Examensarbeten för masterexamen // Master Theses
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- PostDesign of the heat recovery systems at the reconstructed pulp mill Östrand(2015) Ahlström, Johan; Benzon, Marcus; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentThe aim with this master thesis project was to provide a reference for the reconstruction of the heat recovery systems for the future possible reconstructed pulp mill Östrand, owned by SCA and located in Timrå, Sweden. The principle was to design a heat exchanger network and a secondary heating system that are more efficient than those already proposed by consultants. To achieve this Pinch Analysis was used. The required data for this work were gathered during a one-month visit to Östrand. For the majority of the new process equipment, quotations from different equipment producers were used. However, in some cases, current factory data were used and scaled up to the future production levels. With the data gathered, the heat exchanger network proposed by Östrand was analysed first to provide a reference case that was later retrofitted to more energy efficient designs. More specifically, two new designs of the heat exchanger network were proposed. The first retrofit design was performed with the goal of using energy as efficiently as possible, but still creating a network that is possible to implement from a practical point of view. The second retrofit design was obtained by including more detailed practical constraints, according to inputs from plant engineers at SCA Östrand, which could have more chances to be implemented at the reconstructed mill. As a consequence of increased heat recovery, less steam is required for process heating. Since the minimum amount of steam produced is coupled to the amount of black liquor that has to be recovered, increased heat recovery translates into larger steam mass flow rate available for electricity production. This represents a first economic advantage, which should pay back the investment in extra heat exchangers required in the proposed designs compared to the reference prospected design. Additionally, a modified heat exchanger network requires a modified secondary heating system. This is based on a hot/warm water loop and is a common way in pulp mill to collect and deliver heat where direct heat transfer is not possible, e.g. due to large distance between equipment units, or due to different operation times which also requires water tanks to be used. After the two retrofit suggestions for the heat exchanger network were completed, the design of the secondary heating system was therefore investigated. Depending on the heat available at different temperature levels, different amount of hot water can be produced and the mass flow rates of the different segment of the water loop can be optimized. This translates in reality in optimizing the starting and ending temperatures of these segments, which are separated by a tank where water is stored to accommodate process operational flexibility. While such analysis should follow an economic principle, in this work this was conducted following the objective of recovering as much as excess heat as possible and a procedure called the “tank method” was followed, which was previously developed at the div. of Industrial Energy Systems and Technologies. In this thesis three suggestions regarding what to do with the excess heat are discussed: increased production of district heating, increased steam production for electricity production, and heat pumping. The economic result of excess heat utilization provides a second way to pay back the investment in extra heat exchangers required in the proposed designs compared to the reference prospected design. While a profitability analysis should be ultimately conducted to identify the best design solutions for the heat exchanger network and for the secondary heating systems, in this work only a discussion of the economic aspects is provided based on the results of the thermodynamic analysis. These results show that for the ambitious retrofit the electricity production is increased with 24.2 MW and 32.8 MW of excess heat is liberated. For the realistic retrofit, the electricity production is increased with 13.9 MW and 65.7 MW of excess heat is produced. Compared to the relatively small changes to the original design of the heat recovery systems which was the starting point of this work, the results are considered rather promising and show that there is room for Östrand to improve the design of the future plant.
- PostEnergy recovery from destruction of VOC's(2009) Olofsgård, Markus; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and Environment
- PostExperimental and Statistical Investigation of Hydrodynamics of a Falling Liquid Film(2015) ambros, christoph; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentIn falling film evaporators a liquid flows down a heated surface as a thin film under gravity. They can be operated at very low pressures and are thus convenient for the evaporation of viscous and temperature sensitive liquids. Falling liquid films are random in nature and the film response is stochastic. The hydrodynamics haven´t been fully understood so far. Therefore the liquid flow pattern are described by statistical analysis. The flow pattern are investigated at four positions on the outside of a vertical pipe with five meter in length. The dependence on the Reynolds number and viscosity is studied at single positions as well as longitudinal. The experiments are done under non-evaporating- and ambient conditions. The instantaneous film thickness measurements are done by a new laser measurement approach, measuring with a frequency of 500 Hz. A selection of the most promising parameters and statistical methods to describe the liquid flow pattern are determined. A new method has been developed to distinguish between waves with different amplitudes. The results of the liquid flow pattern by using the new measurement approach results in highly resolved film thickness traces. The new method to distinguish between the waves, gives very pronounced points of transition between different flow regimes. The transitions from the capillary-wavy-laminar into the inertia-wavy-laminar, from the inertia-wavy-laminar into the inertia-wavy-turbulent as well as the transition into fully turbulent flow have been investigated. The results of the critical Reynold numbers, marking the transitions between the flow regimes show a high dependency on the position at the pipe as well as viscosity. The work makes a valuable contribution to understand the hydrodynamics of a falling liquid film by investigating the liquid flow pattern.
- PostImproved Resource Utilization at a Kraft Pulp Mill - A case study of Södra Cell Värö(2015) Hedlund, Joel; Ullgren, William; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentThe Södra Cell Värö kraft pulp mill will during 2015 and 2016 be expanded to increase the pulp production capacity. The increased pulp production will generate an even larger amount of by-products and excess heat from the process, thus likely to increase the amount of unused resources compared with the current situation. This master thesis work is an investigation of different alternative solutions to increase the resource utilization at Värö, and by that increase the mill’s economic profitability and environmental performance. A base case of the expanded pulp mill’s energy system was modelled and used as a reference case for the alternative solutions. The following alternatives for increased resource utilization were examined: bark burning, lignin extraction, increased district heating deliveries to Varberg and Kungsbacka, and increased bark drying to use as fuel in the lime kiln. The evaluation was done with respect to energy and mass balances and by using three key performance indicators; resource efficiency, economic performance and CO2 emissions. Furthermore, a description of other possible solutions, which for different reasons were discarded earlier in the work, was made. Several of these solutions showed great potential for further studies. With respect to the economic performance all the alternatives, except increased bark drying, which was not included in the economic analysis; and bark burning, showed better results than the base case. With respect to resource efficiency lignin extraction generally showed the best results. The CO2 emission balances differed a lot for the different alternatives depending on assumptions regarding the surrounding energy system. The investigation showed that all alternatives, except for bark burning, overall gave better results than the base case and implementing anyone of these alternatives would result in increased resource utilization at the Södra Cell Värö pulp mill.
