Mass,energy and material balances of SRF production process. Part 2: SRF produced from construction and demolition waste

In this work, the fraction of construction and demolition waste (C&D waste) complicated and economically not feasible to sort out for recycling purposes is used to produce solid recovered fuel (SRF) through mechanical treatment (MT). The paper presents the mass, energy and material balances of this SRF production process. All the process streams (input and output) produced in MT waste sorting plant to produce SRF from C&D waste are sampled and treated according to CEN standard methods for SRF. Proximate and ultimate analysis of these streams is performed and their composition is determined. Based on this analysis and composition of process streams their mass, energy and material balances are established for SRF production process. By mass balance means the overall mass flow of input waste material stream in the various output streams and material balances mean the mass flow of components of input waste material stream (such as paper and cardboard, wood, plastic (soft), plastic (hard), textile and rubber) in the various output streams of SRF production process. The results from mass balance of SRF production process showed that of the total input C&D waste material to MT waste sorting plant, 44% was recovered in the form of SRF, 5% as ferrous metal, 1% as non-ferrous metal, and 28% was sorted out as fine fraction, 18% as reject material and 4% as heavy fraction. The energy balance of this SRF production process showed that of the total input energy content of C&D waste material to MT waste sorting plant, 74% was recovered in the form of SRF, 16% belonged to the reject material and rest 10% belonged to the streams of fine fraction and heavy fraction. From the material balances of this process, mass fractions of plastic (soft), paper and cardboard, wood and plastic (hard) recovered in the SRF stream were 84%, 82%, 72% and 68% respectively of their input masses to MT plant. A high mass fraction of plastic (PVC) and rubber material was found in the reject material stream. Streams of heavy fraction and fine fraction mainly contained non-combustible material (such as stone/rock, sand particles and gypsum material).     

Comparison of coal/solid recovered fuel (SRF) with coal/refuse derived fuel (RDF) in a fluidized bed reactor

An experimental study was undertaken to compare the differences between municipal solid waste (MSW) derived solid recovered fuel (SRF) (complying with CEN standards) and refuse derived fuel (RDF). Both fuels were co-combusted with coal in a 50 kW fluidised bed combustor and the metal emissions were compared. Synthetic SRF was prepared in the laboratory by grinding major constituents of MSW such as paper, plastic, textile and wood. RDF was obtained from a local mechanical treatment plant. Heavy metal emissions in flue gas and ash samples from the (coal + 10% SRF) fuel mixture were found to be within the acceptable range and were generally lower than that obtained for coal + 10% RDF fuel mixture. The relative distribution of heavy metals in ash components and the flue gas stream shows the presence of a large fraction (up to 98%) of most of the metals in the ash (except Hg and As). Thermo-gravimetric (TG) analysis of SRF constituents was performed to understand the behaviour of fuel mixtures in the absence and presence of air. The results obtained from the experimental study will enhance the confidence of fuel users towards using MSW-derived SRF as an alternative fuel.     

Energy implications of mechanical and mechanical–biological treatment compared to direct waste-to-energy

Primary energy savings potential is used to compare five residual municipal solid waste treatment systems, including configurations with mechanical (MT) and mechanical–biological (MBT) pre-treatment, which produce waste-derived fuels (RDF and SRF), biogas and/or recover additional materials for recycling, alongside a system based on conventional mass burn waste-to-energy and ash treatment. To examine the magnitude of potential savings we consider two energy efficiency levels (state-of-the-art and best available technology), the inclusion/exclusion of heat recovery (CHP vs. PP) and three different background end-use energy production systems (coal condensing electricity and natural gas heat, Nordic electricity mix and natural gas heat, and coal CHP energy quality allocation).The systems achieved net primary energy savings in a range between 34 and 140 MJ_primary/100 MJ_{input waste}, in the different scenario settings. The energy footprint of transportation needs, pre-treatment and reprocessing of recyclable materials was 3–9.5%, 1–18% and 1–8% respectively, relative to total energy savings. Mass combustion WtE achieved the highest savings in scenarios with CHP production, nonetheless, MBT-based systems had similarly high performance if SRF streams were co-combusted with coal. When RDF and SRF was only used in dedicated WtE plants, MBT-based systems totalled lower savings due to inherent system losses and additional energy costs. In scenarios without heat recovery, the biodrying MBS-based system achieved the highest savings, on the condition of SRF co-combustion. As a sensitivity scenario, alternative utilisation of SRF in cement kilns was modelled. It supported similar or higher net savings for all pre-treatment systems compared to mass combustion WtE, except when WtE CHP was possible in the first two background energy scenarios. Recovery of plastics for recycling before energy recovery increased net energy savings in most scenario variations, over those of full stream combustion. Sensitivity to assumptions regarding virgin plastic substitution was tested and was found to mostly favour plastic recovery.     

