Potential Applications of Concentrated Solar Energy Proceedings of a Workshop (1991) / Chapter Skim
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2 SESSION 2 - WASTE TREATMENT
2 SESSION 2 - WASTE TREATMENT
Pages 35-58
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From page 35... ...
The topics covered were the fundamentals of waste treatment economics, high temperature photochemistry, the fundamentals of combustion kinetics, and research and development of techniques -- not necessarily utilizing solar energy -- for destroying hazardous and mixed radioactive and hazardous wastes. In summary, the cession identified two kinds of applications for solar energy in waste treatment: as a source of solar photons for thermal photolytic destruction of organic compounds at high temperatures (but temperatures that are lower than would be required without solar photons)
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From page 36... ...
Dellinger. Lower temperatures provide better control of vaporization of toxic metals and formation of nitrogen oxides; increased destruction efficiency of the parent compound and its by-products; use of excess thermal energy for thermal Resorption of solids and sludges; reduced production of carbon dioxide, carbon monoxide, and toxic organic emissions from conventional fuels; cost savings from lower fuel costs and lower capital costs due to increased materials lifetime and reduced need for air pollution control devices; and increased public acceptance through reduced pollution and use of nonincineration disposal technology.
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From page 37... ...
A possible application of solar energy to this process would be to provide inexpensive heat that would allow molten salt treatment of trace organic contaminants in dilute aqueous or gas waste streams. Another process for destruction of hazardous wastes was described by Terry Galloway of Synthetica Technologies, Inc.
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From page 38... ...
Destruction of toxic organic wastes is one emerging, potentially important, and viable application of concentrated solar radiation. A discussion of the fundamental aspects of this process can also provide a framework for investigation of other high-temperature, photochemical, solarinduced reactions.
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From page 39... ...
Thin observation suggests that the destruction efficiency of a Solar destruction unit can be significantly increased under the proper operating condition" and choice of both gas or operating pressure. Temperature dependent lifetime experiments as well as QRRK and REAM calculations are being conducted to further elucidate the key aspects of high temperature photochemical processes.
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From page 40... ...
The principal absorbing species in this mixture in nitrobenzene; however, effective total destruction of all components of the mixture as well as product" is observed. Aped ~ Asps Available results for the destruction of hazardous waste" using concentrated solar radiation clearly suggest that many compounds are amenable to destruction through direct absorption and unimolecular decomposition, while other weak or nonabsorbing species may also be amenable to destruction through secondary photoinduced, radical molecule reaction pathways.
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From page 41... ...
Specifically, experiments combined with prudent calculations should be performed to prove the listed advantages for a ~olar-based technology. It is felt that a bench scale, rotary drum-photoreactor system should be constructed and tested using a small solar concentrator to further research the practical aspects of hazardous waste treatment using concentrated solar radiation.
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From page 42... ...
Data were obtained on the Thez..,al Photolytic Reactor System (see text) in an atmosphere of flowing air at a gas phase residence time of 10.0 s and simulated solar flux of 95 ~uns(-9.5W/cm2)
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From page 43... ...
kF; and the rate of achieving excited state thermal equilibrium, e.g., keXC and kVr. Some processes are omitted for clarity.
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From page 44... ...
k ab G k_1 [hi] _ _ kF k FIGURE 3 Three state model for thermal-photolytic dissociation in which ken is the rate of absorption; kF in the rate of excited state deactivation; and k~[M]
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From page 45... ...
Reprinted with Permission from: Environmental Sciences Group/University of Dayton Research Institute
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From page 46... ...
Data were obtained on the Advanced Photolytic Reactor System in an atmosphere of flowing helium, gas phase residence time of 10.0 s, and laser flux of 3.00 W/cm2 at 280 nm. Reprinted with Permission from: Environmental Sciences Group/University of Dayton Research Institute
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From page 47... ...
. I 200 300 400 5~00 600 700 Exposure Tesperature, C FIGURE 6 Thermal photolytic destruction of an eight component mixture.
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From page 48... ...
Hazardous waste compounds have different reactivity and reaction intermediates. When this is superimposed onto the basic fuel chemistry, one can derive information on mechanism" for hazardous waste destruction.
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From page 49... ...
In any large concentrations of hazardous wastes, the fo,`~ation of solids will increase the optical density of the media. However, the presence of the particulates may provide a more efficient means of heating the reaction mixture or providing reactive sites for destruction.
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From page 50... ...
1986. Hazardous Waste Destruction.
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From page 51... ...
For the magic to become reality, solar destruction must demonstrate that it competes favorably with current approaches in many ways: Economic Capital cost Operating cost Labor Chemicals Energy Vereatil ity Reliabil ity Environmental Residuals ' production Air emissions Public acceptance Permitting difficulty Among economic factors, versatility and reliability are truly components of both capital and operating costs; they are separated here because of their great importance in chemical waste management applications. Regarding versatility, it i" essential that waste management technologies tolerate extremely wide changes in waste-feed composition.
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From page 52... ...
The price must obviously cover the basic treatment cons, regulatory compliance, feed and product analysis, feed preparation, residuals' disposal, profit, and a host of other factors. In our experience, the central disposal unit process in a chemical waste disposal facility accounts for only about 15% of capital and a third of operating costs (Figure 2 shows some generalized cost distributions am well as actual cost distributions for X*
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From page 53... ...
The intermittent nature of sunlight presents a major problem for solar applications given the importance of reliability in chemical waste treatment. To be compatible with this importance, solar-based systems must shut down during low-nun periods or be equipped with alternative energy sources.
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From page 54... ...
54 One niche that is promising is solar systems for treatment of groundwater at remote sites. In this case, intermittent operation is acceptable, even desirable, and energy costs are high.
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From page 55... ...
55 Table 1 Lagging Chemical Waste Treatment Technologies Technology Prime Reason Not Implemented Plasma destruction In situ vitrification Electric furnaces Moving hearth furnaces Supercritical separators Freeze purification In situ soil cleaning Alkali-metal polyethylene glycol dechlorination Sodium metal dechlorination White-rat fungus for halocarbon destruction Biotreatment, general High fundamental cost and complexity Cost, by-products, uncertain destruction performance Energy cost, capital cost Narrow applicability Narrow applicability, cost Narrow applicability Narrow applicability, uncertain performance Narrow, cost, residuals management Safety and cost Narrow applicability Narrow, failure to achieve low residual standards
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From page 57... ...
FIGURE 2A Typical Hazardous Waste Treatment costs. Reprinted with Permission from: Chemical Waste Management, Inc.
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