H.William Prengle

Optical and thermal analysis of a cassegrainian solar concentrator

Abstract For the storage of solar energy in a chemical system, a Cassegrainian type solar collector is investigated. With generalized geometry, a non-skew ray from the edge of the solar disc is followed through the Cassegrainian configuration to the final image to define the image height. Parametric results are presented in a form which can be used to predict performance based on off-axis optics. Equations and graphs allow the incorporation of angular error into the calculations. Slope of 5 for the limiting tangent to the hyperbolic secondary appears near optimum. The focal length of the hyperboloid is not an important factor as long as it is similar to the focal length of the paraboloid. The required diameter for the hyperboloid is typically half the diameter of the paraboloid. A set of design equations is developed, and their use is demonstrated. Design parameters are calculated for chemical reactor loads of 1.0, 0.5, and 0.1 MW.

Operational chemical storage cycles for utilization of solar energy to produce heat or electric power

Abstract A self-sufficient chemical cycle is required which will take solar energy on an intermittent basis and continuously convert it into heat and/or electric power. This paper presents engineering criteria for selection of suitable chemical reactions, and considers in detail two systems, (a) methanol cycle and (b) ammonium hydrogen sulfate (AHS) cycle. The latter appears very attractive as an operational cycle, has liquid storage on both sides of the cycle, essentially meets all criteria, and has high ΔH (reaction), heat and work efficiencies. Preliminary reactor configurations for the AHS cycle are discussed.

Solar energy with chemical storage for cogeneration of electric power and heat

Abstract U.S.A. energy use by the year 2000 is estimated to be 116–130 quads, compared to 82 quads for 1978. Solar energy, utilized both at the individual residence-building level plus power plant level, along with all other conventional and new energy sources, will be needed to meet future energy demand. In order to make maximum utilization of energy sources to meet national energy-conservation and energy-economic policy, a power plant of the future must cogenerate electrical energy and heat medium, whether it burns fossil fuel or uses solar energy. A solar energy Central Receiver-AHS Chemical Storage cogeneration power plant can be configured to give complete flexibility for day-night and seasonal load combinations, with work efficiencies up to 46 per cent. Such a plant, as a stand-alone or network station, is a real possibility in the not too distant future. Electrical energy and heat medium produced therefrom will be competitive with fossil fuel powered generating plants. A 100 MWe Central Receiver-AHS Cycle cogeneration power plant is discussed in detail; cycle analysis, preliminary cost estimates, and unit energy costs are discussed.

Chemical storage of solar energy kinetics of heterogeneous SO3 and H2O reaction ― reaction analysis and reactor design

Abstract The first energy recovery step in the ammonium hydrogen sulfate (AHS) cycle is the formation of H2SO4(l) from H2O(g) and SO3(g). It has been determined that the optimum way to accomplish this is by the use of a double pipe tubular reactor. In this paper, a mathematical model for the reactor is presented, applied to the three reaction zones, and a method of numerical solution discussed. Three horizontal pilot-scale configurations, 0.234 × 106 to 5.863 × 106 kJ/h energy release, are discussed and sizing presented. Also, the results for a vertical configuration are presented. The need for additional work on two-phase gas-liquid flow in condensing systems and in annuli has been identified. The most important conclusion is that a high temperature can be achieved in the reactor by the use of a front end adiabatic section followed by nonadiabatic sections to recover the heat released.

H2O2VisUV process for photo-oxidation of waterborne hazardous substances — C1C6 chlorinated hydrocarbons

This paper presents results from the first phase development of the H2O2VisUV process for photo-oxidation of waterborne hazardous substances. The technology is generally applicable to numerous situations requiring removal of hazardous substances from: (a) groundwater; (b) drinking water; (c) chemical process water; (d) leakage contamination; and (e) wastewater. However, the first phase research focused attention on drinking water contaminants. The compounds investigated, C1C6, were: tetrachloromethane, tetrachloroethene, dichloroethane, dichloroethene, trichloroethane, trichloroethene and benzene. Dark (no VisUV) oxidation rates and photo-oxidation rates were determined; the latter rate constants were 104–105 greater than dark reaction values. The VisUV photons produce oxidizing free radicals from H2O2 and H2O, and excited state species or free radicals from the reactant compound. The experimental work was conducted in a photochemical batch stirred tank reactor, with 100 W and 450 W mercury vapor lamps, covering the VisUV range, 578.0-222.4 nm. A mathematical model was used to analyze the results and obtain the rate constants. Also, the rate constants were successfully correlated by a molecular composition structure (MCS) model, which permits estimation of rate constants for other C1C6 chlorinated hydrocarbon compounds.

