Page 235 - Boiler plant and distribution system optimization manual

220 Boiler Plant and Distribution System Optimization Manual

B. How much does it cost to operate the 5 hp ENERGY SAVINGS WITH
blower per hour? ADJUSTABLE SPEED DRIVE [ASD]
(Ans.: $0.45/hr)
RPM 100% 90% 85% 80% 75%
C. Assuming 8,000 hours of operation a year, Energy
how much more will it cost to operate the 40 Required 100% 81% 72% 64% 56%
hp blower than the 5 hp blower? Savings 100% 19% 28% 36% 44%
(Ans.: $3.05 x 8,000 HR = $24,400/YR)

Example 2. A plant keeps a 100 hp feed pump on SETTING THE FUEL OIL HEATER
the line continuously where a 30 hp pump could FOR PROPER FUEL OIL VISCOSITY
be used, how much can be saved in a 8,000 hr year AT THE BURNER
by installing a 30 hp pump?
A. How much does it cost to run the 100 hp When the fuel oil temperature is not set to
pump per year? deliver oil at the proper viscosity, the burner can
(Ans.: $10.00/hr x 8,000 hr = $80,000/yr) smoke and foul heat exchange surfaces. Also,
B. How much does it cost to run the 30 hp pump higher levels of excess air will be needed to com-
per Year? pensate for this problem. If the fuel oil heater
(Ans.: $2.75 x 8,000 hr = $22,000/yr) temperature is too high the flame is affected also,
C. What will the annual savings be if the 100 hp becoming ragged with sparklers.
pump is replaced by a 30 hp pump?
(Ans.: $58,000/Yr (approx.)) Situation:
As an economy measure, you have been giv-
As a practical matter you will never get any- en some heavy oil to burn which has a viscosity
one in a boiler plant to downsize equipment. The rating of 4,000 Sabolt Universal Seconds (SUS) at
boiler feed pumps must be able to maintain prop- 100 degrees F. You notice that you have to use a
er water levels and even increase boiler water lot more excess air with this fuel and you have to
level at maximum firing rates and during emer- use your soot blowers more often.
gency conditions. Blowers must be able to pro- Your burner technical manual indicates that
vide enough backup capacity to prevent fuel-rich your burner requires a viscosity of about 150 SUS
firing under all conditions. An adjustable speed for proper atomization.
drive (ASD) controllers will probably be the most What new temperature is required for the
practical and safest approach. fuel oil heater?

Example 3. Pumps and fans follow certain laws Solution:
known as the “Affinity Laws”: Use the viscosity-Temperature Chart.
1. Flow varies with RPM
2. Head Varies with RPM- [Squared] 1. Find 4,000 SUS at 100 degrees F.
3. Horsepower varies with RPM- [Cubed*] 2. Move down a line parallel to the No. 6 fuel
oil line to 150 SUS and read the correspond-
*Experience has shown that actual horsepower requirements may ing temperature for the fuel oil.
with the square function rather than the cube junction when static
back pressure is present. Answer: 220°F

What savings are possible by controlling a Note: If there is a significant piping run between
boiler feed pump with ASD rather than modu- the heater and the burner the actual temperature
lating the Feed Control Valve using the “square” at the burner may be lower and the heater may
relationship? have to be set for a higher temperature.