Browsing by Author "Rindels, Alan J."

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    Analysis of the Elfuel Coal Drying Facility
    (St. Anthony Falls Hydraulic Laboratory, 1990-10) Rindels, Alan J.; Gulliver, John S.; Wetzel, Joseph M.; Voller, Vaughan
    The ELFUEL coal drying facility is designed to utilize the high heat transfer characteristics of a moving packed bed counter-current heat exchanger to efficiently "hot-water dry" lignite coal. Past research into hot water drying of lignite indicates the process is energy inefficient, requiring greater energy input than what can be extracted from the treated lignite. The novel approach of the ELFUEL coal drying facility utilizes the high heat transfer characteristics of a counter-current solid/liquid packed bed to efficiently add and later remove heat to and from descending coal in a pressurized cylindrical vessel. This approach uses raw coal continuously descending in a vertical cylindrical refractory. Coal, upon entering the refractory at the top, gradually heats to process temperatures near the location of hot water injection through contact with hot water flowing upward. Below the point of hot water injection, cool water is forced upward past the descending coal to trap or conserve heat or energy in the system. Sufficient energy is conserved by this design to economically hot-water dry lignite coal. Design of a counter-current energy efficient system which adds and then removes heat has not been reported in the literature. Wonchala and Wynnyckyj (1986) reports counter-current packed bed processes are common in the metallurgical industries. Some important example include the iron blast furnace and iron-ore pelletizing shaft furnace which are very useful since they exhibit a very high potential heat transfer efficiency. However, the metallurgical counter-current gas-solid heat exchangers have not been found to be energy efficient due to channeling of hot gases (Wonchala and Wynnyckyj, 1986). It was the purpose of this study to determine whether the ELFUEL coal drying facility outlined in Minnesota Power's proposal "ELFUEL Demonstration of Low-Rank Coals" to the U. S. Department of Energy, Clean Coal Technology, Round #3 will perform as described and meet the objectives of the process, the economical hot-water drying of lignite coal.
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    An experimental study of critical submergence to avoid free-surface vortices at vertical intakes
    (1983-06) Rindels, Alan J.; Gulliver, John S.
    Free surface vortices at intakes can cause excessive vibration, efficiency loss, structural damage, and flow reduction in hydroturbines, pumps, culverts, etc. They can also be a safety hazard and a potential loss of life. One of the major problems encountered during intake design is the specification of submergence and other design parameters in order to avoid strong free surf ace vortex formation. A properly conceived model study will determine whether free surface vortices are likely to occur. Before that point, however, the engineer needs to develop a preliminary design and then decide if a model study is needed. In order to assist in preliminary intake design, a plot of dimensionless submergence versus intake Froude number is presented for a number of vertical and horizontal intakes from both field and laboratory observations. The pilot is divided into two regions: 1) a region where intake vortices are unlikely and a model study is not required except with extremely poor approach conditions, and 2) a region with a good possibility of intake vortices, and a model study is recommended. Region 2, where intake vortices are a good possibility, is very large; encompassing many intake facilities. This is because minimum intake submergence to avoid vortex formation is highly dependent upon approach conditions, which are site specific. In order to add some clarity to this limited design criteria, an experimental study was undertaken which focused upon typical intake approach conditions. Most hydropower intakes have a forebay to avoid high circulation near the intake, so the experimental study simulated approach conditions with a fore bay or approach channel of varying length and width. The experiments were limited to vertical be11mouth intakes. The tendency for vortex formation is enhanced by separation around the leading edge of the approach channel walls. A long, narrow forebay will reduce the tendency for vortex formation.
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    Hydropower Development alternatives at the Minnesota Falls Dam MN 00152
    (1982-04-02) Rindels, Alan J.; Gulliver, John S.; Garver, Rodrick J.
    The Minnesota Falls Dam is located on the Minnesota R.iver near Granite Falls, Minnesota. The existing dam and 'powerhouse were originally cc;mstructed in 1905 by the Minnesota Valley Power Company. The ownership of the dam and powerhouse has been" transferred' and the current owner is Northern States Power Company. The generation of electric power was discontinued and the powerhouse demolished in 1961. The purpose of this study is to estimate the cost of redeveloping the hydropower potential of the Minnesota Falls Dam, and the energy and power' that a hydropower facility would produce. The economic analysis required to determine project feasibility will be undertaken by the sponsor.
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    Measurements of Oxygen Transfer at Spillways and Overfalls
    (St. Anthony Falls Hydraulic Laboratory, 1989-07) Rindels, Alan J.; Gulliver, John S.
    The oxygen transfer across the air-water interface at a spillway or overfall is an important dissolved oxygen source or sink in a river-reservoir system. Normally many river miles are required for a significant air-water transfer of oxygen to occur, but at a spillway this same oxygen transfer may occur in the short residence time at the spillway/weir. The primary reason for this accelerated oxygen transfer is that air is entrained into the flow, producing a large number of bubbles. Air bubbles greatly increase the surface area available for gas transfer. In addition, the bubbles are transported by the flow to various depths downstream of the structure, increasing gas transfer and the possibility of supersaturation due to an increased saturation concentration at higher pressures. This is not a problem with oxygen, but in the case of dissolved nitrogen this supersaturation may cause fish mortality by nitrogen gas bubble disease. The results of this study are limited to oxygen but can be applied to transfer of any chemical for which transport is controlled by the water side of the interface using procedures described in Gulliver, Thene, and Rindels (1989).