Aprds system

APRDS SYSTEM

BY

SHARAVAN TRIPATHI

JIPT

Auxiliary PRDS System

• Auxiliary PRDS system consists of a TurbinePRDS control system as well as Boiler PRDScontrol system. The controller of these systemare pneumatically controlled. Both thesystems are identical in nature.

• Auxiliary steam is tapped from the mainsteam line and its pressure is reduced and de-superheated to the required temperature andpressure.

Auxiliary PRDS System

• The spray water for de-superheating issupplied from the CEP discharge header.

• In order to obtain better operationalflexibility and controllability range, boththe system have been split into twoidentical PRDS system such as lowcapacity PRDS and high capacity PRDS.

Auxiliary PRDS System Contd..

• The low capacity is of 30% of that of the highcapacity line.

• Each system comprises of the pressurecontroller, one de-superheater and one spray

water flow controller.

• We shall henceforth call the Turbine PRDSsystem as TAS and the Boiler PRDS system asBAS.

System Description- High Capacity• High capacity PRDS comprises of steam pressure

reducing control valve, motorized upstream isolatingvalve, downstream manual isolating valve, one spraywater temperature control valve and one de-superheater.

• A motorized regulating globe valve is provided inbypass line of, which can be operated remote manuallyin case of mal-operation of the pressure control valve.

• A motorized bypass globe valve is provided for spraywater control valve , which can be operated remotemanually in case of mal-operation of spray watercontrol valve.

System Description- Low Capacity• Low capacity PRDS comprises of steam pressure reducing

control valve, motorized upstream isolating valve,downstream manual isolating valve, one spray watertemperature control valve and one desuperheater.

• A motorized regulating globe valve is provided in bypassline of, which can be operated remote manually in case ofmal-operation of pressure reducing control valve.

• A motorized bypass globe valve is provided for spray watercontrol valve, which can be operated remote manually incase of mal-operation of spray water control valve.

TAS/BAS Pressure/ Temperature Control• The auxiliary steam pressure control valve supplies

steam to TAS/BAS header by maintaining TAS/BASline pressure constant at the set point (11 kg/cm2).Downstream pressure of PRDS valve is taken ascontrolled pressure.

• The auxiliary PRDS spray water flow control valve(CD) maintains the TAS / BAS line temperatureconstant at the set point (2600C for TAS & 2200C forBAS). The downstream temperature of PRDS valve istaken as controlled temperature.

Selection of HT & LT PRDS• During unit start up auxiliary steam for turbine is supplied

to Deaerator initial heating & pegging, Turbine GlandSealing. To meet this high demand of auxiliary steam HTPRDS should be put into service.

• After unit synchronization and at about 30 to 40% of unitload deaerator pegging is supplied from CRH / turbineextraction line (CAP) and pegging from TRDS is cut out. Atabout 40% unit load also, turbine gland sealing supply valvefrom TPRDS closes as turbine becomes self-sealingcondition.

Uses of Aux Steam at various locations of plant

LTPRDS:-

1) VAM

2) FO heating

3) HFO Atomizing

4) Mill Inerting

5) Wet steam washing

HTPRDS:-

1) Turbine Gland Sealing

2) Deaerator Pagging

3) APH soot blowing

Vapor Absorber Machine (VAM)



• Absorption refrigeration systems replace thecompressor with a generator and an absorber.Refrigerant enters the evaporator in the form of acool, low-pressure mixture of liquid and vapor (4).

• Heat is transferred from the relatively warm waterto the refrigerant, causing the liquid refrigerant toboil. Using an analogy of the vapor compressioncycle, the absorber acts like the suction side of thecompressor—it draws in the refrigerant vapor (1) tomix with the absorbent. The pump acts like thecompression process itself—it pushes the mixtureof refrigerant and absorbent up to the high-pressure side of the system.

Vapor Absorber Machine (VAM) • The generator acts like the discharge of the

compressor—it delivers the refrigerant vapor (2) tothe rest of the system.

