Preventive measures for material fatigue in subcooled section of gasifier

1. Measures for material fatigue and deformation (stress relief) under frequent alternating cold and hot conditions

At the inlet temperature of - 162 ℃, according to the change of ambient temperature, the heat exchange tube of the gasifier will have a variety of phase transitions (liquid gas / mixed gas) including three stages: liquid phase heating stage, two-phase mixing stage and gas phase heating stage. In order to reduce the stress caused by temperature change, our company adopts the following methods:

① The distance of the elbow in the subcooled section is lengthened to eliminate the stress;

② The frame is made of 6063 aluminum or 304 material, the fasteners are made of 304 stainless steel, and the bolt holes are enlarged;

③ In the liquid inlet section, a collecting pipe is used to make the liquid flow reasonable without bias; The outlet section adopts "collecting pipe collecting" instead of "elbow butt joint", which can reduce the stress caused by boiling phase of gas-liquid mixture to the greatest extent, improve the previous manufacturing method, and completely solve the deformation, even crack and break of elbow.

3A21 aluminum alloy (grade 3003), which is special for low temperature industry in the world, is selected as the material of heat exchange tube and pressure tube. Its low temperature performance and heat transfer performance are excellent; The large spacing and high efficiency gasification heat exchange tube with 200 mm diameter and inner fins is adopted, which effectively changes the flow form of medium in the tube, and the heat exchange effect is excellent. The optimization process design of front smooth 8 fins and back corrugated 12 fins. The overall strength of the equipment at low temperature is better, the heat exchange layout process is more reasonable, the heat exchange efficiency is greatly improved, and the outlet temperature meets and exceeds the rated requirements.

At the same time, this type of aluminum, no noise, no pollution in operation, is an environmental protection and energy saving material!

3A21 is selected for heat exchange, and its characteristics are as follows: 3A21 is al Mn alloy, which is one of the most widely used antirust aluminum. The strength of this alloy is not high (slightly higher than industrial pure aluminum), and can not be strengthened by heat treatment. Therefore, cold working method is adopted to improve its mechanical properties: it has high plasticity in annealing state, good plasticity in semi cold hardening, low plasticity and good corrosion resistance in cold hardening, Good weldability and poor machinability. It is mainly used for low load parts that require high plasticity and good weldability and work in liquid or gas medium, such as mailbox, gasoline or lubricating oil conduit, various liquid containers and other low load parts made by deep drawing. 3003 aluminum sheet has good formability, solubility and corrosion resistance.

The leg is made of 6063 high strength aluminum. The main alloy elements of 6063 aluminum are magnesium and silicon. It has excellent processing performance, excellent weldability, extrusion and electroplating, good corrosion resistance, toughness, easy polishing, coloring film and excellent anodizing effect. It is a typical extruded alloy. 6063 aluminum alloy profiles are widely used in building profiles, irrigation pipes, pipes, bars and profiles for vehicles, platforms, furniture, elevators and fences due to its good plasticity, moderate heat treatment strength, good welding performance and gorgeous color after anodizing treatment.

The two kinds of aluminum materials have high heat transfer performance, but in general, 3A21 has strong plasticity and weldability, which is suitable for the main heat exchange parts; 6063 is not as plastic as 3A21 and has high strength, so it is suitable for outrigger and frame.

The above measures can effectively reduce the phenomenon of material fatigue and stress under the condition of alternate cooling and heating in the subcooling section, and ensure the safe and stable operation of the gasifier within the design life.