Offdesign operation of kraft recovery boiler

A model to solve heat and mass balances during the offdesign load calculations was created. These equations are complex and nonlinear. The main new ideas used in the created offdesign model of a kraft recovery boiler are the use of heat flows as torn iteration variables instead of the current practice of using the mass flows, vectorizing equation solving, thus speeding up the process, using non dimensional variables for solving the multiple heat transfer surface problem and using a new procedure for calculating pressure losses. Recovery boiler heat and mass balances are reduced to vector form. It is shown that these vectorized equations can be solved virtually without iteration. The iteration speed is enhanced by the use of the derived method of calculating multiple heat transfer surfaces simultaneously. To achieve this quick convergence the heat flows were used as the torn iteration parameters. A new method to handle pressure loss calculations with linearization was presented. This method enabled less time to be spent calculating pressure losses. The derived vector representation of the steam generator was used to calculate offdesign operation parameters for a 3000 tds/d example recovery boiler. The model was used to study recovery boiler part load operation and the effect of the black liquor dry solids increase on recovery boiler dimensioning. Heat flows to surface elements for part load calculations can be closely approximated with a previously defined exponent function. The exponential method can be used for the prediction of fouling in kraft recovery boilers. For similar furnaces the firing of 80 % dry solids liquor produces lower hearth heat release rate than the 65 % dry solids liquor if we fire at constant steam flow. The furnace outlet temperatures show that capacity increase with firing rate increase produces higher loadings than capacity increase with dry solids increase. The economizers, boiler banks and furnaces can be dimensioned smaller if we increase the black liquor dry solids content. The main problem with increased black liquor dry solids content is the decrease in the heat available to superheat. Whenever possible the furnace exit temperature should be increased by decreasing the furnace height. The increase in the furnace exit temperature is usually opposed because of fear of increased corrosion.

Heat transfer in superheaters of the bubbling fluidized bed boiler conversions

It is often reasonable to convert old boiler to bubbling fluidized bed boiler instead of building a new one. Converted boiler consists of old and new heat surfaces which must be fitted to operate together. Prediction of heat transfer in not so ideal conditions sets challenges for designers. Two converted boilers situated in Poland were studied on the grounds of acceptance tests and further studies. Calculation of boiler process was performed with boiler design program. Main interest was heat transfer in superheaters and factors affecting it. Theory for heat transfer is presented according to information found from literature. Results obtained from experimental studies and calculations have been compared. With correct definitions calculated parameters corresponded well to measured data at boiler maximum design load. However overload situations revealed to be difficult to model at least without considering changes in the combustion process which requires readjustments to the design program input values.

Predicting overall service quality: a structural equation modelling approach

In this article, the results of a modified SERVQUAL questionnaire (Parasuraman et al., 1991) are reported. The modifications consisted in substituting questionnaire items particularly suited to a specific service (banking) and context (county of Girona, Spain) for the original rather general and abstract items. These modifications led to more interpretable factors which accounted for a higher percentage of item variance. The data were submitted to various structural equation models which made it possible to conclude that the questionnaire contains items with a high measurement quality with respect to five identified dimensions of service quality which differ from those specified by Parasuraman et al. And are specific to the banking service. The two dimensions relating to the behaviour of employees have the greatest predictive power on overall quality and satisfaction ratings, which enables managers to use a low-cost reduced version of the questionnaire to monitor quality on a regular basis. It was also found that satisfaction and overall quality were perfectly correlated thus showing that customers do not perceive these concepts as being distinct

A three dimensional study of heat transfer in a supercritical circulating fluidized bed combustor

From the boiler design point of view, it is imperative to know and understand the operation of the boiler. Since comprehensive measurement of a large furnace is impossible, the furnace can be modeled in order to study its behavior and phenomena. This requires the used model to be validated to correspond with the physical furnace behavior. In this thesis, a three dimensional furnace model is validated to match a bituminous coal utilizing, supercritical once-through circulating fluidized bed combustor based on measurement data. The validated model is used for analyzing the furnace heat transfer. Other heat transfer analysis methods are energy balance method based on tube surface temperature measurements and a method based on measured temperature difference between the tube crest and the fin. The latter method was developed in the thesis using Fluent-software. In the theory part, literature is reviewed and the fundamental aspects of circulating fluidized bed are discussed. These aspects are solid particle behavior in fluidization known as hydrodynamics, behavior of fuel and combustion and heat transfer. Fundamental aspects of modeling are also presented.

