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OSMOTIC POWER GENERATION

ACKNOWLEDGEMENT

I wish to express my sincere gratitude to my seminar coordinator,Prof. Shankar K.S,

Associate Professor in Mechanical Engineering for his guidance and suggestion.

I am extremely grateful to Dr.Abdul Sharee f, Head of Mechanical Engineering

Department for moral support and guidance.

I am extremely grateful to my seminar coordinator, Hemanth Suvarna Department of

Mechanical Engineering for his suggestions and guidance.

I am grateful to the Principal of our college Dr. S A Khan for giving me a chance to

present this Seminar.

I also thank all staffs of Mechanical Department for the constant encouragement. At this

juncture, I gratefully remember the moral support and co operation extended by my

classmates on this seminar presentation. Their active participation really brought life to

my seminar.

Heartfelt thanks to one and all.

RAVIKANT TENDULKAR

(USN: 4PA08ME403)

Dept of Mechanical Engineering Page 1


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ABSTRACT

The need of new energy sources has led to a number of alternatives. Some better

than others. One of those alternatives is energy created by transportation of solutions,

osmotic energy or salinity gradient energy. In the osmotic process two solutions with

different salt-concentrations are involved (often freshwater and salt-water). A semi

permeable membrane, which is an organic filter, separates the solutions. The membrane

only lets small molecules like water-molecules pass. The water aspires to decrease the

salt-concentration on the side of the membrane that contains most salt. The water

therefore streams through the membrane and creates a pressure on the other side. This

pressure can be utilized in order to gain energy, for example by using a turbine and a

generator.

There are several different types of power plants using osmosis (the osmotic

process); both land-based plants and plants anchored to the sea floor. The thing the plants

we have studied have in common is that osmosis is not directly used to generate power.

What the osmosis does is that it creates a flow through the plant and it is that flow that

forces the turbine to rotate.

Energy created by osmosis has very little impact on the environment and that is of

course an important fact to consider when it comes to determine whether osmotic energy

is something to invest in or not. The major fact when it comes to the disadvantages is the

high cost. Osmotic-produced power is much more expensive than for example fossil

fuels. There are also engineering problems to be overcome. The high cost has made us

draw the conclusion that osmotic energy is not something to invest in, at least not in the

nearest future, since no one wants to buy the energy when it is so expensive.

The possibility to use osmotic power from our oceans lies within the technology

that needs to be developed. There are many possible ways to exploit energy from salinity

gradients. It seems, as osmotic pressure will be crucial with each of the possibilities.

Unlike solar, wind, wave and other sources of renewable energy, osmotic power plants

harness a source of energy that is constantly available--fresh water streams running into

the sea--thereby enabling sustainable, renewable power plants that produce constant,

uniform electricity, all day, every day



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CONTENTS

List of Figure 4

Nomenclature 4

CHAPTER1. INTRODUCTION AND HISTORY

1.1 Introduction 5

1.2 History 6

CHAPTER2.THE OSMOTIC PROCESS

2.1 Osmosis principles 7-9

2.2 Types of osmosis 9-10

2.3 Pressure retarded osmosis 10

2.4 Reversed electro dialysis (RED) 11

2.5 Osmotic Pressure 11-12

2.6 Possible Negative Environmental Impact 12-13

2.7 Applications 13-18

CHAPTER3.DIFFERENT POWER PLANTS USING OSMOSIS

3.1 SHEOPP Converter 19

3.2 Underground PRO Plant 20

CHAPTER4. ECONOMIC ASPECTS 21

CHAPTER5.PROS AND CONS 22

CHAPTER6.EXPLOITATION POSSIBILITES 23

CHAPTER8.FUTURE PROSPECTS 24

CHAPTER8.CONCLUTION 25

REFERENCES 26



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LIST OF FIGURE

Fig No. Caption Pg.No

2.1. a osmosis process step 1 7

2.1. b osmosis process step 2 7

2.1. c osmotic power plant overall view 8

2.4. a osmotic pressure 11

2.6. a different cell structure 14

3.1. a schematic diagram of the SHEOPP converter 19

3.2. a schematic diagram of the Underground PRO Plant 20

NOMENCLATURE

Symbol Description

i is the dimensionless vant Hoff factor

M is the molarity (Concentration measured by the number of

moles of solute per liter of solution)

R 0.08206 L atm mol-1 K-1 is the gas constant

T is the thermodynamic (absolute) temperature

CHAPTER 1



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INTRODUCTION AND HISTORY

1.1 Introduction

We can't continue using several of our energy sources we gain energy from today.

