Why are liquefied and compressed gases stored in cylinders? Types of tanks + operating rules

You must admit that blue fuel is very convenient to use and is inexpensive. Its popularity strengthens environmental safety and near-universal accessibility. But have you ever seriously wondered why compressed gases are contained in special cylinders and how this affects your safety?

In our article, you will find detailed, technically sound answers to these questions. We will describe the difference between a liquefied gaseous medium and a compressed analogue. We will familiarize with the technical features of gas tanks, with the rules for refueling and transportation.

Why are gases compressed and how does this affect the cylinders?

In a gaseous state, substances do not have a definite shape, unlike solids. They can only be stored and transported in sealed containers.

But because of the low density, even an insignificant mass of gas takes up a large volume. For example, to transport just 26.9 kg of propane in its usual gaseous state would require a huge capacity of about 14,000 liters.

Propane and butane are the most popular gases in the household sector. They are obtained in the course of oil refining or extracted from oil during its production, for example, using fracking technology.

The problem is solved by compressing the gas by applying external pressure. As a result, its density increases, and the volume decreases. After compression, all the same 26.9 kg of propane fit in a vessel of 50 liters.

When compressed, gases such as propane, butane, ammonia, chlorine, carbon dioxide pass into the liquid state of aggregation, therefore they are called liquefied. Oxygen, argon, methane remain in a gaseous state and are called compressed gases.

Here you need to clarify that any turn gases into liquid by compression, but the pressure force should be higher, and the temperature should be much lower than normal air temperature.

Conventional containers are not suitable for compressed and liquefied gases. In an effort to expand, gas will quickly destroy it and break free, and this is already fraught with explosions, fires, poisoning and financial losses. Therefore, special vessels are used under excessive internal pressure, better known as gas cylinders.

Design features of gas cylinders

The requirements for the design of gas cylinders, including dimensions, wall thickness, determine state technical standards. The higher the pressure applied to compress the gas, the stronger the capacity should be.

The vessel shells for compressed methane, used as fuel for internal combustion engines, have no seams and consist of metal and composite shells. Designed for pressures up to 245 kg / cm².

Oxygen and argon are used for welding. Cylinders for them are made according to GOST 949-73. The material is carbon or alloy steel. Having a volume of 20-50 liters, vessels made of alloy steel with walls 6 mm thick are able to withstand internal pressure up to 19.6 MPa.

According to the accepted standard, they are painted with blue enamel on the outside and have a black “oxygen” inscription on the case. Argon vessels - gray with a green inscription "pure argon."

Welded steel cylinders for liquefied petroleum gas are manufactured in accordance with GOST and meet established safety requirements

Propane, butane and mixtures thereof are contained under a pressure of 1.6 MPa in red welded steel cylinders. Since this gas is widely in demand for domestic and industrial applications, it is worth considering in more detail the features of its storage and transportation, as well as safety rules when refueling cylinders.

The use of liquefied propane-butane

Technical propane-butane (PBT), how it is classified GOST R 52087-2018, belongs to the category of liquefied hydrocarbon gases (LPG). Get it when refining oil. A relatively small increase in pressure is sufficient to transfer PBT to a liquid state. Temperature reduction is not required.

At normal air temperature, a decrease in pressure leads to the evaporation of PBT and its transition to the vapor phase. When filling the cylinders, a two-phase system is formed in them, consisting simultaneously of liquefied gas and its vapor.

This property is an advantage over other types of fuel gases: they store and transport the propane-butane mixture as a liquid in compact containers; they are used immediately as gas, without additional transformations, which gives additional convenience to the consumer.

Liquefied fuel gas in cylinders is delivered to consumers in specialized vehicles with mandatory observance of the rules for handling dangerous goods

In cylinders of an identical volume of liquefied propane-butane fits almost 2 times more than compressed methane. In terms of heat generation, liquefied PBT also surpasses compressed methane with the same volumetric amount.

By reducing the metal consumption, PBT cylinders have less weight. All this reduces the cost of transportation, reduces the number of deliveries and makes the use of propane-butane mixture for domestic and industrial purposes economically feasible.

PBT is in demand in settlements that do not have access to main gas pipelines. For cooking, heating water and coolants in heating systems, it is used by private households, catering and trade enterprises, farms, recreation centers.

Propane-butane mixture cylinders

PBT is in cylinders at a pressure that is tens of times less than that required for storage of compressed gases. Thanks to this, the production technology is simplified, the metal consumption of the cylinders is reduced.Nevertheless, they are also subject to stringent requirements.

