Gasifier type

Advantages

Disadvantage

Updraft

1) Small pressure drop.

2) Little tendency towards slag formation and simplicity in construction.

3) High charcoal burnout with internal heat exchange leading to low gas exit temperature and high gasification efficiencies.

4) Can run on wide range of moisture content and some size variation in feed stock.

1) Moisture Content of fuel.

2) Relatively long time required for start up of engine utilizing syngas.

3) Poor reaction capability with heavy gas load.

4) High amounts of tar and pyrolysis products.

5) Demanding excessive cleaning for the case of engine application.

Downdraft

1) Flexible adaptation of gas production to load.

2) Low sensitivity to charcoal dust and tar content of fuel.

3) Produces gas with low tar content suitable for internal combustion engine.

1) Needs uniform and not very small particle size of fuel 1 - 2 mm.

2) High amount of ash and dust particles remain in gas.

3) The relatively high temperature of exit flue gas.

4) Results in lower gasification efficiency biomass moisture content must be less than 25% on dry basis.

Crossdraft

1) Fast response time to load.

2) Flexible gas production.

3) Can be operated in small scale.

1) High sensitivity to slag formation.

2) Demanding clean charcoal.

3) High pressure drop.

4) Charcoal gasification results in extremely high temperature.