EXPERIMENTAL STUDY OF CASSAVA SUN DRYING

ABSTRACT

Experiments were carried out in Davis, California, USA to compare sun drying of a bed of cassava chips placed in wire mesh trays with those placed in trays made of sheet metal. The wire mesh permitted wind to blow easily through the bed of chips, while the sheet metal constrained the wind to flow across the top of the bed, Drying was faster in the wire mesh trays; the chips reached a moisture content for safe storage after 27 hours of drying, while those in the sheet metal trays took 35 hours. The uniformity of drying was also markedly better in the wire mesh trays. Higher temperatures were attained in the chips contained in the sheet metal trays due to contact heat transfer between the trays and the chips. However the restricted air flow around the chips in the sheet metal trays led them to dry slower than those in the wire mesh trays.     

IMPROVING FLOW PATTERNS IN A DISTILLATION TRAY BY MODIFYING DOWNCOMER APRON SHAPE

A simple modification of the downcomer apron shape has been proposed and experimentally studied. Experiments were carried out in a 40 [cm] diameter tray with water and with no vapor flow. Weir length to diameter ratios were varied from 0.6 to 0.775 and water flow rates between 150 and 600 [cm³/s]. Curved, triangular, trapezoidal and toothed apron shapes were tested. Velocity distributions on the plate were measured using the hydrogen bubble technique up to a flow rate of 200 [cm³/s]. Stagnation point loci were determined for all operating conditions, and the fractional forward-flow area (FFA) was then calculated. The FFA's were considered a measure of the efficiency of the tray, and hence used to compare the performance of the various apron shapes.

Three flow patterns were experimentally observed: regular, inverted and transition. Flow pattern maps were obtained, which permit the selection of an optimum shape when an appropriate scale up criterion is used. To this end, it was found that the best criterion was to use the same liquid residence time in the prototype and model. The results proved that the FFA values for a modified apron were always higher than for the standard or conventional apron. This is important in tray design, since it provides an easy way of improving distillation plate efficiencies.     

贝加莱全自动内部物流中心解决方案

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Understanding maldistribution in 3-pass trays

Understanding 3 pass trays is the key to design of 6 pass trays, such as those in the large towers expected in carbon-capture services. This paper presents a hydraulic distribution model for 3 pass trays with no liquid or vapor equalization. The model is verified by comparison with FRI's test data and with one operating tower. Our paper predicts good distribution for the 3 pass trays tested at FRI, and shows that the poor efficiencies in some of the tests were due to losing the downcomer seals and not tray maldistribution. The model predicts good distribution at maximum rates in the operating tower, but finds that at lower rates, where valves open and close, there is an extreme sensitivity of vapor distribution to small pressure drop variations. This sensitivity precludes reliable modeling of distribution in this region and may define an unstable region in the operation of 3 pass trays.     

CALCULATING DISTILLATION EFFICIENCIES OF MULTICOMPONENT i-BUTANE/ n-BUTANE COLUMN

This paper presents experimental data and estimated distillation efficiencies of an industrial scale distillation column separating i-butane and n-butane. The data gathered from plant instruments and laboratory analysis were reconciled and compared to distillation simulations. The simulations were performed with a number of real plates using the point and the Murphree plate efficiency calculation model. This matrix model of efficiency at first estimates the point efficiencies using the two-film and multicomponent mass transfer theory. The point efficiencies are then converted into Murphree plate efficiencies using a liquid mixing model. The whole method is implemented in a computer program to simulate an industrial distillation column with real plates. Finally the calculated product compositions are compared with reconciled measurements. The values of overall, section, point and Murphree plate efficiencies of multicomponent i-butane/n-butane system are also calculated. The results show that point efficiencies are not adequate for large industrial scale columns. The results also imply that the plate efficiency calculation method can be utilized and employed in the design and simulation of industrial scale columns.     

Separation Tray without Downcomers

The Dualflex tray is a fractionation device without downcomers but with mobile valve plates and top weirs positioned above the perforations of the tray deck, which allows liquid and vapor or gas to pass through. According to the results of systematic experimental investigations, this mass transfer device can be considered as a high capacity tray in comparison with conventional trays; its separation efficiency is also higher than that of a comparable Dualflow tray under identical test conditions. It can be recommended not only for installing in new separation plants, but also for revamps in cases where increasing throughput in existing columns are required. The aforementioned efficiency and capacity studies were carried out in a pilot plant of 600 mm column diameter.     

Froth Porosity and Clear Liquid Height in Trayed Columns

The paper deals with some of the results obtained during experimental research of fluid dynamic behavior of cascade columns. The three most commonly used types of trays (tunnel, sieve, and valve) occupied our attention and 595 experimental runs were performed on a 314 mm inside diameter column with an air‐water system. Analysis of measured values of froth porosity has confirmed that Azbel's equation should be used, despite its theoretical origin. For clear liquid height, a new correlation was established, because statistical parameters of equations taken from literature were not satisfactory. Both equations were tested on experimental data obtained on two rectangular columns, showing good statistical parameters.