Osmotic Power Generation Report

SEMINAR REPORT 2012 OSMOTIC POWER GENERATION

CHAPTER 1

INTRODUCTION

Energy consumption is an important aspect in our day to day life. Energy

consumption rate is increasing very rapidly everyday .If this continues as such then

the world will one day face shortage of energy. So its time to look for more sources

of energy rather than the non-renewable sources of energy and reduce the rate of

consumption of non-renewable energy. There are many forms of renewable energy

sources in the world. The abundant renewable energies include solar energy, tidal

energy, wind energy, Geo thermal energy etc. One of the most recent power

generation techniques is osmotic power generation.

Osmotic power or salinity gradient power is the energy available from the

difference in the salt concentration between seawater and river water. Salinity

gradient power is a specific renewable energy alternative that creates renewable and

sustainable power by using naturally occurring processes.

DEPT OF ME NSSCE, PKD1


CHAPTER 2

PRINCIPLE

The basic principle involved in osmotic power generation is OSMOSIS.

Osmosis is the movement of solvent molecules through a selectively permeable

membrane into a region of higher solute concentration, aiming to equalize the solute

concentrations on the two sides. It may also be used to describe a physical process in

which any solvent moves, without input of energy, across a semi permeable

membrane (permeable to the solvent, but not the solute) separating two solutions of

different concentrations.

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.

Fig 1 Osmosis



CHAPTER 3

METHODS

Two practical methods for osmotic power generation are reverse electro

dialysis (RED) and pressure-retarded osmosis. (PRO).

3.1 Reversed electro dialysis

A method being developed and studied is reversed electro dialysis or reverse

dialysis, which is essentially the creation of a salt battery. This method was described

by Weinstein and Leitz as “an array of alternating anion and cation exchange

membranes can be used to generate electric power from the free energy of river and

sea water.”

The technology related to this type of power is still in its infant stages, even

though the principle was discovered in the 1950s. Standards and a complete

understanding of all the ways salinity gradients can be utilized are important goals to

strive for in order make this clean energy source more viable in the future

3.2 Pressure-retarded osmosis

One method to utilize salinity gradient energy is called pressure-retarded

osmosis. In this method, seawater is pumped into a pressure chamber that is at a

pressure lower than the difference between the pressures of saline water and fresh

water. Freshwater is also pumped into the pressure chamber through a membrane,

which increase both the volume and pressure of the chamber. As the pressure

differences are compensated, a turbine is spun creating energy. This method is being

specifically studied by the Norwegian utility Statkraft, which has calculated that up to

25 TWh/yr would be available from this process in Norway. Statkraft has built the

world's first prototype osmotic power plant on the Oslo fiord which was opened by



Her Royal Highness Crown Princess Mette-Marit of Norway on November 24, 2009.

It aims to produce enough electricity to light and heat a small town within five years

by osmosis. At first it will produce a minuscule 4 kilowatts – enough to heat a large

electric kettle, but by 2015 the target is 25 megawatts – the same as a small wind

farm.

Fig 2



CHAPTER 4

OSMOTIC POWER PROTOTYPE

Fig 3 Osmotic power Prototype

The components of osmotic power prototype are

a) The pre-treatment equipments

Fig 4a Sea water pretreatment Fig4b Fresh water pretreatment

The incoming fresh water and sea water are purified by using these

equipments before being fed into the plant.



b) Membrane Modules:Thin membranes rolled membranes for osmosis

Fig 5 Membrane modules

The membranes employed are mainly of two types of:

(i) Cellulose acetate membrane

A cellulose acetate membrane was prepared as following: the casting

solution is cast on a glass plate and immersed in ice cold water after solvent

evaporation. After solidification the membrane is annealed between 80° and

95°C. A typical casting solution, according to a GKSS patent, consists out of

cellulose diacetate, cellulose triacetate, dioxane, acetone, acetic acid and

methanol. This composition was kept, but due to changing the casting

parameters, both in the lab and in pilot scale, the performance was improved.

Casting parameters like casting speed, changes in the temperature of the

coagulation bath and also the changes of the support material led to the

improved performance. Starting with a membrane performance of

approximately 0.5 W/m2, this type of membrane was improved to a

performance of close to 1.3 W/m2.

(ii) TFC membrane

TFC membranes are made by the interfacial polymerisation of

trimesoylchloride and m-phenylene diamine. Starting with a membrane



performance of approximately 0.1 W/m2, this type of membrane was

improved to a performance of close to 3.5 W/m2.

c) Turbine for power generation

Fig 6 Turbine

d) Pressure Exchangers and booster pumps to provide inlet seawater with

sufficient pressure

Fig 7 Pressure Exchanger

The PX energy recovery device uses the principle of positive displacement

and isobaric chambers to achieve extremely efficient transfer of energy from a high

pressure waste stream to low pressure incoming feed stream. Virtually no energy is

lost in the transfer.



One particularly efficient type of pressure exchanger is a rotary pressure

exchanger. This device uses a cylindrical rotor with longitudinal ducts parallel to its

rotational axis. The rotor spins inside a sleeve between two end covers. Pressure

energy is transferred directly from the high pressure stream to the low pressure stream

in the ducts of the rotor. Some fluid that remains in the ducts serves as a barrier that

inhibits mixing between the streams. This rotational action is similar to that of an old

fashioned machine gun firing high pressure bullets and it is continuously refilled with

new fluid cartridges. The ducts of the rotor charge and discharge as the pressure

transfer process repeats itself.

