The objective of this investigation was to determine the sensitivity of three selected input parameters in the operational control of continuous bottan-fed thickeners used for the treatment of coal refuse slurries. The three variable paramenters were "Feed Flow Rate," "Feed pH," and "Feed Solids Concentration." These three input parameters were studied under three polymeric conditions.
The X-ray analysis of underflow refuse samples from two coal preparation plants showed that the samples contained clays of various types. Kaolinite type clay was chosen as the feed material in this investigation. The static settling tests on the kaolinite-water suspensions using polymers showed that slurries with 5.0% or less feed solids concentration could be separated by all the polymeric conditions (cationic, anionic, and cationic-anionic). The continous solid-liquid separation in the laboratory thickener showed that a 3.0% feed solids was the maximum feed solids concentration that could be used in the continuous thickener operation with the same polymeric conditions. The minimum feed solids concentration was 1.0% solids. The feed pH ranged from 5.0 to 10.0, and the feed flow rate ranged from 915 to 2275 ml/min.
The collective determination of the most and least sensitive variables was based on an experimental design procedure, employing Response Surface Methodology (RSM), to develop mathematical models for the thickener control. The three polymeric conditions used were, cationic polymer, anionic polymer, and a combination of cationic-anionic polymer. For each polymeric condition, two mathematical models were developed: one for overflow response, the other for underflow response.
The formation of small flocs by the cationic polymer produced a sludge bed which prevented the particles from escaping into the overflow. The movement of the sludge bed was rapid. To prevent the bed from passing a pre-determined height, the underflow pump was "on" during most of the experimental time. This situation brought a low solids underflow, but the desired quality of the overflow was reasonably good.
The anionic polymer did not produce a good overflow, because neutralization of the surface charges did not occur and a sludge bed never formed. This condition left the underflow pump "off" at all times, except when samples were to be withdrawn for the analysis. Overflow was the worst quality compared to the other polymeric conditions. The underflow quality was better than the underflow of the cationic tests, and almost as good as the underflow with the combination polymer.
The use of the combination cationic-anionic polymer produced large floes immediately, because of the surface charge neutralization and bridging action that occurred. The time allowed for this action was longer for low to medium flow rates, producing larger flocs which settled and prevented the formation of a sludge bed. However, the desired quality of overflow and underflow remained good. For the majority of the runs with combination polymer, the underflow pump was "off" at all times, except when samples were withdrawn for the analysis. The overflow and underflow quality was the best desired quality for the combination polymer when compared to the results obtained utilizing the cationic and the anionic polymers separately.
The input variables were used to develop six mathematical models. With the aid of the models, contour plots of the main responses were generated; that is, the "suspended solids in the overflow" and the "percent solids in the underflow." The plots gave regions of the best thickener performance within the wide variations of the three mentioned input variables. The plots would allow an operator to control and/or adjust any of the three variables to achieve optimum conditions. The combination polymers produced the best desired quality of overflow and underflow. For this polymeric condition, changes in the feed solids concentration was the most sensitive factor in the maintenance of the overflow quality, and the feed pH was the most sensitive factor for the maintenance of the underflow quality. The role of the feed flow rate for the maintenance of both overflow and underflow quality was proved to be moderate. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/114338 |
| Date | January 1980 |
| Creators | Ghalambor, Ali |
| Contributors | Environmental Sciences and Engineering |
| Publisher | Virginia Polytechnic Institute and State University |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | xv, 237 pages, 3 unnumbered leaves, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 06723148 |
Page generated in 0.0023 seconds