Carbon dioxide 4. Application of carbon dioxide. The effect of carbon dioxide on the human body

Application of carbon dioxide (carbon dioxide)

At present, carbon dioxide in all its states is widely used in all branches of industry and the agro-industrial complex.

In a gaseous state (carbon dioxide)

AT food Industry

1. To create an inert bacteriostatic and fungistatic atmosphere (at a concentration over 20%):
· When processing plant and animal products;
· When packing food and medical products to significantly increase their shelf life;
· When pouring beer, wine and juices as a propellant gas.
2. In the production of soft drinks and mineral waters (saturation).
3. In the brewing and production of champagne and sparkling wines (carbonation).
4. Preparation of carbonated water and drinks by siphons and saturators, for the personnel of hot shops and in the summer.
5. Use in vending machines for the sale of bottled gas and for manual trade in beer and kvass, carbonated water and drinks.
6. In the production of carbonated milk drinks and carbonated fruit and berry juices ("sparkling products").
7. In sugar production (defecation - saturation).
8. For long-term preservation of fruit and vegetable juices while preserving the smell and taste of the freshly squeezed product by saturating with CO2 and storing under high pressure.
9. To intensify the processes of precipitation and removal of salts of tartaric acid from wines and juices (detartition).
10. For the preparation of drinking desalinated water by the filtration method. For saturation of salt-free drinking water with calcium and magnesium ions.

In the production, storage and processing of agricultural products

11. To increase the shelf life of food products, vegetables and fruits in a controlled atmosphere (2-5 times).
12. Storage of cut flowers for 20 or more days in an atmosphere of carbon dioxide.
13. Storage of cereals, pasta, grains, dried fruits and other food products in an atmosphere of carbon dioxide, to protect them from damage by insects and rodents.
14. For processing fruits and berries before storage, which prevents the development of fungal and bacterial rot.
15. For high-pressure saturation of cut or whole vegetables, which enhances the flavor (“sparkling foods”) and improves their shelf life.
16. To improve the growth and increase the productivity of plants in greenhouses.
Today, in vegetable and floriculture farms in Russia, there is an acute question about the implementation of carbon dioxide fertilization of plants in greenhouses. Deficiency of CO2 is a more serious problem than deficiency of mineral nutrients. On average, a plant synthesizes 94% of the dry matter mass from water and carbon dioxide, the remaining 6% is obtained from mineral fertilizers! The low carbon dioxide content is now a factor limiting the yield (primarily in low-volume crops). The air of a 1 ha greenhouse contains about 20 kg of CO2. At maximum light levels in the spring and summer months, the consumption of CO2 by cucumber plants during photosynthesis can approach 50 kg · h / ha (i.e., up to 700 kg / ha CO2 per daylight). The resulting deficit is only partially covered by the influx of atmospheric air through the transoms and leaks in the enclosing structures, as well as by the night respiration of plants. In ground greenhouses, an additional source of carbon dioxide is soil filled with manure, peat, straw or sawdust. The effect of enriching the greenhouse air with carbon dioxide depends on the amount and type of these organic substances that undergo microbiological decomposition. For example, when applying sawdust moistened with mineral fertilizers, the level of carbon dioxide at first can reach high values \u200b\u200bat night, and during the day with closed transoms. However, in general, this effect is not large enough and satisfies only part of the needs of plants. The main disadvantage of biological sources is the short duration of the increase in the concentration of carbon dioxide to the desired level, as well as the impossibility of regulating the feeding process. Often in soil greenhouses on sunny days, with insufficient air exchange, the content of CO2 as a result of intense absorption by plants can fall below 0.01% and photosynthesis practically stops! Lack of CO2 becomes the main factor limiting the assimilation of carbohydrates and, accordingly, the growth and development of plants. It is possible to completely cover the deficit only through the use of technical sources of carbon dioxide.
17. Production of microalgae for livestock. When water is saturated with carbon dioxide in autonomous algae cultivation installations, the rate of algae increases significantly (4-6 times).
18. To improve the quality of the silage. When ensiling juicy forages, the artificial introduction of CO2 into the plant mass prevents the penetration of oxygen from the air, which contributes to the formation of a high-quality product with a favorable ratio of organic acids and an increased content of carotene and digestible protein.
19. For safe disinfestation of food and non-food products. An atmosphere containing more than 60% carbon dioxide within 1-10 days (depending on temperature) destroys not only adult insects, but their larvae and eggs. This technology is applicable to products with a bound water content of up to 20%, such as grain, rice, mushrooms, dried fruits, nuts and cocoa, compound feed and much more.
20. For the total destruction of murine rodents by short-term filling with gas holes, storages, chambers (sufficient concentration of 30% carbon dioxide).
21. For anaerobic pasteurization of animal feed, mixed with water vapor at a temperature not exceeding 83 degrees C - as a substitute for granulation and extrusion, which does not require high energy costs.
22. For the euthanasia of poultry and small animals (pigs, calves, sheep) before slaughter. For anesthesia of fish during transportation.
23. For anesthesia of bee and bumblebee queens in order to accelerate the start of egg-laying.
24. To saturate drinking water for chickens, which significantly reduces the negative impact of high summer temperatures on poultry, promotes thickening of the egg shell and strengthening of the skeleton.
25. For saturation of working solutions of fungicides and herbicides for better action of drugs. This method reduces the consumption of the solution by 20-30%.

