Objectives Discuss Exam Finish with Boilers Discuss low

Objectives - Discuss Exam - Finish with - Boilers - Discuss low temperature energy systems

Coal Boiler

Coal burning method Long time ago: Today: 1) Fluidized bed: http: //www. youtube. com/watch? v=8 n 78 CDI 3 Go. U 2) Powdered coal: http: //www. youtube. com/watch? v=g 1 ojza-nbqs

Coal-fired power plant filters • For Particulate Maters • Electrostatic precipitator • Filter bags • Scrubber for SO 2 (to prevent formation of Sulfuric acid – H 2 SO 4) • Grinded Limestone in water (slurry) sprayed into the gas fluid stream SO 2 + Limestone slurry → Gypsum (used for

Oil – Gas based boilers Gas circulate through tubes water is in-between Water tube boiler

Furnaces For homes Roof tops and induct heaters

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 to 10% for natural gas - ~ 40 for coal

Air Pollutants from Combustion Air-Fuel Ratio - Rich mixture - more fuel than necessary (AF) mixture < (AF)stoich - Lean mixture - more air than necessary (AF) mixture > (AF)stoich Most combustion systems operate under lean conditions! However, lean mixture results in Nox products!

Stoichiometric air/fuel ratio for selected gases

Energy densities of fuels

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!

Condensing vs. noncondensing boilers Example is for a small residential gas powered boiler - wall mount fan coils, or baseboard hearts

Condensing vs. noncondensing boilers ~86% (depends on fuel)

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 …. .

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

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!