Sea Water

Elmosa InvisiHead Intake System vs.
Screening
Comparison between the performance, stability as well as durability and

economics of the InvisiHead and those of screen systems
The Cooling Water Intake at Ventanas Power Station used as a case study (1)
Figure-1: The O&M-Free InvisiHead system
Vs.
Figure 2: The O&M-intensive screening systems

The use of the InvisiHead technology has proved to be more cost-effective than other
existing intake and discharge technologies. Especially after adding the latest
improvements, the InvisiHead is solidifying its position as the best technology
available in the seawater intake and outfall industry. In 2013 the InvisiHead was
further tuned to be more selective – letting only the required flow capacity free of
marine life, sediment and debris. Once the InvisiHead is in position mechanical
screening is no longer needed be it course or fine spaced bar racks, trash rakes, self-
cleaning bar racks or bar screens that consist of stationary bar racks automatically
cleaned by one or more rakes, traveling water screens either dual or center-flow
screens. Complex combined fixed and traveling screens will not prevent sediment-
entrained flow like fine and course sand however from passing the screens over to
accumulate in the screen/pump bays at both Units 1 and 2 in in Ventanas power
station up to one meter deep. Sediment also builds up in the condenser water boxes.
The InvisiHead is a well-engineered proactive intake system which actively uses

natural phenomena to employ biota and sediment flow diversion and to address
operation requirements as well as complying with environmental codes compared to
the highly reactive screening systems that are added onshore to remove part of biota
and debris that should have not moved into the intake system in the first place. The
(1) Courtesy of AES Gener S.A, Chile.
Elmosa Seawater Intake and Outfall Systems

American Eco Systems, LLC., 540 Centre Street , Nutley, NJ 07110 , t. +1 973 563 7270 , f. +1 973 320 5258,
e. elmosa@amecosys.com www.amecosys.com/elmosa Technical sheet 1io/2014
1
Elmosa InvisiHead Intake System vs. Screening
overall performance of the American Eco Systems Elmosa Seawater Intake System
is higher than that of any other systems operating in the water intake industry
including mechanical screening systems. Since the Elmosa InvisiHead system by
design and nature of operation is proactive, it utilizes the natural processes in its
entire operation from the start to the end – from the point where the first water
molecule at the offshore end of the system is drawn in to the downstream end of the
pump bays or NatSep intake basin onshore where that molecule is transferred to the
seawater pump suction bell. The molecule –not associated with any supended
material - is gently drawn in to the InvisiHead and smoothly guided through all the
way to the pump intake at the intake basin. Hence, the need to react to a debris
problem carried in through the water intake system is eliminated and thus the need
for reactive O&M-intensive screening systems is eliminated. This high degree of
performance of the InvisiHead system is also demonstrated when it operates as a
marine outfall to discharge, disperse, mix and dilute effluents to attain local
conditions within the vicinity of the InvisiHead diffuser. In contrast, mechanical
screening has to be supported by a costly O&M-intensive effort as show below to
keep it in operation.
Figure-3: The complete elmosa intake system: InvisiHead, EVE intake line, gravety NatSep; zero
moving parts, zero spareparts for life; meets and exceeds local environmental regulations
Figure-4: Safely dishcharging, dispesing, mixing and diluting effluents

2
Figure-5: InvisiHead can be installed under and supported by loading docks, jetties, and offshore platforms
Figure-6: The O&M-Free InvisiHead Systems
Figure-7: Sequential flow system: Far & Near Approach, Stabilization, Outlet, IH-Intake Pipe Interface

3
Figure-8: A closer look at the O&M-free InvisiHead flow management system with detailed flow
behavior in, to, and out

4
Figure-9: O&M- Intensive screen system

5
Fig-9: Just to remove debris the mechanical screening system can be complex
Figure-10: Sediment accumulation around pump mostly very fine to coarse sand and some algae

6
Technical Comparison: the InvisiHead versus the fixed and traveling Screens
Mechanical
Screening
Issue: Algae and Algae and debris The InvisiHead Intake System Stationary and
biota deposits Management Traveling
How is it resolved? How is it resolved?
Quintero Bay in Chie The far approach, near approach, inlet Using a
has an abundance of red and outlet flow veocities are all lower combination of
algae that enter and clog than the particle fall velocity of the advanced modern
the cooling water intake debris, therefore it will not be sucked fixed and traveling
systems at Ventanas in by the super weak out of phase screens could
power plant. The algae suction forces generated by the remove the design
grow in the bay and onshore seawater intake pumps. These size of debris and
consist of Gracilaria suction forces are as week as 0.017 larger-Figures 2
chilensis (Pellilo) and Gracilaria chilensis, Pellilo millibar – Fig. 7. and 6.
Ceramium rubrum
(banded red weed) are the
primary aquatic
vegetation as the primary
source of debris which
passes over and through
the screens and plug the
condenser tubes
These algae create Ceramium rubrum Banded red

weed
episodes of high debris
loading at the bar racks,
traveling water screens
intake, and condensers.
Algae and sediment pass
through the bar racks
and over, or through, the
traveling water screens
to the condenser tube
Algae collected from intake
sheets. The algae
buildup on the screens
can be so great that the
differential pressure
creates a large gap
between the screen mesh
frame and the guide seal
plates. Debris that
passes through this gap
gets trapped on the Jellyfish
inside of the screen and
is not removed by the
screenwash system.

