topic 4 - boiler operations & maintenance (new update)

7/30/2019 Topic 4 - Boiler Operations & Maintenance (New Update)

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TOPIC 4

4.1 FEEDWATER TREATMENT

4.2 OPERATION4.3 IMPURITIES

4.4 MAINTENANCE

1



BOILER FEED WATER TREATMENT

Boiler feed water treatment = the process by which

suspended and dissolved solids are removedClean condensate and demineralized makeup water

are de-aerated in order to supply boiler feed water

(BFW) to multiple BFW pumps

2 or 3 pumps are used in the boiler operation

Primary pump has 1 or 2 backup pumps that placed

in standby mode

Common boiler water problems:

Foaming

Deposit – tube failure

Corrosion



BOILER FEED WATER



FOAMING

1. Highconcentrations

of dissolved

solids in boiler

water cause

foaming of the

water withinthe boiler

2. Foaming

produces

carryover of

impurities in

the steam &cause deposits

on the turbine

wheels

CORROSSION

1. A complex electrochemicalreaction attack a large or a small

pinpoint area

2. Associated with the reaction of

oxygen with metal & also

contribute by pH, chemical

compounds & others3. Occur when BFW has excess

acidity/alkalinity, high level of O2

and CO2, high temp / high level

of ammonia /sulfur-bearing gases

4. Prevention: maintaining pH

levels in boiler feed water,removing dissolved O2 from

water, use chemical treatment, &

following established out-of-

service & blow-down procedures

DEPOSIT

1. High temp cause

impurities

precipitate &

adhere to the hot

metal surfaces of

the boiler, forming

scale (layer)2. Dissolved

bicarbonate of

calcium &

magnesium break

down & form

insolublecarbonates cause

deposit – tube

failure

3. Carbonate D,

phosphate D,

sulfate deposit &etc

BOILER WATER PROBLEMS



WATER TREATMENT IN BOILER

External Internal

Takes place

before raw water

enters the boiler

Complements the

external process

and helps protectthe internal

components of the

boiler system

Primary location water treatment is at boiler

Common tests on boiler feed water includepH and the presence of particulate matter (measured in ppm), iron, oil and silica



De-aerator – device used to remove air from

water Located at the end of the condensate return header &used as primary boiler feed source

In BFW treatment – Designed to remove

Dissolved Oxygen by heating the water withsteam cause Dissolved O2 leads to boiler corrosion

2 types :

Spray de-aerator :- inject steam directly into the water Tray de-aerator :- steam enters at the bottom & water

enters at the top. Water drops over a series of sievetrays (provide good contact between liquid & heatedvapor

De-aeration



Term used to describe the process in which

water is removed from the boiler system As suspended solids concentrate in the water,

chemical treatment reaches a point at which it isno longer effective. So removal of a portion of the treated water is necessary.

Is depends upon the amount of suspended solidthe boiler can handle (5-10% of total capacity)

Blow-down is controlled through an instrumentdesigned to measure the electric conductivity of the water

Blow-down ports are - located on the bottom of the boiler so accumulated sludge can beremoved

Blow-Down



Physical Properties Of Water

In purest form is colorless, odorless, and tasteless

The only organic substance – occurs in 3 states at atm temp range: ice

(solid), steam (gas), water (liquid)

Boils at 212°F (100°C) at atm pressure

Increase Pressure – boiling point rise

It takes 1 British thermal unit (Btu) to raise the temp of 1 pound (lb) of water one degree Fahrenheit (°F).

It takes 970 Btu to change 1 pound of water to steam

This heat energy (latent heat of vaporization) is stored in the steam &

when it condenses, the energy is given off

Thus much of the heat from burning fuel can be absorbed by boiler

water, transported with the steam, & released at the points of use

E.g: 1 lb of boiler feed water at 72°F requires 140 Btu to reach 212°F &

additional 970 Btu to change to steam. A total of 1,110 Btu is stored in

the steam

BOILER MEDIUM



Steam generators / boilers

–

used to producesteam

Boilers use a combination of radiant,

conductive and convective heat transfer

methods to change water to steam

Steam is used to operate:

steam turbines, distillation systems, and reaction

systems

provide cooling or heating to process equipment

BOILER BASIC OPERATION



SIMPLE BOILER

Consists of :

heat source water-containing drum

water inlet

steam outlet

Operations : As heat is added to the drum, the temp

increases until the water boils

As the steam rises, it is captured in aline & sent on for further processing

Factors that effect boiler operations: density difference for internal circulation

