Resources,Conservation Recycling:X 4(2019)100017 Resource Contents lists available at ScienceDirect tion Resources,Conservation Recycling:X ELSEVIER journal homepage:www.journals.elsevier.com/resources-conservation-and-recycling-x A feasibility assessment of an integrated plastic waste system adopting mechanical and thermochemical conversion processes Maria Laura Mastellone.b.* Department of Environmental,Biological,Pharmaceutical Science and Technology,University of Campania "Luigi Vanvitelli",Via Vivaldi 43,81100 Caserta,Italy Pruvia Fuels GmbH,Rheingoldstr.10a,D-90513 Zirndorf,Germany ARTICLE INFO ABSTRACT Keywords: The large variety and amounts of plastic waste produced worldwide requires to better organize the industrial Plastic waste network devoted to the exploitation of this material by including different processes that allow to recover the Sorting "material"as main target.This paper presents the results of the feasibility study developed for an integrated Pyrolysis system for plastic waste management designed in such a way to deal with the real market and provide for Gasification reliable targets in term of material recovery yields,energy efficiency and waste minimization.The system under Syngas Syncrude study is a combination of mechanical sorting,thermochemical processes and conversion into materials and energy.The quantified block diagrams are used to represent the mass and feedstock energy balances by allowing the calculation of yields of given products.The equipment list for each sub-system is provided together with the installed power for the main component and/or auxiliary;these data allowed to perform the energy balance and to obtain the net energy production by the integrated system.The energy balance demonstrated that the in tegrated system is feasible while,on the contrary,the single processes are not energetic self-sustainable. 1.Introduction and scope economic factors affecting the decision of which route is the most sui- table for a certain waste are the composition in term of polymer type 1.1.Plastic waste management background (HDPE,LDPE,PP,PS,EPS,PET,PVC,...)and the fraction of non- polymeric materials (including multi-layered plastics and composites). The amount of plastic materials produced worldwide reached 348 These characteristics affect the design of the overall system,starting million of tonnes in 2017;about 18%of this amount was produced in with the sorting facility where the commingled plastic waste coming Europe and more than 50%in Asia.A fraction larger than 50%of from the separate collection of municipal and commercial waste is plastic converter demand is constituted by polypropylene (PP),low- realised,until the recycling or recovery process,chosen as suitable tool density polyethylene (LDPE)and high-density polyethylene (HDPE) to convert the waste into valuable materials (Zaccariello et al.,2015). (Plastics Europe Annual Review,2018).The extensive production of The most applied combination of processes in Europe consists of the plastics and the indiscriminate disposal in the environment created also centralised sorting at material recovery facility (MRF)followed by the a question related to plastic waste disposal (Eriksen et al.,2014;Lopez- mechanical recycling for given streams of PET and polyolefins(mainly Lopez et al.,2018;Ritchie and Roser,2019)and several alternatives for HDPE)and by energy recovery for the remaining plastics mixed with recovery and recycling have been proposed and assessed.The large the foreign matters.This latter fraction is not a small amount:the re- variety of plastics and their various utilisation involves the necessity to sidual waste from MRF amounts to 40-60%of the input since it con- find different processes able to obtain an environmental correct dis- tains the foreign matter present in the collected waste and the plastics posal and an optimised material and energy recovery.Depending on not sorted by the sorting line itself. their physical and chemical characteristics,the collected plastic waste This residual waste is preferably sent to energy recovery or to can be sent to mechanical reprocessing,to feedstock/chemical re- production of secondary fuels for cement kilns and steel production cycling process or to energy recovery and landfill (Al-Salem et al., industries as substitute of coals;unfortunately,despite of"landfill ban" 2009).A unique preferred process cannot be chosen for all the com- existing in such Countries (Germany),a large of amount of this waste is mercial plastics introduced in the market nowadays.The main non- sent to landfills.The cost for this final recovery/disposal in Italy,is,by .Corresponding author at:Department of Environmental,Biological,Pharmaceutical Science and Technology,University of Campania "Luigi Vanvitelli",Via Vivaldi 43,81100 Caserta,Italy. E-mail addresses:marialaura.mastellone@unicampania.it,mlm@pruvia.de. https:/doi.org/10.1016/j.rcrx2019.100017 Received 6 June 2019;Received in revised form 16 August 2019;Accepted 23 August 2019 Available online 10 September 2019 2590-289X/2019 The Author(s).Published by Elsevier B.V.This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/)
Contents lists available at ScienceDirect Resources, Conservation & Recycling: X journal homepage: www.journals.elsevier.com/resources-conservation-and-recycling-x A feasibility assessment of an integrated plastic waste system adopting mechanical and thermochemical conversion processes Maria Laura Mastellonea,b,⁎ a Department of Environmental, Biological, Pharmaceutical Science and Technology, University of Campania “Luigi Vanvitelli”, Via Vivaldi 43, 81100 Caserta, Italy b Pruvia Fuels GmbH, Rheingoldstr. 10a, D-90513 Zirndorf, Germany ARTICLE INFO Keywords: Plastic waste Sorting Pyrolysis Gasification Syngas Syncrude ABSTRACT The large variety and amounts of plastic waste produced worldwide requires to better organize the industrial network devoted to the exploitation of this material by including different processes that allow to recover the “material” as main target. This paper presents the results of the feasibility study developed for an integrated system for plastic waste management designed in such a way to deal with the real market and provide for reliable targets in term of material recovery yields, energy efficiency and waste minimization. The system under study is a combination of mechanical sorting, thermochemical processes and conversion into materials and energy. The quantified block diagrams are used to represent the mass and feedstock energy balances by allowing the calculation of yields of given products. The equipment list for each sub-system is provided together with the installed power for the main component and/or auxiliary; these data allowed to perform the energy balance and to obtain the net energy production by the integrated system. The energy balance demonstrated that the integrated system is feasible while, on the contrary, the single processes are not energetic self-sustainable. 