A pharmaceutical factory's 5t/h triple-effect evaporator for pharmaceutical wastewater

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 new 5t/h triple-effect evaporation and crystallization unit (hereinafter referred to as "this unit"), which solves 90% of the wastewater problem 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 Overview

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 material contact surface Ra≤0.6μm, 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% of methanol → ozone catalytic oxidation, reducing COD to 12000mg/L.

·  First-Effect Falling Film: Live steam at 0.6MPa (158℃) enters the shell side of the first-effect process; wastewater is preheated to 45℃ before entering the tube side, concentrating by 1.5 times; secondary steam at 120℃ serves as the heat source for the second-effect process.

·  Countercurrent operation of Effect II/III: Effect II boiling point 95℃, Effect III 72℃, maintained at -0.075MPa using a vacuum pump; overall specific heat transfer coefficient 1800W/(m²·K), evaporation rate 12kg/(m²·h).

·  Crystallization separation: Effect III discharge concentration 28% (near saturation), pumped into an OSLO type forced circulation crystallizer, operating temperature 82℃, slurry density 20%, centrifuged to obtain wet salt with water content ≤3% and whiteness 80%.

·  Mother liquor drying: Centrifuged mother liquor COD 100000mg/L, dried by a paddle dryer to obtain 0.6t/d of mixed salt with water content 5%, 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 + autoclave 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 Technological Highlights

3.1 Thermal Steam Recompression (TVR)

The secondary steam from the first-effect stage, initially at 120℃, is pressurized to 135℃ by a 0.8MPa power steam jet pump before returning to the first-effect shell side, resulting in 18% steam savings and reducing overall steam consumption to 0.32kg/kg water.

3.2 Scale Prevention and CIP

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

3.3 Salt Quality Control

Through OSLO grading and rinsing, the crystal size D50 is 0.7mm; after centrifugation, rinsing with 2℃ cold deionized water for 5 seconds yields NaCl purity of 97%.

3.4 Deep Condensate Treatment

Secondary condensate with COD 300~500mg/L and methanol ≤5mg/L undergoes catalytic ozone + biological filter treatment, resulting in effluent COD ≤30mg/L, which is then reused in the circulating cooling water system with 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".