New underwater pelletizing techniques under development at BKG

New underwater and strand pelletizing technologies are now available to the compounder. Plastics Additives & Compounding reports on some recent activities at a number of companies active in pelletizing.     

Rieter develops die face cut and underwater strand pelletizing expertise

New underwater and strand pelletizing technologies are now available to the compounder. Plastics Additives & Compounding reports on some recent activities at a number of companies active in pelletizing.     

Effect of extractives and storage on the pelletizing process of sawdust

The importance of extractives and storage for sawdust as raw material for wood pellet production was analyzed. Sawdust prepared from eastern white pine (Pinus strobus L.), white oak (Quercus alba L.) and yellow-poplar (Liriodendron tulipifera L.) together with two commercial raw materials were extracted with acetone or stored at 60 °C for 21 days. The effects of the treatments were measured on the pellet strength, and with respect to the energy use requirements of a commercial pellet mill using laboratory dies and methods to measure the different stages of the pelletizing process individually. The results showed that removal of the extractives significantly increased the pellet strength and the energy requirements in all stages of the pelletizing processes corresponding to the samples extractives content, whereas the effect of the storage treatment was indefinite. The study indicates that extractives act as plasticizers and lubricants and thereby decrease the energy requirements for the pelletizing process. On the other hand, extractives seem to prevent close contact between the bonding sites of the lignocellulose particles and thereby decrease the pellet strength. Differences in extractives content can therefore explain differences in pellet mill energy consumption and capacity when raw materials from different wood species are used. The effect of storage with respect to particle surface accumulation of extractives may have little importance compared to the total amount of extractives in the raw material.     

Pelletizing

A wide range of pelletizers is available for the compounder to convert the melt from the extruder into an easily handled form. This month Plastics Additives & Compounding takes a look at some of the new developments in pelletizing.     

Developments at ECON highlight automatic start-up and ease of handling

New underwater and strand pelletizing technologies are now available to the compounder. Plastics Additives & Compounding reports on some recent activities at a number of companies active in pelletizing.     

Fuel pellets from biomass: The importance of the pelletizing pressure and its dependency on the processing conditions

The aim of the present study was to identify the key factors affecting the pelletizing pressure in biomass pelletization processes. The impact of raw material type, pellet length, temperature, moisture content and particle size on the pressure build up in the press channel of a pellet mill was studied using a single pellet press unit. It was shown that the pelletizing pressure increased exponentially with the pellet length. The rate of increase was dependent on biomass species, temperature, moisture content and particle size. A mathematical model, predicting the pelletizing pressure, was in good accordance with experimental data. It was shown that increasing the temperature resulted in a decrease of the pelletizing pressure. Infrared spectra taken from the pellets surface, indicated hydrophobic extractives on the pellet surface, for pellets produced at higher temperatures. The extractives act as lubricants, lowering the friction between the biomass and the press channel walls. The effect of moisture content on the pelletizing pressure was dependent on the raw material species. Different particle size fractions, from below 0.5 mm up to 2.8 mm diameter, were tested, and it was shown that the pelletizing pressure increased with decreasing particle size. The impact of pelletizing pressure on pellet density was determined, and it was shown that a pelletizing pressure above 200 MPa resulted only in minor increase in pellet density.     

两种水下切粒方式的比较

介绍了高聚物切粒工艺中较为常见的两种水下切粒方式——水下拉条切粒和水下模面切粒,比较了它们的优缺点。生产者可根据实际工艺条件和生产条件,选用适合的水下切粒方式,以满足生产要求。     

一种切粒装置的改进设计

文中切粒装置与挤出机配套使用,用于高分子聚合物,尤其是弹性体的挤出成型、切粒。本文针对原有切粒装置存在的诸多问题,对其模套、切刀轴、调距方式进行了改进,并重新确定相关参数,从而使改进后的装置更加适合生产工艺的要求,并达到了满意的效果。     

高聚物挤出造粒形式和原理

本文主要介绍了高聚物熔体挤出造粒的几种形式、工作原理、设备结构和使用范围，并提出了应遵循的原则     

水下切粒设备市场预测及研究

本文叙述了国内聚酯和聚酰胺市场的发展趋势 ,介绍了国内外水下切粒设备发展的最新动向 ,并对明年的国内水下切粒设备市场进行了预测。     

Effect of biomaterial characteristics on pelletizing properties and biofuel pellet quality

Sawdust of conifers as a by-product from saw mills is the most commonly used biomaterial for pellet production in Sweden today. Experiences from the biofuel pellet industry indicate that different biomaterial properties influence the final pellet quality. A systematic study was conducted where five factors were varied according to a two level fractional factorial design. The factors were: tree species (Scots pine, Norway spruce); origin of growth-place (latitudes 57 and 64°N); storage time of sawdust (0 and 140 days), moisture content (9 and 12%) and steam treatment (2 and 6 kg/h). The measured responses bulk density and mechanical durability represented the pellet quality while the press current and the fines produced in the pelletizing process were measures of the pelletizing property.The results showed that low moisture content and long storage time resulted in increased bulk densities and press currents. For mechanical durability and fines, a long storage time and intermediate moisture contents were found favourable. In addition, indications were found that the reduction of fatty and resin acids during the storage also influenced the pelletizing properties and the pellet quality.     

Effect of batch pelletizing on a course of SHS reactions: An overview

Such a simple technological trick as pelletizing (granulating) green powder mixtures (popular in conventional powder technology) has seldom been used in SHS technology. We have demonstrated that pelletizing green powder mixtures can markedly affect the parameters of various SHS reactions (SHS in a mode of infiltration-mediated combustion, SHS with a reduction stage, combustion of thermit mixtures, SHS in aluminum melt) and properties of their products.     

