Document ID: EPA-HQ-OW-2008-0667-3648
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2014-08-15T04:00Z

316B RULE

 TELEPHONE LOG

Name of Caller: 	John Sunda, SAIC

Date: 			October 14, 2008

Company Name: 	Eimco (Brackett Green)

Street Address:	1335 Regents Park Dr., Suite 260

City/State/ZIP:	Houston, TX

Person Contacted:	Trent Gathright

Title:			Group Product Manager

Telephone #:		281-480-7955 Ext 27

                                                                        
                                                             

Trent T. Gathright

Group Product Manager

P&I Screen Products

EIMCO Water Technologies

1335 Regents Park Dr., Suite 260

Houston, TX 77058

Tel: 281-480-7955 Ext. 27

Fax: 281-480-8225

Mob: 832-489-7956

Email: trent.gathright@glv.com

Web: www.glv.com

Called to ask about feasibility of fine mesh screens in high sediment
and debris waterways, technical issues, and examples of fine mesh (<2mm)
traveling screen installations.

He said that it is difficult to nearly impossible to retrofit existing
screens with high screen velocities with fine mesh of 0.5 mm especially
if there is a high debris or sand loading because of the rapid blinding
of the screens. He said the Mississippi and especially the Missouri (big
muddy) have problems with sand and retrofitting high velocity screens
with 0.5 mm mesh would be nearly impossible. I asked about larger mesh
sizes and at what point (size) would the problem diminish. He said the
problems would be significant when mesh size drops below 1.0 mm and that
2.0 mm and above would present no problem with sand. They have done
numerous 1/8 in (3.175 mm) retrofit installations and screen velocity
was not a problem in those cases. Basically, you can have fine mesh
screens with low velocities like around 0.5 fps and coarse mesh screens
with high velocities but you can’t have both fine mesh (0.5mm) and
high screen velocities if there are any chances of debris/sand loading
being a problem. 

Regarding O&M cost issues, one of the biggest O&M cost items associated
with fine mesh is the more frequent need for chain replacement. Factors
that contribute to increased rates are more frequent or continuous
operation, operating at faster rotation speeds, and higher depth
differentials (head loss) across the screen. All of these tend to
increase with reductions in mesh size. Labor is the biggest component
for chain replacement. When asked about the relative increase in O&M for
high debris/fine mesh screens, he said O&M costs should increase by
about 30%.

They recommend installing 2 speed screens so speed can be tailored to
debris conditions, thus minimizing wear on screens.  Typical coarse mesh
screen speed is 10 fps and fine mesh will be around 15 fps and 30 fps.
Their dual flow screens go up to 45 fps since screen panels travel both
down and then up between washes.

Regarding screen velocities he said that 2.5 fps is probably a good
cutoff point for acceptable screen velocities if the screen mesh isn’t
too small. At higher velocities increased head loss across the screen
become an issue.  

I talked about the fact that overseas they use fine mesh but probably
with lower velocities and may use closer spaced bar racks. He said they
also recommend use of closer spaced bar racks but only if the mesh size
is smaller. For example it would make no sense to put 1 inch bar racks
in front of 3/8 in mesh screens.  

Another problem with finer mesh is corrosion. They use stainless steel
but also can use polyester screens but these are less strong and more
easily damaged. He said that puncture of the screens is not that much of
a problem.

Regarding types of debris, with regard to leaves mesh size doesn’t
matter since the leaf will collect on the surface regardless. Algae can
be a problem with fine mesh because it can form a matt on the surface
essentially creating filtering surface that will catch finer particles.
Lake Ontario has problems with algal blooms and the Mississippi and
Missouri rivers can have problems with algae and leaf mats in addition
to sand.

He will send me additional information regarding their experience later
this week via email.