In-depth Analysis of the Whole-Life Cycle Management for Corrosion Prevention in the Gasification Process of Gas Generation Units

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In-depth analysis of the life-cycle anti-corrosion management for the gasification process in gas generation units. As the cornerstone of the modern coal chemical industry chain, gas generation units have complex processes that involve high temperatures and pressures, as well as various highly corrosive substances such as H2S, NH3, chloride ions, and solid particles. It is necessary to establish a life-cycle corrosion prevention management system that covers aspects such as material selection and design, process control, and dynamic monitoring. I. Core corrosion mechanisms: The challenge of multi-factor coupling. Corrosion in gasification processes is not a single-factor phenomenon; rather, it is a process characterized by a high degree of coupling between physical erosion and chemical/electrochemical corrosion: 1. Erosion-corrosion: o Causes: The high-speed impact of solid particles in coal slurry and ash water. o High-risk points: weighing coal feeders, coal mill discharge troughs, flash tanks, etc. Mechanism: The combination of mechanical stripping and chemical corrosion of the medium leads to the formation of grooves, ripples, or horseshoe-shaped indentations on the metal surface. 2. Chloride stress corrosion cracking (Cl-SCC): o Subjects: 300 series austenitic stainless steels. Mechanism: Even at low Cl- concentrations, combined with temperatures above 60°C and tensile stress, stainless steel is highly prone to brittle cracking. This is particularly evident on the inner wall of the gasifier and in the ash water system. 3. Ammonium hydrosulfide (NH4HS) and acidic water corrosion: Characteristics: In conversion condensate and stripping systems, NH4HS, formed from H2S and NH3, is a highly corrosive agent. When the concentration exceeds 2% (wt), the corrosion rate increases significantly, and hydrogen bubbling is likely to occur. 4. High-temperature sulfur and hydrogen corrosion: Conditions: Above 204°C. * Risk: The high-temperature environment in the conversion unit exposes the material to uniform thinning caused by sulfur at high temperatures, as well as internal decarburization and microcracks resulting from high-temperature hydrogen attack (HTHA). II. Anti-corrosion control for key processes: Proactive defense strategies 1. Precise adjustment of the graywater system: By analyzing the levels of ammonia nitrogen, chloride ions, and pH value in the graywater, the amount of water used for system flushing is adjusted dynamically. Maintaining the pH level between 7 and 9 is key to slowing down the thinning of graywater systems. 2. \"Temperature control and separation\" in the shift system: Liquid-water separation – Strict control is exercised over the separation tank at the shift system inlet to prevent liquid water from entering the reactor, thereby eliminating the formation of an environment conducive to corrosion caused by H2S + H2O. Temperature control: Reduce the operating temperature to mitigate high-temperature sulfur/hydrogen corrosion, provided that it does not compromise the catalytic reaction. Medium-pressure deoxygenated water injection: Deoxygenated water is injected in front of the water cooler to dissolve NH4HS and NH4HCO3 crystals, effectively preventing local corrosion caused by scaling. 3. Red-line parameters for circulating cooling water: Flow rate limits – >1.0 m/s on the tube side and >0.3 m/s on the shell side, to reduce sediment accumulation and under-scale corrosion. Temperature limits: The temperature of the process medium is recommended to be below 130°C, while the temperature of the cooling water at the outlet should not exceed 60°C. III. Principles for equipment protection and material selection in humid H2S environments: Materials resistant to hydrogen-induced cracking, such as Q245R, should be preferred. Hydrogen corrosion environment: Use medium-temperature hydrogen-resistant steels (such as 1Cr-0.5Mo, 2.25Cr-1Mo). In areas with severe wear: hardfacing with cemented carbide, tungsten carbide, or high-chromium cast iron is used. Oxygen medium: Austenitic stainless steel or nickel-based alloys must be used. IV. Preventive maintenance: Shutdown protection and monitoring. Nitrogen filling during shutdown: To prevent water vapor from condensing and creating an acidic, wet corrosive environment. Ferrous sulfide passivation: During shutdowns, special treatment is applied to sulfur-containing equipment such as waste boilers to prevent spontaneous combustion of ferrous sulfide.