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