No description available.

No description available.

In the present study, the problem of optimization of thermal cracker (pyrolysis) operation is discussed. The main objective in thermal cracker optimization is the estimation of the optimal flow rates of different feeds (such as, Gas-oil, Propane, Ethane and Debutanized natural gasoline) to the cracking furnace under the restriction on ethylene and propylene production. Thousands of combinations of feeds are possible. Hence the optimization needs an efficient strategy in searching for the global minimum. The optimization problem consists of maximizing the economic profit subject to a number of equality and inequality constraints. Modelling, simulation and optimal operation via optimization of the thermal cracking reactor has been carried out by gPROMS (general PROcess Modelling System) software. The optimization problem is posed as a Non-Linear Programming problem and using a Successive Quadratic Programming (SQP) method for solving constrained nonlinear optimization problem with high accuracy within gPROMS software. New results have been obtained for the control variables and optimal cost of the cracker in comparison with previous studies.

No description available.

No description available.

The current shortage of crude oil from conventional sources has increased interest in developing unconventional resources such as oil sands. Heavy crudes and bitumen are found in Northern Alberta and their exploration, processing, and transport to market pose challenges in the use of these resources. Part of the solution to these challenges involves the reactive thermal processing of heavy crudes and bitumen. This thesis focused on mild thermal cracking reactions, and two studies regarding these reactions were presented. The first was an experimental study performed in a pilot-scale semi-batch reactor. The three crude oils were heated to 350, 400, 425, and 450°C at 1240 kPa. A five-lump reaction model combined with a process simulator with VLE calculations was fitted with the experimental data obtained. The goodness of fit between the model predicted values and experimental values for the Hardisty (MBL), Albian Heavy Synthetic (AHS), and Christina Lake Dilute Bitumen (CDB) were determined to be 0.99, 0.99, and 0.98, respectively. Moreover, 80, 85, and 89% of the optimized model’s predicted values had less than 10% error for MBL, AHS, and CDB, respectively. The second study described the implementation of a mild thermal cracking reaction model to the development of a train car fire-model for the assessment of safety aspects in the design of train cars used to transport crude oil. Case studies were conducted using the UniSim® depressuring utility and a previously developed mild thermal cracking reaction model to demonstrate the effect of compositional change. Three crude oils with varying properties and representative of the types of crudes transported by rail in Canada were used here: MBL, AHS, and CDB. The case studies conducted showed the performance of a train car fire-model to be dependent on the crude oil characteristics: up to -57% and -99% difference in model predicted variables for AHS and CDB, respectively, when compared to MBL. Furthermore, the model’s performance was also shown to be affected by the compositional change of a given crude oil due to mild thermal cracking reactions: up to 42% difference in model predicted variables when compared to the base case.

Thermal cracking is an industrial process sensitive to both temperature and pressure operating conditions. The use of internally ribbed reactors is a passive method to enhance the chemical selectivity of the process, thanks to a significant increase of heat transfer. However, this method also induces an increase in pressure loss, which is damageable to the chemical yield and must be quantified. Because of the complexity of turbulence and chemical kinetics, and as detailed experimental measurements are difficult to conduct, the real advantage of such geometries in terms of selectivity is however poorly known and difficult to assess. This work aims both at evaluating the real benefits of internally ribbed reactors in terms of chemical yields and at proposing innovative and optimized reactor designs. This is made possible using the Large Eddy Simulation (LES) approach, which allows to study in detail the reactive flow inside several reactor geometries. The AVBP code, which solves the Navier-Stokes compressible equations for turbulent flows, is used in order to simulate thermal cracking thanks to a dedicated numerical methodology. In particular, the effect of pressure loss and heat transfer on chemical conversion is compared for both a smooth and a ribbed reactor in order to conclude about the impact of wall roughness in industrial operating conditions. An optimization methodology, based on series of LES and Gaussian process, is finally developed and an innovative reactor design for thermal cracking applications, which maximizes the chemical yield, is proposed

