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
74%
H
13%
E
13%
L
85%
Net heat recovery index (1)
12.8%
Primary Energy Saving index (2)
7,692
kW FF
5,692
kW
1,000
kW Pe
1,000
kW
Sm
3
/h
597
(3)
Sm
3
/h
663.3
Sm
3
/h
143.5
Sm
3
/h
806.8
(
=
0.13
U/Sm
3
0.143
Sm
3
/kWh
1,613
CO
2
kg/h
1,327
CO
2
kg/h
286
CO
2
kg/h
0.286
CO
2
kg/kWh
104.9
U/h
-
86.2
U
=
18.7
U/h
cost for fuel
1.87
cU/kWh
a
O&M cost
1.0
cU/kWh
b
overall production cost
2.87
cU/kWh
c=a+b
reference cost from utility
10
cU/kWh
d
cost saving
7.13
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
428,128
U/year
NACF=e*f (see Chapter 19)
capital cost
1,200
U/kW
i
1,200,000
U
I=i*Pe
payback
2.8
year
I/NACF
(see Chapter 19)
IRR based
on 10 year of life
IRR
34
%
(see Chapter 19)
input data
primaryenergy saving
584
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
3
equivalent oil NHV= 41,860 kJ/kg
2 kgCO
2
/Sm
of natural gas
Fig. 9.7
Cogeneration plant with backpressure steam turbine
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 2
Cogeneration plant with gas turbine
Figure
9.8
shows the energy balance and the economical evaluation of a gas
turbine cogeneration plant with 1,000 kW electric power in typical working
conditions. The heat recovery and electrical efficiency are those shown in Table
9.1
.
Specific consumptions due to the production of electric energy are calculated as
Sm
3
/kWh entering the plant.
The figure shows also primary energy saving (TOE) in comparison with standard
utility plants and variation of the factory energy consumption (additional fuel
consumption and reduction of kWh from utilities).
