3 replies to this topic

[Kanaka Sai]

Usually multiple pads make a set demister unit. Incase of increased pressure drop these have to be taken out of towers handling each pad and similarly handled to place them back forcing long time of plant stoppages . The frequency is more in metallurgical gas based Sulphuric Acid Plants.
Can we design the demister chamber in such a way that as cubicle the demister unit comes out and goes back.

[kkala]

Having worked in a fertilizer factory (1975-81) making H2SO4 from sulfur or pyrites, I do not remember problems of mist eliminators located downstream of absorption towers, even though my "base" was not there but in the phosphoric fertilizer plant. Nevertheless those H2SO4 plants had plenty of idle time for maintenance and cleaning, due to their overcapacity compared to downstream units fed with H2SO4.
The need of interchangeability (for shorter dead time) seemed to gain importance later for several pieces of equipment. Interchangeability, even during operation, has been detected only at the fuel oil strainers to boiler burners: two interlocked strainers, interchanged through a lever. I have not seen the arrangement, though written about it in boiler specification. At any case fuel oil pipe diameter was (say) 2", no comparison to the off gases diameter downstream of the absorption tower. Most probably a similar design has not been developed, concerning demister "cubicle".
Inspite of that, steps have been found out to facilitate demister pad replacement or cleaning, e.g.:
http://www.beggcousl...m?CaseStudyID=7, vertical pads to be removed from outside. One pad can be replaced by a spare during a short plant stoppage.
http://sumitindustri...mister-Pad.html, one piece, horizontal, "easy to clean with air" (according to their saying).
Goggling "sulfuric acid demisters", or similar, could reveal innovative designs with easy cleaning or replacement (price is another cup of tea).

Edited by kkala, 17 July 2011 - 08:09 AM.

[Kanaka Sai]

Thanks for your prompt response. In Sulphuric Acid Plants demisters are located at exit of Drying Tower and candle Filters are provided in Absorption Towers.

[kkala]

Thanks for your prompt response. In Sulphuric Acid Plants demisters are located at exit of Drying Tower and candle Filters are provided in Absorption Towers.

It seems that both plant locations can accept either demisters or candle filters, see http://www.sulphuric...cid/sa_mist.htm and http://www.amistco.c...LES/sulfur.html. Or perhaps modern trend is mist eliminators for air drying tower and candle filters for absorption tower?
I am not sure about the location of mist eliminators in mentioned sulfuric acid plants (1975-81). I had the impression they were located downstream absorption towers, but never seen them; so I might have supposed so. On the other hand Candle filters had not been heard at all. Dealing with specific measurements and surveys on phosphoric fertilizer units, my activities on H2SO4 plants were quite limited.
At any case thanks for sharing the information.

Note: Mist eliminators in mentioned plants, wherever placed, did not have (rather important) problems; otherwise I would have heard of them in the weekly meetings.

Edited by kkala, 17 July 2011 - 12:44 PM.