Possible applications for vacuum pyrolysis in the processing of waste materials

De Jongh, Willem Adriaan (2001-04)

Thesis (MScEng)--University of Stellenbosch, 2001.

Thesis

ENGLISH ABSTRACT: Current global trends in government, industry and popular OpInIOn indicate that recycling will become essential in the future. Vacuum pyrolysis is a new technology with many recycling applications that have not yet been investigated. This study is a contribution towards the better understanding of the vacuum pyrolysis process and also towards finding possible economically favourable recycling applications. A batch operated tube furnace, which allowed the controlled heating of different materials in a vacuum, was designed and built. The gases and vapours passed though a series of progressively colder vacuum traps, condensing the vapours for further study. The products from the process are charcoal, oil, an aqueous phase and noncondensable gases. The charcoal and oils' possible economic values (R2500- R5000/ton of charcoal, while the plant product oil can be sold as a low sulphur fuel, with a retail value of approximately R1.42 per litre) were determined along with the oils' chemical composition. Several possible feedstocks were studied, including intruder plant species, leather wastes, sewage sludge and a simplified representation of municipal solid waste. The three intruder plants studied were Kraalbos (Galenia africane), Scholtzbos (pteronia pallens) and Asbos (Psilocaolon absimile). These plants yielded 40%, 42% and 48% (charcoal per kilogram dry feedstock) respectively at their maximum oil yield temperatures of 380°C, 480°C and 450°C respectively. The maximum oil yields were 36%, 32% and 20% respectively (also on a dry feedstock basis). It was found that the plants with ash contents below 10% yielded commercially competitive charcoal, and that all of the plants yielded oils with heating values in the range of 24MJ/kg, containing several high value compounds. Asbos was the only plant that did not produce usable charcoal, as its ash content of 40% was double that of commercial charcoals. The leather wastes represent a previously unrecognised application of the technology that could bring huge financial rewards to the tanning industry and could provide a more environmentally friendly alternative to lined landfilling. The cost of landfilling for a medium sized tannery can be as high as RIOOO 000 a year. Apart from the volume reductions achieved (up to a factor 8) it was found that landfilling might be totally avoided if the chrome contained in the charcoal product could be extracted and reused. Sewage sludge was studied, as it is a hazardous waste that requires costly disposal in a lined landfill. It was revealed that volume reductions of up to a factor 3.5 were possible with corresponding charcoal and oil yields of 40% and 38% respectively at 500°C. It was also found that the charcoal product could be used as compost, which would then turn a costly waste into a commodity product. The oil from both the leather and sewage sludge had high energy values (26.7MJ/kg and 30.9MJ/kg respectively) and might either be sold as a bunker fuel or used in the process as a make-up heat source. The value of the oil depends on the problems posed by the oils' high nitrogen content (±5%-6%). A further study was also made of the co-pyrolysis of PVC and wood to determine the interaction between the feedstocks and as a simplified representation of municipal solid wastes. It was found that the HCI released from the PVC caused acid hydrolysis of the wood and led to lower charcoal (reduced from 32.6% to 29.7% on dry feedstock basis, at the maximum co-pyrolysis oil yield temperature of 460°C) and much higher oil yields (42.4% for the co-pyrolysis compared to 23.6% for the plant material at 460°C). An existing computer program (CEA by Gordan and McBride) was also employed in order to find explanations for some of the vacuum pyrolysis results. Although large specialist vacuum pyrolysis plants have been designed in the past (mostly to dispose of used tyre waste) it will be necessary to determine the process economics for small-scale applications if the technology is to be applied at the source of the problem. Overall vacuum pyrolysis appears to be a very promising technology that could solve many waste problems in an environmentally friendly and economically beneficial manner.

