Handling, storage and milling. The existing secondary fuel handling system of Kardia PP is capable of handling biomass fuels with characteristics similar to olive kernels (small particle size, grindability comparable to fossil fuels and not herbaceous biomass). On the contrary, it is unsuitable for handling baled biomass, since constant feeding is not assured. Accumulation of biomass appears to be the main issue, while suitable particle size reduction is not guaranteed. The mill recirculation system can be bypassed even by quite large biomass particles. This might be a risk factor. The existing, not for biomass optimised, fuel handling system has little difficulties with olive kernels. Feeding system. No material accumulation was attested in any part of the feeding system during co-firing with olive kernels, whereas significant cardoon quantities were found practically blocked in several places long the feeding line when baled biomass was used. The feeding of a homogenized mixture of chopped cardoons and lignite at Kardia PP and of xxxxxxx and lignite at Meliti PP did not cause any feeding issues; however, it required significant planning on the part of the coal yard operator and increased expenditures for the fuel mixing.
Handling, storage and milling. The RDF has been successfully co-fired at Fusina PP since 2004. In February 2009 the permitting procedure to double RDF annual amount up to 70.000 tons was completed and, as a consequence, RDF has been increased up to 9t/h on each unit at full load on both units 3 and 4. This is one of the first examples of an integrated management and thermal treatment of Municipal Solid Waste (MSW) in Italy. The MSW management system includes a plant for the RDF production, a RDF power plant and a section for compost production, in order to provide suitable treatment for every type of waste. The processes and the main products of the MSW management scheme are shown in Figure 8. Figure 8: Scheme of the MSW management process. At Fusina, the RDF is received at the station (Figure 9), and sent to two large storage silos. The RDF is then fed out of the silos and conveyed through ferrous and non-ferrous metal separation units to four high speed hammer xxxxx. The size grading of the milled RDF varied with time between hammer and screen changes, due to erosion, but the following ranges of values were reported: 100% < 5 mm 50-70% < 2 mm 25-40% < 1 mm 15-30% < 0.5 mm The milled material is then conveyed pneumatically to Units 3 and 4, and in each case the RDF is injected directly into primary air fans. the pulverised coal pipes, at a location just upstream of the The RDF is co-fired through the burners in levels 2 and 3 only, i.e. two of the central burner levels. In this way, there are normally coal flames both above and below the burners co-firing the RDF to support the combustion process. This type of co-firing pattern is commonly employed and helps to maximise the combustion efficiency of the RDF. This helps to minimise the unburned fuel levels in both the furnace bottom ashes in the boiler hoppers and the fly ashes collected in the electrostatic precipitator hoppers.
Handling, storage and milling. Firing of biomass started in 2007, when two fuel lines (fuel bunker, xxxxx and burners) were retrofitted to allow the biomass transportation – mainly wood-chips and saw-dust. Basically, new and larger electric motors were installed to the xxxxx and new burner configuration was applied. In addition, an External Fuel Recirculation (EFR) system was built to recycle solid material from the furnace bottom upstream of the xxxxx. In this way, the heat loss due to the UBC in the bottom ash could be reduced. Two ways are possible to overcome the feeding problems of agricultural by-products to PC plants. One is building a new feeding facility for biomass handling and feeding, which is a very expensive solution and power utilities are reluctant to invest, while the other is pelletising the material near the source of production. In the latter case, also used for the testing activities at Dorog PP, the technology is capable of feeding pellets without major investment at the plant. However, extra costs are due to the pellet production plant, and the price of the pellets, as of now, is higher than that of wood-chips and saw-dust. Biomass/coal co-firing was tested at Dorog PP at 50% biomass thermal input. The biomass fuel consisted in a mixture of barley straw pellets an wood-chips, sunflower hull and wheat bran. The tests were performed at 85% boiler load. Two separate fuel lines were used for coal and for the pellets, so they did not mix before the flame. One bunker fed two biomass xxxxx and one bunker one coal mill. The biomass feeding was not always continuous due to the inhomogeneous mixture. Wood-chips tended to form craters in the bunker and for avoiding plugging, mechanical agitation of the material was necessary. Figure 10: Dorog PP fuel handling and feeding system.
