high pressure boiler operation Flashcards
What is the definition of a boiler?
A closed pressure vessel in which water under pressure is transformed into steam by the application of heat
What is the definition of a pressure vessel
A vessel in which pressure is obtained from an external source to itself
What is the highest pressure a boiler can operate at
The MAWP (maximum allowable working pressure) is the highest pressure a boiler should operate at
Where will scale form in a boiler
Scale will form below the normal water level in a boiler
What is the purpose of the main steam stop valve?
The main steam stop valve is a valve usually connected directly to the boiler for the purpose of shutting off the steam from the main steam line
What is the purpose of a non-return valve
The automatic nonreturn valve cuts the boiler on-line and off-line automatically. The purpose of a non-return valve (NRV), is to allow steam flow in one direction, and automatically prevent backflow, they prevent steam from flowing back to a boiler that has failed or is off-line
What is a slow-opening valve? A quick opening valve
A slow opening valve is a valve that requires 5 complete 360 degree turns to go from fully closed to fully open. A quick opening valve will go from fully closed to fully opened in one quick motion
How do you blow down the water column ang gauge glass
- Slowly open the water column drain wide then close.
- Open the drain on the water glass.
- Close valve on top glass connection to blow out bottom connection
- Close valve on bottom connection
- Open top connection
- Open bottom connection
- Close drain
- Check level in glass with tricocks
How does a pressure gauge work
A pressure gauge uses a bourdon tube which is a closed, spiral tube, connected at one end to the pressure. As the pressure increases, the tube tends to straighten, and, through a linkage and gear, drives an indicating pointer
What is the difference between a blow-down tank and a flash tank
A blow down tank is used to collect blowdown water and cool it before sending down the drain. Flash Tanks are used to flash steam from high temperature condensate prior to introducing into low pressure steam lines and to flash condensate prior to returning to the boiler or condensate
How often would you test the “low water cut-out
At every shift change
What is an open feed water heater? A closed feed water heater?
In an open feedwater heater steam and water come into direct contact with each other. In a closed feedwater heater steam and water do not come into direct contact with each other
Where in the boiler room is a check valve required
On the feedwater line between the boiler feedwater pump and the stop valve
At what temperature is #6 oil preheated before firing
6 oil needs to be preheated to 180 - 200 deg f
Which 2 (two) combustibles have the most heat value
Hydrogen (62,000 btu/lb) and Carbon (14,600 btu/lb) have the highest heat value
What would cause a sudden increase in exit gas temperature
A loss of boiler baffle(s) will allow flue gas to “short circuit” and cause a sudden increase in exit gas temperature
What is the definition of draft
Draft is defined as the pressure difference between to points that causes air or gas to flow
Why is excess air required
Excess air is required for complete combustion
What is excess air
Air required for combustion greater than the theoretical amount
A high CO2 reading in the combustion gases is a indication of
High combustion efficiency
A manometer is used to measure what?
Draft
Which fuel requires the least amount of excess air
Natural gas
What is the minimum discharge pressure of a boiler feed pump
3% above the highest set safety valve
A two element feed water regulator looks at which parameters?
Drum level/steam flow
Foaming in a boiler could be caused by________________________?
High alkalinity, High dissolved solids and Oil or colloidal substances
It may be necessary to prime a pump when
The water level is below the pump
Another name for an open feed water heater is
Deaerator
A pyrometer is used to measure
high temperature
A vacuum is prevented in boilers by opening the
Vent valve
In an inverted bucket trap, as steam enters the trap the bucket will _____?
Rise
What methods are used for the circulation of water and steam through a boiler
Natural/ Thermal Circulation- difference in average density between unheated water and the steam-water mixture
Forced/ pumped- pump used to circulate water into the boiler.
