INSTALLATION

The steam trap, in its most basic concept, must evacuate condensate that arrives without lettingany live steam escape. To achieve this function adequately the points of the installation wheresteam traps must be installed have to be correctly chosen.

In its most general concept, the steam trap is an automatic regulation valve that must control theevacuation of the condensate to reach the maximum energetic efficiency and the optimumoperation of all the equipment that is part of the installation.

The amplitude of this concept joined to the diversity of applications of steam can be translated intovery flexible requirements and, sometimes contradictory, which require different types of steam


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traps to achieve the service specifications. For example, a dryer cylinder in the paper industry canrequire the steam trap to work with a small continuous steam leak while the tracing steam trap inthe fuel line to the boiler generally will discharge condensate at 40C less than the steamsaturation temperature.

2.2 THE IDEAL STEAM TRAP

From a functional point of view, the steam trap must be capable of doing the following functions:

- Evacuate condensate without losing steam- Evacuate air or other incompressible gases- Adjust itself automatically to operation condition changes

Nevertheless, from an operative point of view the steam trap must incorporate additionalperformances, such as:

- High energetic efficiency- Low maintenance- Reliability, robustness and versatility- Self-detection of its own failures- Simple maintenance in line and if possible without interrupting its service- High quality and low price

Obviously, it is impossible in practice to fulfil all these specifications. The traditional steam trapsare valves of purely mechanical type designed to fulfil the most necessary aspects for theapplications to which they are assigned, sacrificing other secondary applications.

Thus, the specification are more and more exigent and include actualised criteria of energy saving,

environmental protection, safety, maintenance, inspection, etc., which causes the evolution of theclassic mechanical steam trap to the modern intelligent BiTherm SmartWatch steam trap.

2.3 INTELLIGENT STEAM TRAPS: BiTherm SmartWatch

They are automatic steam traps which incorporate externally the electronic continuous monitoringsystem SmartWatch.

Though the SmartWatch system can be applied to any type of steam trap its maximal potential isobtained when applied to bi-thermostatic steam traps with external adjustment in operation,described in chapter 3 (Fig. 2.2).

The system has two operation modes:

- Autonomous mode, powered by solar or conventional energy- Network mode, powered by conventional energy

The intelligent steam trap is a device of high technology, unquestionnable technologic leader,which takes advantage of the synergy of the union of the BiTherm bi-thermostatic steam trap withthe electronic continuous monitoring device SmartWatch, controlled by microprocessor.


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Fig. 2.2

INTELLIGENT BITHERM-SMARTWATCH STEAM TRAP

The result produces the higher performances at the moment:

- Systems self-diagnostic- Continuous detection of live steam leaks- Continuous detection of flash steam formation- Continuous detection of the efficiency decrease- Continuous detection of excessive condensate accumulation- Correction possibility of live steam leaks while in operation- Reduction of flash steam formation while in operation- Discharge temperature adjustment while in operation

- Reduction of inspection and maintenance costs- Minimum duration three times higher than the mechanical steam trap

The SmatWatch device incorporates a screwed element, which is connected to the screwed parton top of the steam traps cover. It can be also connected during the steam traps operation. Oncecoupled, the system can initiate its operation alerting about any incidence in its operation.

The external mechanism of adjustment of the steam traps temperature makes it possible toresolve any detected problem while in operation, with no need to isolate the steam trap nor stopthe operation.

One of the most interesting functions of the intelligent steam trap is the control of the pressurisation

of the condensate return collectors.

SOLAR PANELS

YSTRAINER

STRAINER VALVE

EXTERNAL CONNECTION

SMARTWATCH

ALARM SIGNAL

UPPER BIMETALLICTHERMOSTATS

LOWER BIMETALLICTHERMOSTAT

EXTERNAL ADJSTMENT DEVICEWHILE IN OPERATION

BALANCEDPRESSURE VALVE

INDEPENDENT SEAT

BITHERM BI-THERMOSTATICSTEAM TRAP


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Thus, the intelligent steam trap incorporates a system of continuous ultrasound detection thatnormally is activated when a small live steam leak appears. The system also detects increasingrevaporation levels even before reaching the live steam leak. On the other side, the externalmechanism of the steam trap allows to adjust the temperature of evacuation of the condensate,that is, to fix the position of point 2 (Fig. 2.3). From this not only the flash steam formation in thesteam traps discharge can be controlled very easily, but also its evolution in time.