1. Introduction and scope 1.1. Plastic waste management background The amount of plastic materials produced worldwide reached 348 million of tonnes in 2017; about 18% of this amount was produced in Europe and more than 50% in Asia. A fraction larger than 50% of plastic converter demand is constituted by polypropylene (PP), lowdensity polyethylene (LDPE) and high-density polyethylene (HDPE) (Plastics Europe Annual Review, 2018). The extensive production of plastics and the indiscriminate disposal in the environment created also a question related to plastic waste disposal (Eriksen et al., 2014; LópezLópez et al., 2018; Ritchie and Roser, 2019) and several alternatives for recovery and recycling have been proposed and assessed. The large variety of plastics and their various utilisation involves the necessity to find different processes able to obtain an environmental correct disposal and an optimised material and energy recovery. Depending on their physical and chemical characteristics, the collected plastic waste can be sent to mechanical reprocessing, to feedstock / chemical recycling process or to energy recovery and landfill (Al-Salem et al., 2009). A unique preferred process cannot be chosen for all the commercial plastics introduced in the market nowadays. The main noneconomic factors affecting the decision of which route is the most suitable for a certain waste are the composition in term of polymer type (HDPE, LDPE, PP, PS, EPS, PET, PVC, …) and the fraction of nonpolymeric materials (including multi-layered plastics and composites). These characteristics affect the design of the overall system, starting with the sorting facility where the commingled plastic waste coming from the separate collection of municipal and commercial waste is realised, until the recycling or recovery process, chosen as suitable tool to convert the waste into valuable materials (Zaccariello et al., 2015). The most applied combination of processes in Europe consists of the centralised sorting at material recovery facility (MRF) followed by the mechanical recycling for given streams of PET and polyolefins (mainly HDPE) and by energy recovery for the remaining plastics mixed with the foreign matters. This latter fraction is not a small amount: the residual waste from MRF amounts to 40–60% of the input since it contains the foreign matter present in the collected waste and the plastics not sorted by the sorting line itself. This residual waste is preferably sent to energy recovery or to production of secondary fuels for cement kilns and steel production industries as substitute of coals; unfortunately, despite of “landfill ban” existing in such Countries (Germany), a large of amount of this waste is sent to landfills. The cost for this final recovery/disposal in Italy, is, by https://doi.org/10.1016/j.rcrx.2019.100017 Received 6 June 2019; Received in revised form 16 August 2019; Accepted 23 August 2019 ⁎ Corresponding author at: Department of Environmental, Biological, Pharmaceutical Science and Technology, University of Campania “Luigi Vanvitelli”, Via Vivaldi 43, 81100 Caserta, Italy. E-mail addresses: marialaura.mastellone@unicampania.it, mlm@pruvia.de. Resources, Conservation & Recycling: X 4 (2019) 100017 Available online 10 September 2019 2590-289X/ © 2019 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/). T
M.L.Mastellone Resources,Conservation Recycling:X 4(2019)100017 referring to the gate fee only (i.e.transportation not included),reached (Adrados et al.,2012;Haufe et al.,2004;Sogancioglu et al.,2017). very high values such as 145C/t(C.E.A.SpA,private communication, 2019). The huge increase of cost to dispose this kind of waste in Europe was 1.2.Feedstock recycling of polymers due to the so called "plastic ban"of China,following the so-called Green Fence,that introduced,for the first time after decades,quality Polymers are the main component of the "plastics family";they are specifications for secondary materials imported from Europe so dra- constituted by a repeating structure of monomers basically composed matically limiting the plastic waste amount export from European by carbon and hydrogen and,in some cases,by heteroatoms like Countries (Brooks et al.,2018).The restriction of use of landfilling for oxygen,nitrogen,chlorine,...they are generally classified,according plastic waste imposed by the European regulation was another key to their structure and properties,on the basis of thermal-mechanical point in the raising of disposal economic cost. behaviour and on the basis of their processing characteristics in ther Nowadays,it is urgent to strengthen the industrial network devoted moplastics,elastomers and thermosets.They can be also be classified to the plastics'recovery and recycling by including processes that asks according to their mechanism of polymerization as either addition or for a lower degree of purity.The feedstock and the chemical recycling condensation,where: processes,once integrated in the recycling system,allow to use the same "equivalent petroleum amount"several times:as material,feed- a polyaddition consists in the repeating of the same monomer along stock and fuel. the chain; The mechanical recycling of plastics should be preferred when a b condensation requires instead the bond between two different mo- mono-material collection of plastics must be treated,since the cost of lecules. the separation processes,as carried out in the material recovery facil- ities,is very high.Mechanical recycling consists of a series of physical Thermoplastic polymers such as PE,PP,PVC,PS are examples of operations where the recovered material is shredded,washed,melted polyaddition polymers;PET is an example of polycondensed polymer. and re-pelletized.In the case the mechanical recycling is not possible or The polyaddition polymers,with the exception of PVC that has a convenient it is possible to refer to the feedstock and chemical recycling peculiar behaviour(Sheirs and Kaminsky,2006)can undergo thermo- and,as last option,to the energy recovery processes.This last option is lysis in a controlled environment by producing a large spectrum of largely applied today for all the plastics that are not separately collected hydrocarbons having a number of carbon ranging from 1 (methane)to and for plastics that cannot be mechanically recycled.In fact,the het- around 20.The thermolysis of plastic waste is in fact oriented to recover erogeneous mixture of plastic contaminated with other components raw materials for petrochemical industries by means of processes such (such as paper,biowaste,textiles,etc.)is sent to combustion process as liquid and gas phase hydrogenation,steam-cracking,catalytic due to their large high-heating value(about 31.8 MJ/kg for a house. cracking,pyrolysis,coking and gasification. hold plastic mixture)(Themelis et al.,2011).Once energy recovery is A classification of thermolysis process into "feedstock recycling" applied,no other recovery is possible;in order to increase the number and "chemical recycling"(sub-category of feedstock recycling)also of life of fossil carbon,the preferred option is the material recovery that exists with reference to the different process outputs that are obtained. can be obtained by applying mechanical reprocessing and feedstock/ Chemical recycling consists in the depolymerization of certain con- chemical processes densation or addition polymers back to monomers.The chemical re- In all cases the mechanical recycling cannot be applied it is possible cycling allows the re-creating of the chemicals from which the polymers and convenient use the above cited alternative routes (Czajczynska were initially made.If the treatment breaks the polymers into an as- et al.,2017;Demirbas,2004;Panda et al.,2010;Perugini et al.,2005). sortment of chemical species,it can be decided whether to recover In particular,thermolysis processes of selected polymers and plastic specific chemicals for feedstock use or to use the assortment of chemical waste mixture can lead to very good performances in term of energy species for fuel or to use some combination of both end products;in this recovery with a limited environmental impact.Most important,the case the process lays in the more general definition of feedstock re- pyrolysis and gasification processes can be applied even at smaller scale cycling.A special class of feedstock recycling processes yields an im- by making possible the integration with other facilities;for instance, portant raw material called syngas (=synthesis gas,a mixture of hy- gasifiers and pyrolizers can be installed with thermal input