Analysis of the base case design must be able to provide a calculation of the optimization's objective function. Therefore, a calculation of the effect of the decision variables on the objective function must be possible in the base case. An important step at the beginning of the optimization of a process is to choose the scope of the base case to be optimized.
After choosing the base case optimization domain, the next step in the optimization process is to choose the objective function. These parameters will be some of the variables that change in order to optimize for the objective function. Most of the time, reactor section optimization comes first in a chemical process optimization.
The main subject of this thesis is further optimization of the reactor section of this power plant. The sensitivity analysis showed that the changes in fixed asset investment significantly affected the NPV of the process. To begin the optimization and design of the reactor, I set up the process flow diagram for the reactor.
Another specification for the reactor was the length of the reactor or the height of the fluidized bed.
Styrene Production vs. Pressure
The figures below show the effects of pressure, temperature and catalyst bed diameter on styrene production. The process simulator includes a calculator function that has the ability to read out the results of parameter optimizations and to calculate solutions to user-defined formulas.
Styrene Production vs. Temperature
A second calculator displayed the fluidized bed height, diameter, total volume of fluidized catalyst, temperature, and pressure of the reactor. For this volume of catalysts, the optimized system requires the deployment of 15 reactors to keep the superficial gas velocity within the required range. The optimized reactor parameters produced a total flow rate of styrene from the reactor system of 193 kmol/hour and a yield of.
Optimization of Styrene Production Process ChE 451: Process Design
By conducting a sensitivity analysis, we determined that changes in raw materials, revenues, fixed capital investment (FCI) and utilities have the greatest impact on the increase in the net present value (NPV) of the proposed process. An oversight in the design of the base case reactor forced us to make major modifications to our process in the reactor section resulting in an increase in feedstock cost for the optimized plant. Heat integration for the optimized process reduced utility cost by $12 million/year from the base case.
Optimizations in the separation department allowed us to recycle more ethylbenzene and take more of the styrene produced into the actual product without losing it to the fuel gas. Implementation of the above changes resulted in an NPV of -$412 million, which equates to an equivalent annual operating cost (EAOC) of $72.9 million for the optimized case. Process raw material costs actually increased by $19 million/year in the optimized case.
Overall, Table 1 illustrates that the bottom line for our optimized styrene process over the life of the project is -$412 million/year and an EAOC of $72.9 million/year. The process concept diagram in Figure 1 illustrates a simplified version of the styrene process in Unit 500. Initially, we calculated an economic potential, as seen in Table 2, for the process to get an idea of the potential earnings of the process.
The main objective of optimization was to maximize the NPV of the process while satisfying a set of given constraints, which mainly include the production requirements of the styrene and the operating temperatures of the reactor and separation section. To prevent polymerization of the styrene in the separation section, the temperature must remain below 125°C. The results of the sensitivity analysis showed that changes in raw materials, revenue, utilities and FCI most effectively maximize NPV.
After optimizing the reactor and separation sections, we addressed utility costs by integrating heating in order to find the most economical use of energy in the process. Finally, we researched the construction materials of the process equipment and made appropriate changes to reduce FCI. If the molar flow rate of the component is 0, then trace amounts of the component actually exist.
Illustrated above in Figure 2 is a process flow diagram of the optimized process followed by flow tables in Table 4, a partial equipment summary in Table 5, and utility summary in Table 6. As mentioned in the introduction, the optimization of the styrene production process began by a perform economic sensitivity analysis on the base case as illustrated below in Figure 3.
Sensitivity Analysis
To address the sensitivity of the process to changes in raw materials, we began optimization by first focusing on the reactor and optimizing for increased yield of ethylbenzene to styrene. Finally, we analyzed the possibility of changing some of the process equipment's construction materials to try to reduce the FCI. This allowed the process to recycle more ethylbenzene and to take more of the styrene produced in the reactor to the actual product.
After the optimization of the separation work was completed, we integrated heat with the aim of reducing utility costs. This monatomic hydrogen can penetrate the metal of process equipment and create a small pressure pocket. Optimization of the towers and change of construction materials of some equipment of the plant.
The drastic reduction in fuel gas costs due to the inclusion of heat has reduced utility costs for the plant. Optimization of the reactor together with changes in the inlet section setup allowed us to reduce the total amount of low pressure steam required for the process. The overhead vapor stream from the column containing 99% ethylbenzene fed to the column is condensed using cooling water in E-520.
Most of the difference in profit came from the decreasing raw material costs in the adiabatic reactor due to increased recycled ethylbenzene. This allows us to sell the power at 50% of the price of pure benzene and toluene, an option that was not viable in the base case. This reduces raw material costs and directs more of the styrene produced in the reactor to the actual product.
With these considerations in mind, we recommend further process optimization and a more detailed NPV assessment. Further optimization of the reactor to increase the yield of ethylbenzene to styrene is also strongly recommended. High temperatures and pressures exist in many process areas, especially in heat exchangers, reactors and piping.
Careful and regular maintenance of the process control systems is a requirement for any safe process operation. Also, thorough training of operators in the system controls and emergency protocols is very important for the health and safety of the plant and the people in it.
Local Heat Transfer Coefficients
