All power producers, including those operating CHP plants, are looking for new ways to boost performance, raise energy efficiency, lower environmental loads and minimize the use of raw materials. The answer often lies in advanced automation solutions that provide a multitude of tools, writes Jukka Pyykkö.
Automation makes it possible to measure, calculate, estimate and monitor prod-uction efficiency, direct costs, lifetime costs, emissions – and all the interdependencies between them. It enables plants to optimize and control their operations correspondingly.
The operators and contractors of new, large CHP power plants understand well the benefits of automation. But in smaller units, it is not yet clear to every user that a modern automation system gives clear benefits when compared with a simpler PLC system – also in financial terms. A good time to upgrade an automation system is, for instance, in connection with the modernization of boiler combustion technology or the steam turbine controller.
The prerequisite for enjoying the fruits of advanced solutions is an automation and information platform that is expandable and allows integration with various processes. It should also cover all process controls and plant information management needs, as well as mechanical condition monitoring in a single platform. Metso’s solution is Metso DNA, which during the past years has gained a strong foothold, especially in European biomass-fired CHP plants.
The company has recently delivered CHP automation systems to Belgium, Estonia, Finland, France, Germany, Poland, Slovakia, Sweden and the United Kingdom.
ALL FOR MORE EFFICIENT PROCESS OPERATION
In today’s economic environment, power plant operation must be cost-effective and undisturbed. Every plant aims for top performance and higher availability. However, this is possible only if you know your plant efficiency at all times and are able to react to problems immediately. Today, there are numerous automation applications that assist in all areas of power plant operation, from management to production and maintenance.
For example, Metso’s Plant Management Applications provide modern tools for optimizing and automating plant reporting routines, for improving performance and availability, and for maximizing revenues and minimizing production costs.
The solid fuel management application integrates process data from the DCS (distributed control system), load data from the weighing system and laboratory analyses of fuel quality. It automatically reports fuel amounts, costs and energy use. Reliable and seamless management of solid fuel data is the basis for quality monitoring and efficient reporting of fuels, as well as for follow-up of the overall plant performance.
An up-to-date performance monitoring application cal-culates, stores and displays the main performance parameters that indicate the condition and operating efficiency of a process component or unit. It can be applied to boilers, steam turbines, gas turbines, heat recovery steam generators (HRSGs), pumps and fans, flue gas desulphurization plants, heat exchangers, and more.
Energy management controls play a major role in every CHP plant; it is important to be able to balance between different energy forms in real time. As the plant generates electricity with district heat and/or process steam, it must satisfy all the energy consumers at all times. Energy can be lost in many ways through reduced energy efficiency due to a lack of coordination in the plant’s energy production. Energy management controls for CHP plants include an optimal coordination of boilers and turbines to minimize production costs while maintaining environmental compliance.
ENVIRONMENTAL REPORTING THE EASY WAY
As all power plant operators know, EU directives on environmental performance will tighten in the future and place more demands on emission monitoring. However, with the help of modern automation, this will not be a problem. Online emission management applications, such as Metso’s emission monitoring and reporting solutions, provide power plants with real-time information about current emission levels and limit infractions, and forecast flue gas emissions, making it possible to react proactively to potential problems on time.
The solutions fulfil the requirements of the EU directives for large combustion plants and waste incineration, thus also enabling effective authority reporting.
BETTER PERFORMANCE THROUGH OPTIMIZATION
Getting the most out of heat and/or electricity production over the entire plant life cycle is at the top of every power producer’s priority list. It can be achieved through advanced process control applications.
Stable and efficient combustion is a primary requirement for successful boiler operation. Variations in combustion conditions and fuel quality together with changing loads upset combustion. Boiler efficiency decreases and flue gas emissions as well as flue gas oxygen content increase. By optimizing combustion, it is possible to manage the combustion process against variations in production, fuel amount, fuel quality and combustion circumstances. This stabilizes the combustion process, improves boiler efficiency and minimizes flue gas oxygen content, NOx emissions and CO emissions.
Another common challenge is how to exactly measure the quality and amount of solid fuel fed to the boiler. Typically, only conveyor speed is used as a measurement for fuel power. Metso has developed a fuel power compensator application with which it is possible to compensate for disturbances in fuel feed to stabilize combustion and steam production. It is based on estimating fuel power (fuel energy input to the boiler). Fast and accurate estimation is produced with a combination of boiler balance calculations and oxygen consumption calculations.
GOODBYE TO STEAM NETWORK UPSETS
But what about the steam network? Is there a way to improve steam availability and quality, minimize steam venting losses and optimize steam production?
Certainly. By supervising and regulating the whole steam network with a multi-variable and predictive process control, it is possible to simultaneously control several steam network variables and handle control constraints directly. This brings clear benefits especially for industrial power plants, but also utility CHP plants, with more than one boiler, and, for example, heat storages to control and optimize.
Metso’s steam network management application constantly stabilizes both steam balance and pressures in the steam network. As a multivariable controller, it controls all the equipment to optimize the steam network behaviour and ensure high-quality process steam is always available to satisfy the demand of heat and electricity consumers. It also cuts the risk of unplanned shutdowns as well as the need for operator actions and use of secondary fuels.
COORDINATION BETWEEN THE TURBINE AND BOILERS
Metso has integrated turbine control, turbine protection and turbine management applications within its Metso DNA automation system.
