By: Pascal Decoussemaeker & Victoria Watts, Alstom Power Service, Switzerland
Power producers traditionally take a bottom-up, component-centric approach in optimizing their power plants. As they face a variety of new and changing business environments, such as increased competition, evolving grid requirements, fuel supply disruptions and environmental regulations, it increasingly makes sense to combine this with a top-down approach.
The logic is clear: top-down allows you to identify and address the most important problems first, and this will deliver the optimum and fastest return on investment, in alignment with corporate goals and objectives.
To adapt to new environments and meet such objectives, you first have to determine the full potential and requirements of each plant. This varies substantially from one plant to the next, and if strategic issues are not addressed first, it could be a case of throwing good money after bad.
For example, lower than expected reliability might be consuming all the profits of one producer’s plant, while for another just a little extra power output could make the difference between achieving contract compliance or facing heavy penalty costs.
Alstom supports the top-down approach with a service called Total Plant Assessment (TPA), which is based on a systematic and data-driven methodology, highly dependent on careful analysis of historical data to identify the main issues at stake, and the specific components that merit detailed attention.
Combined-cycle plant, Taranaki, New Zealand
Contact Energy is a leading generator of electricity in New Zealand. The company is focused on responding meaningfully to climate change by ensuring that its combined cycle plants are as efficient as possible.
When Contact Energy ordered a TPA for its combined-cycle gas turbine (CCGT) plant at Taranaki, its objective was to secure increased production capacity and efficiency. Alstom started by collecting historical data covering an operation span of six years, using it to uncover plant improvement potential and to provide the plant owner with a detailed trend analysis report.
New Zealand generator Contact Energy ordered a TPA to increase the efficiency and output of its CCGT plant at Taranaki
In the next phase, Alstom plant experts arrived on-site to perform consistency checks, thermal measurements and a general inspection in close cooperation with Contact Energy while the plant was in operation. When this was complete, Alstom’s team focused their investigation of the data on specific components that appeared to offer the highest potential for improvement during the upcoming planned overhaul.
In particular, the team identified major opportunities for improvement in the fuel gas supply system, the gas turbine compressor and the heat recovery steam generator (HRSG).
As a result of the data analysis and action on subsequent recommendations, Contact Energy could benefit immediately – and significantly – from various improvements made during the overhaul:
- Minimization of flue gas by-pass in the HRSG recovered almost 1 MW efficiency in the water-steam cycle;
- Additional improvements were made to the gas turbine and control logic
- Optimizations on the gas turbine compressor, together with the above improvements, delivered a 3.4 per cent improvement in power output and an efficiency gain of 1.08 per cent absolute.
Identifying optimization potential
This example and similar experiences emphasize the importance of identifying strategies that not only help mitigate potential risks, but also help take advantage of business opportunities arising through changes in the environment.
A TPA is essentially designed to detect and quantify possible optimization potentials. In contrast with traditional component assessment strategies, the philosophy behind TPA is to identify hidden potential, not only in the individual components of the power plant, but also in the synergies arising from the complex interactions between them.
Critical success factors to the TPA approach include having a team of experienced engineers with complementary backgrounds, a pre-defined systematic methodology and data analysis. It is also highly advisable to integrate external views during the assessment, for example by bringing in staff from a different plant to conduct the assessment or, preferably, securing the expertise of the original equipment manufacturer (OEM). As both an OEM and a plant integrator, Alstom is ideally positioned to carry out TPAs and identify the concrete measures required to attain maximum profit from an existing power plant or any part of it.
TPA scope & focus
TPA is very much a collaborative effort. Each project needs to consider plant-specific requirements and history, market situation, plant design, fleet-specific characteristics and so on. Close teamwork between the assessment team and plant staff ensures knowledge exchange and continuous flexibility in the scope of the assessment. Figure 1 visualizes the phases, context and input from both parties. There are often unexpected findings, and responding to these appropriately can deliver huge benefit.
Figure 1: TPA phases, context and contributions from the different team members
The plant assessment team starts by defining the scope of the analysis based on the specific plant history and requirements for the assessment. To define the optimal scope and assessment focus, it is important to understand clearly all the specific objectives of the plant. The scope can stretch from engineering investigations on individual components or systems to a comprehensive assessment of the entire power plant.
In the preparation phase, the multidisciplinary team members gather as much additional input as possible from their areas of expertise. Data can come from plant history (e.g. operational data, RAM, CMMS) or fleet inputs (e.g. control monitoring centre). A multidisciplinary team of experts analyzes the information for a preliminary understanding of the general situation.
