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Mathematical modelling of a neutral sulphite semi-chemical pulping process
Thesis (MEng)--Stellenbosch University, 2020.
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| Format: | Thesis |
| Language: | en_ZA |
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Stellenbosch : Stellenbosch University
2020
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| _version_ | 1867613812220231680 |
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| access_status_str | Open Access |
| author | Pottinger, Ryan |
| author2 | Louw, Tobias M. |
| author_browse | Louw, Tobias M. Pottinger, Ryan |
| author_facet | Louw, Tobias M. Pottinger, Ryan |
| author_sort | Pottinger, Ryan |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MEng)--Stellenbosch University, 2020. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/108471 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:42:05.565Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2020 |
| publishDateRange | 2020 |
| publishDateSort | 2020 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/108471 Mathematical modelling of a neutral sulphite semi-chemical pulping process Pottinger, Ryan Louw, Tobias M. Auret, Lidia Wahl, H Gorgens, Johann F. Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Process Engineering. Sulfite pulping process Heat -- Transmission Mass transfer -- Mathematical models Chemical kinetics UCTD Thesis (MEng)--Stellenbosch University, 2020. ENGLISH ABSTRACT: A general mathematical model was developed for the neutral sulphite semi-chemical process. The model accounts for mass transfer effects and reaction kinetics that occur within solid wood chips. The model took into account a bulk liquid phase and a solid wood chip phase. The mass balances took into account delignification, carbohydrate degradation and deacetylation reactions within the wood chip. The reactions caused sodium sulphite to be consumed and acetic and formic acid to be produced. The model takes the sodium sulphite charge, liquor to wood ratio and sulphite to carbonate ratio as inputs into the system. The model predicts the pH and sodium sulphite concentration of the bulk cooking liquor and the lignin content of the wood. Lab scale experiments were conducted to obtain parameters for the delignification, carbohydrate degradation and deacetylation reaction rates. The experiments were conducted in a batch digester using 30 g of milled wood (fiber length < 0.5 mm) in order to remove diffusion limitations. The temperature range for the experiments was between 156 °C – 184 °C. The initial sodium sulphite charge was between 6.34 % - 17.66 % of oven dry wood. The sulphite to carbonate ratio was kept constant at 10:1. The liquor to wood ratio was kept constant at 8.33:1. The pH and sulphite concentration of the cooking liquor and lignin and carbohydrate content of the wood was measured after 30, 60 and 100 minutes of pulping at the appropriate temperature. Non-linear regression was used to fit a kinetics model to the lab scale experimental data and obtain kinetic parameters for the reaction rates. This model did not take into account diffusion effects. The regressed coefficients were used in the full model with diffusion effects. The model was compared to pilot scale experimental data that used full sized wood chips. The model predicted the pH results with a root mean square error (RMSE) of 6.5 %, lignin content with 25.0 % RMSE and sulphite concentration with 158.8 % RMSE. The predictive capability of the model allows process parameters (liquor to wood ratio, sulphite to Stellenbosch University https://scholar.sun.ac.za v carbonate ratio, temperature and sulphite charge) to be changed and the effect on the system to be qualitatively predicted. The lab scale experimental results provided insight into the pulping process. Mass transfer and heat transfer limitations will negatively affect digester pulping and cause higher sulphite charges to be used to achieve the correct lignin content. More research is required in order to model the process accurately for industrial application. Model improvements include conducting lab scale experiments for transient conditions at lower temperatures during the heating up phase in order to model initial delignification. Diffusion and porosity kinetics can be improved by considering lab scale experiments with wood chips. A population balance model should be added to include different sized wood chips in pulping. The model can be altered for use in a plug flow reactor model that incorporates diffusion