The use and research of renewable fuels has become more important due to the connection between climate changes and the use of fossil fuels. With risks of decline in petroleum production derived from fossil fuels due to limitation of resources in the future, the renewable fuels are even more important in the transport sector. Research regarding gasification of biomass to create a syngas that can be upgraded to a biodiesel for cars is one of the approaches. By gasifying black liquor, it is possible to create a 100 % green fuel diesel. However, as this black liquor might be in limited quantities the idea to create a synthetic black liquor was sparked. The pulp industry where the black liquor originated from also has quantities of wastewater, containing a biomass sludge. Otherwise containing water in so large quantities that it is not possible to combust it without ending up with a negative energy output. One of the paths could be to recover the biomass from the sludge and convert it to a liquid similar to black liquor. Catalytic hydrothermal liquefaction has been recognized as a potential method. While biocrude is usually the target in hydrothermal liquefaction for direct upgrade to biofuel, the aqueous product could prove to be used for the gasification process. This would create a combined liquefaction-gasification process. Using model compounds possibly existing in the waste sludge, hydrothermal liquefaction was performed at different temperatures, together with varied alkali loads (K2CO3) and water the content to see how the different compounds reacted. Model compounds included cellulose and lignin as major compounds. Although the temperature was increased from 240 °C to 340 ° the lignin conversion was lower at 340 °C than at 240 °C. Re-polymerization took place and around 40 % of resulted in solid residue, while the remaining 60 % was partially converted to aqueous phase, oil phase or gas in the process. By not performing the hydrothermal liquefaction it is however possible to dissolve Kraft lignin directly in water and alkali. Cellulose showed an almost full conversion at 290 °C with similar results at 340 °C, with 4 – 5 % remaining as solid. At the higher temperature more gas was produced, which is not optimal for this process where liquid product is wanted. This suggest that 290 °C is enough for cellulose conversion in this process. Using an alkali load of 0.3 times the cellulose mass in the solution the final aqueous product contained about 26 % alkali, which is similar to black liquor. Increase the alkali to 0.9 times however increased the sought aqueous product, in both terms of energy and carbon content. Fiber sludge from a pulp mill, containing mainly cellulose, could therefore most likely be converted to a liquid product that is similar to black liquor for further upgrade

Carryover particles are partially/completely burned black liquor particles entrained in the flue gas in kraft recovery boilers. Understanding how carryover particles form and deposit on heat transfer tube surfaces is critically important in the design and operation of a recovery boiler. The tendency for a carryover particle to deposit on a tube surface depends on the particle temperature and composition at the moment of impact. This study was the first to examine systematically how carryover particle composition changes with the black liquor chemistry and burning conditions. The effect of black liquor composition and particle size, gas composition (O2 and SO2 concentrations) and temperature on the composition of carryover particles were studied using an Entrained Flow Reactor (EFR). Field studies were conducted on three operating boilers, where an air-cooled probe was used to collect carryover samples at the superheater entrance. The results show that the chloride (Cl) and potassium (K) contents in carryover particles were linearly proportional to their contents in black liquor. Cl and K were depleted during black liquor combustion due mainly to the vaporization of NaCl and KCl. The depletion of Cl is about three times greater than that of K. The significant depletion of Cl implies that carryover particles contain much less Cl, and hence, are less sticky than previously expected from black liquor composition. A dynamic model was also developed to predict the composition of carryover particles as a function of black liquor composition and burning conditions. Based on the data obtained experimentally in this study, the kinetic equations for the oxidation of sulphide available in the literature were modified and incorporated into the model to improve its sulphide and sulphate predictions. The model predicts the main components of carryover particles formed in both the EFR and three operating recovery boilers reasonably well, except for the K content, which is slightly over-predicted at high O2 concentrations (or high particle temperatures). Based on the predicted composition, it is possible to determine the thermal properties of carryover and to assess its fouling propensity in the boiler. The information helps boiler manufacturers and operators to identify locations in the boiler where massive carryover deposition may occur and to devise appropriate control strategies to minimize fouling and to improve boiler thermal efficiency.

