Real-time monitoring of volume flow, mass flow and shredder power consumption in mixed solid waste processing.

Real-time material flow monitoring is not yet implemented in mixed solid waste processing, but it is important for an efficient quality assured production and the development of the smart waste factory. The present paper shows results of practical investigation of the Real-Time Material Flow Monitoring in a large-scale Solid Recovered Fuel (SRF) production plant and a semi large-scale processing line (Technical line 4.0) using mixed solid waste. The investigations aimed to research the fundamentals for generating mass flow data from volume flow data and volume and mass flow data from shredder power consumption. It could be shown that a mass determination from volume flow data with the help of density determinations can be practically realized in a good approximation (deviation < 1%) to the gravimetrically determined mass in an SRF production plant. With R2 = 0.47, the power consumption of a shredder in the SRF plant shows a low to medium correlation to the corresponding volume flow. In the 31 tests with the Technical Line 4.0, both, the mass flow and the volume flow could be measured in real-time. Combining these data results in the temporal density curve and shows strong fluctuations for shredded commercial waste. Comparing the mean bulk densities for each test with those from the density determinations of taken samples shows a robust correlation (R2 = 0.82). Analyzes of the material composition of the shredded mixed solid waste show strong correlations to bulk density for the proportions of the fractions rest (positive correlation) and plastics (negative correlation).

Origins of major and minor ash constituents of solid recovered fuel for co-processing in the cement industry.

Solid recovered fuel (SRF) ash consists of element oxides, which are valuable materials for cement manufacturers. When SRF is co-processed in the cement industry, its mineral content is incorporated into the clinker. Therefore, from a technical perspective, SRF ash is recycled. However, since recycling processes for materials that may be present in SRF exist, and since recycling goals are defined for different waste types, understanding the origin of these ash constituents and the contribution of different materials to the Recycling-index (R-index, i.e., the material-recyclable share of SRF) is important. In this work, the origins of Al, Ca, Fe, Si, Ti, Mg, Na, K, S, and P were first reviewed. Subsequently, ten SRF samples were sorted, and the ash content and composition of the sorting fractions (e.g., <10 mm, plastics, paper&cardboard) determined. Additionally, selected samples of polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), polyvinyl chloride (PVC), liquid packaging board (LPB), wood, and paper&cardboard (P&C) extracted from SRF were investigated. The results demonstrated that the materials that contributed most of the valuable oxides and ash content, and thereby to the R-index of SRF, are mixed or composite fractions, for example, the fine fraction, composites, and the sorting residues. Except for the composite LPB, no other material recovery options exist for most of these fractions. For this reason, the recycling of mixed and soiled materials or residues in the cement industry may be considered a complementary option to existing recycling processes.

Efficient derivation of significant results from mechanical processing experiments with mixed solid waste: Coarse-shredding of commercial waste.

Deriving significant experiment-based conclusions on mechanical processing of mixed solid waste is challenging: the input material cannot be downscaled in a way that enables drawing transferable conclusions from lab-scale experiments. Hence experiments need to be conducted in industry-scale, using real waste. Besides the enormous resulting experimental efforts and costs, which economically limit the number of experimental runs, identifying and quantifying significant effects is complicated by the distortion of the data introduced by the waste's variability. The distortion is particularly high for cases where sampling is necessary and in experiments where material cannot be re-used from one run to the next. In the latter case, inter-experimental differences of the waste add to the distortion of the data. In this work, a systematic approach for deriving representative and significant results at the minimum possible effort is described and evaluated, based on the method of Design of Experiments. It is applied to a 32 runs D-optimal industry-scale coarse-shredding experiment with mixed commercial solid waste, based on a reduced cubic design model, examining the influence of the gap width, shaft rotation speed, and cutting tool geometry on the throughput behavior and energy demand. The resulting models are highly significant (model p-values < 0.0001), proving the ability to extract reliable information from industry-scale waste processing experiments. Concerning commercial waste shredding, the models provide new insights into process behavior, for example, the quadratic dependence of the mass flow on the shaft rotation speed, with the highest hourly mass flows at 84% of the maximum shaft rotation speed.