AFRIKAANSE OPSOMMING: Hedendaagse neigmgs in regenng, industrie en populêre opirue toon dat hergebruikstegnologieë al hoe meer noodsaaklik sal word in die toekoms. Vakuum pirolise is 'n nuwe tegnologie met vele moonlike hergebruik toepassings wat nog nie bestudeer is nie. Hierdie studie is 'n bydrae tot 'n dieper begrip van vakuum pirolise en ook tot die verdere soeke na nuwe toepassings vir die tegnologie. 'n Enkellading buis-oond, wat die beheerde verhitting van verskillende materiale in vakuum toegelaat het, is ontwerp en gebou. Die gevormde gasse en dampe het deur 'n progressief kouer reeks van vakuum valle beweeg waar dit vir verdere studie gekondenseer en opgevang is. Die produkte van die proses is houtskool, olie, 'n waterryke fase en nie-kondenseerbare gasse. Die houtskool en olie se moontlike waarde (R2500-R5000/ton houtskool, terwyl die plant produk olie verkoop kan word as 'n lae swael verhittings olie met 'n kleinmaat kommersieële verkoopswaarde van R1.42/1), saam met die chemiese samestelling van die olie fase, is bepaal. Die vakuum pirolise van verskeie moontlike voerstowwe is bestudeer, insluitende indringerplante, leerafval, rioolslyk en 'n vereenvoudigde voorstelling van munisipale afval. Die drie plant spesies wat bestudeer is, is: Kraalbos (Galenia africane), Scholtzbos (Pteronia pal/ens) en Asbos (Psilocaolon absimile). Die plante het opbrengste van 40%, 42% en 48% (houtskool per kilogram droë voerstof) onderskeidelik gelewer by elk van die plante se maksimum olie opbrengs temperature van 380°C, 480°C en 450°C onderskeidelik. Die maksimum olie opbrengste was 36%, 32%, 20% (olie per kilogram droë voerstof) vir die onderskeie plante. Daar is bevind dat die plante met as-inhoude van minder as 10% kommersieel kompeterende houtskool gelewer het. Dit is ook gevind dat die olie van al die plante verbrandingswaardes in die orde van 24MJ/kg lewer en dat die olies ook verskeie waardevolle chemikalieë bevat. Asbos was die enigste van die bestudeerde plante wat nie maklik bruikbare houtskool gelewer het nie. Die Asbos houtskool was minder bruikbaar as gevolg van die uiters hoë as-inhoude van tot 40% met gevolglike lae energie waarde. Die vakuum pirolise van leerafval is 'n toepassing wat nog nie voorheen ondersoek is nie. Dit kan moontlik lei tot groot finansiële voordele vir die leerlooi industrie en kan ook 'n meer omgewingsvriendelike alternatief tot belynde afval storting bied. Die koste verbonde aan die storting van leer afval van 'n medium grootte looiery kan tot R1000 000 per jaar beloop. Behalwe vir die volume verkleining behaal (tot 'n faktor 8), is daar ook gevind dat afvalstorting totaal vermy kan word as die hoë hoeveelheid chroom (12% van die houtskool) uit die houtskool verwyder en hergebruik kan word. Rioolslyk is ook bestudeer, siende dat dit ook 'n probleem afvalstof is wat teen groot koste gestort moet word. Die studie het getoon dat volume verkleinings van tot 'n faktor 3.5 en houtskool en olie opbrengste van onderskeidelik 40% en 38% by 500°C behaal kan word. 'n Ondersoek van die houtskool het getoon dat dit gebruik kan word as 'n kompos, wat dan sal beteken dat 'n probleem afvalstof verander word na 'n omgewingsvriendelike en ekonomies waardevolle produk. Die olie van beide die rioolslyk en leer het hoë energiewaardes (26.7MJ/kg en 30.9MJ/kg onderskeidelik) en kan verkoop word as verbrandingsolie of gebruik word in die vakuum pirolise proses as 'n hulp-hitte bron. Die gebruikswaarde van die olie sal baie afhang van die probleme wat deur die uiters hoë stikstof-inhoud (±5%-6%) veroorsaak gaan word. 'n Verdere studie van die ko-pirolise van PVC en hout is ook gedoen om die interaksie tussen die afvalstowwe te bestudeer en ook om as 'n vereenvoudigde voorstelling van munisipale afval te dien. Daar is gevind dat die HCI wat afkom as PVC verhit word, suur hidrolise van die houtstrukture veroorsaak en lei tot laer houtskool (verminder van 32.6% na 29.7% droë voerstofbasis, by die maksimum olie opbrengs temperatuur van 460°C) en veel hoër olie opbrengste (42.4% vir die kopirolise in vergelyking met 23.6% vir die plant materiaal by 460°C). 'n Studie van die energie wat verkry kan word uit die olie en houtskool het getoon dat 16% tot 28% meer energie verteenwoordig word deur die produkte per kilogram droë voerstof vir die ko-pirolise proses bo normale vakuum pirolise. Alhoewel groot spesialis vakuum pirolise aanlegte in die verlede ontwerp is (meestal vir die verwerking van gebruikte motor buitebande) sal dit nogstans noodsaaklik wees om die winsgewindheid van kleinermaat prosesse te bestudeer sodat vakuum pirolise by die oorsprong van die afvalstoftoegepas kan word. Dit blyk dat vakuum pirolise 'n baie belowende tegnologie IS wat verskeie afval probleme op 'n omgewingsvriendelike en ekonomies winsgewinde wyse kan oplos.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/52407
This item appears in the following collections: