BCIT 5th class boiler engineer quiz 3 Flashcards
A gas fired boiler is started up from cold, and a small amount of water is observed draining from the reversing chamber which stops soon after. This may be due to
a) excessive pressure.
b) condensation of water in the flue gases on the cold boiler surfaces.
c) too high water level.
d) a tube leak in a watertube boiler.
e) too high firing rate.
b) condensation of water in the flue gases on the cold boiler surfaces.
CH011 Q016
When fuels containing hydrogen (such as natural gas) are burned, water is formed. Normally this water is in the form of steam and is carried with the flue gases and discharged up the stack. When a boiler is cold, this water can be condensed on the cold heating surfaces and may drain from the bottom of the boiler for a short time until the boiler warms up. If this drainage is caused by a tube leak it will continue and may become worse as the boiler pressure increases.
Before filling a steam boiler in a plant with other boilers operating you should adjust valves as follows
(select 3 items)
a) open the drum vent.
b) close the gauge glass valves.
c) close the low water cutoff steam and water valves.
d) open the water column steam and water valves.
e) open the main steam outlet valve.
f) close the blowoff valves.
a) open the drum vent.
d) open the water column steam and water valves.
f) close the blowoff valves.
CH011 Q034
Make sure that handhole and manhole covers and/or washout plugs are in place and properly tightened. Check that blow - off valves and drains on the water column, gauge glass, and low - water cutoffs are tightly shut. Valves on the gauge glass must be open. The main steam outlet is not opened until the boiler is up to pressure.
When installing manhole covers after boiler maintenance you should (Select 3 Items)
a) ensure that the surfaces are thoroughly cleaned.
b) ensure that the surfaces are freshly painted.
c) install new gaskets if old ones are severely damaged.
d) apply an adhesive to ensure that a tight seal is produced.
e) use gasket compound or graphite to coat gaskets.
f) ensure that an even gap exists between the opening and the raised part of the manhole cover.
a) ensure that the surfaces are thoroughly cleaned.
e) use gasket compound or graphite to coat gaskets.
f) ensure that an even gap exists between the opening and the raised part of the manhole cover.
CH011 Q018
The surfaces where the manhole cover and manhole opening contact must be cleaned to ensure a good seal.
The gasket must be installed so that there is an even gap all around between the raised part of the manhole cover and the manhole opening.
The gasket should be coated with gasket compound or graphite to ensure easy removal on the next shutdown.
No adhesive is used because the gasket ensures a tight seal and that would make the gasket difficult to remove on the next shut down.
A new gasket is always used no matter how good the old one looks.
The inner surfaces of a boiler are not painted including the manhole opening although the cover may be painted.
Select tasks from below that must be preformed before a watertube steam boiler startup is attempted. (select 5 items)
a) Close boiler up replacing manhole and handhole covers.
b) Start circulating pump to circulate water through heating system.
c) Set combustion controls to low fire position.
d) Close drains and fill boiler after adding startup chemicals.
e) Inspect to ensure maintenance is completed and tools and debris removed.
f) Reset Limit Controls that may have been tripped on shutdown.
g) Close vent valve on boiler steam drum.
h) Operate sootbowers to ensure boiler surfaces are clean.
a) Close boiler up replacing manhole and handhole covers.
c) Set combustion controls to low fire position.
d) Close drains and fill boiler after adding startup chemicals.
e) Inspect to ensure maintenance is completed and tools and debris removed.
f) Reset Limit Controls that may have been tripped on shutdown.
CH011 Q006
Before a steam boiler can be started by a programming control, the following conditions must be fulfilled:
Inspect the fireside and water side to ensure all maintenance is completed and all foreign material has been removed.
Close up boiler ensuring that manhole and handhole surfaces are clean and new gaskets are installed.
Add startup chemicals and fill boiler with treated water. For steam boilers, the water in the boiler drum must be above the cut - off point of the low - water fuel cut – off.
For steam boilers, open water supply to condensate storage feed valve if so equipped. Switch feedwater pump to automatic position and open inlet valve to boiler.
The steam pressure or water temperature must be at or below the cut - in setting of the operating control so its switch is closed. The switch for the high limit control will also be closed.
The main power switch or breaker must be closed so the electronic circuit in the programming control panel is energized, and power is available to the motor starting relays.
Check setting of automatic controls and reset any limit switches that may have been tripped (eg low gas pressure, high steam pressure, flame failure)
On boilers with high-low firing control set controls to low fire. On boilers with modulating control, set selector to manual and adjust flame control switch to low fire position.
The water level in a boiler must be maintained above the highest heating surface at all times because
a) the water keeps tubes from overheating which could rapidly result in damage.
b) excessive scale formation occurs if the heating surfaces are allowed to dry out.
c) the boiler is able to handle rapid load changes with more water volume.
d) the gauge glass is above the highest heating surface.
e) the maximum amount of steam can be produced.
a) the water keeps tubes from overheating which could rapidly result in damage.
CH011 Q044
Overheating of the heating surfaces can lead to disastrous explosions. Normally the water in the boiler covering these surfaces keeps the temperature of the boiler metal well below the danger point, but lack of water causes the temperature of the metal to rise to the point where the metal weakens and the internal pressure ruptures the material, resulting in a massive escape of pressurized steam and water.
To prevent overheating as a result of a low water condition the Boiler Code requires that every automatically fired steam and hot water heating boiler which is not under continuous attendance by a certified operator shall be equipped with an approved low - water fuel cut - off device, that is designed to shut off the fuel and air supply to the burner before the water level drops to a dangerous low level.
