Upgrading and dewatering of raw tropical peat by hydrothermal treatment

In this study, hydrothermal upgrading and dewatering of raw tropical peat derived from Pontianak, West Kalimantan-Indonesia was evaluated at temperatures ranging from 150 to 380 °C, a maximum final pressure of 25.1 MPa and a residence time of 30 min. The moisture content of the raw peat was approximately 90 wt.%. Raw peat was hydrothermally upgraded without the addition of water in the laboratory scale. The yield of the solid products was between 53.0 and 99.7 wt.% and the effective calorific value of hydrothermally dewatered peat was between 17,290 and 29,209 kJ/kg following hydrothermal upgrading. In addition, the oxygen content in the solid product was varied from 38.4 to 15.6 wt.% after upgrading, while the carbon content from 55.2 to 77.8 wt.%. The hydrothermally upgraded peat fuel product also had an equilibrium moisture content of 2.3 wt.% and a maximum equilibrium moisture content of 17.6 wt.%. Upgraded peat is characteristically resistant to moisture adsorption at high humidity, which makes it promising for fuel based combustion. The change in the carbon-functional groups and their properties, as determined by FTIR and ¹³C NMR, are discussed in terms of the hydrothermal upgrading and dewatering process.     

连续式过滤机的新发展

介绍了近年开发的几种先进新型连续式过滤机及其结构、工作原理、特点和应用效果 ,并进行了分析。     

PRESSURIZED ELECTROOSMOTIC DEWATERING IN A FILTER CYCLE

This paper describes the role of pressurized electroosmotic dewatering (EOD) in a filter cycle. A laboratory-scale filter-press was used to filter a highly conductive silica suspension under constant pressure, followed by washing and mechanical precompression of the filter cake and finally by pressurized EOD at constant electric current. The influence of filter cycle parameters (filtration and washing pressure and duration, mechanical pressure, and electric field intensity) on the final cake dryness and energy consumption was studied. Electrodes of different materials, forms, and surfaces were used.

The optimal conditions of each filter cycle operation were found to minimize the energy consumption during EOD and maximize the cake dryness. With mechanical pressure and electric field intensity increasing, the total energy consumption increased, but the specific energy consumption (per kg of expressed water) decreased, and the final filter cake was dryer. The pressurized EOD also used less energy than thermal drying.     

Dewatering Cofferdam for Construction of Olmsted Locks

Twin 110-ft×1,200-ft (SI unit conversions are provided in the Appendix) locks and a dam are being constructed in the Ohio River near Olmsted, IL. Construction of these locks required digging a 1,200-ft-wide and 2,200-ft-long excavation in the Ohio River to 100 ft below the design river stage. The size of the cofferdam required for lock construction, and the depth of excavation, made control of groundwater of paramount importance to excavation safety. The work included removing and/or controlling all ground and surface water within the cofferdam; controlling seepage through or beneath the coffercells and from the open cut along the Illinois bank; reducing the artesian head in an underlying stratum of highly jointed, indurated clayey silt and/or siltstone; and lowering the water level in the coffercells. The dewatering was accomplished by installing and pumping deep wells with submersible pumps, with vacuum, within the cofferdam area. The dewatering system was pump tested and evaluated before unwatering the excavation. Evaluation of the pump test data showed that the dewatering system as designed and installed would be adequate for the maximum design river stage with the addition of a few wells in the bottom of the excavation.     

Modelling the electro-osmotically enhanced pressure dewatering of activated sludge

The mechanical dewatering of biological materials, such as activated sludge, is troublesome due to their high compressibility. The dewatering can be improved drastically by the use of electro-osmosis, a technique in which a direct current electric field is applied to the filter cake, inducing an electro-kinetic displacement of the liquid phase. In this article, a model is presented which describes this process for a one-dimensional, one-sided filter press. The model starts from two existing models, each describing a part of the process [Iwata, M., Igami, H., Murase, T., 1991. Analysis of electroosmotic dewatering. Journal of Chemical Engineering of Japan 24(1), 45-50; Sørensen, P.B., Moldrup, P., Hansem, J.A., 1996. Filtration and expression of compressible cakes. Chemical Engineering Science 51(6), 967-979]. A robust solution scheme for the basic flux and continuity equations is used to describe filtration and expression. Regarding the electro-osmosis, an adapted form of the Darcy equation, expressing electro-osmotic induced flow as well as pressure induced flow, is integrated into the former solution scheme. This permits the simulation of the overall process using a single model. Validation of the model revealed that the experimental piston height during dewatering can be described accurately provided that temperature effects are taken into account.     

