04 Combustion of biomass

Combustion

Oxidation of fuel with oxygen —> Output: Energy in the form of heat

Components

• Oxygen

• Combustible components (Carbon, Hydrogen, Sulphur)

• Non-combustible components (Nitrogen, Chlorine, Ash, Heavy metals, Water)

  
  

3 equations —> all exotherm (get energy out of it)

1. Carbon + Oxygen —> CO2

2. Hydrogen + Oxygen —> H2O

3. Sulphur + Oxygen —> SO2 (Sulfur dioxide)

   
   

Complete

—> Each fuel particle is oxidized

• Overstoichiometric: More oxygen than the fuel needs

Incomplete

—> Not every fuel particle gets an oxygen particle

• Substoichiometric: Less oxygen than the fuel requires —> Always incomplete combustion

• Stoichiometric: Exactly as much oxygen as the fuel requires —> Usually incomplete combustion

  
  

• High nitrogen in the air is only heated during combustion

• High fraction of losses in the flue gas

• High air ratio —> high losses, higher temp. (danger of formation of NOx)

—> Target: Small lambda (1) BUT: Risk of incomplete combustion (fomation of CO)

• Dry fuel is heated up (1—>2)

• CmHn = other hydrocarbons

• Most important losses —> Exhaust gas losses

• Higher exhaust gas mass flow —> Higher air ratio

• Exhaust gas losses determine the efficiency of a heat generator

Parameters

• Air ratio / excess air

• Return temp. (of the heated water)

• Fuel humidity