Teses / dissertações sobre o tema "Chemical pulp mill"

The photooxidation of a Thermo-Mechanical (TM) pulp and paper mill effluent with hydrogen peroxide $ rm(H sb2O sb2)$ was investigated at different experimental conditions by using a batch photochemical reactor operating at a dominant UV light wavelength of 253.7 nm. Photolysis of $ rm H sb2O sb2$ produces hydroxyl radicals ($ cdot$OH), which are very powerful oxidizing species. The effluent consisted of a "heat condensate" obtained from toxic vapors generated during various stages of the pulping process. Several operational parameters were varied and their effects on the process were observed and analyzed, in order to achieve its optimization. In addition, heterogeneous photocatalysts such as cupric oxide (CuO) were also investigated as a complement to the photooxidation process.
The main parameter used to determine the quality of the wastewater before and after photooxidation was the Chemical Oxygen Demand (COD), using a closed reflux standard procedure. COD values of the treated solution were determined at subsequent time intervals and used to draw curves illustrating the rate of oxidation of the wastewater. Other parameters, such as Dissolved Organic Carbon (DOC) and dissolved lignin concentration, were investigated towards the end of the research in order to obtain a more complete characterization of the quality of the wastewater after treatment.
The experimental data reveal that there is an optimal $ rm H sb2O sb2$ concentration that is best suited for the photooxidation of the effluent. Moreover, an increase in temperature accelerates the rate of elimination of COD. An increase in effluent concentration is detrimental to the speed of the process, since it causes an increase in its absorbance which can act as a barrier against UV light. The efficiency of the photooxidation process is not affected by variations in the initial pH of the wastewater. Cupric oxide (CuO), when exposed to UV light, efficiently catalyzes the production of OH radicals and is therefore very beneficial to the photooxidation process.

The secondary milling circuit at Waterval UG2 Concentrator had undergone a circuit change with the commissioning of the IsaMill, a horizontally stirred mill, in parallel with the secondary ball mill. The operation treats the PGM bearing UG2 ore type and produces a final concentrate enriched with PGM's. The concept was to treat the finer silicate rich fraction in the IsaMill and the coarser chromite rich fraction through the ball mill. This circuit is typical of a UG2 plant in which maximum silicate with minimal chromite breakage is targeted. As a result of the circuit change an opportunity for optimisation around the industrial scale ball mill was considered for this study. Of concern in this study were new operating conditions for the mill in the changed circuit at which improved performance could be obtained. Another objective was to investigate if a difference in breakage response for the silicate and chromite fractions could be identified for different operating conditions in the ball mill. The secondary mill at Waterval UG2 Concentrator was already fitted with an online ball and pulp load sensor, the Sensomag. The information obtained from the sensor is in the form of shoulder and toe positions for the ball and pulp filling in the rotating ball mill. The mill was surveyed at various ball filling and mill % solids conditions and information from the online sensor was used to understand the mill performance, particularly with regards to mill load behaviour. Hence a final objective was to demonstrate that the information obtained from the online sensor could be related to mill operating conditions. The sensor output was envisioned to eventually form part of the mill control philosophy. Samples were taken of the mill feed and discharge streams at the different operating conditions and analysed for grind as well as PGM and Cr₂O₃ content. The majority of the PGM's in the UG2 ore are in the silicates and thus the PGM distribution results would indicate the amount of breakage in the silicate fraction. Cr₂O₃ is used as an indicator of the chromite content in UG2 ore. In order to identify optimum mill performance the results were analysed using different measures which include general grind, particle and species distributions, reduction ratios, sieve efficiencies and specific energy. By comparing the results the differences and limitations of certain techniques were identified. It was found that the mill performance varied at different operating conditions. The optimum ball filling was found to be around 30%, which is similar to site operational target. The optimal % solids for this mill however seems to be higher than what the mill is typically operated at. No peak in % solids for mill performance was obtained. Scope exists to determine how far from the investigated maximum of 75% solids (by mass) does the optimum in-mill density lie for this mill. Thus new optimum conditions in terms of % solids do exist for the mill in the modified circuit. Results also showed that the size reduction of the silicates increased with an increase in mill % solids and ball filling degree. For chromite, the mill % solids did not appear to have any effect at low ball fillings, but a slight shift was observed at the higher ball fillings tested. The trend suggests that the size reduction of both silicates and chromite increased with an increase in ball filling, albeit at different rates. Finally, the test work has demonstrated that the online sensor outputs can be related to mill performance. Differences in shoulder and toe positions for the ball and pulp loads were distinct between operating conditions. Improved grind performance was observed at conditions that resulted in lower free pulp angles. Thus the sensor could be used as a control tool to identify and maintain optimum mill operational conditions. The Sensomag should be incorporated into a mill controller that looks at more than just mill ball filling. Conditions that result in optimum mill efficiency can be identified and the mill may be controlled using the sensor data. It is recommended that the mill continue to be run at 30% ball filling and at higher mill % solids than the maximum reached in this work.

