Page 293 - Boiler_Operators_Handbook,_Second_Edition

278 Boiler Operator’s Handbook

loose when exposed to the rapid movement of water ment of the designs and why they’re made that way.
and steam can block flow resulting in loss of circulation Not only is a teapot a simple boiler, it’s representa-
and boiler failure so don’t let those broken bolts and tive of many of the earliest designs of boilers. They were
supports go, get them fixed. nothing more than an enclosed pressure vessel full of
One of the ships I sailed had a special baffle in water suspended above a fire with some piping leading
the top of the side waterwall header. The tubes sloped off to the user of the steam. Some, like the early Roman
up from the front of the boiler to the back between two baths, were even simpler, separating the fire from the wa-
headers. The purpose of the baffle was to scoop some of ter by a simple row of mud bricks, the earliest refractory.
the descending water into the top rows of tubes. It was Any fired boiler has some refractory in it so it’s
discovered that the velocity of the water coming down appropriate to explain what it is. It’s material that can
the downcomer to the header was so great the water withstand the heat right next to a fire. Looking like
shot past the inlet of the top rows and they were starved cement or regular brick it contains chemicals to bind
for water. it that will not melt under normal furnace conditions.
I doubt if you’ll encounter a boiler with water There are very few that can stand to be right next to a
circulation baffles but if you do find some strange look- fire and none can tolerate the highest possible flame
ing piece of metal bolted in a boiler don’t remove it. If temperatures. Refractory materials come in different
you’re like the engineers on that ship some time before grades based principally on the temperature they can
I sailed her and find the piece loose in the bottom of the reach without melting or failing. They range from
boiler, go looking for where it should be and put it back. 1200°F stuff on the low end to 3200°F material. Nor-
They didn’t and the top waterwall tube failed on the mally the higher grade materials are used closest to the
next ocean crossing after they found the baffle and left it fire and lower grades are used where the temperature
laying on a workbench. will be lower. Upsets in flame shape, openings in baffle
There are watertube boilers that are designed in a walls and other problems in a furnace can direct hot
manner that doesn’t permit natural circulation. They’re burning gases against refractory that can’t tolerate the
equipped with boiler water circulation pumps that are higher temperature resulting in early, and sometimes
designed to operate at the high pressure and tempera- quick, failure of the boiler.
ture of a steam boiler and produce the differential that’s There are basically three types of refractory, brick
required for the boiler to operate properly. You’ll also or tile, plastic, and castable. Brick or tile are preformed
find small boiler water circulating pumps on hot water and fired at the factory. A burner throat is normally
boilers that serve a different purpose. That’s explained made up of tile. Plastic is moldable, usually applied
in the chapter on operation. by positioning chunks of it then beating it into posi-
tion with a hammer. Castable is mixed and poured into
forms like cement.
BOILER CONSTRUCTION In any large wall of refractory special “anchors”
are furnished with steel or alloy material that penetrates
The construction of a boiler can be attributed to any back-up insulation and attaches to the setting, cas-
many things but the principle ones are code compliance ing or buckstays for support. Some anchors are made
and cost. The manufacturer has to build a boiler that up of a combination of metal and a piece of tile (Figure
complies with the applicable section of the ASME BPCV 5-6) to provide better attachment to the refractory. Set-
but the key to building a boiler is to make the cheapest ting is the name used for a boiler and furnace enclosure
one that will do the job. Low price can be as simple as that consists of brick stacked up like walls to enclose the
first cost but should be based on life cycle cost where the boiler and furnace.
selected boiler should provide the required steam or hot Casing is the name we use to describe the outside of
water with the lowest combined price, installation, fuel the boiler enclosure when it’s typically made up of steel
and maintenance cost over its expected life. plate. It’s not the same as Lagging. Lagging can range
There is always an ongoing effort to design a better from steel plate to painted canvas but is normally thin
boiler and it has resulted in many changes during my sheet metal covers used to protect insulation applied to
lifetime so you can expect to see more changes in boiler a boiler. Buckstays are structural steel components that
construction in the future. There are many books that stiffen the casing of a boiler or provide attachments for
show the extent of construction variations so I’ll only panels of water tubes.
touch on this subject to give you an idea of the develop- There was a time when all boilers were enclosed in