In most of the world today, power producers are operating in uncertain times. As traditional operating models are upended by new sources of energy, particularly the wind, solar and steam power plant operators find themselves running plant and equipment in ways never intended by their designers. This stresses not only the equipment but also budgets and resources. The uncertainty produced by today’s markets also leads to shifting priorities from management and lack of operational predictability.
The result is an increasingly complex operating environment and fragmented marketplace driven by inconsistent and fluctuating demand. Operators face new challenges every quarter. Deregulation, power trading, decentralised power markets, competition from renewables, price volatility, fast ramping, retiring workforce, loss of institutional knowledge and the constant threat of cyberattacks are amongst the most critical of these challenges. This is especially true in mature markets where many steam power plants operate as back-ups to a power grid increasingly supplied by renewables. This leads to inefficient operations where plants must frequently ramp up and shut down as load demand fluctuates. In these markets, the days of plants operating continuously at the base load are coming to an end.
In markets where steam power plants (ie, fossil-fired boiler with steam turbine) still run at full capacity, optimising performance to eliminate unplanned downtime, meeting regulatory burdens and increasing power output are still priorities that must be met, offering significant improvements in profitability. Markets where plants participate in intra-day and day-ahead energy trading, providing reliable power generation schedules and the capability to deliver ancillary services are the key to profitability.
Technology drivers and market demands
The advances in power plant control and optimisation are being driven by a combination of technological (ie, Internet of Things, cloud, faster computer processors, broadband networks, etc) and market forces. Of these market forces, three are paramount: renewable generation, fuel costs and environmental targets. Renewable generating capacity is growing rapidly. At first in Europe and the US, but now in most parts of the globe. With high renewable energy penetration comes greater challenges to grid management. For traditional baseload plants, this means changing output quickly. Only performance optimisation solutions make this economical.
Global fuel prices are another factor. In order to maximise profits, all power plant operators want their plants to burn the least amount of fuel for the highest amount of energy output. This is a critical issue in some global power markets. In the US, for example, cheap natural gas from shale makes it increasingly difficult for coal plant operators to compete. While in Europe, high natural gas prices are challenging gas-fired plant operators with the same problem. In both cases, optimisation that allows operators to maintain tight control over the combustion cycle, while minimising equipment stresses and holding maintenance costs down, can be the difference between operating economically or not.
The one thing all power generators in every market have in common is they are meeting these challenges head-on with digitalisation. Finally, the same environmental concerns around climate change that have stimulated the rise in renewable generation are driving de-carbonisation of steam power plants. Much tighter emission restrictions increase cost pressures on older coal-fired plants in particular. Newer plants find compliance less of a burden, but cost control still depends on the effectiveness of control and optimisation systems.
Digital solutions to common problems
From integrated control systems drawing data from an army of sensors, to remote collaborative management of operations from anywhere on the globe, digital is how operators reduce costs and increase margins. Advanced Process Control (APC) for power plants has become increasingly sophisticated over the past 20 years. Where once a power plant was controlled by an operator facing a bank of gauges and levers, today’s plant control systems run on real-time data from thousands of sources. Today’s operators serve more of an executive or orchestration role – overseeing operations to ensure safety and intervening only as needed. The result is a more accurate control over all of a plant’s processes, not just a select few as in the day’s past. APC and new digital solutions allow for greater optimisation of a greater number of parameters, leading to higher efficiency and greater flexibility to meet market demands than ever before.
How APC systems help operators meet these demands
The secret of a low heat rate and, hence, high thermal efficiency, is to maintain operation with as little variation as possible. Any variation leads to a loss of efficiency and revenue. That is why APC-based performance optimisation is focused on maximising efficiency and reducing variability. Efficiency is at the core of all power plant operations and drives technological advances across the entire power generation spectrum, from coal-fired plants to solar and wind.