Mineral wool waste in Europe: a review of mineral wool waste quantity,quality, and current recycling methods

The construction and demolition (C&D) industry has been identified as a major source of waste. European Union legislation states that, by 2020, 70 % of C&D waste must be prepared for reuse, recycled or recovered. European Union member states must increase their C&D waste recycling percentages in order to meet this binding target. Utilization of mineral wool waste, often considered unrecyclable, could improve the recycling percentage of C&D waste. In this article, mineral wool production and waste volumes are estimated based on information from the Eurostat database. A literature survey is conducted to collect information about mineral wool material properties, current recycling methods, and barriers to recycling of mineral wool, and suitable methods for separating mineral wool from C&D waste streams and the economic viability of mineral wool recycling are discussed. It is noted that accurate estimation of mineral wool waste volumes is problematic due to the fragmented nature of available data. Based on the literature review, current methods for recycling mineral wool waste include utilization of mineral wool waste as a raw material in various products. Barriers to recycling include economic questions and issues related to the purity and health effects of mineral wool waste. Material properties of mineral wool waste, such as fire resistance, could provide improved properties in products utilizing mineral wool waste as a raw material.     

The use of commercial and industrial waste in energy recovery systems - A UK preliminary study

With 2020 energy targets set out by the EU fast approaching, the UK is trying to source a higher proportion of its energy from renewable resources. Coupled with this, a growing population and increasing trends in consumer demand have resulted in national waste loads increasing. A possible solution to both issues is energy-from-waste (EfW) technologies. Many studies have focused on municipal solid waste (MSW) as a potential feedstock, but appear to overlook the potential benefits of commercial and industrial waste (C&IW). In this study, samples of C&IW were collected from three North West waste management companies and Lancaster University campus. The samples were tested for their gross and net calorific value, moisture content, ash content, volatile matter, and also elemental composition to determine their suitability in EfW systems. Intra-sample analysis showed there to be little variation between samples with the exception two samples, from waste management site 3, which showed extensive variation with regards to net calorific value, ash content, and elemental analysis. Comparisons with known fuel types revealed similarities between the sampled C&IW, MSW, and refuse derived fuel (RDF) thereby justifying its potential for use in EfW systems. Mean net calorific value (NCV) was calculated as 9.47 MJ/kg and concentrations of sulphur, nitrogen, and chlorine were found to be below 2%. Potential electrical output was calculated using the NCV of the sampled C&IW coupled with four differing energy generation technologies. Using a conventional incinerator with steam cycle, total electrical output was calculated as 24.9 GWh, based on a plant operating at 100,000 tpa. This value rose to 27.0 GWh when using an integrated gasification combined cycle. A final aspect of this study was to deduce the potential total national electrical output if all suitable C&IW were to be used in EfW systems. Using incineration coupled with a steam turbine, this was determined to be 6 TWh, 1.9% of the national demand thereby contributing 6.5% towards the UK’s 2020 renewable electricity target.     

Closed cycle construction: an integrated process for the separation and reuse of C&D waste