Investigation of the role of interfacial chemistry on particle interactions, sedimentation and electroosmotic dewatering of model kaolinite dispersions

The influence of pulp chemistry on particle interactions and dewatering behaviour of colloidal kaolinite dispersions has been investigated under coagulation conditions. The dispersion shear yield stress, settling rate and consolidation showed strong dependence upon pH and ionic strength, indicating a maximum at ∼pH 3.2 which was established as the isoelectric point (iep) by particle zeta potential analysis. A “gel point” solid concentration at which the dispersion began to be significantly networked and gravity-driven consolidation of the pulp was completely suppressed, occurred at 13 vol.% (∼28 wt.%). The dewatering rates due to coagulation were significantly lower than those commonly achieved by polymeric flocculation, however the sediment consolidation was ∼25% higher when compared with flocculated pulps. Electroosmosis was found to be effective in consolidating pre-sedimented pulps to spadeable pastes (∼30 vol.%) at pH values away from the iep where zeta potential was higher and ionic strength low (10^− 3 M). This pulp consistency or markedly improved consolidation behavior is not achievable under coagulation and/or flocculation conditions.     

Improved estimates of power consumption during dewatering of mine tailings using electrokinetic geosynthetics (EKGs)

Electrokinetic geosynthetics (EKGs) were developed about a decade ago, producing a material that did not experience the same corrosion problems as metal electrodes when used in electro-osmotic (EO) dewatering applications. The conductive polymeric material from which EKGs are made has the additional advantage of being able to be formed into a variety of shapes, including drainage tubes such as those used in this study. One of the primary concerns regarding EO dewatering applications is the rate of energy consumption. This paper reports experiments at three different scales, on different mine tailings materials, that illustrates the potentially misleading results obtained from small scale laboratory tests. Using large, outdoor tests, power consumption rates for treating a kaolinitic mineral sands tailings and a smectitic diamond tailings were found to be up to 30 times lower than the power consumption rates obtained from laboratory tests using small samples in a purpose built EO cell. The primary reason for the improved performance is thought to be the lower voltage gradient used in the field tests, plus the geometric advantages offered by a field layout where a greater volume of material is exposed to the EO effect than only the material directly between the electrodes, which is the case in the EO cell tests. Finally, in the field tests the EO treatment caused the early development of vertical cracks in the tailings, resulting in increased exposure of the tailings to the effects of solar drying. This effect cannot obviously be reproduced in the EO cell laboratory tests, and can be a major advantage for the in situ treatment of mine tailings lagoons, where in some materials the onset of cracking is significantly delayed by the development of an impermeable surface crust.     

某超高层建筑深基坑管井降水的应用与探讨

随着南通地区高层建筑的增多,深井降水利用较为普遍,某些深基坑在设计计算过程中未考虑降水深度范围内土层对降水的影响,易造成降水失败,结合具体工程,对深井降水方案进行分析和探讨,可供相关工程参考。     

离心甩水法测量UO_2颗粒的假密度

本文介绍一种新的颗粒密度测量方法。该方法适用于测量直径在 300μ 以上的陶瓷颗粒的假密度。对五种不同密度的 UO_2 小球进行了测试,所得结果的相对标准偏差为±0.16%,最大相对误差不超过±1%。     

深基坑降水施工中防止相邻建筑沉降的技术措施

本文结合漳州银冠大厦基坑护壁降水的工程实例,论述了基坑与邻近建筑物距离过近时,采用截水帷幕,改基坑边缘井为内部井以调整降水曲线和配合回灌等三项措施,确保相邻建筑不发生沉降。