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Bologna waste-to-energy plant

Via del Frullo 5, Granarolo dell'Emilia (BO)

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Company “FEA”

The Bologna waste-to-energy plant is located at Via del Frullo 5 in Granarolo dell´Emilia. It disposes of municipal solid waste and hazardous (contagious diseases) and non-hazardous special waste.

The plant dates back to 1971 when three disposal lines were built, each with a potential capacity of 200 metric tonnes of waste per day. The first two lines began operating in 1973, while the third began to be used the following year. From 1987 to 1997, the plant went through various engineering and technological upgrades to come into compliance with constantly evolving European regulations.

A modernisation and technological upgrade project was undertaken at the Bologna waste-to-energy plant in 2001, which has retained the same plant configuration since that time. The structure includes two parallel, independent waste-to-energy lines, each of which treats 300 metric tonnes of waste per day, from which energy is recovered through a cogeneration plant. The plant generates close to 130 million kWh of electricity per year, which is sent to the national grid, and close to 30 million Mcal of thermal energy per year for the district heating network.

The new plant´s technological characteristics were selected while paying close attention to the criteria of the highest degree of environmental protection, reliability and operating safety, technological process and product innovation and high energy efficiency.

Page updated 26 August 2015

 
    Number of waste-to-energy lines
    2
    Surface area of the FEA site
    83,184 m2
    Total thermal capacity
    Approximately 81.41 MWt
    Combustion technology
    Water- and air-cooled moving grate incinerators
    Waste disposal capacity
    600 tonnes/d with LCV of 2,800 Kcal/Kg
    Annual operation
    Approximately 14,925 hours
    Rated electric power
    22 MW
    Recovery code
    R1
    Type of waste accepted
    Municipal waste; non-hazardous special waste; hazardous special waste (or hospital waste with infection risk and cancer chemotherapies) up to a maximum of 3,500 tonnes/year


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

    The waste-to-energy plant makes it possible to dispose of a variety of waste through combustion. The heat this generates is exploited to produce heat and electricity.

    1 - Waste receipt and storage.
    The plant is equipped with a storage pit with a volume of 5,400 m3, which has 10 discharge doors. Of these, the first two are used exclusively to unload high-risk hospital waste to avoid mixing it with the other waste located in the pit. At twenty-five metres from the ground, a crane operator operates the hydraulic bridge crane, which lifts the waste and then puts it into the feed hoppers. The waste falls through the loading channel towards the combustion chamber´s loading device (pusher).

    2 - Combustion.
    The waste advances to the combustion chamber by way of a single moving grate inclined at 18°, divided into two parallel sectors with five zones each, which can be adjusted independently of each other according to the process parameters set. The waste on the grate undergoes drying, combustion and scorification treatments. The waste´s progress can be adjusted with devices that change the speed of movement of the grate bars. Heat is removed by the boiler integrated with the combustion chamber, the walls of which are lined with boiler tubes down to the base of the grate. The combustion air from the incinerators is extracted, therefore maintaining the pit in a vacuum to prevent odours from being dispersed outside. If both lines are shut down, a special deodorising plant can be turned on which extracts the air and, after purifying it through filters, releases it back into the atmosphere. The combustion process occurs with processes automatically regulated by the supervision and control system, which establishes the coordinated criteria for the speed of the various grate sectors, the flow and distribution of primary air, secondary air and fume recirculation, to thereby ensure the optimal temperature and oxygen concentration in each zone of the combustion chamber. When combustion is finished, the residual slag falls into the water of a well to stop it from burning, to then be placed on a vibrating surface which conveys it to the dedicated slag pit. From there, the slag is removed by the crane operator using a polyp-grab and is then loaded onto lorries which transport it to the authorised special waste landfill. The gases produced by combustion are conveyed to the post-combustion chamber, the size of which ensures that fumes remain at a temperature above 850°C for at least two seconds. Nozzles located at the entry of the post-combustion chamber inject at high velocity the recirculation fumes (in order to reduce nitrogen oxides), and the secondary air, which completes the fume oxidation. Two methane-fuelled support burners which turn on automatically based on the fume temperature ensure that the temperature is maintained, even if there is waste with a low calorific value. The control room is responsible for monitoring and it monitors all stages of the process and all parts of the plant 24 hours per day, continuously ensuring that they are safe and operating correctly.

    3 - Steam generation.
    The water-tube steam generator consists of three vertical channels followed by a horizontal area where the superheaters and economisers are located. The boiler is designed to achieve high thermal efficiency, and therefore it is equipped with a superheater to increase thermal efficiency and an economiser to recover heat from the fumes.
    The superheated steam produced at 440°C and 50 bar is sent to the turbo-alternator to generate electricity and heat. The economisers and superheaters are cleaned by a mechanical percussion cleaning system. The fly ash coming from the boiler is collected and sent to a grinder to reduce the size of any crusts and subsequently to the two particle storage silos, together with the particles extracted from the fume cooling tower and those filtered by the bag filter. The particles, classified as hazardous waste, are then sent to a neutralisation plant.

