Compressed air and compressors. Application of compressed air - Knowledge Hypermarket

Air supply system for industrial enterprises.

Topic 2

Compressed air is one of the main energy resources and is used as a working medium in technological processes (for example, in chemical industries) and as an energy carrier (pneumatic tools, pneumatic equipment, pneumatic automation, etc.) in almost all enterprises. Compressed air is used in electrical substations to actuate pneumatic actuators of switches and disconnectors. In air circuit breakers, compressed air is used to extinguish the electric arc and ventilate the internal cavities of the circuit breakers to remove moisture deposited on them. In circuit breakers with an air-filled separator, as well as in circuit breakers of the VVB, VNV and other series, compressed air acts as the main insulating medium between the main contacts of the circuit breaker in the off position.

Potential energy is imparted to the air during its compression and is then used in pneumatic actuators to perform mechanical work. Potential energy is converted into kinetic energy of the expanding compressed air jet.

For the operation of air installations, compressed air is accumulated in the tanks of these installations. In turn, the tanks are replenished from systems designed to produce compressed air.

The selection of the optimal distribution scheme and rational modes of production and consumption of compressed air leads to savings, which cannot but have a significant impact on the energy balance of the enterprise as a whole. Since the production of compressed air consumes electricity, its saving entails a reduction in the cost of purchasing energy resources.

A feature of compressed air production is that the performance of compressor equipment depends on seasonal changes in atmospheric air density (in summer, air density is 15-17% lower than in winter) and discharge pressure.

An increase in pressure from 5.0 to 6.0 kgf/cm2 leads to a decrease in compressor productivity by 4-7%, while the energy costs for compression increase by 7-10%. A significant factor negatively affecting the operation of compressor equipment is the irregular consumption of compressed air, the volume of which reaches up to 40% at some compressor stations. To ensure the stable operation of consumers, in the presence of significant volumes of irregular consumption, the personnel of compressor stations are forced to maintain an increased pressure of compressed air at the sources. In addition, alternating loads on equipment with frequent cycles of "loading and unloading" of compressors lead to premature failure of individual components, the restoration of which requires significant financial resources, time and labor costs.

Compressed air, due to its properties, differs significantly from other energy resources:

1. Compressed air does not have its own calorific value, which characterizes the volumes of steam and heat supply;

2. Compressed air does not have a calorific value, which is the main characteristic of all types of fuel;

3. Compressed air is not used in chemical reactions like oxygen and solid fuel;

4. Due to its multicomponent nature, compressed air cannot be used to form a protective environment like nitrogen and argon;

5. Compressed air does not have a sufficiently high specific heat capacity (like water), which characterizes the volumes of industrial water pumping;

6. Compressed air, in part, like electricity, is used in drives of various operating principles for transformation into mechanical work;

7. A distinctive feature is the possibility of converting the kinetic energy of the energy carrier jet (air jet receivers) into mechanical energy.

All these differences determine the specifics of the use of compressed air as an energy resource. The main characteristic of the resource is the ability to perform work by a unit of volume at operating parameters. This implies a direct dependence of resource consumption on its density in a compressed state. In turn, the density of the consumed air depends on pressure and temperature.

The properties of compressed air listed above as an energy resource and the specific features of its production determine the need to organize work on energy saving at consumers, in networks and at sources of compressed air. It is necessary to find and implement the most effective ways to carry out this work, aimed at changing and adjusting the distribution system (configuration and parameters of compressed air networks) in the face of a changing structure of the main consumers and constantly changing requirements for resource parameters. Currently, this work includes the following main areas:

Reducing the volume of non-rhythmic consumption of the resource by transferring consumers to local supply;

Transfer of consumers who do not have increased requirements for the parameters of the resource to the supply of compressed air of lower parameters;

- reduction of pressure at sources (main air pipelines) due to the redistribution of the supply of consumers with similar requirements for energy carrier parameters.

Compressed air pressure regulation is an effective energy saving method. Reducing the pressure by 0.1 kg/cm2 reduces compressed air consumption by approximately 2%. There are various ways to regulate:

- installation of restrictive devices;

- installation of regulators and control valves;

- throttling on shut-off valves.

The second method is the most effective, but also the most costly.

The installation of control valves allows you to accurately maintain a given pressure or its differential. The installation of restrictive devices requires a preliminary calculation, as well as certain manufacturing costs, but this method does not allow precise maintenance of the parameters at a given level. A similar effect is produced by throttling on shut-off valves.