For example fossil fuels contaminate our environment and we are also running out of

them. It is therefore necessary to find other ways of producing energy. This report focuses

on one of those alternatives, osmotic energy.

Osmosis means passage of water from a region of high water concentration (often

freshwater) through a semi permeable membrane to a region of low water concentration

(often NaCl). The membrane only lets water molecules pass. Salt molecules, sand, silt

and other contaminants are prevented to do so.

Several physiological processes use this osmotic effect. For instance, our body

uses it to bring water back from the kidneys, and plants use osmosis to keep the water

pressure inside the plant at a fixed level.

Since scientists have found a way to build semi permeable membranes, we can use

the osmotic effect and convert it to mechanical energy. We will give examples of

different ways of doing this later on in the report. But first we will explain how osmosis

really works.

1.2 History

The process of osmosis through semi permeable membranes was first observed in

1748 by Jean Antoine Nollet. For the following 200 years, osmosis was only a



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phenomenon observed in the laboratory. In 1949 the University Of California At Los

Angeles (UCLA) first investigated desalination of seawater using semi permeable

membranes. Researchers from both UCLA and the University of Florida successfully

produced freshwater from seawater in the mid-1950s, but the flux was too low to be

commercially viable. By the end of 2001, about 15,200 desalination plants were in

operation or in the planning stages worldwide.

The world's first osmotic power plant officially opened in Tofte, Norway,

providing sustainable, renewable electricity generation 24/7.

Osmotic power generation harnesses the chemical energy locked in the gradient

between salt water and fresh water by using an osmosis process. This pilot plant was

designed by Statkraft (Oslo) to produce 10 KW of energy, but the Norwegian renewable

energy company plans to expand that to a full-scale osmotic power plant capable of

producing continuous 25 megawatts of energy.

"Our pilot facility is a significant step towards the commercialization of a game-

changing renewable energy source," said Stein Erik Skilhagan, vice president of osmotic

power at Statkraft, "The global production potential of osmotic power could exceed 1,600TW-h, or the equivalent to half of Europe's entire energy demand."

CHAPTER 2

THE OSMOTIC PROCESS



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2.1Osmosis Principle

Diffusion of molecules through a semi permeable membrane from a place of

higher concentration to a place of lower concentration until the concentration on both

sides is equal. Osmosis is a process by which water moves through a membrane which

blocks other particles, which is how it is used to purify water. For osmotic power it works

in reverse, with osmosis drawing fresh water through the membrane to mix with salty

water, thereby increasing its pressure which can be harnessed to drive electricity turbines.

The main thing with osmotic energy is transportation of solutions (often pure

water and salt-water), separated by a special filter, a membrane. In the osmotic process it

is not possible to use an ordinary filter. You need a "Semi permeable membrane".

A semi permeable membrane is an organic filter with extremely small holes. The

membrane will only allow small molecules, like water molecules, to pass through. The

thin layers of material cause this and that is what the osmotic energy process is all about.

Fig (2.1.a) osmosis process step 1

The picture here on the top shows a simple test rig for this process. The left side contains

pure water. The right side contains a solvent with water and salt (NaCl). The only thing

that separates them now is the semi permeable membrane. The process is about to begin.

Fig (2.1.b) osmosis process step 2

When the process gets started the pure water on the left side aspires to decrease

the salt-concentration on the right side of the membrane. The amount of water on the right



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side will now increase and create an "Osmotic head pressure". We can use this pressure,

for example, to force a water- turbine to rotate.

The amount of freshwater that will pass through the membrane depends on the

salt-concentration in the salt-water, before the osmotic process begins. For instance, if the

salt-concentration from the beginning is 3.5%, the osmotic pressure will be about 28 bars.

The problem with the test rig is that the salt-concentration in the salt-water will

decrease and the process will slow down. The only way to fix this is to continuously,

empty and refill both the left and the right side. This must be done very quickly to avoid

run-interference.

Another problem is that the membrane can, and will wear out because of all silt

and other contamination that will get stuck in the membrane. If we don't consider this fact

a membrane's length of use is about 6 months. This sort of process could not only be used

for energy purpose. The main use area today is Reverse Osmosis, where you create a

pressure larger than the osmotic head pressure and push the salt water through the

membrane. From this process you gain fresh water out of salt-water.

