Steam boilers: principle of operation and device

A steam boiler is a device for converting water into steam, used both in everyday life and in industry. Steam is used for heating rooms, apparatus and pipelines, as well as for rotating turbomachines. Let's find out in more detail what steam boilers are. The principle of operation, device, classification, scope and much more - all this will be discussed below.

Definition

As you already understood, a steam boiler is a steam generating unit. Moreover, boilers of this type can produce two types of steam: saturated and superheated. In the first case, its temperature is about 100 degrees, and the pressure is about 100 kPa. The temperature of superheated steam rises to 500 degrees, and the pressure - up to 26 MPa. Saturated steam is used for domestic purposes, mainly for heating private homes. Superheated steam has found application in industry and energy. It transfers heat well, so its use significantly increases the efficiency of the installation.

Scope of application

There are three main areas of application for steam boilers:

1. Heating systems. Steam acts as an energy carrier.
2. Energy Industrial steam engines, or, as they are also called, steam generators, are used to produce electrical energy.
3. Industry. Steam in industry is used not only for heating the "shirts" of apparatuses and pipelines, but also for converting thermal energy into mechanical energy and moving vehicles.

Domestic steam boilers are used for heating residential premises. In simple words, their task is to heat the water and move the steam through the pipeline. Such a system is often equipped with a stationary furnace or boiler. Typically, household appliances produce saturated non-superheated steam, which is quite enough to solve the tasks assigned to them.

In industry, steam is overheated - it continues to warm after evaporation in order to further increase the temperature. Such installations have special quality requirements, since when the steam overheats, the container risks exploding. Superheated steam received from the boiler can be generated by electricity or mechanical movement.

Electric current using steam is formed as follows. Evaporating, the steam enters the turbine, where it, thanks to the dense flow, rotates the shaft. Thus, thermal energy is converted into mechanical energy, and that, in turn, is converted into electrical energy. This is how the turbines of power plants work.

The rotation of the shaft, which occurs during the evaporation of large quantities of superheated steam, can be transmitted directly to the motor and wheels. So steam transport is set in motion. Popular examples of the operation of a steam engine include a steam locomotive or a ship steam boiler. The principle of operation of the latter is quite simple: when coal is burned, heat is generated, which heats the water and forms steam. Well, the steam, in turn, rotates the wheels, or in the case of the ship, the screws.

Steam boilers: principle of operation

Let's consider in more detail how these boilers work. The source of heat necessary for heating water can be any type of energy: electric, solar, geothermal, heat from the combustion of gas or solid fuel. The steam generated in the process of heating the water is a coolant, that is, it transfers thermal energy from the place of heating to the place of use.

Despite the variety of designs, the basic structure and principle of operation of steam boilers do not differ. The general scheme for heating water with its subsequent conversion into steam looks like this:

1. Purification of water on the filters and its supply to the tank for heating using a pump. The tank is usually located at the top of the installation.
2. From the tank, through pipes, water enters the collector, located, respectively, below.
3. Water rises again, only now not through pipes, but through the heating zone.
4. Steam forms in the heating zone. Under the influence of the pressure difference between the liquid and gaseous substances, it rises up.
5. Above, heated steam is passed through a separator, where it is finally separated from the water. The remaining liquid is returned to the tank, and the steam goes to the steam line.
6. If this is not an ordinary boiler, but a steam generator, then its pipelines are additionally heated. The methods for heating them will be discussed below.

Device

Steam boilers are containers in which water is heated and forms steam. Usually they are made in the form of pipes of various sizes. In addition to a pipe with water, the boiler always has a chamber for burning fuel (firebox). Its design may vary depending on the type of fuel used. If it is wood, or hard coal, then in the lower part of the furnace a grate is installed, on which the fuel is laid. From the lower part of the grate, air enters the combustion chamber. And at the top of the furnace they equip a chimney, which is necessary for efficient traction - air circulation and fuel combustion.

The principle of operation of solid fuel boilers is somewhat different from devices in which liquid or gaseous material is used as a heat carrier. In the second case, the combustion chamber involves a burner that works like the burners of a domestic gas furnace. The grate and chimney are also used for air circulation, because regardless of the type of fuel, air is the most important condition for combustion.

Combustible gas obtained from the combustion of fuel rises to the tank with water. It gives its heat to water and exits through the chimney into the atmosphere. When the water is heated to boiling point, it begins to evaporate. It is worth noting that water also evaporates earlier, but not in such quantities and not with such a vapor temperature. Evaporated steam enters the pipes on its own. Thus, the circulation of steam and the change in the state of aggregation of water occurs naturally. The principle of operation of a steam boiler with natural circulation requires minimal human intervention. All that the operator needs to do is to ensure stable heating of the water and control the process using special devices.

In the case of electric boilers, water heating is easier. It is heated using heating elements such as heating elements or acts as a conductor and heated according to the Joule-Lenz law.

Classification

Steam boilers, the operating principle of which we are considering today, can be classified according to several parameters.

