Distributed mixed-integer fuzzy hierarchical programming for municipal solid waste management. Part II: scheme analysis and mechanism revelation.
The scope of this work is to study the co-combustion of a solid recovered fuel (SRF) produced from household wastes and packaging wastes recovered from selective collection (SC) in the autonomous community of Navarra, located in the northeast of Spain. The municipal solid waste (MSW) is subjected to a mechanical biological treatment (MBT) in order to stabilize the organic matter and recover the recyclable materials as it is done for packaging wastes. Afterwards, rejects from this treatment plant were preconditioned and compressed by a pelletizing process to produce a secondary fuel according to quality and classification criteria of EN 15359, producing the so-called SRF. A fuel characterisation was carried out according to CEN standards and the SRF was classified as follows: NCV 2; Cl 3; Hg 1. SRF pellets were cofired with residual biomass pellets from olive tree pruning (OTP) in a bubbling fluidised bed combustor, as an option of energy recovery. The mixture of fuels, with a mixing ratio close to 50% by weight, showed a significant calorific value of 18.25 MJ/kg at 8% of moisture content. In addition, elemental composition of the mixture based on nitrogen (N), sulphur (S) and chlorine (Cl) (1% N, 0.2% S and 0.4% Cl) was not far from some herbaceous biomasses. The co-combustion showed good results as an energy recovery technology because of the synergies of both fuels, improving notably the combustion conditions and reducing significantly CO concentration, regarding to the combustion of OTP, though other contaminants such as NOx and HCl increased. During eight hours of stable operation, the concentration of dioxins and furans was measured obtaining a value of 7.68 ng/Nm(3) (toxic equivalence: i-TEQ of 0.33 ng/Nm(3)). Proportions of SRF lower than 50% in the mixtures should be tested in order to cut down the emissions of these pollutants, or an abatement system for organochloride compounds may be required.