Home
W&WW Blog Case Histories Books Shop Amazon  Member Survey Advertise
Buyer's Guide News Help Forum Ask Tom! Jobs Videos Newsletters

Search

News Center Links

 News Center Home

  Industry News
  Case Histories
  Air Quality
  Chemicals
  Coatings
  Cogeneration
  Controls
  Conveying
  Dewatering
  Piping
  Pumping
  Software
  Systems
  Tanks
  Valves
  Water Supply
  Wastewater

More Links

  Industry Directory
 
Plants Directory
 
Video Center
 
This Week's Newsletter
 
Water Blog
 
Ask Tom! Archive
 
Trade Shows & Events
 
Industry Associations
 
Journals & Magazines
 
Tank Size Calculators
 
Add Your Plant Now
 
Add Your Company
 
Add Your Resume
 
Contact Us

Sign Up Free!

Click here to read past issues
Industry Newsletter

Enter your business email
address & click to sign up
Read Past Issues Here

Featured Book
From
Amazon

Click here for more

Free Shipping
on all orders over $25.

 
 
Case Histories : Water Supply


Shared Infrastructure Benefits Desalination Economics
By Nikolay Voutchkov
Jul 27, 2005
  E-mail article
Printer friendly page
  .
Stamford, CT -- Remarkable improvements in membrane and energy recovery technologies over the last ten years have yielded a significant reduction in the seawater desalination costs, turning the ocean into a viable water supply source for many arid areas of the world. One of the innovative approaches for improving the economics of seawater desalination is the collocation of desalination plants with coastal power generation stations.

How the Co-location Works?

The key feature of the collocation concept is the direct connection of the desalination plant intake and/or discharge facilities to the discharge outfall of an adjacently located coastal power plant. This approach allows using the power plant cooling water both as source water for the seawater desalination plant and as blending water to reduce the salinity of the desalination plant concentrate prior to the discharge to the ocean. Figure 1 illustrates the collocation concept at the 50 MGD seawater desalination plant in Carlsbad California, which development currently is at permitting and planning phase.

Desalination Plant Intake and Discharge Colocation With Power Plant Discharge

As shown in the above figure, under typical operational conditions the seawater enters the power plant intake facilities and after screening is pumped through the power plant condensers to cool them and thereby to remove the waste heat generated during the electricity generation process. The cooling water discharged from the condensers is 5 to 15 0C warmer than the source ocean water and is usually conveyed to the ocean via a separate discharge canal.

Under the co-location concept, the intake of the seawater desalination plant is connected to the discharge canal of the power plant to collect a portion of the cooling water for desalination. After the desalination plant source seawater is pretreated, it is processed in a reverse osmosis membrane desalination system, which produces two key streams low salinity permeate, which after conditioning is conveyed for potable water supply, and concentrate which salinity is typically two times higher than the source seawater. Under the co-location configuration, the desalination plant concentrate is conveyed to the power plant discharge outfall downstream of the point of desalination plant intake connection.

Co-location with a power station in a large scale was first used by Poseidon Resources for the Tampa Bay Seawater Desalination Project, and since than has been considered for numerous plants in the United States and worldwide. The intake and discharge of the Tampa Bay Seawater Desalination Plant are connected directly to the cooling water discharge outfalls of the Tampa Electric (TECO) Big Bend Power Station.

Co-Location of Tampa Bay Seawater Desalination Plant Intake and Discharge and TECO Power Plant Discharge

The TECO power station discharges an average of 1.4 billion gallons of cooling water per day of which the desalination plant takes an average of 44 MGD to produce 25 MGD of fresh potable water. The desalination plant concentrate is discharged to the same TECO cooling water outfalls downstream from the point of seawater desalination plant intake connection.

Benefits of Sharing Intake Facilities

Usually, coastal power plants with once-trough cooling use large volumes of seawater. Because the power plant intake seawater has to pass through the small diameter (typically 7/8-inch) tubes of the plant condensers to cool them, power plant discharge cooling water, used as a source water for the desalination plant, is already screened through bar racks and fine screens similar to these used at surface water intake desalination plants. Therefore, a desalination plant which intake is connected to the discharge outfall of a power plant, does not require the construction of a separate intake structure, intake pipeline and bar screening facilities (bar-racks and coarse screens). Since the cost of a new surface water intake for a desalination plant is typically 5 to 20 % of the total plant construction expenditure, power plant co-location yields significant construction cost savings.

Sharing intake infrastructure also has environmental benefits because it avoids the need for new construction in the ocean and the seashore area near the desalination plant. The construction of a separate new open intake structure and pipeline for the desalination plant could cause significant disturbance of the benthic marine organisms on the ocean floor in the vicinity during construction. The use of intake beach wells instead of open intakes would have similar negative environmental impact on the seashore marine organisms during the beach well construction.

Another clear environmental benefit of the collocation of power and desalination plants is the reduced overall entrainment, impingement and entrapment of marine organisms as compared to construction of two separate intake structures one for the power plant and one for the desalination plant. This benefit stems from the fact that total biomass of the impacted marine organisms is typically proportional to the volume of the intake seawater. By using the same intake seawater twice (once for cooling and second time for desalination) the net intake inflow of seawater and marine organisms is minimized.