In The Netherlands, construction and demolition (C&D) waste is already to a large extent being reused, especially the stony fraction, which is crushed and reused as a road base material. In order to increase the percentage of reuse of the total C&D waste flow to even higher levels, a new concept has been developed. In this concept, called 'Closed Cycle Construction', the processed materials are being reused at a higher quality level and the quantity of waste that has to be disposed of is minimised. For concrete and masonry, the new concept implies that the material cycle will be completely closed, and the original constituents (clay bricks, gravel, sand, cement stone) are recovered in thermal processes. The mixed C&D waste streams are separated and decontaminated. For this purpose several dry separation techniques are being developed. The quality of the stony fraction is improved so much, that this fraction can be reused as an aggregate in concrete. The new concept has several benefits from a sustainability point of view, namely less energy consumption, less carbon dioxide emission, less waste production and less land use (for excavation and disposal sites). One of the most remarkable benefits of the new concept is that the thermal process steps are fuelled with the combustible fraction of the C&D waste itself. Economically the new process is more or less comparable with the current way of processing C&D waste. On the basis of the positive results of a feasibility study, currently a pilot and demonstration project is being carried out. The aim is to optimise the different process steps of the Closed Cycle Construction process on a laboratory scale, and then to verify them on a large scale. The results of the project are promising, so far.     

Investigations on mechanical biological treatment of waste in South America: towards more sustainable MSW management strategies

This work presents an analysis on the suitability of mechanical biological treatment of municipal solid waste in South America, based on two previous experimental investigations carried out in two different countries. The first experiment was performed for determining the mass and volume reduction of MSW in the province of Concepción (Chile). The implemented bench-scale process consisted of a manual classification and separation stage, followed by an in-vessel biological degradation process. The second experiment consisted of a full-scale experiment performed in the city of Estrela (Brazil), where the existing municipal waste management facility was adapted to enhance the materials sorting and separation. Expressed in wet weight composition, 85.5% of the material input in the first experiment was separated for biological degradation. After 27 days of processing, 60% of the initial mass was reduced through degradation and water evaporation. The final fraction destined for landfilling equals 59% of the total input mass, corresponding to about 50% of the initial volume. In the second experiment, the fraction destined to landfill reaches 46.6% of the total input waste mass, whilst also significantly reducing the total volume to be disposed. These results, and the possible recovery of material streams suitable for recycling or for preparing solid recovered fuels, are the main advantages of the studied process.     

Sample preparation and biomass determination of SRF model mixture using cryogenic milling and the adapted balance method

The biogenic fraction of a simple solid recovered fuel (SRF) mixture (80 wt% printer paper/20 wt% high density polyethylene) is analyzed with the in-house developed adapted balance method (aBM). This fairly new approach is a combination of combustion elemental analysis (CHNS) and a data reconciliation algorithm based on successive linearisation for evaluation of the analysis results. This method shows a great potential as an alternative way to determine the biomass content in SRF. However, the employed analytical technique (CHNS elemental analysis) restricts the probed sample mass to low amounts in the range of a few hundred milligrams. This requires sample comminution to small grain sizes (<200 μm) to generate representative SRF specimen. This is not easily accomplished for certain material mixtures (e.g. SRF with rubber content) by conventional means of sample size reduction.This paper presents a proof of principle investigation of the sample preparation and analysis of an SRF model mixture with the use of cryogenic impact milling (final sample comminution) and the adapted balance method (determination of biomass content). The so derived sample preparation methodology (cutting mills and cryogenic impact milling) shows a better performance in accuracy and precision for the determination of the biomass content than one solely based on cutting mills. The results for the determination of the biogenic fraction are within 1–5% of the data obtained by the reference methods, selective dissolution method (SDM) and ¹⁴C-method (¹⁴C-M).     

Estimating construction and demolition debris generation using a materials flow analysis approach

The magnitude and composition of a region’s construction and demolition (C&D) debris should be understood when developing rules, policies and strategies for managing this segment of the solid waste stream. In the US, several national estimates have been conducted using a weight-per-construction-area approximation; national estimates using alternative procedures such as those used for other segments of the solid waste stream have not been reported for C&D debris. This paper presents an evaluation of a materials flow analysis (MFA) approach for estimating C&D debris generation and composition for a large region (the US). The consumption of construction materials in the US and typical waste factors used for construction materials purchasing were used to estimate the mass of solid waste generated as a result of construction activities. Debris from demolition activities was predicted from various historical construction materials consumption data and estimates of average service lives of the materials. The MFA approach estimated that approximately 610–780 × 10⁶ Mg of C&D debris was generated in 2002. This predicted mass exceeds previous estimates using other C&D debris predictive methodologies and reflects the large waste stream that exists.     

