Page 134 - Boiler_Operators_Handbook,_Second_Edition

What the Wise Operator Knows 119

can be a significantly different condition when compared can treat it as a constant value. Refer back to that earlier
to operating at varying loads in automatic. discussion on knowing your load.
Okay, so you have a steam plant but no steam flow If your boiler is serving an industrial plant you
meter. Well, you’re not unusual. There are still ways of have the potential for a variety of plant efficiency com-
determining the amount of steam generated. A simple parisons. There are pounds of product per pound of
one in many plants is achieved by installing a twenty steam, a very common measure, and complex calcula-
dollar operating hour meter on the boiler feed pump tions that vary depending on the industry, method of
motor starter. This will work in all cases where the production, and product manufactured. Usually these
pumps are operated to control the boiler water level. plants are large enough that process steam metering is
The pump has a listed capacity in gallons per minute justified so you can work with a Plant Rate, pounds of
which, when multiplied by 60 gives you gallons per steam delivered to the plant divided by the quantity of
hour then multiply by 8.33 (or the actual density) to get fuel consumed.
pounds per hour. Multiply differences in hour meter No fuel meters? If you’re firing oil then all you
readings times the pump capacity, 60 minutes per hour need do is sound the tanks regularly and after every
and density to determine how many pounds of steam delivery. If you’re firing gas the gas company always has
you made then divide that by the amount of fuel burned a meter you can use. If firing coal there has to be some
to get evaporation rate. If you have a lot of blowdown way to get an idea of the weight burned.
then calculate it’s percentage, subtract that from 100, In plants that are so small that the price of a fuel
divide the result by 100 then multiply that result by the meter isn’t justified the boilers usually fire at a fixed rate
meter reading to get steam generated. so another twenty dollar operating hour meter connect-
Oh, it’s a hot water plant; well, that’s a little more ed to the fuel safety shut-off valves will give you a read-
difficult. If the water flow through the boiler is constant ing. You can go to the trouble of determining how many
a recorder for the water temperatures will provide you gallons or therms were burned but a formula as simple
with an average temperature difference and you can as hours of operation divided by degree days will give
multiply that by the water flow to determine how many you a performance value you can monitor. Put another
Btu’s went into the water. If the boiler water flow varies operating hour meter on the feed pump and you’re com-
you’ll need a Btu meter that calculates the heat added paring fuel input to steam output. Don’t bother with all
based on flow and temperature. Any decent sized plant the other math, just divide the difference in readings of
will have a Btu meter that makes that calculation. one meter by the difference in readings of the other.
Check out your situation, since a Btu is the amount Always make sure the ratios you use are quanti-
of heat added to one pound of water to raise the water’s ties divided by quantities or flow rates divided by flow
temperature one degree you just have to get the degree rates. I sometimes think we should use a different word
rise and number of pounds figured out. Number of for some of these ratios because A “rate” implies flow
pounds times temperature rise gives you heat out and when, in fact, it has nothing to do with flow rate in this
dividing that by fuel used provides Heat Rate. Since context.
most hot water plants are heating plants you may find Keep in mind that, unlike your car, the boiler plant
you can get along with a degree day ratio. is in operation 8,760 hours a year so a little change in
Plant efficiency can also have a relative parameter fuel consumption represents a significant change in cost
that’s easy to calculate. In many cases it’s not so easy of operation. Monitoring the performance using one
but we’ll get to that later. If the plant is used solely for of the several ratios available to you will allow you to
heating then you can use a degree day ratio. Divide the make those little differences in plant performance that
quantity of fuel burned by the number of Degree Days can amount to significant reductions in operating cost.
in the same period. You will probably find that the ratio
changes with load so you should always compare gal-
lons per degree day or therms per degree day to periods MODERNIZING AND UPGRADING
with the same or a similar number of degree days. That
value is the opposite of evaporation rate, you want to There are two ways of looking at modernizing and
keep it as small as possible. upgrading. An operator either arrives for work one day
If the boilers are also used to heat hot water, the hot to find contractor’s personnel swarming around the
water use is reasonably consistent with variances that plant or the operator simply sits and dreams of what
are insignificant compared to the heating load so you would be nice to have. Occasionally there is some blend