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Industrial ETP & ZLD

Industrial effluent treatment and ZLD plant process flow diagram showing pump and mechanical seal locations

Process Overview

Industrial ETP & ZLD — Process Overview

Industrial effluent treatment plants (ETP) treat wastewater from chemical, pharmaceutical, textile, distillery and other industries. Effluent is equalised, neutralised and clarified, treated biologically and polished in tertiary filters. In zero liquid discharge (ZLD) plants, reverse osmosis (RO) recovers most of the water, and the RO reject is concentrated in a multiple-effect evaporator (MEE), crystallised and separated as salt, with the final mother liquor dried in an agitated thin-film dryer (ATFD).

For municipal water and sewage see Municipal Water & Sewage; for seawater RO see Desalination & RO; for distillery spent wash see Distillery Spent Wash & ZLD.

Key Sealing Challenges

  • Crystallisation: brine and mother liquor form crystals on the faces and atmospheric side; condensate flush, quench or a pressurised barrier is needed.
  • Hot chlorides: MEE brine at 60–110 °C pits stainless steel; super duplex or titanium metal parts are used.
  • Solids and vacuum: crystalliser and later MEE effects run under vacuum with crystal slurry, so double seals keep air out and faces clean.
  • Variable chemistry: effluent composition changes with production, so materials are chosen for the worst case.

What mechanical seal is used on ZLD crystalliser and MEE pumps?

Crystalliser and MEE brine pumps typically use a double cartridge seal on a pressurised condensate barrier (API Plan 53A), or a slurry cartridge with a condensate flush (Plan 32), with sintered SiC vs. sintered SiC faces and super duplex or titanium metal parts. The barrier or flush keeps crystals off the faces, and the double seal stops air entering under vacuum.

Root-Cause Failure Analysis — Field Example

Symptom: MEE brine circulation pump seal leaks within weeks; salt crust on the atmospheric side, faces chipped.
  ├── Incorrect Response: "Fit harder face material."
  ├── Diagnostic Evidence Required:
  │     ├── Is salt crystallising on the atmospheric side because there is no quench?
  │     ├── Is the seal chamber under vacuum, drawing air and drying the faces?
  │     └── Check metal parts for chloride pitting at operating temperature.
  └── Engineered Solution:
        ├── Condensate flush (Plan 32) with a Plan 62 condensate quench, or a double seal with Plan 53A barrier.
        ├── Sintered SiC vs sintered SiC faces.
        └── Super duplex or titanium metal parts for hot chloride brine.

Frequently Asked Questions

Why is condensate used as flush or barrier in ZLD plants?

Condensate is clean, available on site and compatible with the brine. It dissolves crystals instead of adding more salt, and it does not add impurities to the recovered salt.

Which metal parts suit hot brine?

Chlorides at 60–110 °C pit 316L. Super duplex stainless steel or titanium metal parts are selected according to chloride level and temperature.

Related: Municipal Water & Sewage · Desalination & RO · Distillery Spent Wash & ZLD · General Chemical Plants.

Request a Seal Selection

Send your pump make and model, fluid, temperature, pressure, shaft size and speed 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.

Equipment solutions: Slurry Pumps · Vertical & Sump Pumps · Overhung Pumps.

Pump Duty & Mechanical Seal Selection Matrix

Typical values for selection guidance only. Final selection is made against the customer duty sheet.

Pump duty Fluid Typical temp. Typical pressure (bar) Seal arrangement Faces / elastomer API piping plan
Raw Effluent / Equalisation Pump Mixed effluent with solids, variable pH Ambient–50 °C 2–4 bar Slurry cartridge, external springs (catalogue ref. HS860) SiC vs SiC / EPDM or FKM, per effluent chemistry API Plan 32 (clean water flush) or Plan 62 quench, per seal design
Neutralised Effluent Transfer Pump pH-adjusted effluent Ambient–45 °C 2–5 bar Balanced multi-spring cartridge SiC vs SiC / EPDM or FKM API Plan 11
Sludge / Filter Press Feed Pump Chemical or biological sludge Ambient–40 °C Cyclic, rising to 7–15 bar at end of filter cycle Double cartridge, back-to-back (pressurised) SiC vs SiC / EPDM API Plan 53A (barrier ≥ 1.4 bar above the maximum cycle pressure)
RO High-Pressure Pump (effluent RO) Treated effluent, high TDS Ambient–40 °C Discharge 20–60 bar; seal sees seal-chamber pressure — confirm per pump High-pressure balanced cartridge, stationary springs (catalogue ref. HP760) with duplex or super duplex metal parts SiC vs SiC / EPDM API Plan 11
MEE Feed / Brine Circulation Pump Concentrated brine with suspended crystals 60–110 °C Often under vacuum in later effects — confirm per pump Slurry cartridge, external springs (catalogue ref. HS860) with super duplex or titanium metal parts Sintered SiC vs sintered SiC / EPDM API Plan 32 (condensate flush) + Plan 62 condensate quench against crystallisation
Forced-Circulation Crystalliser Pump Salt crystal slurry in saturated brine, under vacuum 50–110 °C Low suction pressure — confirm per pump Double cartridge, back-to-back (pressurised) with super duplex or titanium metal parts Sintered SiC vs sintered SiC / EPDM API Plan 53A (condensate barrier ≥ 1.4 bar above seal chamber)
Condensate / Recovered Water Pump Process condensate 50–90 °C 2–5 bar Balanced multi-spring cartridge SiC vs carbon / EPDM API Plan 11
Mother Liquor / ATFD Feed Pump Highly concentrated mother liquor with organics 60–100 °C 2–5 bar Double cartridge, back-to-back (pressurised) Sintered SiC vs sintered SiC / FFKM API Plan 53A (barrier ≥ 1.4 bar above seal chamber)

Reviewed by Gipfel Engineering’s technical team.

Technical Information Disclaimer

The information on this page, including process descriptions, flow diagrams, operating ranges, seal arrangements, materials and piping plans, is general technical guidance for information only. Values shown are typical industry ranges, not guaranteed ratings or specifications of any Gipfel Engineering product. Each application differs. Seal selection, material compatibility, installation and operation must be verified by qualified personnel against the specific equipment data sheet, process conditions, applicable codes and the pump manufacturer’s instructions. A binding recommendation is given only in a written quotation or technical offer from Gipfel Engineering.

References to standards (such as API 682, ISO 21049, ISO 3069, FDA 21 CFR 177.2600 and NACE MR0175 / ISO 15156) describe common industry practice. They do not mean that any product is certified, qualified or approved to that standard unless this is confirmed in writing for a specific order. Third-party company and product names, including “equivalent to” references, are used for identification only and remain the trademarks of their owners. No affiliation, endorsement or OEM approval is implied.

Compliance with safety, hazardous-area, environmental and statutory requirements at the user’s site remains the responsibility of the plant owner or operator. To the extent permitted by law, Gipfel Engineering accepts no liability for loss or damage arising from reliance on this general information without a confirmed written recommendation. Content may change without notice.

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