Power Production Efficiency Research Articles

97/00691 An evaluation of disposal and utilization options for advanced coal utilization wastes

If the US is to continue to effectively use its substantial coal reserves, new clean coal technologies must be developed to improve power production efficiency and reduce emissions from power plants. In order to gain information about wastes produced by advanced coal utilization processes, a research project is being conducted to characterize the geotechnical and geochemical properties of advanced coal process wastes. The University of North Dakota Energy and Environmental Research Center (EERC) analyzed 34 of these wastes for their bulk chemical and mineral compositions and for the disposal-related physical properties listed in a table. This paper discusses potentially useful waste management practices for eight bulk waste samples obtained from four different clean coal processes: gas reburning with sorbent injection (GRSI); pressurized fluidized-bed combustion (PFBC); SO{sub x}, NO{sub x}, RO{sub x}, BOX (SNRB); and coal reburning (CR). All four processes have been demonstrated at either full-scale or pilot-scale facilities in the US. Since the properties of advanced process wastes are different from conventional coal combustion wastes, an analysis was performed to identify any potential problems that could occur when standard, off-the-shelf waste management technologies are used for handling and disposal of advanced process wastes. When potential problems were identified, possible alternative technologies were evaluated.

Potential beneficial effects of potassium channel blockade by tedisamil in isolated perfused working rat heart with coronary artery ligation

Tedisamil, a potassium channel blocker, is known to produce bradycardia. The hypothesis tested was that tedisamil-induced bradycardia should improve the mechanical and metabolic properties of the ischemic myocardium. Using isolated perfused rat heart with coronary-artery ligation, tedisamil was compared with alinidine, verapamil, and propranolol. The end points were myocardial mechanical function and oxygen uptake. In coronary-ligated hearts, tedisamil (1.83×10-6 M) decreased heart rate, increased left ventricular dP/dtmax, and increased pressure power production. Efficiency of work rose with tedisamil. Alinidine (7×10-6 M) also decreased heart rate without altering left ventricular dP/dtmax, power production, or myocardial efficiency. Verapamil (1.5×10-7 M) did not alter heart rate but decreased left ventricular dP/dtmax, while power production and myocardial efficiency also fell. Propranolol (1×10-5 M) caused changes similar to verapamil, except that the heart rate also fell. Dobutamine (1.18×10-7 M) increased cardiac output and oxygen uptake without altering mechanical efficiency. Of the drugs tested and in the concentrations used in the coronary ligated rat heart, it was only tedisamil that had the capacity to cause less decrease in mechanical work and in myocardial efficiency than in controls.

Efficiency of power production in simple nonlinear electrochemical systems

Efficiency of power production in simple nonlinear electrochemical systems

Theory and experiments on the effects of perturbations on nonlinear chemical systems: Generation of multiple attractors and efficiency

Periodic perturbations are applied to the input fluxes of reactants in a system which exhibits autonomous oscillations, the combustion of acetaldehyde (ACH) and oxygen, and a system which exhibits damped oscillations, the combustion of methane and oxygen. The ACH system is studied by experiments and numerical analysis and the methane system is studied by numerical analysis. The periodic perturbations are in the form of a two-term Fourier series. Such perturbations may generate multiple attractors, which are either periodic or chaotic. We discuss two types of bistable responses: a new phase bistability, in which a subharmonic frequency is added to a sinusoidal perturbation at different phases relative to the periodic response; and jump phenomena, in which the resonant frequency of a nonlinear oscillator depends on the amplitude of the periodic perturbation. Both the ACH and the methane systems confirm the phase bistability. The additional complex behavior of bistability due to jump phenomena is seen only in calculations in the methane system. In both types of bistability a hysteresis loop is formed as we vary the form of the periodic perturbation. In the methane system, we find period doubling to chaos occuring on one branch of the hysteresis loop while the other branch remains periodic. The methane system has been studied in the context of the efficiency of power production. We calculate the efficiency corresponding to each bistable attractor and find one branch of each pair to be the more efficient mode of operation. In the case of the coexisting periodic and chaotic attractors the chaotic attractor is the more efficient mode of operation.

Optimization of kinetic and thermodynamic properties in irreversible open chemical and thermal engines

Periodic variations of an external parameter or constraint of open chemical systems have been shown to induce changes in time averaged kinetic and thermodynamic quantities. We examine the effects of the analytic form of the periodic variation on the time averaged quantities and find the maximum changes obtainable through periodic variations. A variational procedure is proposed, based on a Fourier expansion of the form of the periodic perturbation, the laws of thermodynamics, conservation of matter, and the kinetics. The efficiency of power production in a combustion system is examined with this method in a numerical example. A unique maximum in the efficiency is found, with the gains achievable for more complex functions exceeding those for a sinusoidal perturbation. We interpret the changes in efficiency in terms of the magnitude of the response of the system (resonance) and phase shifts between the periodic perturbations and the response of the system. We illustrate the mechanisms of efficiency changes in this system with two examples; one in which the periodic perturbation affects the phase relations and one in which the periodic perturbation affects the magnitude of the response. Finally, we note that multiple attractors may coexist in this system for certain forms of the periodic perturbation, each with a distinct efficiency.

Efficiency of Human Power Production by Vertical Pumping

Mechanical efficiencies are calculated for a human doing work in a standing and stooping cycle while on a movable platform. An unsteady force is generated which does useful work in oscillating the platform on its suspension system. Such a vertical pumping motion has been proposed for a man-powered ornithopter. The theorem of virtual work provides the efficiency expression. Analog simulation reveals that square wave force exitation is more efficient than sinusoidal or triangular. Design curves show some unexpected requirements for matching man and machine, and very poor efficiency if care is not taken. Losses are due to gravity and human inability to store energy in unloading portions of the cycle. A spring-dashpot suspension allows efficiencies of up to 88% in cases involving sinusoidal exitation. If the spring force is set to zero, one obtains a maximum of 64% efficiency for harmonic exitation. Some improvement can be made by adding toe straps to the human and/or by forcing the cage in a square wave. The novel feature, making this work differ from ordinary vibration work, is the switching logic needed to distinguish loading and unloading portions of the cycle.