Suppose an application that allows to eliminate completely the flash steam in the steam trapsdischarge. In this case point 2 must be situated in point 2, in this way point 3 coincides with point4 and there would be no residual energy to revaporate the condensate discharged by the steamtrap.

This would additionally mean to use the energy H2-H3 (condensate partial sensible heat) as usefulenergy, reducing in the same proportion the residual energy in the evacuated condensate. Fromthis significant advantages can be deduced:

- Total decrease of revaporated in the steam traps exit

- Backpressure reduction due to flash steam- Live steam saving (partial use of sensible heat)- Absence of thermal waterhammering caused by flash steam

Suppose now that with the pass of time the steam trap suffers internal damage due to erosion;then the evacuating temperature would increase, that is, point 2 would increase lightly andtherefore point 3 would be in the flash steam area. This fact would immediately detected by theintelligent steam trap alerting the user, who in a couple of minutes could correct the situation usingthe external adjustment of the steam trap while it is in operation, with no need of substituting thesteam trap or its spare parts. To avoid the risk that point 2 is situated under the desired point theintelligent steam trap monitors continuously this point generating the correspondent alarm when itdecreases more than it should. Again

new significant advantages are evident:

- Absence of inspection costs- Reduction of material costs- Reduction of maintenance costs- High energetic efficiency maintained in time- Detection of failures by excessive condensate accumulation

The exposed example is not a theoretical case nor even less infrequent, but the contrary. A highpercentage of steam traps are used in the chemistry industry in steam tracing, where condensateis discharged at between 80C and 100C. The high number of these steam traps generate highbackpressures in the condensate return collectors of very hard solution. The intelligent steam trap

is the ideal solution to resolve all these problems in a profitable, safe and lasting way(Fig. 2.4).

Other advantages of the intelligent steam trap are its great reliability, robustness and versatility.Reliability is achieved through the continuous self-inspection system, alerting of possible failures.

The robustness is guaranteed because it is a bimetallic steam trap resistant to corrosivecondensates, waterhammers, high pressures and high operation temperatures. It incorporates hightechnology materials such as Titanium Nitride. Additionally, its design as balanced pressure valve,independent from the differential pressure, guarantees its operation even in installation with greatbackpressures.


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Fig. 2.3

ENTHALPY-PRESSURE DIAGRAMM OF WATER STEAM

The versatility is assured by the external adjustment mechanism, which makes the condensatedischarge at the ideal wished temperature possible. It is like having a steam trap manufactured foreach specific application, but conserving the advantages of a product in series. This makespossible that the same device can be used for so different applications like tracing, distributionlines or even turbine protection, only by modifying its discharge temperature. This standardiseselements and reduces costs of immobilised in spare part stocks.

2.4 INTELLIGENT VALVES: SmartWatch

The concept of intelligent steam trap can be applied for the monitoring of steam and gas leaks insafety valves and automatic on-off valves, etc.

The SmartWatch system is applied externally to these valves through a collar, which serves assupport for the fixation of the electronic element (Fig. 2.5).

LATENT HEAT

SENSIBLE HEAT

STEAM TRAP

PRESSURE

ENTHALPY


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Fig. 2.4

Smart Watch Steam trapSteam leak detection

Zone of local pressurisationand waterhammering

Steam

CONTINUOUS STEAM LEAK DETECTION

SmartWatch can be integrated forming a powerful network of valve leakage surveillance, integralsafety concept, improving safety significantly in industrial installations, in LPG spheres, etc.

The system stays in continuous surveillance of the valve detecting any gas or steam leak as soonas it appears. Once detected the leak transmits the information to the central control unit, from

where all programmed actions for each case are automatically generated (remote alarms,telephone calls to maintenance centres and safety departments if necessary, etc.).

Bidirectional data transmission is used, which allows the remote configuration of the sensors aswell as its activation or disactivation. Additionally, self-calibration and failure self-detectionfunctions are available, generating the correspondent alarms to facilitate its identification.

Fig. 2.5

INTELLIGENT SAFETY VALVE


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All the information is collected in databases for its analysis and posterior treatment according theusers necessities.

