Cycling your steam power plant is inevitable, so now is the time to learn how to minimize equipment damage and assess the true costs of cycling. Whether cycling is required by the grid operator because of renewable integration or other factors, you must be proactive about updating operating processes and upgrade equipment so the transition to cycling operation goes smoothly.
Few conventional steam plants were designed to follow load, cycle from minimum to full load every day, or shut down and start up daily, as so many plants are called upon to do these days. The challenge for owners of plants required to operate in this way is to fully understand the effects on plant and component life expectancy, and the actual costs, of these new operating profiles. If the actual costs are unknown, making a profit becomes a matter of luck rather than good management.
In a competitive electricity market, not knowing your true generating costs could place your plant or your company in economic jeopardy. For example, if the actual cost of cycling a unit is not included in your bid price, and the plant must cycle, not only are you not being compensated for unknown damage to plant equipment, but you also are not being compensated for future maintenance and unplanned repair outages. Those costs often far exceed the short-term profits gained by submitting an artificially low market bid price.
Furthermore, the bill for the true cost of operation will arrive after the fact, often years later, in the form of lower capacity factors, less generation, and higher production costs. If, at that time you update production costs to reflect your new reality, your plant may no longer be competitive, resulting in even worse economics.
The same scenario applies in a regulated environment: Future higher-than-expected operating and maintenance costs have to be justified to the public utilities regulators and may not be recoverable.
The following discussion applies equally to solid fuel–fired steam plants and natural gas–fired combined cycle plants.
Cycling for Dollars
Cycling your plant without understanding the costs or applying care and expert guidance when cycling often leads to significant damage, frequent forced outages, and loss of power generation. Bad long-term decisions may be driven by short-term or uninformed decisions, making your plant unreliable during high-profit periods. The fatigue damage added to an older baseload power plant causes creep fatigue interaction damage, rapid increase in boiler tube failures, and many other component failures, including turbine generator and balance-of-plant early creep fatigue failures. In effect, excessive cycling will either decrease the life expectancy of your equipment, or the costs to maintain the equipment will rise, sometimes significantly. Also remember that poorly written startup and shutdown operating instructions or a failure to follow standard processes can often contribute to increased cycling damage and resultant costs.
In our experience, about 60% to 80% of all power plant failures are related to cycling operations. If plant management understands the costs and has a process that provides actual operating costs, it is able to take proactive operational measures rather than deal with unexpected costs and poor performance years after damage to plant systems is done (Figure 1).
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| 1. Common problems in cycling plants. A survey of 215 steam plants found many common equipment problems. Source: Intertek-Aptech |
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