Combustion of Poultry Derived Wastes for Smart Energy Recovery

Due to the stringent and explicit European environmental legislation about land spreading of nitrates, the direct land application of the poultry litter is not anymore the most appropriate disposal technique. We investigated the combustion of pure common poultry derived wastes and mixtures of these with olive pomace in a domestic burner optimized for wood pellet combustion. Typical waste and product streams based on combustion tests were characterized for the different mixtures (100%w to 50%w poultry litter content). We observed that the high CO emissions compared to wood pellet combustion but can be reduced by optimizing combustion; the size distribution function of particle is not influenced by poultry litter content; the inorganic elements are mainly concentrated in ashes. Introduction Currently, due to the stringent and explicit European environmental legislation about land spreading of nitrates, the direct land application of the poultry litter is not anymore the most appropriate disposal technique [1]. Composting is an alternative to direct land application, which results in reduced volumes for disposal, improves consistency of waste, and the elimination of pathogens, although additional equipment and handling costs are incurred and the problems of nutrient run off and heavy metal contamination remain [2, 3]. Nevertheless, scientists and poultry industry leaders are being challenged to find alternative ways of managing poultry litter [4, 5]. Many possible alternatives have been investigated and attempted. All have some merit, but one very good solution is utilizing poultry litter as a fuel to generate clean, renewable energy [6]. In such a context, the Italian situation is undergoing a juridical battle in considering poultry litter as a Biomass as done in the European Community law of 2009 for energy production. The question is to consider or not this waste as a biomass for energy production. Setting aside the political and juridical debate, a poultry litter facility is being built in Umbria region of Italy by the Novelli Group. The objective of the technology based on fluidized bed is to manage a large quantity (5 t/day) of poultry litter producing an efficient and economical operation, while keeping low emissions. The worldwide past experiences regarded the commissioning of large power plant fuelled by poultry litter and then presented important problems of soil contamination, bacteriological management of the areas and pollution due to the XXXV Meeting of the Italian Section of the Combustion Institute 2 waste transportation [7]. In alternative, according the recent European guide lines concerning the smart grids, the generation of electricity and heat from poultry derived wastes based on high-temperature thermal destruction techniques, i.e. combustion, could be a promising local waste management solution [8, 9]. An extensive and interesting review of the recent large-scale power plants fuelled by poultry litter present in Europe is presented by Florin et al [10]. Nevertheless, there remain technical and operational challenges associated with the processing of poultry wastes due to the variability of the waste stream and high costs in comparison to direct land utilization. With the increasing tendency for energy generation from renewable sources and the anticipated introduction of more stringent environmental legislation, we contend that combustion will become economically viable option in the future. Opportunities for improving the economic viability also exist with the co-combustion and/or gasification of poultry derived waste with other agricultural and forestry wastes. In this paper we investigate combustion of pelletized common poultry derived wastes (i.e., manure, bedding and a mixture of these with olive pomace). Waste preparation We used the waste production of a medium scale breeding settled in Italy as a representative basis for estimating the potential for energy production from poultry litter. The best solution was to pelletize the raw material. This generated a high versatility of the fuel; it can be easily produced and stocked on-site before being burnt. In this study we used a simple wood pellet machine. Poultry litter (moisture 35 %wt) was preliminary mixed with olive pomace (moisture 5%wt) before being pelletized. Blends