EXPERT INPUT VITAL FOR DESALINATION

Published: March 4, 2015

MED units at Taweelah 1 power & desalination plant (Abu Dhabi, 2007) ©Tractebel Engineering

 

For dry, coastal countries in need of water and power, thermal desalination is an evident solution. But, how best to go about it is always the first question. Experienced expert, Patrick Joie, answers this and other FAQs impacting the desalination decision.

 

EXPERT INSIGHT

While understanding the merits and limitations of one desalination process over another is a first step to ensuring a client’s long-term objectives are met – the installation of any of the most common desalination processes (MSF, MED, RO) is no real mystery to engineers used to complex power plants (PP). More important is the ability to configure the most efficient coupled plant according to the unique end needs of the customer; for the least CAPEX and best OPEX possible. Read more

OTHER FAQs ANSWERED

What are the main advantages of power-coupled desalination?
Can any thermal PP be coupled with desalination?
Can hybrid desalination be considered?
What are the environmental impacts of desalination and can this be mitigated?
What is the impact of imbalanced power and water consumption patterns?
Is there a limit to the size of a power linked desalination plant?
What value can be gained working with Tractebel Engineering in desalination?

 

“In desalination our talent is; understanding the end goal, then taking all factors and configuration options into consideration from the start in order to arrive at the best long-term solution – a highly efficient, large (or small) scale engineered system geared to deliver in terms of construction, dual-operation and return on investment.”
Patrick Joie – Chief Engineer (Power & Gas) Tractebel Engineering


  • RO Desalination Plant ©Tractebel Engineering RO Desalination Plant ©Tractebel Engineering
  • Patrick Joie on Al Dur RO site (Bahrain, 2007) ©Tractebel Engineering Patrick Joie on Al Dur RO site (Bahrain, 2007) ©Tractebel Engineering
  • Al Dur RO filters (Bahrain, 2007) ©Tractebel Engineering Al Dur RO filters (Bahrain, 2007) ©Tractebel Engineering
  • Barka 2 R0 unit (Oman, 2006) ©Tractebel Engineering Barka 2 R0 unit (Oman, 2006) ©Tractebel Engineering

 

EXPERT INSIGHT

 

A VERSATILE APPLICATION…
With the need to supplement fresh water supplies increasing the world over, different countries or regions take different approaches to desalination – some (RO) requiring less or (thermal MSF, MED) more up-front engineering. While Tractebel Engineering’s long PP experience can assist with configuring the auxiliary systems of a standalone RO plant e.g. water intake and outfall and grid connections; where our expertise contributes most is in the development of power-coupled desalination where the need for water; for industry (less-corrosive cooling or process water), human consumption or agriculture, fits with a high need for power.

Consequently key customers are IWPP and State Authorities in the Middle-East and North Africa (the region runs over 50% of the world’s installed desalination plants). Drought-prone parts of India and sub-Saharan Africa also present as markets primed for major development. But the concept of symbiotic power and water production can work anywhere and on any scale: from the large Phase 1 Az Zour North 1500 MW CCGT±480 000 m3/day (MED process) in Kuwait; the incorporation of a small RO plant (linked to the sea-water cooling system) to provide service water on the Vinh Tan 4 supercritical CFPP in Vietnam as part of Tractebel Engineering’s Owners Engineering services. It’s a question of adapting knowledge to need.

…REQUIRES A VERSATILE APPROACH
In every case, what should be a priority for the Plant Owner in developing any such project is that the plant configuration and desalination process fully answers the need to deliver so many MW and so many MIGD (million imperial gallons/day) at the best tariff/CAPEX/OPEX. This depends on multiple parameters, some of which include:

  • The ratio of water to electricity to be produced – while this will be determined by individual market conditions, the technology used for a high power/low water ratio is not the same for a high water/low power ratio.
  • The degrees of freedom needed in operation; how much flexibility is, or is not, needed – enabling management of the balance of power and water consumption peaks and lows.
  • The seasonal temperature, quality and intensity of the feed saltwater – which can be further impacted/mitigated by the design of water intake and outflow systems.
  • The intended end use of the purified water impacting the re-mineralisation process – zero or minimal additives for industrial water, as opposed to meeting WHO standards for potable water, or special mineral content for irrigation.
  • Options for environmentally-safe brine concentrate disposal – e.g. brine dilution using cooling water.
  • The plant location in relation to the use of the water – is it for local consumption or are powered pumping stations needed to transfer water over longer distances to interior cities.