After vacation you have returned to work in a low pressure steam plant on night shift. To determine if any major incidents have occurred you should first
a) contact the boiler inspector.
b) talk with the building manager.
c) check the controls.
d) make a thorough inspection of plant equipment.
e) read the log book.
e) read the log book.
CH011 Q054
Actions in taking over and running the shift in a low pressure steam heating plant are:
Examine the log book to see if there have been any unusual happenings during the previous shift.
Check the boiler, i.e., fire, water level, leaks.
Test the automatic controls, i.e., stack switch or scanner, low water cut-out, pump control, and pressure limit control.
Inspect the feed pump, injector, boiler valves, piping and fittings for leaks and proper operation.
Check for leaks in the system and check that all sections of the system are hot. If any section is cold the cause should be determined and remedied.
Check all other equipment of the system, i.e., pumps, traps, piping controls, etc.
Make required tests and take appropriate action based on the results of these tests.
Maintain log book.
There are two types of explosions of boilers that can cause catastrophic results. These are
(Select two Items)
a) delayed explosions.
b) furnace explosions.
c) thermal explosions.
d) chemical explosions.
e) pressure explosions.
b) furnace explosions.
e) pressure explosions.
Boiler explosions may be listed under two general classifications: furnace explosions and pressure explosions.
Furnace Explosions
These are explosions which occur when an accumulation of combustible gases ignites and explodes within the furnace or gas passages of the boiler. This may be caused by:
- Insufficient purge of the furnace before lighting up.
- Admission of the fuel to the main burner before the pilot flame or other ignition source is established.
- A weak pilot flame.
- Failure of the main fuel valve to close when the main burner flame is lost.
- An insufficient amount of combustion air resulting in incomplete combustion.
Pressure Explosions
Pressure explosions occur when a pressure part of the boiler such as the shell, furnace, or firetube bursts due to too high a steam pressure or a structural weakening of the metal. This weakening may be caused by:
- The effects of corrosion.
- Overstressing of the material due to heating the boiler up too quickly during start-up.
- Overheating of the heating surfaces due to a low water condition (low -water fuel cut-off failure).
- Scale and sludge build up.
- Also, failure of the boiler operating controls combined with an inoperative safety valve may cause the pressure to rise far above the maximum allowable working pressure.
In either case, the results of an explosion are almost always loss of life and/or extensive damage to property.
When a boiler is heated up too quickly, uneven expansion can result in stress in the metal called
a) thermal stress.
b) tube warp.
c) expansive reaction.
d) tensile reaction.
e) expansion stress.
a) thermal stress.
CH011 Q024
Thermal Shock When metal is subjected to a sudden change in temperature, the temperature change will not be even throughout the metal and expansion and contraction will not be equal in all parts of the metal. This will cause strong internal stresses in the metal, called thermal shock. The larger the temperature change and the heavier the metal, the greater the internal stresses will be.
The heating surfaces of boilers, such as furnace walls, firetubes, and tubesheets, are subjected to thermal shock when the fire is started since rapid temperature changes take place. If a cold boiler is started up and the maximum firing rate is applied, the thermal shock may be so strong that it will result in the appearance of tiny cracks in the metal, especially in the tube ends and tubesheets. This condition is worsened by the stresses set up by uneven expansion and by scale build-up.
Thermal shock is also caused by a rapid drop in temperature. This occurs when the water in a hot water boiler is up to operating temperature (90-115°C, 194-239°F) and the operator allows it to be replaced in a matter of minutes by a large flow of cool water from a heating system that has been out of operation.
To reduce the effects of uneven expansion and thermal shock and to protect a boiler against damage, the following precautions should be taken:
Always warm up the boiler slowly.
Keep the boiler free from scale build-up.
Cover the tubesheet with a lining of refractory to protect it from direct contact with the hot gases.
Do not allow a full flow of cool circulating water to pass through a warm hot water boiler. Bypass part of the flow around the boiler until the water temperature difference between the supply and return lines has reached its normal operating value.
Unless otherwise recommended by the manufacture’s instructions, a high/low fire control should be set to low fire when starting.
True
False
True
CH011 Q022
When lighting off a burner, too much fuel can result in a puff that can cause high furnace pressure. Also, a boiler should be warmed up slowly to reduce thermal stress. Therefore it is normal procedure to start a burner on the low fire or minimum fire setting.
In heating system a sudden increase in the amount of water treatment chemicals required would most likely indicate
a) a loss of air cushion in the expansion tank.
b) water is being lost in the system.
c) that scale has formed on boiler tubes.
d) the quality of water supply has deteriorated.
e) the heating load has increased.
b) water is being lost in the system.
CH011 Q040
When water losses from a steam or hot water boiler and heating system become abnormal, as indicated by the makeup water supply meter or by an increased requirement of water treatment chemicals to maintain normal concentrations in the boiler, an investigation should be made immediately to determine the cause. Proper repairs should be made at once rather than simply increasing the water treatment.
When checking the boiler, it is noticed that the water level is below the gauge glass. The correct action to take is
a) shut off the fuel and fill the boiler before restarting.
b) fill the boiler immediately up to the center of the glass.
c) shut down the boiler and inspect for signs of overheating.
d) call the chief boiler inspector and ask for advice.
e) fill the boiler slowly and check the low water cutoff device.
c) shut down the boiler and inspect for signs of overheating.
CH011 Q042
Low Water Level
A rapidly falling water level in the boiler may be caused by a faulty feedwater level controller, feedwater or condensate pump failure, interruption of the water supply to the pump, or leakage from the boiler due to ruptured fire tubes or leaking blow - off valves.
