Books by Sandile Mondli Mtolo
An absorption column is required to recover acrylic and acetic acid from the gaseous reactor effl... more An absorption column is required to recover acrylic and acetic acid from the gaseous reactor effluent by contacting gas with water. Two incoming streams are handled by the column. The first is the gas stream of 5756,14 kmol/h with 0,078 % (wt./wt.) acrylic acid. It enters at a temperature of 280,50 °C and a pressure of 1,79 bar. The second stream contains processed water available from plant available at 30 °C and 1 bar and it is mixed with 500 ppm of hydroquinone inhibitor. The choice of hydroquinone as an inhibitor for this process was facilitated by its known properties to prevent polymerization of acrylic acid that is susceptible to radical-initiated polymerization (Schork, 2006). The preferred inhibitor dilution range is between 300ppm – 700 ppm (Elder J.E, 2006). The column has two exiting streams, gaseous stream and aqueous liquid stream. The gaseous stream exits at a flowrate of 5782,13 kmol/h with 390,3 ppm (wt./wt.) of acrylic acid and 23.98 ppm (wt./wt.) of acetic acid. It exits at a temperature of 70,13 °C and a pressure of 1 bar. The second exiting stream is the product stream at a total flowrate of 1576, 9 kmol/h. This stream contains 55.2 % (wt./wt.) acrylic acid (main product). It exits at a temperature of 81, 86 °C and a pressure of 1 bar. This stream is cooled to 46.5 °C prior to the LLE unit.
The product specification requires 100 000 tonnes per year of ester grade acrylic acid (minimum purity 94% (wt.) by oxidation of propylene (94% purity on molar basis). This acid product requires approximately 817.33 kmol/h of processed water. The use of packing columns is recommended for diameters less than 0.6 m (Seader, et al., 2011). The obtained diameter was 5,21 m, thus, a packed column couldn’t be chosen. Sieve trays (as opposed to bubble or valve-type trays) were chosen because of their ease of installation and lower cost compared to packed columns. The choice of sieve trays was also facilitated by their well-known design procedures, low fouling tendency and large capacity (Seader, et al., 2011). The design specifies a column with approximately 24.8 m of height, and containing 60 sieve plates. Processed water with 300 ppm of hydroquinone inhibitor is added to tray 1 (the top tray), and recycle stream is added at tray 69, one stage above the base stage. Single pass crossflow-type trays are employed for all the plates. The column operating pressure is 1 bar and the operating temperature range is from 69,85°C to 81.8 °C. A safety factor of 10% was accounted for in the design temperature and pressure. The total weight of a column vessel including the shell weight, plates and insulation is 1096,85 kN which is equivalent to 111847,55 kg. The absorption column and its associated structures (insulation, trays and vessel) are expected to cost in the region of R 8,8 million. Detailed calculations concerning the absorption column design are presented in Appendix F.
Papers by Sandile Mondli Mtolo
The aim of this project was to investigate ferrosilicon replacement through the use of spherical ... more The aim of this project was to investigate ferrosilicon replacement through the use of spherical magnetite in water in a wet heavy medium. By replacing this ferrosilicon with a waste product from titanium sand processing (spherical magnetite), it was hoped that higher density media would be achieved in a fluidized bed without reaching a viscous limit. Investigation on whether fine magnetite suspensions could gain an increased density without meeting the viscosity limit by addition of the coarser spherical magnetite was also done. Separations of coal was then tested. Dense medium of about 2000kg/m3 was prepared using fine magnetite and the setting rates of density tracers were measured. Another dense medium of about 1600kg/m3 was prepared using spherical magnetite and settling rates were again calculated. Spherical magnetite did not completely mix with water to form a required dense medium, thus; it was added to a previously prepared fine magnetite medium in increments of 100 kg/m3 to a final set density of 1500 kg/m3 without reaching a viscous limit.
