Basic Deaerator Science Revealed - Cleaver

Basic Deaerator Science Revealed
Presented by Steve Connor
January, 2015
What We Are Covering Today
Hydrological
Cycle
Benefits
Basic
Deaerator
Science
Revealed
Component
Selection &
Sizing
Types &
Operation
What is
Deaeration?
When to Apply
2
The Hydrologic Cycle
3
Water the Universal Solvent
Dissolved
Solids
Dissolved
Gasses
4
Suspended
Solids
CO2
O2
O2
O2
CO2
O2
Carbonates
Iron
Sulphates
Calcium
Magnesium
Sodium
Manganese
Na2SO4
CO2
Aluminum
Silica
Chlorides
Mg(HCO3)2
CaSO
4
5
MgSOFluorides
4
MgCl2
Tolerances are
Based on Pressure & Temperature
Water Constituent Tolerance: 0-300 operating psig
Feed Water
Boiler Water
Oxygen & CO2
Silica
Iron & copper
Total Alkalinity
Total Hardness
Free OH Alkalinity
pH
Specific Conductance
Non-Volatile TOC
(Total Organic Carbon)
Oily Matter
ASME Guidelines:
Broken down by feed water and boiler water, and then by firetube and watertube boilers.
6
Most Economical Long-Term Approach
Mechanical
Chemical
7
Water Quality: Dissolved Gases
Today we’re concentrating on…
2
2
8
Water Quality: Dissolved Gases
Oxygen Corrosion
Iron begins to dissolve when in contact with water.
Fe + 2H2O = Fe(OH)2 +
Iron +
Water
+
2H
= Ferrous Hydroxide + Hydrogen
9
Water Quality: Dissolved Gases
Now add in dissolved O2
Process continues until 1 of 2
things occurs
1. No more dissolved O2
2. No more iron Fe
4Fe(OH)2 +O2 +H2O= 4Fe(OH)3
Ferrous Hydroxide + Oxygen
+ Water
10
=
Ferric Hydroxide (RUST)
Corroded Boiler Tubes
Watertube
Firetube
Holes
Blisters
11
Water Quality: Dissolved Gases
2 times more
corrosive at
122oF than at
86oF
50 F
86 F
122 F
X
X
Courtesy:http://www.engineeringtoolbox.com/oxygen-steel-pipe-...
Water Quality: Dissolved Gases
Carbon Dioxide – Friend or Foe?
2
13
Water Quality: Dissolved Gases
Creation of
CO2 from
Carbonates
Courtesy:http://www.spiraxsarco.com/resources/steam-engineering-tutorials/the-boiler-house/water-treatment-storageand-blowdown-for-steam-boilers.asp
CO2 + H2O = H2CO3
Combines with Water to Create Carbonic Acid
14
Water Quality: Dissolved Gases
CO2 gas combines with condensate
forming carbonic acid; corroding pipes
and heat transfer units.
Carbonic Acid attack
15
Water Quality: Dissolved Gases
Carbon Dioxide AND Oxygen:
Carbon Dioxide together with Dissolved
Oxygen is 40 percent more corrosive than if
the two were acting alone.
O2
CO2
16
Dissolved
Oxygen is
10 times
more
corrosive
than CO2
OK….what do we do?
17
Water Quality: Dissolved Gasses
Solution to Manage These Gasses
2
CO2
Raise the Temperature!
18
Water Quality: Dissolved Gases
Free Gases Are Insoluble At Saturation Temperature
Oxygen Content, ppm
10
8
6
4
2
0
30 50 70
90 110 130 150 170 190 210
19
Temperature,
Degree F.