What is a fire-tube boiler? Describe its operational features
Boiler where products of combustion pass through the tubes as water surrounds them, may be internal or external fire and horizontal or vertical. They are typically less expensive, short install time, easy controls, turn key operation, small foot print, burn oil or gas and maintenance to tubes is easier
If a fire tube boiler is a four pass design, describe the features of such a design
1st Hot gas travels from burner down through furnace during combustion process
2nd Rear head of boiler seals flue gas in lower portion and flue is directed to next
3rd The front head seals flue gas from escaping and directs to the 3rd pass
4th The flue gas is directed to the 4th pass and then out the stack
Identify the major purposes of the steam drum
Separate saturated steam from water-steam mixture that leaves the heat transfer surfaces and enters the drum
Describe the function of a cyclone steam separator in a boiler steam drum
A steam-water separator that has baffles located above each cyclone and there is a series of corrugated scrubber elements at the entrance to the steam outlet. Water from the scrubber elements drains to a point below the normal water level and re- circulated in the boiler.
What is a superheater? What advantages does it serve in the overall power plant operation
A superheater uses steam to increase the temperature in steam. Steam that has been heated above the saturation temperature corresponding to its pressure is called superheated. It contains more energy, heat and no moisture and travel long distances.
What is a radiant type of a superheater? A convection type superheater
A radiant superheater is usually placed close to the furnace where it absorbs the heat from radiation. A convection type is placed in the gas stream where its heat is absorbed through convection
What are the three basic methods for maintaining a constant steam temperature? Which of these is the predominate method? Describe its operation.
Attemperation - Reduces the temperature of superheated steam at higher loads to permit a constant steam temp over a defined load range. This method is predominate.
Flue gas bypass – The use of dampers to bypass flue gas around the superheater to the economizer, boiler or air heater to reduce heat content.
Flue gas recirculation – Heat available to the superheater is regulated by controlling the heat absorption of the furnace. This control is done through recirculating flue gas
What is an economizer? What is the advantage of using an economizer? If an air preheater is part of the overall boiler design, is the economizer located before or after the air heater with regard to the flue gas flow? Why
It’s a heat exchanger that preheats incoming feed water to the steam drum by passing through the stack where it obtains heat from the flue gas. Advantages are recovered heat loss from stack, lower stack temp, efficiency increase and lower fuel costs. Air preheater is located after the economizer because it dries fuel and moisture
Describe the various types of air preheater and their purpose in the boiler design. What are the methods used in the air heater design to minimize cold end corrosion problems? What is the purpose of a steam coil air heater? Where is it located
Tubular air heaters- series of tubes where flue gas pass with air passing around the outside of the tube
Regenerative air heaters- a rotor that turns continuously through the flue gas air stream at slow speed
Methods used to prevent cold end corrosion is greater sheet thickness, low alloy steel, enameled sheets, glazed ceramics, and honeycomb blocks made of ceramics, and tube thickness
Steam coil heaters are used when required to preheat the air prior to entering the air heater, this is located after the forced draft fan.
In reference to the design of super heaters, economizers, and air heater, what is meant by the terms parallel flow and counter flow? What are the advantages of each design
Parallel flow the flue gas and water flow in the same direction. Counter flow the flue gas and water travel in opposite directions. Counter flow is more efficient due to the heat absorption with less heating transfer surface
How are boilers supported to allow for expansion and contraction during operation
- Suspending drums and headers from slings attached to overhead columns
- By supporting the drum at the end, on columns or overhead beams
- Anchoring the lower drum at the floor level, permitting expansion upward
Why are water wall furnaces so important to the boiler design as compared with older refractory furnace boiler designs
Water wall furnaces are more efficient cause they capture the heat transfer that refractory would not. They also reduce the maintenance of the heating surface
What is the difference between a pressurized and a balanced draft boiler design
Pressurized uses forced draft fans to move the flue gas through the boiler and a balanced draft fan is the use of forced draft and induced draft
Describe a dry pipe, it purpose and location on a boiler?
