absa 4th class b help

8/19/2019 ABSA 4th Class B Help

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Part B - Paper 1

1. A firetube boiler has been prepared for inspection, what should you look for on

the:

•Furnace entry refractory - The refractory should adequately protect the end of the tube where it is in the front smoke box section and not cooled

by water on its outside surface.

• Water side - Examine the water side through all the handhole doors for

tube pitting, scale build up, or oily deposits. Oil deposits on tubes will lead

to local overheating and failure.

• Fire tubes - Examine the inside of the tubes with a flashlight for signs of

moisture due to thinning and pitting of the tube from the water side

corrosion.

2. !plain the ad"anta#es of firin# pul"eri$ed coal o"er other %ethods of firin#

coal.

Low grade lignite and subbituminous coals can be burned satisfactorily.

!etter mixing of the coal fuel and combustion air, therefore less excess air needed.

"uperior combustion control.

&a%e three types of pul"eri$ers.

#oll $ill, !owl $ill, !all #ace $ill, Tube Type !all $ill

'. !plain how you would replace a broken #au#e #lass.

%. &solate gage glass

'. Open gage glass drain valve.

(. )nscrew the nuts and remove the broken gage glass and washers.

*. Open gage valves to blow out any fragments of glass. +lose valves.

. +ut new glass to length using glass tube cutter.

-. lace nuts and new washers on gage glass and install into position. /and tighten.

0. 1arm up glass by cracking steam valve. +lose drain valve.

2. +rack open water valve. 1hen water level in glass stabili3es open steam andwater valves fully.

What is the purpose of a water colu%n and #au#e #lass(

To accurately indicate the level of water in the boiler to the boiler operator.The water column dampens level fluctuations, collects sediment, and provides a place

for the try cocks.


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). *ou are in char#e of a lar#e #as fired power boiler with a superheater and

reheater, auto%atic co%bustion control, and a forced draft fan. !plain what

you would do and the reasons why it could happen if:

•

+here is a fla%e failure - +auses of flame failure could be interruptedfuel supply, tripped by another safety device 4i.e. low water, high pressure, etc5,

faulty combustion controls.

The fuel supply to the burner should be shut off immediately, and the furnace

purged. &nvestigate cause of flame failure to determine length of outage. Take careof steam supplied devices 4turbines, processes, etc5 accordingly.

• +here is a low dru% water le"el +auses of low water level could be

faulty water column6gage glass, tube leak, faulty feedwater controller, faulty

pump, blocked feedwater pipe 4valve closed5, &!7 valves open, sudden stop in

steam demand 4shrinkage5.8irst prove proper gage glass indication, if water level proves low, immediately

shutdown the burner and investigate cause. Take care of steam supplied devices

4turbines, processes, etc5 accordingly.

. escribe a eolite /oftener and what it does.

The sodium 3eolite softener uses ion exchange to convert scaleforming salts, in thewater, to nonscale forming salts. The 3eolite in the softener removes calcium and

magnesium cations from the water and replaces them with sodium cations. 1hen the

3eolite has given up all its sodium cations it is regenerated.

What do you watch for durin# nor%al operation(

7uring normal operation the water leaving the softener should be tested regularly toensure all the hardness is removed from the water. &f hardness is detected, then the

3eolite bed is exhausted and needs to be regenerated.


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0. /ketch a block dia#ra% of a low pressure return line trap heatin# syste%

What is the use of the trap(

The return trap is used to force condensate back into the boiler using steam pressure.

This allows the boiler to be operated up to %99 ka without requiring an equivalentstatic head to force the condensate back into the boiler.


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. Weldin# efinitions:

%5 Bra$e - 1here a weld :oint is produced by heating to above *(9o+ and by

using a nonferrous filler metal, which has a melting point below that of the

metals being bra3ed together.

'5 Flu! - "ubstance used to prevent or remove oxides and impurities from the bra3e weld, or blacksmiths weld.

(5 Porosity - ;as pockets or voids trapped in the weld during the welding

process

*5 oated lectrode - +overed electrode consisting of a rod with heavy or light

covering to protect the molten material from the atmosphere and to stabili3e the

arc.

5 /la# 3nclusion - 5 Wea"e Bead - = weld bead made with transverse oscillation of the rod

%95 5ndercut - = groove melted into the plate at the toe or side of the weld

%%5 +oe crack - = crack in the plate at the edge of the weld

%'5 6!y-acetylene uttin# - =n oxygencutting process wherein the cutting ofmetal is caused by the chemical reaction of oxygen with the base metal at high

temperatures. /igh temps created by burning acetylene with oxygen.

%(5 /hielded 4etal Arc Weldin# - "hielding of the weld from the atmosphere is

obtained from the decomposition of the electrode covering, due to the heat of

welding.

%*5 Preheatin# - /eating the base metal immediately before welding to slow thecooling rate of the weld and prevent cracking


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%5 7esidual /tress - "tress remaining in a structure, as a result of welding

%-5 /patter - $etal particles sprayed out during electric resistance welding

8. /ketch and describe a 4a#netic 9ow Water Fuel utoff /witch.

=t normal water levels, the permanent magnet attached to the pivoted mercury switchis drawn toward the magnetic plunger. This causes the mercury switch to tilt to the

right and the mercury inside closes the burner on circuit. 1hen the water level dropsto the point that the magnetic plunger is no longer in the permanent magnets magnetic

field, the tension spring pulls the magnet away from the tube and causes the mercury

switch to tilt to the left. The mercury inside the switch moves to the left side thusopening the burner circuit, closing the alarm circuit and shutting off the gas supply.

!plain 2 wire and ' wire confi#uration, and the operation of the %ercury

switch.

= ' wire mercury switch and a ( wire mercury switch are used on a combination low

water cutoff and pump control device. The ( wire switch is the low water cutoff,

used to interrupt the burner circuit and close an alarm circuit. The ' wire switch is

used to start and stop the boiler feed pump to compensate for fluctuating water levels.

The mercury switch is a small glass bulb under vacuum which contains a small

amount of mercury. +ontacts are mounted inside the bulb on one or both ends. These


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contacts are connected to external wiring and circuits. 1hen the bulb tilts from one

side to the other the mercury inside opens and closes the circuits as it moves back and

forth.


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. /ketch and describe 2 le%ent Feedwater ontrol, and e!plain its ad"anta#es

o"er 1 ele%ent control.

The advantage of a ' element feedwater control is that the added steam flow sensorallows the effects of swell and shrinkage to be minimi3ed. 1hen an increase in steam

demand is reali3ed the steam flow sensor overrides the drum level sensor and the

controller increases the feedwater flow to the drum. +onversely when a decrease insteam demand is reali3ed the steam flow sensor causes the controller to decrease

feedwater flow to the drum. 1hen steam demand is stabili3ed, the drum level sensor

takes over again to make the final ad:ustments on drum level.


