Technical and Economic Comparison of Pyrolysis and Pelleting for Valorisation of Pulper Rejects from a Secondary Tissue Mill, As Alternative to Disposal
Total Page：16
File Type：pdf, Size：1020Kb
Technical and economic comparison of pyrolysis and pelleting for valorisation of pulper rejects from a secondary tissue mill, as alternative to disposal by Joshua Lourens Nel Thesis presented in partial fulfilment of the requirements for the Degree of MASTER OF ENGINEERING (CHEMICAL ENGINEERING) in the Faculty of Engineering at Stellenbosch University Supervisor Prof. Johann Görgens Co-Supervisor Dr. François-Xavier Collard March 2021 Stellenbosch University https://scholar.sun.ac.za DECLARATION By submitting this thesis electronically, I declare that the entirety of the work contained therein is my own, original work, that I am the sole author thereof (save to the extent explicitly otherwise stated), that reproduction and publication thereof by Stellenbosch University will not infringe any third party rights and that I have not previously in its entirety or in part submitted it for obtaining any qualification. Date: March 2021 Copyright © 2021 Stellenbosch University All rights reserved I Stellenbosch University https://scholar.sun.ac.za PLAGIARISM DECLARATION 1. Plagiarism is the use of ideas, material, and other intellectual property of another’s work and to present is as my own. 2. I agree that plagiarism is a punishable offence because it constitutes theft. 3. I also understand that direct translations are plagiarism. 4. Accordingly, all quotations and contributions from any source whatsoever (including the internet) have been cited fully. I understand that the reproduction of text without quotation marks (even when the source is cited) is plagiarism. 5. I declare that the work contained in this assignment, except where otherwise stated, is my original work and that I have not previously (in its entirety or in part) submitted it for grading in this module/assignment or another module/assignment. Initials and surname: J, L Nel Date: 25 February 2021 II Stellenbosch University https://scholar.sun.ac.za Dedication “This thesis is dedicated to my parents, Danté and Prue, whose no waste philosophy inspired me. Even if I had to stand in buckets while showering with lukewarm, solar-powered water that would eventually be used for watering the garden.” III Stellenbosch University https://scholar.sun.ac.za Abstract South African paper mills are researching solutions to divert commercial and industrial waste (C&IW) from landfills. This problem is driven by increasing landfill fees, and pressure from the Department of Environmental Affairs and corporate policy. This study evaluates two recycling methods for one C&IW from secondary tissue mills, known as pulper rejects. Pulper rejects are rich in plastics and contain some fibres. The methods of recycling included secondary (pelleting) and tertiary recycling (pyrolysis) to convert rejects into marketable solid recovered fuel (SRF) and condensable product (fuel oil), respectively. Rejects were pretreated through drying, milling, extracting ferrous metal, and pelleting. The Ø6 mm pellets underwent analysis to test the technical, economic, and environmental factors according to two British SRF standards. The results from analyses proved the pellets to be feasible for cofiring as SRF in the primary burner of cement kilns. This was possible due to the high lower-heating value (LHV of 29.7 MJ/kg), low ash content (8.65 wt.%), and specific concentration of mercury, which was lower than the maximum permissible concentration according to the Air Quality Act 39 of 2004 (0.0574 mg/MJ). Comparatively, the pellets were subject to pyrolysis for conversion to condensable product, char, and gas. The highest condensable product yield of 62.4 wt.% was achieved at 500 °C on bench-scale and the condensable product was 70% wax and the rest, oil. Consequently, temperatures from 450 to 550 °C were tested on pilot-scale, with a condensable product yield of 51.9 wt.% being achieved at 500 °C. This product contained wax, organic phase oil and aqueous phase oil being 47.6, 20.6 and 31.8 wt.% of the total, respectively. The wax and organic phase oil had a higher heating value (HHV) of 38.9 and 43.6 MJ/kg, respectively and formed the fuel oil product. The gross-energy conversion (GEC) represented the energy transfer from feedstock to products. At 500 °C, the GEC to char and condensable product from bench-scale and pilot-scale was 86.5% and 74.1%, respectively with the difference attributed IV Stellenbosch University https://scholar.sun.ac.za to the aqueous phase oil reported for pilot-scale. However, the separation of aqueous phase resulted in improved oil HHV from 20.6 MJ/kg (bench-scale) to 43.6 MJ/kg (pilot-scale). Techno-economic models were developed for the pelleting and pyrolysis processes to compare profitability at mill capacity. The pelleting process was developed according to the recovery factor transform function method to evaluate multiple pelleting lines with the SRF selling price based off its LHV. The pyrolysis process was developed on Aspen Plus, using