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.

Transformações químicas da matéria orgânica durante a compostagem de resíduos da indústria madeireira

Composting of sawdust and paper mill sludge, using a "Kneer" process reactor, was studied in an attempt to elaborate upon organic matter (OM) transformation during the process and to define parameters to measure the compost maturity level. Temperature, electron paramagnetic resonance (EPR) data, ash and C, H, N and S contents, and a spectroscopic method using ultraviolet-visible (UV-VIS) for alkaline (pH = 8.5) and solid samples was used to study the maturity of the compost samples. These parameters were measured in 6 humic acids (HA) extracted from the compost samples during 29 days. The results of this work show that the "Kneer" process is efficient in transforming ligno-celulitic residues in a short time (29 days), into an organic fertilizer material with application perspectives.

Espectrofotometría de absorción atómica con tubo en la llama: aplicación en la determinación total de cadmio, plomo y zinc en aguas frescas, agua de mar y sedimentos marinos

Thermospray flame furnace Atomic Absorption Spectrometry (TS-FF-AAS) was used for the total determination of Cd, Pb and Zn in fresh water and seawater samples at µg L-1 levels, and in marine sediment samples at µg g-1 levels. Using a sample loop of 50 µL and a peristaltic pump the samples were transported into the metallic tube placed over an air/acetylene flame, through a ceramic capillary (o.d. = 3.2 mm) containing two parallel internal orifices (i.d = 0.5 mm). The detection limits determined for Cd, Pb and Zn using a synthetic water matrix (2.5% m/v NaCl, 0.5% m/v MgCl2 and 0.8% m/v CaCl2) were 0.32 µg L-1; 2.6 µg L-1 and 0.21 µg L-1 respectively. The methodology by TS-FF-AAS was validated by determination of Cd, Pb and Zn in certified reference materials of water and marine sediment, and the t-test for differences between means was applied. No statistically significant differences were established in fresh water and seawater (p>0.05), whereas differences became apparent in marine sediment (p<0.03).

Aplicação de lipases no tratamento de águas residuárias com elevados teores de lipídeos

The process of anaerobic digestion has been greatly developed during the last decades for the treatment of wastewater from food industries as for example, wastewaters from sugar and starch manufacturing and from breweries. However, for wastewaters which contain high amounts of fats and proteins, such as those from slaughterhouses and dairies, anaerobic digestion was found to be troublesome, due to the potential of sludge flotation, the formation of scum layers of lipids at the surface of the reactor, which are not digested and the toxicity of the intermediate compounds (long chain fatty acids) generated during the anaerobic digestion of the wastewater. The addition of hydrolytic enzymes, such as lipases prior to the anaerobic digestion can minimize these problems. In this work, this strategy is reviewed and the technical issues that must be considered in determining its feasibility are discussed.

Estudo do nitrogênio na combustão do gás natural

Nitrogen content in natural gas was studied in experimental and computational investigations to identify its influence on the emission level of exhaust gases from combustion facilities. Changes in natural gas composition with different N2 concentrations may result from introducing a new source gas into the system. An industrial burner fired at 75 kW, housed in a laboratory-scale furnace, was employed for runs where the natural gas/N2 proportion was varied. The exhaust and in-furnace measurements of temperature and gas concentrations were performed for different combustion scenarios, varying N2 content from 1-10 %v. Results have shown that the contamination of natural gas with nitrogen reduced the peak flame temperature, the concentration of unstable species, the NO X emission level and the heat transfer rate to the furnace walls, resulting from the recombination reactions.

Tratamento de chorume de aterro sanitário por fotocatálise heterogênea integrada a processo biológico convencional

The chemical and microbiological decomposition of the garbage deposited in landfills leads to the generation of a dark and malodorous liquid residue that shows a chemical composition of extreme variability and complexity. When matured, the leachates show low biodegradability, which makes it difficult to treat by conventional biological processes. In this work a new strategy for the treatment of landfill leachates is proposed, involving a preliminary treatment by heterogeneous photocatalysis followed by an activated sludge system. The results demonstrate that photochemical treatments of 60 and 90 min significantly enhance the leachates' biodegradability favoring subsequent biological treatment. The biodegradability rate (BOD/COD) was also greatly enhanced.