Normally, when the level drops to the low - water cut - off point, the boiler will shut down automatically. However, should the cut - off fail to shut the boiler down, the water level may drop dangerously.
If the operator finds the boiler in operation while unable to see the water level in the gauge glass, it may be that the glass is either completely full or empty. This should be checked quickly by opening the drain on the glass. If the level is found to be below the gauge glass, the boiler must be shut down immediately.
Caution:
Do not feed water into the boiler to raise the level, and do not open the safety valve or vent valve to release pressure.
Let the boiler cool slowly until it is at hand - touch temperature. Drain the boiler and open it to inspect for damage due to overheating. If no damage is found, the boiler can be closed up again and filled. However, it should not be put back into operation until the cause of the feedwater shortage and the failure of the low - water cut - offs to shut the boiler down is found and corrected.
If it appears that damage has been done, the Boiler Inspector must be notified.
To drain a hot water boiler after isolating it, you must open the blowoff valve and
a) close the continuous blowdown.
b) open the gauge glass drain.
c) open the return valve.
d) open the expansion tank drain valve.
e) open the vent.
e) open the vent.
CH011 Q032
If the boiler has to be opened for maintenance or inspection of the waterside, open the blow - off and vent valve after the boiler has completely cooled down. If the boiler is connected to an expansion tank common with other boilers, close the valve in the line connecting the boiler and tank before opening the blowoff valve. After the boiler is drained, remove the manhole and handhole covers or drain plugs and wash the boiler out with a stream of high pressure cold water.
During the annual inspection a boiler operator is not required to provide any information on known boiler defects to the inspector
True
False
False
CH012 Q006
The boiler operator is required to assist the inspector as necessary and to disclose any defect of which they are aware.
To remove baked on scale inside a cast iron boiler would require
a) dismantling sections and scraping.
b) chemical cleaning.
c) scraping and wire brushing.
d) turbining tubes.
e) wire brushing.
b) chemical cleaning.
CH012 Q002
The maintenance requirements for a cast iron boiler at the end of the heating season are: Thoroughly clean boiler of soot and ashes. Trash and other debris should not be allowed to accumulate around the outside of the boiler. Check to make sure that there is room for expansion between the sections. The tie-rod nuts should not be tight but should be backed off several turns or compression washers should be used with the nuts. If sludge and loose scale are present within the boiler, remove plugs from rear and front sections and flush with clean water. Boiler may have to be cleaned chemically if scale is baked on. Fill boiler completely with treated water to prevent corrosion during summer months. If danger of freezing, store dry. Remove fuses from firing circuit. Check all piping, fittings, etc. for cracks, corrosion, or signs of leakage. Thoroughly overhaul gauge glass and low water cut - outs.
The instrument shown in the figure below is used tomeasure
a) furnace pressure.
b) steam flow.
c) boiler pressure.
d) furnace temperature.
a) furnace pressure.
CH013 Q022
U -Tube Draft Gauge
A simple gauge for measuring draft consists of a glass U - tube containing water. One end is open to the atmosphere and the other end is connected to the inside of the furnace or to the flue gas outlet of the boiler. The difference in the levels of the water in the two legs of the U - tube will be the draft in millimetres of water or inches of water depending on the scale used. This type of gauge is also known as a manometer.
The U- tube gauge is connected to measure furnace draft or pressure. If the furnace pressure is less than atmospheric pressure, the atmosphere pushes upon the water so that the level in the U - tube leg connected to the furnace is higher than the level in the leg open to atmosphere. The difference in the levels is approximately 0.75 inches so that the value of the furnace pressure or draft is - 0.75 inches of water. The disadvantage of the simple U - tube draft gauge is the difficulty in reading slight pressure variations.
Advantages of oil when compared to coal as a fuel include (Select 3 Items)
a) less expensive than coal in fuel grades.
b) no storage is required.
c) more is available in nature than coal.
d) flow to furnace more easily controlled.
e) cleaner burning with less ash.
f) less handling equipment is required.
d) flow to furnace more easily controlled.
e) cleaner burning with less ash.
f) less handling equipment is required.
CH013 Q002
Fuel oil has certain advantages over coal as a boiler fuel:
1. Less storage space required.
2. Amount fed to furnace more easily controlled.
3. Less handling equipment and less labour required.
4. Cleaner and more efficient to use.
However, coal is less expensive than oil and there is a much greater abundance of coal.
Select the correct balanced, equation below that represents the incomplete combustion of carbon
a) C + O→CO
b) 2 C + O2→2 CO
c) C + O2→CO2
d) 2 C + O2→CO
e) C2+ O2→2 CO
b) 2 C + O2→2 CO
CH013 Q008
The combustion process can be expressed in simple chemical equations which representthe combination of these combustible elements with oxygen during complete combustion.
Carbon + Oxygen→Carbon Dioxide + heat
C + O2→CO2+ heat
Hydrogen + Oxygen→Water Vapor + heat
2H2+ O2→2H2O + heat
Sulphur + Oxygen→Sulphur Dioxide + heat
S + O2→SO2+ heat
Heat is stated in writing as being a product of the combustion equations. It is not included as a product in the printing of the combustion equations. Note that combustion of sulphur produces sulphur dioxide which is a toxic gas and causes acid rain. Also the heating value of sulphur is very low. Therefore it is considered an undesirable component of fuels.
Before burning, oil must be divided into fine droplets in a spray pattern. This is known as
a) educting.
b) atomizing.
c) aspirating.
d) reduction.
e) oxidation.
b) atomizing.