In medicine

26. a) mixed with oxygen as a respiration stimulator (at a concentration of 5%);
b) for dry carbonated baths (at a concentration of 15-30%) in order to lower blood pressure and improve blood flow.
27. Cryotherapy in dermatology, dry and water carbon dioxide baths in balneotherapy, breathing mixtures in surgery.

In the chemical and paper industry

28. For the production of soda, ammonium salts (used as fertilizers in crop production, additives to feed for ruminants, instead of yeast in bakery and flour confectionery), lead white, urea, hydroxycarboxylic acids. For the catalytic synthesis of methanol and formaldehyde.
29. For neutralization of alkaline waste water. Thanks to the self-buffering effect of the solution, accurate pH control avoids corrosion of equipment and sewage pipes, and there is no formation of toxic by-products.
30. In the production of paper for processing pulp after alkaline bleaching (increases the efficiency of the process by 15%).
31. To increase the yield and improve the physical and mechanical properties and bleaching of cellulose during oxygen-soda cooking of wood.
32. For cleaning heat exchangers from scale and preventing its formation (a combination of hydrodynamic and chemical methods).

In the construction and other industries

33. For rapid chemical curing of molds for steel and iron casting. The supply of carbon dioxide to the casting molds accelerates their hardening by 20-25 times in comparison with heat drying.
34. As a blowing gas in the production of porous plastics.
35. For strengthening refractory bricks.
36. For welding semiautomatic devices in the repair of bodies of passenger and light vehicles, repair of cabins of trucks and tractors, and in the electric welding of products from thin sheet steel.
37. In the manufacture of welded structures with automatic and semi-automatic electric welding in an environment of carbon dioxide as a shielding gas. In comparison with welding with a stick electrode, the convenience of work increases, the productivity increases by 2-4 times, the cost of 1 kg of deposited metal in a CO2 environment is more than two times lower compared to manual arc welding.
38. As a protective medium in mixtures with inert and noble gases in automated welding and cutting of metal, due to which welds of very high quality are obtained.
39. Charging and recharging fire extinguishers for fire fighting equipment. In fire extinguishing systems, for filling fire extinguishers.
40. Charging cans for gas-cylinder weapons and siphons.
41. As a spray gas in aerosol cans.
42. To fill sports equipment (balls, balls, etc.).
43. As an active medium in medical and industrial lasers.
44. For accurate instrument calibration.

In the mining industry

45. For softening the coal massif during the extraction of coal in rockburst-hazardous seams.
46. \u200b\u200bFor blasting operations without the formation of a flame.
47. Increasing the efficiency of oil production by adding carbon dioxide to oil reservoirs.

In a liquid state (low-temperature carbon dioxide)

