Energy-efficient coal dewatering using liquefied dimethyl ether

In this study, we dewatered sub-bituminous coal mined in Warra, Indonesia, by using liquefied dimethyl ether (DME); no heating was required in this dewatering process. We achieved this dewatering both in a laboratory-scale experiment and using previously developed bench-scale equipment. We also examined the properties of the coal before and after dewatering and measured the amount of energy required by the equipment. We found that the maximum water extraction efficiency of liquefied DME was 98.3%. Further, the properties of the coal did not change after the dewatering treatment. The wastewater obtained by dewatering can be treated by existing wastewater treatment technologies. The energy consumed by the bench-scale equipment was 2069 kJ/kg-water; thus, this dewatering process using liquefied DME was confirmed to be effective and energy efficient.     

Experimental Study on Thermal Hydrolysis and Dewatering Characteristics of Mechanically Dewatered Sewage Sludge

After mechanical dewatering, sewage sludge has a moisture content of around 80 wt% and further disposal is required. A new sewage sludge semi-drying (dewatering) process is proposed and verified. It combines thermal hydrolysis and subsequent mechanical dewatering, with less energy consumption than traditional thermal drying. Sludge treated using this new process satisfies further disposal requirements (e.g., landfill or autothermal incineration). In the present study, a high-pressure test reactor was used to study the thermal hydrolysis of dewatered sludge. Thermally hydrolyzed sludge was subsequently dewatered by centrifugal sedimentation or by pressure filtration. The amount of organic compounds returning to the water phase was also measured. According to the results from centrifugal settling tests, the optimal thermal hydrolysis treatment temperature was 180°C. The moisture content then dropped to 1.44 kg/kg dry solids (DS; 59 wt%) after dewatering under relative centrifugal force of 9,000 × g from 5.67 kg/kg DS (85 wt%). Pressure filtration further reduced the moisture content of filter cakes to only 0.5 kg/kg DS (33 wt%, hydrolysis temperature 180°C). After thermal hydrolysis, the heating value of sludge (moisture-free basis) was about 80% that of the untreated sludge.     

21世纪的清洁燃料—二甲醚

介绍了二甲醚的性质、生产技术,特别是二甲醚作为清洁燃料的虎性能,同时认识到开发三甲醚具有巨大的经济和社会效益。     

Critical solubility of dimethyl ether (DME)+diesel fuel and dimethyl carbonate (DMC)+diesel fuel

An experimental apparatus was developed for measuring the critical solubility. The critical solubilities were determined for binary mixtures of DME+diesel fuel and DMC+diesel fuel. For DME+diesel fuel their critical solubility temperatures ranged from 272.83 to 255.13 K while the mass fractions of DME varied from 3.44 to 95.8%; For DMC+diesel fuel, their critical solubility temperatures were between 273.58 and 302.72 K while the mass fractions of DMC varied from 1.22 to 89.6%.     

Dewatering of primary settled urban sludge in a vertical flow wetland

Sludge drying reed beds (SDRBs) are a combination of traditional sludge drying beds and constructed wetlands. Their main advantages include low investment, infrequent biosolids removal (of the order of years), dewatering and mineralization of biosolids, minimization of biosolid volume, simplicity and economy, and production of a beneficial, well-composted side product. A constructed wetland facility is used to treat the sewage from the municipality of Nea Madytos, Thessaloniki Province, North Greece. The primarily produced biosolids in the Imhoff tank of this facility are treated with a vertical flow SDRB. The performance and dewatering efficiency of this system was monitored for 1 year. Over the 12 years of operation of the treatment plant, 7884 m³ of biosolids from the Imhoff tank were transferred to the SDRBs. Until today, no biosolids were removed, and the level of the dewatered sludge on the bed is built to about 20 cm, with a volume of residue sludge of 28 m³. This corresponds to a biosolid reduction of 99.64%. At the end of the examination period the TS (VS) content varied from 55% (40%) in the top layer to 65% (35%) in the bottom layer. The heavy metal concentration meets the European Union standards for heavy metals in case of agricultural disposal of the treated sludge.     

