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

68 Part II: Cogeneration experiences in Asia and elsewhere
undisturbed operation of several power consumers in the plant during any unexpected tripping
by drawing power automatically as and when required up to the extent of 17.6 MVA.
Considering longer outage of the cogeneration plant during major overhauls or during the
recommended inspections, it was decided to include an additional captive power generation
capacity of 20 MW to guarantee power supply without depending on the public utility grid.
Similarly, to avoid the problem of steam shortage during the outage of heat recovery steam
generators, an additional boiler was included as a spare unit. This would also take care of the
start-up constraint of the gas cracker plant when greater amount of steam was required than
during normal operating conditions. Lean gas was considered as the sole fuel for operating
the cogeneration unit. The results of the economic analysis, considering the prevailing costs
of equipment, fuel, O&M, manpower, etc., are summarized in Table 2.1. The cogeneration
case has a clear edge over the existing case as it helps to reduce the energy bill by 36 per
cent and improves the reliability of the production process.
Table 2.1 Economic analysis of cogeneration in the gas cracker complex
Existing Situation:
Process steam from conventional boiler and power purchase from utility grid
Description Annual Cost
Investment:
Boilers (2 x 136 tons/hour of steam)
Operating & Maintenance Costs:
(US$/year)
3,780.00
Electricity purchased from the grid (50 MW)
40,832.00
Fuel gas (6,626 tons/hour)
4,529.00
Other utilities
2,479.00
Maintenance & Chemicals
315.00
Manpower
336.00
Total Costs (existing situation)
52,271.00
Steam cost (US$/ton)
15.37
Power cost (US$/MWh)
Cogeneration Case:
102.08
Power and heat from the cogeneration plant, minimum demand contract with utility grid
Investment:
Boilers (3 x 136 tons/hour of steam)
Gas turbine generators (3 x 20.7 MW)
Steam turbine generator (25 MW)
Operating & Maintenance Costs:
18,267.00
Demand contract with the grid (17.6 MVA)
754.00
Fuel gas (15.148 tons/hour)
10,355.00
Other utilities
1,862.00
Maintenance & Chemicals
1,720.00
Manpower
504.00
Total Costs (cogeneration case)
Steam cost (US$/ton)
Power cost (US$/MWh)
33,462.00
12.30
51.64