Session B4
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ADSORPTION DESALINATION FOR MORE EFFICIENT DESALINATION
John Maclin, [email protected], Vidic, 2:00, Joseph John, [email protected], Mahboobin, 10:00
Abstract— With increasing droughts in many areas of the
world in addition to the general necessity for clean drinking
water, the demand for innovative methods to produce potable
water has increased. The desalination of seawater has
emerged as an effective way to fulfill the needs of many
people. A novel desalination technique called adsorption
desalination (AD) aims to alleviate the strains of typical
desalination. AD is a method of thermal desalination,
specifically evaporation, which involves heating the
seawater, then extracting the salts and other materials from
the steam. AD utilizes silica gel in the last step of the
desalination process to clean the saline water. Silica gel is
an unsaturated adsorbent which has a high affinity for water
vapor and can pull water vapor out of a solution even at low
temperatures, making it ideal for AD. Also, silica gel is
relatively inexpensive when compared to other chemicals
used in desalination.
Other processes similar to AD can be costly and
consume a lot of energy, both of which are not ideal, even if
the product is clean drinking water for thousands. AD is
interesting in that it has the promise of making both the cost
and carbon footprint of desalination decrease--to the point of
making this type of desalination feasible for long term use
and an overall solution to the clean water crisis.
Key Words—Adsorption desalination, cost and energy
effectiveness, low temperature processing, silica gel, thermal
desalination
DRINKING WATER FROM THE OCEAN
Desalination is a process that has been in use for
centuries. Greek sailors would boil seawater, collecting the
steam in sponges, and the Romans used clay filters to trap
salt--both processes resulting in clean drinking water.
[1]. Modern desalination has expanded on the idea of taking
seawater, which is normally inconsumable due to salt
concentration, by introducing more elaborate and innovative
methods of creating water for human consumption, farming,
and industry.
Desalination has become more complex and is not a
single process, but rather an umbrella term for the many
processes that go into removing salt from water. Most
University of Pittsburgh Swanson School of Engineering 1
Submission Date 03.03.2017
desalinated water comes from processes that use either
membranes or filtration. The processes that use membranes
or filtration can be further divided into methods that rely on
pressure and electricity. For example, reverse osmosis utilizes
membranes and pressure; during reverse osmosis, high
amounts of pressure are applied to seawater to force it
through the membrane and produce pure water.
Electrodialysis uses membranes and electricity to pass a
current through water so that ions move through specific
membranes, resulting in desalinated water [2]. A smaller
portion of desalinated water is produced by various, less
popular methods such as freezing [3].
Another major desalination technique is thermal
distillation which involves heating water to produce water
vapor free of salt that can be separated; one popular example
of such desalination is multi-stage flash. Multi-stage flash
begins with heating saline water by applying steam to the
surface of the pipes carrying the seawater. The water is then
passed to another stage where the pressure is lower, causing it
to boil. This process is repeated at subsequently lower
temperatures and pressures until clean water is produced [4].
Another example of thermal distillation is membrane
distillation which combines, as the name implies, both
membrane and distillation techniques; this method relies on
vapor pressure differences and a special membrane to allow
water vapor to pass through it, but not the seawater [2].
The main benefit of desalination is a reliable source of
water. Drought is becoming more common in many parts of
the world and is persisting where it already exists. To make
matters worse, the areas most affected by drought often have
no other sources of freshwater. One area that exemplifies the
water crisis occurring in many parts of the world is San
Diego County in California. The county has lower
groundwater levels than the rest of the state and traditional
sources of water such as the Colorado River and Sacramento
River are being used at such high rates that the state has had
to ration them [5]. However, San Diego, like many droughtstricken areas, is located very close to an ocean, opening the
possibility for desalination. Since desalination uses ocean
water, it stands out as a viable solution to this water crisis by
providing a steady source of water. Similarly, desalination
would provide water autonomy to many regions. Currently,
many urban areas receive their water from distant, rural
John Maclin
Joseph John
regions. This importation opens the possibility of exploitation
of the rural areas for their resources and disruptions to the
urban water supply caused by problems along the supply
route. Desalination would allow the urban centers to have
direct access to a water supply, solving both problems [4].