capacities drogen and carbon monoxide):in this case the common name to from 250 kW to several megawatts,by requiring small footprints and by indicate the thermal conversion process is "gasification".This latter favouring the real circular economy at local and regional scale.Several process is a carried out in an oxidative environment where the oxygen studies have been published on these processes applied to plastic waste content is much less than the stoichiometric demand for complete and waste in general.Gasification processes differ for the applied combustion (Gartzen et al.,2018;Mastellone,2015). technology of main reactor (gasifier),the method to minimize the tar Hydrocarbons and syngas can be used as chemical feedstocks for formation,the cleaning/conditioning of syngas and its use.Gasification further upgrading to commercial products at oil refineries and chemical can be applied to heterogeneous plastic waste with good performances plants. in term of syngas yield and cold gas efficiency (Gershman and B.I. The plastic conversion into a sort of synthetis crude oil (syncrude) 2013;Lopez et al.,2018).Pyrolysis of plastics aims to obtain preferably can be obtained by using commercially available technologies that are materials instead of energy or fuels.In this case the feeding composition reported and compared in term of reactor technology,process type is limited by strict specifications.The most applied and studied process (thermal/catalytic),yields of products,capacities.A list of suppliers for material recovery from plastic waste is pyrolysis of polyolefins that developed the above cited catalytic and non-catalytic thermolysis is reported in the Table 1.The common point of the largest part of the listed technologies is the plastic feedstock specifications:all the poly- 1High-heating value (HHV)indicates the energy content of one unit mass of olefins can be accepted,polycondensed polymers must be avoided, matter that can be released during oxidation.HHV is an intrinsic property of cellulosic materials and moisture must be limited as much is possible. matter since it is correlated to chemical composition.The low-heating value (LHV)is obtained starting from the HHV value by taking into account that the The differences between the technologies are related to the reactor used hydrogen contained in the matter is transformed into water at standard con- for thermolysis,the presence or not of a catalyst and the maximum ditions(25'C)but,since the real temperature reached by oxidation is much capacity of a single reactor that normally does not exceed 25.000 ton/ larger than 100'C,the water is actually present under form of gas.The phase year. transition requires an amount of heat (2257J/g)that is subtracted to HHV by leading to the LHV.LHV is also an intrinsic property of molecules/compounds
referring to the gate fee only (i.e. transportation not included), reached very high values such as 145€/t (C.E.A. SpA, private communication, 2019). The huge increase of cost to dispose this kind of waste in Europe was due to the so called “plastic ban” of China, following the so-called Green Fence, that introduced, for the first time after decades, quality specifications for secondary materials imported from Europe so dramatically limiting the plastic waste amount export from European Countries (Brooks et al., 2018). The restriction of use of landfilling for plastic waste imposed by the European regulation was another key point in the raising of disposal economic cost. Nowadays, it is urgent to strengthen the industrial network devoted to the plastics’ recovery and recycling by including processes that asks for a lower degree of purity. The feedstock and the chemical recycling processes, once integrated in the recycling system, allow to use the same "equivalent petroleum amount" several times: as material, feedstock and fuel. The mechanical recycling of plastics should be preferred when a mono-material collection of plastics must be treated, since the cost of the separation processes, as carried out in the material recovery facilities, is very high. Mechanical recycling consists of a series of physical operations where the recovered material is shredded, washed, melted and re-pelletized. In the case the mechanical recycling is not possible or convenient it is possible to refer to the feedstock and chemical recycling and, as last option, to the energy recovery processes. This last option is largely applied today for all the plastics that are not separately collected and for plastics that cannot be mechanically recycled. In fact, the heterogeneous mixture of plastic contaminated with other components (such as paper, biowaste, textiles, etc.) is sent to combustion process due to their large high-heating value1 (about 31.8 MJ/kg for a household plastic mixture) (Themelis et al., 2011). Once energy recovery is applied, no other recovery is possible; in order to increase the number of life of fossil carbon, the preferred option is the material recovery that can be obtained by applying mechanical reprocessing and feedstock/ chemical processes. In all cases the mechanical recycling cannot be applied it is possible and convenient use the above cited alternative routes (Czajczyńska et al., 2017; Demirbas, 2004; Panda et al., 2010; Perugini et al., 2005). In particular, thermolysis processes of selected polymers and plastic waste mixture can lead to very good performances in term of energy recovery with a limited environmental impact. Most important, the pyrolysis and gasification processes can be applied even at smaller scale by making possible the integration with other facilities; for instance, gasifiers and pyrolizers can be installed with thermal input capacities from 250 kW to several megawatts, by requiring small footprints and by favouring the real circular economy at local and regional scale. Several studies have been published on these processes applied to plastic waste and waste in general. Gasification processes differ for the applied technology of main reactor (gasifier), the method to minimize the tar formation, the cleaning/conditioning of syngas and its use. Gasification can be applied to heterogeneous plastic waste with good performances in term of syngas yield and cold gas efficiency (Gershman and B.I., 2013; Lopez et al., 2018). Pyrolysis of plastics aims to obtain preferably materials instead of energy or fuels. In this case the feeding composition is limited by strict specifications. The most applied and studied process for material recovery from plastic waste is pyrolysis of polyolefins (Adrados et al., 2012; Haufe et al., 2004; Sogancioglu et al., 2017). 