Boiler Expt 2
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Transcript of Boiler Expt 2
1
BANGLADESH UNIVERSITY OF ENGINEERING & TECHNOLOGY
Course No.: ME 404
Course Title: Power Plant Engineering Sessional
Experiment No.: 2
Name of the Experiment:
Study of a Boiler
Date of Performance
18/09/2011
Name: Aashique Alam Rezwan
Student No.: 06 10 012
Date of Submission
9/10/2011
Section: “A” Group: A12
Dept: Mechanical Engineering
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Experiment No.: 2
Name of the Experiment:
Study of a Boiler
Objectives:
The objectives of this experiment are as follows –
o To study the different accessories & mountings of a boiler
o To study the operations of a boiler
o To study the boiler capacities
o To study the water treatment operations for boiler
Specifications
Brand Name Philipp Loos GmbH
Model 12 D-57629 Norken
Country of Make Germany
Capacity 1600 kg/hr
Maximum working pressure 16 bar
Type of Burner Dual Fuel Burner (Natural Gas/Diesel)
Fuel/fuels used Natural Gas
Boiler Mountings & Accessories
Boiler Mountings
1. Water Level Indicator / Water Gauge
2. Pressure Gauge
3. Safety Valve
4. Stop Valve
5. Feed Valve
6. Blow Down Valve
7. Fusible Plug
8. Steam Scrubber
9. Manhole and Handhole Covers
Boiler Accessories
1. Superheater
2. Attemperator
3. Economiser
4. Air Preheater
5. Feed Water Heater
6. Feed Pump
7. Injectors
8. Draught Production Equipment
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Fig. 1: Schematic Diagram of the Boiler
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Boiler Mountings
Pressure Gauge
Fig. 2: Pressure Gauge
A pressure gauge is used to measure the pressure of the steam inside the steam boiler. It is fixed in front of the
steam boiler. The pressure gauges generally used are of Bourden type.
A Bourden pressure gauge, in its simplest form, consists of an elliptical elastic tube bent into an arc of a circle.
This bent up tube is called Bourden’s tube.
One end of the tube gauge is fixed and connected to the steam space in the boiler. The other end is connected to
a sector through a link. The steam, under pressure, flows into the tube. As a result of this increased pressure, the
Bourden’s tube tends to straighten itself. Since the tube is encased in a circular curve, therefore it tends to
become a circular instead of straight. With the help of a simple pinion and sector arrangement, the elastic
deformation of the Bourden’s tube rotates the pointer. This pointer moves over a calibrated scale, which directly
gives the gauge pressure.
Pressure Governor & Water Level Regulator
Fig. 3: Pressure Governor & Water Level Regulator
Thermal energy is transported to the water inside the boiler body by means of heating. The water grows warm
and vaporizes, the steam pressure in the boiler rises. As soon as the working pressure is attained, the pressure
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governors cut of heating. There upon, when pressure drops for approx. 7% in consequences of the extraction of
steam, the pressure governor will connect up the furnace again.
Owing on the extraction of steam the water level in the boiler body drops. As soons as the water level has
dropped to approx. 4 cms above the low water level (NW), the water level regulator gives an electric pulse to
the switch gear. There upon the feed pump will start, it conveys water from the feed water tank into the boiler.
After a short time the water level in the boiler has risen again by this, there upon the water level regulator will
cut off the feed pump by means of an electric pulse.
Safety Valve
Fig. 4: Spring Loaded Safety Valve
These are the devices attached to the steam chest for preventing explosions due to excessive internal pressure of
steam. A steam boiler is, usually, provided with two safety valves. These are directly placed on the boiler. The
function of a safety valve is to blow off the steam when the pressure of steam inside the boiler exceeds the
working pressure.
A spring loaded safety valve is mainly used for locomotives and marine boilers. It is loaded with spring instead
of weights. The spring is made of round or square spring steal rod in helical form. The spring may be in tension
or compression, as the steam pressure acts along the axis of the spring. In actual practice, the spring is placed in
compression.
According to the original prescriptions the valve must be adjusted in such a manner that it begins to let the
steam out exactly when having reached the licensed pressure. Therefore the pressure governors are regulated so
that they cut off the furnace a short time before attaining the licensed pressure.