Every project will present a different scenario. Only by fully addressing every issue, question, and need, ensuring utmost synergy between all power and desalination needs and technologies, can the Plant Owner be sure of consistently achieving the targets critical to long-term business success.



MSF Desalination Plant in Mirfa (Abu Dhabi) ©ADWEA

 

OTHER FAQs ANSWERED

 

What are the main advantages of power-coupled desalination?
Dual purpose power-desalination plants make the most efficient use of energy produced by thermal PP in the form of low-pressure steam. As desalination vaporisation processes work at low temperatures (because of low pressure), they can be efficiently supplied by even relatively low heat recovered from the PP process. It is a natural fit. In addition to steam, electricity generated by the PP can also be drawn for: process pumps, inlet pumps, water treatment process, pumping stations for water transfer etc. As water is often a low tariff commodity (a social obligation) unless industry related, linking production to higher-tariff power generation can help to offset otherwise important water desalination costs.

Can any thermal PP be coupled with Desalination?
Thermal desalination processes require steam – released as a by-product of Combined-Cycle, Gas Turbine, Coal-Fired, Nuclear or even Solar plants (the latter usually has great potential in regions most afflicted by water shortages). Tractebel Engineering’s knowledge and experience in all these thermal technologies assists in determining the best systems integration in any PP to ensure efficiency.

Can hybrid desalination be considered?
Hybrid desalination – combining thermal desalination processes (MED, MSF) with membrane desalination processes (RO) in one plant is increasingly a consideration as membrane technology has improved to allow filtration of previously less suitable high salt/sandy seawaters (such as in Arabian Gulf). Where a hybrid combination makes it possible to achieve a lower water cost it has value – but this is not always the case (see Az Zour) and needs careful evaluation.

What are the environmental impacts of desalination and can these be mitigated?
It has to be acknowledged that thermal desalination processes rely on and are a by-product of (often fossil-fuelled) electricity generation. The challenge therefore is to assure the PP is configured to operate within environmentally acceptable limits. On the desalination process itself, consideration must be given to the water intake, the use of chemicals needed for water treatment and the reject of brine – while quantities re-entering the sea are fairly negligible and are easily absorbed by the oceans, it is possible to design dispersing outfall pipes and/or dilute the concentrate with PP cooling water outflows.

What is the impact of imbalanced power and water consumption patterns?
The management of energy consumption peaks and lows has to be considered for any PP. In Middle East countries power demand is highest in summer and drops in winter while water consumption is more constant. For that, a more flexible configuration of the plant has to be considered, demonstrating the importance of the design/engineering phase – but there are always solutions.

Is there a limit to the size of a power linked desalination plant?
In terms of engineering, no. Desalination units are modular so, whether it is 1 unit or 20, size is decided by the investor and the amount of power and water the market can consume and is willing to pay for.

What value can be gained working with Tractebel Engineering in desalination?
Peace of mind and competitive advantage stemming from an independent and early overview of constraints and process benefits, working up to a configuration proposal that delivers the best possible outcomes in line with primary development goals and offering the most competitive tariffs.

Discover more about how Tractebel Engineering desalination expertise can benefit your project: www.tractebel-engineering-gdfsuez.com

A SMART PROPOSAL

Bid specifications for the Az Zour North 1500 MW CCGT ±480 000 m3/day Power & Desalination plant in Kuwait allowed up to 25% RO process. In developing the bid proposal –Tractebel Engineering experts considered over 60 configuration concepts. Their final proposal was the only one submitted not to include RO technology – yet presented the best configuration and tariff, helping to win the concession for International Power (GDF SUEZ) and Sumitomo.

MED, MSF, RO?

Our experts can advise on the choice of 3 main desalination techniques linked to PP: need to know more? Click here

Tractebel Engineering rates among the world’s top engineering companies for power-desalination expertise: discover more desalination references on www.tractebel-engineering-gdfsuez.com

More information

Patrick JoieChief Engineer (Power & Gas), Tractebel Engineering

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