M. Maldei’s research while affiliated with Ohio University and other places

Solar cell devices have been fabricated with amorphous, hydrogenated carbon (a-C:H) as the primary semiconducting material. These devices clearly demonstrate photovoltaic behavior as determined by their I–V curves. To identify photon energies that contribute to the photogenerated current, quantum efficiency measurements have been performed. The fabricated solar cells exhibit a maximum quantum efficiency response in the ultraviolet region. Using the measured quantum efficiency curves, the short-circuit currents for a global AM1.5 spectrum at an irradiance of 1000W/m2 have been calculated. These values are comparable to the actually measured short-circuit currents.

Dry scrubbing that takes place after the air preheater (<350°F) is the mode of operation that is the primary focus of this chapter. At the relatively low temperatures that occur in this region of operation, the rate of the gas-solid reaction that drives SO2 capture in the convective (800–1200°F) and the combustion (1600–2400°F) zones is too slow to be significant. At lower temperatures, the presence of either liquid-phase or vapor-phase water is required in order to mediate SO2 capture and to produce reasonable capture rates. More specifically, this chapter focuses on work performed in support of the Limestone Emission Control (LEC) process. The LEC process is a unique system employing standard quarry-sized limestone to remove SO2 from coal-fired boiler flue gases. In the LEC process, hot flue gases (<350°F) are contacted with a bed of 1/32 to 1/4 inch limestone granules covered with a thin film of water. Sulfur dioxide is absorbed from the flue gas into the water film where it subsequently reacts with dissolved limestone. A layer of reaction products, primarily calcium sulfate and calcium sulfite, forms on the surface of the limestone as the reaction proceeds. The LEC process has demonstrated the ability to remove in excess of 90% (and under some conditions in excess of 99%) of the SO2 found in coal-combustion flue gases. This chapter includes a description of a mechanistic model for SO2 capture by a wetted limestone particle, process models for both fixed-bed and moving-bed LEC reactors, and support studies dealing with limestone solubilities and dissolution rates.

A novel wet/dry desulfurization post-Furnace process (ETS' Limestone Emission control (LEC) process) for SO[sub 2] removal has been described by Prudich et al.(1988). In this process hot flue gases are contacted with a bed of quarry-sized (1/4in. to 1/32in.) wet limestone granules. This thesis represents the development of a second generation model of ETS' LEC process. The first generation model developed by Prudich et al.(1988) the use of a fixed limestone bed. The work done on this has been well documented by Appell (1989) and Visneski (1991) process under consideration for this thesis involves a continuously moving limestone bed. The moving bed simplifies the process flowsheet and facilitates limestone reactivation. The moving-bed LEC process involves the use of a cross-flow pattern with the flue gas flowing horizontally across the limestone bed at speeds of around 1 to 2 feet per second and the limestone moving vertically downward through the LEC reactor at speeds of around 1 to 15 feet per hour. The primary parameters considered in the mathematical modeling of the moving-bed LEC process are inlet sulfur dioxide concentration, inlet gas-phase water concentration, inlet flue gas and limestone temperatures and water spray addition rate over the bed. For solution of the process, mass and energy balance equations derived as a function of the positions of the flue gas limestone are solved using a predictor-corrector method. The Adams-Bashforth (modified Euler's) method is used with a second order corrector.

A resistance-in-series kinetic model for the low temperature reaction of sulfur dioxide with limestone is presented. The resistances considered are the gas-phase transport of sulfur dioxide, the liquid-phase diffusion of both the sulfur species and the calcium species and the solid-phase dissolution of limestone. The model uses film theory to predict the liquid concentrations of the dissolved species and assumes an instantaneous reaction between the sulfur species and calcium species. The kinetic model incorporates three rate equations for the removal of sulfur dioxide. When the rate of removal is limited by the diffusion of sulfur dioxide across the gas film surrounding the limestone particle, a gas-phase controlled rate equation is used. When the diffusion of the reacting species through the liquid film covering the limestone particle is the predominant resistance, a liquid-phase controlled rate equation is used. When the rate is limited by the dissolution of limestone, a solid-phase controlled rate equation is used. The kinetic model is incorporated into a flow model for the fixed-bed Limestone Emission Control (LEC) system. The LEC system employs a fixed-bed of standard quarry-sized limestone to remove sulfur dioxide from coal-fired boiler flue gases. The flow modeling equations for the fixed-bed LEC system, which include simultaneous heat and mass transfer as applied to water-phase evaporation and condensation are also presented. The combined kinetic and flow model is subjected to a parametric study and the modeling predictions are compared with experimental results.

Dry scrubbing that takes place after the air preheater (