M.A. Doheim

Investigation of the Ring Area Formed Around Cavitation Erosion Pits on the Surface of Carbon Steel

The ring areas formed around micropits in cavitation erosion experiments were investigated. The corrosion behavior and vibratory cavitation erosion tests of mild carbon steel in tap and distilled water were carried out. Thus, the ring areas were densely formed in tap water and scarcely formed in distilled water in cavitation tests. The ring areas formed around micropits in cavitation and free cavitation tests have a similar shape. Moreover, SEM examinations showed that the corrosion products spread within the ring areas. Thus, the ring areas formed around micropits are the result of corrosion effect and are not the result of thermal effects due to bubble collapse.

Fluidized bed roasting of molybdenite-effect of operating variables

The results of an investigation on the fluidized bed roasting of molybdenite are reported. Molybdenite mixed with quartz was subjected to an oxidizing roast in a 22 mm diam stainless steel batch fluidized bed reactor. Enriched air (with O2) or diluted air (with N2) was used as the fluidizing and oxidizing gas. In addition to the MoS2 content of the solids and the O2 content of the gas, the effect of temperature and flow rate was also examined. For the range of variables investigated, it was found that the temperature influences the rate of the roasting reaction greatly. The gas flow rate affects the conversion favorably up to a certain fluidizing flow rate. An increase in the O2 content of the gas and the MoS2 of the solids results in higher conversion levels. The unreacted core kinetic model was applied to the results; and the energy of activation for the reaction was obtained from the Arrhenius plot as 31,100 cal/gmol of MoS2. The data obtained should be useful in the design and operation of larger scale roasting reactors.

Analysis of waste heat and its recovery in a cement factory

Abstract The cement industry is an energy intensive industry. Energy prices necessitate energy efficient systems, i.e. deep consideration of energy conservation and waste-heat recovery must be made. In the present work, a cement industry was examined with respect to thermal energy consumption, losses and the potential of heat saving. The production line investigated involved a cyclone preheater and precalciner prior to the kiln. In carrying out the work, data were obtained from the control room and by direct measurements on the different units. The thermal energy analysis of the system revealed that a considerable amount of fuel heat is dissipated. For recovering the waste heat, it has been proposed to insulate the external surface of the cyclones and ducts in the preheater unit. The optimization study on the insulations indicated that a 2% fuel saving can be achieved with highly viable payback times ranging from 0.07 to 0.72 yr.

Contact time distribution in fluidized-bed reactors part I: Measurements at room and higher temperatures

Abstract The contact time distribution (CTD) is required in order to predict the performance of gas/solid fluidized-bed reactors. By using certain plausible assumptions, the CTD can be determined from two total residence time decay functions for an adsorbable tracer corresponding to different extents of adsorption. The gas-phase residence time distribution (RTD) can also be determined. The total residence time decay functions were measured using a 6 inch diameter fluidized bed of commercial cracking catalyst with air as the fluidizing gas and nitrous oxide as the tracer. The determinations of the CTD and RTD were carried out at various flow rates and temperatures. The fraction bypassing can be obtained from the CTD curves.

Fluidized-bed thermal treatment of phosphate rock: Effect of operating variables

Abstract The presence of huge amounts of low- and intermediate-grade phosphate ore and the need for high-grade ore for industry, necessitates the availability of economic and efficient upgrading techniques. The fluidized-bed technique is most suitable for upgrading, by thermal treatment, of ores having high percentages of organic matter, carbonates, and moisture. In this work, studies were carried out on the process of thermal upgrading of phosphate rock in a fluidized-bed furnace of 10-cm diameter. The studies involve the effect of the important operating variables such as process temperature, air-flow rate, calcine quenching temperature, and the attrition of phosphate particles. A run-of-mine intermediate-grade phosphate ore was used. Batch and continuous runs were carried out and the ore was calcined and washed. It was found that the increase in process temperature favourably affects the % upgrading of the ore, but this should be studied in close connection with the economic aspects, especially in the case of ores with low carbonaceous matter contents. The fluidizing air-flow rate, and thus, the hydrodynamic condition of the bed, slightly affects the upgrading process. The use of high air-flow rates increases the extent of attrition of phosphate particles. The quenching temperature of the calcine was found to have no effect on the process product, within the range investigated.

Examination of single and repetitive impact breakage

Abstract Impact breakage is experienced in many size reduction machines. The crushing behavior of a single bed under single and repetitive impact is studied. Materials with widely differing physical and mechanical properties and varied feed size were used to elucidate their behavior under varied values of impact energy. It is shown that with an increase in the feed size of the materials, the crushability increases at the same applied energy for both single and repetitive impacts. The repetitive impact shows more energy efficiency than the single impact with materials that show differences in compressive strength, depending upon the orientation of the applied impact. On the other hand single impact crushing is more effective than the repetitive one for materials that have no bedding planes or cleavages.

Fluidization in the non-ferrous mineral processing and metal industry

Abstract Fluidized-bed technology has established itself as a major processing technique in the non-ferrous metal industry. The technique is being commercially used or is being developed towards commercial use in ore separation and beneficiation, drying, calcining, roasting, metal extraction and refining, and metal and alloy treatment. This paper describes briefly and discusses the use of fluidization in these different stages. The discussion extends to certain design considerations and the scale-up problem. The problems associated with conducting the different processes are discussed. The pyrometallurgical processes, using fluidized beds, have been well established without significant problems for most of the non-ferrous metals. The use of fluidized beds is being applied to a wide field of different metal and alloy treatment processes.

Energy analysis and waste heat recovery in a refinery

Petroleum refining is an energy-intensive industry and waste-heat recovery is essential. We investigate energy consumption of 4 refining processes: two crude distillation units, a vacuum distillation unit, and a platforming unit. Current heat-recovery practices and a new heat-recovery system are explored. Heat losses ranged from 25 to 62% of total heat input. The proposed heat-recovery methods increased the heat-utilization efficiencies by 12 to 48.5%, with overall heat losses reduced by 9.9 to 37.3%. A rotating regenerative heat exchanger is the heat-recovery unit of choice in terms of fuel saving and pay-back time.

Rapid estimation of corrected cut point in hydrocyclone classification units

Abstract In dressing plants, the rapid determination of the corrected cut point in hydrocyclone classification is desirable, useful, and important. In this work, classification tests have been carried out on white sand using a 10-cm diameter hydrocyclone to examine closely the relation between the recovery to underflow and the corrected separation size, d 50 . The study was carried out at wide ranges of: apex diameter, vortex-finder diameter, solid content of feed, and length of vortex finder. A simple, yet reliable, equation relating the solid recovery of underflow to d 50 , is developed using all the obtained results. The predicted data show good agreement with the experimental.

Effect of Electroless Ni‐Co‐P and Co‐P Coatings on Cavitation Erosion Resistance

In the present work, electroless Ni-Co-P and Co-P coatings were produced on AISI 1045 steel with and without post-heat treatment. The properties of electroless coatings were characterized using an optical microscope, and microhardness tester. The cavitation erosion resistance of coatings was evaluated using a vibratory cavitation test. The test was carried out both in tap water and 3 wt.% NaCl solution, respectively.