Welded steel cylinders with a volume of 5, 12, 27, 50 liters, designed for an internal pressure of up to 1.6 MPa, are intended for the propane-butane mixture.

It is also possible their content in cylinders made of composite material, designed for 2.0 MPa. The design, shape and dimensions of each cylinder part are determined by state technical standards.

An alternative to traditional steel cylinders is newer composite cylinders with a service life of 20 years and a test interval of 5 years.

According to GOST 15860-84, the cylindrical element of the cylinder (shell), its bottom and underlay rings are made of high-strength steel grades. The surface should be free of cracks, sinks and other defects that reduce the thickness of the walls.

The bottom is made by hot or cold stamping. Between themselves, the elements are connected by welding. Locking devices are installed in the neck of the cylinder. To completely seal the compound, lead lithium or red lead is used.

Safety caps can be steel and cast iron with a threaded or threaded connection. The main requirement for them is the ability to provide reliable protection for the locking device.

Assembled cylinder should be:

• durable;
• tight;
• no deformation.

Outside the container is painted with red enamel, resistant to weathering. The name of the content "Propane" is written in white enamel in the center of the cylindrical part of the body. Non-compliance of the inscription and coloring with the established standard is the reason for rejection of the cylinder.

Each cylinder on the collar or neck must have a nameplate indicating the manufacturer, date of manufacture and testing, technical specifications

By GOST R 55559-2013 composite cylinder consists of an internal sealing shell (liner), on which composite material is wound. Other technical solutions are allowed. The color of the composite balloon is also red.

The cylinder is equipped with shut-off and safety valves, including safety devices against increasing pressure and temperature, which increases its safety.

When operating composite cylinders, the principle of operation of safety devices must be taken into account. When the cylinder is overfilled or gas expands due to an increase in temperature, its excess is brought out. This can lead to an increase in gas concentration in the room where the container is located.

To prevent excess gas concentration, a leakage detector with an audible alarm, which is mounted on a wall in a kitchen or other gasified room, will help

Before sending cylinders for sale, manufacturers conduct acceptance tests. In the future, both steel and composite cylinders must undergo a technical examination every 5 years.

Each cylinder is supplied with a passport, which indicates its technical characteristics and the timing of the technical examination.

PBT properties and safety measures

The physical and chemical properties of gases determine not only the requirements for the design of cylinders, but also safety measures during their refueling, transportation and operation.

An increase in the outside temperature leads to the expansion of the liquid fraction of propane-butane; therefore, cylinders are allowed to fill up to a maximum of 85% of their volume. For example, 50 liter bottle, theoretically containing 26.9 kg of liquefied propane-butane, after refueling it actually contains about 21 kg. The free space is filled with the vapor phase.

The lower explosive limits of propane and butane are respectively 2.3% and 1.9% of the volume of the room, which makes their gas-air mixtures extremely explosive. Consumers and personnel of gas filling stations should exclude the formation of explosive concentrations and ignition sources of PBT.

Filling the LPG cylinder by more than 85% is fraught with explosion and fire, the risk is especially high in the autumn-winter period

Propane-butane mixtures are heavier than air and even with small leaks can accumulate in hazardous concentrations in basements and basements. Hence the ban on the installation of gas equipment in such premises.

Rub the laundry soap on a grater, add water, foam with a brush and apply a soap solution to the problem area - the appearance of bubbles indicates a gas leak.

Propane-butane, like carbon dioxide, exerts on humans and animals not a poison but a suffocating effect while reducing the oxygen concentration in the air to 19%. This can lead to poor health and death. PBT is odorless, so odorants are introduced into the composition to help determine its presence in the air.

Non-compliance security measures leads to emergency situations due to gas leakage and ignition. It is also possible the release and explosion of gas with the destruction of the cylinder.

Rules for refueling household gas cylinders

Refueling is carried out at specially equipped stations with mandatory automatic weighing and cutting off of gas with a dispenser. This allows you to control the degree of fullness with high accuracy.

Cylinders are not allowed to refuel in the following cases:

• faulty valve or valve;
• no residual pressure;
• the survey period has expired;
• there are defects on the surface;
• marking and coloring do not comply with GOST.

At gas stations that do not have a separate license and related equipment, gas station prohibited by law.

The filling station equipment is intended only for automobile cylinders equipped with cut-offs (multivalves), which do not allow filling above the norm.