pilot-scale data, and the price of char and fuel oil determined according to their HHV. Neither process was profitable with the economic settings. The minimum fuel selling price (MFSP) of SRF calculated at 25% discount rate was R6 269/ton and more than 5.16 times the current price (R1 214/ton). Similarly, the MFSP for fuel oil was R29 137/ton and 5.85 times the current price (R4 978/ton). Hence, unless waste disposal fee is drastically increased or feedstock capacity increased, both processes will remain unprofitable. V Stellenbosch University https://scholar.sun.ac.za Opsomming Suid-Afrikaanse papiermeule doen navorsing om oplossings te vind wat kommersiële en industriële afval (C&IW) weg van vullisterreine af lei. Die probleem word aangedryf deur verhoogde vullisterreinfooie, en druk van die Departement van Omgewingsake en korporatiewebeleid. Hierdie studie evalueer twee herwinningsmetodes vir een C&IW uit sekondêre weefselmeule, bekend as pulpmasjienuitskot. Pulpmasjienuitskot is ryk in plastiek en bevat sommige vesels. Die metodes van herwinning sluit in sekondêre (korreling) en tersiêre herwinning (pirolise) om uitskot in bemarkbare soliede, herwinde brandstof (SRF) en kondenseerbare produk (brandstofolie), onderskeidelik, om te keer. Uitskot is voorbehandel deur droging, malery, ekstrahering van ysterhoudende metale, en korreling. Die Ø6 mm korrels het analise ondergaan om die tegniese, ekonomiese en omgewingsfaktore na aanleiding van twee Britse SRF-standaarde te toets. Die resultate van die analises het bewys dat die korrels bruikbaar is vir ko-ontbranding as SRF in die primêre brander van sementoonde. Hierdie was moontlik as gevolg van die hoë laer-verhittingswaarde (LHV van 29.7 MJ/kg), lae asinhoud (8.65 wt.%), en spesifieke konsentrasie van kwik wat laer was as die maksimum toelaatbare konsentrasie na aanleiding van die Lug Kwaliteit Beleid 39 van 2004 (0.00574 mg/MJ). In vergelyking, is die korrels onderwerp aan pirolise vir omsetting na kondenseerbare produk, verkoolsel en gas. Die hoogste kondenseerbare produk met ’n opbrengs van 62.4 wt.% is bereik by 500 °C op banktoetsskaal en die kondenseerbare produk was 70% was en die res, olie. Vervolgens is die temperature van 450 tot 550 °C getoets op loodsskaal, met kondenseerbare produkopbrengs van 51.9 wt.% wat bereik is by 500 °C. Hierdie produk het was, organiese fase-olie en waterige fase-olie bevat, wat 47.6, 20.6 en 31.8 wt.% van die totaal verteenwoordig, onderskeidelik. Die was en organiese fase-olie het ’n hoër verhittingswaardes (HHV) van 38.9 en 43.6 MJ/kg gehad, onderskeidelik, en het die brandstof- VI Stellenbosch University https://scholar.sun.ac.za olie produk gevorm. Die bruto-energie-omsetting (GEC) het die energie-oordrag van voermateriaal na produkte verteenwoordig. By 500 °C was die GEC na verkoolsel en kondenseerbare produk van banktoetsskaal en loodsskaal 86.5% en 74.1%, onderskeidelik met die verskil toegeskryf aan die waterige fase-olie gerapporteer vir loodsskaal. Die skeiding van waterige fase-olie het egter tot verbeterde olie HHV gelei, van 20.6 MJ/kg (banktoetsskaal) na 43.6 MJ/kg (loodsskaal). Tegno-ekonomiese modelle is ontwikkel vir die korreling- en piroliseprosesse om winsgewendheid by meulekapasiteit te vergelyk. Die korrelingproses is ontwikkel na aanleiding van die herwinningsfaktor se transformeringsfunksiemetode om verskeie korrelinglyne met die SRF-verkoopsprys te vergelyk, gebaseer op sy LHV. Die piroliseproses is ontwikkel op Aspen Plus, deur loodsskaaldata te gebruik, en die prys van verkoolsel en brandstofolie is bepaal na aanleiding van hul HHV. Nie een van die prosesse was winsgewend met die ekonomiese omgewing nie. Die minimum brandstofverkoopprys (MFSP) van SRF wat bereken is by 25% afslagkoers was R6 269/ton en meer as 5.16 keer die huidige prys (R1 214/ton). Soortgelyk was die MSFP vir brandstofolie R29 137/ton en 5.85 keer die huidige prys (R4 978/ton). Daarom, behalwe as afvalwegruimingfooie drasties verhoog of voermateriaalkapasiteit toeneem, sal beide prosesse nie-winsgewend bly. VII Stellenbosch University https://scholar.sun.ac.za Acknowledgements Foremost I would like to acknowledge and thank my supervisor Prof. Johann F Görgens for his guidance, pragmatism, and swift response in times of trouble. Secondly, I would like to express my gratitude to my co-supervisor Dr. François-Xavier Collard whose expert knowledge, advice and calm attitude helped me to become a better researcher. I acknowledge and am grateful to the Paper Manufacturers Association of South Africa (PAMSA) for their financial support towards this study and sustenance during my studies. My sincere thanks go to the following people: Mr. Jos Weerdenburg, Mr. Anton Cordier and Mr. Bevan Koopman from the Process Engineering workshop for their practical knowledge and insight. Mr. Henrik Solomon, Mr. Heinrich Bock, Mr. Alvin Petersen, and Mr. Oliver Jooste from the Wood Science and Process Engineering departments for helping me with the experimental part of my study and their patience. Mrs. Hanlie Botha and Mr. Jaco van Rooyen from the process engineering laboratory and Mrs. Riana Rossouw, Ms.