Water Quality: Dissolved Gases
Manage pH @ approx. 11
CO2
20
Reducing Surface Tension
21
Mechanical Removal
Deaeration Removes
• Oxygen
• Free Carbon Dioxide
Heat
Agitate
22
Liberate
DA Methods: Operation
•
•
•
•
Spraying or filming – Reduce surface tension
Heating – Losing solubility
Mechanical – Agitation & scrubbing - Liberating
Releasing O2 & CO2 to atmosphere in gaseous form
23
DA & Holding Hot Condensate
24
Saturated Steam Table
Pressure
(psig)
5
10
80
100
Saturation
Temp
227.3
239.5
323.9
337.9
Volume
(ft3/lb)
20.3
16.46
4.66
3.89
Sensible
Heat (btu/lb)
195.5
207.9
294.4
308.9
Latent Heat
(btu/lb)
960.5
952.5
891.9
880.7
Total Heat
(btu/lb)
1156
1160.4
1186.3
1189.4
25
Zero Condensate Returned
800 HP Process Boiler
•
•
•
•
•
•
•
•
Evaporates 27,600#/HR
Incoming feedwater temperature is 50 Deg. F
DA operating at 5# (227 Deg. F)
227 Deg. F – 50 Deg. F = 177 Btu/#
27,600# X 177 = 4,885,200 Btu’s per hour
@ $0.50 per Therm (100,000)
4,885,200/100,000 = 49 Therms/HR X $0.50 = $25.00/HR
$25.00 X 4000 = $100,000/Year in FW heating cost
All Condensate
Dumped!
X
26
Return Some Condensate to Feed System
800 HP Process Boiler
•
•
•
•
Incoming FW Temperature is 125 Deg. F
227 Deg. F – 125 Deg. F = 102 Deg. F
27,600 X 102 = 2,815,200/100,000 = 28 Therms/HR
28 X $0.50 = $14.00/HR X 4000 HRs/YR = $56,000/YR
• Savings is $44,000 per year!
A Blend of Raw
Makeup & Condensate
125 Deg. F
DA
27
Deaerator Applications
• Boiler plants @ at 75 PSIG
or higher
• Plants with no standby
capacity
• Plants with critical loads
• Plants operating with 25%
makeup or more
28
Types of Deaerators
Spray Type
7,000 – 280,000 pph
Spray cone
29
Types of Deaerators
Spray Head Design
30
Types of Deaerators
Packed Column Type
1,500 – 135,000 pph
Deaerating Column
Storage Tank
31
Packed Column DA
O2 & CO2 Vent
Makeup Water In
Spray & Vent Condensing
Section
Deaerating Column
Corrosion Proof Rings
Steam In
Storage Tank
32
Types of Deaerators
Tray Type
30,000 – 1,200,000 PPH
1,000,000 PPH
40,000 PPH
33
Tray DA
Makeup/Condensate In
Vent Condenser
Steam
Inlet
Spray Valve
Assembly
Trays
Deaerated Water
Downcomer
34
High Temp. Returns
Advantages & Disadvantages
Type
Advantages
Spray
•
•
•
•
Head room
Weight
Price
Capacity
Column
• DA consistency
• Reliable
• HP returns
Tray
•
•
•
•
DA consistency
Reliable
HP returns
Highest capacity
35
Disadvantages
• Mechanical
components
• Critical
adjustments to
steam nozzle
• Limited HP returns
•
•
•
•
Head room
Weight
Limited capacity
Price
• Head room
• Weight
• Price
Saturated Steam Table
Pressure
(psig)
5
10
80
100
Saturation
Temp
227.3
239.5
323.9
337.9
Volume
(ft3/lb)
20.3
16.46
4.66
3.89
Sensible
Heat (btu/lb)
195.5
207.9
294.4
308.9
Latent Heat
(btu/lb)
960.5
952.5
891.9
880.7
Total Heat
(btu/lb)
1156
1160.4
1186.3
1189.4
36
High Pressure Receiver Tank
• Takes high pressure
condensate directly
from the user
• No need to deaerate
• Pump directly into
boiler
• Feed the HPCR from
the DA
37
DA Component Selection & Sizing
Spray Type
38
Spray Cone & Tank Assembly
Formulas:
• 200 HP X 34.5 = 6900#/HR
• 6900/8.3 = 831 Gallons/HR
• Tank storage: 10 minutes = 150 Gal.