Sensor-based Particle Size Determination of Shredded Mixed Commercial Waste based on two-dimensional Images.

To optimize output streams in mechanical waste treatment plants dynamic particle size control is a promising approach. In addition to relevant actuators - such as an adjustable shredder gap width - this also requires technology for online and real-time measurements of the particle size distribution. The paper at hand presents a model in MATLAB® which extracts information about several geometric descriptors - such as diameters, lengths, areas, shape factors - from 2D images of individual particles taken by RGB cameras of pre-shredded, solid, mixed commercial waste and processes this data in a multivariate regression model using the Partial Least Squares Regression (PLSR) to predict the particle size class of each particle according to a drum screen. The investigated materials in this work are lightweight fraction, plastics, wood, paper-cardboard and residual fraction. The particle sizes are divided into classes defined by the screen cuts (in mm) 80, 60, 40, 20 and 10. The results show assignment reliability for certain materials of over 80%. Furthermore, when considering the results for determining a complete particle size distribution - for an exemplary real waste - the accuracy of the model is as good as 99% for the materials wood, 3D-plastics and residual fraction for each particle size class respectively as assignment errors partially compensate each other.

Real time material flow monitoring in mechanical waste processing and the relevance of fluctuations.

To achieve the goals of the circular economy, significant improvements in non-hazardous solid waste processing/treatment must be made. Large deficits in the digitalization of mechanical waste treatment plants (smart waste factory) offer great potential for improvement. Real-time material flow monitoring is carried out in very few plants, thus wasting considerable potential for improving plant performance. This article describes results from the authors' own practical analyses using sensor-based technologies for monitoring material flows, an on-site investigation in a large waste treatment plant and also in a pilot-scale plant (Technical Line 4.0) using mixed commercial waste (MCW) from Austria. The obtained data shows that the quantitative monitoring of volume and mass flow (via laser triangulation as well as near-infrared (NIR) based monitoring) and material composition (NIR sensor) is possible. The observed fluctuations were categorised in short-, mid- and long-term fluctuations and were led back to their causes, i.e. discontinuous feeding process, material and machine-specific characteristics. Using the quotient of the 90% (Q90) and 10% (Q10) quantiles of time-resolved volume-flow data for the assessment of fluctuations, for the considered time-intervals, resulted in Q90 / Q10 ratios between 3.39 and 4.58. If short-term fluctuations (within the observed time-intervals) are related to the 29.6 s moving average, deviations between 1.8% and 6.8% result. To verify the relevance of such fluctuations, sensor-based sorting (SBS) experiments were conducted, revealing a reduced product purity of 6% due to short-term fluctuations in the feed of the SBS-Machine using light packaging waste (LPW).

Influence of pre-screening on down-stream processing for the production of plastic enriched fractions for recycling from mixed commercial and municipal waste.

The use of plastic waste as resource gains more and more attention. In this context, material recycling is especially focused on packaging plastics. Further waste streams that contain a significant amount of plastics are mixed commercial and municipal solid waste. To assess the potential of plastics for recycling and energy recovery from these material streams large-scale experiments were conducted. The potential of mechanical pre-processing with the aim of generating a 3D-plastics pre-concentrate was assessed. The focus of these investigations was put on the relevance of the screening stage and its influence on down-stream material processing via ballistic separation and sensor-based sorting. Results demonstrate not only that the screening of both waste streams leads to enrichment of plastics in coarse particle size ranges (especially >80 mm) and transfer of contaminants, organics and minerals to fine fractions (especially <10 mm), but also that sensor-based sorting performance can be significantly enhanced due to cleaning effects on plastics, induced by the material circulation and the resulting interparticle friction in a drum screen. On the downside, the material rotation in a drum screen leads to tail-formation that can create plant down-time through clogging as well as material losses and impairment of pre-concentrates.

Grain size dependent distribution of different plastic types in coarse shredded mixed commercial and municipal waste.

