Les opérations de dragage génèrent d’importants volumes de sédiments à teneur en eau élevée qui sont difficilement transportables. Toute opération de valorisation ou stockage des sédiments implique de réduire la teneur en eau. Le séchage naturel et la déshydratation mécanisée des sédiments répondent à cette attente. Le séchage naturel des sédiments est la technique de déshydratation la plus économique et la meilleure du point de vue environnemental. Le temps de séchage peut être réduit par des moyens techniques adaptés (retournement, scarification) mis en action par l'application de critères d’aptitude au séchage naturel. Pour ce faire, le processus de séchage naturel a été reproduit à l’échelle du laboratoire à l’aide d’essais d’Égouttage et de Séchage et d’essais de Séchage et de Retrait couplés à des essais scissométriques. Ils ont porté sur neuf sédiments : sept sédiments de barrage, deux sédiments marins et une kaolinite. Une relation Su=f(IP) a été établie. Cette relation permet d’obtenir la cohésion non drainée Su à partir d’une mesure de teneur en eau. Elle permet aussi de définir ou cerner le moment le plus propice au retournement des sédiments à l’aide d’engins spécifiques sur site. Une autre méthode mécanique pour réduire le temps de séchage est suggérée. Il s'agit de pratiquer une scarification des sédiments à l’aide d’outils mobiles, voire robotisés, comme un rouleau scarificateur ou d'une rangée d'outils transportés par un treillis mobile adapté. En ce qui concerne la déshydratation mécanisée des sédiments, une nouvelle méthode de déshydratation en continu a été proposée à partir d'une presse à boues KDS®. Pour des raisons de conception et d'application, la presse à boues KDS® n’a jamais été utilisée pour déshydrater des sédiments. Un plan expérimental a été développé. Il est démontré que la presse KDS® est capable de déshydrater un sédiment fin sableux sans une maintenance démesurée. Des adaptations de la presse KDS® à la déshydratation de sédiments et des améliorations sont finalement proposées. / Dredging operations produce large amounts of sediments with high water content, that are difficult to handle. Storage management and future reuses need to reduce the water content of sediments. Natural and mechanical dewatering of sediments meet this need. The most economic and eco-friendly method of dewatering is natural dewatering. Dewatering period can be reduced with suitable technical means such as adapted plough or scarifier for sediments, operating under defined dewatering criteria. The natural dewatering process was investigated and reproduced at the laboratory scale by performing Natural dewatering test and Shrinkage test coupled with shear measurements (vane shear testing). Nine sediments have been considered: seven dam sediments, two marine sediments and a kaolinite clay. A relationship Su = f(IP) has been established. It allows to deduce the undrained shear strength Su from only a measurement of water content. It allows to state on the right moment to put in operation the specific tools for ploughing and returning over or scarifying sediments stored. These tools can move in the sediments (adapted plough) or roll on the sediments (scarifiying roller) or roll on banks of sediment storage basin. Another way to dewater high water content sediments concerns a mechanical device. Thus a new method of continuous dewatering has been investigated using a prototype machine patented and referenced as KDS® sludge press. This type of press was not adapted for dewater sediments. Full of dewatering tests have been undertaken and performed with this prototype concerning some of sediments (see natural dewatering testing) and sandy clayey mixtures. It has been shown that KDS® press is able to dehydrate sediments including fine sandy sediments without excessive maintenance. Some adaptations and improvements of KDS® press to dewatering sediments are finally suggested.