Overall view of osmotic power plant

Fig (2.1.c) osmotic power plant overall view



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The core process is a lot like desalination in reverse. In desalination you are

separating fresh water from salt water, but in osmotic power you are combining fresh

water with salt water. Therefore its called a pressure exchanger.

The pressure exchanger works similarly to a heat exchanger, essentially

transferring the increased pressure from the salty outflow from the osmosis membrane to

the fresh-water diluted output so it can drive a turbine. Without the pressure exchanger,

the efficiency of the process would be too low to create full-scale osmotic energy

generators. The pressure exchanger transfers pressure from a high-pressure stream

to a low-pressure stream with 98 percent efficiency.

Energy Recovery's pressure exchanger devices are currently installed in

desalination plants worldwide, where they serve a similar function in increasing the

efficiency of the osmosis process. Desalination plants discharge water that has higher salt

content than the original sea water, piping the fresh water produced into cities for

drinking.

Osmotic power plants, on the other hand, discharge fresh water diluted with salt

water in exactly the same proportions as would have happened naturally when the streamflowed into the sea anyway. Statkraft plans to build plants where fresh water is already

dumping into the sea, but the output of desalination plants could also be used even more

successfully, since their output is twice as salty as seawater, thereby doubling the energy

generation capability, which is proportional to saltiness.

2.2 Types of Osmosis

Osmotic Power or Salinity Gradient Power is the energy retrieved from thedifference in the salt concentration between seawater and river water. Two practical

methods for this are

I. Pressure Retarded Osmosis (PRO) and

II. Reverse Electro Dialysis (RED).

Both processes rely on osmosis with ion specific membranes. The key waste

product isbrackish water. This byproduct is the result of natural forces that are beingharnessed: the flow of fresh water into seas that are made up of salt water. A new, cheap

http://en.wikipedia.org/wiki/Brackish_waterhttp://en.wikipedia.org/wiki/Brackish_water


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membrane, based on an electrically modifiedpolyethyleneplastic, made it fit for potential

commercial use.

2.3 Pressure Retarded Osmosis (PRO)

Salinity gradient power is a specific renewable energy alternative that creates

renewable and sustainable power by using naturally occurring processes. This practice

does not contaminate or release carbon dioxide (CO2) emissions (vapor pressure methods

will release dissolved air containing CO2 at low pressuresthese non-condensable gases

can be re-dissolved of course, but with an energy penalty). Also there is basically no fuel

cost.

Salinity gradient energy is based on using the resources of osmotic pressure

difference between fresh water and sea water.All energy that is proposed to use salinity

gradient technology relies on the evaporation to separate water from salt. Osmotic

pressure is the "chemical potential of concentrated and dilute solutions of salt". When

looking at relations between high osmotic pressure and low, solutions with higher

concentrations of salt have higher pressure.

Differing salinity gradient power generations exist but one of the most commonly

discussed is Pressure Retarded Osmosis (PRO). Within PRO seawater is pumped into a

pressure chamber where the pressure is lower than the difference between fresh and salt

water pressure. Fresh water moves in a semi permeable membrane and increases its

volume in the chamber. As the pressure in the chamber is compensated a turbine spins to

generate electricity. In Braun's article he states that this process is easy to understand in a

more broken down manner. Two solutions, A being salt water and B being fresh water are

separated by a membrane. He states "only water molecules can pass the semi permeable

membrane. As a result of the osmotic pressure difference between both solutions, the

water from solution B thus will diffuse through the membrane in order to dilute the

solution". The pressure drives the turbines and powers the generator that produces the

electrical energy.

http://en.wikipedia.org/wiki/Polyethylenehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Polyethylenehttp://en.wikipedia.org/wiki/Carbon_dioxide


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2.4 Reversed Electro Dialysis (RED)

Reversed electro dialysis (RED) is the salinity gradient energy retrieved from the

difference in the salt concentration between seawaterand river water

In reversed electro dialysis (RED) a salt solution and fresh water are let through a

stack of alternating cathode and anode exchange membranes. The chemical potential

difference between salt and fresh water generates a voltage over each membrane and the

total potential of the system is the sum of the potential differences over all membranes. It

is important to remember that the process works through difference in ion concentration

instead of an electric field, which has implications for the type of membrane needed.