1.2. Feedstock recycling of polymers Polymers are the main component of the “plastics family”; they are constituted by a repeating structure of monomers basically composed by carbon and hydrogen and, in some cases, by heteroatoms like oxygen, nitrogen, chlorine, …; they are generally classified, according to their structure and properties, on the basis of thermal-mechanical behaviour and on the basis of their processing characteristics in thermoplastics, elastomers and thermosets. They can be also be classified according to their mechanism of polymerization as either addition or condensation, where: a polyaddition consists in the repeating of the same monomer along the chain; b condensation requires instead the bond between two different molecules. Thermoplastic polymers such as PE, PP, PVC, PS are examples of polyaddition polymers; PET is an example of polycondensed polymer. The polyaddition polymers, with the exception of PVC that has a peculiar behaviour (Sheirs and Kaminsky, 2006) can undergo thermolysis in a controlled environment by producing a large spectrum of hydrocarbons having a number of carbon ranging from 1 (methane) to around 20. The thermolysis of plastic waste is in fact oriented to recover raw materials for petrochemical industries by means of processes such as liquid and gas phase hydrogenation, steam-cracking, catalytic cracking, pyrolysis, coking and gasification. A classification of thermolysis process into “feedstock recycling” and “chemical recycling” (sub-category of feedstock recycling) also exists with reference to the different process outputs that are obtained. Chemical recycling consists in the depolymerization of certain condensation or addition polymers back to monomers. The chemical recycling allows the re-creating of the chemicals from which the polymers were initially made. If the treatment breaks the polymers into an assortment of chemical species, it can be decided whether to recover specific chemicals for feedstock use or to use the assortment of chemical species for fuel or to use some combination of both end products; in this case the process lays in the more general definition of feedstock recycling. A special class of feedstock recycling processes yields an important raw material called syngas (=synthesis gas, a mixture of hydrogen and carbon monoxide): in this case the common name to indicate the thermal conversion process is “gasification”. This latter process is a carried out in an oxidative environment where the oxygen content is much less than the stoichiometric demand for complete combustion (Gartzen et al., 2018; Mastellone, 2015). Hydrocarbons and syngas can be used as chemical feedstocks for further upgrading to commercial products at oil refineries and chemical plants. The plastic conversion into a sort of synthetis crude oil (syncrude) can be obtained by using commercially available technologies that are reported and compared in term of reactor technology, process type (thermal/catalytic), yields of products, capacities. A list of suppliers that developed the above cited catalytic and non-catalytic thermolysis is reported in the Table 1. The common point of the largest part of the listed technologies is the plastic feedstock specifications: all the polyolefins can be accepted, polycondensed polymers must be avoided, cellulosic materials and moisture must be limited as much is possible. The differences between the technologies are related to the reactor used for thermolysis, the presence or not of a catalyst and the maximum capacity of a single reactor that normally does not exceed 25.000 ton/ year. 1 High-heating value (HHV) indicates the energy content of one unit mass of matter that can be released during oxidation. HHV is an intrinsic property of matter since it is correlated to chemical composition. The low-heating value (LHV) is obtained starting from the HHV value by taking into account that the hydrogen contained in the matter is transformed into water at standard conditions (25°C) but, since the real temperature reached by oxidation is much larger than 100°C, the water is actually present under form of gas. The phase transition requires an amount of heat (2257J/g) that is subtracted to HHV by leading to the LHV. LHV is also an intrinsic property of molecules/compounds. M.L. Mastellone Resources, Conservation & Recycling: X 4 (2019) 100017 2
M.L.Mastellone Resources,Conservation Recycling:X 4(2019)100017 Table 1 tool for analysing,controlling,and managing material flows within a List of technological suppliers for plastic-to-oil plants. system”. # Company Name Country 1.4.Scope Agilvx Ine. USA 2 Alphakat GmbH Germany This paper aims to demonstrate that the integration of thermolysis Anhui Oursun Environment Technology Corporation China Agile Process Chemicals LLP India processes such as pyrolysis of polyolefins mixture and gasification of 5 BlueAlp bv /(Petrogas,Gas-systems bv) The Netherlands plastic waste coupled with a mechanical sorting is technically and en- 6 Climax Global Energy USA ergetically feasible and reaches targets of material recovery yields, Envion USA energy efficiency and waste minimization GEEP Canada 9 JBI Global Plastic2Oil USA 10 Klean Industries,Inc. Canada 2.System description 11 MK Aromatics Limited India Nexus Fuels USA The system under study aims to recover the largest amount of sec. 13 Plastic Advanced Recycling Corp.(PARC) USA 14 ondary materials and energy from plastic waste.As recalled before,the Plastic Energy Ltd UK+Spain 15 Polymer Energy LLC USA plastic waste taken as reference is the leftover of material recovery 16 PRYME b.v./(BTC b.v.) The Netherlands facilities processing the household/commercial mixed recyclable waste 17 Pruvia Fuels GmbH Germany obtained by means of separate collection;this leftover is highly con- 18 Pyrocrat Systems LLP India taminated by non-recyclable plastics and foreign materials (paper, 19 Renewlogy (Formerly:PK Clean Technologies Inc.(Salt USA Lake City） metals,textiles).The facility that can threat this kind of waste in a 20 Res Polyflow USA sustainable way must be integrated with processes that minimize the 21 Vadxx USA energy consumption,the waste production and that maximise the value and the yield of products.The proposed system is an example of an integration between mechanical and thermochemical processes aiming to obtain the maximum economic revenue with the minimum en- 1.3.Feasibility assessment method vironmental burden. The system is explained with reference to the block diagram of A feasibility study includes a series of stages related to different Fig.1. aspects of a project with the aim to give an orientation to the man- It is basically composed by the following sections: agement devoted to take the "go/no go"decision for the following steps of the project development (generally referred as "gates").A part of a the sorting section (P1),where the plastic waste coming from the feasibility study is dedicated to the"technical assessment"whose target separate collection is sorted and separated into several streams in- is finding answers to questions such as:is the proposed technology or cluding:a)the mono-polymeric streams destined to mechanical re- solution practical?Is the technology mature and reliable?If not,can it cycling (such as PET,HDPE,PP);b)the mixture of polyolefins be obtained?At which risk?And so on.The main question is related to (plastic feedstock)that is too difficult and expensive to separate into the practicality of the proposed solution,its effects on the market and/ mono-material streams for mechanical recycling and that can be or on the system where it is applied,on the environment,on the destined to feedstock recycling to oil and/or feedstock;c)the mix- economy,etc.Whatever are the methods and procedures used to per- ture of residue (plastic waste)containing the polymers not re- form the technical feasibility assessment,the material flow assessment cognized during the sorting,the polymers that are not suitable to be (MFA)carried out at level of goods resulted instrumental for under- recycled,the foreign matter (biowaste,cellulose,composites,multi- standing how the proposed process or system (e.g.a waste management layered. system)functions,facilitating connections and communications be- the pre-treatment section (P2),where the plastic feedstock is tween the stakeholders,authorities,and involved companies.Allesh shredded,dried and melted to be fed into the thermolysis section.In and Brunner (2015)demonstrated that "MFA has become a common, this section the densification and drying of the plastic feedstock is widely used tool to analyse waste management systems on different followed by de-halogenation by means of degradative extrusion. levels (goods and substances)and with various goals.MFA on the level This process helps to reduce the halogen content,and chlorine in of goods is highly useful for understanding WM systems.It represents a particular,lesser than 1%,as required by the process P3. Mechanical Recycling P7.Fractionation P8.Energy PI,Sorting p2.Pre-treatment P3.Thermolysis into fuel gas and syncrude gas Oil Gas P6.Energy P5.Gasification industries Fig.1.Simplified sketch of the system under study
