Nickolas J. Themelis

Waste-to-energy: A review of the status and benefits in USA

The USA has significant experience in the field of municipal solid waste management. The hierarchy of methodologies for dealing with municipal solid wastes consists of recycling and composting, combustion with energy recovery (commonly called waste-to-energy) and landfilling. This paper focuses on waste-to-energy and especially its current status and benefits, with regard to GHG, dioxin and mercury emissions, energy production and land saving, on the basis of experience of operating facilities in USA.

Resource recovery from used rubber tires

Abstract Including car, truck, bus, and airplane tires, 266 million tires were scrapped in the US in 1996 ( Scrap Tire Management Council (STMC), 1997. ). More than three-quarters of these tires were used as fuel, recycled for material applications, or exported. The remainder accumulates in junkyards or landfills where they pose a fire hazard and provide a breeding ground for disease carrying rodents and insects. Using information on scrap tire composition and the current markets using them, we examine the technologies used to recover their value either for energy or as rubber. As the majority of scrap tires are used as fuel, we calculate their life cycle energy budget considering both the energy consumed for tire production and the energy recovered from their use as fuel. Based on our findings, we draw some preliminary conclusions on how to maximize value recovery from this ubiquitous artifact of industrial societies.

Assessment of the state of food waste treatment in the United States and Canada.

Currently in the US, over 97% of food waste is estimated to be buried in landfills. There is nonetheless interest in strategies to divert this waste from landfills as evidenced by a number of programs and policies at the local and state levels, including collection programs for source separated organic wastes (SSO). The objective of this study was to characterize the state-of-the-practice of food waste treatment alternatives in the US and Canada. Site visits were conducted to aerobic composting and two anaerobic digestion facilities, in addition to meetings with officials that are responsible for program implementation and financing. The technology to produce useful products from either aerobic or anaerobic treatment of SSO is in place. However, there are a number of implementation issues that must be addressed, principally project economics and feedstock purity. Project economics varied by region based on landfill disposal fees. Feedstock purity can be obtained by enforcement of contaminant standards and/or manual or mechanical sorting of the feedstock prior to and after treatment. Future SSO diversion will be governed by economics and policy incentives, including landfill organics bans and climate change mitigation policies.

Controlling particle injection in plasma spraying

This paper reviews experimental and analytical techniques that examine the efficiency of systems for the injection of powders in plasma jets used in spray coating. The types of injectors, the experimental techniques for observing particle trajectories and distributions, and the mathematical models used to investigate the momentum and heat-transfer phenomena between particles, carrier gas, and plasma jet are described. Experimental data are presented from numerous examples from the plasma spraying of ceramic powders.

Heat Generation and Particle Injection in a Thermal Plasma Torch

The operation of plasma guns used for plasma spraying involves a continuous movement of the anode arc root. The resulting fluctuations of voltage and thermal energy input introduce an undesirable element in the spray process. This paper deals with the effects of these arc instabilities on the plasma jet, and the behavior of particles injected in the flow. The first part refers to the formation of the plasma jet. Measurements show that the static behavior of the arc depends strongly upon the plasma-forming gas mixture, especially the mass flow rate, of the heavy gas, injection mode, nozzle diameter, and arc current. These parameters control the electric field in the arc column, the arc length, its stability, and the gas velocity and temperature. The dynamic behavior of the arc is examined to determine how the tempeature and velocity of the plasma gas vary with voltage variations. Relationships between the gas velocity at the nozzle exit and the lifetime of the arc roots, and the independent operating parameters of the gun can be established from a dimensional analysis. The second part discusses the interaction between the plasma jet and the particles injected into the flow. The parameters controlling particle injection and trajectory are examined to determine how injection velocity must vary with particle size and density to achieve a given trajectory. The effect of the transverse injection of the powder carrier gas is investigated using a 3-D computational fluid dynamics code. Finally, the effect of the jet fluctuations on particle trajectory is studied under the assumption that the jet velocity follows the voltage variation. The result is a continuous variation of the particle spray jet position in the flow. Experimental observations confirm the model predictions.

The 2016 Thermal Spray Roadmap

Considerable progress has been made over the last decades in thermal spray technologies, practices and applications. However, like other technologies, they have to continuously evolve to meet new problems and market requirements. This article aims to identify the current challenges limiting the evolution of these technologies and to propose research directions and priorities to meet these challenges. It was prepared on the basis of a collection of short articles written by experts in thermal spray who were asked to present a snapshot of the current state of their specific field, give their views on current challenges faced by the field and provide some guidance as to the R&D required to meet these challenges. The article is divided in three sections that deal with the emerging thermal spray processes, coating properties and function, and biomedical, electronic, aerospace and energy generation applications.