This method is the most cost-free.

Compressed air is an air mass that is contained in a container, while its pressure exceeds atmospheric pressure. It is used in industry in a variety of manufacturing operations. A typical compressed air system is one operating at pressures up to ten bar. In such cases, the air mass is compressed ten times its original volume.

general information

At a pressure of seven bar, compressed air is practically safe to operate. It is able to provide sufficient driving force to the tool as well as an electric feed. This requires less cost. In addition, such a system is characterized by faster response, which in the end can make it much more convenient. However, this will require taking into account the parameters below.

Application of compressed air

Quite often, manufacturers use this type of energy to quickly and efficiently clean equipment from dirt and dust. In addition, compressed air is widely used to blow pipes in boiler rooms. It is used to clean rooms, equipment and even clothes from wood dust. In most countries, standards for the use of this type of energy have already appeared, for example, in Europe it is CUVA, and in the USA - OSHA. In addition to using it in production operations, tools that work directly on air are widely used - these are screwdrivers, pneumatic drills, wrenches (during equipment installation and construction), spray guns (during major repairs). In addition, compressed air in canisters is now widely used in pneumatic weapons.

Safety

When using compressed air, the following safety precautions must be observed.

1. Do not direct the jet into the mouth, eyes, nose, ears or other places.
2. Do not treat open wounds with compressed air, because bubbles can form under the skin, if they reach the heart, they will lead to a heart attack, and if they reach the brain, they can provoke. In addition, getting into the wound, air can infect it , which is located in the compressor system or in pipes.
3. It is forbidden to play around and direct the jet of compressed air at other people.
4. Do not overpressure the compressor system.
5. All elements of the pneumatic installation must be carefully secured to avoid breakage and, as a result, injury.
6. It is forbidden to clean the equipment from dust and dirt in the presence of an open flame source and welding. This may cause an explosion due to the presence of dust in suspension.
7. When working with compressed air systems, wear personal protective equipment such as goggles or a mask.
8. It is forbidden to tighten couplings, in knots or on pipes under pressure.
9. When installing the pneumatic system, hoses should be fixed in places with the least risk of damage (on ceilings, walls).

Benefits of compressed air

Now consider what are the advantages of using this type of energy on production lines.

Compressed air networks

For optimal operation and high economic efficiency of the installation, the following requirements must be met. In the pneumatic system, losses should be minimized, in addition, the air should come to the consumers dry and clean, this is achieved by installing a special dehumidifier that allows moisture to condense. Also, special attention should be paid to the main pipelines. Proper installation of air ducts is the key to the durability of operation, as well as reducing maintenance costs. By increasing the pressure level in the compressor, the drop in the pipeline can be compensated.

Calculation of compressed air consumption

Always include so-called receivers (air collectors). Depending on the performance and power of the equipment, the system may contain several receivers. Their main purpose is to smooth out pressure pulsations, in addition, the gas mass is cooled inside the air collector, and this leads to condensate. Calculation of compressed air is to determine the consumption of the receiver. This is done according to the following formula:

• V = (0.25 x Q c x p 1 x T 0) / (f max x (p u -p l) x T l), where:
  - V - the volume of the air receiver;
  - Q c - compressor performance;
  - p 1 - pressure at the outlet of the installation;
  - T l - maximum temperature;
  - T 0 - compressed air temperature in the receiver;
  - (p u -p l) - given pressure difference between loading and unloading;
  - f max - maximum frequency.

Atmospheric air is a mixture of gases that do not react under normal conditions. Mostly nitrogen and oxygen. Therefore, all the properties characteristic of oxygen and nitrogen are also inherent in air.

Nitrogen is a gas that is close in its effect to neutral gases and does not require the use of any protective measures or special materials for objects in contact with it. However, it has an adverse effect on a person who stays in an environment with a high nitrogen content for a long time.

Oxygen, on the contrary, is an active oxidizing agent. Therefore, the design of machines and apparatus for this gas must take into account the corrosiveness, especially of moist air, the possibility of ignition of combustible materials in air, the possibility of self-ignition and explosion in gas communications in the presence of carbon deposits, vapors or oil drops (over 100 atm.).

Air dissolves in lubricating oils, contributes to their premature oxidation, coking, and a decrease in flash point.

