Suitability of part block switching of ambient air vaporizer for propane vaporization in contrast to cryogenic vaporization

Abstract

Ambient air vaporizer (AAV) is preferred for cryogenic vaporization due to its low operating cost and nonpolluting operation. Continuous deposition of frost during the operation of an AAV requires periodic melting. Conventional cryogenic vaporizers use two identical blocks of vaporizers and the defrosting is achieved by switching off the flow through one vaporizer block while the other operates. The temperature difference between the ambient and the vaporizing fluid is large for cryogenic fluids, while it is very small in the case of propane vaporization. As a result, the conventional AAV becomes very large and heating by fossil fuel or electricity is often employed for propane vaporization. To overcome this unsustainable process, this paper proposes a novel configuration of AAV called “Part block switching (PBS)” that takes advantage of the lower frost deposition in case of propane AAVs compared to the cryogenic ones. A dynamic heat and mass transfer model is developed and solved implicitly. PBS system for propane vaporization is found to have a size reduction of 21% or more compared to the conventional design of full block switching regardless of the switching time. A short switching time of 4 h or less, however, works well for liquid nitrogen vaporization.