Search Results (2)

Boiler cinder is a kind of mining waste that may cause environmental pollution. Based on this reason, a processing method needs to be carried out. In this study, the influence of CO₂-cured boiler cinder on the compressive and flexural strengths of reactive powder cement concrete (RPC) under NaCl actions is investigated. The mass loss rates (MLR) and the relative dynamic modulus of elasticity (RDME) are measured to reflect the resistance of NaCl erosion. The thermogravimetric analysis (TGA), scanning electron microscope (SEM), and X-ray diffraction (XRD) spectrum are obtained for revealing the mechanism of the macro performance. Results show that the relationship between the MLR and the mass ratio of CO₂-cured boiler cinder fits the quadratic function with NaCl erosion. Meanwhile, the MLR during NaCl action are decreased by increasing the amount of CO₂-cured boiler cinder. The MLR range from 0% to 5.3% during NaCl action, and the decreasing rate of MLR by CO₂ curing on boiler cinder is 0%–51.3%. The function of RDME and the mass ratio of CO₂-cured boiler cinder accords with the positive correlation quadratic function. The mechanical strengths decrease when NaCl erosion is encountered. The mechanical strengths’ decreasing rates of RPC are elevated with the increasing number of NaCl freeze–thaw cycles and the NaCl dry–wet alternations. The increasing rates of flexural and compressive strengths of RPC by 13.1%–36.3% and 11.2%–50.4% are achieved by adding CO₂-cured boiler cinder. As observed from the TGA and SEM’s results, the addition of CO₂-cured boiler cinder can increase the thermogravimetric value and the compactness of hydration products. Full article

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. Full article