Analytical investigation of the atmospheric radiation limits in semigray atmospheres in radiative equilibrium

We model the wavelength-dependent absorption of atmospheric gases by assuming constant mass absorption coefficients in finite-width spectral bands. Such a semigray atmosphere is analytically solved by a discrete ordinate method. The general solution is analyzed for a water vapor saturated atmosphere that also contains a carbon dioxide-like absorbing gas in the infrared. A multiple stable equilibrium with a relative upper limit in the outgoing long-wave radiation is found. Differing from previous radiative–convective models, we find that the amount of carbon dioxide strongly modifies the value of this relative upper limit. This result is also obtained in a gray (i.e., equal absorption of radiation at all infrared wavelengths) water vapor saturated atmosphere. The destabilizing effect of carbon dioxide implies that massive carbon dioxide atmospheres are more likely to reach a runaway greenhouse state than thin carbon dioxide ones

Arinakattilan lämmönsiirron laskentamallin kehittäminen

Kattilalaitosten polttoaineen syötössä ilmenevät häiriöt ja biopolttoaineiden laatuvaihtelut aiheuttavat epävakaata palamista ja tekevät prosessin hallinnasta vaikeampaa. Polttoaineen laatuvaihtelut vaikuttavat koko prosessiin ja näkyvät lopulta myös höyryntuotannossa. Kompensoinnilla pyritään estämään häiriöiden suuret vaikutukset höyryn tuotantoon. Tarkoituksena on saada kattilan toiminta ja tehon tuotanto tasaisemmaksi ja helpommin hallittavaksi. Tässä diplomityössä tarkastellaan polttoaineen ominaisuuksien, säteilylämmönsiirron sekä säätöjen vaikutusta toisiinsa ja merkitystä kattilan toiminnan kannalta. Työssä muodostetaan säteilylämmönsiirron laskentamalli arinakattilan tulipesälle käyttäen hyväksi hyvin sekoittuneen tulipesän menetelmää. Menetelmällä voidaan määrittääsavukaasujen keskimääräinen lämpötila tulipesässä, lämpövirta tulipesän seiniin tai poltossa vapautuva lämpöteho. Mallin avulla voidaan paremmin ymmärtää prosessin käyttäytymistä polttoaineen laadun muuttuessa sekä helpottaa ja nopeuttaa kattilan käyttäytymisen ennustamista. Laskentamalli tehtiin Excel –laskentaohjelmaan, jossa se testataan. Verifioinnin jälkeen malli on tarkoitus siirtää toimimaan apros –simulointiympäristöön.

Foam-forming properties of Ilex paraguariensis (mate) saponin: foamability and foam lifetime analysis by Weibull equation

Saponins are natural soaplike foam-forming compounds widely used in foods, cosmetic and pharmaceutical preparations. In this work foamability and foam lifetime of foams obtained from Ilex paraguariensis unripe fruits were analyzed. Polysorbate 80 and sodium dodecyl sulfate were used as reference surfactants. Aiming a better data understanding a linearized 4-parameters Weibull function was proposed. The mate hydroethanolic extract (ME) and a mate saponin enriched fraction (MSF) afforded foamability and foam lifetime comparable to the synthetic surfactants. The linearization of the Weibull equation allowed the statistical comparison of foam decay curves, improving former mathematical approaches.

