Objectives -Discuss Final Project - -Possible dates for the final project presentations: May Learn about -Power generation -Boilers

Combined heat and power (cogeneration CHP or three generation CCHP) Here, we use thermal energy for heating and/or cooling

Gas powered turbine

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%

Combined Cycle (gas and steam) yer_embedded&v=D406Liwm1Jc

Steam powered turbine

Ideal Rankine Cycle h 1 =h f saturated liquid W pump (ideal) =h 2 -h 1 =v f (P high -P low ) v f =specific volume of saturated liquid at low pressure q in =h 3 -h 2 heat added in boiler Usually either q in will be specified or else the high temperature and pressure (so you can find h 3 ) q out =h 4 -h 1 heat removed from condenser) w turbine =h 3 -h 4 turbine work

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

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

Further improvements

Analogy with cooling cycles

Coal Boiler

Coal burning method Long time ago: Today: 1) Fluidized bed: 2) Powdered coal:

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 wallboard)

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: Stoichiometric combustion +Q combustion Depends on the fuel: - 5 to10% 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 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!