The feasibility of torrefaction for the co-firing of wood in pulverised-fuel boilers

Torrefaction is the partial pyrolysis of wood characterised by thermal degradation of predominantly hemicellulose under inert atmosphere. Torrefaction can be likened to coffee roasting but with wood in place of beans. This relatively new process concept makes wood more like coal. Torrefaction has attracted interest because it potentially enables higher rates of co-firing in existing pulverised-coal power plants and hence greater net CO2 emission reductions. Academic and entrepreneurial interest in torrefaction has sky rocketed in the last decade. Research output has focused on the many aspects of torrefaction – from detailed chemical changes in feedstock to globally-optimised production and supply scenarios with which to sustain EU emission-cutting directives. However, despite its seemingly simple concept, torrefaction has retained a somewhat mysterious standing. Why hasn’t torrefied pellet production become fully commercialised? The question is one of feasibility. This thesis addresses this question. Herein, the feasibility of torrefaction in co-firing applications is approached from three directions. Firstly, the natural limitations imposed by the structure of wood are assessed. Secondly, the environmental impact of production and use of torrefied fuel is evaluated and thirdly, economic feasibility is assessed based on the state of the art of pellet making. The conclusions reached in these domains are as follows. Modification of wood’s chemical structure is limited by its naturally existing constituents. Consequently, key properties of wood with regards to its potential as a co-firing fuel have a finite range. The most ideal benefits gained from wood torrefaction cannot all be realised simultaneously in a single process or product. Although torrefaction at elevated pressure may enhance some properties of torrefied wood, high-energy torrefaction yields are achieved at the expense of other key properties such as heating value, grindability, equilibrium moisture content and the ability to pelletise torrefied wood. Moreover, pelletisation of even moderately torrefied fuels is challenging and achieving a standard level of pellet durability, as required by international standards, is not trivial. Despite a reduced moisture content, brief exposure of torrefied pellets to water from rainfall or emersion results in a high level of moisture retention. Based on the above findings, torrefied pellets are an optimised product. Assessment of energy and CO2-equivalent emission balance indicates that there is no environmental barrier to production and use of torrefied pellets in co-firing. A long product transport distance, however, is necessary in order for emission benefits to exceed those of conventional pellets. Substantial CO2 emission reductions appear possible with this fuel if laboratory milling results carry over to industrial scales for direct co-firing. From demonstrated state-of-the-art pellet properties, however, the economic feasibility of torrefied pellet production falls short of conventional pellets primarily due to the larger capital investment required for production. If the capital investment for torrefied pellet production can be reduced significantly or if the pellet-making issues can be resolved, the two production processes could be economically comparable. In this scenario, however, transatlantic shipping distances and a dry fuel are likely necessary for production to be viable. Based on demonstrated pellet properties to date, environmental aspects and production economics, it is concluded that torrefied pellets do not warrant investment at this time. However, from the presented results, the course of future research in this field is clear.