The objective of this dissertation was to develop a process for the production of acetic acid in kraft mills. Acetyl groups in hardwood can be hydrolyzed using alkali at 50 °C. The product from this process contains about 15 g/L of sodium acetate and was determined to be suitable for the production of acetic acid.

Experiments performed using aqueous sodium acetate to evaluate the ability of electrodialysis (ED) to separate and concentrate sodium acetate showed that sodium acetate can be concentrated up to 275 g/L starting with an initial concentration of 17 g/L. The transport of water with sodium and acetate ions through ED membranes limited the maximum obtainable concentration.

To avoid the deleterious effects of white liquor on ED, selectivity experiments were performed using synthetic oxidized white liquor extract. These experiments showed a decrease in the efficiency of ED process due to the presence of sodium carbonate and sodium sulphate in the extract. Hence, it was concluded that caustic should be used as the extraction solvent.

Bi-polar electrodialysis (BPMED) experiments performed using sodium acetate showed that up to 200-280 g/L of acetic acid can be produced using BPMED. Although higher concentrations of sodium hydroxide can also be produced using BPMED, 30 g/L concentration was considered to be sufficient for recycle to the extraction process.

Feed and bleed mode BPMED experiments were performed to determine the current efficiencies and the suitable inlet concentration of sodium acetate for the production of up to 200 g/L of acetic acid. Both feed and bleed mode and batch experiments showed that the current density was the major driving force for BPMED.

Two types of concentrated wood extracts; namely (1) clarified and (2) unclarified were prepared with and without the lignin removal pre-treatment, respectively. The results of the ED and BPMED experiments performed using these extracts were similar to those of the synthetic sodium acetate. A major difference involved an increase of about 15% in electric energy consumption arising from the transport of formate, lactate and glycolate salts. The color of the anionic membranes slightly changed after processing unclarified extract through ED and BPMED.

Sustainability of resources such as energy, water and waste have become important drivers in our current economy. For large industries that are water and energy intensive like pulp and paper (P&P) mills, this is a specifically relevant issue. The large and heterogenous volumes of effluents in P&P mills make it a difficult task to properly treat before discharge. Anaerobic digestion is an efficient wastewater technology that cleans the effluent, reduces wasted sludge and simultaneously produces methane that can be further used as energy. The research work described in this thesis aims to enhance the methane production from the anaerobic digestion of different chemical P&P mill effluents. Through effluent characterization, variability of process parameters, promoting agents and the assessment of biochemical methane potential (BMP) tests, the benefits of three potential methods to enhance methane yields of wastewaters were evaluated. In addition, the conversion of chemical pulp fibers directly to methane was explored. The attained results described the different improvements that can be made to enhance methane production. Easily degradable effluents such as hydrolyzed filtrates and evaporator condensates contain high concentrations of sugars and acetic acid respectively, which could encourage an oversaturation of acids during acidogenesis. An inoculum to substrate ratio (ISR) of 2 proved to be the optimal in order to add the required buffering capacity to neutralize the pH and produce significantly high methane yields of up to 333 mLCH4/gVS. The high productivity of these effluents can be then considered for co-digestion with harder to treat effluents such as lignin-rich streams. Lignin clearly hinders methane production indicated by the negative linear correlation found between lignin content and methane yield. The co-digestion of lignin-rich effluent with evaporator condensates from neutral sulfite semi-chemical (NSSC) pulping proved to enhance the overall methane productivity of the mill´s wastewater treatment. Furthermore, the assessment of hydrotalcites (HT) addition indicated a contribution towards an increase in methane yield, faster production rates and a greater lignin removal. The poor performance of calcined HT suggests that the advantages of HT addition came from the layered sheet structure. Finally, besides establishing the methane potential in various P&P effluents, the examination of methane productivity of different pulp fibers and its products proved to be a promising new energy alternative to explore. Brown, oxygen delignified and bleached pulp gathered biodegradabilities of up to 90% and methane yields as high as 380 mLCH4/gVS. With the current changing bio-economy this last approach paves the way in exploring alternative and novel uses for chemical pulp mill products.
La sostenibilidad en la gestión de recursos como la energía, el agua y los residuos se ha convertido en un aspecto clave en nuestra economía actual. Para grandes industrias que consumen mucha agua y energía, como la industria de pulpa y papel (P&P) este es un tema especialmente relevante. Los grandes y heterogéneos volúmenes de efluentes que producen las fábricas de P&P hacen que su adecuado tratamiento sea una tarea difícil. La digestión anaerobia es una tecnología eficiente para el tratamiento de aguas residuales; que limpia el efluente, reduce el lodo producido y simultáneamente produce metano que puede usarse como fuente de energía. El objetivo del trabajo de investigación descrito en esta tesis es aumentar la producción de metano a partir de la digestión anaerobia de diferentes efluentes producidos en fábricas de pulpa. A través de la caracterización del efluente, determinación de parámetros del proceso, agentes promotores y la evaluación de pruebas de producción de metano bioquímico se evaluaron los beneficios de tres métodos potenciales para mejorar los rendimientos de metano de los efluentes. Asimismo, se exploró la conversión directa de fibras de pulpa química a metano. Los efluentes fácilmente degradables, como los filtrados hidrolizados y los condensados del evaporador, contienen altas concentraciones de azúcares y ácido acético, respectivamente, lo que podría provocar una sobresaturación de ácidos durante la acidogénesis. Se ha demostrado que una relación de inóculo a sustrato de 2 resulta óptima para aumentar la capacidad tampón del sistema y neutralizar el pH y producir rendimientos de metano significativamente altos, de hasta 333 mLCH4/gVS. La alta productividad de estos efluentes hace que se puedan considerar para la co-digestión con efluentes más difíciles de tratar, como las aguas ricas en lignina. Claramente la lignina obstaculiza la producción de metano, tal y como indica la correlación lineal negativa encontrada entre el contenido de lignina y el rendimiento de metano. La co-digestión del efluente rico en lignina con el condensado de evaporadores de pulpa semi-química de sulfito ha demostrado mejorar la productividad de metano en el tratamiento de aguas residuales de la planta. Además, la adición de hidrotalcitas (HT) como catatlizadores contribuye hacia un aumento en la producción de metano, tasas de producción más rápidas y una mayor eliminación de lignina. Con HT calcinadas se han obtenido rendimientos bajos, lo que sugiere que las ventajas de la adición de HT provienen de su estructura laminar. Finalmente, además de establecer el potencial de metano que existen en los efluentes de P&P, la evaluación de la productividad de metano de diferentes fibras de pulpa y sus productos ha demostrado ser una nueva alternativa energética para explorar. El uso de pulpa blanqueada, sin blanquear y deslignificada con oxígeno muestran biodegradabilidades de hasta 90% y rendimientos de metano de hasta 380 mLCH4/gVS. Con la cambiante bioeconomía actual, este último enfoque estimula la exploración de usos alternativos y novedosos para productos de plantas de pulpa química.

