Desalination in the year 2000 - Technoeconomic aspects

579

Desalination,67 (1987) 579-588 ElsavierSciencePublishersB.V.,Amsterdam-Printed inTheNetherlands

DESALIWATIOW

1%) THE YEAR 2000 - TECHNOECONOMIC ASPECTS

0 P Kharbanda, Cost & Management Consultant 501 Olympus, Altamount Road, Bombay 400026, India. (A Fellow of the Institution of Chemical Engineers, Dr Kharbanda is a visiting prof, an author of repute and consults worldwide including to UNIDO) The

history of mankind has revolved around water.

water. life

In fact,

consists largely of water.

about 65%, variation can

no water no life.

be

Life bUgan in

Most of the animal and plant

Water content of human body

is

potato 80%, tomato 95% ands jelly fish 99%. Even a 1% in these figures can cause discomfort.

fatal.

A

A 10% variation

man can live without food for

40

Days,

but

without water, perhaps, not for more than four days. WATER FAMINE IN 2000 Famine?

why?

resources. million years.

Basically, exploding poupulation, but finite water

The

years,

first billion population on this earth took and

the next billion will take a mere

thirteen

Add to this the fact that the water requirement increases

much faster than the growth of population. much water today as there ever was. Aristotle

in his METEOROLOGICA

scientific endless

one

calculations.

and

The

But there is only

as

This was first enunciated by

and has since been water

cycle

this is how it supports life.

is

supported continuous

Water is

by and

considered

free, as a birthright, but it is precious, far too precious to be wasted.

If the most serious problem today is food,

2000 it may well be water. wastage, and

poor

management

internationally.

in the

year

The main causes for water problem are and non-cooperation

Groundwater

- both

nationally

is being used up much

faster

than it is being replenished and as an indication of this one has to drill deeper and deeper.

580 Most

of the water on earth,

(97.3%)

extent for

of 71% by oceans,

which is

covered

(90%) is locked up in ice caps.

little

quantity

agriculture, component

(0.27%)

that

is

It is only

Of the the

rest,

remaining

available

normally

for

industry and municipal purposes. Rainfall is a vital

of

practically

the

is seawater containing 3.5% salt unfit

human body which can tolerate only upto 0.5%.

bulk

to

the water cycle,

but it varies considerably

nothing in areas like North Chile,

from

Cape Verde

(Sal

Island) and Saudi Arabia, to a torrential downpour throughout the year in some of the tropical forests. No wonder, then, that there is

either

drought or flood somewhere or

experienced

the

other.

New

York

a drought in 1965 and for the first time New Yorkers

knew the real value of a glass of water.

In 1972 there was

food

deficit arising from a mere 1% water shortage worldwide. BUT QUALITY IS MORE IMPORTANT THAN QUANTITY The

quality

of water is measured

in terms of

dissolved solids/salts. Clean river water, or fresh water, sea

water

for irrigation.

20

brackish water 5000,

Against this,

Lake

the water required by major users 500 for drinking and

1000

Thus clean river water can be used for all these

except that for some special industrial purposes,

for

boiler feed, the dissolved solids have to be reduced to

PPM

through

appropriate

treatment.

directly by the three main users, killed

total

the so-called potable

contains 200 PPM of salts,

should not have 200 PPM for industry,

example,

of

35,000 and the water in Dead Sea and Great Salt

nearly 260,000.

purposes,

amount

If sea

man would die,

water

is

used

crops will get

and industrial equipment will not last long.

so you

can

see the havoc for not using water of the right quality. Ice

caps

are an obvious source of potable water and in fact

an

from Chile

to

iceberg was transported for this purpose in 1890, Peru,

about

4000 km.

But the first serious scientific proposal

581 mooted

in 1955 was-termed

as 'crazy' by the prestigious

Institute. At the first International Conference dealing exclusively with

this subject,

technically and even commercially

Scripps

in 1977 at Paris

the idea was found to

feasable.

