Roker:
First, I have found no difference between a vertical or horizontal LPG vaporizer - the performance is the same from both, so my comments apply to either.
There is more to an LPG vaporizer than just determining the heat transfer surface area required and the heating fluid employed. The mechanical configuration, the type of apparatus used, and the instrumentation are perhaps just as important - if not more. There may be impurities in the LPG that will sediment (or precipitate out) within the vaporizer if allowed to do so. This will foul the heating surfaces. I've always employed my vaporizers connected externally to my LPG storage tank and routed all generated vapor back to the tank, controlling the tank vapor pressure with the flow of my vaporizer heating fluid. If the LPG has impurities, I always try to keep the liquid inlet into the vaporizer slanted back towards the storage tank and let the tank accumulate the heavies in its lower section.
Hot water is ideal for this application. If you use a U-tube exchanger (i.e., TEMA type BEU), this pretty well dictates that you must have a horizontal vaporizer orientation. The U-tube removal is awkward and difficult in the vertical orientation and air traps itself in the top of the "U" when the bundle is pointing upwards. The trapped air is impossible to remove and ultimately affects heat transfer.
For smooth operation and constant, steady LPG vapor pressure availability for draw-off, the instruments selection is important as far as quality and application are concerned. In the instrumentation, I also stress concentrating on the safety relief protection. All these issues are normally handled by a vaporizer supplier. If you do the job yourself, then you inherit these responsibilities also. If you haven't done this before or if you lack the experience, then an outside, experienced supplier who can guarantee the performance is the way I would recommend the project be implemented.