In RED, as in a fuel cell, the cells are stacked. A module with a capacity of

250 kW has the size of a shipping container.

2.5 Osmotic Pressure

Osmotic Pressure is the pressure that must be applied to a solution to prevent the

inward flow of water across a semi permeable membrane.

Jacobus Henricus vant Hoff first proposed a formula for calculating the osmoticpressure, but this was later improved upon by Harmon Northrop Morse.

On a related note, osmotic potential is the opposite of water potential, which is

the degree to which a solvent tends to stay in a liquid.

Potential Osmotic Pressure

Potential osmotic pressure is the maximum osmotic pressure that could develop in

a solution if it were separated from distilled water by a selectively permeable membrane.

It is the number of solute particles in a unit volume of the solution that directly

determines its potential osmotic pressure. If one waits for equilibrium, osmotic pressure

reaches potential osmotic pressure.

http://en.wikipedia.org/wiki/Salinity_gradienthttp://en.wikipedia.org/wiki/Seawaterhttp://en.wikipedia.org/wiki/Electrodialysishttp://en.wikipedia.org/wiki/Fuel_cellhttp://en.wikipedia.org/wiki/Salinity_gradienthttp://en.wikipedia.org/wiki/Seawaterhttp://en.wikipedia.org/wiki/Electrodialysishttp://en.wikipedia.org/wiki/Fuel_cell


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Fig (2.4.a) osmotic pressure

Morse equation

The osmotic pressure of a dilute solution can be approximated using the Morse

equation (named after Harmon Northrop Morse)

= iMRT

Where, i-> is the dimensionless vant Hoff factor

M-> is the molarity (Concentration measured by the number of moles of solute

per liter of solution)

R -> 0.08206 L atm mol-1 K-1 is the gas constant

T-> is the thermodynamic (absolute) temperature

This equation gives the pressure on one side of the membrane; the total pressure on the

membrane is given by the difference between the pressures on the two sides. Note the

similarity of the above formula to the ideal gas law and also that osmotic pressure is not

dependent on particle charge. This equation was derived by vant Hoff.

2.6 Possible Negative Environmental Impact

The impact of the brackish water waste on the local marine and river environment

could cause harm to the environment. That's why it is important that the brackish water is

piped into a point in the sea which has the same salinity, as is planned by Statkraft.

Marine and river environments have obvious differences in water quality, namely

salinity. Each species of aquatic plant and animal is adapted to survive in either marine,

brackish, or freshwater environments. There are species that can tolerate both, but these

species usually thrive best in a specific water environment. The main waste product of



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salinity gradient technology is brackish water. The discharge of brackish water into the

surrounding waters, if done in large quantities and with any regularity, may alter the

aquatic environment significantly. Fluctuations in salinity will result in changes in the

community of animals and plants living in that location. However, while some variation

in salinity is usual, particularly where fresh water (rivers) empties into an ocean or sea

anyway, these variations become less important for both bodies of water with the addition

of brackish waste waters. Extreme salinity changes in an aquatic environment may result

in findings of low densities of both animals and plants due to intolerance of sudden severe

salinity drops or spikes. The disappearance or multiplication of one or more aquatic

organisms as a result of an influx of brackish water has the potential to cause ecosystem

imbalance. According to the prevailing environmentalist opinions, the possibility of these

negative effects should be considered by the operators of future large blue energy

establishments.

2.7 Applications

Osmotic pressure is the basis of filtering "reverse osmosis", a process commonly

used to purify water. The water to be purified is placed in a chamber and put under an

amount of pressure greater than the osmotic pressure exerted by the water and the solutes

dissolved in it. Part of the chamber opens to a differentially permeable membrane that lets

water molecules through, but not the solute particles. The osmotic pressure of ocean

water is about 27 atm.

Osmotic pressure is necessary for many plant functions. It is the resulting turgor

pressure on the cell wall that allows herbaceous plants to stand upright, and how plants

regulate the aperture of their stomata. In animal cells which lack a cell wall however,

excessive osmotic pressure can result in cytolysis.

Cell wall - A rigid layer of polysaccharides enclosing the membrane of plant and

prokaryotic cells; maintains the shape of the cell and serves as a protective barrier.

