POWER October 2013 - 52

COAL-TO-GAS CONVERSIONS
3. Service life is important. The impact of fuel price and capacity factor on the levelized busbar cost of electricity is remarkably different for
different expected plant service life. The top charts assume a service life of 30 years; bottom charts assume a 10-year service life. Charts on the left assume
low escalation in natural gas cost; charts on the right assume faster-rising gas prices. Source: Black & Veatch
Full conversion to gas
12
11
10
9
8
7
6
5
4
30
18
17
16
15
14
13
12
11
10
9
8
7
6
5
30
40
50
60
Capacity factor (%)
guideline, capital costs for implementing a
complete coal to natural gas conversion (outside
of new pipeline costs) can range from
$100,000 to $250,000 per MW.
A complete coal-to-gas conversion virtually
ensures that sulfur and particulate-related
emissions upgrades will not be required, although
in a tight regulatory scheme controls
may be required for NOx
Although CO2
and CO emissions.
than when burning coal, CO2
emissions will be much less
emissions will
be higher than with a modern gas-fired combined
cycle plant (CCP) because the steam
plant has a lower thermal efficiency.
Decommissioning of the coal-related
equipment may not be required from a logistics
and plant operations point of view, although
it may be required by environmental
regulators as part of a revised air emissions
permit. In a worst-case scenario, the coal
yard and ash ponds may need to be environ52
mentally
reclaimed. Demolition, removal,
and remediation costs vary greatly by site,
ranging from $3,000 to $30,000 per MW.
Repowering a Coal-Fired Unit. The nextmost-expensive
option is to repower the unit
by reusing as much as possible of the existing
coal unit to form a new CCP. This is typically
done by refitting the existing steam turbine to
work with one or two gas turbine units in parallel,
and reusing such major equipment as the
condenser and circulating water systems, cooling
tower, site buildings, transformer yard, and
so forth. (See " Repowering South Mississippi
Electric Power Association's J.T. Dudley, Sr.
Generation Complex " in the August 2013 issue.)
The steam turbine may derate 10% to
20% of its original nameplate capacity due to
the differences in steam flow between a conventional
boiler and a multiple-pressure heat
recovery steam generator.
Black & Veatch has found that when a
www.powermag.com
70
80
90
40
50
60
Capacity factor (%)
18
17
16
15
14
13
12
11
10
9
8
7
6
5
30
40
50
60
Capacity factor (%)
lifecycle cost evaluation is performed, the
modest cost savings of the repowering option
is quickly cancelled out by the many project
risks involved with repowering, the plant
outage costs, and the higher efficiency of the
CCP over the lifetime of the plant.
Complete Unit Replacement with a
Combined Cycle Gas Turbine. The most
extreme step in replacing coal-fired generation
with natural gas generation is tearing down or
mothballing the coal-fired unit to replace it with
a new CCP on site or elsewhere in the utility's
service territory. (See " High Bridge Combined
Cycle Project " in the September 2009 issue.)
Three Case Studies: Evaluating
Natural Gas Cofiring
For each of the four options, the expected service
life of the power station is of critical importance
in an economic analysis. Some options
that appear economically attractive in the short
POWER | October 2013
70
80
90
70
80
90
Coal/gas cofiring
Emissions control retrofit
Repower as combined cycle
12
11
10
9
8
7
6
5
4
30
40
50
60
Capacity factor (%)
70
80
90
New combined cycle
Levelized busbar cost (c/kWh)
Levelized busbar cost (c/kWh)
Levelized busbar cost (c/kWh)
Levelized busbar cost (c/kWh)

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POWER October 2013

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