Abstract This thesis aims to increase our knowledge about the characteristics of chemical pulp process and wastewaters and how problematic substances, e.g. wood extractives, could be removed effectively and selectively by coagulation–flocculation with either internal or external water treatment. Characterization was performed by investigating kraft pulp bleaching filtrates, as well as wastewater, before (influent) and after (effluent) the activated sludge treatment by means of a range of chemical analyses and by carrying out size fractionation studies. Cationic polyelectrolytes were used to purify oxygen stage bleaching filtrate, and charge analyses (zeta potential, charge quantity) were carried out in order to understand the coagulation phenomenon. In activated sludge treatment, the enhancement of particle removal, either by filtration or using a chemical in the primary clarifier, would lead to savings in aeration costs and result in a more stable process. Microfiltration already with a large pore size (8 µm) removed 30–50% of the wood extractives from the influent. Separate treatment stages for certain wastewater fractions, e.g. debarking plant effluent, would ensure cost-efficiency. After the activated sludge process, the wood extractives were present as particles (18%) and < 3 kDa fraction (82%). β-sitosterol occurred only in particles in the effluent. The release of harmful components into the environment could be decreased by microfiltration (e.g. 0.45 µm) of the final effluent or using a chemical in the secondary clarifier. Interestingly a huge increase in BOD was realized in the 3 kDa fraction of both influent and effluent, which indicated the presence of toxic substances in the larger fractions. After passing the effluent into the water system, there might be a similar jump in the BOD because the effluent is diluted many-fold. This would contribute to the formation of areas with an oxygen deficit. In the coagulation–flocculation studies, effective and selective removal of wood extractives (92%) from the oxygen stage filtrate was obtained with a cationic polyelectrolyte of medium molecular weight and medium charge density at 72 °C and pH 5–6. The multimodal zeta potential distribution gave more information than the average zeta potential. Aggregation of colloidal particles occurred when only one zeta potential was observed. The number of different zeta potentials diminished with decreasing pH and after exceeding a certain polyelectrolyte dosage level.