effects, chemical flow dynamics and temperature distribution that can potentially be used to improve digester operation. AFRIKAANSE OPSOMMING: ’n Algemene wiskundige model is ontwikkel vir die neutrale sulfiet semi-chemiese proses. Die model geld vir massa-oordrageffekte en reaksiekinetika wat plaasvind binne soliede houtstukkies. Die model neem ook in ag ’n gemengde vloeistoffase en ’n soliede houtstukkiefase. Die massabalanse het lignienverwydering, koolhidraatafbreking en deasetileringreaksies in ag geneem binne die houtstukkies. Die reaksies het veroorsaak dat natriumsulfiet verbruik is en asynsuur en mieresuur geproduseer is. Die model neem die natriumsulfietlading, loog-tot-hout-ratio en sulfiet-tot-karbonaat-ratio as insette vir die stelsel. Die model voorspel die pH en natriumsulfietkonsentrasie van die grootmaat kookloog en die lignieninhoud van die hout. Laboratoriumskaaleksperimente is uitgevoer om parameters vir lignienverwydering, koolhidraatafbreking en deasetileringreaksietempo’s te kry. Die eksperimente is uitgevoer in ’n lotverteerder deur 30 g gemeulde hout (vesellengte < 0.5 mm) te gebruik om diffusiebeperkinge te verwyder. Die temperatuurbestek vir die eksperimente was tussen 156 °C en 184 °C. Die aanvanklike natriumsulfietlading was tussen 6.34% en 17.66% van oondgedroogde hout. Die sulfiet-tot-karbonaat-ratio is konstant gehou by 10:1. Die loogtot-hout-ratio is konstant by 8.33:1 gehou. Die pH en sulfietkonsentrasie van die kookloog en lignien en koolhidraatinhoud van die hout is na 30, 60 en 100 minute van verpulping by die gepaste temperatuur gemeet. Nie-liniêre regressie is gebruik om ’n kintetikamodel tot die laboratoriumskaal eksperimentele data te pas en om kinetikaparameters vir die reaksietempo te kry. Hierdie model het nie die effek van diffusie in ag geneem nie. Die regressiekoëffisiënte is gebruik in die vol model met diffusie-effekte. Die model is vergelyk met loodsskaal eksperimentele data wat volle grootte houtstukkies gebruik het. Die model het pH resultate voorspel met ’n wortel gemiddelde vierkant fout (RMSE) van 6.5%, lignieninhoid met 25.0% RMSE en sulfietkonsentrasie met 158.8% RSME. Die vermoë van die model om te kan voorspel laat prosesparameters (loog-tot-hout-ratio, sulfiet-tot-karbonaat-ratio, temperatuur en sulfietlading) toe om te verander en die effek op die stelsel kwalitatief te voorspel. Die laboratoriumskaaleksperimente se resultate het insig voorsien in die verpulpingsproses. Massa-oordrag en hitte-oordragbeperkinge sal die vertering van pulp negatief beïnvloed en veroorsaak dat hoër sulfietladings gebruik sal word om die korrekte lignieninhoud te bereik. Meer navorsing word benodig om die proses akkuraat vir industriële toepassing te modelleer. Model verbeteringe sluit in laboratoriumskaaleksperimente vir verbygaande kondisies by laer temperature gedurende die verhittingsfase om aanvanklike lignienverwydering te modelleer. Diffusie en porositeitkinetika kan verbeter word deur laboratoriumskaaleksperimente met houtstukkies te oorweeg. ’n Populasiebalansmodel moet bygelas word om verskillende groottes houtstukkies in verpulping te bevat. Die model kan verander word vir gebruik in ’n propvloei reaktor wat diffusie-effekte, chemiese vloeidinamika en temperatuurverspreiding insluit, wat potensieel gebruik kan word om verteerderbedryf te verbeter. Masters 2020-02-25T14:25:32Z 2020-04-28T15:15:15Z 2020-02-25T14:25:32Z 2020-04-28T15:15:15Z 2020-03 Thesis http://hdl.handle.net/10019.1/108471 en_ZA Stellenbosch University xxi, 119 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Sulfite pulping process Heat -- Transmission Mass transfer -- Mathematical models Chemical kinetics UCTD Pottinger, Ryan Mathematical modelling of a neutral sulphite semi-chemical pulping process |
| title | Mathematical modelling of a neutral sulphite semi-chemical pulping process |
| title_full | Mathematical modelling of a neutral sulphite semi-chemical pulping process |
| title_fullStr | Mathematical modelling of a neutral sulphite semi-chemical pulping process |
| title_full_unstemmed | Mathematical modelling of a neutral sulphite semi-chemical pulping process |
| title_short | Mathematical modelling of a neutral sulphite semi-chemical pulping process |
| title_sort | mathematical modelling of a neutral sulphite semi chemical pulping process |
| topic | Sulfite pulping process Heat -- Transmission Mass transfer -- Mathematical models Chemical kinetics UCTD |
| url | http://hdl.handle.net/10019.1/108471 |
| work_keys_str_mv | AT pottingerryan mathematicalmodellingofaneutralsulphitesemichemicalpulpingprocess |