Results

          Several topological cases were considered for the construction of the new plant in Figure 2 . Net Present Values were calculated for each and compared as seen in Figure 3. The optimum case includes the fluidized bed reactor and X-301 (separation unit) with the cooling loop being replaced by a waste heat boiler and a flash vessel. The optimum case has a NPV of $211 million after 10 years of plant operation. This compared with the current plant with a NPV of $157 million, yields an additional $54 million. The NPV was determined by adding cumulative cash flows discounted to the first year of acrylic acid production. The Fixed Capital Investment (FCI) was determined by using the CAPCOST program [1] and the Cost of Manufacturing (COM) was determined using Equation 4:

COM_d = 0.180(FCI _{plant without X-301}) + 2.73 (C_ol, _{plant without X-301})     (4)

+1.23 (C_UT + C_WT + C_RM) _{plant without X-301} + COM _X-301

where C_OL is the operating labor cost, C_UT is the utility cost, C_WT is the waste treatment cost, and CRM is the cost of raw materials. Table 2 summarizes the cost of utilities, raw materials, and the profits from the base case (current plant) compared with the optimum case. Table 3 shows the equipment specifications and costs for the optimum case of the acrylic acid production unit. Tables 4 and 5 show the complete financial analyses of the base case and optimum economics respectively.

           By replacing E-301 from the base case with a waste heat boiler, the duty from the reactor can be used to produce LPS. Table 6 summarizes this change.

Table 1:  Flow Table for Acrylic Acid Process in Figure 2

Figure 3:  Topological Optimization of Acrylic Acid Unit 300

Table 2: Cost Comparison of utilities, raw materials, and profits between base case and optimum case

Table 3: Equipment Summary for Acrylic Acid Unit 300

• Table 4 shows a complete financial breakdown of the Base Case Economics
• Table 5 shows a complete financial breakdown of the Optimum Case Economics

          By replacing E-301 from the base case with a waste heat boiler, the duty from the reactor can be used to produce LPS.  Table 6 summarizes this change.

Table 6: Results of replacing E-301 with a waste heat boiler

          The current acrylic acid process uses a cooling tower and loop to quench the reactor effluent to 40 ⁰C. By replacing this equipment with a process water jet injector and another waste heat boiler along with a flash vessel, the heat from the reactor effluent can be used to produce more LPS. Table 7 shows the results of this change.

Table 7: Replacing cooling tower with water injector, WHB (E-302), and flash vessel

          The flash vessel used to remove the gases from the reactor effluent uses cooling water to remove the duty of 25136 MJ/h to lower the vessel temperature to 55 ⁰C. Figure 4 shows the optimization of the temperature and pressure of the flash vessel (V-301). An optimum value of 55 ⁰C and 400 kPa was found from this optimization. The NPV used to optimize the flash includes the cost of X-301, flash vessel (V-301), gas adsorber (T-301), deionized water, and cooling water to remove flash duty.

          Other parametric optimization includes the reflux ratio, pressure, and feed location of the acid distillation column. Figures 5 and 6 show the results of these optimizations. For the NPV of the acid distillation column, the cost of the column, condenser, reboiler, cooling water, and LPS were included. Table 8 summarizes the results of the optimization and design of the acid distillation column T-302.

Table 8:  Results of T-302 design and optimization

Figure 4: Optimization of Temperature and Pressure of V-301

Figure 5: Optimization of R/Rmin and Pressure in Acid Distillation Column, T-302

Figure 6: Optimization of Feed Stage Location for Acid Distillation Column, T-302

          With the change in column design, the condenser and reboiler specifications have changed significantly. Table 9 shows the comparison between the base case acid column and the column to be used in the new plant. Both acetic and acrylic acid products are meeting their respective purities requirements in both columns.

Table 9: Comparison of base case and optimum case acid distillation columns

          These changes result in an optimum case NPV of $211 million after 10 years of production. The current plant operates at a NPV of $157 million.

Letter of Transmittal
Executive Summary
Introduciton
Results
Discussion
Conclusions
Recommendations
References