900,000 tons/year compound fertilizer ammonium sulfate MVR evaporator

Process Scheme

1. Materials and Thermodynamics

Ammonium sulfate has a boiling point elevation (Δbpe) of 6.5℃. At 55%wt and 90℃, the solution is highly corrosive and rich in organic impurities, exhibiting a strong tendency to foam. The design employs a two-stage MVR (Medium-Vacuum Recycling) system: first, falling film concentration to 35%, followed by forced circulation crystallization to 55%, balancing energy consumption and anti-foaming properties.

2. Process Overview

Ammonium sulfate mother liquor → Basket filter (400μm) → Preheater (recover sensible heat of condensate to boiling point) → First-stage falling film evaporator → Second-stage forced circulation evaporator → Oslo crystallizer → Two-stage piston pusher centrifuge → Fluidized bed dryer → Packaging. Secondary steam is heated to 18℃ by a titanium alloy centrifugal compressor and reused; condensate, with a conductivity ≤30μS/cm after polishing mixed bed treatment, is entirely used as washing water for compound fertilizer granulation, achieving a closed-loop process.

3. Main Parameters

• Evaporation Water Flow Rate: 62t/h

• Feed Concentration: 12%

• Discharge Solid Content: 55%

• Compressor: Single-stage centrifugal, impeller diameter 1.6m, power 5.2MW, isentropic efficiency 86%, speed range 20-105%

• Overall Heat Transfer Coefficient: Falling film section ≥4.2kW·m⁻²·K⁻¹, forced circulation section ≥3.0kW·m⁻²·K⁻¹

• Electricity Consumption per Ton of Water: 26.8kWh

• Annual Standard Coal Savings: 41,000 tons

• CO₂ Emission Reduction: 107,000 tons/year

Equipment Selection and Materials

1. Heater: Falling film section uses φ25×1.5mm 2205 duplex steel heat exchange tubes, 6m long, 11,000 tubes in total, shell side Q345R; forced circulation section is plate type, single plate area 2m², total heat exchange area 3500m².

2. Evaporation Chamber: φ4.2m×14m, 2205 + titanium composite plate, top titanium wire mesh demister with 99.5% retention, lower 60° cone angle + side-mounted axial flow pump with a flow rate of 18,000 m³/h, head of 4m, frequency conversion, crystal slurry flow velocity of 3.5m/s, scaling cycle ≥30 days.

3. Compressor: Impeller integral TA19 titanium alloy, five-axis milled, surface laser-coated with a corrosion-resistant layer; inlet equipped with cyclone + wire mesh dual-stage demister to ensure droplet density ≤20mg/Nm³.

4. Online Cleaning: CIP system equipped with 5% HNO₃, 3% NaOH and special scale inhibitor PAA-Na, 25ppm, automatically starts every 25 days of operation or when pressure drop >50kPa, cleaning time ≤4h.

Energy Saving and Economy: Compared to the original four-effect reactor, it saves 343,000 tons of steam, 2.4 million tons of circulating water, and 58 million yuan in operating costs annually. The unit energy consumption is 28 kWh/t of water.

Environmental Protection and Safety:

1. Exhaust Gas: After secondary steam condensation, non-condensable gases (NH₃ ≤ 2 mg/m³) enter the two-stage pickling tower.

2. Mother Liquor: Organically rich centrifuged mother liquor undergoes small-scale spray drying and rotary kiln incineration. After SNCR denitrification, the flue gas meets emission standards. The waste residue is melted to produce glass, achieving "zero mother liquor" landfill.

3. Noise: The compressor is housed in a soundproof enclosure, and the plant uses sound absorption technology, resulting in daytime boundary noise ≤ 55 dB(A).

4. Safety: The evaporator is equipped with a rupture disc and a safety valve for double pressure relief.

Automation: Utilizing a Kang Jinghui automatic control system with 4,200 I/O points, key parameters such as evaporation intensity, compressor surge line, and crystal particle size are optimized in real time, with power consumption fluctuations < ±1%. The system allows for remote monitoring, enabling unmanned operation and reduced-staff inspections, decreasing the workforce from 18 people per shift to 6.

Operational Results

1. Capacity: Actual evaporation capacity is 64 t/h, exceeding design capacity by 3%; by-product ammonium sulfate is 3.2 t/h, resulting in an annual capacity of 26,000 tons. N ≥ 21%, H₂O ≤ 0.3%, all recycled to the compound fertilizer production line.

2. Wastewater: Condensate COD ≤ 40 mg/L, ammonia nitrogen ≤ 5 mg/L, with an annual recycling capacity of 520,000 tons.

3. Reliability: 98% uptime, planned cleaning cycle of 30 days, maximum operating time of 46 days; equipment failure rate of 0.3 times/month, significantly lower than the industry average of 1.5 times/month.

Customer Value

This project completely replaces traditional multi-effect evaporation with MVR technology, providing a "zero-steam, zero-emission, low-cost" ammonium sulfate concentration solution for a 900,000-ton/year compound fertilizer plant, generating annual economic benefits of 58 million yuan and reducing CO₂ emissions by 107,000 tons.