Here is an example of a revamp solution that came from a solid understanding of the original process, coupled with out-of-the-box thinking. A producer of terephthalic acid (PTA) needed to increase the capacity of its dehydration column, which separates water from acetic acid using traditional distillation. The component separation profile had a pinch near the point of maximum water concentration at the top of the column, as depicted in Figure 5. It was prohibitively expensive to debottleneck the vessel because of the titanium construction material.
The solution to this problem was to decrease the reflux ratio on the column and feed the overhead stream into an LLE unit, which is more effective than distillation in removing water from dilute streams. Furthermore, part of the feedstock is diverted to this new extraction unit, which increases the capacity even more. Because the separation is moved away from the pinch point, the unit will simultaneously reduce the specific energy consumption.
These kinds of ideas come from creative and talented individuals who go beyond the requirements of typical process engineering assignments.
Figure 5: Reducing reflux ratio of a dehydration column, to move it away from a pinch point, led to increased capacity and lower specific energy consumption. The overhead feed now goes to an LLE unit.
Simple is best
Implementing a clever revamp solution requires selling it to others, either inside or outside the company. Engineers are proud of their technical accomplishments, but many of these brilliant ideas go unrealized because of poor selling. The reason may be as straightforward as a manager rejecting a proposal because it looks too complicated. In general, the revamp idea should be packaged to be no more complex than what the least technically capable person in the decision-making chain can readily understand. The solution itself does not have to be simplistic -- but the presentation must be simple and clear. Look at the big picture. The project will never happen if you can't convince people of its value.
Seize the opportunity
Revamping and troubleshooting a chemical plant is a complex task aimed at achieving a simple and measurable objective. So, make sure you approach the effort properly. Know your process; question and then take responsibility for its design; think creatively about solution alternatives; use reliable engineering practices to implement the work. Start with conventional wisdom but check out recent developments which may open up some opportunities. Choose the right people to be involved in your design. Simplicity is always best, even if the means of achieving that simplicity is complicated.
Competition in the marketplace is fierce. Everyone wants to become the "low-cost" producer. Achieving that is tough if your plant uses the same technology as everyone else. A competitor taking a more creative approach may leapfrog you. So, don't be complacent. Spend the time aggressively reviewing the opportunities for improving your plant's operation.
Joseph C. Gentry, P.E., is petrochemical business manager for GTC Technology Inc., Houston, a firm that provides technology licenses to the petrochemical and refining industries.