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1;. !plain the operation and way of testin# the followin#:

•


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11. escribe the procedure for takin# a water tube boiler off line and preparin# it

for inspection and the safety precautions in"ol"ed.

%5 To properly shut down the boiler the load is reduced to 9? and the sootblowersare operated to clean the fireside surfaces as much as possible. 8iring rate is reduced

to minimum and the controls are set to hand control. The boiler is then shut off.

'5 Once the boiler has cooled slowly with air dampers shut and the pressure has

dropped to 09 ka, open the drum vents.

(5 The boiler is now isolated by closing and locking all valves and opening and

locking all circuit breakers which may allow any gas, liquid, or solid to enter the

boiler, or could cause motion of equipment within the boiler. =ll the valves and

breakers isolated and locked are now tagged with @7O 9

o

+, open the blowdown valves anddrain the boiler.

5 Open the steam drum manhole first, then the mud drum manhole. This is to

prevent the steam drum fro pressuri3ing due to the circulating effect.

-5 1ith the blowdown valves wide open, flush out the boiler with a high pressure

water hose. =llow to drain completely then close and tag out the blowdown valves.

05 Open the fireside access door.

25 rovide E where necessary, and ensure any electrical power used within the

boiler is transformed to %'A to eliminate the danger of electrocution to personnel.

12. escribe the startup procedure for a #as fired firetube packa#ed boiler that has

been shut down for the su%%er.

%5 +heck inspection certificate and maintenance record for recent repairs.

'5 7o a walk around the boiler, checking for water leaks and cleanliness of boiler

area.

(5 +heck gauge glass for proper water level and confirm using try cocks. Ensure

water column and gauge glass valves are fully open and drains closed.*5 Ensure air vent is open.

5 Open the steam line drains and open the header steam valve and then open the

nonreturn valve.

-5 Ensure the safety valves are sealed and not tampered with.


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05 Open the main gas cock at the furnace front, ensuring the handle is pointed

correctly in line with the hole in the valve plug.

25 Open the pilot gas cock. Observe pilot and main gas pressure regulators, limitswitches, gas line valves, etc

>5 +heck for correct position of the feed pump valves, condensate return valves,makeup valves, etc. open the feedwater inlet valve on the boiler. +heck and

replenish chemicals for feedwater as required.

%95 Observe the Bhigh steam pressure fuel cutoff@ setting and the Bsteam pressurecontrol@ settings

%%5 +heck that the cable is connected from the ignition transformer to the igniter

plug, and that the flame scanner is in place

%'5 +heck the connection of the sensing line from the forced air chamber to the

low air pressure fuel cutoff switch. Ensure air inlet screen is free of debris

%(5 +heck that the Bboiler start@ switch is in the off position, then close the feed

pump breaker and boiler main power breaker

%*5 =ctuate the boiler start switch, if boiler does not start reset all the safety

switches low water, high gas, low gas, etc

%5 Once the boiler is firing and steam starts to blow, close the air vent

%-5 !low down the water column and gage glass

%05 Once the boiler is up to 0? normal working pressure, operate the safetyvalve try lever for one short blow and one long blow to ensure it reseats

properly

%25 erform a test on the lowwater fuel cutoff switch. The burner should shut

down with % inch showing on the gage glass. !lowdown the low water cutoff drain to clear any sediment. Once boiler feedwater pump is reenergi3ed,

observe the drum level control shuts off the pump at about half glass.

%>5 Once the boiler and steam lines are fully warmed up, close any drains that are

not controlled by a steam trap.

'95 +heck that the boiler handhole and manhole doors are tight

'%5 Observe the condition of the flame, should appear blue. +heck the stack gas

temperature.

''5 +heck and tighten up any gland leaks showing on the valves

'(5 Enter startup time, on header time, and chemicals added in log book

'*5 Take a boiler water sample to ensure it is within proper limits as to chemical

content.


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1'. escribe the procedures for startin# an F fan on a hi#h pressure boiler.

%5 +heck the fan and driver area as well as the inlet screens for debris.

'5 erform a thorough visual inspection of fan and driver components.

(5 +heck the dampers and damper drive connections for tightness

*5 +heck the oil in the fan and driver bearings, fill or change oil if needed

5 Turn on cooling water to bearings.

-5 "tart fan, listen for any unusual noises, and check for vibrations of fan casing and bearings. Look for any oil leaks. Once fan has ran for a while check bearings for

temperature.

=i"e 2 reasons why an 3 fan is lar#er than an F fan.

%5 The &7 fan removes more mass because the flue gas consists of the mass of the

fuel plus the mass of the air.

'5 The volume of the gases is larger due to the temperature difference

(5 The &7 fan handles any leakage into the boiler setting.

iscuss routine inspections on F fans.

%5 Look for leaks of oil, water, and air. Look for any unusual condition

'5 Listen for unusual noises, note any unusual smells like hot bearings, motor

shorts, leakage of gases, etc

(5 +heck oil levels and rotation of bearing oil rings. +heck bearing temperature

and vibrations*5 +heck fan and driver indicators like vibration, temp, pressures, etc

5 ;enerally look for any unusual condition, a change normally indicates

problems

1). Why is it i%portant that the stea% lea"in# a stea% dru% be dry(

=ll moisture must be removed from the steam to prevent any impurities being carried

over with the steam. These impurities will form deposits in the superheater tubes andoverheating of these tubes will result. =lso if a steam turbine is used these impurities

will form deposits on the blades and turbine control valves and cause damage.

!plain why on so%e hi#h pressure boilers feedwater is sprayed into the stea%

before it lea"es the stea% dru%.

This causes a portion of the leaving steam to condense. The condensate formed

absorbs any gaseous impurities present in the remainder of the steam.


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escribe 2 %ethods of re%o"in# %oisture fro% the stea% in the dru%.

%5 +yclone type separator causes the steam to acquire a whirling motion and

the moisture droplets are thrown out of the steam by centrifugal force.

'5 "crubber type separator consists of a number of closely spaced corrugated

plates between which the steam passes with the moisture droplets depositingupon the plates.

1. /ketch and describe a >olute centrifu#al pu%p and a iffuser centrifu#al pu%p.

= volute pump consists of an impeller made up of a number of vanes, which rotates in

a volute stationary casing. The volute casing is one that increases in crosssectionalarea from the impeller to the outlet. Liquid is drawn into the center of the impeller

and by centrifugal force is accelerated to a high velocity and discharged into thecasing. =s the liquid travels through the volute casing the velocity energy is convertedto pressure energy. = low pressure area is created at the impeller eye as the liquid is

forced outward, thereby drawing in more liquid and creating a constant flow.

