Fresh can be classified in two groupsFresh can be classified in two groups

Fresh water is becoming an important worldwide problem due to the
shortage of the potable water sources. Although 75% of the earth surface is
covered by water, but nearly 96.54% of the total water in the earth is oceans salt
water so the fresh water makes the 2.53% of the planet’s water which consists ground
water, poles, lakes and rivers. However, the available fresh water for human
usage is just less than 0.36% of the remained 2.53% fresh water. Because over
two thirds of the fresh water is frozen in polar ice caps, permafrost and glaciers or the unfrozen remained water is hard to
reach in underground and only a small amount is contained lakes and rivers 1, 2.

In many parts of the world great amount of fresh water is needed
for agricultural, industrial and domestic life where the portion of total water
consumption for mentioned items is 70%, 20% and 10% respectively 3. As
of today, almost 25% of the people in the word has insufficient fresh water
supply 4.
Furthermore, the growth of population and industrial development will intensify
water crisis in the next few decades 5. By
2030, the United Nations World Water Assessment Programme (WWAP) estimates that
only 60% of the global water demand can be satisfied under the
business-as-usual (BAU) scenario 6.

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Oceans are the main sources of water but the problem is that the
water of oceans are salty thus they are not drinkable. The mentioned problem
can be solved by desalination of the oceans salty water. Desalinize means to
remove salt from saline water. Most of the available waters in the planet are
salinity up to 10,000 ppm but the salinity of sea water is from 35,000 to
45,000 ppm. The admissible limit of salinity in water according to World Health
Organization (WHO), is 500 ppm and rise to 1000 ppm for special cases 7, 8. Different methods to desalinize which can be classified in two
groups comprised of thermal technologies and membrane technologies are
investigated in 9, 10. In
the thermal technology a thermal energy source such as fossil-fuel source, non-conventional
solar energy source, nuclear energy or nuclear energy is used to desalinize the
salty water. Multi Stage Flash (MSF), Vapor Compression (VC) and Multi Effect Distillation
(MED) are include thermal process. The membrane processes use electricity for ionization
of salts in salty water or to drive high-pressure pumps. The membrane
technologies contain Reverse Osmosis (RO), Microfiltration (MF), Nanofiltration
(NF) and Ultrafiltration (UF). Energy cost, salinity level of feed water and
plant size have significantly influenced the desalination cost of generated
fresh water per unit 11.

Energy and water crisis are two vital problems which have absorbed
lot of attention in recent years. Incremental condition of energy demand and
consequential environmental problems has clarified the significance. Desalination
process consumes significant amount of energy to remove salt from sea water. For
providing 13 million m3 of fresh water per day approximately 130
million tons of oil per year is needed 12, 13. Due to limited sources of fossil fuels, high environmental
pollution, increasing global warming problem and expensive generation cost of
fossil fuels, renewable energy sources like wind, solar and geothermal are good
choices to meet energy demand of desalination for water purification in areas
with lack of water. The total specific energy consumption of desalination
according to the desalination technologies is varied between 0.5-16 kWh/m3
14, 15.

Introducing energy hub concept opened new window to energy management
field 16.
Energy hubs were recognized as a future energy systems in 17
with considerable potential of research work. Generally, energy hub can be
defined as the units with capability of conversion, storage, district
connections of various energy carries such as electricity, natural gas, heating
and so on 18. The
essential question in energy hub operation is that which condition provides
optimal arrangement of entrance energies and devices operational points, to
achieve the minimum cost of providing consumers demands 17.

In multi carrier energy systems, different types of energies has
been considered. Electricity, natural gas and heating are the most famous ones
which have been investigated as input part of hubs, and electricity and heating
are the most common output based on energy consumer’s needs. In this paper the
optimization of hub operation is done in presence of storages, smart grid
conditions such as electricity DRP or integrated electricity-gas DRP, renewable
energy sources and electricity market. The objective function is to minimize
the cost and emission of the hubs while satisfying the constraints. The
proposed mixed integer linear programming (MILP) for energy hub daily scheduling,
which is guarantor of finding global optimum operation work has been solved by
using CPLEX solver of GAMS software.

Remainder of this paper has been organized as following: Section 2
presents brief description of assumed energy hub model. In the Section 3 the
optimization problem with related constraints have been presented by their
explanation. Section 4 is about the case studies and simulation results and
finally the Section 5 is a conclusion part of this paper.