The Waste Framework Directive regulates the recycling of waste in Europe. The definition of waste is specified in different guidelines and regulations. Mixed Commercial Waste is waste from industry which is not collected separately. Currently there is little known about its composition. Mixed Municipal Waste, on the other hand, is household waste that cannot be attributed to any separately collected waste fraction (AdSLR, 2012). Both wastes are currently treated focussing on the generation of refuse-derived fuel rather than on the separation of recyclables (mainly performed for metals). The purpose of this paper is to characterise the amounts of various plastic types contained in different grain sizes of two-dimensional and three-dimensional plastics sorting fractions of both waste types. Nine types of plastics were identified as potential recycling materials for which recycling processes as well as a market are available. Both wastes were shredded, sampled and sieved into nine grain size classes (GSC). Fractions coarser than 20 mm were sorted, generating a 'plastics-2D' and a 'plastics-3D' fraction among others. The two plastics fractions were further characterised as plastic types using a near-infrared sensor and a Fourier-transform infrared spectrometer. The results reveal a potential for plastic recycling through mechanical and feedstock recycling options for the examined wastes. Certain types of plastics, of certain dimensionality, tend to come in certain grain sizes, which is essential for mechanical enrichment and discharge.

Origins and carriers of Sb, As, Cd, Cl, Cr, Co, Pb, Hg, and Ni in mixed solid waste - A literature-based evaluation.

Antimony, arsenic, cadmium, chlorine, chromium, cobalt, lead, mercury, nickel and their compounds are commonly used in the industrial production of various goods. At the end of the product life cycle, these elements enter the waste system as constituents of the products. Mixed municipal and commercial wastes are landfilled, biologically treated, incinerated, and/or processed in mechanical treatment plants to yield solid recovered fuel (SRF). In all these cases, inorganic contaminants that are present in the input waste material play a significant role. In mechanical waste treatment, materials containing high concentrations of these elements (contaminant carriers) can be selectively removed (e.g. by infrared sorters) to improve the output quality, but prior knowledge about the contaminant carriers is required. This paper reviews several waste-related publications in order to identify carriers of Sb, As, Cd, Cl, Cr, Co, Pb, Hg, and Ni in mixed municipal and commercial waste. Identified contaminant carriers are listed alongside ranges for expected concentrations. Furthermore, the data are combined with information on industrial applications and contaminant concentrations in products in order to discuss the reasons for the presence of the respective elements in the carriers. Generally, besides inerts or metals, identified contaminant carriers often include plastics, composite materials, leather products, textiles, rubber, electronic waste, and batteries. Moreover, it is evaluated how individual contaminant carriers are reflected by chemical waste analyses. While the findings of the paper can be applied to different waste treatment options, the discussion focuses on SRF, which is the main output of mechanical treatment plants.

Digitalisation and intelligent robotics in value chain of circular economy oriented waste management - A review.

The general aim of circular economy is the most efficient and comprehensive use of resources. In order to achieve this goal, new approaches of Industry 4.0 are being developed and implemented in the field of waste management. The innovative K-project: Recycling and Recovery of Waste 4.0 - "ReWaste4.0" deals with topics such as digitalisation and the use of robotic technologies in waste management. Here, a summary of the already published results in these areas, which were divided into the four focused topics, is given: Collection and Logistics, Machines and waste treatment plants, Business models and Data Tools. Presented are systems and methods already used in waste management, as well as technologies that have already been successfully applied in other industrial sectors and will also be relevant in the waste management sector for the future. The focus is set on systems that could be used in waste treatment plants or machines in the future in order to make treatment of waste more efficient. In particular, systems which carry out the sorting of (mixed) waste via robotic technologies are of interest. Furthermore "smart bins" with sensors for material detection or level measurement, methods for digital image analysis and new business models have already been developed. The technologies are often based on large amounts of data that can contribute to increase the efficiency within plants. In addition, the results of an online market survey of companies from the waste management industry on the subject of waste management 4.0 or "digital readiness" are summarized.

Dynamic visualisation of municipal waste management performance in the EU using Ternary Diagram method.