By type of fuel:

1. Coal.
2. Gas.
3. Fuel oil.
4. Electric.

By appointment:

1. Household.
2. Energy.
3. Industrial.
4. Recycling.

By design:

1. Gas pipe.
2. Water pipe.

What is the difference between gas and water tube steam boilers

The principle of operation of boilers is based on heating the tank with water. A container in which water changes to a vapor state is usually a pipe or several pipes. Devices in which fuel heats the pipes, rising up, are called gas-tube boilers.

But there is another option - when the combustible gas moves through a pipe located inside the tank with water. In this case, water tanks are called drums, and the boiler itself is called a water tube. In everyday life, it is also called a fire tube boiler. Depending on the location of the water drums, boilers of this type are divided into: horizontal, vertical and radial. There are also models in which different pipe directions are implemented.

The device and principle of operation of a fire tube steam boiler is somewhat different from a gas tube. Firstly, it concerns the size of pipes with water and steam. Pipes for water tube boilers are less overall than gas tube boilers. Secondly, there are differences in power. A gas-tube boiler gives a pressure of not more than 1 MPa and has a heat-generating capacity of up to 360 kW. The reason for this is large pipes. In order for enough steam and pressure to form in the pipes, their walls must be thick. As a result, the price of such boilers is too high. The water tube boiler is more powerful. Thanks to the thin walls of the pipes, the steam heats up better. And thirdly, water tube boilers are safer. They produce heat and are not afraid of significant overloads.

Additional elements of boilers

The principle of operation of a steam boiler is quite simple, however, its design consists of a fairly large number of elements. In addition to the combustion chamber and pipes for water / steam circulation, the boilers are equipped with devices to increase their efficiency (increase in steam temperature, its pressure and quantity). These devices include:

1. Superheater. It serves to increase the temperature of steam above 100 degrees. Overheating of steam increases the efficiency of the apparatus and its efficiency. Superheated steam can reach temperatures of 500 degrees Celsius. Such high temperatures occur in steam plants of nuclear power plants. The essence of overheating is that after evaporation, the steam going through the pipe is reheated. For this, the apparatus can be equipped with an additional combustion chamber or a simple pipeline, which, before withdrawing steam for its intended use, passes several times through the main firebox. Superheaters are radiation and convection. The first ones work 2-3 times more efficiently.
2. Separator. Serves to “drain” the steam - to separate it from the water. This allows you to increase the efficiency of the installation.
3. Steam battery. This device is designed to maintain a constant level of steam output from the installation. When there is not enough steam, it adds it to the system and, on the contrary, takes it in case of excess.
4. Preparatory device for water. In order for the apparatus to work longer, the water entering it must meet specific requirements. This device reduces the amount of oxygen and minerals in the water. These simple measures help prevent pipe corrosion and scale formation on their walls. Rust and scale not only reduce the efficiency of the device, but also quickly render it unusable, especially in case of active use.

Control devices

In addition, the boiler is equipped with auxiliary devices for monitoring and control. For example, a water level limit indicator monitors the maintenance of a constant liquid level in a drum. The principle of operation of the signaling device of the maximum levels of the steam boiler is based on a change in the mass of special cargoes during their transition from the liquid phase to the vapor phase, and vice versa. In the event of a deviation from the norm, it gives a sound signal to alert employees of the enterprise.

For positional regulation of the water level, a level gauge column of the steam boiler is also used. The principle of operation of the device is based on the electrical conductivity of water. The column is a tube equipped with four electrodes that control the water level. If the water column reaches the bottom mark, the feed pump is connected, and if the top - the boiler’s water supply stops.

Another simple device for measuring the water level in a steam boiler is a gauge glass built into the apparatus. The principle of operation of the gauge glass of a steam boiler is simple - it is intended for visual control of the water level.

In addition to the liquid level, temperature and pressure are measured in the system using thermometers and manometers, respectively. All this is necessary for the normal functioning of the boiler and to prevent the possibility of emergency situations.

Steam generators

We have already examined the principle of operation of a steam boiler, now we will briefly get acquainted with the features of steam generators - the most powerful boilers equipped with additional devices. As you already understood, the main difference between the steam generator and the boiler is that its design includes one or more intermediate superheaters, which allows to reach the highest steam temperatures. At nuclear power plants, due to the very hot steam, they transform the decay energy of an atom into electrical energy.

There are two main methods for heating water and converting it to a gaseous state in a reactor:

1. Water washes the reactor vessel. In this case, the reactor is cooled, and the water is heated. Thus, steam forms in a separate circuit. In this case, the steam generator acts as a heat exchanger.
2. Pipes with water pass inside the reactor. In this embodiment, the reactor is a combustion chamber with which steam is supplied directly to the generator. This design is called a boiling reactor. Everything here works without a steam generator.

Conclusion

Today we met with such a useful device as a steam boiler. The device and the principle of operation of this apparatus are quite simple and based on the banal physical properties of water. Nevertheless, steam boilers greatly facilitate the life of a person. They warm buildings and help generate electricity.