The main hitch:

be the

cost for melting which was estimated to be in the same range ($24/1000 gallons) as for desalination, There were other problems,

transport cost being extra.

too, and a realistic comment was:

Iceberg cometh, but give them few years. But

it

seems that the plans of the French company who

promoted

the idea have 'melted' away. The company has gone bankrupt. DESALINATION It

is

- THE ONLY ANSWER

clear

population, problem.

that with finite desalination

Although

water

resources

and

exploding

is the only viable answer to the water

the word desalination has come in vogue

the process has been known and even practiced

recently,

only

through

the ages. In the 4th century BC, Aristotle devised an evaporation method to quench the thirst of Greek sailors. solar

distillation

drinking

water

preparing Crude

Julius Caeser used

during the first century in Egypt to

for soldiers.

An Arab writer is

credited 'with

a treatise on distillation during the eighth

stills

provide

were a comon feature on sailing ships

century.

during

the

17th century.' The first patent for desalination was taken out in 1869

(in

plant

was

set up at Aden.

first

Large plants came in

desalination vogue

and the first 1 million gallons/day plant at

1930's 1970,

Britain) and in the same year the

large scale desalination

in

Kuwait.

the By

plants had been set up in all the

continents. Nature is much wiser than mqn, natural desalination has been with us

ever

osmosis,

since life began. par excellence,

With an in-built system

of

reverse

sea plant, sea fish and sea bird thrive

on sea water. The process is so efficient,

salt being rejected and

582 fresh water taken into the system, that sea fish has to be salted for

dinner

Sounds idea

table.

Can man ever adapt to

like fiction? of

a

drinking

sea

But faction yesterday is fact

communication

water?

today.

satellite was first mentioned

by

noted science fiction writer in 1945 by (now Sir) Arthur but

he never exepcted

(Personal conversation,

Bombay,

The the

Clarke, 1980) to

see it in his life time. It is a reality already and with this we are

at

the threshold of a

thousands

of

years

revolution

in

human body could

ago,

Some

communication. produce

sufficient

vitamin C for its own requirements. But as a result of widespread availability of this vitamin in fruits and vegetables, human body seems to have lost its capacity to generate the vitamin.

In case

of a 'sudden death, however, much more than the normal quantity of vitamin C has been detected,

so the mechanism

still seems to

be

there. This leads us to the thought that human body could perhaps adapt to drinking sea water. Such a radical change, however, tiill be

extremely

desalination

slow will

meanwhile

and

the

conventional

man-made

have to be KeSOKted to in OKdeK to

meet

the

ever increasing requirement of water. Desalination,

however,

is expensive,

and must remain the

last

the prioriyies being water conservation and proper water

KeSOKt,

Both

management. and

effort

these

persons

require considerable

from

various

interdisciplinary

disciplines

of

science,

engineering and huamities will have to work together as a team in order

to

changing

achieve

optimum results.

Perhaps this shift

in the name of Office of Saline Water

(

U

S

led

to

DepaKtment

of Interior) to Office of Water Research & Technology. DESALINATION CAPACITY HAS BEEN LEAPING rhe

worldwide

starting

desalination capacity has been

with a mere 0.2 mgpd in 1935,

i.0 in 1955,

escalating

it rose to 0.7 in

fast. 1945,

76 in 1965, 194 in 1970 and 444 in 1975. Thereafter

583 the number of plants and the capacity are: Year ---

total capacity, w

No of plants

1980

2205

1922

1985

4600

2621

1986

5700

3032

1987

6300 (est)

3400 (est)

At

are nearly 175

in desalination.

engaged the

there

present

in

105

plants,

thus

confirming

BEAUTIFUL.

Bulk of the capacity

multistage

flash

rest

distillation

the

processes

towards

trend

Schumacher's

SMALL

IS

(92%) is based on two processes, (69%) and reverse osmosis

being divided among several proceses

distillation

countries

Nearly 60% of the total capacity is in

Arabian Peninsula and there is an increasing

smaller

the

companies

(23%),

including

other

(e.g., vertical tube) and electrodialysis.