Fig 8 Schematics of Pressure Exchanger



CHAPTER 5

WORKING

In the PRO process, water with no or low salt gradient is fed into the plant

and filtered before entering the membrane modules using the pre-treatment

equipments. Membrane modules could contain spiral wound or hollow fibre

membranes. In the module, 80–90% of the water with low salt gradient is transferred

by osmosis across the membrane into the pressurised salty water. The osmotic

process increases the volumetric flow of high pressure water and is the key energy

transfer in the power production process. This requires membranes with particularly

high water flux and excellent salt retention properties.

The illustration in figure shows salty water pumped from the sea and filtered before it

is pressurised and fed into the membrane module. In the module it is diluted by the

water received from the less salty side of the membrane. The volumetric feed of salty

water is about twice that of the fresh water.



The diluted and now brackish water from the membrane module is split in two

flows. While 1/3 of the brackish water is fed though the turbine to generate power,

2/3 is returned and energy is recycled in the pressure exchanger to add pressure to the

feed of salty water. Optimal operating pressures are in the range of 11–15 bars,

equivalent to a water head of 100–145 metres in a hydropower plant, enabling the

generation of 1 MW per m3 s fresh water. The fresh water feed operates at ambient

pressure.

Pre-treatment of the water will be necessary depending on the water qualities.

In Norwegian water treatment plants, mechanical filtration down to 50 μm, in

combination with a standard cleaning and maintenance cycle has been enough to

sustain the membrane performance for 7–10 years.



CHAPTER 6

INFLUENCING FACTORS

The membrane system is the heart of the osmotic power generation process

Ideal FO membrane system

High water flux

Sufficient salt rejection

Limited fouling

Scalable for mass production

To be fit in modules

Reasonable cheap

The volume of water entering: The more water that enters the system, the

more power can be produced.

Salinity gradient: The higher the gradient between salinity in the fresh- and

saltwater, the more pressure will build up in the system.

Purity of water: It is important that the fresh water and sea water is as clean as

possible. Substances in the water may get captured within the membranes

support structure or on the membrane surfaces, which will reduce the flow

through the membrane causing reduction in power output. This phenomenon,

which is called fouling, is linked to the design of the system, to the

characteristics of the membrane, and to the membrane element.

Flow losses: Flow losses should be minimum



CHAPTER 7

MERITS AND DEMERITS

MERITS

+ Eco Friendly since there is no emission of harmful gases and no disposal of

chemicals.

+ Can be build anywhere where fresh water flows to saline water.

+ High potential.

+ Abundant since water is used for power generation.

DEMERITS

- High cost of membrane

- Maintenance cost is higher

- Discharge of brackish water into the marine environment may alter the

environment and result in changes for animals and plants living in the local

location.



CHAPTER 8

BACKGROUND

1964- Hand Wrapped Membrane introduced

1970- Sidney Loeb develops membrane technology for the desalination of seawater,

and also discovers the possibility of generating osmotic power.

1970s- No membranes suitable for PRO, and hardly for desalination.

1980s- During the eighties. Desalination more cost effective due to better membranes

and systems.

1997- Statkraft together with SINTEF start a feasibility project on osmotic power in

1997 spurring the development of a new, renewable energy source.

During the years since 1997 Statkraft together with several international

partners have made great improvement of the osmotic power membrane.

2003- In 2003, Statkraft is awarded its first patent for osmotic power membranes and

opens a test facility at Sunndalsora, Norway.

2009- In 2009, the world’s first complete osmotic power prototype is constructed at

Tofte, southwest of Oslo, Norway.

In November 2009, the operation of the prototype starts and for the first time the

feasibility of the osmotic power concept is demonstrated.



CHAPTER 8

CONCLUSION AND SCOPE

Osmotic power plants can be constructed anywhere freshwater flows

out into the sea, provided that the salt concentration is sufficiently high. Unlike

solar power and wind power, osmotic power plants are not affected by fluctuations in

the weather and will produce continuous and predictable electricity. Most river outlets

around the world represent a potential location for a plant, even though some rivers

need more cleaning of the water than others.

Enormous potential

The global potential is estimated to be 1,600-1,700 TWh – equivalent to 50%

of EU’s total annual power generation today. In Norway alone, it would be

able to generate 12 TWh per year –equivalent to around 10% of our total

power consumption. Osmotic power can become an important contributor to the

generation of clean, renewable energy.

Environment-friendly energy

Around the world, rivers flow out into the sea in urban and industrial areas

where it will be possible to construct osmotic power plants. A power plant the

size of a football stadium could supply around 30,000 households

with electricity. These power plants can be built underground, e.g. in the basement of

an industrial building or under a park, minimizing their visual impact. Osmotic power

plants produce renewable energy with no polluting discharges to the atmosphere or

water.

In coming years use of renewable energies and thus conserving energy has to

be promoted hugely .Osmotic power generation is indeed a promising technique with

immense potential worldwide.



REFERENCES

1. Osmotic power — power production based on the osmotic pressure difference

between waters with varying salt gradients

Stein Erik Skilhagen*, Jon E. Dugstad, Rolf Jarle Aaberg

Statkraft Development AS, Lilleakerveien 6, No-0216 Oslo, Norway

2. Membrane processes in energy supply for an osmotic power plant

Karen Gerstandta, K.-V. Peinemanna*, Stein Erik Skilhagenb, Thor Thorsenc,

Torleif Holtc

3. www.statkraft.com
