Page 331 - Boiler_Operators_Handbook,_Second_Edition

316 Boiler Operator’s Handbook

air blowers. I don’t like them because it’s very difficult matching drill bits. That’s very important to do before
to balance the fuel distribution to get them to burn closing a burner when refractory work is done because
cleanly and efficiently. The few I’ve encountered can’t there’s a tendency of masons to leave smears of refrac-
seem to fire without a considerable amount of CO. tory on and in the openings of gas rings.
Atmospheric burners are only used on small boil- The gas ring is usually bolted to the boiler front
ers, hot air furnaces, and service water heaters for the plate, that thick piece of steel that seals the front of the
most part because they are normally fixed fired and boiler, provides support or is integrated with support
have very little control of overall excess air. I’ve seen of the refractory front wall. The front plate supports the
large boilers, as big as 150 horsepower, with atmospher- burner throat to keep it centered, and provides means of
ic burners and have shuddered at the thought of what it attaching the burner or windbox. If the gas ring or the
costs to operate them. If they serve a constant load for boiler front plate is distorted then air leakage around the
which they’re well matched then there’s some sense in gas ring at different points can produce very unstable
their application but in any service with a varying load firing conditions. The condition of the gas ring and
the off cycle losses are very large. clearances (if any) between the gas ring and boiler front
Controlling those losses with dampers that shut off plate should also be checked annually.
air flow through the boiler when it’s not firing can pro- If you find a warped front plate or other problems
vide significant reductions in those losses. The dampers with irregular air spaces around a gas ring you can
have to be proved open before the boiler fires. Modern plug them with ceramic fiber rope. Always put the rope
high efficiency heating equipment with pulse combustion on the windbox side and be certain it’s large enough
or power burners should replace most of that equipment it won’t blow through. It’s very embarrassing to have
in the next few years once gas prices rise again. I’ve been someone ask you what that thing is fluttering in the fire.
able to show a boiler with a power burner can pay for it- Gas rings can fail. Failure of adjustments of firing
self over an atmospheric fired unit in less than a year. Any rate, like linkage slipping, and other contributions can
medium to large boiler should have a power burner and produce situations where the heat of the fire is shifted
unless one isn’t available, it should be modulating. into the throat where it can overheat the gas ring to cre-
Fuel gas can be introduced into a power burner via ate cracks in it. Any cracked gas ring should be replaced
a gas ring, spuds or a gas gun. A gas ring is a piece of before the boiler fires gas.
pipe, fabricated steel or a casting surrounding the burn- There was a time when we attempted to deliver
er right at the boiler front plate with holes drilled in it the fuel gas into the flame in the furnace as uniformly
to distribute the gas evenly around the outside diameter as possible to ensure complete mixing and permit low
of the throat. Some gas rings are fitted with spuds while excess air firing. The discovery of NO as a problem has
x
other burners have spuds at the end of pipes which de- resulted in irregular gas delivery schemes, usually us-
liver the gas from the front of the burner or a gas ring ing spuds (Figure 10-50) installed with pairs facing each
located outside the front of the burner. other to produce alternating fuel rich and lean zones in
Spuds are high temperature metal nozzles drilled the burner. See the section on emissions for an explana-
with holes to admit the gas into the passing air stream. tion of why.
A gas gun consists of a pipe central to the burner with a The fuel gas piping has to penetrate the windbox
closed end drilled to admit the gas very similar to an oil or burner to deliver the gas to the gas ring. There was
burner. Some gas guns consist of two concentric pipes a time when we used a flanged connection on the gas
that permit insertion of an oil gun down the center of ring to permit disassembly but it also placed a poten-
them. The arrangement, distribution and mix of holes tial point for leakage of gas inside the burner windbox.
drilled in gas rings, spuds and guns varies with manu- There it could light off producing heat in a windbox
facturer and in many instances is customized during that wasn’t designed to absorb that heat. There are also
startup to achieve smooth stable combustion. many variations in design of packing glands and other
Retaining data on the drilling of your gas burner is means of sealing the gas piping where it penetrates the
essential because your information may be the only ac- windbox. If you ever have problems with air leakage at
curate copy around; it’s not unusual for a manufacturer the gas line entrance the best solution is welding it to
to fail to update the records for changes made by the the windbox. Normally the windbox is flat and flexible
service technician. One element of your annual boiler in- enough at the gas line entrance that thermal expansion
spection should be checking the diameter of the holes in is accommodated by the windbox flexing. If you have
the gas ring, nozzle, spuds or combination thereof with problems with leaking piping joints inside the windbox