Salinity gradient solar ponds - Solar Energy Sciences and Engineering Applications - page 213

the soil was properly compacted. The pond walls and floor have been covered with 8 cm
thick steel reinforced concrete. The smooth concrete walls and the floor of this pond
have been insulated with 0.5 mm thick sheet of Ethylene-Propylene- Diene-Monomer
(S-801EPDM) to prevent brine leakage. This solar pond has an automatic temperature
measurement system installed prior to the start of operation of the pond. Thirty ponds
of similar size are been used to produce lithium carbonate at the same time in Zabuye
(Nie et al., 2011).
7.4.5 Solar ponds - India
A 1200 m 2 pond was constructed at Central Salt and Marine Chemicals Research
Institute (CSMCR) in Bhavnagar, Gujarat in 1970. This solar pond used magnesium
chloride to create the salinity gradient. Magnesium chloride is a waste product from
the process of making edible salt.
In 1980 a 100 m 2 experimental solar pond was constructed and operated for two
years in Pondicherry. This pond used sodium chloride to create the salinity gradient
and used low density polyethylene liners.
In 1980 another solar pond was constructed with a surface area of 1600 m 2 at
CSMCR in Bhavnagar, Gujarat. This pond also used magnesium chloride to create the
salinity gradient and had problems with the clarity of bittern.
In 1984 a 240 m 2 solar pond was constructed and operated for a long period at
the Indian Institute of Science, Bangalore. Study of this pond has produced very useful
performance data for a small solar pond in south India. It has also proven the technical
and economic viability of small solar ponds.
Since the 1980s several small size solar ponds have been installed and operated
for town water heating. A 400 m 2 solar pond was constructed to supply the hot water
needs of a rural community at Masur on the west coast of India. A similar solar pond
with 300 m 2 surface area was constructed to supply hot water to student hostels for
an engineering college at Hubli in Karnataka.
Figure 7.4.6 shows the solar pond at Bhuj, India. The 6000 m 2 solar pond that
was built at a dairy in Bhuj stood out in many regards. This was the first-ever solar
pond in India to have connected itself to an industrial process, supplying heat to the
Kutch Dairy. To reduce the construction cost of the solar pond the project devel-
oped a cost-effective, indigenous lining; it used locally mined clay and plastics. While
the pond attained a record 99.8 ◦ C under stagnation, stability of the salinity gra-
dient was maintained even at such elevated temperatures. With only one injection
diffuser on one side of the pond, the desired salinity profile was achieved even at the
farthest end.
Here an external heat exchanger is used to extract heat from the storage zone
of this pond. Hot brine is withdrawn from the bottom of the pond and is pumped
through a shell-and-tube heat exchanger where it heats the feedwater up to a tem-
perature of 70 ◦ C. Further, this hot water was delivered to the Kutch Dairy plant to
be used as pre-heated boiler feed water as well as for cleaning and washing. The
entire exercise at the Bhuj solar pond successfully demonstrated the expediency of
the technology by supplying 80,000 litres of hot water daily to the plant (Kumar and
Kishore, 1999).