Water Level Indicator
Fig. 5: Water Level Indicator
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It is an important fitting, which indicates the water level inside the boiler to an observer. It is a safety device,
uipon which the correct working of the boiler depends. This fitting may be seen in front of the oiler, and are
generally tow in number.
Feed Check Valve
Fig. 6: Feed Check Valve
It is a non-return valve, fitted to a screwed spindle to regulate the lift. Its function is to regulate the supply of
water, which is pumped into the boiler, by the feed pump. This valve must have its spindle lifted before the
pump is started. It is fitted to the shell slightly below the normal water level of the boiler.
Blow off Cock
Fig. 7: Blow off Cock
The principal functions of a blow off cock are:
1. To empty the boiler whenever required
2. To discharge the mud, scale or sediments which are accumulated at the bottom of the boiler
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Boiler Accessories
Feed Pump
Fig. 8: Boiler Feed Pump
The feed pump is one of the most important accessories for a boiler unit. Its function is to take the feed water
from the reservoir and to force it into the boiler against the steam pressure.
Superheater
Fig. 9: Superheater
A superheater is an important device of a steam generating unit. Its purpose is to increase the temperature of
saturated steam without raising its pressure. It is generally an integral part of a boiler, and is placed in the path
of hot flue gases from the furnace. The heat, given up by these flue gases, is used in superheating the steam.
Such superheaters, which are installed within the boiler, are known as integral superheaters.
Economizer
An economizer is a device used to heat feed water by utilizing the heat in the exhaust flue gases before leaving
through the chimney. As the name indicates, the economizer improves the economy of the steam boiler.
It is a surface heat exchanger where water flows through the cast iron pipes or steel tubes and flue gases pass
around them. There are two general types of economizer namely (i) independent type and (ii) integral type.
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Other Accessories & Mountings
Fig. 10: Flame Sight Hole
Fig. 11: Water Quality Indicator
Fig. 12: Burner
Fig. 13: Gas Pressure Gauge
Fig. 14: Control Panel, Controller Relay
Fig. 15: Water Softener / Water Treatment Plant
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Water Flow Circuit
Fuel Flow Circuit
Gas (Supply Line)
Pressure Gauge
Gas On/Off Valve (Ball
Valve) Gas Filter
Gas Regulator Push Type Pressure
Gauge
Gas Control Valve
(Solenoid) Throttle Valve
Cross Flow Mixing
Chamber Burner
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Boiler Capacity
Tonnage Rating
The Tonnage Rating is widely used as a datum by shell boiler manufacturers to give a boiler a rating which
shows the amount of steam in kg/h. 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 100°C. 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. The
following equation can then be used to calculate the steam output:
(
) ( )
⁄
( ⁄ )
Boiler hp Rating
This unit tends to be used only in the USA, Australia, and New Zealand. A boiler horsepower is not the
commonly accepted 550 ft lbf/s and the generally accepted conversion factor of 746 Watts = 1 horsepower does
not apply.
In New Zealand, boiler horsepower is a function of the heat transfer area in the boiler, and a boiler horsepower
relates to 17 ft² of heating surface, as depicted in Equation:
( )
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 212°F atmospheric conditions.
Operations of Air and Fuel Flow for Firing a Boiler
1. Blow out of the exhaust gas.
2. Checking the water level in the boiler and if level is below the safety level water is refilled.
3. Air is blown in by starting blower.
4. Natural Gas acts as fuel passes through pressure gauge, regulator and solenoid valve and finally enters
into the burner.
5. Air and gas mixes in proportional limit and produce spark in the electric spark rod.
6. Pilot flame is established then full combustion starts.
7. The fire or hot flue gasses from the burner is channeled through tubes that are surrounded by the fluid
to be heated.
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Control of Water Level Indicator
By means of the water level indicator it is possible to control the water level in the boiler. Normally in automatic
mode of operation, this level is approx. 4 – 8 cms. above to low water mark. The water level must nit drop
below this mark, as otherwise the heating surfaces may be destroyed.
The water level indicator consists of the upper and the lower cock respectively sloping spindle valve, and the
glass pipe respectively reflection glass inset, inserted between the same.
For keeping the glass clean it is to be recommended to pen the cleansing tap placed at the lower end of the water
level indicator. The water that escapes under pressure, will rinse the glass.
In case a leakage should exist at the water level indicator, this may be removed by tightening the tension nuts
that caulk the glass, respectively the hand wheel.
