part 1: overview of cogeneration and its status in asia - Fire

76 Part II: Cogeneration experiences in Asia and elsewhere
Though the initial investment becomes higher due to the higher boiler capacity and larger
turbine and generator, condenser, etc., it can be justified by the higher efficiency and plant
load factor. Moreover, the cost of additional fuel will be marginal. The power generated would
be adequate to handle all the critical loads whereas the non-critical loads can draw power
from the grid. Thus the plant productivity will no longer be affected by the utility power outages.
2.4.6 Full power generation
As there was a need to include installation and management of the fuel and ash handling
system, cooling water circuit for the condenser, and power interfacing and distribution, one
more alternative was included to further increase the boiler and turbine capacities to meet all
the heat and power needs of the factory. Though the investment required was higher, power
generation cost became much lower compared with that of the utility or the diesel generator,
mainly due to the low fuel cost. In addition, the option to avail full depreciation of the
investment in the first year made the economic viability of the project particularly attractive.
Hence the factory management retained this last option. The details of the economic
calculations for this alternative are summarized in Table 2.3.
Table 2.3 Technical and economic parameters of the cogeneration facility
Description Units Values
Power plant capacity
Cogeneration plant power consumption
Net power output for the factory
Working hours
Plant load factor
Annual electricity generation
Annual fuel (rice husk) consumption
Annual fuel use for process steam
Annual net fuel supply for cogeneration alone
Investment on the cogeneration facility
Cost of electrical modernization
Price of electricity purchased
Avoided cost of electricity generated
Cost of fuel
Cost of fuel for cogeneration
Operation and maintenance costs
Annual cost saving
Gross payback period
kW
kW
kW
Hours/year
per cent per annum
10 6 kWh
tons/year
tons/year
tons/year
10 3 US$
10 3 US$
US¢/kWh
10 3 US$/year
US$/ton
10 3 US$/year
10 3 US$/year
10 3 US$/year
Year
2,000.00
350.00
1,650.00
8,760.00
0.80
11.56
30,000.00
12,000.00
18,000.00
2,000.00
286.00
9.43
1,090.00
22.86
411.00
114.00
565.00
4.00
It is expected that when the mill capacity is increased to 100 tons/day of paper, the same
cogeneration plant will operate with 20 tons/hour of inlet steam to provide 12-13 tons of
process steam per hour at 4 bar and generate around 2,700 kW of power.
A desuperheater was added near the paper machine to reduce about 100°C of superheat of
the process steam extracted from the turbine. Compared with the earlier process line
pressure of 7-8 bar, the present system operates at 5 bar pressure, thus the steam
consumption is reduced and the power output from the turbo-generator is increased per ton of
steam. In order to extract the maximum benefit from the cogeneration system and to make