The white liquor oxygen reactor is the core equipment for white liquor oxidation in the pulp and paper industry. Its manufacturing process covers multiple technical fields, including material science, welding engineering, pressure vessel design, and safety specifications. Operating long-term under high temperature, high pressure, and strong alkaline corrosion, with high-pressure oxygen contained in the process medium, the reactor presents prominent manufacturing challenges, mainly reflected in material selection, welding process control, structural precision assurance, and internal cleanliness management.
Stringent Requirements for Material Selection
White liquor is primarily composed of sodium hydroxide and sodium sulfide, classified as a strongly alkaline medium that severely corrodes ordinary carbon steel at elevated temperatures. More critically, the presence of high-pressure oxygen inside the equipment further accelerates oxidative corrosion risks.
Therefore, the main structural materials for white liquor oxygen reactors must be duplex stainless steel or austenitic stainless steel with outstanding alkali corrosion resistance. Duplex steel such as 2205 features a balanced dual-phase microstructure of austenite and ferrite, combining high mechanical strength and excellent resistance to stress corrosion cracking, making it the preferred material for high-pressure service.
During material procurement, chemical composition must be strictly controlled — especially carbon, nickel, and chromium content. Materials shall be fully solution-treated to eliminate susceptibility to intergranular corrosion. Any material defects may induce alkali embrittlement (caustic embrittlement) during operation, triggering sudden cracking in stress-concentrated zones.
High-Risk Control of Welding Processes
Welding is the most critical and defect-prone procedure in reactor fabrication. Duplex stainless steel is highly sensitive to welding heat input; interpass temperature and linear heat input must be rigorously regulated throughout welding operations.
Excessive heat input disrupts the phase balance between austenite and ferrite in weld zones. Excess ferrite degrades corrosion resistance, while excessive austenite weakens mechanical strength. Welding procedure qualification shall fully verify the compatibility between welding consumables and base metals. Post-weld solution heat treatment or stabilization heat treatment is generally required to eliminate welding residual stress.
Residual stress drastically increases the risk of stress corrosion cracking during service. This hazard is further intensified under the combined effect of alkaline media and high-pressure oxygen.
Structural Precision and Leak-Proof Design
Internally, white liquor oxygen reactors are equipped with gas-liquid distribution components to achieve uniform mixing of oxygen and white liquor. The machining accuracy and installation alignment of distribution pipes, nozzles and trays directly determine reaction efficiency.
Misalignment of gas distribution components leads to uneven oxygen dispersion, causing localized over-intense reactions or dead flow zones, which impair oxidation performance and may result in local overheating.
In addition, inner wall transitions between the shell and nozzle connections shall be smoothly polished to eliminate sharp corners and gaps, which are typical initiation sites for corrosion fatigue.
Sealing surface treatment is equally critical. The sealing faces of nozzle flanges, manholes and instrument connections must have higher hardness than gaskets, meet specified surface roughness requirements, and be free of radial scratches. All fasteners shall be pre-tightened in accordance with calculated torque values to prevent sealing failure caused by differential thermal expansion during heating and cooling cycles.
Cleanliness Management and Safety Protection
As a pressure vessel operating in an oxygen-enriched environment, the white liquor oxygen reactor demands extremely high internal cleanliness. All media-contacting inner surfaces undergo pickling and passivation to form a dense passive film and enhance corrosion resistance.
Most importantly, no oil or grease residues are permitted inside the equipment. In high-pressure oxygen environments, organic grease can trigger violent oxidation, combustion, and even explosive accidents. For this reason, thorough degreasing treatment is mandatory after fabrication, with key areas inspected and verified via ultraviolet lamps or oil residue detectors.
In terms of pressure testing, hydraulic testing shall be conducted in compliance with codes, with the test pressure generally set above 1.25 times the design pressure to verify overall structural strength. For systems handling white liquor and oxygen, tightness testing is additionally required. Clean dry air or inert gas is used to inspect all welds and sealing points, ensuring zero bubble leakage under operating pressure.
