EXPERIMENT 2: PERFORMANCE OF A STEAM PLANT THERMODYNAMIC (CLB 20704) -1- 1.0 INTRODUCTION 1.1 OBJECTIVES The objectives for this experiment are: i) To determine the performance characteristics of a steam plant. ii) To demonstrate the conversion of energy from one form to another and the measurement of mechanical power. iii) To demonstrate thermodynamic principle as applied to laboratory scale steam plant. 1.2 GENERAL BACKGROUND Steam engine is a heat engine which makes use of the potential energy that exists as pressure in steam, and then converts it to mechanical work that leads to the students understanding on some principles of thermodynamics using a laboratory scale steam plant. Here, a steam plant will demonstrate the principles of thermodynamics. The steam plant consists of several component include a boiler, a steam engine, a condenser and a feed pump. In large power plants, steam turbine are used but for a small scale laboratory set up, a steam engine is used. Steam engines were usually used in pumps, locomotive, train and steam ships. And some are still used it for electrical power generation. Basically, steam is a colorless expansive and invisible gas resulting from the vaporization of water. Below are the classes of steam: a) Saturated steam. b) Dry steam. c) Wet steam.
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EXPERIMENT 2: PERFORMANCE OF A STEAM PLANT
THERMODYNAMIC (CLB 20704)
-1-
1.0 INTRODUCTION
1.1 OBJECTIVES
The objectives for this experiment are:
i) To determine the performance characteristics of a steam plant.
ii) To demonstrate the conversion of energy from one form to another and the
measurement of mechanical power.
iii) To demonstrate thermodynamic principle as applied to laboratory scale
steam plant.
1.2 GENERAL BACKGROUND
Steam engine is a heat engine which makes use of the potential energy that
exists as pressure in steam, and then converts it to mechanical work that leads to
the students understanding on some principles of thermodynamics using a
laboratory scale steam plant. Here, a steam plant will demonstrate the principles
of thermodynamics.
The steam plant consists of several component include a boiler, a steam
engine, a condenser and a feed pump. In large power plants, steam turbine are
used but for a small scale laboratory set up, a steam engine is used. Steam engines
were usually used in pumps, locomotive, train and steam ships. And some are still
used it for electrical power generation. Basically, steam is a colorless expansive
and invisible gas resulting from the vaporization of water. Below are the classes
of steam:
a) Saturated steam.
b) Dry steam.
c) Wet steam.
EXPERIMENT 2: PERFORMANCE OF A STEAM PLANT
THERMODYNAMIC (CLB 20704)
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d) Superheated steam.
e) Highly superheated or gaseous steam.
1.3 THEORY
The cycle of operations in a heat engine is based on Rankine Cycle. The
Rankine cycle more closely approximates to the cycle of a real steam engine
compared to the Carnot cycle. It therefore predicts a lower ideal thermal
efficiency than the Carnot cycle. In the Rankine cycle, heat is added at constant
pressure p1, at which water is converted in a boiler to superheated steam causes
the steam expands at constant entropy to a pressure P2 in a condenser; the water
so formed is compressed at constant entropy to pressure P1 by a feed pump.
Figure 1.3(a): The Rankine Cycle System Figure 1.3(b): Diagram of Rankine Cycle
Based on the figures above, the cycle is consists of four processes whereby:
• From 1 to 2: Isentropic expansion (Steam turbine)
• From 2 to 3: Isobaric heat rejection (Condenser)
• From 3 to 4: Isentropic compression (Pump)
• From 4 to 1: Isobaric heat supply (Boiler)
EXPERIMENT 2: PERFORMANCE OF A STEAM PLANT
THERMODYNAMIC (CLB 20704)
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For this experiment, firstly consider the complete system of boiler, motor
and condenser surrounded by the control surface. The steady flow energy is given
by:
353211 mhmhQQQQW w −+−−−=
• The overall thermal efficiency of the plant is given by
)( 3
1
1
1
hhms
W
Q
W
w
TH−
==η
• The overall boiler efficiency is given by following this formula
1
1 )(
Q
hhm wsB
−=η
• Rankine cycle efficiency
)( 1
1
hhms
W
w
R−
=η
• Quality of steam
x = h [enthalpy after throttling calorimeter] – hf [@boiler pressure ]
hfg [ @boiler pressure]
• Power W :
60
)21(2 NFFRW
−=
π
R= Brake radius (0.056m)
F = spring load (N)
N = Engine speed (rev. min-1)
EXPERIMENT 2: PERFORMANCE OF A STEAM PLANT
THERMODYNAMIC (CLB 20704)
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1.4 OVERALL PROCESS DESCRIPTION
Laboratory scale steam plant is designed in order to leads student to
understand some of principles of thermodynamic. The main components in the
steam plant are such as a boiler, steam engine, condenser and the feed pump.
Steam engine is use to convert potential energy to mechanical energy. Therefore,
water is supplied from the reservoir to the boiler by an electric pump and is heated
inside it by using two immersion heaters (3 kW each). The boiler is to incorporate
a safety valve a water level gauge and a blow-down cock. Boiler to be rated up to
6 kW and to generate up to 8 kg per hour of steam with maximum pressure of 400
kPa.
In this case, the water should be always clean and free from minerals to
prevent any errors or contamination occurs inside it. Here, the steam pressure in
the boiler will rises until it reaches to 4 bars. Then, it will undergo the steam
engine, which by steam engine is a prime mover, and the engine has a totally
enclosed crank case, 2 cast iron trunk pistons and overhead piston valve made of
stainless steel. A simple band brake will absorb this engine power form by steam
engine. This steam is expanded in the steam engine to produce a useful work.
