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I.
INTRODUCTION
Cussons Steam Laboratory Equipment has been designed to provide complete
investigation of a steam power plant. Cussons Mini Steam Power Plant has been specifically
designed to allow institutes of education to study the principles and operations of an industrial
steam power plant. The plant can operate as a steam boiler, turbo-generator or complete power
plant. The energy input to the plant mainly comes from the fuels but the incoming feedwater and
the superheater provides energy input as well. The energy outputs of the plant is composed of the
energy output from the turbine, heat transferred to the condenser cooling water and other losses
such as heat loss and friction loss. The relationship between the energy input and the energy
output can be generalized by the formula:
Ein = Eout
Equation 1: Energy Balance
The objective of the laboratory experiment is to assess the energies going into and
coming out of the plant and to compare the energy balance for the plant as a whole. In this
experiment, the energy balance is used to examine the plant layout and identify and discuss any
energy transfers which have not been considered but are relevant.
II.
METHODS
A.
APPARATUS
The plant has five principal elements. These are: feed pump, boiler, turbine, condenser
and superheater. The basic series of processes in a steam power are:
Water is pumped into the boiler at a certain pressure by the feed pump, where the water is
converted into steam. The steam then travels through the superheater where, at essentially
constant pressure, its temperature is increased. Then, it is expanded to a low pressure in the
turbine thus producing the work output. The steam is then condensed back to water in the
condenser and once more returned to the boiler by the feed pump to complete the cycle for the
plant
Figure 1: Schematic Diagram of the Power Plant
B.
PROCEDURES
i) After the plant has been allowed to warm
986
986
up (it is recommended that at least 1 hour
986
986
should be allowed), set the pressure to 7[Bar]
using the controller keypad.
ii) Set the superheater temperature to 200[C]
using the controller keypad.
iii) Reset the superheater power gauge by
holding down the mode button and start the
SUPER HEATER T4
timer on the control panel.
STEAM LINE P5
Figure 2: Controller
iv) Measure the fuel consumption and the superheater power over a period of say 10 [minutes]
on the control panel.
v) Take all readings as detailed in tile observed results tables
vi) Repeat the above procedure (at 5 minute; intervals say), to provide three sets of data. Then,
for calculation purposes, determine the mean of each parameter in the observed results table.
III.
THEORY AND CALCULATIONS
For an overall energy balance for a plant such as this, a simple "box type" "system and
surroundings" model will be used. This system is shown, schematically, below:
Qfuel
Qsuperheater
(mh)air
(mh)feedwater
PLANT
as
a
SYSTEM
Wturbine
(mh)exhaust stack
Qloss
(mh)condensate
(Excludes cooling tower and ancillaries)
Where Qfuel
= energy input from fuel = m f
x UCV (assumes 100% for combustion
efficiency)
and UCV = 45.5 MJ/kg for class D fuel
Qsuperheater
= input electrical energy for superheater
=
(kW - hr) net reading from meter on panel / time elapsed (say 10 mins = 0
1667 hours) during test
h )=
( m
air
and where m
air
influx of enthalpy with ambient air for combustion (kW) = m
=
estimated airflow (kg/s)
(see below, exhaust calculation)
Cpair
approximates to 1.005 kJ/(kgK)
Tair
ambient air temp (C)
air
Cpair Tair
h)
( m
feedwater =
influx of enthalpy with feedwater (kW)
m
=
m
Where
h1
h1
steam mass flowrate given by :
3.11 P
kg /s
3600 v
enthalpy of water, determined at temperature T1, using steam property
tables (see ref. 1).
Wturbine =
power output from turbine (kW)
2 NT
60
=
where N
T=
angular velocity x output torque
(kW)
rotational speed of turbine, (RPM)
net torque on output shaft (Nm) and is given by the addition of the friction torque
value, Tm, and shaft torque, Tg, as described in accompanying volume of results.
h)
( m
exhaust stack
h)
( m
ex st.
( m
Where ( m
)
+ m
f
enthalpy efflux through the exhaust stack (kW)
) Cp T
+ m
f
ex ex
sum of fuel and air mass flows (kg/s)
Cpex =Specific heat at constant pressure for exhaust gas. To a close approximation this
will be 1.15 kJ/(kgK)
Tex
T11
Exhaust gas temperature measured at stack outlet, C
N. B.
Calculation of mf and ma
(fuel flowrate litre/s) x pfuel
where, pfuel
870 kg/m3 (Class D fuel)
The estimation of ambient airflow,
i)
m
, into the unit must be achieved by:
a
Using a small anemometer to measure the velocity, U a, of air at the, boiler air intake
grill; this will give a distance time equal to a mean velocity.
ii)
Measure the effective area Ag at the boiler air intake grill (m2)
iii)
Calculating air density at intake grill using the perfect gas law:
p=
pa
RT a
where
pa = (absolute) ambient inlet pressure (kPa)
Ta = absolute ambient inlet temperature (K)
R = 0.287 kJ / (kgK) for air
m
h)
condensate =
m
Where
hc
m
h
s c
steam mass flowrate, kg/s (see earlier)
enthalpy of condensate leaving condenser, kJ/kg
hc is determined from steam property tables at temperature T8
This means that hc = hf at a temperature of T8C (see ref. 1)
e.g. for a typical condensate temperature of, say, 40C then hc = hf = 167.5
(kJ/kg)
loss
the sum of all losses from the plant aggregated and comprising:
i)
convection, conduction and radiation losses from all hot surfaces exposed (even
when lagged) to the surrounding atmosphere
ii)
sound emissions (small)
iii)
slight leaks of fluid (rare)
loss
is determined by the solution of the following generalised energy equation:
Input energies
hence:
fuel
+ Q
= W
turbine
Thus,
loss
-( W
superheater
Output energies
h) + (( m
h)
+ (( m
air
feedwater
h)
m
h)
Q
+ (( m
ex stack + ((
condensate +
=( Q
turbine
fuel
+ Q
superheater
loss
h) +( m
h)
+( m
air
feedwater)
h)
m
h)
+( m
ex stack + (
condensate)
_____________________________________________
Once Q
loss
(kW) has been determined from the above energy balance equation, the relative
magnitude, as a percentage of input (or if desired, output) energy may be determined.
Thus:
Relative loss for plant RL is given by
loss
Q
100
RL = Q
fuel + Q
super h eater +( m
h)air +( m
h)feedwater
IV.
RESULTS
These are the data acquired and the results after the experiment.
Table 1: P7690/SP Steam Power Plant Observed Results
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The following are tables of derived results for energy balance.
Table 2: Input Energy
INPUT
Fuel Oil
Feed-water
Superheater
Air influx
Total
POWER [kW]
78.639
3.441
3.060
0.633
85.774
PERCENTAGE [%]
91.682
4.012
3.568
0.739
100.000
OUTPUT
Exhaust stack loss
Turbine output
(W)
Energy in
condensate
POWER [kW]
9.729
PERCENTAGE [%]
11.342
1.834
2.138
3.768
4.393
Other losses Qloss
Total
70.443
85.774
82.127
100.000
Table 3: Output Energy
A pie chart is created to depict the relative proportions of the various inputs and output energies
from the results above.
Figure 3: Pie Charts of Ein and Eout
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V.
DISCUSSION
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VI.
CONCLUSION
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VII.
REFERENCES
http://www.cussons.co.uk/education/products/steam_engineering/steam_power_plant_an
d_steam_benches/p7690_steam_power_plant_1kw.asp