Benefits of Sharing Discharge Outfalls

Under the co-location configuration, the power plant discharge serves both as an intake and discharge to the desalination plant. Four key benefits stem from this arrangement: (1) the construction of a separate desalination plant outfall structure is avoided thereby decreasing the overall costs for seawater desalination; (2) the salinity of the desalination plant discharge is reduced as a result of the mixing and dilution of the membrane concentrate with the power plant discharge, which has ambient seawater salinity; (3) because a portion of the discharge water is converted to potable water, the total amount of the power plant thermal discharge is reduced, which in turn lessens the negative effect of the power plant thermal discharge on the aquatic environment; (4) the blending of the desalination plant and the power plant discharges results in accelerated dissipation of both the salinity and the thermal discharges.

The cost of construction of a separate ocean outfall could be significant and its avoidance would result in measurable reduction of plant construction expenditures. In addition, the length and configuration of the desalination plant concentrate discharge outfall are closely related to the discharge salinity. Usually, the lower the discharge salinity, the sorter outfall and less sophisticated discharge diffuser configuration are required to achieve environmentally safe concentrate discharge. Blending of the desalination plant concentrate with the lower salinity power plant cooling water often allows to reduce the overall salinity of the ocean discharge within the range of natural variability of the seawater at the end of the discharge pipe, thereby alleviating the need for complex and costly discharge diffuser structures.

In addition, the power plant thermal discharge is lighter than the ambient ocean water because of its elevated temperature and therefore, it tends to float on the ocean surface. The heavier saline discharge from the desalination plant draws the lighter cooling water downwards and thereby engages the entire depth of the ocean water column into the heat and salinity dissipation process. As a result the time for dissipation of both discharges shortens significantly and the area of their impact is reduced.

Other Co-location Advantages

One of the key additional benefits of co-location is the overall reduction of the desalination plant power demand and associated costs of water production as a result of the use of warmer source water. The source water of the RO plant is typically of 5 to 15 degrees Celsius higher than the temperature of the ambient ocean water. This is significant benefit, especially for desalination plants with cold source seawater (such as the Pacific Ocean seawater along the West Coast of the United States), because the RO membrane separation of an average of 10 degrees Celsius of warmer seawater requires approximately 5 % to 8 % lower feed pressure for reverse osmosis separation, and therefore proportionally lower energy use and power costs for seawater desalination. Since the power costs are approximately 20 to 40 % of the total costs for production of desalinated water, use of warmer source water could have a measurable effect on the overall water production costs.

As a result of the co-location the desalination plant unit power costs could be further decreased by avoiding the need for power grid transmission and the associated fees. Typically, the power tariff (unit power cost) structure includes two components: fees for power production and for power grid transmission. Often, the power transmission grid portion of the tariff is 30 to 50 % of the total unit power costs. By connecting the desalination plant directly to the power plant electricity generation equipment, the grid transmission portion of the power fees could be substantially reduced or completely avoided, thereby further reducing the seawater desalination costs.

Co-location of power and desalination plants may also have advantages for the power plant host. In addition to the benefit of having a new customer and generating revenue by leasing power plant property to locate the desalination plant, the power plant host also gains a user of a steady power demand and a high power load factor. This continuous high-quality power demand allows the power plant host to operate its power generation units at optimal regime, which in turn reduces the overall costs of power production.

Conclusions

Co-location of desalination plants with large power generation stations may yield measurable improvement of the economics of seawater desalination and offer cost-reduction advantages because of the use of shared intake and discharge facilities and reduced desalination power costs. In addition, this innovative approach can yield significant environmental benefits associated with the accelerated dissipation of the thermal and saline discharges and the reduction of impact on the marine benthic and seashore habitats by avoiding the construction of new facilities.

For more information contact:
Mr. Nikolay Voutchkov
Senior Vice President
Poseidon Resources Corporation
1055 Washington Boulevard
Stamford, CT 06901
Telephone: 203-327-7740, ext. 126
Email: nvoutchkov@poseidon1.com
Web site: http://www.poseidonresources.com/

Copyright 1998 - 2012 Water and Wastewater.com

Top of Page

 
Send news and case histories to:  news@waterandwastewater.com
 

 

I Search News I



I Live Newsfeed I

Increase traffic and add
content to your website
with our exclusive
newsfeed generator.

Our live newsfeed
allows you to
include news
headlines from our
News Center, right
on your homepage.

Headlines update in
real-time, automatically.

Click here to create
your own newsfeed!

 

 

 
 
I

Buyers Guide | News | Help Forum | Ask Tom! Column | Jobs | Resumes | Newsletters

W&WW Blog | Case Histories | Books | Shop Amazon | Member Survey | Advertise

.

Copyright 1998-2011 Camber Southeast, Inc.
Web Site:  http://www.waterandwastewater.com
Privacy Statement

I
Home