The effect of charged additives and heat pretreatment on the dewatering of fuel-grade peat

The addition of salt, mineral acid or polyelectrolyte or the preheating of fuel-grade peat results in significant improvement of the amount of water released during mechanical pressing. The charged species all act by suppressing the charge on the colloidal particles and, for different reasons, organic salts, protons and polyelectrolytes are all more effective than simple inorganic salts. The cations with large organic portions, including surfactants, have an augmented adsorption to the particle surface because of the hydrophobic effect. The polyelectrolytes are strongly associated with the particles because of the chelate effect. Protons are very effective because they can actually neutralize the net charge on the particle surface by forming covalent bonds with the acid functions. The mechanism by which heat pretreatment improves dewatering is not caused by suppression of the surface charge. The effect could be due to melting or softening of peat waxes causing alterations of surface features which improve water release. It is also possible that heating provides sufficient energy to overcome the energy barrier keeping the particles apart.     

A chemical and thermal pretreatment process for the dewatering of fuel-grade peat

Using a batch heating system raw peat was heated to temperatures below 200°C before mechanical dewatering. Variations were made in heat up time, residence time and helding temperature. After heat treatment, dewatering could be further enhanced by the addition of chitosan, a polycationic biopolymer.     

Treatment of fuel peat to enhance moisture removal

Dewatering of peat by mechanical pressing can be greatly improved by treatments, such as addition of electrolytes and freezing and thawing, which break down the colloidal peat structure. Particularly, by addition of 9.4% lime to peat, followed by freezing, thawing and pressing at ≈8.27 MPa, the moisture content can be reduced from 90% to ≈50%. The improvement gained is commercially advantagous.     

Treatment of fuel peat by the addition of lime with a freeze-thaw cycle

Dewatering of fuel peat by mechanical pressing can be greatly improved by treating the peat with lime and then running it through a freeze-thaw cycle. Results are presented for different concentrations of lime and different types of treatment.     

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.     

Modification of filler-matrix interactions by adsorption of surfactants and its effect on the strength of high-density polyethylene/chalk composites

—The interactions between cationic and anionic surfactants and natural chalk were studied by means of adsorption and zeta potential measurements. Using these experimental results, possible orientations of adsorbed surfactant layers on chalk were deduced and the adsorption free energy was estimated. Chalk modified with stearic acid was extracted with different solvents in order to distinguish the individual bond types between stearic acid and chalk. The investigation of the influence of the surfactant constitution and concentration on selected mechanical properties (impact strength, tensile strength, flexural stress) of high-density polyethylene/ chalk composites showed that the efficiency of the modification with surfactants correlated with their ability to adsorb on the filler surface. The decrease in tensile strength and flexural stress caused by surfactants can be described in the same way as the action of surfactants in the textile washing process. The effect is directly proportional to the adsorbed molar amount of the surfactant. The experimental results also allow the effect of adsorbed water on the strength of filled or reinforced polymers to be described. If the bonding energy of the modifier on the filler is of the same order of magnitude as the interaction energy between the filler and the matrix, the modifier decreases the tensile strength. On the contrary, the impact strength is controlled by factors that cannot be deduced primarily from the interaction energy. Different mechanisms are discussed, among them the possibility of a 'zeta correlation'.     

钻井废水的电荷中和絮凝作用研究

研究了钻井废水中悬浮固相颗粒表面电荷被絮凝剂电荷的中和作用,探讨了废水的化学脱稳和絮凝效率．结果表明,当固相颗粒表面 电位分别被2500mg／LAl2(SO4)3和300mg／LCPAM中和为OmV,悬浮液的毛细管抽吸时间CST值被降低到100s以下时,钻井废水达到了化学脱稳。将2300mg／L A12(SO4),与400mg／LCPAM复配使用,对钻井废水中20μm以下细小颗粒的电荷中和絮凝作用能够使其减少到1．2％,分离水的浊度达到30FUN,色度26度,COD95mg／L。     

The catalytic hydrotreatment of peat pyrolysate oils

A 65 wt % yield of hexane-soluble liquid, containing 83% of the feed carbon, was obtained when Finnish Carex-peat pyrolysate was hydrotreated batchwise (21.5 MPa for two hours at 390°C with 10 wt % catalyst, 4% CoO/15.5% MoO₃ on γ-alumina). Oxygen content was lowered from 22% to 3% in the process. Nitrogen and sulphur contents of the product were 4.3% and 0.10%, respectively. Straight-chain material predominated in the upgraded product and C₁₄-C₂₉ n-alkanes have been identified along with some phenols. The peat pyrolysate is also predominantly straight-chain material, but contains polar functionalities such as the carboxyl group.     

