Cost control of operations and maintenance
Power plants that often start, stop, cycle, two shift, and operate above a unit’s rating impact the life of the unit and total associated unit operating costs. Intertek has developed a real-time operations code called cost control of operations and maintenance (COSTCOM) that is specifically calibrated to display the maintenance, capital replacement, and wear-and-tear costs associated with these potentially damaging operations.
Annual cycling costs for nearly 300 power generating plants were analyzed including conventional coal, oil, and gas fired units ranging from 15 to 1300 megawatts (MW) in size from subcritical drum type to supercritical once-through units. Plant types include combined cycle and single cycle units’ gas turbines; heat recovery steam generator (HRSG) units; and hydro, pumped-hydro, and nuclear units.
One conclusion from these analyses is that the financial costs associated with cycling operations are very high for most power plants. These costs should be displayed for the operators and maintenance personnel so they can help minimize and optimize these costs to meet market/plant conditions. Calculating these costs also allows for their recovery through negotiating informed power purchase agreements, contracting with the independent system operator (ISO), bidding into ancillary services markets, and transferring costs to other utilities, if possible.
COSTCOM’s algorithm follows these steps to measure damage on plant components:
- Cycle counting (rainflow counting)
- Ramp rate damage
- Total "fatigue" damage
- Steady state (creep) damage for each component monitored
- Utilize Larson Miller parameter to quantify impact of extreme temperature stresses (adjustment factor)
- Steady state damage + fatigue damage = Total damage.
The precise damage level is unit specific and dependent on design and unit operating practices. The true costs of cycling and high load operations are often not known or not well understood by utility operators because of the complex effects of these operations on additional capital and/or maintenance spending requirements, increased equivalent forced outage rate (EFOR), increased heat rate, and reduced life effects.
Even when a unit is thought to be properly designed for cycling, there are external effects in the balance-of-plant design, water chemistry, etc., that make some units more susceptible to cyclic damage than others. Just as with heat rate testing, cycling units should be subjected to a thorough analysis of their cycling operations and the impact of these on costs in order to optimize operations and determine the true cost of each type of operation. Proper use of this knowledge can then result in significant savings and improved profitability.
COSTCOM’s capabilities and features include:
- Monitoring the temperature, pressure and MW ramp rates for all plant-wide essential and critical equipment
- Advising the operator of the current critical values and the ramp rate value
- Keeping track of and displays the maximum value and actual values as well as the critical do-not-exceed values that cause severe equipment damage
- Monitoring the number of starts, load follows, and shutdowns as well as the time from the last operation in order to determine the type of next start for the equipment
- Displaying critical ramp rate values for each type of start or online operation so an operator can see at a glance if a problem exists with that operation or if all is normal plant-wide
- Displays rapid updates of the wear-and-tear (WT) cost of the loading damage to unit equipment
- Displaying the accumulated cost over the last minute, last 15 minutes, last hour, last 24 hours, last 90 days, and last year(s)
- Displaying the cost of each operational change to the power plant and, with this knowledge, operators can minimize WT costs during times when MW prices are normal. When prices are high and profit critical, the operator is armed with their operational WT costs and critical values that should not be exceeded. This may allow rapid MW response (from 2 to 10 times faster than previously thought possible) during load changes, while minimizing plant damage and costs.
Knowledge of the cost of each type of operation—hot starts, warm starts, cold starts, load follows, shutdowns, and trips—is essential. Accurate and real-time knowledge of costs is critical to the competitive power business. COSTCOM is designed to equipment plant operators with this knowledge and help ensure each type of operation is performed optimally.
Fatma Faham is senior project manager at Intertek, and she specializes in high energy piping systems with nine years of experience in the power industry. This article originally appeared on Interek’s blog. Intertek is a CFE Media content partner. Edited by Carly Marchal, content specialist, CFE Media, firstname.lastname@example.org.