Sewage Sludge Dewatering Process Using Liquefied Dimethyl Ether as Solid Fuel

This article describes the dewatering of sewage sludge using liquefied dimethyl ether (DME), which clarified the effect of sludge type and its particle size. Changes in the heating value of the dewatered sludge were also examined. In addition, the change in dewaterability upon reuse of the liquefied DME was investigated experimentally.

Regardless of the nature of the sludge, its dewatering behavior was similar. The amount of dewatered water could be increased by decreasing the diameter of the sludge cake. Complete drying of the sludge cake via DME dewatering resulted in retention of approximately 96% of the heating value (17.7 MJ/kg-sludge) of the original sludge cake dry base (18.4 MJ/kg db). The DME could be recovered after extraction, and reuse experiments showed that liquefied DME dewatering performance was unchanged after five reuses.     

Dewatering of Biomass Using Liquid Bio Dimethyl Ether

An interesting integrated configuration in a thermochemical conversion biorefinery that is producing dimethyl ether (DME) is to use a small fraction of the BioDME for dewatering of the solid biomass feedstock. Therefore, the use of liquid BioDME was investigated in this study for pressurized dewatering of biomass at room temperature. Water was removed in liquid form from wet sawdust and wet wood chips using liquid DME in a laboratory-scale batch unit. Both the sawdust and the wood chips could be dewatered in a short time (minutes) to a moisture content of 15% (w/w) from an initial content of approximately 55% (w/w). Longer DME treatment times (hours) lowered the moisture content even further down to 8% (w/w), indicating that the transport phenomena in the porous biomass and the solubility of DME in water influence the dewatering characteristics. The DME dewatering performance, 12–22 g DME per g water removed, was similar to literature data on coal dewatering using liquid DME. The present study showed that DME dewatering of the solid biomass feedstock has potential as an energy-efficient dewatering process, especially in an integrated thermochemical conversion biorefinery.     

Hydrothermal dewatering of brown coal and catalytic hydrothermal gasification of the organic compounds dissolving in the water using a novel Ni/carbon catalyst

Brown coals will continue to be important energy resources in the near future, but their high water contents, which sometimes exceed 50 wt%, and their low calorific values restrict their utilization. Development of an efficient treatment method for dewatering and upgrading is desired to utilize brown coals on a large scale. Hydrothermal treatment is believed to be a promising treatment method because it can not only remove water in liquid phase but also improve calorific value of brown coal. However, some organic compounds are inevitably leached out from the coal during the treatment to emit a huge amount of wastewater containing organic compounds in small concentration, which causes a loss of coal energy as well as a serious problem of wastewater treatment. In this paper, an Australian brown coal (Morwell) was hydrothermally treated for dewatering and upgrading at 250-300 °C. When treated at 300 °C, the water content decreased from 1.31 kg/kg on dry matter to 0.59 kg/kg on dry matter and the calorific value increased from 25.8 to 27.8 MJ/kg on dry matter, indicating that the hydrothermal treatment is really effective for dewatering and upgrading the brown coal. The reactivity to oxygen at low temperature was also reduced by the treatment, which will contribute to suppress the spontaneous combustion of the coal. On the other hand, the amount of organic compound dissolved in the recovered wastewater increased with increasing treatment temperature and it reached ca. 1.5% on carbon basis at 300 °C. The wastewater was treated using a novel Ni-supported carbon catalyst developed by the authors. The organic compounds in the wastewater were completely gasified at as low as 350 °C under 20 MPa at the liquid hourly space velocity of as large as 50, producing combustible gas rich in CH₄ and H₂. The proposed hydrothermal gasification process was found not only to be efficient for wastewater treatment but also to be effective for energy recovery from wastewater. The gasification process combined with the hydrothermal treatment process, which is operated under the conditions close to those of the gasification, will be a new and effective brown coal pretreatment process.     

Production of decaffeinated green tea leaves using liquefied dimethyl ether

We developed a new technique for green tea decaffeination involving ingredient extraction and drying of green tea leaves by using liquefied dimethyl ether (DME) as a safe extraction solvent. After hot water extraction with water content of 74.6–76.2%, green tea leaves were tested to verify the DME extraction in both laboratory- and bench-scale processes. The distributions of caffeine and catechins in the extracted residue, organic extracts, and removed water were tested by high-performance liquid chromatography. Caffeine was completely removed from the green tea leaves. Approximately 25.2–56.0% of catechins remained in the residue after DME extraction. In particular, 56.0% of epigallocatechin gallate, which has the greatest activity of all catechins remained in the residue.     