SmartWatch can be applied to on-off automatic valves to identify instantly process gas leaks,which would be burnt in the flare without being detected (Fig. 2.7). This allows to reduce processlosses and, therefore, production costs as well as inspection and maintenance costs.

Fig. 2.6

SMARTWATCH INTEGRAL SAFETY SYSTEM

A notable characteristic of the SmartWatch system is the facility of application integration in auniversal alarm network with a practically unlimited growing capacity (Fig. 2.8). This way, steamtraps, valves of different types and other elements share a unique and powerful informationstructure. This standardisation means an important operative simplification and reduction ofinstallation and conservation costs.

Surveillance 24 h/day, 365 days/year

Simultaneous adviseto the Safety

Dangerousgas leak

SmartWatch

Safety valve

Instant alarm to theMaintenance D t.

Central control unitRemote alarm


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Fig. 2.7

REDUCTION OF PRODUCTION COSTS

Fig. 2.8

SMARTWATCH NETWORK STRUCTURE

FlareRefiningtower

Process units Process units

Up to 16.7 million elements and up to4 parameters per element

Up to 256elements

Up to 256elements

Up to 256

elements

ControlUnit


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CHAPTER 3

MECHANICAL STEAM TRAPS

3.1 INTRODUCTION

The intelligent steam trap has been excluded from this chapter due to the fact that, though amechanical steam trap, it incorporates electronic technology. Nevertheless, the bi-thermostaticsteam trap will be studied here in detail as a mechanical steam trap, basis of the intelligent steamtrap.

Since the first steam trap of history, from the orifice plaque to the intelligent steam trap, there hasbeen a constant evolution of steam traps trying to satisfy all demands and improve therecharacteristics. The evolution of energy costs caused the new mechanical steam trapsappearance, like the bi-thermostatic, to improve their energetic efficiency.

3.2 CLASSIFICATION OF STEAM TRAPS

There are different criteria of steam trap classification, according the concept used to classify them.According to their operation principle, they can be classified in the following way:

The steam traps sensible to density changes are based upon the buoyancy of a float, closed oropen, that activates a valve in dependence with the level reached by the condensate inside thesteam trap.

The group of steam traps that are sensible to the fluids pass velocity are based on the greatdifference between the specific volume of the steam and the condensate. This makes the velocityof the steam pass through an orifice much higher than the one of the condensate; this is translatedto pressure differences that are used to control the steam trap.

At last, the steam traps sensible to temperature changes take advantage of the condensatecooling in relation to the saturation temperature of the steam to activate a thermostat that controlsthe steam trap operation. They behave like automatic thermostatic valves.

TYPE OF STEAM TRAP

Sensible to status changes

Sensible to velocity changesOrifice Plate

Disc ThermodynamicImpulse

Sensible to density changesFloat

Inverted BucketOpen Bucket

Sensible to temperature changes

ThermostaticBimetallic

Bi-ThermostaticCapsule


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In the continuous discharge system, the discharge of the steam trap is adjusted always to thecondensate production, allowing a constant equilibrium between steam trap and process, avoidingstrong pressure oscillations in the condensate return system.

On the other hand, in case of cyclic discharge the steam trap must be overdimensioned tocompensate in the active part the capacity loss of the dead part of the cycle. The intermittentdischarge provokes pressure oscillations and backpressure that can affect other steam traps andproduce strong waterhammering.

In a cyclic system it is normal to find live steam leaks before the steam trap closes. When it opensa cyclic system must rapidly eliminate the accumulated condensate; this causes a decrease ofpressure before the steam trap and, with it, a small decrease of temperature. At the same time, inthe discharge an increase of backpressure is produced, therefore the final differential pressure thatacts upon the steam trap results decreased.

In summary, the evident advantages of a continuous discharge system in comparison to other

cyclic are:

- Equilibrium between the condensate charge of the process and the steam trap- Softer functioning of the installation- Higher energetic efficiency- Better control of the steam traps operation- Better control of steam leakage- Maintenance of a higher differential pressure in steam traps

3.4 ORIFICE PLAQUE STEAM TRAP

It can be considered as the CAR steam trap in history. It is the simplest trap device. It is an orifice

made on a metallic plaque, calibrated according the condensate flow that it is capable ofevacuating (Fig. 3.2).

