Objective
To generate electricity by the use of a gas engine using medium calorific gases obtained by biomas gasification. The electricity will be used by local firms for water pumping and irrigation.
Indirect heating of the gasifier through a wall seems to be attractive route to produce raw synthesis gas if it can be realized on a technical scale at a sufficient rate and degree of biomass conversion. As secondary gasification is done presently with oxygen, much of the attractiveness is lost as a oxygen is still used. However, for medium Joule gas production and with a steam reforming step, the process regains much interest.
In the development step, some modification of the plant were carried out. The most important was the replacement of the hot gas blower with an ejector. This modification allowed to have stable and reliable runs.
When the gasification circuit is about 400 deg. C, the auxiliary recirculation fan is replaced with an ejector system; during this operation it is necessary to take care of the main equipment to avoid problems related to the several thermal expansion of each system.
When the process temperature into the inner bed is reached, the gasification circuitis recirculated with nitrogen to substitute the hot air used during the heating up. Biomass feeding starts only when the oxygen content is less than 0.05% into the circuit.
In order to assure a good seal of the screw feeder, special attention must be devoted to keep it constantly full of biomass. In this way a good sealing to prevent the syngas out coming is obtained.
Gasification tests prove the innovating concept on which the gasification plant is based; undirect heating by fluidized bed.
Besides, the possibility of obtaining a medium heating value gas without using oxygen has been demonstrated.
From the data obtained, heat transfer coefficient figure of about 200-250 Kcal/h m2 deg. C was calculated. The certified gas analysis coming from different laboratories confirmed the expected figures.
The ratio between the syngas and the biomass feed gives the efficiency of the plant from the material point of view :
syngas yield : 67% ./. : 77%
These calculations bringsto the conclusion that the system works very well and it gives higher efficiency and reproducibility if a biomass is feed with less moisture and adjust the parameters of the plant in function of the different conditions of the fed itself.
The plant in the present execution is not easy to handle. The possibility, to go to choose alternative solutions was not taken in consideration because of the high costs involved in each modifications.
Nevertheless the ground idea of the two concentric fluidized bed and the obtained results have proven that it is possible to obtain from biomass a good medium heating value gas, which can be used to supply gas-motor to produce electrical current. The quality of the obtained gas is good. The only matter is that each time that the plant must be put in operation after long period of stop, it needs several days till it can reach the right operating temperature, and this matter involves in three shifts very high operating costs.
An externally heated fluidized bed gasifier is used to transform agricultural residues to produce a gas of 2,600 to 5,300 Kcal/Nm3 in calorific value. The use of air rather than oxygen limits sulphur emissions. Consumption and transformation of biomass at the rate of 15,000 to 20,000 T/y could result in a saving of 1,000 TOE.
Electricity generation amounts to 500 KWE, 100 KWE being consumed by the plant itself.
Call for proposal
Data not availableFunding Scheme
DEM - Demonstration contractsCoordinator
67039 Sulmona
Italy