Investigation of different precipitating agents effects on performance of γ-Al2O3 nanocatalysts for methanol dehydration to dimethyl ether

This research includes synthesis of nano-sized γ-Al₂O₃ catalyst for methanol dehydration reaction to produce DME. A co-precipitation method with four precipitants including sodium carbonate, sodium bicarbonate, ammonium carbonate and ammonium bicarbonate was used for this purpose. The catalysts were characterized by XRD, FTIR, NH₃-TPD, SEM, TEM and N₂ adsorption–desorption techniques. In order to investigate the catalyst activity, they were used in the fixed bed micro reactor for methanol dehydration reaction at different operating conditions. Also, a commercial γ-Al₂O₃ nanocatalyst was utilized for comparison purposes. The catalyst prepared by ammonium carbonate showed the highest yield of DME in comparison with other ones.     

Atomization and Drying Characteristics of Sewage Sludge inside a Helmholtz Pulse Combustor

Sewage sludge of pasty consistency was atomized and dried directly using a high-temperature, highly turbulent gas flow in the tailpipe generated by a Helmholtz gas-fired pulse combustor (PC). Parametric studies were carried out to investigate the effect of drying pipe length and sludge feed tube size on the PC sludge drying process. Experimental results showed that the pulsating gas stream can disperse the sludge into small particles with a narrow size distribution between 0.01 and 4 mm and the granular sludge was dried rapidly due to the increased particle surface area and the high temperature of the drying medium. PC drying of sewage sludge was compared to convective- and microwave-drying processes. The application potential of the PC sludge-drying process is discussed based on the experimental results.     

Drying Kinetics and Characteristics of Sewage Sludge/Rice Straw Mixture

This study aimed at investigating thin-layer drying characteristics of sludge mixed with different rice straw contents (1, 2, 3, and 5% wb). The experimental results showed that adding 1, 2, and 3% (wb) rice straw to sludge is helpful to improve the drying rate of sludge as the surface area and cracks increase but the drying rate of the sludge mixed with 5% (wb) rice straw decreases with a reduction in thermal conductivity. When the content of rice straw is 2% (wb), the increased amplitude of drying rate is the highest, 14.6, 14.8, 16.0, and 17.6% at 100, 120, 140, and 160°C, respectively. The model proposed by this study showed better prediction compared with the other models and satisfactorily described the drying characteristics of sludge/rice straw mixture as well and is applicable under the given experimental conditions. The values of R², root mean square error (RMSE), and χ² varied from 0.99935 to 0.99992, 0.00295 to 0.00830, and 0.00001 to 0.00007, respectively.     

Nonisothermal Kinetics Based on Two-Stage Scheme for Co-Drying of Biomass and Lignite

This study investigates nonisothermal co-drying kinetics of two typical biomasses (cornstalk and red pine) with lignite in the presence of a nitrogen atmosphere using a thermal gravimetric analysis technique. The drying rate can be increased by either decreasing the blending ratio of biomass or increasing the heating rate. The activation energies of cornstalk/lignite blends and red pine/lignite blends in the two falling rate periods are less than that of their parent samples. In the first falling rate period, the dominant mechanisms of drying for lignite are described by the Avrami–Erofeev equation (n = 1.5), while the mechanisms for the cornstalk, red pine, and mixture samples are fitted to the Mample equation (n = 1.0). In the second falling rate period, the mechanisms are described by the Avrami–Erofeev equation (n = 1.5 or n = 2.0). The general kinetic compensation effect correlations are obtained for all samples within heating rates of 10–30°C/min. Significant synergistic interactions between the Chinese lignite and cornstalk or red pine are detected during co-drying.     

The biodrying process of sewage sludge – a review

Abstract

Sewage treatment can be classified into three phases: liquid, gaseous, and solid. Treatment of solids is performed in several steps, and the greatest difficulty in removing water from sewage sludge is due to the bound water present in the sludge. Thus, biodrying, a drying method that can be classified as biological, has been recently applied to treat this type of waste. This review paper aims to report and compile data from 49 biodrying assays of sewage sludge found in the literature (through the present, 2019) into one synthesis table, to discuss and compare the numerous variables found in these papers and their implications for biodrying, and to suggest possibilities for future research. This paper additionally intends to improve knowledge of biodrying and to consequently contribute to the monitoring and understanding of the process.     

