O Technical and Economic Evaluation of Seawater MSF and RO Desalination Processes for Madinat Yanbu

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O Technical and Economic Evaluation of Seawater
MSF and RO Desalination Processes for Madinat
Yanbu Al-SinaiyahAuthors A. Khawaji, J. Wie
and A. Al-MutiriIDA World Congress, Bahrain 2002

• Presented By
• Fawaz Al-Ghamdi
• May 22, 2007

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OUTLINE

• Introduction
• Technical Comparison
• Cost Comparison
• Cost Comparison For The New Unit
• Conclusion

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INTRODUCTION

• The Royal Commission for Jubail And Yanbu
  maintain and operate Madinat Yanbu Al-Sinaiyah
  (MYAS) including the seawater desalination plant
• The existing desalination plant used to support
  community and industry
• Consist of six 380 m3/hr multi-stage flash (MSF)
  unit
• Because of the expected growth of the MYAS
  community and industry, additional seawater
  desalination unit will be required to meet the
  future demand.
• Two major commercial seawater desalination
  process in the area RO and MSF
• In RO Saudi Arabia 4 Large size, Others are
  small

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INTRODUCTION

• Objective
• The objective of this paper is to present
  the results of the technical and economic
  evaluation of the MSF and RO processes and select
  the one that suit MYAS

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INTRODUCTION
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INTRODUCTION
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TECHNICAL COMPARISON

• MSF system is based on the proved technology and
  have demonstrated operational reliability over
  two decades in the Middle East and throughout the
  world
• RO system is increasingly gaining in popularity
  due to simplicity, improved performance,
  capability to handle a wide variety of feed
  water, energy efficiency, less space , less time
  to construct, less manpower required.

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TECHNICAL COMPARISON

• Major Technical Aspects
• Process Steam and Power Availability
• Product Water Requirement
• Energy Efficiency
• Sea Water Feed Condition

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TECHNICAL COMPARISON

• Process Steam and Power Availability
• There are 5 HRSG supply steam and power
• Provision have been made to supply emergency
  steam from STG since it was anticipated that the
  new desalination unit would reduce the
  availability steam to generate electric power.
• Steam Supply for the new unit is adequate.

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TECHNICAL COMPARISON

• Product Water Requirement
• Product water specification is based on the
  required process water quality needed for plant
  equipment.
• If new MSF units is installed, it will meet the
  process water requirement.
• Single stage RO plant is adequate to produce
  water with TDS lt 435 ppm with 99 recovery. So,
  more than one stage will be required.

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TECHNICAL COMPARISON

• Energy Efficiency
• RO plants require only electrical power to run
  the high pressure pumps. (7-8.3 Kwh/m3 of
  product water)
• MSF units require thermal and electrical energy,
  the total consumption is approximately 17 Kwh/m3
  of product water.

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TECHNICAL COMPARISON

• Seawater Feed Condition
• Conditions of seawater are safe for operation of
  both MSF and RO plants since the sea water
  condition is stable.
• An MSF plant would require 3 times more seawater
  than an RO plant equivalent in size.

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TECHNICAL COMPARISON

• Advantages and Disadvantages
• Major advantages of the MSF desalination plants
  are as follows
• 1) Demonstrated operational reliability over
  twenty years in the Kingdom and throughout the
  world.
• 2) Relatively insensitive to the salinity of the
  feed water with production of high quality water
  (less than 10 ppm TDS), which is more suitable
  for use as process water.
• 3) Minimum requirement of feed water
  pretreatment. Unaffected by normal levels of
  suspended or biological matters in the seawater.

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TECHNICAL COMPARISON

• Advantages and Disadvantages
• Major advantages of the MSF desalination plants
  are as follows
• 4) In the winter time as the seawater temperature
  declines, the flash range can be increased
  resulting in higher production of desalinated
  water.
• 5) The use of improved scale control and tube
  cleaning methods have increased operational
  periods between shutdowns, thereby increasing
  plant availability.