Prediction of the air consumption when dewatering a filter cake obtained by pressure filtration

In this communication, we report some data for the dewatering of a coal flotation concentrate in which very fine particles occur Dewatering is carried out by pressure filtration (up to 6 bar) followed by blowing to partially dry the cake (the filtration and dewatering phase respectively). For the systems studied, a reasonable prediction of the air consumption in either a lab filter, or a one-element test filter, or a full-scale continuous filter is possible, based on measurement of the liquid permeability for saturated flow in a lab filter cake. Together with scaling-up characteristics of the filtration step (not reported here), this gives the possibility of a reliable prediction of the required size and energy consumption of a large-scale continuous-pressure filter based on bench-scale test data.     

A study on the direct catalytic steam gasification of coal for the bench-scale system

Various techniques have been developed to increase the efficiency of coal gasification. The use of a catalyst in the catalytic-steam gasification process lowers the activation energy required for the coal gasification reaction. Catalytic-steam gasification uses steam rather than oxygen as the oxidant and can lead to an increased H₂/CO ratio. The purpose of this study was to evaluate the composition of syngas produced under various reaction conditions and the effects of these conditions on the catalyst performance in the gasification reaction. Simultaneous evaluation of the kinetic parameters was undertaken through a lab-scale experiment using Indonesian low rank coals and a bench-scale catalytic-steam gasifier design. The composition of the syngas and the reaction characteristics obtained in the lab- and bench-scale experiments employing the catalytic gasification reactor were compared. The optimal conditions for syngas production were empirically derived using lab-scale catalytic-steam gasification. Scale-up of a bench-scale catalytic-steam gasifier was based on the lab-scale results based on the similarities between the two systems. The results indicated that when the catalytic-steam gasification reaction was optimized by applying the K₂CO₃ catalyst to low rank coal, a higher hydrogen yield could be produced compared to the conventional gasification process, even at low temperature.     

褐煤经四氢化萘处理后的结构及热解-气化特性分析

在小型反应釜上采用非极性有机溶剂四氢化萘(tetrahydronaphthalene, THN)对内蒙古锡林郭勒褐煤进行脱水,获取了不同温度下的脱水试样,运用傅里叶红外光谱(Fourier transform infrared spectroscopy,FT-IR)分析技术对比研究了在不同脱水温度下煤样中有机官能团的变化,通过FT-IR谱图的分峰拟合计算,对脱水煤样的化学结构变化特征进行半定量分析,并结合热重(thermal gravity analysis/differential thermal gravity,TG/DTG)和实验室固定床反应器(fixed bed reactor)考察了不同脱水温度下煤样的热解气化特性和热解气相产物分布规律,并对脱水煤样在最大失重速率区间的动力学参数进行了计算。试验结果显示:四氢化萘溶剂对褐煤的脱水提质是有效的,150~200℃时C O开始分解,而此时芳香环上的C C仍然相对稳定。随着脱水温度的升高,芳香类氢含量先减小后增大,脂肪类氢含量先增大后减小,芳香度和芳香碳在脱水温度范围内逐渐增大。煤样的脱水温度升高,热解气相产物H₂、CH₄、CO累积产率增大,CO₂累积产率减小;脱水煤样热解活化能随着脱水温度的升高而升高,进而导致脱水温度较高煤样热解失重率降低。     

高盐高有机制药废水污泥电渗透高干脱水

为研究高盐高有机制药废水污泥的电渗透脱水效果,深入认识化学污泥的电脱水过程,本文采用电渗透高干脱水技术对经抽滤脱水的高盐高有机制药废水化学污泥进行深度脱水,考察了泥饼初始pH的改变对污泥电渗透高干脱水过程中阴阳极污泥的含水率、电流、电导率、pH、zeta电位与能耗的影响,验证了对高盐高有机制药废水污泥实行电渗透高干脱水的可行性,解析了化学污泥电渗透脱水过程的机制。结果表明,泥饼pH为2、3、4时,zeta电位为正值,电渗流反向流动,无法脱水;pH增至5时,zeta电位为负值,电渗流从阴极脱除,污泥含水率从53.2%降至44.8%,脱水效果最好;但pH增至6时,脱水量有所降低。污泥电导率随pH的增加而降低。pH为5时初始电流最大。脱水15min时,即污泥含水率降至45.5%时,能源利用率最高。     

