Hygro-elasto-plastic behavior of planar orthotropic material

The mechanical and hygroscopic properties of paper and board are factors affecting the whole lifecycle of a product, including paper/board quality, production, converting, and material and energy savings. The progress of shrinkage profiles, loose edges of web, baggy web causing wrinkling and misregistration in printing are examples of factors affecting runnability and end product quality in the drying section and converting processes, where paper or board is treated as a moving web. The structural properties and internal stresses or plastic strain differences built up during production also cause the end-product defects related to distortion of the shape of the product such as sheet or box. The objective of this work was to construct a model capable of capturing the characteristic behavior of hygroscopic orthotropic material under moisture change, during different external in-plane stretch or stress conditions. Two independent experimental models were constructed: the elasto-plastic material model and the hygroexpansivity-shrinkage model. Both describe the structural properties of the sheet with a fiber orientation probability distribution, and both are functions of the dry solids content and fiber orientation anisotropy index. The anisotropy index, introduced in this work, simplifies the procedure of determining the constitutive parameters of the material model and the hygroexpansion coefficients in different in-plane directions of the orthotropic sheet. The mathematically consistent elasto-plastic material model and the dry solids content dependent hygroexpansivity have been constructed over the entire range from wet to dry. The presented elastoplastic and hygroexpansivity-shrinkage models can be used in an analytical approach to estimate the plastic strain and shrinkage in simple one-dimensional cases. For studies of the combined and more complicated effects of hygro-elasto-plastic behavior, both models were implemented in a finite element program for a numerical solution. The finite element approach also offered possibilities for studying different structural variations of orthotropic planar material, as well as local buckling behavior and internal stress situations of the sheet or web generated by local strain differences. A comparison of the simulation examples presented in this work to results published earlier confirms that the hygro-elasto-plastic model provides at least qualitatively reasonable estimates. The application potential of the hygro-elasto-plastic model is versatile, including several phenomena and defects appearing in the drying, converting and end-use conditions of the paper or board webs and products, or in other corresponding complex planar materials.

Intensification of Operation of Inclined Plate Settler at Fertilizer Plant

Fertilizer plant’s process waters contain high concentrations of nitrogen compounds, such as ammonium and nitrate. Phosphorus and fluorine, which originate from phosphoric acid and rock phosphate (apatite) used in fertilizer production, are also present. Phosphorus and nitrogen are the primary nutrients causing eutrophication of surface waters. At fertilizer plant process waters are held in closed internal circulation. In a scrubber system process waters are used for washing exhaust gases from fertilizer reactors and dry gases from granulation drums as well as for cooling down the fertilizer slurry in neutralization reactor. Solids in process waters are separated in an inclined plate settler by gravitational sedimentation. However, the operation of inclined plate settler has been inadequate. The aim of this thesis was to intensify the operation of inclined plate settler and thus the solids separation e.g. through coagulation and/or flocculation process. Chemical precipitation was studied to reduce the amount of dissolved species in process waters. Specific interest was in precipitation of nitrogen, phosphorus, and fluorine containing specimens. Amounts of phosphorus and fluorine were reduced significantly by chemical precipitation. When compared to earlier studies, annual chemical costs were almost eight times lower. Instead, nitrogen compounds are readily dissolved in water, thus being difficult to remove by precipitation. Possible alternative techniques for nitrogen removal are adsorption, ion exchange, and reverse osmosis. Settling velocities of pH adjusted and flocculated process waters were sufficient for the operation of inclined plate settler. Design principles of inclined plate settler are also presented. In continuation studies, flow conditions in inclined plate settler should be modelled with computational fluid dynamics and suitability of adsorbents, ion exchange resins, and membranes should be studied in laboratory scale tests.

Recovery boilers - history and future

Recovery boilers are built all over the world. The roots of recovery technology are longer than the roots of recovery boilers. But it wasn’t until the invention of recovery boilers before the Second World War that the pulping technology was revolutionalized. This led to long development of essentially the same type of equipment, culminating into units that are largest biofuel boilers in the world. Early recovery technology concentrated on chemical recovery as chemicals cost money and if one could recycle these chemicals then the profitability of pulp manufacture would improve. For pulp mills the significance of electricity generation from the recovery boiler was for long secondary. The most important design criterion for the recovery boiler was a high availability. The electricity generation in recovery boiler process can be increased by elevated main steam pressure and temperature or by higher black liquor dry solids as well as improving its steam cycle. This has been done in the modern Scandinavian units.

Bauksiittijätteen neutralointi- ja stabilointimenetelmät

Bauksiittijäte on alumiinin jalostuksessa syntyvä sivutuote, jonka alkalisuus on riski lähiympäristön ekosysteemeille. Alkalisuuden aiheuttamaan riskiin etsittiin ratkaisua perehtymällä bauksiittijätteen käsittelyyn. Kandidaatintyössä esitettiin eri menetelmiä bauksiittijätteen neutraloimiseksi, stabiloimiseksi ja varastoimiseksi. Menetelmien periaatteet määritettiin kirjallisuudesta löytyvien tutkimusten pohjalta, joiden perusteella voitiin määrittää toimivimmat menetelmät bauksiittijätteen käsittelemiseksi. Käytännöllisimmiksi käsittelymenetelmiksi osoittautuivat meriveden ja/tai hiilidioksidin lisääminen bauksiittijätteeseen sen neutraloimiseksi. Bauksiittijätteen stabiloimiseksi siihen tulee lisätä kiinteää materiaalia, kuten kalkkia, kiintoainepitoisuuden nostamiseksi sekä kovettuvien yhdisteiden muodostumiseksi.