De 20 största massabruken i Sverige släpper tillsammans ut ungefär 20 miljoner ton CO2 per år. Dessa utsläpp har biogent ursprung och anses därför vara klimatneutrala. Massa- och pappersindustrin är därmed en lämplig kandidat för implementeringen av BECCS (eng. Bioenergy with Carbon Capture and Storage) och har en betydande potential att nå de, av den svenska regeringen, uppsatta klimatmålen som säger att Sverige inte ska några nettoutsläpp av växthusgaser till atmosfären senast år 2045. I detta examensarbete simulerades kemiska absorptions- och desorptionsprocesser med MEA som lösningsmedel genom att tillämpa den hastighetsbaserade metoden i en rigorös modell i Aspen Plus. Stripper- och absorptionsmodellerna validerades innan standardprocessen modifierades till en konfiguration som möjliggör värmeintegration av koldioxidinfångningens överskottsvärme med, exempelvis, ett sulfatmassabruk. Avskiljningsgraden och laddning hos den mättade lösningen användes som prestandaindikatorer för att validera absorptionskolonnerna. Återkokarens energiåtgång och laddning hos den omättade lösningen användes somprestandaindikatorer för att validera stripperkolonnerna. Samtliga kolonner dimensionerades för att erhålla 90 vikt% avskiljningsgrad. Olika flödeshastigheter av lösningsmedlet testades för att säkerställa effektivt nyttjande av packningen i absorptions- och stripperkolonnerna. Lämpliga temperaturnivåer för värmeintegration, inom och utanför, koldioxidinfångningen erhölls genom att utvärdera olika varianter av en stripper-overhead-kompression konfiguration. Utvärderingen av den modifierade MEA processen tog hänsyn till potentialen för ångbesparing och energieffektivisering. Resultat från simuleringarna tyder på att den modifierade strippern skulle kunna ge besparingar på upp emot 11 % i ånganvändning. Energibesparingar i samma storleksordning kunde även erhållas genom värmeintegration mellan koldioxidinfångningen och en särskild process i ett referensbruk. Implementering av BECCS-konceptet på det här sättet skulle därmed kunna bli ett mer attraktivt alternativ för den svenska massa- och pappersindustrin att bekämpa klimatförändringarna.
The 20 largest pulp mills in Sweden emit around 20 million tonnes of CO2 per year. These emissions are considered carbon-neutral since they originate from biogenic sources. The pulp and paper industry is therefore a good candidate for the application of BECCS (Bioenergy with Carbon Capture and Storage) and has the potential to play a significant role for reaching the long-term mitigation target set by the Swedish government that Sweden should be climate-neutral by year 2045. In this thesis, a MEA-based chemical absorption and desorption process was rigorously modelled in Aspen Plus using the rate-based method. Validation of the absorber and stripper model was conducted before the standard process was modified to a configuration that enables heat integration of a significant amount of excess heat from the capture process in, for example, a Kraft pulp mill. CO2 removal rate and rich solvent loading were used as performance indicators to validate the absorber columns. The reboiler duty and lean solvent loading served as performance indicators in the stripper validation. The columns were dimensioned considering 90 wt% capture rate. Efficient use of the entire packing in the absorber and stripper columns was ensured by testing different solvent flow rates. Suitable temperature levels for heat integration, within and across the capture plant, were obtained through an assessment of different versions of a stripper overhead compression configuration. The evaluation of the modified MEA processes took into account the steam conservation potential and energy efficiency potential. The simulation results indicate that the modified stripper may lead to savings of up to 11% in steam consumption. Heat integration between the capture plant and a specific process in a reference Kraft pulp mill resulted in energy savings of the same order of magnitude. Thereby, making the BECCS concept a more attractive solution for the Swedish pulp and paper industry to mitigate climate change.

The use of ultrafiltration (UF) to treat pulp mill effluents is limited by fouling of membrane surfaces and pores. In prior studies with pulp mill effluents, no efforts were made to relate the molecular-size distribution of the solute molecules to the membrane fouling mechanisms. This dissertation presents a novel protocol for obtaining certain essential size distribution parameters, such as, the average molecular weight (M(w)), average molecular number (M(n)) and heterogeneity index (HI) to describe complex industrial wastewaters including the extraction (E)-stage effluent. This novel molecular sizing protocol was verified using challenge solutions containing solutes of known molecular weight. In these tests, the measured M(w)'s were within ±5% of the expected M(w)'s. A comprehensive model to describe the UF membrane productivity during the treatment of E-stage effluent was developed. This model accounts for variations in membrane, feed water and operational variables. The feed water variables that were incorporated into the model include molecular size distribution, viscosity and concentration. Also, included in the model are the operational variables such as trans-membrane pressure and cross-flow velocity. This model predicted the fluxes for the E- and oxygenated E-stage (E₀) effluents within an error of 9%. The UF membrane fouling by E-stage effluent was quantified employing fouling potential factors. An increase in the molecular weight cut-off (MWCO) of the membranes resulted in increased irreversible fouling possibly by increased pore plugging. Lower irreversible fouling was observed for pulp mill effluents with high M(w)'s. The role of surfactants in reducing the membrane fouling was also discussed. The ratio of M(w) of feed wastewater to the MWCO of the membrane, denoted by λ, effectively represents the ratio of the average diameter of the solute molecule to the nominal diameter of the pore. Membrane rejection and fouling potentials were related to λ. The measured apparent diffusion (D) and mass transfer (k) coefficients for the E- and E₀-stage effluents across the membranes were found to confirm to D ∼ M(w)⁻⁽⁰·³³ ᵗᵒ ⁰·⁴⁸⁾ and k ∼ D⁰·⁶⁶.