Nearly one-third of the total existing capacity has been supplied by

Japanese

(France),

companies

(largely Sasakura )

Ionics and UOP.

User-wise,

followed

by

Sidem

two-thirds of the capacity

is for drinking water, one-fifth for industrial uses and the rest for various other purposes. Reverse

Osmosis

starting

in 1970,

holding

.at 23%.

plants

has been gaining

with a mere 2% share in the total

capacity

with

process

capacities of

ground

quite

installed

fast,

desalting

it jumped to over 25% in 1980 and is currently Its share is much larger (43%) in small

plants

under 0.01 mgpd and smaller (11%) in the

1 mgpd and above range.

And with the

trend

large towards

smaller plants in the future, its share could rise in the future. COST OF DESALINATION The largest MSF installation is that Al-Jubail with

a total

II in Saudi Arabia

capacity of 210 mgpd comprising @f 4 X 10

modules,

each approximately

5 mggd.

The economy of scale beyond this size

appears marginal.

Two of the largest RO installations are

those

584 at

Bahrain

one

(Capacity 10 mgpd) completed in Ott 1984 and the

at Malta

(Capacity 5.3 mgpd) completed an year earlier. The total

capital

cost

services

is

production

reported $4.07

20%.

be $17.5

million

and

the

cost

of

per 1000 gals including amortisation

cost

of

operates

at

800 psi as per the

membrane manufacturer, say

to

including local supplies and

The largest single cost item ($1.62) is electricity.

$1.62. plant

of the Malta plant,

recommendations

This

of

the

DuPont. If operated at a higher pressure, operating cost is reduced by 15-

900 psi which is possible,

than

The membrane can also be operated for a longer period and this will further help in reducing the cost.

recommended addition,

a

cheaper membrane

than that of DuPont can

be

In

used,

with a cost reduction of $0.40 per 1000 gals. Cumulative efecf of these

could

bring the cost down to $1.50 range which

is

quite

the cost of

water

attractive. Assuming

an

interest charge of 7% per year,

from

desalination

in a 5 mgpd plant is estimated

gals

for

MSF and $1.70 for RO.

mgpd,

'at

the same location,

respectively.

$1.50

$0.05/kWh.Higher figures,

For a larger

at

$1.90/1000

installation,

these figures reduce to $1.70

Electricity

charges

are

assumed

energy cost favours RO even further.

however,

have

50 and at

These cost

been arived at by DuPont with a

vested

interest in RO and may therefore be slightly biased in its favour - hence an independent cost calculation that

is

recommended,

MSF with its improved and more eficient versions

knowing continues

to hold its ground. It is interesting to note that the figure of $1.50-2.50/1000 gals has remained unchanged over the years despite the inflation. This has

fortunately

been

counterbalanced

by

improvements

in

technology and eficiency of operation. The future in this respect promises to be even more exciting and we revert to this later.

585 WHAT'S IN STORE TO THE YEAR 20007 We

indicated earlier the desalination

have

with an estimate for 1987. 13

years

to

the

capacity as of

1986

What is likely to happen in the

next

year 2000.

Future is

always

uncertain

forecasts are almost always wrong - thanks to the dynamic of

economy and of the environment.

exciting

to

Despite this,

nature

it is

attempt a forecast if only to get a 'feel'

and

always of

the

situation. The

projections

made

on

of the future desalination

two basis,

exponential

growth and linear

former takes the capacity to dizzy heights, given

the financial constraint

capacity

of the water user

choose the more likely realistic linear

According

to

capacity

the

growth.

replacement and the

growth

new

is likely to reach a plateau in the 90's,

rest being MSF and other variants of distillation 330

of

additional capacity

comprises

new

of

capacity.

185 The

as total

The

countries.

We

rate.

desalination with

order of 330 mgpd and of this ~0 will constitute about

total

been

too good to be true,

therefore

this,

have

annual

24%,

the

processes.