Settling rates of density tracers in this set density were measured. A sample of shale and coal (feed ash content of 17.32%) was used to measure the separation efficiency of the prepared dense medium. Coal and shale ash content was determined using the furnace and thereafter, the necessary calculations were done to generate the tromp curve. The separation inefficiency EP usually lies in the range of 0.02 – 0.08(Wills, 1997). For this project, an EP value of 0.05 (which is within the required range) was assumed. An EP value of 0.06 was calculated from the generated tromp curve and this translated to 94% separation efficiency.
At a set density of 1500 kg/m3, 88.21 % of material reporting to the floats with 11.79% going to the sinks, and 80.02% mass yield was achieved. It was concluded that; the replacement of fine magnetite by spherical magnetite would be feasible since it could reduce the cost of raw materials for a process, spherical magnetite can be used to be replace ferrosilicon in a heavy medium, spherical magnetite could replace some of the fine magnetite at lower densities since it does not have much effect on the viscosity at higher densities and finally, sharp and efficient separation of coal were possible at lower densities. Furthermore, it was recommended that; fine magnetite must be replaced with spherical magnetite to decrease viscosity and process costs, use a pump capable of pumping high density slurries, an effective stirrer with bigger impellers must be used and a bed or column of bigger diameter must also be used to decrease wall effects.
Uploads
Books by Sandile Mondli Mtolo
The product specification requires 100 000 tonnes per year of ester grade acrylic acid (minimum purity 94% (wt.) by oxidation of propylene (94% purity on molar basis). This acid product requires approximately 817.33 kmol/h of processed water. The use of packing columns is recommended for diameters less than 0.6 m (Seader, et al., 2011). The obtained diameter was 5,21 m, thus, a packed column couldn’t be chosen. Sieve trays (as opposed to bubble or valve-type trays) were chosen because of their ease of installation and lower cost compared to packed columns. The choice of sieve trays was also facilitated by their well-known design procedures, low fouling tendency and large capacity (Seader, et al., 2011). The design specifies a column with approximately 24.8 m of height, and containing 60 sieve plates. Processed water with 300 ppm of hydroquinone inhibitor is added to tray 1 (the top tray), and recycle stream is added at tray 69, one stage above the base stage. Single pass crossflow-type trays are employed for all the plates. The column operating pressure is 1 bar and the operating temperature range is from 69,85°C to 81.8 °C. A safety factor of 10% was accounted for in the design temperature and pressure. The total weight of a column vessel including the shell weight, plates and insulation is 1096,85 kN which is equivalent to 111847,55 kg. The absorption column and its associated structures (insulation, trays and vessel) are expected to cost in the region of R 8,8 million. Detailed calculations concerning the absorption column design are presented in Appendix F.
Papers by Sandile Mondli Mtolo
Settling rates of density tracers in this set density were measured. A sample of shale and coal (feed ash content of 17.32%) was used to measure the separation efficiency of the prepared dense medium. Coal and shale ash content was determined using the furnace and thereafter, the necessary calculations were done to generate the tromp curve. The separation inefficiency EP usually lies in the range of 0.02 – 0.08(Wills, 1997). For this project, an EP value of 0.05 (which is within the required range) was assumed. An EP value of 0.06 was calculated from the generated tromp curve and this translated to 94% separation efficiency.
At a set density of 1500 kg/m3, 88.21 % of material reporting to the floats with 11.79% going to the sinks, and 80.02% mass yield was achieved. It was concluded that; the replacement of fine magnetite by spherical magnetite would be feasible since it could reduce the cost of raw materials for a process, spherical magnetite can be used to be replace ferrosilicon in a heavy medium, spherical magnetite could replace some of the fine magnetite at lower densities since it does not have much effect on the viscosity at higher densities and finally, sharp and efficient separation of coal were possible at lower densities. Furthermore, it was recommended that; fine magnetite must be replaced with spherical magnetite to decrease viscosity and process costs, use a pump capable of pumping high density slurries, an effective stirrer with bigger impellers must be used and a bed or column of bigger diameter must also be used to decrease wall effects.