While desalination has incredible positive benefits, it
also comes along with negative consequences, among them
are cost, energy usage, and environmental impact.
Desalination is very expensive and costs much more than
other sources of water. To begin with, desalination has high
initial costs; for example, the Carlsbad plant near San Diego
cost $1 billion to construct [5]. This price tag cannot be
glossed over since operating the plant is also costly. The cost
of desalinated water is so high due to the maintenance
required for the plant and energy usage. Since saltwater has
such a taxing effect on the pipes and membranes, constant
maintenance and cleaning is required for the plant to operate
at full capacity, raising costs. To further ensure the plant is
running smoothly, backups for all the parts are installed in
case one fails, further increasing costs. Finally, the actual
desalination process requires large amounts of electricity,
which accounts for more than half of the plant’s cost. When
these costs are combined, San Diego County ends up paying
between $1,000 and $2,500 per acre-foot for water from the
Carlsbad plant which is about 80% higher than water from
other sources [5] The environmental impacts of desalination
include a high carbon footprint and potential disruption of
aquatic ecosystems; these consequences are analyzed more
deeply in a later section.
highly effective adsorbent due to its porosity and polarity.
Porosity refers to the empty space within a material. Polarity
refers to differences in electric charges of a material. Since
silica gel is highly porous, it can retain a large amount of
water vapor. Silica gel is also quite polar, which allows it to
pull water vapor towards itself more effectively [6].
Adsorption desalination can be divided into two main
steps: adsorption and desorption. During the adsorption
phase, seawater is passed into the evaporator and heated,
producing water vapor that moves into the adsorption beds.
During desorption, the adsorption beds are heated to release
the water, resulting in the final product of potable water.
Potable means fit or suitable for drinking, so potable water is
another way of saying drinking water. Adsorption and
desorption do not take place at the same time; instead, during
one half of a cycle, a certain number of adsorption beds are
dedicated to one of the processes, while the rest are used for
the other process. During the other half-cycle, the roles of the
adsorption beds are switched. A schematic of a typical AD
plant is shown below.
THE PROCESS
How Adsorption Desalination (AD) Works
As the name suggests, the heart of adsorption
desalination is adsorption. Adsorption is the process by which
a gas or liquid is exposed to an optimal pressure and/or
temperature and collects on the surface of a porous, solid
material. The solid is called the adsorbent and the material
that collects on the solid is called the adsorbate. The
collection can occur through one of two processes:
physisorption or chemisorption. Physisorption occurs because
of intramolecular forces, specifically van der Waals forces,
between the gas or liquid and the adsorbent. Van der Waals
forces can occur between any known molecule when a
periodic dipole is created in the atoms that then aligns with
adjacent atoms pulling them together by electric forces. The
van der Waals forces are not covalent or ionic, but occur
randomly with dipoles. Chemisorption occurs when a
chemical reaction occurs between the gas or liquid and the
adsorbent, creating new chemical compounds [6]. In
adsorption desalination, water vapor is the adsorbate that
collects on silica gel, the adsorbent, through physisorption.
An AD plant has a few major components: the
evaporator, condenser, and adsorbent beds containing the
silica gel. Silica gel is used for adsorption because it is a
FIGURE 1 [7]
Schematic of an AD plant
To begin the adsorption step, raw seawater is fed into
the evaporator while clean water is taken out of the
condenser. The total amount of water moving into evaporator
is shown below where Ms,evap is the mass of sea water in the
evaporator, ms, in is the flow rate of feed sea water, mbrine is
the flow rate of brine discharged from the evaporator, cads is
the adsorptive water vapor uptake, Msg is the mass of silica
gel, and θ, γ, and n are shown in figure 2 [8].
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John Maclin
Joseph John
Tchilled,out is the temperature of the chilled water leaving the
evaporator.
EQUATION 1 [8]
Overall evaporator intake
EQUATION 3 [8]
Energy balance in evaporator
The water vapor that is now on the adsorption beds is not yet
clean, however, since its concentration of salt is still
equivalent to that of the raw seawater. To convert this water
vapor into potable water, the desorption stage is required [8].
