VC seawater desalination plant

Desalination, 45 (1983) 39-47 Elsevier Science Publishers B.V., Amsterdam

OPERATING

EXPERIENCE

VTE/VC SEAWATER

B. Ohlemann,

AND PERFORMANCE

DESALINATION

Envirogenics

DATA OF AN ADVANCED

BARGE-MOUNTED

PLANT

Incon Anlagentechnik

D.K. Emmermann,

39 - Printed in The Netherlands

GmbH, Homburg/Saar

Systems

Co., El-Monte,

California

ABSTRACT The floating desalination demonstration plant "MEDA" presents an advanced concept to produce fresh water from seawater with low energy consumption. At first step of its demonstration phase, MEDA was operated at Helgoland in the North-Sea at its design capacity of 5000 ma/day and a performance ratio of 22 to 1 kg/kg. The 24 effect VTE evaporator combined with two vapor compression topping effects operated at a max. feed temperature of 135 "C with sulphuric acid pretreatment. High heat transfer rates were obtained using foamy upflow in double-fluted evaporator tubes without inter-effect pumps. Data were obtained for an alternative pretreatment system for feed make-up using a fluidized bed ion exchanger system operating in the countercurrent mode. Calcium ion content in the feedwater was demonstrably reduced by more than 90 %. This paper presents and analyses the above performance results.

RESUME L'installation flottante demonstrative de desalenisation d'eau de mer "MEDA" a' l'avantage de produire, par l'intermediaire d'un concept trds avance avec peu d'energie, de l'eau potable. Lors de la l&e @tape demonstrative qui a &ti! effectuee en Helgoland, en mer du Nord. M@da montra une capacite de 5000 m3/h et un ratio de performance de 22 a' 1 kg/kg. L'evaporateur 24-Effet-aux tuyaux verticaux avec le condensateur de vapeurs chaudes a et6 opere avec une temperature maximale de l'eau atteignant 135 "C avec la mgme dose d'acide sulphurique le tartre. L'utilisation d'evaporation d'ecume par sustention et de tuyaux aux rainures verticales dans les evaporateurs aux tuyaux verticaux a prouve une augmentation nette des resultats du transfer de chaleur, sans utilisation des pompes inter-effet. Les donnees ont et.5 effect&es pour un systeme alternatif preventif pour la preparation d'eau potable utilisant un systeme d'echange d'ions a' base de fluor operant contre courant. Le contenu en calcium pour cette eau d'alimentation etait reduit de plus de 90 %. Cette explication presente et analyse des resultats de ce procedus.

KURZFASSUNG Die verschwimmbare Meerwasserentsalzungsund Demonstrationsanlage "MEDA" prasentiert ein fortschrittliches Konzept zur Gewinnung von Brauchwasser aus Meerwasser. Der erste Schritt umfaDte die Demonstration der MEDA in der Nordsee vor Helgoland mit der Auslegungskapazitat von 5000 m3/d und einem Leistungsverhlltnis von 22 : 1 kg/kg. Die 24-Effekt-Vertikalrohrverdampferanlage kombiniert mit zwei Briidenverdichtereffekten wurde mit einer maximalen Speisewassertemperatur von 135 'C bei gleichzeitiger Dosierung von Schwefelslure zur Kesselsteinverhijtung betrieben. Die Anwendung von Schaumauftriebverdampfung und Llngsrillenrohren in den Vertikalrohrverdampfern ergab eine betrgchtliche Steigerung der Warmedurchgangszahlen ohne Einsatz von Intereffektpumpen. Daten wurden aufgeOOll-9164/83/$03.00

0 1983 Elsevier Science Publishers B.V.

40 nommen fiir eine nach dem Liftbett-Verfahren arbeitende Ionenaustauscheranlage als alternatives System zur Verhiitung von Kesselsteinablagerungen. Der Kalziumgehalt des Speisewassers konnte urn Uber 90 % reduziert werden. Die vorliegende Abhandlung prasentiert und bewertet die erhaltenen Betriebsdaten.

INTRODUCTION The principle operational

aim of the MEDA project

reliability

desalination

is to demonstrate

and a low energy consumption

plant "MEDA" which presents

an advanced

water from seawater.

