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 learn more in detail what the steam boilers are. The principle of operation, device, classification, scope and much more - all this will be discussed below.

Definition

As you have already understood, the steam boiler is an aggregate producing steam. In this case, boilers of this type can produce pairs of two types: saturated and superheated. In the first case, its temperature is of the order of 100 degrees, and the pressure is about 100 kPa. The temperature of the superheated steam rises to 500 degrees, and the pressure to 26 MPa. Saturated steam is used for domestic purposes, mainly for heating private houses. Superheated steam has found application in industry and energy. It tolerates heat well, so its use greatly 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. Power engineering. Industrial steam engines, or steam generators, as they are called, are used to generate electricity.
3. Industry. Steam in the industry is used not only to heat the "shirts" of apparatus and pipelines, but also to convert thermal energy into mechanical energy and transport vehicles.

Household 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 stove or boiler. Usually household appliances produce saturated non-superheated steam, which is quite enough to solve the tasks assigned to them.

In the industry, the steam overheats - continue to heat after evaporation in order to further increase the temperature. To such installations, special requirements for quality are required, since when the steam is overheated, the capacity risks exploding. Superheated steam from a boiler can be used to generate electricity or mechanical motion.

Electric current with steam is formed as follows. Evaporating, the steam gets into the turbine, where it, thanks to a dense flow rotates the shaft. Thus, thermal energy passes into mechanical energy, and that, in turn, is transformed into electric energy. So turbines of power stations work.

Rotation of the shaft, which occurs when large quantities of superheated steam evaporates, can be transmitted directly to the motor and wheels. So in motion is the steam transport. As popular examples of the operation of a steam engine, a steam generator of a locomotive or a steam boiler can be used. The principle 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: the principle of operation

Let's consider in more detail how I work with such boilers. The source of heat necessary for heating water can be any kind of energy: electric, solar, geothermal, heat from the combustion of gas or solid fuel. The steam produced during the heating of water is a heat carrier, that is, transfers heat energy from the place of heating to the place of use.

Despite the variety of designs, the basic design and operating principle of steam boilers are no different. The general scheme of water heating with its subsequent conversion into steam looks like this:

1. Purification of water on the filters and its supply to the tank for heating with a pump. The reservoir is usually located at the top of the unit.
2. From the reservoir, through the pipes, water enters the collector, located, respectively, lower.
3. The water rises again, only now not through the pipes, but through the heating zone.
4. Steam forms in the heating zone. Under the action of the pressure difference between the liquid and gaseous matter, it will rise upward.
5. At the top, heated steam is passed through the separator, where it is finally separated from the water. The remaining liquid is returned to the tank, and the steam flows into the steam line.
6. If this is not an ordinary boiler, but a steam generator, then its pipelines are additionally heated. The ways of heating them will be discussed below.

Device

Steam boilers are a container in which water is heated and forms steam. They are usually made in the form of pipes of different sizes. In addition to the pipe with water, the boiler always has a combustion chamber (furnace). Its design can vary depending on the type of fuel used. If it is wood, or hard coal, then in the lower part of the furnace there is a grate, on which fuel is laid. From the bottom of the grate, air enters the combustion chamber. And at the top of the firebox they build a chimney, which is necessary for effective traction - air circulation and fuel combustion.

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

The combustible gas obtained from the combustion of the fuel rises to a container of water. It gives its heat to the water and exits through the chimney into the atmosphere. When the water is heated to the boiling point, it begins to evaporate. It is worth noting that the water evaporates earlier, but not in such quantities and not with such a vapor temperature. Evaporated steam enters the pipes by itself. Thus, the circulation of steam and the change in the aggregate states of water occur naturally. The principle of operation of a steam boiler with natural circulation requires minimal human intervention. All you need to do to the operator is to ensure stable water heating and control the process with the help of special devices.

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

Classification

Steam boilers, the 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. Utilization.

By design:

1. Gas tube.
2. Water tube.

What distinguishes gas and water tube steam boilers

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

But there is another option - when the flammable 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 pipe. In everyday life it is also called a fire tube. Depending on the location of the water drums, boilers of this type are divided into: horizontal, vertical and radial. Also there are models in which different directions of pipes are realized.

The device and principle of operation of the fire-tube steam boiler is somewhat different from the gas-tube boiler. First, it concerns the size of pipes with water and steam. At water-tube boilers the pipes are less than the gas pipes. Secondly, there are differences in power. The gas-tube boiler produces a pressure of not more than 1 MPa and has a heat-generating capacity of up to 360 kW. The reason for this are large pipes. In order to form enough steam and pressure 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.

Boiler accessories

The principle of operation of the steam boiler is quite simple, however its design consists of a rather 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, pressure and quantity). These devices include:

1. Superheater. It serves to increase the temperature of the steam above 100 degrees. Overheating of the steam increases the efficiency of the device and its efficiency. Superheated steam can reach a temperature of 500 degrees Celsius. Such high temperatures take place in steam installations of nuclear power plants. The essence of overheating is that after evaporation the steam passing through the pipe is subjected to reheating. For this purpose, the device can be equipped with an additional combustion chamber or a simple pipeline, which several times passes through the main furnace before the steam is taken out to the intended use. Steam superheaters are radiation and convection. The first work 2-3 times more efficiently.
2. Separator. Serves to "drain" the steam - separating it from water. This allows you to increase the efficiency of the installation.
3. A rechargeable battery. This device is designed to maintain a constant level of steam output from the unit. When the pair is not enough, it adds it to the system and, on the contrary, selects it in case of an overabundance.
4. A preparatory device for water. In order for the unit to work longer, the water that enters it must meet specific requirements. This device reduces the amount of oxygen and minerals in the water. These simple measures prevent corrosion of pipes and the formation of scale on their walls. Rust and scum not only reduce the efficiency of the device, but also quickly lead to its uselessness, especially in the case of active use.

Control devices

In addition, the boiler is equipped with auxiliary devices for monitoring and control. For example, the water limit switch monitors the maintenance of a constant level of liquid in the drum. The principle of operation of the limit level detector for a steam boiler is based on a change in the mass of special loads during their transition from the liquid phase to the vapor phase, and vice versa. In the event of a deviation from the norm, he beeps to alert the company's employees.

For position-based water level control, a level gauge column of the steam boiler is also used. The principle 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 lower mark, a feed pump is connected, and if the top one - the boiler water supply stops.

Another simple device for measuring the water level in a steam boiler is a water-glass, built into the body of the apparatus. The principle of operation of the water meter glass of the steam boiler is simple - it is designed for visual monitoring of the water level.

In addition to the liquid level, the system measures thermometers and pressure gauges with temperature and pressure, respectively. All this is necessary for the normal operation of the boiler and to prevent the occurrence of emergencies.

Steam Generators

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

There are two main ways of heating water and converting it into a gaseous state in the reactor:

1. Water washes the reactor vessel. The reactor is cooled and the water is heated. Thus, the steam is formed in a separate circuit. In this case, the steam generator functions as a heat exchanger.
2. Pipes with water pass inside the reactor. In this embodiment, the reactor is a combustion chamber with which the steam is fed directly to the power generator. This design is called a boiling reactor. Here everything works without a steam generator.

Conclusion

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