    4 - Fume purification.
    The combustion fumes exiting the boiler go through the treatment system, which is broken down into several phases: gas humidification in the cooling tower, dry reaction, physical particle separation in the bag filter, fume cleaning in the wet scrubber and DeNOx and DeDiox effect (abatement of nitrogen oxides and dioxins) in the SCR process (catalyser). To ensure effective abatement, the fume temperature is lowered from 160-200°C (temperature at which it exits the boiler) to 150°C in the cooling tower, or quencher. In the first part of the cooling tower, in the shape of a cyclone, the coarse particles carried by the fumes are separated. In the second, the fumes are cooled through the injection of water mist and the resulting evaporation. Downstream from the cooling tower, the reactant is injected into the line, with the dual purpose of improving the abatement of pollutants in the fumes and reducing consumption in the subsequent washing column. The next step is separating particles from the fumes in the bag filter, consisting of several internal cells which work independently. The particles discharged by the filter are partially recirculated and sent to the dry reaction section, in order to maximise the exploitation of reactants, and partially sent to the two particle storage silos with a pneumatic transport system. Outside the filter is a primary heat exchanger, which has the dual function of cooling the exiting fumes to facilitate the absorption of acid substances in the scrubber and of heating the flow coming out of the washing column before being injected into the SCR system. The scrubber is divided into two stages, one acid and one neutral. The acids are absorbed in the lower section. The recirculated watery solution is partially purged and sent to the water treatment plant.
    In the upper stage, SO2 and the remaining traces of acid still present are removed. The stage of neutralisation with a 30% caustic soda solution includes a plate system for fumes/liquid contact. An organic precipitating agent is injected to improve the abatement of heavy metals.
    Before exiting the washing column, the fumes go through a drift eliminator which removes liquid droplets to prevent them from entering the heat exchanger. The fumes exiting the scrubber go through the primary heat exchanger and are sent to the pre-heating system needed to reach the optimal temperature for the catalytic reaction (220-240°C). The system consists of a secondary heat exchanger fuelled by the fumes exiting the SCR reactor and a methane burner, which provides additional heat to reach the desired temperature. The DeNOx DeDiox process (SCR) uses a 25% ammonia solution needed for the reaction to reduce NOx, which results in an abatement of nitrogen oxides and dioxins. Before the purified fumes are sent to the chimney, heat recovery takes place in a third exchanger, which pre-heats the condensate in the thermal cycle. The combustion fumes are extracted through the draught fan found downstream from the fumes washing section and upstream from the catalytic DeNOx (abatement of nitrogen oxides) and the chimney.

    5 - Cogeneration of electricity and heat.
    The waste-to-energy plant is intended to obtain energy from waste through a cogeneration system, which uses steam generated by combustion and transforms it into thermal energy and electricity.
    The superheated steam (440°C and 50 bar A) produced in the waste-to-energy lines is sent to the cogeneration plant consisting of a two-stage turbine with two steam discharges, connected to a synchronous electric generator. The steam released from the turbine is collected in a main vacuum condenser. If the turbocharger is not working, the steam is sent to a by-pass circuit including a desuperheater and an auxiliary condenser. The plant has high thermoelectric efficiency due to the boiler integrated with the combustion chamber and the recovery of heat from fumes, which are cooled to 180°C when released from the boiler. During the procedure, the exchangers located on the condensate circuit carry out a series of heat recoveries. In terms of the most significant thermal absorption, an initial low-pressure steam discharge fuels the exchangers for district heating and the degasser, while a second discharge is sent to the regenerative exchanger which is responsible for increasing the condensate temperature to improve thermal cycle efficiency. A subsequent recovery is carried out on fumes released from the SCR which transfer heat to the condensate before entering the degasser. The condensers are cooled by a circuit of cooling towers mainly fed by surface water from Bonifica Renana. The main circulation pumps send the water to the two condensers connected in succession and subsequently to the cooling towers to be cooled. An auxiliary pump (booster) boosts the water for other users. The energy recovered by the cogeneration plant is converted into electricity to be delivered to ENEL and thermal energy to be transferred to the district heating network which provides heat to the Via del Frullo plant, to a methane gas decompression substation located close to the plant, and to the Agricultural and Food Centre of Bologna (CAAB) and the Pilastro neighbourhood in Bologna.

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    • The plant is equipped with a Continuous Emissions Monitoring System which has automatic analysers functioning 24 hours per day to continuously monitor the quality of atmospheric emissions.
      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 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 and pressure.

      Atmospheric emissions controls have been increased since 2009 through sampling and the occasional analysis of PCDD + PCDF (dioxins) and Hg (mercury) parameters. A back-up chimney gas analysis system was also installed to ensure continuous monitoring even if the main system fails.

      A data acquisition system (SADE) 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. These data are also provided on the group´s website, where they are automatically updated every half hour.

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    Termovalorizzazione dei rifiuti: smaltimento sicuro con recupero di energia
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