The orifice plaque cannot be considered really as an automatic steam trap because it does notincorporate any pressure, temperature or flow regulation element. It is only capable of creating acharge loss that increases with the flow.

The live steam pass at great speed through the orifice produces a charge loss that stops partiallythe current decreasing at certain level the great steam losses that this steam trap can present if itis not well dimensioned.

The advantages of this steam trap are:

- Maximum simplicity- Wide pressure range- Low maintenance

Fig. 3.2

ORIFICE PLAQUE STEAM TRAP


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Its disadvantages are evident:

- Very critic dimensioning- Low flexibility- Great live steam losses- Appearance of great backpressures in the condensate collectors.

3.5 FLOAT STEAM TRAP

It was the first mechanical automatic steam trap used in industry. Basically it is a liquid levelregulation valve (Fig. 3.3).

Its mechanism is constituted by an articulated bar in one of its extremes of length (L) and a float onthe other end that gives an impulsion (E). In an intermediate point the plug of a valve of area (S) issituated. The level of condensate in the steam trap activates the opening and closing of the valve(V).

The articulated bar constitutes an arm bar (L). From the equilibrium of the applied forces to it, it isdeduced that there is a limited differential pressure that acts on the valve and from which thefloating pressure that acts on the float cannot open the valve.

The opening force (Fa = E x L) must be always bigger than the closing force (Fc = P x S).Therefore:

E x L > P x S

For this reason in float steam traps it is always necessary to take into account the section of thedischarge orifice and the maximal differential pressure of operation.

Fig. 3.3

FLOAT STEAM TRAP

To evacuate big flows a valve of great pass section will be needed, which obliges to increase thefloats diameter or the arm bars length and therefore the size of the steam trap.

To evacuate the retained air inside, the steam trap can incorporate a thermostatic air vent (T) ofcapsule, bellow or bimetallic, or a small valve of manual deareation. The thermostat must be ofbimetallic type if it works with overheated steam. Sometimes the air vent is simply a small internal

orifice, which, like a by-pass, substitutes the thermostatic air vent, in this case the steam trap willhave a constant live steam leakage.Consequently, to dimension a float steam trap, the following aspects must be considered:

Shearing (E)

Pressure (P)

Thermostat

Valve

FloatFloat


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It is observed then that the discharge in this steam trap is intermittent and its need of an hydraulicseal in its bottom part to establish the steam pressure inside the bucket, necessary to achieve itsflotation.

Fig. 3.4

INVERTED BUCKET STEAM TRAP

Like in the float steam traps, the size of the valves orifice (V) is critical and determines themaximum differential pressure, at higher pressures the steam traps cannot work because theweight of the bucket that moves the bar isnt capable of opening the valve (V).

Therefore when dimensioning these steam traps the same mentioned indications for the floatsteam traps must be followed.

The advantages of this steam trap are:

- Simplicity, with low possibilities of mechanical failures- Waterhammer resistant- It discharges dirty condensates without difficulty- It requires low maintenance

Its disadvantages are:

- Slow deareation, small orifice to avoid great energy losses in operation- It can lose its water seal and produce great steam losses- Fixed mounting position- Normally it doesnt incorporate filter nor check valve- It works with steam losses by condensation in each cycle- Expensive maintenance and generally it is not repairable in line- Sensible to freezing due to the presence of water inside it- It admits only a small steam overheat if a check valve is installed in its entrance- Its discharge temperature cannot be varied


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3.7 THERMODYNAMIC DISC STEAM TRAP

The disc thermodynamic steam trap deserves special attention because it has been the mostlyused in the past. Its utilisation has descended considerably due to its low energetic efficiency.

The operation of the disc steam trap is very negative because it produces steam losses that areorigin of strong local backpressures in the return collectors that affect very negatively the goodoperation of the installation.

The disc steam traps design is very simple. Its operation is based on the Bernouilli principle. Itconsist of a body, a cover and a disc.

The cover has a protuberance to facilitate the formation of a control chamber between the disc andthe cover when the disc is in the highest position, open.

When the disc is in the lower position, closed, the control chamber remains also closed.