ROLLER PRESS FOR ELECTRO-OSMOTIC DEWATERING OF BIO-MATERIALS

In our preliminary investigations, lab-scale and bench-scale electro-osmotic press dewatering units were tested with multiple test combinations and trials with various bio-materials to study the process parameters and to improve equipment designs. Effects of various pre-treatments and treatment combinations on the dewatering rates were evaluated. Obtained results lead to the development of a pilot scale unit.

Pilot plant operations were carried in Courtenay, British Columbia (Canada) with locally harvested “bull kelp” Nereocystis luetkeana. Operation of the pilot plant included harvesting the kelp, grinding it into a slurry, reacting the slurry with Calcium Chloride, draining the excess water, and combined fields dewatering. The operations indicated that the Calcium Chloride reaction followed by draining was a necessary step for an effective water removal with the combined fields roller press. The pilot plant operations showed to be a viable process for the production of kelp meal for animal consumption     

PRESS DEWATERING OF BROWN COAL: PART 1-EXPLORATORY STUDIES

The large water content of brown coal can be reduced by press dewatering with much lower energy requirement than by alternative methods. The cost of the press need.ed increases with the required pressing pressure, which is det e rmfned by the coal properties. The results of experiments on Victorian brown coals are interpreted with supporting theory to give these properties, and the effects on these of grinding and slurrying and of thermal, mechanical and chemical pretreatments. Brown coals from Victoria are compared with lignites from South Australia and West Germany after slurrying, and with a thickened wash-water effluent containing Victorian brown coal dust. Salt removal from the high-salt South Australian coal was obtained.     

PRESS DEWATERING OF BROWN COAL: PART 1-EXPLORATORY STUDIES

The large water content of brown coal can be reduced by press dewatering with much lower energy requirement than by alternative methods. The cost of the press need.ed increases with the required pressing pressure, which is det e rmfned by the coal properties. The results of experiments on Victorian brown coals are interpreted with supporting theory to give these properties, and the effects on these of grinding and slurrying and of thermal, mechanical and chemical pretreatments. Brown coals from Victoria are compared with lignites from South Australia and West Germany after slurrying, and with a thickened wash-water effluent containing Victorian brown coal dust. Salt removal from the high-salt South Australian coal was obtained.     

Removal of water from brown coal by treatment with steam

It is known that when low rank coals are subjected to elevated temperatures (200–300°C) under saturated steam conditions, water is removed. The greatest uncertainty associated with the procedure centres around the rate at which this dewatering proceeds. In order to predict the overall removal rate in a proposed continuous thermal dewatering plant, a rate model is required. To do this, the physical properties of moist and dewatered Victorian brown coals were measured. The rate of water removal once dewatering temperatures were reached was also measured and found to be very rapid. The process is thus limited by heat conduction within the particle. A mathematical model for heat transfer within and water removal from a long radially-shrinking coal cylinder of variable properties was set up and tested experimentally. It was found that a non-shrinking, constant property model was a slightly better predictor of dewatering performance.     

浅析二甲醚代替LPG用于工业生产的可行性

二甲醚（DME）与石油化工中的燃料产品LPG的物理化学性质和燃烧机理相似,随着液化石油气资源的紧缺及价格上涨等经济问题的加重和清洁环保理念的深入,DME作为一种新兴的清洁燃料将会逐步代替LPG,占领燃料市场的一席之地。本文阐述了DME的应用和物理化学性质,着重介绍了DME的燃烧机理和热力学性质的计算,并提出了DME代替...     

