Monday, 22nd April 2013

Design Characteristics of Innovative ZLD System Based

on Low Temperature Distillation (LTD) Technology

Proposal Submitted for

SONEDE, Tunisia

Dr.-Eng. AbdelHakim Hassabou

Technical Advisor, PROTEC

• Achieving strict wastewater treatment regulations has become one of the most

critical considerations in industry today.

• Numerous environmental regulations, rigorous permitting processes, and lack

of water availability, among other factors, are driving many industrial facilities

to implement zero liquid discharge (ZLD) systems as a solution.

• Zero Liquid Discharge (ZLD)

help to achieve environmental compliance,

reduce carbon footprint,

create positive public perception,

recover high purity water for reuse

Introduction: Mitigation of Environmental

Impacts through ZLD

Desalination-Brine Disposal Options

• Sewer disposal. Done mainly for small-scale municipal desalination plants.

• Deep well injection. Practiced for brackish water desalination where the

adverse impacts of such injections do not harm the quality of aquifers. A detailed

hydrogeological study is a prerequisite to determine the safety of this practice.

• Evaporation pond. Usually applied for small-scale desalination plants and for

brackish water desalination.

• Zero liquid discharge. Tends to be one of the most expensive. Usually

practiced for industrial water desalination, or where desalination plant effluents are

used as inputs for chemical industries such as salt production.

• Land application. Practiced for small-scale plants and where land is relatively

inexpensive and readily available. User should be sure to mitigate any adverse

environmental impacts.

Costs are highly site-specific; general trends in relative costs are indicated; cost for

surface water or sewer discharge can be higher if the distance from desalination facility to

the discharge water body or sewer is large, necessitating long pipelines and/or pumping

facilities.

ZLD Based on Low Temperature Distillation

System

• Direct evaporation and condensing– no tube bundles and no membranes.

–Efficient heat transfer

–Less risk for fouling/scaling

–Simple, robust and efficient operations

• Advanced thermodynamics to process extensive mass flows in a compact space

• Use available low grade stream(s)

The Low Temperature Distillation Concept

The LTD Flow Sheet

– The flow is similar to MSF, but

without heat exchangers in

every stage

– The thermodynamic is similar

to MED, but without the

disadvantage of the tube bundle

– There are no heat exchangers

in the stages

– There is no phase change on

the heat exchangers

– A unique spraying and control

system optimizes the efficiency

Layout LTD plant (e.g. 5 cascades)

Pressure vessel with unique pressure control system

Piping in PP-plastics

External heat exchangers (standard component, made out of Titanium)

Water circulation pumps (standard component)

Process control system (control panel)

LTD desalination plants consist of the following main elements:

Feed water sources

Possible Feed sources for the LTD

– Sea water 35’000- 45’000ppm TDS

– RO- Brine, MED-/MSF –Brine

– Highly polluted produced water 100’000-300’000ppm

– Polluted industrial waste water

– Radioactive ground water

Heat transfer of MED

Thermal resistance of MED

0

0.1

0.2

0.3

0.4

tube inside tube outside tube* fouling

R (

m2K

/kW

)

Thermal resistance MED

Min

Max

*25 x 0.5 mm tubes

Effect of non-condensable gases

Heat transfer

Heat transfer

Tube bundle

Non-condensable gases

Vapor

Condensate

Non-condensable gases

Vacuum pump

Vapor

MED LTD

Free and forced convective heat transfer coefficients

0.00 0.05 0.10 0.15 0.20 0.25 0.30

0

2

4

6

8

10

12

Pressure=1.5 bar

avg. wall subcooling= 8 K

Fig. 18 comparison of free and forced flow heat transfer coefficients

He

at tr

an

sfe

r co

eff

icie

nt (k

W/m

2 K

)

Air mass fraction

Free convective condensation

Forced flow condensation (steam flow-0.003 kg/s)

Forced flow condensation (steam flow-0.004 kg/s)

Comparison of free and forced convective heat transfer coefficients (N.K. Maheshwari, P.K. Vijayan and D. Saha, 2007,

Effect of non-condensable gases on condensation heat transfer)

Thermal surfaces

Min

Min

Max

Max

Min

Min

Max

Max

-

10'000

20'000

30'000

40'000

50'000

60'000

MED LTD

He

at t

ran

sfe

r (W

/m2 K

)

Comparison of heat transferMED vs LTD

full-load

full-load

part-load

part-load

Source: WABAG, 2009, Heat transfer in horizontal tube falling film evaporators, IDA World Congress, UAE) WS LTD plant El Gouna

Heat transfer coefficients of different processes

Type of heat transfer Heat transfer coefficient

(W/m2K)

Boiling water 10’000 – 25’000

Condensing vapour 6’000 – 230’000

Gas on surface 50 - 200

MED tube bundle* 1’700 – 6’000

WS LTD** 8’000 – 50’000

* Source: WABAG, 2009, Heat transfer in horizontal tube falling film evaporators, IDA World Congress, UAE) ** WS LTD plant El Gouna

Specific heat transfer per m3 of reactor volume

0

200

400

600

800

1000

1200

1400

1600

MED LTD

Hea

t tr

ansf

er (

kW/m

3)

Specific heat transfer capabilityMED vs LTD

(1 m3 reactor, 3K, full-load)

Specific cost of heat exchange

MED* WS LTD**

Vacuum pump

Vapor

Surface per MW (m2/MWth 3K)

160 33

Reactor volume per MW (m3/ MWth 3K)

10 0.7

Costs per MW (6K) 100% 18%

Costs per MW (3K) >200% 36%

Costs per MW (1.5K) >400% 72%

* Assumptions: tube diameter: 25 mm; distance factor: 1.5 ** Assumptions: droplet size and volume flow El Gouna, titanium plate heat exchanger include General: if nothing else is figures are based on “WABAG, 2009, Heat transfer in horizontal tube falling film evaporators, IDA World Congress, UAE”

Heat transfer

Heat transfer

Tube bundle

Vapor

Condensate

Comparison of GOR

40

50

60

70

80

90

100

DT

(°C

)

Water production (m3/h)

DT= 4.7 K

DT= 3.1 K

+50%

+100%

MED (12 stages)

MED (18 stages)

WS LTD (24 stages)96

DT= 2.3 K

Feed water flow Circulation volume Distillate rate

110 m3/h 300 m3/h 73 m3/h

Electrical Energy 1kWe/m3

Thermal energy 12 MWth at 95 ºC

Basic Figures: LTD plant El Gouna, Egypt

LTD Module (Pilot plant in El Gouna)

LT (Waste Heat) Dryer

Summary: Advantages of LTD system

Low investment costs

Low maintenance costs due to simple and robust

process

Use of excess heat can generate CO2 benefits

Combination with solar power plant possible due to

low temperature and part-load tolerant process

Low energy costs

Conclusions

Dr. Corrado Sommariva, President of the International Desalination Association

(IDA), The National, 09/01/2013

The LTD technology - an opportunity to invest in a

large and growing market with a unique process

adressing the key challenges of the industry.

The LTD technology is simple, robust, energy efficient and very economical