Most solar sorption systems that have been developed are not yet economically justified. However,
solar thermal adsorption systems are promising and
environmental friendly with low maintenance cost
requirements. This work details aspects of adsorption
refrigeration systems, criteria for choosing an appropriate working pair, challenges with adsorption systems and published performance data and limitations
of these systems.
Commercialization of the technology has been hindered due to comparatively bigger sizes of current
adsorption based cooling units, their low specific cooling power and high manufacturing cost. Efforts to
enhance their performance have focused attention on
improvement of heat and mass transfer and improvements in properties of working pairs among other
strategies.
Steatite (also called saponite or soapstone) is a soft,
magnesium-rich metamorphic rock composed of talc
(Huhta & Kärki, 2018) which can be studied for suitability as a co-adsorbent material. It has been used
for carvings, sculptures, countertops, and architectural
elements, among other uses. However, the cutting and
processing of soapstone produces a large amount of
waste powder, which poses a disposal problem. For
instance, in the production of dimension stones and
other items in Brazil, 60 wt. % of soapstone ends up
as waste and is disposed to landfills (Rodrigues &
Lima, 2012). In Finland, some 110,000 tons of soapstone was produced annually in 2012 (Pokki, 2014)
out of which, the generated waste was 60–75 wt. %.In
Kenya, waste that remains after carving is not disposed which leads to environmental degradation and
pollution (Onyambu, 2013). It is therefore imperative
to consider sustainable ways for utilization of waste
associated with this industry.
Consequently, there have been attempts to find
uses for steatite waste. Some possible uses have been
explored including its application as raw material
in ceramics manufacturing (Cota et al., 2018; Panzera et al., 2011). Steatite is also a potential oil spill
sorbent due to the hydrophobicity of the talc it contains (Souza et al., 2016). Ultrafine steatite powder
is a suitable supplementary cementitious material that
can replace up to 25% of Portland cement (Kumar
et al., 2017). Another application is its use as a
dispersed phase material in composites containing
Portland cement binder (Strecker et al., 2010). Steatitecontaining mortars have been further supplemented
with carbon fibers (Panzera et al., 2011) or thermoset
polymers (Cota et al., 2018) and used in the restoration of historical buildings. However, all of the above
examples rely on either the use of high temperature
(approximately 1,000–1,200
◦ C in ceramics production) or CO 2 -intensive Portland cement as a co-binder,
which decreases the environmental feasibility of these
applications.
Adsorption systems utilize low temperature heat,
which provides a more suitable condition to use steatite
as a co-adsorbent medium in a low carbon footprint
application. This will help develop a method to turn
currently underexploited soapstone waste into a useful
material.
2 LITERATURE REVIEW
The history of solar adsoption system dates back to
1920s when sulfur dioxide and silica gel were used
for the air-conditioning of railway carriages in the
USA. But with the development of cheap reliable compressors and the introduction of CFCs, heat based
sorption systems took a back seat. After the oil crisis
in 1970s and with the restrictions imposed by Montreal (1987) and Kyoto (1997) protocol, research on
heat driven sorption cooling systems started again.
The development of sorption refrigeration systems
powered by solar energy emerged in the late 1970s, following the pioneering work of (Tchernev, 1978), which
observed that zeolite, adsorbs large amounts of water
vapour when cooled and desorbs the water vapour
when heated, thus providing a unique opportunity for
its utilization in refrigeration applications.
Fast forward, Wang et al. (2000) and Zhang (2002)
proposed solar powered continuous solid adsorption
refrigeration and heating hybrid system for water heating and an icemaker. The machine used activated
carbon–methanol as the working pair and 2 m
2 of evacuated tube collectors. The daily ice production was
about 10 kg when the insolation was about 22 MJ/m
2 .
Critoph (2000) used a heat pipe to heat and cool the
adsorber. He concluded that fluids with different physical and chemical properties should be used for cooling
and heating purposes. Different fluids would eliminate the occurrence of possible inward air leaks and
the utilization of thick material to enclose the working
fluid.
Li et al. (2001) performed experiments with a solarpowered icemaker that had activated carbon–methanol
as working pair. This icemaker had a COP ranging
from 0.12 to 0.14, and produced between 5 and 6 kg of
ice per square meter of collector. They concluded that
in order to improve the performance of this system,
the heat transfer properties of the adsorber could be
enhanced by increasing the number of fins or using
consolidated adsorbent.
An adsorption icemaker with activated carbon–
methanol pair was tested in Burkina Faso by Buchter
(2003). The results of this prototype were comparable
to those obtained by (Boubakri, 1992) in Morocco,
with a similar system.
In order to solve the corrosion problem of sea
water in the steel adsorber, a split heat pipe system was designed and constructed in Shanghai Jiao
Tong University (SJTU) (Wang, 2004) using composite adsorbent of CaCl 2 and activated carbon to improve
adsorption performance through incorporating a mass
recovery system. The mass recovery process improved
SCP and COP for the system by 15.5% and 24.1%,
respectively. The heat transfer performance of this system improved by the introduction of the split heat
pipe.
