Emissions of fine particulate matter, PM 2.5 , in both primary and secondary form, are difficult to capture in typical dry electrostatic precipitators (ESPs). Wet (or waterbased) ESPs are well suited for collection of acid aerosols and fine particulates because of greater corona power and virtually no re-entrainment. However, field disruptions because of spraying (misting) of water, formation of dry spots (channeling), and collector surface corrosion limit the applicability of current wet ESPs in the control of secondary PM 2.5 . Researchers at Ohio University have patented novel membrane collection surfaces to address these problems. Water-based cleaning in membrane collectors made of corrosion-resistant fibers is facilitated by capillary action between the fibers, maintaining an even distribution of water. This paper presents collection efficiency results of lab-scale and pilot-scale testing at FirstEnergy's Bruce Mansfield Plant for the membranebased wet ESP. The data indicate that a membrane wet ESP was more effective at collecting fine particulates, acid aerosols, and oxidized mercury than the metal-plate wet ESP, even with ϳ15% less collecting area.

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In this paper the model development, problem specification, constraint formulation, and optimal feedback controller design for a variable-displacement hydraulic pump system are shown using the Quantitative Feedback Theory (QFT) technique. The use of variable-displacement pumps in hydraulic system applications has become widespread due to their efficiency advantages; however, this efficiency gain is often accompanied by a degradation of system stability. Here we develop a QFT controller for a variabledisplacement pump based upon a linear, parametrically uncertain model in which some of this uncertainty reflects variation in operating point-dependent parameters. After presentation of a realistic non-linear differential equation model, the linearized model is developed and the effect of parametric uncertainty is reviewed. From this point, closed-loop performance specifications are formulated and the QFT design technique is carried out. An initial feasible controller is designed, and this design is optimized via a non-linear programming technique. In conclusion, a non-linear closed-loop system response is simulated. This paper is intended to have tutorial value, both in terms of the detailed hydraulic system model development, as well as in terms of the detailed exposition of the QFT controller design and optimal loop shaping processes.1998 John Wiley & Sons, Ltd.

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A critical evaluation of current hydraulic servo system analysis methods indicates a need for alternative methods better able to quantify robust stability. One promising method recently developed for analysing large-scale power systems determines stability robustness in a high-dimensional parameter space by computing the distance to the 'closest' Hopf bifurcation (which corresponds to the birth of a limit cycle oscillation). In this paper a procedure is developed for applying closest Hopf bifurcation theory in the design and analysis of robustly stable hydraulic servo systems. The procedure addresses practical implementation issues such as the impact of an inhomogeneous parameter space and the choice of a metric that yields a meaningful quantitative measure of stability robustness. Results from the new procedure applied to a common position control system compare favourably with published describing function results and new simulation results. Additionally, the new procedure is easier to apply and produces results which are easier to interpret and use. As a demonstration of the design procedure's ability to handle non-linear systems with high-dimensional parameter spaces, a hydraulic servo system with an inhomogeneous seven-dimensional parameter space is designed to meet a robust stability requirement.