Mitigation of climate change and energy security are major driving forces for increased biomass utilization. The pulp and paper industry consumes a large proportion of the biomass worldwide including bark, wood residues, and black liquor. Due to the fact that modern mills have established infrastructure for handling and processing biomass, it is possible to lay foundation for future gasification based bio-refineries to poly-produce electricity, chemicals or bio-fuels together with pulp and paper products. There is a potential to export electricity or bio-fuels by improving energy systems of existing chemical pulp mills by integrating gasification technology. The present study investigates bio-fuel alternatives from the dry black liquor gasification (BLG) system with direct causticization and direct methane production from the catalytic hydrothermal gasification (CHG) system. The studied systems are compared with bio-fuel alternatives from the Chemrec BLG system and the improvements in the energy systems of the pulp mill are analyzed. The results are used to identify the efficient route based on system performance indicators e.g. material and energy balances to compare BLG systems and the conventional recovery boiler system, potential biofuel production together with biomass to biofuel conversion efficiency, energy ratios, potential CO2 mitigation combining on-site CO2 reduction using CO2 capture and potential CO2 offsets from biofuel use, and potential motor fuel replacement. The results showed that the dry BLG system for synthetic natural gas (SNG) production offers better integration opportunities with the chemical pulp mill in terms of overall material and energy balances. The biofuel production and conversion efficiency are higher in the CHG system than other studied configurations but at a cost of larger biomass import. The dry BLG system for SNG production achieved high biomass to biofuel efficiency and considerable biofuel production. The energy ratio is significant in the dry BLG (SNG) system with less biomass demand and considerable net steam production in the BLG island. The elimination of the lime kiln in the dry BLG systems resulted in reduced consequences of incremental biomass import and associated CO2 emissions. Hydrogen production in the dry BLG system showed the highest combined CO2 mitigation potential i.e. on-site CO2 capture potential and CO2 offset from biofuel replacing fossil fuel. The results also showed that the motor fuel replacement potential with SNG as compressed natural gas (CNG) replacing gasoline in the transport sector is significantly high in countries with large pulp industry.
QC 20120528

L’atelier de régénération d’une usine kraft permet d’extraire des liqueurs noires les élémentschimiques nécessaires à la cuisson du bois et de les régénérer sous leur forme active, ainsi quede valoriser la fraction organique dissoute sous forme de chaleur. Les opérations unitaires enoeuvre sont nombreuses, complexes, et souvent mal décrites. Ce travail vise à permettre unemeilleure compréhension de la régénération, par la réalisation de modèles fiables décrivant lesphénomènes et processus dans chaque opération unitaire, leur implémentation algorithmiqueet leur exploitation par la simulation du procédé global
Chemical recovery at the kraft mill is the process whereby the valuable inorganic elements areextracted from spent kraft liquors and regenerated under their form effective to the cooking ofthe wood and energy is producted from the dissolved organic fraction. Many unit operations areinvolved, often poorly described. This work aims at a better understanding of the recovery processes.Reliable models describing the physical phenomena were proposed for each operation andimplemented as a computer algorithm. The whole chemical recovery unit was then simulated

Recycling of bleaching effluents into the black liquor recovery system has become an important step of a closed cycle technology that, in a kraft pulp mill, will result in a reduction in pollutants discharge into receiving waters and also a decrease of fresh water consumption.
In the current work, the combustion of pre-dried solid samples of black liquor (BL), chlorination effluent (C/D), and extraction effluent (E 1) as well as two-component and three-component mixtures was investigated experimentally in a Thermogravimetric Analyzer (TGA) and in a Constant-Temperature Tube Furnace.
Results of the thermogravimetric analyses showed that solids from the C/D stage were similar to those of the black liquor solids in the volatile matter, char, and ash contents, while the solids from the E1 stage contained less volatiles and were richer in their ash content. Results also revealed that both effluents were devolatilized and gasified at lower rates than that of black liquor. The addition of up to 20% of either effluent did not have a significant impact of the TGA behaviour of black liquor. In addition, mixtures containing solids from the three liquors were very close to black liquor in terms of their devolatilization and gasification rates and followed a weight-loss trend similar to that of black liquor.
Effect of temperature, O2, mixing ratio on the chemical compositions of combustion products was investigated in a constant-temperature tube furnace. Chemical analyses of the gaseous and solid phases were performed using a Mass Spectrometer (MS) and an Ion Chromatograph (IC), respectively. Results showed the combustion products of two-component mixtures containing up to 20% of C/D or E1 in black liquor solids would not be significantly different from those of typical black liquor, except that they contained more HCl in the gas phase and larger amounts of chloride in the solid phase, especially when C/D was added. Their amounts were greatly influenced by temperature and oxygen. Combustion of three-component mixtures (BL-C/D-E1) resulted in products very similar to those obtained during the combustion of black liquor alone. The HCl yield was increased with temperature and BL content in the mixture.