1.3. Feasibility assessment method A feasibility study includes a series of stages related to different aspects of a project with the aim to give an orientation to the management devoted to take the “go/no go” decision for the following steps of the project development (generally referred as "gates"). A part of a feasibility study is dedicated to the “technical assessment” whose target is finding answers to questions such as: is the proposed technology or solution practical? Is the technology mature and reliable? If not, can it be obtained? At which risk? And so on. The main question is related to the practicality of the proposed solution, its effects on the market and/ or on the system where it is applied, on the environment, on the economy, etc. Whatever are the methods and procedures used to perform the technical feasibility assessment, the material flow assessment (MFA) carried out at level of goods resulted instrumental for understanding how the proposed process or system (e.g. a waste management system) functions, facilitating connections and communications between the stakeholders, authorities, and involved companies. Allesh and Brunner (2015) demonstrated that “MFA has become a common, widely used tool to analyse waste management systems on different levels (goods and substances) and with various goals. MFA on the level of goods is highly useful for understanding WM systems. It represents a tool for analysing, controlling, and managing material flows within a system”. 1.4. Scope This paper aims to demonstrate that the integration of thermolysis processes such as pyrolysis of polyolefins mixture and gasification of plastic waste coupled with a mechanical sorting is technically and energetically feasible and reaches targets of material recovery yields, energy efficiency and waste minimization. 2. System description The system under study aims to recover the largest amount of secondary materials and energy from plastic waste. As recalled before, the plastic waste taken as reference is the leftover of material recovery facilities processing the household/commercial mixed recyclable waste obtained by means of separate collection; this leftover is highly contaminated by non-recyclable plastics and foreign materials (paper, metals, textiles). The facility that can threat this kind of waste in a sustainable way must be integrated with processes that minimize the energy consumption, the waste production and that maximise the value and the yield of products. The proposed system is an example of an integration between mechanical and thermochemical processes aiming to obtain the maximum economic revenue with the minimum environmental burden. The system is explained with reference to the block diagram of Fig. 1. It is basically composed by the following sections: • the sorting section (P1), where the plastic waste coming from the separate collection is sorted and separated into several streams including: a) the mono-polymeric streams destined to mechanical recycling (such as PET, HDPE, PP); b) the mixture of polyolefins (plastic feedstock) that is too difficult and expensive to separate into mono-material streams for mechanical recycling and that can be destined to feedstock recycling to oil and/or feedstock; c) the mixture of residue (plastic waste) containing the polymers not recognized during the sorting, the polymers that are not suitable to be recycled, the foreign matter (biowaste, cellulose, composites, multilayered. • the pre-treatment section (P2), where the plastic feedstock is shredded, dried and melted to be fed into the thermolysis section. In this section the densification and drying of the plastic feedstock is followed by de-halogenation by means of degradative extrusion. This process helps to reduce the halogen content, and chlorine in particular, lesser than 1%, as required by the process P3. Table 1 List of technological suppliers for plastic-to-oil plants. # Company Name Country 1 Agilyx Inc. USA 2 Alphakat GmbH Germany 3 Anhui Oursun Environment & Technology Corporation China 4 Agile Process Chemicals LLP India 5 BlueAlp bv / (Petrogas, Gas-systems bv) The Netherlands 6 Climax Global Energy USA 7 Envion USA 8 GEEP Canada 9 JBI Global / Plastic2Oil USA 10 Klean Industries, Inc. Canada 11 MK Aromatics Limited India 12 Nexus Fuels USA 13 Plastic Advanced Recycling Corp. (PARC) USA 14 Plastic Energy Ltd UK + Spain 15 Polymer Energy LLC USA 16 PRYME b.v. / (BTC b.v.) The Netherlands 17 Pruvia Fuels GmbH Germany 18 Pyrocrat Systems LLP India 19 Renewlogy (Formerly: PK Clean Technologies Inc. (Salt Lake City) USA 20 Res Polyflow USA 21 Vadxx USA Fig. 1. Simplified sketch of the system under study. M.L. Mastellone Resources, Conservation & Recycling: X 4 (2019) 100017 3
M.L.Mastellone Resources,Conservation Recycling:X 4(2019)100017 the thermolysis section (P3),where the molten polymer flow is electrical conversion efficiency for engine. converted into pyrolysis products(P3)and then,by using a series of condensers,is fractionated at least into syncrude (F18)and fuel gas 2.1.Mechanical sorting (F15),or in more streams having different boiling points.The term syncrude is used to highlight that the destiny of this product is its The mechanical sorting process (P1)is realized by using both phy- use as blending component of crude oil in the refinery industry or as sical and chemical properties of the materials.First of all,the plastic a raw material to be processed in the chemical industry. waste bales are opened and roughly shredded.After this preliminary the gasification section(P5),preceded by a densification(P4)of the treatment a separation of flows by density is made by using an air drum plastics and other burnable leftovers discharged from sorting sec- separator.The flows having different density are addressed to optical tion,where the waste,otherwise destined to landfilling of in- sorting that is carried out by using Near-InfraRed(NIR)equipment that cineration,is converted into a synthetic gas i.e.syngas (F6); detects the chemical composition of materials on the belts and fires by the energy recovery section,that includes an engine (P8)fed by the high-pressure air jets those detected as "positive"flows.The rest of pyrolysis gas(F15)and an engine (P6)fed by syngas.The properties materials constitutes the“negative'”flow.The sign“+”indicates that of the two fuel gas streams are quite different:the fuel gas from the the equipment is able to detect as positive a given flow (Fig.2);gen. process P3 is similar to LPG;the syngas is a mixture of carbon erally,the detection of materials as positive flow ensures a high level of monoxide and hydrogen.Studies about their use as blended fuel gas purity of the flow if the distribution on the accelerating belt is guar- in a unique engine are not available. anteed.The densimetric separation has been chosen because of the huge presence of films(LDPE,PP)that can envelope the heavy but The mass and feedstock energy balance and the total energy as- smaller materials by decreasing the purity of the flows.The light den- sessment are presented in the following paragraphs.To obtain these sity flow is sent to a unique NIR because the presence of PET/PVC/ data,a series of input data have been set up,the input data of the whole glass,etc.is expected to be in the higher density fractions that is sorted modelling are: with more accuracy. The composition of plastic feedstock needs to meet specifications so plastic mixed waste (PMW)composition entering the integrated that the design of the sorting plant must be