Waste to Energy Technologies

In this paper, a linear active disturbance rejection controller is proposed for a waste heat recovery system using an organic Rankine cycle process, whose model is obtained by applying the system identification technique. The disturbances imposed on the waste heat recovery system are estimated through an extended linear state observer and then compensated by a linear feedback control strategy. The proposed control strategy is applied to a 100 kW waste heat recovery system to handle the power demand variations of grid and process disturbances. The effectiveness of this controller is verified via a simulation study, and the results demonstrate that the proposed strategy can provide satisfactory tracking performance and disturbance rejection. Full article

An experimental study on converting municipal solid waste (MSW) into chlorine-free solid fuel using a combination of hydrothermal processing and water-washing has been performed. After the product was extracted from the reactor, water-washing experiments were then conducted to obtain chlorine-free products with less than 3000 ppm total chlorine content. A series of combustion experiments were then performed for the products before and after the washing process to determine the chlorine content in the exhaust gas and those left in the ash after the combustion process at a certain temperature. A series of thermogravimetric analyses were also conducted to compare the combustion characteristics of the products before and after the washing process. Due to the loss of ash and some volatile matter after washing process, there were increases in the fixed carbon content and the heating value of the product. Considering the possible chlorine emission, the washing process after the hydrothermal treatment should be necessary only if the furnace temperature is more than 800 °C. Full article

The landfill of Bellolampo is located in northern Sicily and serves the greater area of Palermo (Sicily). In the recent past, the landfill has been progressively renovated in order to align the waste disposal process with the state-of-the-art technology. During the past years, the site had been equipped with seven biogas engines, fuelled with the biogas produced at the oldest part of the landfill. More recently, another two engines of the same type have been installed for a total of 9 MW electrical power installed at the landfill. The landfill of Bellolampo faces a significant leachate disposal problem. Some 250 m³ of contaminated leachate are produced daily and transported by ships and trucks to an area about 1000 km away before being treated and disposed. The disposal of this extremely polluting fluid causes significant nuisance in the integrated waste management process and significant disposal expenses (in excess of € 60 per ton of fluid disposed and € 4.5 mln per year). Furthermore, the recent legislation strongly suggests the landfill manager to activate fully integrated systems and 100% landfill auto-sustainability. On the other hand, the above mentioned biogas engines produce a great quantity of unused thermal energy yearly. This study demonstrates that this energy could be effectively and efficiently used to enable the sustainable in-house treatment of the leachate. The treatment is aimed to significantly reduce leachate volume in order to reduce fluid disposal costs. A thorough economical analysis is also performed. The study demonstrates that a medium sized landfill can sustainably and cost-effectively be managed through a fully integrated system thus producing substantial economies. Full article

This paper describes a kinetic study of the decomposition of waste printed circuit boards (WPCB) under conventional and microwave-induced pyrolysis conditions. We discuss the heating rates and the influence of the pyrolysis on the thermal decomposition kinetics of WPCB. We find that the thermal degradation of WPCB in a controlled conventional thermogravimetric analyzer (TGA) occurred in the temperature range of 300 °C–600 °C, where the main pyrolysis of organic matter takes place along with an expulsion of volumetric volatiles. The corresponding activation energy is decreased from 267 kJ/mol to 168 kJ/mol with increased heating rates from 20 °C/min to 50 °C/min. Similarly, the process of microwave-induced pyrolysis of WPCB material manifests in only one stage, judging by experiments with a microwave power of 700 W. Here, the activation energy is determined to be only 49 kJ/mol, much lower than that found in a conventional TGA subject to a similar heating rate. The low activation energy found in microwave-induced pyrolysis suggests that the adoption of microwave technology for the disposal of WPCB material and even for waste electronic and electrical equipment (WEEE) could be an attractive option. Full article

The performance analysis of a supercritical organic Rankine cycle system driven by exhaust heat using 18 organic working fluids is presented. Several parameters, such as the net power output, exergy efficiency, expander size parameter (SP), and heat exchanger requirement of evaporator and the condenser, were used to evaluate the performance of this recovery cycle and screen the working fluids. The results reveal that in most cases, raising the expander inlet temperature is helpful to improve the net power output and the exergy efficiency. However, the effect of the expander inlet pressure on those parameters is related to the expander inlet temperature and working fluid used. Either lower expander inlet temperature and pressure, or higher expander inlet temperature and pressure, generally makes the net power output more. Lower expander inlet temperature results in larger total heat transfer requirement and expander size. According to the screening criteria of both the higher output and the lower investment, the following working fluids for the supercritical ORC system are recommended: R152a and R143a. Full article

