This report outlines the steps taken to separate a 50:50 by volume ethanol and isopropanol side stream. The resulting separation must contain no more than 3% alcohol impurity in each product. A laboratory column, run at total reflux, was utilized to scale up to a forty foot high by one foot diameter column. The laboratory column allowed the team to determine vapor velocities and HETP values for the 0.24 inch Pro-Pakq packing. HETP is defined as the height of packing divided by the number of theoretical column stages. The column consisted of four main sections: packing, controls, a reboiler, and a condenser.
To complete the vapor velocity vs. HETP relationship, the vapor velocity must be found. The vapor velocity was found using a system energy balance. The design vapor velocity was determined to be 4.85 ft/hr. However, this vapor velocity did not result in the column flooding; therefore the scaled-up column is not designed to its full potential. Ideally, distillation columns should be designed at 70-80% of the flooding velocity. The column HETP was found by use of the Fenske equation and was determined to be an average of 4.55 inches.
As a result of the design parameters from the experimental column, the following design is proposed: the column will run at a vapor velocity of 4.85 ft/hr and will have a HETP of 4.30 inches. This will result in a packing height of 38.7 feet. The reboiler will have an area of 113.52 ft2 and the area of the condenser will have a value of 45.54 ft2 in which heat exchange will take place.
Operating Procedure for packed Column22
Intermediate Number Tables (R&D) B4
Intermediate Number Tables (Design) C1
A chemical plant spends approximately 50 to 90% of capital investment on separation equipment (1,1) Therefore, the ability to utilize a small laboratory column and to scale-up a column is an important skill for a chemical engineer.
This report will outline the steps taken to design a packed distillation column. The column needs to separate a 50:50 mixture of ethanol and isopropanol into a distillate stream containing no more than 3 wt% isopropanol and a bottoms stream containing no more than 3 wt% ethanol. The design of the full-scale column was based on a laboratory simulation column. This column allowed the team to determine vapor velocities and HETP values for the 0.24 inch Pro-Pakq packing.
Once the simulation vapor velocities are determined, they can be translated to the column design and used in the design of the reboiler and condenser. Areas for the reboiler and condenser will be found and costs will be calculated. Finally, the actual packing height will be determined for the scaled-up column.
The primary goal of this project was to deterimine the design specifications for a one foot diameter by forty foot high packed distillation column. The laboratory was run at total reflux. Total reflux occurs when the entire overhead vapor flow is returned as reflux and all of the bottoms liquid is returned as boil up. Total reflux is useful for starting up columns, maintaining column operation when all or part of a plant is shut down, or for our purposes: determining column efficiency. However, since our column was a packed column and not a tray or sieve plate column, efficiency is measured not in terms of overall efficiency, but in terms of HETP. HETP is defined as follows:
HETP = height of column packing y number of theoretical stages(1)
There are two basic ways to determine the number of theoretical stages (Nmin): McCabe Thiele analysis and/or using the Fenske equation. Both of these methods will give Nmin, however, McCabe Thiele utilizes a graphical analysis and Fenske utilizes a numerical analysis.
To use McCabe Thiele graphical analysis, the condition of constant molal overflow (CMO) must be met. The assumptions behind CMO are as follows (1, 117):
2.The specific heat changes are negligible compared to latent heat changes
3.The heat of vaporization per mole, l, is constant
An additional criterion for utilizing McCabe Thiele analysis is the existence of good equilibrium data. Ideally, empirical equilibrium data can be found in several sources, but this data was not available for isopropanol and ethanol. To determine our equilibrium curve, we had to incorporate a different method. All of the equilibrium data was found