= diffuser pump consists of an impeller like the volute pump, but also has a stationary

diffuser ring. =s the high velocity liquid leaves the impeller by centrifugal force it

passes through the diffuser vanes. The diffuser vanes gradually increase in area andconvert the fluids velocity energy into pressure energy. The fluid is then discharged

into the casing. "ome diffuser pumps have a volute casing as well which serves to

increase the pressure even further.

escribe two ways to stop end thrust.

7ouble inlet impeller balances the forces on the impeller, although a light thrust

bearing is still required.

Opposing singleinlet impellers used on multistage pumps with single inlet

impellers. The inlets of one half of the impellers face one direction and the other halfface the other direction thereby counteracting each others axial thrust.


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10. /ketch and describe different rotary pu%ps.

External gear pump two gears rotate in opposite direction inside the casing. Liquid

is drawn in and trapped between the teeth and the casing as it travels around thecasing and is discharged out the inlet.

&nternal gear pump an external cut gear meshes with an internal cut gear on one sideand is separated by a crescent shaped partition on the other to prevent liquid from

passing back to the suction. Liquid fills the spaces between the teeth as they unmesh,

and is forced out the discharge when they mesh again.

"liding vane pump has an off center mounted rotor with slots containing sliding

vanes. The vanes are forced out by centrifugal force to seal against the casing wall. =s

the fluid is drawn in due to the increasing area of the rotor to the casing, it is trapped by the vanes and carried around to the discharge where the rotorcasing area is

reduced thereby forcing the liquid out the discharge.

Three lobe pump same as external gear pump only lobes instead of gears

Two screw pump has two opposing spiral rotors. Liquid is carried from the inlet to

the discharge as the spirals rotate and mesh.


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1. /ketch a stea% dru% showin# all internals and flows.

escribe the flow of stea% and water in the dru%.

The steam6water mixture from the risers enters the drum behind a baffle and thenenters the cyclone separator at the side. The water, thrown out by centrifugal force,

drains from the bottom of the cyclone below the drum water level. The steam leaves

the top of the cyclone and passes through the chevron drier to remove any residualmoisture, before leaving the drum.

8eedwater enters through the feedwater distribution pipe or pipes which run thelength of the drum for uniform distribution. The water makes up the drum level and is

used as needed by the boiler as the water circulates down the downcomers and to the

generating tubes.


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18. What are the types of bladin# on an F and 3 fan(

%5 =irfoil 87

'5 !ackwardcurved 87(5 "traight radial &7

*5 #adial tip &7

5 8orward curved &7

escribe ' %ethods of fan output control.

%5 &nlet damper control using inlet vanes to control the airflow through the fan.

'5 Outlet damper control throttling the airflow from the fan

(5 Aariable speed control varying the driver speed through variable frequency

drives or by using fluid drives, magnetic couplings, or steam turbines

/ketch a balanced draft boiler

!alanced draft boiler


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1. 9ist reasons for black s%oke.

Too much fuel supplied


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2;.


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21. What are the ad"anta#es and disad"anta#es of hot water heatin# co%pared with

stea% heatin#(

=dvantagesC

• !oiler and piping is smaller

• iping pitch or slope not as critical

• +hanging system temperature more easily

• Less maintenance costs

7isadvantagesC

• $ust run at higher pressures in multistory buildings if boiler in basement

• $ore power required to circulate the water

• ;reater danger of damage due to free3ing

• $ore damage caused if leak develops

What are 2 different types of heatin# syste% control(

&ntermittent circulation method and +ontinuous circulation method, described below.

What are the differences between continuous and inter%ittent flow syste%s(

&ntermittent +irculation This method keeps the boiler water temperature at a

constant value by an immersion thermostat 4aquastat5 which controls the operation of

the burner. The circulator is controlled by a thermostat located in the heated 3one.

1hen the air temperature drops below the desired setting, the thermostat starts thecirc pump thus supplying hot water to the convectors. Once desired temperature us

reached the thermostat shuts off the pump.

+ontinuous +irculation This method keeps the circulation constant, and the

thermostat controls the temperature of the supply water by manipulating burner

operation.


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22. Pu%p efinitions:

%5 /tatic /uction 9ift - The vertical distance from the liquid supply level tothe pump centre line when the pump is above the supply source.

'5 /tatic /uction


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%*5 &et Positi"e /uction


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2. efine ) ad"anta#es and 2 disad"anta#es of %echanical draft co%pared to

natural draft.

=dvantagesC

%5 !etter control of airflow

'5 =llows use of superheaters, economi3ers, and air heaters, increased efficiency

(5 "maller less expensive stack can be used

*5 !etter fuel6air mixing, higher heat output per si3e of furnace

5 !etter purging of furnace, safer operation

-5 7raft produced independent of atmospheric conditions

7isadvantagesC

%5 &nitial cost higher

'5 +loser supervision necessary, more mechanical equipment involved

(5 $ore unit outages because of equipment breakdowns.

9ist ' factors which influence the power reCuired to dri"e a fan.

%5 The amount of air or gas to be moved in a unit time

'5 The pressure difference across the fan

(5 The efficiency of the fan and its drive

!plain why perfor%ance cur"es are reCuired for fans.

= performance curve is required in selecting a fan for any purpose since each fan has

its own performance curve which defines exactly how the machine will perform.

What ) Cuantities are shown on a typical fan perfor%ance cur"e chart(

%5 Efficiency

'5 ower

(5 ressure

*5 capacity


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20. escribe the correct procedure for startin# up a balanced draft, #as-fired water-

tube boiler and put it on line with a battery of boilers already in ser"ice.

%5 erform prechecks on boiler and auxiliary equipment. This includes watersample, deaerator level, stroking all control valves, 87 and &7 fan checks and

proper damper control, fuel pressure, make sure drum vent is open and all

permissives are met.

'5 "tart &7 fan then 87 fan

(5 repurge the furnace

*5 #educe air flow and light the pilot

5 Light main burner and ensure a stable flame

-5 eep flame low to provide for a slow controlled warmup, may test L18+O

05 Once steam emits from the vent, close vent

25 =s the boiler starts to build pressure warm up the steam line between the main

stop and the header. This is done by opening the drain at the main stop andcracking open the header valve to allow the header steam to flow back to themain stop and out the drain. "lowly open the header valve wide open once the

pressure has equali3ed between the header and steam line.

>5 Once boiler pressure is slightly below header pressure back of the main stop

spindle about F the way.

%95 Once boiler pressure exceeds header pressure and the disc piston opens,slowly open the main stop the rest of the way and close the drain. The boiler is

now on line.

escribe the correct procedure for takin# this boiler out of ser"ice.