• The refrigerant vapor (2) leaving the generatorenters the condenser, where heat is transferred towater at a lower temperature, causing therefrigerant vapor to condense into a liquid. Thisliquid refrigerant (3) then flows to the expansiondevice, which creates a pressure drop that reducesthe pressure of the refrigerant to that of theevaporator. The resulting mixture of liquid andvapor refrigerant (4) travels to the evaporator torepeat the cycle.

How Absorption Machine Works • Absorption system employs heat and a

concentrated salt solution (lithium bromide) toproduce chilled water. In its simplest design theabsorption machine consists of 4 basic components:

1. Generator

2. Condenser

3. Evaporator

4. Absorber

Function of Components Generator: • The purpose of the generator is to deliver the refrigerant

vapor to the rest of the system.• It accomplishes this by separating the water (refrigerant) from

the lithium bromide-and-water solution.• In the generator, a high-temperature energy source, typically

steam or hot water, flows through tubes that are immersed ina dilute solution of refrigerant and absorbent.

• The solution absorbs heat from the warmer steam or water,causing the refrigerant to boil (vaporize) and separate fromthe absorbent solution.

• As the refrigerant is boiled away, the absorbent solutionbecomes more concentrated. The concentrated absorbentsolution returns to the absorber and the refrigerant vapormigrates to the condenser.

Condenser:

• The purpose of condenser is to condense therefrigerant vapors. Inside the condenser, coolingwater flows through tubes and the hot refrigerantvapor fills the surrounding space.

• As heat transfers from the refrigerant vapor to thewater, refrigerant condenses on the tube surfaces.The condensed liquid refrigerant collects in thebottom of the condenser before traveling to theexpansion device.

• The cooling water system is typically connected toa cooling tower. Generally, the generator andcondenser are contained inside of the same shell.

Expansion Device:• From the condenser, the liquid refrigerant flows

through an expansion device into the evaporator. Theexpansion device is used to maintain the pressuredifference between the high-pressure (condenser) andlow-pressure (evaporator) sides of the refrigerationsystem by creating a liquid seal that separates the high-pressure and low pressure sides of the cycle.

• As the high-pressure liquid refrigerant flows throughthe expansion device, it causes a pressure drop thatreduces the refrigerant pressure to that of theevaporator. This pressure reduction causes a smallportion of the liquid

• refrigerant to boil off, cooling the remaining refrigerantto the desired evaporator temperature. The cooledmixture of liquid and vapor refrigerant then flows intothe evaporator.

Absorber:

• Inside the absorber, the refrigerant vapor is absorbedby the lithium bromide solution. As the refrigerantvapor is absorbed, it condenses from a vapor to aliquid, releasing the heat it acquired in the evaporator.

• The absorption process creates a lower pressure withinthe absorber. This lower pressure, along with theabsorbent’s affinity for water, induces a continuousflow of refrigerant vapor from the evaporator. Inaddition, the absorption process condenses therefrigerant vapors and releases the heat removed fromthe evaporator by the refrigerant. The heat releasedfrom the condensation of refrigerant vapors and theirabsorption in the solution is removed to the coolingwater that is circulated through the absorber tubebundle.

• As the concentrated solution absorbs more andmore refrigerant; its absorption ability decreases.The weak absorbent solution is then pumped to thegenerator where heat is used to drive off therefrigerant. The hot refrigerant vapors created inthe generator migrate to the condenser. The coolingtower water circulating through

• the condenser turns the refrigerant vapors to aliquid state and picks up the heat of condensation,which it rejects to the cooling tower. The liquidrefrigerant returns to the evaporator and completesthe cycle.

FO Heating

Viscosity

• The viscosity of a fluid is a measure of its internalresistance to flow. Viscosity depends ontemperature and decreases as the temperatureincreases.

• Any numerical value for viscosity has no meaningunless the temperature is also specified.

• Viscosity is measured in Stokes / Centistokes.Sometimes viscosity is also quoted in Engler,Saybolt or Redwood.

