Vapouriser FAQS
Do vapourisers 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 vapourisations 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 vapourisers 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 vapouriser? 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.