In the food industry

1. For quick freezing, to a temperature of -18 degrees C and below, food products in contact freezers. Along with liquid nitrogen, liquid carbon dioxide is most suitable for direct contact freezing different types products. As a contact refrigerant, it is attractive because of its low cost, chemical passivity and thermal stability, does not corrode metal assemblies, is not flammable, and is not hazardous to personnel. Liquid carbon dioxide is supplied to the product moving on the conveyor belt from nozzles in certain portions, which, at atmospheric pressure, instantly turns into a mixture of dry snow and cold carbon dioxide, while the fans constantly stir the gas mixture inside the apparatus, which, in principle, is capable of cooling the product from +20 degrees. From to -78.5 degrees C in a few minutes. The use of contact freezers has a number of fundamental advantages over traditional freezing technology:
· Freezing time is reduced to 5-30 minutes; enzymatic activity in the product quickly stops;
· The structure of tissues and cells of the product is well preserved, since ice crystals are formed much smaller and almost simultaneously in cells and in the intercellular space of tissues;
· With slow freezing, traces of the vital activity of bacteria appear in the product, while with shock freezing they simply do not have time to develop;
· Weight loss of the product as a result of drying is only 0.3-1% (versus 3-6%);
· Volatile valuable aromatic substances will be retained in much larger quantities. Compared to freezing with liquid nitrogen, when freezing with carbon dioxide:
No cracking of the product is observed due to too large temperature difference between the surface and the core of the frozen product
· In the process of freezing CO2 penetrates into the product and during defrosting protects it from oxidation and the development of microorganisms. Fruits and vegetables, subjected to quick freezing and packing on the spot, most fully retain their taste and nutritional value, all vitamins and biologically active substances, which makes it possible to widely use them for the production of products for baby and diet food. It is important that non-standard fruit and vegetable products can be successfully used for the preparation of expensive frozen mixtures. Fast freezers on liquid carbon dioxide are compact, simple in design and inexpensive to operate (if there is a nearby source of cheap liquid carbon dioxide). The devices exist in mobile and stationary versions, spiral, tunnel and cabinet types, which are of interest to agricultural producers and processors. They are especially convenient when the production requires the freezing of various food products and raw materials at different temperature conditions (-10 ... -70 degrees C). Quick-frozen foods can be dried under high vacuum - freeze drying. Products dried in this way are of high quality: they retain all the nutrients, have an increased regenerating capacity, have a slight shrinkage and a porous structure, and retain their natural color. Freeze-dried products are 10 times lighter than the original ones due to the removal of water from them, they are stored in sealed bags for a very long time (especially when the bags are filled with carbon dioxide) and can be delivered cheaply to the most remote areas.
2. For rapid cooling of fresh food products in packed and unpackaged form up to + 2 ... + 6 degrees C. With the help of installations, the operation of which is similar to the operation of freezers: when injecting liquid carbon dioxide, the smallest dry snow is formed, with which the product is processed for a certain time. Dry snow - effective remedy a rapid decrease in temperature, which does not lead to the drying out of the product, like air cooling, and does not increase its moisture content, as occurs when cooling with water ice. Dry snow cooling provides the required temperature reduction in just a few minutes, not hours as with conventional cooling. The natural color of the product is preserved and even improved due to the slight diffusion of CO2 inside. At the same time, the shelf life of products is significantly increased, since CO2 inhibits the development of both aerobic and anaerobic bacteria and molds. It is convenient and profitable to refrigerate poultry meat (cut or in carcasses), portioned meat, sausages and semi-finished products. Plants are also used where the technology requires rapid cooling of the product during or before forming, pressing, extruding, grinding or cutting. Devices of this type are also very convenient for use in poultry farms of in-line ultra-fast cooling from 42.7 degrees C to 4.4-7.2 degrees C from freshly laid chicken eggs.
3. For peeling berries by freezing.
4. For cryopreservation of semen and embryos of cattle and pigs.

In the refrigeration industry

5. For use as an alternative refrigerant in refrigeration plants. Carbon dioxide can serve as an effective refrigerant because it has a low critical temperature (31.1 degrees C), a relatively high triple point temperature (-56 degrees C), a high pressure at the triple point (0.5 MPa) and a high critical pressure ( 7.39 MPa). As a refrigerant it has the following advantages:
· Very low price in comparison with other refrigerants;
· Non-toxic, non-flammable and non-explosive;
· Compatible with all electrical insulating and construction materials;
· Does not deplete the ozone layer;
· Makes a moderate contribution to the increase in the greenhouse effect in comparison with modern halogenated refrigerants. High critical pressure has a positive aspect associated with a low compression ratio, as a result of which the efficiency of the compressor becomes significant, which allows the use of compact and low cost design solutions for refrigeration units. At the same time, additional cooling of the condenser electric motor is required, the metal consumption of the refrigeration plant increases due to the increase in the thickness of the pipes and walls. The use of CO2 in low-temperature two-stage installations for industrial and semi-industrial use, and especially in air conditioning systems for cars and trains, is promising.
6. For high-performance frozen grinding of soft, thermoplastic and elastic products and substances. In cryogenic mills, products and substances that cannot be ground in their usual form, such as gelatin, rubber and rubber, any polymers, tires, are frozen quickly and with low energy consumption. Cold milling in a dry, inert atmosphere is required for all spices, cocoa beans and coffee beans.
7. For testing technical systems at low temperatures.

