6t/h Acetic Acid Concentration and Phosphorus Removal Triple-Effect Evaporation System for Phosphorus-Containing Wastewater

This fine chemical company, located in the Yangtze River Delta Chemical Industrial Park in China, primarily produces pharmaceutical intermediates and specialty acetate esters. During production, it generates approximately 140 tons of dilute acetic acid wastewater daily, with an acetic acid concentration of only 5% to 8%, making direct outsourcing treatment prohibitively costly. Simultaneously, the esterification reaction section discharges phosphorus-containing process wastewater with a total phosphorus concentration as high as 800 to 1200 mg/L, far exceeding the wastewater treatment plant's discharge standards. To achieve the dual goals of dilute acetic acid resource recovery and phosphorus-containing wastewater treatment to meet standards, the company invested in and constructed a triple-effect evaporation system with a processing capacity of six tons per hour in 2025. Designed, manufactured, installed, and commissioned by Kang Jinghui, the system was successfully delivered. Through segmented design and cascaded utilization of thermal energy, the key links in clean production and cost reduction/efficiency improvement were successfully addressed.

This triple-effect evaporation system employs a combination of falling film and forced circulation processes, with modular design for both acetic acid concentration and phosphorus removal from phosphorus-containing wastewater. The dilute acetic acid concentration section utilizes a triple-effect co-current evaporation system. The first effect uses live steam for heating, with the evaporation temperature controlled below 85 degrees Celsius, effectively preventing high-temperature decomposition and volatilization losses of acetic acid. The second and third effects sequentially utilize the secondary steam generated in the previous effect as a heat source, continuously evaporating at decreasing temperatures and pressures. After triple-effect concentration, the acetic acid solution reaches a concentration of over 40%, allowing for direct reuse in the esterification reactor. Annual acetic acid recovery is equivalent to over 2,000 tons of raw solution, significantly reducing raw material procurement costs. The system's flow-through components are made of a composite material of 316L ultra-low carbon stainless steel and duplex steel, exhibiting excellent resistance to acetic acid corrosion; no significant corrosion thinning has been observed since the equipment began operation.

The phosphorus removal section for phosphorus-containing wastewater employs a triple-effect forced circulation evaporation and crystallization path. After entering the evaporator, the phosphorus-containing wastewater flows through the heating pipes at high speed and turbulent flow under the drive of a circulating pump, preventing the deposition of scale such as calcium phosphate and magnesium ammonium phosphate on the heat transfer surface. As water evaporates stage by stage in the triple-effect system, the phosphate concentration continuously increases until it becomes supersaturated, precipitating crystals in the crystallizer. After centrifugation, the moisture content is below 8%, making it suitable for sale as a raw material for phosphate fertilizer. The total phosphorus concentration in the evaporation condensate is reduced to below 5 mg/L, meeting the park's strictest discharge standards. Over 90% of this condensate is recycled for workshop cleaning and circulating cooling water replenishment, achieving near-zero wastewater discharge.

The core advantage of this system lies in the cascade utilization of thermal energy and intelligent switching of operating conditions. The triple-effect series design reduces steam consumption per ton of water to only 30% to 35% of that of single-effect evaporation, saving over four million yuan in steam costs annually. Addressing the differences in the physicochemical properties of the two materials, the control system is preset with a low-temperature concentration mode for dilute acetic acid and a phosphorus removal crystallization mode for phosphorus-containing wastewater. Automatic switching is achieved through online density meters, conductivity meters, and pH monitoring, eliminating the need for manual cleaning and material transfer. A single unit can cover the treatment needs of both main types of wastewater for the entire plant. In addition, each evaporator is equipped with a high-efficiency demister at the top to prevent product loss and pipeline blockage caused by mist entrainment. The vacuum system uses a water ring vacuum pump set to maintain a high vacuum in the final effect, keeping the evaporation temperature between 45 and 55 degrees Celsius, further inhibiting the deterioration of heat-sensitive materials.

Since its official commissioning, the 6-ton-per-hour triple-effect evaporation system has operated smoothly, processing over 48,000 tons of mixed wastewater annually. The comprehensive acetic acid recovery rate reached 92%, and the phosphorus removal rate remained stable at over 99.5%, reducing total phosphorus emissions by approximately 45 tons annually. The project not only helped the company eliminate environmental compliance risks but also, through acetic acid reuse and the sale of phosphate byproducts, expects to recover the entire equipment investment within three and a half years. This case fully demonstrates that for complex, high-volume fine chemical wastewater, triple-effect evaporation technology, with its mature heat recovery mechanism and flexible process adaptability, has become a reliable industrial solution for achieving high-value component recovery and stringent phosphorus removal requirements.