No description available.

A systematic study has been made of the factors which influence compressibility in cake filtration. A fully automated dead-end pressure filtration rig was designed, constructed and assembled at Loughborough and used to provide accurate data for an experimental matrix. The parameters investigated included pressure, feed concentration, time, surface charge, size and shape of the particulate material and scale of filtration. A proven electrical resistance measuring technique was used to determine transient solids concentrations through a filtering cake/suspension and subsequently interpret filtration performance. The particulate materials calcite and zinc sulphide dispersed in water were used to span a range of filter cake compressibility. The initial results from experiments using calcite were found to be reproducible and generally followed the expected trends. More compressible materials, such as zinc sulphide, were subsequently filtered at different pHs to investigate the influence of surface charge. Filter cells of different filter sizes were used to examine the influence of scale on filtration. Several curious observations were made such as sudden increases in filtrate rate at apparently stable process conditions and lower concentration measurements near the base of the cake. The importance of considering all scale-up parameters and their relation to each other is highlighted in the work. Further points such as the definition of compressibility over a narrow range of pressure and the structure of the filter cake have been discussed. The results were analysed with the use of conventional and new filtration theories. The conventional and modem theories generally gave good predictions of cake height for all the materials tested but for unstable/compressible suspensions the prediction of the concentration profile was less accurate. The use of the maximum solids concentration value at the base of the cake has been suggested to reduce this error and so help prevent filter under sizing. Results indicating retarded packing compressibility have been discussed along with volume-time data which suggest an influence of scale on filtration. Scale-up constants were found to vary considerably in some cases. Large changes in cake resistance were seen for small changes in cake concentration suggesting a need to use other structural characterising parameters as well as macroscopic cake concentration values. The Koenders and Wakeman model gave good predictions of the first linear part of the volume-time relationships for stable suspensions. Conclusions are drawn on the influence of each of the studied parameters on the filtration of compressible materials.

Call number: LD2668 .T4 1986 N47 / Master of Science / Human Nutrition

Please read the abstract in the section, 00front of this document / Dissertation (MInst Agrar (Food Processing))--University of Pretoria, 2008. / Food Science / MInst Agrar / Unrestricted

Call number: LD2668 .T4 1978 Y45 / Master of Science

Full and partial substitution of sucrose with polydextrose, and its effects on properties of batters and structure development of cakes were studied. Although substitution levels around 25% did not alter the properties of the system, higher levels of replacement resulted in significant changes in batter and cake properties. The effects of sucrose replacement by polydextrose on starch gelatinization and egg protein denaturation temperatures were studied by differential scanning calorimetry in model systems. Experiments showed that polydextrose raises gelatinization temperature more than sucrose. No significant difference was found between the two solutes with respect to their effect on egg protein denaturation. Dynamic oscillatory experiments showed that the viscoelastic profile of cake batters is altered when polydextrose is used to replace sucrose. A clear tendency towards permanent deformation and fluid-like behaviour was observed with increasing levels of replacement by polydextrose. Changes in rheological properties of batters with increasing polydextrose concentration were related to bubble size and distribution of cake batters. Microscopical techniques were developed to assess the foam characteristics of batters, before and during heating. Increasing level of replacement increased the mean size of bubbles and introduced large variation in bubble size distribution. The lack of uniformity in bubble distribution of polydextrose batters increased the rate of gas diffusion from the small bubbles to larger ones. During heating, bubble population of conventional batters expanded more than that of polydextrose substituted batters. Changes in bubble expansion rates resulted in cakes of lower volume with increasing levels of replacement. Assessment of textural properties of cakes indicated that sucrose replacement at levels around 50% or greater contributes to weakening the mechanical strength of crumb structure. Scanning electron microscopy of crumb samples demonstrated changes on the degree of starch granules swelling, cell wall structure and matrix development, as a result of sucrose replacement by polydextrose

