5th sodium chloride MVR evaporator in pharmaceutical plant

I. Project Overview

A pharmaceutical raw material plant produces 800 tons of antiviral drugs annually, discharging 120 m³ of high-COD, high-salt process wastewater daily. This wastewater contains 6-8% NaCl, 0.5% methanol, 1000-3000 mg/L of API intermediates, and 20000-35000 mg/L of COD. The original outsourced disposal cost was 380 RMB/ton, with significant transportation and storage risks. In 2023, the company constructed a 5 t/h triple-effect evaporation crystallization unit (hereinafter referred to as "this unit"), which solves 90% of the wastewater volume in one go, recovers and reuses the condensate, and outsources the resource utilization of by-product industrial wet salt, reducing the overall disposal cost to 85 RMB/ton.

II. Process Route

2.1 Process Summary

The process consists of five stages: pretreatment → triple-effect countercurrent falling film concentration → forced circulation crystallization → centrifugal separation → mother liquor drying. The entire system is constructed of 316L/2205 duplex stainless steel, with a surface area Ra≤0.6μm in contact with materials, meeting GMP requirements for easy cleaning.

• Pretreatment: Wastewater is filtered through a 100μm basket filter → low-temperature vacuum degassing (45℃, -0.085MPa) to recover 95% methanol → ozone catalytic oxidation, reducing COD to 12000mg/L.

• I-Effect Falling Film: Live steam at 0.6MPa (158℃) enters the shell side of I-Effect; wastewater preheated at 45℃ enters the tube side, concentrating 1.5 times; secondary steam at 120℃ serves as the heat source for II-Effect.

• II/III-Effect Countercurrent: II-Effect boiling point is 95℃, III-Effect boiling point is 72℃; a vacuum pump maintains the pressure at the last effect at -0.075MPa; overall specific heat transfer coefficient is 1800W/m²·K, evaporation rate is 12kg/m²·h.

• Crystallization Separation: The discharge concentration from III-Effect is 28% (near saturation), pumped into an OSLO-type forced circulation crystallizer; operating temperature is 82℃, slurry density is 20%; centrifugation yields wet salt with a water content ≤3% and a whiteness of 80%. ⑤ Mother liquor drying: The centrifuged mother liquor, with a COD of 100,000 mg/L, is dried using a paddle dryer to obtain 0.6 t/d of mixed salts with a water content of 5%, which is then sent for hazardous waste incineration.

2.2 Equipment Configuration

• Evaporation Capacity: 5t/h (8% salinity in influent)

• Heat Exchange Area: Effect I 180m², Effect II 160m², Effect III 140m²

• Steam Consumption: 0.32kg steam/kg water (triple-effect + thermocompression pump)

• Cooling Water Circulation: 60m³/h (28℃→35℃)

• Vacuum System: Water ring + Roots two-stage, ultimate vacuum -0.085MPa

• Material: Tube side 2205, shell side 316L

III. Key Technical Highlights

3.1 Thermocompression Steam Recompression (TVR)

The secondary steam from Effect I at 120℃ is pressurized to 135℃ by a 0.8MPa power steam jet pump before returning to the shell side of Effect I, saving 18% of steam and reducing overall steam consumption to 0.32kg/kg water.

3.2 Scale Prevention and CIP

Online CIP uses alternating cleaning at 80℃ with 2% NaOH + 1% HNO₃, with a cycle of 10 days and a cleaning time of 4 hours. 3.3 Salt Quality Control

Chemicals are processed using an OSLO grading and washing process, resulting in a crystal size D50 of 0.7 mm. After centrifugation, the crystals are rinsed with 2°C cold deionized water for 5 seconds, achieving a NaCl purity of 97%.

3.4 Condensate Deep Treatment

Secondary condensate with a COD of 300~500 mg/L and methanol ≤5 mg/L is treated with a catalytic ozone + biological filter, achieving an effluent COD ≤30 mg/L. This effluent is then reused in the circulating cooling water system, achieving a reuse rate of 95%.

IV. Operational Results The unit successfully started up on the first attempt in November 2023. 72-hour performance evaluation data:

• Evaporation rate: 5.2 t/h (design 5 t/h)

• Steam consumption: 0.31 kg/kg water

• Salt production: 0.42 t/h

• Condensate recovery rate: 95%

• Unit availability: >98% (4320 hours of operation over 6 months)

V. Economic and Environmental Benefits

5.1 Economic Indicators

Annual operating cost: approximately RMB 1.28 million (steam RMB 180/t, electricity RMB 0.65/kWh, labor + chemicals). Annual savings in outsourced disposal costs: approximately RMB 12.6 million. After deducting operating costs, the annual net profit is approximately RMB 11.32 million.

5.2 Environmental Indicators

Annual reduction of 36,000 tons of high-salinity wastewater discharge and 1,080 tons of COD emission reduction; 95% methanol recovery and 55 tons of VOCs reduction; 2,800 tons of CO₂ emission reduction per year; and 180 tons of hazardous waste salts are incinerated in compliance with regulations, achieving "reduction and resource utilization".