Apostolos Kantzas

The dynamic calibration of an electrical capacitance tomography sensor applied to the fluidized bed drying of pharmaceutical granule

Electrical capacitance tomographic data collected in a lab-scale fluidized bed used for the drying of pharmaceutical granule have been corrected for the influence of moisture on the permittivity of the drying material. The correction is based on a linear least-squares fit to measurements of capacitance in a packed bed of granule at various moisture contents. X-ray tomography has been used to independently verify this correction procedure. The influence of permittivity models and number of iterations used for the reconstruction of tomograms have also been examined. It has been determined that the Bottcher permittivity model performs best at bed moistures above approximately 5 wt% while the parallel model is superior at bed moisture below this value. The reconstruction technique based on iterative linear back-projection utilized for the reconstruction of ECT data required approximately 50 iterations to successfully reproduce the density behaviour seen in the x-ray tomographs. Instability in the reconstruction technique at higher numbers of iterations indicates that a linear least-squares fit does not completely capture the response of the sensor to moisture changes. For future applications, changes in bed voidage associated with the drying of pharmaceuticals must be addressed and included in this calibration procedure in order to implement this calibration technique throughout the drying process. Nevertheless, the viability of this technique for on-line calibration of an ECT sensor applied to the drying process has been demonstrated.

Quantification of channelling in polyethylene resin fluid beds using X-ray computer assisted tomography (CAT)

Abstract The determination of fluid distributions in fixed and fluidized beds was given a new dimension with the implementation of tomographic imaging techniques. Of particular interest is the time-averaged macroscopic determination of solids and gas in gas-phase polymerization reactors. The voidage distribution coupled with appropriate kinetic models can provide an estimate of deviation from expected fluid behaviour, which is due to the presence of hot spots or gas by-passing. In this study, the fluidization characteristics of commercially available LLDPE and HDPE resins were investigated using X-ray CAT scanning. The experiments were run in a small column with a diameter of 10 cm (D) and variable bed heights at L D ratios of one, two and three. The fluidization velocities were varied between one and three times the minimum fluidization velocity for each sample. All experiments were performed at ambient conditions. The X-ray CAT scanner images describe the solid and gas distributions at a resolution of 400 μm by 400 μm in cross-section and 3 mm in thickness. Hundreds of images were collected and analysed. It is very important to note that in most cases the slice-average voidage is constant through the column length. However, there is considerable radial variability within each slice. This variability is measured as a function of position, and in fixed positions as a function of time. In this paper, we try to quantify these observations through comparisons of the voidage distribution of a fluid bed to the expected corresponding distribution of a uniform bed. Deviations from the expected mean are classified in distinct categories. The areas of consistently high gas concentration are identified as areas of gas channelling. Having identified these areas, we proceeded with the determination of the formation and propagation of gas channels in a fluid bed both in the spatial and temporal domains. We found that the simple fluid-bed systems we used in the laboratory exhibited a complicated gas channelling picture at relatively low L D and relatively low fluidization numbers. Channels can appear in the bed and can have a variety of characteristics and relative positions in the bed while the operating conditions vary only slightly. The implication of such channels in the operation of gas-phase polymerization reactors is also presented.

Heavy Oil Waterflooding: Effects of Flow Rate and Oil Viscosity

Many countries in the world contain significant heavy oil deposits. In reservoirs with viscosity over several hundred mPa·s, waterflooding is not expected to be successful due to the extremely high oil viscosity. However, in many smaller, thinner reservoirs, or reservoirs at the conclusion of cold production, thermal enhanced oil recovery methods will not be economic. Waterfloods are relatively inexpensive and easy to control; therefore, they will still often be employed in high viscosity heavy oil fields. This paper presents experimental findings of waterflooding in laboratory sandpacks for two high viscosity heavy oils of 4,650 mPa·s and 11,500 mPa·s at varying water injection rates. The results of this work show that capillary forces, which are often neglected due to the high oil viscosity, are important even in heavy oil systems. At low injection rates, water imbibition can be used to stabilize the waterflood and improve oil recovery. Waterflooding can therefore be a viable non-thermal enhanced oil recovery technology, even in fields with very high oil viscosity.

