Cost Impacts of Cycling Coal-Fired Power Plants 33rd USAEE/IAEE North American Conference Pittsburgh, PA October 27, 2015

Key Takeaways Operation of existing coal units at partial load factor negatively impacts heat rate, which increases fuel costs. Operating at 50% load factor increases heat rate by nearly 10%. Units designed for a single annual cold start can expect a cost of ~$13-14k/MW for this cold start. However this cost per start could increase by 14-29% for coal units that do a monthly cold start. This is due to increased fuel usage for startup, and increased failure/inspection costs for mechanical components. This increase in fuel use, O&M costs is sufficient to force otherwise profitable existing coal units to (or beyond) the margin in PJM during periods of low gas price, such as shoulder months.

Study Objective Identify which mechanical components in the power plant are most susceptible to early failure (and replacement) due to more frequent ramping and starts/stops. The cost of these components will be developed, and the frequency with which these need to be replaced should also be identified. This information should be reflected in an updated O&M cost ($/MWh basis) for a typical existing coal unit. Evaluate the impact that ramping/load following has on heat rate. This revised heat rate should be used to reflect an updated fuel cost ($/MWh basis) for a typical existing coal unit. Since the extent to which existing coal units will be load following in the future is unknown, consider a range of outputs (percentage of maximum annual kilowatt-hour production) and to reflect the reduction in revenue resulting from being on (or near) the margin.

Time Between Replacement/Major Repair (Years) Component Time Between Replacement/Major Repair (Years) Replacement/ Major Repair Cost (1000$/MW) Annual (Routine) Maintenance and Inspection Cost (1000$/MW/year)   1 Start 6 Starts 12 Starts Coal Pulverizer 6 5 4 1.33 0.92 1.0 Steam Drum Annual maint. only N/A 1.8 2.2 Boiler Refractory 1.5 Superheater/Headers/Tubes 10 9-10 8-10 8-30.6 0.067 0.080 Reheater Tubes 10-23.3 Economizer Tubes 9 8-9 7-8 5.0-10.0 Lower Furnace Tubes 7-9 6-8 0.15-1.05 Windbox Supports 0.33-0.50 Feedwater Heaters 15-20 18 15 0.67-4.33 0.25 Boiler Feed Pumps 0.50 0.30 Steam Turbine Generator (STG) 0.030 Minor Overhaul 2-4 2-3 0.53 Major Overhaul 5-10 5-8 Admission Valves Incl. in minor overhaul cost Incl. in STG cost Turbine Rotor Incl. in major overhaul cost LP Turbine Blades Generator

Change in Heat Rate as a Function of Load Factor

Maintenance and Startup Fuel Cost as a Function, per Start

Annual Maintenance and Startup Fuel Cost as a Function of Startup Frequency

Total Annual Fixed O&M and Startup Fuel Costs

Impact of Capacity Factor Reduction Strategy on Fuel, O&M for a Single Cold Start If a single annual cold start is expected, cheaper to shut the unit down and restart when needed, instead of operating at partial load factor.

Impact of Capacity Factor Reduction Strategy on Fuel, O&M for Multiple Cold Starts Combined effects of heat rate degradation due to frequent starts/stops or partial load operation, combined with increased O&M/maintenance costs, can negatively impact dispatch costs of existing coal units

PJM Dispatch Curve (5-22-15) Average gas price: ~$2.50/MBtu Existing coal units have reasonably economic dispatch position

PJM Dispatch Curve (5-22-15) Average gas price: ~$2.50/MBtu Additional cost of $4/MWh from increased starts/stops pushes otherwise profitable coal units to the margin. More frequent stops/cold starts negatively impacts heat, which adds fuel cost, and increases maintenance costs from added wear-and-tear on susceptible components.