Basics & FAQ

Many technical gases are liquefied for storage and transport. A distinction is made between cryogenic liquefied gases and gases liquefied under pressure. Liquefaction under pressure is achieved by compression. When a gas is liquefied under pressure, both the liquid and the gaseous phase are present in the tank or cylinder. When gas is withdrawn from the vapour phase, the pressure in the storage vessel drops, and the liquid gas vaporizes naturally in line with its vapour pressure curve to refill the space that has been freed up.

The change from the liquid to the gaseous state requires a substance-specific amount of energy in the form of heat (enthalpy of vaporization), which in simple tank installations with low withdrawal rates is drawn from the surroundings. If more heat is required than can be transported from the surroundings into the tank, the medium cools down and the operating pressure falls until the pressure of the medium is too low for technically practical operation of the system. Gas can then no longer be withdrawn.

A vaporizer is needed to withdraw larger quantities of gas. For this purpose, the gas is withdrawn from the tank in liquid form and only becomes gaseous in the vaporizer. The tank does not cool down, and with propane/butane mixtures the composition of the gas remains the same, instead of the propane vaporizing first. The vaporizer either improves the absorption of ambient heat by means of suitably designed structures or supplies the heat required for vaporization by external heating.

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No. A vaporizer is essentially a passive component. It provides the liquid gas with an environment in which, up to the respective rated capacity, it finds sufficient heat transfer surfaces and heat energy to vaporize at constant pressure within the temperatures required by codes and standards or by physical necessity.

No capacity or quantity can be set on the vaporizer itself. In the standard case, with direct withdrawal from the tank, the vaporizer operates at the temperature-dependent system pressure according to the vapour pressure curve, i.e. at saturation conditions. With direct withdrawal from the tank and the liquid line open back to the tank, there is no pressure increase: the gas leaves the vaporizer at the pressure at which it enters (‘at unchanged pressure’). The rated capacity in kg/h indicates the maximum quantity the unit can safely vaporize.

If, on the other hand, the liquid gas is pressurized by a pump above its temperature-dependent vapour pressure, it is outside saturation conditions. The unit must then be sized separately by us.

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In principle, yes. Small quantities can be withdrawn from the vapour phase of the tank without difficulty. The withdrawal rate actually possible depends on the tank size, the type of storage (underground/above-ground) and the ambient temperature.

The expansion of the gas causes a drop in pressure, and therefore also in temperature, inside the vessel along the vapour pressure curve. The temperature difference that develops at the contact surface between the gas vessel and its surroundings (soil or ambient air) is balanced by a heat flow from the surroundings into the liquid phase of the gas vessel. The withdrawal flow from the vapour phase and the heat flow from the surroundings are thus in direct equilibrium.

The rate of this heat flow is limited by the size of the contact surface, the vessel size and the heat capacity and temperature of the surrounding medium. If more liquefied gas is withdrawn than can vaporize naturally via the heat flow from outside, the vessel cools down and the pressure falls in line with the vapour pressure curve until the gas flow stops. A heated vaporizer is then needed.

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No. Ambient-air (atmospheric) vaporizers are not part of our product range.

Their most common application is the vaporization of cryogenic liquefied gases such as oxygen, nitrogen or argon. Because of the very low vaporization temperature of these gases, the heat flow can be reliably obtained from the ambient air even in winter, but only with very large transfer surfaces. At high withdrawal rates, the units can ice up.

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A heated vaporizer is needed as soon as more gas is required than the tank can vaporize naturally from ambient heat (Why do you need a vaporizer?). It is always needed for media with a higher boiling point, such as alcohols, and also when defined gas temperatures must be reached to prevent recondensation.

As required by technical regulations, the heating is indirect. The heat is transferred to the gas by means of a solid or a liquid; the liquid is heated electrically, with heating water or with steam. Vaporizers for liquefied petroleum gas (LPG) differ in size and capacity, in heating method and in the resulting safety requirements. Which model is suitable depends on the application:

• solid heat transfer medium, electrically heated: dry-type vaporizers ET8TO (12–100 kg/h propane) and ETA8TO (5–30 kg/h ammonia)
• water bath, electrically heated: wet-type vaporizers ES (60–1,400 kg/h propane) and ESA (30–320 kg/h ammonia); the electrical connected load of up to 227 kW must be available at the site
• heating water from the heating network or a dedicated boiler: hot-water vaporizers WW (300–2,000 kg/h propane, special sizes up to 4,000 kg/h) and WA (100–660 kg/h ammonia)
• steam from an existing steam network: steam-heated vaporizer DS (60–800 kg/h propane, special sizes up to 1,000 kg/h); WW and WA can also be heated with steam via a steam heat exchanger

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Dry-type vaporizers use a solid block for heat transfer, usually made of aluminium. The liquid gas flows through tubes that are in contact with this block and absorbs the heat as it vaporizes. This design is particularly compact, low-maintenance and quickly ready for use.