Effects of pre-treatment technologies on quantity and quality of source-sorted municipal organic waste for biogas recovery

Source-sorted municipal organic waste collected from different dwelling types in five Danish cities and pre-treated at three different plants was sampled and characterized several times during one year to investigate the origin of any differences in composition of the pre-treated waste introduced by city, pre-treatment technology, dwelling type or annual season. The investigated pre-treatment technologies were screw press, disc screen and shredder+magnet. The average quantity of pre-treated organic waste (biomass) produced from the incoming waste varied between the investigated pre-treatment technologies: 59%, 66% and 98% wet weight, respectively (41%, 34% and 2% reject, respectively). The pre-treatment technologies showed differences with respect to distribution of the chemical components in the waste between the biomass and the rejected material (reject), especially for dry matter, ash, collection bag material (plastic or paper) and easily degradable organic matter. Furthermore, the particle size of the biomass was related to the pre-treatment technology. The content of plastic in the biomass depended both on the actual collection bag material used in the system and the pre-treatment technology. The sampled reject consisted mostly of organic matter. For cities using plastic bags for the source-separated organic waste, the expected content of plastic in the reject was up to 10% wet weight (in some cases up to 20%). Batch tests for methane potential of the biomass samples showed only minor variations caused by the factors city, pre-treatment technology, dwelling type and season when based on the VS content of the waste (overall average 459STPm(3)/tVS). The amount of methane generated from 1t of collected waste was therefore mainly determined by the efficiency of the chosen pre-treatment technology described by the mass distribution of the incoming waste between biomass and reject.     

A holistic life cycle analysis of waste management scenarios at increasing source segregation intensity: The case of an Italian urban area

Life cycle analysis of several waste management scenarios for an Italian urban area was performed on the basis of different source segregation collection (SS) intensities from 0% up to 52%. Source segregated waste was recycled and or/recovered by composting. Residual waste management options were by landfilling, incineration with energy recovery or solid recovered fuel (SRF) production to substitute for coal. The increase in fuel and materials consumption due to increase in SS had negligible influence on the environmental impact of the system. Recycling operations such as incineration and SRF were always advantageous for impact reduction. There was lower impact for an SS of 52% even though the difference with the SS intensity of 35% was quite limited, about 15%. In all the configurations analyzed, the best environmental performance was achieved for the management system producing SRF by the biodrying process.     

Optimal utilization of waste-to-energy in an LCA perspective

Energy production from two types of municipal solid waste was evaluated using life cycle assessment (LCA): (1) mixed high calorific waste suitable for production of solid recovered fuels (SRF) and (2) source separated organic waste. For SRF, co-combustion was compared with mass burn incineration. For organic waste, anaerobic digestion (AD) was compared with mass burn incineration. In the case of mass burn incineration, incineration with and without energy recovery was modelled. Biogas produced from anaerobic digestion was evaluated for use both as transportation fuel and for heat and power production. All relevant consequences for energy and resource consumptions, emissions to air, water and soil, upstream processes and downstream processes were included in the LCA. Energy substitutions were considered with respect to two different energy systems: a present-day Danish system based on fossil fuels and a potential future system based on 100% renewable energy. It was found that mass burn incineration of SRF with energy recovery provided savings in all impact categories, but co-combustion was better with respect to Global Warming (GW). If all heat from incineration could be utilized, however, the two alternatives were comparable for SRF. For organic waste, mass burn incineration with energy recovery was preferable over anaerobic digestion in most impact categories. Waste composition and flue gas cleaning at co-combustion plants were critical for the environmental performance of SRF treatment, while the impacts related to utilization of the digestate were significant for the outcome of organic waste treatment. The conclusions were robust in a present-day as well as in a future energy system. This indicated that mass burn incineration with efficient energy recovery is a very environmentally competitive solution overall.     

Preliminary study for the management of construction and demolition waste

This paper refers to the management of the construction and demolition (C&D) waste since, according to the EU Waste Strategy, C&D waste is considered to be one of the priority waste streams and appropriate actions need to be taken with respect to its effective management. Initially, the paper presents the state-of-the-art of the problem of C&D waste, including the amount and composition of C&D waste in EU countries, differences in the characteristics of this waste stream depending on its origin, as well as collection and management practices that are applied. A methodology is described for the estimation of the quantities of the waste stream under examination, since in most cases quantitative primary data is not available. Next, the fundamentals for the development of an integrated scheme for the management of C&D waste are presented and discussed, such as appropriate demolition procedures and location of waste management (off-site waste management, on-site waste management, direct on-site recovery, centralized on-site recovery). Finally, taking into consideration all relevant parameters, alternative systems that could be applied for the management of the C&D waste are suggested.     

