Chemical & Glass-Lined Reactors

Chemical & Glass-Lined Reactors — Sealing Overview

Reactors are agitated pressure vessels in which chemical reactions take place: batch reactors in pharmaceutical and fine-chemical plants, glass-lined reactors (GLR) for acids and corrosive intermediates, hydrogenation reactors, polymerisation and resin reactors, gas-induction reactors and special horizontal or photochemical designs.

The reactor shaft seal has to contain the product through vacuum distillation, pressure steps and reaction peaks, keep air out under vacuum, and survive the same runout and slow speed as any agitator seal. On glass-lined reactors the seal must also protect the glass: no metal parts that the product can attack, clamping that does not stress the glass-lined nozzle, and connection dimensions to DIN 28136, DIN 28137 and DIN 28159. Almost all reactor duties therefore use a pressurised double seal with a barrier system.

Key Sealing Challenges

• Corrosion: wetted parts are chosen for the product, for example PTFE-lined parts or Hastelloy C on acid duties.
• Pressure swings: barrier pressure must stay at least 1.4 bar above the highest vessel pressure, including reaction peaks, or product will cross the product-side faces.
• Hydrogen: hydrogen escapes through very small gaps and can blister elastomers on rapid venting, so pressurised double seals and suitable elastomers are needed.
• Batch contamination: barrier fluid entering the batch can spoil it. Choose a product-compatible barrier, or a Plan 74 gas barrier seal.

Fault Diagnosis Example

Symptom: GLR seal leaks product to atmosphere during the pressure step of each batch, but is dry under vacuum.
  ├── Incorrect Response: "Replace the seal faces every batch."
  ├── Diagnostic Evidence Required:
  │     ├── Log barrier pressure against vessel pressure through a whole batch; does vessel pressure overtake the barrier?
  │     ├── Check the seal pot nitrogen regulator and level.
  │     └── Inspect the product-side faces and wetted parts for chemical attack.
  └── Engineered Solution:
        ├── Set barrier pressure at least 1.4 bar above the highest vessel pressure in the batch.
        ├── Fit low-pressure and low-level alarms on the seal pot.
        └── Confirm wetted-part materials against the product chemistry.

Frequently Asked Questions

Why do glass-lined reactors need special seals?

Glass resists almost every chemical the reactor handles, so the seal must not introduce a less resistant material. Wetted parts must resist the product, and the seal must be clamped without stressing the glass-lined nozzle, whose connection dimensions follow DIN 28136 and DIN 28137.

Is a single seal ever acceptable on a reactor?

Only on non-hazardous, atmospheric duties. Most reactors run under vacuum or pressure with hazardous products, so a pressurised double seal is the normal choice.

How is a hydrogenation reactor seal different?

Hydrogen escapes far more easily than liquids, so the seal is a pressurised double seal with the barrier above maximum hydrogen pressure. Elastomers must resist damage from rapid gas decompression when the reactor is vented.

Related: Agitators · Dryers & ANFD · API & Bulk Drug · Chemical Plants · All reactor solutions.

Request a Seal Selection

Send the reactor and agitator drawings, nozzle standard, shaft size and speed, vessel design pressure and temperature, and the product to info@gipfelengg.com or use our enquiry form. Gipfel Engineering (ISO 9001:2015, NSIC-registered MSME, Mumbai) designs and manufactures mechanical seals, seal support systems and process pumps.