In metallurgy

8. For cooling difficult-to-machine alloys when machining on lathes.
9. To create a containment environment for suppressing smoke from smelting or spillage of copper, nickel, zinc and lead.
10. When annealing hard copper wire for cable products.

In the extractive industry

11. As a weakly blasting explosive in coal mining, which does not lead to the ignition of methane and coal dust during an explosion, and does not produce poisonous gases.
12. Prevention of fires and explosions by displacing air by carbon dioxide from containers and mines with explosive vapors and gases.

Supercritical

In extraction processes

1. Capturing aromatic substances from fruit and berry juices, obtaining extracts of plants and medicinal herbs using liquid carbon dioxide. In traditional methods of extraction of plant and animal raw materials, various organic solvents are used, which are narrowly specific and rarely ensure the extraction of a full complex of biologically active compounds from raw materials. Moreover, in this case, the problem always arises of separating the residual solvent from the extract, and the technological parameters of this process can lead to the partial or even complete destruction of some components of the extract, which causes a change not only in the composition, but in the properties of the isolated extract. Compared to traditional methods, extraction processes (as well as fractionation and impregnation) using supercritical carbon dioxide have a number of advantages:
· Energy-saving nature of the process;
· High mass transfer characteristic of the process due to low viscosity and high penetrating power of the solvent;
· High degree of extraction of the corresponding components and high quality of the resulting product;
· Practical absence of СО2 in finished products;
An inert dissolving medium is used when temperature conditionsthat does not threaten thermal degradation of materials;
· The process does not produce waste water and waste solvents; after decompression, CO2 can be collected and reused;
· Provides unique microbiological purity of the products;
· Lack of complex equipment and multi-stage process;
· A cheap, non-toxic and non-flammable solvent is used. The selective and extraction properties of carbon dioxide can vary within wide limits with changes in temperature and pressure, which makes it possible to extract most of the spectrum of biologically active compounds known to date from plant raw materials at low temperatures.
2. To obtain valuable natural products - CO2-extracts of aromatic substances, essential oils and biologically active substances. The extract practically copies the original plant raw materials, as for the concentration of the substances included in it, we can say that there are no analogues among the classic extracts. Chromatographic analysis data show that the content of valuable substances exceeds classical extracts by tens of times. We have mastered the production on an industrial scale:
· Extracts from spices and medicinal herbs;
· Fruit aromas;
· Extracts and acids from hops;
Antioxidants, carotenoids and lycopenes (including those from tomato raw materials);
· Natural dyes (from fruits of red pepper and others);
· Wool lanolin;
· Natural plant waxes;
· Sea buckthorn oils.
3. For the isolation of highly refined essential oils, in particular from citrus fruits. During the extraction of essential oils with supercritical CO2, highly volatile fractions are successfully extracted, which give these oils fixing properties, as well as a fuller aroma.
4. To remove caffeine from tea and coffee, nicotine from tobacco.
5. To remove cholesterol from food (meat, dairy products and eggs).
6. For the manufacture of fat-free potato chips and soy products;
7. For the production of high quality tobacco with specified technological properties.
8. For dry cleaning of clothes.
9. To remove uranium compounds and transuranic elements from radioactively contaminated soils and from the surfaces of metal bodies. At the same time, the volume of water waste is reduced by hundreds of times, and there is no need to use aggressive organic solvents.
10. For environmentally friendly technology for etching printed circuit boards for microelectronics, without the formation of toxic liquid waste.

In fractionation processes

The separation of a liquid substance from a solution, or the separation of a mixture of liquid substances is called fractionation. These processes are continuous and therefore much more efficient than the separation of substances from solid substrates.
11. For refining and deodorizing oils and fats. To obtain marketable oil, it is necessary to carry out a whole range of measures, such as removing lecithin, mucus, acid, bleaching, deodorization and others. When extracting with supercritical CO2, these processes are carried out during one technological cycle, and the quality of the oil obtained in this case is much better, since the process proceeds at relatively low temperatures.
12. To reduce the alcohol content of beverages. The production of non-alcoholic traditional drinks (wine, beer, cider) is in increasing demand for ethical, religious or dietary reasons. Even though these low alcohol drinks are often of inferior quality, the market is large and growing rapidly, so improving such technology is a very attractive issue.
13. For energy-saving production of high-purity glycerin.
14. For energy-saving production of lecetin from soybean oil (with a phosphatidyl choline content of about 95%).
15. For flowing purification of industrial waste water from hydrocarbon pollutants.