%5 ;ive the boiler a good blowdown

'5 ut controls in hand and slowly reduce firing rate. Ensure other boilers on theheader take up the required load. $ain stop will close once header pressure

exceeds boiler pressure.

(5 Once firing rate is reduced to minimum, shut off the main fuel or test L18+O

to trip the boiler.

*5 =llow the fans to post purge for the determined time then shut down the 87fan then the &7 fan.

5 +lose the header stop valve

-5 Open drum vent once boiler pressure drops to slightly above atmospheric to

prevent a vacuum forming in the drum. !oiler is now shutdown.


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2. efine the followin# boiler repair ter%s:

• Arrow head bit - +utter bit with arrow shaped cutting edges for drilling out

plugged or heavily scaled, straight, heat exchanger tubes.

• 6"er rollin# - Excessive tube expanding work hardens tube metal, causes

flaking and induces stress fatigue. "hortens tube life. The expanded part of thetube is beyond the drum thickness.

• +ube bellin# - 8laring of a tube end.

• ontrolled rollin# - Expanding tubes utili3ing a portable motor that will

sense torque and stop rotation of an expander when a specified torque or tightness of the tube is reached.

•

6yster knife - = chisel shaped tool operated by impact. )sed to collapse a boiler tube inward by being forced between the tube end and the drum.

• Wall reduction - The thinning of a tube wall when tube expanding.

• Fish tail - 4whips5 8lexible wire type of holder used between the motor and

cleaning accessory.

• 7attler ?"ibrator@ - = device rotated by an air motor that causes vibration

inside the firetubes to remove the external scale from the tubes.

• 3nsert - "hort length of tube, inserted into an end of an air preheater tube to

attempt the salvage of the unit without complete tube replacement.

• /erratin# tool - = tool for cutting grooves or serrations on the inside of a tube

sheet hole.

28. escribe the principle of operation of 2 types of auto%atic air "ents used on hot

water heatin# syste%s.

%. 8loat operated air vent with water present in the vent body the float will hold the

vent valve shut. 1hen air enters the vent body the water level drops and the float

drops thus opening the vent valve.'. /ygroscopic disc vent when water is in contact with the disc it will swell and

seal off the air vent. 1hen air enters the vent, the disc will dry out and shrink thus

opening the vent port.


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With the aid of a sketch, describe the operation of a diaphra#% air "ent.

The sealed cylinder attached to the needle valve is filled with a volatile fluid. 1hensteam surrounds the cylinder, the volatile liquid vapori3es and a pressure is produced

within the cylinder. This forces the diaphragm out against the stop beneath it causing

the cylinder and needle valve to rise and the port is shut off preventing steam fromescaping. 1hen air enters the vent the volatile liquid will not be vapori3ed due to the

lower temperature. This causes the diaphragm to collapse and the cylinder and needle

valve move downward opening the port to allow the air to escape.


25/53

2. +he 2 types of sootblowers are stationary and retractable. !plain where each

type is installed and e!plain why that type is selected.

"tationary soot blowers are installed in the lower temperature 3ones of the boiler suchas the economi3er and air heater sections. The temperatures do not get severe enough

in these areas to damage the sootblower if it is left in.

#etractable sootblowers are installed in the high heat areas of the boiler such as the

superheater and reheater sections and the furnace walls. The temperatures in these3ones are too high, so the sootblower must be retracted when not in use to avoid

overheating.

!plain ) precautions to be taken to ensure %a!i%u% sootblower and boiler

tube life.

%5 !oiler load is at least 9? maximum capacity so fine dust is removed quickly

'5 Ensure induced draft is increased until furnace pressure is 0 mm water gaugeabove normal. To prevent blowback through openings.

(5 7o not allow traversing or rotating sootblowers to remain in one position andimpinge directly upon tubes or baffles while discharging steam, as the steam

will erode the tubes and a leak may result.

*5 &f air is used it must be dry, if steam is used it must be superheated

escribe the procedure for %anually soot blowin# a hi#h pressure water tube

boiler burnin# pul"eri$ed coal. +he boiler is fitted with a superheater,

econo%i$er and an air heater.

%5 Ensure boiler load is at least 9? and increase induced draft so furnace

pressure is 0mm water gauge above normal. Then close isolating cocks on

draft indicators and +O' sampling points.'5 +lear all dust and ash hoppers

(5 Open drain valve on main steam supply header to remove any condensate

*5 +rack open the mainsteam supply header isolation valve, when allcondensate removed close drain and fully open isolation valve.

5 +lose all boiler inspection windows

-5 Operate each sootblower individually beginning with those nearest the bottomof the furnace and working systematically towards the rear of the boiler unit

05 Open and close the steam stop valve on each sootblower immediately before

and after the blower is used

25 $ake sure that retractable sootblowers are fully traversed into the gas pass

before opening the steam stop valve, and they are fully withdrawnimmediately after use

>5 Once soot blowing cycle has completed, close the main steam header isolationvalve

%95 =d:ust draft back to normal conditions

%%5 +lear all dust and ash hoppers

%'5 Open isolation cocks for draft and +O'


26/53

';. efine the followin# water treat%ent ter%s:

• +urbidity - articles of suspended matter in water

• olloidal particles - Aery small particles of insoluble material suspended in

water

• eioni$ation - The removal of harmful ions from a solution using an ion

exchange process. =lso known as deminerali3ation

• oa#ulation - The process where finely divided particles of turbidity are

combined by chemical means into masses sufficiently large to settle out of

suspension.

• Floc - = spongy substance produced from the addition of a coagulant to water

containing particles of turbidity. The product of coagulation. The floc has a

large surface area which traps fine suspended particles in the water, thus

forming larger particles.

With the aid of a sketch, e!plain the operation of a coa#ulatin# water clarifier.

The raw water and the coagulant enter the top of the clarifier and are mixed together by agitators. =s the mixture travels down the mixing 3one of the clarifier the particles

coagulate. The coagulated particles form a sludge blanket in the bottom portion of the

upflow 3one effectively acting as a filter for the upflowing water. The clarified water is collected at the top of the upflow 3one by a collector pipe. The sludge collects in

the conical section at the bottom and is removed by periodically opening the

desludging valve.


27/53

'1. escribe the differences between two types of %echanical seals.

#otating $echanical "eal has the mating ring held stationary in the pump housing

and the sealing ring held by a shell secured by set screws to the shaft turns with theshaft.

