This document describes a zero liquid discharge (ZLD) system based on low temperature distillation (LTD) technology proposed for SONEDE in Tunisia. Key advantages of LTD over traditional multi-effect distillation include more efficient heat transfer through direct evaporation and condensing without tube bundles, use of low-grade heat sources, lower costs, and simpler operation. The system aims to help facilities achieve environmental compliance while reducing costs, footprint and increasing water recovery for reuse.

1. 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

2. • 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

3. 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.

4. 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.

6. ZLD Based on Low Temperature Distillation
System

7. • 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

8. 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

9. 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:

10. 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

11. Heat transfer of MED

12. 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

13. Effect of non-condensable gases
Heat transfer
Heat transfer
Tube bundle
Non-condensable
gases
Vapor
Condensate
Non-condensable
gases
Vacuum
pump
Vapor
MED
LTD

14. 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
Heattransfercoefficient(kW/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)

15. Thermal surfaces
Min
Min
Max
Max
Min
Min
Max
Max
-
10'000
20'000
30'000
40'000
50'000
60'000
MED LTD
Heattransfer(W/m2K)
Comparison of heat transfer
MED 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

16. Heat transfer coefficients of different processes
Type of heat transfer Heat transfer coefficient
(W/m2
K)
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

17. Specific heat transfer per m3 of reactor volume
0
200
400
600
800
1000
1200
1400
1600
MED LTD
Heattransfer(kW/m3)
Specific heat transfer capability
MED vs LTD
(1 m3 reactor, 3K, full-load)

18. 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

19. 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

20. 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

21. LTD Module (Pilot plant in El Gouna)

22. LT (Waste Heat) Dryer

23. 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

24. 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