Sequential polymer dosing for effective dewatering of ATAD sludges

Dewatering problems associated with the sludge from autothermal thermophilic aerobic digestion (ATAD) of sludge, result in large chemical conditioning costs for effective dewatering. A variety of chemical conditioners were used to improve dewatering, but none of them were able to dewater the sludge as desired at acceptable conditioning doses. It was found that during the digestion process, chemical precipitation of divalent cations occurred. Some of the ATAD sludge colloids were found to have a positive zeta potential and these were thought to be the precipitated divalent cations. Sequential polymer dosing using either iron or cationic polymer, followed by anionic polymer, was found to improve dewatering. The use of anionic polymer is essential and allows the use of smaller amounts of iron or cationic polymer for effective dewatering. The use of the less expensive anionic polymer along with cationic polymers has the potential to make the use of the ATAD process more economical.     

LAB-SCALE IMPULSE DRYING EXPERIMENTS WITH EXTENSION TO HIGHER IMPULSE

Impulse drying uses high temperature and high impulse in the press section of the paper machine. The technique can increase the water removal rate and thereby minimize the size of the dryer section or alternatively increase production capacity. Additionally, the technique improves paper properties compared to conventional wet pressing. This paper contains a discussion of the value associated with extending the press impulse in impulse drying. Experiments were conducted in a lab-scale press simulator. Experiments with 150 g/m² liner were conducted with four different press impulses, 160, 260, 360 and 450 kPa s. The impulse was varied by changing the dwell time between the pressurization and the depressurization phase. It was shown that increasing the nip length and press load beyond conventional shoe press limits gave noteworthy press dryness and sheet strength advantages. The impulse drying experiments were also compared with single and double-felted wet pressing experiments.

     

Freeze-thaw and consolidation tests on Suncor mature fine tailings (MFT)

This paper presents the findings of a laboratory investigation of the effects of freeze-thaw, and sulfuric acid and quicklime amendment on Suncor mature fine tailings (MFT) post-thaw geotechnical behaviour and soil micro and macro-fabric. This paper gives the results of a consolidation test program on Suncor MFT using a large strain consolidation apparatus along with constant head flow tests to evaluate the void ratio versus effective stress and void ratio versus hydraulic conductivity data for three types of MFT specimens. The large scale and small scale fabric (macro-fabric and micro-fabric) of these specimens were also examined. The results indicated that freeze-thaw can effectively reduce the initial void ratio and the compressibility of untreated and amended MFT. Freeze-thaw can also significantly increase the hydraulic conductivity of MFT, which in combination with reduced compressibility enhances the MFT consolidation. These results were supported by changes observed in the macro and micro-fabric of the tested MFT specimens.     

“九五”选煤研究成果对中国选煤技术的影响

回顾了“九五”课题立项背景和立题指导思想，介绍了“九五”期间选煤科学研究在５个技术领域的国家“九五”攻关和部级课题分布，重点介绍了高硫难选煤脱硫、大型高效全重介简化工艺、干法与节水型选煤、细粒煤粉选、传统技术升级运用技术等领域的研究成果内容、特点及使用范围，并分析了这些研究成果对中国选煤技术的影响及其将对选煤业的推动作用。     

LAB-SCALE IMPULSE DRYING EXPERIMENTS WITH EXTENSION TO HIGHER IMPULSE

Impulse drying uses high temperature and high impulse in the press section of the paper machine. The technique can increase the water removal rate and thereby minimize the size of the dryer section or alternatively increase production capacity. Additionally, the technique improves paper properties compared to conventional wet pressing. This paper contains a discussion of the value associated with extending the press impulse in impulse drying. Experiments were conducted in a lab-scale press simulator. Experiments with 150 g/m² liner were conducted with four different press impulses, 160, 260, 360 and 450 kPa s. The impulse was varied by changing the dwell time between the pressurization and the depressurization phase. It was shown that increasing the nip length and press load beyond conventional shoe press limits gave noteworthy press dryness and sheet strength advantages. The impulse drying experiments were also compared with single and double-felted wet pressing experiments.     