39
Vent
Makeup Valve
•
•
•
H.P. Return
Steam
Exhaust Or
Flash Steam
Mechanical
Pneumatic
Electronic
Cold Make-Up
Water
Make-Up Valve
Check Valve
L.P. Condensate
Formula:
SQ Root of inlet press. – tank press. – nozzle press X
Cv = GPM
To
Boiler
Boiler Feed
Water Pump
Overflow
Drainer
Example: (50# - 5# - 7#) = 6.1 X 12 = 73.2 GPM
SQ Root
40
Vent
H.P. Return
PRV
Steam
Exhaust Or
Flash Steam
Cold Make-Up
Water
Make-Up Valve
Check Valve
L.P. Condensate
Selection Sequence:
To
Boiler
Boiler Feed
Water Pump
Overflow
Drainer
1.
2.
3.
4.
Maximum pumping rate of DA
Estimate Average mix temperature of FW
Determine amount of steam to heat FW to saturation
Determine PRV size based on boiler operating
pressure
41
Centrifugal Pumps
Flow:
•
•
BHP X Evaporation Rate = GPM
GPM X Safety Factor
- Continuous = 15%
- Intermittent = 50%
TDH
•
•
(In pounds or 2.31 feet of head )
Total Dynamic Head or…
Discharge Pressure Requirement
for the pump to attain
Specific gravity
NPSHR
•
•
Vertical Multi-Stage
Net Positive Suction Head Required
2.31 Feet per pound
Close Coupled
Flexible Coupled
42
43
Centrifugal pumps
Formulation Example:
Flow
200 HP X 0.069 = 13.8 Gal
Continuous: X 15% = 16 GPM
Intermittent: X 50% = 21 GPM
TDH Duty
Vertical Multi-Stage
Boiler operating pressure + FW valve loss +
Line loss = Total pressure loss X 2.31 = Total loss in Feet of Head/SG
<100# + 25# + 5# = 135 X 2.31 = 301 Feet of Head/0.95 = 317’>
NPSHR
Read from the pump curve at the respective duty points
44
Pump Curve
3' Centrifugal
4'
5'
6'
7'
8'
NPSHR
500
10” Dia.
400
Head in Feet
9” Dia.
300
280
8” Dia.
7”Dia.
200
180
100
6” Dia.
5” Dia.
20
40
60
80
45
Capacity in GPM
100
120
140
160
Pump Curve
3' Centrifugal
4'
5'
6'
7'
8'
NPSHR
500
10” Dia.
400
Head in Feet
9” Dia.
300
8” Dia.
7”Dia.
6” Dia.
100
X
X
200
5” Dia.
20
40
60
80
46
Capacity in GPM
100
120
140
160
Stand
Height depends on NPSHR for Pumps versus NPSHA
47
Safety Valve(s)
Sizing considerations:
1. Normally set at DA design pressure
2. Must handle full output from PRV @ boiler’s safety valve setting
48
Summary
DA Benefits:
-
Hotter boiler feedwater saves fuel energy (10 Deg. F rise = 1%)
Saves on chemical costs
Reduces blow down; saves water, chemicals and sewer charges
Better protects the boiler and piping system; reduces downtime &
capital expense
- Reduces thermal shock
MAJOR TAKE-A-WAYS
- DA removes O2 & CO2
- O2 corrosion increases with temperature
- CO2 is 40% more corrosive with O2 present
- DA’s reduce water surface tension, heat, agitate & liberate gasses
- Three types; Spray, Tray & Column
- Return condensate as hot as possible
- Spray is limited in the amount of high temp condensate it can handle
- Changing duty points on a pump can cause cavitation.
- Safety valves are the last line of defense!
49
Contact Us
Thomas Leunig
Product Manager-Packaged
Water Systems
tleunig@cleaverbrooks.com
414-577-3197
cleaverbrooks.com
Jesse Steffen
Sales Engineer-Packaged
Water Systems
jsteffen@cleaverbrooks.com
414-577-2728
cleaverbrooks.com
50