Biomass Gasifier: Syngas Production

Feedstock

Process Controls

Equivalence ratio (ER) 0.28

Moisture content 15%

Feed rate 20 kg/h

Syngas Composition (vol%, dry)

H₂

CH₄

CO₂

N₂

Reactor State

Syngas LHV

0.0 MJ/Nm³

Cold-gas efficiency

Oxidation zone peak T

0 °C

Gas yield

0.0 Nm³/kg

How it works

This is a fixed-bed downdraft gasifier: biomass fed at the top falls through four zones while air enters near the throat. Unlike direct combustion (burning biomass to release heat), gasification deliberately starves the reaction of oxygen so the carbon converts into a combustible gas — syngas — instead of just CO₂ and heat.

Drying   (~100-200°C): free water driven off
Pyrolysis(~200-500°C): volatiles crack into tar, char, gas
Oxidation(~700-1250°C): partial combustion of char supplies process heat
Reduction(~600-900°C): char + hot gas react endothermically

The reduction zone is governed by two real gas-phase reactions:

Boudouard:       C + CO2  ⇌ 2 CO
Water-gas shift: CO + H2O ⇌ CO2 + H2

The equivalence ratio (ER) is the actual air supplied divided by the air needed for full stoichiometric combustion. Low ER (~0.2) starves oxidation of heat; high ER (~0.4) pushes the process toward combustion, diluting syngas with N₂ and CO₂. Moisture content shifts the water-gas-shift reaction toward more H₂ but consumes ~2.26 MJ/kg to evaporate, lowering peak temperature and efficiency.

Heating value uses the standard per-species lower heating values (MJ per Nm³ of gas):

LHV_syngas = (H2%·10.8 + CO%·12.6 + CH4%·35.8) / 100

Cold-gas efficiency (CGE) compares the chemical energy leaving as syngas to the chemical energy that entered as wet biomass — the standard figure of merit for a gasifier.

Biomass / char / ash Oxidation glow Rising syngas

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