Agglomerate formation is a common phenomenon that can cause operating problems in the fluid coking reactor. When agglomerates form they provide longer diffusion paths of the reaction products through the liquid layers and liquid bridges within the agglomerate, which leads to higher mass transfer resistance, trapping of the reaction products and increasing the undesired coke formation reactions. Surviving agglomerates in the reactor can also cause fouling of the reactor interior and defluidization of the bed. The ultimate coke yield was determined for agglomerates of Athabasca vacuum residue and solid particles by heating on Curie-point alloy strips in an induction furnace at 503 oC and 530 oC and in a fluidized bed reactor at 500 oC until all toluene-soluble material was converted. Coke yields from agglomerates were compared to the results from reacting thin films of vacuum residue. The average coke yield from the agglomerates was 23%, while the coke yield from thin films of 20 m thickness was 11%, which supports the role of mass transfer in coke formation reactions. The ultimate coke yield was insensitive to vacuum residue concentration, agglomerate size, reaction temperature and agglomerate disintegration. The temperature profile within agglomerates was measured by implanting a thermocouple at the agglomerate center, and a heat transfer model was used to describe the temperature variation with time. The effective thermal diffusivity of the agglomerates was 0.20 x 10-6 m2/s. Control experiments on reactions in thin liquid films confirmed that heating rates in the range of 14.8 to 148 K/s had no effect on the ultimate yield of coke

Thermal stimulation of geothermal wells is a production enhancement technique that is an attractive option to operators of geothermal fields as a way to enhance and revitalize well performance capabilities through injection of cold water into the geothermal reservoir. This thesis presents a review of thermal stimulation procedures that have been carried out at various geothermal fields worldwide, and then sets out to demonstrate through laboratory experiments the effects of thermal stimulation on typical reservoir rocks. Thermal damage to crustal rocks is important in many fields of practical engineering applications. Thermal fractures have been discussed in many studies, however their formation under fully water saturated conditions as a result of rapid quenching is not fully understood. In this study, a new methodology is designed to replicate thermal stimulation in such an environment, using an apparatus that allows rocks to be heated to 350°C at up to 22 MPa confining pressure and rapidly quenched with cold water to ambient temperature while maintaining system pressure. The results indicate that through thermal cycling in the apparatus, porosity was increased, density decreased, acoustic velocities attenuated and mechanical properties significantly altered. Maximum damage occurred during the first thermal cycle, a product of the thermo-mechanical Kaiser effect such that rocks should not experience additional damage unless a previous maximum stress is surpassed. The thesis details a comprehensive evaluation of the Rotokawa Andesite sourced from the Rotokawa Geothermal field located in the Taupo Volcanic Zone, New Zealand. The importance of microstructural fabrics on the physical properties of this reservoir lithology is demonstrated. The mineralogical and petrological fabrics of the rocks are coupled with detailed studies of the microstructural fracture networks, including measurements of porosity, density and permeability. Acoustic wave velocities and dynamic elastic moduli were determined. Uniaxial compressive strength testing coupled with acoustic emission have helped to determine the behavior of the rock under deformation and provided data to characterize the static elastic moduli of the rocks. These data are then utilized to build empirical, micromechanical and geometric relationships. To better constrain important engineering concerns such as wellbore stability, reservoir forecasting and stimulation procedures, thermal property measurements were carried out on samples recovered from the Rotokawa Andesite. In particular, measurements of linear thermal expansion, thermogravimetric analysis, and differential scanning calorimetry were measured utilizing varied experimental heating rates of 2, 5 and 20 K/min. The property analyses were carried out to determine if heating rates influenced the measurement of thermal properties, specifically thermal expansion coefficients and strain rate in the samples. Results indicate that thermal expansion is not heating rate dependent within the range investigated though the strain rate is significantly dependent on heating rate, with higher strain rates observed in conjunction with higher heating rates. By using a one dimensional stress model, a failure criterion can be established for the Rotokawa Andesite when subject to thermal stressing. The importance of this study is to further understand the critical heating and cooling rates at which thermal stress causes cracking within the Rotokawa reservoir. This can enhance permeability but can also affect wellbore stability, so constraining these conditions can be beneficial to resource utilization. To test effects of thermal stimulation in the laboratory, Rotokawa Andesite core was heated to 325ºC at pressure of 20 MPa and quenched rapidly to 20ºC while maintaining a pressure of 20 MPa. Permeability increased by an order of magnitude over original pre-treatment values. Ultrasonic velocities also reflected a significant change after stimulation testing. Scanning electron microscopy showed significant microstructural change to samples and supplemented physical property investigations. The results imply that thermal stimulation can be successfully repeated in the laboratory and is coupled with both thermal and chemical components. The results of these investigations are of profound importance for effective utilization and maintenance of the Rotokawa Geothermal field and the results also have implications for geothermal fields worldwide.

No description available.