Page 242 - Boiler_Operators_Handbook,_Second_Edition

Chapter 7

Consumables

fuel oils and coal, water and ash. An analysis of fuel oil
Few people realize the value of consumables. The will also list “BS&W” which stands for bottom sediment
typical boiler plant consumes a million dollars worth in and water (I’ll admit I normally call it brown stuff and
each year. Boiler operators can have a significant impact water except I abbreviate the second word a little).
on their consumption. The laboratory will usually include the higher
I’m not talking about the illegal activities that can heating value of the fuel as well. Results are typically
involve things as simple as rags or pallets. I will only say listed as pounds of an element per pound of fuel, a value
that operators that entered into those have, in my experi- that is readily converted to percent by multiplying by
ence, always been caught and the punishment is severe. 100. The values for the fuel are dependent on the fuel
There is significant trust placed in operating per- source and any treatment it endures before it is deliv-
sonnel to protect the income of their employer and, as ered to you to burn. When fuel gas is analyzed and you
a result, their fellow employees. The use, or abuse, of don’t ask for an ultimate analysis you will be given a list
consumables is where the true value of operation is mea- of the gases in the fuel and their respective percentages
sured. by volume. Normally methane is listed as the primary
constituent of natural gas with much smaller fractions
of other gases.
FUELS It’s a simple matter to convert a volumetric analy-
sis (one that shows the percent by volume) to a gravi-
The principle purpose of most boilers is to convert metric analysis (one that shows percent by weight)
the chemical energy in a fuel to heat absorbed in water, and to use those analysis. It’s only essential for a boiler
steam, or another medium for use in the facility served operator to know what the words mean and to be aware
by the boiler plant. (We can’t forget that there are elec- that the ratio of hydrogen to carbon in fuel will vary to
tric boilers). A wise operator should know as much as affect boiler operation. The reason is clear when you do
possible about the fuel he’s burning both to get it done an efficiency calculation, see the chapter on efficiency.
safely and to get the most out of that fuel. We’ll cover the Sulfur in fuel contributes a small amount to the
most common fuels first then touch on some of the oth- energy released in combustion. The problem with sulfur
ers you might encounter. In the process you should get is its products of combustion, sulfur dioxide (SO ) and
2
an understanding of what’s required to burn any fuel sulfur trioxide (SO ) combine with the water in the flue
3
so you’re comfortable working with something that is gas and atmosphere to produce sulfurous (H SO ) and
2 3
unusual. sulfuric (H SO ) acids. When surface temperatures in
2 4
Oil, gas and coal are called “fossil” fuels because the boiler and ductwork are so low that the acid gas can
they are found in the ground where they were trapped condense the acids attack the metal and extreme damage
as vegetable and animal matter hundreds of thousands due to corrosion is the result. The last half of the twen-
of years ago. As they decayed they became the fuels we tieth century saw a concerted effort to reduce the sulfur
know of today. Wood, bagasse, corn and similar fuels, all content of fuels to reduce the problems with acid rain
produced from living plants are called “biomass” fuels. caused by the burning of the sulfur in fuels.
The ultimate analysis of a fuel is a determination of Liquid water in fuel can create all sorts of prob-
the percentage of each element in a fuel. An element is a lems. It absorbs a lot of heat from combustion to convert
material that consists entirely of one kind of atom. The it to a vapor (the hydrogen in fuel burns to a vapor, not a
determination is made in a laboratory using standard liquid) and it creates corrosive conditions that can dam-
procedures which are included in the appendix. An ulti- age the fuel handling and storage system. Water in coal
mate analysis will normally list the amount of Hydrogen, is a major problem in the winter because it will freeze to
Carbon, Sulfur, Oxygen, and Nitrogen in the fuel along convert a pile of coal to one solid chunk that can’t be fed
with any other element of significant quantity and, for to the boilers. Similarly it can freeze in gas or oil systems
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