I think there is indeed a world of difference between an industrial sized air conditioning plant which, if not maintained correctly, can become a breeding ground for legionella bacteria, particularly in the drain system, feeding a high or medium pressure ship's boiler, and my workshop dehumidifier supplying a model boiler. This is precisely why modern industrial AC plant have a number of anti-bacterial devices built into the heat exchange units and the drain systems to combat this, such as UV lights and chemical dosing systems.
I once sailed on a vessel that had solid welded grey water drain lines pass through the double bottom boiler feed tank. Unfortunately the grey water corroded through the pipe and leaked into the feed water after a few years and contaminated the feed water. By the time we saw the feed water analysis go through the roof and identified where it was coming from it was already too late to prevent the boiler requiring retubing. I joined the ship to find the boiler top plate upwards hanging from chain blocks and the furnace sat on the tank tops with nothing in between and the instruction, "Look after the other boiler"
The vessel in my case was about 2 years old at the time of my first joining as part of the 2nd crewchange after reflagging. The crew I took over from accepted the vessel at flag change, and were confronted with a horribly non-cooperative steam system fighting them at every step of the way. The burners worked, pressure controls worked, the boilers produced steam, but other than that, none of the automation worked properly. Literally NONE. Circulation pumps, level controls, level alarms, make up systems, all erratic.
That first crew was unfamiliar with the type, and made a few pretty panic-inspired modifications.
The situation was so bad, that preparing the engine and machinery for manouvering and departure required all engineroom staff, people manning pumps and filling hoses in order to keep the boilers from shutting down (heavy fuel, so no steam=>no hot fuel=> no propulsion or electrical power).
I happened to have served on a near identical sister vessel, so I was a bit more familiar with what should be expected, and what kind of chemical dosage SHOULD be normal. The other crew was unaware of that and therefore, they focused on the mechanical side of the malfunctions.
I found floatswitches but also levelglasses and such completely blocked, making it impossible to operate the system manually on the visual indications, because there were none.
I had all those floatswitches and level glasses and other stuff fixed, undid the mods, but the chemical values remained, which worried me but at the time I really was at a loss as to why.
I discovered the fairly well hidden drain rerouting hose one or two contracts later by sheer luck, stumbling over a piece of "garden hose" that should not be there when working on the AirCon. Following that hose (it was only about 25 metres long but sigzagged along several bulkhead penetrations (and had been painted over white as to not stand out?) to find it end up in a big unmarked pipe that turned out to be the ventpipe of the feedwater tank.
Removing it, the chemical test values dramatically dropped within 2 weeks.
Fortunately, at next drydock the boilers proved to be relatively undamaged (some slight pittings along the waterlevel line not requiring retubing).
In my 32 years at sea, I have never seen any treatment system for AirCon drainwater systems, or other measures to prevent bacterial growth. In drinking water systems it is pretty common nowadays, but for some reason, AirCons are overlooked when it comes to that.
But mind you, it is NOT the difference between "industrial" and "domestic" that determines water quality, but the type of air that is being handled. More specific, the number of people living in the conditioned space, and the amount of recirculation of air. An airconditioned unmanned switchboard room is different from living quarters where people live, eat, drink, prepare food, take showers, smoke, excercise etc etc. A condensing tumbledryer in an empty shed at the outskirts of town produces different water than one on the 10th floor of an appartmentbuilding in town centre.
That is why in general, unless conditions are known and the water is tested, I do not recommend such condensate because "it is condensed water form a tumbledryer/dehumidifier so it should be OK" is not automatically valid.
That is my SOLE intention with posts like this. Do not trust things to be such&so, "just because". Steam plants are expensive, and we put a LOT of effort and money in them. Skimping on feedwater is penny wise, pound foolish.
Author
Topic: Cheddar Automatic Boiler Control (Read 3023 times)