Sieman's Mulitwash Systems

[QualityTime]

Does anybody have any experience with the Sieman's multwash system. They are promoting a simultaneous water and air backwash. They have "wings" on their backwash troughs and short plate settlers.

 

[WaterTechnology]

Full disclosure: I work for Siemens.

Saw your post and if you need more information on Siemen's Multi Wash System, these 2 links could be of value to you.

the attached Siemen's Multi Wash System URL has information and a link to the multi wash brochure which has more indepth information.

 

[QualityTime]

Hi, I have seen this brochure already. I just wanted some input into whether there is any media carryover on the backwash. I have heard stories second hand. The system to prevent media carryover looks pretty elaborate. Just looking at it you kind of wonder is the particles are trapped under the trough with nowhere to go

 

[sbush]

If I may be so bold as to answer your last question ahead of the General Filter salesman's pending response. Their trough is surrounded by curve-plate baffles (what you called wings). These two plates overlap underneath the trough, but at the same time, they are off-set in the vertical orientation across their lower edges to form a covered opening or large slot running the length of the trough. Thus, upcoming air bubbles cannot turn and enter the trough zone; while at the same time, media that enters the trough zone from above, falls back into the fluidized bed through the covered opening below. The media never settles or gets trapped; instead there is a continuous circular or rolling movement of the fluidize bed.

After the simultaneous air-water cycle is finished, the disturbed bed is backwashed at a normal water-only rate (15 - 20 gpm/sf) for a short period to re-stratify multi-layer beds and to bring the top of the bed back to its ideal pancake-level condition. The final backwash also removes any trapped or entrained air bubbles from the bed, prior to service.

These air-water separator baffles (General Filter's Multi-wash and other brands) function well in square, rectanular, and circular walled, vertical tanks and vessels. However, they have been known to have media loss problems in horizontal pressure vessels. Due to the continuous tappering shape of the horizontal shell, as water rises to the overflow, there is a rapid acceleration of the rise rate that can result in what appears as a "boil over" condtion (even at what might be thought to be low "sub-fluidizing" rise rates recommended for these systems).

A lot of these "better mouse traps" are driven by marketing. You know--get your brand specified with a unique feature that the competition cannot match. Less competition means...well you know what that means.

Simultaneous air-water does not necessarily result in the best scouring action (although it looks very impressive from above). The secret to scouring is maintaining intimate contact between the granules of media. With air and water the close contact is lost to a large degree. On the otherhand, air-water backwash does expand the bed tremendously to allow for removal of loosened debris, particularly from the deeper regions of the bed.

If you don't have wings, you can have your cake and eat it too, by using a method that first drains the freeboard water level to about 1" or so above the resting filter bed, then by scouring with air only the media remains in close contact (think of it like a "sandblasting" effect)with granules scrubbing each other. This step is followed, in sequence, by upflowing with water and air (i.e., simultaneous air/water backwash) until the water level reaches a safe point just beneath the overflow trough. The proper termination level can be sensed automatically/remotely by a water level probe or by visual observation in an open-top filter. At this point, the air flow is stopped. Water continues upward at a progressively increasing rate of flow until the standard 15 - 20 gpm/sf velocity is acheived. Thus the loosened debris, from deep within the bed, is carried away without media loss. With this method, there are no "winged" baffles to obscure the viewing ability of the top of the filter bed or to interfere with the laminar flow path of water entering the filter enroute to the bed area. Unfortunately, for salesmen, this method isn't proprietary and anyone can build it or adapt it to their own filters.

I hope this answer is what you were looking for, when you asked your questions. Like a lot of the URL links on this and other sites, I didn't find any first hand information or "Eng-tips". Do you ever wish people would keep their Googlizations to themselve? I take it with a grain of salt myself, but I worry about the impressionable souls out there.

Oh shoot! I'm rambling again.

Bye.

S. Bush

http://www.water-eg.com

 

[QualityTime]

sbush:

Thanks....that is exactly my feeling with this system. There is a large installation which just got installed and the jury is still out. I am watching with interest. Lots of marketing hype?? The whole setup looks pretty elaborate when simplicity is the best. I would assume that continuing the air water wash as the water overflows the trough is to really make sure you get the particles out because they are now travelling at a higher velocity upwards

As far as for what you have suggested if you do not have water wings I am in complete agreement with you.

 

[QualityTime]

I am hearing different stories about this system using more backwash water than a conventional wash. Can anyone add to this