One of the main interests in commercial methane production is to maximize the gas yield, and it is thus appealing to use material with relative high methane potential. However, such material often results in process instability whereas ammonia inhibition is common. Removal of ammonia through adsorption is a fairly unexplored method in the field of biogas production, and could prove to be cost-effective.The adsorption capacity of pulp fibres from the paper making industry were investigated through batch adsorption experiments. Additionally, the fibres effect on small scale batch digesters in terms of methane production and cellulase activity was explored. Overall, the adsorption capacity of the pulp fibres was low, whereas Kraft hardwood had the highest adsorption capacity in both an aqueous ammonium solution and digester fluid at 11±3 and 60±20 mg g-1, respectively. The initial total ammonium nitrogen concentration had the highest effect on the adsorption capacity with a positive correlation. The pulp fibres seemingly had no effect on the ammonia inhibited anaerobic digestion systems. However, the cellulase activity was higher after day 5 in the anaerobic digestion systems with a high ammonia concentration.In essence, the overall results showed that the adsorption of the fibres was relatively low and most likely not suitable as a material to prevent ammonia inhibition in an AD.

Syftet med den här studien är att göra en teknoekonomisk utvärdering av processer för förvätskning av CO2 med hjälp av Aspen Plus. Ett flertal förvätskningsprocesser från tidigare studier jämfördes och från dessa valdes två förvätskningsprocesser ut för fortsatta studier och simuleringar. Dessa två förvätskningsprocesser var ett internt kylt förvätskningssystem och ett externt kylt förvätskningssystem av Øi et al., Energy Procedia 86 (2016) 500-510, som kallats system A, samt av Seo et al., International Journal of Greenhouse Gas Control 35 (2015) 1-12 kallat system B. Dessa två olika processer simulerades för teknisk analys med hjälp av Aspen Plus. Aspen Economical Analyzer (AEA) användes för att göra den ekonomiska analysen. I dessa simuleringar användes ett massflöde på 45 ton/h inkluderat vatteninnehåll, i jämförelse med tidigare studier med högre massflöden runt 100 ton/h. Elektricitet-och kylbehovet undersöktes i ett flertal olika fall med varierande kyltemperatur mellan kompressorerna. Två fall med integrering av fjärrvärme samt två fall med en värmepump undersöktes också med varierande återgående temperatur på fjärrvärmevattnet. Detta gjordes för att undersöka hur mycket värme som kan tillvaratas från förvätskningsprocessen. Vidare bestämdes även investeringskostnader samt driftskostnader med hjälp av AEA. Från detta bestämdes även den årliga kostnaden av kapitalet, CAPEX, och kostnaden att förvätska CO2 räknades ut i form av €/ton.  Resultaten visade att integrering av fjärrvärme samt värmepumpar är användbart för att tillvarata på så mycket värme som möjligt från förvätskningssystemen. I de fall med en värmepump samt en återgående temperatur på 47°C i fjärrvärmenätet hade ett COP på 3.07 samt 3.15 för system A samt system B vardera. Kostanden att förvätska CO2 var 17.42 €/ton för system A samt 17.75 €/ton för system B utan använding av en värmepump samt en återgående temperatur på 47°C i fjärrvärmenätet. Vid integrering av en värmepump gick kostnaden av förvätskning upp till 20.85 €/ton för system A samt 21.69 €/ton för system B. Kostnaden av förvätskning dominerades av driftskostnader med kostnaden av kapitalet har en mindre påverkan. Utnyttjandegraden har även en stor påverkan på kostanden av förvätskning, då lägre kapaciteter visade sig leda till markant högre förvätskningskostnader. När intäkterna från fjärrvärmeproduktionen adderades till kostnadskalkylen, minskade kostnaden av förvätskning, speciellt för de system med en värmepump, där priset minskade till 10.26 €/ton för system A eller 10.98 €/ton för system B. I linje med tidigare studier pekar även dessa resultat på att det ekonomiska optimumet sammanfaller med energioptimum. Resultaten visade även att system A, det internt kylda systemet, hade den lägsta förvätskningskostanden och minsta elektricitetsförbrukningen med och utan värmepump, och därför är system A optimalt för småskalig CO2 förvätskning.
The aim of this study is to do a technoeconomical analysis on CO2 liquefaction systems using Aspen Plus. Several liquefaction systems from previous studies were compared, and from these, two liquefaction systems were chosen for further studies and simulations. These liquefaction systems were namely an internal liquefaction system and an external liquefaction system by Øi et al., Energy Procedia 86 (2016) 500-510, called system A and Seo et al., International Journal of Greenhouse Gas Control 35 (2015) 1-12, called system B. These systems were simulated for technical analysis using Aspen Plus, and Aspen Economical Analyzer (AEA) was used for economical studies. A small-scale liquefaction system was studied with a mass flow rate of 45 tonne/h including the water content, as compared to other studies with higher mass flow rates of around 100 tonne/h. The electricity demand and cooling demand were studied in several cases of interstage cooling between compressors. Furthermore, two cases of district heating as well as two cases of heat pumps were studied with varying return temperatures of the district heating water. This was done to study how much heat could be recovered from the liquefaction process. Furthermore, the capital expenses as well as the operating expenses were also determined using AEA. From this, the annual CAPEX and the cost of CO2 was calculated in terms of €/tonne CO2.  The results showed that district heating and heat pumps can be useful to recover heat from the liquefaction processes. The simulations that included a heat pump and assumed a return temperature of 47°C had a COP of 3.07 and 3.15 for system A and B respectively. The determined cost of production was 17.42 €/tonne for system A and 17.75 €/tonne for system B when not using a heat pump and a return temperature of 47°C in the district heating grid. However, when adding a heat pump the total production cost (TPC) increased to 20.85 €/tonne for system A, and 21.69 €/tonne for system B. It was also shown that the TPC is highly dominated by the operating expenses while the total capital investment has a smaller impact on the TPC. The capacity is also important for the TPC as lower capacities was shown to lead to significantly increased production costs. When taking the revenue streams from district heating into account the TPC was decreased, in particular for the systems including the heat pumps, where the TPC for system A was 10.26 €/tonne while for system B it was 10.98 €/tonne. In accordance with previous studies it was shown that the economical optimum is closely related to the energy optimum. It was concluded that as system A, the internal liquefaction system, had the lowest TPC and electricity input with and without the heat pump and thus it is the optimal configuration for small-scale CO2 liquefaction.

