Plant intervention – optimising operations20 August 2014
Today’s market conditions have made power plant optimisation an increasingly important way for operators to reduce costs, but this process is not all about technological upgrades, as Elly Earls finds out, speaking to Alstom’s Bill Miller and Nuon Energy’s Adriaan Temmink.
Power plant optimisation, the improvement of an existing steam plant's performance by tuning or projects involving the installation of upgraded components or systems, is becoming an increasingly important way for operators to reduce costs, not only because of tighter margins and recent shifts in the structure of the industry, but also the growing need for plant cycling to meet the requirements of an energy mix, which is getting more diverse by the year.
According to Bill Miller, director, boiler chief engineering office, Alstom Power Thermal Services, the company's research in many markets has shown that the main impetus for this increased focus on optimisation has come from the narrowing of generation margins that occurred concurrently with structural changes in the industry, which split ownership of generation and transmission.
In Europe, for example, the 'Third Energy Package', which came into force in 2009, stipulated the separation of companies' generation and sale operations from their transmission networks. And, in China, similar reform was passed far earlier, in 2002, when the Chinese Government decided to set up separated business units responsible for generation, transmission and services.
"This reduces the ability to internally trade generation and transmission margins," Miller explains.
Moreover, while the overall power output capability of generators is often still required, the increasing influence of non-dispatchable generation - for example, from wind and solar sources - has led to more plant cycling than was anticipated when power plants were originally built.
"This has called for the need to tune for many multiple operating scenarios," Miller notes.
Essentially, conventional power plants increasingly need to be able to perform efficiently in part-load operation, just as they do at base load, in order to balance out the energy fluctuations in the grid created by the increased use of renewable sources.
"Management of such units are now studying possibilities to operate the plant at lowest possible load to prevent restarting costs and/or increase starting efficiency by reducing start-up time and costs," explains Adriaan Temmink, process technologist at Nuon Energy. "By adjusting existing plants' parameters, allowing them to start more rapidly, and raise and decrease load more dramatically, such installations might survive this transition period to a period where sustainable power production will be the trend, and where gas-fired power plants could prove to be indispensble to ensure back-up capacity in the occasion of violent weather changes, such as a sudden lack of wind combined with low solar power on a cloudy day."
"Operators now face multiple challenges, with reduced running hours for return on the investment, markets with lower wholesale prices, and greater demands on the plant operation parameters," summarises Miller. "Cost reduction therefore becomes essential for maintaining the plant designed on a different business model for future profitability.
"All of these challenges, in turn, have given plant-owners a driver on what they can now control, one of which is to optimise and 'sweat' their existing asset in a changed environment rather than necessarily have expenditure on large new projects."
Magic number: three categories of optimisation
So what are the most effective ways of optimising existing power plants? According to Miller, the technologies that can help improve plant performance can be divided into three categories - limited intervention, minor intervention or major intervention.
Limited interventions typically involve tuning or changes in practice identified by studying a plant.
"These studies can be used, for example, to provide robust feedback on operating and maintenance practices as well as being able to predict the future reliability of a plant given different maintenance scenarios," says Miller. "This reliability can then be compared with the business plan of the owner to provide direction on necessary changes in outage intervals and scope."
A well-devised monitoring and diagnostics plan could also have a significant impact on a plant's costs, as it allows the facility's owners to get advanced warning of any issues before a fault becomes a failure.
"In addition, with advancement in technology, it is now possible to do some inspection work without large-scale disassembly of equipment," Miller adds.
For example, if you could eliminate the need to remove a generator rotor to perform an inspection, the savings could range (depending whether this activity is on the outage critical path) from the direct cost (and risk) or removing and re-installing the generator rotor, to the direct benefit of additional available generation.
Meanwhile, minor interventions include improved air preheater and economiser technologies, which reduce losses to the atmosphere; turbine valve upgrades, which reduce losses to turbines; and boiler tramp air in-leakage control programmes. Increased steam temperature due to a more precise measurement could also lift plant efficiency.
Finally, major interventions could take the form of turbine-cylinder retrofits, which can eliminate reliability issues and increase efficiency and flexibility; boiler fuel changes - for example, from coal to gas or from one coal type to another; the addition of additional recovery surfaces at the boiler back-end; or the retrofitting of fabric filters for environmental compliance.
"Retrofitting the lifetime-limited major components like turbines, boiler panels and headers as well as the main steam pipework allow operators to use the remaining equipment of the plant for an extended period," says Miller, adding - with strong emphasis - that the best efficiency improvements can only be achieved if the plant is looked at as a whole.
"A holistic plant view is important," he notes. "The necessary segregation of plant areas and disciplines often means that the best solution has difficulty in being seen unless all of the costs and benefits are taken into account. It is therefore important to have an integrated view of the life cycle of the plant, and to have an asset management plan that accounts for all drivers whether these are market opportunities, environmental compliance, fuel costs, maintenance costs and so on."
Of course, with a new build, the latest technology can be installed, giving market-leading efficiency and reliability, whereas with refurbishment, there will sometimes be technical compromises, as the existing infrastructure was not originally designed for the new service.
As Temmink explains: "Adjusting plant parameters, such as turbine inlet temperature (TIT) of the gas turbine, reducing stack temperature of the heat-recovery steam generator (HRSG), raising steam and reheat temperatures or reducing condenser pressure will increase the overall efficiency significantly, but, without exception, this will be at the cost of increased lifetime consumption.
"Adjusting the manner of operation of the assets, therefore, has to be done in close cooperation with the department of maintenance engineering and, most likely, a new reliability-centred maintenance (RCM) procedure has to be executed."
Yet, given today's market conditions, the benefits of optimisation over new builds often outweigh these challenges.
"These changes can be enough to improve the relative merit order of the plant, such that in an environment of excess capacity markets, the plant can still have a future role," Miller explains.
Temmink clarifies: "By occupying a higher place in the merit order, chances increase that the particular asset will be asked earlier and/or more often; the plant is at lower market prices sooner in the market. When at the end of the year the installation ran for, say, 2,000 hours, resulting in a positive exploration figure and having consumed as many effective operating hours as it would have, had it run for 8,000 base load hours, finally no harm is done."
Power plant optimisation is not all about technology; however, staff training is equally critical to success.
"The reason often is that for existing plants, there is an embedded history and culture of how a plant performs and is operated," explains Miller. "Introducing new technology that can change what was previously considered as the normal practice requires the staff's understanding, in addition to the technology change itself."
Indeed, as Temmink emphasises, lack of investment in human capital can have a hugely detrimental effect on a power plant's operations: "As everybody will agree, there is a relationship between the amount of money invested in the scientific level of knowledge available to all operational personnel and the failure rate of the installation caused by its malfunctioning. For instance, malfunctioning caused by means of 'pushing the wrong button at the wrong moment' or such as the result of a lack of knowledge."
The investment must be optimal, he adds, or more harm than good could result.
"It can be feared that with insufficient investment, or investment by management in the wrong training courses, a temporary increase in failures of the installation may be expected to occur," he notes. "It might therefore even be better not to invest in human capital at all rather than invest in insufficient, wrong or inferior training programmes."
But in the non-scientific field of staff training, how can a power-plant operator be sure they've got it right? According to Miller: "A staff training programme should meet the plant owner's objectives, with the overall technical process changes, the reason those changes are achievable, how they contribute to the objective and what actions are required from each staff function to achieve the outcome."
Temmink adds: "Most helpful is the determination of the intellectual levels of personnel, the scope of the technological requirements and the performance circumstances of the installation. Training requirements and training programmes can then be carefully adjusted, and effectively and efficiently executed and implemented in the organisation."