Design framework for dimethyl ether (DME) production from coal and biomass-derived syngas via simulation approach

A comprehensive thermodynamic study was conducted to evaluate the comparative efficacy of methanol and dimethyl ether (DME) synthesis using CO₂ rich syngas feed. The first part of our study included assessing the relative performances of the methanol synthesis system, two step DME synthesis system, and one step DME synthesis system in terms of the CO_x conversion and product yield (methanol/DME) based on the Gibbs free energy minimization approach. The wide range of composition of CO₂-enriched syngas feed produced by the coal and biomass gasification was simulated using Aspen Plus and the following evaluation parameters were analyzed for a broad parameter range: reaction temperature (180–280°C), reaction pressure (10–80 bar), stoichiometry number (SN) (0–11), and CO₂/(CO₂ + CO) molar feed ratio (0–1) for isothermal as well as adiabatic conditions. Based on the equilibrium yield, one-step DME synthesis was discovered as the most viable process to utilize the co-gasification derived syngas effectively. In the second part of our study, the overall process efficiency was inspected through the process design of 1 tonnes per day (TPD) DME plant inclusive of heat integration, resulting in significant CO₂ abatement and DME production with high product purity and minimum energy consumption. Consequently, one-step DME production via CO₂-enriched syngas obtained through the coal or biomass gasification process is identified as the leading technology based on energy utilization and CO₂ abatement.     

用于城市污水处理用浓缩脱水一体机

机械浓缩脱水已被广泛用于城市及工业污水的污泥脱水中,目前被广泛采用的脱水设备有带式压榨过滤机、卧式螺旋卸料沉降离心机、板框厢式压滤机等,由于脱水工艺的要求,为了减少因浓缩过程时间较长,结合在污泥中的氮磷重新释放后进入水体,造成藻类的繁殖和对水系的进一步污染,要求机械脱水设备能够对沉淀池中底流进行直接处理,即浓缩脱水一体化处理。     

二甲醚在工业和民用领域中的应用

二甲醚作为清洁燃料和新能源在替代液化石油气和柴油等方面有良好的应用前景。如何应用二甲醚、如何开发二甲醚下游产业是摆在人们面前很现实的问题。实践证明在液化石油气中掺混二甲醚的道路走不通,二甲醚纯烧是一条健康发展之路,二甲醚应在工业和民用工业用领域找到自己的位置。     

热压过滤完善选煤工艺

论述了热压过滤干燥脱水机具有过滤与干燥的双重作用、脱水效率高等特点;分析了干燥压滤机内脱水峰面的形成和移动过程,以及物料中液体饱和度与时间的关系;介绍了热压过滤干燥工艺系统与装备,并通过应用实例说明其完善选煤工艺的意义。     

A Review of Dehydration of Various Industrial Sludges

Wastewater characteristics and sludge generation potential of point source categories are reviewed critically. Novel industry-specific sludge dewatering/drying solutions necessary to establish a sustainable model are examined through a detailed literature survey. Knowledge of sludge properties is one of the most critical issues needed to design dewatering/drying equipment. This study focuses on industrial wastewater/sludge characterization. In addition, a comprehensive review of current drying models and technologies is also presented. A summary of the results derived from a novel thin-film-based photonic sludge dewatering/drying study is outlined as an alternative approach for industrial sludge control. Sludge was dried in a tubular quartz reactor (TQR), the inner surface of which was coated with a TiO₂ thin film. The TQR was irradiated with UV A, UV B, and UV C lamps. The consumed and generated energy fluxes through endergonic and exergonic reactions driven by photolysis and photocatalysis were investigated. In addition, the variations in sludge dewatering/drying characteristics were also examined and compared with conventional methods to evaluate the energy requirements.     

污泥脱水设备在污水处理厂中的应用

污泥脱水是减小污泥体积的关键工艺技术,而枵泥脱水设备的选型对污泥脱水效率的高低和脱水工艺的正常运行最为重要。文章以广州某水厂为例,在介绍常见污泥脱水设备的基础上,选择了合适的污泥脱水设备,在污泥脱水工艺流程中发挥了稳定的脱水效果,该厂的污泥脱水问题也得到了有效的解决。     

Energy efficiency improvement of dimethyl ether purification process by utilizing dividing wall columns

The alternative fuel, dimethyl ether (DME), which can be synthesized from natural gas, coal or biomass syngas, has been traditionally used as a diesel substitute or additive. DME purification processes with a conventional distillation sequence consume a large amount of energy. We used dividing wall columns (DWCs) to improve the energy efficiency and reduce the capital cost of the DME purification process. Various possible DWC arrangements were explored to find the potential benefits derived from thermally coupled distillations. The results show that utilizing DWCs can significantly reduce both the energy consumption and investment cost of the DME purification process. The lower energy consumption also results in the reduction of the CO₂ emission.