Browsing by Author "Enqvist, Eric"

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Comparison of alternative pulping methods on straw, bamboo and eucalyptus
(2001) Enqvist, Eric
Helsinki University of Technology | Master's thesis
Imeytyksen antama keittopotentiaali sulfaattikeitossa
(2003) Vehmas, Mari
Helsinki University of Technology | Master's thesis
Tämän työn tavoitteena oli selvittää laboratoriomittakaavan imeytyslaitteistolla eri tehdasmäntyhakkeiden penetroitumista ja höyryfaasikeittoja suorittamalla imeytyksen antamaa keittopotentiaalia. Työssä perehdyttiin hakkeiden ilmanpoiston, imeytyspaineen, imeytyslämpötilan ja imeytyslipeän alkalipitoisuuden vaikutuksiin hakkeiden penetroitumisprosessissa. Lisäksi selvitettiin, minkälainen delignifiointiaste on mahdollista saavuttaa pelkästään imeytyksessä hakkeen sisään saadulla alkalilla. Imeytystavan, alkaliannoksen, höyryfaasikeiton lämpötilan ja keittoajan yhteisvaikutuksia keitetyn massan laatuun analysoitiin saannon, rejektin määrän ja massan ligniinipitoisuuden avulla. Kirjallisuusosassa tutustuttiin puun rakenteeseen, puun ja hakkeiden tiheyksiin sekä puun kemialliseen koostumukseen. Käsiteltiin puun hiilihydraattien ja ligniinin reaktioita sekä alkalin kulutusta ja alkaliannoksen vaikutuksia sulfaattikeitossa. Kirjallisuuskatsauksen loppuosassa tarkasteltiin hakkeiden imeytystä ja penetraatioon vaikuttavia seikkoja sekä käytiin läpi höyryfaasikeiton ominaisuuksia ja vaikutuksia massan ominaisuuksiin. Imeytyskokeissa havaittiin, että paineen nosto imeytyksessä sekä nopeuttaa penetroitumista että nostaa lopullista penetraatioastetta. Ilma puun kapillaareissa puristuu enemmän korkeamman paineen vaikutuksesta. Höyrytyksen penetraatiota parantava vaikutus havaittiin ilmeiseksi. Imeytyslipeän lämpötilan kasvaessa penetraatioaste kasvaa ja se saavutetaan nopeammin. Sahahake penetroituu paremmin kuin kuitupuu. Valkolipeää imeytyy enemmän hakkeeseen kuin vahvistettua kuumamustalipeää. Tähän vaikuttavat mm. lipeiden erilaiset viskositeetit ja kuumamustalipeän sisältämät orgaaniset molekyylit. Lipeästä ja haketyypistä riippuen tehollisen alkalin pitoisuus vaihtelee puun sisällä. Pelkällä imeytyksessä hakkeeseen saatavalla alkalilla voidaan saavuttaa höyryfaasikeiton jälkeen kappataso 30 ja jopa hieman matalampikin. Tällöin imeytysolosuhteiden täytyy olla optimaaliset. Hakkeiden höyrytys ennen imeytystä on välttämätön. Havaittiin, että imeytyspaineen on oltava suuri, mieluiten noin 9 bar. Korkealla imeytyspaineella ja -lämpötilalla sekä höyrytyksellä voidaan parantaa massan tasaisuutta eli pienentää rejektin määrää. H-tekijä malli toimii höyryfaasikeitossa paremmin korkeammilla EA-annoksilla kuin alhaisemmilla annoksilla.
From vapour to gas: Optimising cellulose degradation with gaseous HCl
(2018-06-01) Pääkkönen, Timo; Spiliopoulos, Panagiotis; Knuts, Aaro; Nieminen, Kaarlo; Johansson, Leena Sisko; Enqvist, Eric; Kontturi, Eero
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
A cellulose degradation technique utilizing a pressurized HCl gas (up to 100 kPa) device is introduced. High pressure HCl quickly degraded cellulose in purified cotton linters, reaching the so-called levelling-off degree of polymerisation (LODP) in less than 1.5 h. LODP marks the point where the disordered portions of cellulose microfibrils have been degraded and only the crystalline portions remain, generally signalling the end of cellulose degradation unless remarkably high concentrations are used. In the present high pressure system, however, continued hydrolysis following the LODP was detected by incremental release of sugars from the hydrolysate after its exposure to water, supposedly caused by erosion from the cellulose crystallite ends. With minimal water consumption and the ease of recycling the gaseous acid, the technique could be a potential candidate for pre-treatment considering the future production of cellulose nanomaterials, particularly cellulose nanocrystals.
