Energy and Steam

8/11/2019 Energy and Steam

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Energy and Steam


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Introduction

Steam is mainly used in industries for power

generation and drying. To design any

application which is based on steam, it isimportant to understand the behaviour of

steam under different conditions.


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FORMATION OF STEAM


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Steam boilers

The steam boiler may be defined as a closed

vessel which is used to convert water into

steam at required temperature and pressure

by the application of heat.

The fuel used in boiler may be solid, liquid or

gas. The fuel is burnt in a furnace to produce

heat. This heat is used to convert water in to

steam at required temperature and pressure.


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Classification of a Boiler1) Horizontal, vertical or inclined

If the axis of the boiler is horizontal is known as horizontal. If the axis of theboiler is vertical is known as vertical boiler. If the axis of the boiler isinclines is known as inclined boiler.

2) Fire tube boiler and water tube boiler Fire tube boiler: In fire tube boiler the hot gases flows inside the tube andthe water surrounds the tube.

Water tube boiler: In water tube boiler the water flows inside the tube andthe hot gases flows around the tube.

3) Internally fired and externally fired boilerInternally fired boiler:If the furnace is located inside the boiler shell is

known as internally fire boiler.Externally fired boiler: If the furnace is located outside the boiler shell is

known as externally fired boiler.

4) Forced circulation and natural circulationForced circulation: In forced circulation boiler, the water is circulated in theboiler is done with the help of pump in known as forced circulation.

Natural circulation: In natural circulation boiler, the water is circulated inthe boiler is due to convection currents is known as natural circulationboiler.


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5) High pressure boiler and low pressure boilerHigh-pressure boiler: The high-pressure boiler is designed toproduce steam at very high pressure is known as high-

pressure boiler.Low-pressure boiler: The low-pressure boiler is designed toproduce steam at low pressure is known as low-pressureboiler.

6) Single tube and multi tube boiler

Single tube boiler: If the boiler contains only one fire tube isknown as single tube boiler.

Multi tube boiler: If the boiler contains more than one firetube is known as multi tube boiler.

7) Stationary and portable (locomotive) boilerStationary boiler: If the boiler is located at factory siteExample, power generation plant and the boiler used intextile mills are known as stationary boiler.

Portable boiler: Portable boiler is a small boiler, which canbe used as a locomotive or temporarily used at factory

sites.


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Lancashire boiler

The Lancashire boiler is a horizontal axis, fire

tube, multi tubular, low pressure, natural

circulation, internally fired, and stationary

boiler.

The parts of Lancashire boiler are flue tubes,

safety valve, steam stop valve, pressure gauge,

furnace, feed check valve, man hole, water level

indicator, fusible plug and blow off valve.


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Construction and Working of Lancashire

Boiler


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Babcock and Wilcox Boiler

Babcock and Wilcox boiler is horizontal boiler,multi tube, externally fired, water tube, stationary,

low-pressure boiler and natural circulation boiler


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Boiler mountings

The boiler mountings are necessary for the proper function and safety

of a boiler; with out mountings boiler will not function. The various

boiler mountings are listed below.

1. Safety valve

2. Water level indicator

3. Pressure gauge

4. Blow off valve

5. Steam stop valve

6. Feed check valve

7. Man hole


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a) Safety valve : The boiler is designed for a pressure, but the workingpressure of a boiler is always less than the design pressure. Thefunction of a safety valve is to protect the boiler from excess pressure,when the pressure inside the boiler exceeds the working pressure, the

safety valve opens and the excess pressure is released to atmosphere.

b) Water level indicator:The function of a water level indicator is toindicate the actual level of water in the boiler. For proper function of aboiler the water level in the boiler has to be maintained betweenminimum and maximum level but, if the water level falls less than theminimum results in rapid increase in pressure of steam leads toexplosion of a boiler. Always the water level indicator is located nearerand easily visible for the operator.

c) Pressure gauge: The function of a pressure gauge is to indicate theactual pressure inside the boiler. The pressure rating of a pressuregauge, which is mounted on a boiler, should be twice the working

pressure of a boiler.d) Blow off valve: The function of a blow off valve is to drain the

sediments from a boiler. This operation is carried out when the boileris not in use. Always the blow off valve is located at the lowest positionof a boiler so that it is easy to drain the sediments from the boiler.


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e)Steam stop valve: The function of a steam stop valve is toregulate the quantity of steam that is going to the application.Always the boiler generates more steam than the quantity ofsteam required for the application, hence steam stop valveregulates the flow and delivers the required quantity of steamto the application.

f) Feed check valve:The feed check valve is a unidirectionalvalve; it allows the water from tank to the boiler and blocksthe steam from boiler to the water tank. When the pump ison it feeds the water to the boiler and, when the pump is offthe high-pressure steam flows towards the feed check valvebut it blocks the leakage of steam from boiler to the watertank.

g) Man hole: The boilers may be either water tube or fire tube

boiler. In both the boilers hot gases flow in or out side thetubes leaves behind some quantity of ash. This ash depositwill reduce the heat transfer rate, which leads to decrease theefficiency of a boiler. When the boiler is not in use a personenters the boiler through a man hole and cleans the surfaces

of the tubes.


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Boiler accessories

Boiler accessories are auxiliary parts used in

steam boilers for their proper function and to

improve the efficiency of the power plant. The

various boiler accessories are listed below.

a) Super heater

b) Economizer

c) Air pre heaterd) Steam separator

e) Steam trap


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a) Super heater: The function of a super heater is to increase the temperature of the steam

above its saturation temperature. The steam, which is delivered from the boiler is known as

wet steam, if wet steam is used for the application results in corrosion of parts and erosion of

turbine blades. The steam separator is in the form of U-tube, which is located just above thefurnace where the temperature is maximum.

b) Economizer:The function of a economizer (heat exchanger) is used to recover the waste heat

from the gases going to chimney, this is also known as waste heat recovery system. The heat

recovered from gases is used to heat the boiler feed water. The supply of preheated water to

the boiler reduces the amount of fuel required to raise water temperature from atmospheric

temperature to preheated water temperature.

c) Air pre heater:Air preheater is another heat exchanger is used to recover waste heat from the

gases. The air, which is fed to the furnace, is preheated to few degrees more than

atmospheric temperature. Due to this, the amount of heat to be added to the air in the

furnace is considerably reduced.

d) Steam separator:The function of a steam separator is used to separate the water particles

present in the steam. The presence of water particles in the steam gives rise to blades

erosion in turbines and corrosion of parts in steam engine.

e) Steam trap: The function of a steam trap is to drain the condensed steam automatically from

the steam pipes and steam separators with out permitting any water to escape to the

application

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