Min. Bed Height in IX, WHY?

[mohtogh]

Why we have a minimum bed height in IXs?
Also that minimum height is different for co-current and counter-current operation.why?
Thanks for replies.

 

[25362]

Could the sites

http://www.water-eg.com/

and

http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-66322003000400008

and

thread164-96776, thread127-37319, thread127-44495, thread124-29497

be of help ? I hope so.

 

[mohtogh]

Probably my question is not clear.
I like to know , why resin manufactureres declare minimum bed height should be e.g. 600 mm? If I choose 400 mm as bed height, what problem faced?
Thanks, especially for 25362.

 

[cub3bead]

mohtogh,

Several reasons:

1. It takes a certain amount of time for the ions to diffuse into the resin, exchange and diffuse back out into the water stream.

2. The deeper resin beds tend to minimize channeling which results in partially treated or untreated water exiting the vessel.

3. The resin manufacturer usually has little control over the design of the vessel inlet distributor and underdrain collector.

Operators hate regenerating IX beds. This is not a manufacturer's issue but from a technology application viewpoint regeneration more than once every 24 hours while it may save capex will likely cost more in labor and regenerant costs.

IF you want a thinner resin bed look at Eco-Tec.

http://www.eco-tec.com/

They use a very fine, proprietary resin in their units. They regnerate frequently but the beds are only about 150 mm deep.

Many years ago I learned a very important principal in the application of ion exchange technology. TINSTAAFL: The is no such thing as a free lunch; trying to do more with less in ion exchange will only lead to problems. If you scrimp on resin volume or regenerant chemicals for the job everybody will be dissatisfied with the results. I have made a pretty good living fixing problems where others have cut corners.

 

[GarySCWSVI]

It is always best to follow the resin manufacturers recommendations. One can have shallower bed depths but all of the resin manufaccturers specifications are based, in general, on a minimum bed depth . This is to ensure an adequate contact time as previously mentioned by cub3bead.

One can always use a shallower bed but one can then expect not to see the resin perform per the resin manufacturers specifications. Contact time is a very important part of ion exchange resin application. In most cases the minimum resin bed depth will be 600 mm/30 inches. Shallower beds usually mean less contact time and therefre less cspacity and higher leakages.

Gary Schreiber, CWS VI
The Purolite Co.

 

[mohtogh]

Thanks all.
I think the only reason could be "chanelling prevention" (As cub3Head said), because for satisfying kinetic, I have to keep BV/hr(which is exactly inverse of residence time).I mean If I want to have enough residence time, I could decrease the bed height (whatever I want) and increase bed diameter, but I am not allowed to decrease bed height less than a specified number.Am I right?

 

[xinmin]

I think it is easier to control the flow distribution by uing smaller beds. In addition, sometimes, the land area is more critic than the height.

 

[cub3bead]

The smaller bead size may be acceptable if you are prepared to accept the higher pressure drop and the much higher price of the resin.

I for one will continue to follow manufacturer recommendations and deliver systems that delight my customers because they operate well.

In the grand scheme of IX systems the land cost is usually not that big a factor.

TINSTAAFL

 

[sbush]

I believe that a minimum bed depth is necessary to allow for the "zone of ion exchange activity" that travels through the depth of the ion exchange bed during service. I'm not certain of the actual working depth of this zone, but I would guess it has a lot to do with contact time and hydraulic loading rate.

Please take a look at another thread on a related topic:

http://eng-tips.com/viewthread.cfm?SQID=95205&SPID=194&page=2

S. Bush

http://www.water-eg.com