Human impact

When the pressure drops to 140 mm Hg, signs of oxygen starvation appear, and at 110 mm Hg - hypoxia, up to 50 - 60 mm - it is already life-threatening.

An increase in the partial pressure of N2 in the air causes narcotic effects.

A high concentration of CO2 causes asphyxia, and when
14 - 15% of it death occurs. In residential premises, the content of carbon dioxide should not exceed 0.1%.

4.2 Importance of air in human development

4.2.1 Development of compressed air technologies

Even 3,000 years ago, blowing air with bellows was used for smelting metals and ventilation of mines (there are other Egyptian drawings).

Hero of Alexandria introduced the concept of "pneumatics" - the use of compressed air.

In the Middle Ages, the bellows drive from the water wheel began to be used.

In the middle of the 18th century, a steam engine and a piston compressor similar to it were invented, which created a pressure of up to 0.2 MPa (2 atm).

In 1741 Gelier built a primitive fan with blades rotating on an axis - a blower.

Then came pneumatic mail, a diving suit, caissons.

At the beginning of the XIX century. they could already compress air to a pressure of 0.5 - 0.6 MPa, and began to transmit it at a distance. Compressed air began to be widely used in various technical devices.

In 1845 a pneumatic machine was invented, and in 1872 - a pneumatic brake.

In 1857 a pneumatic tool appeared - a drill hammer - for laying a tunnel in the Alps.

Soon the first CS appeared - in Paris N=1470 kW,
p= 0.6 MPa, network length up to 48 km - provision for factories and plants. Later, the power was increased to 18500 kW - with a steam drive.

4.2.2 Purpose of compressed air

Today, not a single industrial enterprise can do without the use of compressed air, which is an affordable and cheap source of both raw materials and energy. Especially widely compressed air is used in industry and construction. Compressed air sources are both small mobile units and large stationary compressor stations connected to consumers through a network of air ducts, which together form the air supply system of an industrial enterprise.

Air supply systems are designed to generate compressed air of the required parameters and uninterruptedly provide it with the technological needs of the enterprise.

Depending on the profile of the enterprise, production, compressed air is used today for:

Implementation of the main technological processes (as a component of chemical technology, for example, for the production of oxygen and nitrogen, for blasting in metallurgy, etc.);

Energy applications associated with the use of air as an oxidizing agent for the combustion of various fuels or as a heat carrier for heating or cooling gases and liquids;

As a working fluid in internal combustion engines, gas turbines;

Ensuring the operation of pneumatic tools and pneumatic actuators, supplying machines for foundry and forging industries, construction machines and mechanisms, performing blowing, sandblasting, painting and other works at manufacturing enterprises of various types of activity;

Ensuring the operation of technological complexes and devices (conveyors, pneumatic transport systems, drilling rigs, etc.);

Ensuring the operation of pneumatic systems, instrumentation and A systems, and much more in technology.

Note that in some industries, for example, at chemical plants, compressed air for the main technological processes has parameters different from those of the air supply system, and is produced by special compressors that are part of the equipment of production lines.

The course "Compressor stations" deals with the use of compressed air as an energy carrier in various industries. This use of it is difficult to overestimate. But there are other uses as well. The most significant of them is the use of air as reagents in metallurgy and chemistry, as well as in pneumatic transport.

4.3 Application of compressed air in metallurgy

Here, air is used as a reagent containing O2. The main function is blast, that is, the supply of compressed air to various units - blast furnaces, open-hearth furnaces, converters. This is essential for combustion in all metallurgical processes.

Ore enrichment- (1st process) - increasing the content of iron or other metal in the ore and reducing harmful impurities. One way to enrich flotation.

Compressed air is blown through the pulp. During froth flotation, useful mineral particles are not wetted by water and rise along with air bubbles, while others are wetted and settle to the bottom - this is waste rock (Fig. 4.4).

Widely used for beneficiation of non-ferrous metal ores (% low), but also for iron too.

Agglomeration" href="/text/category/aglomeratciya/" rel="bookmark"> agglomeration machine (Fig. 4.5).

The coke starts to burn, the ore heats up and turns into a strong porous mass - it “sticks together” - this is the agglomerate, which then makes it possible to carry out a more efficient process of iron smelting in the blast furnace.

Figure 4.5 - Scheme of agglomeration

domain process(Fig. 4.6). Iron in the ore is in the form of oxides. Therefore, it is necessary to free iron from the O2 associated with it - recovery.