The activity in the adsorption bed is the same as the
evaporator. The energy balance equation of an adsorption bed
connected to the evaporator and desorping bed connected to
the condenser is shown in equation 4 where Cp,sg is the
isosteric heat of the silica gel, MHX is the mass of the
adsorption bed, cp,a is the specific heat of adsorption, Qst is
the isosteric heat of adsorption, cp is the specific heat
capacity, Tcw./hw, in is the temperature of the water entering the
adsorbing or desorbing bed, and T''cw./hw, out is the temperature
of the water leaving the adsorbing or desorbing bed.
FIGURE 2 [8]
Table of constants of overall evaporator intake
Heat is then applied to this water, producing water vapor that
evaporates onto the silica gel. The heat used for this step can
come from waste heat from other processes or renewable
sources such as geothermal or solar; the possibility of using
heat derived from renewable sources further adds to the
environmental benefit of AD. The brine produced from this
step is discarded once the salt concentration in the evaporator
reaches a specific level; brine refers to highly saline water.
The concentrations of raw seawater, seawater in the
evaporator, and vapor can be added to relate the mass of
seawater and the rate of change of the concentration of
seawater in the evaporator as shown in the equation below
where Xs, in is the concentration of raw seawater, Xs, evap is the
concentration of seawater in the evaporator, and XD is the
concentration of the vapor.
.
EQUATION 4 [8]
Energy balance in adsorption bed
During the desorption phase, the adsorption beds are heated
and the water vapor stored here moves out of the silica gel
and into a condenser. While in the condenser, the vapor is
cooled by water supplied by a cooling unit, generating the
desired product of drinkable water. Equation 5 represents the
energy balance
of the
condenser where
Tcond is
the temperature of the condenser, MHX,cond is the mass of the
condenser, Md is the mass of distillate leaving condenser, and
cdes is the new adsorptive water vapor uptake [6].
EQUATION 2 [8]
Relationship between masses and concentrations in
evaporator
The energy balance of this entire step can be expressed
through equation 3 [8]. The energy balance is simply a
mathematical way to represent that energy can neither be
created nor destroyed, only transformed [9]. Cp,s is the
specific heat of seawater, Tevap is the temperature of the
evaporator, MHX,Evap is the mass of the evaporator, cp,HX is the
specific heat of the evaporator, hf is the enthalpy of the
seawater, hfg is the enthalpy of evaporation, mchilled is the rate
of change of the mass of chilled water, Tchilled,in is the
temperature of the chilled water entering the evaporator,
EQUATION 5 [8]
Energy balance in condenser
Adsorption Desalination Combined with Other
Desalination Methods
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AD can be easily combined with already existing types
of desalination, namely those that utilize a similar thermal
method. AD itself comes from extensive research into better
methods of thermal desalination to try to produce the same
amount of water at lower temperatures.
the brine discharge of reverse osmosis (RO). The RO portion
of this system is simple. First, raw seawater is taken in and
passed through multiple filters including sand and gravel. The
water then goes through another round of filtering where
smaller particles are removed. After this step, only the salt
remains in the water [11]. Then, the water moves to a pump
where it is subjected to extremely high pressures and sent off
to multiple RO "modules" where the actual desalination takes
place. A more detailed schematic of a single RO module can
be seen in the figure below. The brine left over after the water
has passed through all the RO modules will then be sent to
the AD portion of the system. The clean water is sent to
posttreatment. This process is depicted in the figure below
where Mf is the mass flow rate of feed water, Xf is the
concentration of feed water, Mb is the mass flow rate of brine,
Xb is the concentration of brine, Mp is the mass flow rate of
permeate (clean water), and Xp is the concentration of
permeate [7].
