沙漠研究 22-1, 153 -155 (2012 )"ICAL 1 / DT X"

Journal of Arid Land Studies－Refereed Paper－

Vacuum Distillation System Aiming to Use Solar-Heat for Desalination
Takahisa JITSUNO*1) and Kaoru HAMABE2)
Abstract: A simple vacuum distillation system has been developed for the desalination of the seawater and for the purification ofcontaminated well water. This system can be operated by solar heat, and the production of salt is possible in this vacuum still.
Because no consumption parts are required, the system should work more than 30 years. This simple system had the thermal
efficiency of 70% which is equivalent to the generation of 10 kg/m2 of water per day.
Key Words: Desalination, Freshwater, Solar-distillation, Vacuum distillation

2. Solar Desalination Methods
1. Introduction
In the desert area, many desalination systems are working
to produce fresh water from seawater. The most costeffective desalination method is Reverse-Osmotic (RO)method using organic filters. The other is the Multi-Stage
Flash (MSF) method using petroleum fuel. These methods
are good for producing a large amount of fresh water (up to470000 tons/day).
However, conventional desalination
systems consume a lot of fuel, electricity or filters in operation.
Those systems are good for the well-progressed oroil-producing countries, but not suitable for theunder-developed countries without oil fields because of thehigh running cost.
On the other hand, many solar-powered desalination
schemes have been proposed to prevent above-mentioned
disadvantages of conventional desalination systems (Qiblaweyand Banat, 2008). However, these schemes have small yields,
and have many difficulties in the operation such as thecondensation of salt and the removal of condensed saline-water.
We wanted to develop a simple solar-powered vacuum
distillation system for producing fresh water using only pipes
as the main device. This system contains a evaporating pipe
heated by solar-radiation and a cooling pipe cooled by air.
This system only contains pipes, and no elements areconsumed during operation. We have developed several
variations of heating and cooling schemes, and the details arepresented in this paper.
Our first priority was to develop a distillation system
suitable for arid and rural areas in developing countries. For
this purpose, the cost of the machine should be low enough tointroduce them into the rural desert.

2.1. Previous schemes
For reducing the energy consumption for the saline-wateror contaminated water desalination, many schemes using thesolar-power have been proposed (Kunze, 2001, Tanaka et al.,2000). These methods were the basin types, the vacuum
distillation systems, and the solar-heated tube schemes.
However, the yields of water for these schemes were verysmall, and these systems required heavy maintenance work tooperate.
As an example, a solar-heated vacuum-desalination system
was proposed (Abi-Jabal et al., 2001). This system used amulti-stage vacuum-distillation scheme with solar-heat, and120 kg/day of water was obtained. However, for operating
the multi-stage distillation, a complicated vacuum control wasrequired in the large-scale vacuum system. The empty
weight of the system was 5 tons, and the operating weight was12 tons. This meant the total cost of the system was verylarge, and it brought difficulty for wide-spread use in the ruralarea.
2.2. Operation principle of new approach
The solar-distillation systems using U type tube have been
proposed by many researchers in many papers (Midili andAyhan, 2004a, 2004b) or patentsA) B). This principle is very
common and is very simple. However, this scheme is notfound in use because of the difficulty in maintaining thesystems. These schemes employed complicated heating andcooling systems, for example, multi-stage and indirect heatingof saline-water. For this reason, the heating efficiency waslow, and the complicated structure of heating tube provided adifficulty in cleaning of the device.
In our system, the sunlight is directly received at the boilingpipe, and boiling pipe is a simple tube. This provides highheat efficiency because the sunlight heats the heating pipe,* Corresponding Author: jitsuno@ile.osaka-u.ac.jp
2-6 Yamadaoka, Suita Osaka 565-0871
1) Institute of Laser Engineering, Osaka University, Japan

2) Environmental Management and Technology Center in Kansai, Japanadded to the condenser for long term operation.
At the beginning of the operation, this tube is evacuated to1/100 atmosphere with a vacuum pump, and the devise is usedin seal-off condition. The vacuum pump is used only oncefor a whole day of operation.
After the evacuation, the saline-water or contaminatedwater is supplied to the boiling pipe. Then, the electric heaterand cooling fans are operated for the distillation. During theoperation, the raw-water is supplied to the boiling pipe formaintaining the water level in the boiling pipe. The distilledwater is also removed from the condenser to the additional
reserve tank. In actual distillation, condensed saline-water
should be removed from the boiling pipe for preventing
deposition of too much salt. These operations are simply
done by opening valves of the inlet and the outlet ports of this
distillation system.

