12. Eureka! We have Steam!!!!
Mass Balance
Makeup Water In = Steam Out
Energy Balance
Fuel Energy In = Steam Energy Out
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13. Water Mass Balance
Makeup Water In = Steam Out??????
What’s left behind?
• Contaminants
Dissolved Solids: Calcium, magnesium, sodium, chloride, phosphate,
bicarbonate, carbonate, iron, manganese, etc.
–Retrograde solubility
Suspended Solids: Silts, corrosion by-products, precipitated salts, etc.
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14. Boilers Cycles
Cycles begin when water evaporates. As water evaporates, solids stay behind.
When the solids = twice the MU solids, So forth, and so on.
you have 2 cycles of concentration.
19. How to Control Scale?
Blowdown
• Continuous/surface blowdown
Control dissolved solids/conductivity
• Bottom blowdown
Control sludge
New Mass Balance
• Makeup Water In = Steam + Blowdown
New Energy Balance
• Fuel Energy In = Steam Energy Out + Blowdown Energy Out
+ radiant losses + stack losses + combustion inefficiencies
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21. Blowdown vs. Cycles of Concentration
10 Cycles of Concentration = 10% Blowdown
• 10% of the boiler makeup water is going down the drain
20 Cycles of Concentration = 5 % Blowdown
• 5% of the boiler makeup water is going down the drain
50 Cycles of Concentration = 2% Blowdown
• 2% of the boiler makeup water is going down the drain
100 Cycles of Concentration = 1% Blowdown
• 1% of the boiler makeup water is going down the drain
How high can you go?
• American Society of Mechanical Engineers (ASME) Guidelines
• Steam quality
• Scale forming salts solubility
• Current boiler conditions
• ASME recommends 100 maximum 21
22. Wait!!! There’s More!
Maximizing Cycles of Concentration
• Saves water
• Saves FUEL!
Boiler @ 50 psig
• Blowdown heat content = 267 BTU/lb
Boiler @ 150 psig
• Blowdown heat content = 338 BTU/lb
Boiler @ 250 psig
• Blowdown heat content = 381 BTU/lb
Maximizing Cycles of Concentration Minimizes the Heat
Going Down the Drain!
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23. Maximizing Cycles of Concentration
Improve Makeup Water Quality
• ASME: “Where a choice is available, the reduction or removal of
objectionable constituents by pretreatment external to the boiler
is always preferable to, and more reliable than, management of
these constituents within the boiler by internal chemical
treatment.”
• Water Softener
• Dealkalizer
• Demineralization
• Reverse Osmosis
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24. Maximizing Cycles of Concentration
Maximize Control of Cycles
• Automatic blowdown controller
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30. Economizers
Extract more heat from fuel
Not all energy absorbed by boiler
Economizer transfers waste boiler stack heat to boiler
feedwater
For every 40-50°F drop in stack temperature
• 1% gain in boiler efficiency
Dew point of acids and water the limiting factor
• Unless use corrosion resistant materials
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31. Blowdown Flash Tank & Heat Exchanger
Recover heat from the blowdown!
• Example: 150 psig Blowdown heat content = 338 BTU/lb
366°F
Blowdown Flash Tank
• Lower Pressure = Flashing of portion of blowdown to low pressure
steam.
Can use in Deaerator
–E.g., 10 psig at 240°F
Blowdown Heat Exchanger
• Exchange remaining heat with incoming
makeup water
• 20°F approach temperature
Typically, 80% of waste heat in
blowdown can be recovered
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34. Energy Saving Summary
Maximize Cycles of Concentration
• Pretreatment
• Automatic blowdown control
• Chemicals
• Maximize condensate return
Economizers
• Extract remaining amount of heat out of fuel
Blowdown Flash Tank & Heat Exchanger
• Keep heat from going down the drain
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