The objective of this investigation was to utilise water pinch analysis as a tool for the optimisation of fresh water use in an integrated pulp and paper mill. The investigation was carried out at Mondi Paper in Merebank, south of Durban. The pulp and paper manufacturing process is a large consumer of fresh water and minimising the amount of fresh water used in the processes is beneficial from both a cost and environmental point of view. There are examples of mills which have "closed" their water systems to the extent that fresh water make up is minimal and most of the water is recycled and reused in a closed loop. These examples provide guidance on the basis of proven methods for reducing water consumption in the pulp and paper industry and can be used as a reference for mills wishing to reduce water consumption by making use of tried and tested methods. This investigation sought to provide an alternative method to identifying potential savings in fresh water consumption by making use of water pinch analysis. This was done at Mondi Paper by analysing individual parts of the mill and then a larger section of the mill which included both pulp and paper production. Flow rates of water streams and fibre content in those streams were obtained from plant data, where available, and this data was used to produce.a mass balance using the Linnhoff-March software, Water Tracker. The balance produced using Water Tracker provided the missing flow and fibre content data and this data was used as the input for the Linnhoff-March software, Water Pinch , to perform the water pinch analysis. The results achieved when analysing the individual parts of the mill did not demonstrate potential for significant savings in fresh water consumption, however the analysis of the integrated section of the mill identified a potential reduction in fresh water. It was found that the application of a single contaminant analysis to the larger section of the mill identified a possible reduction in the freshwater requirement of 8.1% and a reduction in effluent generated of 5.4%. This is a savings of R1 548 593 per annum based on 2003 costs of fresh water and effluent disposal. This analysis was conducted using the most simplified representation possible to produce meaningful results in order to evaluate the effectiveness of water pinch analysis in optimising the fresh water consumption in an integrated pulp and paper mill. It is demonstrated that water pinch analysis is potentially a useful tool in determining the minimum fresh water requirement of a site.
Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.

Pulp and paper mills are facing the possibility of stricter effluent discharge limits. End-of-pipe treatment for discharge no longer guarantees compliance, nor is it the most cost-effective way of solving mills' effluent problems. In this dissertation, water pinch analysis is used as a tool to determine the optimum effluent treatment conditions to ensure compliance at the least cost to the mill. It is also shown that the environment and the mill can benefit simultaneously if the correct effluent discharge philosophy is implemented. Mill simulation results were used to set up a water pinch analysis model. Maximum permissible inlet concentrations were specified for all process units. Mass transfer equations were used to describe the relationships between inlet and outlet concentrations of the process units. A number of generic effluent treatment units with preset performance specifications were added to the pinch model. These treatment units can be sized and used in an optimal way by the pinch model to obtain an optimum effluent treatment and recycling scheme. Capital and operating costs for different treatment units were included in the analysis. The capital cost for treatment units decrease as the volume treated by the unit decreases. The operating cost is generally expressed in terms of volume; however, certain treatment units have treatment cost expressed on load treated rather than volume. The validity of the results obtained from WaterPinch™, the pinch analysis software used for building the pinch model, was checked by using a process simulation package, WinGEMS™, to simulate the proposed effluent treatment scenarios. This step ensured that the mass transfer relationships used in the water pinch model were valid. This was an important part of the work, as the results generated by the optimisation model have to be reliable in order to make the results obtained applicable to the mill. The verified water pinch model was used to find optimum treatment plant layouts for different effluent discharge volume and concentration specifications. This resulted in an optimum-cost profile for a range of effluent discharge volumes and concentrations. Optimum-cost profiles could be a decision making tool in the negotiation between the mill and the regulatory authority to set effluent discharge regulations in such a way that the environment benefits without unnecessarily restricting economical and social development of the region. Using optimum-cost profiles, the differences between a load-based and a concentration-based discharge permit was illustrated. Comparing the pinch analysis results for these scenarios showed that the mill has no financial incentive to reduce effluent volume if a concentration-based permit is in place. However, a load-based permit could make it financially viable for a mill to reduce effluent volume and load rather than to simply treat and discharge. It is also shown that both the mill and the environment (river) benefit from a load based permit. The impact of possible future waste discharge charges on the economical feasibility of various effluent treatment options is also investigated. The results indicate that the implementation of waste discharge charges will only benefit the environment if it is linked with a load-based effluent discharge permit. This illustrates the usefulness of pinch analysis as a basic risk analysis and risk management tool.
Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2005.

