Posted by Tony Conner on January 05, 2002 at 13:58:16:
In Reply to: Re: Miura Boilers: Pros and Cons posted by Vern on January 05, 2002 at 08:55:56:
I don't think that Miura boilers are particularly any better or worse than any low water content boiler. Low water content boilers will work. However, a lot of plants have ongoing problems due to factors that are NOT the fault of the boiler itself.
A huge chunk of the problems people have with low water content boilers, is that they select units that are way too big for the load, then, to compound the situation, fail to mechanically install them correctly.
Steam quality is an issue with most low water content boilers. In conventional boilers, there's a steam space above the water line, that often contains screens & separators to knock water droplets out of the steam flow. Low water content boilers do not have this big space above the water line, and there's no room for anything internal to dry the steam out before it hits the header. This is where proper piping comes in. They typically need oversized steam leads, with a specified minimum length of vertical piping. Failure to pipe these units EXACTLY as specified leads to no end of problems.
Another prime source of problems is that boilers of this design are (like most other steam equipment) GROSSLY OVERSIZED. This causes the units to cycle on & off constantly. Compounding this, is the fact that many of these boilers do not have modulating burners. They are low fire/ high fire/off. I think the constant purging of the furnace, and draft loss up the stack while off really eats into the effeciency of this type of boiler. Nobody who buys & installs low water content boilers ever puts accurate (or any) steam flow meters in. I think if they did, the actual effeciency would be far less than the advertised figure. (I don't doubt the advertised effeciency figures are correct - under controlled lab conditions.)
The water treatment aspect is a measure of the overall sensitivity that this type of boiler has in pretty much every aspect - there is very little margin of tolerance for any kind of chemical or mechanical miscalculation, or upset.