A pipe installed on top of the drum to separate the moisture from the steam before the steam passed to the steam outlet
Why are water tube boilers considered less dangerous than fire tube boilers
Water tube contains less water than fire tube boilers
In describing the capacity or size of a boiler, how is it best defined in modern boilers
Lbs of steam per hour (lb/hr)
What is the best method for the determination of leak tightness on the water/ steam side of a boiler
Hydrostatic test-fill boiler with water and check for leaks
Describe a flame safety system
An electronic monitor (fire eye) detects Uv/Ir rays and makes corrective action to the burner. It the pilot/burner doesn’t light the fire eye will shut the fuel supply valve
What are some of the major operating problems that can occur in the operation of a fuel-oil-burning power plant
Failure of the oil to flow to the pumps from the tank, clogged strainers, pump failure, vapor formation due to high temp in tank, oil too heavy to flow to pumps due to insufficient heating, faulty atomization and smoke/poor combustion and flame striking
In a fuel-oil-burning plant, what is the primary source of NOx, and how is the NOx controlled
NOx is formed during combustion by two methods, thermal NOx and Fuel NOx. It’s controlled by lowering excess air and two stages of combustion
Natural gas is being used as a primary fuel to power gas turbines in a cogeneration system. What are the advantages and disadvantages of this system
Advantages would be low cost fuel (natural gas now), initial cost, and schedule for install is short, reliability and low maintenance costs.
Disadvantages are cost of fuel (variable); supply must be available, lower heating value, need gas regulators and clean flows
How is NOx formed when firing natural gas, and how is NOx controlled
Same as oil fuel burning. Thermal NOx is the primary source of NOx formation because natural gas and other gaseous fuels generally are low in or absent of nitrogen. Flue gas recirculation is used to reduce NOx emissions
What is the most important function of a burner-control system? Describe the three types of burner-control systems
The most important function is the combustion control which regulates the fuel to meet the demands of steam or hot water and maintains the ration of air to fuel. Manual control system requires the operator to maintain the burner at the burner platform with visual and manual operating. The second system is a remote manual sequence which uses instrumentation and switches to control fuel equipment (what my plant has). Lastly is an automatic sequence control which uses an automatic controller to start up, shut down and regulate the burner. These are equipment with set points and automatic safety shut downs
What is draft and draft loss? In a boiler, how is draft created
Draft is the difference in pressure usually from the inside of a vessel in relation to the atmosphere (outside). Draft loss is the reduction in static pressure due to friction or other pressure losses as it travels through the exhaust system. Draft can be created in forced draft (fan on outside of boiler pushing air through), induced draft (fan located after boiler but before stack, sucking air through), balanced draft (the use of forced and induced fans) and natural draft (draft loss is low and the stack is high
Describe a forced-draft fan and an induced draft fan. How are these fans part of a pressurized furnace and a balanced draft boiler design
A forced draft fan (pressurized furnace) is located on the outside of the furnace and blows causing flue gas to travel out the stack. Induced draft fan is located after the furnace and before the stack and pulls flue gas through to the stack. Balanced draft fans are the use of a forced draft fan and induced draft fan, pressure is slightly negative in the furnace
Describe the operation of a steam atomized oil burner
Steam is used to atomize fuel oil by breaking up the oil into small droplets which makes the fuel easier to burn because it increases the surface area. The steam is projected across the jet which forms a conical spray of fuel oil before its ignited. Inside mixing burners have the oil and steam mingle before leaving the burner tip and outside burners have them mixing just as they leave the burner tip
Describe the operation of a high pressure oil atomized burner
Oil flows at high pressure in the center of the tube and is discharged through tangential slots in the sprayer-plate swirling chamber. Swirling oil passes through the sprayer plate orifice into the space between the two plates. Some oil is forced back to the return line by centrifugal action which is controlled by a FCV. The oil that doesn’t return back goes through an orifice plate which forms a hollow cone shaped spray where it’s ignited
What is the purpose of a flame detecting device for automatic burners
A fire eye is used to automatically control shut down features in a furnace if the flame is lost while running or the pilot fails to light the burner. This system is an interlock for operating the boiler and will switch the blower on when flame is lost to purge boiler of combustible gases. This fire eye will also open/close the main fuel valves as needed
What is understood when a boiler is on full automatic control
The process is automated where the purging, burners, dampers, valves, pumps and operating equipment are all controlled electronically without hand manipulation. This type of system is usually found in smaller to medium size boilers. Different devices or switches come back to a main system where logic operates the boiler depending on its current status.
