An innovative hybrid energy system consisting of a waste-to-energy unit and a coal-fired power unit is designed to enhance the energy recovery of waste and decrease the investment costs of waste-to-energy unit. In this integrated design, partial cold reheat steam of the coal-fired unit is heated by the waste-to-energy boiler’s superheater. The heat required for partial preheated air of waste-to-energy unit and its feedwater are supplied by the feedwater of CFPU. In addition, an additional evaporator is deployed in the waste-to-energy boiler, of which the outlet stream is utilized to provide the heat source for the urea hydrolysis unit of coal-fired power plant. The stand-alone and proposed designs are analyzed and compared through thermodynamic and economic methods. Results indicate that the net total energy efficiency increases from 41.84% to 42.12%, and the net total exergy efficiency rises from 41.19% to 41.46% after system integration. Moreover, the energy efficiency and exergy efficiency of waste-to-energy system are enhanced by 10.48% and 9.92%, respectively. The dynamic payback period of new waste-to-energy system is cut down from 11.39 years to 5.48 years, and an additional net present value of $14.42 million is got than before.
According to the waste-to-energy (WTE) valorization and circular economy principles, the use of waste oil and grease (WOG) for obtaining biofuels shows the tendency towards sustainability, makes the interest in green chemistry, and the development of environmentally friendly processes grow. Three different fatty wastes (from the fat trap of a sewage station, lard waste, and frying oil) were analyzed and this work showed they have no potentially toxic metals. The frying oil sample and residual lard waste showed a higher percentage of triacylglycerides resulting in higher biodiesel conversion. The samples showed physical and chemical properties (density, viscosity, and ash) within the limits established by current regulations. Bio-oil samples formed a mixture of carboxylic acids, with high acidity. However, the parameters that deviated from the maximum permitted by the standard could be adjusted blending with petroleum diesel, replacing partially the fossil energy carriers with biomass-derived energy carriers which could bring positive impacts from multiple perspectives, i.e., economic, environmental, and health.