A. Boiler Formulas
Boiler Horse Power (HP):
BHP = (Lb/hr) * FE / 34.5
where Lb/hr is pounds of steam per hour and FE is the factor
of evaporation.
Steam:
S=HP * 34.5 * t
where HP is boiler horsepower and t is time (h).
Cycle of
Concentration of Boiler Water:
CYC=Bch / FCh
where Bch is
ppm water chlorides
and FCh is ppm feedwater chlorides.
Differential Setting
(lb):
Delta S = P1 - P2
where P1 is the cutout pressure and P2 is the cut in
pressure
Factor of
Evaporation:
FE = SH + LH / 970.3
where SH is the sensible heat and LH is the latent heat.
Force (lb):
F=P / A
where P is pressure (psi) and A is area (in^2).
Horsepower (HP):
HP=(d * t) / (t * 33000)
where d is distance, F is force, and t is time.
Inches of Mercury
(in):
InHG=P / 0.491
where P is pressure
Percent of Blowdown:
%BD=(PP - RP) / PP
where PR is popping pressure and RP is reseat pressure
Rate of Combustion
(Btu/hr) RC=H / (Vf * t)
where H is heat released (BTU), Vf is volume of furnace
(ft^3), and t is time (hr).
Return Condensate
Percentage in Feedwater RC%=(MC – FC) / (MC – CC)
where MC is the makeup conductivity (μohms), FC is the
feedwater conductivity (μohms), and CC is the condensate conductivity (μohms).
Static Head Pressure
(lb)
SHP= Bpr * 2.31
where Bpr = boiler pressure (psi)
Temperature
Conversions:
F to C
C = (F – 32) / 1.8
C to F
F = (1.8 * C) + 32
Total Force (lb)
TF = P*A
where P is pressure (psi) and A is the area of valve disc
exposed to steam (sq. in.)
Water Column (in)
WC = P / 0.03061
where P is pressure (psi).
Flue gas analysis:
|
Boiler flue
gas analysis is used to determine
combustion efficiency.
|
|
|
Carbon Dioxide
(CO2)
|
Indicates
complete combustion
|
|
Carbon Monoxide (CO)
|
Indicates incomplete combustion
|
|
Oxygen (O2)
|
Indicates the presence of excess
air
|
|
Oxides of
Nitrogen (NOx)
|
A product of high temperature combustion
|
|
Combustibles
|
Material that burns
when exposed to oxygen and heat
|
It is
typical to target oxygen levels of 8% in low fire and 3% in high fire for gas
fired burners.
It is typical
to target oxygen levels of 6% in low fire and 4% in high fire for oil fired
burners.
Johnston
Boiler Company recommends no greater level than 200 ppm of Carbon
Monoxide in its burner operation. The acceptable “Industry Standard” level is
400 ppm or less.
Johnston
Boiler Company recommends zero combustibles for a gas fired burner.
Johnston
Boiler Company recommends a maximum #2 Smokespot (Ringelmann Chart) in its oil
fired burner.
For a burner
originally adjusted to 15% air, changes in combustion air temperature and barometric pressure cause the following in
excess air:
|
Air Temperature
|
Barometric Pressure (In. HG)
|
Resulting
Excess Air %*
|
|
40
|
29
|
25.5
|
|
60
|
29
|
20.2
|
|
80
|
29
|
15.0
|
|
100
|
29
|
9.6
|
|
120
|
29
|
1.1
|
|
80
|
27
|
7.0
|
|
80
|
28
|
11.0
|
|
80
|
29
|
15.0
|
|
80
|
30
|
19.0
|
|
40
|
31
|
34.5
|
|
60
|
30
|
25.0
|
|
80
|
29
|
15.0
|
|
100
|
28
|
5.0
|
|
120
|
27
|
-5.5
|
* Expressed as a
percent of the Stoichiometric air required.
|
ENERGY
LOSS
FROM
SCALE DEPOSITS IN BOILERS
|
|
|
SCALE THICKNESS (INCHES)
|
EXTRA FUEL COST (PERCENT)
|
|
1/32
|
8.50
|
|
1/25
|
9.30
|
|
1/20
|
11.10
|
|
1/16
|
12.40
|
|
1/8
|
25.00
|
|
1/4
|
40.00
|
|
3/8
|
55.00
|
|
1/2
|
70.00
|
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