In case of the sloping spindle valve water level indicator the tension nuts for the glass inset are to be found at the
back of the inset. Here it is recommendable to tighten crosswise from the middle.
When tightening, the connection valves of the water level indicator at the boiler must be blocked, because, at
improper handling, the glass may crack, and the escaping hot water or steam mixture may endanger persons.
To test a gauge glass, the following procedure should be followed:
Close the water cock and open the drain cock for approximately 5 seconds.
Close the drain cock and open the water cock. Water should return to its normal working level
relatively quickly. If this does not happen, then a blockage in the water cock could be the reason, and
remedial action should be taken as soon as possible.
Close the steam cock and open the drain cock for approximately 5 seconds.
Close the drain cock and open the steam cock. If the water does not return to its normal working level
relatively quickly, a blockage may exist in the steam cock. Remedial action should be taken as soon as
possible.
The authorized attendant should systematically test the water gauges at least once each day and should
be provided with suitable protection for the face and hands, as a safeguard against scalding in the event
of glass breakage.
Functions and Pressure Setting of Safety Valve
These are the devices attached to the steam chest for preventing explosions due to excessive internal pressure of
steam. A steam boiler is, usually, provided with two safety valves. These are directly placed on the boiler. The
function of a safety valve is to blow off the steam when the pressure of steam inside the boiler exceeds the
working pressure.
The safety valve installed is of a tested type and spring-loaded. By means of the spring
1. The surface of packing is pressed upon the packing ring
2. The power of the spring is arranged in such a manner that the contact surface is lifted only at an
adjusted pressure of 10 or 13 bar for example. Then the overpressure will escape and the spring brings
the packing surfaces back to the packing position.
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According to the official prescriptions the valve must be adjusted in such a manner that it begins to let the steam
out exactly when having reached the licensed pressure. Therefore the pressure governors are regulated so that
they cut off the furnace a short time before attaining the licensed pressure. Thereby it is prevented that the safety
valve is set in operation in case of each slight pressure rise.
Examination of readiness for function
It is recommendable to let the safety valve blow off from time to time by means of lifting the level in order to be
sure of the readiness for function of the valve and in order to prevent that boiler scale can deposit.
Relief in case of leakage
It may occur that, after blowing-off, dirt may deposit between the contact surfaces, in this case some steam will
continue to escape through the valve. Open again the safety valve by lifting the lever. The contact surface is
lifted from the packing seat; steam will escape and will eventually take off the substances. By releasing the
lever, the valve is closed again.
If this does not help one should, only under pressure, turn the cone on its seat to an for approx. ¼ turn by means
of square at the upper spindle end. Therefore the cover must be unscrewed and taken off. The cone on its seat
may only be turned if the safety valve is below the blowing-off pressure or a pressure being only slightly below
the blowing-off pressure. If this is not noted, one turn of the cone will destroy the contact surface. A tight
closing will not be guaranteed any more.
Fig. 16: Safety Valve
Hydraulic Test of a Boiler
The equipment should have been hydrostatically tested to a minimum of 1½ times the design pressure, in the
factory, and copies of the Manufacturer's Data report, signed by the Authorized Inspector witnessing and
evidencing the test forwarded to all jurisdictional bodies as well as to the Client. However, the complete system,
along with all interconnecting piping, should be hydrostatically tested before start-up to comply with code
requirements and to check for leaks that may have occurred during shipping and handling. This test should be
completed under the supervision of and witnessed by an Authorized Inspector who should represent the State or
municipality having jurisdiction or the insurance company covering the installation. At the option of this
inspector, the hydrostatic test may be at 1½ times the design pressure of the equipment, or at a pressure slightly
less than the setting of the lowest safety valve. The latter test will avoid the necessity of blanking or gagging of
safety valves, removing piping and plugging various pipe openings, removing controls and gage glasses, etc
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The boiler and process lines must be completely vented in order to fill them with water. The following is a
recommended procedure for hydraulic testing:
1. Open the steam drum vent valve and gag the safety valves in accordance with safety valve manufacturer's
recommendations. In lieu of gagging, the safety valves may be removed and replaced with test plugs or blind
flanges.
2. Open the vents on the interconnecting piping. Close steam outlet valve.
3. Isolate pressure switches, gauge glasses or control components that are not intended to be subjected to a
hydrostatic test.