Cytolysis - Pathological breakdown of cells by the destruction of their outer

membrane.

Pfeffer cell

Plasmolysis The study of parasitic protozoan of the genus Plasmodium that causes

malaria in humans.

http://en.wikipedia.org/wiki/Cell_wallhttp://en.wikipedia.org/wiki/Cytolysishttp://en.wikipedia.org/wiki/Wilhelm_Pfefferhttp://en.wikipedia.org/wiki/Plasmolysishttp://en.wikipedia.org/wiki/Cell_wallhttp://en.wikipedia.org/wiki/Cytolysishttp://en.wikipedia.org/wiki/Wilhelm_Pfefferhttp://en.wikipedia.org/wiki/Plasmolysis


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Turgor pressure - The normal rigid state of fullness of a cell or blood vessel or

capillary resulting from pressure of the contents against the wall or membrane.

For the calculation of molecular weight by using colligative properties, osmotic

pressure is the most preferred property.

Osmotic pressure is an important factor affecting cells. Osmoregulation is the

homeostasis mechanism of an organism to reach balance in osmotic pressure.

Hypertonicity is the presence of a solution that causes cells to shrink.

Hypotonicity is the presence of a solution that causes cells to swell.

Isotonic is the presence of a solution that produces no change in cell volume.

Fig (2.6.a) different cell structure

When a biological cell is in a hypotonic environment, the cell interior accumulates

water, water flows across the cell membrane into the cell, causing it to expand. In plant

cells, the cell wall restricts the expansion, resulting in pressure on the cell wall from

within called turgor pressure.

Drinking Water Purification

Around the world, household drinking water purification systems, including a

reverse osmosis step, are commonly used for improving water for drinking and cooking.

Such systems typically include a number of steps:

a sediment filter to trap particles including rust and calcium carbonate

optionally a second sediment filter with smaller pores

an activated carbon filter to trap organic chemicals and chlorine, which will attack

and degrade TFC reverse osmosis membranes

a reverse osmosis (RO) filter which is a thin film composite membrane (TFM or

TFC)

http://en.wikipedia.org/wiki/Turgor_pressurehttp://en.wikipedia.org/wiki/Tonicity#Hypertonicityhttp://en.wikipedia.org/wiki/Tonicity#Hypotonicityhttp://en.wikipedia.org/wiki/Tonicity#Isotonicityhttp://en.wikipedia.org/wiki/Turgor_pressurehttp://en.wikipedia.org/wiki/Tonicity#Hypertonicityhttp://en.wikipedia.org/wiki/Tonicity#Hypotonicityhttp://en.wikipedia.org/wiki/Tonicity#Isotonicity


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optionally a second carbon filter to capture those chemicals not removed by the

RO membrane

optionally an ultra-violet lamp for disinfecting any microbes that may escape

filtering by the reverse osmosis membrane

In some systems, the carbon pre-filter is omitted and cellulose triacetate

membrane (CTA) is used. The CTA membrane is prone to rotting unless protected by

chlorinated water, while the TFC membrane is prone to breaking down under the

influence of chlorine. In CTA systems, a carbon post-filter is needed to remove chlorine

from the final product water.

Portable reverse osmosis (RO) water processors are sold for personal water

purification in various locations. To work effectively, the water feeding to these units

should best be under some pressure (40 psi or greater is the norm). Portable RO water

processors can be used by people who live in rural areas without clean water, far away

from the city's water pipes. Rural people filter river or ocean water themselves, as the

device is easy to use (Saline water may need special membranes). Some travelers on long

boating trips, fishing, island camping, or in countries where the local water supply is

polluted or substandard, use RO water processors coupled with one or more UV

sterilizers. RO systems are also now extensively used by marine aquarium enthusiasts. In

the production of bottled mineral water, the water passes through an RO water processor

to remove pollutants and microorganisms. In European countries, though, such processing

of Natural Mineral Water (as defined by a European Directive) is not allowed under

European law. (In practice, a fraction of the living bacteria can and do pass through RO

membranes through minor imperfections, or bypass the membrane entirely through tiny

leaks in surrounding seals. Thus, complete RO systems may include additional water

treatment stages that use ultraviolet light or ozone to prevent microbiological

contamination.)

