3. Тексты для чтения и перевода Текст 1. Basics of boilers and boiler processes

In a traditional context, a boiler is an enclosed container that provides a means for heat from combustion to be transferred into the working media (usually water) until it becomes heated or a gas (steam). One could simply say that a boiler is as a heat exchanger between fire and water. The boiler is the part of a steam power plant process that produces the steam and thus provides the heat. The steam or hot water under pressure can then be used for transferring the heat to a process that consumes the heat in the steam and turns it into work. A steam boiler fulfils the following statements:

1. It is part of a type of heat engine or process

2. Heat is generated through combustion (burning)

3. It has a working fluid, a.k.a. heat carrier that transfers the generated heat away from the boiler

4. The heating media and working fluid are separated by walls

In an industrial/technical context, the concept “steam boiler” (also referredto as “steam generator”) includes the whole complex system for producing steam for use e.g. in a turbine or in industrial process. It includes all the different phases of heat transfer from flames to water/steam mixture (economizer, boiler, super- heater, reheater and air preheater). It also includes different auxiliary systems (e.g. fuel feeding, water treatment, flue gas channels including stack).

The heat is generated in the furnace part of the boiler, where fuel is com- busted. The fuel used in a boiler contains either chemically bonded energy (like coal, waste and biofuels) or nuclear energy. Nuclear energy will not be covered in this material. A boiler must be designed to absorb the maximum amount of heat released in the process of combustion. This heat is transferred to the boiler water through radiation, conduction and convection. The relative percentage of each is dependent upon the type of boiler, the designed heat transfer surface and the fuels that power the combustion.

Текст 2. A simple boiler

In order to describe the principles of a steam boiler, consider a very simple case, where the boiler simply is a container, partially filled with water. Combustion of fuel produce heat, which is transferred to the container and makes the water evaporate. The vapor or steam can escape through a pipe that is connected to the container and be transported elsewhere. Another pipe brings water (called “feed- water”) to the container to replace the water that has evaporated and escaped.

Since the pressure level in the boiler should be kept constant (in order to have stable process values), the mass of the steam that escapes has to be equal to the mass of the water that is added. If steam leaves the boiler faster than water is added, the pressure in the boiler falls. If water is added faster than it is evaporated, the pressure rises. If more fuel is combusted, more heat generated and transferred to the water. Thus, more steam is generated and pressure rises inside the boiler. If less fuel is combusted, less steam is generated and the pressure sinks.