The effect of mixed surfactants on enhancing oil recovery

Micelles composed of mixed surfactants with different structures (mixed micelles) are of great theoretical and industrial interest. This work pertains tomaximizing interfacial tension (IFT) reduction via surfactant pairs. In this respect, four types of fatty acid amides based on lauric, myristic, palmitic, and stearic acids were blended with dodecyl benzene sulfonic acid at a molar ratio of 4∶1 and designated as A₁, A₂, A₃, and A₄, respectively. The IFT was measured for each blend at different concentrations using Badri crude oil. The most potent formula (A₄) was evaluated for using in enhanced oil recovery (EOR). The IFT was tested in the presence of different electrolyte concentrations with different crude oils at different temperatures. Finally several runs were devoted to study the displacement of Badri crude oil by A₄ surfactant solution using different slug sizes of 10, 20, and 40% of pore volume (PV). The study reveled that Badri crude oil gave ultra-low IFT at lowest surfactant concentration and 0.5% of NaCl. The recovery factor at a slug size of 20% PV was 83% of original oil in place compared with 59% in case of conventional water flood.     

Kinetics of precipitation of surfactants. I. Anionic surfactants with calcium and with cationic surfactants

Isoperibol calorimetry was used to measure the rates of precipitation for aqueous solutions of several anionic surfactants with calcium and of anionic and cationic surfactants. A monomer concentration-dependent supersaturation ratio was used to describe the relative rates of precipitation for the surfactant systems studied. This supersaturation ratio allows for the relative rates of precipitation of any surfactant solution to be compared whether micelles are present in solution or not. In general, as the supersaturation ratio increases, the rate of precipitation decreases and the induction time decreases, bot above and below the critical micelle concentration (CMC). The rate of precipitation of sodium dodecyl sulfate (SDS) with dodecyl pyridinium chloride is much slower than the rate of precipitation of the anionic surfactants with calcium for similar supersaturation ratios. The rate of precipitation of SDS with calcium is slightly faster than the rate of precipitation of sodium octyl benzene sulfonate for similar supersaturation ratios. Studies of precipitate crystals, conducted using image analysis, showed that size and shape dependent on the initial supersaturation, the precipitating surfactant molecule, and the extent of aging (until an equilibrium size and shape was reached). Also, differences in the appearance of crystals formed from solutions above and below the CMC were observed. These were most likely due to the difference in supersaturation of these solutions. The crystals formed due to precipitation of SDS with calcium at a concentration above the CMC formed flat trapezoidal, rhombic and hexagonal shapes. These aged into clusters by 1 wk. For a solution that was precipitated at concentrations beginning below the CMC, the crystals began as elongated and rhombic flat plates and aged into trapezoidal, rhombic, and needle-like structures.     

污泥深度脱水技术研究进展

随着经济的发展和国民生活水平的提高,污水污泥的排放量逐年增加,环境问题愈发严重,污泥的处理处置成为焦点问题,污泥脱水是制约污泥处置处理进一步发展的关键。本文针对目前污泥深度脱水技术开展,首先简述了不同来源污泥的分类及其基本特性,然后重点阐述了不同污泥预处理技术,分析了各污泥深度脱水技术作用机理,并对各自脱水效果及优缺点进行比较分析。结果表明,物理法中水热预处理对污泥的可脱水程度提升最大。较低声强、短时间的超声波处理对污泥脱水性能有着明显的改善。化学法在污泥过滤性能以及脱水速率方面有很大优势,酸碱处理后污泥zeta电位上升,污泥过滤性能及脱水速率得到改善。高级氧化法处理后污泥脱水效果高于酸碱处理,微生物细胞被溶解释放出有机物,可脱水程度改善。生物法处理污泥除改善污泥脱水性能外,还有对环境污染小等特点,但耗时较长。最后对污泥的后续脱水工艺进行综述,介绍了现存的主流脱水工艺,包括机械脱水、热干化技术、水热脱水工艺等;并针对不同的污泥后续利用方法,选取合适的预处理技术,提出相应优化的污泥处理工艺流程。     