3. Experimental Results

Fig. 1. Photograph of distillation system.

which is cooled by evaporation inside the pipe. This also
provides a very simple structure which is easy to maintain.
The cooling tube (condenser) is also a very simple pipe.
The operation principle is simple, and the system works as
a conventional vacuum distillation device used in chemical
processes, namely a combination of the boiling flask andcondenser. The heating pipe contains saline-water inside, andgenerated water vapor is transmitted to the condenser. The
water vapor is cooled in the condenser to produce water.
For the purpose of continuous operation, a 10 m of watercolumn can be used for taking out the distilled water from thevacuum. However, this scheme is also an old idea reported
previously (Al-Kharabsheh and Goswami, 2003a, 2003b).
2.3. Details of the experimental device
The photograph of system is shown in Figure 1. Thissystem is using an electric heater of 500W. This heating partwill be replaced with a solar heater in the actual device. The
condenser is cooled by electric fans of 50W. Between theboiling pipe and the condenser, a set of combined baffles isinserted to preventing the surge of boiling saline-water. Boththe boiling pipe and condenser have reserve pipes forsaline-water and distilled water. An additional reserve tank is

3.1. Fresh-water distillation
The system was first tested with the freshwater as theraw-water. The tap-water colored by watercolor (orangecolor) was used to see the contamination of raw-water todistilled water. The heat efficiency was measured by theproduction rate of distilled water, and the measured value washigher than 80%. Without good baffles, raw-water is easily
surged into the distilled water. Multi-stage baffles are foundeffective to prevent this surge. This baffles worked perfectly.
3.2. Saline-water distillation
Because the final application of this system is thedistillation of seawater, we must know the applicability of thissystem to seawater. Unfortunately, the actual seawater isdifficult to obtain, saline-water for the tropical fish was used atthe 3.5% concentration. For observing the problem in highcondensation situations, the system was operated to a very highconcentration (35%). The average heat efficiency was about
70% because of higher operating temperature at the mostcondensed condition. The boiling temperature was increased
up to 70 degree Celsius. After the experiment, a lot of salt
powder was observed at the bottom of the boiling tube. The
contamination of distilled water was also not observed in thisexperiment.
3.3. Distillation of CaCl2 solution
Instead of the saline-water, the Calcium chloride (CaCl2)
solution, which was used as a desiccant of the home closet,
was distilled to obtaining water from the air. In thisexperiment, the distillation was done normally with somewhat
higher temperature. This means we can obtain water fromthe air even in the most arid area without any kind of water.

4. Discussion
A very simple distillation system has been demonstrated
the ability of distillation using electric heater. The proof
experiment with solar-heat is not performed as yet, but theprinciple is the same with the achieved experiment. Becauseof the cost of this scheme is very cheap, this scheme seams toadaptable to the very rural area of the arid countries. Thismethod is applicable to making drinking water, and the waterproduction for the agriculture with the drip irrigation. Using
this method, we can grow Jatropha or Pongamia tree for theproduction of botanical oil for the bio-diesel-fuel in the veryarid rural area such as Somalia in Africa.
Since this method is distillation, this scheme is also usefulfor purifying drinking water in the contaminated well water
area. In India and Bangladesh, many wells are contaminatedwith Arsenic, and the measure to remove this contamination isurgently requiredC). We strongly believe our method should
be used in such cases.
The amount of water production of this system is not large
as conventional methods (MSF or RO), but this scheme
requires almost no running cost for more than 30 years. The
size of 30 kg/ day system should be 3 (L) × 1 (W) × 1.5 (H) m.
This size machine is very suitable for home use in the aridareas.
If the system is operated in parallel, we can obtain 1~10 ton
water par day. This water should be enough to maintain a
few hundreds meter square orchard of Jatropha or Pongamia
tree. This provides a large amount of employments for ruralareas.
Finally we want to mention our system is freely modified
in the case of application. If we have electricity, the coolingshould be done using electric fan because it provides a verysmall system. If we have no electricity, we can construct asystem without the electric fan. In this case, cooling finsshould be large as compared to the fan-type system. If themaintenance for the vacuum system is difficult, we canconstruct the distilling system at atmospheric pressure, but it
requires high boiling temperature (100°C) causing lower heatefficiency.
We are now planning to perform the solar-heat experiment,
and it will be reported soon.
NotesA) R. E. Snyder: US Patent 2490659 (1949).
B) H. A. Wilson: US Patent 5552022 (1996).
C) http://www.daiwa.jp/water/index.html

References
Abu-Jabal M.S., Kamiya L., Narasaki Y. (2001): Proving test
for a solar-powerd desalination system in Gaza-Palestine.
Desalination, 137: 1-6.
Al-Kharabsheh S., Goswami D.Y. (2003a): Analysis of an
innovative water desalination system using low-grade solar
heat. Desalination, 156: 323-332.
Al-Kharabsheh S., Goswami D.Y. (2003b): Experimental
study of an innovative solar water desalination systemutilizing a passive vacuum technique. Solar Energy, 75:
395-401.
Kunze H. (2001): A new approach to solar desalination forsmall- and medium-size use in remote areas. Desalination,
139: 35-41.
Midili A., Ayhan T. (2004a): Natural vacuum distillation
technique-Part I: Theory and basics. Int. J. Energy Res., 28:355-371.
Midili A., Ayhan T. (2004b): Natural vacuum distillation
technique-Part II: Experimental investigation. Int. J. EnergyRes., 28: 373-389.
Qiblawey H. M., Banat F. (2008): Solar thermal desalination
technologies. Desalination, 220: 633-644.
Tanaka H., Nosoko T., Nagata T. (2000): A highly productivebasin-type-multiple-effect coupled solar still. Desalination,
130: 279-293.