The present work deals with some aspects of the fluidmechanics of paper-making,more specifically partial dewateringduring roll forming. The study is mainly experimental. Pressureand wire position measurements have been carried out in anexperimental facility, the KTH-Former,which models the rollforming zone of a paper machine. Measurements are carried out with pure water for threedifferent wires (fabrics): A non-permeable,a semi-permeable anda conventional wire. Although not used in paper making,thenon-permeable wire is useful when trying to understand thefundamental mechanics of roll forming.The semi-permeable wirewith finite but low permeability is used to model the effectsof the fibre web on the drainage. Tests have mainly been carried out for different wiretensions and different jet speeds. It is shown that the localcurvature of the wire is strongly correlated to the dewateringpressure. The conventiona wire shows a single pressure peak causingcomplete de- watering in the first part of the dewateringzone.The pressure distributions for the non-and semi-permeablewires are found to show two consecutive pressure peaks followedby a suction peak where the wire is taken of the roll.Thisoscillating behaviour is due to capillary waves where the wiretension plays the role of surface tension on a free surface.Thewavy behaviour of the wire is recovered from an analyticalmodel and the effect is governed by a dimensionless Webernumber. The measured wave lengths correspond well to thosegiven by the theory. When the wire tension is high,i.e.a high dewateringpressure,the flow in the impingement region collapses when thedynamic pressure of the headbox jet is about half of thedewatering pressure. It is shown experimentally that the localdrainage shows a correlation to the dewatering pressure andhence to the wire curvature. / NR 20140805

Master of Science

Student Number : 0418764K - MSc (Eng) dissertation - School of Civil and Environmental Engineering - Faculty of Engineering and the Built Environment / Increasing quantities of finer wastes often contain reactive sulphide minerals and high water contents that pose stability and environmental concerns. This study investigates how electrokinetic process can be improved, to make it more viable towards dewatering finer coal slurries. In the electrokinetic process, a direct current induces the movement of water out of a porous material. A wooden test box was filled up to two-thirds with fine coal slurries. Electrokinetic Geotextiles (EKGs) and brass were used as electrodes. The conducting wires were attached to each electrode and connected to a DC source to form an electro-osmosis cell. Current was passed through the cell and water moved to the cathode where it was withdrawn. The dewatering efficiencies ranged from 13.13 to 109.84 ml/Ah. The energy consumptions ranged from 5.23 to 14.03 kWh/m3 and are in line with those recorded by Johns (2005). Conductivity and pH measurements were taken. EKGs performed better than brass electrodes.

In modern coal preparation plants, solid-solid and solid-liquid separation processes used to treat fine coal are least efficient and most costly operations. For example, field studies indicate that the froth flotation process, which is normally used to treat minus (-0.2 mm) fine coal, often recovers less than 65 to 70% of the organic matter in this size range. Fine coal separation processes are also inherently less effective in removing pyrite than that of coarse coal separations. Moreover, while fines may represent 10% or less of the total run-of-mine feed, this size fraction often contains one-third or more of the total moisture in the delivered product. In order to address these issues, several multistage coal processing circuits were set up and experimentally tested to demonstrate the potential improvements in fine coal upgrading that may be realistically achievable using an "optimized" fine coal processing flowsheet. On the basis of results obtained from this research, engineering criteria was also developed that may be used to identify optimum circuit configurations for the processing different fine coal streams. In the current study, several fine coal cleaning alternatives were evaluated in laboratory, bench-scale and pilot-scale test programs. Fine coal processes compared in the first phase of this work included spirals, water-only cyclones, teeter-bed separators and froth flotation. The performance of each technology was compared based on separation efficiencies derived from combustible rejection versus ash rejection plots. The resulting data was used to identify size ranges most appropriate for the various alternative processes. As a follow-up to this effort, a second phase of pilot-scale and in-plant testing was conducted to identify new types of spiral circuit configurations that improve fine coal separations. The experimental data from this effort indicates that a four-stage spiral with second- and fourth-stage middlings recycle offered the best option for improved separation efficiency, clean coal yield and combustible recovery. The newly developed spiral circuitry was capable of increasing cumulative clean coal yield by 1.9 % at the same clean coal ash as compared to that of achieved using existing conventional compound spiral technology. Moreover, the experimental results also proved that slurry repluping after two turns is not effective in improving separation performance of spiral circuits. The third phase of work conducted in this study focused on the development of methods for improving the partitioning of pyrite within fine coal circuits. The investigation, which included both laboratory and pilot-scale test programs, indicated that density-based separations are generally effective in reducing sulfur due to the large density difference between pyrite and coal. On the other hand, the data also showed that sulfur rejections obtained in froth flotation are often poor due to the natural floatability of pyrite. Unfortunately, engineering analyses showed that pyrite removal from the flotation feed using density separators would be impractical due to the large volumetric flow of slurry that would need to be treated. On the other hand, further analyses indicated that the preferential partitioning of pyrite to the underflow streams of classifying cyclones and fine wire sieves could be exploited to concentrate pyrite into low-volume secondary streams that could be treated in a cost effective manner to remove pyrite prior to flotation. Therefore, on the basis of results obtained from this experimental study, a combined flotation-spiral circuitry was developed for enhanced ash and sulfur rejections from fine coal circuits. Finally, the fourth phase of work conducted as part of this investigation focused on evaluating a new mechanical, non-thermal dewatering process called Nano Drying Technology (NDT"). Experimental results obtained from bench-scale testing showed that the NDT" system can effectively dewater fine clean coal products from more than 30% surface moisture to single-digit moisture values. Test data obtained using a pilot-scale NDT" plant further validated this capability using a continuous prototype facility. It was also observed that, unlike existing fine coal dewatering processes, the performance of the NDT" system is not constrained by particle size. / Ph. D.