Figure 4.6 - Domain process

The oxygen contained in the hot air blown into the furnace interacts with the carbon of the coke, forming CO2. It rises higher, interacts with coke, forming CO, it takes oxygen from iron oxides of the ore and binds it. And the released iron interacts with carbon, forming cast iron. For 1 ton of cast iron, 2500 - 3500 m3 of air is needed, i.e. V=8000 m3/min. To prevent the air from cooling the oven, it is preheated to 1100 - 1300ºC in cowpers.

The nozzle is heated by burning fuel. Then the fuel supply is stopped and air is pumped. In order for the feeding process to be continuous, several cowpers are installed. Note that the air contains 4/5 nitrogen, i.e. 80% of the energy is wasted, since only 20% of oxygen is used for combustion.

Obviously, it is more profitable to enrich the air with oxygen. But this became possible only in the 1930s and 1940s with the advent of powerful separation plants.

Converter method cooking steel (Bessemer). Molten liquid iron is blown with compressed air, and the O2 contained in it combines with carbon, silicon and manganese (Fig. 4.7 a). This process is the reverse of the blast furnace process - oxidative. Thus, unnecessary components are bound into oxides and removed.

When blown with air, carbon quickly burns out and steel is formed from cast iron. And Si and Mn, when combined with O2, release heat to support the reaction, that is, the converter is a “furnace without fuel” (Mendeleev). Disadvantages - saturation of steel with nitrogen - brittleness of steel, tendency to aging. There are also harmful impurities S and P. Cast iron was not suitable for this, but only with Si and Mn. Scrap metal in the converter cannot be melted down.

So it's better - open-hearth method- for the processing of cast iron and scrap (Fig. 4.8).

Here, heat for the melting process must be supplied by burning fuel oil, coke oven gas, and Kalashnikov gas. The mixture of gas and air is heated in the regenerators due to the heat from the combustion products leaving the furnace. The nozzles are heating up. Intermittent devices. Therefore, they are placed in pairs and switched after 15 - 20 minutes. Open-hearth capacity - 100 tons of steel per hour. This method is more advanced.

Technological shops of a metallurgical plant are consumers of a large amount of compressed air. Compressed air is used for blowing into blast furnaces, for the operation of pneumatic machines and pneumatic tools, for burning fuel in roasting, heating and thermal furnaces.

Compressed air consumption in blast-furnace shops significantly exceeds air consumption in any other industries. So, to obtain 1 ton of cast iron, about 3000 m3 of air is needed under normal conditions. For blowing into blast furnaces, air with a pressure of 0.3-0.4 MPa is required; it is produced at PVA steam-blowing stations, usually combined with a thermal power plant (CHP-PVS).

Blower units designed to supply air to blast furnaces are installed at blower stations.

These stations come in different versions:

steam-blowing (PVS), including boiler units, steam turbines and blast-furnace blast units;

combined, steam-blowing and electric (PVA as part of CHP-PVA), consisting of blast-furnace blast units and steam turbines;

PVA or CHPP-PVA, which include blast-furnace blast compressors with an electric drive;

blower stations, including only electric driven air compressors (EVS).

Blower stations are equipped with multi-stage centrifugal blowers. The number of stages is determined by the required pressure. The main element of centrifugal blowers is an impeller with blades that eject air during rotation of the wheel due to centrifugal forces from the center to the periphery, while the air is supplied with energy that increases its pressure. Due to the significant heating of the air, the compressors are supplied with water cooling.

The main type of drive for blast-furnace blowers is a steam turbine. The turbines used for these purposes operate on steam at a pressure of 3.5 MPa or 9 MPa with a temperature of 435 0 C or 535 0 C, respectively. Sometimes other types of drives are used. Before being fed into the blast furnace, air after compression is heated to a temperature of about 1000 0 C in blast furnaces (coopers).

The main manufacturer of centrifugal compressor machines used as blower units is the Nevsky Machine-Building Plant, St. Petersburg. The productivity of machines produced by this enterprise is from 2500 to 6900 m 3 /min, air pressure is 0.45-0.53 MPa, the drive is a steam condensing turbine with a capacity of 12-30 MW.

