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.     

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.     

清洁燃料二甲醚的合成技术

介绍了清洁燃料二甲醚的性质与用途、合成技术、所涉及的催化剂以及合成反应器,并提出了生物质制取二甲醚的可能性.     

汽车用清洁燃料——二甲醚

二甲醚是柴油发动机理想的替代燃料,可以由天然气和煤为原料合成制取.综述了二甲醚的两种合成工艺:一步法和二步法.     

合成气直接合成二甲醚的工艺研究

本文考察了二氧化碳浓度、空速、温度在合成气直接合成二甲醚过程中对双功能催化剂的影响，结果表明，合成比2．85，在CO2浓度4．2％－7．15％范围内，随着CO2浓度增加，CO的转化率和DME的选择性逐渐下降，在进气空速1300－3200h^-1范围内，CO的转化率和DME的选择性随空速的增加而减小，但在1500h^-1左右CO的转化率和DME的选择性较高；在反应温度265－300℃范围内，CO的转化率和DME的选择性随浊度的升高而增加，但在285－300℃之间两者变化不大，最佳条件：CO2浓度5．2％，空速1500h^-1,温度285℃。     

液化石油气、二甲醚产品标准述评

介绍了我国现行有效的液化石油气、二甲醚产品的国家标准、行业标准的关键内容。现行有效的液化石油气、二甲醚产品的国家标准、行业标准以及部分省市DME与LPG复合燃料的地方标准推动了燃气产业发展,为DME与LPG复合燃料国家标准的发布实施奠定了坚实基础。     

二甲醚作为二次能源的前景分析

论述了二甲醚作为二次能源替代民用燃料和车用燃料的可行性和重大意义,阐述了我国能源短缺的危害和开发二次能源的必要性和紧迫性,简述了二甲醚的性质和制备,分析了二甲醚作为二次新能源开发的资源优势和对环境的重大意义及开发前景。     

直接二甲醚燃料电池的研究进展

综述了近几年来关于最具商业前景的直接二甲醚燃料电池的研究成果,文中主要探讨了新型阳极催化剂的开发,膜电极结构对电池性能的优化以及操作条件对电池性能的影响。建议在深入对催化剂、电池结构和操作条件的研究基础上,采用碱性电解质饱和二甲醚为燃料和双氧水替代氧气为氧化剂等方法进一步提高电池性能。     

LPG掺混DME燃烧特性研究

为研究液化石油气掺混二甲醚的混合燃料的燃烧特性,依据GB16410—2007《家用燃气灶具》,对二甲醚质量分数分别为15%、20%和25%的混合燃料进行燃烧特性测试,通过实验室测试及理论计算得出:在一定的二甲醚掺混比例下,混合燃料的燃烧特性与液化石油气基本相同,并对混合燃料的应用提出了相关建议。     

清洁燃料型二甲醚的开发具有重要战略意义

二甲醚特有的物理化学性质决定了清洁燃料二甲醚的开发对我国国民经济发展具有重要战略意义。随着世界各国环保意识的增强 ,二甲醚将进一步替代氟氯烃用于气雾剂、致冷剂和发泡剂。由于我国能源资源匮乏 ,二甲醚作为民用燃料用于醇醚燃料、液化气和柴油汽车燃料的代用品的条件也日趋成熟 ,到 2 0 10年二甲醚在中国的需求量将超过 30 0 0万t。截至 2 0 0 3年底 ,全球二甲醚总生产能力约为 30万t。二甲醚的开发已成为世界能源技术研究的热点。     

Hydrothermal Carbonization of Sewage Sludge: Analysis of Process Severity and Solid Content

Hydrothermal carbonization of sewage sludge was carried out with the aim to evaluate the influence of process severity and initial solid content. Response surface methodology was applied to model yield and C yield responses. Enhanced dewaterability performance was recorded under mild processing conditions. The treatment promoted concentration and immobilization of Pb, Cd, Ni, Zn, and Cu. Variation of the solid content showed a stronger influence than severity on average yield and C yield. Higher heating values (HHVs) and energy retention efficiencies (EREs) of hydrochars obtained at the lowest solid content displayed the lowest values. Hence, the energy requirements of a first dewatering step should be compared with the related improvement in terms of HHV and ERE when sludge is used as feedstock.     

二甲醚燃料汽车的研究和应用进展

从二甲醚燃料发动机的特性、二甲醚燃料的排放指标等方面论述了国外二甲醚燃料汽车的研发进程,介绍了国内在二甲醚燃料喷雾、燃料特性、发动机性能等方面的研究和应用。上海将成为国内首先推广二甲醚燃料汽车的城市。     

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.     