In impregnation processes

Impregnation process - the introduction of new substances, in essence, is a reverse extraction process. The required substance dissolves in supercritical CO2, then the solution penetrates into the solid substrate, when the pressure is released, carbon dioxide instantly evaporates, and the substance remains in the substrate.
16. For environmentally friendly technology for dyeing fibers, fabrics and textile accessories. Staining is a special case of impregnation. Dyes are usually dissolved in a toxic organic solvent, so dyed materials must be thoroughly rinsed, which either evaporates the solvent into the atmosphere or ends up in wastewater. For supercritical dyeing, water and solvents are not used, the dye is dissolved in supercritical CO2. This method provides an interesting opportunity to dye different types of synthetic materials at the same time, for example, plastic prongs and fabric zipper lining.
17. For environmentally friendly technology, paint application. The dry dye dissolves in a stream of supercritical CO2, and with it flies out of the nozzle of a special gun. Carbon dioxide immediately evaporates and the paint settles on the surface. This technology is especially promising for painting cars and large equipment.
18. For homogenized impregnation of polymer structures with drugs, thereby ensuring constant and prolonged release of drugs in the body. This technology is based on the ability of supercritical CO2 to easily penetrate into many polymers, saturate them, causing micropores to open and swell.

In technological processes

19. Replacement of high-temperature water vapor with supercritical CO2 in extrusion processes, in the processing of grain-like raw materials, allows using relatively low temperatures, introducing dairy ingredients and any heat-sensitive additives into the formulation. Supercritical fluid extrusion allows the creation of new products with an ultra-porous internal structure and a smooth, dense surface.
20. For obtaining powders of polymers and fats. A jet of supercritical CO2 with some polymers or fats dissolved in it is injected into a chamber with a lower pressure, where they "condense" in the form of a perfectly homogeneous finely dispersed powder, the finest fibers or films.
21. To prepare for drying greens and fruits by removing the cuticular wax layer with a jet of supercritical CO2.

In the processes of carrying out chemical reactions

22. A promising area of \u200b\u200bapplication of supercritical CO2 is its use as an inert medium in the course of chemical reactions of polymerization and synthesis. In a supercritical environment, synthesis can take place a thousand times faster than the synthesis of the same substances in traditional reactors. It is very important for industry that such a significant acceleration of the reaction rate, due to high concentrations of reagents in a supercritical medium with its low viscosity and high diffusion capacity, makes it possible to accordingly reduce the contact time of the reagents. In terms of technology, this makes it possible to replace static closed flow reactors, of a fundamentally smaller size, with cheaper and safer ones.

In thermal processes

23. As a working fluid for modern power plants.
24. As a working fluid of gas heat pumps that produce high-temperature heat for hot water supply systems.

Solid (dry ice and snow)

In the food industry

1. For contact freezing of meat and fish.
2. For contact quick freezing of berries (red and black currants, gooseberries, raspberries, black chokeberry and others).
3. Sale of ice cream and soft drinks in places remote from the power grid, with dry ice cooling.
4. During storage, transportation and sale of frozen and chilled food products. The production of briquetted and granulated dry ice for buyers and sellers of perishable products is developing. Dry ice is very convenient for transportation and when selling meat, fish, ice cream in hot weather - the products remain frozen for a very long time. Since dry ice only evaporates (sublimates), there is no melted liquid, and the transport containers remain always clean. Autorefrigerators can be equipped with a small-sized dry-ice cooling system, which is characterized by the utmost simplicity of the device and high operational reliability; its cost is many times lower than the cost of any classic refrigeration unit. This cooling system is the most economical when transporting over short distances.
5. For pre-cooling containers before loading products. Blasting dry snow in cold carbon dioxide is one of the most effective ways to pre-cool any container.
6. For air transportation as a primary refrigerant in insulated containers with an autonomous two-stage refrigeration system (granular dry ice - freon).

