Plastics recycling has become an established national industry in Korea. However, it is still in its infant stage and experiences growing pains. Mixed plastic wastes generated from households after hand picking and/or mechanical sorting processes amount to 2,000,000 ton per year in 2012 Most of thes...
Plastics recycling has become an established national industry in Korea. However, it is still in its infant stage and experiences growing pains. Mixed plastic wastes generated from households after hand picking and/or mechanical sorting processes amount to 2,000,000 ton per year in 2012 Most of these wastes end up in landfills and/or incineration due to the lack of separation technology and high cost. Due to their high PVC content, there plastic can not be used as raw materials, chemical and/or thermal recycling. In the present work, gravity separation system has been developed to remove PVC from the mixed plastic waste and recover individual plastics. The separation system mainly consists of air classification, crushing, feeding system at fixed rate and wet-type gravity separation system. The gravity system based on centrifugal separation also consists of mixing, precleaning, separation, dewatering, recovery system, wastewater treatment system, etc. The main objective of this process is to achieve high separation efficiency of polyolefin (PE, PP) with less than 0.3 wt.% PVC content and less than 10% moisture content. The system with a capacity of 0.5 ton per hour is developed and operational results are analysed. • The process with a capacity of 0.5 ton/h was developed in the present work and it consists of air classification, crushing, paper and fines separation, feeding, mixing, precleaning, gravity separation with a centrifuge, dewatering, and lighter and heavier fraction recovery. • The material obtained after air classification is crushed down to a particle size of minus 15㎜ by using a specially designed crusher. The crusher is designed with one-shaft shredder with 8 rotors, a compression feeding unit and a forced discharge unit. The crusher has a throughput rate of over 0.6 tons per hour and capable of crushing the film-type plastics. • The crushed fractions are fed into the gravity separation system at a fixed rate. The gravity separation system is designed to capacity of 0.5 ton/h of the mixed plastic fractions. In feeding system, fine size fractions such as paper, glass, ceramics, etc. can be removed from the crushed materials before feeding into the gravity separation system to improve the separation and dewatering efficienies of the final products. • The gravity separation system consists of mixing, precleaning, separation, dewatering and recovery of lighter and heavier products. The suspension after precleaning is fed to the gravity separator, which is based on the centrifuge. Inside of the centrifuge, the material is separated by specific gravity value of the plastics as described above, i.e. lighter fractions (polyolefin, i.e. LDPE, HDPE and PP) are separated out of other heavier ones (PET, PVC, ABS and other non polyolefin). In this system, PS fraction (S.G. = 1.03∼1.06) can also be recovered as heavier fractions. Both fractions are discharged from the centrifuge at opposite conical ends to send the dewatering units. In particular, lighter fractions are freely discharged to the flow direction due to high fluidity of water medium. The water is only used as separating medium and then recycled to the mixing tank after removing the suspended solids. • The dewatering units for heavier and lighter fractions are used respectively. The basic mechanisms for the dewatering are centrifugation and/or eddy force instead of compression and/or air blowing. The moisture contents for the heavier and lighter fractions after dewatering are less than 5 and 10 wt.%, respectively. The moisture content of the lighter fractions is normally 4~5% higher than that of the heavier fractions because of high content of films in the lighter fractions. • One of the major advantages for this system is that thermal drying is not applied to the final products after dewatering. In addition, paper, fibrous materials and fine particles are removed as a dry base in advance before feeding to the gravity system to enhance the separation and dewatering efficiencies. The gravity separation system we developed is one-step process with low water and energy consumption. • Based on the separation results, it was possible to achieve high separation efficiency (over 99.65%) with PVC content of less than 0.3 wt.%. The obtained lighter fraction after gravity separation could be used as a raw material for material , thermal and/or chemical recycling. • Cost benefit analysis was also carried out based on the results of the system operation. The annual profit will be amount to 362million won. • The system we developed is useful for recycling of agricultural films, ASR treatment, PU recovery from waste electrical and electronic products, PVC removal from mixed plastic wastes, etc. Further development of this system will be continued, and should contribute to improving efficiencies and growth of the recycling industry in the near future.
