Objectives

1
Objectives

• Discuss Exam
• Finish with
• Boilers
• Discuss low temperature energy systems

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Coal Boiler
3
Coal burning method
Long time ago
Today 1) Fluidized bed http//www.youtube.com/
watch?v8n78CDI3GoU 2) Powdered
coal http//www.youtube.com/watch?vg1ojza-nbqs

4
Coal-fired power plant filters

• For Particulate Maters
• Electrostatic precipitator
• Filter bags
• Scrubber for SO2 (to prevent formation of
  Sulfuric acid H2SO4)
• Grinded Limestone in water (slurry) sprayed into
  the gas fluid stream SO2 Limestone slurry ?
  Gypsum (used for wallboard)

5
Oil Gas based boilers
Gas circulate through tubes water is
in-between
Water tube boiler
6
Furnaces
For homes
Roof tops and induct heaters
7
Fuel combustion - Stoichiometry

• Boiler efficiency as a function of excessive air
• Stoichiometry
• Chemistry of reactants, products and energy in
  chemical reactions
• A stoichiometric ratio of a reagent is the
  optimum amount or ratio where, assuming that the
  reaction proceeds to completion

Q combustion
Stoichiometric combustion
Depends on the fuel - 5 to10 for natural
gas - 40 for coal
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Air Pollutants from Combustion
Air-Fuel Ratio

• - Rich mixture
• - more fuel than necessary
• (AF) mixture lt (AF)stoich
• - Lean mixture
• - more air than necessary
• (AF) mixture gt (AF)stoich
• Most combustion systems
• operate under lean conditions!
• However, lean mixture
• results in Nox products!

9
Stoichiometric air/fuel ratio for selected gases
10
Energy densities of fuels
11
Higher heating value (HHV) vs. Lower heating
value (HHV)

• HHV is the heat of combustion of the fuel when
  the water product is at liquid state (water vapor
  from the product are condensed)
• LHV is the heat of combustion of the fuel when
  the combustion product contain water vapor
• For methane 10 difference!

12
Condensing vs. noncondensing boilers
Example is for a small residential gas powered
boiler - wall mount
fan coils, or baseboard hearts
13
Condensing vs. noncondensing boilers
86 (depends on fuel)
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Boiler Efficiency Definitions

• ASHRAE Standard 90.1-2004 describes the minimum
  acceptable ratings for new boilers
• Combustion Efficiency ((Fuel Input Stack
  Losses) / Fuel Input) x 100
• Thermal Efficiency (Output / Input) x 100
• Annual or Seasonal Efficiency
• ..

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Boiler and Furnace Efficiency Definitions
Example (for large coal based boilers)
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Typical boiler and furnace efficiency (based on
the higher heating value)

• Condensing boilers
• manufacturers claim up to 98 (be careful with
  this number check for which conditions)
• Older conventional boilers 70-80
• Typical new models around 90
• New gas furnaces are in the rage of 80-90
• These numbers are for well maintained and tuned
  boilers furnaces. Also, Seasonal Efficiency can
  be significantly smaller!

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Combined heat and power(cogeneration CHP or
three generation CCHP)
Boiler (or heat generation system )
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Low temperature energy systems

• Waist heat is part of almost every CHP
• Many new micro CHP system use Stirling engine

http//www.viessmann.com
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Stirling cycle
Closed Cycle Engine No phase change Working
fluid air, hydrogen, or helium
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Stirling engine
Theoretical efficiency of up to 25 (for 500ºC)
Real efficiency in residential application
between 6-8