"tationary $echanical "eal has the shell containing the sealing ring held stationary

in the pump housing and the mating ring is fastened rigidly against a shoulder to theshaft, so that it rotates with the shaft.

efine ) ad"anta#es of %echanical seals

%5 They require much less maintenance'5 They do not produce wear of the shafts or shaft sleeves as does packing

(5 They reduce leakage to a minimum

*5 They can work under very high temperatures and pressures

efine 2 disad"anta#es of %echanical seals

%5 ;reater first cost

'5 1hen seal fails, greater downtime to replace seal than packing

/ketch a %echanical seal and e!plain how it operates

= stationary mechanical seal contains springs and a sealing ring which is heldstationary in the annular space of the pump housing. The mating ring, which is

mounted to the shaft against a shoulder, rotates with the shaft. The sealing ring is

forced against the mating ring by the springs thereby preventing leakage between

them. Orings are installed between the sealing ring and the shell and the mating ringand the shaft to prevent leakage.

9ist ) causes of leakin# in %echanical seals.

%5 "eal faces are scored or grooved'5 7istortion of the rings due to unevenly tightened bolts of the seal housing

(5 Excessive pumpshaft vibration

*5 Orings or other gaskets nicked during installation

5 $isalignment of piping resulting in distortion of pump parts


28/53

'2. efine packa#ed boiler

= boiler supplied complete with burner, draft fan, feed pump, controls and other

accessories by the boiler manufacturer.

/ketch and describe a ) pass firetube boiler showin# the water le"el, flue #as

flow, water flow, and all fittin#s.


29/53

''. What is the che%ical co%position of acetylene(

>'.(? +arbon and 0.0? /ydrogen gravimetric. +'/'

What %easures are taken to enable safe stora#e of acetylene in a cylinder(

The acetylene cylinders are initially packed with a porous filler to which acetone is

added. The acetone will absorb ' times its volume of acetylene per atmosphere of

pressure. The acetylene that is dissolved into the acetone is also divided up into cellswithin the cylinder. This stabili3es the acetylene.

What is the purpose of the fusible plu# on an acetylene cylinder(

To release the combustible gases slowly instead of causing a violent exploding in the

event that a cylinder is caught up in a fire.

At nor%al te%peratures, what is the stora#e pressure of acetylene(

%099 ka

What is the difference between the threaded hose connection on an acetylene

cylinder and the threaded hose connection on an o!y#en cylinder(

The acetylene connection has left hand threads and the oxygen connection has right

hand threads

What is the stora#e pressure of o!y#en at nor%al te%peratures(

%999 ka

What is the si#nificance of the nu%ber sta%ped on an o!y-acetylene torch tip(

The number indicates the pressure in psi required from both the acetylene and the

oxygen. 8or example a number ' tip requires ' psi acetylene and ' psi oxygen


30/53

'). /ketch and describe a sin#le ele%ent feedwater control

1ith single element feedwater control a differential pressure transmitter senses a

change in head pressure in the drum due to the water level. 1hen a change in level is

detected, it is compared to the set point in the controller. &f any deviation from set

point is detected, the controller output will reposition the feedwater control valveaccordingly to compensate.

/ketch and e!plain water ha%%er

1ater hammer is a series of shocks produced by a sudden change in velocity of wateror condensate flowing through a pipeline. This can be caused by the sudden starting

and stopping of water flow. =nother way water hammer is produced is by steam being

admitted to a pipe containing water or condensate. The steam will pass above thesurface of the water and create a steam pocket behind the water. =s the steam rapidly

condenses a vacuum will be formed in the pocket. The water will rush in to fill the

void and produce water hammer.

!plain how water ha%%er is pre"ented.

To prevent water hammer, all water and condensate should be drained from any piping that steam will be admitted to. This is accomplished by the use of steam traps

and manual bypass valves to ensure positive drainage.


31/53

'0. iscuss an alkaline boil out on a watertube boiler and reasons why.

=n alkaline boil out is used to remove oil and grease type contaminants present in the

boiler after its erection or if the boiler gets contaminated during operation.

iscuss an inhibited acid cleanin# on a watertube boiler and reasons why.

&nhibited acid cleaning is used to remove scale from inside the tubes. =n inhibitor isadded to the acid to prevent or minimi3e the attack of the acid on the metal.

iscuss reasons why che%ical cleanin# is preferred in a watertube boiler.

%5 Less time and manpower required

'5 #eaches hard to reach areas

(5 !oiler can be designed with no special provisions for manual cleaning

*5 Less costly than mechanical

5 !etter quality cleaning is achieved

9ist precautions when dealin# with acid cleanin#.

%5 =ssure correct acid for the :ob

'5 !oiler isolated from steam header

(5 !rass or bron3e parts replaced with steel parts

*5 The spent solvent is safely disposed of

5 ersonnel handling the acid wear appropriate E

'. /ketch and describe wear rin#s on a centrifu#al pu%p.

1ear rings are renewable pieces of material made of a softer substance than the

impeller and pump casing. 1ear rings are placed between the impeller and the casing

to provide a sacrificial layer between them. This provides a minimal clearance between the impeller and the casing to prevent excessive leakage from the discharge

into the suction. 1ear rings are often made of bron3e or cast iron since these materials

wear in a smooth manner.


32/53

'8. escribe a wet layup and a dry layup of a boiler.

1et layup of a boiler is used when the boiler is placed in a standby condition. The

boiler is either completely or partially filled with deaerated feedwater with oxygenscavengers added to absorb any oxygen in the feedwater. = pressure slightly above

atmospheric is maintained during the storage period. &f the boiler is only partially

filled with water, the remaining space above the water is filled with an inert gas and pressuri3ed to approximately ( ka.This method is used when the boiler may be required for service on short notice. 1et

layup cannot be used if the boiler may be sub:ected to free3ing temperatures.

7ry layup of a boiler is used when the boiler will be out of service for an extended

period of time or if the boiler will be exposed to free3ing temperatures during the

standby.7ry layup involves cleaning and thoroughly drying the boiler to prevent the onset of

corrosion. The vents on the drum, superheater, and economi3er as well as other water

side vents are open to completely drain all the water from the boiler. The boiler is

then dried out by a small flame until no moisture is present at the drum vent. $oistureabsorbent material is then placed in the drum to absorb any moisture present in the

air. The boiler is then sealed up and pressuri3ed with nitrogen gas to ( ka.

'. /ketch and describe a lar#e watertube boiler ?stea% #enerator@ with a

superheater, econo%i$er and air heater.


33/53

);. iscuss the differences between:

• Anthracite coal - "hiny black, contains little or no volatile gas which makes

it hard to light off. +onsidered a smokeless fuel suitable for firing in cities.

Over >9? carbon content. Over (9 $G6kg /A. /ard to find.

• Bitu%inous coal - +ontains a fair percentage of volatile gases including

hydrogen and carbon mixtures. Easy to light off. $ost popular power plant

fuel. /A of '9 (9 $G6kg.

