M.L.Mastellone Resources,Conservation Recycling:X 4(2019)100017 of plastic waste by using thermolysis processes,applied to the flows N Name Installed power,kW that are not mechanically recyclable to new valuable goods,has been 1 Feeder 75 carried out.The data sources are mainly obtained by literature,in- 1 Ash discharge 100 dustrial applications and Companies active in the related fields with Thermal cracker (plasma) 100 demo plants installed;the model to simulate the mass flows is the 3 Pumps 25 Material Flow Analysis.A feedstock energy flow assessment is also 11 Air compressor 85 Analysers applied in order to evaluate which part of material energy content is Cooling water system 110 exploited and transferred to fuels and secondary materials.Data about the installed power necessary to operate a modelled integrated plant is also provided to establish which is the external energy request The engines can reach 35%of conversion efficiency in electricity by and,then,the opex. self-producing all the electric power and by feeding the excess into the The most important result of the feasibility study is that the plastic grid. waste used as reference input to the system is the residue coming from The energy balance(Table 10)helps to assess the economic feasi- the existing material recycling factories that sorts the plastics collected bility of the integrated system with regard to the operating cost and, at households and commercial sources;this residue is addressed to specifically,to the electricity cost that constitute the most relevant disposal such as landfilling or incineration with municipal solid waste contribution to the operating cost (opex).The operating cost can be with a corresponding high costs and impacts.The conversion into considered as obtained by adding the following items: secondary fuels is also applied to substitute the fossil fuels into cement kiln or(rarely)in the steel production factories;in this case the sorted ·human resources plastics substitutes the coal as fuel for production of heat after a sorting ·electricity and densification stage (so called CSS production).Today the cost of ·waste disposal these stages is about 806/t that have been added to the transportation raw materials\additives costs between the MRF and the CSS facility and from CSS to cement facility licensed to use the CSS fuel.The large cost of treatment of All the financial items are not considered. plastics and the limited number of authorized facilities,led to a massive The economical assessment has been made by comparing the opex landfilling calculated for the integrated facility and for the three separated sub- The material and energy balances allowed to verify that a com- processes:mechanical sorting,plastic-to-oil,gasification.Each fa- bination between energy-intensive processes,like mechanical sorting, cility opex is obtained by assuming that the operating time is 7920 h/ can be energetically and economically sustained by integrating them year(i.e.three shifts for day,330 days/year),the annual gross mean in a network where the non-recyclable materials can be exploited in salary is 48.000 E/year,the electricity cost is 120C/MWh.The value form of materials and energy.The complete exploitation of mixed of opex has been calculated for the facilities considered as standalone plastic waste,containing polymers that cannot be mechanically re- installations (columns 2,3 and 4 of Table 11)and for integrated fa- cycled with a sustainable industrial cost or havening no real market to cility.The human resources for this latter have been considered as the be sold,cannot be obtained by recurring to a unique process that sum of those necessary for the three process's sections but this as- inevitably results in a not sustainable gate fee.The building of an sumption can be considered conservative because the shift super- integrated and sustainable network allows to apply for real the cir- visors,extraordinary maintenance workers,administrative people cular economy principles and the results obtained in this paper give a can be shared. demonstration of this statement. The data of Table 11 demonstrate that the integration between the In the examined case,two thermochemical processes have been mechanical sorting of low-quality waste with the gasification and used for the flows (polyolefins-based flow and commingled plastic plastic-to-oil units allow to decrease the cost for waste disposal and for waste flow)resulting from the sorting of a typical plastic waste electrical energy.All the waste that is not suitable to be converted into coming from household and commercial separate collection:a)a syncrude(from which kerosene and other petrochemical feedstocks are plastic-to-oil process based on pyrolysis of polyolefins and fractio- produced)can be converted into syngas (from which energy and/or nation of obtained vapor products;b)a gasification process of the other petrochemical feedstocks can be produced). flow containing all the other components of the sorting line,including composites,elastomers,foreign matter,etc.,with the aim to produce 5.Summary and conclusions a high-calorific syngas. The use of the pyrolysis gas from the plastic-to-oil and the syngas The assessment of an integrated system allowing the exploitation from gasification to produce electricity,allows to cover integrally the Table 11 Operating cost evaluation for single installations and for the integrated facility. ITEM SORTING PRETREATMENT-P20-ENERGY DENSIFICATION-GASIFICATION-ENERGY RECOVERY INTEGRATED RECOVERY FACILITY Capacity t/h 17.87 6.90 8.22 17.87 Human resources (technical # 15 9 9 33 staf的 E/t 5.09 7.91 6.64 11.19 Electricity kWh/t 65.9 374.2 262.9 -462.8 E/t 7.90 44.91 31.55 -55.54 Waste disposal t/h 15.12 0.55 0.58 1.13 e/t 122.6 32.0 28.0 25.2 Raw materials\additives E/t 5 5 4.2 Total E/t 135.64 89.81 71.19 -14.89N° Name Installed power, kW 1 Feeder 