FIGURE 3 [8]
Categories of desalination
The figure above shows the different types of
desalination and how they are connected. AD is under the
umbrella of thermal desalination of evaporation making the
process similar to Multi-Stage-Flash, Multi-Effect and Vapor
Compression. During the water cycle, the heat from the sun
evaporates sea water, separating it from the salt, which then
precipitates as potable water. Thermal desalination mimics
the water cycle by boiling the water and separating the steam
from the ions dissolved in it, thus making it potable. One of
the interesting parts of AD is that it has the capacity to run on
solar power [8]. Making an artificial process that can operate
on the same type and amount of energy as the natural process
basically frees it from the need of energy input. AD has also
been made to make use of the waste heat from traditional
thermal desalination, making a part of the process essentially
free of charge by saving energy [8]. This idea would be most
useful with the combination of Multi-Effect desalination.
(MED). MED is already considered the most efficient
desalination process in use regarding energy consumption
because it can operate on waste heat or very low heat. MED
works in a series of chambers; an external heat source heats
the first chamber to bring the water inside to a steam. Then
the steam is used to heat more water and bring it to a boil and
the process continues into a third chamber [10]. AD can
make this process even more efficient by adding adsorption
beds to the chambers allowing the initial temperature of the
first chamber to be lower and the pressure in each chamber to
be lower. Combining AD with MED is the most probable use
since the addition of the AD process would be relatively
inexpensive [8].
Combinations with other methods is not limited to
thermal desalination, however. Ali et al have conducted a
simulation that used AD to extract more potable water from
FIGURE 4 [7]
RO portion of RO-AD System
FIGURE 5 [7]
Single RO module
The RO system can be analyzed mathematically through
many equations. The mass balance of the system is given in
equation 6 [7].
EQUATION 6 [7]
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John Maclin
Joseph John
pressure, Πcave is the average feed side osmotic pressure, Kw is
the water permeability, and Am is the membrane area [7].
Mass balance of RO system
The salt balance can be found by multiplying each flow rate
by their given concentrations as shown in equation 7 [7].
EQUATION 10 [7]
Flow of permeate through each RO module
EQUATION 7 [7]
Salt balance of RO system
The overall performance of the RO system can be measured
using the following metrics below. [7].
One phenomenon that was observed was a lowering of the
feed pressure as the water passed through subsequent RO
modules. Equation 8 gives the pressure drop where Pcd is the
pressure drop across each RO module and N is the number
RO module [7].
EQUATION 11 [7]
RO overall performance measures
EQUATION 8 [7]
Pressure drop across RO module
The AD portion of this system is the same process as detailed
in the earlier section on AD.
The schematic of the complete RO-AD system can be
seen in figure 6. The mass balance, salt balance, and recovery
for the total system are also shown where Mb,RO is the flow
rate of brine in the RO system, Mp,AD is the flow rate of
permeate in the AD system, Mb,AD is the flow rate of brine in
the AD system, Xb,RO is the concentration of brine in the RO
system, Xp,AD is the concentration of permeate in the AD
system, and Xb,AD is the concentration of brine in the AD
system [7].
Certain osmotic pressures which will be needed in later
calculations can be found using the equations in equation 9
where ΠP is the permeate osmotic pressure, Πf is the feed
osmotic pressure, SR is the salt rejection, CP is the
concentration polarization factor, Xfc is the average
concentration factor, Xf is the concentration of feed water,
and Ri is the permeate recovery where I is the number RO
module [7].
EQUATION 12 [7]
Performance of RO-AD system
EQUATION 9 [7]
Osmotic pressure calculations and their intermediate
calculations
Equation 10 models the flow of clean water through each RO
module where Pf is the feed pressure, Pp is the permeate
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John Maclin
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Advantages of Adsorption Desalination
The primary benefit of AD is that it uses significantly
less energy than more popular forms of desalination. To help
compare the energy usage of AD and other methods, a
distinction between payable and non-payable energy is
drawn. This distinction is most easily described by explaining
the concept of non-payable energy; non-payable energy is
derived from heat sources that remain after other processes
have finished and would go unused. Non-payable energy can
also come from renewable sources such as solar panels.
Payable energy comprises energy from other sources and is
used mainly for operating the pumps and moving the potable
water to other sources. In terms of non-payable energy, AD
has a lower usage than nearly all other forms of desalination,
as shown in the figure below [8].
