Boiler is an important heat energy supply equipment in the national economy. Power, machinery, metallurgy, chemical, textile, paper, food and other industries, as well as industrial and civil heating, require boilers to supply a large amount of heat energy.
A boiler is a device that uses a thermal energy or other energy released from the combustion of a fuel to heat a working medium (intermediate heating medium) to a certain parameter. Boilers used to heat water and turn it into steam are called steam boilers, also called steam generators. Boilers used to heat water to increase its temperature into hot water are called hot water boilers, and boilers used to heat organic heat carriers are called organic heat carrier boilers.
From the perspective of energy utilization, a boiler is an energy conversion device. In a boiler, the chemical storage of primary energy (fuel) can be converted into the thermal energy contained in the combustion products (fume and ash) through a combustion process, and then transferred to an intermediate heating medium (such as water) through a heat transfer process. And steam), relying on it to transfer heat to heating equipment.
This intermediate heat carrier that transfers heat is a secondary energy source, because its purpose is to provide energy to energy-using equipment.
When the intermediate heating medium is used to perform heat-to-power conversion in a heat engine, it is called a "working medium". If the intermediate heating medium only transfers heat to the heat equipment and provides heat for heat utilization, it is usually called "heat medium".
According to their uses, boilers can be divided into four categories: power station boilers, industrial boilers, marine boilers and locomotive boilers. The first two types are also called fixed boilers because they are installed on a fixed foundation and cannot be moved. The latter two types are called mobile boilers. This article describes a stationary industrial boiler.
Three main processes take place in the boiler:
(1) The fuel is burned in the furnace, and its chemical storage can be released in the form of heat energy, so that the flame and combustion products (fume and ash) have a high temperature.
(2) High-temperature flame and smoke transfer heat to the working medium (heating medium) through the "heating surface".
(3) The working medium (heating medium) is heated, its temperature rises or vaporizes into saturated steam, or it is further heated to become superheated steam.
The above three processes are interrelated and carried out at the same time, realizing the conversion and transfer of energy.
With the transformation and transfer of energy, there is also a flow and change of matter:
(1) Working fluid, such as feed water (or return water), enters the boiler and is subsequently supplied in the form of steam (or hot water).
(2) Fuel, such as coal, enters the furnace for combustion. After the combustible part is burned, it is converted into flue gas with the original moisture content, and the original ash content remains as ash residue.
(3) Air is sent into the furnace, where oxygen participates in the combustion reaction, and excess air and inert gas remaining in the reaction are mixed in the flue gas and discharged.
The three main systems of the boiler are the water first steam system, the coal one ash system and the wind two smoke system. The work of these three systems is performed simultaneously.
The processes performed on the fuel and flue gas side (including combustion, heat release, slag removal, gas flow, etc.) are generally referred to as "in-furnace processes"; the processes performed on the water and steam side (water and steam Flow, endothermic, vaporization, vapor-water separation, thermochemical processes, etc.) collectively referred to as "in-pot processes"