Small quantities of reduced sulphur compounds (RSCs) emitted from Kraft pulp mills can affect air quality due to low odour thresholds. Chromatographic methods were developed for individual RSCs at ppt to ppb concentrations. Analyses of ambient air samples showed that while H2S, CH3SH, DMS and DMDS were linked to the pulp mill, the majority of COS and CS2 was due to other sources unrelated to the mill. The fluxes of individual RSCs from kraft wastewater clarifiers were quantified for the first time. DMDS and DMS were the major RSCs emitted from the primary and secondary clarifiers, respectively. RSC fluxes were one to three orders of magnitude higher at the primary clarifier than at the secondary one. Clarifier emissions were, however, insignificant compared to point sources in the mill. Statistically significant correlations were found between the DMS emission and BOD, COD, as well as TSS in the secondary treatment system.

Sappi's Ngodwana integrated Kraft pulp and paper mill was used as case study for the application and evaluation of the water pinch technique. The technique of water pinch originates from energy pinch, but uses mass flow and contaminant concentration to identify water and effluent reduction opportunities. The classical meaning of pinch, as defmed by energy pinch has however been changed to a more modem meaning. Historically the terms water or energy pinch was used to refer to the points where two composite curves touched on energy or water graphs. This graphical meaning of pinch is gradually being replaced to refer to the optimal po int proposed by a numerical solver beyond which improvement of the water network is no longer possible for the given inputs. The water pinch technique was applied by means of a numerical solver that used mixed integer non-linear programming to optimise to the minimum cost for running the water network under investigation. The problem defmition was defined in terms of costs associated with the use of utilities, raw material, treatment facilities and process units. It was also possible to define factors such as environmental impact, corrosion, fouling, scaling, cooling tower treatment cost, legal risk etc in terms of a penalty cost. The water pinch technique has been refined in software packages that are user friendly, ca~ble of handling multi-contaminants and suitable for varying flows. The software package WaterPinch by Linnhoff March was used. The case study was applied on Ngodwana mill that has an already highly closed water system with effluent generation rates as low 20 kL per ton of pulp and paper. The pinch study included sodium, chloride, calcium, suspended solids and COD as contaminants. The study investigated different applications of the pinch technique. The following was concluded: • The mill's understanding of its current restrictions, ()l pinch points, of its water network was confirmed. No new pinch points have been identified of which the mill was not aware. This indicates that the mill was already highly knowledgeable about its water system. This was expected of a mill that has a very low specific-effluent-generation rate. Water pinch was unable to significantly improve on the effluent generation rate of the mill. • The pinch analysis has identified opportunities of mixing small quantities of waste streams into process water streams to replace fresh water. These changes can introduce minor water savings and new risks to the process that have to be understood better before implementation. • The mill has progressed far with the design and costing of a proposed effluent treatment plant (ERPl). The integration of this treatment plant into the water network was investigated using the pinch technique. The pinch solver suggested a totally different approach to the integration of the ERPI plant compared to design of the mill. The mill's design revolves around the treatment of low chloride streams in the ERPl plant and using of the treated water as make-up to the cooling towers. Sodium was recovered as raw material from the cooling towers' blow-down. Pinch proposed treatment of the high cWoride containing streams and returning the streams to users suitable of using high chloride water. The network proposed by mill's design generates 8.2 MLlday effluent less than the pinch proposal, and recovers sodium as raw material. The proposal presented by pinch is not recommended and points to the difficulty in simulating factors, such as raw material recovery, in a pinch analysis. • Users for the excess storm water were identified using water pinch and will be suitable for implementation. The mill has mwever decided on alternative sinks for the storm water based on considerations such as process inter-dependency, risks associated with contamination and general management philosophy for the different systems in the mill. These considerations could have been included into the pinch solver, but were not because it was of interest what the second best option would be. • The pinch investigation proved useful to confirm certain understandings of the mill. The investigation confirmed the difficulty of improving the water systems of the mill due to the fact that Ngodwana is already a highly closed and integrated mill. Numerous smaller process changes have been identified by the pinch solver and could be investigated further for smaller process improvements. • It i; recommended that pinch technology be applied again when the mill plans to make major process changes or expansions. It is also recommended to use water pinch on a more frequent basis in smaller sections of the mill or for other evaluations in the mill. As a group Sappi could benefit from the use of water pinch, especially in situations where the water network of the mill is not already water efficient. • The recommendations and conclusions in this report have not been subjected to technical and economical feasibility studies. Extensive further studies must be conducted before implementation of any of the results. Further studies must include impacts from process dynamics, long term effects, impacts from other contaminants that have not been simulated, etc.
Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2009.