CH014 Q010
Oil must be broken up into a fine spray before entering hte furnace so that it can be heated and vaporized quickly for combustion. This process is called atomizing.
Two mediums that are used to atomize oil in high pressure oil burners are
(Select 2 Items).
a) boiler steam.
b) natural gas.
c) steel pellets.
d) compressed air.
e) high pressure nitrogen.
a) boiler steam.
d) compressed air.
CH014 Q012
Air atomizing burners require a compressed air supply. Usually a small rotary air compressor is mounted on or near the front of the boiler. The compressor is driven either directly by a small electric motor or by a V-belt and motor combination which also drives a fan supplying the secondary air to the furnace.
This type of burner can be used for light oils and also for heavier oils that are preheated.
Most industrial burners use steam for atomization instead of air (primary air). Basically the principle of operation of a steam atomizing burner is much the same as that of the air atomizing burner.
One advantage that cast iron has over steel as a piping material is that it is
a) stronger.
b) easier to bend.
c) more resistant to erosion.
d) lighter.
e) easier to weld.
c) more resistant to erosion.
CH015 Q006
Steel
Advantages: Steel piping is moderately priced as compared to piping made of other materials.
Disadvantages: Low resistance to the corrosive effects of water.
Cast Iron
Advantages: Has a high resistance to corrosion and to abrasion.
Disadvantages: It is quite brittle and not suitable for the pressure piping of most building systems.
Copper
Advantages: Copper and copper alloys offer great resistance to corrosion.
Disadvantages: Much more expensive than carbon steel and its use is restricted to low and moderate temperature service.
Plastic
Advantages: Plastic piping is reasonably inexpensive, light weight, easy to assemble and it offers great resistance to corrosion.
Disadvantages: Its use is restricted to low and moderate temperature and low and moderate pressure service. Also it is not permitted in commercial buildings in some jurisdictions – check local building codes before use.
To prevent leakage of flanged joints, they are normally sealed using
a) gaskets.
b) grease.
c) Teflon tape.
d) packing.
e) caulking.
a) gaskets.
CH015 Q014
In order to prevent leakage at flanged connections, the flange faces which butt together would have to be absolutely flat and smooth. While it is theoretically possible to grind the faces to this condition it is a time consuming and expensive proposition. Therefore, ring - shaped gaskets are usually used between flange faces. These are made of a comparatively soft material which, when the flanged connection is tightened, will fill any small depressions in the flange faces and thus prevent leakage.
The figure below represents
a) a float trap.
b) a bimetallic trap.
c) a thermodynamic trap.
d) an inverted bucket trap.
e) a thermostatic trap.
e) a thermostatic trap.
CH017 Q004
Thermostatic Steam Trap
This trap consists of a chamber containing an element consisting of a flexible bellows containing a small amount of volatile liquid. A valve is attached to the bottom of the bellows. As shown, the trap is open and condensate flows through and out the outlet. Air will also be allowed to escape. When steam enters the chamber, the steam heats the bellows causing the volatile liquid to evaporate pressurizing the bellows. This causes the bellows to expand forcing the valve down against the seat and trapping the steam. If the trap again fills with condensate or air, it will cool off and the volatile liquid will condense allowing the valve to open, expelling the air or condensate.
A valve which allows flow in one direction but closes if the flow is reversed is the
a) gate valve.
b) check valve.
c) needle valve.
d) globe valve.
e) butterfly valve.
b) check valve.
CH018 Q004
The check valve is a valve which prevents reversal of flow in piping. The flow of the fluid keeps the check valve open while reversal of flow will cause the valve to close. The swing check valve features a straight line flow and therefore offers little resistance to flow. The disc which is hinged at the top, swings freely in an arc from the fully open to closed position. The flow holds the disc opened but if reversed, the disc drops closed by gravity and will be held closed by the higher pressure on the downstream side of the valve.
The reason for leaving the suction valve on the standby pump of a hot oil system open is to
a) keep the pump hot and ready for start-up.
b) prevent contaminants from blocking the suction strainer.
c) prevent air bubbles from forming in the pump.
d) ensure the safety valve protects the pump from excessive pressure.
a) keep the pump hot and ready for start-up.
CH019 Q014
The suction valve of the standby pump should be left open all the time to allow a small amount of hot oil to flow backwards through the pump around the discharge check valve. This is recommended in order to maintain the standby pump at operating temperature, as it would otherwise be difficult to start in cold weather because of the high viscosity of the hot oil at low temperatures.
In hot oil systems, low oil flow shutdown sensors are usually installed
a) in the pump suction line.
b) in the inlet line to the oil heater.
c) in the outlet line from the oil heater.
d) in the convection tube bundle.
e) in the surge tank line.
c) in the outlet line from the oil heater.
CH019 Q008
Low hot oil flow (FSDL). Since severe overheating and probable tube failure would occur if hot oil stopped flowing through the heater, a low hot oil flow device is always installed in the outlet line from the heater.
Foaming is a low pressure steam boiler can normally be reduced by
a) increasing the firing rate.
b) raising the water level.
c) blowing the boiler down several times.
d) addition of oxygen scavenging chemicals.
e) addition of caustic soda.
c) blowing the boiler down several times.
CH011 Q038
Mild cases of foaming can be controlled by the use of antifoam chemicals. More severe foaming is usually controlled by blowdown. Lower the level in the boiler
5 - 7.5 cm (2-3 in) and refill to the normal level. Repeat this several times. In persistent cases, it may be necessary to take the boiler out of service and to cool, drain, and wash it out thoroughly. Then refill the boiler and put it back into service.
