Issues regarding gypsum rain and water contamination at the outlet of the flue stack of the desulfurization tower, i.e., problems related to the demister
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This post was last edited by SeaWolf_GUVX on 2019-7-19 at 15:33. Question: 1. Is it serious that the flue gas discharged from the desulfurization tower contains liquid droplets (including slurry)? 2. Does all the water used for flushing the demister escape from the chimney outlet? Description of the internal functional areas of the absorption tower: The absorption tower is capable of handling 72,000 Nm3/h of flue gas. Its dimensions are 5m in diameter by 15.5m in height, with a section of variable diameter measuring 5m in diameter by 2m in height; the exhaust chimney has a diameter of 2m and a height of 25m. The lower 3m of the tower consists of a circulating slurry tank, while the upper part features one cyclone unit and three spray layers. In the section with variable diameter (at 4m in diameter), there is one flat-plate mist remover; at 3m in diameter, another flat-plate mist remover is installed; and at 2m in diameter, a wire mesh dust and mist removal device is present. Current situation: When one or two circulation pumps are in operation, gypsum rain is produced at the chimney outlet, and it turns into white spots on the ground a few seconds after falling. If the process water pump (with a flow rate of 12.5 m3/h and a head of 45 m) is used to flush the demister, the chimney outlet will experience heavy rainfall-like conditions, while the liquid level inside the tower remains completely unchanged. I earnestly request assistance from professionals in this field; thank you!
We have encountered this problem as well; by removing about one-third of the adsorption balls from the demister and adjusting the angle of the blades used for dust treatment, things improved significantly. Which design firm are you using?
The swirl plates in a desulfurization tower come in external rotation and internal rotation types. Based on our many years of experience in constructing desulfurization towers, it is recommended that the swirl plates inside the tower should be of the internal rotation type. You can take a look; if it’s an inward-rotating swirl plate, it’s recommended to switch to an outward-rotating one. Direct the airflow to spread along the tower walls, rather than concentrating it in the center.
The suggestions we put forward ourselves, designed by the demister manufacturers
There are no swirl plates at the top of the absorption tower; it is covered with a layer of mesh
As you described, the position of the demister is incorrect; the flow velocity at the area where the diameter changes is significantly higher than that inside the tower. The flow velocity at the demister is usually around 4, and such a high velocity is likely too high to enable it to function properly
There’s no such thing as an abnormally high tower flow rate of 3.5 M/S; this one is only around 1.5 M/S, I think
You are calculating for an empty tower; also calculate the flow velocity between the blades of the demister. Perhaps due to the pressure difference between the empty tower and the demister, a Venturi effect is created, which allows liquid droplets to escape
Such problems are quite common these days. Our facility specializes in flue gas desulfurization, and the root cause of this issue is that neither mist eliminators of the mesh type nor those of the plate type are able to effectively remove the free water particles carried in the flue gas. Mesh-type mist eliminators can remove over 95% of the free water, so the remaining free water is discharged through the chimney and falls to the ground, where the salts contained in it precipitate, forming white spots on the surface. The solution is to replace or add a demister. Feel free to message me if needed.
The flow velocities in the two-layer demister are approximately 1.89 m/s and 3.3 m/s
This speed is still quite different from the flow velocity in the empty tower; it seems that a negative pressure has been created at the location of the demister, preventing water from reaching the demister at all