For steam power plants, this has led to the development of supercritical and ultra-supercritical boiler technologies based on ever higher steam temperatures and pressures that rely on ever more sophisticated materials and technologies. In a coal-fired plant, for example, optimum plant efficiency depends on maintaining the plant within a narrow range of steam cycle operating conditions. The more tight the control, the easier it becomes to maintain efficient generation. When talking about power plant efficiency, steam cycle efficiency is the headline figure that is mentioned the most. But optimising efficiency stretches well beyond this. Power plants are large users of electricity, which is used to drive a whole range of auxiliary systems, such as pumps, fans, compressors, drives, etc. If the operation of all these energy consuming components can be controlled as part of the overall optimisation scheme, there are enormous savings to be had. This underscores one of the strongest business cases for optimisation. By operating each component of a plant as efficiently as possible, an APC solution can pay for itself in as little as one to two years.
Steam power plants benefit the most
APC solutions are available for all types of power plants, but it is in steam power plants that they offer the greatest advantages. For example, APC allows boilers to maintain low nitrogen oxides (NOx) emission conditions and high carbon burnout, both of which are critical for plant emission performance and efficiency. Depending on how they are configured, APC systems can also manage steam temperatures and pressures throughout the steam cycle, allowing the best achievable efficiency while minimising mechanical stresses. Optimising coordinated boiler/turbine control for grid frequency support also can be achieved. At the same time, system parameters and KPIs are collected to support predictive and prescriptive maintenance activities, lowering maintenance costs significantly.
APC solutions can be used to control gas turbine and combined cycle power plants, too. But modern gas turbines often operate at the limits of their material capabilities and are already closely controlled to ensure that they do not exceed these limits. Because of this, there is less room for operational changes which improve efficiency at base load. Instead, APC can improve load response (eg, start up and ramping) as well as the low load capability of such units. With cogeneration plants, APC will also improve plant economics by maintaining optimum efficiency for multiple fuel changes and for frequent power and steam demand fluctuations.
Holistic approach is key
Each of these improvements can lead to considerable operational improvement. In this approach, integration is the key to APC system effectiveness. It is always the goal of power plant operators to achieve the best heat rate and highest level of flexibility. But the inability to automate and optimise all the different parts of the plant as one is often an insurmountable challenge to achieving these goals. Any integration that does occur relies on the expertise of plant operators. Thus, the whole plant model, if there was one, resides in an operator’s head. However, today’s solutions are capable of optimising the whole plant (or fleet of plants) as a single unit. So, when plant operators talk about power plant optimisation today, they are talking about this holistic view of ‘plant control’.
Solutions independent of the control system
This holistic approach is made possible by performance optimisation solutions that are control system agnostic. In the past, software applications ran directly on the control system infrastructure. Today, these applications are model-based and are implemented on top of the control system (usually running on a PC or server) and interact with the control systems via industry standard real-time interfaces to read inputs and send outputs to the underlying basic controls. This allows the use of a variety of digital modelling techniques (eg, data based or physical equations), to create a ‘digital twin’ of the plant.
Lowering maintenance expenses
Because of fast ramping and other operational demands, power plants today are subject to stresses that exceed their original design criteria. This leads to increased equipment wear and higher maintenance costs. Digital twins and other APC systems help keep these expenses under control by ensuring the plant always operates within certain limits. During start up, for example, if the temperature gradients within the boiler can be limited, thermal stresses are reduced. By maintaining tight control of conditions during start up, shutdown and when a plant is ramping, APC solutions extend the lifetime of plant components. In addition, the data collected during each cycle can be used to build up a historical picture of component health that can be used to predict equipment failure before it happens – keeping unplanned downtime to a minimum and allowing maintenance personnel to schedule needed repairs at optimum times.
Speed & solution
Even though the future for steam power plants is challenging, there is a path forward. Driven by market forces beyond their control, plant operators are embracing digitalisation to improve performance, save money and reduce emissions. This is nothing new. The power industry has been adopting technological solutions to solve problems for years. What has changed is the urgency at which they must now proceed. Speed is essential. Steam power plant operators in particular are facing market demands their facilities were never designed to meet. ABB believes that today’s APC solutions provide the best route to success, empowering flexible, economical operation for years to come. The challenges are here now but, fortunately, so are the solutions.