When starting up a steam boiler in an operating multi-boiler steam plant the main steam valve should be
a) cracked open when the boiler approaches header pressure and then opened fully when the pressure equalizes.
b) cracked open before starting the boiler and opened fully when up to pressure.
c) open quickly as soon as the pressure in the boiler reaches header pressure.
d) open fully before starting the burner.
e) opened fully when the boiler vent is closed.
a) cracked open when the boiler approaches header pressure and then opened fully when the pressure equalizes.
CH011 Q036
When the heating plant has two or more boilers supplying steam to a common header and one or more boilers are already in operation, the steam stop valve of the boiler that is being started up must be kept closed during warm up. The boiler is started using the normal procedures. When the boiler pressure is nearly equal to the pressure in the common supply header, open the stop valve slightly so that the pressure in the boiler will equalize with the header pressure. When the pressures are equal, the stop valve can be opened wide.
A combination altitude - pressure gauge has two pointers. One indicates the current pressure in the boiler and the other indicates
a) the maximum allowable working pressure.
b) the static pressure in the boiler when shutdown and cold.
c) the pressure due to the circulating pump.
d) the pressure setting of the safety valve.
e) the operating pressure when the boiler is running.
b) the static pressure in the boiler when shutdown and cold.
CH011 Q020
The moving pointer on a combination altitude – pressure gauge indicates the pressure in the boiler. After filling the boiler with water and opening the regulating valve from the city water system this pressure will be shown on the moving pointer and depends on the height of the water in the heating system above the boiler. At this time the stationary pointer should be set to match this pressure which will be the lowest pressure at which the boiler should operate. When operating, the pressure in the boiler will increase as the water is heated and expands into the expansion tank. The operator can see at a glance where the pressure is, in relation to the minimum required pressure.
The formation of scale on boiler tubes can cause severe damage because
a) it may result in reduced boiler circulation.
b) it can restrict the flow of flue gases.
c) it can result in too high boiler pressure.
d) it may result in tube leaks.
e) it may result in overheating of tubes.
e) it may result in overheating of tubes.
CH011 Q30
A small rise in flue gas temperature lowers boiler efficiency but will not harm the boiler. An excessive temperature rise, however, will lead to serious trouble. When ills caused by heavy soot build-up, the combustion conditions in the furnace are affected and this may result in a furnace explosion. When it is caused by heavy scale build-up, the reduced heat transfer from tubes to boiler water will cause the tube temperature to rise above the safe limit and the tubes may become seriously damaged.
If a flame failure occurs on a gas fired boiler the first step that should be taken is to
a) shut off the fuel and stop the fan.
b) re-establish ignition by energizing the electrodes.
c) relight the burner off the hot refractory.
d) shut the fuel off and purge the furnace.
e) switch to oil firing immediately.
d) shut the fuel off and purge the furnace.
CH011 Q046
When flame failure occurs, the flow of the fuel to the burner must be stopped immediately to prevent the furnace from filling with unburned fuel which could cause an explosion. Most boilers are now equipped with flame detection devices which will shut off the fuel supply within a few seconds after the flame fails. Regular testing of the operation of these devices is a must. Before attempting to re-ignite the flame, the furnace must be purged by blowing air through until all combustible gases have been removed.
A firetube boiler has a stack thermometer and the temperature has been rising over the last couple of weeks. This could be an indication that
a) the water level in the boiler is too low.
b) the water level in the boiler is too high.
c) the fan dampers needs adjustment.
d) the continuous blowdown valve is draining too much water.
e) there is a buildup of soot inside the tubes.
e) there is a buildup of soot inside the tubes.
CH011 Q028
Check the temperature of the flue gases by means of the stack thermometer. The stack temperature is a good indication of the effectiveness of the heat exchange between the flue gases and the water in the boiler. When the heating surfaces are clean on fire and water sides the maximum amount of heat is transferred and stack temperature will be at its lowest value for each specific firing rate.
By keeping a log of the stack temperature, a gradual increase in temperature will tell the operator that the heating surfaces are fouling up and that the heat transfer, and thus the boiler efficiency, is dropping and that cleaning may be required.
Soot and Scale deposits on the fire-side caused by improper combustion or scale and sludge deposits on the water - side caused by insufficient or improper water treatment will foul up the heating surfaces and reduce heat transfer. The gases will then leave the boiler at a higher temperature and boiler efficiency will be reduced.
A small rise in flue gas temperature lowers boiler efficiency but will not harm the boiler. An excessive temperature rise, however, will lead to serious trouble. When ills caused by heavy soot build-up, the combustion conditions in the furnace are affected and this may result in a furnace explosion. When it is caused by heavy scale build-up, the reduced heat transfer from tubes to boiler water will cause the tube temperature to rise above the safe limit and the tubes may become seriously damaged.
A hot water boiler having a relief valve setting of 400 kPa should be operated at
a) 350 kPa.
b) 331 kPa.
c) 440 kPa.
d) 400 kPa.
e) 300 kPa.
e) 300 kPa.
CH011 Q026
The operating pressure of low - pressure hot water heating boilers varies considerably because of the many different types of buildings they have to serve. It is, however, recommended that the differential between the safety relief valve set pressure and the boiler operating pressure is kept to a minimum of 69 kPa (10 psi) or 25 % of the relief valve setting, whichever is greater. For example:
If the safety relief valve is set to open at 207 kPa (30 psi), the operating pressure should not exceed 138 kPa (20 psi).
If the safety relief valve is set to open at 827 kPa (120 psi), the operating pressure should not exceed 620 kPa (90 psi).