FIGURE 6 [7]
RO-AD system
THE IMPORTANCE
Adverse Environmental Impacts of Desalination
The environmental impacts of desalination are
concerning. Desalination is an energy-intensive process; the
Carlsbad reverse osmosis plant uses the same amount of
energy as 30,000 homes, contributing to desalination’s high
cost [5]. Desalination consumes a large amount of energy and
part of its environmental effects stem from that energy usage;
because the energy that powers a plant is produced from
unclean sources, such as the burning of fossil fuels,
desalination results in a large carbon footprint. There are
advancements being made that could reduce energy usage;
for example, at the Massachusetts Institute of Technology,
engineers are working on creating extremely thin membranes
so that less energy is required for saline water to pass through
it. However, these researchers have yet to prove that this
membrane can successfully desalinate water. Further, they
have only been able to produce a 1 cm2 membrane [5]. This
research reveals the larger problem of scaling up
technological developments made in the lab to industrial
scales that could provide water for entire regions. Thus, for
the foreseeable future, reverse osmosis will continue to be the
primary desalination process.
Desalination can also have strong ecological impacts.
The intake pipes used to retrieve seawater can kill small
organisms such as “plankton, fish eggs, fish larvae and other
microbial organisms that constitute the base layer of the
marine food chain” [12]. Even larger animals such as fish and
possibly mammals can be killed [4]. This disruption of local
ecosystems is concerning and should be avoided as much as
possible. Further potential ecological deterioration, such as
the death of certain organisms, can arise from pouring the
brine produced after desalination back into ocean because this
solution contains a very high salt concentration and
potentially other foreign elements introduced by agricultural
runoff [12].
FIGURE 7 [7]
Energy usage by different desalination methods
These large amounts of energy savings can have a
significant impact on climate change. Since most of the
energy that powers desalination is derived from the burning
of fossil fuels, the reduction in energy usage means a lower
carbon footprint and thus, a lower contribution to climate
change. To help quantify this impact, the output of different
desalination methods can be related to their production of
greenhouse gases. The unit used to numerically describe
carbon emissions is gCO2eq/kWh, which is read as grams of
carbon dioxide equivalent per kilowatt hour; this unit relates
greenhouse gas emissions of a process to the amount of
carbon dioxide that would be produced in the same process
[13]. To connect greenhouse gas output to water output, the
average energy usage of a desalination method, given by
kWh/m3, can be multiplied by the average carbon dioxide
equivalency, given by gCO2eq/kWh. Using the median
gCO2eq/kWh of coal power plants in the United Kingdom,
846 gCO2eq/kWh, we find that AD produces 1167.48
gCO2eq/m3 of water, compared to 1692 gCO2eq/m3 for multieffect distillation (MED). Carbon footprint reduction can be
calculated using equation 13.
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John Maclin
Joseph John
some research has been carried out to explore the use of other
materials, namely AQSOA-Z02. AQSOA-Z02 is a synthetic
zeolite developed by Mitsubishi and tested by Youssef et al to
compare its effectiveness to silica gel as an adsorbent [15]. A
zeolite is a hydrated mineral made of links of AlO4 and SiO4
and other metals such as sodium or potassium. These
minerals also have many openings in them and allow
materials of a certain size to pass through them while
restricting others. Since AQSOA-Z02 is synthetic, it is
manufactured in such a way to make its structure of a specific
shape and equal size throughout, thus tailoring it to a specific
purpose [16]. These properties make zeolites a good match
for AD since large amounts of water vapor can be held in
them.
To study AQSOA-Z02, Youssef et al created a
simulation of a four-bed AD system equipped with an
evaporator and condenser [15]. Two of the beds are used for
adsorption while the other two are used for desorption. While
adsorption is taking place in the respective beds, water is
passed through them to absorb heat released from adsorption.
Simultaneously, the desorption beds are treated with hot
water to retrieve the clean water vapor. This water vapor then
travels to the condenser where it becomes liquid water [16].
Figure 8 depicts the simulation created.
EQUATION 13 [8]
Energy saving calculation
AD results in a 31% reduction in greenhouse gas emissions
(GHGE) when compared to MED. These reductions only
increase when AD is compared to other desalination methods;
AD reduces GHGE by 44.8% compared to multi-stage flash,
72.4% to reverse osmosis, and 87.6% to vapor-compression
[13].