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Formate-based mud has been used to drill deep gas wells in Saudi Arabia since 2004. This mud typically contains XC-polymer, starch, polyanionic cellulose, and a relatively small amount of calcium carbonate particles, and is used to drill a deep sandstone reservoir (310°F). Calcium carbonate particles are frequently used as weighting material to maintain the pressure that is required for well control and minimize the leak-off. Such solids become consolidated and trapped in the polymeric material and this makes the filter cake a strong permeability barrier. Various cleaning fluids were proposed to remove drilling mud filter cake; including: solid-free formate brine and formate brine doped with organic acids (acetic, formic, and citric acids), esters, and enzymes. The main objective of this research is to assess the effectiveness of these cleaning fluids in removing drilling mud filter cake. A dynamic high-pressure/high-temperature (HPHT) cell was used to determine characteristics of the drilling mud filter cake. Drilling mud and completion fluids were obtained from the field. Compatibility tests between potassium formate brine, cleaning fluids, and formation brine were performed at 300ºF and 200 psi using HPHT visual cells. Surface tensions of various cleaning fluids were also measured at high temperatures. The conventional method for cleaning the filter cake is by circulating solid-free formate brines at a high flow rate. This mechanical technique removes only the external drilling fluid damage. Citric acid at 10 wt%, formic acid, and lactic acid were found to be incompatible with formate brine at room temperature. However, these acids were compatible with formate brine at temperatures greater than 122°F. Only acetic acid was compatible with formate brine. A formula was developed that is compatible at room and reservoir temperature. This formula was effective in removing filter cake. A corrosion inhibitor was added to protect downhole tubulars. In general detail, this research will discuss the development of this formula and all tests that led to its development.

The main goal of drilling a horizontal well is to enhance productivity or injectory by placing a long distance drain-hole within the pay-zone. Poor drilling fluid design results in difficulties such as poor hole cleaning, excessive torque or drag, wellbore instability, stuck drill string, loss of circulation, subsurface pressure control, poor cement jobs, and difficulties associated with running electric logs and formation damage can result. Neither of the conventional chemical cleaning methods can overcome problems for filter-cake removal in long horizontal and maximum reservoir contact wells because of limitations such as the complex geometry of wells, non-uniform chemical distribution, low contact between cleaning fluids/filter cake, and high chemical reaction rate, especially at high temperatures. This study describes a novel self-destructing drilling fluid system. Filter cakes are formed from a formula of drilling fluid that have a mixture of solid acid precursor and particulate solid acid-reactive materials. Then in the presence of water, the solid acid precursor (polylactic acid) hydrolyzes and dissolves, generating acids that then dissolve the solid acid-reactive materials (calcite). It effectively stimulates the horizontal section right after drilling and eliminates acidizing, resulting in significant cost savings, and improves filter-cake removal, thus enhancing the performance of the treated wells. A series of experiments have been run in the lab to determine the efficiency of this new system. Properties of this drilling fluid are measured. Experiments on solid acid particle size showed that the best size-distribution of solid acid precursor and solid reactive material to make a self-destructing filter cake is fine particles of calcium carbonate used as weighting material with 150 microns polylactic acid as solid acid precursor. By comparison of the results of the experiments at different temperatures, 230 degrees F has been chosen as the best temperature for running experiments. The self-destructing drilling fluid systems need enough time for the solid acid to be hydrolyzed and therefore remove the filter cake. After 20 hours of contact with the water as the only cleaning solution, about 80 percent of the filter cake was removed. Calcite is found to be the dominant compound in the sample of remained filter cake, which was proved by x-ray diffraction tests. Secondary electron microscopy (SEM) results show the morphology of the remained filter cake sample and confirm the crystalline area of calcite.

Food and eating are often associated with both positive and negative emotions: pleasure and enjoyment, and also worry and guilt. Guilt has the potential to have both adaptive and maladaptive consequences on health behaviours. The present study aimed to further explore the relationship between a default association of guilt with a ‘forbidden’ food item (i.e., chocolate cake) and healthy eating behaviours, attitudes, intentions, and perceived behavioural control. Individual difference variables (self-control, self-compassion, and neuroticism) and stress were also examined in relation to guilt. This study investigated the influence of a default guilt association on hypothetical and actual food choices. The findings suggest that food-related guilt can have both adaptive and maladaptive consequences on healthy eating behaviours and on individual difference variables. Individuals with chocolate cake-guilt associations reported healthier eating intentions and higher perceived behavioural control in relation to healthy eating. Those with guilt associations did not report more positive attitudes toward healthy eating nor higher self-control. They reported lower levels of self-compassion and higher levels of neuroticism and perceived stress. In regard to a hypothetical food choice, no differences were found between those with guilt or celebration associations. With one exception, guilt did not have adaptive effects during a taste test in regard to sweet and savoury food intake and post-eating guilt. Self-control appeared to be a protective factor from the maladaptive effects of guilt: self-control moderated the relationship between a guilt association and healthy eating intentions and savoury food intake. The overall findings from this research indicate that an alternative approach to promoting healthy eating and living should be considered.