Electrocatalytic oxidation of methanol by the [Ru3O(OAc)6(py)2(CH3OH)]3+cluster: improving the metal-ligand electron transfer by accessing the higher oxidation states of a multicentered system

The [Ru3O(Ac)6(py)2(CH3OH)]+ cluster provides an effective electrocatalytic species for the oxidation of methanol under mild conditions. This complex exhibits characteristic electrochemical waves at -1.02, 0.15 and 1.18 V, associated with the Ru3III,II,II/Ru3III,III,II/Ru 3III,III,III /Ru3IV,III,III successive redox couples, respectively. Above 1.7 V, formation of two RuIV centers enhances the 2-electron oxidation of the methanol ligand yielding formaldehyde, in agreement with the theoretical evolution of the HOMO levels as a function of the oxidation states. This work illustrates an important strategy to improve the efficiency of the oxidation catalysis, by using a multicentered redox catalyst and accessing its multiple higher oxidation states.

Solving Schrödinger equation for two dimensional potentials using supersymmetry

The formalism of supersymmetric Quantum Mechanics can be extended to arbitrary dimensions. We introduce this formalism and explore its utility to solve the Schrödinger equation for a bidimensinal potential. This potential can be applied in several systems in physical and chemistry context , for instance, it can be used to study benzene molecule.

Electron transfer by singlet excited state of porphyn and electron acceptor affinity in rigid medium: photoacoustic phase angle analysis

Photoacoustic spectroscopy provides information about both amplitude and phase of the response of a system to an optical excitation process. This paper presents the studies of the phase in the electron transfer process between octaethylporphyn (OEP) and quinone molecules dispersed in a polymeric matrix. It was observed a tendency in the phase behavior to small values only in the spectral region near to 620 nm, while for shorter wavelength did not show any tendency. These measurements suggested that the electron transfer to acceptor occurred with the participation of octaethylporphyn singlet excited state.

Electron migration in DNA matrix: an electron transfer reaction

This paper brings an active and provocative area of current research. It describes the investigation of electron transfer (ET) chemistry in general and ET reactions results in DNA in particular. Two DNA intercalating molecules were used: Ethidium Bromide as the donor (D) and Methyl-Viologen as the acceptor (A), the former intercalated between DNA bases and the latter in its surface. Using the Perrin model and fluorescence quenching measurements the distance of electron migration, herein considered to be the linear spacing between donor and acceptor molecule along the DNA molecule, was obtained. A value of 22.6 (± 1.1) angstroms for the distance and a number of 6.6 base pairs between donor and acceptor were found. In current literature the values found were 26 angstroms and almost 8 base pairs. DNA electron transfer is considered to be mediated by through-space interactions between the p-electron-containing base pairs.

Role of culture in knowledge transfer and sharing - case ERP implementation

The main objective of this study was to examine how culture influences knowledge transfer and sharing within multicultural ERP project implementation in China. The main interest was to explain how national culture and knowledge are linked by understanding how culture influences knowledge transfer and sharing in a project organization. The other objective of this work was to discuss what Chinese cultural characteristic inhibit and en-hance knowledge sharing in ERP project. The perspective of this study was qualitative and the empirical material was collected from theme interviews among Stora Enso employees. Conclusion of this thesis is that Finns have a very direct style of communication and sharing knowledge whereas Chinese respect face shaving and indirect communication. Another conclusion is that knowledge sharing does not “just happen”, it is needed that project members understand national culture to get all project members commitment to project. In China most important is understand local business processes and understand role of trust and guanxi.

