Objective
To demonstrate the gasification of RDF using two 19 MWe circulating fluidised bed gasifiers. RDF from a nearby waste processing plant is fed to each unit at 4. 2 T/H. Heat from the primary and secondary combustion chamber is used to produce superheated steam. The plant will generate 6. 7 MWe. Gasification takes place at 875 deg. C in the circulating bed. Total energy output is estimated at 11265 TOE/Y, however, the saving with respect to a conventional RDF facility is 1651 TOE/Y. The innovation lies in the high combustion efficiency of the CFBG. An energy conversion efficiency of 96. 3 % is claimed.
The Greve in Chianti plant is the first experience of industrial RDF gasification and this led to a considerable risk for Aerimpianti which "suitably" considered it in the planning phase with the choice of the best equipment available on the market to construct an industrial type plant. Although some parts still require considerable improvement, it is believed that the overall results are satisfactory, at least from a technical point of view, and that in the future, it will be possible to express a positive judgment from an economic point of view. Since it can be foreseen that the RDF available will continue to have variable characteristics in terms of density, presence of metallic materials and heat value, some modifications have already been made and have been shown to improve the reliability of the systems considerably, these are :
- increase the tolerance between the blades and casing of the RDF rotary valves feeding
- insertion of inspection door for quickly removing of plugsand/or unwanted material in the RDF feeding system
- increase of the speed control range of the RDF feeding screw
- increase the tolerance between the blades and casing of the ash discharge screw conveyor
- installation of manual type block breakers at the gasifier bottom
- parallel arrangement of the RDF rotary valves feeding in order to have two possible feeding lines for gasifier n.1 : one service line and a back-up line
- remodelling of the gasifier bottom to avoid the accumulation of metallic material in the dead points not reached by the air flow
- replacement of the boiler superheater tubes arranged to a "quinconce" with an other type of arrangement in order to avoid dust accumulation.
The fact that the innovative part of the project, i.e. the gasifiers, did not show any problems even in the case of RDF having an L.H.V. of 5,400 Kcal/kg leads us to be reasonably optimistic about the immediate future, also considering the success of the "gas supply to the cement-factory" test, since next year RDF disposal in the conditions described in par. 4.2.1 and 4.2.2. are forecast.
In the short time, when some necessary modifications, in order to minimize the costs and reestablish the original efficiency, have been carried out along with the operations for supply the process gas to the cement-factory industrially, a consistent use of the two gasifiers is foreseen :
- the first dedicated to the electrical energy production line
- the second dedicated to the production of gas to be sent to the cement-factory.
These configurations require a considerable availability of RDF; the managing company "SAFI", committed to search for that fuel, is also aiming to RDF disposal produced from the industrial waste available in the "Florence" area. The preliminary sample examined seems to be of a suitable quality for the capacity power and characteristics of the plant.
The plant, realized in the Greve in Chianti Council area, is located at the "SACCI" cement-factory area and is placed inside the suitably restructured existing industrial buildings. The plant, at the actual project financed phase, is composed by :
- n. 2 circulating fluidized bed gasifiers having each a thermal power rating of 18 KWt
- n. 1 combustion and heat recovery line made up of :
- primary combustion chamber fitted with dual gas burner
- post-combustion chamber
- heat recovery section for steam production
- n. 1 flue gas treatment line
- n. 1 turbogenerator unit with capacity 6.7 MWh
- n. 1 "Therma" polyfunctional package
- n. 1 ash stabilization line complete of rotary kiln with after burner chamber and flue gas treatment line associated
This unit also represent a third potential line for RDF disposal or other type of waste, since that the ash at outlet of gasifier are totally inertized.
- RDF storage and transportation plants
- general auxiliary equipments and/or services for the overall plant.
The gasification reactions take place in the fluidized bed sand of the reactor when fuel is input the hot bed and air is used as fluidization. Each gasifier is composed of a main fluidized bed reactor and two recirculated external fluid bed systems which ensure, by means an U-beam particle separator and an hot cyclone separator, a recycle of the dust and solid material into the main fluidized bed reactor.
The fuel introduced into the gasifier reactor reaches the bed material and is thus first dried and volatized, and then partially oxidized and/or gasified. The temperature in the bed is ensured by the partial controlled combustion and is controlled by fuel/air ratio.
The gasification produces a "lean gas", that is conveyed to the primary combustion chamber of the combustion and heat-recovery system where, with addition of secondary combustion air, a complete combustion reaction is obtained under stoichiometric control and at hightemperature.
The flue gases then pass into the post-combustion chamber designed in order to provide the operating conditions in accordance with Italian law requirements. RDF material is supplied to the plant by normal transportation means. Feeding each gasifier at the maximum design flow rate of 4.2 ton/h of RDF it is possible to satisfy the electrical energy production line and simultaneously send the surplus of the L.H.V. fuel gas produced to cement-factory.
The connection between gasification plant and cement factory is realized by a transportation gas duct of about 800 meters length, in order to burn the gas into rotary kiln saving conventional fuel. Circulating bed gasifier is maintained at an operating pressure slightly above atmospheric pressure. The fuel gas produced, at 850 ./. 870 deg. C temperature, is 3.900 ./. 8.400 Ncm/h with net heating value range of 6500 ./. 9000 KJ/Ncm, the gas is used for primary combustion without any further treatment.
Call for proposal
Data not availableFunding Scheme
DEM - Demonstration contractsCoordinator
20135 Milano
Italy