不同微生物发酵剂及木醋液在草炭发酵中应用效果研究

草炭与硬杂木锯末以2．6：1比例混匀后，接种不同微生物发酵剂和喷施500倍木醋液，在温室里容积为2．5m^3的发酵槽中进行对比试验，试验结果：喷施500倍木醋液比对照最高发酵温度高7℃，平均发酵温度高4℃；大于40℃以上中高发酵温度多7天；HA总比对照增加11．47％，HA游含量也略高于对照。在只接种微生物发酵剂的处理中，最高发酵温度是酵素菌56℃〉高温纤维分解菌55℃〉秸秆速腐剂54℃〉EM53℃〉对照46℃；在喷施木醋液条件下接种发酵剂，最高发酵温度是高温纤维分解菌57℃=酵素菌57℃〉速腐剂50℃〉EM48℃。HA总及HA游含量也是高温纤维分解菌＋木醋液与酵素菌＋木醋液两个处理明显高于对照及其他接种剂处理。     

The oxidation of peat and its thermal accompaniment

The oxidation of peat is monitored thermally and the ignition phenomenology investigated. Ignition theory is applied to the results and are an extrapolation made to induce safe stockpiling quantities.     

The effect of hydrothermal dewatering of Pontianak tropical peat on organics in wastewater and gaseous products

This paper describes a study of the effects of hydrothermal dewatering of raw tropical peat from Pontianak, West Kalimantan-Indonesia, on the amounts of organic compounds released into wastewater and gaseous products. Hydrothermal upgrading and dewatering of the peat was carried out in a batch-type autoclave reactor at temperatures between 150 and 380 °C at a maximum pressure of 25.1 MPa for 30 min. It was found that the extent of decomposition of organics during hydrothermal dewatering depended on temperature increase.Wastewater from hydrothermal dewatering was found to contain organic carbon (TOC) ranging from 800 ppm at low temperatures, to 7504 ppm at high temperatures. A number of sugars and furans were detected in the wastewater at 250 °C, and organic acids and alcohols at all temperatures. Phenol and phenolic derivatives were observed at 250 °C, and significant amounts of CO₂, CO and H₂ were detected at all temperatures studied; CH₄ was detected only at 380 °C, but at this temperature CO₂ was no longer detected.A simplified schematic diagram of the decomposition behavior of tropical peat in the hydrothermal dewatering process is discussed with respect to the change in the concentration of organics in wastewater and gaseous products as determined by TOC, GC, GC–MS and ¹³C NMR analyses of the solids produced.     

Effect of zeta potentials of oil droplets and bubbles on flotation of oil-in-water mixtures

The effects of surface charges of oil droplets and bubbles in the oil-in-water flotation process were studied by a zeta potential apparatus which was specially designed to measure the zeta potential of bubbles. To measure the electrophoretic velocity of bubbles accurately, small bubbles whose rising velocities were less than 1 mm/s were introduced into an electrophoresis cell by a method of pressure reduction of a solution containing dissolved air, and the movement of the bubble in the cell was followed by moving the cell vertically at the same velocity as that of the rising bubble. It was found that the separation efficiency, n, for the flotation was strongly dependent on the zeta potentials of both the oil droplets and the bubbles. n increased as the zeta potentials of both the oil droplets and the bubbles decreased. Also n became the largest when the oil droplets were negatively charged and the bubbles were positively charged. Furthermore, a critical adhesion parameter, m=4π?ζ_pζ_b/kA, between oil droplets and bubbles was calculated by the heterocoagulation theory, using the value of the experimentally determined Hamaker constant, A=3.38x 10^?20J, and the dependence of n on m was examined.     