• 9i#nite coal - !rown in color, young, surface coal. /igh moisture and ash

content. Only used in plant is ad:acent to coal field. /A of %- $G6kg or lower.

Where are ash and sla# collected( ?' locations@

=sh and slag collects on the furnace walls, superheater section, reheater section,economi3er section and the air heater section. =ll these areas need to be sootblown to

remove the ash or slag.

iscuss the ad"anta#es of pul"eri$ed coal o"er nor%al coal for co%bustion

control.

ulveri3ed coal firing allows for a more intimate mixture of coal and air in the

furnace. This increases the efficiency and controllability of the heat release rate of thefuel.

Why is bitu%inous coal easy to li#ht off(

7ue to its high volatile gas content.

/ketch and describe a ba# house filter syste%.

= bag house system uses several filter bags, in parallel, and the principle is the sameas a vacuum cleaner. The fabric of the bags is large enough to allow the flue gas

molecules to pass through but small enough to catch the dust particles. Gets of air or a

rapper system is used to dislodge the dust particles which are carried away fordisposal.


34/53

)1. /ketch and describe a hot li%e water softener with a backwash filter syste%.

#aw water and chemicals enter the top of the softener through sprays, which

thoroughly mixes them together. "team is introduced and deaerates the incoming

water. The chemical reactions occur almost instantaneously and the compounds form

sludge. =fter about a onehour retention time the softened water is carried out throughand inverted weir to the outlet. =s the sludge collects in the bottom some of it is

discharged to waste while some is recirculated to help reduce the amount of

chemicals needed for the process. The filters are arranged to be backwashed withwater from the softener and this water is returned to the softener, after backwashing.


35/53

)2. What is weldin# flash(

/aving the eyeballs burned from the ultraviolet rays emitted by electric arc welding

What causes weldin# flash(

The contact of the ultraviolet rays from the E#1 process and unprotected eyes

What are the effects of weldin# flash and how is it treated(

1elding flash causes the eyeballs to blister and is very painful. &f medical aid is not

immediately available then castor oil may be applied to the eyes to provide

lubrication for the eyelid over the eyeball. Teabags 4used5 applied to the eyes also

give some relief. "unglasses should be worn for a few days after the flash occurs.

What safety precautions can be taken to pre"ent weldin# flash(

1ear suitable eye protection. 7ark eyeglasses for the observers, and a proper welding

helmet for the welder.

What precautions should be taken when weldin# #al"ani$ed steel or cad%iu%plated steel(

1hen welding galvani3ed or cadmium plated steel, toxic fumes are produced andshould be drawn away from the operator with adequate ventilation.


36/53

)'. /ketch and describe the operation of a pop action safety "al"e.

The valve disc is held on its seat by the pressure of the spring. &n the closed position

the pressure from the boiler acts on the area of the disk that is inside the seat area

only. 1hen boiler pressure exceeds the preset spring pressure the disc is lifted off itsseat. =s the disc lifts, the area the steam acts upon is increased thus increasing the

force on the disc. This increased force causes the valve to pop wide open. The valve

will remain open until boiler pressure has reduced sufficiently to allow the spring pressure to return to the disc to its seat.

!plain how to adEust the blowdown

!lowdown is ad:usted using the blowdown ad:ustment ring. The ring is ad:usted up or

down to vary the amount of port opening, to allow steam to escape. &f the ring is

ad:usted upwards the blowdown will be longer as less steam will flow through portand continue to act on the lip of the disc holding it open longer. &f the ring is ad:usted

downwards more steam is allowed to escape out the ports and less steam acts on the

lip of the disc and the valve closes sooner.

Why does the superheater safety "al"e pop before the boiler safety "al"e(


37/53

The superheater safety valve pops before and closes after the boiler safety valve in

order to keep a constant flow of steam through the superheater to prevent overheating.


38/53

)). 9ist the ad"anta#es and disad"anta#es of econo%i$ers.

=dvantages

%5 &ncreased boiler efficiency due to the fact that heat is recovered from the flue

gases that would otherwise be lost up the stack.'5 Less thermal shock to the steam drum from the feedwater.

7isadvantages

%5 &ncreased resistance to flue gas flow, bigger fan required

'5 &ncreased resistance to feedwater flow, bigger pump required

(5 +orrosion problems

*5 Economi3er heat surfaces must be clean for efficient operation

o%pare an econo%i$er "s. additional #eneratin# tubes for heat absorption.

Economi3ers are used instead of additional steam generating tubes because thefeedwater temperature is below the saturated steam temperature. =dditional heat is

thus recovered from the flue gas leaving the boiler to the stack.

). efine pressure e!plosion and furnace e!plosion

8urnace explosions occur when an accumulation of combustible gases ignite and

explode within the furnace 4fireside5, or gas passes of the boiler.

ressure explosions occur when a pressure part of the boiler 4waterside5 fails due tosteam pressure, or structural weakening of the metal.

9ist 0 causes of pressure e!plosions

%5 Overstressing of material due to too rapid heating up of the boiler at startup.

'5 Overheating due to low water level.

(5 Overheating due to build up of scale, sludge, or oil on heating surfaces.

*5 Overheating due to faulty water circulation in the boiler

5 1eakening of the material due to corrosion.

-5 !oiler pressure above $=1

9ist causes of furnace e!plosions

%5 8ailure to purge the furnace adequately before startup

'5 =dmission of fuel to main burner before pilot flame is established

(5 The main flame gets blown out

*5 =ttempting to light one burner off another in operation

5 =ccumulation of combustibles due to incomplete combustion


39/53

)0. escribe the test for a low water fuel cutoff switch.

The low water fuel cutoff is tested by isolating the water supply to the boiler and

draining the water from the drum. The burner should shut down when the water level

is one inch above the bottom of the gauge glass.

escribe the care and %aintenance that %ust be taken for a low water cut off(

One reason that the low water fuel cutoff may not work properly is the collection of sediment in the float chamber. To prevent this, the chamber should be blown out

regularly. =nother reason for malfunction is corrosion in the electrical contacts. This

can be prevented by a regular inspection and maintenance of the contacts. =nother

reason for malfunction could be a binding of the linkage on the float due to corrosion.roper feedwater treatment should eliminate this problem.

). /ketch and describe a ' ele%ent feedwater control syste% and its ad"anta#e o"era 2 ele%ent syste%.

= threeelement feed water control is superior to the twoelement feedwater control

because it overcomes the effect of swell and shrinkage as well as responds to

feedwater upsets by measuring feedwater flow using an orifice plate and differential

transmitter.


40/53

)8. iscuss the followin# stea% traps:

• 4echanical - made of either a ball float or a bucket float to open and close

the trap outlet valve, depending upon whether any condensate is present

within the trap body.