Initially, in the installation start-up, the steam trap discharges with no difficulty until live steamreaches the steam trap. In its pass through the steam trap the steam runs under the disc at greatspeed to the exit of the steam trap generating an increase of the dynamic pressure and therefore adecrease of the static pressure in the bottom side of the disc, because according Bernouillisprinciple the total pressure in the fluid remains constant.

At the same time a small amount of steam reaches the small control chamber between the discand the cover. The steam flow speed in this chamber decreases and for the same reason beforementioned, but inversely, an elevation of the static pressure in the chamber is produced.

As a consequence of these facts the disc falls violently against the seat of the steam trap, pressedfrom above and absorbed from below, producing the steam traps closure.

In this position the control chamber, the entrance and exit orifice remain isolated one from eachother. On all the discs top surface acts the pressure of the control chamber in the closing directionwhile in only a small part of the inferior side of the disc acts the steam pressure and thebackpressure, both in direction of opening. The result is a net closing force.

This unbalance of forces remains until the pressure in the control chamber decreases sufficiently,due to the condensation of the retained steam, to open the disc. This cycle is repeatedsuccessively.

It is important to mention that the steam traps discharges are repeated in cycles independentlyfrom whether it flows condensate to the steam traps or not.

Fig. 3.5

THERMODYNAMIC DISC STEAM TRAP


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This fact is easily confirmed when some water drops fall on the steam trap; it immediatelycondenses the steam retained in the control chamber and the steam trap opens open over andover again even if there is no condensate in front of it.

For this reason protection caps are installed on the steam traps when it is installed in cold or humidareas, to reduce it opening rhythm which would produce great energy losses.

Advise that sometimes this steam traps operation is described wrongly when affirming that the itsclosing is produced by the condensates revaporation effect inside the steam trap. This is incorrectbecause the flash steam is produced after the steam trap and cannot progress counter-currentwhere the pressure is higher. Therefore, it is the live steam escape, not flash steam, the one thatproduces the steam trap closure, like demonstrated experimentally (see work published inPetrogas, September 1979, p. 43).

The advantages of a disc steam trap are:

- Wide pressure range- Robust construction and low price- Insensible to waterhammering- It works with overheated steam- Insensible to freezing- Very resistant to corrosion

Disadvantages of the disc steam trap:

- Low deareation capacity- It doesnt admit a backpressure higher than 80% (50% maximum for low service

pressures)- Sensible to failures due dirtying- Cyclic operation. Fast deterioration of the disc and/or seat due to the violence of the

closing with important and increasing steam losses.- Important energy losses specially in low flow services like line and tracing with steam.- Very sensible to climate adverse conditions, rain and wind- Creation of high backpressures in return collectors

As observed, the disadvantages of this type of steam trap are based repeatedly on the excessiveenergy consume, being nowadays considered as one of the steam traps with the lowest energeticefficiency.

3.8 IMPULSE STEAM TRAP

The mechanism of the impulse steam trap (Fig. 3.5) is constituted by a cylindrical piston or plug(P), that has a central orifice (O) along its symmetry axis, communicating the entrance with the exitof the steam trap. This plug (P) incorporates a circular horizontal wing in its top part.

The plug (P) can move upwards and downwards inside a cylinder of conical internal surface. In thetop part the plug closes the valves orifice (V).

The condensate that reaches the steam trap flows through the central orifice of the plug. At thesame time the condensate flows around the cylindrical wing of the piston onto the top controlchamber of the steam trap, producing steam loss in the straight part between the horizontal plugand the conical cylinder.


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As a consequence the pressure in the top control chamber, over the plug, is lower than thepressure in the lower part of the plug wing and the plug rises opening the valve (V).

When steam reaches the steam trap, the central orifice (O) of the plug produces a higherresistance to the steam pass due to its high flow speed compared to the condensate; this makesthe pressure in the top control chamber increase and the plug (P) descends strangling the flowsection of the valve (V).

The free section between the plug and the guide cylinder varies with the movement of the firstcaused by the conicity of the second, acting as a tube of variable section. This allows certainflexibility to flow variations, resulting therefore to be an organ of regulation because the valve (V)depends on the vertical position that the plug (P) adopts each time, this position will depend on thecondensate flow.

Fig. 3.6

IMPULSE STEAM TRAP

Note that the position of the steam trap must be always vertical not to interfere in the upward anddownward movement of the plug.

