(12) RATE PHENOMENA IN A SLAG RESISTANCE ELECTRIC FURNACE (Miscellany)

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Stochastic and physical modeling of motion of municipal solid waste (MSW) particles on a waste-to-energy (WTE) moving grate

a b s t r a c t Numerical analysis of the mixing of municipal solid waste (MSW) particles as they travel on the grate of a mass-burn waste-to-energy (WTE) combustion chamber is necessary for understanding the parameters that control the combustion processes and designing the grate. In order to characterize the heterogeneous particle behavior, a 2-dimensional stochastic model of MSW particle mixing within a WTE combustion bed was developed. This model was calibrated and validated by means of a full-scale physical model of the Martin reverse acting grate, using tracer particles of sizes ranging from 6 to 22 cm. It was found that different particle sizes result in different residence times according to the Brazil Nut Effect (BNE). The motion of the reverse acting grate, in the speed range of 15e90 reciprocations/h, increases the mean residence time of small and medium particles by 69% and 8%, respectively and decreases that of large particles by 19%. Also, within this speed range, the mixing diffusion coefficient of each particle size was quantified. The ratio of particle diameter to the height of moving bar, d/h, was found to be a major parameter for the mixing diffusion coefficient and the particle residence time at reciprocation speeds exceeding 30 recip./h. Based on these quantitative results and the local MSW particle size distribution, the grate motion and the moving bar height can be designed for optimum operation

Combining Anaerobic Digestion and Waste-To-Energy

Abstract A large fraction of the municipal solid wastes (MSW) stream in the U.S. comprises of natural organic compounds (i.e., food and plant wastes) with high moisture content and low heating value. While these properties are undesirable during the combustion of MSW in waste-to-energy (WTE) plants, they are required for anaerobic digestion (AD). During AD, methane gas is produced that can be captured and used for energy generation. The required long residence times limit the throughput of an AD plant but further development may result in increasing the rates of bioreactions. This paper introduces current AD practices and identifies possible synergies between AD and WTE. It is suggested that co-siting of WTE and AD facilities may result in mutual benefits

Transport And Chemical Rate Phenomena

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Studies of the reduction of iron oxides in particulate systems.

The reduction of iron oxides has been investigated extensively, mainly by virtue of its industrial significance. Nevertheless, despite the large amount of experimental evidence, there has been as yet no agreement as to the mechanism of the reaction, nor has a generalized correlation for the reaction rate been suggested. As a matter of fact, many workers appear to assume that the complexity of the system makes the formulation of such a correlation impossible. One of the main objects of this study has been to attempt an analysis of the mechanism of the reduction, from which a correlation could be derived. To this end, a thorough search of the relevant literature was conducted and the results are presented in the form of a critical review in the first section of this Thesis

The case for WTE as a renewable source of energy

Abstract The combustion of municipal solid wastes for generating electricity (Waste-To-Energy) has been recognized by several states as a renewable source of energy. Yet, there has been determined opposition by some environmental groups to including WTE in the portfolio of renewable energy sources that will benefit from a tax credit designed to decrease reliance on non-renewable fossil fuels. While WTE is considered worldwide as a solid waste management option, the recognition and acceptance of WTE as a clean source of energy still requires public involvement and education. This paper will examine the "pro" and "con" arguments for considering WTE as a renewable energy source

Waste as a renewable source of energy: current and future practices

Abstract Municipal Solid Waste (MSW) has been recognized by several states as a renewable source of energy. Worldwide, about 130 million tons of MSW are combusted annually in waste-to-energy facilities that produce electricity and steam for district heating and also recover metals for recycling. While being linked to environmental pollution prior to the implementation of Maximum Available Control Technology (MACT) regulations, Waste-toEnergy (WTE) was recently named one of the cleanest sources of energy by the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Energy (DOE). However, the WTE industry often faces resistance and preconceptions based on past experience rather than current performance. Due to economic considerations that do not include environmental benefits, most of the U.S. MSW still ends up in landfills despite the fact that for every ton of MSW landfilled greenhouse gas emissions increase by at least 1.2 tons of carbon dioxide. While implemented research and development strategies focused on emissions, there is still a tremendous need for more efficient yet durable combustion technologies including flue gas recirculation and oxygen enrichment, environmentally and economically competitive reuse options for WTE residues, and also public education. The importance of WTE in the universal effort for sustainable development and its need for research and development resources has led to the formation of the Waste-toEnergy Research and Technology Council. Its principal goal is to improve the economic and environmental performance of technologies that can be used to recover materials and of waste during production and distribution of goods, it is almost certain that a minimum quantity of waste will be generated. Because it is believed that the global community will continue to produce industrial products, there will be a continuous stream of new waste, which therefore could be considered to replenish the previously generated garbage. After its generation waste has to be managed appropriately. In the past, the dominant technique to deal with the waste stream was the disposal or dumping in landfills, either controlled or without any regulation. It was soon realized that the waste dumped would turn the land into unusable space and means to reduce the MSW volume were sought. Waste was incinerated or separated into different fractions that could be reused directly or treated to become reusable. At some point, it was recognized during combustion energy was generated and the first waste-to-energy plants were established. While the energy demand has grown rapidly since the beginning of industrialization, the environmental impacts of our consuming society started to be investigated mainly in the second half of the 20th century. Incineration gained a negative image through toxic air emissions and become less favorable. Fossil fuels have remained the dominant means of generating energy

The case for WTE as a renewable source of energy

The combustion of municipal solid wastes for generating electricity (Waste-To-Energy) has been recognized by several states as a renewable source of energy. Yet, there has been determined opposition by some environmental groups to including WTE in the portfolio of renewable energy sources that will benefit from a tax credit designed to decrease reliance on non-renewable fossil fuels. While WTE is considered worldwide as a solid waste management option, the recognition and acceptance of WfE as a clean source of energy still requires public involvement and education. This paper will examine the "pro" and "con" arguments for considering WTE as a renewable energy source. Waste as a renewable source of energy In the traditional sense, renewable sources of energy are those that nature can replenish, such as waterpower, windpower, solar radiation and biomass (wood and plant waste). However, the U,S, municipal solid wastes (MSW) contain a large fraction of paper, food wastes, cotton and leather, all of which are renewable materials under proper stewardship of the Earth. Municipal solid wastes also contain man-made plastics, rubber and fabrics that were produced using non-renewable fossil fuels. All these materials were produced because they were needed by humanity. Although it is desirable to minimize the amount of materials used per capita, and also the generation of wastes during production and distribution of goods, a certain quantity of wastes will always be generated