• Each type of oil has its own temperature - viscosityrelationship. The measurement of viscosity is madewith an instrument called Viscometer.

• Viscosity is the most important characteristic in thestorage and use of fuel oil. It influences the degreeof pre-heat required for handling, storage andsatisfactory atomization. If the oil is too viscous, itmay become difficult to pump, hard to light theburner, and tough to operate.

• Poor atomization may result in the formation ofcarbon deposits on the burner tips or on the walls.Therefore pre-heating is necessary for properatomization.

Pressure Reduce Steam.

OIL GUN

ATOMISINGSTEAM VALVE

HFO NOZZLEVALVE SCAVENGE

VALVE

AB ELEVATION

CD ELEVATION

EF ELEVATION

Oil Gun Connection

Atomizing Steam Scheme

HFO Automizing

Oil Gun on Elevation AB

Oil Gun on Elevation CD & Above

Mill Inerting system

Wet Steam Washing

• During operation, deposits occur on the turbineblading to a greater or lesser degree depending onthe steam purity [1] and the pressures andtemperatures of the operating steam. Thesedeposits cause a reduction of the turbine generatorunit’s efficiency due to:

Changes in the flow profiles

• Thicker boundary layers in the steam

• flow as a result of rough surfaces.

• In extreme cases the flow area of turbine may get reducedwith consequent reduction in the maximum possible steamflow through the turbine, and corresponding output. Chokingof blade flow path can be detected on the basis of internalefficiency measurement

• If deposit leads to an increase in stage pressures, themaximum stage pressures shown in the Technical Data shouldnot be exceeded. If necessary, the output must be reduceds.

• water-insoluble, silicate deposits occur in a temperaturerange between 500°C and 350°C. Alkali silicates and silicic acidare deposited between 350°C and 60°C.

• Salt deposits occur at temperatures ranging from 480°C to theblading stages where condensation begins. Salt deposits arewater-soluble and can be removed by steam washing withsaturated steam. Depending on their composition, silicatedeposits are either water-soluble (e.g. alkali silicates) or occuras a hard Water-insoluble coating. In latter case the depositscan only be removed mechanically during overhauls.

Steam Washing of IP Turbine

• All stop and control valves and all valves in the extractionlines remain closed during steam washing of the IP turbine.

• Any isolating valves present upstream of the feed waterheaters must also be closed.

• The drains from the IP turbine between the reheat controlvalves and the IP outlet, the extraction valves or the swingcheck valves in the extraction lines must be vented duringsteam washing only to the extent required to allow thecondensate arising to drain off whilst preventing excessiveloss of steam.

• All other drains from the turbine generator must be full open.After the saturated steam line (Fig.1, item 2) has been joinedup at the connection points (3), the washing steam can berouted into the IP turbine, from there via the cross-aroundlines to the IP turbine and then to the condenser.

Steam Washing of HP Turbine• The main control valves must be open during steam washing

of the HP turbine.• All drains (7, 8) from the HP turbine situated between the

main stop valves and the HP outlet may be vented duringsteam washing only to the extent required to allow thecondensate arising to drain off while preventing excessive lossof steam.

• All other drains particularly those in the cold reheat line, mustbe fully open.

• Local drainage may also be provided so that no steam canenter the Reheater of the Boiler, if at all possible. After thesteam line (6) has been joined up at the connection points (3),the stream can be routed into the HP turbine.

• The steam leaving the HP turbine is exhausted to thecondenser via the drains (9). The condensate is dischargedand samples are taken to determine the salt content asdescribed in steam washing of IP turbine, the completioncriteria remaining same.

Gland Sealing System

FUNCTION• This system ensures the sealing of glands in HP, IP and

LP turbine under various load conditions. The turbineglands are self seal type (refer gland sealing scheme).Upto 40% load, steam from an auxiliary source throughvalve (MAW10AA001) is taken to seal all the HP,IP andLP glands.

• During this period the valve (MAW50AA001)connecting this header to condenser is kept closed.After 40% load, seal steam valve (MAW10AA001) isclosed and the leak steam valve (MAW50AA001) isopened.