Alternative strategies for energy recovery from municipal solid waste Part B: Emission and cost estimates

This two-part paper assesses four strategies for energy recovery from Municipal Solid Waste (MSW) by dedicated Waste-To-Energy (WTE) plants. In strategy 1, the residue of Material Recovery (MR) is fed directly to a grate combustor, while in strategy 2 the grate combustor comes downstream of light mechanical treatment. In strategies 3 and 4, the MR residue is converted into Refuse Derived Fuel (RDF), in a fluidized cumbuster bed. The results of Part A, devoted to mass and energy balances, clearly show that pre-treating the MR residue in order to increase the heating value of the feedstock fed to the WTE plant has marginal effects on the energy efficiency of the WTE plant. When considering the efficiency of the whole strategy of waste management, the energy balances show that the more thorough the pre-treatment, the smaller the amount of energy recovered per unit of MR residue. Starting from the heat/mass balances illustrated in Part A, Part B examines the environmental impacts and economics of the various strategies by means of a Life Cycle Assessment (LCA). Results show that treating the MR residues ahead of the WTE plant does not provide environmental or economic benefits. RDF production worsens almost all impact indicators because it reduces net electricity production and thus the displacement of power plant emissions; it also increases costs, because the benefits of improving the quality of the material fed to the WTE plant do not compensate the cost of such improvement.     

Use of wastes derived from earthquakes for the production of concrete masonry partition wall blocks

Utilization of construction and demolition (C&D) wastes as recycled aggregates in the production of concrete and concrete products have attracted much attention in recent years. However, the presence of large quantities of crushed clay brick in some the C&D waste streams (e.g. waste derived collapsed masonry buildings after an earthquake) renders the recycled aggregates unsuitable for high grade use. One possibility is to make use of the low grade recycled aggregates for concrete block production. In this paper, we report the results of a comprehensive study to assess the feasibility of using crushed clay brick as coarse and fine aggregates in concrete masonry block production. The effects of the content of crushed coarse and fine clay brick aggregates (CBA) on the mechanical properties of non-structural concrete block were quantified. From the experimental test results, it was observed that incorporating the crushed clay brick aggregates had a significant influence on the properties of blocks. The hardened density and drying shrinkage of the block specimens decreased with an increase in CBA content. The use of CBA increased the water absorption of block specimens. The results suggested that the amount of crushed clay brick to be used in concrete masonry blocks should be controlled at less than 25% (coarse aggregate) and within 50-75% for fine aggregates.     

Metals, non-metals and PCB in electrical and electronic waste--actual levels in Switzerland

The chemical composition of waste of small electrical and electronic equipment (s-WEEE), a rapidly growing waste stream, was determined for selected metals (Cu, Sb, Hg etc.) and non-metals (Cl, Br, P) and PCBs. During a 3-day experiment, all output products and the s-WEEE input mass flows in a WEEE recycling plant were measured. Only output products were sampled and analyzed. Material balances were established, applying substance flow analysis (SFA). Transfer coefficients for the selected substances were also determined. The results demonstrate the capability of SFA to determine the composition of the highly heterogeneous WEEE for most substances with rather low uncertainty (2 sigma +/- 30%). The results confirm the growing importance of s-WEEE regarding secondary resource metals and potential toxic substances. Nowadays, the thirty times smaller s-WEEE turns over larger flows for many substances, compared to municipal solid waste. Transfer coefficient results serve to evaluate the separation efficiency of the recycling process and confirm--with the exception of PCB and Hg--the limitation of hand-sorting and mechanical processing to separate pollutants (Cd, Pb, etc.) out of reusable fractions. Regularly applied SFA would serve to assess the efficacy of legislative, organizational and technical measures on the WEEE.     