Mathematical equation correction to spectral and transport interferences in high-resolution continuum source flame atomic absorption spectrometry: determination of lead in phosphoric acid

In this work, a new mathematical equation correction approach for overcoming spectral and transport interferences was proposed. The proposal was applied to eliminate spectral interference caused by PO molecules at the 217.0005 nm Pb line, and the transport interference caused by variations in phosphoric acid concentrations. Correction may be necessary at 217.0005 nm to account for the contribution of PO, since Atotal217.0005 nm = A Pb217.0005 nm + A PO217.0005 nm. This may be easily done by measuring other PO wavelengths (e.g. 217.0458 nm) and calculating the relative contribution of PO absorbance (A PO) to the total absorbance (Atotal) at 217.0005 nm: A Pb217.0005 nm = Atotal217.0005 nm - A PO217.0005 nm = Atotal217.0005 nm - k (A PO217.0458 nm). The correction factor k is calculated from slopes of calibration curves built up for phosphorous (P) standard solutions measured at 217.0005 and 217.0458 nm, i.e. k = (slope217.0005 nm/slope217.0458 nm). For wavelength integrated absorbance of 3 pixels, sample aspiration rate of 5.0 ml min-1, analytical curves in the 0.1 - 1.0 mg L-1 Pb range with linearity better than 0.9990 were consistently obtained. Calibration curves for P at 217.0005 and 217.0458 nm with linearity better than 0.998 were obtained. Relative standard deviations (RSD) of measurements (n = 12) in the range of 1.4 - 4.3% and 2.0 - 6.0% without and with mathematical equation correction approach were obtained respectively. The limit of detection calculated to analytical line at 217.0005 nm was 10 µg L-1 Pb. Recoveries for Pb spikes were in the 97.5 - 100% and 105 - 230% intervals with and without mathematical equation correction approach, respectively.

Leaf-Targeted Ferredoxin-NADP+-Oxidoreductase (FNR): Electron Transfer Properties and Thylakoid Association in Arabidopsis thaliana

Photosynthetic reactions are divided in two parts: light-driven electron transfer reactions and carbon fixation reactions. Electron transfer reactions capture solar energy and split water molecules to form reducing energy (NADPH) and energy-carrying molecules (ATP). These end-products are used for fixation of inorganic carbon dioxide into organic sugar molecules. Ferredoxin-NADP⁺ oxidoreductase (FNR) is an enzyme that acts at the branch point between the electron transfer reactions and reductive metabolism by catalyzing reduction of NADP+ at the last step of the electron transfer chain. In this thesis, two isoforms of FNR from A rabidopsis thaliana, FNR1 and FNR2, were characterized using the reverse genetics approach. The fnr1 and fnr2 mutant plants resembled each other in many respects. Downregulation of photosynthesis protected the single fnr mutant plants from excess formation of reactive oxygen species (ROS), even without significant upregulation of antioxidative mechanisms. Adverse growth conditions, however, resulted in phenotypic differences between fnr1 and fnr2. While fnr2 plants showed downregulation of photosynthetic complexes and upregulation of antioxidative mechanisms under low-temperature growth conditions, fnr1 plants had the wild-type phenotype, indicating that FNR2 may have a specific role in redistribution of electrons under unfavorable conditions. The heterozygotic double mutant (fnr1xfnr2) was severely devoid of chloroplastic FNR, which clearly restricted photosynthesis. The fnr1xfnr2 plants used several photoprotective mechanisms to avoid oxidative stress. In wild-type chloroplasts, both FNR isoforms were found from the stroma, the thylakoid membrane, and the inner envelope membrane. In the absence of the FNR1 isoform, FNR2 was found only in the stroma, suggesting that FNR1 and FNR2 form a dimer, by which FNR1 anchors FNR2 to the thylakoid membrane. Structural modeling predicted formation of an FNR dimer in complex with ferredoxin. In this thesis work, Tic62 was found to be the main protein that binds FNR to the thylakoid membrane, where Tic62 and FNR formed high molecular weight complexes. The formation of such complexes was shown to be regulated by the redox state of the chloroplast. The accumulation of Tic62-FNR complexes in darkness and dissociation of complexes from the membranes in light provide evidence that the complexes may have roles unrelated to photosynthesis. This and the high viability of fnr1 mutant plants lacking thylakoid-bound FNR indicate that the stromal pool of FNR is photosynthetically active.