• Pipings are so sized that the leak off steam from frontand rear ends of HP turbine goes to the condenserthrough the valve (MAW50AA001), while steam fromthe two IP glands is utilised for sealing the LP glands,thus avoiding the use of a desuperheater.

• The leak off steam and air from the last chambers ofeach rotor is sucked into a gland cooler. Building up ofvacuum in the condenser is the first step during startup. For building up vacuum, it is necessary to seal theturbine glands by supplying steam to the shaft throughthe valve (MAW10AA001).

• The control system opens the gland steam supply valve(MAW10AA001) until the pressure in the headeracquires a preset value. Subsequently when the setpicks up load, the pressure of steam inside HP and IPturbine builds up resulting in the leakage of steam fromthe turbine into gland steam supply header which inturn would result in increase of pressure in the header.

• The controller gradually closes the gland steam supplyvalve (MAW10AA001) and opens gland leak off valve(MAW50AA001), if required.

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Why Deaeration?

Corrosion in boilers is caused by three factors:

1. Feed water temperature

2. Feed water pH value

3. Feed water oxygen content

Temperature and pH value influence the aggressiveness ofcorrosion. The higher the temperature, and the lower the pHvalue the increased aggressiveness of the feed water. Thedissolved oxygen content of the feed water is a large factor indetermining the amount of corrosion that will take place. Thepresence of oxygen, and other non-condensable gases, in the feedwater is a major cause of corrosion in the feed water piping,boiler, and condensate handling equipment.

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Why Deaeration?

• Reduce corrosion by dissolved gas: oxygen,carbon dioxide. Oxygen is the mostaggressive even in small concentrations.

• Sources of oxygen: makeup water,condensate return system.

• Pitting corrosion. Degree of oxygen attackdepends on concentration of dissolvedoxygen, the pH and the temperature of thewater.

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Removal of oxygen, carbon dioxide and othernon-condensable gases from feed water.

What is Deaeration?

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Deaerator PrinciplesDeaeration is the mechanical removal of dissolved gases from the boiler feedwater. There are three principles that must be met in the design of anydeaerator.

1. The incoming feed water must be heated to the full saturation temperature,corresponding to the steam pressure maintained inside the deaerator. Thiswill lower the solubility of the dissolved gases to zero.

2. The heated feed water must be mechanically agitated. This is accomplished ina tray deaerator by first spraying the water in a thin film into a steamatmosphere. Creating a thin film reduces the distance, the gas bubble has totravel to be released from the water. Next, the water is cascaded over a bankof slotted trays, further reducing the surface tension of the water. This allowsfor the removal of any gases not liberated by the initial spraying.

3. Adequate steam supply must be passed through the water, in both the spraysection and the tray section to sweep out the gases from the water.

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The easiest way to de-aerate is to force steam into the feed water,

this action is called scrubbing. Scrubbing raises the watertemperature causing the release of O2 and CO2 gases that arethen vented from the system. In boiling section steam is used to"scrub" the feed water as

(1)steam is essentially devoid of O2 and CO2,

(2)steam is readily available and

(3)steam adds the heat required to complete the reaction.

Deaerator Principles

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For efficient operation, de-aerating equipment must satisfy thefollowing requirements:

(1)Heating of the feed water: The operating temperature in the unitshould be saturation temperature. If this temperature andpressure cannot be economically achieved then it is important toget as close to it as possible.

(2)Agitation decreases the time and heat energy necessary toremove dissolved gases from the water.

(3)Maximization of surface area by finely dispersing the water toexpose maximum surface area to the steam. This enables thewater to be heated to saturation temperature quicker andreduces the distance the gases have to travel to be liberated.

(4)The liberated gases must be vented to allow their escape from thesystem as they are released.

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DEAERATION

Oxygen reacts with water ( H20 ) to give ( OH- ) ION

Fe = Fe+ + e-

O2 + 2H2O + 4e- = 4OH-

Fe+ + 2OH - = Fe(OH)2

2Fe + O2 + 2H2O = Fe(OH)2

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DEAERATION

Carbon dioxide is an acidic gas andcould form carbonic acid with water,

carbonic acid liberates H+ ions that

attacks on metal.