Revamping Dimethyl Ether Separation to a Single‐Step Process

Process intensification techniques were recently proposed to improve the eco‐efficiency of the conventional dimethyl ether (DME) purification and methanol recovery distillation sequence, but they all require new specific equipment and hence rather high investment costs leading to several years of payback time. However, the alternative of reusing the existing equipment to revamp the two distillation columns of the downstream processing section into a single‐step separation was so far overlooked in the open literature. To solve the problem of costly DME separation, a novel single‐step DME separation taking place in a dividing‐wall column (DWC) is proposed that effectively integrates in one shell the tasks of DME purification and methanol recovery. The new process is optimized in terms of minimal energy requirements, taking into account the restrictions caused by reusing one distillation column like, such as limited diameter or reboiler/condenser heat duty. The results demonstrate that the DWC alternative is feasible and has better performances as compared to the classic sequence, i.e., 28 % lower operating costs and 20 % less capital investment.     

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.     

城市污泥热风与微波干化特性研究

采用热风和微波加热两种方式对城市污泥进行薄层干化实验研究,分别考察污泥薄层厚度和其他操作条件对污泥干燥特性及能耗的影响。研究发现:在热风干燥过程中,由于污泥的塑性,污泥表面容易结壳,从而严重阻碍了水分向外迁移,使得干燥速率呈阶梯状下降。微波干燥污泥具有时间短、干燥速率大,同时节省能源。     

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。     

Sewage Sludge Solar Drying: Experiences from the First Pilot-Scale Application in Greece

Increasingly strict regulations governing sludge management have raised interest in drying technologies. The feasibility of sewage sludge solar drying was experimentally evaluated in a 66-m² pilot-scale greenhouse plant under typical weather conditions in Greece. The greenhouse was equipped with ventilation fans to maximize the drying process efficiency and a turning drum for efficient sludge mixing. The obtained results proved the applicability and the high performance of the solar drying technology. The time necessary to achieve a dry product with a dry solids content up to 95% ranged between 8 and 31 days, depending on the weather conditions. During drying, sludge organic matter was reduced by 5–21%, and total and fecal coliform content was also decreased up to three orders of magnitude. By taking into consideration the sludge content in heavy metals, the final product can partially or totally replace commercially available inorganic fertilizers in agricultural applications, in accordance with the restrictions imposed by national and European regulations. Based on a preliminary cost analysis concerning the construction of a solar drying facility covering a sum of 80,000 population equivalent (PE), a corresponding capital cost of 24 €/PE is anticipated.     

Investigation on Convective Drying of Mixtures of Sewage Sludge and Sawdust in a Fixed Bed

This work is part of a project aiming to develop a renewable fuel for gasification purposes, through convective drying of sludge/wood mixtures. The first step consists of characterizing the behavior of sawdust/sludge mixtures during the application of convective drying. The influence of the mixing step (no mixing versus 30 s at 40 rpm), as well as the sawdust : sludge ratio (1:9, 2:8, 3:7, and 4:6 on a dry basis) and the effect of drying temperature (50, 80, and 110°C) were investigated. In this study, X-ray tomography, a noninvasive imaging technique, is used to assess changes in the volume, void, and exchange surface at the beginning and the end of the drying process. Results first confirm the importance of the mixing step on the drying behavior: the drying rate of the mixed sludge is lower than that of the original sludge. Nevertheless, the addition of sawdust is shown to have a positive impact on the drying process from a mass ratio of 2:8, with drying rates higher than that of the original sludge. With increasing amounts of sawdust, the initial and final bed volumes, initial and final total exchange surfaces, and initial void fraction increase linearly, but the bed volume shrinkage and final void fraction decrease linearly.     

Dimensionless Formulation of Convective Heat Transfer in Fry‐Drying of Sewage Sludge

Fry‐drying is an alternative for heat and mass transfer intensification. The process reuses waste oil as a heating medium for drying by contact with the wet sludge. At the end of the process, a stable derived fuel is obtained, a granular solid composed of the dried indigenous sewage solid and the impregnated oil. The fry‐dried sludge is storable and transportable without any pathogen elements. Knowledge about heat and mass transfer rates during the frying process is essential in order to assess the quality of the final product such as calorific value, oil uptake, porosity changes, etc. The heat transfer properties including transfer by free convection between the solid and the frying oil are fundamental for the process design and manufacturing of the fry‐dried product. The convective heat coefficient by temperature measurement and overall energy balance calculation is determined. The heat flux is calculated from the fry‐drying kinetics including moisture loss and oil intake kinetics. Various hydrodynamic regimes for convective heat transfer during the frying process are discussed (non‐boiling, boiling, and low‐boiling regime). A dimensionless formulation for estimating the convective transfer is proposed.