The

replacement installed

and

145

as

desalination

in the year 2000 would seem to be of the order of

5500-

6000 mgpd. Financial constraint could well restrict it to a lower figure. by

On the other hand,

with some creative financial package

the plant suppliers - and they are capable of devising one

-

even the higher projected figure could be exceeded. In

any

case

suppliers to

update

there is an atractive market

awaiting

the

plant

during the period to the year 2000 and they will their technology and improve it further in

order

need to

hold their ground. PUTURR PROMISES TO BE EXCITIWG We

have noted earlier that the two main contending

for desalination

are

MSF

technologies

(distillation) and RO (reverse osmosis).

566 technologies have come a long way since

These and

have

been

improved

since

then.

introduced In

case

to the reuse of vapour for increasing production to as

as

8

tons

balanced

of fresh water per ton of steam,

against

the extra cost of additional

but

this

use

of

cheaper

TO hold its

materials.

own

mush

has

stages.

cost economies are possible through change of process and

of

for example, introduction of multiple stages , have

distillation, led

constantly

first

to

Further

parameters against

the

formidable RO process, further improvements in operation and cost likely to be affected in the 90's with particular

are to

of scale formation and use of

prevention

reference

automatic

process

control. Other possibilities holding great potential include: * Dual purpose MSF plants, power plus desalination. * The above could include a nuclear or oil fired power plant. One such

plant

is already operating in the USSR,

MW

a 150

metal fast breeder reactor) with a 32 mgpd desalination plant

design developed in France,

liquid

plant.

A

though smaller scale and skid

mounted promises great economies. *

A highly cost-effective

effect

successor of MSF is the MES

evaporation) with energy

stack

(multiple approaching

consumption

that for ~0. *

Combine

MSF

with vapour compression either

by

a

mechanical

compressor or by an adsorption system.

*

Other energy saving devices,

such as vapour heat evaporation,

the half stage evaporation and hybrid evaporation etc. *

Combining

heating

MSF

value,

with wet air oxidation of fuels e.g.,

of

very

peat or coal with an excessive amount

low of

water. And more. no

bounds.

Sky is the limit and engineers innovative ability know In

case

of

RO,

improvements in the membrane,

there

have

been

considerable

with increased life and capable of

581 Also with the growing competition,

operating at higher pressure. there

have

been

better and even

cheaper

types

of

membranes

offering the designer a host of choices. Both the processes, MSF and RO, have kept a lead over all others. They

have

have

go

proved to be the best in their own spheres. one step further and aim for having best

worlds? Several possibilities

of

Why

not

both

the

have and are being explored in this

respect. These include: *

A hybrid MSF/RO combining the synergetic benefits of the

MSF yields a much purer product (over

350

ppm).

two.

(less than 25 ppm solids) than RO

For many purposes these could be blended

with

each other and/or with brackish water - for optimum results. Such combination

leads to better efficiency,

load following capability

and also use of excess electricity. * Combined RO/VC.

The combined system yields 40% more production

than the RO process alone, with only 29% aditional energy. * Combined RO/MES.

This combines the simplicity of MES with

low energy consumption

the

of RO. But so far only few small plants of

this type have ben designed because of the complexity

involved.

CONCLUDING The

exploding a

population and the finite fresh

water

point

to

There

could even be a water famine in the year 2000,

serious water problem in many parts of

resources the

world.

unless

we

is esential to desalinate brackish and sea water in order

to

take appropriate action NOW, It

provide

safe drinking water for healthy condition.

ever be considered too high, for

any

capacity continue,

nation. around but

To meet

NO cost

can

for health must be the top priority this

requirement,

the

the world has been growing fast and

desalination this

will

is likely to level off by the end of the century.

Both the leading processes, distillation

and reverse osmosis will

to grow with constant improvements,

continue winner

well

may

be

an optimum combination

and of

the the

ultimate two

- to

'tailor' to the requirements of any specific location. The

real

long-term

management are

called

close water,

solution,

including water conservation. for and these have to be used

internatinal cooperation. even

however,

lies in

proper

Some radical in

water

measures

conjunction

with

with adequate supply of potable

arid areas can be made fertile and this will add

new dimension to the solution of the food problem.

a