This has been achieved

with the combination

of well-known

pression

(VC), vertical

efficiency

TECHNICAL

necessary

plant is a VC-VTFE-MSF

equipment

(VTFE) and multi-

desalination

plants.

fired boiler,

the necessary

has been designed

supply of the desalination

whereby

the high pressure

the vapor compressor electricity

from a central

With the features

control

outlined

by an oil

through a turbine

Plant operation

and accommodation

provide

is remotely

con-

a workshop,

for operating

seawater

as well

continuous

diesel generators

room. The barge also contains

above, the floating

all

hose. The storage

for one month's

steam is expanded

for plant start-up.

can be put in operation local conditions

and distillate

plant is provided

and a generator.Three

storage for spare parts, a laboratory

of 5000

unit. This includes a seawater

fresh water to land using a flexible

The energy

capacity

on a barge which also contains

tanks for fuel, chemicals,

for fuel and chemicals

operation.

unit with a nominal

It is installed

storage

as a pump to transfer

trolled

system

vapor com-

process with a total

thermal

to make it a self-supporting

intake with screens,

driving

fresh

FEATURES

(1.3 mgd) fresh water.

capacity

to produce

processes:

is a desalting

seawater

a new desalting

with foamy upflow

(MSF). The result

2 to 3 times higher than conventional

The desalting m3/d

concept

by developing

and proven thermal

tube evaporation

stage flash evaporation

the feasibility,

of the floating

desalination

in a very short time, almost completely

personnel. plant "MEDA"

independent

of

and facilities.

PROCESS DESCRIPTION The basic details process diagram topping

of the process

is presented

(vapor compression)

ly oriented

feed heater

have been given elsewhere

in Figure 3. The VC/VTFE effects and twenty-four

is located

(ref. 1). A

unit consists

VTFE effects.

in each VTFE effect,

except

of two

One vertical-

in effect twenty-

four. A trim heater is used to heat the feed water up to the top brine temperature. The vapor generated denser.

in effect

Brine and distillate

twenty-four

is further

brine cooler also serves as precondenser densable

gases are removed

cooled

is condensed

in the reject con-

in a three stage MSF cooler. The

for the venting-system

by a water ring vacuum pump.

before non-con-

41 Raw seawater denser.

High pressure

as cooling

water

seawater

is utilized

by the vapor compressor

of the total distillate

turbine

is used to generate

turbine

generator

output.

electrical

effect.

Both quantities

the topping

is condensed

effects.

Vapor generated

The bus

steam is uti-

in the first VTFE effect. in the first topping

(vapor compres-

this effect with the top brine

and flows as heating

of condensed

by the

to a common

The turbine exhaust

Part of the feed water entering

is evaporated

The

a large per-

with the diesel generators

lized as main heat input and is condensed

sion) effect.

and produces

Part of the power produced

power can be transferred.

Steam from the compressor

in the system.

through a turbine.

power up to 875 kVA at 50 cycles.

can be synchronized

so that electrical

temperature

in the MSF cooler and reject con-

is used as feed water

steam of 50 bar and 505 "C is expanded

power provided centage

is utilized

Part of the preheated

steam to the second

topping

steam form the total amount of product in topping

in

effect two flows to the compres-

sor. OPERATION

AND PERFORMANCE

After construction

the system were carried conditions

DATA

in the North Sea shipyard

was completed

out at the port of Emden. Because

at the Emden docks,

several

tests of

of the brackish

the barge was towed to Helgoland,

water

an island 70 km

off the German North Sea coast. The floating conditions.

seawater

desalination

An initial set-back

(a) The injection

plant was operated

in plant operation

pumps of the diesel generators

from the specification

in the electrical

a self-acting

several

installation,

boiler

week of operation.

trips.

Thereafter

Both problems

No problems termined

arose with the seawater

during operation,

matter

of the fuel oil pump

filter

including

installed

with a quantity

pumps worked

properly,

pump serving

the ion exchanger

Electrical brine cooler

equipment

worked

continuous

while operating

tubing materials

less steel claddings

in the feed make-

except for failure

operation

satisfactorily,

gave false level signals.

the level transducer Various

effecting

system.

of a pack-

The packing

of the desalination

unit.

only the level float in the MSF

This problem was eliminated

brine control

no. 1.4439/1.4571)

by cleaning

valve manually.

(CuNi 70/30, CuNi 90/10, Al-Brass)

(Material

screen. As de-

in the local seawater.