• +her%odyna%ic - = disk type thermodynamic trap allows condensate to flow

by the force of the condensate lifting the disk off its seat. The condensate thentravels underneath it. 1hen steam enters the trap, the steam expands and

travels at high velocity across the underside of the disk. "ome of the steam

also passes up to the small space above the disk. The steam passing at high

velocity under the disk causes a pressure reduction in that area and the steamabove the disk, being at full pressure, forces the disk down, thus closing off

the outlet of the trap.

• +her%ostatic - utili3e a bellows filled with a volatile fluid. 1hen steam is in

the trap body, the volatile fluid boils and expands the bellows and closes offthe outlet valve. 1hen cooler condensate enters the trap body, the volatile

fluid stops boiling and the bellows contract to open the outlet port and the

condensate exits.

). escribe the procedure for replacin# the packin# on a pu%p.

%5 "hut down, isolate and drain pump

'5 #emove gland ad:usting nuts and slide gland away from the stuffing box.Then remove all the old packing using a packing puller. $ake sure stuffing

box is thoroughly clean.

(5 +heck condition of the shaft, resurface if necessary

*5 7etermine the correct si3e of packing

5 +ut the required number of rings of packing, using an old shaft if possible as atemplate.

-5 &nstall the packing rings one at a time after putting a light coating of oil or

grease on the inner diameter of each ring. Tamp the rings into the stuffing box

one by one using a split wooden bushing or metal ring to push each ring into place. $ake sure the ring :oints are staggered.

05 ut gland into place and compress the packing slightly by tightening the gland

nuts. Then slacken them off to :ust finger tight.

25 rime and start the pump. =llow the packing to leak freely for a few minutes,

and then gradually tighten the gland until leakage is reduced to that necessaryfor lubrication during normal operation.


41/53

1@ iscuss the procedures for the followin# nondestructi"e tests:

• 7adio#raphic - &n this method xrays or gamma rays are used to penetrate the

weld on one side and a sensiti3ed photographic paper is placed on the other side. 7ifferent amounts of radiation will come through depending on the

thickness and type of metal and show up on the film. +racks, porosity, or light

slag inclusion in the weld will show up as darker areas on the film due to thefact that more light will be let through in these areas.

• 5ltrasonic - &n this method high frequency sound waves are directed into the

metal to be tested, and are reflected back and measured. =nomalies and

defects in the metal will reflect the sound waves in a different pattern. 1ith

the use of a screen these waves can be seen as a wave signal and the defects

can be seen.

• ye-Penetrant - &n this method dye is applied to the surface of the weld and

allowed to absorb into the flaw. The excess is wiped off and a Bblack@ light is

beamed onto the affected area. The defect is revealed by means of the

fluorescent material absorbed in the flaw.

1. !plain why boilers reCuire a #ood foundation

To ensure there is no movement due to settling which would result in extra stress in

the connecting pipe work, and cracking of any brickwork

What is the desi#n that pul"eri$ed coal fired, hi#h pressure, watertube boilers

use for support and why do they use it.

They are top supported and allowed to expand downwards

Why are tie bar and buck stay arran#e%ents used on furnace casin#(

To strengthen the casing in order to withstand the internal pressure on a forced draft boiler.

/ketch and describe a tie bar and buck stay arran#e%ent on a furnace corner

Tiebars or channels and buckstays surround the boiler hori3ontally. These buckstaysare steel beams that are bolted together on the corners in a manner that allows

expansion and contraction to take place.


42/53

2. Why is a de#asifier used with a hydro#en $eolite softener(

The effluent from a hydrogen 3eolite softener contains +arbonic acid. +arbonic acidwill quickly break down into +O' and water. This +O' must be removed from the

water to prevent corrosion. The degasifier does this :ob.

With the aid of a sketch, e!plain the operation of the de#asifier.

The degasifier removes the +O' by passing the water through a tower in which the

water flows down over trays and is scrubbed by upward flowing air, from a blower,and the +O' is released to the atmosphere. The treated water falls into the clearwell

below the tower for storage.


43/53

'. /ketch and describe any re%ote le"el indicator

3#e%a re%ote water-le"el indicator

The steam condenser maintains a constant head of water acting at the top of the

indicator glass that contains a colored indicating liquid. The right column of water or

varying head is exposed to the liquid level in the drum and the right side of the )

tube containing the indicating liquid. 1hen the level in the boiler steam drum is atminimum, the pressure differential between the two heads will be the greatest. The

indicating liquid will be forced downward to the bottom of the indicator glass. =s the

level rises in the drum, the indicating liquid will also rise in the glass, giving acolored indication of the level to the operators on the operating floor.

What is the purpose of the e!pansion pipe and the condenser cha%ber(

The expansion or equali3ing pipe prevents the indicator from being sub:ected to

boiler pressure on one side only. The condenser chamber is used to maintain a fixed

head of water on the steamspace side. "urplus condensate returns to the level of

water in the boiler.


44/53

. /ketch and describe a %ulti-ele%ent co%bustion control syste% on a hi#h

pressure boiler

=n increase in firing rate demand is sent by the high selector to be the set point for

the air flow and the low selector sends the airflow process variable to be the set pointfor the fuel flow. This ensures that the airflow leads and the fuel follows to prevent a

rich condition.

= decrease in firing rate demand is sent by the low selector to be the set point for thefuel flow and the high selector sends the fuel flow process variable to be the set point

for the air flow. This ensures that the gas decreases first, then the air to prevent a rich

condition.The O' controller ensures that the percentage of excess air will be reduced at

increased steam demand, and increased, at a decrease in steam demand.


45/53

0. What is the purpose of an air heater on a lar#e stea% #enerator(

To recover heat from the flue gas and use it to preheat the combustion air to the

burners

escribe 2 types of air heaters

= recuperative air heater has heat transferred directly from the flue gases on one sideof the heating surface to the inlet air on the other side of the heating surface.

= regenerative air heater absorbs heat from the flue gasses onto a metal, or other solid

surface, and then this surface is repositioned to allow the heat to be transferred to the

combustion air.

!plain where and why corrosion occurs in an air heater

!oiler flue gases contain sulphur compounds. 1hen the flue gases are cooled to a

certain point 4dew point5, sulphuric acid will condense and form on the air heater

surfaces and cause corrosion. =reas most vulnerable are at the cold end of the unit,

the flue gas exit.

What can be done to pre"ent or %ini%i$e corrosion in an air heater(

eep the flue gas temperatures above the dew point. This can be done by re

circulating the air from the heater outlet to the heater inlet, or bypassing a portion of

the inlet air around the heater and mixing it afterward with the heated air.

. 9ist characteristics of a plant fuel and e!plain how they effect plant operation.

