Objectives

1
Objectives

• Discuss Final Project
• http//www.caee.utexas.edu/prof/Novoselac/classes/
  CE397b/Hw.html
• Possible dates for the final project
  presentations May 13 - 16
• Learn about
• Power generation
• Boilers

2
Combined heat and power(cogeneration CHP or
three generation CCHP)
Here, we use thermal energy for heating and/or
cooling
3
Gas powered turbine
http//www.youtube.com/watch?featureplayer_embedd
edvrxps0sZ8T3Y
4
Combustion product gas powered turbines

• Limited to gas or oil as a major source of fuel
• Approximately 55 to 65 of the power produced by
  the turbine is used for compressor.
• Gas temperatures at the turbine inlet can be
  1200ºC to 1400ºC
• Because of the power required to drive the
  compressor, energy conversion efficiency for a
  simple cycle gas turbine plant is 30

5
Combined Cycle(gas and steam)
http//www.youtube.com/watch?featureplayer_embedd
edvD406Liwm1Jc
6
Steam powered turbine
7
Ideal Rankine Cycle
h1hf saturated liquid Wpump (ideal)h2-h1vf(Ph
igh-Plow) vfspecific volume of saturated liquid
at low pressure qinh3-h2 heat added in
boiler Usually either qin will be specified or
else the high temperature and pressure (so you
can find h3) qouth4-h1 heat removed from
condenser) wturbineh3-h4 turbine work
8
Reheat Cycle

• It allows increase boiler pressure without
  problems of low quality at turbine exit

9
Regeneration

• Preheats steam entering boiler using a feed-water
  heater, improving efficiency

10
Further improvements
11
Analogy with cooling cycles
12
Coal Boiler
13
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

14
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)

15
Oil Gas based boilers
Gas circulate through tubes water is
in-between
Water tube boiler
16
Furnaces
For homes
Roof tops and induct heaters
17
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
18
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!

19
Stoichiometric air/fuel ratio for selected gases
20
Energy densities of fuels
21
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!

22
Condensing vs. noncondensing boilers
Example is for a small residential gas powered
boiler - wall mount
fan coils, or baseboard hearts
23
Condensing vs. noncondensing boilers
86 (depends on fuel)
24
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
• ..

25
Boiler and Furnace Efficiency Definitions
Example (for large coal based boilers)
26
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!