Practical experience is the best teacher for the next generation25 March 1999
Amid the rice fields of the Lomellina area, in the small town of Parona some 24 km southwest of Milan, Italy, Foster Wheeler is building what may be a benchmark integrated waste-to-energy plant for the new millennium. Design of the 16 MWe plant has benefitted from experience gained at the Robbins facility in the USA.
There is now limited choice between landfill and the burning of Municipal Solid Waste (MSW) in Europe. Most European countries now have or soon will have two mandates in place: first, that no waste can be landfilled without first having undergone a thorough treatment process that is aimed to recycle and recover any available resource, second, that any facilities burning MSW must meet new, more stringent emissions requirements. The first limits the opportunities for landfill; the second makes incineration a technically challenging operation.
The Lomellina waste-to-energy (WTE) plant, located near Milan, Italy, is being jointly designed and built by Foster Wheeler Italiana and Foster Wheeler Power Systems. The design of the Lomellina plant has been influenced by the experience which has been gained by Foster Wheeler from the Robbins waste-to-energy/recycling facility, in Illinois, USA, owned and operated by Foster Wheeler Illinois. Since the plant began commercial operation, the technology incorporated in the Robbins facility has been used as a showcase for the environmental advantages of an integrated waste-to-energy/recycling facility over landfill.
The Robbins plant has shown that experience is still the best teacher, and has helped guide the design philosophy of Foster Wheeler's waste-to-energy plants.
The Lomellina project
Lomellina is a unique project in several ways. It is a build-own-operate project developed and financed by Foster Wheeler. It will also be designed, constructed and operated by Foster Wheeler. It will have the first circulating fluidized bed (CFB) boiler in Italy, and is the first WTE plant financed through limited recourse project financing.
The Lomellina facility will only accept MSW from some 30 surrounding communities within a 30 mile radius of the site. It will not accept industrial or hazardous waste.
Lomellina will have a single boiler train and one turbine generator. Work on the project began in the first quarter of 1998, and the facility is scheduled to begin pretreatment operation by late 1999, and complete commercial operation by mid 2000. When fully operational, it will burn 400 tons of refuse derived fuel (RDF) daily, equivalent to 200 000 tons annually of municipal solid waste. It will have an electric capacity of 16 MWe, which will be sold entirely to ENEL.
Foster Wheeler Italiana worked closely with local governments during the planning and engineering phase, and is continuing that effort now that construction is progressing. For example, Lomellina will have a two phase start up. In order to ease landfill problems for the nearby communities that will be sending their MSW to the Lomellina facility, Foster Wheeler has agreed to begin receiving the MSW as early as October 1999. This will also work to Foster Wheeler's advantage, since it will allow the facility to begin fuel preparation early, ensuring that there is a more-than-adequate supply of fully prepared RDF when commercial operation begins.
The plant has been designed to burn only RDF; no supplementary fuel will be required for normal operations. The boiler will require natural gas as a start-up fuel to bring the furnace to the temperature that is required for efficient burning of RDF (which will take about 6 hours, according to the current calculations), and for a shorter period to burn all RDF that remains in the furnace prior to the boiler being shut down for maintenance procedures. The natural gas is needed as a start up and shut down fuel because RDF has to be burned at a certain temperature, which is high enough to ensure that the plant meets mandated emissions limits.
Foster Wheeler recognised that a good deal of the Robbins facility could be used to design Lomellina. Robbins could provide data needed to determine what had worked well, what areas could use improvement, and where changes would be necessary for the Lomellina plant. In effect, Robbins would provide the starting point and become the stepping stone to the next generation of integrated waste-to-energy plants.
Lessons from Robbins
Foster Wheeler engineers assigned to the Lomellina project spent a lot of time at the Robbins facility studying the physical plant and every phase of its operations. Perhaps the one fact that became most clear to everyone during this 'analysis phase' was the enormous impact the quality of the fuel used has on the overall operations and efficiency of a WTE facility. High quality fuel is vital if operating and maintenance problems are to be eliminated. This understanding played a key role in the eventual design of the fuel preparation system at Lomellina.
WTE plants are becoming increasingly popular in Europe. This is mainly because there is limited space for landfills, severe restrictions on waste to be landfilled, and growing recognition that these plants provide the most efficient means of recovery of all recyclable content of MSW. The more stringent emissions requirements that have recently been mandated in Europe also favour the use of circulating fluidized bed (CFB) boilers. The Robbins facility demonstrated that CFB technology is capable of burning RDF efficiently, and that it has no problem meeting mandated emission levels.
When it is operational, the Lomellina plant will remove glass, organic material, aluminium and other non-ferrous/ferrous metals first for recycling. All compostable materials in the MSW itself will be separated and delivered to the composting facility. Other organic materials, such as grass clippings, leaves and tree limbs, will be chopped and then also deposited for composting. The site will include a very large state-of-the-art composting facility for this waste.
The inert and organic separation and the RDF preparation will be carried out through low-speed shredders, trommels and high-speed shredders. Magnetic and eddy current separators along the conveyor lines will reduce to a minimum metals in the fuel.
Emphasis was placed on fuel quality during the design of Lomellina, as this considerably reduces other problems. For example, experience at Robbins showed that the key to avoiding problems in ash-removal was proper fuel preparation. One of the most important factors in fuel preparation is the elimination of ferrous materials. It is believed that the Lomellina design, which contains a two-stage shredder/trommel fuel preparation system, should efficiently eliminate ferrous materials. Central to the design concept at Lomellina, therefore, is to provide the highest possible quality of fuel to the facility.
Design of the emissions control system was another area that has been heavily influenced by the experience gained from the Robbins plant. It was decided that, unlike Robbins, Lomellina would have an 'all-dry' emissions control system. One consideration in the design of Lomellina was the fact that most emissions limits are lower in Italy than the USA.
The Lomellina plant will have flue gas temperature control, a dry scrubber that will use injected lime to reduce acid gases such as SO2 and HCl, and activated carbon injection into the scrubber system to reduce mercury emissions. Finally, a baghouse will be used to collect particulate matter such as dust and fly ash to prevent them escaping up the stack. This results from the fact that, in addition to lower emissions levels in Europe, fly ash is also considered and treated as a hazardous material in most of Europe.
In Europe, bottom ash can be used, as in the USA, for road aggregate or for landfill cover. However, fly ash has to be treated differently in Europe than in the USA. It is mixed with cement and a neutralising agent, and formed into concrete blocks that encapsulate both the ash and the heavy metals that were captured. These blocks are then deposited in landfills.
Comparing the two plants
The Robbins waste to energy facility, with a capacity of 600 000 t/year of MSW, is considerably larger than Lomellina. With the decision to build the Lomellina facility, Foster Wheeler recognised that there was an opportunity to implement a new generation of WTE plants. There was enough history at the Robbins plant to recognise that improvements could be made for the next generation of such facilities.
The question of fuel preparation, and in particular putting more emphasis on the removal of metals and other inert materials, was perhaps the most visible improvement. Robbins has two boiler trains, with the fuel preparation system consisting of two parallel lines, each with one shredder and two trommels. By contrast, Lomellina has one boiler train with two parallel fuel preparation lines consisting of two shredders and one trommel. At the Robbins plant, the MSW is delivered and dumped on a flat floor, which requires a large space. The Lomellina facility was designed with a large pit for the MSW, considerably reducing the amount of land required for MSW storage.
These are only the most visible differences. The Robbins facility was used as a test ground for the technology. As a result, everything from the boiler downwards was examined and evaluated to see where improvements could be made.
TablesKey dates Basic data for Lomellina waste to energy plant