Then, the condenser will condense the exhaust steam from the steam engine from
saturated steam to water. This water is then returned back to the reservoir and
pump back into the boiler and the cycle continues.
Furthermore, this apparatus is also consists of a tachometer to measure
speed, an electrical power meter for measuring the heater power input,
thermocouples with read-outs for steam and cooling water temperatures, and
pressure gauges for boiler and engine inlet pressures. This compressive
instrumentation will provide the user with all the reading necessary to perform
experiment in thermodynamics and efficiency.
EXPERIMENT 2: PERFORMANCE OF A STEAM PLANT
THERMODYNAMIC (CLB 20704)
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2.0 METHODOLOGY
2.1 APPARATUS
Figure 2.1: Steam Motor and Energy Conservation Test Set
2.2 OPERATIONS
2.2.1 SETUP & CHECKS
1. The cooling water supply was supplied to the inlet pipe of the
condenser and the outlet pipe was connected to a suitable drain.
The outlet from the condensate collector was connected to a
suitable drain or container.
2. The unit was connected to the electrical supply.
3. The filter on the end of the boiler pump suction pipe was checked
in place and clean. The end of the pipe was placed into the
reservoir tank supplied. The tank was filled with the clean soft
EXPERIMENT 2: PERFORMANCE OF A STEAM PLANT
THERMODYNAMIC (CLB 20704)
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water to at least half way. The reservoir was kept half full to ensure
no air is drain in to the pump
4. The upper and lower valves on the boiler sight gauge and the steam
outlet valve on the boiler was opened.
5. The temperature display was switched on.
6. The red emergency stop button was pulled out. The mains supply
and the boiler feed pump was switched on.
7. The pump bleed valve was opened and the pump was operated.
When there is a steady flow of water, with no air bubbles, the
bleed valve was closed and begins to fill the boiler to the upper
mark on the sight gauge. The boiler should fill in 8 to 10 minutes.
When the boiler is full, the boiler steam valve was closed.
8. The band brake was slackening to ensure that the engine is not
loaded. The spring balances was zero.
9. The both heaters was switched on, the indicator lamps will light up
to show the heaters are working. The boiler pressure will rise as
indicated on the boiler pressure gauge. The calorimeter valve was
closed.
2.2.2 START UP
1. When the boiler pressure has reached approximately 60 kN/m2 (0.6
bar), the boiler steam valve was opened until the engine inlet
pressure has reached 40 kN/m2 to 50 kN/m
2 (0.4 bar to 0.5 bar)
2. In one swift movement, the starting knob was pulled upward and
let go. The engine was started to turn. If the engine does not turn:
• Try the starting knob again
• Check the inlet pressure is correct
• Check that the band brake is not too tight
EXPERIMENT 2: PERFORMANCE OF A STEAM PLANT
THERMODYNAMIC (CLB 20704)
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• Check that the steam engine is not seized- the pulley was watch
at the front of the engine and see if it turns as you pull the
starting knob upwards.
3. The condenser cooling water was turned on and a flow rate for
about 100 liters/hour was adjusted. As the steam pressure rises, the
engine speed will increase, the steam valve was used to keep
engine ticking over at a pressure of between 40kN/m2 and
50kN/m2
4. The heater was switched on in order to keep the boiler pressure up
to sufficient level. The boiler safety valve will begin to operate at
approximately 340kN/m2 (3.4 bars) but will not be fully open until
400kN/m2. The steam at higher boiler pressure was vented through
the safety valve.
5. The apparatus was run for at least 10 minutes to stabilize before
the reading is taken. The level of water in the boiler was checked
regularly. The feed pump was switched on when necessary so that
the level lies between the permitted limits.
2.2.3 EXPERIMENT PROCEDURES
1. The engine was run at the constant speed 2000 rev per min-1 at
varying engine load with:
a) The right hand spring balance was loaded with 2N stages to
20 N.
b) The boiler pressure was varied to achieve constant speed.
(+ 100 rev. min-1)
2. The parameter was recorded in the data sheet
(The volume of condensate was collected in a measuring cylinder
with 1 minute’s interval for the condensate flow rate.)
3. The results were analyzed.
EXPERIMENT 2: PERFORMANCE OF A STEAM PLANT
THERMODYNAMIC (CLB 20704)
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4. After used:
a) The electrical and water supplies were disconnected.
b) The boiler was allowed to cool down and the boiler drain
valve was opened.
c) The water from the apparatus was drained.
d) The temperature display was switched off.
EXPERIMENT 2: PERFORMANCE OF A STEAM PLANT
THERMODYNAMIC (CLB 20704)
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3.0 DATA & RESULTS
Table 1: Data for Operating Parameters
*Condenser Cooling Water flowrate, mw = 0.0284 kg/s
Spring
Load
Boiler
Pressure
Boiler
Temp
Engine
Inlet
Pressure
Engine
Speed
Calorimeter
Temp
Condenser
Cooling
H2O inlet
Condenser
Cooling
H2O outlet
Condensate
Flow Rate
Electrical
Power
Condensate
Temp
F1
(N)
F2
(N) P1 (bar) T1 (°C) P2 (bar)
N
(rev/min) T2 (°C) T3 (°C) T4 (°C) Ms (kg/s) Q1 (kW) T5 (°C)