The system is constituted by a combined cycle power station (gas cycle: Brayton, steam cycle: Rankine), intended to the production of electricity and steam.
This power station consists of two gas turbines and a steam condensation turbine with extraction; each machine has its own electric generator with a total authorized capacity of approx. 148.5 MW and steam for the factory of about 30 t/h in normal conditions.
The rated thermal power authorized by the Power Station is 299 MW thermal, equivalent to approximately 148.5 MW electric.
The plant is designed for a continuous operation; the production of electricity is sold at 132 kV voltage.
The medium and low pressure steam is transferred to the plant for technological uses depending on the demand of the production plants.
Gas turbines (no. 2-60 MW of rated power), use natural gas as the only fuel taken from the pipeline. The exhaust of each turbine is conveyed to a steam generator which recovers the sensible heat of the gas discharged for the production of steam on two pressure levels, 60 bar and 6 bar.
Then the fumes are cooled to a temperature of approx. 110°C and are introduced into the atmosphere through no. 2 chimneys 40 m tall.
The steam produced by the boilers is sent to a steam turbine (54.7 MW rated power), and, when required, a portion is entered to the distribution networks of the industrial facility in addition to what produced by the power station.
The steam discharged from the turbine is condensed in an air cooled heat exchanger.
Each turbine, gas and steam, activates its own electric generator (each 70 MVA), whose combined production is fed into the national grid.
The demineralized water, which is necessary to produce steam in the boiler, is acquired by the plant, which produces it using raw water taken from the river.
Then water from the cooling tower is used to remove the heat from the closed loop cooling cycle of the machine lubrication circuits. After passing in the heat exchangers water is returned to the cooling tower.
Gas cycle and recovery boiler section
The power station is composed of two sections (lines) each comprising a gas turbine and a boiler (150 MW thermal), which produces steam (85 t/h in high pressure and 16 ton/h in low pressure), recovering the heat of fumes discharged from the turbine.
The recovery boiler is considered together with the gas turbine because, since there is no by-pass chimney, the gas turbine and boiler always operate together.
In the gas turbine it is possible to clearly distinguish the three sections: air compressor, combustion plant and turbine. The environment air sucked by the compressor undergoes a filtration process to remove the most of the suspended particles that can dirty the compressor blades decreasing its efficiency. Therefore, the compressed air enters the two combustion chambers, where the temperature is increased by burning natural gas. The gas coming out from the combustion chambers, with residual oxygen around 15% by volume, invests the turbine blades rotating at 5430 rpm. The turbine is rigidly connected to the compressor on the same shaft which transmits the motion to the electric generator with the interposition of a reduction gear.
The gas discharged from the turbine at a temperature of approx. 540°C enters into the recovery boiler, where steam is produced from the heat recovered, that is then sent to the next section of the steam turbine (steam cycle). There is no additional combustion in the boiler. Then the gas is sent to the atmosphere by means of a chimney, 40 meters high, placed on top of the boiler, at a temperature of approx. 110°C.
On each flue is installed an analyzer for the continuous monitoring of the NOx and CO pollutants, in addition to residual oxygen and humidity from the fumes, data required to return the NOx and CO values to the dry fumes reference and 15% of O2.
A single lubrication oil circuit serves the main machines of the section: gas turbine/compressor, speed reducer and electric generator, for each individual gas turbine.
The vapors that are generated by the oil casing are largely reduced by an electrostatic filter and recycled in the same casing.
Continuous water discharges are generated from this section due to the production process. They are the continuous drains from the cylindrical boiler bodies that contain phosphorus, residue of the boiler water alkalizing treatment. These discharges are sent to water treatment together with any contaminated waste oil.
These drains, conveyed into the sewer system of the plant, then flow into the local channel.
As solid waste originating from the production process only the filter panels for the suction air of gas turbines are indicated, which are disposed at the end of life by specialized companies, and other solid wastes originate during the power plant maintenance.
Finally the solid waste similar to urban waste are sent to the Public Service provider. The raw materials used in this section are:
Natural gas: only authorized fuel, taken with the pipe directly from pipeline.
Ambient air: drawn directly from the surrounding environment and used, after compression and heating, as a motor fluid of gas turbines.
Demineralized water: used for the production of steam in the boiler and directly withdrawn by piping from the neighboring water treatment plant.
Steam cycle section
The power station is composed of a single steam cycle section.
In this section convey the high and low pressure steam flow produced by the recovery boiler to be entered in the steam turbine.
Part of the steam can be sent to the distribution network of the industrial facility, if it consists of medium pressure (18 ate) it is laminated by the boiler high pressure, if it consists of low pressure it is extracted from the steam turbine or, if insufficient, sent directly from the boiler production. After working in the turbine, the steam is condensed in an air exchanger, and the condensate is recovered to be re-entered in the boiler circuits.
During the initial stages of start-up of the power plant, the steam is sent directly to the condenser by- passing the steam turbine.
The steam turbine drags an electric generator rigidly connected on the same axis. Water discharges are those described in the previous section.
Auxiliary systems and infrastructure
In addition to all the components which are part of the production cycle of the process, the power plant is equipped with the following infrastructure and auxiliary plants:
1. Electrical substation for connection to the 132 kV national grid.
2. Natural gas decompression station, where the gas withdrawn from pipeline has reduced pressure and then sent to the system.
3. Lighting systems, telephone, intercom, door phone, closed circuit cameras (for safety), ground network and cathodic protection where necessary;
4. Water pumping plant, for the whole multi-company plant, and managed by company;
5. Emergency electric generator with 480 kW diesel engine.
6. Fire detection and extinguishing system.
7. All detection systems, alarm and automatic fire-extinguishing system, provided within the power station are monitored by a directed control panel, installed internally to the Control Room always manned by the Power Station operators.
Plant consists of following main equipment:
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