Fluid Mechanics, Heat Transfer, and Thermodynamics Design Project
Production of Acrylic Acid
We are investigating the feasibility of constructing a new, grass-roots, 50,000 metric tons/year, acrylic acid production facility. As part of the feasibility study, we would like you to investigate some of the details of the feed and reaction sections of the proposed plant.
Acrylic Acid Production Reactions
The reactions are given below. The primary reaction is:
C H O C H O H O3 6 2 3 4 2 215+ ® +. acrylicacid
The secondary reactions are:
C H O C H O CO H O3 6 2 2 4 2 2 225+ ® + +. acetic acid
C H O CO H O3 6 2 2 245 3 3+ ® +. (3)
For the purposes of this preliminary evaluation, it is assumed that the reactions occur in a fluidized bed of catalyst particles. Due to the characteristics of fluidized bed reactors, a maximum propylene conversion of 90% is possible in the reactor. The selectivity for acrylic acid/acetic acid is 13.5. The selectivity for acrylic acid/carbon dioxide formed in the combustion reaction (Reaction (3)) is 1.6.
The PFD for the reaction section is given in Figure 1. The propylene is stored in tanks which are not shown. There are two tanks, each holding a one-day supply, one in a filling mode and the other in a feeding mode. The propylene is stored at ambient temperature (which may be assumed to be 25°C) as a vapor/liquid equilibrium mixture, and the feed to the process may either be vapor (drawn from the top of the tank) or liquid (drawn from the bottom of the tank). The feed to the reactor must be at 4.3 bar and the crude acrylic acid product (in the liquid phase) may not exceed 90°C. The pressure drops across process units at base case
conditions are given in Table 1.
Table 1: Pressure Drops across Process Units in Feed Section Unit DDP (bar)
mixing points 0.05 Reactor 0.80
any heat exchanger 0.35
The reactor feed must be at 4.3 bar and 190°C. Heat generated in the reactor is removed by Dowtherm AÔ, which is thermally regenerated in E-301. If the Dowtherm pressure is maintained above 10 bar, it is not volatile up to 400°C. The reactor exit temperature is 290°C. Following the reactor, the reaction products are quenched with sufficient deionized water to bring the temperature of the stream to 200°C. The crude acrylic acid product is obtained by flashing the quenched reactor effluent. It may be assumed that all light gases (N2, O2, CO2) leave in the vapor phase. All other components distribute between the vapor and liquid phases. The temperature of any liquid stream containing acrylic acid may never exceed 90°C to avoid spontaneous polymerization.
Your assignment consists of three "mini-designs."
1. Optimization of the Feed Section. (ChE 110(fluids) and 142(thermo)) Refer to Figure 1. You are to determine the optimum pipe sizes for Streams 1-4. Equivalent pipe lengths can be determined from the attached plot plan (Figure 2). Pipe runs are at ...