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BOILER SYSTEMS
A boiler is often the largest consumer of fuel
in a manufacturing plant. Any improvements that maintenance
can make in its operation are immediately reflected in decreased
energy consumption and decreased energy cost. A boiler and
its system components that are optimized to run at peak efficiency
reduce operational and production costs compared to a system that
is neglected. The following module containing the recommendations
below illustrate the potential savings that can be achieved.
General Rules of Thumb:
- The average cost of electricity is $0.05/kWh
($15/MMBtu)
- The average cost of natural gas is $0.35/CCF
- The average cost of #2 fuel oil is
$4/MMBtu
- There are 2000 hours per year per shift
(based on the assumption that one shift is 8 hours per day,
5 days per week, 50 weeks per year)
- A typical boiler or furnace has
a combustion efficiency of 80%
- 90% of the heat loss from a hot,
uninsulated surface can be economically eliminated by installing
insulation.
- Cost of high pressure (125 psig)
steam leaks are on the order of $150 to $500/leak/shift/year
- Cost of low pressure (15 psig)
steam leaks are on the order of $30 to $110/leak/shift/year
- Cost of heat lost through hot,
uninsulated pipes: (associated per 100 feet of uninsulated pipe)
25 psig: $375/100ft/shift/year
50 psig: $430/100ft/shift/year
75 psig: $480/100ft/shift/year
100 psig: $515/100ft/shift/year
- Switching from electric heat to
natural gas or #2 fuel oil can reduce heating costs by 78%
Notes:
Before choosing the following targeted recommendations READ THE
FOLLOWING:
Payback estimates for the following recommendations will use the
equation below. They will vary depending on the, application,
type of installation, and purchase quantity of material and labor
associated with each recommendation. It will be up to the
person doing the analyses to use the URL references below each
equation to help estimate an implementation cost.
The data correlating to
the variables below each equation will be prompted for in order
to execute a calculation. Frequently the fuel cost (FC)
associated with the specific recommendation will be prompted for
in order to calculate the annual cost savings (ACS). Unless otherwise
specific to a particular recommendation the ACS will calculated
as follows:
- Improve boiler efficiency
with fuel change
- Minimize boiler blow
down with improved feed water treatment
1. Improve boiler efficiency with fuel change
When possible use a fuel with a higher heating value so that the
boiler's firing efficiency is optimized. Perform a tune-up
to increase efficiency, and institute a maintenance program.
A maintenance program in general should include 1) an establishment
of a tube clean out cycle, 2) inspection of the burner head and
orifice once a month with cleaning if necessary, 3) frequent soot
blow-out, 4) adjustment of excess air if necessary, and 5) implementation
of blow down procedures to insure that blow down frequency is
appropriate for the condition of the boiler feed water.
The following equation describes the potential savings that can
be achieved. The URL's below can be used to research an
appropriate implementation cost.
Power
Engineering Books
ASHRAE
ABMA
Thomas Register
GY = gallons of fuel consumed per year
HVF = heating value of fuel oil, BTU/gal (see table below)
| Fuel Grade |
Common Name |
HHV* (BTU/Gal) |
Specific Gravity |
| 1 |
Kerosene |
137,000 |
0.81 |
| 2 |
Distallate |
141,000 |
0.865 |
| 4 |
Very light residual |
146,000 |
0.90 |
| 5 |
Light residual |
148,000 |
0.94 |
| 6 |
Residual |
150,000 |
0.96 |
* Higher heating value (Ref: Industrial Boiler Management,
Kenneth G. Oliver,1989)
h1= anticipated combustion
efficiency of boiler
h2 = current combustion efficiency
of boiler
Calculator?
Data Conversions?
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2. Minimize boiler blow down with improved feed
water treatment
Establish optimum
blow down levels to maintain acceptable boiler-water quality and
to minimize hot water losses; continuously maintain blow down
at minimum acceptable level by manual adjustments or by installing
automatic blow down controls.
Power
Engineering Books
ASHRAE
ABMA
Thomas Register
HY = hours per year boiler is operated
STM = lb/hr of steam output from boiler
CAB = cost of actual blow down, $/hr per 100,000 lb/hr
of steam generated*
CMB = cost of minimum required blow down, $/hr per 100,000
lb/hr of steam generated * From
charts, given % blow down, drum pressure, unit efficiency, makeup
temperature, and fuel cost. (ref. - Energy Management Handbook,
W.C.Turner, editor, pg. 143)Calculator?
Data Conversions?
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Follow the procedure outlined below:
A. Determine actual blow
down, BD:
MU = lb/hr of makeup water to deaerator
from the water treatment plant (obtain from flow indicator)
BFW = lb/hr of boiler feed water
A = T x %MU
A = ppm of impurity in BFW
T = ppm of impurities in makeup water to deaerator from
the treatment plant (obtain average value through lab tests)
B = ppm of concentrated impurities
in boiler drum water (obtain average value through lab tests)
STM = lb/hr of steam output from each boiler (obtain
from flow indicator)
B. Determine required
blow down, BDR
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