Squeeze More From Your Process

Process intensification can enhance distillation, heat transfer and other operations

By Rocky C. Costello, R. C. Costello & Associates, Inc.

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Among the typical reactions where a byproduct prevents the reaction from going to the right are: esterification, transesterification, hydrolysis, acetalization and amination. Other types of reactions that could benefit from reactive distillation include: alkylation/transalkylation/dealkylation, isomerization and chlorination.

We expect installations using reactive distillation to continue to increase at a moderate pace in this decade. Again the driver will be less metal on the ground, ultimately reducing installed costs.

Other separation uses

 

Figure 4. High shear and centrifugal forces create extremely small droplets that enhance dearation. Source: GasTran Systems.

Another application of PI is for removing dissolved gases from process water.
GasTran Systems has developed a novel mechanical approach to single-stage vacuum deaeration to achieve extremely low levels of dissolved gases (Figure 4).

The technology imparts high shear and centrifugal forces on a liquid to create extremely small droplets, thus exposing a large surface area through which efficient gas absorption and gas removal can occur. Once the small droplets are created, a vacuum pump is used to remove dissolved gases to levels reportedly unachievable with other vacuum deaeration designs.

Performance improves with deeper vacuum level; Number of Transfer Units (NTU) values of 4.3 – 4.5 and dissolved oxygen levels of 235 ppb are possible across only a few inches of rotor packing.

Figure 5. Flash evaporation of low boiling solvents from the extract obviates a distillation column. Source: R. C. Costello & Assoc.

Applications include: dissolved gas removal from boiler feedwater, water for ion exchange and ultrapure services, and many other process water pretreatment jobs. The technology also may serve as a low cost alternative for removal of carrier solvents or a low boiler from reaction products.

Extraction offers another opportunity for PI. Figure 5 shows an experimental system for extracting chemicals from botanicals offered by R. C. Costello & Associates, Redondo Beach, Calif.. This system can be modified to separate organics from water. The technology utilizes low boiling point solvents that are flash evaporated from the extract. Typically 1,1,1,2-tetrafluoroethane is used because it’s very refractory, has a boiling point of -15.3°F (-26.3°C), and isn’t flammable. This eliminates a costly distillation column and related auxiliary heat transfer equipment, pumps and process instrumentation. Combining the approach with a Podbielniak extractor (which most likely was the first PI device invented) can further simplify and miniaturize the extraction system. The Podbielniak could be used to contact the solvent with the heavy liquid instead of using an extraction column.

Hot prospects

 

Figure 6. No over-sizing to compensate for plugging is necessary thanks to ongoing scouring taking place within this unit. Source: Klaren BV.

PI already plays a role in heat transfer. For instance, Klaren BV, Hillegom, the Netherlands, offers self-cleaning heat exchangers that require significantly less heat transfer area than traditional shell-and-tube units (Figure 6). The company says that chopped wire circulated through the downcomer and up through the tubes of its shell-and-tube exchanger scour the surfaces clean, removing scale as quickly as it forms. So, there’s no need to oversize the exchanger to compensate for fouling and pluggage.

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