EFFECTS OF VARIOUS PROCESS PARAMETERS ON TEMPERATURE PROFILE OF ADIABATIC FIXED BED REACTOR FOR PRODUCTION OF DIMETHYL ETHER (DME) FROM METHANOL

Catalytic dehydration of methanol for production of dimethyl ether (DME) is an exothermic reaction. Therefore, the temperature of the adiabatic reactor of DME production will be increased by the progress of the reaction. In this article, effects of various process parameters are considered on the temperature profile of a fixed catalyst bed in a laboratory-scale reactor of DME production from methanol. Acidic gamma alumina is used for DME production, and effects of inlet feed temperature, flow rate of the feed, pressure of the reactor, and catalyst particle sizes on the temperature profile of the catalyst beds are investigated.     

DRYING OF MOCK SPENT NUCLEAR FUEL ELEMENTS

Spent nuclear fuel elements are stored in underwater cooling pools until the elements can be safely handled and prepared for interim dry storage. The fuel was intended for short-term storage in water before it was to be reprocessed. However, the fuel will no longer be reprocessed, and extended storage in water has caused many of the aluminum-clad elements to degrade, exposing the uranium fuel. In addition, sludge, comprised of corroded aluminum and sediment, has accumulated in and around the fuel plates. The water in the sludge must be removed before the spent fuel elements can be placed in dry storage. Experiments have been performed on mock spent fuel elements with simulated corrosion product applied between the plates. A series of vacuum and heating cycles were used to dry the elements, and a mixture of clay and aluminum oxide was used to simulate corrosion products on the elements.

The procedures used in the experiments were determined to be adequate to dry the mock spent fuel elements, and the temperature behavior of the simulated corrosion product within the fuel elements could be used to determine when the element was dry. On plates where areas of wet simulant were found, a sharp drying front was observed that separated the wet and dry parts of the simulated corrosion product. The drying front propagated inward towards the center of the mock fuel elements over time.     

DRYING OF MOCK SPENT NUCLEAR FUEL ELEMENTS

Abstract

Spent nuclear fuel elements are stored in underwater cooling pools until the elements can be safely handled and prepared for interim dry storage. The fuel was intended for short-term storage in water before it was to be reprocessed. However, the fuel will no longer be reprocessed, and extended storage in water has caused many of the aluminum-clad elements to degrade, exposing the uranium fuel. In addition, sludge, comprised of corroded aluminum and sediment, has accumulated in and around the fuel plates. The water in the sludge must be removed before the spent fuel elements can be placed in dry storage. Experiments have been performed on mock spent fuel elements with simulated corrosion product applied between the plates. A series of vacuum and heating cycles were used to dry the elements, and a mixture of clay and aluminum oxide was used to simulate corrosion products on the elements.

The procedures used in the experiments were determined to be adequate to dry the mock spent fuel elements, and the temperature behavior of the simulated corrosion product within the fuel elements could be used to determine when the element was dry. On plates where areas of wet simulant were found, a sharp drying front was observed that separated the wet and dry parts of the simulated corrosion product. The drying front propagated inward towards the center of the mock fuel elements over time.     

LW450×1810—N型卧式螺旋卸料沉降离心机在市政污水中的应用

对LW450×1810-N型卧式螺旋卸料沉降离心机在市政污水中的应用作了详细的分析,并且对该机的一些结构特点、电气控制等方面作了较全面的介绍。另外,还介绍了该机在污水处理厂中的试验情况,试验结果证明该机的结构是合理的,设计是成功的。     

城市污泥快速干燥工艺研究进展

热干化是一种城市污泥安全处置的重要途径。塑化是城市污泥热风干燥常见现象,对污泥干燥过程产生重要负面影响。污泥塑化阻碍了内部水分向外迁移,增加污泥干燥时间和干燥能耗。本文概括了近三年天津科技大学机械工程学院课题组在避免或降低污泥"塑化"影响,发展污泥快速干燥工艺的研究进展。新污泥干化工艺包括城市污泥油炸干燥和脉动燃烧雾化干燥。     

城市污泥处理利用现状研究

城市污水处理厂污泥产量巨大且成分复杂,如何把污泥进行合理利用已经越来越受人们的关注。描述了目前城市污水处理厂污泥处理与综合利用的现状。并介绍了几种新兴的污泥处理工艺。为今后污泥的资源化利用提供参考。