All applications are engineered using the standard engineering tools of the plant DCS, and executed using redundant process controllers. The steam turbine automation consists of special turbine control features, such as a fast governor control and integrated simulator. Protection functions include overspeed protection and machine protection. Tools for mechanical condition and performance monitoring of the turbine can be included in the package as integrated features of the automation system.
|The layout of the Metso DNA automation system|
PERFECT MATCH: AUTOMATION AND EQUIPMENT
Working plant automation builds on advanced solutions that all link together perfectly. But to ensure the most efficient overall plant performance, automation must be well integrated into the plant equipment. A perfect match brings the best results.
The main automation system in a CHP plant covers the whole process, including the boiler island, turbine island, balance of plant, fuel handling and auxiliary processes. Plants can gain from a supplier such as Metso that can offer a complete delivery from fuel handling to the tip of the smokestack.
AND THE FUTURE?
Automation today is playing a major role in a CHP plant’s operation. But how far will the development go? What could the automation level be, let’s say, in 2050? I think different kinds of green or greener energy supply processes will be connected to the common district heating/cooling net-works and national grids. They will be controlled optimally and operated remotely with advanced automation solutions. Power plants will run with biomass, solar energy, process heat, biogas, waste-to-energy, wind, heat pumps, natural gas, energy storages, gasification or coal with carbon capture. Automation’s role is to take care of the optimum power and heat production based on capacities and costs.
Jukka Pyykkö is Product Manager at Metso’s Automation business line, Finland. Email: email@example.com;
Optimized combustion control improves efficiency at Oulun Energia
Oulun Energia’s Toppila cogeneration power plant in Finland improved its high combustion efficiency even further by applying optimized combustion control to its process. Toppila has two power boilers. Toppila 1, originally built in 1977 by Tampella and converted into a BFB boiler in 1996, features a fuel capacity of 267 MW. Toppila 2, an Ahlstrom boiler from 1995, is a CFB boiler with a fuel capacity of 315 MW. About 85% of the fuel consists of peat, while the rest is wood.
In 2008-2009, Metso supplied combustion optimizers for both boilers and implemented them in the existing Metso DCS system. Combustion Optimizer is a multi-variable control application based on fuzzy logic. The fuzzy controllers are connected to the base level controls through parameters and controller set points.
|The Toppila cogeneration power plant in Finland, where Metso supplied combustion optimizers that have further increased a high combustion efficiency|
The delivery also included a fuel power compensator application to adjust for disturbances in the fuel feed in order to stabilize combustion and steam production. It is based on an estimation of the fuel energy input to the boiler through a steady-state boiler energy balance and dynamic oxygen consumption.
The applications have now been used full time in both boilers since spring 2009. In Toppila 2, residual oxygen has dropped on average from 0.3 to 0.5 percentage points, and is now 2%. Improved combustion efficiency has brought direct cost savings, since more energy can now be produced from the same amount of fuel.
In Toppila 1, the original target of controlling the front pass better has been reached, resulting in a higher cyclone temperature and thus better boiler steam efficiency. This, in turn, means more electricity and steam produced. With the latter, it has been possible, for example, to replace oil-fuelled reserve heat plants that had been needed during the coldest winter periods in Oulu.
In addition to combustion optimization, Metso also supplied a turbine controller to the Toppila 1 Zamech turbine from 1977. The old hydraulic control system was removed, and all the turbine controls, such as speed, load, steam pressure, and the automatic run-up controller as well as turbine protection, were implemented in the power plant’s DCS system. The benefits of the modernization were more accurate controls and easier start-up of the steam turbine, not to mention overall benefits for maintenance and operation due to an integrated solution.
Under control – from incoming biofuel to customer invoicing
The brand new, 200 MW multi-fuel, biopower production plant in Pori, western Finland, is a great example of the current trend towards environmentally sustainable solutions in energy production. The new plant mainly uses domestic biofuels, such as peat and wood-based fuels. Metso was chosen as the main process supplier for both the power boiler and process automation.
The drivers transporting biofuel to the plant all have a bar code card, which forms the basis for automatic fuel handling. The process control system controls the incoming fuel and transfers the information to the users and the information management system. The system calculates the heat value of the delivery based on moisture analyses and weight measurements.
Metso’s automation scope included plant-wide automation and an information management system, both based on the Metso DNA platform. This encompasses solutions and hardware from the control room to cross-connect cabinets. The automation system network is physically large: the remote district heat pumping stations controlled and monitored by the system are located several kilometers from the main power plant. The information management system includes a DNAhistorian database and several Plant Management Applications for monitoring and reporting, such as fuel data management, boiler and turbine performance monitoring, emission reporting according to the EU directives, as well as balance and cost allocation reporting.
The power plant is located next to a large titanium dioxide supplier, Sachtleben Pigments. Another large customer is the City of Pori, which utilizes the excess heat from the plant for district heating. The network also comprises the Aittaluoto power plant, located in the city center. A third user is the Pihlava industrial area. Excess electricity produced at the plant is sold to the national network.
One of the beauties of the information system relates to invoicing the customers for their share. The cost and profit follow-up starts from calculating the heat value of each incoming material supply. This is recorded in the information management system. The plant owners have agreed on how to share the costs and profits, and the information system automatically produces the monthly shares of purchased and used energy to enable invoicing.