Educación

In the development of the economic aspects of a power plant, both the initial capital costs of the plant and the operating costs must be eval-uated carefully. Of these costs, the fuel cost is the highest of all costs over the life of the plant, and thus the overall plant efficiency is extremely important. This, therefore, involves the careful selection of the primary fuel for the plant and of the operating and environmental equip-ment that must perform at high efficiency as well as high reliability.

The costs of a power plant include the initial capital costs and the continual operating and maintenance (O&M) costs. These costs include the following:

Figure 1.11Heat recovery steam generator (HRSG) arrangement for a combined cycle gas turbine facility. (Vogt Power International, Inc., a Babcock Power, Inc., company.) Ch01_Lammers_1418466 10/8/04 11:34 AM Page 29

Steam and Its Importance

Capital Costs

■ Steam generating system

■ Environmental control systems

■ Fuel preparation and handling equipment

■ Air and flue gas handling systems, including FD and ID fans

■ Structural support steel

■ Buildings

■ Instrumentation and controls

■ Ash handling systems

■ Turbine generator

■ Condenser

■ Cooling tower

■ Condensate system, including feedwater heaters and pumps

■ Water treatment systems

■ Electrical system

■ Insulation

■ Stack

■ Transportation costs

■ Site preparation

■ Construction

■ Taxes

■ Engineering and project management

■ Startup

■ Performance and efficiency testing

The O&M costs of a power plant are significant and affect the overall power plant costs. These costs must be evaluated carefully together with the capital costs of the power plant to determine the proper selection of the systems to be used and the fuel to be burned during the lifetime of the plant. O&M costs are both variable and fixed and include the following:

Variable Costs

■ Fuel costs

■ Auxiliary power requirements for equipment such as fans, pumps, pulverizers, etc.

■ Water treatment, including chemicals

■ Ash and by-product effluent handling and treatment

The preceding fixed O&M costs are incurred whether or not the plant is operational, and such costs increase over time. The variable costs are extremely time dependent as well as material availability dependent. The availability of low-cost fuel, for example, must be evaluated carefully for the life of the plant in order to determine the best economical selection of a power plant type and its fuel. With an expected plant life of 40 years and more, making the proper decision on the type of power plant and its fuel is critical to the economic viability of the project. This decision is often complicated when plant site envi-ronmental requirements force a decision toward a more expensive fuel.

1.7 Summary

Steam is generated for many useful purposes from relatively simple heating systems to the complexities of a fossil fuel–fired or nuclear–fueled electric utility power plant. All types of fuels are burned, and many different combustion systems are used to burn them efficient-ly and reliabefficient-ly.

This book will describe the various systems and equipment of a steam power plant that are so important to everyday life, whether it be for the generation of electricity, for heating, or for a process that leads to a product. The environmental control systems that are a necessary part of a modern plant are also thoroughly described because their reliability and efficiency are necessary to the successful operation of these plants.

Questions and Problems

1.1 Why are the study and understanding of steam power plants so important?

1.2 Describe the various forms of energy input to a power plant. Provide examples of the plant output that uses this energy.

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1.3 Provide a list of the major uses of steam in industry.

1.4 What are the sources of heat that are used to generate steam?

1.5 What is a British thermal unit (Btu)?

1.6 Why is air pollution control equipment so important in the production of steam?

1.7 Provide a sketch and describe the operation of the Rankine steam cycle.

What is the advantage of superheating the steam?

1.8 Define dry saturated steam and superheated steam.

1.9 What are the major systems of a coal-fired power plant? Provide a brief description of each.

1.10 What is the purpose of an air heater?

1.11 Why is condensing the steam from the turbine and returning it to the boiler so important?

1.12 Why is a natural gas–fired boiler far less complex than a boiler that burns coal?

1.13 For a coal-fired or other solid fuel–fired boiler, what additional systems are necessary to account for the ash contained in the fuel?

1.14 What percentage of the total electric production results from steam power plants?

1.15 Why would a coal-fired plant be more difficult to obtain an operating per-mit for as compared with a plant fired with natural gas? Provide ideas on how this can be overcome.

1.16 For large utility boilers burning natural gas and oil, why has their use declined except for certain parts of the world?

1.17 Why is coal used to such a large degree, even with its complications?

1.18 Why are water treatment systems important to a well-operated power plant?

1.19 For most industrial-type boilers, what is the most distinguishing feature of this design? What is its purpose?

1.20 From an environmental point of view, what are the advantages of a flu-idized bed boiler?

1.21 Name the two types of fluidized bed boilers and briefly describe their characteristics.

1.22 Describe a combined cycle system that uses a gas turbine. What are the advantages of this system? What is the single most important disadvantage?

1.23 Of all the power plant costs, which one has the most significant cost impact?

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Steam and Its Importance