Impregnation, vapor phase and methanol as means of intensifying the softwood kraft pulping process
(2006-10-27) Enqvist, Eric
Doctoral dissertation (monograph)
The objective of the research was to find ways to shorten the cooking time, i.e. intensify the kraft pulping process. The reason for undertaking such a study lies in the long standing trend of ever increasing reactor size in the kraft pulping industry. The huge digester size in use presently has lead to severe problems in understanding the behavior of the chip column inside the digester. An intensified process with a drastically shorter pulping time would give a more manageable process and greater freedom in reactor design. The study was performed using a new experimental digester giving a much greater control over temperatures than what can be achieved with other types of digesters. This enabled experiments that clarify the impact of impregnation, heat-up time, cooking temperature and cooking time to a greater degree than what has been possible earlier. The research on actual intensification centered on understanding the impact of impregnation and the impact of alcohols (methanol) on the overall rate of pulping. This research supports earlier research that shows how the cooking time can be shortened using alcohols as additives in pulping. It also supports results showing that a fast process can be achieved by using impregnation with high concentrations of cooking chemicals followed by a cooking stage performed with direct steam heating. The fact that the effects work in synergy so that the fastest pulping process identified was one that employed high concentration impregnation followed by heating using methanol steam is a new finding. The decrease in cooking time compared to a conventional liquid phase batch process without proper impregnation is close to 70%. The present research was aimed only at shortening the cooking time and does not address questions related to actual digester and process design and economical feasibility of the process. Especially the regeneration of cooking chemicals and methanol are an area that will need further study before such question can be addressed.
Single fiber swelling behavior for natural and man-made cellulose fibers under alkaline treatment
(2021-12) You, Xiang; Chen, Feng; Ma, Yibo; Roselli, Annariikka; Enqvist, Eric; Hassi, Heikki
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Swelling behavior of cotton, dissolving wood pulp (DWP), viscose staple fiber, and Tencel staple fiber in varying sodium hydroxide (NaOH) concentration were investigated by means of optical microscopy and were characterized by molecular mass distribution, X-ray diffractometer, and dynamic vapor sorption. The effect of temperature (20–45 °C) and duration (0–120 min) was studied. The results reveal that the swelling ratio of fiber in alkali solution depends on fiber accessibility and NaOH concentration. Viscose staple fiber exhibited the highest swelling ratio and lowest swelling ratio observed for dissolving wood pulp fiber among all the materials. The cotton or DWP fibers provide maximum swelling during alkaline steeping (18wt % lye) at higher temperatures, i.e., 45 °C. As for viscose staple fiber and Tencel staple fiber, using 12 wt% lye concentration and steeping at lower temperatures, i.e., 20 °C maximum swelling behavior.
Validation of chip bed property measurements in a laboratory digester
(2004) Laakso, Ville Valtteri
Helsinki University of Technology | Master's thesis
In this work, a digester system equipped with a hydraulic compression piston was taken into operation and developed further for studying the behaviour of the chip column during kraft cooking. In particular, the effects of chip bed porosity and kappa number on the liquid flow resistance were measured. The tests consisted of 16 cooks with carefully screened chips. The volume of the chips was measured with an optical chip analyser (VisiChipsTM from Metso Paper) and the average porosity of the chip bed was then calculated from this volume. The cooking conditions were the same for all cooks: alkali dose 21 %, sulfidity 43 %, liquid to wood ratio 4.5, and cooking temperature 170°C. The relationship between H-factor and kappa number was determined with precooks. The actual test cooks were performed so that the temperature was lowered to 130°C after the desired H-factor was reached. This slowed down the cooking reactions and the compression tests could be carried out at virtually constant kappa number (20 or 70). During the compression tests, the chip column was compressed with a perforated steel plate, which was moved by a hydraulic piston. Liquid was circulated through the compressed chip column with different velocities (superficial velocity 0-11.4 mm/s) and the generated pressure difference was measured. Chip bed porosities between 0.5 and 0.05 were tested with an interval of 0.05. Compression tests were first performed on a digester full of chips and the liquid flowing upwards. In this set-up, the direction of liquid flow was opposite to the direction of compression force. The pressure drops measured (kPa/m) were substantially higher than those found in the literature. It was also discovered, that a chip column at higher kappa number produced higher pressure difference than a chip column at lower kappa number in the same porosity. When the height of the chip column was reduced by half, the pressure difference decreased more than half. It suggests that the porosity was not evenly distributed. This phenomenon was emphasized at higher kappa number. The direction of the liquid flow was changed to down flow and compression cooks were repeated at both kappa number levels with both full and half-full digester. Down flow produced lower pressure difference than up flow at the same kappa number and porosity. The difference was greater particularly with a full digester. A chip bed at higher kappa number produced higher pressure loss than a lower kappa number chip bed at the same porosity also with down flow. The relatively high flow resistance may have been caused by a thin but dense chip layer, which has formed due to the friction between the digester wall and chips. Down flow apparently evened out the porosity close to the compressing plate and hereby decreased the total pressure loss. With the equipment used, it was not possible to measure the distribution of porosity. The height of the cylindrical digester was 981 mm and the diameter was 202 mm, and it is possible that the ratio of digester height to diameter was too high. This could have increased the uneven vertical distribution of porosity in the chip column. Due to technical reasons, the flow resistance of the chip bed under constant compaction pressure was not measured. It was not possible to accurately measure the compaction pressure needed to compress the chip bed to certain porosity either. However, this compaction pressure was estimated graphically. Based on these estimations, the pressure losses caused by the chip bed under certain compaction pressures were compared. Chip columns at lower kappa numbers produced higher flow resistances under fixed compaction pressures. This has been reported in previous studies. The conclusion is that a chip bed at higher kappa number produces higher flow resistance at fixed porosity. The reason is that a chip bed at high kappa number is harder and more force is needed to compress it to certain porosity and it is more deformed. Due to friction, deformations concentrate on the end of the chip being compressed.