When cleaning surfaces

8. Cleaning of parts and assemblies, engines from contamination by treatment plants using dry ice granules in a gas stream. For cleaning the surfaces of assemblies and parts from operational contamination. Recently, there has been a great demand for non-abrasive express cleaning of materials, dry and wet surfaces with a jet of finely granulated dry ice (blasting). Without disassembling the units, you can successfully carry out:
· Cleaning of welding lines;
· Removal of old paint;
· Cleaning of casting molds;
· Cleaning of units of printing machines;
· Cleaning of equipment for the food industry;
· Cleaning of molds for the production of polyurethane foam products.
· Cleaning of molds for the production of automobile tires and other rubber products;
· Cleaning of molds for the production of plastic products, including cleaning of molds for the production of PET bottles; When dry ice pellets hit a surface, they instantly evaporate, creating a micro-explosion that removes contamination from the surface. When removing brittle material such as paint, the process creates a pressure wave between the coating and the substrate. This wave is strong enough to remove the cover, lifting it up from the inside. When removing viscous or viscous materials such as oil or dirt, the cleaning process is similar to rinsing with a strong jet of water.
7. For deburring rubber and plastic stamped products (tumbling).

During construction work

9. In the process of manufacturing porous building materials with the same size of carbon dioxide bubbles, evenly distributed throughout the entire volume of the material.
10. For freezing soil during construction.
11. Installation of ice plugs in pipes with water (by freezing them outside with dry ice), for the duration of repair work on pipelines without draining the water.
12. For cleaning artesian wells.
13. When removing asphalt pavements in hot weather.

In other industries

14. Obtaining low temperatures down to minus 100 degrees (when mixing dry ice with ether) for testing the quality of products, for laboratory work.
15. For cold fit of parts in mechanical engineering.
16. In the manufacture of plastic grades of alloyed and stainless steels, annealed aluminum alloys.
17. When crushing, grinding and preserving calcium carbide.
18. To create artificial rain and get additional precipitation.
19. Artificial dispersion of clouds and fog, the fight against hail.
20. For the formation of harmless smoke during performances and concerts. Obtaining a smoke effect, on the stage during the performances of artists, using dry ice.

In medicine

21. For the treatment of certain skin diseases (cryotherapy).

Carbon dioxide CO 2 (carbon dioxide, carbon dioxide, carbon dioxide, carbonic anhydride), depending on pressure and temperature, can be in a gaseous, liquid or solid state.

In its gaseous state, carbon dioxide is a colorless gas with a slightly sour taste and odor. The Earth's atmosphere contains about 0.04% carbon dioxide. Under normal conditions, its density is 1.98 g / l - about 1.5 times the density of air.

Diagram. Phase equilibrium of carbon dioxide

Liquid carbon dioxide (carbon dioxide) is a colorless, odorless liquid. At room temperature, it only exists at pressures above 5850 kPa. The density of liquid carbon dioxide is highly temperature dependent. For example, at temperatures below + 11 ° С liquid carbon dioxide is heavier than water, at temperatures above + 11 ° С it is lighter. As a result of the evaporation of 1 kg of liquid carbon dioxide, under normal conditions, approximately 509 liters of gas are formed.

At a temperature of about -56.6 ° C and a pressure of about 519 kPa, liquid carbon dioxide turns into a solid - "dry ice".

In industry, there are 3 most common methods for producing carbon dioxide:

• from waste gases of chemical industries, primarily synthetic ammonia and methanol; the exhaust gas contains approximately 90% carbon dioxide;
• from the flue gases of industrial boilers burning natural gas, coal and other fuels; the flue gas contains 12-20% carbon dioxide;
• from waste gases generated during fermentation in the process of obtaining beer, alcohol, in the splitting of fats; the off-gas is almost pure carbon dioxide.

According to GOST 8050-85, gaseous and liquid carbon dioxide is supplied in three types: the highest, first and second grades. It is recommended to use carbon dioxide of the highest and first grade for welding. The use of carbon dioxide of the second grade for welding is allowed, but the presence of gas dryers is desirable. The permissible content of carbon dioxide and some impurities in various brands of carbon dioxide is shown in the table below.

