The Ecoenergia SRL WtE plant is located in Corteolona of Pavia in Italy and has been in operation since 2004. The Plant has first designed to treat 7,5 t/h of Municipal Solid Waste Residual Fraction.

At the Plant the combustion and recovery sections are integrated to each other since furnace walls are of membrane design. In the following a short description of the system is provided.

System Description

In the bubbling fluidised bed boiler (BFB), combustion takes place in a bed consisting of bed material and fuel ash. The bed is held in suspension by an upward flow of combustion air. The air flow and velocity are chosen to give intense mixing of material with minimum of carry-over of particles out of the furnace. The combustion in the BFB takes place in the dense bottom bed except for the fines in the fuel which burn in a particle suspension above the bed.

To further enhance the combustion and reduce the emissions, the front, rear and side walls of the furnace are equipped with asymmetrically placed arches through which combustion air and re-circulated flue gas is introduced. The intense mixing allows the BFB to operate at low excess air levels.

Membrane wall construction provides a fully water-cooled and gas tight furnace enclosure.

To achieve the right bed temperature and to protect the lower part of the furnace from erosion and corrosion, the lower part of the walls are lined with refractory material (rammed or gunned refractory).

To ensure that the temperature of the flue gas is at least 850°C for at least two seconds after the last injection of combustion air, the major part of the upper furnace walls will be covered by refractory lining.

Primary air is fed to the boiler windbox below the furnace and up through the reactor bottom in a large number of aligned erosion resistant nozzles. The overfire air is supplied in several stages. Secondary, tertiary and cross air (side walls) is supplied through nozzles located above the fuel inlet on the front and rear wall to maintain a good penetration throughout the entire load range, The secondary and tertiary air nozzles are directed to promote circulation of bed material above dense bed.

Special flue gas swept plates are located below the fuel chutes in order to provide an increased distribution of the fuel into the combustion chamber.

Downstream furnace an empty pass cavity is installed. The empty pass ( radiation cavity) is made of membrane walls and it is designed to reduce the flue gas temperature prior to the superheaters to avoid sticky components from building up on the tubes. The radiation pass is divided in several parallel gas passes by vertical water cooled tube screens.

Flue gas coming from the empty cavity enters the rear convection pass enclosure. The rear convection path enclosure is of similar membrane wall design as that of the furnace. It contains orizontal exchange surfaces and in particular:

• Superheater
• Boiler bank
• Economiser

Air Pollution Control System

The airpollution control system includes 2 cyclones in parallel and one bag house filter for the removal of particles (dust control) that achives more thatn 99.99% reduction. Moreover the unit is equipped with a semi dry type Scrubbing to conduct chemical gas cleaning. In addition NH₃ in water solution is injected in the combustion section by means of compressed air distributing lances to remove NOx. NOx reduction is achieved by 55-60%. Activated carbon is used for Hg removal.

Treatment of the Produced Ash

• Cyclones ash is treated on line. Cement, water and additives are injected directly in the ash extraction system which is installed on the bottom of the cyclones .Treated ash is discharged in closed container and disposed in the landfill which is available nearby the combustion plant.
• Boiler ash is disposed in the landfill.
• Bag house filter treated by external authorized plants.
• Bottom ash undergoes metal separation (ferrous and non ferrous), sand recovery and recirculation in the fluidized bed.