SBREFRA Presentation
Wayne Penrod
Executive Manager, Environmental Policy
Sunflower Electric Power Corporation
Unit design is unchangeable
• Unit design is determined (fixed) by the owner’s
engineer before any major components are ordered
and before any construction is commenced.
• Conditions are influenced by the required size, the
expected usage (peaking, intermediate, or base - often
called the duty-cycle), and the need to minimize the
initial cost of the generating facility.
• The most critical of these factors, steam pressure,
steam temperature, and condenser back-pressure
cannot be altered without deep reconstruction of the
plant.
Sub-critical steam cycle
• Modern sub-critical pulverized coal units (>100 MW) were first
constructed in the late 1940’s, initially by the larger investor-owned
utilities.
• These subcritical units operated at pressures of 1600 psi to 1800 psi
and temperatures of 1000F.
• Larger, more efficient subcritical pulverized coal units, operating at
increased pressures (2450 psi) and temperatures (1000-1020F)
began to be constructed in the mid-1970’s. These became typical
design conditions for smaller investor-owned and cooperative
generating facilities.
• Smaller subcritical units operate at pressures of 1200 to 1600 psi
and 950 to 1000F.
• Older, subcritical units may operate at pressures of 400 to 1000 psi,
and 800 to 900F.
Supercritical steam cycle
• Supercritical operating pressures are greater than 3600 psi.
• Throttle steam temperatures were initially at 1000F.
• Supercritical pulverized coal units were first constructed in the mid1960’s by the larger investor-owned, and federal governmentowned utilities. AEP, Duke, Southern, and TVA are the leading
examples. Because of higher initial cost these units tend to be
large, generally above 600 MW.
• These early units were much plagued by scale-up design problems
and water chemistry.
• Further advancement occurred with foreign development beginning
in the 1990’s.
• Newer, more efficient units, such as AEP’s John Turk, operate at
higher throttle steam temperatures - approaching 1100F.
Factors affecting unit operating
efficiency
• Best generating unit efficiency obtained when
new, at design conditions defined in the
specifics of the contract guarantees.
• Units almost never operate at those
conditions. Operation below design, or
optimum conditions necessarily introduces
thermal inefficiencies, thereby increasing the
determination of the unit’s heat rate.
Ambient and maintenance factors
affecting efficiency
• Higher ambient air temperature and humidity negatively
impacts a unit equipped with cooling towers; higher
surface water temperature negatively impacts the
performance of a once-through cooled unit.
• Mechanical issues related to steam generator or turbine
generator operation can further introduce thermal
inefficiencies (i.e., turbine steam packing leakage, air
heater leakage, furnace slagging, etc.).
• Components or sub-components of a generating unit will
deteriorate with age and small incremental losses of
efficiency will occur. (Condenser tube fouling and pluggage,
and loss of air heater basket materials through corrosion
are some examples.)
Operating factors affecting efficiency
• Peaking, or intermediate duty operation, by design, are undertaken
at substantial penalties to the thermal efficiency of a steam turbine
generator.
• Load (or frequency) regulation, or automatic governor control, is
used to match an individual electric company energy supply to their
instantaneous customer load; this necessary function requires the
assignment of certain portions of a generating units capacity to
“reserve requirements” established by the power pools. This
decrease in unit load decreases the efficiency of each connected
generator to the grid.
• Small systems, with one or two operating units, experience this
impact more fully. Larger systems may reassign reserve
requirements and limit the impact to a smaller percentage of their
fleet.
New factors affecting operating
efficiency
• Regulated versus unregulated markets may have an effect
on dispatch of unit; a base load unit may become a load
following unit.
• Integrating renewable resources into the supply portfolio
causes increased cycling duty for existing resources.
• Required installation of 316(b) cooling towers on units
designed for once-through cooling dramatically decreases
the overall unit efficiency.
• Increased auxiliary loads due to the required installation of
new tail-pipe control technologies for CATR and EGU MACT
will decrease the overall unit efficiency.
Case studies
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Marion 123
Chamois
Fort Dodge
San Miguel 1
Genoa 3
Garden City Gas Steam
Take-home message
• Design efficiencies were fixed in the development
phase of the plant, and any improvements are at
best marginal and at worst hindered by the
specter of NSR review.
• Regulatory influences either indirectly hinder the
maintenance of original design efficiencies (NSR
review) or directly require the addition of
equipment which penalizes the thermal efficiency
of a facility.
• A output-based GHG standard (lb-CO2/MWh) is
not a plausible metric for NSPS purposes.