Vaporizers are devices which heat and vaporize a working fluid. In many cases, they are similar to industrial boilers except that they do not build up high pressures. Vaporizer units are most commonly used for low pressure heat transfer by incorporating the vaporized stream as the heat exchange fluid. They can also be used to vaporize liquid fuels or cryogenic liquids.
Types of Vaporizers
The most fundamental distinction between different types of vaporizers is function. Vaporizers are used for one of two basic purposes: to generate a vapor or to transfer heat.
Vaporizers designed solely for generating a vapor from a liquid stream are used in a broad range of applications. Propane vaporizers, for example, are designed to vaporize liquid propane (lp) in order to supply propane gas to equipment. This is essential for cold environments where natural vaporization from storage is insufficient, or in systems where vapor requirements are very high. Vaporizers can be used similarly with other fuels such as gasoline and kerosene, most notably in applications such as fuel-injection for engines. They may also be used in cryogenic applications for superheating or vaporizing low temperature fluids (between -280 and -420 °F) such as liquefied natural gas or liquid nitrogen. Or they may simply be used for generating steam or other hot gases by heating liquid feeds.
Vaporizers can also be used specifically as heat transfer devices which use heat transfer fluids and refrigerants in their vapor form. Using vapors over liquids or solid surfaces allows for lower pressure heat exchange as well as better temperature uniformity. These units typically incorporate a shell and tube heat exchanger and may incorporate the vaporized fluid either inside or outside the tubes. Heat exchange vaporizers may use either single or multi-component heat transfer fluids, including Dowtherm®, Therminol®, and other common organic fluids.
Vaporizers can be distinguished based on the heating source for the vaporized fluid.
Ambient vaporizers channel heat from the surrounding air to vaporize cryogenic and other low temperature liquids.
Electric vaporizers use electrically powered resistance heating coils or electrode-type surfaces to transfer heat for vaporization.
- Hot water vaporizers (water bath vaporizers; circulating hot-water vaporizers) use pre-heated water or another hot liquid as the heat source for vaporization. This allows for more precise temperature control.
- Radiant heat vaporizers utilize radiant energy from a combustion source or other heat source as an alternative to convection or conduction heating.
Steam vaporizers use pre-heated steam or another hot gas as the heat source for vaporization. This allows for more precise temperature control and more efficient heat transfer to the boiling liquid.
Image Credit: Alternate Energy Systems, Inc.
Vaporizer performance is defined by a few key specifications.
Capacity is the rate at which liquid can be vaporized by the device, specified in gallons per hour (gph), kilograms per hour (kg/h), or similar units of quantity (mass or volume) per time. This specification is typically used to rate vaporizers design for generating vapor, rather than those for heat transfer.
Maximum temperature is the maximum operating temperature of the vaporizer, or the highest temperature the system (or heat transfer fluid) is designed to reach.
Power requirements are specified for vaporizers which use electric heat or have other equipment requiring electric power. Power is typically specified in kilowatts (kW).
Operating pressure describes the maximum pressure conditions under pressurized operation at a specified temperature (typically the maximum temperature). Pressure is typically specified in pounds per square inch (psi).
Features and Auxiliary Equipment
In some applications, it may be important to consider whether a vaporizer incorporates certain features or auxiliary equipment.
Condensate pumps are installed to provide the option to pump excess fluid or collected condensate back into the vaporizer system.
Gravity return indicates that the vaporizer does not require a pump to move the condensed fluid back through the system loop.
Hartford loops are plumbing designs used in most vaporizer systems to prevent liquid from flowing in the wrong direction due to gravity.
Power controllers are used to control power (voltage and/or current) supplied to the vaporizer system.
Removable elements allow parts to be replaced without the need for draining the system of fluid first, making maintenance and repair less time consuming and expensive.
Industrial vaporizers should adhere to various standards set by the American Society of Mechanical Engineers (ASME). These standards are meant to ensure equipment is designed to perform safely and efficiently. Industrial vaporizers may also be registered with the National Board of Boiler and Pressure Vessel Inspectors for further proof of reliable construction.