Idiomit Ingo Schulzen romaanissa ”Adam und Evelyn” sekä sen suomennoksessa

Pro gradu -työni käsittelee idiomeja ja niiden kääntämistä. Tutkimusaineistona on Ingo Schulzen romaani ”Adam und Evelyn” (2008), sekä sen suomennos ”Adam ja Evelyn” (2011), jonka on laatinut suomentaja Jukka-Pekka Pajunen. Työn tarkoituksena on selvittää, miten paljon ja minkälaisia idiomeja kummassakin tekstissä esiintyy, sekä tarkastella, minkälaisia käännösratkaisuja suomentaja on käyttänyt. Työn teoriaosa jakautuu kahteen osaan. Ensin käsittelen idiomia yleisemmin, ja paneudun muun muassa idiomien piirteisiin ja luokitteluun. Sitten tarkastelen idiomia kääntämisen näkökulmasta. Aineiston analyysi on toteutettu lukemalla molemmat romaanit useaan otteeseen ja poimimalla vastaan tulleet idiomit erikseen kummastakin tekstistä. Luokittelen tutkimusaineistostani keräämäni idiomit Marja Nenosen (2002) mukaan verbillisiin, verbittömiin ja muihin idiomeihin. Käännösratkaisut jaan Rune Ingon (1990) mallin mukaan neljään luokkaan, jotka ovat: idiomi käännetty idiomilla, idiomi käännetty normaali-ilmauksella, idiomi käännetty sananmukaisesti ja normaali-ilmaus käännetty idiomilla. Lisäksi tapauksissa, joissa idiomi on käännetty idiomilla, tarkastelen, missä määrin lähtö- ja kohdekielinen idiomi vastaavat toisiaan. Lähtöhypoteesinani on, että idiomien suuren kielikohtaisuuden vuoksi suurin osa lähtökielisistä idiomeista on käännetty normaali-ilmauksella, ja että kuitenkin myös idiomilla kääntämistä esiintyy runsaasti. Idiomeja esiintyy kummassakin romaanissa runsaasti. Kummassakin tekstissä idiomeista ylivoimaisesti suurin osa lukeutuu verbillisiin idiomeihin. Normaali-ilmauksella kääntämistä on suomennoksessa käytetty ratkaisuna runsaasti, mutta idiomilla kääntäminen on kuitenkin aineistoni yleisin käännösratkaisu. Niinpä lähtöhypoteesini piti paikkansa vain osittain. Sananmukaisia käännöksiä esiintyy suomennoksessa vain vähän. Huomionarvoista on, että normaali-ilmauksen kääntäminen idiomilla, on aineistossani huomattavan yleinen käännösratkaisu.

Enhancement of ultrafiltration process by pretreatment in recovery of hemicelluloses from wood extracts

Hemicelluloses are potential raw material for several items produced in future wood-based biorefineries. One possible method for recovering hemicelluloses from wood extracts is ultrafiltration (UF). However, low filtration capacities and severe fouling restrict the use of tight UF membranes in the treatment of wood extracts. The lack of suitable commercial membranes creates a need for pretreatment which would decrease fouling and increase the filtration capacity. This thesis focuses on the evaluation of the possibility to improve the filtration capacity and decrease fouling with the pretreatment of wood extracts. Methods which remove harmful compounds and methods which degrade them are studied, as well as combinations of the methods. The tested pretreatments have an influence on both the concentration of different compounds and the molecular mass distribution of the compounds in the extract. This study revealed that in addition to which kind of compounds were removed, also the change in molecular size distribution affected the filtration capacity significantly. It was shown that the most harmful compounds for the filtration capacity of the hydrophobic 5 kDa membrane were the ones capable of permeating the membrane and fouling also the inner membrane structure. Naturally, the size of the most harmful compounds depends on the used UF membrane and is thus case-specific. However, in the choice of the pretreatment method, the focus should be on the removal of harmful compound sizes rather than merely on the total amount of removed foulants. The results proved that filtration capacity can be increased with both adsorptive and oxidative pretreatments even by hundreds of per cents. For instance, the use of XAD7 and XAD16 adsorbents increased the average flux in the UF of a birch extract from nearly zero to 107 kg/(m2h) and 175 kg/(m2h), respectively. In the treatment of a spruce extract, oxidation by pulsed corona discharge (PCD) increased the flux in UF from 46 kg/(m2h) to 158 kg/(m2h). Moreover, when a birch extract batch was treated with laccase enzyme, the flux in UF increased from 15 kg/(m2h) to 36 kg/(m2h). However, fouling was decreased only by adsorptive pretreatment while oxidative methods had a negligible or even negative impact on it. This demonstrates that filtration capacity and fouling are affected by different compounds and mechanisms. The results of this thesis show that filtration capacity can be improved and fouling decreased through appropriate pretreatment. However, the choice of the best possible pretreatment is case-specific and depends on the wood extract and the membrane used. Finding the best option requires information on the extract content and membrane characteristics as well as on the filtration performance of the membrane in the prevailing conditions and a multivariate approach. On the basis of this study, it can be roughly concluded that adsorptive pretreatment improves the filtration capacity and decreases fouling rather reliably, but it may lead to significant hemicellulose losses. Oxidation reduces the loss of valuable hemicelluloses and could improve the filtration capacity, but fouling challenges may remain. Combining oxidation with adsorptive pretreatment was not a solution for avoiding hemicellulose losses in the tested cases.

Förteckning öfver böcker, hufvudsakligen af juridiskt och oeconomiskt innehåll, som komma att genom auction försäljas i Helsingfors den 21 april och följande auctionsdagar 1838

Imprimatur: Carl N. Keckman.