Table. Characteristics of carbon dioxide brands

Safety measures when working with carbon dioxide:

• Carbon dioxide is non-toxic and non-explosive, however, when its concentration in the air exceeds 5% (92 g / m 3), the proportion of oxygen decreases, which can lead to oxygen deficiency and suffocation. Therefore, you should beware of its accumulation in poorly ventilated areas. To register the concentration of carbon dioxide in the air of industrial premises, gas analyzers are used - stationary automatic or portable.
• When the pressure decreases to atmospheric, liquid carbon dioxide turns into gas and snow with a temperature of -78.5 ° C and can lead to damage to the mucous membrane of the eyes and frostbite of the skin. Therefore, when sampling liquid carbon dioxide, it is necessary to use protective glasses and gloves.
• Inspection of the internal container of a previously operated tank for storing and transporting liquid carbon dioxide must be carried out in a hose gas mask. The tank must be warmed up to temperature environment, and blow out the inner container with air or ventilate. It is allowed not to use a gas mask only after the volume fraction of carbon dioxide inside the equipment falls below 0.5%.

The use of carbon dioxide in welding

Carbon dioxide is used as an active shielding gas in arc welding (usually in semi-automatic welding) with a consumable electrode (wire), including in the composition of a gas mixture (with oxygen, argon).

Welding stations can be supplied with carbon dioxide in the following ways:

• directly from an autonomous station for the production of carbon dioxide;
• from a stationary storage vessel - with significant volumes of carbon dioxide consumption and the enterprise does not have its own autonomous station;
• from the transport carbon dioxide tank - with lower volumes of carbon dioxide consumption;
• from cylinders - with insignificant volumes of carbon dioxide or the impossibility of laying pipelines to the welding station.

An autonomous station for the production of carbon dioxide is a separate specialized workshop of an enterprise that produces carbon dioxide for its own needs and supply to other organizations. Carbon dioxide is supplied to the welding stations through gas pipelines laid in the welding shops.

With large volumes of carbon dioxide consumption and the enterprise does not have an autonomous station, carbon dioxide is stored in stationary storage vessels, into which it is supplied from transport containers (see figure below).

Drawing. Scheme of supplying welding stations with carbon dioxide from a stationary storage vessel

With lower consumption volumes, the supply of carbon dioxide through pipelines can be carried out directly from the transport tank. The characteristics of some stationary and transport containers are shown in the table below.

Table. Characteristics of tanks for storage and transportation of carbon dioxide (carbon dioxide)

With small volumes of carbon dioxide consumption or the impossibility of conducting pipelines to welding stations, cylinders are used to supply carbon dioxide. In a standard black cylinder with a capacity of 40 liters, 25 kg of liquid carbon dioxide is poured, which is usually stored at a pressure of 5-6 MPa. As a result of the evaporation of 25 kg of liquid carbon dioxide, approximately 12 600 liters of gas are formed. The storage scheme for carbon dioxide in a cylinder is shown in the figure below.

Drawing. Scheme of storage of carbon dioxide (carbon dioxide) in a cylinder

To take gas from a cylinder, it must be equipped with a reducer, gas heater and gas dryer. When carbon dioxide leaves the cylinder as a result of its expansion, adiabatic cooling of the gas occurs. At a high gas flow rate (over 18 l / min), this can lead to freezing of the water vapor contained in the gas and blockage of the reducer. In this regard, it is advisable to place a gas heater between the reducer and the cylinder valve. When the gas passes through the coil, it is heated by an electric heating element connected to a network with a voltage of 24 or 36V.

A gas desiccant is used to extract moisture from carbon dioxide. It is a body filled with a material (usually silica gel, copper sulfate or alumogel) that absorbs moisture well. Dryers are available in high pressure upstream of the pressure reducer and low pressure downstream of the pressure reducer.

(Iv) carbon dioxide or carbon dioxide. It is also called carbonic anhydride. It is a completely colorless and odorless gas with a sour taste. Carbon dioxide is heavier than air and does not dissolve well in water. At temperatures below -78 degrees Celsius, it crystallizes and becomes like snow.

From a gaseous state, this substance passes into a solid, since it cannot exist in a liquid state under atmospheric pressure. The density of carbon dioxide under normal conditions is 1.97 kg / m3 - 1.5 times higher. Carbon dioxide in solid form is called "dry ice". It turns into a liquid state in which it can be stored for a long time when the pressure rises. Let us consider in more detail this substance and its chemical structure.

Carbon dioxide, the formula of which is CO2, is composed of carbon and oxygen, and it is produced by burning or decaying organic matter. Carbon monoxide is found in the air and underground mineral springs. Humans and animals also emit carbon dioxide when they breathe out air. Plants release it without light, but during photosynthesis they intensively absorb it. Due to the metabolic process of cells of all living things, carbon monoxide is one of the main components of the surrounding nature.