adapted until the obtained system; plastic feedstock composition complies with the specifications.For in- yields obtained by mechanical equipment and by chemical reactors stance,PVC,PET,multi-layered compounds,etc.must be removed with (pyrolizer and gasifier); large efficacy so that the optical sorters have to be placed with such a composition of pyrolysis products and syngas; redundancy. In the block diagram of sorting plant under study,the PET and PVC polymers are detected as positive flow in an optical sorter dedicated to the medium density flow.A second optical sorter is added in series to the first one in order to remove all the other impurities by detecting polyolefins as positive flow. The composition of material flows obtained by the sorting has been obtained by applying a mathematical modelling reported in the para- hredder graph "Materials"with reference to the detailed block diagram of Fig.2. The magnetic separator removes ferrous metals while the ECS is able to remove the non-ferrous materials by allowing to obtain a clean flow of polyolefins.After an intense shredding and homogenization,the flow of polyolefins becomes a plastic feedstock suitable to be addressed to a plastic-to-oil (Pto)section. PL4 P1.5 NIR 2 + 9 2.2.Plastic-to-oil section P7 The thermolysis section is organized to produce a mixture of hy- drocarbons ranging between Cl and C30 that undergoes a fractionation based on the boiling temperature (Tp)of components;three fractions PII P1.12 P13 are obtained:a fraction from C1 to C4 (non-condensable gas or NCG),a PETPVC storage fraction from C5 to C21(similar to the crude oil and then utilized for F段RP 2 blending with it at the refinery inlet named syncrude)and a heavier 下4， fraction that constitutes a bottom residue (T>350C)recirculated to ECS the cracking reactor.The reactor is fed by polyolefins with a limited amount of foreign matter (cellulose,glass,paper,etc.)and traces of undesired polymers such as PET or PVC.The thermal cracking in a P1.16 Metals storage reactor is operated at a temperature between 450 and 480'C.More specifically a temperature of 480'C is used in the primary cracking 23 zone (heterogeneous zone)and a slight lower temperature (450-460'C) F10.RM is established in the homogenous zone.The kinetic model used to P117 Plasnc Feedstock predict the products distribution and the reaction time is based on YF2.PF model available in the literature (Al-Salem and Lettieri,2010)as modified on the basis of a global reaction model not presented here. Fig.2.Block diagram of sorting section P1.Details of main equipment com- The resulting yields of products are:61.3%of waxes,18.5%of liquids, posing this section of the overall system under study.The flows indicated by 7.6%of aromatics,10%of NCG.On the basis of industrial experiences, larger arrows are:input data F1 (PMW);output data F4(W_1),F9(RP),F2 a certain amount has been considered as a process loss due to tar for- (PF). mation during cooling and partial condensation;this led to consider,for
• the thermolysis section (P3), where the molten polymer flow is converted into pyrolysis products (P3) and then, by using a series of condensers, is fractionated at least into syncrude (F18) and fuel gas (F15), or in more streams having different boiling points. The term syncrude is used to highlight that the destiny of this product is its use as blending component of crude oil in the refinery industry or as a raw material to be processed in the chemical industry. • the gasification section (P5), preceded by a densification (P4) of the plastics and other burnable leftovers discharged from sorting section, where the waste, otherwise destined to landfilling of incineration, is converted into a synthetic gas i.e. syngas (F6); • the energy recovery section, that includes an engine (P8) fed by the pyrolysis gas (F15) and an engine (P6) fed by syngas. The properties of the two fuel gas streams are quite different: the fuel gas from the process P3 is similar to LPG; the syngas is a mixture of carbon monoxide and hydrogen. Studies about their use as blended fuel gas in a unique engine are not available. The mass and feedstock energy balance and the total energy assessment are presented in the following paragraphs. To obtain these data, a series of input data have been set up, the input data of the whole modelling are: • plastic mixed waste (PMW) composition entering the integrated system; • yields obtained by mechanical equipment and by chemical reactors (pyrolizer and gasifier); • composition of pyrolysis products and syngas; • electrical conversion efficiency for engine. 2.1. Mechanical sorting The mechanical sorting process (P1) is realized by using both physical and chemical properties of the materials. First of all, the plastic waste bales are opened and roughly shredded. After this preliminary treatment a separation of flows by density is made by using an air drum separator. The flows having different density are addressed to optical sorting that is carried out by using Near-InfraRed (NIR) equipment that detects the chemical composition of materials on the belts and fires by high-pressure air jets those detected as “positive” flows. The rest of materials constitutes the “negative” flow. The sign “+” indicates that the equipment is able to detect as positive a given flow (Fig. 2); generally, the detection of materials as positive flow ensures a high level of purity of the flow if the distribution on the accelerating belt is guaranteed. The densimetric separation has been chosen because of the huge presence of films (LDPE, PP) that can envelope the heavy but smaller materials by decreasing the purity of the flows. The light density flow is sent to a unique NIR because the presence of PET/PVC/ glass, etc. is expected to be in the higher density fractions that is sorted with more accuracy. The composition of plastic feedstock needs to meet specifications so that the design of the sorting plant must be adapted until the obtained plastic feedstock composition complies with the specifications. For instance, PVC, PET, multi-layered compounds, etc. must be removed with large efficacy so that the optical sorters have to be placed with such a redundancy. In the block diagram of sorting plant under study, the PET and PVC polymers are detected as positive flow in an optical sorter dedicated to the medium density flow. A second optical sorter is added in series to the first one in order to remove all the other impurities by detecting polyolefins as positive flow. The composition of material flows obtained by the sorting has been obtained by applying a mathematical modelling reported in the paragraph “Materials” with reference to the detailed block diagram of Fig. 2. The magnetic separator removes ferrous metals while the ECS is able to remove the non-ferrous materials by allowing to obtain a clean flow of polyolefins. After an intense shredding and homogenization, the flow of polyolefins becomes a plastic feedstock suitable to be addressed to a plastic-to-oil (PtO) section. 2.2. Plastic-to-oil section The thermolysis section is organized to produce a mixture of hydrocarbons ranging between C1 and C30 that undergoes a fractionation based on the boiling temperature (Tb) of components; three fractions are obtained: a fraction from C1 to C4 (non-condensable gas or NCG), a fraction from C5 to C21 (similar to the crude oil and then utilized for blending with it at the refinery inlet named syncrude) and a heavier fraction that constitutes a bottom residue (Tb > 350 °C) recirculated to the cracking reactor. The reactor is fed by polyolefins with a limited amount of foreign matter (cellulose, glass, paper, etc.) and traces of undesired polymers such as PET or PVC. The thermal cracking in a reactor is operated at a temperature between 450 and 480 °C. More specifically a temperature of 480 °C is used in the primary cracking zone (heterogeneous zone) and a slight lower temperature (450–460 °C) is established in the homogenous zone. The kinetic model used to predict the products distribution and the reaction time is based on model available in the literature (Al-Salem and Lettieri, 2010) as modified on the basis of a global reaction model not presented here. The resulting yields of products are: 61.3% of waxes, 18.5% of liquids, 7.6% of aromatics, 10% of NCG. On the basis of industrial experiences, a certain amount has been considered as a process loss due to tar formation during cooling and partial condensation; this led to consider, for Fig. 2. Block diagram of sorting section P1. Details of main equipment composing this section of the overall system under study. The flows indicated by larger arrows are: input data = F1 (PMW); output data = F4 (W_1), F9 (RP), F2 (PF). M.L. Mastellone Resources, Conservation & Recycling: X 4 (2019) 100017 4