For more operative flexibility the steam trap normally incorporates in its top part a adjustmentscrew that fixes the position of the guide conical cylinder able to vary the top control chambersvolume and, in consequence, the pressure in the chamber.

It is evident that a watertight plug closure is never achieved, because the control orifice (O)maintains a live steam leak permanently (control steam), which makes the steam trap operationpossible. For this reason, the leak detection through ultrasound in impulse steam traps is alwayspositive.

The advantages of this type of steam trap are:

- Small and robust- Air and incondensable discharge- Wide operation range- It can be used with overheated steam

Its disadvantages are:

- Live steam losses and low efficiency- Increase of backpressure in return collectors- Fast waste of internals by erosion

- Doesnt support well backpressures higher than 40%- Great sensibility to staining


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3.9 THERMOSTATIC STEAM TRAP

It includes a wide group of steam traps that use a thermostat of solid expansion, liquid expansion(bellow or capsule) or bimetallic to control its operation.

The thermostatic solid expansion steam traps use a resin of high dilatation coefficient that in itsexpansion activates the valve of the steam trap. Its use is very limited.

The liquid expansion steam traps (Fig. 3.7) are formed by a capsule (C) or a corrosion resistantbellow of stainless steel or other materials, in which there is a mixture of water and alcohol or otherliquid with a boiling point that is a few degrees under the one of the water.

The operation is very simple; when condensate reaches the steam trap at a temperature close tothe saturation point, the internal liquid of the capsule evaporates and the capsule dilates closingthe steam traps valve.

When the condensate cools, the internal fluid of the capsule condenses and the capsule contracts

opening the valve.

Advantages of the bellow or capsule steam traps:

- Great evacuation capacity- Great precision and fast response- Operation in any position- Automatic deareation- Insensible to staining- Insensible to freezing- They follow the steam saturation curve without readjustments- They admit great backpressures

Disadvantages:

- Fragility of the thermostatic element- They do not support well waterhammering and overheated steam- High maintenance cost; expensive spare parts and of short duration

Fig. 3.7

CAPSULE THERMOSTATIC STEAM TRAP


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The third group of thermostatic steam traps, the bimetallic, deserves a special mention due to itswide utilisation and the evolution grade they have suffered.

They are constituted by a thermostat of bimetallic plates that react with the different condensatetemperatures transmitting its movement to the internal valve plug of the steam trap.

They are very versatile steam traps due to the possibility of adjusting their condensate evacuationtemperature to the optimum value for the service they must fulfil and their use has allowed theachievement of great energetic efficiency of the installations.

The bimetallic thermostat can present diverse configurations. Generally the internal regulatingorgan of the steam trap or bimetallic regulator is formed by a packet of bimetallic plates more orless robust, according the pressure they must support, a valve with its plug and a temperatureadjustment device that is used also to join all the other elements. Fig. 3.8 shows a classicbimetallic steam trap with differential pressure valve. Its operation is as follows:

When cold condensate reaches the steam trap the bimetallic plates are relaxed, plain, allowing the

movement of the plug that is pushed in the direction of opening by the fluid own pressure. Whenthe condensates temperature starts to rise the bimetallic sheets curve, they act in pairs oneagainst the other, pulling up the plug that is pressed in opposite direction. The plugs position, andtherefore the opening of the valve, depends continuously on the equilibrium of the closing forces(thermal) and the opening forces (differential pressure over the plug). When the condensatetemperature is close to the steams saturation point the bimetallic regulator closes the valvehermetically; this process is continuous and the closing point depends on the adjustment given tothe thermostat.

Fig. 3.8

CLASSIC THERMOSTATIC BIMETALLIC STEAM TRAP

The valve of this steam tarp is of differential pressure type; the plug in on the exit side of the valve,where the condensate expansion is produced and the fluid flow speed is very high andconsequently the erosive action over the plug is very aggressive.

The advantages of the bimetallic steam trap are:- Optimum energy efficiency- Continuous discharge and wide pressure range- Great robustness, resistance to waste and to waterhammering

- Insensible to corrosive condensates and freezing- Automatic deareation and great capacity of start-up in cold- Mounting in any position

Bimetallicpackage


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- It supports overheated steam- High reliability and versatility

The disadvantages of these steam traps are:

- Sensibility to staining- Slow response to strong pressure or operation condition changes

The most innovative of the bimetallic steam traps is the bi-thermostatic steam trap of balancedpressure (Fig. 3.9).