Based on this background information, a site visit provides the opportunity to collect additional information and insights. Depending on the focus areas, the site visit can include workshops, tests on the running plant or the visual inspection of certain components.
After analyzing the collected data and test results, a detailed report shows areas of improvement potential. The report should also sketch a roadmap for improvement that shows concrete measures to deliver on this potential. Team members review and discuss its content to clarify any remaining questions and decide on the next steps to take.
Involvement of an OEM, plant integrator and in-house experts ensure that all of the steps in the TPA process – including preparation, data collection and analysis – are carried out according to highly disciplined and systematic techniques. Success depends on both in-house experience and the application of industry best practices.
To take full advantage of the improvement potential identified, it is recommended that a TPA is conducted at least 18 months before the next major overhaul. This allows optimal implementation of any recommendations on modifications, repair and upgrade possibilities.
TPA focus areas
The power plant owner’s individual market situation, requirements and issues at hand determine the focus of the TPA. The focus is set on one or more of these areas: performance, reliability, asset condition, environment, operation and maintenance, and operational flexibility.
The performance assessment determines system and component measures that can bring about fuel savings and/or an increase in power output. The team carries out detailed efficiency measurements for selected components (such as HRSGs) and identifies critical items that require special off-line inspections.
The plant reliability assessment addresses in a pro-active way reliability issues according to the specific site’s operational profile. The scope definition is based on a reliability, availability and maintainability (RAM) analysis, combined with fleet inputs from various domain experts, as well as the experience of the plant operator. Once the scope has been reduced to the most critical systems in the plant, a reliability-centered maintenance (RCM) workshop drills down to the required level of detail using a failure mode effects and criticality analysis (FMECA). This workshop is a moderated team exercise going through all aspects of the production process. Again, it is recommended that the team is set up in such a way that the know-how covers the different viewpoints of the equipment (design and practice).
The plant asset condition assessment determines the current operating condition of specific components of the power plant. Plant owners can thereby estimate the remaining life-cycle costs more precisely for planning and optimization purposes, and can review the effects of changes in the operating regime and the associated risks. FMECA provides the methodological approach, and verification through inspections and measurements show to what extent they are relevant for a given plant.
A TPA also looks at the compliance of various measures taken in the plant with the externally set environmental requirements (such as catalyst, noise reduction measures, emissions reduction measures and water treatment). This is another reason why a total plant approach pays dividends; the solution often does not lie in the component that seems to be directly responsible, but in the interaction process surrounding it (for example, accelerated ageing of the NOx catalyst because of its operation in a sub-optimal temperature region).
The staff responsible for a plant’s operation and maintenance (O&M) is a further critical success factor for profitable plant operation. Therefore it is important to have an overview of the current O&M plant status in the areas of strategy definition, store management, infrastructure, manpower, planning, condition monitoring and continuous improvement. Interviews and observation enable the team to measure current O&M activities against best practices. Of course, it is highly advantageous to have an external expert view during this assessment, for example to employ an O&M team from a sister plant, or to engage an O&M operator to carry out the observations and agree actions and improvements with the local O&M team.
The plant operational flexibility assessment identifies possible modifications of the plant operation concept that would enable the plant operator to benefit from business opportunities or respond to new constraints resulting from changes in market and grid conditions. These could include, for example, start-up time reduction, increased fuel flexibility, environmental compliance or improved frequency support.
Holistic approach identifies optimization potential
TPAs take a holistic, data-driven and methodological approach to plant assessment, designed to uncover untapped optimization potential. A TPA provides recommendations on modifications, repair and upgrade packages to realize the plant’s full potential. The methodology includes a range of focus areas, which are required to cover specific requirements. The approach differs from traditional methods by assessing not only the individual components, but also their interactions. Furthermore, the iterative review of assessment scope based on previous TPA findings offers a customized assessment with individual results and propositions. Working together with an interdisciplinary team of experts and the resources from a company like Alstom allows effective learning and knowledge transfer to the plant team.
A TPA approach enables plant owners to achieve the best possible overall solution by optimizing the business according to the operating regime and market requirements (demand, fuel prices, regulations, etc). In this way, they can identify and achieve synergies that would be missed using a traditional component-based approach.
Plant owners will find that they can more successfully pursue their chosen business strategies based on the knowledge generated, and actions implemented, in response to a TPA. These include lifetime extension, optimization of maintenance strategies, investment planning, life-cycle costs, environmental performance improvement and operational flexibility.