M.L.Mastellone Resources,Conservation Recycling:X 4 (2019)100017 the following calculations,a fraction of liquid product (syncrude)equal particularly for plastics (Mastellone and Arena,2008;Sjostrom et al., to 80%and NCG equal to 10%.The rest of the matter is converted into 1999). char and tar (Mastellone et al.,2002;Scheirs and Kaminsky,2006) The heat released by exothermal reactions increases the environ. The PtO plant (based on the Pruvia Fuels GmbH technology)is ment temperature until values depending by the equivalence ratio, preceded by a pre-treatment that removes moistures and halogens from proximate and ultimate analysis of waste and its net chemical energy. the plastic feedstock.This pre-treatment is carried out by using a The operating temperature of the waste gasifiers is generally in the combination between densifiers and degassing extruders(AMUT Group, range 850-1200'C depending by the above recalled parameters and by 2019).The densifiers allow to manage polyolefins having very light heat losses.The oxygen supplied to the gasifier is generally 25-40%of bulk density (LLDPE)and heterogeneous mechanical properties.The the stoichiometric demand.The reducing environment promotes the extrusion is a pre-treatment that allows to remove moisture with 99% partial oxidation of carbon and hydrogen element in the fuel by pro- efficacy if the initial content is less than 10%,to remove organic viding the heat necessary to the cracking of waste/fuel component.The chlorine by breaking the C-Cl bonds in the initial part of machine by fraction between the oxygen provided for gasification reactions and the allowing the degassing together with moisture,to bring the tempera- stoichiometric demand is known as equivalence ratio and its value ture up to 350C so favouring the input to the thermolysis reactor depends on ultimate analysis of the waste.The main product of gasi. (pyrolizer).Downstream the extruder,the following equipment is in- fication process is the synthesis gas also identified as "synthetic gas or stalled: syngas".This term is used when it is used as a feedstock for production of synthetic natural gas(SNG),Fischer-Tropsch liquids(FTL),hydrogen 1)Heated/insulated feeder to bring the plastic feedstock in the reactor or any other material or fuel;the term "producer gas"is used when the over the melting temperature gas is used to energy production.Anyway,whatever is the final utili- 2)Thermolysis reactor zation,the term syngas can be used to indicate the gaseous product of 3)Carbon/ash discharge system gasification.The syngas composition can vary depending on waste and 4)Cooling of pyrolysis products operating conditions,but the main constituents are carbon monoxide 5)Fractionation of pyrolysis products hydrogen,methane,C2-C6 hydrocarbons,carbon dioxide and water. 6)Light fuel gas energy recovery (heat,electricity or both) The general layout of a gasification plant includes: 7)Auxiliaries (scrubber,cooling water production,...) 1)Mechanical feeder at ambient temperature The reaction enthalpy necessary to break the chemical bonds of 2)Gasification reactor polymers can vary (Brems et al,2011);a mean value of 250 MJ/t has 3)Bottom ash discharge system been used by considering a prevailing amount of polyethylene.Starting 4)Cooling of syngas from ambient temperature,a sensible heat of 1200 MJ/t needs to be 5)Cleaning upgrading of syngas (thermal/catalytic cracking,tar added to reach the reaction temperature (total energy:1450 MJ/t).It is absorption,.…) noteworthy that the sensible heat acquired by the molten polymer in 6)Syngas energy recovery (heat,electricity or both) the extruder is in the range 60-70%of the total need.This means that 7)Auxiliaries (scrubber,cooling water production,...) the electricity used to operate the extruder is used to increase the en- thalpy of the plastic flow and only a limited amount is transferred to the The data used to model the performance of the gasifier section in the pyrolizer by using waste heat from engines (e.g.by using heat ex- following paragraphs come from an extensive series of experiments changers crossed by hot diathermic oil as heat vector). carried on the plastic waste by using a pilot-scale fluidized bed gasifier (Arena et al.,2010,2008;Mastellone and Zaccariello,2013).The main 2.3.Gasification process description performance parameters for the gasification of plastic waste mixture are reported in the following($4.3)and are related to a specific pilot plant Gasification is a thermochemical process that transforms a carbon operated with an oxidizing stream constituted by air having an based material into a gaseous mixture of low molecular weight species. equivalent ratio of about 0.3.The tar content in the syngas has been What's left is a clean "synthesis gas"that can be converted into valuable considered negligible thanks to use of catalytic reaction in the gasifier products and electricity.In particular,gasification of waste is an eco- (Arena et al.,2009).In the case of gasification,the absorbed process nomical and environmental viable solution to produce cleaner energy energy can be evaluated by considering that the exothermic reactions together with a remarkable waste weight reduction.The most simplistic uses a fraction of the feedstock energy of the input waste to guarantee a way to consider gasification is as an alternative to the combustion to given temperature and to promote the endothermic reactions;this obtain heat and power with a lesser environmental impact.In this case fraction of energy is the complement of the Cold Gas Efficiency para- the gasification process is used to transform a heterogeneous fuel (solid meter (CGE). waste,sludge,biomasses,low-rank coal,...into a homogeneous syn- thetic gaseous fuel to be utilized in an industrial burner,an engine or a 3.Materials gas turbine to produce electricity and heat.The loss of chemical energy necessary to promote the endothermic reactions of gasification is ba- The input material to which this paper refers is the plastic waste lanced by the higher performance of the homogeneous combustion.The residual from the centralized sorting at material recovery facility general concept and the technologies utilized to gasify a material is (MRF).This plastic waste has a low content of PET and a high content of similar to that reported for incineration facilities,but the operating polyolefins,other polymers and foreign matter.The sorting of this parameters of the plant are completely different. waste with the only aim to recover the PET and the HDPE,that are the First of all,the gasification process cannot be represented by a single only polymers suitable for the mechanical recycling,would be not main reaction,as for the combustion process,but by reactions involving economically convenient because of the largest part of the flow(about different reactants (oxygen,carbon dioxide,water)and characterized 90%)that should be addressed to disposal (landfilling or incineration). by different reaction's enthalpies (Mastellone,2015).Moreover,the By referring to the integrated system under study,where the sorting is interaction between intermediates and minerals must be considered, finalized to prepare the feedstocks for PtO and gasification processes
