122、preventive measures for material fatigue in subcooled section of gasifier (part 2) -威尼斯2299

preventive measures for material fatigue in subcooled section of gasifier (part 2)

(1) . anti eccentric design

during the operation of the air heated gasifier, the gasifier itself is subject to two different forces of gravity and gas buoyancy (other wind forces are not considered); 8 fins are used in the inlet section and 12 fins are used in the heating section. the weight of 12 fins is greater than 8 fins; generally speaking, gravity is greater than buoyancy; but the buoyancy of the liquid inlet end is small, and the frosting during operation increases the gravity, so the center of gravity will shift slightly to the liquid inlet end. in the design of our company, under the condition of continuous operation without icing, we try to use more 12 fins in the reheating section, so as to balance the gravity and keep the center of gravity at the center of the equipment as far as possible, so as to prevent adverse effects such as equipment tilt caused by different forces during operation.

(2) anti icing design of subcooled section

during the operation of the air heated gasifier, when the low temperature liquid lng enters the finned tube, the temperature of the tube wall (finned tube) decreases sharply near the inlet doer to the large temperature difference between the liquid lng and the tube (finned tube) (about 170 ℃), and the water vapor in the surrounding air condenses into frost layer quickly when it is cold. at the same time, along the length of the pipe, the fluid absorbs the heat of the pipe wall, first goes through the supercooling section, gasification area and then to the reheating area, and the temperature rises continuously. the farther away from the inlet, the higher the temperature is, so the temperature difference between the pipe wall and the fluid gradually decreases, so the frosting degree and speed away from the inlet become smaller and smaller.

therefore, it can be seen that in the subcooled section, ice is most likely to form; and it is not difficult to find out the main factors that affect the frost thickness are: ambient temperature, ambient humidity, air flow rate and continuous working time.

the working time of vaporizer is set as 8 hours, and other factors are uncertain.

on the basis of slightly increasing the cost, our company has carried out special surface treatment (forced oxidation) of aluminum in the supercooled section. doer  to the small adhesion between the treated 8-wing and smooth fin and frost layer, when the frost layer reaches a certain thickness, it is more conducive to the fall of frost layer, so as to control the growth of frost layer thickness to the greatest extent, so as to prevent icing. at the same time, the treated equipment is still as white as new after long-term use. advanced special surface treatment, greatly improve product life, suitable for seaside and corrosive harsh environment.

therefore, it is very reasonable to use aluminum alloy material for heat exchange tube (smooth 8 fins) in subcooling section and 3a21 material for heat exchange tube (corrugated 12 fins) in heating and reheating section.