Since 25% of 400 is 100 which is greater than 69 kPa, the boiler should operate at 400 – 100 = 300 kPa
The reason for this recommendation is that a large pressure differential will assure a tight closing of the valve. With a small pressure differential, the spring often is not able to seat the disk properly after the valve has released excess pressure and, as a result, a slight leakage or weeping of the valve may occur. This, in turn, may cause corrosive deposits to build up between and around the disk and seat. These deposits may prevent the valve from opening at the set pressure.
The low water cutoff should be dismantled, cleaned and inspected at least
a) once a day.
b) once a month.
c) twice a year.
d) once a year.
e) once every two years.
d) once a year.
CH011 Q050
Have your serviceman dismantle the low - water cut - off of a heating boiler for a complete overhaul at least once a year or more often if boiler water conditions are less than ideal and a considerable amount of sediment is formed.
During ignition of a gas fired boiler the pilot flame is established but the main flame does not come on and the boiler shuts down. This may be a result of (select 3 correct answers)
a) the programming control being set to MANUAL mode.
b) the water level being too low in the boiler.
c) a manual valve in the main gas line not having been opened.
d) the scanner not detecting the pilot flame.
e) the atomizing air compressor not being engaged.
f) the fuel gas valve not at minimum fire.
c) a manual valve in the main gas line not having been opened.
d) the scanner not detecting the pilot flame.
f) the fuel gas valve not at minimum fire.
CH011 Q014
The atomizing air compressor is only required when burning oil.
If the scanner is does not detect the pilot flame, the main flame will not be ignited. The pilot flame will light, however, and it will be shut down after a few seconds when not detected.
If the ignition electrodes are damaged there will be no spark to ignite the pilot burner.
To light the main flame, the fuel gas valve must be in the minimum fire position or an excess flow of fuel at ignition may cause a furnace explosion.
If a manual or automatic valve on the main gas line is closed, there will be no gas supply to the main burner.
If the programming control is in manual or automatic mode, the unit will start up normally. When cold, it should be started in manual mode and remain at minimum fire until the boiler is warmed up.
If the water level is low the programming control will not even attempt to light the boiler and no pilot flame will be established nor will the fan start.
The water level in a boiler must be maintained above the highest heating surface at all times because
a) the maximum amount of steam can be produced.
b) the boiler is able to handle rapid load changes with more water volume.
c) excessive scale formation occurs if the heating surfaces are allowed to dry out.
d) the water keeps tubes from overheating which could rapidly result in damage.
e) the gauge glass is above the highest heating surface.
d) the water keeps tubes from overheating which could rapidly result in damage.
CH011 Q044
Overheating of the heating surfaces can lead to disastrous explosions. Normally the water in the boiler covering these surfaces keeps the temperature of the boiler metal well below the danger point, but lack of water causes the temperature of the metal to rise to the point where the metal weakens and the internal pressure ruptures the material, resulting in a massive escape of pressurized steam and water.
To prevent overheating as a result of a low water condition the Boiler Code requires that every automatically fired steam and hot water heating boiler which is not under continuous attendance by a certified operator shall be equipped with an approved low - water fuel cut - off device, that is designed to shut off the fuel and air supply to the burner before the water level drops to a dangerous low level.
After vacation you have returned to work in a low pressure steam plant on night shift. To determine if any major incidents have occurred you should first
a) check the controls.
b) read the log book.
c) contact the boiler inspector.
d) talk with the building manager.
e) make a thorough inspection of plant equipment.
b) read the log book.
CH011 Q054
Actions in taking over and running the shift in a low pressure steam heating plant are:
Examine the log book to see if there have been any unusual happenings during the previous shift.
Check the boiler, i.e., fire, water level, leaks.
Test the automatic controls, i.e., stack switch or scanner, low water cut-out, pump control, and pressure limit control.
Inspect the feed pump, injector, boiler valves, piping and fittings for leaks and proper operation.
Check for leaks in the system and check that all sections of the system are hot. If any section is cold the cause should be determined and remedied.
Check all other equipment of the system, i.e., pumps, traps, piping controls, etc.
Make required tests and take appropriate action based on the results of these tests.
Maintain log book.
There are two types of explosions of boilers that can cause catastrophic results. These are
(Select two Items)
a) pressure explosions.
b) thermal explosions.
c) furnace explosions.
d) delayed explosions.
e) chemical explosions.
a) pressure explosions.
c) furnace explosions.
CH011 Q048
Boiler explosions may be listed under two general classifications: furnace explosions and pressure explosions.
Furnace Explosions
These are explosions which occur when an accumulation of combustible gases ignites and explodes within the furnace or gas passages of the boiler. This may be caused by:
* Insufficient purge of the furnace before lighting up.
* Admission of the fuel to the main burner before the pilot flame or other ignition source is established.
* A weak pilot flame.
* Failure of the main fuel valve to close when the main burner flame is lost.
* An insufficient amount of combustion air resulting in incomplete combustion.
Pressure Explosions
Pressure explosions occur when a pressure part of the boiler such as the shell, furnace, or firetube bursts due to too high a steam pressure or a structural weakening of the metal. This weakening may be caused by:
* The effects of corrosion.
* Overstressing of the material due to heating the boiler up too quickly during start-up.
* Overheating of the heating surfaces due to a low water condition (low -water fuel cut-off failure).
* Scale and sludge build up.
* Also, failure of the boiler operating controls combined with an inoperative safety valve may cause the pressure to rise far above the maximum allowable working pressure.
In either case, the results of an explosion are almost always loss of life and/or extensive damage to property.