Influence of multi-phase phenomena on semibatch crystallization processes of aqueous solutions

Crystal properties, product quality and particle size are determined by the operating conditions in the crystallization process. Thus, in order to obtain desired end-products, the crystallization process should be effectively controlled based on reliable kinetic information, which can be provided by powerful analytical tools such as Raman spectrometry and thermal analysis. The present research work studied various crystallization processes such as reactive crystallization, precipitation with anti-solvent and evaporation crystallization. The goal of the work was to understand more comprehensively the fundamentals, phenomena and utilizations of crystallization, and establish proper methods to control particle size distribution, especially for three phase gas-liquid-solid crystallization systems. As a part of the solid-liquid equilibrium studies in this work, prediction of KCl solubility in a MgCl2-KCl-H2O system was studied theoretically. Additionally, a solubility prediction model by Pitzer thermodynamic model was investigated based on solubility measurements of potassium dihydrogen phosphate with the presence of non-electronic organic substances in aqueous solutions. The prediction model helps to extend literature data and offers an easy and economical way to choose solvent for anti-solvent precipitation. Using experimental and modern analytical methods, precipitation kinetics and mass transfer in reactive crystallization of magnesium carbonate hydrates with magnesium hydroxide slurry and CO2 gas were systematically investigated. The obtained results gave deeper insight into gas-liquid-solid interactions and the mechanisms of this heterogeneous crystallization process. The research approach developed can provide theoretical guidance and act as a useful reference to promote development of gas-liquid reactive crystallization. Gas-liquid mass transfer of absorption in the presence of solid particles in a stirred tank was investigated in order to gain understanding of how different-sized particles interact with gas bubbles. Based on obtained volumetric mass transfer coefficient values, it was found that the influence of the presence of small particles on gas-liquid mass transfer cannot be ignored since there are interactions between bubbles and particles. Raman spectrometry was successfully applied for liquid and solids analysis in semi-batch anti-solvent precipitation and evaporation crystallization. Real-time information such as supersaturation, formation of precipitates and identification of crystal polymorphs could be obtained by Raman spectrometry. The solubility prediction models, monitoring methods for precipitation and empirical model for absorption developed in this study together with the methodologies used gives valuable information for aspects of industrial crystallization. Furthermore, Raman analysis was seen to be a potential controlling method for various crystallization processes.

Characterization of the filter media used in the dual media filter

The removal of organics from copper electrolyte solutions after solvent extraction by dual media filtration is one of the most efficient ways to ensure the clean electrolyte flow into the electrowinning. The clean electrolyte will ensure the good quality cathode plate production. Dual media filtration uses two layers of filter media for filtration as anthracite and garnet respectively. The anthracite layer will help the coalescing of the entrained organic droplets which will then float to the top of the filter, and back to the solvent extraction process. The garnet layer will catch any solids left in the electrolyte traveling through the filter media. This thesis will concentrate on characterization of five different anthracites in order to find some differences using specific surface area analysis, particle size analysis, and morphology analysis. These results are compared to the pressure loss values obtained from lab column tests and bed expansion behavior. The goal of the thesis was to find out if there were any differences in the anthracite which would make the one perform better than the other. There were no big differences found on any aspect of the particle characterization, but some found differences should be further studied in order to confirm the meaning of the porosity, surface area, intensity mean and intensity SD (Standard Deviation) on anthracites and their use in dual media filtration. The thesis work analyzed anthracite samples the way that is not found on any public literature sources, and further studies on the issue would bring more knowledge to the electrolyte process.

Kartoitus Kaakkois-Suomen jätelietteistä, lietteen tuottajista ja käsittelymenetelmistä

In this thesis the sludge of Southeastern-Finland, the companies which produce sludge and the current methods and those still in development have been surveyed. 85 % of the waste sludge from industry comes from forest industries. The sludge from municipal waste water treatment plants is mostly used as a raw material for bioplants. The sludge from forest industry is mostly incinerated. New circulation methods increase the recycling value of the waste by creating new products but they still lack a full-scale plant. The political pressure from Europe and the politics driven by the government of Finland will drive circular economy forward and thus uplifting the processing options of waste slurries. This work is divided in two parts, first contains the survey and the second contains the experimental part and the operational methods based on the survey. In the experimental part wet hard sheet waste sludge was de-watered with shaking filter and the applications for waste sludge from cellulose factory were considered. The results are, that the wet hard sheet waste sludge can be dewatered to high enough total solids content for the inteded use. Also, the cellulose waste sludge has too high Cd content in almost all of the batches to be used as a land improment.