G.K. Lausterer

Improved maneuverability of power plants for better grid stability

Abstract The interaction between power systems and power plants is becoming more and more important as power system operators look at the properties of power plants with respect to their response and maneuvering capabilities, whereas plant operators look at the expenses that are incurred with frequency support operation. The new unit control method presented here is designed to improve power plant response. The thermodynamic losses usually associated with rapid frequency control can be avoided if, in addition, condensate throttling is used. The proposed method has been proved over several years. Experimental results are presented, demonstrating the validity of the approach.

On-line thermal stress monitoring using mathematical models

Abstract Thermal stresses of thick-walled components in power plants are the limiting factors for rapid start-up, shut-down or load changes. In current industrial practice, thermal stresses are calculated from differential temperature measurements. In this paper a method is described to calculate thermal stresses from readily available plant measurements. Mathematical models of the critical thickwalled components were used for unit 8 at the GKM power plant in Germany in order to reduce the instrumentation costs and improve the quality of the thermal stress calculation. Operational experience has shown that the estimated inner and mean temperatures are considerably more accurate than the previously used measured values.

Temperature Control using State Feedback in a Fossil Fired Power Plant

Abstract State feedback control is one of the modern control methods with the potential to improve power plant control. This paper especially deals with the problems resulting from transforming state feedback theory into an easy to handle product. Firstly, the structure of controller and observer and the special design algorithm (pole placement with one tuning factor) for a general SISO (Single Input / Single Output) system are described. Then, suggestions for integrating the state feedback controller into a modem process control system are made. Also, control results and economic benefits are discussed.

Modular Modelling Applied to a Benson® Boiler

Abstract A comprehensive nonlinear model for a once-through steam generator (OTSG) of BENSON design is presented. A modular “first-principles” modelling technique is applied and the basic equations describing the boiler, combustion chamber and flue gas system as well as the turbine are stated. The emphasis is placed on consistent modelling, i.e. developing a model consistent with the intended application. The implicit numerical scheme employed to solve the extremely stiff system of equations is briefly outlined. Superheater temperature control and decoupling boiler control is discussed. Compari son of actual and simulated data shows good agreement supporting the validity of the model. Two special dynamic events, the rupture of a fccdwater pipe and the loss of a coal mill are analyzed in details. It is concluded that first-principles modelling can provide detailed physical insight into complex dynamical phenomena thus enabling improved boiler design.

MATHEMATICAL MODELLING OF A STEAM GENERATOR

Abstract A detailed nonlinear model of a once-through steam generator of BENSON® type is presented with special emphasis placed on accurate modelling of two-phase heat transfer. The nonlinear coupled partial differential equations were derived from first principles and thus permit predictions of the dynamic response of the unit already in the planning stage. The model equations, comprising a stiff two-point boundary value problem, are solved by means of an implicit Runge-Kutta-method featuring step-size control with prespecified numerical error. Using an optimized solution algorithm, computational requirements are kept modest. Comparison of simulation results to actual data shows good agreement and demonstrates the validity of the model. In addition, new insight into the physical phenomena occuring in the two-phase region is gained.

Improved Power Plant Control Using a Digital Process Control System

Abstract The advent of microprocessor-based distributed process automation systems has paved the road for the application of advanced control schemes. The example of a modern fossil-fired power plant is used to describe the features of such a system. The capabilities and advantages of this system are highlighted using two application cases: - a state feedback controller with observer for improved superheater temperature control and - an extended dynamic decoupling scheme improving unit dynamic response and considerably reducing commissioning time. Practical experiences with the implementation of the algorithms are reported. Comparison to conventional control schemes shows a reduction in mean control deviation by a factor of two to ten. Finally, reasons for the persisting gap betwesen control science and industrial practice are stated and the economic benefits of improved control are discussed.

Improved Maneuverability of Power Plants for Better Grid Stability and Economic Dispatch

Abstract The interaction between power systems and power plant becomes more and more important as power system operators look at the properties of power plants with respect to their primary and secondary control capabilities whereas plant operators look at the expenses that are incurred with frequency support operation. The New Unit Control method presented guarantees an exceptionally careful operation of the plant. Scheduled load variations will be realized according to the natural transfer response. Because there are less movements of the actuators you have less wear and tear on the plant. The smoother pressure and temperature control reduces the thermal stress of the plant thus increasing lifetime. The firing will become even more smooth if Condensate Throttling (C.T.) is used. C.T. is used not only on major frequency drops, but also during normal operation. Overfirring with the fuel controller can then to a large extend be reduced and replaced by the load reserves of the condensate throttling circuit. The New Unit Control has been proven over several years. It can be installed instead of any conventional unit control in any fossil-frred power plant. Experimental results are presented demonstrating the validity of the approach.

Knowledge-Based Monitoring of Coal-Fired Power Plants

Abstract The increasing complexity of coal-fired power plants especially due to added environmental protection equipment like flue gas desulphurization (FGD) plants places high demands on control roon1 operators. These problems may be alleviated using a knowledge-based system (KDS) for process monitoring and operator support. Such a system is currently being developed under the name KNOBOS ( KNO wledge- B ased- O perator System). It provides the following functions: acquisition and monitoring of process status, prediction of incipient malfunctions. diagnostic and prognostic functions, instruction on preventive or remedial actions. consulting and optimizing functions. The real-time expert system shell G2 was used to implent KNOBOS. First experience with knowledge aquisition for an FGD plant is reported (pilot project).

ADAPTIVE NONLINEAR COMPENSATORS FOR POWER PLANT CONTROL

Abstract Automatic control of modern power stations is generally not achieved with single control loops, but requires strongly interacting, hierarchical multi-loop control schemes. In these complex control systems, sustained oscillations may arise due to nonlinearities in the low-level control loops, if the control is designed improperly. It is shown by means of the method of harmonic balance, why continuous oscillations arise and how they may be avoided by implementing adaptive nonlinear compensators. A power station unit serves as an example that demonstrates the use of adaptive nonlinear compensators to prevent continuous oscillations without a degradation in control performance of the unit. As an additional benefit, the control is very steady during regular operation (small disturbances) resulting in a low switching rate of the actuators and thus reduced wear on the equipment. After large disturbances, however, hard control action is still ensured. Practical experience with these nonlinear compensators during several years in various units of different size and make are very satisfactory.

Sienergy-the Homogeneous Solution for Power Plant Management

Abstract The liberalization of the energy market gradually softens the local monopolies and competition between utilities emerges more and more. A deregulated energy market compels the utilities to increase their competitiveness. This requires cutting of generation costs, an increase of productivity and securing of the investments earned out. Siemens encourages this objective. The solution is called Sienergy, a series od modules for a cost optimized plant management. The artificial word is composed of Siemens and Engergy. The echo to synergy signifies: • here the combined knowledge of the Siemens AG will be introdced (e. g. of KWU, plant automation, energy distribution) as from other companies (e. g. STEAG in connection with KETEK) • the software modules offered complement and reinforce each others, they are together more than the sum of their pails. • a close cooperation of manufacturer and utilities (the modules contain plenty of engineeriiig)leads to further synergy-effects. Consequently, the Sienergy-modules provide a bundle of tools, with which cost transparency and decision competence was increased essentially. The modules themselves have proven their usefulness already in many applications.