%5 "pecific ;ravity the higher the specific gravity, the lower the hydrogencontent and the harder it is to ignite the fuel

'5 /eating Aalue this is needed to calculate the boiler efficiency

(5 8lash oint determines the safe temperature at which the fuel can be stored*5 +ongealing or our oint determines the temperature at which the oil will

refuse to flow

5 Aiscosity measure of resistance to flow, the higher the reading the moretrouble it is to burn. 4heaters, etc5

). What is post weld heat treat%ent ?PW


46/53

8. !plain the startup procedure of a 1 ;;; kPa stea% ato%i$in# boiler usin#

Bunker oil.

%5 Ensure oil tank temperature is (9o+

'5 erform a proper purge of the furnace 4mins5

(5 +heck all burner connections

*5 +heck water level and position of all boiler valves, open superheater drains

5 Open oil circulating valve at burner and start fuel oil pump

-5 ut heating steam on fuel oil heater, raise temp to >9 >*o+

05 +lose oil circulating valve

25 Open back draft damper

>5 7rain steam line to burners

%95 Open air register slightly

%%5 Open steam valves and blow steam through the burner until steam is dry

%'5 Ensure boiler clean out valve is shut and throttle steam to burner

%(5 lace a lighted torch through the observation door near the burner tip

%*5 +arefully open the oil valve to allow enough oil to pass to ignite the burner, atthe same time increase the air register opening and increase the atomi3ing

steam

%5 1hen the burner is properly ignited, withdraw the torch.

What are interlocks which will cause the fuel solenoid "al"e to trip(

%5 8an failure

'5 Low oil supply pressure

(5 Low combustion air pressure

*5 Low water level

5 8lame failure

-5 $=1 exceeded


47/53

. /ketch a reducin# "al"e station of a boiler producin# 2;;; kPa down to 1;;; kPa

for process usa#e and down to 1;' kPa for heatin#.

/ketch and describe a sprin# pressure reducin# "al"e

0;. !plain the purpose of the followin# water tests:

•


48/53

• onducti"ity - To measure the total dissolved solids in the boiler water. This

is important since too much dissolved solids in the water can lead to carryover

from the boiler .

01. /ketch and describe the operation of a pressure #a#e.

The bourdon pressure gauge contains an oval tube in the form of a B+@, having an arc

of about '09o. One end of the tube is sealed and the other is connected to the steam

pressure. =s the pressure increases it forces the oval tube into a more circular shape.

This causes the free end of the tube to move linearly. The free end of the tube isattached to a pointer and indicator assembly to record the pressure applied.

What is the purpose of the siphon tube(

The purpose of the steam gauge siphon is to prevent steam from entering the gaugeand damaging it. The siphon is basically a loop in the pipe between the boiler and the

gauge. This allows the steam to condense in the upper part of the pipe, and preventsteam from entering the gauge.

Where are the inspectors test #a#e connected(

The connection for the &nspectorHs test gage is a tee fitting with one branch plugged,and is located between the siphon tube and the gage connection.

What is the procedure to test a #a#e(

One method is to use the test connection while the boiler is in operation and compare

the boiler gage to the inspectorHs test gage. This only compares the current pressure.

= more accurate method involves removing the gage from the boiler and using adeadweight tester to test the gage throughout its entire range.


49/53

02. /ketch and describe a direct positionin# co%bustion control syste%

= direct pressure combustion control system senses changes in boiler load and

regulates the fuel6air supply to the burners to match load. One controller is used for both fuel and air, so the fuelair ratio trim has to be manually ad:usted for different

firing rates.

!plain why this syste% cannot be used on lar#e hi#h pressure boilers.

The control of the fuelair ratio is not precise enough for large pressure boilers as aslight increase in boiler efficiency can save a lot of money.


50/53

0'. /ketch and describe an in"erted bucket stea% trap.

The bucket initially hangs down and holds the discharge valve open. +ondensate enters

the trap and flows under the bottom edge of the bucket to fill the trap body. Then thecondensate will flow out through the open discharge valve at the outlet. =ny steam that

enters the trap will collect at the top of the inverted bucket giving it buoyancy and

causing it to rise, thus closing the discharge valve. =ir and +O' gas will also collect at thetop of the inverted bucket and will pass through the vent at the top of the bucket to the

upper part of the trap body.

0). !plain the purpose and ad"anta#e of:

• losed feedwater heater - To increase plant efficiency by preheating the

boiler feedwater. !eing a closed design allows them to be placed anywhere inthe plant cycle including the discharge of the boiler feed pumps. /igher

temperatures are obtained over open feedwater heaters.

• "aporator - To remove the dissolved solids from the feedwater. )ses

exhaust heat from the turbine to distill the water instead of using chemicals

and deminerali3ers.

• eaerator - To remove O' and +O' from the water and serve as a feedwater

heater. #emoves the gases which otherwise would need to be removed bychemical means.


51/53

/ketch and describe a deaerator.

&n a combination spray and tray type deaerator, the water is first sprayed into the

upper heating section, and then allowed to trickle down over a series of steam swepttrays. This way the released gases and remaining steam traveling to the vent will pass

through the incoming water spray, condensing most of the steam. This section is

called the internal vent condenser.


52/53

0. What are ' ad"anta#es and ' disad"anta#es of continuous and inter%ittent

blowdown(

=dvantages%5 #emoval of dissolved solids from the steam drum 4+!75

'5 #emoval of suspended solids from the mud drum 4&!75

(5 rovides drainage of the waterside of the boiler 4&!757isadvantages

%5 /eat loss causing a decrease in overall steam system efficiency

'5 Loss of treated water, thus requiring more makeup water (5 #equired piping and blowdown tank, extra costs

/ketch a sin#le line drawin# of an inter%ittent blowdown

What is the difference between a Cuick openin# and slow openin# "al"e(

= quick opening valve is one which is opened or closed by moving a lever or wrench

through a small arc.

= slow opening valve is one which requires at least (-9o turns of the operating

mechanism to change from full closed to full open and viceversa.

00. A stea% dri"en feedwater pu%p starts and stops i%%ediately durin# startup,

then the relief "al"e opens. What is the cause and how are you #oin# to correct

it(

The cause is that the exhaust or L steam valve is closed. The relief valve opens asthe casing builds pressure and has no place to go, this is also why the rotor stops

turning. To correct this first close the intake valve and then open the exhaust valve

wide open 4assuming the casing and piping are drained of condensate and warmedup5.


53/53

08. /ketch and describe sub%er#ed arc weldin#.

=n arc welding process where the welding occurs beneath a protective layer of

granular and molten mineral material. This is normally an automatic process that produces seams which are neat and uniform in appearance

absa 4th class b help

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