7
How the InvisiHead Intake System How the

manages the problem Mechanical
Screening
Sediment and Debris
Sediment Deposits Stationary and
Management Traveling
Systems deal with
the problem
180 cubic meters of fine Since it utelizes the natural The use of all types
to coarse sediment phenomena in its flow management, of screening
accumulated around the InvisiHead uses local marine systems may reduce
pump in one year currents to flush marine life, debris or eliminate flow of
and sediment out of its system and get algae but definitely
Ventanas experiences back into the ambiant again. The will not affect
operating and standard InvisiHead secifications call sediment transport
maintenance problems for an entrance veocity of 0.091m/s action. Use of
related to sediment and local currents to flush out debris dedicated sediment
entering the intakes. with fall velocity lower than 0.09m/s. removal equipment
Sediment accumulates 0.02m/s is the fall velocity of fine- was recommended.
up to one meter deep in very fine sand in the pile shown in
the screen/pump bays at Fig.10. No sufficient data is available
both Units: Unit1 and about current velocities in Quintero
Unit2. Sediment also Bay. In standard conditions of local
builds up in the marine currents one InvisiHead
condenser water boxes. system of 5.67m for Unit 1 and 1-
6.55m or 2-4.63m for unit 2 of the
Ventanas power plant to deliver the
required flow capacities unattended at
all times free of algae, debris, and
sediment. Due to the ack of sufficient
current data 0.02m/s woud be the
design criterion of the InvisiHead
entrance velocity for both units.
Units1 and Unit2 woud need a total of
11-5.5m InvisiHead systems to supply
the required capacities of clean water
free of sediment and algae.

8
Mechanical
Costs Sediment, Algae and
The InvisiHead Intake System
Screening
Debris Management Stationary and
Traveling
Total Sediment and Equipment: Equipment:
algae management
costs OPTION I: Total cost is at
Under standard conditions the about $11.3
entrance velocity is made at million
0.09m/s to use one-5.67m to
supply 45,000 GPM to Unit1 and
one-6.55m to supply 60,000 GPM Annual O&M:
to Unit2 $612,000
Both InvisiHead systems operating
under standard conditions to
supply cooling water free of algae
and sediment.
Total cost is about $1.68million
OPTION II:
But since no sufficient site data for
marine currents in Quintero Bay is
available supplying Unit1 with 5-
5.5m systems and Unit2 with 6-
5.5m systems using 0.02m/s as
the sizing criterion.
Total cost is at about $8.4 million
The systems will not admit algae

or any sediment greater in size
than fine sand (0.05mm). Chances
are great that marine currents
even as slow as 0.03m/s will exist
at the InvisiHead site to do self
sediment flushing operations – Fig.
7 and 8. The systems are O&M-
free for life.
Payback Period O&M costs to remove Since the InvisiHead system is

algae, sediment and O&M-Free, it pays back its capital
debris by screening and investment in terms of O&M cost
other mechanical means : savings as follows:
$612,000/yr. Option 1: 2.75 years or 33 months

Option II: 13.7 years

9

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Elmosa InvisiHead Intake System vs.

Comparison between the performance, stability as well as durability and

Figure-1: The O&M-Free InvisiHead system

Figure 2: The O&M-intensive screening systems

The InvisiHead is a well-engineered proactive intake system which actively uses

(1) Courtesy of AES Gener S.A, Chile.

Elmosa Seawater Intake and Outfall Systems

Figure-4: Safely dishcharging, dispesing, mixing and diluting effluents

Elmosa Seawater Intake and Outfall Systems

Figure-6: The O&M-Free InvisiHead Systems

Elmosa Seawater Intake and Outfall Systems

Elmosa Seawater Intake and Outfall Systems

Figure-9: O&M- Intensive screen system

Elmosa Seawater Intake and Outfall Systems

Elmosa Seawater Intake and Outfall Systems

These algae create Ceramium rubrum Banded red

Elmosa Seawater Intake and Outfall Systems

How the InvisiHead Intake System How the

Elmosa Seawater Intake and Outfall Systems

Total cost is about $1.68million

Total cost is at about $8.4 million

The systems will not admit algae

Payback Period O&M costs to remove Since the InvisiHead system is

$612,000/yr. Option 1: 2.75 years or 33 months

Elmosa Seawater Intake and Outfall Systems

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