Page 234 - Boiler_Operators_Handbook,_Second_Edition

Maintenance 219

We did it occasionally on ships using boiler wa- picture should be the only time you see a tube turbine.
ter. A heavy steel reinforced hose was connected to High pressure washers are used to remove scale
the blowdown of an operating boiler. A valve and from the water side of fire tube boilers. Operating with
homemade lance was attached to the other end and we nozzle pressures as high as 40,000 psig they blow the
proceeded to try to wash the soot accumulations from scale away and sometimes take some metal as well.
the boiler. The hot boiler water would help dissolve the These are best handled by contractors experienced with
deposits and the caustic solution would help neutralize their operation. The application usually requires a vacu-
the acidic soot. That’s also a very dirty, and hot, job that um system and truck to remove the scale from the boiler
shouldn’t be necessary with proper firing, properly ad- as it’s washed off and separate it from the wash water to
justed soot blowers, and fuel treatment. allow recycling of the wash water.
Another boiler expert I know insists soot blowers The third method for scale removal is acid wash-
are installed on boilers only to give operators time to ing. An inhibited hydrochloric acid is used to eat the
learn how to operate the boiler. That’s not true, but he scale off the tubes. The application requires care and reg-
usually gets a snicker when he says it. ular testing to ensure the acid is removing scale and not
There are three methods for cleaning water side boiler metal. The acid solution is heated and circulated
scale from boiler tubes but none should be required and the entire boiler has to be flooded so all the boiler
under normal circumstances. If you have adequate pre- metal is exposed to the acid. Any mistakes don’t result
treatment facilities and adequate boiler water chemical in just tube replacement. This method is also best left to
treatment you should never need tube cleaning. Turbin- contractors with the equipment and skill necessary to do
ing is the method I was introduced to when I started and the task. They also haul off the spent acid and dissolved
is occasionally used as a general maintenance method in scale when they’re done.
plants with very poor water pretreatment. When cleaning fails, and so much energy is wasted
Turbining tubes is accomplished with a special by scale that something has to be done, plugging or re-
water powered tool that rotates a set of small sharp placement of the tubes is required. If you have a modern
gears around inside the tube (Figure 6-10). The water flexitube boiler then all you need is a wrench, special
not only powers the tool but flushes the debris away. A tool, and big hammer. They’re designed to be replaced
tube cleaning turbine will remove most of the scale but by individuals with a reasonable mechanical sense.
leave small pieces unless you repeatedly run it up and Otherwise your boiler tubes are installed by rolling or
down the tube until you’ve removed a lot of metal as a combination of rolling and welding, processes that
well. They’re not difficult to operate. It’s just difficult require more skill.
to control the enthusiasm of young people that might When you have only one or two defective tubes
remove half the tube metal. Of course they only work it’s usually easier and more frugal to plug them than to
for removing waterside scale from inside water tubes. I replace them. Some tubes can’t be plugged because they
should say from inside round water tubes. If you have serve purposes other than heat transfer. Tubes that form
a very old boiler you may find the tubes are closer to boiler walls or flue gas baffles can’t be plugged because
square where they’re bent. Turbines will jam in them they will melt down or burn off without water cooling
and you tend to poke holes in the flats of those squar- and allow heat and flue gases through.
ish tubes. With modern water treatment methods, this For watertube boilers it’s a little more than simply a
matter of obtaining some machined
steel plugs that fit into the ends of
the tubes and inserting them. The
first, and a very important, thing to
do is to make sure you have located
the leaking tube at both ends. Test-
ing using rubber plugs and a water
hose is recommended. To be certain
the plugs don’t blow out because
steam is generated in the tube from
water leakage you should drill or
chisel a hole in the tube so any leak-
Figure 6-10. Tube turbine age is bled into the flue gas. You