Thermal degradation of paper industry wastes from a recovered paper mill using TGA. Characterization and gasification test.

In this survey, a refuse derived fuel (RDF) was produced from paper industry wastes through a mechanical treatment (MT). The two main wastes generated from a recovered paper mill were rejects and de-inking sludge, which were produced principally in the pulping and de-inking processes, respectively. This work presents raw wastes characterization, fuel preparation and gasification tests performed in a circulating fluidized bed (CFB) gasifier pilot plant. The characterization was carried out by proximate and ultimate analysis. Several blends of pre-conditioned rejects and de-inking sludge were densified by means of pelletizing, studying the energy consumption and its quality properties. Besides, thermal degradation of blends was studied under thermogravimetric analysis (TGA). The experimental runs were made from 30 to 900°C in nitrogen atmosphere at three heating ranges, ß=5, 10 and 20°C/min. Two thermal stages were identified during the thermal degradation, which are linked to cellulose and plastic degradation. In addition, kinetics parameters were estimated by the application of non-isothermal methods: Kissinger-Akahira-Sunose (KAS), Flynn-Ozawa-Wall (FOW) and Coats and Redfern. The activation energy values were about 140-160 kJ/mol and 60-80 kJ/mol for plastic and cellulosic materials, respectively. Regarding waste valorisation, a blend composed of 95% of rejects and 5% of de-inking sludge was selected for gasification tests. The energy consumption during the preparation was recorded and a gasification tests were done to prove the usability of these pellets in a CFB gasifier. The main results were a net calorific value (NCV) of 5 MJ/Nm(3) and a total tar content of 11.44 g/Nm(3) at an equivalence ratio (ER) of 0.3.

Classification and characterisation of SRF produced from different flows of processed MSW in the Navarra region and its co-combustion performance with olive tree pruning residues.

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.