In TORPEDO dry-type vaporizers, the vaporizer coil is cast into an aluminium block together with the heating system, and the block is indirectly electrically heated. Neither the heater nor the tube coil can be replaced. The vaporizer does not need an external control unit. It is easy to connect and ready for use straight away. It is well suited to commercial kitchens, small businesses and heating plants with a consumption of up to 100 kg/h propane. For ammonia, our dry-type vaporizers are suitable for a withdrawal rate of up to 30 kg/h.

Suitable vaporizers: ET8TOETA8TO

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A wet-type vaporizer uses a liquid heat transfer medium, usually a water bath to which an inhibitor and antifreeze have been added. In the electrically heated wet-type vaporizers ES and ESA, this water bath is indirectly electrically heated, and the vaporizer coil is immersed in the bath. In the DS, steam heats the heat transfer medium; in the hot-water vaporizers WW and WA, heating water flows through the shell around the tube coil.

The advantage is that heater ratings and heat transfer surfaces are easier to adapt, including for demanding applications. The vaporizer coil and the heating element terminal box are flanged to the front end of the vaporizer and can be withdrawn for servicing. The tube coil and the heating system are separate and fully repairable. The control cabinet with thermostat and relay technology is low-maintenance and can be adapted to different requirements.

Suitable vaporizers: ESESA

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Hot-water vaporizers are heated with hot water circulating in a closed circuit. They are well suited to large throughputs, especially if waste heat or a heating system is available anyway. At TORPEDO, they are the largest models, preferably designed for flow/return temperatures of 90/70 °C.

Operation generally requires a heating network. The vaporizer is easy to integrate. If the heating system has more than one heat consumer, the vaporizer circuit must be hydraulically separated. The heat transfer medium circuit with heat exchanger and pump is usually provided by the customer on site. If the vaporizer is the only heat consumer in the heating circuit, the heat exchanger can be omitted.

Because flow temperatures continue to fall, separate heating systems dedicated to the vaporizer are sometimes necessary.

A heating system is not essential: the intermediate circuit can also be heated via a steam heat exchanger. This means the hot-water vaporizers WW and WA can also be heated with steam.

Suitable vaporizers: WWWA

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Steam heating only makes sense if a steam network already exists. Generating steam solely for the vaporizer is generally not economical.

In the TORPEDO vaporizer type DS, the steam does not heat the gas directly but a liquid heat transfer medium based on a mixture of antifreeze, inhibitors and water. A self-acting steam temperature regulator ensures that this heat transfer medium is kept at a constant operating temperature.

Hot-water vaporizers of types WW and WA can also be heated with steam: the intermediate circuit is then heated via a steam heat exchanger.

Suitable vaporizers: DSWWWA

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The electrically heated vaporizer is the easiest to operate. However, it also requires high electrical connected loads, which the power supply of the premises must be able to provide. For high power requirements, the connection options should be checked in advance.

You will find the connected loads of the individual sizes in the tables on the unit pages.

Suitable vaporizers: ET8TOESETA8TOESA

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In that case, the solenoid valves close, in all designs, and no more liquid gas enters the vaporizer. This also applies in the event of severe voltage fluctuations. Overload means that more gas is being withdrawn than the vaporizer can handle. The heat transfer medium cools down, and if it falls below the minimum temperature, the valves close to prevent liquid from entering the gas line.

In these cases, the gas supply to the consumers is interrupted. Where it must not fail, we will advise you individually when planning your gas supply system, based on your case and the required capacity (What information do you need to size a vaporizer?).

In normal operation, the solenoid valves only open once the heat transfer medium has reached the required vaporization temperature. Heating and monitoring are thermostatically controlled within specified limits. An additional safety temperature limiter monitors the heat transfer medium and prevents its temperature from rising to an impermissible level.

