Liquid carrying problems in spray packed towers and cyclone towers
Thread Content
This post was last edited by Xianshen on 2016-12-7 at 15:26. What are the common causes of liquid presence in spray packing towers? We have a project tower DN1400×5000, with two spray layers; each layer uses DN50 Boulton ring packing 50 cm in length. The mist removal layer features DN50 Boulton ring packing 30 cm long. The air flow rate is 3000 cmh. It is used for oil removal, with a spray rate of 3 L/M3. There is always liquid present, and a lot of water accumulates in the filters at the back. There is also a cyclone tower (which makes use of the customer’s existing tower; it has three layers of cyclone plates, with the top layer used for mist removal). Alkali is added to remove paint fumes and acidic gases. The diameter of the tower is 3000×6000, and its air handling capacity is 15,000 cmh; the spraying rate is 2 L/M3. There is also a significant amount of liquid involved. I would like to seek advice from all of you!
No way, right? The empty tower velocity for the packed tower is 0.54 m/s at 3000 cmh, while for the cyclone tower it’s 15000 cmh with an empty tower velocity of 0.59 m/s, right?
Two factors need to be considered: the first is the gas velocity; when this velocity is greater than the settling speed of the droplets, the droplets are carried away. The higher the gas velocity, the greater the liquid carryover. In the tower, assuming that the effects of positive and negative process pressures are not considered, the droplets fall due to their own gravity. The greater the upward \"force\" exerted by the gas on the droplets, the larger the droplets that can be carried away, and thus the higher the amount of liquid entrained. Secondly, there is the issue of separation space: after leaving the packing layer or demisting layer, larger droplets fall naturally, but most of the smaller droplets continue to move with the gas flow. During this movement, they combine randomly due to their irregular motion, and once they form larger droplets, those too fall. If there isn’t enough separation space, the above process becomes essentially pointless, leading to entrainment.
It is also closely related to the nozzles in the spray tower; if the particle size of the mist is much smaller, more material will be carried away.
It can be considered from two aspects: one is the droplet capture efficiency, which requires thorough calculations; there are experts in this field who need to conduct further re-evaluations； Secondly, considering the water content in the gas, if the water content in the gas is already saturated or near-saturated at that temperature, liquid water will precipitate due to temperature differences during pipeline transportation.
The nozzle does have some impact, but I personally think it shouldn’t be very significant. We’ve used spiral nozzles of 1/4, 3/8, and 1/2 inch sizes, as well as pipe holes; we’ve tried those out, but there’s no quantitative analysis – just a qualitative estimate, since the normal pressure for our nozzles is around 1–1.5 kilograms