Membrane pore sizes can vary from .1 to 5,000 nanometers (nm) depending on

filter type. "Particle filtration" removes particles of 1,000 nm or larger. Microfiltration

removes particles of 50 nm or larger. "Ultrafiltration" removes particles of roughly 3 nm

or larger. "Nanofiltration" removes particles of 1 nm or larger. Reverse osmosis is in the

final category of membrane filtration, "Hyperfiltration", and removes particles larger than.1 nm.



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In the United States military, R.O.W.P.U.'s (Reverse Osmosis Water Purification

Unit, pronounced "roh-poo") are used on the battlefield and in training. They come

ranging from 1500 GPD (gallons per day) to 150,000 GPD and bigger depending on the

need. The most common of these are the 600 GPH (gallons per hour) and the 3,000 GPH.

Both are able to purify salt water and water contaminated with N.B.C.

(Nuclear/Biological/Chemical) agents from the water. During a normal 24 hour period,

one unit can produce anywhere from 12,000 to 60,000 gallons of water, with a required 4

hour maintenance window to check systems, pumps, R.O. elements and the engine

generator. A single ROWPU can sustain a force of a battalion size element or roughly

1,000 to 6,000 soldiers.

Water and Wastewater Purification

Rain water collected from storm drains is purified with reverse osmosis water

processors and used for landscape irrigation and industrial cooling in Los Angeles and

other cities, as a solution to the problem of water shortages.

In industry, reverse osmosis removes minerals from boiler water at power plants.

The water is boiled and condensed repeatedly. It must be as pure as possible so that it

does not leave deposits on the machinery or cause corrosion. The deposits inside or

outside the boiler tubes may result in under-performance of the boiler, bringing down its

efficiency and resulting in poor steam production, hence poor power production at

turbine.

It is also used to clean effluent and brackish groundwater. The effluent, is in larger

volumes (more than 500 cu. meter per day) should be treated in effluent treatment plant

first and then the clear effluent is subjected to reverse osmosis system. it helps in bringing

down the treatment cost significantly and increase the membrane life of the RO system.

The process of reverse osmosis can be used for the production of deionizer water.

In 2002, Singapore announced that a process named NEW water would be a significant

part of its future water plans. It involves using reverse osmosis to treat domestic

wastewater before discharging the NEW water back into the reservoirs.



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Dialysis

Reverse osmosis is similar to the technique used in dialysis, which is used by

people with kidney failure. The kidneys filter the blood, removing waste products (e.g.

urea) and water, which is then excreted as urine. A dialysis machine mimics the function

of the kidneys. The blood passes from the body via a catheter to the dialysis machine,

across a filter.

Food Industry

In addition to desalination, reverse osmosis is a more economical operation for

concentrating food liquids (such as fruit juices) than conventional heat-treatment

processes. Research has been done on concentration of orange juice and tomato juice. Its

advantages include a low operating cost and the ability to avoid heat treatment processes,

which makes it suitable for heat-sensitive substances like the protein and enzymes found

in most food products.

Reverse osmosis is extensively used in the dairy industry for the production of

whey protein powders and for the concentration of milk to reduce shipping costs. In whey

applications, the whey (liquid remaining after cheese manufacture) is pre-concentratedwith RO from 6% total solids to 10-20% total solids before UF (ultra filtration)

processing. The UF retentate can then be used to make various whey powders including

WPI (whey protein isolate) used in bodybuilding formulations. Additionally, the UF

permeate, which contains lactose, is concentrated by RO from 5% total solids to 1822%

total solids to reduce crystallization and drying costs of the lactose powder.

Although use of the process was once frowned upon in the wine industry, it is

now widely understood and used. An estimated 60 reverse osmosis machines were in use

in Bordeaux, France in 2002. Known users include many of the elite classed growths

(Kramer) such as Chteau Loville-Las Cases in Bordeaux.



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Car Washing

Because of its lower mineral content, Reverse Osmosis water is often used in car

washes during the final vehicle rinse to prevent water spotting on the vehicle. Reverse

osmosis water displaces the mineral-heavy reclamation water (municipal water). Reverse

Osmosis water also enables the car wash operators to reduce the demands on the vehicle

drying equipment such as air blowers.

Maple Syrup Production

In 1946, some maple syrup producers started using reverse osmosis to remove

water from sap before being further boiled down to syrup. The use of reverse osmosis

allows approximately 54-42% of the water to be removed from the sap, reducing energy

consumption and exposure of the syrup to high temperatures. Microbial contamination

and degradation of the membranes has to be monitored.

