1 / 20

Objectives

This discussion explores the different methods of coal burning in boilers, such as fluidized bed and powdered coal, and the efficiency of low temperature energy systems. Topics include air-fuel ratios, combustion pollutants, energy densities of fuels, and the efficiency of condensing and non-condensing boilers.

dcalderon
Download Presentation

Objectives

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Discuss Exam Finish with Boilers Discuss low temperature energy systems Objectives

  2. Coal Boiler

  3. Coal burning method Long time ago: Today: 1) Fluidized bed: http://www.youtube.com/watch?v=8n78CDI3GoU 2) Powdered coal: http://www.youtube.com/watch?v=g1ojza-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

  8. 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!

  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)

  14. 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 …..

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

  16. 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!

  17. Combined heat and power(cogeneration CHP or three generation CCHP) Boiler (or heat generation system )

  18. Low temperature energy systems • Waist heat is part of almost every CHP • Many new micro CHP system use Stirling engine http://www.viessmann.com

  19. Stirling cycle Closed Cycle Engine No phase change Working fluid: air, hydrogen, or helium

  20. Stirling engine Theoretical efficiency of up to 25% (for 500ºC) Real efficiency in residential application between 6-8%

More Related