Power Plant Synthesis

Dimitris Al. Katsaprakakis

• Publisher: CRC Press
• Year: 2020
• ISBN:
  9781351682183
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Mechanics

Power Plant Synthesis provides an integrated approach to the operation, analysis, simulation, and dimensioning of power plants for electricity and thermal energy production. Fundamental concepts of energy and power, energy conversion, and power plant design are first presented, and integrated approaches for the operation and simulation of conventional electricity production systems are then examined. Hybrid power plants and cogeneration systems are covered, with operating algorithms, optimization, and dimensioning methods explained. The environmental impacts of energy sources are described and compared, with real-life case studies included to show the synthesis of the specific topics covered.

1

Introductory Concepts

1.1 Energy and Power

1.1.1 Energy

Energy is one of the most well-known physical magnitudes, while at the same time it remains one of the most difficult concepts to understand. It necessarily accompanies every change in the physical world, from the simplest ones, such as throwing a stone, to the most complicated ones, like various biological procedures. Energy is not perceptible from our senses, unlike other common physical attributes, such as temperature, volume, or length of an object. Unlike these magnitudes, energy cannot be seen, cannot be caught, cannot be heard, and cannot be tasted. The only way energy can be perceptible is through its results.

Yet, what is energy? How can energy be defined? Often mentioned in scientific or educational texts, the following definition covers to a large extent the concept of energy:

Energy is the ability of a body or system to produce work or to cause a change.

How exactly is this definition understood? Before trying to answer this question, let's recall some fundamental concepts from physics. When a force applied to an object makes it move for a distance , with an angle φ between the directions of the vectors and , then we say that this force produces work W which is equal to the internal product of and (Figure 1.1):

(1.1)

Figure 1.1 Work production.

The units of work arise from the product of the units of the involved magnitudes in the above definition relationship:

W=F·S⇔W=Nt·m=Joule

(1.2)

Consequently, work and energy have the same units; hence, work and energy are equivalent magnitudes. Specifically, the production of work requires the consumption of at least an equal amount of energy. Having recalled the concepts of energy and work and having understood that the work production implies the consumption of at least equal energy, we can now try to present some physical interpretations of the energy definition given above.

A moving object produces work; hence, it must have or it must be provided with at least equal energy. Therefore, a human who walks and covers a specific distance produces work, which obviously is given by the internal product of the covered distance with a total resultant force applied in the human body. In this case, the force is applied by the human's muscular system, mainly by the muscles of the legs, and should be as high as required in order to overcome the ground and the air resistances and the body's weight component opposite to the direction of movement (Figure 1.2). Where does this energy come from? In this case, it is provided by the energy that the human body has either stored in the form of fat, or has recently received from foods. Is there any case where a human body is not able to produce work due to not having enough energy availability? Certainly there is, although these conditions that can make a human body unable to move because of its remarkably degraded energy level, in current times and in most parts of the modern world, are uncommon. Yet, it is clear that for a human body that is not provided with the required energy for a long time period (starvation), the body will reach a point at which it will not be able to perform any kind of movement. Hence, it will not have the ability to produce work.

Figure 1.2 Work production from a human body.

Similar to a human body, a moving car that covers a distance produces work, which equals the internal product of the covered distance with the resultant applied force to this, in order to overcome the ground and the air resistances and the car's weight component opposite to the direction of movement. In this case, the applied force is provided by the car's engine. Work is produced as a result of the car's available energy content, practically the chemical energy contained in the stored fuel in the car's fuel tank. Obviously a car with an empty tank cannot move; hence, there is no possibility for work production precisely because there is no energy available.

An object dropped (without any initial push) from the roof of a building to perform a free fall to the level of the ground will cover a distance equal to the height h of the building. During this free fall, the only force applied to the object is its weight . The vectors of the applied force and the covered distance have the same direction, namely the angle between these vectors will be 0^°. Because the object moves, there will be work produced, which is given by the relationship:

(1.3)

where m is the mass of the object and g the acceleration of gravity. For this movement there was neither an initial boost nor any fuel consumed to provide the required energy. What was the source of energy consumed for the production of the above calculated work? The answer is provided by Equation 1.3: The dynamic energy due to the gravitational field of earth that the object has due to its position at the roof of the building versus the ground level. Indeed, the produced work equals the dynamic energy of an object with a mass m located at height h versus the reference level. Consequently, the work production in this case is possible exactly due to the dynamic energy of the object. During the object's free fall, the initial dynamic energy is totally consumed for the production of equal work.

Energy is a physical magnitude that can be perceptible only from its results. We may say that it is well-hidden in bodies and systems, such as the fuel in the car's reservoir, and is revealed only when bodies and systems take part in physical or chemical processes. During these processes, energy is usually converted from one form to another, causing, thus, conceivable results to the surroundings. For example, nobody can realize the dynamic energy contained in the flowerpot at the sill of a balcony. If, however, a clumsy hand forces this flowerpot to change position and land on the roof of the parked car below the balcony, making a dent, the initial dynamic energy will be conceivable from this result.

1.1.2 Power

Power equals the rate that energy is produced or consumed by a body or a system, or, more accurately, the rate of energy transferred or converted:

P=dEdT

(1.4)

Having grasped the concept of energy, power seems to be more easily understood and can be explained with a number of examples. Let's assume two runners with identical physical constitutions and the same mass, comp...

Table of contents

• Cover
• Half Title
• Series Page
• Title Page
• Copyright Page
• Dedication
• Contents
• Preface
• Acknowledgments
• About the Author
• Chapter 1 Introductory Concepts
• Chapter 2 Conventional Power Plants for Electricity Production
• Chapter 3 Electricity Production Hybrid Power Plants
• Chapter 4 Hybrid Plants for Thermal Energy Production
• Chapter 5 Cogeneration Power Plants
• Chapter 6 Smart Grids
• Chapter 7 Energy as a Consumptive Product
• Index