All process and metering

without

the first

of about 20 ma/h due to a

ing of the brine regenerant was replaced

during

running up to the end

problems.

intake system,

the self-cleaning

up line had to be rinsed continuously high level of suspended

shut-down

were eliminated

operational

of the quality

and (b) due to an error

the plant was continuously

of the test period with only negligible

by two problems:

failed because

of the fuel used which differed

created

for 30 days in seawater

was caused

and rubber

as well as stain-

lined piping caused

42 no problems.

Some corrosion

was noticed

No scaling at all was observed

in the carbon

neither

steel MSF cooler.

in the evaporator

tubes nor in the

feed heater tubes. Surfactant subsequent

dosing did not cause any operating

multi-stage

operation

MEDA was operated test sequence formance

flash brine cooler.

due to barge movement

was carried

at design conditions

obtained TABLE

before an extensive

out in order to obtain additional

operating

cooling

inlet temperature

water and/or

under these operating

data on system per-

conditions.

To meet the design point, a seawater ed by recirculating

There was also no effect on plant

even in stormy weather.

continuously

under various

problems with regard to the

product water.

conditions

are summarized

of 30 'C was simulat-

Plant performance in Table

data

1.

1

Performance

data Helgoland

Product water:

Economy

flow rate

m3/d

5250

ppm

<25

ratio a

electrical

Max. operating

1982

TDS

Spec. fuel consumption Overall

August/September

b

.

power consumption

kg dist/kg

steam

22.3

kg oil/m3 dist

3.9

kW

550

temperature

"C

135

kg/h

270 000

330 000

Cooling water temperature

kg/h "C

Seawater

temperature

OC

15

Seawater

concentration

pw wm

33 500

Feed water rate Cont. factor Cooling

5

water rate

Surfactant

(~0s)

dosing rate

One stage radial compressor

30

IO

with inlet guide vane:

Volume flow

m3/s

6.2

Suction

pressure

bar

2.60

Suction

temperature

"C

128.8

kW

400

Pressure

ratio

1.22

Power consumption

(shaft)

Speed

min

-1

7375

EAt steam conditions of 50 bar and 505 "C Including overall electrical power consumption The economy

ratio under design conditions

ure steam of 50 bar and 505 'C and includes

has been calculated the electrical

at high pres-

power provided

by

43 the turbine actual

driven generator.

primary

energy

the desalination

The specific

demand.

plant as well as the overall

pumps, etc. and all auxiliaries The feed water entering centration

ratio enables

ment systems liquid

process

at an increased

possible

The addition the scaling there

of 10 ppm surfactant

design

tubes of various

An alternative the partial

process

removal

sists of five identical

pumps. Vertical

operated

in parallel

to remove suspended (blow-down)

supplied

seawater

whole system

is self-acting

The ion exchanger

hardness desired

start-up

Figures

by ion exchanger

by the evaporator

and controlled

with double

heat trans-

to avoid scaling

involving

The system con-

The third column was backwashed with concentrated

unit. The last column was rinsed again. The

by micro-processor. within

number of cycles were required

level. The successful

linked

heat transfer

and feed heater.

the filter was ready for operation

in the feed water and finally

the removal

overall

for effects

of

brine as

have been equipped

column was regenerated

system was put into operation

a certain

in a reduction

to overall

was tested.

ratio.

each filled with 20 m' resin. Two columns

Another

before

made it

performance

tube foam evaporation

4 and 5 present

for feed water softening. solids.

the multi-effect

tube evaporation

of feed water pretreatment

with treated

initial

utilizing

increase

under design conditions

vessels

a smaller

drop in the evaporating

gave a significant

of Calcium

Furthermore

to the feed water results

materials.

obtained

5-fold. This condosing and pretreat-

hence the overall

(ref. 2, 3, 4, 5). Effects and feed heaters

fer coefficients

for

of 135 'C. These facts and the

with vertical

and tube side pressure

tube geometry

supply for

time.

temperature

is no need for inter-effect

fluted

brine

was concentrated

the number of effects

tendency

with advanced rates

operating

energy

power consumption

in costs for chemical

an evaporator

of foamy upflow combined

to increase

electrical

volumes and pump sizes.

start-up

realized

is based on the

the thermal

on the barge.

