The power generation industry is changing rapidly. Growing power demand, deregulation, and economic and environmental pressures are creating significant demand to modernize existing plants and optimize processes, as well as building new plants.
Large utility power companies are upgrading and modernizing to meet efficiency and environmental guidelines.
Small power plants are being built to serve local markets. Many process industries (e.g., chemical, pulp and paper, refining, and food and beverage) are generating their own power and using the surplus steam for other purposes such as heating office buildings or sterilizing equipment, or injecting into their processes.
Guide to Level Measurement Series
Ultimately, the efficiency of a power generation system is measured by the amount of fuel burned versus the amount of electricity (measured in megawatts [MW]) produced. The balance between the energy used and the electricity generated is called the heat rate. Improvements in process control instrumentation can provide more accurate information for use in heat-rate monitoring and reduction of the plant heat rate.
Power Basics
Steam power generation involves four basic stages:
- Heat is produced.
- The heat transfers to liquid water to produce steam.
- Steam drives a turbine that turns a shaft connected to a generator.
- The generator converts mechanical energy to electricity.
From a process measurement and control perspective, these stages may be thought of as two interrelated processes:
- Steam and water process.
- Fuel, air, and flue gas process.
The Steam and Water Process
The large boilers found in a power generation plants are normally water tube boilers, in which water passes through a set of tubes suspended in the boiler furnace. The heat in the furnace converts the water in the tubes in to steam by a process called evaporation.
As evaporation begins, water and steam exist together. The steam and water are separated in the boiler steam drum. The water is recirculated into the water tubes, and the steam, called saturated steam, is routed to another set of tubes that are located in the hottest part of the furnace. This set of steam tubes is called a superheater.
The finished product of the boiler is called dry superheated steam. The dry superheated steam exits the boiler through a pipe called the main steam header. In a power plant, the main steam header leads to a series of turbines.
Emerson Process Management
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