4. Fill the system with treated water in accordance with recommendations from the Clients water treatment
consultant. The test water temperature range must be 70°F minimum to 120°F maximum (100°F to 120°F water
temperature is preferred). Care should be taken so that all air is vented while the equipment is being filled. Fill
the equipment until water overflows the vent, then close the vent.
5. Apply pressure slowly. The recommended rate of pressure increase is less than 50 psi per minute. Proper
control must be maintained so that pressure does not exceed the desired setting of the local steam boiler
inspecting agency. Do not subject any pressure part to more than 1½ times the design pressure rating of any
component.
6. When the proper test pressure is reached, inspection in accordance with the test objective can begin. Examine
the system for any leaks. If no leaks are visible, hold the system in a pressurized static condition for a period
long enough to satisfy the code requirement.
7. Upon completion of the test, release pressure slowly through a small drain valve. Then fully open vents and
drains when the pressure drops to 20 psig. Particular
Care must be given to make sure that parts not normally containing water during Operations are drained free of
water. The system should be drained fully after hydrostatic testing, to prevent freezing, if the unit is installed in
a cold weather area, and to minimize corrosion of the metal surfaces.
8. If temporary handhole or manway gaskets were used for the test, they should be replaced with regular service
gaskets before readying the unit for operation. Gaskets should never be reused. Replace gage glass if necessary
and make sure that the gauge cocks are open. Remove all blanks or gags from safety valves and install relief
valves, if removed.
9. Additional inspection at this time by the Authorized inspector will determine whether the installation
including piping arrangements, valve gauges and controls and other equipment on the unit meets Code and/or
other jurisdictional requirements.
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Discussion
In this experiment we have been studied in great details of a fire tube boiler. Boiler is one of the most important
appliances for any industry. It is also an essential part of a power generation plant. The boiler or steam boiler is
equipment used for producing steam. The American Society of Mechanical Engineers (ASME) gives the
following definition of the steam generating unit:
“A combination of apparatus for producing, furnishing or recovering heat together with the apparatus for
transferring the heat so made available to the fluid being heated and vaporized”
A steam boiler is a closed vessel in which steam is produced from water by the application of heat. Heat is
usually produced due to the combustion of fuel in a furnace. The hot gas generated in a furnace is called furnace
gas. It is also known as flue gas as it passes through a pipe called the flue.
The volume occupied by the water in the boiler drum is called the water space and the space above the water
surface is known as steam space. Heating surface is that part of the boiler which is exposed to hot gases on one
side and water or steam on the other.
The steam produced in a boiler is used for
► Power Generation: Mechanical work or electrical power may be generated by expanding steam in the
steam engine or steam turbine.
► Heating: The steam is utilized for heating the residential and industrial buildings in cold weather and
for producing hot waters for hot water supply.
► Utilization of steam for industrial processes such as for sizing and bleaching etc. in textile industries.
Steam is also used in many other industries like sugar mills and chemical industries.
The boiler we studied in our Boiler Laboratory is essentially of a fire tube type boiler. It can also be classified
by the number of passes present in the boiler. The boiler, we studied is a three pass boiler having five tube in
each pass.
Fig. 17: Three Pass Principle of Boiler
The characteristics of a water tube boiler are discussed below:
o The hot gases from the furnaces pass through the tubes which are surrounded by water
o For a given power, the floor area required for the generation of steam is more than a water tube boiler
o Overall efficiency with economizer is up to 75%
o The transportation and erection is difficult
o It can cope reasonably with sudden increase in load but for a shorter period
o The water does not circulate in a definite direction
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o The operating cost is less
o The bursting chances are less
o The bursting produces greater risk to the property
o It is not suitable for large plant
The boiler, steam boiler, is one of the most important and essential part of equipment for any industrial process.
So, the knowledge of a boiler, in many respects, is very important. In this experiment we have learnt
accessories, mountings and also the operating procedures of a steam boiler. These knowledge will certainly help
in our professional life.
References:
1. Operations Manual, Steam Boiler, Philipp Loos GmbH
2. Boiler’s Manual, Philipp Loos GmbH
3. Dampfkessel, Loos, Bosch Group
4. Khurmi, R., S., Gupta, J., K., “Thermal Engineering”, 2006
5. Roy, K., P., “Elements of Heat Engines”, 1988
6. Vasandani, V., P., Kumar, D., S., “Heat Engineering”, 1995