The flow resistance of fiber sheet during initial dewatering

In this work, a novel experimental filtration device with pressure profiling was used for analyzing water removal from the fiber network in the forming section of a paper machine. The experimental data were used to develop a stratified model for the flow resistance of the developing fiber sheet during the filtration process. The new model was verified with both laboratory- and pilot-scale measurements and excellent agreement was observed between them. It was also observed that there is a strong linear correlation between the maximal attainable solid content of a filtered sheet after the forming section and the instantaneous response to pressure of the flow resistivity of the furnish.     

The relationship of the environmental effect of surfactants to their interfacial properties

In an investigation of possible relationships between interfacial properties of surfactants and their environmental effect, using several anionic and nonionic surfactants, a linear correlation was found between the parameters, ΔG ⁰ _ad/A _min, and rotifer toxicity. ΔG ⁰ _ad is a standard free energy of adsorption at the air/aqueous solution interface, and A _min is the minimal hydrated cross-sectional area of the surfactant molecule. Both quantities were evaluated from surface tension data. This correlation is much better than attempted correlations of the toxicity with the negative logarithm of the critical micelle concentration (−log CMC) or with ΔG ⁰ _ad or A _min alone. The ΔG ⁰ _ad/A _min correlation with rotifer toxicity is also better than the correlation with the analogous parameter, Δ _s ^| G _ads ^0| A_min, obtained from adsorption isotherms of the surfactants on a solid immobilized membrane simulating a cell membrane. The data support our hypothesis that toxicity is determined both by adsorption tendency and ease of cell membrane penetration.     

Municipal sludge dewatering by belt filter press: effect of operating parameters

A belt filter press is commonly used to dewater sewage sludge but few data concerning this process have been published. A laboratory‐scale investigation was carried out to highlight the main process parameters affecting belt filter press efficiency as measured by the dry solid content of the final cake, percentage of solids recovered, and lateral sludge migration on the belt. Belt speed was determined to be the most important parameter: a low belt speed produces drier cakes with lower lateral sludge migration on the belt and also improves filtrate quality. At low belt speed, pressure is gently applied to the initial sludge, enabling a slow structuring of the cake and leading to better water release. Copyright © 2005 Society of Chemical Industry     

Electrochemical Aspects of Electroosmotic Dewatering of Clay Suspensions

ABSTRACT

An attempt is made to elucidate the electrochemical aspects of the electroosmotic dewatering (EOD) of clays as reported in some recent work, especially that on interrupted DC power electroosmotic dewatering published by Rabie, Mujumdar and Weber (2). These authors showed that the dewatering by EOD stops after the DC power has been on for several minutes or hours; on interruption of their power and on short-circuiting of the electrodes, conditions can be created again for some further dewatering by DC power EOD. This discovery, of Rabie et al. is interpreted as a fuel cell effect and it is shown that it affords clues to several other electrochemical strategies for the possible enhancement of the efficiency of the EOD by DC power.

Further, the open circuit potentials observed by Rabie et al. (2) on the interruption of DC power are given an electrochemical interpretation which leads to quantitative estimates in agreement with the experimental values.     

Electrochemical Aspects of Electroosmotic Dewatering of Clay Suspensions

An attempt is made to elucidate the electrochemical aspects of the electroosmotic dewatering (EOD) of clays as reported in some recent work, especially that on interrupted DC power electroosmotic dewatering published by Rabie, Mujumdar and Weber (2). These authors showed that the dewatering by EOD stops after the DC power has been on for several minutes or hours; on interruption of their power and on short-circuiting of the electrodes, conditions can be created again for some further dewatering by DC power EOD. This discovery, of Rabie et al. is interpreted as a fuel cell effect and it is shown that it affords clues to several other electrochemical strategies for the possible enhancement of the efficiency of the EOD by DC power.

Further, the open circuit potentials observed by Rabie et al. (2) on the interruption of DC power are given an electrochemical interpretation which leads to quantitative estimates in agreement with the experimental values.