Hydrogen production

For small scale production of hydrogen, reverse osmosis is sometimes used to

prevent formation of minerals on the surface of electrodes and to remove organics from

drinking water.



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CHAPTER 3

DIFFERENT POWER PLANTS USING OSMOSIS

3.1 SHEOPP Converter

The picture below shows a SHEOPP Converter, which is a submarine

hydroelectric power plant anchored to the sea floor. Fresh surface water, from a river

mouth or an aqueduct, is conveyed through a penstock (standpipe) to a hydraulic turbine.

After generating electric power, the fresh water is discharged and depressurized into a

submarine tank. Finally the fresh water diffuses out in the sea by osmosis, through a

barrier of semi permeable membranes.

For pure fresh water and perfect semi permeable membranes a flushing pump

would not be necessary and the electric power produced in the SHEOPP Converter would

be maximized. In real situations, however, the fresh water will generally contain non-

tolerable amounts of dissolved salts and particles like sand, silt and other contaminants. It

may then be necessary to pre-treat the fresh water and a flushing pump would be required

to prevent accumulation of unwanted solutes and contamination on the fresh water side of

the membranes, to keep them in good working condition for as long as possible.

The efficiency for the SHEOPP will reach its maximum at a depth of 110 meters.

Fig (3.1.a) schematic diagram of the SHEOPP converter



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3.2 Underground PRO Plant

If an osmotic flow passes through a semi permeable membrane, which separates

the two solutions and forces a turbine to rotate, the process is called pressure-retarded

osmosis, PRO. Both these plants described here use PRO, but the plant below is land-based while the SHEOPP Converter is anchored to the sea floor.

Fresh water at sea level flows vertically downward through a penstock. The lower

end of the penstock is situated about 90 meters below the sea surface where the pressure

is 9 bars. This pressure forces a turbine to rotate and the pressure drops to 0 bar. Seawater

is pumped from the surface to a barrier of semi permeable membranes (an osmotic unit).

By osmosis the fresh water is driven through the membranes, trying to even out the

amount of dissolved salt in the seawater. The flushing solution is pressurized to 9 bars

and is pumped up to the surface. The diluted solution returns to the seawater by the

osmotic pressure.

The osmotic effect is thus used to force the turbine to move. When the water is

pressed out through the membranes a sucking effect, a stream appears. It is that stream,

created by osmosis that makes the turbine spin. Thus, in neither of these plants osmosis is

used for the direct generation of electric power. It is the sucking effect, the flow, whichgenerates electric power.

Fig (3.2.a) schematic diagram of the Underground PRO Plant



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CHAPTER 4

ECONOMIC ASPECTS

Due to the fact, that the material we have is old, it is hard to give an estimate of

the cost of osmotic-produced electricity with any accuracy. And another difficulty in

determine the costs is the large variety of cost estimates for reverse osmosis. Reverse

osmosis is when you make fresh water out of seawater, also known as desalination.

Osmotic inc. gave a rough estimate for the cost of the membranes in 1977. This

amounted to about $0.20 /m2 if 2km2 of membrane area were produced. The power output

for 1 km2 would, by 1977 amount to 1.62 MW. This number has been calculated from the

values given by several tests on semi permeable membranes.

We don't know how much, or in which direction these price-estimates have

changed since 1977, but we guess that the costs haven't changed so much, because there

have not been that much research in this area, since then. At least not what we have heard.

We do know that Norway are doing some research now on how to use osmotic plants in

their fiords, but this is new and classified, so we couldn't get any material from them.

To this, many other costs will appear, for instance, pumping costs, installing costs.

According to a calculation made by a scientist an osmotic plant is estimated to cost about

$36.000 per installed kilowatt. Our conclusion is, that osmotic power plants, is nothing to

invest money in.



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CHAPTER 5

PROS AND CONS

There are many attractive features about using salt for power. A big advantage is

that it is renewable. There is no risk what so ever to run out of salt because of osmotic

produced power. (Salt-water evaporation leads to precipitation over land.) The process

creating energy, does not consume the salt, it only utilizes it to force water to move.

Another advantage is that osmotic-produced energy has a minimal environmental impact.

It is a very "clean" process and this is of course a big plus. The amount of heat that occurs

in the process would raise the temperature less than half a degree Celsius, which is not

harmful to the marine organisms.