The objective of this paper was to provide a preliminary analysis of energy utilization from biological wastewater treatment sludge (biosludge) in Taiwan, a densely populated country (estimate 640 persons/km²) with a high dependence (over 99%) on imported energy. The discussion focused on the status of biosludge generation and its management in the years 2004–2010. Findings showed that the main types of combustible waste (i.e., biosludge) produced by the industrial and agricultural sectors of Taiwan included food processing sludge, wine brewery sludge and agricultural sludge which may be reused as auxiliary fuel in the utilities (e.g., generator, boiler and incinerator). Furthermore, two conceptual biosludge-to-energy systems have been addressed with regard to the thermochemical conversion processes. One is to adopt direct combustion for power generation in the combined heat and power system. Another system uses pyrolysis and gasification for producing biochar (solid fuel), bio-oil (liquid fuel) and syngas (gas fuel). Based on their thermochemical properties and reported generation quantities, the energy potential and the environmental benefits of mitigating CO₂ emissions were also analyzed in the study, showing around 1.1 × 10³ TJ/year and 57 Gg CO₂/year, respectively. Full article

Nowadays, on average, two thirds of the fuel energy consumed by an engine is wasted through the exhaust gases and the cooling liquid. The recovery of this energy would enable a substantial reduction in fuel consumption. One solution is to integrate a heat recovery system based on a steam Rankine cycle. The key component in such a system is the expander, which has a strong impact on the system’s performance. A survey of different expander technologies leads us to select the reciprocating expander as the most promising one for an automotive application. This paper therefore proposes a steady-state semi-empirical model of the expander device developed under the Engineering Equation Solver (EES) environment. The ambient and mechanical losses as well as internal leakage were taken into account by the model. By exploiting the expander manufacturer’s data, all the parameters of the expander model were identified. The model computes the mass flow rate, the power output delivered and the exhaust enthalpy of the steam. The maximum deviation between predictions and measurement data is 4.7%. A performance study of the expander is carried out and shows that the isentropic efficiency is quite high and increases with the expander rotary speed. The mechanical efficiency depends on mechanical losses which are quite high, approximately 90%. The volumetric efficiency was also evaluated. Full article

This paper presents an extensive review of the scientific literature associated with various microwave pyrolysis applications in waste to energy engineering. It was established that microwave-heated pyrolysis processes offer a number of advantages over other processes that use traditional thermal heat sources. In particular, microwave-heated processes show a distinct advantage in providing rapid and energy-efficient heating compared to conventional technologies, and thus facilitating increased production rates. It can also be established that the pyrolysis process offers an exciting way to recover both the energetic and chemical value of the waste materials by generating potentially useful pyrolysis products suitable for future reuse. Furthermore, this review has revealed good performance of the microwave pyrolysis process when compared to other more conventional methods of operation, indicating that it shows exceptional promise as a means for energy recovery from waste materials. Nonetheless, it was revealed that many important characteristics of the microwave pyrolysis process have yet to be raised or fully investigated. In addition, limited information is available concerning the characteristics of the microwave pyrolysis of waste materials. It was thus concluded that more work is needed to extend existing understanding of these aspects in order to develop improvements to the process to transform it into a commercially viable route to recover energy from waste materials in an environmentally sustainable manner. Full article

In industrialized countries, it is expected that the future generation of bioenergy will be from the direct combustion of residues and wastes obtained from biomass. Bioenergy production using woody biomass is a fast developing application since this fuel source is considered to be carbon neutral. The harnessing of bioenergy from these sources produces residue in the form of ash. As the demand for bioenergy production increases, ash and residue volumes will increase. Major challenges will arise relating to the efficient management of these byproducts. The primary concerns for ash are its storage, disposal, use and the presence of unburned carbon. The continual increase in ash volume will result in decreased ash storage facilities (in cases of limited room for landfill expansion), as well as increased handling, transporting and spreading costs. The utilization of ash has been the focus of many studies, hence this review investigates the likely environmental and technological challenges that increased ash generation may cause. The presence of alkali metals, alkaline earth metals, chlorine, sulphur and silicon influences the reactivity and leaching to the inorganic phases which may have significant impacts on soils and the recycling of soil nutrient. Discussed are some of the existing technologies for the processing of ash. Unburned carbon present in ash allows for the exploration of using ash as a fuel. The paper proposes sieve fractionation as a suitable method for the separation of unburnt carbon present in bottom ash obtained from a fixed-bed combustion system, followed by the application of the gasification technology to particle sizes of energy importance. It is hoped that this process will significantly reduce the volume of ash disposed at landfills. Full article