Multiple Effect Evaporators (MEE) are used in kraft pulp mills to concentrate black liquor. In order to verify if the MEE is operating at an optimum condition, thermal performance of evaporators is calculated. Due to the interconnection of many variables involved, this can be a challenging task. Thus, this work involved the study of operating data from two Canadian pulp mills using Multivariate Data Analysis (MVDA) techniques: Principal Component Analysis (PCA) and Partial Least Squares Analysis (PLS). Moreover, the evaporation system was modelled using a dynamic simulation software called CADSIM. MVDA determined that the thermal performance of the evaporators was positively correlated with the weak black liquor flow rate and negatively correlated with the steam pressure (to the first effect). The CADSIM model confirmed these findings. Therefore, these two techniques show to be useful tools in identifying operating variables that may be adjusted to improve thermal performance of evaporators.

Multiple Effect Evaporators (MEE) are used in kraft pulp mills to concentrate black liquor. In order to verify if the MEE is operating at an optimum condition, thermal performance of evaporators is calculated. Due to the interconnection of many variables involved, this can be a challenging task. Thus, this work involved the study of operating data from two Canadian pulp mills using Multivariate Data Analysis (MVDA) techniques: Principal Component Analysis (PCA) and Partial Least Squares Analysis (PLS). Moreover, the evaporation system was modelled using a dynamic simulation software called CADSIM. MVDA determined that the thermal performance of the evaporators was positively correlated with the weak black liquor flow rate and negatively correlated with the steam pressure (to the first effect). The CADSIM model confirmed these findings. Therefore, these two techniques show to be useful tools in identifying operating variables that may be adjusted to improve thermal performance of evaporators.

Carryover particles are partially/completely burned black liquor particles entrained in the flue gas in kraft recovery boilers. Understanding how carryover particles form and deposit on heat transfer tube surfaces is critically important in the design and operation of a recovery boiler. The tendency for a carryover particle to deposit on a tube surface depends on the particle temperature and composition at the moment of impact. This study was the first to examine systematically how carryover particle composition changes with the black liquor chemistry and burning conditions. The effect of black liquor composition and particle size, gas composition (O2 and SO2 concentrations) and temperature on the composition of carryover particles were studied using an Entrained Flow Reactor (EFR). Field studies were conducted on three operating boilers, where an air-cooled probe was used to collect carryover samples at the superheater entrance. The results show that the chloride (Cl) and potassium (K) contents in carryover particles were linearly proportional to their contents in black liquor. Cl and K were depleted during black liquor combustion due mainly to the vaporization of NaCl and KCl. The depletion of Cl is about three times greater than that of K. The significant depletion of Cl implies that carryover particles contain much less Cl, and hence, are less sticky than previously expected from black liquor composition. A dynamic model was also developed to predict the composition of carryover particles as a function of black liquor composition and burning conditions. Based on the data obtained experimentally in this study, the kinetic equations for the oxidation of sulphide available in the literature were modified and incorporated into the model to improve its sulphide and sulphate predictions. The model predicts the main components of carryover particles formed in both the EFR and three operating recovery boilers reasonably well, except for the K content, which is slightly over-predicted at high O2 concentrations (or high particle temperatures). Based on the predicted composition, it is possible to determine the thermal properties of carryover and to assess its fouling propensity in the boiler. The information helps boiler manufacturers and operators to identify locations in the boiler where massive carryover deposition may occur and to devise appropriate control strategies to minimize fouling and to improve boiler thermal efficiency.