One of the differences with respect to the classic bimetallic steam trap is that the bi-thermostaticsteam trap incorporates two antagonistic thermostats. The thermostat on top consists of variousbimetallic plate pairs guided by the plugs stem, and the inferior thermostat is formed by onebimetallic sheet that leans and is guided in its edges by the body of the steam trap.

The bimetallic plate pairs of the superior thermostat act one against the other; each pair is

separated from the next by a ring that distances them 1mm and that protects the regulator fromfailures caused by staining.

The fittings of the valve are covered with Titanium Nitride in steam traps of high pressure,increasing its surface hardness until 84 HRC to enlarge the steam traps life.

The valve is guided in its flow direction, therefore the steam trap can work in any position (thesteam trap works even if the entrance and exit connections are exchanged, in this case the steamtrap would operate like a differential pressure valve with the thermostat in the exit side).

The valve is of balanced pressure type, the plug is situated before the valve, in an area wherethere is only condensate circulating at low speed and, therefore, does not suffer the erosive effects

of the flash steam, formed at the exit of the valve. As a consequence the duration of the bi-thermostatic steam trap is three times longer than the one of the classic bimetallic steam trap.

The superior thermostat expands with the increase of temperature pressing the plug in the closingdirection; at the same time, the inferior thermostat arches itself allowing the movement of the valvein the same direction. The combined result of both actions is the progressive strangulation of thecondensate flow as the condensate temperature rises till it reaches its complete closure when itarrives to the previously adjusted temperature.

When the condensate temperature decreases the thermostats act inversely; The superiorthermostat contracts decreasing its pressure over the plug while the inferior thermostat decreasesits curvature pushing the plug in the direction of valve opening. As a consequence the flow section

of the valve increases.

Both thermostats always fulfil an antagonistic equilibrium function without intervening in any waythe differential pressure. The condensate discharge is modulated according the amount ofcondensate produced in the installation. The balance point can be fixed with the steam trap inoperation through the external temperature adjustment mechanism, which allows to convert aseries steam trap into a specific steam trap for each application.

While in a classic bimetallic steam trap, the bimetal is constantly submitted to the opening force,fact that requires a more robust design, with higher thermal inertia and that limits the pressurerange of the steam trap. In bi-thermostatic steam traps both thermostats are never submitted topressure forces, but exclusively to thermal effects, which only affect the intrinsic property of thebimetal, thus its operation pressure range is much higher and its duration much longer.


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Fig. 3.9

BI-THERMOSTATIC BALANCED PRESSURE STEAM TRAP

Also as a difference with the classic bimetallic steam trap, all the components of the bi-thermostaticregulator are independent and can be substituted separately, fact that reduces very much therepairing cost. Additionally, the external adjustment mechanism makes repairs in operationpossible, with no need of substituting any internal element, reducing enormously the maintenancecost.

The failure of a classic bimetallic steam trap due to accumulation of dirt between the plates of thethermostat has been eliminated in the bi-thermostatic steam trap, which include separating ring of1mm between bimetallic plate pairs.

Finally, the steam trap incorporates an external connection for the continuous monitoring electronicsystem, described in chapter 1, that converts it in a super-steam-trap of high technology with muchhigher performances than any other known steam trap.

As the principal advantages we can mention:

- Optimum energetic efficiency- External adjustment mechanism while in service- Possibility of repair while in operation- Very long duration- High reliability and versatility- Great robustness, resistance to waste and to waterhammering

- Insensible to staining and to corrosive condensates- Insensible to freezing- Automatic deareation- Great security coefficient in cold start-up- They admit great backpressures- They support overheated steam and great differential pressures- Reduced maintenance and spare part cost

The disadvantages of these steam traps are:

- They follow with small retard to strong pressure or regime changes

The bi-thermostatic steam trap adds therefore new advantages to the classic bimetallic steam trap,li i ti l it d f t

External adjustment devicewhile in operation

SmartWatch

connection

Upper thermostat

Lower thermostat

Pressure balancedbimetallic acka e

steam traps manual

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