Civil Engineering Reference
In-Depth Information
NOT RECOVERABLE HEAT
COMBUSTION AIR
COGENERATION PLANT
ELECTRIC GENERATOR
LOSSES
NATURAL GAS
ELECTRICAL ENERGY
LOSSES
HEAT RECOVERY
100%
F
50%
H
30%
E
20%
L
63%
Net heat recovery index (1)
23.40%
Primary Energy Saving index (2)
3,333
kW FF
1,667
kW
1,000
kW Pe
667
kW
Sm
3
/h
174.8
(3)
Sm
3
/h
194.2
Sm
3
/h
155.4
Sm
3
/h
349.6
(
=
0.13
U/Sm
3
0.154
Sm
3
/kWh
699
CO
2
kg/h
388
CO
2
kg/h
311
CO
2
kg/h
0.311
CO
2
kg/kWh
45.8
U/h
-
25.5
U
=
20.3
U/h
cost for fuel
2.03
cU/kWh
a
O&M cost
1.5
cU/kWh
b
overall production cost
3.53
cU/kWh
c=a+b
reference cost from utility
10
cU/kWh
d
cost saving
6.47
cU/kWh
e=d-c
operating hours
6,000
h/year
f
electric energy production
6,000,000
kWh/year
g=f*Pe
yearly cost saving
3,87,687
U/year
NACF=e*f
(see Chapter 19)
capital cost
1,300
U/kW
i
1,300,000
U
I=i*Pe
payback
3.35
year
I/NACF
(see Chapter 19)
IRR based
on 10 year of life
IRR
27
%
(see Chapter 19)
input data
primaryenergy saving
526
TOE/year
(
(1) H/(H+E)
(2) (1-F/(E/
p
+H/
b
))*100
(5)=(2)*FF*(E/η
p
+H/η
b
)*3,600*f/41,860/1,000
(4)= (3)/
b
where h
p
=electrical production and transmission efficiency=40% and h
b
=efficiency of the boiler to replace=90%
natural gas LHV=34,325 kJ/Sm
3
2 kgCO
2
/Sm
3
of natural gas
equivalent oil NHV= 41,860 kJ/kg
Fig. 9.8
Cogeneration plant with gas turbine
The recoverable heat form flue-gases varies according to end user requirements:
hot air for drying, steam and hot water, with or without additional burners.
The reference costs of electric energy and fuel are used for the economic
evaluations. A preliminary evaluation can be made on the basis of the average
cost of electric energy purchased from utilities (see Table
20.3
); for a more detailed
analysis, it is necessary to calculate the purchased energy and the consequent cost
corresponding to the new demand profile of the plant for utilities-energy. Local
regulations concerning the selling of energy to the utilities and its purchase from
them in emergency must also be considered.
Maintenance costs, too, must be taken into account, typically a fixed cost per unit
of kWh produced.
Example 3
Cogeneration plant with reciprocating engine
Figure
9.9
shows the energy balance and the economical evaluation of a
reciprocating engine cogeneration plant with 1,000 kW electric power in typical
working conditions. The heat recovery and electrical efficiency are those shown in
