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- South African Journal of Chemical Engineering
- OA African Journal Archive
- Volume 13, Issue 2, 2001
South African Journal of Chemical Engineering - Volume 13, Issue 2, 2001
Volume 13, Issue 2, 2001
Using a Turbine Expander to Recover Exothermic Reaction Heat - a Case Study on a Phthalic Anhydride ProcessAuthor F.J.J.G. JanssenSource: South African Journal of Chemical Engineering 13, pp 1 –14 (2001)More Less
Phthalic anhydride (PA) is produced from alkyl-substituted- or multinuclear aromatic compounds such as o-xylene or aphthalene by partial oxidation. With reaction enthalpies as high as -1 793 kJ/mol naphthalene reacted, there are many opportunities for energy recovery making these systems attractive for process integration research.<p>The production of PA from naphthalene is used to investigate two energy recovery schemes. The first is a Rankine cycle that uses steam, raised during the cooling of the reactor, to produce power. The second also includes a turbine expander at the reactor exit. It expands hot reactor product gases to deliver additional power and reduces the pressure of the reactor product before it enters the separation section.<p>Simulation results showed that, under certain operating conditions, the steam cycle alone could not supply the feed compression power requirement. However, when a turbine expander is included in the process, all of the power requirements can be fulfilled and as much as 2 651 MJ/ton PA can be exported for use elsewhere.<p>Unlike power generation from fossil fuels, no carbon dioxide is emitted to the atmosphere when an expansion turbine is used. Savings in CO<sub>2</sub> emissions between 0.46 and 0.75 ton CO<sub>2</sub>/ton PA are estimated for this unit.<p> An exergy analysis showed that the thermodynamic loss of the process with the second energy recovery scheme is 4.5% lower than that of the first. The reason being that power can be recovered when expansion takes place in a turbine instead of an isenthalpic expansion valve.
Author S. SimukangaSource: South African Journal of Chemical Engineering 13, pp 15 –25 (2001)More Less
The experimental Residence Time Distribution (RTD) curves were obtained using sodium chloride as a tracer during the comminution of apatite ore in a ball mill. The generalized number of cycles distribution (NCD) and the inverse Laplace transform for a perfectly mixed reactor and a pure time delay unit were used in curve fitting of RTD with internal circulation and RTD with dead space. The iterated parameters of the NCD probability mass functions and the corresponding number of cycles as well as the time constants in the two units were used to simulate the experimental RTD curves. The values of the probability mass functions and the corresponding number of cycles obtained in the simulation were used to calculate the moments of the NCD. The moments of the NCD were then used to calculate the moments of the theoretical RTD and these were then compared with the moments of the experimental RTD curves. Any malfunctioning of the comminuting unit, such as dead space in the mill, can result in an uneconomical utilization of the equipment, loss of optimum output of material per given time and a high recycle ratio. It is therefore essential from time to time to check for any malfunctioning of the equipment using for example a tracer to determine the RTD of the material through the comminuting unit. Any deviation from the normal RTD curve means unsatisfactory performance of the unit.