Plastics recycling has become an established national industry in Korea. However, it is still in its infant stage and experiences growing pains. Mixed plastic wastes generated from households after hand picking and/or mechanical sorting processes amount to 2,000,000 ton per year in 2012 Most of these wastes end up in landfills and/or incineration due to the lack of separation technology and high cost. Due to their high PVC content, there plastic can not be used as raw materials, chemical and/or thermal recycling. In the present work, gravity separation system has been developed to remove PVC from the mixed plastic waste and recover individual plastics. The separation system mainly consists of air classification, crushing, feeding system at fixed rate and wet-type gravity separation system. The gravity system based on centrifugal separation also consists of mixing, precleaning, separation, dewatering, recovery system, wastewater treatment system, etc. The main objective of this process is to achieve high separation efficiency of polyolefin (PE, PP) with less than 0.3 wt.% PVC content and less than 10% moisture content. The system with a capacity of 0.5 ton per hour is developed and operational results are analysed. • The process with a capacity of 0.5 ton/h was developed in the present work and it consists of air classification, crushing, paper and fines separation, feeding, mixing, precleaning, gravity separation with a centrifuge, dewatering, and lighter and heavier fraction recovery. • The material obtained after air classification is crushed down to a particle size of minus 15㎜ by using a specially designed crusher. The crusher is designed with one-shaft shredder with 8 rotors, a compression feeding unit and a forced discharge unit. The crusher has a throughput rate of over 0.6 tons per hour and capable of crushing the film-type plastics. • The crushed fractions are fed into the gravity separation system at a fixed rate. The gravity separation system is designed to capacity of 0.5 ton/h of the mixed plastic fractions. In feeding system, fine size fractions such as paper, glass, ceramics, etc. can be removed from the crushed materials before feeding into the gravity separation system to improve the separation and dewatering efficienies of the final products. • The gravity separation system consists of mixing, precleaning, separation, dewatering and recovery of lighter and heavier products. The suspension after precleaning is fed to the gravity separator, which is based on the centrifuge. Inside of the centrifuge, the material is separated by specific gravity value of the plastics as described above, i.e. lighter fractions (polyolefin, i.e. LDPE, HDPE and PP) are separated out of other heavier ones (PET, PVC, ABS and other non polyolefin). In this system, PS fraction (S.G. = 1.03∼1.06) can also be recovered as heavier fractions. Both fractions are discharged from the centrifuge at opposite conical ends to send the dewatering units. In particular, lighter fractions are freely discharged to the flow direction due to high fluidity of water medium. The water is only used as separating medium and then recycled to the mixing tank after removing the suspended solids. • The dewatering units for heavier and lighter fractions are used respectively. The basic mechanisms for the dewatering are centrifugation and/or eddy force instead of compression and/or air blowing. The moisture contents for the heavier and lighter fractions after dewatering are less than 5 and 10 wt.%, respectively. The moisture content of the lighter fractions is normally 4~5% higher than that of the heavier fractions because of high content of films in the lighter fractions. • One of the major advantages for this system is that thermal drying is not applied to the final products after dewatering. In addition, paper, fibrous materials and fine particles are removed as a dry base in advance before feeding to the gravity system to enhance the separation and dewatering efficiencies. The gravity separation system we developed is one-step process with low water and energy consumption. • Based on the separation results, it was possible to achieve high separation efficiency (over 99.65%) with PVC content of less than 0.3 wt.%. The obtained lighter fraction after gravity separation could be used as a raw material for material , thermal and/or chemical recycling. • Cost benefit analysis was also carried out based on the results of the system operation. The annual profit will be amount to 362million won. • The system we developed is useful for recycling of agricultural films, ASR treatment, PU recovery from waste electrical and electronic products, PVC removal from mixed plastic wastes, etc. Further development of this system will be continued, and should contribute to improving efficiencies and growth of the recycling industry in the near future.
※ AI-Helper는 부적절한 답변을 할 수 있습니다.