the evaporator

a reduction

reduces

The MEOA project

application

utilized

as well as vessel

inventory

fuel consumption

This incorporates

in the regenerating

one hour. After until the residual brine reached

the

operation of the ion exchanger system resulted in 2+ 2+ and 70 % Mg . Calcium content in the treat-

of more than 90 % Ca

ed feed was measured

by atomic

sorption

that such systems

can be applied

brine temperature

of 135 "C and above.

in the on board laboratory.

for operating

without

acid-dosing

This shows at a maximum

CONCLUSIONS The practical

feasibility

of advanced

desalting

technology

as presented

on a full-scale

production

size plant. This

has been successfully

demonstrated

has also demonstrated

that performance

process are achievable.

ratios 2 to 3 times higher

This will result

in considerable

benefit,

here

than MSF in that over-

44 all costs on large scale desalination successful VTFE

demonstration

plants can be substantially

of MEDA at Helgoland

or VTFE for single and dual purpose

supports

reduced.

the acceptance

The

of VC/

plants.

ACKNOWLEDGEklENTS The authors generous

and Incon Anlagentechnik

financial

support

(BMFT) of the Federal

Republic

ment. They are also indebted seewerke

GmbH, without

ions to the execution

GmbH, acknowledge

of the Ministry

for Research

with gratitude

of Germany as well as their continuous

to Incon's Joint Venture

whose active

involvement,

the

and Technology

partner,

Thyssen

from inception,

encourageNord-

and contribut-

of the work, the MEDA project may not have been realized.

REFERENCES

1 2 3 4 5

D.K. Emmermann, An advanced barge mounted VTE/VC for the desalination of seawater,'International Congress on Desalination and Water Re-Use, Bahrain Nov. 29 - Dec. 3, 1981 E. Kirschbaum et al: WarmeUbergang im senkrechten Verdampferrohr, VDI Forschungsheft 375, 193-i. E. Kirschbaum, Der WarmeUbergang im senkrechten Verdampferrohr, Chem. Ing. Techn. Nr. 1, 1954 E. Kirschbaum, Der WPrmeUbergang im senkrechten Verdampferrohr, Chem. Ing. Techn. Nr. 5, 1955 H.H. Sephton, Development of vertical tube foam evaporator for desalination, OWRT report - PB-248 667, June 1975

Fig. 1. Barge-mounted VC/VTFE seawater capacity of 5000 m'/day fresh water.

Fig. 2. Plant operation

is remotely

desalination

controlled

plant MEDA with a nominal

from this central

room.

HP-steam from boiler

Feed water

pretreatment

f---------1

I

t

loo-qf~12 6

Vapor compression

I

I

I

I---J

cycle

I

1

I

I

I

I r--I

1 I

I I

I I

7

:

'31

MSF -

16 .

evaporator

1 Seawater intake 2 Reject condenser 3 Cooling water discharge L Ion exchanger 5 Decarbonator

system

7 Feed water pump 0 Feed water to topping effect 1 9 Vapor compression effect Is.1 10 Compressor 11 Turbine I Generator

3.

Process

12 HP-steam by-pass 13 LP-steam to 19 VTFE-effect IL Distillate out off V&nit 15 Brine to 1st VTFE-effect 16 Distillate to MSF-unit 17 Brine to MSF-unit

6 Deaerator

Fig.

17

diagram

18 Non-condcnsiblcs

from VTFE-unit

19 Blow down 20 Product water 21 Vacuum pump 22 Steam condensate

pump

2 i

_II-w

Loo0

v 2000 5 r c1 z 1000

*

.

% I” 0

Fig.4

1

“‘.’ 1 2

3

1

5

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 No. of feed heoter

tubes based on outside

range 45 - 135 "C, average

Fig.5.

8

. Overall heat transfer coefficients

with double-fluted

z ii

7

6

0

',.""."""."'.",.' 1 2 3 L 5 6 7

Overall

on outside

velocity

heat transfer

tube diameter

loading 4 l/min/tube,

0

for vertically tube diameter

oriented

feed heater

of 19 mn. Temperature

1.5 m/s, tube wall thickness

0.9 mm.

9 IO ll 12 13 IL 15 16 17 18 19 20 21 22 23 2.L Na of VTFE -Effect

coefficients

for vertical

of 50 mm. Temperature

10 ppm surfactant,

tube foamy upflow

range 50 - 130 "C, average

tube wall thickness

0.9 mn.

based liquid