Steam Boilers

Question 1

List the characteristics of an ideal boiler

Answer 1

1. Simple construction
2. Good workmanship
3. Made from materials which have low maintenance
4. Design and construction must incorporate the expansion and contraction properties of materials
5. Adequate steam and water space
6. Steam must be delivered that is clean
7. Good water circulation
8. A furnace that is set for efficient combustion
9. Maximum rate of heat transfer
10. Must respond to sudden demands and overloads
11. Easy to repair and clean
12. At least one code safety factor

Question 2

What two groups can boilers be classified into

Answer 2

1. Water tube type

2. Flame tube type

Question 3

Describe the flame tube type boiler

Answer 3

This boiler has a number of smoke tubes through which the products of combustion pass, heating the water around it

Question 4

What are flame tube type boilers best used for

Answer 4

Smaller quantities of steam - such as steam locomotives

Question 5

Flame tube type boilers are further divided into…

Answer 5

• Vertical tubular

- Horizontal tubular

Question 6

Describe water tube type boilers

Answer 6

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

Question 7

What are water tube type boilers best used for

Answer 7

Large quantities of super-heated steam - such as at a power station

Question 8

Water tube type boilers are further divided into…

Answer 8

• Vertical
• Vertically inclined
• Horizontal
• Combination of all three

Question 9

List the parts that make up a boiler

Answer 9

• Economiser
• Evaporator
• Superheater
• Other components such as an air heater

Question 10

Describe the economiser

Answer 10

A heat exchanger designed to recover some of the heat from the products of combustion

Question 11

What is the purpose of the economiser

Answer 11

Provide hot water supply to the evaporator, this increasing the efficiency of the plant

Question 12

Describe the evaporator

Answer 12

Transforms the nearly boiling feed water from the economiser into wet steam at a constant pressure

Question 13

Describe the superheater

Answer 13

Transforms large quantities of wet steam at constant pressure into superheated steam at the desired temperature

Question 14

What is superheated steam

Answer 14

Steam that is heated above the temperature that corresponds to the boiling point of water at that pressure

Question 15

Describe the air heater

Answer 15

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

Question 16

What are two common types of air heaters

Answer 16

• Tubular

- Regenerative

Question 17

What impurities are commonly found in feed water

Answer 17

• Mud
• Lime and magnesium
• Foam forming impurities
• Corrosive impurities like acids
• Gases in solution like oxygen and carbon dioxide

Question 18

Why must feed water be treated

Answer 18

• To prevent formation of deposits
• To reduce corrosion of metals
• To prevent boiler water carry-over

Question 19

What are the consequences of impure feed water

Answer 19

• Scale formation
• Corrosion
• Carry-over
• Foaming
• Priming
• Caustic embrittlement

Question 20

Define scale

Answer 20

Scale sticks to the surfaces of the boiler and tubes, slowing down the rate of heat transfer

Question 21

List the different methods to treat waste water

Answer 21

• Water treatment processes (clarification, filtration, lime softening)
• Ion exchange
• Complete demineralization
• Thermal treatment
• Removing corrosive gases
• Chemical treatment (corrosion control, deposit control)
• Blowdown

Question 22

Describe the different water treatment processes

Answer 22

• Clarification (removal of suspended solids by coagulation, flocculation and sedimentation
• Filtration (reduces suspended solids)
• Lime softening (reduction in total dissolved solids which cause scale)

Question 23

Describe ion exchange

Answer 23

This process substitutes or exchanges more desirable ions for less desirable ones

Question 24

What is the most common form of ion exchange

Answer 24

Water softening in which dissolved hardness is removed by the exchange of calcium and magnesium ions for sodium ions

Question 25

Describe demineralization

Answer 25

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.

Question 26

Define thermal treatment

Answer 26

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

Question 27

Describe blowdown

Answer 27

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.

Question 28

Define boiler efficiency

Answer 28

The ratio of the thermal heat supplied to the steam and the thermal heat obtained per kilogram of fuel

Question 29

Define equivalent evaporation

Answer 29

The amount of steam produced by the boiler plant per kg of fuel that is used

Question 30

Define a boiler

Answer 30

A closed vessel in which water under pressure is transformed into steam by the application of heat

Question 31

What’s the total of kilograms in one Ton

Answer 31

1000