The technological advantages of AD over other methods
also extend to water output. Since the chemical makeup of
bodies of water vary, it is crucial that desalination methods be
flexible enough to accommodate various salinities. Due to the
basic principles of AD, it has been shown to be able to
produce 6.7 m3 of water per tonne of silica gel per day
regardless of the salinity of the feed water; since AD is driven
by the temperature and pressure conditions, those are only
conditions that determine output. Compare this to another
method such as MSF, which is driven by thermal properties,
thus subjecting its output to the salinity of the feed water [8].
With regards to ecological impacts on marine life, AD
can alleviate a few of the problems such as brine discharge as
mentioned in the section covering the combination of AD and
reverse osmosis. However, it cannot solve problems such as
loss of marine life. It is inevitable that aquatic organisms will
be killed during the process because the problem arises from
the fundamental process of taking in ocean water to
desalinate. However, marine biologists have argued that
problems such as these do not pose a major risk to ocean
ecosystems. Dr. Daniel Cartamil states that the killing of
plankton due to water intake from desalination "accounts for
only about 1 percent or 2 percent of plankton mortality in a
given area. In other words, the actual effect on marine life is
negligible" [14]. Cartamil goes on to discuss the issue of
brine, mentioning how current methods only leave areas
directly around the area of discharge with higher salinity
levels. Even then, these levels are not high enough to cause
damage to organisms [14].
FIGURE 8 [15]
Schematic of the system used by Youssef et al
To mathematically determine how AQSOA-Z02 and
silica gel perform, adsorption isotherms and adsorption
kinetics are analyzed. Adsorption isotherms refer to the
highest amount of adsorbate that can be held by a dry
material at a given vapor pressure. The isotherms of silica gel
are given by the equation below.
WHATS NEXT?
Different materials used as adsorbents
Despite all the work being done on AD, there is not
much research concerning what other materials can be used
as an adsorbent. In most of the studies researched, silica gel
was used because of its ideal porosity and polarity. However,
EQUATION 14 [15]
Dubinin-Astakhov equation and its constants.
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John Maclin
Joseph John
clean water cannot detract from the issue of sustainability.
For desalination, sustainability can be defined as the ability to
create clean drinking water at an efficient pace, while being
generally inexpensive to achieve and environmentally safe
and conscious. Most common desalination techniques such as
reverse osmosis are efficient in providing a large amount of
drinking water from the ocean, but are not very sustainable
practices in many senses. As stated earlier, reverse osmosis
requires tons of energy, is very costly to carry out, and has a
large environmental impact through its carbon footprint and
effects on marine life.
To expand on what was stated
earlier, AD will increase the general sustainability of
desalination as a water source because it will be less
expensive in regards to energy consumption.
When
combined with existing desalination methods such as MED,
AD can lower the amount of energy needed for operation by
about 72% [7]. With less energy consumption, the cost of
operation will decrease along with the environmental impact
because the energy that is needed to run the plants comes
primarily from the burning of fossil fuels. With this decreased
energy usage, there is a lower demand for fossil fuels such as
coal, meaning that less of it will be mined. This decrease
further helps the environment due to the deleterious effects of
mining. For example, during one form of mining that
involves blowing off the tops of mountains with explosives,
bodies of water can be filled with sediment from the
explosion [17]. These particles harm not only the ecosystem
in direct contact with the stream, but also other streams that
receive water from the polluted source and other streams they
feed into, thus exponentially increasing the effects of mining.
Underground mines are not much better with regards to the
environment. The methane, a greenhouse gas, escaping from
these coal mines account for a sizeable 10% of methane
emissions in the United States. Even after a mine closes,
acidic water can drain from it and pollute water sources [17].
AD can reduce all of these effects by decreasing the demand
for coal. Therefore, AD makes desalination more sustainable
from both the monetary and environmental standpoints.