Energy recovery from New York City municipal solid wastes

This work was part of a major study that examined the policy and technology implications of alternatives for managing the municipal solid wastes (MSW) of New York City. At this time, of the 4.1 million metric tons of MSW collected by the City annually, 16.6% are recycled, 12.4% are combusted in Waste-to-Energy (WTE) plants, and the remaining 71% are landfilled. Despite the heterogeneity of organic materials in MSW, the composite molecular structure can be approximated by the organic compound C6 H10 O4. A formula was derived that allows the prediction of the heating value of MSW as a function of moisture and glass/metal content and compares well with experimentally derived values. The performance of a leading Waste-to-Energy plant that utilises suspension firing of shredded MSW, processes one million tons of MSW per year, and generates a net of 610 kWh/metric ton was examined. The results of this study showed that WTE processing of the MSW reduces fossil fuel consumption and is environmentally superior to landfilling.

MATERIAL AND ENERGY BALANCES IN A LARGE-SCALE AEROBIC BIOCONVERSION CELL

On the basis of earlier experimental studies of the aerobic bioconversion of organic wastes, the preferred values of operating parameters and the biochemical rate constants of oxidation to CO2 and H2O were identified. Energy and material balances were then constructed for a large, 3 m deep aerobic cell holding 1,440 tons of the ‘wet’ component of organic wastes (major organic constituent: [C6H10O4]n). It was found that conduction/convection and radiation losses to the surroundings amount to a relatively small fraction of the chemical heat released by oxidation. Therefore, the surplus chemical heat must be removed by means of an upward water-saturated air flow that is several-fold the stoichiometric requirement for biodegradation. This study has quantified a basic process difference between anaerobic and aerobic bioconversion of organic matter: In the former, most of the chemical energy in the converted organic matter is stored chemically in the generated methane gas. In the latter, this energy is released in the cell and must be carried out in a relatively large air/water vapour flow through the cell.

A Perspective on Plasma Spray Technology

Plasma spraying is often assumed to be a mature technology in which all the important phenomena have been observed and described adequately. However, the intricate interactions between the electrically conducting fluid and electromagnetic, thermal and acoustics phenomena that affect the operation of the plasma torch are not fully understood as yet. Also, variants of the plasma spray process are emerging and raise new scientific questions. These technologies include the spraying of liquid feedstock in the form of submicrometric particles or chemical precursors in a solvent and, coatings formed by vapor condensation onto the substrate. These relatively novel techniques make possible the production of thinner coatings than in air plasma spraying with a fine and even nanostructured microstructure. This paper attempts to define some of the current important issues and research priorities in the plasma spray field.

A basin-wide approach to dredged material management in New York/New Jersey Harbor

In the last decade, an area of increasing estuarine research in the New York/New Jersey Harbor has been the identification of toxic contaminant sources, mapping of contaminant levels in water and sediments, and assessment of contaminant accumulation in biota. The accumulation of anthropogenic contamination in the harbors sediments has occurred for centuries, primarily from land-based municipal and industrial sources. Contaminants from land-based sources introduced into surface waters rapidly become scavenged by suspended particles that then tend to settle to the bottom, primarily in deep areas, such as berths and navigation channels. Several million cubic meters of sediments must be dredged annually to clear navigation channels. In the past, the dredged material was disposed in a designated ocean site. However, in1992, new testing procedures were implemented, and much of the harbors dredged material was determined to be unsuitable for ocean placement. It is ironic that these restrictions came at a time when the quality of harbor sediments is improving, largely because of pollution controls implemented as a result of the Clean Water Act and other environmental measures put in place by government and industry. For example, the harbor-wide concentration of mercury has decreased to 0.7-0.8ppm, a level that is approaching the pre-industrial background level. Nevertheless, in certain areas of the harbor, there remain sufficiently high concentrations of contaminants to merit concern and to create serious problems for sponsors of dredging projects. Development of a basin-wide sediment management strategy is necessary to guide port decision-makers in their efforts to clean-up contaminant sources, to dredge regional waterways, and to ameliorate the contaminated sediment disposal problem. The backbone of this strategy is the integration of the data from an ongoing field monitoring and modeling program with a parallel investigation of watershed and airshed sources and sinks using industrial ecology methodology.