This contribution describes the dynamic visualisation of European (EU 28) municipal waste management performance, using the Ternary Diagram Method. Municipal waste management performance depends primarily on three treatment categories: recycling & composting, incineration and landfilling. The framework of current municipal waste management including recycling targets, etc. is given by the Waste Framework Directive - 2008/98/EC. The proposed Circular Economy Package should stimulate Europe's transition towards more sustainable resources and energy oriented waste management. The Package also includes a revised legislative proposal on waste that sets ambitious recycling rates for municipal waste for 2025 (60%) and 2030 (65%). Additionally, the new calculation method for monitoring the attainment of the targets should be applied. In 2014, ca. 240 million tonnes of municipal waste were generated in the EU. While in 1995, 17% were recycled and composted, 14% incinerated and 64% landfilled, in 2014 ca. 71% were recovered but 28% landfilled only. Considering the treatment performance of the individual EU member states, the EU 28 can be divided into three groups, namely: "Recovery Countries", "Transition Countries" and "Landfilling Countries". Using Ternary Diagram Method, three types of visualization for the municipal waste management performance have been investigated and extensively described. Therefore, for better understanding of municipal waste management performance in the last 20years, dynamic visualisation of the Eurostat table-form data on all 28 member states of the EU has been carried out in three different ways: 1. "Performance Positioning" of waste management unit(s) at a specific date; 2. "Performance dynamics" over a certain time period and; 3. "Performance development" expressed as a track(s). Results obtained show that the Ternary Diagram Method is very well suited to be used for better understanding of past developments and coherences, for monitoring of current situations and prognosis of future paths. One of the interesting coherences shown by the method is the linked development of recycling & composting (60-65%) with incineration (40-35%) performance over the last 20years in the EU 28.

Design, quality, and quality assurance of solid recovered fuels for the substitution of fossil feedstock in the cement industry.

This paper describes the requirements for the production, quality, and quality assurance of solid recovered fuels (SRF) that are increasingly used in the cement industry. Different aspects have to be considered before using SRF as an alternative fuel. Here, a study on the quality of SRF used in the cement industry is presented. This overview is completed by an investigation of type and properties of input materials used at waste splitting and SRF production plants in Austria. As a simplified classification, SRF can be divided into two classes: a fine, high-calorific SRF for the main burner, or coarser SRF material with low calorific value for secondary firing systems, such as precombustion chambers or similar systems. In the present study, SRFs coming from various sources that fall under these two different waste fuel classes are discussed. Both SRFs are actually fired in the grey clinker kiln of the Holcim (Slovensko) plant in Rohoznik (Slovakia). The fine premium-quality material is used in the main burner and the coarse regular-quality material is fed to a FLS Hotdisc combustion device. In general, the alternative fuels are used instead of their substituted fossil fuels. For this, chemical compositions and other properties of SRF were compared to hard coal as one of the most common conventional fuels in Europe. This approach allows to compare the heavy metal input from traditional and alternative fuels and to comment on the legal requirements on SRF that, at the moment, are under development in Europe.

Production, quality and quality assurance of Refuse Derived Fuels (RDFs).

This contribution describes characterization, classification, production, application and quality assurance of Refuse Derived Fuels (RDFs) that are increasingly used in a wide range of co-incineration plants. It is shown in this paper, that the fuel-parameter, i.e. net calorific value [MJ/kg(OS)], particle size d(90) or d(95) [mm], impurities [w%], chlorine content [w%], sulfur content [w%], fluorine content [w%], ash content [w%], moisture [w%] and heavy metals content [mg/kg(DM)], can be preferentially used for the classification of different types of RDF applied for co-incineration and substitution of fossil-fuel in different industial sectors. Describing the external production of RDF by processing and confectioning of wastes as well as internal processing of waste at the incineration plant, a case study is reported on the application of RDF made out of different household waste fractions in a 120,000t/yr Waste to Energy (WtE) circulating fluidized bed (CFB) incinerator. For that purpose, delivered wastes, as well as incinerator feedstock material (i.e. after internal waste processing) are extensively investigated. Starting with elaboration of sampling plan in accordance with the relevant guidelines and standards, waste from different suppliers was sampled. Moreover, manual sorting analyses and chemical analyses were carried out. Finally, results of investigations are presented and discussed in the paper.