Steam Boilers Flashcards
List the characteristics of an ideal boiler
- Simple construction
- Good workmanship
- Made from materials which have low maintenance
- Design and construction must incorporate the expansion and contraction properties of materials
- Adequate steam and water space
- Steam must be delivered that is clean
- Good water circulation
- A furnace that is set for efficient combustion
- Maximum rate of heat transfer
- Must respond to sudden demands and overloads
- Easy to repair and clean
- At least one code safety factor
What two groups can boilers be classified into
- Water tube type
2. Flame tube type
Describe the flame tube type boiler
This boiler has a number of smoke tubes through which the products of combustion pass, heating the water around it
What are flame tube type boilers best used for
Smaller quantities of steam - such as steam locomotives
Flame tube type boilers are further divided into…
- Vertical tubular
- Horizontal tubular
Describe water tube type boilers
Products of combustion pass around tubes that are filled with water. The water is circulated from the drum by a means of a number of tubes and the heat surrounding the tubes heats the water in the tubes
What are water tube type boilers best used for
Large quantities of super-heated steam - such as at a power station
Water tube type boilers are further divided into…
- Vertical
- Vertically inclined
- Horizontal
- Combination of all three
List the parts that make up a boiler
- Economiser
- Evaporator
- Superheater
- Other components such as an air heater
Describe the economiser
A heat exchanger designed to recover some of the heat from the products of combustion
What is the purpose of the economiser
Provide hot water supply to the evaporator, this increasing the efficiency of the plant
Describe the evaporator
Transforms the nearly boiling feed water from the economiser into wet steam at a constant pressure
Describe the superheater
Transforms large quantities of wet steam at constant pressure into superheated steam at the desired temperature
What is superheated steam
Steam that is heated above the temperature that corresponds to the boiling point of water at that pressure
Describe the air heater
Uses the last energy from the fuel to heat the air - increasing the efficiency. Fuel burns better if the air is heated, and the overall effect is that the fuel consumption is reduced
What are two common types of air heaters
- Tubular
- Regenerative
What impurities are commonly found in feed water
- Mud
- Lime and magnesium
- Foam forming impurities
- Corrosive impurities like acids
- Gases in solution like oxygen and carbon dioxide
Why must feed water be treated
- To prevent formation of deposits
- To reduce corrosion of metals
- To prevent boiler water carry-over
What are the consequences of impure feed water
- Scale formation
- Corrosion
- Carry-over
- Foaming
- Priming
- Caustic embrittlement
Define scale
Scale sticks to the surfaces of the boiler and tubes, slowing down the rate of heat transfer
List the different methods to treat waste water
- Water treatment processes (clarification, filtration, lime softening)
- Ion exchange
- Complete demineralization
- Thermal treatment
- Removing corrosive gases
- Chemical treatment (corrosion control, deposit control)
- Blowdown
Describe the different water treatment processes
- Clarification (removal of suspended solids by coagulation, flocculation and sedimentation
- Filtration (reduces suspended solids)
- Lime softening (reduction in total dissolved solids which cause scale)
Describe ion exchange
This process substitutes or exchanges more desirable ions for less desirable ones
What is the most common form of ion exchange
Water softening in which dissolved hardness is removed by the exchange of calcium and magnesium ions for sodium ions
Describe demineralization
A cation exchanger removes all the cations and replaces them with hydrogen ions. The water leaving the system contains carbon dioxide. The water then passes into a degassifier where CO2 is removed. The acidic water then passes through an anion exchanger which removes all the anions and replaces them with hydroxyl ions. The treated water goes to a mixed bed unit. It leaves this unit nearly pure.
Define thermal treatment
Water is heated before it enters the boiler. Dissolved gases like oxygen and CO2 are driven off. The heaters that heat the water are called deareators
Describe blowdown
If water boils, all impurities are left behind when the steam evaporates. The impurities will continue to concentrate in the boiler and eventually reach a level where the impurities are dangerously high. They are then blown out of the boiler.
Define boiler efficiency
The ratio of the thermal heat supplied to the steam and the thermal heat obtained per kilogram of fuel
Define equivalent evaporation
The amount of steam produced by the boiler plant per kg of fuel that is used
Define a boiler
A closed vessel in which water under pressure is transformed into steam by the application of heat
What’s the total of kilograms in one Ton
1000
