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

Agree, blue fuel is very convenient to use and inexpensive.Its popularity is strengthened by environmental safety and almost universal availability. But have you ever seriously thought about why compressed gases are contained in special cylinders and how this affects your safety?

In the article we present you will find detailed, technically sound answers to these questions. We will tell you the difference between a liquefied gaseous medium and its compressed counterpart. We will introduce you to the technical features of gas containers, the rules for filling and transporting them.

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

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

But due to the low density, even a small amount of gas by mass occupies a large volume. For example, to transport only 26.9 kg of propane in its usual gaseous state, a huge container with a volume of about 14,000 liters will be required.

Propane and butane are the most popular gases in the domestic sector. They are obtained during oil refining or isolated 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 its volume decreases. After compression, the same 26.9 kg of propane fits in a 50-liter vessel.

When compressed, gases such as propane, butane, ammonia, chlorine, and carbon dioxide transform into a liquid aggregate state, which is why they are called liquefied. Oxygen, argon, methane remain in a gaseous state and are called compressed gases.

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

For compressed and liquefied gases, ordinary containers are not suitable. Striving to expand, the gas will quickly destroy it and break free, and this is already fraught with explosions, fires, poisoning and financial losses. Therefore, special vessels under excess internal pressure, better known as gas cylinders, are used.

Design features of gas cylinders

Requirements for the design of gas cylinders, including dimensions and wall thickness, are determined by state technical standards. The more pressure applied to compress the gas, the stronger the container must be.

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

Oxygen and argon are used for welding work. Cylinders for them are manufactured 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 inscription “oxygen” on the body. Vessels for argon are 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 their mixtures are contained under a pressure of 1.6 MPa in red welded steel cylinders. Since this gas is widely in demand for municipal and industrial use, it is worth considering in more detail the features of its storage and transportation, as well as safety rules when refilling cylinders.

Application 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). It is obtained from oil refining. A relatively small increase in pressure is sufficient for PBT to transform into a liquid state. No temperature reduction is required.

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

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

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

Cylinders of the same volume of liquefied propane-butane can hold almost 2 times more than compressed methane. In terms of heat release, liquefied PBT is also superior to compressed methane at the same volumetric quantity.

Due to the reduction in 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, and recreation centers.

Cylinders for propane-butane mixture

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

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

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

An alternative to traditional steel cylinders are newer cylinders made of composite materials with a service life of 20 years and a test period of 5 years.

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

The bottom is made by hot or cold stamping. The elements are connected to each other by welding.Locking devices are installed in the neck of the cylinder. To completely seal the connection, lead litharge or red lead is used.

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

The assembled cylinder should have:

• durable;
• sealed;
• without deformation.

The outside of the container is painted with red enamel, which is weather-resistant. The name of the contents “Propane” is written in white enamel in the center of the cylindrical part of the body. Failure to comply with the established standard in the inscription and coloring is a reason for rejecting the cylinder.

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

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

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

When using composite cylinders, it is necessary to take into account the operating principle of safety devices. When the cylinder overflows or the gas expands due to increased temperature, its excess is discharged outside. This may lead to an increase in gas concentration in the room where the cylinder is located.

A leak detector with an audible alarm, which is mounted on the wall in the kitchen or other gasified room, will help prevent excess gas concentrations.

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

Each cylinder is supplied with a passport, which indicates its technical characteristics and the timing of 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 outside temperature leads to the expansion of the liquid fraction of propane-butane, so cylinders are allowed to be filled to a maximum of 85% of their volume. Eg, 50 liter cylinder, 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 2.3% and 1.9% of the volume of the room, respectively, which makes their gas-air mixtures extremely explosive. Consumers and personnel of gas filling stations must prevent the formation of explosive concentrations and ignition sources of PBT.

Filling an LPG cylinder 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 basements and basements in dangerous concentrations. Hence the ban on installing gas equipment in such premises.

Grate the laundry soap, add water, lather with a brush and apply the soap solution to the problem area - the appearance of bubbles indicates a gas leak.

Propane-butane, like carbon dioxide, does not have a poisonous, but a suffocating effect on humans and animals when the oxygen concentration in the air decreases to 19%. This can lead to deterioration in human health and death. PBT is odorless, so odorants are added to the composition to help detect its presence in the air.

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

Rules for refilling household gas cylinders

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

Cylinders are not allowed to be refilled in the following cases:

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

At automobile gas filling stations that do not have a separate license and appropriate equipment, refilling household cylinders prohibited by law.

Gas filling station equipment is intended only for automobile cylinders equipped with cut-off valves (multi-valves) that do not allow filling above the norm.

Refilling household gas cylinders requires special equipment, which differs from that of a conventional gas filling station.

It should be remembered: if at subzero temperatures you fill a propane-butane cylinder more than 85% and then take it into a warm room, an explosion is possible.

When moving, the cylinders are protected from falls and impacts and are not turned upside down with their caps.Loading and unloading from the vehicle is performed with the engine turned off.

Safety of heating and hot water supply using 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 heating devices. It is cheaper than electricity. Unlike firewood, coal or diesel, it does not pollute the air with solid combustion products, that is, it is more environmentally friendly.

Instead of cylinders in private households, you can use gas tanks with a volume of up to 20,000 liters, if there are no problems with refilling them

When organizing a heating and hot water supply system using 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:

• a gas boiler;
• gearboxes;
• shut-off valves;
• gas pipeline components;
• radiators.

The boiler can be single- or double-circuit, but must have 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 double-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, the water vapor generated during the combustion of gas is converted into liquid, which makes it possible to obtain additional thermal energy.

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 volume of gas and extends the interval between refills

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

To prevent the pressure in the system from dropping during severe frosts, the cabinets must be insulated with non-flammable materials, and minimal heating must be provided in the room.

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

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

The color of the reducer must match the color of the cylinder, that is, be red (for propane-butane). It must not become clogged, otherwise the pressure may increase and the equipment may fail. Once a week, the gearbox is checked for gravity flow and the functionality of the safety valve.

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

To create a gas pipeline, steel pipes with walls no less than 2 mm thick are used. The section of pipe that passes through the wall is placed in a protective case.A flexible connection can be used to connect to the gas pipeline of a heating boiler. The reducer is connected to the gas pipeline using a durite hose (rubber-fabric sleeve).

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

LPG for water heating

Flow columns and storage gas water heaters (boilers), like heating boilers, can operate on propane-butane. Conversion from main gas to liquefied gas is also carried out by replacing burner nozzles. There are models available for sale that are supplied by the manufacturer with kits for LPG. Connection to gas cylinders is carried out through a reducer.

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

Equipping water dispensers and boilers with automatic control and adjustment devices increases their efficiency and safety. Modern models have protection systems against overheating and switching on without water, and control for the presence of flame. LED display displays important information, such as 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:

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

After compression, hydrocarbon gas is in a cylinder at elevated pressure and is capable of rapid expansion as the temperature rises.

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

Tell us about how you use bottled gas at your dacha or country house. Please leave comments, ask questions, post photos in the block form below. Share valuable information on the topic of the article that is worth sharing with site visitors.