Some of the items that are checked during a fireside inspection include (Select 3 Items)
a) signs of flame impingment.
b) drum internals.
c) refractory damage.
d) signs of leakage.
e) scale formation due to hardness.
f) handhole and manhole openings.
a) signs of flame impingment.
c) refractory damage.
d) signs of leakage.
CH012 Q004
Fireside Inspection
When inspecting the fireside of the boiler, the inspector may require the removal of sections of refractory or insulation in order to facilitate inspection of tube or drum surfaces.
- The surfaces are examined for bulges or blisters which would indicate overheating.
- Ends of firetubes are checked for signs of leakage and the tube-sheet ligaments for cracking.
- Tubes adjacent to sootblowers are examined for signs of erosion due to direct impingement of steam from blowers.
- Refractory and brickwork of the burners, baffles, and furnace walls are checked for deterioration.
The internal inspection requires that the boiler be shut down, cooled, and drained; also, manholes and handholes have to be opened.
ASME Boiler and Pressure Vessel Code, Section VII, Recommended Rules for the Care of Power Boilers, states the recommended procedures for a boiler inspection.
Chemical cleaning of boilers is normally carried out by a specialist because several precautions are required including
- the right acid must be determined by analyzing the deposits.
- adequate piping must be installed for circulation and temperature control.
- brass and bronze parts must all be removed.
- spent solvent must be disposed of in a safe and environmentally friendly manner
- ventilation must be provided to ensure no accumulation of hydrogen or H2S.
a) 2, 3, 4, and 5 only.
b) 1, 2, 4, and 5 only.
c) 1, 2, 3, 4, and 5.
d) 2, 3, and 4 only.
e) 2, 4, and 5 only.
c) 1, 2, 3, 4, and 5.
CH012 Q018
When employing an acid cleaning method, the proper technique must be followed and the necessary precautions must be taken. It is advisable that the procedures be performed under the direction of experienced personnel to assure that:
- The right type of acid is used for the deposit to be removed (which means the deposit must be analyzed first).
- Adequate piping systems are installed for the admission, temperature control, circulation, and removal of the acid.
- The boiler is isolated from the steam header.
- Brass and bronze parts are replaced with steel parts.
- The spent solvent can be disposed of safely.
- The boiler is adequately vented, because hydrogen is produced by the reaction of acid with iron. The hydrogen could cause a fire or explosion. In addition, poisonous gases such as hydrogen sulphide (H2S) can also be generated.
- Personnel handling the acids and inhibitors are supplied with proper safety clothing, including masks, goggles, rubber gloves, and aprons.
The heat generated by combustion of one kilogram of a solid fuel is the fuels
a) combustion temperature.
b) specific heat.
c) heating value.
d) latent heat.
e) heat of combustion.
c) heating value.
CH013 Q004
When a unit amount of fuel is burned completely, the heat produced by this combustion is called the heating value of the fuel. The unit amount can be a mass unit (kg or pound) or a volume unit (cubic metre or cubic foot), depending on the type of fuel. For liquid and solid fuels mass units are used (kJ/kg) and for gaseous fuels volumes are used (kJ/m3).
The heating value of a fuel depends primarily on the amount of carbon, hydrogen and sulphur in the fuel.
The use of a chimney to create draft and supply air to the boiler furnace for combustion without the need for fans is called
a) force draft.
b) natural draft.
c) balanced draft.
d) induced draft.
e) mechanical draft.
b) natural draft.
CH013 Q016
Natural Draft
When air or other gases are heated, they expand and, as a result, the weight of each unit volume of hot gas will be less than the weight of a similar unit volume of unheated, cool air or gas. When a boiler chimney contains heated gas, the column of hot gas surrounded by the cooler, denser air of the atmosphere causes these hot gases to rise. The hot gases will rise up through the chimney and are replaced by the air outside the furnace which is cooler and less dense. This air, in turn, becomes part of the hot combustion gases and will rise up into the chimney. In this way, a continuous draft or pressure difference is produced. The higher the chimney, the taller the column of hot gases, the greater the difference between the pressure in the furnace and the surrounding atmosphere, and the greater the draft.
Mechanical Draft
Mechanical draft is draft that is produced by a fan or blower which, when used for a heating boiler, is usually driven by an electric motor.
In most smaller heating boilers, the gases flow through a fairly simple pathway which offers little resistance to flow. The draft required to produce the gas flow can be small and a short chimney will be sufficient to produce this draft. In larger boilers such as multi-pass firetube boilers, the path of the gases through the boiler is long and offers considerable resistance. It would require a high and costly chimney to produce sufficient natural draft to overcome this resistance. Also the draft produced by a chimney varies with wind and weather conditions. By using mechanical draft instead of natural draft, the need for a tall chimney is eliminated and a more definite draft control becomes possible.
Two arrangements of fans may be used for mechanical draft; the forced draft fan and the induced draft fan.
Force Draft
With forced draft, a fan is used to supply combustion air to the boiler furnace. This causes the furnace pressure to be increased above atmospheric pressure and is referred to as a pressurized furnace boiler. The furnace pressure then forces the combustion products through the boiler and out the uptake to the stack.
Induced Draft
In an induced draft boiler a fan is used to draw combustion products out of the boiler and discharge them up the stack. This, in turn reduces the furnace pressure so that it is lower than atmospheric pressure. The atmospheric pressure then pushes air through registers around the burner and into the furnace to supply the air required for combustion.
Balanced Draft
In a balanced draft boiler two fans are used. The force draft fan supplies air for combustion of the fuel and an induced draft fan draws the products of combustion out of the furnace and discharges them up the stack. In this system, the induced draft fan is controlled to maintain the furnace pressure just slightly below atmospheric pressure.