Monitoring the fluidization characteristics of polyolefin resins using X-ray Computer Assisted Tomography scanning

Flow visualization of chemical reactor phenomena was given a new direction with the implementation of process tomography techniques. These techniques can provide valuable information on flow phenomena in heterogeneous reactors. In particular, visualization and understanding of flow phenomena in gas phase polymerization reactors can aid us in achieving a better temperature distribution in the reactor and higher quality of products. In this study, the fluidization characteristics of a series of commercially available LLDPE, HDPE and IPP resins were investigated. The experiments were run in a small column of 10 cm in diameter (D) and variable bed heights (L), at L/D ratios of one, two and three. The fluidization velocities were varied between one and three times the minimum fluidization velocity of each sample. The particle size distributions varied from very narrow mesh sizes to full particle size distributions as they came out of commercial gas phase polymerization reactors. The resins also varied in sphericity. In several samples, there was some rubber present in the particles resulting in a “stickiness” characteristic of the resin. All experiments were performed at ambient conditions and inside the x-ray Computer Assisted Tomography (CAT) scanner facility. The CAT scanner images provided areal gas voidage distributions as a function of position and operating conditions at a resolution of 400 μm by 400 μm in cross section and 3 mm in thickness. A large number of images were collected and analyzed. Experimental results clearly established a set of fluidization experiments that gave relatively uniform voidage distributions, whereas other experiments had extremely non-uniform voidage distributions. Segregation and channeling were also observed under various operating conditions. It was found that certain regions of the bed were characterized by high voidage while others by very low voidage. These regions varied with experiments using the same resin but different velocities and L/Ds. The spatial variability of the voidage was also described in terms of statistical moments, frequency distributions and variograms. The voidage distributions were found to vary from wide unimodal to tri-modal of the same range for experimental conditions that, at first sight, did not appear to be significantly different. This paper describes the various categories of voidage distributions observed and provides some first correlations between voidage and operating parameters. A discussion of the implications of such phenomena to the performance of a gas phase polymerization reactor is also presented.

Viscosity Determination of Heavy Oil and Bitumen Using NMR Relaxometry

Knowledge of oil viscosity is important when estimating hydrocarbon reserves and evaluating the potential for water-flooding of EOR processes. This information is especially important in heavy oil and bitumen, as viscosity is usually the major impediment to recovery of these reserves. As oil viscosity increases, obtaining a laboratory measured in the lab may not be prone to error, and viscosities measured in the lab may not be representative of field conditions. Nuclear magnetic resonance (NMR) is therefore presented as an attractive alternative method for determining oil viscosity. Several correlations already exist for determining oil viscosity using NMR. Some of these correlations compare the geometric mean T 2 relaxation time to oil viscosity, while others relate viscosity to the apparent hydrogen index. This paper examines these different models on a suite of conventional and heavy oil samples. It is concluded that none of the existing models can accurately predict oil viscosity for both conventional and heavy oils, especially for oils with viscosity higher than 20,000 cP. All the measured oil sample show a correlation between oil viscosity and the geometric mean T 2 relaxation time, and also between viscosity and relative hydrogen index. This is consistent with what other experimenters have noticed. An empirical model is developed, correlating oil viscosity to both of these parameters. Unlike previous models, this model can accurately predict oil viscosity for both conventional and heavy oil. The wider range of this model makes it useful for laboratory analysis of oil viscosity using NMR. If the results of this model can be applied to in situ oils. NMR can be used as a logging tool to characterize heavy oil and bitumen formations. The model presented in this paper is the first step towards succesfully predicting viscosity in situ.

Porosity distributions in carbonate reservoirs using low-field NMR

Alberta contains significant deposits of oil and gas in carbonate formations. Carbonates tend to have fairly tight matrix structures, resulting in low primary porosity and permeability. Laboratory characterization of carbonate properties is a slow and tedious process, however, core data is often collected in order to augment and tune logging tool predictions. In this application, having a good understanding of carbonate pore systems at the core analysis level is key to proper reservoir characterization. Low-field NMR is an emerging technology that shows great promise for rock characterization measurements. In this paper, low-field NMR technology is investigated for determining primary and secondary porosity through the interpretation of NMR spectra. This data was also used to establish the bound and mobile fluid distributions existing in the porous medium. The data set for this experimental work consists of a large collection of core samples from various fields in Alberta and Saskatchewan. CT data were analyzed to obtain the primary and secondary porosity fractions, which were used to find corresponding NMR cutoff values that separate the NMR spectra into primary and secondary porosity. A distinct relationship was observed between the primary porosity fraction and the irreducible water saturation, S wi . The fraction of NMR amplitude in the last peak of the NMR spectra can also be correlated to CT secondary porosity. Another important relationship observed is that the geometric mean relaxation time of the last NMR peak correlates well with the cutoff between primary and secondary porosity. The bound and mobile fluid distributions are generally distinguished through the identification of T 2cutoff values. A correlation was found to predict T 2cutoff for this wide range of samples. This study shows that information from the fully saturated NMR spectrum can be used to estimate primary and secondary porosity fractions in carbonates, as well as bound and mobile fluid fractions.