CO2 + H20 H2CO3 H+ + HCO

2H+ + 2e- = H2

-3

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TYPES OF DEAERATION

1. Physical deaeration.

2. Chemical deaeration.

PRINCIPAL FOR PHYSICAL DEAERATIONThe principle of deaeration is based on the following laws

• HENERY’S LAW

• DALTON’S LAW OF PARTIAL PRESSURE

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Dalton’s Law of Partial PressureIt states that the pressure in a container having amixture of a gas and vapour, is the sum of partialpressure of the vapour at the commontemperature and the partial pressure of the gas,at any point inside.

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HENERY’S LAW

• The mass of gas with a definite mass of liquid,which will dissolve at a given temperature, isdirectly proportional to the partial pressure ofthe gas in contact with the liquid.

• This hold with in the close limit for gases whichdon’t unite chemically with water.

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Decreasing the partial pressure of the gas in watermay be achieved by following methods:

Use of another gas to remove the undesirablegases e.g. Nitrogen can be used to removeoxygen.

Decreasing the total pressure so as toapproach the vapour pressure of the water.

Increasing the vapour pressure by heatingthe water

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(A) According to working pressure under which they operate:

Vacuum deaerator

Atmospheric deaerator

High pressure deaerator

Classification of Deaerator

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Vacuum Deaerator

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Classification of Deaerator

(B) Also deaerator can be classified in accordance with the

mode of steam-water distribution:

Atomizing ( spray ) type

Tray type

Film type ( combination of both spray and tray type)

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Tray Type Deaerator

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Tray Type Deaerators

These are composed of a deaerating section and a feed water storagesection. Incoming water is sprayed through a perforated distribution pipe intoa steam atmosphere where it is atomized. There it is heated to within a fewdegrees of the saturation temperature of the steam. Most of the non-condensable gases are released to the steam as the water enters the unit. Thewater then cascades through the tray section, breaking into fine droplets,which immediately contact incoming steam. The steam heats the water to thesaturation temperature of the steam and removes all but a trace ofoxygen. Deaerated water falls to the feed water storage section below and isprotected from recontamination by a blanket of steam. As the non-condensable gases are liberated, they as well as a small amount of steam arevented to atmosphere. It is essential that sufficient venting is provided at alltimes or deaeration will be incomplete.

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Tray Type Deaerator

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Trays

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Spray Type Deaerators

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The spray-type deaerators do not use trays for dispersion of the water. In thiscase, spring loaded nozzles located in the top of the unit spray water into a steamatmosphere which is heated to within a few degrees of the saturation temperatureof the steam. Most of the non-condensable gases are released to the steam, andthe heated water falls to a water seal and drains to the lowest section of the steamscrubber. The water is scrubbed by large quantities of steam and heated to thesaturation temperature prevailing at this point. The intimate steam to watercontact achieved in the scrubber efficiently strips the water of dissolved gases. Asthe steam-water mixture rises in the scrubber, a slight pressure loss causes thedeaerated water temperature to remain a few degrees below the inlet steamsaturation temperature. The deaerated water overflows from the steam scrubberto the storage section below. The steam, after flowing through the scrubber,passes up into the spray heater section to heat the incoming water. Most of thesteam condenses in the spray section to become part of the deaerated water. Asmall portion of the steam, vented to atmosphere, removes non-condensablegases from the system.

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Spray Valve

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Counter & Parallel Flow Deaerator

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1. In this design, the inlet water is sprayed into a steam atmospherespray nozzles.

2. This action heats the water to liberate most of the dissolved gases.3. This flows down through water seals for distribution over the tray

bank, which serve two functions.4. First they prevent gases liberated in the initiate heating, from

entering the tray bank.5. Second they direct the steam to flow down through the trays,

before entering the upper heating section.6. The main function of the tray bank is to remove the remaining

amounts of dissolved gases, not liberated in the initial heating.

