220t/d rubber additives DZ wastewater triple-effect evaporator

I. Project Overview

Project Name: 220t/d Rubber Additive DZ Wastewater Triple-Effect Evaporator

Owner Industry: Rubber Vulcanization Accelerator DZ (N,N-Dicyclohexyl-2-benzothiazole sulfenamide) Production Line

Construction Location: Shandong Province

Commissioning Time: May 2023

Design Scale: Influent 220m³/d, containing sodium chloride 14-18%, COD 45000mg/L, benzothiazoles 3000mg/L, cyclohexylamine 800mg/L, pH 11-12

Core Process: "Pretreatment for oil removal → MVR pre-concentration → Triple-effect forced circulation evaporation and crystallization → Centrifugal drying → Deep treatment of condensate"

Target Requirements: Sodium chloride recovery rate ≥97%, condensate reuse rate ≥93%, NaCl ≥97.5% (meeting GB/T5462-2015 Industrial Wet Salt Grade 1), no mother liquor discharge, achieving zero discharge.

II. Detailed Process Route

1. Pretreatment Oil Removal: DZ wastewater contains residual cyclohexylamine, benzothiazole, and trace amounts of resin oil. It first undergoes acid precipitation + dissolved air flotation to remove floating oil and colloids before entering a ceramic membrane oil separator, ensuring the effluent oil content is ≤20mg/L to prevent subsequent evaporation foaming and coking.

2. MVR Pre-concentration: An 8t/h single-stage MVR forced circulation evaporator is used to concentrate the wastewater from 18% to 26%, with a power consumption of 38kWh per ton of water. All secondary steam is reused, reducing subsequent live steam consumption.

3. Triple-Effect Forced Circulation Evaporation Crystallization: 

• First effect: Live steam 0.5MPa(g), temperature 105℃; Second effect: 85℃; Third effect: 65℃. Each effect uses an axial flow pump + high-flow forced circulation, with a circulation ratio of 4~5, ensuring a crystal flow velocity ≥2.5m/s within the heating tubes, inhibiting scaling.

• Crystallizer: A triple-effect, bottom-mounted Oslo-type DTB crystallizer is used. The solid content of the crystal slurry is controlled at 25-30%, with an average particle size of 0.45mm. After centrifugation and dehydration, the water content is ≤3%.

• Salt Leg Washing: Countercurrent washing with condensate removes organic matter from the crystal surface, ensuring whiteness ≥80 and TOC ≤100mg/kg.

4. Condensate Deep Treatment: The triple-effect mixed condensate has a COD of approximately 1200mg/L. After "ozone catalytic oxidation + BAF," the COD is ≤50mg/L, and the conductivity is ≤200μS/cm. All of this condensate is recycled for flushing workshop equipment and replenishing circulating cooling water.

5. Mother Liquor Drying: The system is equipped with a 200L/h scraped film evaporator to concentrate the mother liquor to a solid content of 90%, producing 1.2t/d of mixed salts. This is sent to the park's hazardous waste center for co-processing, achieving zero mother liquor discharge.

III. Key Equipment and Materials

Operating Data (Average of 12 consecutive months from June 2023 to May 2024) 

• Processing capacity: 228 m³/d (design margin 103%)

• Steam consumption: 0.29 t/t water (triple-effect + drying total)

• Comprehensive power consumption: 22 kWh/t water (including MVR, circulating pump, drying)

• Salt production: 38 t/d, NaCl 97.8%, whiteness 82, TOC 85 mg/kg, sold to local chlor-alkali plant at 280 yuan/t

• Condensate reuse rate: 94%, annual primary water saving of 75,000 tons

• System uptime: 96.4%, unplanned shutdowns 2 times/year, each <4 hours

• Operating cost: 42 yuan/t wastewater (steam + electricity + chemicals + labor)

• Investment payback period: 1.9 years

Technological Innovations

1. High-salt, high-COD co-treatment: MVR pre-concentration + triple-effect crystallization staged energy consumption, reducing operating cost per ton of water by 58% compared to traditional single-effect systems.

2. Titanium tube + 2205 duplex stainless steel composite material: Solves the problems of pitting and crevice corrosion at Cl⁻150g/L and high temperature of 105℃, extending equipment life to over 10 years.

3. Oslo DTB particle size controllable technology: Average particle size increased by 30%, centrifugal dehydration power consumption reduced by 15%, and salt whiteness increased by 20%.

4. Zero discharge of mother liquor drying: Scraped film dryer coupled with triple-effect thermal system, utilizing the latent heat of secondary steam, drying energy consumption ≤60kWh/t of mixed salt.

5. Intelligent anti-scaling algorithm: DCS built-in "temperature difference-flow rate-vibration" multi-parameter model, providing 72-hour advance warning of scaling, online switching cleaning, reducing annual cleaning frequency from 12 times to 4 times.

Customer Benefits

Environmental Benefits: Annual reduction of COD emissions by 3600t, and reduction of hazardous waste mixed salt by 85%. Economic Benefits: Annual savings of 75,000 tons of primary water and 21,000 tons of live steam; a reduction of 12 million yuan in hazardous waste disposal costs; and a comprehensive benefit of 16.2 million yuan.

Conclusion: 

The 220t/d rubber additive DZ wastewater triple-effect evaporator project, with "high efficiency, low consumption, long cycle, and zero emissions" as its core objectives, successfully solved the problem of treating high-salt, high-COD organic wastewater through integrated technologies such as titanium corrosion protection, forced circulation, Oslo crystallization, and mother liquor drying. It provides a replicable and scalable paradigm for the rubber additive industry. In the future, we will continue to iterate on cutting-edge technologies such as steam compression-multi-effect coupling, AI intelligent scale prevention, and mixed salt resource utilization to help more chemical enterprises achieve green and low-carbon transformation.