The release of sodium during the combustion of black liquor is a significant source of fume formation in a kraft recovery boiler, affecting efficiency in a pulp and paper mill. The fume is deposited on the surface of heat exchanger tubes in the upper furnace, causing fouling and corrosion, especially to the superheaters. This thesis reports on work done to develop improved understanding of fume formation. The mechanisms of sodium release during each stage of black liquor combustion are influenced by the surface temperature. The addition of boron to the black liquor, which debottlenecks the recausticizing plant by a reduction in lime usage, also influences the characteristics of black liquor combustion, such as combustion time and swelling. Previously, no effective measurement technique has been available to quantify sodium concentration in the plume of a burning black liquor droplet with or without boron, or to record the distribution of surface temperature through the time history of a burning droplet. This thesis reports on the adaptation of two techniques for the measurement of the release of atomic sodium and the temperature history, and their application to investigate several aspects of the release of atomic sodium during combustion of black liquor in a flat flame environment. The simultaneous employment of a planar laser-induced fluorescence (PLIF) technique with an absorption technique has been adapted to allow quantitative measurement of the release of atomic sodium. The absorption technique has been employed to correct for both fluorescence trapping due to absorption and attenuation by high concentration of the atomic sodium in the plume, and for collisional quenching by the other major gas components present in the flat flame. An independent assessment was performed using kinetic calculations, based on measured total sodium that is residual in a particle obtained at different stages in the combustion process. These independent assessments were used to provide greater insight in to the release process and to cross-check. The influence of both the initial diameter of the droplet and addition of boron to the black liquor on the temporal release and the release rate of atomic sodium during the combustion have been performed using the present PLIF technique. The second technique, two-dimensional two-colour optical pyrometry, has been adapted to measure the distribution of surface temperature and the swelling (change in surface area) of a burning black liquor droplet. The influence of surface temperature or the change in the external surface area of the droplet on the release of atomic sodium during the combustion of black liquor has been assessed through concurrent use of both adapted techniques. The highest concentration of atomic sodium was measured in the final stage of combustion that of smelt coalescence, where it is an order of magnitude greater than in the other stages combined. While the extensive release of atomic sodium at high temperature in this final combustion stage occurs in only a relatively small percentage of droplets in a kraft recovery boiler, the effect could still be significant in fume formation. This is because the extensive release is expected to occur in the very small droplets, predominantly generated by splitting or physical ejection. Small droplets will have a very short combustion time and so could remain in suspension within hot gases for sufficient time for extensive release of sodium. These measurements outcomes can be used to support the future development of sub-models for computational fluid dynamics (CFD) models in order to better understand and optimise fume formation in a kraft recovery boiler. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1474431 / Thesis (Ph.D.) - University of Adelaide, School of Mechanical Engineering, 2009

The release of sodium during the combustion of black liquor is a significant source of fume formation in a kraft recovery boiler, affecting efficiency in a pulp and paper mill. The fume is deposited on the surface of heat exchanger tubes in the upper furnace, causing fouling and corrosion, especially to the superheaters. This thesis reports on work done to develop improved understanding of fume formation. The mechanisms of sodium release during each stage of black liquor combustion are influenced by the surface temperature. The addition of boron to the black liquor, which debottlenecks the recausticizing plant by a reduction in lime usage, also influences the characteristics of black liquor combustion, such as combustion time and swelling. Previously, no effective measurement technique has been available to quantify sodium concentration in the plume of a burning black liquor droplet with or without boron, or to record the distribution of surface temperature through the time history of a burning droplet. This thesis reports on the adaptation of two techniques for the measurement of the release of atomic sodium and the temperature history, and their application to investigate several aspects of the release of atomic sodium during combustion of black liquor in a flat flame environment. The simultaneous employment of a planar laser-induced fluorescence (PLIF) technique with an absorption technique has been adapted to allow quantitative measurement of the release of atomic sodium. The absorption technique has been employed to correct for both fluorescence trapping due to absorption and attenuation by high concentration of the atomic sodium in the plume, and for collisional quenching by the other major gas components present in the flat flame. An independent assessment was performed using kinetic calculations, based on measured total sodium that is residual in a particle obtained at different stages in the combustion process. These independent assessments were used to provide greater insight in to the release process and to cross-check. The influence of both the initial diameter of the droplet and addition of boron to the black liquor on the temporal release and the release rate of atomic sodium during the combustion have been performed using the present PLIF technique. The second technique, two-dimensional two-colour optical pyrometry, has been adapted to measure the distribution of surface temperature and the swelling (change in surface area) of a burning black liquor droplet. The influence of surface temperature or the change in the external surface area of the droplet on the release of atomic sodium during the combustion of black liquor has been assessed through concurrent use of both adapted techniques. The highest concentration of atomic sodium was measured in the final stage of combustion that of smelt coalescence, where it is an order of magnitude greater than in the other stages combined. While the extensive release of atomic sodium at high temperature in this final combustion stage occurs in only a relatively small percentage of droplets in a kraft recovery boiler, the effect could still be significant in fume formation. This is because the extensive release is expected to occur in the very small droplets, predominantly generated by splitting or physical ejection. Small droplets will have a very short combustion time and so could remain in suspension within hot gases for sufficient time for extensive release of sodium. These measurements outcomes can be used to support the future development of sub-models for computational fluid dynamics (CFD) models in order to better understand and optimise fume formation in a kraft recovery boiler. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1474431 / Thesis (Ph.D.) - University of Adelaide, School of Mechanical Engineering, 2009

