BANGLADESH UNIVERSITY OF ENGINEERING & TECHNOLOGY

Course No.: ME 404 Course Title: Power Plant Engineering Sessional

Experiment No.: 02 Name of the Experiment: Study of a Boiler

Name: Mohammed Naimul Hoque Student No.: 0910089 Department: Mechanical Engineering Group: B14 Date of Performance: 05.05.2015 Date of Submission: 19.05.2015

Objectives:

To study the different accessories & mountings of a boiler.

To study the operations of a boiler.

To study the boiler capacities.

To study the water treatment operations for boiler.

To study the thermal balance of the boiler.

Specifications:

Brand Name: Philipp Loos GmbH

Model: Rekord-1600

Country of Make: Germany

Capacity: 1600 Kg/Hr

Maximum working pressure: 14 bar

Type of Burner: Dual Fuel Burner (Natural Gas/Diesel)

Fuel/fuels used: Natural Gas

Boiler Mountings & Accessories:

Boiler Mountings:

These are different fittings and devices necessary for the operation and safety of a boiler. Boiler

mountings are generally mounted over the boiler shell. The following mountings are usually

installed on a boiler-

1. Water level indicator

2. Pressure gauges

3. Pressure relief valves

4. Steam stop valve

5. Feed check valve

6. Blow down valve

7. Low water alarms

8. Fusible plug

9. Man and mud holes covers, etc.

Boiler Accessories:

These are auxiliary plants and devices required for the proper and efficient operation of boilers.

Commonly used accessories are-

1. Air pre-heater,

2. Economizer,

3. Super heater,

4. Feed pump,

5. Injector, etc.

Schematic Diagram of a Boiler:

Figure: Schematic Diagram of a Fire Tube Boiler

Function, Location and Working Principle of Mountings and Accessories:

Mountings:

Water Level Indicator: The function of

the water level indicator is to ascertain

constantly and exactly the level of water

in the boiler shell. It is fitted in the front

of the boiler from where it is easily visible

to the operator. The water gauge is

needed to ascertain the water level of a

boiler two water gauges should be fitted

for each boiler in such a place that the

water level can be constantly seen.

The unit consists of a strong glass tube

whose ends pass through stuffing boxes

consists of heat resisting rubber packing

to prevent leakage steam and water. The

flanges are bolted to front end plate of

the boiler, the upper flange being fitted

to the steam space and the lower to water space in the boiler. There are two cocks namely

steam cock and water cock which communicate the boiler shell spaces to the gauge glass tube.

When the handle of the cocks are vertical, they are in operation and the water level in the tube

corresponds to water level in the shell. A red mark on the glass tube indicates the safe water

level.

Pressure Gauge

A pressure gauge is fitted in front of boiler in such a

position that the operator can conveniently read it. It reads

the pressure of steam in the boiler and is connected to

steam space by a siphon tube.

Elliptical spring tube (also called Bourdon tube) is made up

of special quality Bronze. Plug (P) is provided for cleaning

the siphon tube. Siphon is filled with cold water to prevent

the hot steam entering into the bourdon tube and spring

tube remains comparatively cool.

Fig: Pressure Gauge

Figure: Water Level Indicator

Pressure relief valves: The pressure relief valve is used in a boiler to

relieve the pressure of steam when it is above the working pressure. It

is also called the safety valve. Its function is to discharge a portion of

the steam from the boiler automatically when the steam pressure

exceeds the normal limit. It is mounted on the top of the shell. As per

boiler regulation two safety valves are required to be fitted in each

boiler.

Stop Valve: The function of the steam stop valve is to shut

off or regulate the flow of steam from the boiler to the

steam pipe or from the steam pipe to the engine. When

used for the former purpose, it is called junction valve.

Usually the junction valve means a regulating valve of

larger size and a stop valve refers to a regulating valve of

smaller size.

The junction valve is mounted on the highest part of the

steam space of the boiler and is connected to the steam

pipe, which carries the steam to the engine.

Feed check valve:

The feed check valve is used to control the supply

of water to the boiler and to prevent the escape of

water from the boiler when the pump pressure is

less or the pump is stopped. It is fitted over the

shell slightly below the normal water level of the

boiler.

Fig: Safety Valve

Figure: Stop valve

Fig: Feed Check Valve

Blow-Off Cock: The blow of cock serves to drain out the

water from the boiler periodically for any one of the

following reasons:

1) To discharge mud, scale and other impurities which

settle down at the bottom of the boiler.

2) To empty the boiler for internal cleaning and

inspection.

3) To lower the water level rapidly if the level becomes

too high.

The unit is fitted at the lowest portion of the boiler. It

may be mounted directly to the boiler shell or through an

elbow pipe, which is fitted to the boiler shell.

Fusible Plug: The function of the fusible plug is to extinguish the

fire in the event of the boiler shell failing below a certain specified

limit. We know that when the water on heating transforms into

steam, the level of water in the boiler falls down. If the water is

not replenished and the steam generation continues then the

parts, which have been uncovered by water uncovered by water

may get overheated and subsequently are melted. To safeguard

against this eventuality we use fusible plug.

The fusible plug is inserted at the box crown or cover the

combustion chamber at the lowest permissible water level.

Man Holes: These are door to allow men to enter inside the boiler for inspection and repair

purposes.

Fig: Blow-off Cock

Figure: Fusible Plug

Accessories:

Air Preheater: Air heater or air pre-heater is

waste heat recovery device in which the air on

its way to the furnace is raised in temperature

by utilizing the heat of the exhaust gases. Air

pre-heater are classified into the following two

categories.

Recuperative Air heater

Regenerative Air heater

Economizer: The economizer is a device, which serves to recover some of the heat being

carried by exhaust flue gases. The heat thus recovered is utilized in raised temperature in feed

water being supplied to the boiler. If the water is raised and thus there is a saving in the

consumption of fuel.

The economizer unit is installed in the path of the flue gases between the boiler and the

chimney.

Steam Super Heater:

It is a heat exchanger in which heat of combustion products is used to dry the wet steam,

pressure remains constant, its volume and temperature increase. Basically, a super heater

consists of a set of small diameter U tubes in which steam flows and takes up the heat from hot

flue gases.

Figure: Air preheater

Figure: Economizer

Superheating results in increased efficiency and economy of the steam plant.

Feed Water Pump:

It is used to feed the water at a high pressure against the high pressure of steam already existing

inside the boiler.

Water Flow Circuit:

Figure: Super heater

Fuel Flow Circuit:

Capacity of Boiler:

Tonnage Rating:

It is the amount of water evaporated from feed water at 100 C and formed into dry and

saturated steam at 100 C at normal atmospheric pressure. Each kilogram of steam would then

have received 2.257 kJ of heat from the boiler. Shell boilers are often operated with feed water

temperatures lower than 100C. Consequently the boiler is required to supply enthalpy to bring

the water up to boiling point

KW Rating:

Some manufacturers will give a boiler rating in kW. This is not an evaporation rate, and is

subject to the same Tonnage Rating. To establish the actual evaporation by mass, it is first

necessary to know the temperature of the feed water and the pressure of the steam produced,

in order to establish how much energy is added to each kg of water.

(

) = ()

3600 (

)

()

Boiler hp rating:

Boiler horsepower is a function of the heat transfer area in the boiler, and a boiler horsepower

relates to 17 ft of heating surface, as depicted in equation:

= (1

17) (2)

In the USA and Australia the readily accepted definition of a boiler horsepower is the amount of

energy required to evaporate 34.5 lb of water at 212F atmospheric conditions.