Uso de lodo de estação de tratamento de água centrifugado em matriz de concreto de cimento portland para reduzir o impacto ambiental

An alternative application of the humid sludge from the Passaúna WTP, located in Curitiba's metropolitan area, is proposed for concrete structures, partially replacing aggregates and cement. For the investigation, a reference concrete and four concrete mixtures with sludge were produced, and from these, two mixtures, containing 4% and 8% of sludge (m/m), were analyzed by different techniques: X ray fluorescence, X ray diffraction, thermo-gravimetric analysis, physicochemical analysis, compressive strength, etc. The properties were evaluated and the results indicate that the mixtures can be applied in different situations as cast structures for construction of concrete walls. Mixtures with more than 4% of sludge are restricted to applications where the workability of the concrete is not required, such as for residential pavements, sidewalks and stepping floors.

Determinação direta de molibdênio em comprimidos polivitamínicos por voltametria em meio não aquoso

Adsorptive stripping voltammetry carried out in a homogeneous ternary solvent composed of N,N-dimethylformamide, water and ethanol, with alpha-benzoinoxime (alphaBO) as the complexing agent for Mo(VI) and a 0.5 mol L-1 acetic acid - sodium acetate buffer as supporting electrolyte was successfully used for the determination of molybdenum in polyvitamin-polymineral tablets. Tablet samples were analyzed and the results were compared with those obtained both by graphite furnace atomic absorption and by recovery tests, with good correlations, indicating that this may be considered as an alternative procedure for routine determination of Mo(VI) in pharmaceutical samples.

Modern recovery boiler design criteria

Engineering and pricing of large recovery boiler were studied in this work. Engineering was carried out with Anita 4.2 which is an engineering program of Andritz. Key initial values were chosen with previous studies. Primary target of this work was to find out the consequences that furnace dimensions and furnace screen vertical part has to boiler pricing. Boilers that were engineered had different rate of furnace width and depth and different heat transfer plate count. Boiler balances were invariable. Boilers with different vertical screen construction were also calculated. First variation was boiler with vertical screen up to furnace roof. Other variation was to connect vertical screen to Pre-boiler generating bank inlet tubes. Total prices were calculated to engineered boilers. Pricing was sort out to heat transfers, high pressure pipes, steel structures, auxiliary equipments and civil/structural costs. This study did not notice parts of the boiler which costs do not vary with the construction of the boiler. Heat transfers had the largest share of costs. Boiler building had the most significant differences between the boilers. Furnace screen had also significant role especially to costs of the boiler building.

Decolorization and toxicity of municipal waste by horseradish (Cochlearia armoracia)

The Municipal Station of Americana, SP, Brazil, treats a volume of 400 l s-1 of effluent, of domestic and textile origin, and produces about 20 t of sludge per day. The plant horseradish, which contains high amount of peroxidases, was able to decolorize this effluent in 2 h and the solid waste in 2 days, at concentrations of 10 and 50%, respectively. However, there was an increase in the toxicity for the bioassays with Hydra attenuatta, Selenastrum capricornutum and lettuce seeds, indicating formation of more toxic substances. Since horseradish showed the ability to decolorize these residues, it can be used as pre-treatment resulting in a sludge of less complex composition.

Liuottajasäiliön hönkien käsittely täytekappalepesurilla

Soodakattilan liuottajasäiliön hönkä on ongelmallinen kaasu sen sisältävän suuren vesihöyrypitoisuuden, pölyn sekä rikkiyhdisteiden vuoksi. Nykyisin sitä ei voida johtaa ilmakehään käsittelemättömänä. Tässä diplomityössä kuvatun järjestelmän avulla liuottajasäiliön hönkä hävitetään soodakattilan tulipesässä. Liuottajasäiliöstä tulevasta höngästä poistetaan kosteutta sekä kiintoaineita jäähdyttämällä sitä täytekappalepesurissa. Tähän diplomityöhön liittyen suunniteltiin koeohjelma. Kokeiden tarkoituksena on tarkastella sekä hönkäpesurin että koko järjestelmän toimintaa erilaisilla kaasun ja nesteen virtauksilla. Lisäksi koeohjelmaan otettiin mukaan höngän esipesurin, sulan hajotushöyryn ja kiertonesteen lämmönsiirtimen toiminnan vaikutus koko järjestelmään. Diplomityössä kuvattujen kokeiden tuloksia ei julkaista tässä työssä. Lopuksi työssä on tarkasteltu höngän ja kiertonesteen laadun vaikutusta täytekappalepesurin sekä koko järjestelmän toimintaan.

