Analysis of the Ammonium Sulfate Evaporation and Crystallization Process

I. Primary Process Flow

Preprocessing stage

Water Quality Adjustment: Adjust the pH of wastewater to an appropriate range (typically slightly acidic or neutral), and remove suspended solids, oils, and heavy metal impurities to prevent adverse effects on subsequent evaporation efficiency.

Concentrate Preparation: Adjust the ammonium sulfate solution to a specific initial concentration to facilitate subsequent evaporation and crystallization operations.

Evaporation Concentration

Multi-effect evaporation: Utilizing three-effect or four-effect evaporators, this process harnesses the cascading thermal energy of steam to achieve stepwise evaporation, thereby reducing energy consumption. For instance, a three-effect evaporator employs the secondary steam from the preceding effect as the heat source for the subsequent effect, significantly enhancing energy utilization efficiency.

MVR Technology: By utilizing mechanical vapor recompression (MVR) to recover latent heat from secondary steam, the compressed and heated vapor is recycled as a heat source, reducing energy consumption by 30% to 50% compared to traditional evaporators.

Crystallization and Separation

Continuous crystallization process: Combining plate and tube evaporators, the solution is rapidly evaporated to critical saturation in the plate evaporator before passing through the tube evaporator to promote crystal growth and prevent pipe blockage.

Solid-liquid separation: Crystals are separated from the mother liquor using centrifuges or filter presses. The mother liquor is returned to the evaporation system for recycling, while the ammonium sulfate crystals are dried and packaged.

II. Core Elements of Process Design

Equipment Material Selection

Ammonium sulfate solutions are corrosive to stainless steel, necessitating the use of duplex steel or titanium materials (such as in tube evaporators and separators) to enhance corrosion resistance. Plate evaporators, due to manufacturing constraints, predominantly utilize titanium plates.

Dynamic Control Parameters

Supersaturation Gradient Control: Adjusting the supersaturation of the solution through evaporation rate ensures uniform crystal growth and minimizes the formation of fine crystals.

Seed addition and agitation: Introduce seed crystals during the late evaporation stage while controlling agitation speed to promote the formation of large crystals (particle size up to 2.0–2.5 mm), thereby enhancing product flowability and anti-caking properties.

III. Typical Application Scenarios

Industrial Wastewater Treatment

Recover coke oven gas scrubbing solutions containing ammonium sulfate, metallurgical waste liquids, and other materials to achieve resource utilization, thereby reducing wastewater salinity and subsequent disposal costs.

Agricultural Fertilizer Production

Granular ammonium sulfate is produced via an evaporation-cooling crystallization process, yielding a product with high purity and excellent flowability, making it suitable for mechanized fertilization.

Purification of Chemical Byproducts

Processing ammonium sulfate mother liquor from caprolactam and other production processes to enhance the value of by-products.

IV. Technical Advantages and Challenges

Energy-saving advantages: MVR technology combined with multi-effect evaporation design reduces steam consumption by 40% to 60%, and condensate can be reused.

Operational Challenges: Strict monitoring of solution pH, supersaturation, and seed crystal dosage is required to prevent equipment scaling or crystal agglomeration.

Through optimized evaporation processes and equipment selection, the ammonium sulfate evaporation crystallization system demonstrates remarkable performance in energy efficiency, product quality, and environmental benefits, establishing itself as a key technology in both industrial and environmental sectors.