When we come to the disadvantages one big obstacle is the costs. Compared to

other energy-producing processes osmotic energy is extremely expensive, about 36 times

as expensive as a conventional power plant. There are also engineering problems to be

overcome. It is difficult to build a large plant and lower it in the sea as deep as 110

meters, in the SHEOPP converter-case, and about 90 meters down in the ground, when it

comes to the underground plant described earlier. Further there is a problem with the

protection of the marine organisms from the turbine and other machinery.



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CHAPTER 6

EXPLOITATION POSSIBILITIES

There are many possible ways to exploit the energy from salinity gradients. With each of

the possibilities it seems as osmotic pressure will be crucial. Here are two brief

descriptions of possible approaches:

Reverse Electro Dialysis: This process involves direct electrochemical

conversion in dialectic cells. Dialectic cells use the potential found between

solutions of different salt concentrations, which are separated by charged

membranes. For instance, fresh water has, in general, 850 parts per million

dissolved salt water. That is equal to a potential of 80 mill volts at the interface

(the membrane). By putting many cells in series it is possible to create more

power.

Vapour Pressure Differences: Another approach is to build a device that can use

the difference in vapour pressure between fresh water and salt water. The

difference can be used to run a turbine. There are many limitations to this system,

but there are advantages too. For example no membranes are required (in order to

use the vapour pressure differences).



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CHAPTER 7

FUTURE PROSPECTS

The possibility to use the salinity gradient in the ocean for power lies within the

technology that needs to be developed. There are currently two hurdles to overcome,

which includes the membrane water part and sunlight. If we could develop the membrane

to use salt-water as fresh water and brine with a higher salt-concentration as the

concentrated solution, then it would be more feasible to use salinity for power. Or, the

vapour pressure technique could be further developed. However, the biggest hurdle that

needs to be overcome is the cost. Salinity power is not economically feasible compared to

fossil fuels

Currently, more effort is being put into developing salt-gradient solar ponds for

energy (where osmosis is used). Therefore in the world of salt, there is more potential in

using salt from the solar ponds as opposed from the ocean. The salt percentage will be

much higher, which will increase the osmotic head pressure and more energy can be

extracted.



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CHAPTER 8

CONCLUSION

The conclusion we have reached during this project is that osmotic energy is not

something we can use in the nearest future. The disadvantages, the obstacles, are too big

to be overcome at the moment. The cleaning of the membranes and the cost are good

examples of such obstacles. However in the future if the technology is further developed

and the costs will decrease, osmotic energy might be an alternative to the energy sources

we use today.



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REFERENCE

Brochures

MT Freshwater AB "Desalination with reverse osmosis" 1995

SYCON Research material by Fredrik Axby

Internet

http://naring.regeringen.se/

http://world-wide-water.com/index2.html

http://taipan.nmsu.edu/aght/soils/soil_physics/tutorials/wp/wp_comp.html

http://www-ib.berkeley.edu/IB/instruction/IB150/material/lectures/lecture22/

http://edie.cprost.sfu.ca/~rhlogan/osmotic.html

http://www.seas.ucla.edu/~sechurl/CP/sld001.htm

http://www.purchon.co.uk/science/osmosis.html

Literature

National encyclopedia volume 14
http://naring.regeringen.se/http://world-wide-water.com/index2.htmlhttp://taipan.nmsu.edu/aght/soils/soil_physics/tutorials/wp/wp_comp.htmlhttp://www-ib.berkeley.edu/IB/instruction/IB150/material/lectures/lecture22/Osmosis.htmlhttp://edie.cprost.sfu.ca/~rhlogan/osmotic.htmlhttp://www.seas.ucla.edu/~sechurl/CP/sld001.htmhttp://www.purchon.co.uk/science/osmosis.htmlhttp://naring.regeringen.se/http://world-wide-water.com/index2.htmlhttp://taipan.nmsu.edu/aght/soils/soil_physics/tutorials/wp/wp_comp.htmlhttp://www-ib.berkeley.edu/IB/instruction/IB150/material/lectures/lecture22/Osmosis.htmlhttp://edie.cprost.sfu.ca/~rhlogan/osmotic.htmlhttp://www.seas.ucla.edu/~sechurl/CP/sld001.htmhttp://www.purchon.co.uk/science/osmosis.html

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