Frequently Asked Questions (FAQs)
Do vaporizers build pressure?
Yes and no. There are two types of vaporization systems – Feed-out and Feed-back.
Feed-back systems add heat to the liquid LPG and allow it to return to the storage vessel as vapor and/or liquid. The process of adding heat to the fluid results in a pressure rise in the storage vessel. Feed-back systems require specially configured vaporizers sometimes referred to as tank heaters or feed-back vaporizers.
Feed-out vaporizers do not build pressure – they simply add heat to convert the liquid to vapor as it passes through, but they do allow the storage vessel to maintain a higher pressure that corresponds to the ambient temperature. Without a vaporizer all storage vessels will naturally refrigerate resulting in lower pressures.
What type of vaporizations system is best - Feed-out or Feed-back?
There are benefits to both types of systems, but the deciding factor is usually energy waste.
With Feed-back systems the energy added to the LPG returns to the tank resulting in a higher storage tank pressure and temperature. The higher storage temperature results in heat loss to the atmosphere.
With Feed-out systems the amount of energy used is a direct factor of the amount of LPG consumed by the downstream process. Heat is added at the rate necessary to convert the liquid LPG to vapor only as it is consumed.
The other factor is product consistency. If LPG is used, it is comprised of butanes and propane each having distinctly different partial pressures. Because of the different partial pressures, the butanes and propane will vaporize at different rates inside the storage vessel. In a Feed-back system vapor for the downstream process is taken from the vapor space in the storage vessel which initially results in higher propane concentrations and gradually shifts toward greater butane concentration as the tank is emptied. The end result is inconsistent combustion properties. Feed-out systems send out only vaporized liquid which maintains a homogeneous form in the storage vessel.
Do vaporizers increase combustion efficiency?
In some cases. When LPG comprised of butanes and propane is used, vaporization without a Feed-out vaporizer will result in early vaporization of the propane followed later by more concentrated butane-rich LPG vapor. Combustion resulting from the varying product composition will yield changing efficiency and combustion properties. A feed-out type vaporizer will provide consistent LPG vapor quality that will allow the combustion equipment to be optimized.
If the LPG being used is strictly propane then a vaporizer will not yield improved combustion efficiency. It is important to note, however, that a reduction in combustion output can occur without a vaporizer if the system pressure drops because of a lack of natural vaporization. This often happens with changes in climate such as when the temperature drops at night or as winter approaches. A vaporizer will allow the combustion equipment to continue at full output.
Can I put a check valve between the storage vessel and the vaporizer?
NO! Liquid and vapor must be allowed to return to the storage vessel. All vaporizers operate with a flywheel effect which means they have heat (energy) available after a downturn in the use of gas. The remaining heat is transferred into the liquid LPG left in the vaporizer. The heat converts the liquid into vapor causing rapid expansion. This expansion results in a pressure rise that if unable to return to the tank will force the over-pressure relief valve to vent.
If air is mixed with propane to form a mixture suitable for replacing natural gas, is it flammable?
No. The appropriate mixing ratio for using propane to replace natural gas is 46-48% propane and 54-52% air. The limits of flammability for propane are roughly 2.5 – 9.5% propane in air. Propane above 9.5% concentration in air will not ignite.
What is the useable life of a vaporizer?
The question of vaporizer design life is a very popular and appropriate question which has been asked many times in the past by our customers. LP-Gas suppliers and end users alike need to know what they can expect as the typical life expectancy for a particular type of vaporizer placed on site under given conditions. This information is needed to both establish the front-end economics and to establish a safe and responsible maintenance and replacement program.
As the manufacturer, we can anticipate a variety of site and operating conditions and incorporate that information into our design basis. However, as the manufacturer it is not practical to calculate the life of the vaporizer under every possible set of field and site conditions. The most appropriate approach for permanent installations is to use the formula below to establish the expected physical lifespan:
Expected Physical Lifespan = Vaporizer Design Life x (1- (Environmental Factor + Maintenance Factor))
Vaporizer Design Life:
ZIMMER – 8 years
TORREXX – 8 years
TORREXX w/hermetic relay – 10 years
POWER P-Series – 10 years
Direct Fired – 8 years
Environmental Factor (0 = best to 0.3 = worst): Evaluated based on the severity of the physical atmosphere where the vaporizer is placed. Considerations – salt air, acid atmosphere, flooding, etc.
Maintenance Factor (-0.5 = best to 0.5 = worst): No maintenance over the life of the vaporizer results in the worst case and a regular maintenance program, appropriate for the type of vaporizer and one that effectively addresses and prevents problems including those related to LPG quality, results in the best case. For example, a vaporizer processing HD-5 propane beginning with a new (un-used) tank and a regular periodic preventive maintenance program would use a factor of -0.5.
A TORREXX vaporizer w/ hermetic relay is placed at an inland factory using propane. The installation is new beginning with a new (un-used) tank and a regular periodic preventive maintenance program is implemented. What is the expected lifespan?
Vaporizer Design Life = 10 years
Environmental Factor = 0
Maintenance Factor = -0.5
Expected Physical Lifespan = 10 years x (1 – (0 + (-0.5))) = 15 years
Naturally the environmental and maintenance factors are subjective and require some experience to effectively predict. All of our factory authorized representatives are experts in the field of vaporizers and are capable of helping you assess these values.
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