Refueling household gas cylinders requires special equipment that differs from that of conventional gas stations

It should be remembered that if, at negative temperatures, the tank is filled with propane-butane by more than 85% and then brought into a warm room, an explosion may occur.

When moving, the cylinders are protected from falls and bumps, do not turn down caps. Loading and unloading from the car is performed with the engine turned off.

Safety of heating and domestic hot water on bottled gas

In the absence of access to a centralized gas supply, liquefied gas can be used as fuel for autonomous heating systems and water heaters. It is cheaper than electricity. Unlike firewood, coal or diesel does not pollute the air with solid combustion products, that is, it is more environmentally friendly.

Instead of cylinders in private households, gas tanks with a volume of up to 20,000 liters can be used if there are no problems with refueling

When organizing a heating system and hot water supply for LPG, it is necessary to take into account the requirements of SNiP 42-01-2002.

In addition to cylinders (50 l), the following equipment is used:

• gas boiler;
• gearboxes;
• shutoff valves;
• gas pipeline components;
• radiators.

The boiler can be single or double circuit, but always with a burner for liquefied gas. If bottled gas is a temporary solution and the house is planned to be connected to a centralized gas supply, it is rational to buy a boiler for main gas and additional equipment for LPG. A dual-circuit boiler will provide both domestic hot water and space heating.

It is possible to install a highly efficient condensing boiler equipped with two heat exchangers for heating the coolant and hot water supply. In such a boiler, water vapor generated during gas combustion is converted into liquid, which allows for additional thermal energy to be generated.

The boiler power is selected based on the area of ​​the heated room and preference is given to models with higher efficiency.

Several gas cylinders are connected to gas boilers, which increases the total gas volume and extends the interval between refueling

At the same time, several of the most capacious 50-liter cylinders are used, combined into a single battery. Cylinders are placed in metal, ventilated cabinets on the street on the north side of the house, in order to avoid heating by solar radiation. Another option is a separate non-residential premises.

So that in severe frosts the pressure in the system does not drop, the cabinets must be insulated with non-combustible materials, and the room must be kept at a minimum.

It is important to ensure that the distance from the boiler is at least 2 meters and that the equipment has free access for inspection. There should be no drain pits, cellars, basements, ditches near gas equipment. Gasification of basements and basements is prohibited.

Cylinders are connected to the gas pipeline through gas reducer, which allows you to adjust the gas pressure during its selection. It can be separate for each cylinder or common to all.

The color of the gearbox must match the color of the cylinder, that is, be red (for propane-butane). It must not be allowed to clog, otherwise the pressure may rise and equipment malfunction. Once a week, the gearbox is checked for gravity and the safety valve.

When combining cylinders into a single battery, it is rational to use a pressure stabilization ramp consisting of a connection module, a reducer, a filter, a valve, a stabilizer

To create a gas pipeline, steel pipes with walls at least 2 mm thick are used. The pipe section that passes through the wall is placed in a protective case. Flexible connection can be used to connect the boiler to the gas pipeline. The reducer is connected to the gas pipeline using a dyuritic hose (rubber-fabric sleeve).

It is written in detail about which gas mixture is best used for storage in a gas tank in the next articlewhich we recommend that you familiarize yourself with.

LPG for heating water

Flow columns and storage gas water heaters (boilers), like heating boilers, are able to work on propane-butane. The transfer from the main to liquefied gas is also carried out by replacing the burner nozzles. On sale there are models equipped with manufacturer sets for LPG. Connection to gas cylinders is carried out through a reducer.

The column is installed in a non-residential room with ventilation and exhaust hood. The minimum distance from the gas column to the surrounding objects is determined by the regulations and must be observed for safety reasons. Installation in the bathroom is prohibited.

Equipping the water columns and boilers with automatic control and adjustment devices increases their efficiency and safety. Modern models have protection systems against overheating and against switching on without water, and control the presence of flame. LED-display, displays important information, for example, the temperature of the water entering the taps.

Conclusions and useful video on the topic

Checking the gas cylinder for safety, service life and rejection:

The reasons for the gas pressure drop in the system at -42 ° C and ways to combat the freezing of gas cylinders:

After compression, the hydrocarbon gas is in the cylinder at elevated pressure and is capable of sharp expansion with increasing temperature.

Compliance with safety rules and the use of gas cylinders that meet established standards helps to avoid accidents and efficiently use blue fuel for cooking, space heating and hot water supply of private houses.

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