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Pozzilli waste-to-energy plant

Via dell'Energia - Pozzilli (IS)

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The thermoelectric power plant of Pozzilli is classified as a Plant Powered by Renewable Sources (RES power plant), pursuant to Italian Legislative Decree no. 79 of 16 March 1999 and no. 387 of 29 December 2003, as well as a co-incineration plant in accordance with Italian Legislative Decree no. 133 of 11 May 2005, implementing the European Directive 2000/76/EC, specifically relating to the production of electricity.

The current plant is the result of the renovation of the pre-existing facility located at the same site and deactivated at the end of 2005 in accordance with the provisions of Decree no. 79 of 16 March 1999, in order to obtain the IAFR classification by the Electricity System Operator (GSE) and including an appropriate improvement of the plant's energy and environmental performance, pursuant to the Ministerial Decree of 11 November 1999.

This renovation implied the replacement of the steam generator boilers and of the turbine-alternator-condenser unit, requiring a thorough and systematic review of all the design and construction criteria, in light of the most recent operational and environmental regulations, including the provisions of Legislative Decree no. 133 of 11 May 2005.

The maximum authorised capacity is 93,500 tonnes of incoming waste per year.

Page updated 26 August 2015

 
    Number of lines
    1
    Total thermal capacity
    Approximately 47 MWt
    Combustion technology
    Martin grate incinerator
    Waste disposal capacity
    Max. approximately 280 t/d with LCV of 15,000 kJ/kg
    Annual operation
    8,000 hr
    Rated electric power
    11.5 MW
    Recovery code
    R1
    Type of waste accepted
    WDF - waste-derived fuel

    Environmental compatibility with current regulations (Legislative Decree 152/06)

    The plant makes it possible to recover waste (RDF) through combustion of the waste itself. The heat generated by this process is exploited to produce electricity.

    1 - Waste receipt and storage.
    Combustible waste is normally received at the plant by means of specially equipped and authorised vehicles. The possibility of managing the logistics via rail is also under evaluation, since the services at the Industrial Consortium of Isernia - Venafro, where the plant is located, in principle allow this solution to be adopted.
    The incoming material is identified and recorded in accordance with the statutory procedures and subjected to a preliminary examination in order to verify it is conforming to the specifications according to internal management and control procedures based on the ISO 14001 and EMAS standards.
    If it is found to be suitable and conforming to the predefined chemical, physical and merceological properties, after being weighed on a weighbridge, the product is unloaded in a specifically dedicated storage facility.
    The storage facility consists of a 2,200 m2 reinforced concrete structure, fully enclosed and equipped with an air extraction system which provides an hourly renewal appropriate to the volume of the facility, thereby ensuring the best environmental conditions.
    Also the primary combustion air is taken directly from inside the storage facility, so that no odours or volatile substances are dispersed into the surrounding environment.
    The RDF is stored solely inside e storage facility: biomasses not housed in the facility are placed under cover to protect them from atmospheric precipitation.

    2 - Steam generator boiler
    The boiler is the unit in which the thermal energy generated by combustion is used to convert water into superheated steam, at high pressure and temperature, which is used to operate a steam turbine coupled to a power generator.
    The Pozzilli plant boiler, with a thermal power of 47 MWt, consists of a Martin grid on which the fuel is burnt: the high-temperature gaseous fraction of combustion, or fumes, first follows an ascending path in the combustion chamber consisting of continuous walls of pipes set side-by-side and connected by membranes containing water being converted into steam. The temperature of the fumes in the hottest part is never less than 1,100°C, and is in any case guaranteed to remain at a temperature of more than 1,100°C for at least two seconds, in accordance with current standards: this helps to prevent the formation of noxious gases such as dioxins and furans.
    Subsequently, the fumes pass through another four vertical heat-exchanging zones in which, by progressively giving up their heat, they allow the steam to be brought to the temperature and pressure levels required for injection into the turbine; at the same time, the water is preheated and sent to the boiler in a closed cycle.
    The solid residues of the combustion consist of the ashes collected on the grid and some lighter-weight residues borne by the fumes, together with the unburnt particles collected along the circuit in the boiler until a final filtering stage in a special filter system.

    3 - Turbo-alternator unit
    This consists of a steam turbine-alternator-condenser unit.
    The triple-spillback, multistage steam turbine transforms the energy of the high pressure/temperature steam into mechanical energy; in practice, it is a motor coupled to a three-phase power generator.
    The steam that drove the turbine is discharged into a water-cooled heat exchanger, the condenser, where it returns to the liquid state and is sent back to the boiler in a closed cycle.
    The three-phase alternator, with rotating-diode type excitation, including a water-cooling system, is coupled to the turbine by means of a mechanical speed reducer.
    The 6 kV electricity produced by the alternator is converted to 20 kV and fed into the ENEL distribution network.
    The energy is partially absorbed by the plant itself to operate its auxiliary services: pumps, transport and collection systems, air blowers and fume extractors.
    The net electric power available to be fed into the grid is 11.5 MW.

    4 - Fume treatment and emissions monitoring
    Much care has been devoted to the design and to the methods for management of the fume treatment and emission monitoring systems, in compliance with the rules included in Legislative Decree no. 133 of 11 May 2005 and in implementation of European Directive 2000/76/EC on waste incineration.
    The treatment system includes:

    • injection of urea into the combustion chamber to lower NOx emissions;
    • injection of sodium bicarbonate and active carbons upon release of fumes from the economiser to reduce acid (HCl and SO2) and heavy metal emissions;
    • final filtration to restrain the particulate matter carried by the fumes before transfer to the chimney stack.
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    • The plant is equipped with a Continuous Emissions Monitoring System which has automatic analysers functioning 24 hours per day to monitor the quality of atmospheric emissions from one moment to the next.
      A suitably heated sample probe continuously transports a sample of the gas from the plant´s chimney to the analysis booth where the instrumentation is installed. The sample is put into the Fourier transform infrared spectroscopy (FTIR) analyser, which continuously detects the absorption spectra of the compounds to be measured. A mathematical process is used to compare the spectra with the stored typical spectra of the substances being investigated. The comparison makes it possible to determine the quantitative values (concentrations) of the elements and compounds analysed. Besides the FTIR system, there are other continuous analysers and meters needed to complete the fume analysis by determining other parameters such as: particles, organic compounds, mercury, oxygen, temperature, flow rate and pressure.
      After the analysis system, a data acquisition system continuously provides the values obtained by calculating the half-hourly and daily averages of the concentrations measured, which are compared with the maximum admissible limit values set by the Control Bodies.

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