This gas is not toxic, but if it accumulates in high concentration, suffocation (hypercapnia) can begin, and if it is lacking, the opposite condition develops - hypocapnia. Carbon dioxide transmits and reflects infrared. He is the one that directly affects global warming. This is due to the fact that the level of its content in the atmosphere is constantly increasing, which leads to the greenhouse effect.

Carbon dioxide is produced industrially from flue or furnace gases, or by decomposition of dolomite and limestone carbonates. The mixture of these gases is thoroughly washed with a special solution consisting of potassium carbonate. Then it passes into bicarbonate and decomposes when heated, resulting in the release of carbon dioxide. Carbon dioxide (H2CO3) is formed from carbon dioxide dissolved in water, but in modern conditions it is obtained by other, more progressive methods. After the carbon dioxide is purified, it is compressed, cooled and pumped into cylinders.

This substance is widely and widely used in industry. Food workers use it as a leavening agent (for example, for making dough) or as a preservative (E290). With the help of carbon dioxide, various tonic drinks and soda are produced, which are so loved not only by children, but also by adults. Carbon dioxide is used in the manufacture of baking soda, beer, sugar, sparkling wines.

Carbon dioxide is also used in the production of effective fire extinguishers. With the help of carbon dioxide, the active medium is created, which is necessary at high temperatures of the welding arc, carbon dioxide decomposes into oxygen and carbon monoxide. Oxygen interacts with liquid metal and oxidizes it. Carbon dioxide in cans is used in air guns and pistols.

Aircraft builders use this substance as fuel for their models. With the help of carbon dioxide, you can significantly increase the productivity of crops grown in a greenhouse. It is also widely used in industry in which food is preserved much better. It is used as a refrigerant in refrigerators, freezers, electric generators and other heat and power plants.

Carbon dioxide is normally a colorless, non-aromatic gas with a slightly sour taste. At atmospheric pressure, the compound does not exist in a liquid state, but passes from a solid to a gaseous state. Carbon dioxide is called dry ice in the solid phase. Other names for the substance are carbon dioxide, carbon dioxide, carbon monoxide, carbonic anhydride.

The compound is contained in mineral springs, air, and is released during respiration of plants and animals. In living nature, matter plays an important role, taking part in the metabolic processes of living cells. Carbon dioxide is produced by oxidative reactions in mammals and is released with respiration into the atmosphere. The main source of carbon for plants is atmospheric carbon dioxide.

Carbon dioxide is produced commercially from flue gases by absorption with monoethanolamine or potassium carbonate. In addition, the compound is produced in special air separation plants as a by-product in the extraction of argon, oxygen, and nitrogen.

Applications for carbon dioxide

Due to its properties, carbon dioxide has been used in the food industry since the 19th century. One of the brewers discovered a build-up of gas under the lid of a beer barrel. He decided to try it, therefore he enriched water and beer with this chemical compound. Afterwards, new drinks were served to the guests, who liked the sparkling water. This is how the use of carbon dioxide in the beverage industry begins. Subsequently were thoroughly studied chemical properties and the composition of the compound.

Carbon dioxide, known as a food additive under the number E290, is used as a leavening agent for dough when baking confectionery. Carbon dioxide is actively used in the production of soft drinks. Its addition has a positive effect on the refreshing qualities and properties of beverages. In winemaking, the fermentation process is controlled by the addition of carbon dioxide. Some of the wines are specially enriched with this compound. For better storage of juices, carbon dioxide is also used in a small concentration. In addition, the substance is used as a shielding gas during the transportation and storage of food products.

Due to its properties, carbon dioxide is used in cylinders of fire extinguishers, during welding with wire, in pneumatic weapons, as a source of energy for engines in aircraft models. In solid form, the compound is used to keep cold in freezers.

The additive under the number E290 is approved in almost all countries for use in food production.

The effect of carbon dioxide on the human body

Carbon dioxide is found in many living cells in the body and in the atmosphere. In this regard, the E290 additive can be classified as relatively harmless.

But remember that carbon dioxide promotes the absorption of various substances into the gastric mucosa. This explains the rapid intoxication as a result of the consumption of alcoholic carbonated drinks.

The harm of carbon dioxide is manifested by side effects such as bloating and belching when drinking carbonated drinks. There is another opinion regarding this food additive, which is as follows: the harm of carbon dioxide lies in the fact that highly carbonated drinks are able to flush calcium from the bones.

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