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.

Balancing effluent quality, economic cost and greenhouse gas emissions during the evaluation of (plant-wide) control/operational strategies in WWTPs

The objective of this paper was to show the potential additional insight that result from adding greenhouse gas (GHG) emissions to plant performance evaluation criteria, such as effluent quality (EQI) and operational cost (OCI) indices, when evaluating (plant-wide) control/operational strategies in wastewater treatment plants (WWTPs). The proposed GHG evaluation is based on a set of comprehensive dynamic models that estimate the most significant potential on-site and off-site sources of CO2, CH4 and N2O. The study calculates and discusses the changes in EQI, OCI and the emission of GHGs as a consequence of varying the following four process variables: (i) the set point of aeration control in the activated sludge section; (ii) the removal efficiency of total suspended solids (TSS) in the primary clarifier; (iii) the temperature in the anaerobic digester; and (iv) the control of the flow of anaerobic digester supernatants coming from sludge treatment. Based upon the assumptions built into the model structures, simulation results highlight the potential undesirable effects of increased GHG production when carrying out local energy optimization of the aeration system in the activated sludge section and energy recovery from the AD. Although off-site CO2 emissions may decrease, the effect is counterbalanced by increased N2O emissions, especially since N2O has a 300-fold stronger greenhouse effect than CO2. The reported results emphasize the importance and usefulness of using multiple evaluation criteria to compare and evaluate (plant-wide) control strategies in a WWTP for more informed operational decision making

Comparison of a deterministic and a data driven model to describe MBR fouling

Membrane bioreactors (MBRs) are a combination of activated sludge bioreactors and membrane filtration, enabling high quality effluent with a small footprint. However, they can be beset by fouling, which causes an increase in transmembrane pressure (TMP). Modelling and simulation of changes in TMP could be useful to describe fouling through the identification of the most relevant operating conditions. Using experimental data from a MBR pilot plant operated for 462days, two different models were developed: a deterministic model using activated sludge model n°2d (ASM2d) for the biological component and a resistance in-series model for the filtration component as well as a data-driven model based on multivariable regressions. Once validated, these models were used to describe membrane fouling (as changes in TMP over time) under different operating conditions. The deterministic model performed better at higher temperatures (>20°C), constant operating conditions (DO set-point, membrane air-flow, pH and ORP), and high mixed liquor suspended solids (>6.9gL-1) and flux changes. At low pH (<7) or periods with higher pH changes, the data-driven model was more accurate. Changes in the DO set-point of the aerobic reactor that affected the TMP were also better described by the data-driven model. By combining the use of both models, a better description of fouling can be achieved under different operating conditions

Towards integrated operation of membrane bioreactors : effects of aeration on biological and filtration performance

Two experimental studies evaluated the effect of aerobic and membrane aeration changes on sludge properties, biological nutrient removal and filtration processes in a pilot plant membrane bioreactor. The optimal operating conditions were found at an aerobic dissolved oxygen set-point (DO) of 0.5mgO2L-1 and a membrane specific aeration demand (SADm) of 1mh-1, where membrane aeration can be used for nitrification. Under these conditions, a total flow reduction of 42% was achieved (75% energy reduction) without compromising nutrient removal efficiencies, maintaining sludge characteristics and controlled filtration. Below these optimal operating conditions, the nutrient removal efficiency was reduced, increasing 20% for soluble microbial products, 14% for capillarity suction time and reducing a 15% for filterability. Below this DO set-point, fouling increased with a transmembrane pressure 75% higher. SADm below 1mh-1 doubled the values of transmembrane pressure, without recovery after achieving the initial conditions