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

74 Part II: Cogeneration experiences in Asia and elsewhere
2.3.6 Comparison of the different options
Table 2.2 summarizes the results of the analysis of the 4 options considered. As it can be
seen from the payback periods calculated, the diesel engine option has a clear edge over the
others. The results could however have been quite different had natural gas been available at
the site at a reasonable price.
Table 2.2 Comparison of the cogeneration options retained for the textile mill
Alt. Technical Power Percentage Investment + 40 Main Payback
Option Output Demand Met Per Cent Taxes Fuel Period
(MW) ( per cent) (10 6 US$) (Year)
1 Steam turbine 0.8 10 6.0 HFO 20
2 Gas turbine 4.7 60 7.6 Diesel 20
3 Combined cycle 6.8 80 13.6 Diesel 20
4A Diesel engine 12.7 160 12.6 HFO 6
4B Diesel engine 8.7 120 10.4 HFO 6
4C Diesel engine 6.4 80
9.6 HFO 6
On the basis of the analysis and in order to minimize the investment, the factory decided to
purchase a new diesel generator of 5 MW capacity and operate it along with the existing
generator to meet all the low-pressure steam demand of the factory. The existing highpressure
boiler met the demand for high-pressure steam.
2.4 Cogeneration in a Paper Mill 3
Cogeneration is widely used in paper mills around the world. Steam generated is used at
different pressures and temperatures for cooking of chips in digesters in the pulping process
and for drying of paper in paper machines. In addition, some amount of steam is used for
concentration of black liquor in multiple effect evaporators.
A small paper mill in India with an installed capacity to produce 60 tons of writing, printing and
duplex quality paper per day, uses agro-industrial residue based cogeneration to meet all the
process energy requirements. Waste paper is mainly used as the raw material and a small
quantity of pulp is produced from bagasse, the residue from the cane sugar mills.
2.4.1 Existing energy supply facility
Steam demand of about 7 tons/hour at 4 bar is met by two boilers, each with a capacity to
produce 6-7 tons of steam per hour, using coffee and rice husk as fuel. The utility grid met
electricity demand of about 2,500 kVA. During power interruptions, a stand-by diesel generator
set with an installed capacity of 1,525 kVA was used to take care of the essential power
needs.
Frequent power cuts, lasting for as much as 25-30 per cent of the year, forced the factory
management to look for an alternative economic source of power than the stand-by diesel
generator. Coinciding with the plan to increase the production capacity to 100 tons of paper
per day, a study was conducted to assess the viability of cogeneration. With the expansion
plan of the factory, the process steam demand was estimated as 13 tons/hour and the power
demand was expected to increase to 2,700 kW.
3 M.M. Patel and P. R. Raheja, “Case study presentation on cogen project and benefits at South India
Paper Mills”, paper presented at the CII Energy Summit ’96, Chennai, 11-14 September 1996.