the following calculations, a fraction of liquid product (syncrude) equal to 80% and NCG equal to 10%. The rest of the matter is converted into char and tar (Mastellone et al., 2002; Scheirs and Kaminsky, 2006). The PtO plant (based on the Pruvia Fuels GmbH technology) is preceded by a pre-treatment that removes moistures and halogens from the plastic feedstock. This pre-treatment is carried out by using a combination between densifiers and degassing extruders (AMUT Group, 2019). The densifiers allow to manage polyolefins having very light bulk density (LLDPE) and heterogeneous mechanical properties. The extrusion is a pre-treatment that allows to remove moisture with 99% efficacy if the initial content is less than 10%, to remove organic chlorine by breaking the C-Cl bonds in the initial part of machine by allowing the degassing together with moisture, to bring the temperature up to 350 °C so favouring the input to the thermolysis reactor (pyrolizer). Downstream the extruder, the following equipment is installed: 1) Heated/insulated feeder to bring the plastic feedstock in the reactor over the melting temperature 2) Thermolysis reactor 3) Carbon/ash discharge system 4) Cooling of pyrolysis products 5) Fractionation of pyrolysis products 6) Light fuel gas energy recovery (heat, electricity or both) 7) Auxiliaries (scrubber, cooling water production, …) The reaction enthalpy necessary to break the chemical bonds of polymers can vary (Brems et al., 2011); a mean value of 250 MJ/t has been used by considering a prevailing amount of polyethylene. Starting from ambient temperature, a sensible heat of 1200 MJ/t needs to be added to reach the reaction temperature (total energy: 1450 MJ/t). It is noteworthy that the sensible heat acquired by the molten polymer in the extruder is in the range 60–70% of the total need. This means that the electricity used to operate the extruder is used to increase the enthalpy of the plastic flow and only a limited amount is transferred to the pyrolizer by using waste heat from engines (e.g. by using heat exchangers crossed by hot diathermic oil as heat vector). 2.3. Gasification process description Gasification is a thermochemical process that transforms a carbonbased material into a gaseous mixture of low molecular weight species. What’s left is a clean “synthesis gas” that can be converted into valuable products and electricity. In particular, gasification of waste is an economical and environmental viable solution to produce cleaner energy together with a remarkable waste weight reduction. The most simplistic way to consider gasification is as an alternative to the combustion to obtain heat and power with a lesser environmental impact. In this case the gasification process is used to transform a heterogeneous fuel (solid waste, sludge, biomasses, low-rank coal, …) into a homogeneous synthetic gaseous fuel to be utilized in an industrial burner, an engine or a gas turbine to produce electricity and heat. The loss of chemical energy necessary to promote the endothermic reactions of gasification is balanced by the higher performance of the homogeneous combustion. The general concept and the technologies utilized to gasify a material is similar to that reported for incineration facilities, but the operating parameters of the plant are completely different. First of all, the gasification process cannot be represented by a single main reaction, as for the combustion process, but by reactions involving different reactants (oxygen, carbon dioxide, water) and characterized by different reaction’s enthalpies (Mastellone, 2015). Moreover, the interaction between intermediates and minerals must be considered, particularly for plastics (Mastellone and Arena, 2008; Sjöström et al., 1999). The heat released by exothermal reactions increases the environment temperature until values depending by the equivalence ratio, proximate and ultimate analysis of waste and its net chemical energy. The operating temperature of the waste gasifiers is generally in the range 850–1200 °C depending by the above recalled parameters and by heat losses. The oxygen supplied to the gasifier is generally 25–40% of the stoichiometric demand. The reducing environment promotes the partial oxidation of carbon and hydrogen element in the fuel by providing the heat necessary to the cracking of waste/fuel component. The fraction between the oxygen provided for gasification reactions and the stoichiometric demand is known as equivalence ratio and its value depends on ultimate analysis of the waste. The main product of gasification process is the synthesis gas also identified as “synthetic gas or syngas”. This term is used when it is used as a feedstock for production of synthetic natural gas (SNG), Fischer-Tropsch liquids (FTL), hydrogen or any other material or fuel; the term “producer gas” is used when the gas is used to energy production. Anyway, whatever is the final utilization, the term syngas can be used to indicate the gaseous product of gasification. The syngas composition can vary depending on waste and operating conditions, but the main constituents are carbon monoxide, hydrogen, methane, C2-C6 hydrocarbons, carbon dioxide and water. The general layout of a gasification plant includes: 1) Mechanical feeder at ambient temperature 2) Gasification reactor 3) Bottom ash discharge system 4) Cooling of syngas 5) Cleaning / upgrading of syngas (thermal/catalytic cracking, tar absorption, …) 6) Syngas energy recovery (heat, electricity or both) 7) Auxiliaries (scrubber, cooling water production, …) The data used to model the performance of the gasifier section in the following paragraphs come from an extensive series of experiments carried on the plastic waste by using a pilot-scale fluidized bed gasifier (Arena et al., 2010, 2008; Mastellone and Zaccariello, 2013). The main performance parameters for the gasification of plastic waste mixture are reported in the following (§4.3) and are related to a specific pilot plant operated with an oxidizing stream constituted by air having an equivalent ratio of about 0.3. The tar content in the syngas has been considered negligible thanks to use of catalytic reaction in the gasifier (Arena et al., 2009). In the case of gasification, the absorbed process energy can be evaluated by considering that the exothermic reactions uses a fraction of the feedstock energy of the input waste to guarantee a given temperature and to promote the endothermic reactions; this fraction of energy is the complement of the Cold Gas Efficiency parameter (CGE). 3. Materials The input material to which this paper refers is the plastic waste residual from the centralized sorting at material recovery facility (MRF). This plastic waste has a low content of PET and a high content of polyolefins, other polymers and foreign matter. The sorting of this waste with the only aim to recover the PET and the HDPE, that are the only polymers suitable for the mechanical recycling, would be not economically convenient because of the largest part of the flow (about 90%) that should be addressed to disposal (landfilling or incineration). By referring to the integrated system under study, where the sorting is finalized to prepare the feedstocks for PtO and gasification processes, M.L. Mastellone Resources, Conservation & Recycling: X 4 (2019) 100017 5