Batch Reactor and Overhead Condenser Evaluation

Project Synopsis

Project Summary

Process Engineering Associates, LLC (PROCESS) was asked by the client, a pharmaceutical ingredients manufacturing company, to evaluate the operation of a batch reactor and accompanying overhead condenser. The system routinely has trouble maintaining a permit-specific condenser vent gas-side outlet temperature. Additionally, the exchanger vent line, routed to a conservation vent, frequently has condensed vapor running down the side of a sight glass. Condensate in the vent line produces high reactor back-pressure and poor reactor performance.

Operation of the system is straightforward. A small purge of nitrogen is applied to the reactor. Reactants are charged to the reactor. The reactor is heated. The desired reaction is initiated, generating a saturated vapor phase. Saturated vapor is partially condensed in the overhead co-current exchanger. Condensate is returned to the reactor while the process vapor stream is routed through a sight glass and flame arrestor. The condensate return line is not insulated nor properly sloped. Condensate is returned to the reactor through a dip tube.

PROCESS noted the following issues/incidents occurring during system operation:

• Most every batch experiences periods where the temperature of the condenser process cold-side exceeds the permit-specified value.
• Condensate return flow through the sight glass is characterized by quick short-lived pulses. A continuous liquid flow is not typically visible.
• Condensate “drizzle” is frequently observed in the conservation vent vapor line sight glass.
• High reactor pressure has been recorded by the data collection system.  The coincident conservation vent differential pressure was high as well.
• On occasion, liquid flows out of the seal legs on the conservation vent taps.

PROCESS analyzed the batch data, modeled the system in CHEMCAD and concluded that the system was constrained thermodynamically (exchanger) and hydraulically (piping arrangement and lack of insulation). After the analysis, PROCESS offered the following recommendations:

1. Equalize pressure in top of the dip tube with the reactor pressure (remove the bottom liquid seal in condensate return line) by retooling the top section of the dip tube with slots or round holes. This will relieve pressure buildup in the condensate return line by giving vapor an “escape” path.
2. Insulate the condensate return line.
3. Reduce the flow of nitrogen to the reactor. This will drop the condenser load by a significant amount.
4. Modify the condenser for counter-current operation.
5. Slope the condensate return line as much as possible. This will decrease the amount of vapor formed and liquid accumulated in the pipe and result in better draining of the condensate line.

Changes were implemented by the client during a Fall outage. Operations resumed in November and all operational deficiencies were mitigated. Operations in January have revealed control system problems. PROCESS will be looking to mitigate instrumentation and control issues in a subsequent project.

Industry Type

Utilized Skills

• Process troubleshooting
• Process evalution
• Batch process improvement.