An approximate model for sizing and costing a solar thermal collector-central receiver system

Abstract An approximate generalized theoretical model is presented for the geometry and energy transfer of a solar thermal collector-central receiver system. Equations permit sizing the receiver, tower, and heliostat field. Cost functions correlate data from Department of Energy studies. Based on a set of assumed conditions, simplified, optimized sizing equations yield the minimum capital cost. The costs of the tower and central receiver will change with plant and equipment cost indices, while heliostat costs are expected to diminish as annual production increases. The heliostat cost is the major cost component even at lowest projected unit cost; therefore optimization tends toward minimum heliostat area. The model permits order-of-magnitude cost estimates to be made very quickly, compared to detailed simulation.

Chemical storage of solar energy—kinetics of heterogeneous NH3 and H2SO4 reactions II. Process and reactor design

Abstract An important energy recovery step in the ammonium hydrogen sulfate (AHS) cycle is the recombination reaction producing NH4HSO4. It has been determined that the optimum way to accomplish this, and prevent side reactions, is by the heterogeneous gas-liquid reaction of H2SO4 and NH3. A mathematical model is presented and applied to the two reaction zones and a method of numerical solution is discussed. Three horizontal pilot-scale configurations, 0.17 × 106 to 4.2 × 106 kJ/h energy release, are discussed and sizing is presented. The most important conclusion from the work is that the energy can be released most effectively by carrying out the reaction in a double pipe tubular reactor operating in the annular flow regime with both gas and liquid in turbulent flow.

H2O2/VisUV photo-oxidation process for treatment of waterborne hazardous substances—Reaction mechanism, rate model, and data for tubular flow and flow stirred tank reactors

Abstract This paper presents the chemical reaction engineering development of the H 2 O 2 /VisUV photo-oxidation process for treatment of hazardous waterborne substances, that occur in groundwater, leachates, and industrial wastewater. Reaction results, on benzene (BNZ), dichlorobenzene (DCB), trichloroethene (TCE), trichloroethane (TCA), and carbon tetrachloride (CTC), have been obtained, providing engineering data and models that can be used to size full-scale equipment. A photochemical flow stirred tank reactor (pcfSTR) and a photo-chemical tubular flow reactor (pcTFR) were used in the experimental work. Two experimental discoveries were made in the course of the work: (1) conventional thermal kinetics do not apply, the rate controlling variable is the photon flux, and (2) for the photo-chemical reactors used, the pcfSTR was more effective than the pcTFR. The following sub-topics are discussed: reaction mechanism, reactor hydrodynamics, photon flux effects, typical reaction data (on benzene and trichloroethane), and rate constants.

Chemical storage of solar energy—Kinetics of heterogeneous NH3 and H2SO4 reactions I. Analysis of experimental reaction and mass transfer data

Abstract The exothermic heterogeneous reaction of ammonia vapor and liquid sulfuric acid (H2O + SO3) to produce ammonium hydrogen sulfate and ammonium sulfate is important for the recovery of stored energy in the small molecules, H2O, SO3 and NH3. As the first part of a chemical reaction engineering analysis, literature data on the reaction and mass transfer were analyzed. The reaction rate constant as a function of temperature and the mass transfer coefficient as a function of the dynamical variables in a flow system were determined. The reaction mechanism in concentrated liquid phase is pseudo-second order and the rate is extremely fast. However, for the heterogeneous system with ammonia transferred from the vapor phase the mass transfer is rate controlling. A broad range of mass transfer data, covering packed columns and dispersed phase droplets, was correlated over 15 orders of magnitude by the j D -factor correlation method.

Solar-fuel fired cogeneration plants—Sizing and costing model for molten salt storage systems

Abstract The large-scale utilization of solar energy will be facilitated by economical and efficient energy storage. The proposed energy storage systems have been critically reviewed, and capital cost estimates compared on a common basis. A model for sizing an energy storage system is proposed and used to determine the size range of practical interest. Based on selection criteria and relevant data two storage systems have been investigated: an all sodium system and a molten salt system. The design equations, cost estimates, and correlations indicate that, for the energy storage systems developed to date, in the capacity range of 700–2100 MWh, a molten salt, two-tank isolated-type system is the most cost effective and technically feasible for a solar, central receiver, hybrid cogeneration plant. At the extremes of the above range the unit capital cost for the molten salt storage system was found to be 22.8–26.7