EDTA, Chemical Formulas, and Boiler Cleaning Calculations
Conversions and Miscellaneous Formulas
- 1 Cubic foot = 7.48 gallons
- Cubic feet = Length x Width x Height
- PSI = Elevation x 0.433
- 1 PSI = 2.31 Feet
- 454 grams per pound
- Grams to Pounds: grams x 0.0022046
- Liters to Gallons: Liters x 0.26417
Nitrogen Displacement
Volume in gallons x 0.134 = SCF N2 needed to displace a vessel
EDTA
Molecular weight = 292
Dividing the molecular weight of EDTA acid by the atomic weight of the metal being complexed will result in obtaining the required amount of EDTA necessary to complex one (1) pound of a given metal.
-
Iron (Fe): 55.85
- 292 / 55.85 = 5.23
- 5.23 / 0.40 = 13.07 gallons of ICOR 500 to dissolve 1# Fe
-
Copper (Cu): 63.54
- 292 / 63.54 = 4.60
- 4.60 / 0.40 = 11.5 gallons of ICOR 500 to dissolve 1# Cu
ICOR 500 / 510
- 10 lbs/gallon
- 4 pure lbs/gallon
ICOR 500
- Cleaning temperature: 180-200°F
- Passivation temperature: 140-160°F
ICOR 510
- Cleaning temperature: 250-300°F
- Passivation temperature: 140-160°F
Inhibitor Calculation
Boiler volume x 0.1% = X gallons inhibitor
or
Boiler volume x 0.001 = X gallons inhibitor
Saturation point: 10%
EDTA Calculation
System volume x 8.34 = Boiler Weight of Water (BWOW)
BWOW x 1% = 1% pure EDTA
1% pure EDTA / 0.40 = 40% of pure EDTA
40% pure EDTA / 10 = Gallons of ICOR 500
Take 1% and multiply to get initial EDTA injection
or
8.34 x system volume x desired % / 0.4 / 10 = gallons ICOR
Back Calculation of Spent EDTA
4,170# Fe
4170 x 5.23 = 21,809 lbs pure EDTA spent
% pure EDTA in boiler
21,809 x BWOW = x (multiply by 100 to get %)
Passivation
SWAG: 15-20 gallons aqua ammonia per 1,000 gallons volume to raise pH for passivation
Oxygen required for passivation: 2.0 – 2.5 SCF per # Fe to passivate in 1 hour
Required SCF / 60 minutes = SCFM
Example with 1036# FE
1036 x 2.5 / 60 = 43 SCFM
1036 x 2.5 / 90 = 29 SCFM to passivate in 90 minutes
If flow rate exceeds 250 SCFM, dilution of Fe may be required. Please consult.
Always start O² blow on opposite side of steam drum sample point
Corrosive range: -500mV / -350mV
Minimum Fe to passivate: 0.02%
Maximum Fe to passivate: 1.6%
Minimum EDTA to passivate: 1.5%
Maximum EDTA to passivate: 2.0% (if above, EDTA becomes corrosive)
Material Balance
EDTA% / 100 * BWOW = X
lbs Fe x 5.23 = Y or lbs Cu x 4.60
X + Y = Z
Divide Z by total EDTA injected = % Material Balance
Example: 1.9% EDTA, 961# Fe, 13440# EDTA
1.9% / 100 * 300,240 = 5704.56
961 lbs Fe x 5.23 = 5026.03
5704.56 + 5026.03 = 10730.59
10730.59 / 13440 = 0.798 * 100 to get % (79.8%)
Corrosion Rate
- O²: 0.018 lbs / FT² / Day
- Air & Sodium Nitrite: 0.022 lbs / FT² / Day
Wetted Surface Area
- Natural Circulation (N/C): Volume x 2.44 FT²
- Controlled Circulation (C/C): Volume x 3.26 FT²
- Super Critical (S/C): Volume x 6.11 FT²
Wetted Surface area x volume = “Factor”
“Factor” x 0.018 (O²) = lbs/hr Base Metal Corrosion
# Fe x 5.23 = pure lbs EDTA
Pure lbs EDTA / BWOW = % EDTA to be consumed during passivation (move decimal point 2 places)
Example: 130,000 gallon N/C, BWOW 1,084,200
130,000 x 2.44 = 317,200 FT²
317,200 x 0.018 = 5,709 #Fe
5,709 / 24hrs = 237 #Fe per hour (Until EMF goes to -300 or more +)
237 x 5.23 = 1,244 pure lbs EDTA
1,244 / 1,084,200 = 0.0011 * 100 or 0.11% EDTA
Make adjustment lbs/hr for longer passivation (Max 2 hours)
Make sure to account for Cu you are going to pick up during passivation and EDTA you will consume.
Example
500lbs Cu will consume 2,300lbs EDTA
Convert pure EDTA in to %
Pure lbs EDTA ÷ BWOW = X * 100 = % EDTA to be consumed for Cu
Cuprox
29% Aqua Ammonia
- 1 gallon = 7.4 lbs/gallon
- Pure lbs ammonia in 1 gallon = 2.2 lbs/gallon
- Specific Gravity: 0.90
1% aqua ammonia in 50,000 gallon boiler by weight
BWOW * 1% / 2.2 = X gallons
50,000 * 8.34 = 417,000
417,000 * 1% = 4170 lbs pure ammonia needed
4,170 / 2.2 lbs/gallon = 1.895 gal aqua ammonia
O² agitation 10-20 SCFM / 10,000 gallon boiler volume