What are the fireman’s duties when a boiler is on full automatic control
Maintain drum level, steam pressure, air/fuel mixture, equipment, rounds/ readings, clean fuel burning equipment, blow tubes, room clean, lubricate equipment, observe all operating equipment, blow down gauge glass/ columns, test feed water, repair leaks as needed and report to engineer in charge
Describe natural and forced draft
Forced draft is the use of a fan on the outside of the boiler that forces flue gas through the boiler and out the stack. Natural draft is when the system draft loss (reduction in static pressure from friction or other pressure losses) is low and the stack is tall.
Give ten reasons why a boiler will smoke
Dirty burner tip, not enough air, dirty tubes, heavy ash accumulation, improper draft, air/fuel mixture, incomplete combustion, moisture in fuel, fuel pressure, furnace leaks
How do you light off an oil fired boiler, with no automatic controls, after you have lost fire
Confirm all equipment is running properly and boiler level is met then purge furnace and attempt to re-fire
How do you determine the temperature of fuel oil at the burner for proper atomization
A heater is located on the high pressure side of the pump which lowers viscosity of the oil so that it can be atomized effectively by the burners. Oil heaters are supplied with thermostats that maintain a constant outlet oil temperature
What is the heat content of coal, oil and natural gas
Coal 17% volatile
Oil 13.8%
Gas 11%
Why is maintenance of a correct water level one of the most important criteria for safe and reliable boiler operation
If the level is too high you can have carry over which water droplets enter the steam outlet and could cause damage to equipment (turbine) down stream. If the level is to low there’s a risk of over heating the tubes from direct hot flue gas exposure. Both can ruin equipment which is costly and cause the process to be stopped
Describe the operation of float and probe type water columns
The float style was the first design and consisted of a float assembly that was connected to a linkage that would release steam from the column through an external whistle if you had a low or high condition. The probe type has replaced the float system and uses electronics to display current water levels. This style is favored because there is no moving parts which could fail
Explain the purpose and operation of a feed water regulator
Feed water regulator maintains proper water levels in the boiler or preheater. A feed water switch usually located on the water column (package boilers) sense low level and turns the feed water pumps on which allows heated water from the preheater to flow to the boiler until the water level switch is satisfied. The original feed water regulators consisted of a float with a linkage tied to a valve
Explain the difference between a two and three element feed water regulator. Which is the most commonly used system
A two element feed water regulator takes into account steam flow and feed water flow. A three element feed water regulator takes into account steam flow, feed water flow and drum level. This is the most commonly used control system
Explain the swelling and shrinkage characteristics of water and why these are important in the control of the boiler drum level
As the boiler load increases and the saturated vapor increases you will get swelling in the boiler. The opposite is shrinkage when the load demands decreases and the saturated vapor decreases. Both these effects are important because they change the water level in the boiler and adjustments might need to be made to the system to ensure proper water level at all times
An operator with two 500 BHP boilers
Can not leave the boiler room
How do we know a boiler has been inspected
Valid Certificate of Inspection
Are dual pressure controls allowed on boilers
No
A cyclone separator operates on which principle
Centrifugal force
A licensed operator is required for boilers over 15 PSI. What HP
> 9 HP
Water tube boiler
What is boiler heating surface
Parts of the boiler with water on one side and products of combustion on the other side. Measured in 〖ft〗^2 and the side receiving heat
What surface is used when calculating water wall heating surface
Extended surface
Boiler tubes are measured based on which dimension
Outside diameter
What is the size of an oval manhole
11 x 15” or 12 X 16”
What size is a handhole
2 ¾ X 3 ½
Superheaters increase the temperature of?
Saturated steam
What does OS+Y stand for
Outside stem and yoke
Which valve limits flow in one direction
Check valve
Which valve offers the least resistance to flow
Gate valve
Which valve offers the most resistance to flow
Globe valve
What are trycocks used for?
Determine water level in boiler
What is minimum pipe size to water column
1” (1” to 2 ½ “)
What is minimum size of water column drain/blow-off
¾ “
What is minimum size of gage glass drain/blow-off
½ “
Gage glass breaks, what valve do you close first
Bottom water valve, hot water might burn you
When replacing gage glass which valve is opened first
Top steam valve, to temper glass
Two (2 bottom blowdown valves are required when?