266
solar thermal adsorption systems are promising and
environmental friendly with low maintenance cost
requirements. This work details aspects of adsorption
refrigeration systems, criteria for choosing an appropriate working pair, challenges with adsorption systems and published performance data and limitations
of these systems.
Commercialization of the technology has been hindered due to comparatively bigger sizes of current
adsorption based cooling units, their low specific cooling power and high manufacturing cost. Efforts to
enhance their performance have focused attention on
improvement of heat and mass transfer and improvements in properties of working pairs among other
strategies.
Steatite (also called saponite or soapstone) is a soft,
magnesium-rich metamorphic rock composed of talc
(Huhta & Kärki, 2018) which can be studied for suitability as a co-adsorbent material. It has been used
for carvings, sculptures, countertops, and architectural
elements, among other uses. However, the cutting and
processing of soapstone produces a large amount of
waste powder, which poses a disposal problem. For
instance, in the production of dimension stones and
other items in Brazil, 60 wt. % of soapstone ends up
as waste and is disposed to landfills (Rodrigues &
Lima, 2012). In Finland, some 110,000 tons of soapstone was produced annually in 2012 (Pokki, 2014)
out of which, the generated waste was 60–75 wt. %.In
Kenya, waste that remains after carving is not disposed which leads to environmental degradation and
pollution (Onyambu, 2013). It is therefore imperative
to consider sustainable ways for utilization of waste
associated with this industry.
Consequently, there have been attempts to find
uses for steatite waste. Some possible uses have been
explored including its application as raw material
in ceramics manufacturing (Cota et al., 2018; Panzera et al., 2011). Steatite is also a potential oil spill
sorbent due to the hydrophobicity of the talc it contains (Souza et al., 2016). Ultrafine steatite powder
is a suitable supplementary cementitious material that
can replace up to 25% of Portland cement (Kumar
et al., 2017). Another application is its use as a
dispersed phase material in composites containing
Portland cement binder (Strecker et al., 2010). Steatitecontaining mortars have been further supplemented
with carbon fibers (Panzera et al., 2011) or thermoset
polymers (Cota et al., 2018) and used in the restoration of historical buildings. However, all of the above
examples rely on either the use of high temperature
(approximately 1,000–1,200
◦ C in ceramics production) or CO 2 -intensive Portland cement as a co-binder,
which decreases the environmental feasibility of these
applications.
Adsorption systems utilize low temperature heat,
which provides a more suitable condition to use steatite
as a co-adsorbent medium in a low carbon footprint
application. This will help develop a method to turn
currently underexploited soapstone waste into a useful
material.
2 LITERATURE REVIEW
The history of solar adsoption system dates back to
1920s when sulfur dioxide and silica gel were used
for the air-conditioning of railway carriages in the
USA. But with the development of cheap reliable compressors and the introduction of CFCs, heat based
sorption systems took a back seat. After the oil crisis
in 1970s and with the restrictions imposed by Montreal (1987) and Kyoto (1997) protocol, research on
heat driven sorption cooling systems started again.
The development of sorption refrigeration systems
powered by solar energy emerged in the late 1970s, following the pioneering work of (Tchernev, 1978), which
observed that zeolite, adsorbs large amounts of water
vapour when cooled and desorbs the water vapour
when heated, thus providing a unique opportunity for
its utilization in refrigeration applications.
Fast forward, Wang et al. (2000) and Zhang (2002)
proposed solar powered continuous solid adsorption
refrigeration and heating hybrid system for water heating and an icemaker. The machine used activated
carbon–methanol as the working pair and 2 m
2 of evacuated tube collectors. The daily ice production was
about 10 kg when the insolation was about 22 MJ/m
2 .
Critoph (2000) used a heat pipe to heat and cool the
adsorber. He concluded that fluids with different physical and chemical properties should be used for cooling
and heating purposes. Different fluids would eliminate the occurrence of possible inward air leaks and
the utilization of thick material to enclose the working
fluid.
Li et al. (2001) performed experiments with a solarpowered icemaker that had activated carbon–methanol
as working pair. This icemaker had a COP ranging
from 0.12 to 0.14, and produced between 5 and 6 kg of
ice per square meter of collector. They concluded that
in order to improve the performance of this system,
the heat transfer properties of the adsorber could be
enhanced by increasing the number of fins or using
consolidated adsorbent.
An adsorption icemaker with activated carbon–
methanol pair was tested in Burkina Faso by Buchter
(2003). The results of this prototype were comparable
to those obtained by (Boubakri, 1992) in Morocco,
with a similar system.
In order to solve the corrosion problem of sea
water in the steel adsorber, a split heat pipe system was designed and constructed in Shanghai Jiao
Tong University (SJTU) (Wang, 2004) using composite adsorbent of CaCl 2 and activated carbon to improve
adsorption performance through incorporating a mass
recovery system. The mass recovery process improved
SCP and COP for the system by 15.5% and 24.1%,
respectively. The heat transfer performance of this system improved by the introduction of the split heat
pipe.
266