Suitable vaporizers: ET8TOESWWDSETA8TOESAWA

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Yes, in hazardous area Zone 1 or Zone 2, depending on the design. Where LPG or ammonia can escape, an explosive mixture can form with the ambient air. The operator therefore classifies the installation area into hazardous area zones. This is done in the operator’s risk assessment and recorded in the explosion protection document (Section 6 of the German Hazardous Substances Ordinance, GefStoffV). For gases, there are three zones:

• Zone 0: An explosive atmosphere is present continuously, for long periods or frequently.
• Zone 1: It is likely to occur in normal operation occasionally.
• Zone 2: It is not likely to occur in normal operation and, if it does occur, only rarely and for a short period.

The TORPEDO dry-type vaporizers ET8TO and ETA8TO are designed for Zone 2 (equipment category II 3G). The wet-type vaporizers ES, ESA, DS, WW and WA are suitable for Zones 1 and 2; their control cabinet must be installed outside the hazardous area. We will be glad to help you select the right unit for your zone classification.

Suitable vaporizers: ET8TOESWWDSETA8TOESAWA

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All TORPEDO vaporizers are available as an individual unit or as a vaporizer system, with a tailored scope of supply.

Our dry-type vaporizers are series-produced units with a type-examined design. We essentially build all other designs as custom-built units, tailored to the customer and the order. For special models, for example for other media or in special sizes, we carry out our own conformity assessment: to Module B + F (EU-type examination and product verification) or as unit verification to Module G. With a complete system, by contrast, special requirements of all kinds can be taken into account, and the most suitable components can be selected and optimally integrated. You do not have to source the components yourself, all parts are matched to one another, and installation is simple and quick. More on this under Systems.

Suitable vaporizers: ET8TOESWWDSETA8TOESAWA

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Yes, on request. Since 2025 we have been building LPG vaporizers compatible with renewable dimethyl ether (rDME), currently on separate request. In future, all units designed for propane are also to be suitable for rDME.

Because the physical and chemical properties of rDME differ from those of pure propane/butane mixtures, vaporization systems must be specifically designed for these requirements, for example in terms of seals, diaphragms and hoses. Drawing on our many years of experience with vaporizers for various special gases, we have developed our vaporizers accordingly. We can also build complete rDME-compatible systems, as we manufacture systems even for ammonia, which is more corrosive still. We are currently working on lower-cost versions, because the materials for DME do not need to be quite as resistant as for ammonia. More on this under rDME.

Suitable vaporizers: ET8TOESWWDS

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To size your vaporizer or vaporizer system correctly, we need some information, above all:

• the gas and its exact composition
• the storage (above-ground or underground tank, drum, cylinders)
• the climatic conditions at the site
• the inlet pressure: operation at saturation conditions or with a pressure increase, e.g. by a pump
• the maximum and minimum gas demand in kg/h and the outlet pressure
• the preferred energy source (electricity, heating water, steam)
• requirements for availability, redundancy and explosion protection

You will find the complete checklists in the planning notes for propane / LPG and for ammonia.

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Vaporizer and LPG installations are, as a rule, installations subject to monitoring. Their inspections are governed by the German Ordinance on Industrial Safety and Health (BetrSichV). The installation must be inspected before initial commissioning and after modifications requiring inspection. Periodic inspections are then to be carried out, the maximum intervals of which are also laid down in the BetrSichV.

For the pressure vessels themselves, external inspection, internal inspection and strength test depend on the classification of the unit. The operator sets the specific intervals, which may be shorter, in the risk assessment. We determine and document the appropriate scope of inspection for you. More under Maintenance & inspections.

Suitable vaporizers: ET8TOESWWDSETA8TOESAWA

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Yes, for the dry-type vaporizer ET8TO. A vaporizer whose pressure-bearing part consists solely of tube coils and whose medium is non-corrosive is exempt from the periodic external inspection. Internal inspection and strength test are only due when the unit is taken out of service for repair work.

We do not apply this relaxation to the ammonia dry-type vaporizer ETA8TO, as ammonia is corrosive. The wet-type vaporizers are pressure vessels; the regular inspection intervals apply to them.

The inspection of the pressure installation as well as the explosion protection inspections and the electrical inspections remain mandatory.

Suitable vaporizers: ET8TO

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Statutory inspections keep you within the legal framework; maintenance keeps your production running. In continuous operation, electrical parts are subject to natural wear and contact erosion. Malfunctions of control valves often go unnoticed until the system shuts down.

We recommend annual maintenance of all units to ensure system availability in the long term. You will find our complete recommendations under Maintenance & inspections.

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