Parallel Down Flow

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7. Since very little, or no heating takes place in the trays, the entirevolume of steam is used to scrub out the remaining gases.

8. The trays are slotted, and provide a great amount of spillingedge.

9. This allows for a great amount of water surface area to beexposed to the steam.

10.Water and steam flow downward through the trays.11.The steam, after exiting the tray bank, steam is condensed by

the colder inlet water, and a small amount is vented toatmosphere, along with the dissolved gases.

Parallel Down Flow

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Packed Column Type

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1. Inlet water is sprayed into a steam atmosphere through avariable orifice & spring loaded spray nozzle.

2. water heating liberate dissolved gases & heated waterflows down onto a distribution plate, which evenlydistributes the water over the entire cross-sectional areaof the tower packing.

3. As the water flows down through the distribution plate itenters a steam chest area, where it is further heated byup flowing steam and more of the dissolved gases areliberated.

Packed Tower

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1. Remaining dissolved gases are removed when the waterflows down from the steam chest and then down throughthe packing tower.

2. The packing tower exposes a greater surface area of thewater; while up flowing steam completes the deaerationprocess. The water leaving the bottom of the packingtower is given a final scrubbing of steam.

3. The steam, entering the deaerator from below the packingtower, is introduced through a fixed orifice steamdistributor. This steam distributor directs high velocitysteam through the down flowing water leaving the bottomof the packing tower.

Packed Tower

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Deaerator Functions

Deaerator has to meet following needs.

It does deaeration

Acts as a feed water heater.

Acts as a storage tank (reservoir)

Accept the leak-off flows from the BFP.

Accept the H.P. Heater drains.

Heat the tank content from cold to providehot deaerated water for unit start-up.

Ensure NPSH for BFP

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DEAERATING RATIO

O2 Content in Condensate at

inlet to deaerator= 6

O2 Content in feed water at outlet S.T.

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TECHNICAL PARTICULARS OF DEAERATOR

1. Type Tray with external vent condenser

2. Design Pressure Kg/cm2 7.4

3. Design Temperature OC 250

4. Hydraulic Test Pressure Kg/cm2 11.1

5. Storage capacity M3 90

6. No. of perforated trays 5

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Operating Conditions of Deaerator

Temperature of deaerated water must be equal tosaturation temp. of water corresponding to thepressure at which deaerator operates.

Sufficient heating steam must be delivered to thedeaerator to ensure continuous boiling of waterundergoing deaeration.

The feed water charge to deaerator must bedisintegrated into fine droplets to ensure better heat –transfer

Deaerator must be provided with sufficient venting topurge all the non-condensing gases out of the systemand to ensure minimum partial Pressure of these gasesin the upper part of the deaerator.

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Causes of High O2/CO2 Concentration

Inadequate deaerator vent leading to accumulation ofnon-condensing gases and increase in their partialpressure.

High feed-water flow rate.

Delivery of O2 - containing condensate directly intothe storage tank.

Frequent pressure drop in the deaerator.

Faulty deaerator internals.

Delivery of relatively “cold” flows with higher O2 -content to deaerator.

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While the most efficient mechanical deaeratorsreduce oxygen to very low levels (.005cc/l or 5ppb), even trace amounts of oxygen may causecorrosion damage to a system. Consequently,good operating practice requires removal of thattrace oxygen with a chemical oxygen scavengersuch as sodium sulfite or hydrazine.

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Chemical Deaeration

The addition of an oxygen scavenging chemical (Sodium Sulphite or Hydrazine) will remove the remaining oxygen and prevent corrosion.

Na2SO3 + O2 = Na2SO4

Sodium Sulphite Oxygen Sodium Sulphate

Now obsolete, as it increases the total dissolved solids.

Modern Practice: Hydrazine is used for chemical Deaeration.