刀盘结构对水下切粒水室流场分布的影响

对于特殊材料的水下切粒加工,采用立式爪形刀盘的独特结构.运用有限元分析软件fluent,对水下切粒水室进行数值模拟,对比分析立式爪形刀盘与传统刀盘的水室流场分布,探究不同的刀盘结构以及刀盘位置的变化对于切粒水室流场分布的影响.     

Reactive sintering of U1−yAmyO2±x in overstoichiometric conditions

In the framework of Partitioning & Transmutation (P&T), U_1?yAm_yO_2±x materials are promising fuels for Am recycling. In this context, these materials were fabricated in the ATALANTE facility by a process which consists of pelletizing and reactive sintering. Since it was effective in studies conducted on UO_2+x, sintering in overstoichiometric conditions was investigated. In this work, three Am contents (10, 20 and 30%) and four temperatures (from 1000 to 1300 °C) were studied. It was shown that low-density and multiphasic compounds were obtained. Moreover, XRD and XAFS analyses pointed out that the total reduction of Am(+IV) to Am(+III) and solid solution formation occur during sintering at temperatures inferior to 1300 °C. Although previous studies on UO_2+x showed that high oxygen potential enhanced the diffusion process, this work proved that this effect is clearly modified by the presence of Am. Finally, sintering in overstoichiometric conditions is not yet suitable for Am-bearing fuel fabrication.     

The influence of raw material characteristics on the industrial pelletizing process and pellet quality

Industrial pelletizing of sawdust was carried out as a designed experiment in the factors: sawdust moisture content, fractions of fresh pine, stored pine and spruce. The process parameters and response variables were energy consumption, pellet flow rate, pellet bulk density, durability and moisture content. The final data consisted of twelve industrial scale runs. Because of the many response variables, data evaluation was by principal component analysis of a 12 × 9 data matrix. The two principal component model showed a clustering of samples, with a good reproducibility of the center points. It also showed a positive correlation of energy consumption, bulk density and durability all negatively correlated to flow rate and moisture content. The stored pine was more related to high durability and bulk density. The role of the spruce fraction was unclear. The design matrix, augmented with the process parameters was a 12 × 6 matrix. Partial least squares regression showed excellent results for pellet moisture content and bulk density. The model for durability was promising. A 12 × 21 data matrix of fatty- and resin acid concentrations measured by GC–MS showed the differences between fresh and stored pine very clearly. The influence of the spruce fraction was less clear. However, the influence of the fatty- and resin acids on the pelletizing process could not be confirmed, indicating that other differences between fresh and stored pine sawdust have to be investigated. This work shows that it is possible to design the pelletizing process for moderate energy consumption and high pellet quality.     

聚丙烯挤压造粒系统问题分析与改造

就装置从国外引进的聚丙烯粉料挤压造粒系统的工艺及在生产中遇到的问题进行分析,提出有针对性的解决方法;同时对不同牌号下运行参数进行比较归纳,为该系统优化操作提供指导。     

Radial distribution of porosity in spherical activated carbon particles

The radial distribution of porosity in spherical activated carbon particles and its relationship to both activation temperature and conversion of the reaction C-CO₂ are discussed. Char spheres, obtained by pelletizing Quercus agrifolia powdered char, were activated using CO₂ as activating agent at 820 and 860 °C. For both temperatures, the gasification reaction was run until the desired conversion (30, 50 and 70%) was reached. The activation process was performed using TGA apparatus. The porosity of the samples was measured by physical adsorption of nitrogen at −196 °C. BET and Dubinin-Raduskhevich equations were used to analyse the results. From each activated carbon sphere several samples were prepared, corresponding to different layers of the sphere; an outer layer, a middle layer and the core of the particle. From these results, the radial porosity evolution as a function of activation temperature and reaction conversion was obtained and a mathematical expression that correlates pore volume evolution and reaction conversion is proposed.     

Processing highly filled pre‐compounded pellets on single screw extruders

This article discusses, in general terms, several approaches to producing highly filled plastics. Emphasis is on wood flour, with polyolefins as an example. Processing other highly filled polymer and filler choices follows the same logic. Successful approaches include the single screw machine being fed pre‐pelletized material. A large pelletizing twin screw compounder selected for compounding for its output rate isolates the complexities of the compounding step from the profile lines, which have their own unique challenges, such as sizing and cooling the part at good quality and with good tolerances. Operating a few big pelletizing twin screw machines would allow the simple single screw lines of various sizes to run at decent efficiencies on big or small profiles. Since not one machinery approach has monopolized this application to date, some of the major processing and equipment comparisons are discussed. J. VINYL. ADDIT. TECHNOL. 12:83–86, 2006. © 2006 Society of Plastics Engineers     

基于CFD⁃DEM的水下切粒装置水室内颗粒流动过程数值模拟

基于CFD?DEM耦合方法,研究了颗粒在水室内的流动状态,分析了不同刀盘转速、粒子水通入量和水室出口角度对造粒过程的影响,发现提高刀盘转速、增加粒子水通入量和水室出口倾斜一定的角度都有利于水室内颗粒的排出。进一步研究了颗粒与碎屑在水室内的流动,发现在水室出口处二者的流动基本呈现出一定的分离角度。     

Strand pelletizers aim to meet compounders' needs

Some basic research in polymer behaviour during the pelletizing by Rieter Automatik has led to an improvement in the quality of pellet cuts. Along with other innovations, the development has now been incorporated in the company's latest range of strand pelletizers for the compounding industry. Mark Holmes reports.