containing up to 70%wt of poultry litter were prepared. Higher poultry content lead to a squashy product definitively not suitable for the whole process management. Moreover, the mechanical properties of the so-prepared pellet were not satisfactory and they did not allow the pellet to be correctly fed by the screw conveyor. Then, further experiments were performed on the optimization of the mechanical properties of the blends. The best conditions were obtained with a moisture content of 10 %wt in the poultry litter. Blends from 100%wt down to 50%wt of poultry litter were then possible with satisfactory feeding to the burner. The characteristics of the different blends (Poultry Litter PL/Olive Pomace OP) are presented in table 1. Table 1. Average composition and chemical properties of the pellets. pellet 100%PL pellet 70%PL pellet 60%PL pellet 50%PL Pellet 100%OP Gross heat value, kcal/kg 3,198 3,895 4,064 4,407 4,931 Net heat value, kcal/kg 2,834 3,350 3,455 3,963 4,752 Moisture, %wt 10 8 8 8 5 Ash content(dry basis), %wt 27 23 17 15 4 C %wt 34.8 39.6 41.1 45.0 51.8 H %wt 4.26 4.91 4.88 5.52 6.22 XXXV Meeting of the Italian Section of the Combustion Institute 3 N %wt 1.79 1.38 1.41 0.91 0.59 O %wt 43.7 44.5 44.9 42.7 39.2 S %wt 0.65 0.63 0.61 0.60 0.51 Cl %wt 0.87 0.90 0.84 0.70 0.52 Ca ppm 74,879 38,427 27,596 20,405 2,348 K ppm 37,675 27,395 24,296 18,986 12,154 P ppm 16,454 10,014 8,369 5,733 541 Mg ppm 6,067 3,857 3,203 2,372 221 Na ppm 3,981 2,522 2,087 1,458 58 Al ppm 2,799 2,255 1,370 1,230 271 Fe ppm 1,657 1,161 889 802 513 Mn ppm 622 399 315 168 10 Cu ppm 280 118 100 69 12 Zn ppm 322 252 174 117 6 Ba ppm 29.7 50.4 22.8 14.3 4.0 Cr ppm 22.2 13.3 14.0 17.8 1.6 Co ppm 3,2 1,9 1,5 1,1 0.1 Ni ppm 10.3 5.7 6.0 7.3 2.1 V ppm 9.8 6.6 5.2 3.7 0.3 Na+Ca+K+Si+Mg+Cl, %wt 13.13 8.12 6.56 5.02 2.00 Combustion results Experimental set-up The experiments were performed in a 50 kW house-built pellet burner inserted in a water-cooled closed fire-place. The pellets were fed to the burner head by mean of two screw conveyors. The pellet flow rate was kept constant for all the experiments. The energy exchanged to cooling water was kept constant. The combustion air was also kept constant and was fixed to the oil pomace value in the electronic remote control. The burner parameters were previously optimized for the oil pomace combustion. The objective of this paper is to compare combustion performances of the different pellets keeping constant the combustion parameters. During the experiments the exhaust gas temperature and the stable gases concentrations (CO, CO2, NO, SO2) were continuously measured. Sampling was performed tree times for each blend in order to measure the average concentration and the size distribution of the particles. The determination of the particulate matter was performed according to the EN 13284-1:2003. Isokinetic sampling was performed at the exhausts of the boiler and the samples were size-segregated by means of an 8-stages Andersen impactor. No dioxin analysis was performed due to its time consuming procedure not compatible with laboratory scale. Finally, a complete chemical analysis of the ash was performed after each run. XXXV Meeting of the Italian Section of the Combustion Institute 4 Test results The first comment regards the ignition of the pellet. Only pellets for blends up to 50%wt of poultry litter (PL) can normally ignite, while higher PL content in the pellets generates smoke without ignition. Combustion of 100%wt PL pellet was possible but it suffered from coarse stability. On figure 1.A-D are represented the observed flame for 100%wt PL, 70%wt PL, 60%wt PL, and 50%wt PL respectively. Figure 1. Flame aspect for the different poultry litter content: 100%wt PL (a), 70%wt PL (b), 60%wt PL (c), 50%wt PL (d). We can clearly observe from the figure 1 that the flame intensity increases while decreasing the poultry litter content. For PL content higher than 60%wt we have a large presence of smoke around the flame; and we can note a more important ash accumulation in the bed of the burner. The combustion performances were followed by continuously sampling exhaust gas. The time evolution of the CO, NOX, O2 concentrations are presented in Figure 2. All the results are on dry basis. 0 20 40 60 80 100 120 Time, [min] 0.1 1 10 C O , [ % ] 100% 50% 0 20 40 60 80 100 120 Time, [min] 10 10