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TECHNICAL COMPARISON

• Disadvantages Of MSF
• 1) Relatively higher costs in both capital cost
  and OM cost.
• 2) Require more energy (both electrical and
  thermal energy) than RO Plants.
• 3) Require more seawater (about three times more)
  than RO Plants
• 4) Require larger space for a given capacity
  plant.
• Encounter more corrosion problems than RO plants
• Longer construction time.

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TECHNICAL COMPARISON

• Advantages of RO
• 1) Relatively lower capital cost because of
  simpler system.
• 2) Less overall energy consumption
• 3) Require about one third the seawater needed
  for MSF plants.
• 4) Operate at ambient temperature without any
  adverse impact on environment (i.e. thermal
  pollution).
• 5) Scheduled maintenance can be performed without
  shutting down the entire plant because of modular
  design.
• 6) Use more plastics and non-metals, therefore
  reducing corrosion related problems.

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TECHNICAL COMPARISON

• Advantages of RO
• 7) Less space requirement than a similar capacity
  MSF Plant.
• 8) Has fewer components, resulting in less repair
  and replacement parts.
• 9) Faster startup and shutdown
• 10) Shorter construction time
• 11) Easier capacity increase for future expansion

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TECHNICAL COMPARISON

• Disadvantages of RO
• 1) Predominant cause of most failures is
  unsatisfactory pretreatment of feed water.
  Therefore, RO Plants require constant attention,
  careful monitoring and good attitude by operating
  personnel.
• Biological activity of the seawater feed system
  must be kept under rigid control, as opposed to
  MSF plants
• Chemical addition for pretreatment must be
  carefully monitored and adjusted to match the
  seasonal change in seawater quality.
• 4) Membrane performance monitoring should be
  rigidly followed to satisfy the manufacturers
  warranty requirements.
• RO membranes are expensive.

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COST COMPARISON

• Based on literature review, the cost ratios for
  MSF and RO

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COST COMPARISON

• The various factors that are significant in
  comparing the production cost of water in MSF and
  RO include
• Energy Cost
• Chemicals Cost
• Metals Cost
• Membrane Replacement Cost
• Land Use Cost
• Construction time
• Fuel Price

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COST COMPARISON

• Energy Cost
• RO 7 Kwh/m3
• MSF 17 Kwh/m3
• Chemicals Cost
• The cost of chemicals in an RO plant is higher
  than that of chemicals in an MSF Plant, depending
  on the pretreatment and scale control method
• Metal Cost
• Many of the corrosion problems encountered with
  MSF plants in the past have been overcome by
  selection of improved materials, and a s a
  result, MSF plants can be adversely affected by
  the high cost of alloy material
• The high pressure pumps and piping in RO unit
  requires stainless steel material.

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COST COMPARISON

• Membrane Replacement Cost
• Only applicable to RO plants
• Average life 5 years
• An accurate membrane replacement frequency is
  difficult to predict as it is tied up with
  feedwater treatment and operation.
• Land Use and Construction
• RO uses less land and its construction time is
  shorter than an MSF plant
• Fuel Price
• Related to energy
• RO is more energy efficient process

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COST COMPARISON FOR THE NEW UNIT
Estimated Water Production Cost
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COST COMPARISON FOR THE NEW UNIT

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CONCLUSIONS

• This evaluation of MSF and RO is not to establish
  superiority of one system or technology over the
  other, but to select a process based on its cost
  effectiveness, simplicity in operation and
  maintenance, and compliance with the requirement
  for potable water
• For the production of potable water of a 570
  m3/hr, the capital cost for s single stage RO
  plant is estimated to be about 27 percent lower
  that an identical size MSF plant
• Ro is more energy efficient that MSF
• RO unit chemical costs were determined to be
  lower that those of the MYAS MSF plant

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CONCLUSIONS (cont.)

• Sea water requirement for RO unit is about 1/3
  sea water requirement for the MSF unit.
• RO plants require less space, less construction
  time and more flexible
• RO unit have not adverse impact in environment as
  it is operate at atmospheric temperature
• As a result of this evaluation, RO is determined
  to be more cost-effective in both initial capital
  cost and water production cost
• On the basis of this evaluation and the best
  available data, a decision was made to install a
  seawater RO plant at MYAS

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• Thank You