Pressure

temperature

water level



More complicated boiler (modified shell

and tube heat exchanger)

Heat is transferred to the fluid medium Composed of a shell and a series of

tubes designed to transfer heat from the

fire tubes (waste gases pass through) &

into boiler feed water

Combustion gases exit through a

chamber similar to an exchanger head &pass out of the boiler

The water level in the boiler shell ismaintained above the tubes to protectthem from over heating

Heat is transferred from within the tube to

the surrounding fluid Components: boiler shell with feed inlet &

outlet connections, fire tubes, acombustion tube, burner, feed water inlet, steam outlet, combustion gasexhaust port and tube sheets

FIRE TUBE BOILER



Consists an upper & lower drum

connected by tubes

Lower drum & water tube –

filledcompletely with water, the upper drum

only partially full

This arrangement allows steam to pass

through mechanical separators in the

upper drum, flow to a superheater sectionand exit the boiler

As heat is applied to the boiler firebox,

water flows from the upper drum through

downcomers into the lower drum

Tubes, called risers, cause water and

steam to flow into the upper drum

because of density differences

WATER TUBE BOILER



Operates under the principal of differential

density

When a fluid is heated, it expands andbecomes less dense

Cooler water flows from the upper drum

through the downcomers to the lower drum

and then rises as some steam is generated

Circulation continues and make up water isadded to the upper drum to replace the

steam that is generated

Circulation continues because steam bubbles

in lower drum move up the riser tubes &

cause the density of the water to decrease

The cooler water in the downcomer flow into

mud drum

Steam move up the riser & steam generating

tube & into the upper steam generating drum

Boiler Water Circulation

Steam and water drum circulation



MainComponents

of Boiler

Furnace

Tubes

Drums Gas and oil

burners

Economisizer

section



Boiler start

upprocedures

Fill the steam

drum withwater to thenormal level

Start the

fan

Purge thefurnace

Check furnacefor percentage

of flammables Light theburners

Bring theboiler up topressure

Place the

boiler online



As steam flows from the boiler to the plant, it begins to cool & formed

condensate

Condensate cause problems as it flows with the steam

Slugs of water can damage equipment and lead to a condition known

as water hammer

Device known as steam traps are used to remove condensate.

Steam traps are grouped into 2 categories: Mechanical

Thermostatic.

Mechanical steam traps include :

inverted buckets

floats

Thermostatic traps include

bellows-type traps

Steam System

I t d B k t St T



Inverted Bucket Steam Traps • Use to remove condensate from steam and return it

to a condensate header

• The position of the bucket determines whether the

valve is open or shut

• An air vent & outlet valve is located on the top of

the bucket & Gases escape through this hole and

into the outlet line

• Bucket in the lower position – valve is open

• Bucket in the upper position – the valve is closed

• Operation:

– the steam enters the bottom of the trap via the inlet and fills the inverted

bucket

– Condensate in the steam drops to the bottom of the inverted bucket, and

gases escape out the vent

– When the body of the bucket trap is full of condensate, the inverted bucket

rests on the bottom & the outlet valve on the top in the open position

–

As steam fills the inverted bucket, it rises and valve closes

Fl t St T



Float-type traps have a float that rests on the top of the condensate A rod to the outlet valve attaches the float. The position of the float

determines the position of the valve

As the level in the trap increases, the float lifts, allowing condensate to flow

Components:

A body,

An inlet & outlet

A bonnet

A float

A rod

A valve

Float Steam Traps

B ll Th t ti St T



One of the popular steam traps is the thermostatic steam trap because itcheaper and selected more frequently than other type

This type of trap responds to the temperature differences between

condensate and steam

Operation:

steam enters the bottom of the trap and comes into contact with the bellows

Condensate causes the bellows to contract and open. Steam causes the bellows to

expand and close

Bellows trap can handle condensate & noncondensable gases

Bellows Thermostatic Steam Traps

topic 4 - boiler operations & maintenance (new update)

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