Page 144 - Handbook of Energy Engineering Calculations

overall heat sink is identical—25 percent larger than the base case—because
the steam extracted from the l-p turbine reduces the required cooling
capacity. Note that this also reduces steam-turbine output by 2 MW
compared to the mechanical chiller, but has less effect on overall plant
output.

Cost estimates summarized in Table 1 show that the absorption chilling
system required here costs about $4-million, or about $230/kW of added
output. Compared to the base case, raw-water consumption increases O&M

costs by $35/h when the chiller is operating. Disposal of additional cooling-
water blow-down adds $17/h.
Compared to mechanical chillers, absorption units may not handle load
changes as well; therefore they may not be acceptable for cycling or load-
following operation. When forced to operate below their rated capacity,

absorption chillers suffer a loss in efficiency and reportedly require more
operator attention than mechanical systems.
Refrigerant issues affect the comparison between mechanical and

absorption chilling. Mechanical chillers use either halogenated or
nonhalogenated fluorocarbons at this time. Halogenated fluorocarbons,
preferred by industry because they reduce the compressor load compared to
nonhalogenated materials, will be phased out by the end of the decade
because of environmental considerations (destruction of the ozone layer). Use

of nonhalogenated refrigerants is expected to increase both the cost and
parasitic power consumption for mechanical systems, at least in the near
term. However, absorption chillers using either ammonia or lithium bromide

will be unaffected by the new environmental regulations.
Off-peak thermal storage is one way to mitigate the impact of inlet-air
chilling’s major drawback: high parasitic power consumption. A portion of
the plant’s electrical or thermal output is used to make ice or cool water
during off-peak hours. During peak hours, the chilling system is turned off

and the stored ice and/or cold water is used to chill the turbine inlet air. A
major advantage is that plants can maximize their output during periods of
peak demand when capacity payments are at the highest level. Thermal

storage and its equipment requirements are analyzed in Section 13 of this
handbook.

5. Compare steam and water injection alternatives