Life cycle assessment of solid refuse fuel production from MSW in Korea

Solid refuse fuel (SRF) produced from waste materials is a promising fuel that can be utilized for energy recovery in industries. This study considered both characterization and weighting modeling as life cycle assessment (LCA) results. This study aimed to analyze the flows of materials and energy and to evaluate the environmental impact of SRF plants using LCA and compared them with an incineration plant. Based on the results of material and energy flow analysis, SRF products had various energy potentials depending on the treatment method of municipal solid waste (MSW) and replaced the current fossil fuels by SRF combustion. Global impacts were mainly influenced by energy consumption, especially drying methods in the production of SRF, and affected the results of the weighting analysis. The SRF plant with a bio-drying option was evaluated as the best effective practice in the weighting analysis. The LCA results in this study indicated 0.021–9.88 points according to drying methods for SRF production and 1.38 points for incineration. In the sensitivity analysis, the environmental impact of SRF production was found to be significantly affected by the drying methods for MSW and the utilization of fossil energy. Thus, improvement of the drying options could significantly reduce the environmental impact.     

Estimation of building-related construction and demolition waste in Shanghai

One methodology is proposed to estimate the quantification and composition of building-related construction and demolition (C&D) waste in a fast developing region like Shanghai, PR China. The varieties of structure types and building waste intensities due to the requirement of progressive building design and structure codes in different decades are considered in this regional C&D waste estimation study. It is concluded that approximately 13.71 million tons of C&D waste was generated in 2012 in Shanghai, of which more than 80% of this C&D waste was concrete, bricks and blocks. Analysis from this study can be applied to facilitate C&D waste governors and researchers the duty of formulating precise policies and specifications. As a matter of fact, at least a half of the enormous amount of C&D waste could be recycled if implementing proper recycling technologies and measures. The appropriate managements would be economically and environmentally beneficial to Shanghai where the per capita per year output of C&D waste has been as high as 842 kg in 2010.     

Technical specifications for mechanical recycling of agricultural plastic waste

Technical specifications appropriate for the recycling of agricultural plastic wastes (APWs), widely accepted by the recycling industry were developed. The specifications establish quality standards to be met by the agricultural plastics producers, users and the agricultural plastic waste management chain. They constitute the base for the best economical and environmental valorisation of the APW.The analysis of the APW streams conducted across Europe in the framework of the European project “LabelAgriWaste” revealed the inherent characteristics of the APW streams and the inherent constraints (technical or economical) of the APW. The APW stream properties related to its recycling potential and measured during pilot trials are presented and a subsequent universally accepted simplified and expanded list of APW recycling technical specifications is proposed and justified. The list includes two sets of specifications, applied to two different quality categories of recyclable APW: one for pellet production process (“Quality I”) and another one for plastic profile production process (“Quality II”). Parameters that are taken into consideration in the specifications include the APW physical characteristics, contamination, composition and degradation. The proposed specifications are focused on polyethylene based APW that represents the vast majority of the APW stream. However, the specifications can be adjusted to cover also APW of different materials (e.g. PP or PVC) that are found in very small quantities in protected cultivations in Europe. The adoption of the proposed specifications could transform this waste stream into a labelled commodity traded freely in the market and will constitute the base for the best economical and environmental valorisation of the APW.     

Pyrolysis of municipal plastic wastes II: Influence of raw material composition under catalytic conditions

In this work, the results obtained in catalytic pyrolysis of three plastic waste streams which are the rejects of an industrial packing wastes sorting plant are presented. The samples have been pyrolysed in a 3.5 dm(3) reactor under semi-batch conditions at 440 °C for 30 min in nitrogen atmosphere. Commercial ZSM-5 zeolite has been used as catalyst in liquid phase contact. In every case, high HHV gases and liquids which can be useful as fuels or source of chemicals are obtained. A solid fraction composed of the inorganic material contained in the raw materials and some char formed in the pyrolysis process is also obtained. The zeolite has shown to be very effective to produce liquids with great aromatics content and C3-C4 fraction rich gases, even though the raw material was mainly composed of polyolefins. The characteristics of the pyrolysis products as well as the effect of the catalyst vary depending on the composition of the raw material. When paper rich samples are pyrolysed, ZSM-5 zeolite increases water production and reduces CO and CO(2) generation. If stepwise pyrolysis is applied to such sample, the aqueous liquid phase can be separated from the organic liquid fraction in a first low temperature step.