In modern coal preparation plants, solid-solid and solid-liquid separation processes used to treat fine coal are least efficient and most costly operations. For example, field studies indicate that the froth flotation process, which is normally used to treat minus (-0.2 mm) fine coal, often recovers less than 65 to 70% of the organic matter in this size range. Fine coal separation processes are also inherently less effective in removing pyrite than that of coarse coal separations. Moreover, while fines may represent 10% or less of the total run-of-mine feed, this size fraction often contains one-third or more of the total moisture in the delivered product. In order to address these issues, several multistage coal processing circuits were set up and experimentally tested to demonstrate the potential improvements in fine coal upgrading that may be realistically achievable using an "optimized" fine coal processing flowsheet. On the basis of results obtained from this research, engineering criteria was also developed that may be used to identify optimum circuit configurations for the processing different fine coal streams. In the current study, several fine coal cleaning alternatives were evaluated in laboratory, bench-scale and pilot-scale test programs. Fine coal processes compared in the first phase of this work included spirals, water-only cyclones, teeter-bed separators and froth flotation. The performance of each technology was compared based on separation efficiencies derived from combustible rejection versus ash rejection plots. The resulting data was used to identify size ranges most appropriate for the various alternative processes. As a follow-up to this effort, a second phase of pilot-scale and in-plant testing was conducted to identify new types of spiral circuit configurations that improve fine coal separations. The experimental data from this effort indicates that a four-stage spiral with second- and fourth-stage middlings recycle offered the best option for improved separation efficiency, clean coal yield and combustible recovery. The newly developed spiral circuitry was capable of increasing cumulative clean coal yield by 1.9% at the same clean coal ash as compared to that of achieved using existing conventional compound spiral technology. Moreover, the experimental results also proved that slurry repluping after two turns is not effective in improving separation performance of spiral circuits. The third phase of work conducted in this study focused on the development of methods for improving the partitioning of pyrite within fine coal circuits. The investigation, which included both laboratory and pilot-scale test programs, indicated that density-based separations are generally effective in reducing sulfur due to the large density difference between pyrite and coal. On the other hand, the data also showed that sulfur rejections obtained in froth flotation are often poor due to the natural floatability of pyrite. Unfortunately, engineering analyses showed that pyrite removal from the flotation feed using density separators would be impractical due to the large volumetric flow of slurry that would need to be treated. On the other hand, further analyses indicated that the preferential partitioning of pyrite to the underflow streams of classifying cyclones and fine wire sieves could be exploited to concentrate pyrite into low-volume secondary streams that could be treated in a cost effective manner to remove pyrite prior to flotation. Therefore, on the basis of results obtained from this experimental study, a combined flotation-spiral circuitry was developed for enhanced ash and sulfur rejections from fine coal circuits. Finally, the fourth phase of work conducted as part of this investigation focused on evaluating a new mechanical, non-thermal dewatering process called Nano Drying Technology (NDT™). Experimental results obtained from bench-scale testing showed that the NDT™ system can effectively dewater fine clean coal products from more than 30% surface moisture to single-digit moisture values. Test data obtained using a pilot-scale NDT™ plant further validated this capability using a continuous prototype facility. It was also observed that, unlike existing fine coal dewatering processes, the performance of the NDT™ system is not constrained by particle size. / Ph. D.

