Abstract
The present work studies the possibility of energy recovery by thermal conversion of combustible residual materials, namely tires and rubber-plastic, plastic waste from outdoor luminaires. The waste has great potential for energy recovery (HHV: 38.6 MJ/kg for tires and 31.6 MJ/kg for plastic). Considering the thermal conversion difficulties of these residues, four co-combustion tests with mixtures of tires/plastics + pelletized Miscanthus, and an additional test with 100% Miscanthus were performed. The temperature was increased to the maximum allowed by the equipment, about 500 °C. The water temperature at the boiler outlet and the water flow were controlled (60 °C and 11 L/min). Different mixtures of residues (0–60% tires/plastics) were tested and compared in terms of power and gaseous emissions. Results indicate that energy production increased with the increase of tire residue in the mixture, reaching a maximum of 157 kW for 40% of miscanthus and 60% of tires. However, the automatic feeding difficulties of the boiler also increased, requiring constant operator intervention. As for plastic and rubber waste, fuel consumption generally decreased with increasing percentages of these materials in the blend, with temperatures ranging from 383 °C to 411 °C. Power also decreased by including such wastes (66–100 kW) due to feeding difficulties and cinder-fusing problems related to ash melting. From the study, it can be concluded that co-combustion is a suitable technology for the recovery of waste tires, but operational problems arise with high levels of residues in the mixture. Increasing pollutant emissions and the need for pre-treatments are other limiting factors. In this sense, the thermal gasification process was tested with the same residues and the same percentages of mixtures used in the co-combustion tests. The gasification tests were performed in a downdraft reactor at temperatures above 800 °C. Each test started with 100% acacia chip for reference (like the previous miscanthus), and then with mixtures of 0–60% of tires and blends of plastics and rubbers. Results obtained for the two residues demonstrated the viability of the technology, however, with mixtures higher than 40% it was very difficult to develop a process under stable conditions. The optimum condition for producing a synthesis gas with a substantial heating value occurred with mixtures of 20% of polymeric wastes, which resulted in gases with a calorific value of 3.64 MJ/Nm3 for tires and 3.09 MJ/Nm3 for plastics and rubbers.
Highlights
For the development of a country, high investments are required for electric power generation
Rubber produced a greater amount of synthesis gas than forest biomass. These results suggest an important role for the co-gasification of plastics of biomass and rubber additions when working at high temperatures
Tire combustion tests have shown that SO2 emissions are constantly increasing to about 1.3 g/Nm3 with a 60% mixture of polymers, exceeding that defined in Table 4, Annex A, of the Ordinance No.675/2009 of June 23, making it necessary to mitigate SO2 emissions
Summary
For the development of a country, high investments are required for electric power generation. Seeking to meet this current demand and respecting the integration between man and nature, it is necessary to generate clean, renewable and efficient energy generation. The search for economic and social development must be linked to environmental preservation for sustainable development [1]. Legislations seek the reduction and even banishment on the future use of landfills, since waste disposal is an environmentally critical situation looking for recycling alternatives incorporated into strategies oriented towards a circular economy [3]. As a way to reduce the amount of waste sent to landfills, recycling, recovery, and energy recovery are viable options [4]
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