75 1 Ash discharge 100 2 Thermal cracker (plasma) 100 3 Pumps 25 1 Air compressor 85 1 Analysers 5 Cooling water system 110 The engines can reach 35% of conversion efficiency in electricity by self-producing all the electric power and by feeding the excess into the grid. The energy balance (Table 10) helps to assess the economic feasi￾bility of the integrated system with regard to the operating cost and, specifically, to the electricity cost that constitute the most relevant contribution to the operating cost (opex). The operating cost can be considered as obtained by adding the following items: • human resources • electricity • waste disposal • raw materials\additives All the financial items are not considered. The economical assessment has been made by comparing the opex calculated for the integrated facility and for the three separated sub￾processes: mechanical sorting, plastic-to-oil, gasification. Each fa￾cility opex is obtained by assuming that the operating time is 7920 h/ year (i.e. three shifts for day, 330 days/year), the annual gross mean salary is 48.000 €/year, the electricity cost is 120€/MWh. The value of opex has been calculated for the facilities considered as standalone installations (columns 2, 3 and 4 of Table 11) and for integrated fa￾cility. The human resources for this latter have been considered as the sum of those necessary for the three process’s sections but this as￾sumption can be considered conservative because the shift super￾visors, extraordinary maintenance workers, administrative people can be shared. The data of Table 11 demonstrate that the integration between the mechanical sorting of low-quality waste with the gasification and plastic-to-oil units allow to decrease the cost for waste disposal and for electrical energy. All the waste that is not suitable to be converted into syncrude (from which kerosene and other petrochemical feedstocks are produced) can be converted into syngas (from which energy and/or other petrochemical feedstocks can be produced). 5. Summary and conclusions The assessment of an integrated system allowing the exploitation of plastic waste by using thermolysis processes, applied to the flows that are not mechanically recyclable to new valuable goods, has been carried out. The data sources are mainly obtained by literature, in￾dustrial applications and Companies active in the related fields with demo plants installed; the model to simulate the mass flows is the Material Flow Analysis. A feedstock energy flow assessment is also applied in order to evaluate which part of material energy content is exploited and transferred to fuels and secondary materials. Data about the installed power necessary to operate a modelled integrated plant is also provided to establish which is the external energy request and, then, the opex. The most important result of the feasibility study is that the plastic waste used as reference input to the system is the residue coming from the existing material recycling factories that sorts the plastics collected at households and commercial sources; this residue is addressed to disposal such as landfilling or incineration with municipal solid waste with a corresponding high costs and impacts. The conversion into secondary fuels is also applied to substitute the fossil fuels into cement kiln or (rarely) in the steel production factories; in this case the sorted plastics substitutes the coal as fuel for production of heat after a sorting and densification stage (so called CSS production). Today the cost of these stages is about 80€/t that have been added to the transportation costs between the MRF and the CSS facility and from CSS to cement facility licensed to use the CSS fuel. The large cost of treatment of plastics and the limited number of authorized facilities, led to a massive landfilling The material and energy balances allowed to verify that a com￾bination between energy-intensive processes, like mechanical sorting, can be energetically and economically sustained by integrating them in a network where the non-recyclable materials can be exploited in form of materials and energy. The complete exploitation of mixed plastic waste, containing polymers that cannot be mechanically re￾cycled with a sustainable industrial cost or havening no real market to be sold, cannot be obtained by recurring to a unique process that inevitably results in a not sustainable gate fee. The building of an integrated and sustainable network allows to apply for real the cir￾cular economy principles and the results obtained in this paper give a demonstration of this statement. In the examined case, two thermochemical processes have been used for the flows (polyolefins-based flow and commingled plastic & waste flow) resulting from the sorting of a typical plastic waste coming from household and commercial separate collection: a) a plastic-to-oil process based on pyrolysis of polyolefins and fractio￾nation of obtained vapor products; b) a gasification process of the flow containing all the other components of the sorting line, including composites, elastomers, foreign matter, etc., with the aim to produce a high-calorific syngas. The use of the pyrolysis gas from the plastic-to-oil and the syngas from gasification to produce electricity, allows to cover integrally the Table 11 Operating cost evaluation for single installations and for the integrated facility. ITEM SORTING PRETREATMENT-P2O-ENERGY RECOVERY DENSIFICATION-GASIFICATION-ENERGY RECOVERY INTEGRATED FACILITY Capacity t/h 17.87 6.90 8.22 17.87 Human resources (technical staff) # 15 9 9 33 €/t 5.09 7.91 6.64 11.19 Electricity kWh/t 65.9 374.2 262.9 −462.8 €/t 7.90 44.91 31.55 −55.54 Waste disposal t/h 15.12 0.55 0.58 1.13 €/t 122.6 32.0 28.0 25.2 Raw materials\additives €/t 5 5 4.2 Total €/t 135.64 89.81 71.19 −14.89 M.L. Mastellone Resources, Conservation & Recycling: X 4 (2019) 100017 10