AD can also make desalination more economically
viable because of its easy addition to already existing
desalination methods. The cost of creating a desalination
plant can be around $1 billion, and is also very costly to run
[5]. Making new plants where they already exist is not an
option because of the high cost of production, but AD can
bypass this issue by simply being added to already existing
RO and MED plants [8]. By adding the new AD technology
to the already existing plants, the investment is vastly lower
than that of building a new plant. Furthermore, the plants that
are receiving these additions now have better sustainability
values.
Lastly, AD can increase sustainability in
environmental aspects because it is a very low power process
and can even be run on just solar power [8]. Therefore, if
added to an existing plant the energy waste will be lower
because AD can either utilize or lessen waste produced.
Again, this makes the need for fossil fuel energy lower, thus
making the carbon footprint on the plant lower. AD has been
The intake of water vapor by AQSOA-Z02 is given by
equation 15.
EQUATION 15 [15]
Water vapor intake by AQSOA-Z02
Since adsorption depends on time, temperature, and pressure,
kinetics is used to determine the rate process using equation
16.
EQUATION 16 [16]
Rate process of adsorption
FIGURE 9 [15]
Rate of adsorption constants
From these experiments, the authors concluded the
following: "Results showed that for heat source temperatures
above 75 °C and evaporator temperature below 20 °C suitable
for cooling applications, AQSOA-Z02 outperforms silica gel
in terms of higher SDWP and SCP [specific daily water
production and specific cooling power] [16]. Research like
this proves that there is room for advancement in AD in areas
such as the choice of adsorbent which bodes well for the
technology.
Expansion in Sustainability for Desalination
The idea of having a sustainable water source from the
ocean is very tantalizing because of the vast abundance of salt
water available. However, the allure of a consistent source of
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John Maclin
Joseph John
getting attention from the science community because it will
greatly improve the sustainability of desalination itself and
may make it a viable option for clean water in places that
have little water at all.
Singapore.
2003.
Accessed
3.2.2017.
http://www.scholarbank.nus.edu.sg/bitstream/handle/10635/1
3716/Thesis-Qiu_Jiayou(ME).pdf?sequence=1.
[7] Ali, et al. “Recycling brine water of reverse osmosis
desalination employing adsorption desalination: A theoretical
simulation.” Desalination. Vol. 408. 1.8.2017. Accessed
1.26.2017.https://www.engineeringvillage.com/share/docume
nt.url?mid=cpx_M75380f57159cc1abc71M7f881017816317
1&database=cpx&view=abstract.
[8] K. Ng, K. Thu, Y. Kim, A. Chakraborty, G. Amy.
“Adsorption desalination: An emerging low-cost thermal
desalination method.” Desalination. Vol. 308. 1.2.2013.
http://www.sciencedirect.com/science/article/pii/S001191641
2004018. pp. 161-179.
[10] R. Levicky. “Chapter 7 – Energy and Energy Balances.”
New
York
University.
Accessed
3.2.2017.
http://faculty.poly.edu/~rlevicky/Handout6.pdf.
[10] “MED—Multi-Effect Distillation.” Wabag. 2016.
Accessed 3.2.2017. http://www.wabag.com/performancerange/processes-and-technologies/med-multi-effectdistillation/.
[11] C. Lewis. “How It Works.” Carlsbad Desalination
Plant. 2016. 3.3.2017. http://carlsbaddesal.com/how-it-works.
[12] “The Impacts of Relying on Desalination of Water.”
Scientific
American.
Accessed
1.10.2017.
https://www.scientificamerican.com/article/the-impacts-ofrelying-on-desalination/.
[13] “Carbon Footprint of Electricity Generation.”
Parliamentary Office of Science and Technology. Vol. 383.
6-2011.
Accessed
3.2.2017.
https://www.parliament.uk/documents/post/postpn_383carbon-footprint-electricity-generation.pdf.
[14] D. Cartamil. “Marine environmental damage will be a
minimal trade-off.” The San Diego Union-Tribune.
11.28.2015.
Accessed
3.2.2017.
http://www.sandiegouniontribune.com/opinion/commentary/s
dut-desalination-carlsbad-marine-life-cartamil-2015nov28htmlstory.html.
