How does an updraft gasifier work?

The updraft gasifier consists of a top fed fuel bed through which the “gasification agent” (steam, oxygen and/or air) flows in from the bottom and exits through the top as gas. The updraft gasifier has been the standard of coal gasification for 150 years and it’s also popular in biomass cook stoves.

What is the difference between updraft and downdraft gasifier?

In downdraft gasifiers, both fuel and the gas move downward. In updraft gasifiers, fuel moves downward and gas upward. In co-current gasifiers, the fuel and gas move in the same direction, usually downward (downdraft gasifiers), but the movement can also be upward.

Is gasification more efficient than combustion?

If the lessons from coal gasification help enlighten biomass gasification, the comparison will be as follows: In theory, gasification has several advantages compared to combustion, including increased efficiency (up to a 50% increase), easier pollutant removal, and the ability to use the syngas/producer gas for …

How do you calculate the efficiency of a gasifier?

mass rate of CO=15.46*0.0727=1.124 lb/min. CO2=7.62*0.115=0.876 lb/min. CH4=2.14*0.0417=0.089 lb/min. %conversion=output/input=0.78675/0.7988=98%.

What is the purpose of downdraft gasifier?

Downdraft gasifiers generate a synthesis gas more suitable for use in engines or turbines, cooling being required due to the high temperature at which it occurs, and which may affect the operation of the engine.

Why is gasification better than combustion?

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.

How is gasification different from combustion?

Gasification process converts solid fuel into a gaseous fuel through a process of high temperature oxidation-reduction reactions. Combustion process converts solid fuel into gaseous products of combustion through high temperature oxidation reactions.

What is gasification efficiency?

The thermal efficiency for biomass gasification varies from 70-80%. The fuel gas composition ranges from 30-55% N2, 16-30% CO2, 12-30% CO, and 2-10% H2. Air blown gasification produces 2 Nm3 fuel gas/kg of dry biomass. The gas yield reaches 4 Nm3 of fuel gas/kg of polyethylene.

What is cold gas efficiency of gasifier?

Maximum cold gas efficiency of the TBCFB gasifier is 85.0%–80.9% at 800–900 °C. Required gasification time and BFB gasifier volume greatly increase below 850 °C.

How does a gasifier wood stove work?

A wood gasification boiler. Wood is burned in the firebox (top), and gases travel downward and are burned at 1,800 to 2,000 F in the ceramic chamber below. The hot gases then pass through a fire-tube heat exchanger to transfer heat to water stored in a large tank.

Where does the feed come from in an updraft gasifier?

Updraft gasifiers [ 73, 81, 82 ]: A schematic of the updraft gasifier is shown in Figure 14.4a. In these gasifiers, the feed is introduced from the top, and air is introduced from the bottom through grate.

What’s the difference between updraft and downdraft gasification?

One of the differences between updraft gasifiers and downdraft is that it doesn’t take as long for the start-up procedure for the downdraft gasifier setup; this is the process that many reactors must go through before going into daily operations, where the best temperatures/conditions for gasification are reached.

How is the temperature of an updraft gasifier controlled?

The gasification temperature may be controlled by mixing steam and/or flue gas with the gasification medium. The hearth load of an updraft gasifier is generally limited to 2.8 MW/m 2 or 150 kg/m 2 /h for biomass ( Overend, 2004 ).

Why is the tar content lower in updraft gasifiers?

As the exit of the producer gas is close to the combustion zone of the gasifier with maximum temperature, the tar formed during devolatilization of biomass is thermally cracked to some extent. Thus, the tar content of the producer gas from downdraft design is lower than that in the updraft design.