Kraft pulping, also known as sulphate pulping is a complex process where the wood components are liberated from each other facilitated by chemical reactions. During the pulping process some dissolved and degraded compounds end up together with the spent cooking chemicals in the black liquor. In kraft pulping of hardwood, the black liquor contains substantial amounts of dissolved hemicellulose, especially xylan due to the wood composition. The xylan content is of high value due to its ability to re-deposit by adsorption on cellulose fibres and its tendency to increase pulp strength and yield. In this work, the possibility of introducing xylan rich, hardwood black liquor from the hardwood digester into the softwood digester at the process of SCA – Munksund was studied. The objective was to investigate if hardwood black liquor addition in a softwood cook can increase the yield and pulp strength. The theoretical feasibility of altering the process was investigated by a literature review and a brief process investigation. During the study a total of eight lab cooks were conducted to obtain information on how hardwood black liquor addition changes the pulp quality of regular softwood cooks. The wood chips, white liquor and hardwood black liquor used were collected at Munksund and the process conditions in the lab cooks were chosen to simulate the actual process in the Munksund mill. In addition to the cooking, chemical and physical evaluation on pulps, cooking liquors and wood chips were performed. The theoretical evaluation indicates that the process in Munksund is well suited for introducing the hardwood black liquor in to the softwood digester. The chemical analysis of the black liquors show a xylan content that is approximately four times higher in the hardwood black liquor compared to the softwood black liquor. In the kappa number range of approximately 80-90, a total yield increase of 0.4%-units was obtained for two cooks with hardwood black liquor addition compared to their corresponding reference cooks. A carbohydrate analysis showed a higher xylan content in the pulp cooked with addition of hardwood black liquor compared to the corresponding reference pulp. One pulp with hardwood black liquor addition and its corresponding reference cook were refined in an Escher Wyss lab mill. The pulp with hardwood black liquor addition exhibits an increase or retained strength for all strength evaluation tests made on handmade pulp sheets. Strength increases of approximately 5% were obtained for tensile index and ISO-Z strength for a pulp with hardwood black liquor addition.   The results conducted in this study shows that it can be possible to slightly increase both the yield and some pulp strength parameters when adding hardwood black liquor in to the softwood cook in lab scale. It is also shown that the increase in the total yield most likely depends on xylan adsorption on the cellulose fibres. The calculated increased revenue for this process change could be over 400 000 Euro per year.

In this study, a numerical model is used to investigate the evaporation and flow characteristics of heated liquid sheets and films. The liquid is modeled as water and as black liquor, a byproduct produced by paper mills. In the pulping process, black liquor is concentrated in an evaporator as a falling film. The effectiveness of the evaporator is reduced due to fouling on heat transfer surfaces. Two flow arrangements are studied: falling films, where the liquor and steam are separated by a heat transfer surface; and liquid curtains, which is a thin sheet of liquid falling due to gravity surrounded by steam. For the liquid curtain, the liquid and gas come into direct contact, therefore there is no place for fouling to occur allowing for a more consistent operation of the evaporator. This type of arrangement is not currently used in paper mills but is being investigated in this work to determine its feasibility. The fluid system is simulated using the finite volume method with a single-fluid field to capture the liquid-gas interface. This study investigates how the breakup of a liquid curtain is affected by flow parameters and how the breakup into droplets influences the evaporation characteristics of the liquid curtain. It is found that the falling film evaporator has a much higher liquid evaporation rate than evaporating as a liquid curtain. However the falling film evaporator has an entrance length with no evaporation, and liquid curtains allow for evaporation to start occurring very near the inlet. If reducing length of the evaporator is a priority, liquid curtain evaporators can obtain a higher evaporation rate than falling films within the same distance. Falling film evaporation has a higher steam efficiency than a liquid curtain evaporator. However, for short evaporator lengths the rate at which water is removed from a liquid curtain evaporator is much greater, but at the cost of a higher steam consumption rate.