Advances in Magnetic Resonance Relaxometry for Heavy Oil and Bitumen Characterization

This paper offers a summary of the advances in heavy oil and bitumen reservoir characterization and fluid stream monitoring using low field magnetic resonance tools. Both laboratory and field advances are presented. Although the bulk of the work discussed was performed in our laboratory, a selection of other pertinent technologies is also presented. This overview aims at offering the reader a quick reference of what has been achieved in the past ten years and it is hoped that it will be used as a guide for future development in this area.

Measurement of hydrodynamic data of gas-phase polymerization reactors using non-intrusive methods

The hydrodynamic characteristics of polyethylene resins are studied in detail through a combination of different techniques in our laboratory. Computer Assisted Tomography is used to determine voidage distribution under different operating conditions. Radioactive particle tracking is used to determine the solid particle trajectories, the horizontal and vertical velocities of the solids and the residence time distribution of the solids. X-ray fluoroscopy is used to determine bubble frequency and velocity. All these techniques are then combined with the information obtained through monitoring pressure fluctuations in the fluidized bed columns. All experiments are performed in Plexiglas columns of diameters that vary between 10 and 30 cm in diameter. The materials used are polyethylene and air, respectively. The combination of these techniques provides the unique opportunity to study the fluidized bed systems in great detail. Unfortunately, all techniques cannot be implemented in a single experiment. As a result, the same experiment is repeated as many times as necessary to collect the required data. The column is moved from one imaging system to the next and the experiment is repeated under the same operating conditions. It is believed that the data collected can be used as if all the data were collected during the same test. This paper presents preliminary experimental results for each set of experiments along with the nature and limitations of each set of experimental data. The results from each different system are combined in an effort to describe the complex hydrodynamics of the bed. The incremental information obtained in each set of experiments compared to the macroscopic measurements (flow rate and pressure drop) is demonstrated.

Effect of Temperature and Pressure on Contact Angle and Interfacial Tension of Quartz/Water/Bitumen Systems

Thermal-recovery methods (e.g., steam injection) are commonly used to recover bitumen from oil sands. The injected steam contacts the oil sand and forms an interface. The steam changes to water, transferring its heat to bitumen across this interface. The heated bitumen will have a lower viscosity, which allows for oil to be mobilized and recovered from the reservoir. Studies that explain hot-water/bitumen interfaces are crucial for understanding thermal-recovery methods. The strength and energy of hot-water/bitumen interfaces are expected to play important roles in the recovery of bitumen from oil sands. However, measurements on hot-water/bitumen interfaces are scarce in the literature. A relevant measurement would be the contact angle and interfacial tension (IFT) of the water/bitumen interfaces at different temperatures. In this paper, it has been attempted to reveal and present the results of several water/bitumen contact-angle and IFT measurements. The measurements cover a temperature range from ambient to 100°C for a given pressure. The experiments are run in X-ray transparent cells, and images are taken using a microcomputed-tomography (microCT) scanner. The results of contact angle and the IFTs of the hot-water/bitumen interface are produced by using the axisymmetric drop shape-analysis (ADSA) method.

In Situ Viscosity of Heavy Oil: Core and Log Calibrations

Having knowledge of oil viscosity variation within reservoirs would be of considerable benefit when producing from heavy oil fields. Previous work has demonstrated that low field NMR bench-top instruments can be used to perform measurements of in situ viscosity. Ideally, if these measurements could be performed on NMR logging tools, viscosity characterization studies could be carried out using fewer core samples. In this paper, data is presented for a heavy oil reservoir in northern Alberta. A methodology is presented for tuning NMR viscosity estimates to the field in question, and core analysis results are collected, showing that in situ viscosity predictions are possible in the laboratory. NMR spectra measured in the laboratory are compared to NMR logging tool spectra, in order to determine if results obtained using bench-top instruments can be extrapolated to logging tool data.