[15] P. Youssef, A. Mahmoud, R. AL-Dadah. “Performance
analysis
of
four
bed
adsorption
water
desalination/refrigeration system, comparison of AQSOAZ02 to silica-gel.” Desalination. Vol. 375. 11.2.2015.
http://www.sciencedirect.com/science/article/pii/S001191641
5300400. pp. 100-107.
[16] C. Woodford. “Zeolites.” Explain that Stuff. 12.28.2016.
Accessed
3.2.2017.
http://www.explainthatstuff.com/zeolites.html.
[17] “Coal and the Environment,” U.S. Energy Information
Administration.
Accessed
3.30.2017.
https://www.eia.gov/energyexplained/?page=coal_environme
nt.
INCREASE IN DESALINATION
EFFICIENCY
The recent increase in both frequency and intensity of
droughts all over the world makes the process of desalination
itself very appealing. Humans have been looking to the
oceans for centuries, wishing that these massive bodies of
water could be consumed [1]. Even though ancient societies
figured out primitive ways to perform desalination, their
techniques are unable to produce enough water to solve the
current water crisis and are also too inefficient to be
economically viable. Modern desalination is very promising
for regions with intense droughts and has been in use for a
few centuries, but the process is expensive and can produce a
large carbon footprint. Adsorption desalination is the
solution to the problems that face modern desalination. AD is
inexpensive because it utilizes inexpensive adsorbents such
as silica gel, can run on waste heat, and is more efficient than
the most commonly used desalination methods. AD also
helps reduce the carbon footprint of desalination by running
at a lower temperature and possessing the ability to operate
on solar power, reducing the dependency on fossil fuels. AD
can be added to the desalination processes already in use,
making it a highly versatile technology and one that should
be considered essential to this conference and to the future of
desalination.
SOURCES
[1] “Desalination history.” Australian Department of
Environment and Primary Industries. 10.28.2016. Accessed
3.2.2017.
http://www.depi.vic.gov.au/water/urbanwater/desalination-project/desalinationbackground/desalination-history.
[2] “Water Desalination Process.” American Membrane
Technology Association. 2016. Accessed 3.2.2017.
http://www.amtaorg.com/Water_Desalination_Processes.html
[3] H. Cooley. “Seawater Desalination: Panacea or Hype?”
Action
Bioscience.
4-2010.
Accessed
1.10.2017.
http://www.actionbioscience.org/environment/cooley.html?pr
int=1.
[4] “MSF—Multi-Stage Flash.” Wabag. 2016. Accessed
3.2.2017.
http://www.wabag.com/performancerange/processesand-technologies/msf-multi-stage-flash.
[5] D. Talbot. “Desalination out of Desperation.” MIT
Technology Review. 12.16.2014. Accessed 1.10.2017.
https://www.technologyreview.com/s/533446/desalinationout-of-desperation/.
[6] Q. Jiayou. “Characterization of silica gel-water vapor
adsorption and its measuring facility.” National University of
9
John Maclin
Joseph John
ADDITIONAL SOURCES
“Desalination project wins Global Innovation Challenge at
Saudi Water & Power Forum.” King Abdullah University of
Science and Technology. Accessed 1.11.2017.
https://www.kaust.edu.sa/en/news/desalination-project-winsglobal-innovation-challenge.
G. Maciulevičiūtė. “Recent Developments in Adsorption
Desalination: Process Configurations.” Linkedin. 11.27.2015.
Accessed 1.10.2017. https://www.linkedin.com/pulse/recentdevelopments-adsorption-desalination-processmaciulevi%C4%8Di%C5%ABt%C4%97.
J. Wei. “A Study of Silica Gel Adsorption Desalination
System.” The University of Adelaide. 2012. Accessed
1.10.2017.
https://digital.library.adelaide.edu.au/dspace/bitstream/2440/8
2463/8/02whole.pdf. pp. 11-45.
ACKNOWLEDGMENTS
We would like to acknowledge our writing instructor for
the conference paper, Keely Bowers, for her support and
guidance through this process. We would like to also
acknowledge our co-chair, Abigail Kulhanek, for leading us
in the right direction when we were struggling with certain
parts of developing our final product.
10