What are the four main types of gasifiers?
The process of gasifying involves turning organic waste or fossil fuels into gases. These gases include carbon dioxide (CO2), hydrogen (H2), and carbon monoxide (CO) (CO). High temperatures are used to oxidize and reduce organic materials during the procedure. The finished item is a fuel or gas mixture known as producer gas or syngas. The product burns more effectively than virgin fuels because it is flammable at greater temperatures. Electricity is produced using the method in many different sectors.
What are the four main types of gasifiers?
In a gasifier, the fuel interacts with air or oxygen and steam. Therefore, gasifiers are classified according to the way in which air or oxygen is introduced. On a larger scale, there are four types of gasifiers as follows
1.updraft gasifier or counterflow gasifier
The countercurrent or updraft gasifier is the earliest and most basic type of gasifier. The top is where the gas exits and the bottom is where the gas enters. The reduction reaction occurs further up in the gasifier after the combustion reaction, which happens close to the grate at the bottom. Due to forced convection and radiant heat transfer from the bottom zone, the feedstock is heated and pyrolyzed in the gasifier’s top section. The gas stream carries the tars and volatiles created during this process. The ash is taken out of the gasifier’s bottom.
a: The main advantage is its simplicity.
b: Internal heat exchange and high carbon release of gas at low temperatures.
c: High efficiency of gasification equipment.
a: If there are channels in the equipment, an explosion may occur. This may be the cause of oxygen breakthrough. This is extremely dangerous and is one of the main disadvantages of this type of gasifier.
b: Tar may be burned if the gas is used in applications where it is directly heated.
c: Disposal of condensate containing tar may also be a minor problem.
2. Downflow or parallel-flow gasifiers
By designing down-flow or downdraft gasifiers, where primary gasification air is supplied into or above the oxidation zone in the gasifier, solutions to the issue of tar entrainment in the gas stream have been identified. In order for the fuel and gas to travel in the same direction, the generator gas is evacuated from the unit’s bottom. In order to become the permanent gases hydrogen, carbon dioxide, carbon monoxide, and methane, the acid and tar distillation products from the fuel must pass through the flaming charcoal bed during the descent. The amount of tar that has been degraded varies depending on the hot zone’s temperature and how long the tar fumes have been present.
a: The product obtained is a tar-free gas that can be used in engine applications.
b: These gasifiers are less affected by any environmental obstacles due to the low content of organic components in the condensate.
a: Unable to use most unprocessed fuels.
b: They encounter problems due to the use of fuels with high ash content.
c: Lack of internal heat exchange compared to updraft gasifiers.
d: Lower efficiency due to the low calorific value of the gas.
e: Gasifiers become inefficient at high uniform temperatures and may become impractical for power ranges above 350 kW.
3. Crossflow gasifier
Cross-flow gasifiers are suitable for use with charcoal. Charcoal gasification leads to very high temperatures in the oxidation zone (1500 °C or higher), which can lead to material problems. In a cross-vented gasifier, the fuel (charcoal) itself provides insulation against these high temperatures.
a: These units are economically viable in the power range up to 10 kW.
b: It can be operated on a very small scale.
c: These types of gasifiers can fit into small engines.
a: It requires a concomitant supply of good quality charcoal.
b: These gasifiers have a minimal tar conversion capacity.
4.Fluidized Bed Gasifier
The operation of both top and bottom suction gasifiers is influenced by the morphology, physical and chemical properties of the fuel. Common problems are the absence of fuel flow, slagging and extreme pressure drops on the gasifier. One design approach designed to eliminate these difficulties is the fluidized bed gasifier. Air is blown through the bed of solid particles at a rate sufficient to keep them in suspension. The bed is initially heated from the outside and once a sufficiently high temperature is reached the feedstock is introduced. Fuel pellets are introduced to the bottom of the reactor and are quickly mixed with the bed material, which is heated almost instantaneously to bed temperature. As a result of this treatment, the fuel is pyrolyzed very rapidly, resulting in the mixing of components with relatively large amounts of gaseous material. Further gasification and tar conversion reactions take place in the gas phase. Most systems are equipped with an internal cyclone to minimize coke ejection.
a: Feedstock flexibility as the temperature is easily controlled and the temperature can be kept at or below the melting point of the ash (rice husk).
b: Ability to handle fluffy and fine-grained materials (sawdust, etc.) without pretreatment. Some biomass fuels may have feeding problems, bed instability and fly ash sintering in the gas channel.
a: High tar content of the gas (up to 500 mg/m³ gas), incomplete carbon combustion and poor response to load changes.
b: There are no very small fluidized bed gasifiers, and the application range must be tentatively set at 500 kW (shaft power) or more.
c: Fluidized bed gasifiers are currently available on a semi-commercial basis from a number of manufacturers in Europe and the USA.
What factors depend on the choice of gasifier?
5.Moisture and ash content
6.Oxygen flow in the gasifier
What are the other types of gasifiers?
A number of other biomass gasifier systems (dual fuel, sandwich, melt cell), partly derived from coal gasification technology, are currently under development. In some cases, these systems contain unnecessary improvements and complications, and in other cases, near-term applications in developing countries are not possible due to the size and complexity of the equipment. For these reasons, these systems are not mentioned in this report.