N2H4 + O2 = N2 + 2H2O

3N2H4 = 4NH3 + N2

Additional ammonia reacts with

2NH3 + CO2 + H2O = (NH4)2CO3

(acidic) Ammonium Carbonate (Neutral)

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FST - Deaerator

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Disadvantages of Counter Flow Deaerators

• Inability to deliver 0.007 ppb outlet quality in applications with alow inlet water temperature, or when 100% make-up isrequired.

• Low tray loading. This reduces the flow rating for a givendiameter deaerator vs. a parallel down flow unit.

• High vent rate. This reduces operating efficiency

Advantages of Counter Flow Deaerators

• The counter flow deaerator is cheaper to manufacture.

• The higher capacity and the ability to perform under varying steamand water conditions make the parallel down flow (and packedtower for smaller applications) design competitive, and the onlylogical choice.

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Disadvantages of Atomizer Deaerators

• Inability to deliver 7 ppb outlet quality when plant conditionsvary from design specifications. Requires constant plantconditions.

• Failure rate of the atomizer valve, and maintenance required tokeep it operating properly.

Advantages of Atomizer Deaerators

• 1. Low cost

• 2. Low overall height

The atomizer type deaerator is only effective when applied to an application with no plant or process swings. Along with the maintenance required, this type deaerator, while inexpensive, has only limited applications.

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Disadvantages of Parallel Down Flow

• More complicated design, resulting in slightly higher cost.

Advantages of Parallel Down Flow

• Time proven design

• Thousands of installations worldwide

• Design suitable for small to medium size plants

• Can meet outlet guarantees at varying plant conditions.

• High tray loading, resulting in higher outlet capacity for anygiven diameter.

• Large tray spilling edge, resulting in high deaerating efficiency

• Low vent rate, resulting in increased operating efficiency.

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Disadvantages of Packed tower

• Height requirement

• Typically considered for small size plants.

Advantages of Packed tower

• Low cost

• Low maintenance

• Ability to handle varying plant conditions

• This design can meet the requirements for a reliabledeaerator capable of producing completely deaeratedwater for small plants. Packed tower design includesmulti-stage deaeration, to deliver top performance.

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CORROSION is defined as the destruction of a metal by chemical orelectromechanical reaction with its environment. Corrosion dramaticallyincreases maintenance costs and can cause unnecessary safety risks. It willoccur when levels of oxygen or carbon dioxide are high, where pH values arelow, where contact occurs between dissimilar metals and in corrosiveatmospheres. Corrosion is an electrochemical process in which electricity flowsthrough a solution of ions between areas of metal. Deterioration occurs whenthe current leaves the negatively charged metal or anode and travels throughthe solution to the positively charged metal or cathode, completing anelectrical circuit in much the same manner as a battery cell. The anode and thecathode can be different metals or areas of the same metal. Corrosion occurswhen there is a difference in the electrical potential between them.

SCALE is a very hard substance that adheres directly to heating surfacesforming a layer of insulation. This layer of insulation will decrease heat transferefficiency. Scale also results in metal fatigue/failure from overheating, energywaste, high maintenance costs and unnecessary safety risks. A one-sixteenthinch thickness of scale in a fire tube boiler can result in a 12.5% increase in fuelconsumption.

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FOULING occurs when a restriction develops in piping and equipmentpassageways and results in inefficient water flow. The fouling of boiler roomequipment directly impacts energy efficiencies and cost of operations.

FOAMING is a condition in which concentrations of soluble salts, aggravatedby grease, suspended solids or organic matter, create frothy bubbles or foamin the steam space of a boiler. When these bubbles collapse it creates aliquid that is carried over into the steam system. Foaming degrades steamquality and in some cases can create a water slug that is discharged into thesteam lines.

CAUSTIC GAUGING will occur when there is a high concentration of alkalinesalts (a pH value of 11 or greater) that will liberate hydrogen absorbed bythe iron in the steel. It will be more evident in high temperature areas of theboiler's waterside and manifests itself in the form of hairline cracks.

HYDROGEN EMBRITTLEMENT occurs in the event of lower pH value of thewater in evaporator

Thank you

Aprds system

Engineering