Objective
Construction and operation of a gasifiers which, fed with 70 kg/h of a wooden fuel, gives a gas flow equivalent to a thermal power of 200000 Kcal/h (836 GJ/h). Two different prototypes have been planned and achieved:
1. A thermic unit, feeding a dual-fuel (methane-wood gas) burner,
2. An electricity generating unit, where the produced gas (cooled, washed and filtered) is fed to a four-stroke engine powering an electrical generator (up to an electric power of 35 kW). Initially the marketing target was to use the gasifiers in the pine nuts factories: in this case the fuel can be either the pignolia shells (as they come from the crushing machines), either the pine-cones "stumps & scales" (coarsely milled and sieved). Later on, a larger utilization field has been found: the winter heating of the greenhouses (beyond 100000 units are operated in Italy). In this case, other more abundant biomasses must be made available as fuel by means of a morphological conditioning (pelletization).
The thermic unit has been completely achieved in Dec.1994 and, since Jan.1995 is operated for demonstrations. Up to April 1st, 1996, it has been used for 22 "demonstrations", each of them about a week long. The gasifier operation is very flexible: the unit can be used only a half of its capacity. To ignite the gasifier and to put it in a steady regimen, about two hours are necessary, whithout any close watch. Once in steady regimen, the gasifier can be stopped at any moment just by putting "off" the main switch. A break up to 24 hours is allowed: to start again, the main switch has to be put again "on". The unit is easy to be moved and to be towed. The maximum capacity (200000 KCal/h) is reached when the gasifier is fed with 100 Nm³ of air: the fuel consumption will be about 70 Kg/h and the gas produced will be 160 Nm³/h.
The electricity generating unit has been achieved only in Feb. 1996. Up to April 1st, the unit had been running for three "demonstrations" of about 12 hours each. The most serious problem in the tuning of this unit arose from the fact that the static pressure available downstream the gasifier appeared to be too low to overcome the resistences existing through the scrubbing, cooling and filtering apparatus. Of course it was possible to increase the gas pressure by means of the blower feeding with air gasifier, but in this case a return gas towards the fuel hopper takes place. This happens because of the relatively high porosity of the fuel grains present inside of the tube where the endless screw is mounted. Increasing the lenght of the feeding screw the feeder becomes almost "gas-thight" but, after several tests, a more acceptable solution has been to increase the gas pressure by means of turbine sucking the gas and feeding the washing paddler and the filtration line.
A negative performance of the electricity generating unit is due to the fact that a continuous watch is necessary during all the starting phase.
THERMIC UNIT :
The gasifier, coupled with its burner, is mounted on an easy-towing three-wheel carriage. The body of the gasifier is a cylindrical steel vessel made with 10 mm thick steel sheet. The inner walls of the vessel are lined by a 80 mm thick refractory layer. Also the lid (welded) is protected by a refractory lining. Outside, a light thermal protection is obtained by means of a layer of ceramic fibres, covered by a zinc-plated sheet. The inner diameter of the gasification chamber is about 60 cm. On the lid, a touch-down probe is mounted, which controls the embers level in the chamber (and the fuel feeder). From an external hopper, by means of an endless-screw feeder, the woody granulated fuel is fed to a burning bowl placed on the bottom of the chamber. To start up the gasifier a small quantity of fuel is manually placed in the bowl through a side inspection door and lit by means of a butane gas torch introduced through a side manifold. Once a first core of flaming embers is obtained, the feeder and the air blower are switched on. Within two hours a steady regimen is reached and the feeder maintains, automatically, a constant level of the embers in the gasification chamber. When fed with an inlet air flow-rate of 100 Nm³/h, the gasifier reaches its highest capacity, producing 160 Nm³/h of gas. The gas heating value (GHV) is around 5 GJ/Nm³ (1200 KCal/Nm³).
ELECTRICITY GENERATING UNIT.
The gas generation section is identical as for the thermic unit. The hot gas leaving the gasification chamber comes through a cyclone, entering the bottom of a spray washing scrubber where a circulating pump feeds a spray nozzle placed on the top. This scrubber carries out a first cooling and washing: an important fraction of the combustion water and of the less volatile tar is condensed, collected through a finned tubes cooling radiator, and withdrawn. The gas pressure is then raised by a turbine, which blows the gas through washing paddler, followed by a filter box.
Programme(s)
Call for proposal
Data not availableFunding Scheme
DEM - Demonstration contractsCoordinator
55048 Torre del Lago Lucca
Italy