Chapter 1: When Environmental Subsidies Backfire: The Case of Black Liquor and the Alternative Fuel Mixture Tax Credit: In 2005, the US government introduced the Alternative Fuel Mixture Tax Credit (AFMTC), which paid fifty cents/gallon for alternative fuel that was mixed and burned with traditional fuel. The American chemical pulp industry, which has traditionally burned ‘Black Liquor’, a residue of the pulping process, was able to make large claims on this subsidy in 2009 by mixing diesel fuel into a process where it was not required. This scenario exhibits two main downfalls of environmental subsidies: (i) the majority of the subsidy is paid to free-riders, and (ii) there are strong incentives towards overproduction and increased pollution. In this paper, the value of the AFMTC per tonne of chemical pulp is computed and used in a simulation using the Global Forest Products Model (Buongiorno, 2001) to calculate the effects of the AFMTC on the American and Canadian chemical pulp industries. The simulation suggests that the total amount paid to the American chemical pulp industry was US$7.63 billion, that American chemical pulp production rose by 2.5 million tonnes from the baseline, and Canadian production and exports to the US fell by 285,000 and 255,000 tonnes respectively, costing Canadian chemical pulp producers US$132 million in lost production. Using Canadian chemical pulp production and pollutant release data, production/release averages were developed. These averages suggest that the increase in American chemical pulp production led to significant increase in releases of greenhouse gases, hydrogen sulfide, sulfur oxides, nitrogen oxides and particulate matter. Chapter 2: The Alternative Fuel Mixture Tax Credit and the Pulp and Paper Green Transformation Program: A Policy Comparison: In 2009, chemical pulp mills in the US and Canada were able to take advantage of two subsidy programs that paid mills fifty cents for every gallon of ‘Black Liquor’ burned during the pulping process. Black Liquor is a residue product from the production of chemical pulp, and is traditionally used as a fuel in further pulp production. These subsidies were the Alternative Fuel Mixture Tax Credit (AFMTC) in the US and the Pulp and Paper Green Transformation Program (PPGTP) in Canada. Even though the AFMTC was a subsidy that applied to many industries, and the PPGTP was only available to chemical pulp mills, in the context of the chemical pulp industry only, the subsidies were almost identical: Both paid mills the same amount for undertaking the same activity, and mills were able to claim the subsidies for roughly the same amount of time. The key difference between the two programs was stipulations on how the money was to be spent. In the US, the AFMTC was a refundable tax credit, and simply another source of revenue for a recipient mill. In Canada, a recipient of PPGTP funds was required to spend the money on some form of capital investment that would increase energy efficiency or lower pollution emissions from the mill. In this paper, we develop a theoretical model with a representative chemical pulp mill in order to compare the effects that these two subsidies would have on the mill’s production of pulp (and in turn its production and use of black liquor), and its decision in whether to invest in a one-time capital improvement that would increase energy efficiency at the mill. The results from this model show that the PPGTP was a more effective policy than the AFMTC, in that it encouraged increased investment in energy efficiency, whereas the AFMTC did not. However, the PPGTP provides incentives to increase production, similar to the AFMTC, in two out of three possible outcomes. Even though the PPGTP is shown to be more effective than the AFMTC, it still exhibits several properties inherent in a second-best policy - because the subsidy is tied to production, it encouraged increased production, and may not have allocated funding in an efficient manner. Chapter 3: Naming, Shaming, and Abatement: Do Published ‘Top Emitter’ Lists Provide Incentive for Increasing Pollution Prevention Activities? Several works have measured the effects that publically disclosed pollutant release information has on the firms and facilities reporting the information. Most of these studies quantify the negative response that the information garners with the media, through some measure of media coverage, and measure the negative impact that this attention has on the firm; for example, by showing a negative effect on the respective company’s publically traded stock performance. Subsequent studies have then shown how these negative impacts from publicity cause firms to report lower emissions levels in following years. What is currently missing from this body of literature, however, is an examination of the step in between the firm receiving negative press and reporting lower emissions, namely, increased pollution abatement efforts on behalf of the publically labeled facility. In this paper, we attempt to gain a better understanding of this relationship by examining Canadian self-reported facility level data on pollution prevention activities from the National Pollutant Release Inventory. Two consistent samples of data are used to empirically test the effects that ‘Top Ten’ emitter lists, published by Environment Canada in the late 1990’s, had on the number of pollution prevention activities undertaken by facilities in the following year. The results from this work were inconclusive: Between these two samples, there was a noticeable decrease in the amount of pollution prevention activities reported in years after the cessation of the Top Ten publications. Under certain model specifications, a facility that was labeled as a Top Ten emitter is estimated to have 20% more pollution prevention activities undertaken compared to a facility that was not so labeled. It was also shown that a firm that reported new pollution abatement activities also had a significant reduction in releases. This finding, along with the decreasing trend in reported activities, raises a significant policy issue, as measures that clearly reduce reported emissions are being reported with less frequency in Canada.