The correct and balanced equation for complete combustion of carbon is
a) C + O2 → CO2
b) 2C + O2 → 2 CO
c) C + O2 → 2 CO
d) C + O → CO
e) 2C + O2 → 2 CO2
a) C + O2 → CO2
CH013 Q006
The combustion process can be expressed in simple chemical equations which represent the combination of these combustible elements with oxygen during complete combustion.
Carbon + Oxygen → Carbon Dioxide + heat
C + O2 → CO2 + heat
Hydrogen + Oxygen → Water Vapor + heat
2H2 + O2 → 2H2O + heat
Sulphur + Oxygen → Sulphur Dioxide + heat
S + O2 → SO2 + heat
Heat is stated in writing as being a product of the combustion equations. It is not included as a product in the printing of the combustion equations. Note that combustion of sulphur produces sulphur dioxide which is a toxic gas and causes acid rain. Also the heating value of sulphur is very low. Therefore it is considered an undesirable component of fuels.
The figure below represents
a) an air atomizing oil burner.
b) an atmospheric burner.
c) a rotary cup oil burner.
d) a refractory gas burner.
e) a ring gas burner.
e) a ring gas burner.
CH014 Q004
A type of burner commonly used in packaged firetube boilers is called a ring burner.
It is a ring - shaped, hollow casting mounted in the firing opening of the furnace. Small openings are drilled in the face of this ring through which the gas is directed into the furnace. The combustion air is supplied through the centre of the gas ring.
Deflector vanes give the air a swirling motion before it enters the furnace in order to promote intensive mixing with the gas.
This type of burner is known as an after - mix or outside mixing type since the gas and air mix together after they leave the burner.
In a pre-mix atmospheric gas burner, air is supplied to the burner for combustion by
a) a forced draft fan.
b) momentum from the flow of gas.
c) an induced draft fan.
d) a the stack effect of a chimney.
e) an steam powered eductor.
b) momentum from the flow of gas.
CH014 Q006
The principle of operation is quite simple. Gas passes through the small orifice or nozzle into the mixer head, exits as a straight flowing, high velocity jet and enters the throat of the Venturi tube. (A Venturi tube is a tube with a gradually increasing cross - sectional area). When the gas enters the tube, it spreads out and draws in, or aspirates, part of the air needed for combustion.
The momentum of the gas carries the air - gas mixture through the tube and into the burner head from where it issues through the ports. The mixture burns at the ports and additional air is supplied from the surrounding atmosphere to complete combustion. The air coming in through the Venturi is the primary air and that supplied around the flame is the secondary air. On smaller burners the gas flow through the orifice or nozzle is not adjustable with the amount depending on the size of the orifice or nozzle and the gas supply pressure. The gas flow in larger burners can be adjusted by a small needle valve. The amount of primary air can be adjusted by enlarging the air opening in the mixing head by means of a disc or plate.
A 76.2 mm (3 inch) pipe has a wall thickness of 5.5 mm. Its outside diameter is
a) 87.2 mm.
b) 81.7 mm.
c) 65.2 mm.
d) 70.7 mm.
e) 76.2 mm.
a) 87.2 mm.
CH015 Q004
Pipe up to 12 inch is sized as its nominal inside diameter. Therefore the outside diameter is the inside diameter plus the wall on both sides = 76.2 + (2 x 5.5) = 76.2 + 11 = 87.2 mm.
The figure below of a threaded pipe fitting represents a
a) union.
b) cross.
c) 45° elbow.
d) street elbow.
e) 90° elbow.
d) street elbow.
CH015 Q010
The figure is of a threaded street elbow.
To allow condensate out when a trap fails it should be piped in
a) using couplings.
b) in-line with a strainer.
c) using threaded fittings.
d) between unions.
e) with a parallel by-pass valve.
e) with a parallel by-pass valve.
CH017 Q006
Inlet and outlet gate valves permit isolating the trap for inspection and cleaning. Bypass line with globe valve, makes it possible to rid the system of condensate by hand throttling while the trap is out of service. Unions should be placed before and after the trap to allow the trap and strainer to be removed easily. A test valve allows the operator to open it to see that the trap is working.
When a steam boiler is connected to a common header with other boilers the main outlet must be fitted with a
a) non-return valve.
b) butterfly valve.
c) check valve.
d) double block and bleed.
e) gate valve.
a) non-return valve.
CH018 Q006
The non-return stop valve, also referred to as a stop - and - check valve, is installed at the boiler outlet in cases where the boiler is connected to a common main with other boilers. In principle, it is a stop valve which includes a device for preventing a reversal of flow through the pipe line when the valve is open. The check valve will prevent a reverse flow of steam into the boiler from the common main.
The heaters in a hot oil system should be inspected every
a) 3 months.
b) 6 months.
c) 12 months.
d) l8 months.
e) 24 months.
c) 12 months.
CH019 Q018
Hot oil heaters should normally be inspected annually.
The purpose of the concrete dike around the base of a hot oil heater is
a) to keep water from collecting under the heater.
b) to contain any oil leaks and direct them away from the heater.
c) to provide a source of quench water in the event of a fire.
d) to provide a bed of sand used to retard any fire.
e) to support the vertical columns used to hold up the heater.
b) to contain any oil leaks and direct them away from the heater.
CH019 Q006
A concrete dike surrounds the foundation to prevent hot oil from spreading beyond the immediate confines of the heater in the event of a tube rupture. A drain is provided from within the diked area to a pit located about 50 m from the heater; this permits hot oil to drain to a safe area.