Boiler(s) operating at 100 psi or above.
What is the purpose of blowdown valves
Remove sludge/sediment
Where do you find a longitudinal joint
Running the length of the shell/drum.
What keeps the boiler from dry firing
Low Water Cut Out (LWCO)
Best time to blowdown boiler is
Low load full pressure
The range of a pressure gauge should be
1.5 to 2 times the MAWP
Economizers and Air Preheaters are examples of what
Heat Recovery equipment
Before blowing down the boiler you should
Find true water level
Before blowing down the boiler you should
Blowdown water column and gauge glass
Purpose of an economizer is to?
Heat feedwater
The purpose of the water column is to
Dampen oscillating water in the gage glass
Nitrogen has what value in the combustion process
No value (Inert gas)
What is a Fire Eye or Flame Safeguard
Flame detector/scanner
The internal resistance a material offers to external force is known as
Stress
When two forces of equal intensity pull in opposite directions
Tensile stress
Forces pushing towards the center of an object is known as
Compressive stress
Three types of stress found in boilers are
Compressive, Shear and Tensile stress
what to know for 3rd engineer license
All of that pertaining foregoing grades: Types, purpose, operation of the following: Non- condensing steam turbines, impulse blading, reaction blading, velocity-compounding, pressure compounding, journal bearings, forced feed lubrication, reduction gears, shaft seals, throttle-trip valves, emergency governors, overpressure protection devices. Understanding of causes of vibrations and critical speeds in turbines. Turbine horsepower determination as per Chapter 146.
Knowledge of direct acting centrifugal and electronic type speed governors. A knowledge of water treatment. The effect of scale, sludge and other contaminants in boilers. An understanding of water side and fire side corrosion and its prevention. A thorough knowledge of positive and non-positive displacement pumps. A knowledge of heating systems using outside air
admission. Methods of removing scale and oil from boilers. Knowledge of boiler safety valve code requirements; including capacity determination, permissible mountings, set pressures, stamping, etc. Ability to order a safety valve and checking safety valve capacity three ways. A knowledge of gagging a safety valve. A knowledge of power plant repairs, including the procedure for making welded and mechanical repairs in accordance with state laws. A thorough knowledge of boilers, boiler control systems both combustion and feedwater. Understanding of code jurisdictional limits for piping drum type boilers as required by ASME Code, Section I PG-58.
Typical fuel oil and gas piping arrangements. Knowledge of two and three element feedwater level control systems. Knowledge of bearings used in turbines. Knowledge of indicators, recording devices, and associated instrumentation for monitoring and controlling combustion process. Knowledge of safety controls to prevent unsafe boiler conditions. Knowledge of flue gas analysis and boiler efficiency. Skill in math and simple algebra. Knowledge of surface and air-cooled condensers. Basic methods of superheat temperature control. Safety rules for entering boilers for inspection. Basic steam and water cycle for a condensing turbo generator.
Procedure to hire a boiler repair and other licensed contractors. Understanding of ASME Code Section I & National Board Code as it applies to the normal duties and responsibilities of a Third Class Engineer. Complete understanding of “Responsibilities of being a Chief Engineer.” A knowledge of Gen.. Laws Chapter 146, knowledge of CMR’s 522 & 310, knowledge of B31.1 piping code, knowledge of Gas Turbines. Knowledge of Piping and Instrumentation Drawings (P&ID’s)
Questions concerning the plant in which the applicant is presently employed or where they have been employed in the past may be asked during the oral portion of the exam.
What is a boiler
A BOILER IS A CLOSED VESSEL IN WHICH WATER, UNDER PRESSURE, IS TRANSFORMED INTO STEAM BY THE APPLICATION OF HEAT.
What is a pressure vessel
A PRESSURE VESSEL IS A CLOSED VESSEL IN WHICH THE SOURCE OF PRESSURE IS EXTERNAL TO ITSELF. ANY PRESSURE VESSEL NOT IDENTIFIED AS A BOILER