- PostModelling of Black Liquor Evaporator Cleaning - A case study of Skärblacka pulp mill(2015) ANDERSSON, MIKAELA; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentTo maintain good operation of a chemical pulp mill, efficient removal of sodium scales attached to the heating surfaces in the black liquor evaporators is necessary. Increased knowledge about the cleaning process for the scales can lead to overall improved performance for the mill, with reduced production losses and increased heat economy as main advantages. Making the black liquor evaporation process more efficient will not only reduce the running cost of the plant, it will also influence the global environment in a positive way since resources are used in a more efficient way. Within this thesis, an existing modelling tool that simulates the dissolution of sodium scales in black liquor evaporators have been further developed and modified for industrial operation. The updated modelling tool enables the scale distributions to be determined from the boiling point rise, and the probability with each scale distribution to be verified via analysis of the heat transfer coefficient. A case study was done at BillerudKorsnäs’ mill in Skärblacka and a full scale test was performed where liquor samples and online process data were collected during one wash sequence. The aim was to utilize the updated cleaning model, together with data obtained from the case study, to gain fundamental understanding of the dissolution process of the scales in an effort to improve evaporator cleaning. Furthermore the work also aimed on being able to predict how the scales were distributed within the evaporator. It was found that the most reliable parameters to monitor were boiling point rise from online process data and dry solids content from laboratory analyses. The previous showed high sensitivity towards changes in scale thickness and was concluded to be the most effective parameter to monitor trends during the wash and to follow to determine it the wash is finished or not. Dry solids content from lab analyses on the other hand showed better performance to predict absolute values. Another finding made was that if it is desirable to have a short cleaning time, the evaporation rate should be low.
- PostProcess Stream Data Analysis: Data Reconciliation and Gross Error Detection for Process Integration Studies(2015) Murcia, Cristina; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentOne of the major challenges for energy companies is to adapt their process plants to the continuous improvements of available technologies, so as to make their old plants as competitive and cost-efficient as the new ones. Along these lines, process stream data was recently collected for analysing opportunities for improved process integration of the Hydrocracker Unit of a major oil refinery located in Lysekil on the West Coast of Sweden. However, inconsistencies in the process data measurements, e.g. energy balances that do not add up, made the study cumbersome. For analysing heat exchanger networks it is essential to establish sets of process data with balanced heat balances for the existing heat exchangers. The aim of this thesis project was to develop a computer-based solution for systematic analysis, identification and correction of the “raw” data obtained from process data measurements in order to acquire such a consistent set of data. With this purpose, a tool for Data Reconciliation and Gross Error Detection for process stream data was developed using Visual Basic in Microsoft Excel. The tool is based on the Modified Iterative Measurement Test. A second tool, which is easier for handle large data sets and especially designed for networks with non-linear constraints was also developed. This second tool is only able to solve Data Reconciliation problems, so it is targeted for sets of data where there are exclusively random errors. Both developed tools were used to analyse the data set collected from the refinery’s Hydrocracker Unit with the purpose of generating a consistent set of data with balanced heat exchangers. The solution proposed is an energy balanced network, where from the 32 temperature measurements, all the reconciled values, except two, are within the specified bounds indicated. The two reconciled temperatures outside the bounds are the ones in which the presence of a gross error has been confirmed. Since this is a preliminary study, the solution proposed must be taken as a recommendation.
- PostWater Pinch Analysis of a Lignocellulosic Ethanol Production Process - Development of an Excel application for multiple contaminants(2015) Rolén, Alexandra; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentThe renewable fuels industry is faced with significant challenges related to increasing concerns about global warming and environmental impact. Bio-ethanol is a renewable fuel produced in large quantities, and its productions needs to be improved continuously, in particularly with respect to fresh water usage and waste-water effluent. This thesis uses a methodology for establishing targets and identifying design configurations for reduced fresh water usage and waste water effluent for a lignocellulosic bio-ethanol production plant. One of the major challenges for this type of analysis is the ability to take multiple contaminants into account. The objective of this thesis was to develop an analysis tool that is able to handle up to three types of contaminants. The work resulted in an application for Microsoft Excel that calculates targets for the minimum fresh water usage and waste water effluent release of a given process and proposes a water network configuration that is able to achieve these targets. The tool is based on methodologies proposed by Zhang et al. (2013). A simpler analysis and design tool with the capacity to handle a single contaminant only based on Foo (2013) was also developed for comparison purposes. Trying to perform a water pinch analysis revealed problems related to setting reasonable constraints for the maximum level of contaminant concentrations that the process units in the ethanol production process can tolerate. The results presented should only be considered as preliminary suggestions for opportunities to improve this type of process. For the lignocellulosic bio-ethanol process investigated, the single contaminant analysis tool indicates that the fresh water usage could be decreased by up to 23%. However, when three different types of contaminant are considered in the analysis, the potential fresh water savings are reduced to 13%, which underlines the importance of considered multiple contaminants in the analysis. The potential savings presented for single contaminants are on the same order of magnitude as numbers found in the literature.