A simplified parameter extraction technique using batch settling data to estimate suspension material properties in dewatering applications

Batch settling tests are considered in order to obtain dewatering material properties of suspensions/sludges towards the low end of the range of solids fractions. Plausible functional forms are considered for fitting batch settling test (height vs. time) data. In particular, power law and exponential decay functions are shown to be reasonable fits to simulated synthetic batch settling data. These forms are subsequently employed to reconstruct functional relationships between a settling flux function and suspension solids fraction. The functional relationships so obtained are found to be faithful representations of the flux function used to generate the simulated settling data, with improved agreement being achieved by restricting the interval of solids fraction across which the reconstruction is performed. The results suggest that general features only (and not fine details) of batch settling curves are required to reconstruct settling flux functions. In the particular case where power law fits are employed to describe the settling height data, an analytic formula can be derived linking the settling flux function explicitly and directly to the power law fitting parameters. This simplifies immensely the technique for extracting parameters for the settling flux. When applied to real experimental data, errors arising from using the power law fits tend to be small compared to those inherent in the experimental measurements themselves.     

Electro-Kinetic Technology as a Low-Cost Method for Dewatering Food By-Product

Increasing volumes of food waste, intense environmental awareness, and stringent legislation have imposed increased demands upon conventional food waste management. Food by-products that were once considered to be without value are now being utilized as reusable materials, fuels, and energy in order to reduce waste. One major barrier to the valorization of food by-products is their high moisture content. This has brought about the necessity of dewatering food waste for any potential re-use for certain disposal options. A laboratory system for experimentally characterizing electro-kinetic dewatering of food by-products was evaluated. The bench scale system, which is an augmented filter press, was used to investigate the dewatering at constant voltage. Five food by-products (brewer's spent grain, cauliflower trimmings, mango peel, orange peel, and melon peel) were studied. The results indicated that electro-kinetic dewatering combined with mechanical dewatering can reduce the percentage of moisture from 78% to 71% for brewer's spent grain, from 77% to 68% for orange peel, from 80% to 73% for mango peel, from 91% to 74% for melon peel, and from 92% to 80% for cauliflower trimmings. The total moisture reduction showed a correlation with electrical conductivity (R² = 0.89). The energy consumption of every sample was evaluated and was found to be up to 60 times more economical compared to thermal processing.     

Effect of Hydrodynamics During Crystallization on Mechanical Dewatering of Salicylic Acid

Mechanical cake dewatering is always desired to reduce the load on thermal dewatering (drying). Any change in the upstream process such as crystallization can have a significant influence on the filtration as well as cake dewatering characteristics. The present study deals with the effect of hydrodynamics (mixing intensity) during salicylic acid crystallization on the air dewatering characteristics in the subsequent pressure filtration. The mixing conditions during crystallization were varied by using three different types of agitators (anchor impeller [AI], curved blade turbine [CBT], and bar turbine [BT]) and by varying the speed of agitation. The effect of operating pressure and dewatering time on the final moisture content of the cake was also studied.

The crystal properties (crystal size and size distribution) were found to vary with the mixing intensity, which further influenced the cake dewatering kinetics as well as the residual moisture content. An AI, which is a laminar flow impeller, produced crystals with a wide size distribution and higher mean particle size, which resulted in cake with high porosity and hence higher moisture content. The high porosity (as well as high cake permeability) caused early air breakthrough, which resulted in ineffective dewatering of cake. Therefore, in this case the residual moisture in cake was found to be higher (27%) even at higher dewatering pressure (1.5 bar gauge) and longer dewatering time (90 s). A BT creates high turbulence during mixing and produced crystals with a relatively narrow size distribution and lower mean particle size, which provided low-porosity cakes. Such cakes could be efficiently dewatered and the final cake moisture content was found to decrease to about 15%, a significant improvement in the filterability of the cake. The dewatering data were modeled according to the correlation between irreducible cake saturation and capillary number for predicting the cake dewatering characteristics (residual moisture as well as dewatering kinetics) and the results were compared with the experimental data.     

低廉充填胶凝材料的开发与应用研究

开发了以炉渣、黄土、石灰为主要原料的低廉充填胶凝材料，试验了多孔直管滤网振动预脱水和分流沉降预脱水新技术，实现无水泥或少水泥胶结充填，大幅度降低胶充成本，经济效益和社会效益显著．     

沙特阿拉伯MA’ADEN取水口基坑降水

对沙特MA’ADEN取水口降水工程的设计、施工、运行、降水效果以及与预期的水文地质参数的比较及取值等方面进行了介绍、分析，希望对今后类似工程有所帮助。