To drive pneumatic machines and pneumatic tools, air with a pressure of 0.6-1.0 MPa is used. Compressed air of such pressures is obtained centrally at compressor stations using reciprocating and centrifugal compressors. Centrifugal compressors are preferable because they provide a continuous supply of gas, are reliable and easy to maintain, and do not pollute the compressed air with oil. Reciprocating compressors provide a higher degree of gas compression with the same dimensions as centrifugal compressors, but they have lower productivity and are less reliable. In this regard, modern compressor stations, as a rule, are equipped with centrifugal compressor machines. The Nevsky Machine-Building Plant produces compressors with a capacity of 345 to 3200 m 3 /min, air pressure up to 1.4 MPa.

Compressed air is transported to consumers using a developed network of air pipelines, from the blower and compressor stations separately. Air ducts to the blast furnace are thermally insulated, as the air temperature after compression rises to 200 0 C. These air ducts have diameters reaching 2500 mm.

For burning fuel in roasting, heating and thermal furnaces, compressed air with a pressure of 0.003-0.01 MPa is used, supplied by centrifugal blowers (fans) installed in close proximity to the consumer.

The general requirement for compressed air is the absence of mechanical impurities, moisture, oil vapors. Cleaning from mechanical impurities is carried out with the help of filters, and from moisture and oil vapors - by cooling the compressed air. However, not all moisture condenses, and its presence in pipelines can lead to the formation of ice plugs in winter.

Obtaining compressed air requires significant costs (for example, the cost of blast furnace blast is 30% of the cost of pig iron).

Pneumatic tools, i.e., tools driven by compressed air, are widely used in the construction, shipbuilding, mining and other fields of technology. In any large plant, pneumatic hammers and drills are used; mines use pneumatic jackhammers.

Each such tool is connected with a rubber hose to a line - a pipe into which air is continuously pumped from a central compressor station. The simplest diagram of a pressure pump-compressor is shown in fig. 302. When the flywheel rotates, piston 1 moves in the cylinder to the right and left. When the piston moves to the right, compressed air opens valve 2 and is injected into the line; when moving to the left, a new portion of air is sucked into the cylinder from the atmosphere, and valve 2 closes, and valve 3 opens. On fig. 303 shows the device of a pressure gauge used to measure the pressure of compressed air or other gases. A hollow metal tube 1 of oval section, bent in the form of a ring, is connected with an open end 2 to the volume in which the pressure is to be measured. Near end 2 is a tube rigidly attached to the pressure gauge body. The closed end 3 is connected to a mechanism that drives the pointer of the device. The greater the gas pressure, the more the tube 1 straightens and the more the arrow deviates. Usually, the position of the arrow corresponding to atmospheric pressure is marked with zero on the scale. Then the manometer shows how much the measured pressure exceeds the atmospheric pressure: the readings of the device give the so-called "excess pressure". Such pressure gauges are used, for example, to measure steam pressure in steam boilers.

Rice. 302. Compressor diagram

Rice. 303. Manometer device for high pressures

Let's point out a few more applications of compressed air.

Air (pneumatic) brakes are widely used on railways, in trams, trolleybuses, subways, and motor vehicles. In pneumatic brakes on trains, brake pads 1 are pressed against the wheel tires with compressed air located in tank 2 located under the car (Fig. 304). The brakes are controlled by changing the air pressure in the main pipe, which connects the cars with the main compressed air tank located on the locomotive and filled with a compressor. The control is designed so that when the pressure in the line decreases, the distribution valve 3 connects the tank 2 to the brake cylinder 4 and thereby brakes. Reducing the pressure in the line can be carried out by the driver, who disconnects the line from the compressor and connects it to the atmosphere. The same result can be achieved if the emergency braking valve is opened in any car or a line break occurs.

Rice. 304. Scheme of the air brake device on railway trains

Compressed air is used in the oil industry during oil production. In the area of ​​oil deposits, compressed air is pumped underground, displacing oil to the surface. Sometimes, due to some processes occurring in the oil-bearing layer, compressed gas accumulates in the underground layers. If a well is drilled in the ground, reaching the level of oil, the gas will displace the oil to the surface of the earth. The pressure difference between the underground gas and the atmosphere is so great that it causes the oil that has risen through the well to spurt like a high fountain.

Rice. 305. Device for pouring distilled water

The same principle is used for the apparatus often used in laboratories for pouring distilled water from a vessel. If you blow into the tube 1 of the device (Fig. 305), then water will pour out of the tube 2. Since the vessel is always closed with a cork, the liquid can be stored for a long time without becoming contaminated.

To free the ballast compartments of a submarine from water (“purge”), water is displaced by compressed air stored on board the boat in special cylinders.