What is the difference between fixed bed gasifier and moving-bed gasifier?
Moving-bed gasifier In moving-bed gasifiers, also referred to as a ‘fixed-bed’ gasifiers, oxidant and steam are introduced in the lower part of the gasifier and flow vertically upward, while feedstock is introduced at the top of the gasifier. The feedstock is heated by up-flowing hot syngas.
What are the three main types of gasifiers?
2.3 Types of gasifiers
- 1 Updraught or counter current gasifier. The oldest and simplest type of gasifier is the counter current or updraught gasifier shown schematically in Fig.
- 2 Downdraught or co-current gasifiers.
- Cross-draught gasifier.
- Fluidized bed gasifier.
- 5 Other types of gasifiers.
Why downdraft gasifier has lower tar than that of updraft gasifier?
Because the gases leave the gasifier unit at temperatures ∼900–1000 °C, the overall energy efficiency of a downdraft gasifier is low because of the high heat content removed by the hot gas. The tar content of the product gas is lower than for an updraft gasifier but the particulate content of the gas is high.
Which is the oldest and simplest type of gasifier?
Explanation: The oldest and simplest type of gasifier is the counter current or up draught gasifier. The major advantage of this type of gasifier are its simplicity, high charcoal burnout and internal heat exchange leading to low gas exit temperatures and high equipment efficiency.
What is the oldest gasifier?
Lurgi gasifier
The Lurgi gasifier is the oldest gasifier technology that is still widely used in commercial practice. Sasol, a South African firm, still uses this gasifier to produce synthetic liquid fuels from coal. This gasifier produces a considerable quantity of tar, which complicates operations.
Which gasifier is found the most suitable for engine application?
The downdraft gasifiers or cocurrent gasifiers are the most common type of gasifiers. In cocurrent gasifiers, biomass feedstock is fed from the top while air is passed downwards and producer gas leaves from the bottom of the gasifier.
What is gasifier and its advantages?
In summary, gasification has inherent advantages over combustion for emissions control. Emission control is simpler in gasification than in combustion because the produced syngas in gasification is at higher temperature and pressure than the exhaust gases produced in combustion.
Which gasifier has better converting capacity?
Answer: Compared to the updraft gasifier, the Downdraft fixed bed gasifier (DFBG) has the main advantage of a lower tar concentration and a higher carbon conversion rate, which is beneficial for the engine in generating electricity.
What are the disadvantages of gasification?
There is a lack of internal heat exchange in comparison to the updraught gasifier. Less efficiency due to the low heating value of gases. The gasifier can turn inefficient under high uniform temperatures and may become impractical for power ranges above 350 kW.
How does a fixed bed gasifier work?
Feedstocks in the form of large coal particles 1 and fluxes are loaded into the top of the refractory-lined gasifier vessel and move slowly downward through the bed, while reacting with high oxygen content gas introduced at the bottom of the gasifier that is flowing countercurrently upward in the gasifier.
Where does the syngas go in a fixed bed gasifier?
In the updraft gasifier the air is provided on the bottom, while the syngas leaves the gasifier at its top; contrarily, in the downdraft configuration the air is fed in a furnace located at the bottom and the syngas leaves the gasifier at its top.
How can you tell the updraft from the downdraft in a fixed bed gasifier?
Depending on the direction of the air, from bottom to top or vice versa, it is possible to distinguish the downdraft and the updraft configurations.
What happens in the drying zone of a gasifier?
Reactions within the gasifier occur in different “zones”. In the “drying zone” at the top of the gasifier, the entering coal is heated and dried, while cooling the product gas before it leaves the reactor. The coal is further heated and devolatized by the higher temperature gas as it descends through the “carbonization zone”.