This objective of this project was to develop a new dewatering device that could produce a lower moisture content and better fine particle recovery than current technology. To meet this goal, a hyperbaric horizontal belt filter was designed and constructed over the course of 18 months. Once built, the filter was then thoroughly tested to determine operational capabilities. The test data showed that the lowest moisture content that could be achieved with a coarse feed (minus 1 mm screen-bowl centrifuge feed) was 8.8%. This value could be further reduced to 8.2% and capacity increased with the use of dewatering aids. When testing with a fine feed (minus 0.15 mm column product feed), the lowest moisture content was 35% without chemicals and 29% with chemicals. A 50/50 mixture by volume of coarse and fine feeds was artificially created and provided a moisture of 10.8%, which was reduced using reagents to 8.4%. The machine provided a very high recovery rate for all feed materials. Of the coal input, no less than 94% of it reported to the dry product. The pressure used to dewater the coal was the controlling factor for the air consumption of the unit. The data from these tests suggest that a full size production unit is feasible, although the power requirements for gas compression would be high. / Master of Science

A vast majority of coal and mineral cleaning and upgrading processes involve the addition of water. The water allows the movement of particles throughout the processing plant and the upgrading of the material. When the process is complete the finished product must be dewatered. This is due to storage concerns, in which the water takes up a majority of the space, and high transportation costs, in which no compensation is obtained from the buyer for the shipment of the liquid. Dewatering is accomplished by many devices, with the two most common pieces of equipment being the screen-bowl centrifuge and disk filter. This thesis tests and compares the effect of reagents on dewatering using the screen-bowl centrifuge and disk filter. Coal was obtained from the Upper Banner, Pittsburgh No. 8, Taggart, and Dorchester seams, crushed and ground to the desired size, and run through the dewatering circuits. The results showed that the moisture content of the product can be greatly reduced in the disk filter while being only slightly reduced in the screen-bowl centrifuge. It was also shown that the recovery can be slightly increased in the screen-bowl centrifuge. Overall, with the addition of reagents, the disk filter outperformed the centrifuge in both recovery and moisture content. A model was also developed for the screen-bowl centrifuge. The results from the screen-bowl tests helped in the development of this model. This model can be used to predict the moisture content of the product, the recovery, particle size distribution of the effluent and particle size distribution of the product. The model also predicted how the product moisture and recovery were affected by changing the feed flow rate, feed percent solids, centrifuge speed, and particle size distribution. / Master of Science

No description available.

The main objective of this research was to identify the compounds responsible for persistent odors in biosolids during long-term storage using olfactometry measurements and to determine their generation pattern with regard to time of appearance and decline using gas chromatography-mass spectrometry (GC-MS). Another objective of this study was to investigate the effect of various digestion and dewatering techniques on odors and determine if there is a correlation between the peak concentration and time of appearance of short-tem organic sulfur odors and persistent odors. Headspace analysis was used to quantify short-term odor-causing organic sulfur compounds and persistent odors from compounds such as indole, skatole, butyric acid and p-cresol for an incubation period up to 150 days. A unique odor generation pattern was observed for each of the compounds analyzed for all the dewatered cakes tested in this study. Dewatered cake samples were also analyzed to determine their detection threshold by a trained odor panel and the results were consistent with the general pattern of odor generation observed in this study. Positive correlations were observed between the peak concentration of organic sulfur and persistent odor compounds whereas little or no relationship was observed between their times of appearance. The type of sludge used in digestion (primary sludge, WAS and mix) was found to affect the production of odor-causing compounds significantly. Primary sludge produces the highest odors followed by mix. WAS was found to produce biosolids with a low odor concentration. Positive correlation was observed between odor concentration and digestion SRT. Significant reduction in odor concentration was observed when the SRT was increased from 12-days to 25-days. At 45-day SRT, further reduction in odors was not very significant. Moreover, the results from this study indicate that methanogens play an important role in the degradation of both organic sulfur and persistent odors. Although the highest odors during biosolids incubation came from sulfur compounds, the persistent odors must be managed as part of a comprehensive sludge management approach. / Master of Science